Effect of α-tocopherol on the processability, tensile properties, and structure of fully bio-based poly (butylene succinate)/Brewer’s spent grain composites

Renewable and biodegradable plastics are of interest to the scientific community as a solution to the environmental pollution caused by petroleum-based plastics. This aspect, combined with the need to dispose of enormous quantities of agri-food industrial waste (such as brewer's spent grains, or BSG), has led to the consideration of the direct use of polybutylene succinate (PBS, a bio-derived and biodegradable bioplastic) blended with BSG (at 25% by weight) to utilize "green" materials and recycle agri-food waste. Alpha-tocopherol (TOC) is added to the PBS/BSG biocomposite blend at 2–10% by weight. The blends' structure-property correlation was performed through chemical, physical, rheological, and tensile mechanical characterization. The results show that TOC performs the dual function of plasticizer and physical compatibilizer, due to the hydrogen bonding between PBS and BSG. This effect is attributed to the dual chemical structure of TOC (polar head and nonpolar tail), which should not exceed 4% by weight, as higher amounts reduce the crystallinity degree of PBS and destabilize its macromolecular structure, compromising its mechanical properties. Amounts lower than 4% by weight are insufficient for the compatibilizing/plasticizing effect. TOC at 4% by weight reduces the viscosity of the mixture (by ~2 orders of magnitude), mechanical stress during processing (-56%), improves deformability by 33%, and improves the toughness of the blend by 43%.