Quantitative Analysis of Epoxy Resin Cure Reaction: A Study by Near-Infrared Spectroscopy

Abstract

Near-infrared spectroscopy was used to quantify the cure reaction of 4,4′-methylene- bis-(2,6-diethylaniline) (MDEA)–epoxy resins (E/A = 1.4) carried out at 72 and 160 °C. The absorption bands of the functional groups of interest in MDEA–epoxy resins are assigned according to the literature. A new assignment at 6580 cm−1 is also proposed for the secondary amine: it was supported by a synthesized model compound. Two different spectrum treatments were proposed. The first one is based only on a normalization at 4610–4620 cm−1, while the second one needs the subtraction of the normalized spectrum of a post-cure sample. To follow the curing process, amines and epoxy were studied at the same time in the combination and the overtone regions. The results are compared. In the combination region, quantitative results are obtained from absorbance measurements, while in the overtone region spectrum decompositions and area measurements are necessary. Complementary and reliable information are so obtained and allow us to calculate conversions of epoxide and amine I and concentrations in amine II, amine III, hydoxyl groups, and ether links. Kinetics are also established. The curing process mechanism is at last discussed for both curing temperatures.

Another look at epoxy thermosets correlating structure with mechanical properties

“…This leads to a performance limiting factor especially regarding toughness or force distribution over longer distances and shorter time scales as the building blocks become restricted in their mobility. Differential scanning calorimetry (DSC), infrared spectroscopy (IR), Raman spectroscopy, and fluorescence spectroscopy have been used to study the extent of epoxy reaction and its kinetics . Cure kinetics via DSC indicates the overall extent of chemical change but does not provide specifics regarding cure chemistry at molecular level.…”

“…Mid‐FTIR (600–4000 cm −1 ) characterization has been used to measure epoxy functional group reaction kinetics; however, the methods are not capable of providing clear distinction between epoxy, primary, and secondary amine concentration changes due to band overlap. Conversely, near infrared (NIR) spectroscopy characterization can differentiate among distinct bands specific to each epoxide, primary amine, phenyl, combined primary–secondary amine, and the resulting hydroxyl groups during cure of epoxy‐amine systems . The cure kinetics and mechanisms of epoxy‐amine reactions studied via NIR spectroscopy have been reported by some researchers .…”

<b>Preparation and reactivity studies of maleimidophenyl glycidylether with amines</b>

“…Thus, both the intercrossed and the interpenetrating systems (IPN) based on bismaleimides and epoxy resins were prepared and exhibited good thermal and mechanical properties. Additionally [8,9], since imide groups could provide char formation in the condensed phase to improve polymers flame retardant properties, epoxy resins modified with imide compounds through chemical reactions or physical blending have been reported to show good flame retardant properties [10][11][12].…”

Curing reaction of glycidylthioether resins: Kinetic model study by near infrared spectroscopy and multivariate curve resolution

“…Although this is essentially an off‐line technique, it is often used for the kinetic investigation of reactions that do not evolve toward solid products. Spectroscopic techniques, such as Fourier transform infrared spectroscopy,17, 18 fluorescence,19, 20 and near infrared spectroscopy (NIR)21, 22 enable the process to be monitored on‐line and provide useful information about the kinetics of the curing reaction that can be used for mechanistic studies. In particular, NIR spectra are much simpler than mid‐IR spectra.…”

“…Also, relatively large amounts of sample can be used because molar absorptivities are much lower in this region. 17 Most studies in the literature 17,22 use the spectral data in a univariate mode. This analysis provides data for evaluating the total degree of conversion but does not explain how many steps are involved in the overall process, how the concentration of the species evolves over time (concentration profiles), or what the spectral profile of each compound is.…”