Applications of terahertz spectroscopy in the plastics industry

The worldwide production volume of polymers is still rising exponentially and the number of applications for plastic components steadily increases. Yet, many branches within the polymer industry are hardly supported by non-destructive testing techniques. We demonstrate that terahertz (THz) spectroscopy could be the method of choice to ensure high-quality polymer products. Applications range from the in-line monitoring of extrusion processes and the quality control of commodities in a mass production up to a total inspection of high-tech safety relevant products. Furthermore, we present an extension to THz time-domain spectroscopy in the form of a new data extraction algorithm, which derives the absorption coefficient, the refractive index and the thickness of a sample with very high precision in a single pass. Apart from that, we discuss the ability of THz systems for quality control of polymeric compounds. Here, it is essential to monitor the additive content as well as additive inhomogeneities within the mixture. Recently, we built a fiber-coupled THz spectrometer for in-line monitoring of compounding processes. Additionally, we demonstrate the potential of THz systems for the non-destructive and contactless testing of structural components. THz imaging is capable of analyzing material thicknesses, superstructures, the quality of plastic weld joints, and of detecting flaws in components. Plastics and THz form a very fruitful symbiosis. In return, plastics industry can provide THz systems with custom-tailored components, which have very attractive properties and extremely low costs. Examples of this development are photonic crystals or polymeric Bragg filters, which have recently been demonstrated.