Lignin-Rubber Blends
Lignin has attracted most attention as filler in natural and synthetic rubbers, and in this application lignin is used as a component of a multiphase mixture, not as a homogeneous blend. A number of research groups have studied this application, generally known as compounding rubber with lignin [90-93]. Lignin has been applied as filler in butadiene-styrene-butadiene and isoprene-styrene-buta- diene rubbers for shoe soles and in natural rubber. In these studies soda lignin and calcium lignosulfonate were compared as fillers in natural rubber, and it was reported that lignin had properties entirely comparable to carbon black; soda lignin had better filler properties than calcium lignosulfonate and showed potential as a low-cost substitute for carbon black [91,92]. Low molecular weight lignins have been shown to be more effective in improving the tensile strength of natural rubber than of styrene-butadiene rubber. Kramarova and coworkers reported that lignin is significantly more effective than starch or protein as a filler for natural rubber, but not for styrene-butadiene rubber [92].