John M. Chalmers

FT-IR imaging of polymers: an industrial appraisal

Chemical structure and conformation and physical property anisotropy at the microscopic level can have a major influence on the macroscopic performance characteristics of polymer products. Images based on infrared spectral differences and changes generated using FT-IR microscopy techniques are becoming increasingly used to highlight both chemical structure variations and morphology gradients within polymer articles. This paper illustrates potential industrial applications to polymer characterisation and analysis using mid-infrared FT-IR microscopy systems fitted with focal plane array (FPA) detectors.

Fourier transform infrared microscopy: some advances in techniques for characterisation and structure–property elucidations of industrial material†

FTIR-microscopy has become one of the foremost vibrational spectroscopy techniques for problem-solving and analysing and mapping the chemical structure and physical characteristics associated with industrial materials and their fabricated products. Many recent advances have utilised the attributes of reflection techniques, such as specular reflection spectroscopy approaches, while emerging capabilities becoming available to the industrial spectroscopist include both spectral imaging and use of synchrotron radiation as a source. This paper seeks to illustrate each of these recent advances and developments through applications of FTIR-microscopy to industrial problem-solving case studies.

FTIR, FT-Raman and chemometrics: applications to the analysis and characterisation of polymers

Abstract Within an industrial spectroscopy laboratory, two of the more significant advances in recent years have been the allying of FT-Raman alongside FTIR capabilities, coupled with the ready availability of multivariate data analysis software. Whether charged with developing rapid, cost effective methods for the quality assurance of products, or providing simple, efficient means to characterising their physico-chemical properties, these developments have proven particularly valuable to the spectroscopist concerned with the analysis and characterisation of polymers. This article will highlight the potential of these important advances through novel applications evaluated for the compositional and physical structure characterisation of polymers.

Measurement of surface orientation in uniaxial poly(ethylene terephthalate) films using polarised specular reflectance Fourier transform infrared microscopy

Abstract Polarised Fourier transform infrared (FT-IR) external-reflection spectroscopy has been used to measure molecular orientation at the surface of uniaxially drawn poly(ethylene terephthalate) (PET) films as a function of draw ratio. The spectra, which were obtained using an FT-IR microscope operating in the reflectance mode, were of high signal-to-noise ( S N ) ratio, and contained only the specular component of the reflected radiation. The dichroic ratio of the 1019 cm−1 ring stretching band was used to measure the PET orientation function, P200. Prior to quantifying band intensities, the reflectance spectra were either transformed using the Kramers-Kronig algorithm, or simply differentiated; it was found that the dichroic ratios obtained using either pretreatment were similar. It was shown that the P200 values obtained using the FT-IR method compared well with those obtained using surface refractive index measurements, provided that the intensity of the 1019 cm−1 band was normalised relative to a non-dichroic band in the spectrum prior to computing dichroic ratios. The use of a reflecting microscope to perform the analysis of surface orientation not only simplifies sample alignment compared with “macro” reflectance accessories, but also allows awkward-shaped or small samples to be examined with relative ease. Unfortunately, a significant current limitation is that samples must be sufficiently “optically thick” to prevent double-pass (“transflectance”) radiation reaching the detector and yielding non-specular features in the reflectance spectrum. For polyaromatics, this probably means thicknesses in excess of 50 μm to obtain good spectra in the fingerprint region. Polarised attenuated total reflectance microscopy may present an alternate approach for examining thinner films.

In situ Identification of Thin-Layer Chromatography Fractions by FT Raman Spectroscopy

The use of near-IR-FT Raman spectroscopy for the in situ analysis of fractions on TLC plates is described. The detection of additives in use in the plastics industry is used as an example. Reasonable-quality spectra were obtained from sample loadings equivalent to about 3 μg mm−2 in the most favorable case. Background fluorescence was not a problem, either from the adsorbent or the adsorbate, even when fluorescor was present to aid spot visualization. Similarly, staining with iodine to identify spot positions did not degrade the FT Raman spectra. When a mixture of three additives (200 μg of each) was eluted on a silica TLC plate, two of the additives gave good Raman spectra, sufficient for identification. The third component, a weaker scatterer, had spread over such a large area that the concentration was too weak to give a Raman spectrum visible above the background features from the TLC adsorbent. The concentration of the eluted spot is the limiting factor in this approach since the Raman experiment samples only about 1 mm2 of the total sample area. However, component detection is clearly feasible with the use of this technique, and advances in detector technology should substantially reduce the sample loadings required to effect identification, although it must be realized that background Raman features from the TLC adsorbent will ultimately obscure the spectrum of very dilute loadings of additives. In such cases, sample concentration on the plate will be necessary. A brief comparison with conventional Raman spectra obtained with 514-nm excitation is also made. While good spectra of one additive on silica were obtained, this approach could not be used with plates that contained added fluorescor or that had been stained with iodine for spot visualization, owing to intense background fluorescence. The approach was also prone to fluorescence form the TLC fraction itself and sample degradation.

Improved Chromatographic Resolution for Gas Chromatography/Matrix Isolation Infrared Spectroscopy

When gas chromatography/matrix isolation infrared spectroscopy (GCV MI-IR) is carried out with a fixed cryodisk rotation speed, chromatographic resolution may be substantially degraded. In this research, an approach allowing dynamic programming of disk rotation speed is shown to result in much improved resolution in reconstructed chromatograms. Use of up to 254 different speeds during a single chromatographic run is possible. Thus, the analyst can match the requirements of any specific separation problem with an appropriate set of cryocollector movement speeds. As a consequence, much improved analytical performance without loss of sensitivity is possible for mixture analysis by GC/MI-IR, as is up to 30% higher apparent chromatographic resolution than is observed with a flame ionization detector. In addition, careful matching of sample spot size and detector area with the appropriate cryodisk speed leads to the detection of as little as 40 picograms of hexachlorobenzene.

Polymer Analysis and Characterization by FTIR, FTIR-Microscopy, Raman Spectroscopy and Chemometrics

Abstract FTIR-microspectroscopy and Raman spectroscopy, including FT-Raman spectroscopy, are now commonplace tools in many major industrial laboratories. When coupled with multivariate data analysis procedures, the spectroscopic data they produce can be utilized to provide not only rapid, cost-effective quality assurance methods for products, but also to enable simple, efficient or novel means to characterize physicochemical properties. In this paper we discuss these advantages and illustrate them through novel applications and case studies developed for the compositional analysis and physical structural characterization of polymeric products.

Resin characterisation in carbon fibre reinforced prepregs using photoacoustic-FTIR

The use of photoacoustic-FTIR spectroscopy for resin characterisation in carbon fibre reinforced prepregs is discussed, and examples given of its application to both thermoset and thermoplastic systems.