Abstract
Peanut meal (PM) has recently emerged as a potential protein source for wood adhesives, owing to superior features such as high availability, renewability and eco-friendliness. However, the poor properties of unmodified PM-based wood adhesives, compared with their petroleum-derived counterparts, limit their use in high-performance applications. In order to promote the application of PM-based wood adhesives in plywood industry, urea (U) and epichlorohydrin (ECH) were used to enhance the properties of the adhesives and the modification mechanism was investigated. PM-based wood adhesives made with U and ECH were shown to possess sufficient water resistance and exhibited higher apparent viscosity and solid content than without. Fourier-transform infrared spectroscopy results suggested that U denatured PM protein and expose more reactive groups, allowing ECH to react better with U-treated PM protein to form a dense, cross-linked network which was the main reason for the improvement of the properties. The crystallinity increased from 2.7% to 11% compared with the control, indicating that the molecular structure of the resultant adhesive modified by U and ECH became more regular and compact owing to the cross-linked network structure. Thermogravimetry tests showed that decomposition temperature of the protein skeleton structure increased from 307°C to 314°C after U and ECH modification. Scanning electron microscopy images revealed that using U and ECH for adhesives resulted in a smooth protein surface which prevented moisture penetration and improved water resistance. PM-based adhesives thus represent potential candidates to replace petroleum-derived adhesives in the plywood industry, which will effectively promote the rapid development of eco-friendly adhesives and increase the added value of PM.
Highlights
With the rapid development of the artificial plywood industry, the production and use of wood adhesives have steadily increased in recent years
We suggest that ECH reacted with functional groups of the Peanut meal (PM) protein unfolded by U to form a dense, three-dimensional network structure that resisted water intrusion
A novel PM-based wood adhesive with superior properties was prepared by U and ECH treatment of PM
Summary
With the rapid development of the artificial plywood industry, the production and use of wood adhesives have steadily increased in recent years. Methods that can modify plant protein-based adhesives to enhance their properties include denaturation [12] or modifications with cross-linking agents [13], synthetic resins [14], nanomaterials [15,16] and biomimetic materials [17,18]. These modifications have produced effective improvements in the properties of plant protein-based adhesives [19]. Considering the high content of reactive groups in peanut protein, chemical modifications were selected to enhance the properties of PM-based adhesives. The corresponding modification mechanism was characterized by various analytical methods
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