Electronic Thesis and Dissertation Repository


Doctor of Philosophy


Chemical and Biochemical Engineering


Prof. Dr. Chunbao (Charles) Xu


This doctoral study was aimed to produce bio-polyols from Kraft lignin (KL) and hydrolysis lignin (HL) via depolymerization and utilize the lignin-derived bio-polyols in the preparation of bio-based rigid polyurethane (BRPU) foams at high percentage of bio-contents (50-70 wt.%). This study demonstrated that depolymerization is a practical and effective approach to unleash the potential of utilization of lignin, of complex structures and low reactivity/functionality, for bioproducts and biomaterials.

Depolymerization of KL was realized in alkaline medium using water alone as a solvent or employing water-ethylene glycol (EG) mixture via a low pressure (psig) proprietary process, both effective for producing low molecular weight depolymerized KL (DKL). The KL depolymerization process conditions were optimized. BRPU foams were prepared by incorporating DKL via two routes: (1) direct utilization of DKL by replacing 50 wt.% of sucrose polyol and PPG400 and, (2) oxypropylation of DKL to make a single polyol feedstock for the foam preparation.

Similarly, HL was effectively depolymerized employing water alone or water-ethanol (50:50, v/v) mixture with or without catalysts, or employing EG as a solvent under acidic conditions via a low pressure (psig) process. The obtained depolymerized HL (DHL) products were also used as bio-polyols for the preparation of BRPU foams via two routes: direct replacement or oxypropylation.

The main academic contribution of this work is that this study has led to the development of a novel/proprietary process for efficient and cost effective depolymerization of KL and HL under low pressure (psig), viable approaches to prepare BRPU foams containing 50-70 wt.% of bio-contents. All BRPU foams exhibit good physical, mechanical and thermal properties for their potential application as an insulation material. The major industrial significance of this project is that it helps transform the largely available KL and HL resources into value-added bioproducts i.e., bio-polyols and BRPU foams. As a result, it will help reduce the dependency of RPU foams production on petroleum derived polyols, generate additional revenue streams to the associated industries (particularly, pulp/paper mills and cellulosic ethanol plants), and also improve their sustainability.