Structural impact on some physical properties of cellulose-based films

Sammanfattning: Cellulose is a natural material that can be used both in its original form and as a building block for creating new types of materials. This work focused on regenerated cellulose (RC) and cellulose acetate butyrate (CAB) in which the hydroxyls on the cellulose backbone were substituted with ester groups. In this work both RC and CAB were formed as free-standing films via initial dissolution and characterized with respect to their structural and morphological aspects, as well as some other material properties. Cellulose pulp was dissolved in cold aqueous alkali urea solution and regenerated in either alcohols or esters to form RC films. Variations of commercially available CAB were dissolved in acetone and solvent cast to form CAB films.This work strove to understand the structural relations of cellulose-based films, the fundamental principles of these materials and how they affect the material properties. This work examined the effect of the polarity of the regeneration liquid on the crystallinity and on other material properties of dried RC films (Papers I and III). This work also investigated the variation in degree of substitution of butyrate and the variation in molecular weight of commercially available CAB and how those could affect the microstructural order of a solvent cast film to the degree that a measurable change in material properties could be observed (Paper II). This was done via structural analysisusing solid-state nuclear magnetic resonance (ss-NMR), x-ray diffraction (XRD), and temperature-modulated differential scanning calorimetry (TOPEM DSC), on RC and CAB films. The qualitative concept of “film formability” was used in this work to determine the practical film properties (related to the ease of handling a film) based on subjective observations.Both the RC films and the CAB films were transparent, with some variations. The CAB films were more fragile than the RC films, even when theCAB films were almost triple the RC films’ thickness. The RC films could be bent considerably, even sharply folded, whereas the CAB films were only slightly bendable before they snapped.The crystallinity of the RC films varied with the regeneration liquid used,and an increase in crystallinity was observed in the following order: EtOH