Study on Thermal and Mechanical Properties of Biodegradable Blends of Poly(ε-caprolactone) and Lignin

Abstract

The phase structure and physical property were investigated for blends of poly(ε-caprolactone) (PCL) and lignin, both of which were biodegradable polymers. The blend was prepared by mechanical mixing and solution casting. The thermal analysis (DSC and DMTA) indicated there was no detectable evidence that PCL/lignin blends prepared by mechanical mixing was miscible obviously. But it was found the obvious shift of glass transition temperature Tg of the blends prepared by solution casting. This was the strong evidence to support the fact that these two polymers were at least partially miscible. According to the results of FT-IR, no obvious changes in the shape and peak position of carbonyl absorption caused by formation of hydrogen bond between PCL carbonyl and lignin phenol hydroxyl groups were observed due to the fact that the number of phenol groups in lignin molecule is too small to induce detectable changes of carbonyl absorption. With increasing the lignin content in the blends, the position of O-H stretching band obviously shifted from 3397 to 3412 cm−1. This shift to lower frequency was characteristic for intermolecular hydrogen bonding. Studying the mechanical property of the blends, we found that the maximum strength, elongation at maximum strength and elongation at break decreased but Young’s modulus increased with the increasing content of lignin. Within the lignin content of 25%, the material had good mechanical property. It was also found that the samples prepared by solution casting had better mechanical properties because of the higher dispersity. The result suggested that to blend PCL with lignin could contribute to increase Young’s modulus and reduce the production cost of PCL materials.