Producing Lignin-Based Polyols through Microwave-Assisted Liquefaction for Rigid Polyurethane Foam Production

Bai-Liang Xue; Jia-Long Wen; Run-Cang Sun

doi:10.3390/ma8020586

Producing Lignin-Based Polyols through Microwave-Assisted Liquefaction for Rigid Polyurethane Foam Production

Materials (Basel). 2015 Feb 10;8(2):586-599. doi: 10.3390/ma8020586.

Authors

Bai-Liang Xue¹, Jia-Long Wen², Run-Cang Sun^{3

4}

Affiliations

¹ Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing 100083, China. xuebailiang@bjfu.edu.cn.
² Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing 100083, China. wenjialong@bjfu.edu.cn.
³ Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing 100083, China. rcsun3@bjfu.edu.cn.
⁴ State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou 510641, China. rcsun3@bjfu.edu.cn.

Abstract

Lignin-based polyols were synthesized through microwave-assisted liquefaction under different microwave heating times (5-30 min). The liquefaction reactions were carried out using polyethylene glycol (PEG-400)/glycerol as liquefying solvents and 97 wt% sulfur acid as a catalyst at 140 °C. The polyols obtained were analyzed for their yield, composition and structural characteristics using gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectra. FT-IR and NMR spectra showed that the liquefying solvents reacted with the phenol hydroxyl groups of the lignin in the liquefied product. With increasing microwave heating time, the viscosity of polyols was slightly increased and their corresponding molecular weight (M_W) was gradually reduced. The optimal condition at the microwave heating time (5 min) ensured a high liquefaction yield (97.47%) and polyol with a suitable hydroxyl number (8.628 mmol/g). Polyurethane (PU) foams were prepared by polyols and methylene diphenylene diisocyanate (MDI) using the one-shot method. With the isocyanate/hydroxyl group ([NCO]/[OH]) ratio increasing from 0.6 to 1.0, their mechanical properties were gradually increased. This study provided some insight into the microwave-assisted liquefied lignin polyols for the production of rigid PU foam.

Keywords: Polyurethane (PU) foam; lignin; liquefaction; microwave heating.