Hydrothermally Treated Lignin as a Sustainable Biobased Filler for Rubber Compounds

Increasing emphasis in the rubber world on the production of environmentally friendly products has created a demand for alternative reinforcing fillers. Industrial lignin side-stream of lignocellulosic biomass has gained significant interest in this respect due to its abundancy and eco-friendly nature. In the present study, a recently developed, biobased hydrothermally treated (HTT) lignin was investigated as a potential functional filler for a solution styrene butadiene and butadiene rubber blend. Commercial reinforcing fillers N330 carbon black and ULTRASIL 7000 precipitated silica were used as references. Bis(triethoxy silylpropyl)tetrasulfide silane was used as a coupling agent for in situ surface compatibilization of this hydrothermally treated lignin with the hydrophobic rubber, as is commonly done for hydrophilic silica. The influence of unmodified and silane-modified lignin on the vulcanization, morphological, static and dynamic mechanical properties was investigated and examined with the reference fillers. The overall in-rubber properties exhibited by the silane-modified hydrothermally treated lignin are superior in comparison with those of the unmodified version. In comparison with reference fillers, this modified lignin shows semireinforcing behavior. The reinforcing properties are primarily due to networking of HTT lignin particles with rubber trapped-in or formation of sponge-like HTT lignin textures in the presence of silane, as observed with atomic force microscopy. The present work describes the complex reinforcement phenomena of using a silane as coupling agent for hydrothermally treated lignin and outlines its potential as an alternative rubber reinforcing filler.