Starch as Co-Plasticizer in Blends Based Polyvinyl Alcohol/Corn Starch: Influence of Starch Content and Process Method Steps on Thermal and Composted Degradation Properties

Abstract

Processing biodegradable polymer films implies challenges, including thermal sensitivity, complex flow behavior, and the need to add plasticizers to confer properties similar to conventional plastics. Two extrusion processes were compared and studied to evaluate the processability of polyvinyl alcohol (PVA) and corn starch (CS) blends. The first method consisted of the mixing of PVA, CS, and glycerol by a one-step extrusion process to obtain PVA/CS 1S blends, and the second method involved the plasticization and processing of PVA and CS, each one with glycerol separately, and then they were extruded again to obtain PVA/CS 2S blends. CS content was varied at 30, 40, 50, 60, and 70 wt-3%. Finally, PVA/CS blends were processed by blown extrusion to produce films. The effect of the extrusion method and CS content on the thermal, morphological, rheological, and mechanical properties of PVA/CS blends was studied. Crystallization and melt temperatures (DSC) decreased with higher CS content. The degradation temperature increased from 210°C to 270°C and 295°C for one-step and two-step processes, respectively, indicating that CS acted as a plasticizer and disrupted PVA crystallinity. One-step extrusion had viscosities closer to PVA, while two-step extrusion resembled CS, resulting in complete starch granule plasticization. The Young's modulus increased by 168% and 146% for one and two-step blends, respectively. Although incorporating 30 wt-% starch via a two-step process leads to a higher disintegration rate (83.8%) and method-dependent property improvements, the one-step extrusion method holds greater industrial promise. Its advantages include lower costs by skipping pre-plasticization, reduced drying requirements, and the ability to use more glycerol.