Abstract

Electrochemical Degradation in Rubber

T.J. Pond

Micrographs are shown of some typical types of structural damage that can occur in a vulcanisate as a result of electrochemical degradation (ECD) in the material. The importance of the carbon black content, the operating temperature, the coolant composition, a vulcanisates cure system and other compound ingredients on the size of the current that can flow through a vulcanisate and its impact on ECD were discussed as well as the effects of crosslink density on volume resistivity and current flow. Results from SEM X-ray analysis of ECD damaged material on the depletion of zinc and sulphur by ECD and the associated effects on current flow through a compound are also discussed.

A Universal Method to Predict Wet Traction Behaviour of Tyre Tread Compounds in the Laboratory

Michael Heinz

Wet grip is one of the most important properties relevant to tyre safety. The slip dependency of the side force coefficient was investigated with extra attention to Antilock Braking System (ABS)-breaking. A set-up which enables the simulation of wet road properties leads to a fair prediction of wet grip. A laboratory test method has been developed which uses a rotating disk against which a rubber sample wheel runs under a given load, slip angle and speed. The side force component acting on the wheel during the tests was recorded. The surface can be wetted with water at different temperatures and the side force at a slipping wheel is measured over a wide range of temperatures, slip and speed. Low water temperatures and low slip speed settings in the laboratory produce side force ratings, which correlate excellently with ABS braking on the road. Median and high slip speeds give ratings in close agreement with locked wheel braking on the road.

Hydrogenated Natural Rubber from Different Types of Preserved Latex

B.N. Krishna Veni and M.S. Ma’zam

One of the major disadvantages of natural rubber (NR) is poor ozone and ageing resistance besides poor oil and chemical resistance. These weaknesses are partly caused by the double bonds present in the rubber molecules. However the number of double bonds can be reduced by hydrogenation. This paper discusses the effect of preservation systems of NR latex used as the starting materials and also the effect of hydrogen peroxide on the efficiency of the hydrogenation reaction. The hydrogenated NR was prepared by reacting NR latex with hydrazine hydrate and hydrogen peroxide. The rubber was characterised by using proton Nuclear Magnetic Resonance (NMR). The results showed that the hydrogenation level is significantly affected by the different preservation systems and the concentration of hydrogen peroxide. The optimum level of hydrogen peroxide concentration was found to be in the range of 20-30% for all types of preservation systems. The use of field latex as a starting material achieved a much higher hydrogenation level (67%) compared to other types of preserved latex examined.

Mechanical and Rheological Properties of Short Nylon Fibre NR/SBR Composites

S. Soltani, G. Naderi and M.H.R. Ghoreishy

NR/SBR composites were prepared with virgin and waste short nylon fibre using a two-roll mill. The effects of the fibres and bonding agent content on the microstructure, mechanical and rheological properties of the composites were investigated. The curing characteristics of the composites were determined and subsequently vulcanised at 150ºC using a hot press. The cure and scorch times of the composites decreased while the maximum torques increased with increasing fibre loading. The adhesion between the fibre and rubber was enhanced by using a dry bonding agent consisting of resorcinol, hexamethylenetetramine and hydrated silica (HRH). The bonding agent provided a shorter curing time and enhanced mechanical properties. The fracture surfaces of samples were examined by scanning electron microscopy (SEM). The presence of fibres in the matrix influenced the fracture modes leading to pull out and breakage of fibres. Anisotropic swelling studies were carried out to study the fibre matrix interaction and fibre orientation. The restriction to swelling is higher for composites containing bonding agent and the preferential orientation of the fibres is in the milling direction. For composites prepared with virgin and waste fibres, the dependence of the storage modulus (G’) on angular frequency followed a clear non-terminal behaviour.

Effect of Filler on Physical Properties and Surface Morphology of Natural Rubber Latex Films

R. Roslim and M.Y. Amir Hashim

The physical properties of unfilled and filled natural rubber latex (NRL) films were investigated. The presence of calcium carbonate in latex films, determined by ash content method that was lower than the amount of filler added to the compound, suggested that the filler tended to sediment. Images obtained from Field Emission Scanning Electron Microscope System (FESEM) on the filled latex film confirmed agglomerates in the latex films especially with higher filler loading and hence, influencing the appearance of the films whereby the dense colour was observed. The stress on the latex films due to the filler was investigated using Mooney Rivlin (C1) stress-strain relaxation measurement method. The clear difference in the C1 values obtained from the test sample before and after being stretched indicated possible breaking at the polymer-filler interphase, especially in natural rubber latex films with high filler loading. It was confirmed that the addition of calcium carbonate up to 20 parts per hundred rubber (p.p.h.r.) into compounded natural rubber latex produced films with some improvements in strength and stiffness. The improvement in strength, however, ceased and decreased on higher filler content and the elasticity of the film reduced drastically.

High Temperature-mechanical Mixing to Prepare Electrically Conductive Sulfur-vulcanised Poly(butadiene-co-acrylonitrile)-polyaniline dodecylbenzenesulfonate Blends

K.C. Yong and Che Su Mt Saad

High temperature-mechanical mixing method (by using the combination of internal mixer and two-roll mill) was successfully used for the first time in order to prepare sulfur-vulcanised poly(butadiene-co-acrylonitrile)-polyaniline dodecylbenzenesulfonate [NBR-PAni.DBSA] blends. The addition of sulfur as the vulcanising agent did not affect the electrical properties of all these vulcanised blends (with good electrical conductivity up to 10^–2S.cm^–1 and low conductivity percolation threshold at only 5.0 wt %/4.5 volume % of PAni.DBSA loadings). The FT-IR spectra of the vulcanised NBR-PAni.DBSA blends resembled a superposition of the spectra of constituent NBR and PAni.DBSA, but with some notable peak shifts due to changing intermolecular interactions between the two polymer components. Blends with ≤30 wt % of PAni.DBSA gave the best compatibility, i.e. with largest peak shifts for their FT-IR spectra and largest temperature shifts for their DSC recorded thermal events. The scanning electron microscopy study of the vulcanised blends showed that the level of electrical conductive network formation was enhanced with increase of PAni.DBSA content.

A Cost Effective Solution for Treatment of Rubber Factory Wastewater

K.V.V.S. Kudaligama, W.M. Thurul and P.A.J. Yapa

Crepe rubber industry is one of the major water polluting industries in all rubber growing countries. There is a necessity to develop suitable treatment technologies for the management of this problem. Covered Activated Ditch (CAD) type test reactors set with Bio-brush media are very effective in rubber factory wastewater treatment. Out of four organic loading rates (OLR) and five specific surface areas (SSA) of media tested respectively, Bio-brush media with 200 m²/m³ SSA under 1.0 COD kg/m³/d OLR was selected as the best for CAD reactors and the average COD removal achieved was about 89%. Results revealed that at higher OLR, correction of pH could be avoided for an efficient treatment and reactors with higher SSA of media were able to tolerate organic shock loads comparatively. The efficiency of treatment increased with increasing SSA of media and no special cycles were observed in removing biomass from the test reactor under any of the four OLRs tested. During maturation, chemical oxygen demand (COD), pH and suspended solids (SS) of treated effluent with 200 m²/m³ SSA were about 100 mg/L, 6.7 – 7.2 and 26 – 43 mg/L respectively which were below the maximum desirable levels stipulated by the Central Environmental Authority of Sri Lanka. Apart from the rubber industry, CAD reactors could also be used for treating biodegradable liquid waste such as waste from the palm oil industry, rice processing industry, sugar industry and others.

Synthesis, Characterisation and Performance of Nanosilica as Filler in Natural Rubber Compounds

Low particle size silica in the nanometer range was synthesised in an aqueous medium by the sol-gel method using dilute hydrochloric acid and sodium silicate, and characterised using X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Infrared Spectroscopy (IR). This synthetic nanosilica had a lower number of hydroxyl groups than commercial silica and hence underwent reduced silica-silica agglomeration. The nanosilica was used as a reinforcing filler in natural rubber compounds, its cure characteristics and mechanical properties were evaluated. Minimum torque, maximum torque, scorch time and cure time were increased with silica loading. Mechanical properties such as tensile strength, Young’s modulus, tear strength, abrasion loss, hardness, resilience and compression set were better than those of natural rubber vulcanisates filled with commercial silica. Volume fraction of rubber in a solvent-swollen sample was also higher for the nanosilica compounds.

Tear Strength of Pre-stressed NR Black-filled Vulcanisates

Azemi bin Samsuri

Parallel-sided test-pieces prepared from conventional natural rubber (NR) sulfur vulcanisates filled with 50 p.p.h.r. HAF black were pre-stressed to a pre-determined stress level for one minute, after which the loading stress was removed. They were swollen in toluene for 72 hours after which time they were deswollen to remove residual strain, and to allow for rapid elastic recovery. The test-pieces were dried down to a constant weight before carrying out the tear test. Tear deviations from the intended tear path took place if the stress level during pre-stressing was lower than 18 - 20 MPa (ca. 350% strain). Above 20 MPa stress level, the tear did not deviate but propagated along the intended tear path. However, if the samples were cycled a few times even below 18 MPa, no tear deviations from the intended path were observed. Tear measurements on all samples pre-stressed to 23 MPa were conducted at four different temperatures and at various different test speeds. Within the range of test speeds and test temperatures covered in this investigation, tearing energy increased with increasing test speeds. The tearing energy data were amenable to WLF transformations indicating that the tearing process was predominantly associated with viscous processes. Tearing energy of the pre-stressed samples was closely associated with the amount of permanent set produced during pre-stressing (single loading or cyclic loading). The higher the amount of set, the lower the tearing energy.

A Study on Deformation Micromechanics of Kenaf Fibre and Kenaf/Epoxy Composite using Raman Spectroscopy

Siti Salina Sarkawi and S.J. Eichhorn

The deformation micromechanics of kenaf fibre and model kenaf/epoxy composites were investigated using Raman spectroscopy. The mechanical properties of kenaf fibre were evaluated. A well defined peak at 1095 cm^–1 was observed in Raman spectra of the kenaf fibre. This peak was found to shift to a lower wavenumber upon fibre deformation. The Raman peak position was also noted to decrease linearly with respect to an increase in strain and stress. The same trend was also observed during the deformation of kenaf fibre-epoxy resin composite using a four-point bending test. The 1095 cm^–1 peak position returned to its original position after the fibre was deformed in the composite. This indicated that the stress was being transferred from the matrix to the fibre.

Characterisation of Natural Rubber Cup Coagula Maturation Conditions and Consequences on Dry Rubber Properties

J. Intapun, J. Sainte-Beuve, F. Bonfils, V. Tanrattanakul, E. Dubreucq and L. Vaysse

The maturation conditions of cup rubber coagula stacked in the form of a stocking pile in an industrial plant have been characterised. It was found that temperature and relative humidity of the air increased with depth within the pile. In contrast, oxygen content of the air within the pile decreased as depth increased. The effects of these parameters on the properties of processed cup coagula maturation were studied. Effects of 24-day maturation on rubber properties were found to vary with the position of cup coagula within the pile. The pH of maturated cup coagula decreased significantly with depth in the pile. An inverse pattern was observed for Wallace initial plasticity (P_o), Plasticity retention index (PRI), gel content and weight average molar mass (M_w). Moreover, the maturation period, especially at the deepest layers, was found to have a positive effect on the standardised properties of rubber such as P_o and PRI.

Use of Approximate Calculations and Finite Element Analysis to Estimate the Stiffness of Rubber Bushes and Cylindrical Mountings

Julia Gough

Rubber bushes consist of a hollow rubber cylinder bonded on the inside and outside to rigid metal sleeves and are widely used as mountings to provide compliance. Four modes of deformation are commonly defined: axial, torsional, radial and tilting. Formulae, available in the literature for calculating the small strain stiffnesses of such bushes, are briefly reviewed. Sometimes two voids are introduced on opposite sides, running along the length of the bush, to give a directional dependence to the radial and tilting stiffness. An approximate theoretical treatment for such bushes is presented, together with predictions of the stiffnesses from FEA. Mountings in which the inner and outer sleeves are connected by two blocks of rubber, in effect bushes with very large voids, are also considered. It is shown that reasonable predictions of the bush stiffnesses may be obtained from the approximate formulae. Such formulae may therefore be used in design calculations to provide an initial estimate of the required dimensions of the bush and FEA may then be used to refine the initial design.

