Biodegradable extruded thermoplastic maize starch for outdoor applications

In the recent years, great progress was achieved in the development of biodegradable products based on agricultural raw materials. Among them, one of the most promising and diffused biomaterials is represented by starch. For this reason, different approaches have already been explored to use starch as a natural source for the production of biodegradable thermoplastic polymers. However, there is still a lack of a controlled, easy and cheap procedure to process maize native starch in order to obtain a highly performing thermoplastic polymer. The purpose of this paper is the development of a simple and reproducible method able to produce a thermoplastic starch that can be easily transformed into extruded objects, suitable for several potential applications. To reach this aim, a proper plasticizer was added to a commercial maize starch at different concentrations corresponding to mass fraction from 50 to 70% (in the following text %). The effect of the different amounts of the plasticizer on the processability of the starch powder was assessed by varying the parameters during the extrusion process. The interaction of the structure of starch with the plasticizer, firstly, and the final thermal and physical–mechanical properties of the extruded thermoplastic starch samples, secondly, were analysed by using several techniques: differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, UV transmittance, moisture absorption, colorimetric and mechanical tests. The samples containing 50% of plasticizer, in possess of the best physical and thermal performances, were further characterized in terms of durability, in order to predict their lifetime in outdoor conditions, by using artificial ageing tests, such as moisture absorption and QUV accelerated weathering tests.