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Abstract  

Kinetics of thermosetting polymers curing is difficult to study by isothermal methods based on the differential scanning calorimetry (DSC) technique. The difficulty is due to the low sensitivity of the equipment for total reaction heat measurements during high temperature process. The aim of this paper is to display the equivalence between a dynamic model, the Ozawa method, and an isothermal isoconversional fit, which allows predicting the isothermal behavior of the resol resins cure through dynamic runs by DSC. In this work, lignin–phenol–formaldehyde and commercial phenol–formaldehyde resol resins were employed. In addition, the isothermal kinetic parameters for both resins were performed by means of transformation of the data obtained from the dynamic Ozawa method.

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Abstract  

The effect of both formaldehyde content and catalyst type used in the synthesis of several resole type phenolic resins has been studied by using differential scanning calorimetry. In this study Kissinger-Akahira-Sunose (KAS), Ozawa-Flynn-Wall (OFW) and Friedman model-free kinetics are applied in order to correlate the dynamic cure behaviour with the mentioned synthesis variables. Strong upward dependency of activation energy on conversion has been detected in all cases up to a maximum value. Lower the formaldehyde content fewer changes in activation energy have been detected, revealing a more homogeneous polymerization. As formaldehyde content increases, stronger variations of energy values have been observed and the maximum value is shifted to lower conversions. By comparing triethylamine and sodium hydroxide catalysts similar behaviour has been observed, with higher energy values and shifting of the maximum in the latter. Friedman approach has been resulted in more convenient and accurate for the energy values determination and KAS method seems useful for the dynamic cure prediction of that type of thermoset.

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Journal of Thermal Analysis and Calorimetry
Authors:
C. Peña
,
K. de la Caba
,
A. Retegi
,
C. Ocando
,
J. Labidi
,
J. Echeverria
, and
I. Mondragon

Abstract  

Autocondensation reactions of mimosa and chestnut tannin extracts solutions have been analysed at several pH by differential scanning calorimetry (DSC). Alkaline pH promotes autocondensation reaction of these tannins. Curing reactions between these tannins and hexamine at acid and not strongly alkaline pH have been proved by DSC. Thermal analysis gives insights not only on reactions between tannin and hexamine, but also about water presence on solutions and degradation reactions of tannins. Products obtained from reactions between tannins and hexamine have been analysed by Fourier transform infrared spectroscopy (FTIR). The obtained chemical structures are influenced by both chemical structure of tannin and pH of solution. For mimosa tannin amine and ether groups are obtained while for hydrolysable chestnut tannin amide groups have been detected.

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Journal of Thermal Analysis and Calorimetry
Authors:
M. López
,
M. Blanco
,
A. Vazquez
,
J. Ramos
,
A. Arbelaiz
,
N. Gabilondo
,
J. Echeverría
, and
I. Mondragon

Abstract  

The curing kinetics of nanocomposites based on phenolic resol cured with triethylamine (TEA) containing different amounts of organic montmorillonite was analyzed by differential scanning calorimetry. Kissinger-Akahira-Sunose (KAS) model-free kinetics has been applied to correlate the dynamic cure behaviour in the presence of modified montmorillonite. The effect in the curing of the use of different clay modifiers has also been studied. A commercial clay with hydroxyl groups (Cloisite 30B) and a customized montmorillonite (PheMMT) whose reactive groups induce condensation reactions with the resol matrix have been used. Strong dependency of activation energy on apparent conversion has been observed for all compounds.

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