Lignin Based Rubber Composites towards Production of Energy Efficient Compounds for Tire Industry

Lignins are derived from wood, possess strong mechanical properties, and contain a number of reactive functional groups, such as phenolic –OH and alcoholic -OH.  These reactive functional groups aid chemical modification of lignin so that they can be used as fillers in development of composites of thermoplastic and thermosetting resins.  In the present study, unmodified and modified lignins are being used in rubber formulations with the specific aim of reducing the rolling resistance. The rubber compounds were prepared using different amounts of kraft lignin (15, 30, 45 and 60 phr) and the effect of lignin on the mechanical properties, cure behavior, and crosslink density was determined. Rolling resistance of the compounds was estimated through viscoelastic damping characteristics of cured compounds by dynamic mechanical studies. It was found that lignin shows significant reinforcing behavior with 33% increase in 100% modulus and more than 50% increase in both elongation at break and tensile strength. Also, it caused a reduction in the cure time of rubber compounds by 20% and an increase in the extent of cure. The reduction of optimum cure time was attributed to participation of lignin in the crosslinking reaction via the reactive functional groups and sulfur present in its structures. These findings were supported by bound rubber and crosslink density measurements. The study hence highlights lignin as a potential candidate for producing energy efficient compounds for tire industry.