Tailoring the properties of regenerated cellulose films

Abstract

The production and waste management challenges of fossil-based plastics contribute to the environmental problems such as pollution and greenhouse gas emissions. New European Union (EU) directives limit the use of single use plastics and set new strategies for packaging materials in order to reduce the environmental burden the petroleum-based plastics are causing. Therefore, there is an urgent demand to find alternative materials especially in the packaging applications. Biopolymers, such as cellulose, is considered as a potential replacement material in the packaging industry. Cellulose is nontoxic, biodegradable, and sustainable polymer that can be found in nature. It is not thermoformable, but it can be processed via dissolution and regeneration in order to produce, for example, regenerated cellulose films (RCF). In this master’s thesis the effect of degree of polymerization (DP), blending samples with different DP values, removal of undissolved cellulose and addition of cellulose fibers on mechanical on barrier properties of RCFs were evaluated. Four samples from eucalyptus kraft pulp with different DP values (209-509) were used. Non-derivatizing aqueous alkali solvent system was used to dissolve the samples. The formed cellulose solution was evaluated with optical microscopy and rheological properties were determined. Tensile strength and elongation at break were determined for both wet non-plasticized and dry plasticized RCFs with a tensile test. Also, the morphology was evaluated by scanning electron microscopy and the oxygen transmission rate (OTR) and grease resistance (GR) were measured for certain RCFs. It was found that none of the studied factors significantly affected the barrier properties against oxygen and grease. In addition, no films could be prepared from the sample with the lowest DP due to the brittleness of the films. It was assumed that the polymer chain size was too short to form entanglements and interact with each other. Blending cellulose samples with different DP values was shown to decrease the mechanical properties as the amount of smaller DP containing sample was increased and in other cases no significant changes were observed. Undissolved cellulose seemed to have mechanical properties decreasing effect because removing it by centrifuging and filtering increased the strength and ductility in both wet and dry films. The addition of cellulose fibers did not significantly change the mechanical properties of dry films. In wet films the effects were not clear which was suspected to be due to the undetermined and uncontrolled amount of moisture in the wet films. The tensile strength and elongation at break in wet non-plasticized films varied between 0.6-1.8 MPa and 5-45 %, respectively. In dry films the corresponding results ranged between 30-58 MPa and 3-11%, respectively. The respective OTR and GR results were less than 10 cc/m2 ·day and > 11 days for all measured films. The tensile strength and oxygen barrier of the dry films were significantly higher than for commonly used fossil-based plastics polypropylene and polyethylene. Based on this, the RCFs could be used as a sustainable alternative to replace these fossil-based plastics in certain packaging applications.