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Formulations for Heat Resistant Chlorinated Chlorination is widely used for producing powder-free gloves. One of the advantages of the process is that it reduces the water extractable protein contents(EP) of latex products to very levels1. Such reduction of EP is highly desirable in view of the allergy problem2,3. Although its exact mechanism is not clearly understood,chlorination is by far the most effective method for EP reduction4,5,6. The process is also widely used in the manufacture of catheters and household gloves as an additional process to eliminate the usage of powders. Due to the thick physical profile of these products,problems of physical deterioration caused by chlorination is minimal. However when it is applied to medical gloves where their thickness is approximately 0.2mm and below,judicious control of the process is essential. Otherwise, it will result in the gloves having poor physical properties particularly after high temperature ageing at 100°C for 22 h. A paper was published in 1993 on chlorination of gloves1,explaining the theoretical and practical aspects of chlorination and changes in physical properties after chlorination at different level of free chlorine concentrations. Under the process conditions studied, the properties of the final product were shown to be below specification as required by the ASTM standard. Further storage of the product above the ambient temperature is expected to result in further deterioration in properties. The purpose of this work is to overcome these problems by developing suitable formulations to give latex films which are resistant to high temperature ageing. GENERAL PROCESS OF CHLORINATION In general, the chlorination process involves attachment of chlorine atoms onto the backbone of natural rubber molecules on the surface of the latex films. Free chlorine atoms required can be produced by either dissolving chlorine gas in water or by reacting hypochlorite solution with acid to release the chlorine. A general procedure for producing chlorinated gloves is given as follows:
a : If double chlorination is required,repeat process.b : Optional.Gloves should posses good physical properties and may be washed with water if necessary prior to the chlorination process. EXPERIMENTAL A series of formulations with different curative systems were prepared, as shown in Table 1. Formulation A uses a single accelerator system and Formulations B,C,D and E have either two or three combinations of accelerators amongst which synergistic effects were expected to take place. Films of thicknesses 0,1,0.2, and 0.4mm were prepared by the normal coagulant dipping. After leaching for approximately 5 min at 70°C, the dipped films were cured at 100°C for 20 min. They were then exposed to various concentrations of chlorine solutions for 15 min, washed with water, neutralised and washed again before drying at 50°C in an air circulated oven. The dried films were then kept for 24 h in a dessicator before the unaged properties were measured. The ageing process was carried out under two conditions, 22 h at 100°C and 7 days at 70°C, after which the tensile properties of the films were tested. The water extractable protein values of the films were determined by the Rubber Research Institute of CMalaysia modified Lowry microassay against Bovine Serum Albumin (BSA) standard. RESULTS AND DISCUSSION Figures 1-15 show the plots of tensile strength values of latex films of varying thickness versus chlorination concentrations for the five formulations investigated. Tensile Strength Values Unaged samples. As shown in Figures 1,4,8,10, and 13 the tensile strength values of unaged samples ranged from 22 Mpa to 38 Mpa. They were not affected by increase in chlorine concentration or change in film thickness. The unaged values for Formulations A and B were approximately 25 Mpa improved to above 30 Mpa in Formulations C,D and E. The required value byASTM specification is 21 Mpa, indicating that all formualtions are capable of meeting the specified requirements. Aged for 22 h at 100°C. All samples of Formulations A and B were severly affected by ageing as illustrated in Figures 3 and 6. The tensile strength values deteriorated by approximately 30% to 50%. The deterioration was most marked when the film thickness was 0.1 mm. Since the values after ageing were below 16Mpa,Formulations A and B were not suitable for chlorinated gloves. Nowever better performance was observed in Formulation Cas shown in Figure 9. All the values were above the specification with the exception of samples with thickness of 0.1 mm, which again exhibited poor heat resistance. Formulations D and E exhibited higher aged tensile strength values, (approximately above 70%), as shown in Figures 12 and 15. The retention was also unaffected by changes in chlorine concentration and sample thickness. It is worth noting that the results for Formulation D were more consistent than those of Formulation E: the aged tensile strength values decreased monotonically with increasing chlorine concentration. They were however all above the minimum specification. Aged for 7 days at 70°C. The retention in tensile strength values after ageing at 70°C for 7 days was above 80% for all samples. It was not significantly affected by changes in sample thickness and chlorine concentration. As shown in Figures 2,5,8,11 and 14, the values ranged from 17 Mpa to 33 Mpa and were above the minimum requirement. Extractable Protein Contents The extractable protein (EP) content of all chlorinated film ranged from 0.009 to 0.030 mg/g sample. However for Formulation E, the value was slightly higher as compared to other samples. In view of this, only Formulations C and D were found suitable for production of chlorinated gloves with good heat resistance and low EP contents. Tables 2 and 3 below show the other tensile properties of chlorinated films of Formulations C and D (unaged and aged at 70°C for 7 days and 100°C for 22 h). The EB (%) and modulus values were satisfactory and met the requirements of standard specifications. CONCLUSION Changing the accelerator system or increasing the thickness of latex films was found to improve the ageing resistance of the films. For less severe ageing conditions (for 7 days at 70°C) all five formulations studied passed the ASTM specification. However, when severe ageing condition (for 22 h at 100°C) was used on thin latex films of 0.1 mm thickness, only Formulations C, D and E met the specified requirements. Of the three formulations, C and D are the best in the terms of heat resistance and extractable protein content and are therefore recommended. ACKNOWLEDGEMENT The author wishes to thank Dr Lai Pin Fah for his advice and comments on this paper and En.Juseph Ambrose,Pn.Norhanam Sulong,En.Chua Swee Hong for their assistance. REFERENCES
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