Adhesive-Free Cornhusk-Based Biocomposites via Alkali Retting–Pressing Strategy

Cornhusks are widely employed as reinforcing fillers in biocomposite fabrication, where conventional manufacturing processes rely on petroleum-derived resins or adhesives. This reliance not only poses substantial risks to human health and ecological environments, but also leads to the unsatisfactory mechanical performance of the final products. Developing a feasible strategy to eliminate petroleum-based binders while simultaneously enhancing the mechanical strength of the biocomposites remains a challenge. In this paper, we present an adhesive-free approach to produce high-performance, sustainable biomass structural materials directly from raw cornhusks, without prior pulverization, via a combined alkaline retting and hot-pressing treatment. Benefiting from the synergistic effects of highly aligned cellulose fibers and a densely compacted multi-layer structure, the resulting structural material exhibits a tensile strength of 136 MPa and a flexural strength of 127 MPa. These values are higher than those of conventional density fiberboards (approximately 20 MPa and 40 MPa). After 72 h of water immersion, the material shows a water absorption rate of 38% and a thickness swelling rate of 16%, both of which are lower than the corresponding parameters of traditional density fiberboards (around 60% and 20%). Its initial thermal degradation temperature reaches 251 °C, showing good thermal stability. Furthermore, the as-fabricated cornhusk-based structural material, which combines high mechanical strength, water resistance, and thermal resistance, exhibits zero formaldehyde emissions. It can serve as a promising alternative to traditional petroleum-bonded biomass density boards, for applications in furniture manufacturing and interior decoration.