Effect of Urea/Polyethylene Glycol Freeze-Activation Treatment on Bonding Mechanism and Properties of Adhesive-Free Straw Fiberboard

Self-bonding plant fiber boards harness the natural properties of plant fibers to develop adhesive strength through specific procedures, thereby minimizing or eliminating the need for chemical adhesives. This environmentally sustainable engineered board has significant potential for practical applications. In this study, adhesive-free straw-based fiberboards were fabricated using the freeze activation method, where straw fibers were treated with a composite activator of urea and polyethylene glycol (PEG) under low-temperature freezing conditions (−15°C,1 h). The resulting boards exhibited desirable mechanical properties. Mechanical testing indicated that a 20% activator content yielded fiberboards with enhanced mechanical properties: tensile strength of 8.25 MPa, flexural strength of 18.46 MPa, internal bonding strength of 0.23 MPa, and an increased contact angle of 82.37°. Surface analysis via SEM and XRD indicated SiO2 enrichment on the fiber surface and enhanced cellulose crystallinity post-freeze activation treatment, optimizing the mechanical stability of the fiberboard. The activator promoted the oriented alignment of hydroxyl groups on the fiber surface, reinforcing hydrogen bonds and van der Waals forces, thereby improving the mechanical strength through enhanced surface structure and chemical composition.