Synthesis and characterization of lignin–HTPB copolyurethane

Lignin–HTPB copolyurethanes have been synthesized from hydroxyl terminated polybutadiene (HTPB) and varied quantities of lignin and toluene diisocyanate. IR spectroscopy and estimation of isocyanate groups have established the formation of HTPB polyurethane and lignin–HTPB copolyurethane. The crosslink density, sol fraction, diffusion coefficient, mechanical properties and X-ray crystallinity of lignin–HTPB copolyurethane have been measured and compared with those of HTPB polyurethane. Tensile strength improvement of lignin–HTPB copolyurethane was observed up to 3-wt.% lignin incorporation. High hydroxyl value of lignin has been found responsible for the decrease in tensile strength with the increase in lignin content of lignin–HTPB copolyurethane.