Thermal and Adhesive Characteristics of Acetone-Formaldehyde/Phenol- Formaldehyde Resins

Addition of varying amounts of acetone-formaldehyde (AF) resin to a standard phenol-formaldehyde (PF) plywood resin resulted in an adhesive with reduced gelation temperatures and times compared with the standard PF resin. Differential thermal analysis (DTA) thermograms of these mixtures showed the presence of an exothermic peak in the range 70-90?C, while endothermic peaks occurred in the regions 115-135?C (major) and 150-175?C (minor). The magnitude of the exothermic peak is dependent upon AF to PF ratio and on sodium hydroxide content. For a 30/70 mixture of AF/PF resin, passage of the exothermic peak corresponded to resin gelation and a softening temperature of 30?C. Adequate cure, resulting in a softening temperature of 150?C, required heating until the second endothermic region was passed. Plywood-bonding experiments indicated that up to 25 percent AF substitution in PF resin afforded a boiling-water-resistant bond when properly cured. AF/PF glue mixtures accelerated plywood shear strength development compared with PF glues.

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