Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Charles Chunbao Xu

Abstract

The phenol-formaldehyde (PF) resin manufacturing industry is facing a growing challenge with respect to concerns over human health, due to the use of carcinogenic formaldehyde and sustainability due to the use of petroleum-based phenol in PF resin manufacture. Glucose and its derivative, 5-hydroxymethylfurfural (5-HMF), have proven to be potential substitutes for formaldehyde in the synthesis of phenolic novolac resins.

This thesis investigated a number of glucose and 5-HMF resin systems including the curing of phenol-glucose novolac resin (PG) with a bis-phenol-A type epoxy. The curing process was modeled according to the Sestak-Berggren equation (S, B) using Málek methods. This was followed by a novel one-pot two-step approach for the synthesis of phenol-5-hydroxymethylfurfural (PHMF) resin by reacting phenol with HMF generated in-situ from glucose. The catalytic effect of CrCl2/CrCl3 and tetraethylammonium chloride (TEAC) in the process was studied and found to facilitate both glucose dehydration and phenol-aldehyde polycondensation reactions. The resulting PHMF resins had a weight average molecular weight (Mw) in the range of 700-900 g/mol and a structure similar to novolac PF resins. Moreover, an attempt was made to make the system greener by using lignin as a bio-based curing agent for the synthesized PHMF resin. The curing mechanism was elucidated using spectral methods and a lignin model compound. A void-free polymer matrix was produced from the PHMF resin and bis-phenol-A epoxy resin upon curing. In addition, bio-phenolic compounds were produced from woody biomass by hydrothermal liquefaction or hydrolytic depolymerisation of lignin. These bio-phenolic feedstocks were used to partially replace the petroleum-based phenol in the production of bio-based PHMF (BPHMF) resins.

Differential scanning calorimetry (DSC) was used to study the curing kinetics of all the cross-linking reactions for the PHMF and BPHMF resins. The kinetic parameters obtained using model-free methods and model-predicted reaction rates are in good agreement with the experimental results. The effects of different process parameters including curing temperature and reaction time were discussed, and the amount of hardener (i.e., curing agent) was optimized.

Glass fiber reinforced composites of PHMF and BPHMF resins were prepared by impregnating glass fibers with the PHMF or BPHMF resins. The thermal, mechanical, dynamic mechanical and rheological properties as well as chemical and water resistance of the matrix and the composites were studied.