Near-infrared spectroscopy chemical properties

Many different methods can be used to measure the degree of crosslinking within an epoxy specimen. These methods include chemical analysis and infrared and near infrared spectroscopy. They measure the extent to which the epoxy groups are consumed. Other methods are based on the measurements of properties that are directly or indirectly related to the extent and nature of crosslinks. These properties are the heat distortion temperature, glass transition temperature, hardness, electrical resistivity, degree of solvent swelling and dynamic mechanical properties, and thermal expansion rate. The methods of measurement are described in Chap. 20. 

Baley C, Busnel F, Grohens Y, Sire O (2006) Influence of chemical treatments rai surface properties and adhesion of flax fiber-polyester resin. Compos A 37(10) 1626-1637 Barton F, Akin D, Morrison W, Ulrich A, Archibald D (2002) Analysis of fiber content in flax stems by near-infrared spectroscopy. J Agric Food Chem 50(26) 7576-7580 Basu S, Bhattacharyya J (1951) Mildew of complex vegetable fibers. J Sci Ind Res 10B(4) 91-93 Berkley E (1949) Certain variations in the structure and properties of natural cellulose fibers. Text Res J 19(60) 91-93... 

Interpretive spectroscopy provides a basis for the establishment of cause-and-effect relationships between spectrometer response and the chemical properties of the samples. While many books available on NIR cover a range of applications and topics from a broad perspective, most of them barely touch on structure correlation and interpretation of spectra. The first, and arguably the only, book to tackle this intriguing and challenging area, Practical Guide to Interpretive Near-Infrared Spectroscopy presents the most detailed discussion of the subject to date. 

Schrampf E, Leitner E (2010) Prediction of rheological and chemical properties of different starches used in the paper industry by near infrared spectroscopy (NIRS). Macromol Symp 296 154-160... 

Near-infrared spectroscopy (NIRS) can be used for product identification, classification and quality control, as well as for the determination of product properties (chemical and physical) and component concentrations in process applications, all with the object of rapid analysis. Near-IR analysis was born of a need to solve practical quality control problems rather than the desire to perform high-resolution molecular structure analysis in the laboratory. The samples subjected to NIRS are often very complex mixtures and are studied without any sample preparation. Competitor analysis is not possible. 

Raman spectroscopy has been widely used to study the composition and molecular structure of polymers [100, 101, 102, 103, 104]. Assessment of conformation, tacticity, orientation, chain bonds and crystallinity bands are quite well established. However, some difficulties have been found when analysing Raman data since the band intensities depend upon several factors, such as laser power and sample and instrument alignment, which are not dependent on the sample chemical properties. Raman spectra may show a non-linear base line to fluorescence (or incandescence in near infrared excited Raman spectra). Fluorescence is a strong light emission, which interferes with or totally swaps the weak Raman signal. It is therefore necessary to remove the effects of these variables. Several methods and mathematical artefacts have been used in order to remove the effects of fluorescence on the spectra [105, 106, 107]. 

Reflectance spectroscopy has proven to be the most powerful and versatile remote-sensing technique for determining surface mineralogy, chemical compositions and lithologies of planetary objects, as well as constituents of their atmospheres. Table 10.1 summarizes information that has been deduced for the terrestrial planets based on spectral properties of light in the visible and near-infrared regions reflected from their surfaces. 

Applied Spectroscopy 53, No.5, May 1999, p.557-64 COMPARISON OF NEAR-INFRARED AND RAMAN SPECTROSCOPY FOR THE DETERMINATION OF CHEMICAL AND PHYSICAL PROPERTIES OF NAPHTHA Min-Sik Ku Hoeil Chung SK Corp. 

Quantitative infrared spectroscopy can provide certain advantages over other analytical techniques. This approach may be used for the analysis of one component of a mixture, especially when the compounds in the mixture are alike chemically or have very similar physical properties (for example, structural isomers). In these instances, analysis using ultraviolet/visible spectroscopy, for instance, is difficult because the spectra of the components will be nearly identical. Chromatographic analysis may be of limited use because separation, of say isomers, is difficult to achieve. The infrared spectra of isomers are usually quite different in the fingerprint region. Another advantage of the infrared technique is that it can be non-destructive and requires a relatively small amount of sample. 

Dias et al., used, what they called, a hyphenated rapid real-time dynamic mechanical analysis (RT DMA) and time resolved near-infi ared spectroscopy to simultaneously monitor photopolymerization of acrylate coating compositions. This allowed them to determine the rate of conversion and the mechanical properties of the finished films. It is claimed that up to 374 near infrared spectra and to 50 dynamic analysis points can be accumulated within a second. They observed that modulus buildup does not linearly follow chemical conversion of acrylate bonds. The gel point is detected after passing a certain critical acrylate conversion. Their experimental data revealed a critical dependence of the mechanical property development during the later stage of acrylate conversion. 

Raman spectroscopy has recently gained popularity for advanced chemical analysis of surfaces. In nanoscience, Raman spectroscopy is used to characterize surface properties of materials, measure temperature, and determine crystallinity. Raman spectroscopy is a spectroscopic technique used in material science to study vibrational and rotational frequencies in a system. The technique measures shifts in inelastic scattering, or Raman scattering, of light from a visible, near infrared or near ultraviolet light source and the shift in energy provides information about the material s surface characteristics. The Raman signal unit is a measurement of the ratio between the Stokes (down-shifted) intensity and anti-Stokes (up-shifted) intensity peaks. 

Near-infrared (NIR) spectroscopy has taken its place among other proven spectroscopic tools, especially for determining chemical and physical properties of foods and food products. Covering the small region of the electromagnetic spectrum from 780 to 2500 (nm) (Sheppard, 1985 354), producing spectra with only 860 data points spaced 2 nm apart, NIR spectroscopy has experienced phenomenal growth over its short history from 1905 (the year Coblentz produced the first official NIR publication) to the... 

Near-infrared (NIR) spectroscopy has been found to be a useful technique to characterize raw materials and finished textile products, and NIR methods and techniques continue to find increasingly diverse and wide-ranging quantitative and qualitative applications in the textile industry. Quantitative analyses determine the amount (or quantity) of the property/species of interest in a substance or material. Qualitative analyses can be used to either identify a specific species or subsfance present in a material (i.e., coating on a fiber), the type of material itself (i.e., cotton, nylon, or polyester), or the quality of the material. NIR quantitative and qualitative methods allow the user to rapidly, accurately, and precisely monitor key chemical, physical, and morphological properties of textile fibers, yarns, fabrics, and chemical textile auxiliaries. Chemical properties are specific chemical species or groups present in the material (i.e., CH, OH, NH) that result in NIR spectral absorbencies at distinctive... 

Rinnan, R. and Rinnan, A. (2007). Application of near infrared reflectance (NIR) and fluorescence spectroscopy to analysis of microbiological and chemical properties of arctic soil. Soil Biol. Biochem., 39,1664-1673. 

---