Application Of Modified Alkali Lignin In Natural Rubber

Alkali lignin was used in rubber as a new type of filler because of its ageing resistance, low cost and environment-friendly properties. But its dispersion in non-polar rubber was poor because of the polar group on its surface. Therefore, it’s of importance to develop a reasonable modification way to improve the dispersion effect. In this paper, the laws of alkali lignin treated by two ways filling in natural rubber were investigated. The two ways were dynamic heat treatment and pre-dispersion treatment, respectively. Maleic anhydride(MAH) and silane coupling agent(Si69) were used for surface modification of alkali lignin. We used rubber processing analyzer to investigate the effect of the filler network structure characteristics on the dynamic mechanical properties. Also the microstructure properties of vulcanizates were observed by scanning electron microscopy(SEM).The results showed that there was hardly no filler-filler interaction in the natural rubber filled with alkali lignin and the bound rubber content was also very low. So its Payne effect mainly depended on the rubber-rubber interaction. Mechanical properties of the vulcanizates decreased with the increase of the dosage of alkali lignin, but the aging resistance increased with an increase in the amount. If the alkali lignin was used with the carbon black, when the dosage of alkali lignin was 10phr(the ratio of the two was 1:4),the dynamic mechanical properties of rubber, mixing characteristics, Mooney viscosity and mechanical properties were similar with the rubber filled with carbon black only. With the increase of alkali lignin proportion in the filler, all of the properties showed an obvious degradation compared with the rubber filled with carbon black. So we can use a small amount of alkali lignin to replace the carbon black in the carbon black filled system. It was not only environmental friendly and economical but can also improve the hot-oxygen aging properties of rubber on the premise that it can sustain the basic mechanical strength. Then the alkali lignin was treated by dynamic heat treatment and the results showed that the mechanics performance of rubber filled with AL1- MAH was much better than that of the rubber filled with AL1- Si69.With the analysis of the dynamic mechanical properties, the rubber filled with AL1-MAH has a higher energy storage modulus and a lower loss factor that that of AL1- Si69,so the MAH modification effect was better than that of Si69 modification. Finally, with the MAH as modifier, we compared the two types of treatments. It showed that the effect of pre-dispersion treatment was much better than that of dynamic heat treatment in that the pre-dispersion treatment can provide more opportunities for hydroxyl groups of alkali lignin to react with MAH at the molecular level although its process was much more complicated. So the crosslinking density of the rubber, bound rubber content, the storage modulus and comprehensive mechanical properties of rubber of pre-dispersion treatment were higher than that of dynamic heating treatment. When the dosage of MAH was 3phr, the rubber compound had the highest storage modulus and the lowest loss factor. And the tensile strength, tear strength, abrasion resistance, and stress at definite elongation were the best. But the ageing-resistant performance became bad.