Qualitative and quantitative evaluation of epoxy systems by Fourier transform infrared spectroscopy and the flexibilizing effect of mercaptans

Abstract

Epoxy systems are widely applied as adhesives in the aerospace industry. They have excellent adhesion properties, however, being thermosetting, epoxy systems show fracture brittleness characteristics. Polysulfi de and polymercaptans are good options to increase the fl exibility of the epoxy adhesive. Thermal analysis techniques are generally used to evaluate the curing degree of epoxy systems. In most cases, when infrared (IR) analysis is used, it is employed qualitatively. This paper presents the reaction study of a DGEBA epoxy prepolymer with diethylenetriamine (DETA) and linear and branched dodecyl mercaptans as fl exibilizers. Conversion data and curing time were assessed qualitatively and quantitatively by Fourier Transform Infrared Spectroscopy (FT-IR) in the medium infrared region (MIR) and in the near infrared region, using near infrared refl ectance accessory (NIRA). NIRA methodology showed satisfactory results, with errors between 3 and 7%, especially in samples with lower amine contents. Mechanical tests confi rmed the fl exibilization of the cured epoxy system by the addition of mercaptans, indicating a lower crosslinking degree in the matrix. Young's modulus (E) signifi cantly decreased from 2017 MPa to 578 MPa with the addition of approximately 20 wt% of normal dodecyl mercaptan to the epoxy system.

The role of organoclay in the diffusion of epoxy‐amine oligomers and in the cross‐linking density of the resulting network

“…DGEBA_DETA resin and the epoxy nanocomposites were analyzed by infrared spectra in the NIR region to confirm the variation in the epoxide ring content after the curing cycle and post‐curing treatment. The NIR region is more sensitive than the MIR region, allowing lower epoxide ring contents to be detected 51–53 . The band at approximately 4530 cm −1 shows less interference than the band of the epoxide ring in the MIR region at 916 cm −1 51,52 .…”

“…The NIR region is more sensitive than the MIR region, allowing lower epoxide ring contents to be detected. [51][52][53] The band at approximately 4530 cm À1 shows less interference than the band of the epoxide ring in the MIR region at 916 cm À1 . 51,52 The band at 4530 cm À1 has been assigned either to the combination of the CH 2 angular deformation band, at 1460 cm À1 , with the CH axial deformation from the epoxide ring at approximately 3050 cm À1 , or to the combination of the second overtone of the epoxide ring stretch at 916 cm À1 with the CH group stretch at 2725 cm À1 .…”

High Ion Conducting Dobule Network Crosslinked Gel Polymer Electrolytes for High‐Performance Supercapacitors

“…In the FT‐IR data, before the curing of the DNE(4:0) (black line in Figure 2a), the vibration peak of the C–O–C epoxide ring band was clearly observed at ≈926 cm −1 . [ 26 ] After the thermal curing (red line in Figure 2a), the intensity of the peak, corresponding to the epoxide ring, weakened in both DNEs. This indicates the occurrence of epoxy cross‐linking by epoxide ring opening reaction.…”

Investigation and assessment of epoxy resin adhesives using Fourier‐transform infrared spectrometry

“…Epoxy resins are widely used in many industries as adhesives, coatings and matrices in advanced polymer composites owing to their good electrical insulation properties and good chemical and thermal resistance [1]. Additionally, epoxies exhibit high tensile, flexural, compressive, and fatigue strengths, good adhesion to a broad variety of substrates, low shrinkage during curing, good corrosion resistance and the ability to cure over a wide range of temperatures [2][3][4][5][6][7][8].…”

“…Several studies have investigated the curing of epoxy resins using different curing agents [1,3,[20][21][22][23][24][25][26][27]. Most of these studies included epoxy resins cured with amines.…”