Abstract
Soybean meal (SM)-based adhesive exhibited a great potential to replace petroleum-derived ones to alleviate the energy crisis and eliminate carcinogenic formaldehyde. However, the bad water resistance (caused by low crosslinking density) and inherent brittleness of SM adhesive severely hindered its application. However, improving crosslinking density is generally accompanied by a toughness reduction of the adhesive. Herein, we developed a flexible long-chain starch with a hyper-branched structure (HD), and incorporated it with SM and a crosslinking agent to prepare a novel SM adhesive. Results showed that this adhesive exhibited both excellent water resistance and enhanced toughness. The wet bond strength of plywood fabricated using this adhesive was 354.5% higher than that of SM adhesive. These achievements are because introducing HD with hyper-branched groups enhanced crosslinking density, while HD’s flexible long-chain structure improved toughness of the adhesive. This HD can promote the development of tough and hydrophobic bio-based composites.
Highlights
Formaldehyde-based adhesives, play a dominant role in wood-based panel manufacturing, as they exhibit a high bond strength and low cost [1]
The active groups in Soybean meal (SM), such as –NH2, –COOH, and –OH, can form hydrogen bonds with –OH in the wood to produce a bonding effect [5]. These hydrogen bonds are weakened with moisture, resulting in a SM adhesive with poor water resistance and low bond strength, the plywood fabricated using these adhesives cannot meet the strength requirement for indoor use [6]
The crosslinking agent, i.e., triglycidyl isocyanurate (TGIC), is a triazine epoxy compound derived from epichlorohydrin and isocyanuric acid [12]
Summary
Formaldehyde-based adhesives, play a dominant role in wood-based panel manufacturing, as they exhibit a high bond strength and low cost [1]. Application to wood-based panels creates indoor pollution concerns due to continuous formaldehyde release [2]. The active groups in SM, such as –NH2 , –COOH, and –OH, can form hydrogen bonds with –OH in the wood to produce a bonding effect [5]. These hydrogen bonds are weakened with moisture, resulting in a SM adhesive with poor water resistance and low bond strength, the plywood fabricated using these adhesives cannot meet the strength requirement for indoor use [6]. In order to improve the performances of SM adhesive, the most effective method is crosslinking agent modification; epoxides, such as ethylene
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