lignin is one of the most abundant biopolymers on earth, constituting approximately 30% of the dry weight of softwoods and 20% of hardwoods. it is a renewable, non-toxic, commercially available and low cost natural resource that has significant potential for being utilized as a basic raw material for the polymer industry. lignin has potential for serving as a reinforcement agent in rubber because of its relatively large molecular weight, low surface reactivity and high water resistance. however, unmodified kraft lignin is generally incompatible with the rubber matrix, causing well known hysterisis problems in filled tires. therefore, modification is required to improve the potential application of kraft lignin as a rubber filler. to date, lignin has been used primarily as a low-grade fuel for the pulp and paper industry due to the lack of effective modification and depolymerization methods.