Abstract
A simple and useful approach by using non-toxic and water-soluble raw material to improve the bonding properties of soy protein adhesive has attracted much attention recently. The objective of this research was to provide a simple and environmentally friendly approach for preparing a high adhesion performance soy protein adhesive in aqueous solution by using waterborne-epoxy resin, soy protein and water-soluble polyacrylamide (PAM). The chemical structure and curing characteristics, as well as the initial viscosity and adhesion performance of the resulted soy protein adhesive were characterized by 1H nuclear magnetic resonance (1H-NMR), differential scanning calorimetry (DSC), a rotary viscosity meter and a plywood panel test. The 1H-NMR analysis results confirmed that epoxy resin was successfully crosslinked with the –NH2 groups of the soy protein molecule to form a water-resistance network structure, and the resulting adhesive contains active epoxy groups. It was found that the addition of PAM can decrease the apparent viscosity, lower curing temperature, and enhancing the wet shear strength of soy protein adhesives effectively, which were capable of facilitating their application as wood adhesives. The resulting soy protein adhesive containing 4% epoxy resin and 0.05% PAM dosage had a reasonable viscosity and lower cure temperature, and showed good water resistance and wet shear strength, which met the requirement for interior use plywood of the Chinese Industrial Standard. These results suggested that waterborne-epoxy resin can be used to prepare high-performance environmentally friendly soy protein adhesives, which might provide a feasible methodology to prepare bio-adhesive adhesives for plywood industrial applications.
Highlights
Industrial interest in bio-based polymeric materials from renewable agricultural products has received increased attention over the past decade
According to the ndings shown in Table 1, the apparent viscosity of pure SPI and EPOXYSPI adhesives showed relatively low viscosity compared to other soy protein adhesives,[19] which indicates good owability and penetrability into the veneer, The introduction of epoxy resin led to a marked decrease in the viscosity of SPI adhesive, which agrees with a previous study.[18]
The peaks intensity of the epoxy group become much weaker compared with the epoxy resin, which might be a result of the consumption on some amount of epoxy group via the crosslinking reaction of epoxy groups with –NH2 and –COOH groups on the SPI molecules.[28]. These results above indicated that the epoxy groups of epoxy resin were able to react with the active groups of SPI molecules (e.g., –NH2) during adhesive synthetic process by a ring opening reactions of epoxy groups, and that the resulting adhesive contained a certain amount of epoxy groups, which can further react with hydroxyl group of wood to form better bonding property during its curing process
Summary
Industrial interest in bio-based polymeric materials from renewable agricultural products has received increased attention over the past decade. Soy proteins are among the most investigated natural compounds for various industrial applications such as wood adhesives, food packaging, bio-based composites and coatings, etc. Due to their plentiful supply, excellent properties and high functionality.[1] In recent years, soy proteins have attracted great attention to prepare bio-adhesives for bonding wood composite materials.[2] the low bonding strength and poor water resistance of soy protein bioadhesives limited their more extensive application in highperformance wood adhesives. To form a cross-linked network structure.[8,9] This method can markedly improve the water resistance of soy protein adhesive, the main drawback is the complex preparation procedures, which makes it impractical for application in the plywood production For soy protein molecular modi cation, high activity groups were normally gra ed onto soy protein molecules through esteri cation, acylation reaction, etc. to form a cross-linked network structure.[8,9] This method can markedly improve the water resistance of soy protein adhesive, the main drawback is the complex preparation procedures, which makes it impractical for application in the plywood production
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