Despite growing extensive applications, until now the poor thermal stability and flame retardancy properties of wood−plastic composites (WPC) remain effectively unsolved. Meanwhile, industrial lignin has emerged as a potential component for polymer composites due to many advantages including abundance, rich reactive functional groups, high carbon content and tailored capability for chemical transformations. Herein, we have fabricated one biobased flame retardant based on industrial lignin chemically grafted with phosphorus, nitrogen and copper elements, as the functional additive for the WPC. Compared with unmodified lignin (O-lignin), functionalized lignin (F-lignin) is more effective to improve the thermal stability and flame retardancy of WPC because of presence of the flame retardancy elements (P and N) and the catalytic effect of Cu 2+ on the char-formation. The presence of F-lignin not only reduces the heat release rate, total heat release and slows down the combustion process but also decreases total smoke production rate during combustion. The char residue shows that it is the increased char residues and its continuous compact char formed during burning that are responsible for enhanced flame retardancy properties. This work suggests a novel green strategy for improving flame retardancy performance of WPC and promoting the utilization of industrial lignin.

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Despite extraordinary mechanical properties and excellent biodegradability, poly­(lactic acid) (PLA) still suffers from a highly inherent flammability, restricting its wide applications in the electric and automobile fields. Although a wide range of flame retardants have been developed to reduce the flammability, so far, they normally compromise the mechanical strength of PLA. Herein, we have demonstrated the fabrication of a novel core–shell nanofibrous flame-retardant system, PN-FR@CNF, through in situ chemically grafting the phosphorus–nitrogen-based polymer onto the cellulose nanofiber (CNF) surface. The results show that adding 10 wt % PN-FR@CNF enables PLA to achieve a V-0 flame resistance rating during vertical burning tests and to exhibit a dramatically reduced peak heat release rate in cone calorimetry measurements, indicating a significantly reduced flammability. In addition, the tensile strength of PLA also increases by around 24% (about 72 MPa). This work offers an innovative methodology for the design of the unique integration of extraordinary flame retardancy and mechanical reinforcement into one hierarchical nanostructured additive system for creating advanced green polymeric materials.

The inherent flammability of biodegradable polybutylene succinate (PBS) extremely restricts the growing applications as packaging and construction materials; meanwhile, only a minority of industrial alkali lignin has been effectively utilized until now. To address these two challenges, herein we have converted alkali lignin into one biobased additive for PBS by chemically modified lignin with phosphorus, nitrogen, and the zinc­(II) ions. Cone calorimetry results show that addition of 10 wt % modified lignin (PNZn-lignin) reduces the peak heat release rate and total heat release of PBS strikingly by 50 and 67%, respectively. Moreover, the total smoke production is decreased noticeably by 50%. Observations of char residues indicate that adding PNZn-lignin leads to a compact, intact, and thick char layer that is responsible for such enhanced properties. This work offers a new strategy for reducing the flammability and smoke release of PBS, promoting high-value-added utilization of industrial lignin, and designing biobased advanced polymeric materials.

The combination of high strength, great toughness, and high heat resistance for polymeric materials is a vital factor for their practical applications. Unfortunately, until now it has remained a major challenge to achieve this performance portfolio because the mechanisms of strength and toughness are mutually exclusive. In the natural world, spider silk features the combination of high strength, great toughness, and excellent thermal stability, which are governed by the nanoconfinement of hydrogen-bonded β-sheets. Here, we report a facile bioinspired methodology for fabricating advanced polymer composite films with a high tensile strength of 152.8 MPa, a high stiffness of 4.35 GPa, and a tensile toughness of 30.3 MJ/m in addition to high thermal stability (69 °C higher than that of the polymer matrix) only by adding 2.0 wt % of artificial β-sheets. The mechanical and thermostable performance portfolio is superior to that of its counterparts developed to date because of the nanoconfinement and hydrogen-bond cross-linking effects of artificial β-sheets. Our study offers a facile biomimetic strategy for the design of integrated mechanically robust and thermostable polymer materials, which hold promise for many applications in electrical devices and tissue engineering fields.