Preparation of Flaxseed Meal Protein Renewable Bioadhesive by Using Small Proportions of Trimethylolpropane Trigglycidyl Ether and Ethylenediamine

The main raw material utilized in wood adhesives comes from petrochemical extractives. However, due to the excessive dependence on petrochemical resources and the adverse impact on the ecosystem and human well-being, there is an increasing trend to develop byproduct protein-based adhesives in the current global food safety context. In this research, flaxseed meal was subjected to pretreatment, and trimethylolpropane triglycidyl ether (TTE) and ethylenediamine (EN) were utilized as crosslinkers to establish a more compact adhesive layer and to prevent water intrusion. The pretreatment decreased the FM/UB viscosity by 60% compared to FM. The combination of CD analysis indicated that the Urea-NaOH pretreatment effectively stretched the flaxseed meal protein. According to Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and differential scanning calorimetry (DSC) were used to analyze the resulting adhesive’s reaction mechanism and thermal response. Furthermore, the physical properties of the adhesive were characterized using wet shear strength testing and SEM observation. Remarkably, the dry bond strength increased from 0.72 to 2.12 MPa, representing a 194.4% increase. The wet bonding strength of the adhesive was improved from 0.22 to 1.21 MPa, representing a 550% increase compared to the original flaxseed protein-based adhesive, which far exceeded the minimum requirement for plywood of Type II (≥0.7 MPa, by GB/T 9846-2015). This study demonstrated an eco-friendly and sustainable method for the development of protein adhesives as viable substitutes for petrochemical resins.