Nanoparticle-free, recyclable, and photothermal-responsive castor-oil-based shape memory polyurethane with regulatable mechanical properties and antibacterial activity

Abstract

Photothermal shape memory polyurethanes (SMPUs) have attracted more and more attention due to their precision, flexibility, and remote control. However, the current photothermal SMPUs often rely on petroleum-based resources and utilize inorganic or metal nanoparticles as photothermal agents, which would not only cause a resource crisis but also pollute the environment. In addition, their own non-recyclability would further expand the drawbacks mentioned above. Herein, we report nanoparticle-free, recyclable, and photothermal-responsive castor oil (CO)-based shape memory polyurethanes (denoted BPUs), which are synthesized by CO, 1,4-benzoquinone dioxime (BQDO), and 4,4′- methylenedicyclohexyl diisocyanate (HMDI). Benefits from the rational molecular design, the mechanical properties of BPUs can undergo a wide range of changes from soft to tough and then to hard. Compared with the control sample, the σ and E of BPUs are increased by 9.6–29.8 times and 3–854 times, respectively. They also showed exceptional malleability, reprocessability, recyclability, and dual-shape memory due to dynamic oxime-carbamate bonds formed by BQDO reacting with isocyanate. Specifically, after several thermal remodeling BPUs, their mechanical properties can basically return to more than 92% of the original sample. Moreover, BPUs can maintain Rf and Rr above 90% after several shape memory-reconstruction cycles. More importantly, BPUs have excellent photothermal performance due to the color and conjugate structure of BQDO. For example, BPU-2 can reach 102.1 °C after being exposed to NIR light with a power density of 0.8 W/cm2 for about 50 s. At the same time, several functional applications of BPUs have been developed based on the excellent photothermal performance of BQDO, such as photothermal shape memory, photothermal engines, and photothermal antibacterial (sterilization rate is around 99%). This work provides new enlightenment for the high-value utilization of CO-based SMPUs; and certain reference significance for the sustainable development of photothermal SMPUs.