A comparison of different synthesis routes for starch acetates and the resulting mechanical properties

Abstract

Starch acetate based on a sustainable native polymer can be used as a thermoplastic substance to produce e.g. commodity material. This work investigates the influence of the synthesis routes and starch species on the mechanical properties of starch acetate with 20 w% triacetin as a plasticizer after thermoplastic processing. For better comparison, acetic acid anhydride was used both as a reactant and a solvent for all reactions. Three activators, acetic acid, aqueous sodium hydroxide and potassium carbonate, were applied in order to compare the esterification of the polysaccharide. The activators strongly determine parameters like reaction time and molecular degradation of the starch backbone. The modification of starch into starch acetate in acetic acid anhydride with potassium carbonate as an activator was analyzed in detail. To reach highly substituted starch acetates (DS Acetate > 2), the addition time of potassium carbonate, as well as the penetration of the acetic acid anhydride into the starch granule was of great importance. The analytical methods of titration, SEC-MALLS, 13C NMR, X-ray and FT-Raman spectroscopy were applied and the mechanical parameters of tensile strength, elastic modulus and elongation at break were determined in the resulting specimens. A strong correlation between the mechanical data and the synthesis route was found.