Nursery Performance of Full and Half-sib Progenies and Juvenile Screening for Selection in Rubber (Hevea brasiliensis Muell. Arg.) Breeding

T.R. Chandrasekhar*# and T. Gireesh**
In order to report growth and yield performance of progenies of 2002-hand pollination programme and to discuss the observations vis-à-vis juvenile screening in hevea breeding, test tapping at three years was carried out. Latex volume, instead of dry rubber, was collected as yield from each tapping. Dry rubber content (DRC) of top selections was determined for calculation of rubber yield. Distribution of seedlings in different girth, yield and DRC classes were studied. Mean range in latex yield noted in the full-sib progenies of Wickham Χ Wild accessions was 0.1 to 4.5 mL t^–1 t^–1 (mL per tree per tapping) while in Wickham Χ Wickham progenies it was 0.1 to 19.6 mL t^–1 t^–1. In the clonal half-sibs (HS), mean yield was low in HS progenies of RRII 105 and PB 330 while in RRII 414 and RRII 429 it was higher. Maximum latex yield noted from a tapping was 33.0 mL t^–1 t^–1. Dry rubber yield in the top 20% selections showed a range of 0.7 to 4.1 g t^–1 t^–1 (grams per tree per tapping). Mean yield from 10 tappings ranged from 7 to 41 g t^–1 10t^–1 (grams per tree per 10 tappings). DRC among the top 20% selections varied from 14.3% to 38%. In the low girth class only one was included in the top 20% of selections. Moderate and average girth classes each contributed 41 and 38 seedlings that included most of the top 20% of selections. It was concluded that test-tapping at age three, rather than at two, was more useful. Measurement of yield in terms of latex volume as opposed to that of dry rubber yield, can result in more accurate yield recording. Latex can be used for determining rubber content and biochemical and physiological determinants of yield that can further boost the probability of potential selections. For maximum genetic gain in juvenile selection, seedlings of moderate to high girth class and average yield seemed more promising.

Secondary Somatic Embryogenesis in Hevea brasiliensis (Müll. Arg.): An Alternative Process for Long-term Somatic Embryogenesis

L. Lardet, F. Dessailly, M.P. Carron, M.A. Rio, N. Ferrière and P. Montoro

A procedure for long-term somatic embryogenesis called Maintained Somatic Embryogenesis (MSE) was previously described in Hevea brasiliensis to obtain embryogenic callus lines directly from integument explants. However, the frequency with which embryogenic friable callus lines are directly established from the inner integument of immature fruit is low and restricted to the clones PB 260 and RRIM 703. In this study, the ability of somatic embryos to develop friable callus lines with proliferating and embryogenic capacities was highlighted. Histological analyses revealed dedifferentiation of the epidermal and perivascular cells, giving rise to the formation of friable embryogenic callus on the periphery of somatic embryo explants. Cell proliferation induced by subsequent subcultures of calli on maintenance medium resulted in the establishment of embryogenic callus lines. This new procedure is called indirect Secondary Somatic Embryogenesis (SSE). The potential of embryo-derived embryogenic callus lines was assessed in comparison with the integument-derived embryogenic callus line produced using the MSE procedure. Embryogenic callus lines were established with the clones PB 260 and RRIM 703 for the new process with a higher frequency than those obtained with the MSE procedure. In addition, the number of subcultures needed to establish callus lines was shortened. Secondary somatic embryogenesis also enabled the production of friable callus lines for the PB 217 clone, which was recalcitrant to the previous process. This alternative procedure opens the way for applications of long-term embryogenesis to many other clones for which primary somatic embryogenesis is successful.

NRESTdb: Access to the Transcriptome of Natural Rubber Latex

Mohd-Noor Mat-Isa, Keng-See Chow, Ahmad-Fuad-Hilmi Mohamad, Mohd-Yunus Shahrum, Chee-Chong Hoh, Mohd-Rashdi Mohd-Amin, Khairil-Anuar Zainal, Hoong-Yeet Yeang and Kiew-Lian Wan

Current technological advancement of DNA sequencing has afforded opportunities to analyse genes on a larger scale. In natural rubber research, DNA sequencing technology has been used in the generation of approximately 10,000 DNA sequences representing genes expressed in the latex of Hevea brasiliensis (Muell. Arg.) clone RRIM600. These sequence data, more popularly known as expressed sequence tags (ESTs), can be analysed using bioinformatics tools to facilitate gene discovery and provide information regarding the putative function and expression profile of latex genes. We have developed NRESTdb, a Natural Rubber EST database, to provide easy access and rapid analysis of these data. To our knowledge, this is the first publicly available EST database for H. brasiliensis. In addition to serving as a repository for individual latex EST and clustered sequences, this database allows users to view, mine and retrieve useful information regarding: the transcriptome of natural rubber latex including matches with existing domains and gene sequences available in public databases; description based on the Gene Ontology nomenclature; homologues identified via comparative sequence analysis; and enhanced data sets of special interest, namely rubber biosynthesis and latex allergy.

Susceptibility Of Hela (Cancer-Origin) Cells to a Sub-Fraction of Latex B-serum

M.T. Ong, K.L. Yang, K.L. Lam G.A. Ong and E. Sunderasan

An increasing amount of cancer research is being directed towards the investigation of plant-derived anticancer compounds, many of which have been used in traditional herbal treatments for centuries. Extracts of Hevea brasiliensis, the natural rubber tree, had been demonstrated previously to have anti-cancer properties. In the present study, latex fractions, namely B- and C-sera were found to have anticancer properties in cell-based assay. Based on this result, further screening was carried out using sub-fractions of latex B- and C-sera. This has led to the findings that one of the B-serum sub-fractions, BHM, is highly selective in reducing the growth of HeLa (cancer-origin) cells compared to that of Vero (non-cancer-origin) cells in MTT cell-based assay. The outcome has also paved the way for further investigations to elucidate the mechanisms of the BHM sub-fraction in reducing the growth of cancer-origin cells, as well as to evaluate its potential role in cancer treatment.

Molecular Characterisation of the Sucrose Transporter HbSUT1B in Relation to Rubber Production in Latex Cells

A. Dusotoit-Coucaud, N. Brunel, J. Franchel, F. Granet, H. Chrestin and S. Sakr

The rubber synthesis in latex cells requires sucrose. These particular cells are heterotrophic ones and are apoplastically connected to other tissues. Such features imply that the rubber yield may depend on the latex cell efficiency to absorb and to use the imported sucrose. This study investigates the sucrose transporters as key genes for rubber biosynthesis involved in the ethylene-stimulated rubber yield. Seven putative sucrose transporters had been isolated from a latex-derived cDNA library of PB 217. Expression profiling of these sucrose transporters under ethylene stimulation in PB 217 underlined the role of one sucrose transporter: HbSUT1B (Hevea brasiliensis Sucrose Transporter 6) (Dusotoit-Coucaud et al., 2007). This paper reports the next stage in HbSUT1B, molecular characterisation. Its expression in different parts of the rubber tree was studied. It was preferentially expressed in leaves and bark. This result was completed by in-situ hybridisation experiments. In addition, promoter cloning and analysis revealed some clues for the wounding regulation of HbSUT1B. The HbSUT1B expression was analysed in response to different treatments in latex or bark tissues. HbSUT1B was considerably up-regulated by hormones and wounding in bark but not in latex. This regulation appeared to be tissue-specific.

Early Selection of Promising High Yielding Hevea Progenies based on Selected Physiological and Stomatal Characteristics

Bastiah Ahmad, Hashima Idris and Siti Hawa Sulong

Leaf physiological and stomatal parameters were studied from immature plants grown in the ground nursery. These Hevea clones differed widely in mature yield. Significant differences were detected in some of the parameters such as light saturated photosynthesis (Psat), stomatal conductance (SC), transpiration rate (TR), mesophyll conductance (MCond) and instantaneous water use efficiency (WUEg) among the clones. The variation in mature yield, girth at opening as well as physiological parameters and stomatal characteristics were not affected by weather. The mature yield showed a positive correlation with Psat, SC, TR and MCond while the girth at opening was positively correlated with instantaneous WUEg. A step-wise multiple regression confirmed results of the simple correlation. About 34% of the differences in mature yield was explained by Psat. The addition of potential conductance index (PCI), a product of stomatal frequency (SF) and square of length of stomatal complex (LSC), as an independent variable increased the predictive power for mature yield by about 55%. The results indicated that Psat singly could identify high yielding clones with 63% accuracy and an error rate of 17% for wrongly identifying low yielders as high yielding clones. When both Psat and PCI were used, all high yielding clones could be identified. It is concluded that both Psat and PCI, which together have successfully identified high yielding clones, have a potential to be used as indirect selection criteria for yield of Hevea progenies during the early stages of growth in the nursery.

Physical Properties of Polyamide 6 Fibre Coated with Thermoplastic Polyurethane Thin Film

Mutsuhisa Furukawa and Baiju John

Polyamide 6 (PA6) monofilament fibres were coated with thermoplastic polyurethane (TPU) thin film. The TPU was prepared from poly (ethylene adipate) glycol, 4, 4’-diphenylmethane diisocyanate (MDI) and 1, 4-butanediol (BD) with an NCO Index of 1.05. The structural changes in the fibre were analysed by the microscope FT-IR ATR scanning mode. It was found that structural changes occurred in the PA6 fibres due to TPU coating. There was a transformation from an amorphous phase to the α-crystalline phase resulting in the increase of crystallinity of PA6 fibre. An increase in strength as well as elongation was observed in the case of TPU coated fibres. The Young’s modulus too showed an increase in strength. The improvement in the mechanical properties of coated PA6 was due to the crystalline changes in the fiber, the annealing effect, the interface stiffening due to the interaction of the urethane group of TPU and the amide group of polyamide fiber as well as the role played by micro-cracks. The blending method is usually used for the performance improvement of PA6 fibres. The improvement of mechanical properties with a soft thin TPU coating seems very interesting and important. Also the TPU coated PA6 fibres had enhanced mechanical properties and possess a degradable nature when compared to the normal PA6 fibres.

Spatial Dependence of Selected Physico-chemical Properties in a Major Rubber Growing Soil in Sri Lanka

R.S. Dharmakeerthi, T.R. Attygalle, R.B. Mapa, S.P. Perera and S.N. Silva

If soil properties are spatially dependent, this information could be used to delineate management units for site-specific fertilizer application. Spatial dependency of soil pH, organic carbon (OC), gravimetric water content ( θ _g ), available P (P_a ), exchangeable K, Mg and Ca (K_ex, Mg_ex, and Ca_ex, respectively) were evaluated using geostatistical methods in a rubber field on Red Yellow Podsolic soils (Typic Paleudults), a major rubber growing soil in Sri Lanka. Soil samples were collected at 5 m intervals along a linear transect of 150 m from crest to bottom in a hilly landscape. Soil pH, OC and θ_g showed a low variability (CV<15%), P_a and Ca_ex showed a very high degree of variability (CV>50%), while K _ex and Mg _ex showed a medium variability. Variation in measured soil properties showed some spatial structure. Spatial dependence of available P was poor (81% nugget variance), while that of pH was very high (6% nugget variance). The distance within which the soil properties were spatially correlated ranged from 10.6 m (pH) to 69 m ( θ _g ). In general, there was a high degree of randomness in plant available nutrients in this field, particularly at distances less than 5 m. The usefulness of this information in site-specific fertilizer application is discussed.

Effects of Added Ammonium Laurate Soap on Natural Rubber Latex

K. Manjula Dilkushi Silva and S. Walpalage

Low quality natural rubber latex, matured with different levels of well known long chain fatty acid salt showed variations in properties. Mechanical stability time, foaming height and viscosity were significantly altered by the added ammonium laurate soap level. Potassium hydroxide number and conductivity showed existence of a similar effect apparently up to a certain level of the added soap. Soap levels above 0.5 X 10^-4 moles per 100 g of latex enhance the mechanical stability time as well as foaming height. Magnitude of the effect depends upon the amount of the added soap. Initial viscosity was decreased by soap addition but a progressive increase and corresponding decrease was observed thereafter. Both potassium hydroxide number and conductivity increased with increasing levels of soap and attained a constant value after 5 X 10^-4 moles of soap per 100 g latex. Soap levels between 4.2 X 10^-4 and 5 X 10^-4 moles per 100 g latex were the critical levels with rapid changes in properties. There was no effect of fatty acid soap on MST on matured latex.

