Infrared spectroscopy epoxy resin

Molecular structure of epoxy resins. Infrared spectroscopy (IR) is used to determine the epoxide content of resins as well as their structure. A compilation of IR spectra of uncured resins has been published (86) and their use in quality control and identification of components of resin blends has been described. Recently, near IR (NIR) has emerged as a useful tool to characterize epoxy resins (87). 

This article will review the impact of two powerful new techniques for characterizing epoxy resins at the molecular level — Fourier transform infrared spectroscopy (FT-IR) and high resolution nuclear magnetic resonance (NMR) of solids. Fortunately, these two techniques are not inhibited appreciably by the insoluble nature of the cured resin. Consequently, substantial structural information at the molecular level can be obtained. In this article, the basis of the methods will be briefly described in order to appreciate the nature of the methods followed by a description of the work on epoxies to date and finally some indication will be given of the anticipated contributions of these methods in the future. 

All of the usual sampling techniques used in infrared spectroscopy can be used with FT-IR instrumentation. The optics of the sampling chamber of commercial FT-IR instruments are the same as the traditional dispersive instruments so the accessories can be used without modification for the most part. To make full use of the larger aperature of the FT-IR instrument, some accessories should be modified to accomodate the larger beam. The instrumental advantages of FT-IR allow one to use a number of sampling techniques which are not effective using dispersive instrumentation. Transmission, diffuse reflectance and internal reflectance techniques are most often used in the study of epoxy resins. 

Commercial cylindrical quartz cells can be adapted for gas-phase work as illustrated in Fig. 9.18. Such a cell finds use in the near infrared for the determination of overtone vibrational frequencies, and also in visible and ultraviolet spectroscopy. A much less expensive cell which is adequate for most gases may be constructed from Pyrex along the lines of the cell shown in Fig. 9.18. Quartz windows may then be attached by epoxy resin. A cell which is filled from a conventional vacuum line will generally contain mercury vapor which absorbs at 2537 A. Once the origin of this absorption is recognized, it causes little difficulty because of its narrow bandwidth. 

O Brien and Hartman (26) studied the interface of a model system—epoxy resin, regenerated cellulose fibers—by attenuated total reflectance infrared spectroscopy. They compared spectra of the components to spectra of epoxy cured on cellulose and found for the mixture a diminished hydroxyl absorption (3,350 cm 1) and C-0 stretching (1,050 cm"1), and disappearance of the epoxy band (915 cm 1). From this they concluded that covalent bonding does occur between the epoxide groups and cellulose hydroxyls. 

The hydroxyl equivalent weight of epoxy resins can be determined by several methods. The most common is esterification with acids, reaction with acetyl chloride, and reaction with lithium aluminum hydride. Infrared spectroscopy may also be used. 

Epoxy Resins by Near-Infrared Spectroscopy", SPE Transactions... 

Analysis of Cure. Infrared spectroscopy was utilized to examine film cure and the effect of stabilizers upon the cure of the epoxy acrylate. Pre-cured material has absorptions at 1635, 1410 and 810 cm-1 which clearly diminish after the resin is UV-irradiated (Figure 6). The 1635 cm-1 absorption can be assigned to the carbon-carbon stretch of an olefinic bond in conjugation with a carbonyl group the 1410 cm-1 can be assigned to the CH2 in-plane deformation of a vinylic group. The 810 cm-1 can also be assigned to some aspect of vinylic... 

In addition to HPLC, elemental analysis, vapor phase osmometry. Fourier Transform Infrared Spectroscopy (FTIR), GC/MS, and NMR techniques were applied to verify the purity of the resin samples. Epoxy equivalent weights (EEW) were determined by the standard nonaqueous titration method (J ) using chloroform as the solvent. A correction for tertiary amine was obtained by conducting the titration in the absence of the quaternary halide. ... 

Recently/ the crosslinking reactions of tetrafiinctional epoxy resins with aromatic primary diamines was investigated. The crosslinked polymers were characterized by UV visible and fluo> rescence spectroscopies after gelation. The amount of tertiary amine fluorescence intensity of the spectra shows significant amounts of such amines in the finished products. The infrared spectra confirm the overall reaction of epoxides with amines, but also show that ether formation becomes significant only late in the cure. In addition, during the cure, especially in air, some oxidations and degradations occur. This results in color formation. 

Musto, P. Mascia, L. Ragosta, G. Scarinzi, G. Villano, P. (2000). The transport of water in a tetrafunctional epoxy resin by near-infrared Fourier transform spectroscopy. Polymer, Vol. 41, No.2, Qanuary 2000), pp.565-574, ISSN 0032-3057. 

Xu, L.S. Schlup, J.R. (1998). Etherification versus amine addition during epoxy resin amine cure An in situ study using near-infrared spectroscopy. Journal of Applied Polymer Science, Vol.67, No.5, 0anuary 1998), pp. 895-90, ISSN 0021-8995. 

Infrared spectroscopy was used to follow the ageing processes of two epoxy resins. Resin samples were exposed to ionising radiation and the effects at the molecular level, and how the resins modified their hydration mechanisms was discussed. Aromatic amine cured resins are only slightly affected by the radiation, but those cured by alkyl diamines are more sensitive and thus absorb more water.molecules. 14 refs. 

Polymer Bulletin 42, No.5, May 1999, p.579-86 RHEO-OPTICAL FOURIER TRANSFORM INFRARED SPECTROSCOPY OF DIOL-MODIFIED DIGLYCIDYL ETHER OF BISPHENOL-A EPOXY RESINS Scherzer T... 

Detailed near-infrared spectra of PET exposed to different relative humidities indicated three different subbands of the first overtone of water at 7080 cm 7010 cm and 6810 cm The comparison with the water spectmm of bulk water suggested that most of the water is only weakly bonded with PET (89). The analysis of difference spectra of dry nylon and nylon exposed to different humidities, indicated that there were distinct populations of hydrogen-bonded water in it (90). Recently, Musto et al. (91) investigated the nature of molecular interactions of water in epoxy resins by means of near-infrared spectroscopy as proposed by Eukuda et al. (89,90). They found three subbands at 7076 cm 6820 cm and 6535 cm evidencing two kinds of water adsorbed in the polymer (mobile water localized in micro vide and water molecules firmly bonded to the network). However, hydroxyl groups of epoxy may complicate the analysis of water content in polymers because they absorb also in the same overtone region as water. 

B. Chabert, G. Lachenal C. Vinh-Tung. Epoxy resins and epoxy blends studied by near infrared spectroscopy. Mocmmo/Symp 94 145-158, 1995. 

BUlaud, C., R. Legras, and V. Carher, Quantitative Analysis of Epoxy Resin Cure Reaction A Study by Near-Infrared Spectroscopy. A/ / /. Spectrosc., 2002. 56 1413-1421. 

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