Abstract
This work analyzes the effect of the anhydride excess on the nonisothermal curing kinetics and on the final properties of synthetic and biobased epoxy resins. Diglycidyl ether of bisphenol A (DGEBA) and epoxidized soybean oil (ESO) were crosslinked using methyltetrahydrophthalic anhydride (MTHPA) as a curing agent and 1-methylimidazole (1MI) as an initiator. It was shown that the ESO/MTHPA/1MI system reacts slower than the DGEBA/MTHPA/1MI system, giving place to a more significant evaporation of the curing agent during the reaction. As a result, an excess of anhydride improves the final thermal properties of the ESO/MTHPA/1MI network, contrary to the behavior observed for DGEBA/MTHPA/1MI. The knowledge of the kinetics of the curing process and the optimal amount of the curing agent for each system is of critical importance for a more efficient processing of these materials.
Highlights
The production of polymeric materials has evidenced a very fast and continuous growth since the mid-20th century aimed at satisfying an increasing demand [1, 2]
It was shown that the epoxidized soybean oil (ESO)/methyltetrahydrophthalic anhydride (MTHPA)/1MI system reacts slower than the Diglycidyl ether of bisphenol A (DGEBA)/MTHPA/1MI system, giving place to a more significant evaporation of the curing agent during the reaction
We study the effect of different amounts of anhydride excess on the properties of thermosetting polymers obtained using synthetic and bio-based epoxy precursors
Summary
The production of polymeric materials has evidenced a very fast and continuous growth since the mid-20th century aimed at satisfying an increasing demand [1, 2]. There are many available modifications for vegetable oils that have been studied and developed so far, including epoxidation, hydroxylation, acrylation, and maleinization among others [6] These modified oils can be used to obtain different kinds of polymeric materials like epoxy thermosets, [7, 8] polyurethanes [9,10,11], or polyacrylates, [12] as well as other products such as adhesives and lubricant greases [13, 14]. It is known that anhydride evaporation can take place during the polymerization reaction, leading to an undesired change in the stoichiometric relation and yielding a final material with a lower curing agent/epoxy resin ratio This change in the proportion of the curing agent with respect to the epoxy precursor must be accounted in order to properly explain the material behavior. We discuss how the different reaction kinetics lead to different anhydride evaporation rates and affect the network stoichiometry and performance
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