Effect of Adhesive Content and Modification Method on Physical and Mechanical Properties of Eucalyptus Veneer-Poly-beta-Hydroxybutyrate Film Composites

Formaldehyde-based resin and petroleum-based plastic are often used as an adhesive in plywood manufacturing, which has an adverse effect on people's health and the global environment. We have investigated the plywoodlike composite with wood veneer (WV) and poly-b-hydroxybutyrate film (PHBF) as a novel formaldehyde-free and environmentally friendly composite (WV-PHBF). The composite was prepared with three veneers, and the PHBF placed between adjacent veneers varied from 22.5 to 112.5 g/m(2). The composite was hot pressed at 170 degrees C for 70 s/mm under a pressure of 1.0 MPa. Furthermore, the WV-PHBF with an adhesive dosage at 67.5 g/m(2) was modified with three modification methods: silane coupling agent (KH-550), alkaline solution (NaOH), and polydiphenylmethane diisocyanate (p-MDI). Results showed the following: (1) under the untreated condition, a composite with more than 67.5 g/m(2) adhesive will meet the Chinese National Standard (GB/T) 9846-2015 of bonding and bending strength requirements, and 90.0 g/m(2) was the best; (2) the KH-550 and p-MDI treatment had a positive effect on WV-PHBF, but NaOH mainly had an adverse effect; (3) the physical-mechanical properties of the composite with 67.5 g/m(2) adhesive content being processed by 1 percent by weight (wt%) KH-550 or 2 wt% p-MDI was better than WV-PHBF with 90 g/m(2) adhesive content, especially in bonding strength; (4) statistical analysis shows that 1.0 wt% KH-550 significantly improved the bonding strength properties of WV-PHBF, and water-resistance properties were significantly improved by 2.0 wt% of p-MDI also; and (5) morphological observation shows that KH-550 and p-MDI treatments increase the interfacial compatibility between WV and PHBF of the composites.