Self-Neutralizing Citric Acid–Corn Starch Wood Adhesives

Very acidic pHs are not allowed in wood adhesives. The development of new self-neutralizing adhesives has therefore become a priority. The corn starch–citric acid adhesive (CACS) was developed recently to be an environmentally friendly biomass adhesive. In this work, we propose to prepare self-neutralizing corn starch adhesives using the CACS adhesive as the matrix and morpholine/maleic acid (MM) and morpholine/d-lactic acid (DM) as the neutralizing agents. The results showed that the MM neutralizing additive is more effective than the DM in eliminating the residual acid on the glue line. When the addition of the MM neutralizer was 10%, the pH of the adhesive system increased to about 4.5 and an adhesive with stable water resistance, good durability, and high bonding strength and durability acceptable to the relevant standards could be maintained. Structural analysis proved that MA was also involved in the esterification reaction of corn starch (CS). Therefore, the MM-CACS adhesive developed in this study has the potential to replace traditional petroleum-based adhesives as a new type of biomass self-neutralizing adhesive.