Effect of lignin-based monomer on controlling the molecular weight and physical properties of the polyacrylonitrile/lignin copolymer

In this work, lignin was grafted with acrylonitrile to control the molecular weights and molecular architecture of polyacrylonitrile (PAN)/lignin copolymer. Lignin-acrylonitrile monomer (LA-AN) and its copolymers with AN were synthesized successfully. First, lignin was aminated (LA) and then grafted with 2-chloroacrylonitrile to prepare LA-AN. The copolymerization of LA-AN and AN was carried out using 2,2-azobis(2-methylpropionitrile) as initiator. The modification, grafting, and copolymerization were confirmed with Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and X-ray photoelectron spectroscopy. Contrary to the previous studies, gel permeation chromatography showed that the molecular weight of the copolymers was increased significantly due to the presence of lignin (up to 203,944). Viscosity analysis revealed that the addition of lignin reduces the viscosity of the copolymer solution. While thermogravimetric analysis showed improvement in the degradation temperature, and lowering of the melt temperature, as revealed by differential scanning calorimetry. These findings indicated that the attaching acrylonitrile on lignin molecules result in control of the molecular weight and molecular structure of PAN/Lignin copolymers which results in enhanced solubility, spinnability, and other properties associated with molecular weight.