Characterisation of Foulants in a PVDF Tubular Cross Flow Ultrafiltration Membrane by ATR/FTIR Spectrometry

V. Devaraj, I. Ahmad Fauzi and M.N. Zairossani

Attenuated Total Internal Reflection Fourier Transform Infrared Spectrometry (ATR-FTIR) was used to study the chemical nature of the deposits on the fouled polyvinylidene Fluoride (PVDF) tubular membrane after the concentration of natural rubber skim latex by cross-flow ultrafiltration process. The subtraction spectroscopy analysis (subtraction of spectrum of the fouled membrane by the spectrum of the unused clean membrane) indicated that the major composition of the foulants found on the interior surface of the membrane could be of natural rubber latex protein derivatives (amino acids; bonded NH; NH2 and amine) and the smaller rubber particles that plugged the membrane pores. The chemical nature of inorganic foulants originating from metallic ions from the preservation system of the natural rubber latex could not be determined. The current membrane cleaning procedure is not effective enough to remove all the organic foulants. This study only provides a preliminary identification of the functional groups and needs further confirmation by other analytical tools for a full characterisation of the foulants for formulating a more effective membrane cleaning procedure.

Zinc-Complexes in Natural Rubber Latex Sulphur Vulcanisation System

M. Siti Nor Qamarina and M.Y. Amir Hashim

Zinc-complexes are essential ingredients in natural rubber latex (NRL) sulphur vulcanisation systems as they enhance the vulcanisation efficiency and improve the vulcanisate properties. Sulphur, zinc-type accelerators and zinc oxide (ZnO) are the main chemical ingredients utilised in a vulcanisation system. Zinc type accelerators accelerate the vulcanisation process in many rubber products manufacturing, while ZnO, enhances the vulcanisation efficiency. However, these chemicals may form residuals and could be released from the vulcanisates, either during the product manufacturing process or from the finished products. These chemicals may contribute towards environmental pollution, while some residuals are known to induce Type IV skin sensitivity. Thus, understanding the role of these zinc-containing chemicals in the processing of NRL based products can help the optimisation on the amount of chemicals needed for the latex products. This study showed that the amount of residual carbamate (DEC) extracted from vulcanised NRL films reduced with increased amount of ZnO content. The physical properties and crosslink densities of NRL films improved with addition of zinc diethyl dithiocarbamate (ZDEC) and ZnO. The study also confirmed the effect of heating whereby NRL films heated at high temperature demonstrated prominent differences in physical properties and residual DEC.

Agronomic Performance of the Clone IRCA 111 of Hevea brasiliensis under Different Frequencies of Tapping and Stimulation in South-West Côte d’Ivoire

S. Obouayeba, E.F. Soumahin, M. Dobo, R. Lacote, O. Gabla and A. Doumbia

Clone IRCA 111 was developed in Côte d’Ivoire in 1975 to contribute in increasing the rubber production. Nine years of study were conducted on a large scale to identify the optimal tapping system for its exploitation before being released to the producers. The experimental design was that of a Randomised Complete Bloc (RCB). Among the six tapping systems tested (½ S d/2 6d/7; ½ S d/3 6d/7. ET 2.5%. Pa 1 (1). 4/y; ½ S d/4 6d/7. ET 2.5%. Pa 1 (1). 4/y; ½ S d/4 6d/7. ET 2.5%. Pa 1 (1). 8/y; ½ S d/5 6d/7. ET 2.5%. Pa 1 (1). 8/y and ½ S d/6 6d/7. ET 2.5%. Pa 1 (1). 10/y) tapping twice per week with 4 annual stimulations (½ S d/3 6d/7. ET 2.5%. Pa 1 (1). 4/y) turned out to be the optimal exploitation system for IRCA 111. Nevertheless, with a limited number of tappers, weekly tapping with 10 annual stimulations (½ S d/6 6d/7. ET 2.5 %. Pa 1 (1). 10/y) was the most appropriate. The production of rubber per tree and per tapping (g/t/t) was in logarithmic relation with the intensity of tapping. The rate of tapping panel dryness (TPD) was related to the intensity of tapping by a quadratic polynomial function. The study also demonstrated that IRCA 111 had a high yield, a fast growth rate and an active metabolism as compared to the standard clone PB 235.

Special Communication: Revised International Notation for Latex Harvest Technology

K.R. Vijayakumar, Eric Gohet, K.U. Thomas, Wei Xiaodi, Sumarmadji, Lakshman Rodrigo, Do Kim Thanh, Pichit Sopchoke, K. Karunaichamy and Mohd Akbar Md. Said

Tapping notation that was revised by Lukman in 1983 is revised again. Rainguarding and gaseous stimulation have been incorporated as new items. For a tapping period of less than a year, it is shown exactly from the starting month to the ending month. Number of tappings realized against the possible maximum number of tapping days is shown as a fraction. Similarly, actual number of stimulations given against the scheduled number is also shown as a fraction. Changes have been brought about in the expressions for cut length and frequency of tapping. Use of arrows for expressing directions of tapping cuts and for change of tapping have been changed to more convenient ones. The terminology, 'exploitation technology' is changed to 'latex harvest technology'.

Comparison between Sodium Dodecyl Sulfate and Polyfructose Surfactant Systems in Urea Deproteinisation of Natural Rubber Latex

Manroshan, S., Asrul Mustafa, Mok, K.L., Kawahara, S., Amir-Hashim M.Y. and Booten, K.

The use of surfactants in addition to proteolytic enzymes and other protein removing agents such as urea is a common practice in acquiring deproteinised natural rubber latex. In the present work, sodium dodecyl sulphate and a hydrophobically modified polyfructose surfactant were used and compared in urea-deproteinisation of natural rubber latex. The resulting deproteinised NR latex were evaluated for their mechanical stability, protein content, nitrogen content, swelling index, tensile strength and surface morphology. The results showed that the mechanical stability, surface morphology and mechanical properties after aging improved when both sodium dodecyl sulphate and hydrophobically modified polyfructose surfactants were used together. Furthermore, the combination of both surfactants also reduced the extractable protein content, nitrogen content and weight swelling index of the urea deproteinised latex.

Assessing Effects of Thermoset Polyester Resin Waste Powder on the Processing and Mechanical Properties of Natural Rubber

A. Ansarifar, L. Wang, M. Osmani and A. Pappu

Products made of glass fibre reinforced polymers are often disposed off in landfills, incinerated or processed into waste powders at the end of their service life. Waste powders can be recycled as fillers for use in virgin polymers. The effects of up to 50 parts per hundred rubber by weight thermoset polyester resin waste powder on the viscosity, cure and mechanical properties of a sulphur-cured natural rubber compound were studied. The powder had resin polymer particles and glass fibre fragments ranging from approximately a few microns to 700 microns in size. The viscosity remained unchanged and the cure properties deteriorated when the powder was added to the rubber. The hardness, Young’s modulus and tensile modulus increased whereas, the tensile strength, elongation at break, stored energy density at break and tearing energy decreased. There was also evidence of poor adhesion between the powder and rubber. The waste powder could be recycled as an extender filler to replace a portion of the raw rubber in the compound.

Comparison of Properties of Natural Rubber Compounds with Various Fillers

Mazlina Mustafa Kamal, Jane Clarke and Md Aris Ahmad

One of the most important phenomena in rubber science is the reinforcement by rigid entities such as carbon black, clays, silicates and calcium carbonate. Thus, these fillers are added to rubber formulations to optimise properties that meet a given service application or a set of performance parameters.

In this study, it was observed that the degree of reinforcement by addition of fillers depended on the filler characteristics which in turn affected the strength of the rubber:filler interaction. The two main filler characteristics that affected reinforcement were the filler particle size and surface activity. The reinforcing effect of starch was considerably lower than that of carbon black due to its large particle size and its low dispersive component of surface energy.

Establishment and Characterisation of Hevea Cell Suspension Cultures

W. Ziyun, T.D. Huang, H.S. Huang and Y.W. Hua

A simple and rapid protocol for establishment of Hevea suspension cultures is presented. H. brasiliensis ´ H. nitida suspension cultures with uniformly dispersed cells and cell aggregates were obtained after one to two months of culture. The growth kinetics study showed a typical sigmoidal profile including lag phase, log phase or exponential phase, linear phase and deceleration phase, while the doubling time was 2-5 days. Sedimented cell volume (SCV), fresh weight (FW), growth index (GI) of FW, the decrease of electrical conductivity (EC) in the medium had a very good linear correlation with dry weight (DW) or GI of DW. The optimum maintenance medium for Hevea suspension cultures was the modified MS medium supplemented with 0.2 mg/L 2,4-D, 2 mg/L NAA, 1 mg/L kinetin, 50 g/L sucrose, 0.2 g/L L-Asparagine and 0.4 g/L casein hydrolysate and coconut water 5% (v/v), in which suspension cultures were still well grown with multiplication after incubating in optimised suspension medium (OSM) for more than one year. This cell suspension cultures would be used for protoplast isolation, large-scale clonal propagation, preservation of genetic resources, genetic transformation and establishment of bioreactors in Hevea.

Properties of Kenaf Fibre Reinforced Natural Rubber Composites

Gunasunderi Raju, Ma'zam Md Said and Md Aris Ahmad

Kenaf has recently been seen as a competitive reinforcing material for conventional synthetic fibre, such as glass fibre in polymer composites. The usage of kenaf has increased due to its biodegradability and environmental compatibility. The cure characteristics and mechanical properties of kenaf bast fibre-reinforced natural rubber composites with and without bonding agent were investigated. Kenaf bast fibre composites were prepared by mixing kenaf with natural rubber (NR). The composites were vulcanised at 150°C according to their respective cure times. It was found that fibres with the smallest particle size exhibited the highest modulus at 100% (M100 ), tensile strength, and elongation at break. The values were higher in the longitudinal direction than that of in the transverse direction of fibre orientation. Increasing the fibre loading resulted in a rise in the torque value, tensile strength and hardness of the composite. The mechanical properties were further enhanced when a dry bonding system comprising resorcinol, hexamethylene tetramine and silica was used as a bonding agent in the composites. Scanning electron microscopy (SEM) micrographs confirmed that the bonding agent helped to improve interfacial strength of the fibre composites. Vulcanisates containing kenaf bast fibre exhibit better mechanical properties compared to that containing kenaf core fibre.

Epoxidised Natural Rubber-Stabilised Gold Colloids Prepared in an Organic Mixture of Toluene and 2-propanol

M. Abu Bakar, J. Ismail, C.H. Teoh, W.L. Tan and S. Ong

A direct synthesis of gold nanoparticles in a purely organic environment using 2-propanol as the reducing agent and epoxidised natural rubber (ENR-50) as the polymer stabiliser is described. Experimental parameters such as reaction temperature and concentration of gold ions were scrutinised in order to study the effect on size, morphology and dispersion of the gold nanoparticles. Preparations at temperatures £ 70°C or employing high concentrations of gold ions produced large particles of various geometrical structures with some of sponge like appearance while those prepared at ³ 80°C or at low concentrations of gold ions produced fine particles of spherical or near spherical shape. The particles were well dispersed in the ENR matrix. The formation of ENR-stabilised gold organosol was relatively fast ca. 1-3 hrs. Therefore synthesis of ENR-gold composite in organic solvent was capable of producing small sized and spherical particles when the synthesis was carried out at high temperatures and low concentration of gold ions was used.

Plasticisation of Carbon Black Filled Acrylonitrile-butadiene Rubber Using Cardanol

Mary Alexander, Beena T. Abraham and Eby Thomas Thachil

The comparative performance of cardanol, the main ingredient of cashew nut shell liquid (CSNL) for plasticising carbon black-filled acrylonitrile – butadiene rubber (NBR) is presented. The performance of dioctyl phthalate (DOP), a common plasticiser for NBR was compared with that of cardanol in terms of the cure characteristics, mechanical properties, thermal ageing properties, crosslink density and extractability. While both these plasticisers showed almost equivalent performance in respect of most properties, a clear superiority was bodytextd for cardanol in the case of extractability after varying periods of ageing at 100°C. This alludes to the resistance of cardanol-plasticised NBR to ageing and a lessened possibility of it being leached out / blooming out on prolonged use. The demonstrated usefulness of cardanol, a renewable, agro-byproduct for NBR processing is significant.

