Evaluation of Bio/pMDI Wood Adhesives
Loading...
Date
2018-09-20
Authors
Zhang, Che
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
With the increasing concerns about formaldehyde emissions from wood-based panels and the demands of the sustainable products, the potential of synthetic wood resins derived from biomass resources has sparked enormous interest. To date, extensive efforts have been devoted to investigating the mechanism, the properties, and the modification approach of the bio-adhesives. To overcome the limitations of pure bio-adhesives (low reactivity, low moisture resistance, and biodegradation), many approaches have been developed to partially replace the bio-polymer with synthetic thermosetting adhesives. In this project, a functional experimental grade binder, made from the reactive extrusion modification process of biopolymers with other reagents, is used as a co-binder in combination with polymeric methylene diphenyl diisocyanate (pMDI) resin, to study the resulting performance of the system for wood adhesive applications.
To evaluate the influence of the experimental grade biopolymer binder on the performance of the pMDI adhesive, a pMDI adhesive blended with water was first investigated. The effect of water content on emulsion morphology and viscosity was characterized. For bonded samples, formulations obtaining the highest bonding strength of the water/pMDI adhesives was determined by comparing the pull-off stress and the lap-shear stress. To further improve the bonding performance, the wood substrate was modified by the silane coupling agent, (3-aminopropyl) triethoxysilane (APTES). The penetration depth of pMDI in the different wood substrates (neat wood, 1wt% APTES-treated wood, 3wt% APTES-treated wood) was accurately determined. These studies indicate that both strong interactions between the adhesives and wood substrate, and a certain level of penetration of the adhesives, are required for the good bonding performance of the water/pMDI adhesives.
The biopolymer/pMDI adhesives were prepared and investigated based on the protocols from the industry partner Ecosynthetix. By comparing the biopolymer/pMDI adhesives with the water/pMDI adhesives, the effect of the biopolymer to the pMDI was determined. The biopolymer can work as a thickener, emulsifier of the system to reduce the dosage of pMDI. In terms of bonding performance, the bonding strength of the biopolymer/pMDI adhesive is comparable with the highest stress achieved by water/pMDI resin, indicating the experimental grade biopolymer can be applied as an effective wood adhesive binder to partially replace pMDI without reducing the overall bonding performance.
Description
Keywords
pMDI, Wood adhesives, Bonding strengths, Biopolymer