Epoxy resin spectroscopy

Network properties and microscopic structures of various epoxy resins cross-linked by phenolic novolacs were investigated by Suzuki et al.97 Positron annihilation spectroscopy (PAS) was utilized to characterize intermolecular spacing of networks and the results were compared to bulk polymer properties. The lifetimes (t3) and intensities (/3) of the active species (positronium ions) correspond to volume and number of holes which constitute the free volume in the network. Networks cured with flexible epoxies had more holes throughout the temperature range, and the space increased with temperature increases. Glass transition temperatures and thermal expansion coefficients (a) were calculated from plots of t3 versus temperature. The Tgs and thermal expansion coefficients obtained from PAS were lower titan those obtained from thermomechanical analysis. These differences were attributed to micro-Brownian motions determined by PAS versus macroscopic polymer properties determined by thermomechanical analysis. 

Patrikis. A.K., Andrews, M.C. and Young, R.J. (1994). Analysis of the single fiber pull-out test by the use of Raman spectroscopy part I Pull-out of aramid fibers from an epoxy resin. Composites Sci. Technol. 52, 387 396. 

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. 

DSC is increasingly being applied to the study of epoxy resin cure in combination with other analytical methods such as nuclear magnetic resonance and Fourier transform infra-red spectroscopy, chromatographic methods, and dynamic mechanical or dielectric studies. It is probably as part of such combined investigations that DSC can be used most effectively in basic research, and in quality control and assessment. 

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. 

Van Overbeke, E. Devaux, J. Legras, R. Carter, J.T. McGrail, P.T. 8t Carlier, V. Raman Spectroscopy and DSC Determination of Conversion in DDS-Cured Epoxy Resin Application to Epoxy-Copolyethersulfone Blends Appl. Spectrosc. 2001, 55, 540-551. 

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. 

Hydroxyl equivalent. The hydroxyl equivalent is the weight of epoxy resin containing one equivalent of hydroxyl group. It is important in calculating average molecular weights. It is determined by various methods (Lee and Nivelle, 1967), such as esterification with acids, reaction with lithium aluminium hydride, reaction with acetyl chloride and near-infra-red spectroscopy. 

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

The problem of reliably analysing the epoxy-resin component of a carbon-fibre epoxy prepreg has also been addressed by using FT-IR emission spectroscopy (FTIES)... 

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