Influence of Flame Retardant Additives on the Flammability Behaviour of Natural Rubber (NR)

Dayang Habibah Abg Ismawi, J.F. Harper and A. Ansarifar

A combination of decabromodiphenyl oxide (DBBO) and antimony trioxide (Sb₂O₃) is a widely used flame retardant system for rubber compounds. In addition to cost effectiveness, thermal and mechanical performance, halogen content is responsible for its low flammability characteristics. Nevertheless, there are concerns on the corrosiveness and toxicity of smoke and other emission products generated during the combustion of rubbers utilising these materials. Fillers such as aluminium hydroxide (ATH), organoclay and zinc hydroxystannate (ZHS) have been used as alternative halogen-free flame retardants. This paper describes the effect of these flame retardants on flammability behaviour and tensile strength of natural rubber (NR). ZHS is an alternative to Sb₂O₃ because of the former’s smoke suppression properties. However, similar to Sb₂O₃, it does not have flame retarding properties on its own. ZHS loaded at 20 p.p.h.r. in combination with 40 p.p.h.r. chlorinated paraffin (CP) showed better flammability performance. Results from the National Bureau of Standard (NBS) smoke box showed that this compound gave lower smoke density compared to a similar compound with antimony trioxide in place of the ZHS. In general however, partial replacement of flame retardant (FR) additives in NR compounds by ZHS produced no synergistic improvement in fire retardant behaviour.

Adaptability Analysis of Rubber (Hevea Brasiliensis Muell.-Arg.) Clones via GGE Biplot

Yield of rubber (Hevea brasiliensis Muell.- Arg.) in Tripura, a sub-optimal area, has low and high yielding regimes. Data on overall means, low and high yielding periods for 11 years (1990 to 2001) were separately analysed via GGE biplot to judge specific adaptation of clones. Stability estimates viz., ecovalence, stability variance, s2, Huehn’s non-parametric statistics and Lin and Binn’s superiority measure were also calculated. These estimates were comparable except for Huehn’s non-parametric statistics. GGE biplot analysis was conducted under symmetrical, entry-focused and tester-focused procedures. While entry-focused scaling for overall means kept years towards a single cluster presuming that all clones were performing comparably over the years, under tester-focused scaling, the years were well spread, indicating the climates of all the years were not same. Overall genotype means were high for PB 235, RRII 203, RRIM 600, RRII 118 and RRIM 703. The symmetrical scaling of data of regime II showed 1999 and 2000 exhibiting higher principal component analysis (PCA) 1 values. Clones RRII 105, RRII 118, RRIM 703 and PB 235 were high yielders under this regime. The performance of clones was different when mean values were plotted against PCA values. While RRII 105, RRIM 703, RRIM 600 and RRII 118 were most stable under regime I, RRIM 605 had a higher stability under regime II. Under both circumstances, PB 235 and RRII 203 were high yielders. When overall means were plotted, RRII 105, RRIM 703, RRII 118 and PB 235 were bodytextd to be most stable over 11 years. Under all these years, PB 235, RRII 203 and RRIM 600 were high yielding.

In-situ Ultrasonic Enhancement of Flux During Natural Rubber Skim Latex Recovery by Ultrafiltration

S. Anitha, V. Devaraj and M. N. Zairossani

A study was conducted to investigate flux behavior during a cross-flow ultrafiltration (UF) process to concentrate natural rubber skim latex, with in-situ sonication. Tubular polyvinylidene fluoride (PVDF) membranes with 200kD molecular weight cut-off (MWCO) were selected for this study. Experiments were conducted to study the effect of skim latex preservation level with and without sonication at a transmembrane pressure (TMP) of 2 bar. Results showed the permeate flux remained constant with sonication, and a decline in flux was observed without sonication. This study was also able to determine the ideal preservation level where the in-situ sonication improved the permeate flux without affecting the stability of the feed. This ideal preservation becomes the optimum preservation level required for skim latex recovery by ultrafiltration with in-situ sonication. The study showed that the flux with an intermittent ultrasonic application with sonication ratio of 1 was comparable to that for continuous sonication.

Biobased Surfactant as a Colloid Stabiliser in 50% Zinc Dibutyldithiocarbamate Dispersion

Manroshan, S., Amir-Hashim M.Y. and Booten, K.

Recent development in surfactant technology has made it possible to produce surfactants based on plant extracts. A new material based on polyfructose extracted from roots of chicory was used as a stabiliser in 50% ZDBC dispersion and the properties were evaluated and compared with other systems. Although results of the light scattering technique did not show much difference in the particle size, a marked difference in the particle shape was observed when Transmission Electron Microscopy (TEM) was used. TEM micrographs of ammonium caseinate stabilised dispersion showed formation of uneven, saw like shaped particles with a wide particle size distribution whereas polyfructose stabilised dispersion showed formation of very even, circular shaped particles with a narrow particle size distribution. Viscosity results of polyfructose stabilised dispersion showed a pseudoplastic behavior similar to normal dispersion systems. Although a hard sediment formed with ammonium caseinate stabilised dispersion, no caking was observed in the polyfructose stabilised dispersion.

A Study on the Use of Linseed Oil as Plasticiser in Natural Rubber Compounds

Raju, P., Nandanan, V. and Sunil, K.N. Kutty

Plasticisers such as minerals oils and synthetic oils were used in rubber compounds for improved processability, filler uptake and to reduce cost. Mechanical properties and thermal degradation of natural rubber compounds containing linseed oil had been studied to evaluate its suitability as a plasticiser. Naphthenic oil was used as a reference plasticiser. Tear strength, modulus, resilience and compression set of mixes containing linseed oil were improved compared with those containing naphthenic oil. Thermal studies showed an increase of 7°C in the temperature of initiation of degradation and an increase of 4°C in temperature at which peak rate of degradation occurred. The peak rate of degradation was comparable to that of the reference compound.

Improvement of Productivity of Rubber Trees in Smallholding by the Introduction of Upward Tapping in the South-East of Côte d’Ivoire

S. Obouayeba, E.F. Soumahin, A.M.C. Boko, G.B. Dea, K. Dian and Y.M. Gnagne

In smallholdings nine to twelve years of downward tapping was carried out on virgin barks followed by downward tapping on renewed barks, a total period of exploitation not exceeding 20 years. However in industrial plantations, downward and upward tapping of rubber trees resulted up to 36 years of exploitation. The study was conducted to assess the feasibility of upward tapping in smallholding conditions in four locations. Downward tapping on renewed barks (½ S d/3 6d/7 ET 2.5% Pa 1(1) 10/y(m)) was compared to upward tapping on virgin barks: ¼ S ↑ d/3 6d/7 ET 5% Pa 1(1) 10/y(m) and ½ S ↑ d/6 6d/7 ET 2.5% Pa 2(1) 10/ y(m). The performance of these tapping systems were assessed for rubber production, vegetative growth, physiological profile and the tapping panel dryness (TPD) susceptibility of rubber trees. The productivity of downward tapping was satisfactory, but significantly lower than that of upward tapping systems. In fact, compared to downward tapping, upward tapping increased the rubber tree productivity by 34% and 36% for the quarter cut and half spiral cut respectively. Generally, the physiological profile of all tested systems were good, with little occurrence of TPD. Thus, in smallholdings, nine years of downward tapping followed by upward tapping, especially the upward quarter spiral, turned out to be the best tapping system in Côte d'Ivoire.

Static Modelling Approaches to Predict Growth (Girth) of Hevea Brasiliensis as Tools for Extension Activities in Malaysia

Yahya Abd Karim

Rubber (Hevea brasiliensis) is one of the most important agricultural industries in Malaysia. Its production provides the livelihood of large segments of the Malaysian population consisting of smallholders, estate workers and their families. Being a complex agricultural system, a model would help to organise available information or knowledge in order to identify gaps and direct future research in rubber based systems. It may also help in the process of dissemination of the technology to farmers as well as rubber planters. Hence, an attempt is made to develop a model to predict the growth of rubber under different planting densities, climate, clones and management. Validation results show that the model is able to simulate growth (girth) from different range of environment and rubber clones from Malaysia with the modelling efficiency (EF) of 0.87.

Electrically Conductive Epoxidised Natural Rubber-polyaniline dodecylbenzenesulfonate Blends Prepared by Solution Mixing

K.C. Yong, P.J.S. Foot, H. Morgan, S. Cook, A.J. Tinker and Md Aris Ahmad

Epoxidised natural rubber (ENR) and polyaniline dodecylbenzenesulfonate (PAni.DBSA) were predicted to be miscible, on the basis of simple solubility parameter calculations. Blends with electrical conductivities up to
10^–3S.cm^–1 were prepared for the first time by solution mixing. The lowest estimated electrical conductivity percolation threshold for these blends was 2.9 wt% or 2.5 volume% of added PAni.DBSA. NMR spectroscopy showed that the epoxide level of the host, ENR decreased with increasing PAni.DBSA loading (due to the sensitive nature of ENR to acidic conditions). This decrease was a direct sign of ring opening in the ENR molecular structure. The ring opening of ENR was also identified indirectly through the increasing absorption value of FT-IR peaks in the region of 3390 cm^–1 and through the trends observed by differential scanning calorimetry (DSC). Electrical conductivity measurement and morphology studies [by optical microscopy and transmission electron microscopy (TEM)] revealed that the ring opening did not affect the electrical properties of the blends.

Synthesis of Polyisoprene-Grafted Silicas by Free Radical Photopolymerisation of Isoprene Initiated from Silica Surface

Daniel Derouet and Chi Nhan Ha Thuc

Synthetic silicas are used increasingly in tyre tread compounds. However, their use as fillers for hydrophobic rubbers (synthetic polydienes, natural rubber) is questionable unless a silanecoupling agent is introduced to bind the silica to the rubbers and to prevent it from interfering with the reaction mechanism of the sulphur-cure system. In order to improve the interphase strengths between silica and hydrophobic rubber, as well as to suppress the effects of silanol groups on sulphur-cured systems, polyisoprene-grafted silicas were synthesised. The principle of the synthesis was based on the “living” radical photopolymerisation initiated from the silica surface. For that, a two-step procedure was adopted. First, silica particles were functionalised with N,N-diethyldithiocarbamate iniferter groups, by using a SN2 substitution of chlorine atoms previously bound on silica surface. Following this, photopolymerisation of isoprene was carried out from the N,N-diethyldithiocarbamate iniferter groups and the polymerisation progress was simultaneously followed by HPLC and NMR. Functionalised silicas and polyisoprene-grafted silicas were characterised by solid-state ¹³C and ²⁹Si CP/MAS NMR.

Modification of Deproteinised Natural Rubber by Graft-copolymerisation of Methyl Methacrylate

Nurul Hayati Yusof, Seiichi Kawahara and Ma'zam Md Said

Natural Rubber (NR) latex was deproteinised by incubation with urea in the presence of sodium dodecyl sulfate (SDS). Urea deproteinised natural rubber (U-DPNR) latex was graft-copolymerised with Methyl Methacrylate (MMA) at a monomer feed of 5, 10, 15 and 20 wt % on rubber. The monomer content, monomer conversion and grafting efficiency of the copolymerisation reaction were determined. The resulting graft copolymers were characterised by FT-IR spectroscopy and morphology observed using a transmission electron microscope (TEM). The monomer content, conversion and grafting efficiency of NR-graft-PMMA, U-DPNR-graft-PMMA and E-DPNR-graft-PMMA were compared as well. The results showed that, MMA feed of 15 wt % on rubber, initiator concentration of 6.6 X 10^–5 mol/g-rubber and reaction temperature at 30ºC were found to be suitable conditions to obtain high MMA content, high conversion and high grafting efficiency. The highest grafting efficiency was about 80% at 15 wt % on rubber feed of MMA for U-DPNR-graft-PMMA and E-DPNR-graft-PMMA.

Amidino Phenyl Thiourea as a Secondary Accelerator for the Vulcanisation of Natural Rubber - Polychloroprene Blends

A.P. Susamma, A.M. Mini and A.P. Kuriakose

All rubbers have shortcomings in one or more properties. There are therefore technical reasons for blending different elastomers as it makes it possible to obtain the desired compromise in properties. Natural rubber (NR) is a versatile raw material on account of its unique chemical and physical properties. Polychloroprene rubber (CR) is known for its good flame resistance, resistance to oil and ozone but is more costly. A blend of NR and CR will make a desirable compromise in the individual properties. Thiourea (TU) and its derivatives are widely used in CR and NR latex vulcanisation. Ethylene thiourea (NA22), the conventional accelerator used in CR vulcanisation is reported to be toxic in nature.

We synthesised a thiourea derivative viz. N-amidino-N’-phenyl thiourea (APT) which is a non-toxic chemical and attempted the use of APT, as a secondary accelerator for the vulcanisation of NR-CR blends. Systems with varying concentrations of APT along with tetramethyl thiuram disulphide (TMTD) and other compounding ingredients were prepared in unfilled and filled systems. TMTD-TU and TMTD-NA22 binary combinations were taken as controls. Different cure characteristics and various physical properties of the experimental and control systems were investigated.

Studies showed that APT could be advantageously used as a secondary accelerator along with TMTD. The different vulcanisates prepared with this non-toxic accelerator showed better/ comparable tensile and other physical properties compared with the reference formulations.

