PBS-Based Green Copolymer as an Efficient Compatibilizer in Thermoplastic Inedible Wheat Flour/Poly(butylene succinate) Blends

Considering the current context of research aiming at proposing new bioplastics with low costs and properties similar to fossil-based commodities currently on the market, in the present work, a hybrid blend containing a prevalent amount of cheap inedible cereal flour (70 wt %) and poly(butylene succinate) (PBS) (30 wt %) has been prepared by a simple, eco-friendly, and low-cost processing methodology. In order to improve the interfacial tension and enhance the adhesion between the different phases at the solid state, with consequent improvement in microstructure uniformity and in material mechanical and adhesive performance, the PBS fraction in the blend was replaced with variable amounts (0-25 wt %) of PBS-based green copolymer, which exerted the function of a compatibilizer. The copolymer is characterized by an ad hoc chemical structure, containing six-carbon aliphatic rings, also present in the flour starch structure. The two synthetic polyesters obtained through two-stage melt polycondensation have been deeply characterized from the molecular, thermal, and mechanical points of view. Copolymerization deeply impacts the polymer final properties, the crystallizing ability, and stiffness of the PBS homopolymer being reduced. Also, the prepared ternary blends were deeply investigated in terms of microstructure, thermal, and mechanical properties. Lastly, both pure blend components and ternary blends were subjected to disintegration experiments under composting conditions. The results obtained proved how effective was the compatibilizer action of the copolymer, as evidenced by the investigation conducted on morphology and mechanical properties. Specifically, the mixtures with 15 and 20 wt % Co appeared to be characterized by the best mechanical performance, showing a progressive increase of deformation while preserving good values of elastic modulus and stress. The disintegration rate in compost was found to be higher for the lower amount of copolymer in the ternary blend. However, after 90 days of incubation, the blend richest in copolymer content lost 62% of weight.