Effects of Treatments on the Structure of Camellia oleifera Cake Protein and the Properties of Adhesives

Abstract

Although the preparation of wood adhesives from protein in oilcake has significant advantages in terms of environmental protection and cost control, it still faces many challenges that need to be addressed in practical applications. This study used Camellia oleifera cake protein extracted from C. oleifera seeds as raw material to prepare adhesives through thermal, alkaline, acidic, and enzymatic treatments, which were then applied in the production of plywood. The results showed that thermal treatment increased the viscosity of the protein adhesive and improved the bonding strength to 1.12 MPa. Fourier transform infrared spectroscopy analysis indicated partial transformation of the secondary structure of protein molecules, while differential scanning calorimetric analysis showed an increase in curing temperature. Alkaline treatment slightly reduced the viscosity but achieved a bonding strength of 1.14 MPa, disrupting some of the crystalline structures of the protein and lowering the curing temperature. Acidic treatment greatly reduced the viscosity but resulted in the highest bonding strength of 1.36 MPa, partially hydrolyzing peptide bonds and reducing both the curing temperature and crystallinity. Enzymatic treatment decreased the viscosity of the protein adhesive but lowered the bonding strength to 0.82 MPa, with extensive hydrolysis of peptide bonds. Different treatment methods altered the rheological properties and bonding properties of the adhesives by affecting the molecular structure, aggregation state, and chemical reactivity of C. oleifera protein.