Wood Hydrolysate for Renewable Products

Abstract: Renewable biomass has been used by mankind for a long time for different purposes, from simply food to industrial products. Among a large family of polysaccharides, hemicellulose is non-edible but has shown a potential in many industrial fields such as medicine, agriculture and packaging. However, a complicated process is usually required to extract highly purified hemicellulose for further applications, which makes it not practical and economical for real industrial applications.This thesis presents the utilization of a wood hydrolysate which was simply upgraded and recovered instead of being highly purified from the liquid by-product in the pulp industry. This softwood hydrolysate is rich in hemicellulose, O-acetyl galactoglucomannan (AcGGM), and also contains some lignin.Films and coatings were produced based on this wood hydrolysate by blending with two other polysaccharide co-components, carboxymethyl cellulose (CMC) and chitosan. Different recipes with a variety of concentrations and compositions were prepared. For comparison, highly purified AcGGM-based films and coatings were also produced.Mechanical properties and water vapor and oxygen barrier properties of the films and coatings were investigated. It was found that as a co-component, chitosan improved the mechanical properties best, and CMC gave better oxygen barrier properties at both 50% and 80% relative humidity. The wood-hydrolysate-based films gave much lower oxygen permeability (OP) values than AcGGM-based films.In order to reveal why the less purified wood hydrolysate gave a better oxygen barrier, both theoretical and experimental studies were carried out. A group calculation based on Hansen’s Solubility parameter theory (HSP) showed that there were strong interactions between lignin and AcGGM in the wood hydrolysate and also that CMC was more compatible with wood hydrolysate/AcGGM than chitosan. These led to an affinity between components and gave a more compact molecular structure, and thus a smaller free volume in the matrix. This interpretation was in agreement with the Positron annihilation lifetime spectra (PALS) data, which showed that wood-hydrolysate-based films had a smaller free volume (hole size) and narrower distribution than AcGGM-based films. It also showed that CMC-co-component films had smaller hole radii in the matrix than chitosan-co-component films. Thermal properties and FTIR also shed light on the influence and nature of these interactions.