Biodegradable composites from poly(butylene adipate‐<i>co</i>‐terephthalate) with soybean protein isolate: Preparation, characterization, and performances

Abstract Soy protein isolate (SPI), a widely available and inexpensive natural polymer, can be used as a filler to reduce the cost of poly(butylene adipate‐ co ‐terephthalate) (PBAT) materials. To improve the compatibility between SPI and PBAT, a series of polycaprolactone‐based polyurethane prepolymers (PCLPUs) with different soft segment molecular weights were synthesized and used as compatibilizers to prepare SPI/PBAT composites. At the same time, the effect of PCLPU soft segment molecular weight on the properties of SPI/PBAT composites was studied. Structural, morphological, and property analyses were carried out on the composite materials; the results showed that PCLPU was an effective compatibilizer for SPI/PBAT composite materials. The –NCO group at its end forms a urethane bond with the hydroxyl group in SPI and PBAT. At the same time, the soft segment of PCLPU is physically crosslinked with PBAT to produce a dual physical and chemical effect. The lower the soft segment molecular weight of PCLPU added, the better the performance of the SPI/PBAT composite materials. This is observed because PCLPU with a lower soft segment molecular weight contains more –NCO functional groups, which can better achieve compatibilization between SPI and PBAT through chemical crosslinking. The addition of 5% PCLPU‐500 content to the SPI/PBAT composite material increased its tensile elongation, impact strength, and tensile strength by 867%, 264%, and 150%, respectively, compared with those of the SPI/PBAT composite material without a compatibilizer, achieving toughening and strengthening with good processability and biodegradability. This work provides a simple, effective solution for preparing high‐performance, green, and low‐cost biodegradable composite materials. Highlights PBAT composites were prepared using soy protein isolate (SPI) as filler. Different types of PCLPU exist as a reactive compatibilizer for PBAT and SPI. Polycaprolactone‐based polyurethane prepolymer significantly improves the interfacial compatibility of PBAT composites. SPI/PBAT film has good degradability and is a rich source of nitrogen.