Preparation and characterization of resorcinol-dialdehyde starch-formaldehyde copolycondensation resin adhesive.

A resorcinol-dialdehyde starch-formaldehyde (RDSF) copolycondensation resin adhesive was prepared by substituting high reactive dialdehyde starch for a portion of formaldehyde in the formulation. Fourier transforms infrared spectrometer (FTIR) analysis results confirmed that the copolycondensation reaction of the dialdehyde starch with resorcinol and formaldehyde was successful. The curing property, thermal stability, permeability and crystal structure of the RDSF adhesive were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscope (SEM), X-ray diffraction (XRD). The solids content, viscosity, curing time, bonding strength were also obtained. The results showed that the RDSF adhesive had a higher solids content, moderate viscosity, shorter curing time and better bond strength than a standard resorcinol-starch-formaldehyde (RSF) adhesive. It was found that dialdehyde starch could accelerate the curing rate, while decreasing the curing temperature and heat release during the curing process of RDSF. The dense cross-linked structure of the dialdehyde starch and resorcinol-formaldehyde (RF) system produced improved thermal stability. SEM results showed that the RDSF adhesive formed a thin and continuous adhesive layer on the surface of a poplar board, and filled the pores of the wood, which improved the bond strength. The crystal structure of the RDSF was not altered by addition of the starch, and the physicochemical properties of the adhesive were similar to those of a normal resorcinol-formaldehyde resin.