The Effect of Scragging Strain on the Dynamic Mechanical Properties of Filled Rubber

J. Kingston

A series of tests have been carried out on two example filled natural rubber (NR) and styrenebutadiene rubber (SBR) compounds in which the rubbers were scragged to a series of increasing shear strains and the effect of this on the dynamic properties at the lower strains were measured. After a long period, the tests were repeated to measure the recovery in the materials. It was found that increasing the scragging strain caused the rubber stiffness at lower strains to fall continuously, with no sign that it would reach a constant value and that while there was some recovery over time, it is not thought that the rubber would ever recover its initial stiffness.

Assessing Effects of Mixing Parameters on Interphases in Blends of Dissimilar Rubbers Using M-TDSC

S. Ostad-Movahed, A. Ansarifar and M. Song

A modulated-temperature differential scanning calorimetry (M-TDSC) method was used to calculate the mass fraction of interphase and determine its composition in some SBR/BR and NR/BR blends. Effects of mixing time, mixing temperature, rotor speed, silica nanofiller, and mass fraction of pure rubbers on the mass fraction and composition of the interphase in the blends were investigated. It emerged that increases in mixing time and temperature, incorporation of the filler in the rubbers, and changes in the blend composition affected the properties of the interphase. Furthermore, M-TDSC was found to be a useful technique for studying interphases in blends of dissimilar as well as partially miscible rubbers and estimating their compositions. The measurements were also sensitive to the mixing conditions, rubber composition and silica filler in the rubbers

An Assessment of the Endotoxin Contents of Natural Rubber Latex Medical Gloves

A. Ikram and M.Y. Amir-Hashim

The endotoxin levels of Malaysian Natural Rubber (NR) latex medical gloves were determined by a kinetic turbidimetric Limulus Amoebocyte Lysate (LAL) assay. The samples evaluated were 39 pairs of sterilised surgical gloves from 10 commercially-available brands and 21 pairs of non-sterilised examination gloves from 8 brands. The endotoxin concentrations ranged from 3.2 to 114.1 EU/glove pair for surgical gloves and from < 8.4 to 9,632 EU/glove pair for the examination gloves. In the case of surgical gloves, 72% had endotoxin activity below the specified FDA standard of 20 EU/device, while in the case of the non-sterilised examination gloves, only 38% had values below the specified level. There was no correlation between endotoxin concentrations and the presence of glove powders in the present study.

Blends of Sulphur Prevulcanised Natural Rubber Latex and 2-(Dimethylamino) ethyl methacrylate-grafted latex for Improved Static Dissipative Properties

K. Vivayganathan, M. Asrul and M.Y. Amir-Hashim

Improvement in static dissipative properties of cast films prepared from blends of natural rubber latex and 2-(Dimethylamino) ethyl methacrylate (DMAEMA)-grafted NR latex was demonstrated. The relative changes in surface properties of the cast films prepared from latex blends were investigated using surface resistivity measurements, contact angle and Fourier Transform Infrared-Attenuated Total Reflectance (FTIR-ATR). The results indicated that static dissipative properties and surface related properties, such as surface energy and wettability could be enhanced provided that an appropriate blend ratio of the DMAEMA-grafted NR latex and an effective amount of monomer was used in the preparation of the grafted NR latex. Differences in the properties of film surfaces, the air-facing and former-facing surfaces are also described.

Relationship between Rate of Laticifer Differentiation, Number of Laticifer Rows and Rubber Yield among 1981 IRRDB Germplasm Collections of Hevea brasiliensis

Jun-Hong Yu, Xia Zeng, Shu-Guang Yang, Hua-Sun Huang and Wei-Min Tian

Early selection based on parameters related to yield is important in the Hevea breeding program. In an attempt to characterise such parameters, we investigated the variation in TNLD (time needed for laticifer differentiation) of the 1981 IRRDB germplasm collections by means of an experimental system for the induction of secondary laticifer differentiation in relation to RLCL (ratio of laticifer rows to the cell layers of the functional phloem) and rubber yield of the corresponding mature germplasm collections. The results demonstrated that TNLD varied among the 63 germplasm collections examined and was correlated to RLCL (r=0.5795, highly significant) and rubber yield (r=0.4558, significant level) of the mature plants. TNLD is expected to be a parameter candidate for early selection, which is better than the leaflet latex method in that it is related to the secondary laticifer differentiation and also better than test-tapping yield method in that early selection can be carried out with one-year-old epicormic shoot in the nursery. Large scale experiment is necessary to confirm this conclusion.

Latex as Yield may be Better than Rubber Yield in Juvenile Screening for Selection in Rubber (Hevea brasiliensis Muell. Arg.)

T.R. Chandrasekhar and T. Gireesh

The usefulness of collecting latex as yield in test-tapping of Hevea seedlings for juvenile selection was assessed. Latex volume was recorded as yield instead of dry rubber. Data were recorded from each tapping for each of the test-tapped seedlings using graduated microcentrifuge/ centrifuge tubes. Dry rubber content (DRC) of top selections was determined for calculation of rubber yield. Mean range in latex yields among the tapped seedlings was 0.07 mL t^–1 t^–1 to 16.46 mL t^–1 t^–1 (mL per tree per tapping). Mean rubber yields in the top 20% selections from 10 tappings varied from 4.25 g t^–1 10t^–1 to 41.37 g t^–1 10t^–1 (grams per tree per 10 tappings). DRC among the top 20% selections varied from 14.3% to 38%. It was concluded that in juvenile selection of Hevea seedlings, yields determined as latex volume could result in more accurate yield recordings. Furthermore, the latex could be used to determine rubber content for eliminating the very low DRC seedlings. Information on biochemical and physiological determinants of yield could also be extracted in an effort to enhance probability of potential selections.

The Role of Zinc Compound Residues in the Environmental Degradation of Prevulcanised Natural Rubber Latex Films

A. Ikram, K.P. Ng, M.Y. Amir Hashim and M.S. Fauzi

The effect of residual diethyldithiocarbamate on the environmental degradation of prevulcanised natural rubber latex films was studied in the presence of zinc oxide and a conventional phenolic antioxidant. The films were buried in a clayey soil at 40% field capacity and retrieved after 24 and 48 weeks. The overall degradation was significantly greater for films without zinc oxide and without Wingstay L^®, as well as for films prepared at longer vulcanisation process times. Films prepared with zinc oxide and Wingstay L^®showed generally smooth surfaces after 24 weeks, compared to films prepared without zinc oxide or Wingstay L^®that had cracks and voids across the surfaces. The concentrations of residual dithiocarbamates remaining could offer an explanation as to why some of the film pieces were slow to degrade, despite the higher degree of crosslinking formed.

Ballistic Response of Natural Rubber Latex Coated and Uncoated Fabric Systems

Mohd Rozi Ahmad, Wan Yunus Wan Ahmad, Azemi Samsuri and Jamil Salleh

The intrinsic properties of natural rubber latex (NRL) such as excellent strength, adhesion and flexibility make it very suitable for coating on textile fabrics. In this study, high strength fabrics were coated with NRL and assembled with uncoated fabrics into several fabric systems. The fabric systems were shot with 9 mm bullets at 367 ± 9 m/s to assess the blunt trauma performances. The results showed that both the 18-layer and 21-layer uncoated fabric systems failed the blunt trauma test. However, fabric systems with NRL coated fabric layers gave lower blunt trauma of between 25 mm – 32 mm indentation depths. The modes of failure after the ballistic impact were believed to be closely related with friction among the yarns in the NRL coated fabrics. The relative measure of friction was evaluated through the yarn pull-out strength and puncture resistance tests on the uncoated and NRL coated fabrics. Higher frictional effects were evident from the NRL coated fabrics in comparison with the uncoated fabrics.

Changes in the Micro-Structure and Tensile Properties of Peroxide Prevulcanised Natural Rubber Latex Films during Thermal Oxidative Ageing

D. Dazylah, M.S. Ma'zam and M.Y. Amir Hashim

The effect of ageing on tensile properties and micro-structure of peroxide prevulcanised natural rubber latex (PPVL) films (with and without antioxidant Irganox 1520^®) was studied. The modulus of peroxide prevulcanisates containing Irganox 1520^®generally decreased with increasing ageing time at 100ºC. However, there appeared a cyclical increase and decrease of modulus at about one hour intervals over the 0-12 hours ageing time studied. FTIR analysis of films showed evidence of oxidative reaction in aged films whereby the relevant FTIR peaks of natural rubber, C=CH₂at 845 cm^-1and polyisoprene peak at 2958 cm^-1, 1576 cm^-1, 1470 cm^-1, 1126 cm^-1and 845 cm^-1, weakened gradually with ageing time. The observation was supported by an NMR study which showed appearance of extra peaks in the spectra, identified as belonging to the relevant degradation products. As the ageing process progressed, the NMR analysis showed a film with a minimum line broadening measure the hydrogen percentage calculated from NMR (H%), indicating a high polymer chain mobility, corresponding to high tensile strength with a modulus at 300 (M300) value of about 0.85 MPa. Transmission Electron Micrographs (TEMs) of unaged peroxide prevulcanised natural rubber latex films showed a mesh of stained network surrounding white domains, whilst aged films tended to show a more distinct staining over the entire surface of the particles. However, this phenomenon was not observed in films protected by Irganox 1520^®antioxidant.

Electrophoretic Characterisation of Hevein

H.Y. Yeang, S.A.M. Arif, Y.H. Loke, N.P. Chew and S.M. Mohsin

Although the latex protein, hevein, has received much research interest, its analysis by conventional SDS-polyacrylamide gel electrophoresis has been problematic. Hevein does not migrate at a rate that commensurates with its molecular weight and it does not always produce a sharp band on a polyacrylamide gel. To compound this problem, hevein is difficult to stain because it has a tendency to diffuse out of the gel during the de-staining process. Moreover, hevein Western blot is difficult to perform because, as a small protein, it easily passes through a nitrocellulose membrane during electro-transfer. Using the tricine SDS-polyacrylamide gel electrophoresis system that is optimised for small proteins and peptides, hevein migrated in the gel at a rate consistent with its molecular weight of 4.7 kDa, although the migration rate was significantly reduced under non-reducing conditions. Addition of phosphotungstic acid to the Coomassie blue stain fixed hevein and prevented its loss by diffusion out of the gel. Hevein could be effectively Western blotted on to the PVDF membrane and fixed with glutaraldehyde, after which, the protein was detectable using anti-hevein antibody. Although hevein is an unglycosylated protein, it was found to be associated with carbohydrate, probably through its lectin property in binding carbohydrate.

Proteins Bound to Rubber Particles and Sensitivity to the Tapping Panel Dryness in Hevea Brasiliensis

K.M. Okoma, K. Dian, A. Sangare and S. Ake

The rubber tree, Hevea Brasiliensis, is an Euphorbiaceous species from the Amazonian basin cultivated for latex production. The physiological syndrome, tapping panel dryness, which stops latex flow, affects natural rubber production. Sensitivity of Hevea brasiliensis to this syndrome depends on the clone. To understand the molecular level of this sensitivity difference, the polypeptides of rubber particles were analysed in different clones using two-dimensional electrophoresis. The present study highlighted a relation between the clonal sensitivity and the variation of the accumulation of six acidic polypeptides. These polypeptides correspond probably to isoelectric variants of two, 14.5 kDa and 26.0 kDa major proteins. Five among these polypeptides (P2, P4, P5, P8 and P9) were expressed abundantly in the most sensitive clones while the latter (P3) presented a very weak expression among these clones. These polypeptides that fluctuate according to the sensitivity of the clones can be used as markers for tapping panel dryness sensitivity and serve as tools for precocious selection of tolerant clones.

An Investigation, using Finite Element Analysis, of the Effect of Swaging on Stiffnesses of Rubber Bushes

Julia Gough

common practice in the manufacture of cylindrical rubber bushes is to apply a radial contraction to the outer sleeve or a radial expansion to the inner sleeve after moulding – a process known as swaging. This relieves tensile stresses which arise due to differential thermal contraction of the rubber and the sleeves and, if a sufficiently large swaging strain is applied, this compresses the bush which improves its fatigue life. A Finite Element Analysis (FEA) investigation of the effect of swaging on the small strain stiffnesses of some representative, initially stress-free, bushes was carried out. The axial and torsional stiffnesses reduce slightly as the swaging strain increases, contrary to the effect of dimensional changes alone, whereas the radial and tilting stiffnesses increase as predicted from dimensional changes. The reduction in the axial and tilting stiffness was attributed to the effect of compressive stresses introduced by swaging. An approximate estimate of the bush stiffnesses may be obtained from existing theoretical formulae if the original dimensions are used in the calculation of the axial and torsional stiffness and the swaged dimensions are used in the calculation of radial and tilting stiffness.

