Abstract:
Since proteins existing in natural rubber were reported to cause allergy to some people using natural rubber products, synthetic cis-1,4-polyisoprene which is designed to have similar structure and properties to natural rubber is preferably chosen in some applications due to the absence of proteins. However, deproteinization of natural rubber latex can reduce extractable antigenic proteins, giving rise to less allergic reaction. In this respect, a deproteinized natural rubber is of interest as an alternative raw material for producing low allergen natural rubber products. In this research, gum and carbon black-filled deproteinized natural rubber and synthetic cis-1,4-polyisoprene vulcanizates having various crosslink densities were prepared by varying the curative contents. Whole natural rubber having various crosslink densities was also prepared for comparison. The mechanical properties such as tensile strength, tear strength, flex-cracking resistance, abrasion resistance and heat buildup of all vulcanizates were determined and their properties at a similar degree of crosslink density were also compared.
For both gum and carbon black systems, deproteinized natural rubber was found to possess a lower crosslink density than both synthetic cis-1,4-polyisoprene and whole natural rubber at a specific level of curative content. Tensile and tear strengths of the vulcanizates passed through a maximum with the increase in crosslink density and then declined as crosslink density further increased. In addition, flex-cracking resistance of all vulcanizates decreased as crosslinking increased. The results indicated that deproteinized natural rubber performed better flex-cracking resistance than synthetic cis-1,4-polyisoprene and whole natural rubber at a specific level of curative content because deproteinized natural rubber had a lower modulus. In gum system, synthetic cis-1,4-polyisoprene exhibited an abrupt drop in tear strength at lower crosslink density and had a narrower peak than did the other two. This might be due to its lower crystallizability compared to the others. For carbon black system, it is found that tensile strength, tear strength and heat buildup of all vulcanizates were comparable at a given crosslink density. This means the reinforcement by carbon black overshadows the intrinsic properties of each rubber. At optimum crosslink density, most mechanical properties of deproteinized natural rubber and whole natural rubber for both gum and carbon black systems were comparable to those of synthetic cis-1,4-polyisoprene except for the flex-cracking resistance of the carbon black-filled deproteinized natural rubber and whole natural rubber was inferior to that of carbon black-filled synthetic cis-1,4-polyisoprene due to their higher modulus. However, the improved flex-cracking resistance of carbon black-filled deproteinized natural rubber without much drop in tensile and tear strengths can be achieved by preparing it with a slightly lower modulus. From the results, most mechanical properties of deproteinized natural rubber were competitive with those of synthetic cis-1,4-polyisoprene. Thus, deproteinized natural rubber might be used as an alternative raw material for producing low allergen natural rubber products."