Study on Synthetic and Bio-Based Phenol-Formaldehyde Adhesives for the Wood-Based Industry

Abstract

Wood-based panels, like plywood (PW), particleboard (PB), oriented strand board (OSB), medium-density fiberboard (MDF), etc., are traditionally manufactured with formaldehyde-based adhesives like urea-formaldehyde (UF), melamine formaldehyde(MF) and phenol-formaldehyde (PF). These adhesives not only are synthesized by raw materials derived from petroleum, that is a finite recourse, but also give rise to the public concern about the free formaldehyde emissions of the panels produced with them. This study investigates the performance of phenol-formaldehyde adhesives where 15% of the phenol has been replaced by any of the natural derived materials: soy protein isolate (SPI), tannin, lignin, cashews nut shell liquid (CNSL) and pyrolysis oil of forestry residues. The experimental adhesives were produced on laboratory scale under the same specifications while their physical characteristics were determined using standard laboratory analysis and thermal analysis techniques like Thermogravimetric/Differential Thermogravimetric Analysis (TGA/DTG) and Differential Scanning Calorimetry (DSC). Their adhesion property was investigated through the fabrication of 3-layer plywood panels which were subjected to testing for their shear strength, wood failure and free formaldehyde emissions performance. These tests were conducted according to the procedures determined by the standards used in the industrial practice and in particular: the European standards EN 314.1 & 314.2, the British standard BS6566 and the Japanese standard JIS A1460. An overall comparative evaluation of the adhesives was carried out using the performance of a conventional phenol-formaldehyde adhesive as a standard. Last, a linear regression statistical analysis was implemented for the location of the most significant physical characteristic of the adhesives relative to their performance in plywood panel application. The experimental adhesives were found to be able to replace successfully a conventional phenol-formaldehyde adhesive on plywood panel application showing also promising flame retardation. The pH of the adhesives was found to be the property with the highest correlation to wood failure performance of the plywood panels.