A New Flexible Soy-Based Adhesive Enhanced with Neopentyl Glycol Diglycidyl Ether: Properties and Application.

Jing Luo,Yuanyuan Bai,Jianlin Luo,Qiang Gao,Jianzhang Li,Li Li,Jizhi Zhang

doi:10.3390/polym8090346

Jing Luo, Yuanyuan Bai + Show 5 more

Open Access

https://doi.org/10.3390/polym8090346

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Journal: Polymers	Publication Date: Sep 21, 2016
Citations: 31	License type: CC BY 4.0

Affiliation: Beijing Forestry University, Shandong University

Abstract

Soy-based adhesives inherently possess low water resistance and brittleness, which limit their application on plywood fabrication. This investigation involves using a long chain cross-linker, neopentyl glycol diglycidyl ether (NGDE), to produce an intrinsic toughening effect to reduce the brittleness and improve the water resistance of a soybean meal–based adhesive. The solids content, viscosity, functional groups, fracture surface micrographs, and thermal stability of the adhesives were measured. Three-layer plywood was fabricated using the resultant adhesive, and the tensile shear strength of the plywood was measured. All adhesive properties were compared with a soybean meal/polyamidoamine-epichlorohydrin (PAE) adhesive and commercial melamine urea formaldehyde resin. The results showed that adding 6 g NGDE improved the water resistance of the soybean meal-based adhesive by 12.5%. This improvement is attributed to the following reasons: (1) a dense cross-linked network is formed by the chemical reaction between NGDE and protein molecules; (2) the toughness of the adhesive increases and a smooth and homogeneous fracture surface is created, which effectively prevents moisture intrusion; (3) the addition of NGDE increases the thermostability of the cured adhesive. The tensile shear strength of the plywood bonded with the soybean meal-based adhesive with 6 g NGDE was 286.2% higher than that without NGDE and attained 1.12 MPa, which was attributed to the reduction in the adhesive’s viscosity, and the improvement in the water resistance and toughness of the adhesive. The tensile shear strength of the plywood bonded with 6 g NGDE was 19.1% higher than that with 6 g PAE and was similar to the MUF resin, which validated the novel adhesive being suitable for use as an industrial plywood adhesive.

Highlights

Formaldehyde-based resins play a dominant role in the present plywood fabrication industry because of their advantages, such as good water resistance, fast curing, and good age resistance.the formaldehyde emission issue and over-reliance on fossil resources of these adhesives have created a need to develop adhesives based on environmentally friendly, renewable resources [1,2,3,4].As a renewable product, soy protein has the advantages of being abundant, inexpensive, and environmentally friendly, so it offers great potential as a raw material for wood adhesives
The viscosity of the soybean meal-based (SM) adhesive was recorded at 35,310 mPa·s
This is due to the sodium dodecyl sulfate (SDS) partially unfolding the soy protein molecules and exposing active groups inside of the protein molecule

Summary

Introduction

Soy protein has the advantages of being abundant, inexpensive, and environmentally friendly, so it offers great potential as a raw material for wood adhesives. The efforts to improve the water resistance of the soy protein–based adhesives can be classified into four categories: denaturing agent modification, protein molecular modification, reactive cross-linker and synthetic resin modification. Denaturants, such as urea, sodium dodecyl sulfate, and alkali, can unfold the protein molecule and in some cases create a more crystalline domain to prevent water intrusion, which improves the water resistance of the adhesive [8,9,10,11,12]. The resultant plywood bonded with the soy protein–based adhesive containing denaturants cannot meet interior use requirements

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Conclusion