ผลของอัตราส่วนระหว่างกำมะถัน และสารเร่งต่อสมบัติเชิงกลของยางสไตรีน-บิวทาไดอีนและยางบิวทาไดอีน / ทวนทน ทวยมาตร = Effects of sulfur to accelerator ratio on mechanical properties of styrene-butadiene rubber and butadiene rubber / Tuanton Tuaymas
This research studied the effects of sulfur to N,N'-Dicyclohexyl-2-benzothiazole sulfenamide accelerator (S/A) ratio on mechanical properties of styrene-butadiene rubber (SBR) and butadiene rubber (BR). The weight ratios of S/A used in this study were 6.67, 3.20, 1.92, 1.17, and 0.26. The first three S/A ratios were classified as conventional vulcanizing system (CV). The next two ratios were counted as semi-efficiency vulcanizing (Semi-EV) and efficiency vulcanizing system (EV), respectively. In addition, one more rubber compound cured with EV system was prepared using a sulfur donor, tetramethylthiuram disulfide (TMTD), acting as sulfur and accelerator, rather than using sulfur accompanied with accelerator. For each S/A ratio, a series of compounds with crosslink densities varying from 25 to 250 mol/m3 was prepared. The results showed that the effects of S/A ratio on mechanical properties of SBR were close to those of BR with a slight difference under some circumstances. For both SBR and BR, when decreasing the S/A ratios from 6.67 to 3.20, 1.92, and 1.17, tensile and tear strength were nearly the same. Moreover the strengths of these compounds were independent of the crosslink density. For SBR cured with EV system, the tensile strength of the compound cured with sulfur and accelerator at the ratio of 0.26 was similar to that of the one cured with TMTD. Compared with other curing systems, SBR cured with EV system had the lowest tensile strength. And the increase in crosslink density now significantly caused the reduction of the tensile strength. For tear strength, the result showed that when crosslink density was less than 100 mol/m3, SBR cured with TMTD showed the highest tear strength whereas the rest had nearly the same tear strength. However, above 100 mol/m3, SBR cured with EV system no matter using sulfur and accelerator at the ratio of 0.26 or TMTD had the lowest tear strength. The increase in crosslink density reduced the tear strength of SBR cured with EV system significantly. For BR with crosslink density less than 50 mol/m3, the one cured with sulfur and accelerator at ratio of 0.26 showed highest tensile and tear strength. But above 50 mol/m3, both curing system and crosslink density did not have any significant effect on the strength. Comparison amongst rubbers which had the same crosslink density, it was found that when temperature was lower than -40 oC, SBR cured with TMTD had lowest storage modulus while SBR cured with sulfur and accelerator at various ratios had the same storage modulus. The glass transition temperature (Tg) decreased with decreasing of S/A ratio. And SBR cured with TMTD showed lowest Tg. The cut growth resistance of SBR and BR decreased with increasing of cut size. The cut growth resistances of SBR cured with sulfur and accelerator at ratio of 0.26 and cured with TMTD were the same but lower than those of SBR cured with the other cure systems. On the other hand, for BR, the difference in curing systems did not effect on the cut growth resistance. The position of sulfur peak of SBR and BR detected by XANES shifted to the higher energy with the decreasing of S/A ratios. This indicated that the decreasing of S/A ratios resulted the cured rubber in having the higher proportion of monosulfidic and disulfidic linkages.
