Combined effects of starch dry heat treatment (DHT) and chitosan blending on materials produced by extrusion

Starch is a biodegradable polysaccharide with potential application as bio-based plastic. However, its utilization is limited due to poor mechanical properties and high-water affinity. This study evaluated strategies to address these limitations: (1) starch modification through dry heat treatment (DHT); (2) blending starch with chitosan; and (3) combining DHT-modified starch with chitosan. Unlike previous reports describing a two-step extrusion process for producing chitosan/starch materials, this study developed a single-step extrusion process, based on two feed streams - a dry (wheat starch and chitosan - up to 45 %) and a wet (water, glycerol and acetic acid) mixture. Experiments were conducted to determine the minimum amount of acetic acid required to solubilize chitosan, as well as the maximum chitosan concentration capable of forming a homogeneous blend with the starches. Results showed DHT enhanced tensile strength (TS) by 25 % and Young's modulus (YM) by 110 %, while reducing elongation at break (EB) by 25 % and water uptake by 40 %. Blending native starch with chitosan enhanced water-stability (reducing water uptake by 69 %) and improved YM by 370 %, but reduced TS and EB by 15 and 80 %, respectively. Combining DHT-modified starch with chitosan did not provide additional advantages compared to blending native-starch. These findings demonstrate DHT-modified starch is promising for enhancing mechanical properties and water stability, while blending native starch with chitosan enhances water stability, highlighting their potential as packaging.