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  • 1 WOOD Carinthian Competence Center (W3C), Kompetenzzentrum Holz GmbH, Klagenfurterstrasse 87-89, 9300, St. Veit an der Glan, Austria
  • | 2 School of Applied Chemistry, Reutlingen University, Alteburgstrasse 150, 72762, Reutlingen, Germany
  • | 3 Department of Wood Science and Technology, University of Natural Resources and Life Sciences, Peter Jordan Strasse 82, 1190, Vienna, Austria
  • | 4 Department of Chemistry of Polymeric Materials, University of Leoben, Otto-Glöckel-Straße 2, 8700, Leoben, Austria
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Abstract

The thermal cure kinetics of an epoxidized linseed oil with methyl nadic anhydride as curing agent and 1-methyl imidazole as catalyst was studied by differential scanning calorimetry (DSC). The curing process was evaluated by non-isothermal DSC measurements; three iso-conversional methods for kinetic analysis of the original thermo-chemical data were applied to calculate the changes in apparent activation energy in dependence of conversion during the cross-linking reaction. All three iso-conversional methods provided consistent activation energy versus time profiles for the complex curing process. The accuracy and predictive power of the kinetic methods were evaluated by isothermal DSC measurements performed at temperatures above the glass transition temperature of the completely cured mixture (Tg). It was found that the predictions obtained from the iso-conversional method by Vyazovkin yielded the best agreement with the experimental values. The corresponding activation energy (Ea) regime showed an increase in Ea at the beginning of the curing which was followed by a continuous decrease as the cross-linking proceeded. This decrease in Ea is explained by a diffusion controlled reaction kinetics which is caused by two phenomena, gelation and vitrification. Gelation during curing of the epoxidized linseed/methyl nadic anhydride system was characterized by rheological measurements using a plate/plate rheometer and vitrification of the system was confirmed experimentally by detecting a significant decrease in complex heat capacity using alternating differential scanning calorimetry (ADSC) measurements.

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