Thermo-Responsive Polymers-Based on Source-Selective Lignins

Abstract

In this study, thermomechanical properties of hardwood and softwood lignin-nitrile butadiene rubber composites were controlled by a thermal annealing process. The presence of thermally unstable linkages within the selected lignins provides free radical sources for crosslinking reactions. The measured dynamic mechanical properties demonstrated substantial improvement in glass transition temperatures (Tg) and storage moduli (E’) of 50 wt. % softwood lignin- and 50 wt. % hardwood lignin-rubber composites after thermal annealing at 180°C. An increase in Tg of approximately 18°C and more than 230% increasing E’ was achieved after annealing the 50 wt. % hardwood lignin-rubber for 5 h. The chemical crosslinking reactions between lignin-nitrile butadiene rubber and lignin-lignin were characterized by in-situ dynamic mechanical analysis and Fourier transform infrared (FTIR) spectroscopy. A mechanism of crosslinking reactions was revealed.