Regenerated cellulose films from a binary solvent system

Abstract

In this thesis, the cellulose films regenerated from various solvent systems and the main properties of such films were reviewed based on the recent literatures. Among the different solvent systems, it has been found that a certain class of ionic liquids are more environmentally friendly, since the processing conditions of cellulose are much milder and only small amounts of degradation products are generated from the solvent and solute. In general, the regenerated cellulose films from ionic liquids are transparent with relatively high mechanical properties. In addition to their biodegradability and thermal stability, the regenerated cellulose films are considered to have a great potential to be used as packaging materials. This thesis focused on the dissolution of birch prehydrolyzed kraft pulp (Enocell) in 1,5-diazabicyclo [4.3.0] non-5-ene acetate ([DBNH]OAc) and the fabrication of regenerated films by casting without extensive stretch. Various cellulose concentrations, different coagulation media and different drying methods were explored to optimize the process, and to improve the comprehensive properties of the regenerated films. It was found that the best films were obtained from a concentration of 5.6 wt% to 5.8 wt%. The most appropriate regeneration conditions were coagulation in aqueous ethanol (80%) and drying at a constant humidity of 30% RH (relative humidity) and at a temperature of 23 °C. With slight stretching, these films showed a high tensile strength of 75 MPa, an elongation of 3% and a Young’s Modulus of 6.5 GPa. The optical transmittance was over 88%, which was comparable to that of the commercial cellophane. 10 wt% Betulin based on Enocell pulp was mixed with the solution, resulting in an enhanced contact angle from 27.5° to 71.5°, due to the aggregates of Betulin dispersed evenly on the surface. However, both films (with and without the addition of Betulin) showed poor water vapor barrier properties, which were between 3000 and 4000 g∙μm/m^2∙day∙kPa.