The aim of the study was to develop lightweight and strong composite materials from nanocellulose and water-soluble polysaccharides (WSPs). The composites have potential in replacing oil-based materials in packaging, electronics, and medical applications. The used materials are renewable and the chemical modification methods are environmentally friendly. First a way to make good quality thin films from only cellulose nanofibrils was developed, where after the focus was to optimize the type, modification and mixing ratio of added water-soluble polysaccharides. The made composites were characterized in nano- to micron size scales and their relationship with e.g. macroscopic tensile and thermal properties were investigated. Various WSPs such as galactoglucomannan (GGM) and guar gum (GG) were used as such and after enzymatic modification, as soft adhesive component in the film raw material. GG was enzymatically oxidised and gas chromatography-mass spectrometry (GC-MS) was used to study the degree of oxidation of modified GGs. The characterization of the composite materials was done in two levels: CNF model surfaces were used to study the details of WSP adsorption and interfacial forces between CNF and WSPs. Macroscopic tensile properties of the free-standing composite films were studied using tensile testing, and structural features were measured by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The adsorption of WSPs on CNF model surfaces was studied by quartz crystal microbalance (QCM-D). The surface interactions between the constituents of the composites were studied using colloidal probe atomic force microscopy (CPM). All tested WSPs adsorbed on cellulose surfaces. The interactions in pure CNF model films were successfully explained by DLVO theory, whereas the interactions in CNF+WSP films were well described by a polyelectrolyte brush (PEB) model. Adsorbing WSP on the surface had a small lubricating effect by lowering the friction of model films. GGM, and hydrolysed and oxidised GG, added to CNF, had significant reinforcing effect on the wet strength composite films even after the composites had been soaked for extended period. Multilayer composites were made by laminating CNF+WSP films with epoxy and it was shown to improve the mechanical properties compared to only CNF-epoxy laminates and increased the application temperature range by raising the glass transition temperature of the epoxy matrix. Finally, to summarize, the work showed that only small modifications to CNF films can enhance the properties of the films. The work combined nano -and macroscopic features of the films for creating better understanding of the composites. The renewable materials are needed to replace plastic and for high level applications.
|Publication status||Published - 2019|
|MoE publication type||G5 Doctoral dissertation (article)|
- guar gum