Effect of Rubber Chemicals on the Surface Free Energy of NR and NR–SBR Rubber Blends

A. Ansarifar, G.W. Critchlow, R. Guo, R.J. Ellis, S.P. Kirtley and B. Seymour

Rubber chemicals are added to raw rubbers to improve their mechanical, environmental and processing properties. These chemicals often migrate to the surface and alter its free energy and ultimately its contact adhesion properties. In this study, some industrially important rubber chemicals were mixed with natural rubber and a blend of natural rubber and styrene-butadiene rubber, and the contact angle measured using drops of water and diiodomethane on the rubber surface. The data from these measurements were subsequently used to calculate the surface free energy of the rubbers. Some of the chemicals had a detrimental effect on the surface free energy of the rubbers. This was also confirmed by static secondary ion mass spectrometry, which indicated a substantial surface modification of the rubbers.

The Effect of Hydrophobically Modified Inulin on the Properties of Natural Rubber Latex Concentrates

Manroshan, S., Amir-Hashim M.Y. and Booten, K.

Natural rubber (NR) latex is a dispersion of rubber particles in an aqueous phase. By virtue of the naturally occurring surface active materials surrounding each particle, the rubber particles are therefore prevented from coalescing together. However, microbe activities in non-preserved latex may destroy the surface active properties of these natural materials. Hence, NR latex is typically preserved with ammonia to maintain its alkalinity of pH 10 and above. In this study, a biobased surfactant was added to the deammoniated natural rubber latex concentrate to enhance the stability of the latex. The hydrophobically modified polyfructose (Inutec^®SP1), thought to be similar to some of the naturally occurring surfactants on the rubber was incorporated into the latex at different ratios and its effect on some of the important properties of the latex were investigated. The addition of 0.25 p.h.r. of the surfactant increased the mechanical stability time (MST) of the latex concentrates by 500 s. Up to six weeks of storage, not much change was observed in the viscosity although the volatile fatty acid number (VFA No.) of the concentrates increased slightly. However, as the pH reduced further below 10, the effectiveness of the surfactant decreased. The MST reduced whereas the VFA No. and viscosity of the latex concentrates increased.

Preparation and Properties of Low Protein NR Latex using Stabilised Liquid Papain

K. Mariamma George, G. Rajammal, Geethakumary Amma and N.M. Mathew

An attempt was made to produce low protein natural rubber (NR) latex suitable for making surgical gloves with low levels of extractable protein content in a single centrifuging process. Stabilised liquid papain from papaya plant (Carica papaya) at two dosages viz., 0.25 p.h.r. and 0.5 p.h.r. was used for latex deproteinization. A process was standardised for the deproteinization of NR latex by conducting laboratory, pilot plant and plant trials. Processing and technological properties of these low protein latices were assessed. Surgical gloves were prepared in an automatic dipping plant under different conditions of leaching. The extractable protein content and physical properties of the gloves were determined. The results showed that low protein latex prepared using 0.25 p.h.r. of liquid papain produced gloves of extractable protein (EP) content less than 50 µg/dm². Antigenic protein content obtained for the samples were also less than 10 µg/dm². Continuous production of surgical gloves from this latex by on line wet gel and post-cure leaching was found to give low protein gloves with good physical properties. The effect of slurry dip on protein content could be controlled more effectively using this latex as the amount of EP content in the original latex was low and hence the amount of proteins leaching into the slurry would also be less.

Storage behaviour of this latex and its vulcanizates was studied in comparison to normal centrifuged latex (cenex). Changes in raw latex properties such as volatile fatty acids, mechanical stability time, potassium hydroxide number and zinc oxide viscosity were comparable for both the latices. But the change in EP content for low protein latex vulcanizates was from 68 to 88 µg/dm² where as for the cenex, the increase was from 150 to 368 µg/dm². Physical properties of latex film vulcanizates were more or less unaffected by storage.

Estimating Growth (Girth), Yield and Above-ground Biomass of Hevea brasiliensis: Validation of the WaNuLCAS Model

Yahya Abd Karim

An effort was made to validate the WaNuLCAS (Water, Nutrients, and Light Capture in Agroforestry Systems) model in order to test its efficiency to predict growth (girth), yield, above-ground biomass as well as leaves and twigs biomass of Hevea brasiliensis. The model was run for 20 years, representing the economic life span of rubber. The output of the simulation was compared with the observed data for validation purposes. Results from the statistical analysis showed that the model was able to simulate girth, rubber production, above-ground biomass and leaves and twigs biomass with efficiencies (EF) of 0.83, 0.97, 0.70 and -0.15 respectively. EF measures the accuracy of the model in performing simulation as compared to experimental data. The optimum value of EF is 1. The negative value for leaves and twigs biomass indicated that the observed mean value was better than the predicted value.

Non-linear Viscoelastic Characterisation of Natural Rubber Gum through Large Amplitude Harmonic Experiments

J.L. Leblanc

Standard dynamic testing requires strict proportionality between stress and strain for valid resolution of the (measured) complex modulus into its elastic and viscous components. Thus, it is restricted to material and/or testing conditions that correspond to linear viscoelastic behaviour; otherwise ‘apparent’ results are obtained, with therefore limited meaning, if any, in terms of material science. Correct non-linear harmonic testing under large amplitude oscillatory strain is however feasible today using purposely modified torsional rheometers to capture full strain and torque signals which are appropriately treated in order to extract pertinent and useful information. Harmonic techniques that require signal processing to convert the response of the material in the time domain into a material property in the frequency domain are usually referred to as Fourier Transform (FT) rheometry, i.e. a development of the so-called dynamic (or harmonic) testing to investigate both the linear and the non-linear viscoelastic domains of polymer materials. It consists essentially of considering the frequency spectrum of the torque signal obtained when submitting a material to high strain. Contrary to standard dynamic testing, no validity condition is needed for FT rheometry. In principle, any dynamic rheometer can conveniently be modified for FT testing, but implementation of the technique on a commercial torsional rheometer, operating with a closed test cavity, proved to give repeatable and reliable results on a number of polymer systems. A series of natural rubber gum samples were tested in order to further illustrate the capabilities of the technique.

Modified Natural Rubber Latex via in situ Polymerization of Lignin Related Compound in thePresence of Lignosulfonate Salt

Asrul, M.*#, Kawahara, S.** and Amir-Hashim M.Y.*

Modified natural rubber latex having relatively high resistance to thermo-oxidative ageing was prepared from in situ polymerization of lignin related compounds in the presence of styrene and lignosulfonate salt. High tensile strength retention of the modified rubber latex films on ageing were shown to be attainable by addition of appropriate lignin related compounds in the modification reaction. Molecular weight and gel content determination indicated that the simultaneous effect of rubber degradation as a side effect of modification was negligible in the batches comprising ferulic acid and coumaric acid. The viability of the modified rubber in the use as technological rubber latex products which requires higher resistance to oxidative ageing was assessed.

Deciphering Rubber Particle Destabilisation by Hevea Bark Extract

E. Sunderasan*,#, S.K. Ling**, Siti Arija Mad Arif* And H.Y. Yeang*

Filtration of Hevea bark extract through Millipore spin cartridge (molecular weight cut-off at 100 kDa) yielded a brown slurry retentate and a clear liquid in the flow through fraction. The retentate was then separated by preparative reverse phase high performance liquid chromatography (HPLC) and the brown bark pigment was recovered in a broad peak. The whole bark extract, the spin cartridge retentate, and the brown HPLC fraction, readily destabilised the high density rubber particles (Zone 2 and Zone 3) suspensions but only negligible destabilising activity was observed with the clear spin cartridge flow through fraction. Destabilisation of Zone 1 rubber particles by whole bark extract, spin cartridge retentate, and the brown HPLC fraction occurred only when C-serum was substituted with Zone 3 rubber particles in the reaction mixture. Polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG), which are known to bind phenolic compounds/tannins, effectively precipitated the brown pigment of the bark extract. The clear supernatant recovered from the PVP and PEG treated bark extract also failed to induce rubber particle destabilisation. The presence of substantial levels of phenolics in the bark extract was confirmed by a modified Folin-Ciocalteau assay. Analyses on thin layer chromatography indicated that the brown pigment of the bark extract consists of highly polymeric condensed tannins. Analytical reverse phase HPLC revealed that three different peaks with UV spectra similar to those of tannins, and one peak that resembles phenolics could be separated from the bark extract, and its spin cartridge retentate.

Biochemical Mechanisms Associated with Low Yield During Stress in Hevea Clone RRII 105

S. Sreelatha*#, Sheela P. Simon*, G. Muraleedhara Kurup** and K.R. Vijayakumar***

Variation in yield, latex physiological parameters, enzymes involved in carbohydrate and thiol metabolism, antioxidant enzymes and enzymes related to cessation of latex flow were studied in clone RRII 105 during peak yielding and low yielding stress (summer) seasons. A significant reduction in dry rubber yield was observed during the stress period compared to the peak yielding season. Latex flow characteristics, metabolism of carbohydrate and thiols, and activities of antioxidant enzymes showed significant variation between seasons. The present study revealed that even though thiol metabolism is activated during stress, decline in cytosolic invertase, superoxide dismutase, catalase and B-serum N-acetyl glucosaminidase activity lead to lower yield during the stress period in clone RRII 105. The significance of these physiological and biochemical parameters are discussed in relation to yield obtained during the peak yielding and stress seasons.

Tillage Effects on Growth Performance of Hevea Seedling Rootstock and some Fertility Area of Nigeria

I.K. Okore*#, F.A. Akpobome*, H. Tijani-Eniola** and E.A. Oghide*

Vast amount of resources are devoted annually for the establishment of Hevea seedling rootstock nursery through conventional tillage, despite global disposition of conservative tillage. A field experiment was carried out to evaluate the effect of tillage methods, namely, plough+harrow, plough only, bed and without tillage on the growth performance of Hevea brasiliensis (natural rubber) seedling rootstock and the nutrient status of sandy acid soil in a forest area (Benin) of Nigeria for two years. In both cropping years (2003/2004 and 2004/2005) , the effect of tillage methods on seedling height and stem girth did not differ significantly (P³0.05). However, seedling dry matter and budding success (69.8 g/tree and 78% on the average, respectively) were significantly higher in the ploughed plots. The plots with no tillage, followed by raised seedbed treatments, had significantly higher values of organic C, available P and exchangeable bases with low levels of Al³⁺and H⁺at 0 cm ¾ 15 cm depth. Having recorded no significant difference in crop performance between the nil-tillage and plough+harrow plots, but higher soil nutrient levels in the treatments without tillage for two years; it could be predicted that land preparation without tillage, in addition to ploughing only or raised seed-bed was a better alternative to plough+harrow which often caused soil degradation in the sandy acid soil of high rainfall areas.

SHORT COMMUNICATION Hev b 11, a Peculiar Class I Chitinase?

J.J. Beintema*#

The recently identified rubber allergen Hev b 11, which is a class I chitinase, may be a cytosolic (C-serum) protein. This is a rather unique feature, as all other known plant class I chitinases are vacuolar proteins.

A Study on the Use of Coconut Oil as Plasticiser in Natural Rubber Compound

Raju, P., Nandanan, V. and Sunil, K.N. Kutty

Mechanical properties and thermal degradation characteristics of natural rubber compounds containing coconut oil were compared with that of a control compound containing naphthenic oil. Cure time was marginally lower in the case of coconut oil mixes, probably due to the presence of free fatty acids. Tensile strength, tear strength, resilience and abrasion resistance were better than the naphthenic oil-based compounds. Compression set and hardness were marginally inferior. The coconut oil mixes had a crosslink density comparable to that of the reference compound. Thermal studies showed that the temperature of initiation of degradation was increased by 10ºC and the temperature at which the peak rate of degradation occured was increased by 7ºC. The peak rate of degradation was comparable to the control compound.

Measurement of Dry Rubber Content of Natural Rubber Latex with a Capacitive Transducer

R. Reji Kumar, S. Najamul Hussain and J. Philip

A new method to determine the dry rubber content (DRC) of natural rubber latex using a capacitive transducer is presented. The capacitance of a capacitor is directly proportional to the area of the plates, permittivity of the medium and inversely proportional to the separation between the plates. If the area of the plates and the separation between them are kept constant, the capacitance is directly proportional to the permittivity of the medium. Based on this physical principle, a capacitive transducer was specially designed and fabricated. The capacitance of the capacitor with latex samples as the dielectric was measured with a high impedance LCR meter. Simultaneously, the DRC of the same latex samples was determined following standard laboratory procedures. Statistical analysis of the results showed that there was a good correlation between the capacitance with Hevea latex as the dielectric and the corresponding DRC values. Related parameters such as dissipation factor, electrical resistivity, impedance and susceptibility were found to be proportional to the DRC values of latex.

