Tuning the Adhesive Properties of Soy Protein Wood Adhesives with Different Coadjutant Polymers, Nanocellulose and Lignin

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.

Improved soy protein adhesives by lignin and polyamide‐epichlorohydrin: Adhesion performance and properties

“… 31 Protein adsorption on solid surfaces is driven by different types of nonspecific interactions such as hydrophobic forces, electrostatics, and hydrogen bonding 32,33 . Therefore, lignin has been utilized as a water resistance improvement for protein‐based adhesives 34–37 . The wet adhesion strength improved approximately 50% with unmodified lignin in our previous study 38 .…”

“…32,33 Therefore, lignin has been utilized as a water resistance improvement for protein-based adhesives. [34][35][36][37] The wet adhesion strength improved approximately 50% with unmodified lignin in our previous study. 38 Further water resistance improvement was achieved by using modified lignin.…”

Effects of soy protein isolate on the physicochemical properties of Fresh extruded rice- shaped kernels

“…The G' and G" declined at the temperature of 75 °C ~ 80 °C. Podlena et al [25] found that the thermal analysis transition temperature of unmodi ed SPI was 73.8 °C. Therefore, it could be preliminarily speculated that the rheological properties of FER may be caused by the denaturation of SPI.…”

Lignin oligomers from mild base-catalyzed depolymerization for potential application in aqueous soy adhesive as phenolic blends

“…However, the formaldehyde emission has caused environmental and health concerns because of its possibility of causing cancer. 3 Recently, soy protein adhesive was revived because the adhesive system did not contain any formaldehyde. Thus, how to overcome the disadvantages such as relatively low bonding strength and poor water resistance has become the focus of research in soy-based adhesive systems.…”