Influence of the Stoichiometric Ratio on the Curing Kinetics and Mechanical Properties of Epoxy Resin Cured with a Rosin‐Based Anhydride

Abstract

Bio‐based alternatives for petroleum‐based epoxy resin curing agents, such as maleopimaric acid (MPA), are indispensable for sustainable fiber reinforced polymer composites with thermosetting matrices. However, previous investigations disregarded the importance of choosing the right stoichiometric ratio R between the anhydride groups in the rosin‐based curing agent and the epoxy groups in the resin. Therefore, the influence of R on the curing kinetics and mechanical properties of an epoxy resin cured with a rosin‐based anhydride is studied. Here, Fourier‐transform infrared spectroscopy (FT–IR) indicates that for R ⩾ 0.9 unreacted anhydride groups are present in the thermoset. Consequently, the network density decreases and the glass transition temperature Tg drops by about 40 °C. On the other hand, the steric hindrance of unreacted functional groups for R ⩾ 0.9, increases the flexural modulus and the reduced network density improves fracture toughness. The results indicate that the best R for overall high mechanical performance and good processability is preferably low (R ⩽ 0.7). Here, a low R results in a high Tg and good processability due to a low viscosity. However, the latency of the mixtures is low and therefore, the mixtures are not fit for processing via prepreg technology.

High-Impact Epoxy Resins with Superior Hydrophobicity Toughened by Epoxy Functionalized Poly(olefin-alt-maleimide) Derivatives

“…Moreover, it is easy to obtain the initial curing temperature ( T i ), curing peak temperature ( T p ), and curing finish temperature ( T f ) of these blends at different heating rates from Figure a–e, and the detailed data are listed in Table S3. As shown in the insets of Figure a–e, the gel temperature ( T i0 ), curing temperature ( T p0 ), and postcuring temperature ( T f0 ) could be derived from the values of the intercepts by extrapolation of the fitting curves to β = 0 °C/min . The experimental results are summarized in Table S4.…”

“…Obviously, the T i0 , T p0 , and T f0 values of the PHMIEP/E51/DDM blends were also slightly lower than those of the E51/DDM blend, which also suggested the relatively lower curing temperature and the higher curing reactivity of the PHMIEP/E51/DDM blends. In order to accurately compare the curing reactivity, Kissinger’s method (eqs S1–S3) was employed to calculate the apparent activation energy ( E a ), − reaction order ( n ), and preexponential factor ( A ) of the curing reaction, and the calculated results are given in Table S4.…”

An algae-derived partially renewable epoxy resin formulation for glass fibre-reinforced sustainable polymer composites

“…7 A hardener is selected among multifunctional amines or anhydrides based on the target application and provides an exothermic ring-opening reaction with multifunctional epoxy monomers to form a thermoset. 8,9 Additives such as reactive diluents (low viscosity epoxy compounds) and accelerators (imidazoles) are found in delicate industrial resin recipes to adjust processability and curing cycles. 10 Bisphenol A (BPA) is a substance of concern as it possesses major toxicity as an endocrine disruptor.…”