Status of Macro-elements in Latex, Bark and Leaf of Clone RRIM 901, Panel BO-1, in Relation to Gaseous Stimulation

Mohd Akbar Md Said and Mohd Fauzi Ramlan

The effect of different methods of latex extraction (T) and stimulation (S) on the status of nutrient present in the latex, bark and leaf of clone RRIM 901, Panel BO-1 was studied to establish a relationship between the status of nutrient in tissue and tree productivity. The results showed no consistent pattern on the influence of the interaction effect of T X S on the drainage of elements from the latex and removal of nutrient from the bark. The influence of T X S interaction on N and Mg was observed both in the latex and the bark, while for P and K, the influence was confined solely in the latex or the bark. The study indicated that nutritional stress possibly caused the declining yield response as obtained from gaseous stimulation on young Hevea trees of clone RRIM 901, Panel BO-1. Therefore, to achieve sustainable crop production, it is essential to have a balanced situation between the amount of crop harvested and the ability of the tree to replenish, not only the crop harvested but also the amount of elements lost in the latex and bark after completion of tapping.

Impact of Conservation Pits on Growth and Yield of Mature Rubber

Sherin George, Jacob John, Phebe Joseph, Annie Philip and K.I. Punnoose

Runoff and erosion substantially and seriously limit crop production in a tropical country like India. Appropriate runoff management techniques that enhance water conservation and reduce erosion to acceptable rates minimise these effects. The effect of conservation pits on soil moisture conservation and growth and yield of rubber was evaluated in a field experiment conducted from 1998 to 2005 in a mature rubber plantation in the central region of the traditional rubber growing tract in India. The treatments comprised conservation pits taken at the rate of 100, 150, 200 and 250 ha^–1and a control without pits. The experimental field was well drained with an average gradient of 17% – 22%. Growth and yield of rubber were significantly influenced by the presence of pits. Yield of rubber was enhanced by 15% in the plots with 250 pits ha^–1. Soil moisture storage estimated at depths of 10, 20, 30, 40, 60 and 100 cm, was substantially higher where pits were at the rate of 250 ha^–1, indicating the contribution of pits towards ground water recharge. The presence of pits positively influenced the leaf water potential. The quantity of soil conserved in the pits ranged from 4.58 t ha^–1– 10.42 t ha^–1as the number of pits increased from 100 to 250. The quantity of nutrient conserved ranged from 12–29, 6–13 and 27–62 kg ha^–1of N, P and K respectively. The proposed field water harvesting technique was proved to be quite useful in the conservation of soil and water in rubber.

Rubber Seed Oil for Partial Substitution of Mineral Oil Used as Carrier for Copper Fungicide in the Management of Abnormal Leaf Fall Disease of Rubber

C.K. Jacob, P. Srinivas, E.E. Prem, M.J. Manju, S.K. Mushrif and S.P. Idicula

Rubber seed oil (RSO) was evaluated for its potential use in oil-based spray formulations against abnormal leaf fall disease of rubber (Hevea brasiliensis) which could influence the economics of disease management. A mixture of RSO and mineral spray oil (SO) in a proportion of 1:2 was assessed as a carrier for the fungicide copper oxychloride (COC), in comparison with SO alone. The scope for reducing the dosage of COC, when RSO and SO were mixed (1:2 proportion) for spraying against abnormal leaf fall disease, was investigated in field trials in two endemic locations over six years. Results indicated that the use of RSO for partial substitution of SO was promising and resulted in similar disease control as provided by the use of SO. Lower dosage (6 kg/ha) of COC was found to be comparable to the recommended dosage of COC (8 kg/ha) when RSO + SO was used as carrier. RSO had no phytotoxic effect on the rubber leaves either alone or in combination with spray oil. Reduction in cost was evident when a combination of partial complementation with RSO and a reduced dosage of COC was applied.

Comparative Study of the Epoxidation of Natural and Synthetic Rubber Latices

D Derouet, S Mulder-Houdayer and J-C Brosse

Epoxidation performed with performic acid generated in situ from the couple hydrogen peroxide/ formic acid was studied for synthetic polyisoprene latex (LIR-700) and natural rubber (NR) latex. Various parameters of the reaction (nature and concentration of surfactant used, reaction temperature, and quantities of formic acid and hydrogen peroxide used to form performic acid) were studied and the results obtained for the respective latices were compared. At similar epoxidation conditions, the results obtained with LIR-700 and NR latices were shown to be very close. NR and LIR-700 latices showed the same behaviour during the epoxidation performed with performic acid. Optimal conditions to carry out epoxidation for the preparation of stable latices were also established. This was achieved when the epoxidation was carried out on latices previously stabilised with 3 p.h.r. of a non-ionic surfactant (Sinnopal NP 307^®for example) at a temperature of 60ºC, with equimolar quantities of formic acid and hydrogen peroxide.

Effect of Low Temperature Curing on Short Isora Fibre Reinforced Natural Rubber Composites

Lovely Mathew, Shiny Palatty and Rani Joseph

‘Isora’ a natural fibre obtained from Helicteres isora plant is used for reinforcement of rubber composites. The fibre is separated from the bark of the plant by a retting process. Composites were prepared using chopped untreated and alkali treated isora fibre of lengths 10 mm at different fibre loadings in natural rubber (NR) using both low temperature curing accelerators (ZDC/ xanthates) and conventional accelerators (CBS/TMTD). The bonding between the fibre and rubber was improved by the use of RF resin. Cure characteristics of the composites heated to various temperatures were studied. The mechanical properties of the composites prepared using a conventional system were compared with those of the composite prepared using xanthates, at different temperatures from 80ºC–140ºC. Composites with the conventional accelerator system were vulcanised at 150ºC. The results showed that the xanthates were effective in low temperature curing of NR and the composite vulcanised at 100ºC showed optimum properties. At high temperature, fibre and rubber showed a tendency to degrade and hence a decrease in properties. Alkali treated fibre composites showed enhancement of mechanical properties in both systems. Properties are improved by the use of bonding agent. The tensile fractured surface has been investigated by SEM studies and the failure mechanism has been explained. The swelling behaviour of these composites were also studied in toluene and it was found that low temperature cured composites restrict swelling considerably.

IgE Antibody Binding to the Carbohydrate Moiety of Hev b 13

S.A.M Arif, RG Hamilton and HY Yeang

Previous work has indicated the involvement of Hev b 13 glycan in the binding of specific human IgE antibodies. Further evidence is presented here to show that IgE binding to Hev b 13 is due to its epitope(s) that reside(s) on the glycans covalently bound to the amino acid structure of the glycoprotein. Oxidative degradation of native Hev b 13 carbohydrate structures by periodate disabled most of the IgE antibody reactivity. To further study the role of the Hev b 13 glycan in IgE antibody-recognition, an unglycosylated recombinant version of the protein was synthesised in Escherichia coli, using the pMal-c2 vector. An 88 kDa protein was obtained which corresponded to the expected size of the MBP-Hev b 13 fusion protein. The recombinant protein was recognised by the monoclonal and polyclonal antibodies specific for Hev b 13, thus confirming its identity. However, human IgE antibody failed to react with the unglycosylated recombinant Hev b 13 protein. Competitive inhibition of IgE binding to Hev b 13 by patatin was shown to result from cross-reacting carbohydrate determinants. These results indicated that the carbohydrate moiety of the glycoprotein played a principal role in human IgE antibody reactivity and allergenicity to Hev b 13.

Efficacy of Glyphosate and its Mixtures against Weeds under Young Rubber Forest Plantation

M A Ahmad Faiz

Weed infestation is a major problem during the early stages of establishment of rubber forest plantation. Currently, information on effective weed control system in young rubber forest plantation is limited. As the rubber forest plantation is often located in remote areas, a weed control system which provides longer duration of weed control is preferred. Trials were conducted to determine effective rates of glyphosate isopropylamine and its mixtures against mixed weeds. Glyphosate isopropylamine at 1.08 kg ae/ha mixed with metsulfuron methyl at 0.03 kg ai/ha, was safe and effective against weeds in rubber less than a year old. In rubber above two years old, glyphosate isopropylamine at 1.08 kg ae/ha mixed with metsulfuron methyl (0.03 kg ai/ha), fluroxypyr (0.3 kg ae/ha), dicamba (0.6 kg ae/ha) or premixed picloram + 2,4-D (0.097 kg ae/ha + 0.36 kg ae/ha) were effective. Glufosinate ammonium at 0.9 kg ai/ha gave shorter duration of control against mixed weeds compared to glyphosate (1.08 kg ae/ha) + metsulfuron methyl (0.03 kg ai/ha). Glyphosate isopropylamine (1.08 kg ae/ha) + metsulfuron methyl (0.03 kg ai/ha) at two or four rounds per year provided more effective weed control than slashing. Slashing at two or four rounds was ineffective and at two rounds per year gave rise to serious weed regeneration.

Yield Stimulation of the Rubber Tree (RRIM 600) with Ethephon does Not Increase Latex Hev b 6 Protein or mRNA

P Arokiaraj and H Y Yeang

Hevea brasiliensis latex hevein is an allergenic protein designated the allergen name Hev b 6 by the International Union of Immunological Societies. A study was undertaken to determine if latex flow stimulation by ethephon increased Hev b 6 concentration in the latex from mature rubber trees. A two-site immunoenzymatic assay with antibodies specific for hevein revealed no significant differences in Hev b 6 content in control trees and Hevea trees stimulated with ethephon. The mRNA transcript levels of hevein determined by northern analysis appeared similar for control and stimulated trees. Using the relative ratio method for Real Time PCR assessment, the steady-state transcript levels of hevein were also similar for control and stimulated trees. It was concluded that latex from mature Hevea trees stimulated with ethephon did not result in an increase in hevein mRNA transcripts or in the translated protein. There was therefore no evidence from this study that ethephon stimulation increased allergenicity of latex by increasing Hev b 6 content.

The Factor Contributing to Higher Extractable Protein Content in Natural Rubber Latex Glove as Determined by ASTM D5712-99 over ASTM D5712-95 and its Relation to Allergen Content

H Hasma, D Dazylah and M Nor Qamarina

Values for glove extractable protein content determined by ASTM D5712-99 were generally higher than corresponding values obtained by ASTM D5712-95. This resulted from the different procedures used in the two assays. Among all the variables investigated, it was ascertained that differences in extraction medium were the main contributing factor. Extraction with 25 mM phosphate-buffered saline, as in ASTM D5712-99, gave higher protein content than extraction with water, as in ASTM D5712-95. The same was true of the allergen values of the extracts.

Mechanical Properties of Sulphur Prevulcanised and Gamma Radiation Vulcanised Natural Rubber and Carboxylated Styrene Butadiene Rubber Latices and Their Blends

Ranimol Stephen, Kuruvilla Joseph and Sabu Thomas

Blends of natural rubber and carboxylated styrene butadiene rubber latex with varying blend ratio were prepared. The blends were vulcanised by different techniques which include sulphur prevulcanisation, and gamma radiation vulcanisation. Morphology of the blends was investigated from scanning electron micrographs. Mechanical properties such as tensile strength, tear strength, elongation at break and modulus were studied with reference to blend ratio and vulcanisation techniques. The crosslink density of the blends and individual components were determined from the swelling and stress-strain measurements. The sulphur prevulcanisation of latices was carried out at 70ºC for 2 h.The radiation vulcanisation of various systems was carried out using n-butyl acrylate as sensitiser at a dose of 15 kGy/h. The swell ratio of the samples was calculated. The radiation vulcanised systems showed comparable properties as that of sulphur prevulcanised systems. However, the modulus of radiation vulcanised latex films was lower than prevulcanised samples. The gamma radiation vulcanised latices are eco-friendly due to the absence of curing agents. Applicability of various theoretical models were investigated to predict the modulus of the blends.

