A Comparative Study on the Mechanical and Physical Properties of Plywood Panels Prepared by Chitosan as Bio-Adhesive

Abstract

This study aims to make environment-friendly plywood panels acceptable in terms of both mechanical and physical properties using chitosan as a natural binder. Five-layer poplar plywood specimens were prepared with two different commercial adhesives, namely urea-formaldehyde (UF) and methylene diphenyl isocyanate (MDI), and compared with chitosan (CH). For evaluation, mechanical properties such as modulus of rupture (MOR), modulus of elasticity (MOE), glue line shear strength, surface soundness, and physical properties such as thickness swelling (TS), water absorption (WA) of the samples were studied. Variable parameters were: adhesive type (UF, MDI, and CH), adhesive content (2, 4, and 6 wt%), and adhesive spread rate (150 and 180 g/m²). Other parameters such as pressing time (10 min), press pressure (30 kg/cm²) and press temperature (140 ºC) were held constant. Data analysis revealed that the mechanical properties differed significantly among the board types. Based on the findings of this study, the MOR properties of the panels slightly increased when the resin content increased from 150 to 180 g/m². The results of shear strength and surface soundness showed that boards made with chitosan as a binder, had the same results as those made with UF resin. In general, WA and TS decreased (improved) with the increase of resin content. The test results showed that the lowest TS observed in chitosan boards was 4% chitosan with a 180 g/m² spread rate, which is better than UF plywood and, close to the results of MDI specimens. According to the measured parameters, 4% chitosan with a spread rate of 180 g/m² can be considered the optimal binder composition for plywood manufacturing. The overall results show that chitosan has potential as a replacement resin material for plywood manufacturing.