Abstract
The current production of wood composites relies mostly on formaldehyde-based adhesives such as urea formaldehyde (UF) and phenol formaldehyde (PF) resins. As these resins are produced from non-renewable resources, and there are some ongoing issues with possible health hazard due to formaldehyde emission from such products, the purpose of this research was to develop a formaldehyde-free plywood adhesive utilizing waste protein as a renewable feedstock. The feedstock for this work was specified risk material (SRM), which is currently being disposed of either by incineration or by landfilling. In this report, we describe a technology for utilization of SRM for the development of an environmentally friendly plywood adhesive. SRM was thermally hydrolyzed using a Canadian government-approved protocol, and the peptides were recovered from the hydrolyzate. The recovered peptides were chemically crosslinked with polyamidoamine-epichlorohydrin (PAE) resin to develop an adhesive system for bonding of plywood specimens. The effects of crosslinking time, peptides/crosslinking agent ratio, and temperature of hot pressing of plywood specimens on the strength of formulated adhesives were investigated. Formulations containing as much as 78% (wt/wt) peptides met the ASTM (American Society for Testing and Materials) specifications of minimum dry and soaked shear strength requirement for UF resin type adhesives. Under the optimum conditions tested, the peptides–PAE resin-based formulations resulted in plywood specimens having comparable dry as well as soaked shear strength to that of commercial PF resin.
Highlights
Production of wood-based panel products such as plywood, oriented strand boards (OSB), medium-density fibreboards (MDF), particleboards, and hardboards requires the use of wood adhesive binders
A thermal hydrolysis procedure that was previously developed in our lab was used in this study, which was based on a Canadian Food Inspection Agency (CFIA) approved protocol for specified risk material (SRM)
SRM, the primary feedstock for our adhesive formulations, was subjected to thermal hydrolysis, followed by extraction and purification of the resulting peptides, using procedures developed in our laboratory [8]
Summary
Production of wood-based panel products such as plywood, oriented strand boards (OSB), medium-density fibreboards (MDF), particleboards, and hardboards requires the use of wood adhesive binders. In 2013, global wood-based panel production reached 367 million m3 [1], requiring. 16.2 megatonnes of wood adhesives and binders [2]. Formaldehyde-based resins such as urea formaldehyde (UF), phenol formaldehyde (PF), resorcinol formaldehyde (RF), melamine formaldehyde (MF), and melamine–urea–formaldehyde (MUF) resins are currently the most common type of wood adhesives. Urea–formaldehyde products accounted for over 30% of the global wood adhesives consumed in 2013 [2]. The use of wood adhesive resins is on the rise due to increasing demand of engineered wood products [1]. Consumption of formaldehyde-based resins is on the Polymers 2016, 8, 285; doi:10.3390/polym8080285 www.mdpi.com/journal/polymers
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