Tung oil-derived polyurethane composite foams based on dual dynamic phenol-carbamate exchange with desirable mechanical properties, flame retardancy and recyclability

Abstract

At present, thermoset polyurethane foams were mainly derived from petroleum-based resources and faced inherent challenges such as difficulty in recycling and fire hazard. In this study, tung oil and catechol were used to prepare tung oil-derived polyphenols via Friedel-Crafts alkylation reaction. These polyphenols were combined with isocyanate to synthesize tung oil-derived polyurethane (TPU) foam. With the presence of dual dynamically cross-linked phenol-carbamate bonds, the TPU foam could be hot-pressed several times into a smooth and homogeneous TPU film. To improve the fire resistance and compressive strength of TPU foam, phytic acid functionalized metal-organic frameworks (UiO-66-NH₂@PA) flame retardants were successfully synthesized by one-pot solvothermal method. By adding 20 wt% of flame retardants, the TPU composite foams achieved a UL-94 V-0 flammability rating with a limiting oxygen index of 28.1 vol%. The total heat release, total smoke release, CO production and CO₂ production of the TPU composite foams were reduced by 43.1 %, 57.8 %, 63.6 % and 62.1 %, respectively, compared to the pure TPU foam. Furthermore, the compressive strength of the TPU composite foam continued to increase with increasing flame retardants content, reaching a maximum of 0.55 MPa. Importantly, the introduction of the flame retardants didn't affect the hot-press recycling performance of the TPU foam, but instead improved the tensile strength and flame retardancy of the recycled TPU film. This work paved the way to produce bio-based PU foam with excellent flame retardancy and recyclability.