Biodegradable composites from poly(butylene adipate-co-terephthalate) with soybean protein isolate: Preparation, characterization, and performances

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.