Characterization and Performance of Soy-Based Adhesives Cured with Epoxy Resin

Abstract

Soy-based adhesives have attracted much attention recently because they are environmentally safe, low cost, and readily available. To improve the gluability and water resistance of soy-based adhesives, we prepared an enzyme-treated soy-based adhesive modified with an epoxy resin. We investigated the wet shear strength of plywood bonded with the modified adhesive using the boiling-water test. Fourier transformed infrared spectroscopy (FTIR) and 1 H nuclear magnetic resonance analysis were used to characterize the reaction between epoxy groups and -NH 2 groups in the modified soy-based adhesives. FTIR analysis confirmed the cross-linking structure in the cured adhesives. Viscosity and the solid content of soy-based adhesives gradually increased with the increasing amount of epoxy resin, but had little effect on its operability. Wet shear strength of plywood samples increased as the amount of epoxy resin was increased, whereas the inverse trend was observed regarding the water absorption of cured adhesives. Compared to an unmodified adhesive, the addition of 30% of epoxy resin increased the wet shear strength of plywood samples by 58.3% (0.95 MPa), meeting the requirement of the Chinese National Standard for exterior plywood. Differential scanning calorimetry and thermogravimetric analysis showed the improved thermostability of the cured adhesives after curing at 160 • C. These results suggest that epoxy resin could effectively improve the performance of enzyme-treated soy-based adhesives, which might provide a new option for the preparation of soy-based adhesives with high gluability and water resistance.

Preparation and characterization of a soy protein based bio-adhesive crosslinked by waterborne epoxy resin and polyacrylamide

“…Thus, the recommended viscosity of soy protein adhesive is around 6000 to 20 000 mPa s for sprayline coaters. 23 According to the ndings shown in Table 1, the apparent viscosity of pure SPI and EPOXY-SPI 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 With the additive amount of epoxy resin, the viscosity of EPOXY-SPI adhesive gradually decreased by 18.1% from 19 753 to 16 159 mPa s, and further decreased by 68.5% to 6229 mPa s when 7 wt% of epoxy resin was loaded, which met the operating viscosity requirements of soy protein adhesive.…”

“…As can be clearly seen, the shear strength of all adhesives increased with increase of epoxy resin addition amount, indicating that the bonding performances of the resulted adhesives were improved by epoxy resin. Two reasonable interpretation for this were probably that: (1) epoxy groups of epoxy resin were capable of reacting with the amino and hydroxyl groups to form three-dimensional crosslinked network structure of the resulted adhesives; 19,28 (2) the hydrophilic groups (-COOH, -NH 2 ) of soy proteins were consumed by epoxy group to increase relative hydrophobic property. When the addition amounts of epoxy resin were increased to/or more than 4 wt%, the shear strengths were higher than 0.70 MPa, which met the GB/T 9846-2015 standard requirements for interior use plywood.…”

“…18 Enzymetreated soy-based adhesive was blended with commercial epoxy resin before the application, and a water resistance crosslinked structure was formed during its curing process, resulting in the improvement of plywood bonding strength. 19 In addition, the addition of epoxy resins to soy-based adhesives was found to improve its gluability and owability. These efforts mainly focus on physical mixing of soy-based adhesive directly with cross-linker before its application, whose water-resistant structure was formed during its hot-press curing process.…”

Specific oxidants improve the wood bonding strength of soy and other plant flours

“…Of the many plant materials, most of the research has been with soy because of its ready availability as a low‐cost flour with acceptably consistent composition. Most recent research has focused on addition of co‐reacting adhesives, such as phenolics, polyamidoamine‐epichlorohydrin, isocyanates, and epoxies, but other research has used aldehydes, or added reactive functionality to the protein . Often, this research has used commercial soy protein isolate, which is readily available but can be a poor model compound for the native proteins in soy flour because of the processing involved in commercial isolate production, especially jet‐cooking for increased performance in food applications .…”

Development of Eco-Friendly Soy Meal Adhesives Enhanced by Ethylene Glycol Diglycidyl Ether

“…Soy-based adhesives were developed in 1923 and widely used in commercial production of plywood between 1930s and 1960s, but later they were placed by petroleum-based adhesives owing to the poor adhesion property and water resistance [1,2]. In recent years, however, the dwindling of fossil resources and the growing concerns about the pollution of petroleum-based adhesives have been driving the development of renewable and eco-friendly materials [3,4]. Soybean is considered as an alternative because of its abundance, low cost, operability, renewability, and environment friendliness [5][6][7][8][9].…”