Lignin as a Compounding Ingredient for Natural Rubber

Abstract

Abstract Important claims have been made in recent years regarding the capacity of lignin to reinforce natural and synthetic rubber. In 1949 Dawson reviewed the literature on the use of lignin in rubber and drew particular attention to the work of Keilen and Pollak who had shown that in certain circumstances lignin could be considered to rival EPC black in its ability to yield strong GR-S vulcanizates with high resistance to tear. Raff and his coworkers subsequently showed that the reinforcement of GR-S by lignin is enhanced if the lignin, before coprecipitation with the latex, is subjected to oxidation; other workers studied the application of lignin to the reinforcement of different elastomers, the influence of coprecipitation conditions on the properties of the product, and the problem of overcoming the delaying effect of lignin on vulcanization of lignin-natural rubber coprecipitates. Keilen and Pollak in their experiments incorporated lignin into rubber by coprecipitation at the latex stage, but they indicated that similar results could be obtained if lignin “in the gelled state” was added to rubber by milling. No reinforcement was observed however when lignin was added to rubber as a dry powder. Lignin is potentially an abundant and cheap material which according to the above claims should extend the range of useful compounds available to rubber manufacturers. The present paper describes work undertaken to gain firsthand knowledge of the technique of coprecipitating lignin with natural rubber from preserved latex, to learn something about the properties of natural rubber compounds prepared from lignin coprecipitates, and to study possible ways of incorporating lignin into rubber by means other than coprecipitation. It also records test results for masterbatches prepared by the Rubber Research Institute of Malaya from fresh latex on a pilot plant scale.