Utilization of softwood lignin as both crosslinker and reinforcing agent in silicone elastomers

Abstract

Lignin, the second most abundant naturally occurring organic polymer on earth, is normally used only as a source of fuel because of the difficulties in processing it for other applications. While the Piers–Rubinsztajn reaction of phenols and alkoxybenzene groups with hydrosilanes can lead to highly degraded hardwood lignin, under different conditions, the process permits partial reduction of surface-presenting groups on softwood lignin. The method requires no pre-modification of the lignin surface, which reacts with silicon-hydride functional groups on silicone polymers in a process catalysed by B(C₆F₅)₃. Simultaneously, crosslinking of the silicone occurs to give a reinforced elastomer. Lignin plays dual roles as crosslinker and reinforcing reagent. The mechanical performance of lignin crosslinked/reinforced composites, depending on formulation, is comparable to some commercially available silicone elastomers and can be readily tuned by lignin content and molecular weight of silicones used in the formulation. The composites demonstrated acceptable resistance to solvent extraction and excellent resistance to high temperature aging.