How the compatibility between polyethylene and thermoplastic starch can be improved by adding organic acids?

Thermoplastic starch (TPS) can be added to a synthetic polymer, including linear low-density polyethylene (LLDPE), as a low-cost renewable and biodegradable source, to reduce the PE content. Nevertheless, this mixture leads to a mechanical performance decrease due to the immiscibility between both polymers. The aim of this work was to investigate the effect of three different organic acids (3% phr): citric, capric, and palmitic on LLDPE/TPS blends, with a mass ratio of 70/30. The introduction of capric or palmitic acid strengthened TPS and LLDPE interfacial adhesion and improved the mechanical properties of the blends. The glass transition of the glycerol-rich phase (measured by DMA) occurs at higher temperatures for LLDPE/TPS/CITRIC blends, suggesting a plasticizer effect of this acid. It also could be seen by SEM, the images showed that improvements in the compatibility between the immiscible components were achieved by capric or palmitic acid incorporation. TPS's incorporation had increased the water absorption because of its hydrophilic characteristic; however, acid incorporation reduced this property. In relation to colorimetric aspects, all blends had loss of brightness, but the ones with citric acid were darker, presenting higher color change than the blends with others acids.