Study on Acid Hardening of Resol Type Phenolic Resins by Infrared Spectrometry

Abstract

Acid hardening of resol type phenolic resins are used in adhesives for wood working. abrasives and other several fields. Mechanisms of the reaction had been studied by several workers, but there were almost no work published in which instrumental analysis were used. In this papar, mechanisms of acid hardening of phenolic resins were studied by infrared spectrometry. Resol type phenolic resins were prepared by the use of NaOH catalyst, and their mole. ratios (F/P) were 1.0, 1.5, 2.0. The samples were acidified by 1 N HCl. Heating temperatures were 60 and 120° C. To follow the reaction quantitatively, intensity ratio method was used taking the 1610 cm^-1 band as intensity standard. The results were as follows.1.60° C hardening The main reactions were formation of methylene linkage (active p-position+methylol group) and dimethylene ether linkage (methylol group+methylol group). Small amount of carbonyl group was detected, which formed by the oxidation of methylene linkage.2.120° C hardening Samples of mole ratio (F/P) 1.5 and 2.0: The reactions were divided into two stages. At the first stage, formation of dimethylene ether linkages was remarkable. At the second stage, dimethylene ether linkages were decomposed, and phenolic hydroxyl groups decreased. At this stage, formation of quinone and quinone methide type carbonyl groups was suggested. Absorption intensity at 1650 cm^-1 (carbonyl group) increased remarkably. Sample of mole ratio (F/P) 1.0: At early stage, methylol group and dimethylene ether group disappeared, and after that intensities of out of plane deformation band of benzene rings were almost unchanged. Carbonyl group was made mainly through the oxidation of methylene group.