The mechanical properties of films based on differently modified potato starches

In recent decades, interest in bio-based materials as substitutes for plastics has grown significantly. Polysaccharides as part of an arsenal of biodegradable, renewable and edible biopolymers have shown great potential as plastic substitutes. Starch has gained some popularity among the polysaccharides as it seems to fit for these purposes surprisingly well despite its weaknesses. This thesis offers an insight into starch as a biopolymer and reviews its film-forming properties and strengths as a film former while pointing out the weaknesses and suggesting strategies to overcome these disadvantages. Modification of starch by focusing on the preparation of cationic and amphoteric starches by etherification and esterification is discussed followed by an insight into the usage of polyols as plasticizers in the starch films and a novel plasticizer used in the starch films will be presented. Lastly, applications and properties of starch-based biopolymer films will be shortly reviewed. The study was built around the commercial modified potato starch-based biopolymer products which are traditionally used as strengthening agents in paper and board industry. The main samples included both cationic and amphoteric liquid like products. For comparison, native potato starch together with a low cationic powder like product were studied alongside the other samples. The aim was on the utilization of these starches in film preparation and to examine the differences between the samples. The composition of the starch products was confirmed by spectral analysis and investigation of the properties of the films concentrated on thermal and mechanical analysis. Additionally, the work presents a novel use of (2,3-dihydroxypropyl) trimethylammonium chloride (DHPTAC) as a plasticizer for potato starch and modified potato starch based biopolymer films. Major outcome from the mechanical analysis was that the mechanical properties of the starch films were clearly dependent on two things: the amount of DHPTAC in the film and degree of the modification of starch. However, the results from the thermal analysis were not so consistent