Hempseed Protein is a Potential Alternative Source for Plant Protein-Based Adhesives

Hempseed meal, a co-product of hemp oil extraction, contains about 40% proteins, which has recently become abundant because of the large demands of hemp oil related products. It has been an acute issue for hemp industries to utilize the hempseed meal for value-added products. On the other hand, wood industries are constantly seeking plant protein alternatives not only to secure plant protein sources but also to improve wet adhesion properties. In this study, native hempseed protein was identified to have great potential for wood adhesive applications. Hemp proteins were extracted from two types of hempseed meals: Hlesia and commercial hempseed meals. Then the extracted hemp proteins with and without modification were used to prepare wood adhesives. Glutaraldehyde, previously identified as a toxic but effective crosslinker for soybean protein adhesives, was used as the crosslinking reagent for hemp protein in this study. Results showed that the wet adhesion strength of hemp proteins without modification was similar or superior compared to published data such as modified soy protein-based adhesives. Glutaraldehyde crosslinker only improved wet adhesion of commercial hemp protein at low press temperature such as 150°C and 150-170°C for Hlesia hemp protein. At press temperature 170-190°C, wet adhesion of commercial hemp protein was not affected by glutaraldehyde crosslinker, while for Hlesia hemp protein, wet adhesion was not affected by glutaraldehyde crosslinker at 190°C. The highly hydrophobic amino acid contents of hempseed proteins were identified to attribute to the unique wet adhesion performance for low water solubility and water resistance, which is essential for plant protein-based adhesive application. This is the first time to demonstrate that native hemp proteins could be a feasible and valuable alternative source of plant protein-based adhesives.