Effects of hydrolysis degree of soy protein isolate on the structure and performance of hydrolyzed soy protein isolate/urea/formaldehyde copolymer resin

The hydrolyzed soy protein isolate (HSPI) with different hydrolysis degree was applied to modify urea‐formaldehyde resins (UF) via copolymerization process. The properties of HSPI were characterized by attenuated total reflection Fourier transform infrared spectroscopy (ATR‐FTIR) and TGA. The results show that HSPI with different hydrolysis degree is obtained. 1H NMR and ATR‐FTIR spectra indicate that HSPI with different hydrolysis degree can incorporate into the structure of cured and uncured UF. The UF modified with higher hydrolysis degree of HSPI possess more stable units and contribute to the lower exothermic peak temperature in DSC curves. The bonding strength of HSPI modified UF increases as the hydrolysis degree of HSPI increases at the hot‐press temperature of 120°C and decreases at the hot‐press temperature of 150°C. The best bonding strength is 1.53 MPa at the hot‐press temperature of 135°C and improved 56.12% compared with UF. In addition, the formaldehyde emission is dramatically reduced.