Blends of Poly (Butylene Adipate-Co-Terephthalate) and Thermoplastic Whey Protein Isolate: A Compatibilization Study

This work assesses the influence of the plasticizer polyethylene glycol (PEG) on the compatibilization of poly (butylene adipate-co-terephthalate) (PBAT) and thermoplastic whey protein isolate (WPIT) blends. To prepare the blends, WPI was denatured at 90 °C, in the presence of PEG, to become a thermoplastic material. Dried WPIT was later mechanically blended with PBAT using a torque rheometer at 160 °C and 80 rpm. Two blends were prepared: 90% of PBAT/10% of WPIT (90_10) and 70% of PBAT/30% of WPIT (70_30). Scanning electron microscopy (SEM) analyses showed a homogenous blend morphology and good interaction between the dispersed phase and the matrix. Atomic force microscopy-based infrared spectroscopy (AFM-IR) showed PBAT and WPIT bands in all studied regions of both blends, which suggests that these materials presented partial miscibility. The viscosity ratio of the PBAT/WPIT system was less than 3.5 in the high shear rate region in complex viscosity curves, which indicates that droplet break-up of WPIT may occur by the drop fibrillation mechanism. The addition of WPIT reduced the degree of crystallinity of PBAT in the blends in comparison to pristine PBAT as shown by X-ray diffraction (XRD). Mechanical tests showed that blend tensile strength and elongation at break decreased with the addition of WPIT. Elastic modulus of the blends increased compared to pristine PBAT. Barrier properties were also evaluated showing that the oxygen permeability coefficient reduced by 20% for the blend with 30% of WPIT and vapor water permeability increased with the addition of WPIT.