Effect of Silane Coupling Agent on the Mechanical Properties of Flyash-filled Natural Rubber

Nabil A N Alkadasi

This paper describes the utilisation of flyash as a filler after being treated with silane coupling agent and used as fillers in NR. The properties considered were tensile strength, modulus at 100% and 400%, Young's modulus and hardness. Composites were made with varying proportion of untreated and treated flyash. A two-roll mill was used for dispersing the filler in the rubber and compression moulding technique was used to cure the compounds in sheet forms. Tensile properties were measured on a computerised UTM using ASTM procedure. Comparison of properties of composites filled with treated and untreated flyash established that treatment of flyash imparted better reinforcing properties. Tensile strength improved by 83% while modulus at 400% improved by 100% and Young's modulus improved by 29%. Similarly elongation at break also improved by 50%. The silane coupling agent used here promoted adhesion between flyash and NR.

NR Gloves in Contact with Food: Factors Affecting the Protein Transfer

H Hasma

Some NR latex gloves have been reported to transfer proteins to certain food on contact with gloves. The situation, however, could not be applied to all types of food and NR latex gloves. This study showed that no glove proteins were transferred to dry non-sticky food whereas the amount of proteins transferred to moist food is dependant on the extractable protein (EP) or antigenic protein (AP) content of the glove surface in contact with food.

Glove contact surface of EP content < 60 µg/dm² or AP content of < 1.5 µg/dm² could not transmit a measurable amount of proteins to nitrocellulose membrane which was used to simulate food with high binding affinity for proteins. On the other hand, only gloves with a higher AP level of >10 µg/dm² was found to transfer detectable amount of proteins to tomato and cheese. This inferred that NR gloves, especially powder-free gloves, with EP of < 60 µg/dm² and/or AP < 10 µg/dm² could be used in food handling.

Sucrose and Metabolism Distribution Patterns in the Latices of Three Hevea brasiliensis Clones: Effects of Tapping and Stimulation on the Tree Trunk

U Silpi, P ChantUma, P Kasemsap, P Thaler, S ThaniSawanyangKUra, A Lacointe, T Améglio and E Gohet

This study describes the sucrose balance between supply and demand in the bark of the rubber tree, along with concurrent latex metabolic activity. Experiments were designed using three hevea brasiliensis clones (PB 235, RRIM 600 and GT 1) in the same polyclonal plot at the Chachoengsao Rubber Research Centre (CRRC-DOA) in Thailand. Treatments were carried out on previously untapped trees (growth potential control), trees tapped without stimulation (½S d/3 6d/7 9m/12, physiological control), and trees tapped with ethephon stimulation (½S d/3 6d/7 9m/12 ET 2.5% 5/y and 12/y). Tapping had a marked effect on latex physiology in the whole trunk. Sucrose concentration was significantly reduced. The Latex Diagnosis Mapping (LDM) method was used to describe the shape and size of the latex regeneration area and of the metabolically active bark area. For the three clones, rubber production correlated with the estimated latex regeneration area. It took around 100 cm²of latex regeneration area to regenerate 1 g of rubber. As it assesses the impact of any tapping system on whole trunk latex physiology, the LDM method was used to develop new tapping systems, such as systems involving ethylene gas stimulation, micro-tapping cut systems, and multi-tapping cut systems.

Greater Sensitivity of Detecting Glove Defects Using Soap Solution and the Role of Non-rubber Constituents in Needle Puncture Tear

H. Hasma, Alias Othman and Mohd Noor Shafie

The higher percentage of failure in the palm region of commercial gloves than in the fingers was partly attributed to the sensitivity of the 1 litre water leak test rather than merely to the higher number of defects in the palm. Incorporating 0.1% sodium dodecyl sulphate, Teepol®, Triton X-100® or Tween-80® in water increased the sensitivity of detecting finger defects. The smallest leak detectable by the 1 litre soap leak test was equivalent to 2 µL virus FX174 penetration. Needle punctured NR gloves exposed to cyclic stress offered a better protection than vinyl and nitrile gloves under similar conditions. The non-rubber constituents present in NR gloves were shown to have some effect on the amount of virus penetrating through the punctured tear.

Reinforcement of Silicone Rubber with Precipitated Amorphous White Silica Nanofiller—Effect of Silica Aggregates on the Rubber Properties

A. Ansarifar and B.Y. Lim

Silicone rubbers often possess poor mechanical properties and must be reinforced with fillers such as synthetic silicas for industrial applications. The effect of up to 60 parts per hundred rubber by weight precipitated amorphous white silica nanofiller on the properties of a peroxidecured polydimethyl siloxane rubber was studied. The rubber also contained a small amount of vinyl groups. The mechanical properties of the rubber vulcanisate were enhanced noticeably when the filler was added. This was mainly due to a strong filler-filler interaction which produced large silica aggregates in the rubber. The addition of the filler was also beneficial to the crosslink density of the rubber.

Shape Factor and Carbon Black Loading Effect on FEA Prediction of Bearing Behaviour

V. Luksameevanish, M. Seadan and S. Kopoonpat

Four natural rubber compounds varying in carbon black content from 10 p.h.r. to 70 p.h.r. were characterised and moulded for bearings, having four different values of shape factors ranging from approximately 0.33 to 1.73, according to the number of reinforcing plates used. The approximate area of the bearing and thickness were 50 mm 3 106 mm and 50 mm, respectively. Three deformation modes were predicted, namely compression, shear and compression-shear. Good agreement was found between the 12 compression model predictions and the corresponding experimental values for bearings containing 10 p.h.r., 20 p.h.r. and 40 p.h.r. of carbon black for each of the four different arrangements of reinforcing metal plates (0, 1, 2 and 3 layers). However, for bearings containing 70 p.h.r. carbon black, differences between experimental and predicted results could clearly be visible. The percentage difference increased with the number of reinforcing plates included with the increase of the shape factor. Therefore, an improved FEA model which included an imaginary elastic-glue layer between the rubber block and metal plate as a compensation for glue failure was examined. The optimum elastic layer value of Young’s modulus was 8 MPa while the thickness of the layer depended on the total thickness or total volume of the rubber block. This model was able to predict the behaviour of bearings containing 70 p.h.r. carbon black with shape factors ranging from 0.5 to 2.35 for 11 cases. The FEA prediction of shear behaviour showed good agreement with the experimental data for all four bearing compounds and no effect of shape factor on shear stress was observed. Moreover, shear stress did not depend on the compressive force to which the bearing was subjected before shear, and the FEA results agreed with the corresponding experimental results.

The Merits of Using Advanced Planting Materials in Rubber Forest Plantation

Bastiah Ahmad, Naimah Ibrahim and Ramli Othman

The growth of three types of planting materials, namely buddings and seedlings with different number of whorls and ‘core’ stumps, in a rubber forest plantation system was studied in three trials. In the first trial, two- and four-whorled buddings of three clones (RRIM 2020, RRIM 2025 and RRIM 2027) were compared. The second trial compared growth of seedlings (PBIG GG 4, 5 and 6) and three- and six-whorled buddings of RRIM 2001 and RRIM 2026. In another trial, the growth of three types of planting materials namely two- and six-whorled buddings and ‘core’ stumps were also compared. Generally, buddings planted as advanced planting materials (with four or six whorls) had better girth than two- or three-whorled buddings or seedlings. However, advanced seedlings did not indicate the same trend. Clone RRIM 2020 had significantly better girth than RRIM 2027 in the first trial. The girth superiority of ‘core’ stumps over those of twowhorled buddings was maintained for 2.5 years after planting whilst the six-whorled buddings caught up with the ‘core’ stumps in girth size as early as two years after planting. The significance of these findings in relation to the use of advanced planting materials to reduce the period of immaturity of rubber and for rubber forest plantation is discussed.

Synthesis of Modifed Natural Rubber-stabilised Silver Organosols via Liquid-to-liquid Transfer Techniques

M. Abu Bakar*#, W.L. Tan*, N.J. Azizi* and N.H.H. Abu Bakar*

A simple one- and two-step phase transfer technique in synthesizing silver nanoparticles is described. The silver ions are reduced using sodium borohydride either before (one-step method) or after (two-step method) adding the organic phase. 2-propanol was employed as a transferring agent whereas tetraoctylammonium-bromide and 50% epoxidised natural rubber (ENR-50) was used as the stabiliser in aqueous and organic layer, respectively. Both of the methods described are of comparable efficiency in transferring ions/particles whereby based on the atomic absorption spectroscopy determination, more than 93% of the silver ions/particles were transported into the toluene layer. The samples were characterised by UV-vis, FTIR, TEM and XRD. The UV-vis spectra and XRD pattern indicated the formation of silver nanoparticles. Size and size distribution analysis of the as-formed silver nanoparticles showed that two-step phase transfer method gave smaller particle size as well as narrower size distribution. The average size and standard deviation of silver nanoparticles for the one-step and two-step method in the organic layer was 18.4 nm ± 9.5 nm and 15 nm ± 5.8 nm, respectively.

Epoxidised Natural Rubber as a Coupling Agent in in situ Precipitated Silica–Natural Rubber Composites

Maya, K.S.*,**, Rani Joseph*#, Jacob K. Varkey*** and Benny George***

Natural rubber (NR) compounds were prepared with in situ precipitated silica in the presence of epoxidised natural rubber (ENR) as a coupling agent. In situ silica masterbatches were prepared from NR latex along with ENR. For this, NR latex was mixed with a suitable amount of ENR latex and precipitation of silica was carried out using sodium silicate and ammonium chloride. Compounds were prepared with these masterbatches. The mechanical properties of the vulcanisates were compared with two reference compounds prepared from NR and commercially available silica with and without a silane-coupling agent Si-69^®. The NR-silica composites prepared with ENR as the coupling agent showed better mechanical properties and improved rubber-filler interaction.

Influence of Effluent from Rubber Processing Factories on the Chemical, Physical and Microbiological Properties of Soil

Mohd. Zin Abdul Karim*

The high concentration of nitrogen and potassium in effluent of rubber processing can be utilised as fertiliser for crops such as oil palm. A study was carried out to monitor the effects of effluent on the chemical, physical and microbiological properties of the soil during the initial two years of application in areas planted with oil palm. Effluent application revealed higher content of potassium in the soil compared to the fertiliser-applied soil. The effluent also enriched the soil to a depth of 20 cm with organic carbon and total nitrogen as compared to the fertilised soil. Concentrations of total phosphorus, total magnesium and total calcium of the effluent-applied soil were comparable to the fertiliser-applied soil. Cation exchange capacity of the soil applied with effluent was higher than the fertiliser-applied soil but the difference was not significant. Total bacteria and fungi population of the effluent-applied soil were comparable to the fertiliser-applied soil. The fertiliser-applied soil had a significantly higher population of ammonium oxidiser than the effluent-applied soil.

Relationship between Methods of Latex Extraction and Stimulation on Yield of RRIM 901, Panel BO-1

Mohd Akbar Md Said*# and Mohd Fauzi Ramlan**

Five-year-old trees of clone RRIM 901, Panel BO-1 were used to study the relationship between methods of latex extraction and stimulation on tree and land productivity with emphasis on gaseous stimulation. The study compared three different extraction methods viz. 1/2S, 1/6S and 3PI with two stimulation methods namely 2.5% ethephon and REACTORRIM technique while nil stimulation was the control. All the treatments were tapped with d/3 tapping frequency. There was a strong relationship between the surface area severed and the method of stimulation employed. No significant advantage of stimulation was observed since the young Hevea trees used in the study did not response positively to the gaseous methods of stimulation used in the study specifically when the trees were tapped with the 1/2S d/3 system. The two-year study signified that the most practical method of extracting latex from young Hevea trees was the conventional 1/2S d/3 system without or with mild ethephon stimulation.

An Assessment of Stimulation of Hevea brasiliensis Rubber Biosynthesis by eIF-5A Protein-enriched Bacterial Lysates

K.S. Chow*#, Faridah Yusof**, Salimah Mohd. Lim* and Latifah Abdullah*

The effect of six unique isoforms of Hevea brasiliensis eukaryotic translation initiation factor 5A (eIF-5A), previously reported as a rubber biosynthesis stimulator protein (RBSP) was evaluated using biosynthesis assays containing zone 2 rubber particles and radiolabelled isopentenyl diphosphate ([¹⁴C]-IPP). Recombinant RBSP proteins were over-expressed as N-terminal glutathione-S-transferase (GST)-tagged proteins in a bacterial system. Crude extracts of six RBSP-GST isoforms were added to rubber biosynthesis assays in increasing volumes. Results showed that increases in the amount of each RBSP-GST isoform corresponded with increases in the level of [¹⁴C]-IPP incorporation above that of the control which contained no recombinant protein. Statistical data analysis revealed that three RBSP isoforms increased [¹⁴C]-IPP incorporation significantly compared to the GST control where the RBSP isoform with the highest stimulatory effect produced a 45% increase in IPP incorporation compared to GST.