Abstract
The curing reactions of epoxy resins are a complex process that defines thermosets final properties and are affected by any additive present on its formulation. Considering this, the aim of this study was to analyze the influence of the solvent addition on the curing kinetics of an epoxy system. The epoxy samples were prepared using different percentages by weight of acetone: 0, 2, 5 and 10 wt.%. From DSC and DMA tests, followed by the Borchardt-Daniels kinetic analysis it was reported that the addition of acetone can decrease the reactions rate, activation energy, Tg and elastic modulus. The presence of solvent, even in small amounts, can affect the curing mechanisms of epoxy resins. The changes on the curing behavior and the low quality of the final properties for the sample with 10 wt.% of solvent indicates that this may be a limit for acetone addition on the epoxy formulations.
Highlights
Epoxy resins are defined as a low-molecular-weight prepolymer based on epoxide groups capable to be converted on a thermoset or a three-dimensional network structure[1]
Based on the Costa (1999) review about curing kinetic methods for epoxy resins, the mathematical approach chosen to analyze the kinetics involved on the curing reactions of the epoxy samples was the Borchardt-Daniels method, that is simpler than other kinetic models, as it allows to calculate the reaction order (n), pre-exponential factor (A) and activation energy (Ea) from one single dynamic DSC run, following the relations described on the ASTM E2041[22,31]
This behavior is similar to that reported on other works from literature which have concluded that the addition of solvent on epoxy systems can affect the crosslinking mechanisms due to the presence of residual solvent that may difficulty the curing process and decrease the crosslink density, affecting some kinetic parameters such as the reaction order (n) and activation energy (Ea)[6,29,30]
Summary
Epoxy resins are defined as a low-molecular-weight prepolymer based on epoxide groups capable to be converted on a thermoset or a three-dimensional network structure[1]. This transformation, known as curing process, occurs due to the reaction between the free epoxide groups and curing agents which causes irreversible changes on the polymer network and will define the final properties of the material[1,2]. The presence of resins must be avoided on recycled fibers since this contamination can reduce the adhesion between fibers and matrix in a later production of other composites[7,9]
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