Effect of alkalinity on the structure of phenol–formaldehyde resol resins

Abstract

Two phenol-formaldehyde resol resin series with different methylationand condensation-stage alkalinities were studied. The first series was impregnation resins having a methylation alkalinity between 0.5 and 1.5 wt % and a condensation alkalinity of 1.5 wt %. The second series was adhesive resins with a methylation alkalinity between 0.5 and 3.5 wt % and a condensation alkalinity of 6.0 wt %. The chemical structure was analyzed by 13 C-NMR spectroscopy, and reactivity, by differential scanning calorimetry (DSC). The methylation alkalinity was found to affect the distribution of the structural groups of both phenol-formaldehyde impregnation and adhesive resins, but not to the same extent as did the total condensation alkalinity. Also, the results of the DSC analysis illustrate best the reactivity differences due to the condensation alkalinity.

Bio-based nanocomposites by in situ cure of phenolic prepolymers with cellulose whiskers

“…9, the samples exhibit one main exotherm during DSC temperature scan with perhaps another broad shoulder, in agreement with the literature reports on the curing behavior of resoles (Luukko et al 2001). The low-temperature exotherm peaks at 146-149°C, while the shoulder centers at approximately 221°C.…”

“…Indeed the catalytic role of CNWs on PF curing behavior has been recently noted (Hong et al 2010). The hypothesis of a simple pH effect (Pizzi 1994;Luukko et al 2001) was however discarded since CNWs addition did not alter the resole pH. The increase in the heat of cure is very significant (ca.…”

Online monitoring of synthesis and curing of phenol–formaldehyde resol resins by Raman spectroscopy

“…The methylolation stage of the synthesis is followed by the condensation stage, in which the methylol groups react with the free sites of other phenolic species yielding methylene bridge structures between the phenolic rings [1,2]. The formation of dibenzyl ether bridges resulting from the reactions of two methylol groups is not favored in highly alkaline conditions [3][4][5]. The resol resin synthesis is halted when the appropriate degree of condensation in the resin (viscosity) has been achieved.…”

Comparison of model‐fitting kinetics for predicting the cure behavior of commercial phenol–formaldehyde resins

“…During a differential scanning calorimetry (DSC) temperature scan phenol-formaldehyde (PF) resoles typically exhibit two exotherms. 5 Although a subject of controversy, the first exotherm is often ascribed to hydroxymethylphenols formation and condensation, while the second exotherm is attributed to dimethylene ether linkages decomposition into methylene linkages between phenolic moieties. 5 To model resin cure kinetics, model-fitting (MF) 6 and model-free kinetics 7 can be used in combination with DSC.…”

“…5 Although a subject of controversy, the first exotherm is often ascribed to hydroxymethylphenols formation and condensation, while the second exotherm is attributed to dimethylene ether linkages decomposition into methylene linkages between phenolic moieties. 5 To model resin cure kinetics, model-fitting (MF) 6 and model-free kinetics 7 can be used in combination with DSC. 8 For commercial PF resins, model-free kinetics has recently demonstrated excellent modeling and prediction abilities for both degree of cure and reaction rate during dynamic and isothermal cure.…”