Evaluation of hydrolytic and thermal stability of plywood, bonded with urea-formaldehyde resins with tire pyrolysis char, wheat flour and coconut shell powder as novel filler systems

Abstract

The objective of this study was to evaluate the properties of the plywood, bonded with urea formaldehyde (UF) resins with added novel filler systems. 3-ply and 5-ply plywood panels were produced with rotary-peeled rubberwood veneers using UF resin as binder. Three UF resins were prepared by varying the F:U mole ratios viz., 1.0 1.2 and 1.4 (a control and two innovative high molar ratio) by a conventional alkaline-acid two-step process, with the second addition of urea. Resins were analyzed for their specifications with FTIR measurements and thermogravimetric analysis both in their liquid and cured states. Five different fillers viz., (wheat flour, coconut shell powder, commercial charcoal-N660, tire pyrolysis charcoal and treated tire pyrolysis charcoal with phenol, etc.) were selected and %wt. of filler was added to each resin varied as 10, 15 or 20. Mechanical properties and dimensional stability, i.e., water absorption and thickness swelling of the plywood varying with the % filler and the variety was investigated. The shear strengths of plywood boards of 1.4 F/U were observed as 2.50, 2.55, and 3.15 MPa when wheat flour filler was used as 10, 15, and 20 %wt. These strengths were increased to 4.64, 5.09, and 5.60 MPa respectively when the filler is changed to the coconut shell powder. Tire pyrolysis char shows better mechanical properties than wheat flour but lesser than coconut shell powder as the filler. This work showed %wt. and the variety of bio-fillers added to UF resin bonded plywood have a huge impact on their physicochemical properties.