# Isolation and Characterization of Lignin from Sapele (Entandrophragma cylindricum): Application in Flexible Polyurethane Foam Production

## TL;DR

This paper describes a method to isolate lignin from sapele wood and use it to create flexible polyurethane foams with potential applications in automotive and flooring industries.

## Contribution

The study introduces a novel hybrid pulping process to isolate lignin and produce bio-polyols for polyurethane foam with improved mechanical and thermal properties.

## Key findings

- Bio-polyols with high -OH groups were produced using a PEG-glycerol mixture and sulfuric acid catalyst.
- Increasing liquefaction temperature improved thermal stability and mechanical performance of the foams.
- The foams showed potential for use in automotive and flooring applications due to their structural properties.

## Abstract

Lignin used in this work was isolated from sapele (Entandrophragma cylindricum) wood through a hybrid pulping process using soda/ethanol as pulping liquor and denoted soda-oxyethylated lignin (SOL). SOL was mixed with a polyethylene glycol (PEG)–glycerol mixture (80/20 v/v) as liquefying solvent with 98% wt. sulfur acid as catalyst, and the mixture was taken to boil at 140 °C for 2, 2.5, and 3 h. Three bio-polyols LBP1, LBP2, and LBP3 were obtained, and each of them exhibited a high proportion of -OH groups. Lignin-based polyurethane foams (LBPUFs) were prepared using the bio-polyols obtained with a toluene diisocyanate (TDI) prepolymer by the one-shot method. Gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and carbon-13 nuclear magnetic resonance spectroscopy (13C NMR) were used characterize lignin in order to determine viscosity, yield, and composition and to characterize their structure. The PEG-400–glycerol mixture was found to react with the lignin bio-polyols’ phenolic -OHs. The bio-polyols’ viscosity was found to increase as the liquefaction temperature increased, while simultaneously their molecular weights decreased. All the NCO groups were eliminated from the samples, which had high thermal stability as the liquefaction temperature increased, leading to a decrease in cell size, density, and crystallinity and an improvement in mechanical performance. Based on these properties, especially the presence of some aromatic rings in the bio-polyols, the foams produced can be useful in automotive applications and for floor carpets.