The development of continuously degradable and recyclable polymeric composites with superb mechanical properties, which can extend the service life of materials and reduce the environmental impact, will make a significant contribution to global sustainability. In this study, poly(vinyl alcohol) (PVA)-based composites (DPVA-Fe-TA) with degradability, recyclability and excellent mechanical properties are prepared by complexation of 3,4-dihydroxybenzaldehyde-grafted PVA (D-PVA), tannin (TA) and Fe3+ ions in dimethyl sulfoxide (DMSO), and then dialysis in deionized water and glycerol (Gly). The two-step dialysis process, playing a crucial role in reducing the free water of D-PVA-Fe-TA composites, enhances the formation of reversible of hydrogen-bonding and the reinforcement of self-assembled Fe(3+)chelation between TA and D-PVA, and facilitates the fabrication of PVA-based composites with a breaking strength of approximate to 18.7 MPa, an elongation at break of similar to 812 % and a toughness of approximate to 86.81 MJ/m(3); Meanwhile, the resulting homogeneous and dense structure of D-PVA-Fe-TA composites hinders the penetration of Gly solution, thereby enhancing the bonding strength and environmental adaptability of D-PVA-TA-Fe composites within the temperature range of-20 degrees C to 60 degrees C. Furthermore, the as- prepared D-PVA-TA-Fe composites exhibit recyclability for multiple cycles. When placed under soil culture medium, the resulting composites can be degraded without the need for manual interference. This study presents a novel strategy for the fabrication of materials possessing excellent mechanical strength, environmental adaptability, recyclability and degradation, which have great potential for taking the place of conversional composites in specific conditions.

The increasing demand for environmentally-friendly products has led to a growing focus on the development of high-performance biodegradable materials. However, achieving a balance between mechanical strength, water resistance, and biodegradability remains a challenge. Herein, the successful preparation of exceptional biodegradable poly(vinyl alcohol) (PVA)/starch (ST) composites using alkaline-regulated crystalline engineering is reported. The findings demonstrate that the alkali promotes ST gelatinization while inhibiting its recrystallization, resulting in improved compatibility and good dispersion in the PVA matrix. In contrast, the alkali enhances the crystallization of PVA, thereby improving the composites' water resistance. The composites exhibit outstanding mechanical properties, with a strain at break of approximately 400 % and a toughness of 54 MJ/m3, surpassing most reported works. Even in high humidity and water environments, the composites maintain their mechanical strength, with a strength of 13 MPa after soaking in water for 1 d, significantly higher than films without the addition of alkali. Moreover, the composites exhibit excellent biodegradability, with a degradation rate exceeding 40 % after a 60-d natural soil burial test. The flame retardancy is also greatly enhanced, with a limiting oxygen index (LOI) of 30 %. This study offers a promising avenue for the development of highperformance biodegradable materials such as dip-coating fabric, fire retardant coating, and industrial packaging.

Rubber can improve the mechanical properties of the coated nitrogen fertilizers (CNFs), but the biomass components cause holes in the urea release process, thus accelerating the release of urea. In this study, a self-healing rubber (SHR) shell/hydrogel core based on a supramolecular network was fabricated as a coating material for CNFs to improve the above problems. The core of CNFs consists of vanillin(Van)-cross-linked poly(vinyl alcohol) (PVA)/carboxymethyl chitosan (CMCS) hydrogel, prepared by a freeze-thaw cycle. The shell of CNFs was prepared by soaking Van-cross-linked natural rubber (NR)/chitosan (CS)/PVA material in Zn2+ solution. A green core-shell structured CNF with hydrogen bonding and metal coordination was finally prepared, which has improved the mechanical properties, slow-release effect, and soil water retention capacity of the CNF. The effects of CS and PVA contents and the impregnation of Zn2+ on the physical and chemical properties of the SHR supramolecular composite and its self-healing ability were investigated, and the urea release kinetics were analyzed. The CNFs could reach release equilibrium in water for 10 days, with a slow-release rate of 62.7%, and the urea release kinetics were in accordance with the Korsmeyer-Peppas model (R-2 >= 0.90), with a possible release mechanism of Fickian diffusion.