Using bio-based chemicals and recycling waste plastics are essential components of the circular economy. Wood−plastic composites (WPCs), fabricated from recycled plastic and wood-processing wastes, are new, green, and environmentally friendly materials. However, their flammability causes potential fire risks and hazards. Although bio-based flame retardants possess the essential advantage over inorganic or petroleum-based chemicals, their application, particularly that of fully bio-based flame retardants, in WPC has been seldom reported. Herein, we designed and synthesized a fully bio-based flame retardant, phytic acid-tyramine salt (referred to as PATA), using a green and environmentally friendly approach with only deionized water as the reaction solvent. PATA is subsequently utilized in conjunction with ammonium polyphosphate (APP) to synergistically impart flame-retardant properties to WPCs. PATA/APP shows a good flame-retardant effect, improving the flame retardant and smoke suppression properties of WPCs. The PATA/APP system can increase the limiting oxygen index by 31% and achieve a vertical combustion V-0 rating. Furthermore, the PATA/APP system can reduce the peak heat release rate, total heat release, and maximum smoke density by 49, 22, and 15%, respectively. The PATA/APP system can generate phosphoric acid substances during combustion, which promote the decomposition of wood flour to form stable char layers containing P−N−C or P−O−C structures. Consequently, we provide an environmental-friendly approach to enhance the flame retardancy of WPCs.

The emergence of 4D-printing technology provides a new opportunity for the development of shape memory polymers (SMPs) with sophisticated or individualized architectures in the most material-saving way. Fused deposition modeling (FDM) has been regarded as a feasible and facile printing technology to print thermoplastics, but the low adhesion between interlayers of the obtained objects is an unavoidable problem caused by its printing principle. Fortunately, abundant biobased chemicals with a variety of reactive groups make it easy to design ecofriendly linear SMPs with active sites, which are ready for in situ reactions during FDM printing. Herein, we developed fully biobased shape memory copolyesters (PBSe-co-PBIs) by polycondensation of dimethyl itaconate, dimethyl sebacate, and 1,4-butanediol. The flexible and crystalline PBSe may serve as a molecular switch to ensure the desirable shape memory effect (SME) of the materials, and the PBI moiety with double bonds forming cross-linking points between layers during the printing process under UV irradiation acts as net points for SMPs and enhances interlayer adhesion. The shape memory performance and the enhanced interlayer adhesion of printed materials by this strategy were verified by DMA analysis and tensile tests. Finally, a 4D-printed "Sanxingdui bronze mask" and an overheating protection cover were demonstrated, which indicated a great potential in high-temperature protection devices.