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Dedicated to Professor Dr. K. W. BOER on the occasion of his 70th birthday Thermal infrared sensors with maximal sensitivity and minimal response time require radiation absorbing layers with small heat capacity and high absorbance. In the near infrared these conditions are well met by black gold layers. In order to examine the question whether black gold layers are suitable absorbers as well in the far infrared, their reflectance is measured in a wave number range from k = 14 to 650 cm-', corresponding to a range in wavelength 1 = l / k between 15 and 710 pm.The samples are prepared at various residual gas pressures. The influence of tempering o m the absorbance and the spectral absorption behavior at low temperatures is discussed. The experimental results may be accounted for by a dielectric function according to the Bergman formalism. The spectral dependence of the absorption coefficient and the real and imaginary parts of the refractive index following from it are presented.

The identification of black polymers which contain about 0.5 to 3 mass percent soot or black master batch is still an essential problem in recycling sorting processes. Near infrared spectroscopy (NIRS) of non-black polymers offers a reliable and fast identification, and is therefore suitable for industrial application. NIRS is consequently widely used in polymer sorting plants. However, this method cannot be used for black polymers because small amounts of carbon black or soot absorb all light in the NIR spectral region. Spectroscopy in the mid infrared spectral region (MIR) offers a possibility to identify black polymers. MIR spectral measurements carried out with Fourier-transform infrared spectrometers (FTIR) are not fast enough to meet economic requirements in sorting plants. By contrast, spectrometer systems based on the photon up-conversion technique are fast and sensitive enough and can be applied to sort black polymer parts. Such a system is able to measure several thousand spectra per second hence is suitable for industrial applications. The results of spectral measurements of black polymers are presented.

Near-infrared (NIR) spectroscopy was evaluated as a rapid method of predicting fiber components (hemicellulose, cellulose, lignin, and ash) and selective compounds of hydrochar and corresponding process liquor produced by hydrothermal carbonization (HTC) of maize silage. Several HTC reaction times and temperatures were applied and NIR spectra of both HTC solids and liquids were obtained and correlated with concentration determined from van-Soest fiber analysis, IC, and UHPLC. Partial least-squares regression was applied to calculate models for the prediction of selective substances. The model developed with the spectra had the best performance in 3-7 factors with a correlation coefficient, which varied between 0.9275-0.9880 and 0.9364-0.9957 for compounds in solid and liquid, respectively. Calculated root mean square errors of prediction (RMSEP) were 0.42-5.06mg/kg. The preliminary results indicate that NIR, a widely applied technique, might be applied to determine chemical compounds in HTC solid and liquid.

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NIR spectroscopy has become an analytical tool frequently used in many chemical production processes. Its use in polymer processing applications such as polymer extrusion would greatly increase product quality. Parameters of interest in this application are composition of the processed polymer, moisture or reaction status in reactive polymeric systems, as well as rheological parameters such as melt flow index (MFI) or viscosity. The measurement of NIR spectra could provide a way to control the processes. For this purpose a transmission sensor was developed for the application of NIR spectroscopy to extrusion processes. This sensor includes fibre optical probes and a measuring cell that can be adapted to the various extruders for in-line measurements. In contrast to mid-infrared sensors, it uses optical quartz components, which provides a low-cost solution. Extrusion processes at temperatures up to 300°C and pressures up to 35 MPa have been investigated. The application of multivariate analysis for PE/PPblending demonstrated the performance of the system with respect to process monitoring. In this case deviations between predicted and actual polymer composition were below 2%. Together with an AOTF spectrometer that was also developed, the complete system is suitable for harsh industrial environments and could lead to improved extrusion processes.

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