Hydrochar as an environment-friendly additive to improve the performance of biodegradable plastics.

Plastic additives affect the properties of plastics, which further determine the application range of plastics. However, most plastic additives have environmental friendliness or performance issues limiting their application. Hydrochar (HC) from waste biomass by hydrothermal carbonization has been proved to contain organic matter as function substances, like a binder, and is environment-friendly material. Currently, hydrochar as a plastic additive has not been previously reported. In this study, the HC/PBAT composites were produced by hydrochar blending with poly (butylene adipate-co-terephthalate) (PBAT) which is a biodegradable polymer. The hydrochar produced at different hydrothermal carbonization temperatures (180 °C, 210 °C, 240 °C, 270 °C, and 300 °C) and the addition of hydrochar (10 wt%, 20 wt%) were investigated. The results showed that the elastic modulus of the composites was increased by 27.4 MPa and 32.5 MPa compared with virgin PBAT while adding 10 wt% and 20 wt% hydrochar, respectively. Moreover, the stiffness of the composite was improved, and the balance of stiffness and toughness of the composites was effectively maintained when adding 10 wt% hydrochar treated at 300 °C. The elongation at break, tensile strength, and the elastic modulus of its composites were 630.8 ± 13.7%, 23.0 ± 0.4 MPa, and 100.5 ± 2.7 MPa, respectively. Furthermore, the crystallization temperature of the composites was increased after hydrochar was added into PBAT, and the maximum was 87.9 °C. It also means that hydrochar has a great nucleation effect during plastic processing. Therefore, hydrochar can be used as an environment-friendly additive to promote the performance of biodegradable plastic and promise to be applied in the field of biodegradable plastics.