PETplanet Insider Vol. 22 No. 11/21 www.petpla.net 39 EVENT REVIEW About quality control and IR spectroscopy Compact FT-IR spectrometers in recycling Incoming goods inspection and the verification of raw materials have become vital tools of quality control. Where does the raw material come from? Has it been processed correctly? Does it meet the quality requirements? All these questions must be thoroughly answered if optimal production parameters and high-quality results are to be guaranteed. In this respect, the industry’s requirements for chemical analysis are clearly defined: it must be fast, reliable, at- or in-line, cost-effective, timesaving and, of course, easy to use. Infrared (IR) spectroscopy fulfils virtually all these conditions by default. It allows nondestructive chemical analysis of all types of polymers down to the additives and fillers they contain. An analysis usually takes less than a minute, is highly reproducible and requires no chemicals or consumables. At the push of a button, IR spectroscopy can even deformulate complex mixtures into their components. IR spectroscopy basics IR spectroscopy works by irradiating the sample material (e.g. pellets, shavings or even whole moulded parts) with IR light and checking the reflected or transmitted portion for certain molecular vibration patterns. Since the functional groups in the polymer, such as hydrocarbons, esters, ethers, ketones, etc., only absorb particular wavelengths of infrared light, one ends up with an IR spectrum that features a highly characteristic pattern. With this, it is possible to identify a polymer unambiguously, similar to a human fingerprint. This way, IR spectra can tell the information beyond the chemical identity as well. A real-life IR application is differentiation between different polyamides. Despite their very different material properties, the Polyamides 6.6, 6.10 and 6.12 are chemically very similar. Although they only differ in the chain length of the monomers used, this is already sufficient to recognise clear differences in an IR spectrum and to correctly assign the polyamides. Assessing the crystallinity (e.g. HDPE/ LDPE) or quantification of ingredients is also feasible, as long as the constituents in question are present within single-digit percentage range. IR and its role in recycling With the new DIN SPEC 91446, FT-IR spectroscopy has a strong presence in the quality control of recyclates and recycled products. Among other things, the new standard describes how IR spectrometers can be used to classify recycled plastics according to their purity. Users can assess the actual value of the recyclate in a few minutes through a quick chemical analysis. Much to their delight of course, since a pure and chemically well-defined recycled product fetches a significantly higher price. (FT-) IR spectrometers and instrumentation Robust benchtop IR spectrometers like Bruker’s Alpha II are no bigger than a shoebox these days and still offer full performance. The Alpha II is durable, easy to transport, virtually maintenance-free and offers true plugand-play qualities through automatic methods, dedicated reference libraries and intuitive touch operation said Bruker. Like all FT-IR spectrometers, it is based on an interferometer, which can rightfully be called the heart of the instrument. FT-IR stands for Fourier Transform Infrared and is nowadays the most common technique of acquiring and recording infrared spectra. The Alpha II’s interferometer is wearfree and offers permanent alignment for high quality results, less downtime and high stability. It is important to note that FT-IR analysis is not at all a black box. Although autonomous evaluation and analysis routines are common and practical, all results can be traced and understood at any time, even by inexperienced users. The Alpha II’s software logs all procedures on the instrument and can individually identify both, samples and users. www.bruker.com/alpha
RkJQdWJsaXNoZXIy NTY0MjI=