Catalytic and ortho-directing effect of Zn2+, Mg2+, Ba2+, and Ca2+ metal hydroxides on the preparation of phenolic-formaldehyde resin

Abstract

A one step method was employed to prepare PF (phenol-formaldehyde) resin adhesive from phenol and formaldehyde with Zn2+, Mg2+, Ba2+, and Ca2+ hydroxides as catalysts, and the physicochemical properties of the resulting polymeric material were analyzed. The viscosity of the liquid adhesive decreased at intermediate catalyst concentrations, while the polymerization rate decreased at the highest concentrations; no clear pattern could be observed between catalyst concentration and solid content. Differential scanning calorimetry (DSC) performed on the PF resin catalyzed by Ba2+ showed that the polymer had a curing exothermic peak at around 110 °C, while the initial curing temperatures of PF resins were affected by the type of metal hydroxide used, and were in the order Ca2+ < Mg2+ <control sample. FTIR spectroscopy was used to monitor the degree of ortho/para substitution during the synthesis of PF resin with Ba2+, Ca2+, and Mg2+ hydroxides. The highest ortho/para ratio was achieved with Ba2+ at a concentration of 0.45 wt.%, which also resulted in the most significant increase in the polymerization rate for the formation of PF resin.