Abstract
Commercial wood adhesives are based on products that contain formaldehyde; however, environmental and health concerns about formaldehyde emissions from wood products have influenced research and development efforts in order to find alternative, formaldehyde-free products for wood adhesives. In this work, different soy protein-based wood adhesives are proposed, and their performance is compared to commercial urea formaldehyde (UF) adhesive. Soy protein-based wood adhesives were prepared using either soy protein isolate (SPI) or soy protein flour (SF) with different coadjutant polymers: polyethylene oxide (PEO), hydroxypropyl methylcellulose (HPMC), cellulose nanofibrils (CNF) or polyvinyl alcohol (PVA) with and without addition of kraft lignin. The effects of the type of soy protein, solids content, coadjutant polymer and lignin addition were investigated. The wood adhesive formulations were tested on the bonding of hardwood (white maple) and softwood (southern yellow pine) and the dry shear strength of test specimens was measured according to method ASTM D905-08. The adhesive formulations with SPI achieved significantly higher values than those with SF. The dry shear strength of the adhesives varies depending on the coadjutant polymer, the wood species and the addition of lignin.
Highlights
Wood adhesives represent a large portion of the global adhesives market; for example, in 2018 the global wood adhesives market size was valued at USD 4.60 billion [1]
The results of dry shear strength show that the adhesive performance of the formulations is different if they are applied to southern yellow pine or maple
The addition of lignin has a different effect depending on the coadjutant polymer in the formulation
Summary
Wood adhesives represent a large portion of the global adhesives market; for example, in 2018 the global wood adhesives market size was valued at USD 4.60 billion [1]. Wood adhesives are used in products such as plywood, particleboard, oriented strand board and medium density fiberboard, which are used in wood furniture and the construction industry. Emission Standards for Composite Wood Products, intended to reduce formaldehyde emissions from different wood products including but not limited to hardwood plywood, medium-density fiberboard, particleboard and/or finished products containing these composite wood materials [4]. Among the challenges in alleviating this problem is the development of wood adhesives that are formaldehydefree, but that can perform well as those containing formaldehyde. This includes the tuning of the material adhesive properties [5]. Soy protein adhesives have been extensively studied for their natural biobased potential [6,7,8]
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