Characterization of plywood made from heat-treated rubberwood veneers bonded with melamine urea formaldehyde resin

Abstract

The objective of the study is to evaluate the properties of the plywood made from rubberwood veneers thermally treated at various temperatures. Rotary-peeled rubberwood veneers were thermally treated at 160, 170, 180, and 190 °C under 1 bar pressure. 5-ply plywood panels were produced using melamine urea formaldehyde (MUF) resin as binder. Dimensional stability, i.e., water absorption (WA) and thickness swelling (TS) as well as mechanical properties of the plywood were assessed. The results demonstrated that the dimensional stability of the plywood made from thermally treated rubberwood veneers improved as indicated by lower WA and TS values. The reduction in WA and TS values increased along with treatment temperatures. Darkening in the plywood as a result of heat treatment was observed. Meanwhile, heat treatment at 170 °C and 180 °C resulted in plywood with the highest modulus of rupture (MOR), modulus of elasticity (MOE) and shear strength. However, beyond that temperature, the mechanical strength of the plywood started to decline. Based on the findings in this work it appears that heat treatment of rubberwood veneers at temperatures ranging from 160 to 180 °C could have a potential to improve overall properties of plywood panels.