On the physico-chemical properties of softwood hemicellulose and compounds derived from it

Abstract: Hemicellulose is the second largest polysaccharide group available in nature after cellulose. Hemicellulose is present in plant cell walls along with cellulose and lignin. It is an abundant and biodegradable material that could potentially replace fossil-based products. The focus of this thesis is the properties and valorization of softwood hemicellulose (galactoglucomannan).In the first part of the thesis, the nature of the interactions between hemicellulose and cellulose was investigated. The adsorption studies of several types of hemicelluloses to cellulose model surfaces were performed using ellipsometry, QCM-D and neutron reflectometry. The results showed that the binding between hemicellulose and cellulose involves specific interactions facilitated by similarity in the backbone unit conformation. The adsorption showed the molecular weight dependency with the largest adsorbed amount obtained for a hemicellulose with the largest molecular weight at a low concentration regime. The opposite trend was observed at higher concentrations. Neutron reflectometry results demonstrated that lower molecular weight hemicellulose samples with higher flexibility were able to more extensively diffuse into the amorphous parts of the cellulose layer.In the second part of this work, the properties of various hemicellulose-based colloidal systems were evaluated. Softwood hemicellulose extract provided excellent stabilizing effect to lipid liquid crystalline phase nanoparticles. These nanoparticles showed high colloidal stability over the period of at least 42 days with no major changes in the hydrodynamic diameter and the polydispersity index.Inclusion of mannans derived from hemicellulose in the structure of thermoresponsive NIPAm-based copolymers shifted the transition temperature to higher values. Mannan side groups were here suggested to create a hydrophilic shell around the hydrophobic particle that provided a stabilizing effect at the elevated temperatures up to 70°C.Finally, the hemicellulose-based surfactant mixture demonstrated surface active properties with formation of two separate kinds of micelles as evidenced by the two inflection points in the surface tension curve.