Spectroscopy is adapted to meet more demanding materials characterisation.
Currently many analytical tests are either limited in the information they can give or are time consuming and expensive. Typically, businesses have to make choices between increasing cost and delays by carrying out detailed analysis or reducing the amount of analysis and running the risk of shipping off-spec material. This can have repercussions along the whole supply chain; similar problems also occur with asset management, such as in the aerospace and power sectors, where identification and qualification of material is vitally important. Recyclers face similar concerns.
A new group of technologies called Transpec has been designed to address these issues. The fundamental principle is that molecular vibrations and electronic transitions give information relating to specific compounds and functional groups and their interaction with the environment. The most powerful and rapid tool for measuring this is spectroscopy: Transpec offers both Raman and WideWavelength devices.
The transpec "principle" builds databases of known materials and then uses multi-variate statistical analysis (MVSA) on the whole of the spectral data and regresses it against known material characteristics such as concentration of additives, physical properties, processability and performance.
The benefits from Transpec's spectrographic method are: rapid results (typically within seconds), no need for sample preparation, and high portability -meaning multiple measurements can be carried out anywhere on site. The ability for Transpec to make multiple component measurements and property predictions in one analysis means fewer tests are required.
Transpec is a two component system -a software package which runs either of two complementary spectrometers, WideWavelength and Raman.
Transpec-WideWavelength uses the UV-Vis-NIR reflectance spectrum, which means it can pick up information on colour and dispersity as well as the molecular structure. Transpec-Raman uses the Raman scattering effect from a laser source that gives high resolution spectra and is suitable for detailed component analysis of a wide range of organic and inorganic materials and compounds.
Transpec Raman tends to be more useful for compounders and masterbatchers while WideWavelength finds more use in composites and colour-based needs and where water may be an issue.
Transpec principles can be applied universally to materials in that any characteristics of interest can be examined for correlations with the spectral data; this can be any of the "soft" metrics such as good/bad to "hard" metrics such as physical properties. This means that there is a wide range of possible applications from simple identification to complex property predictions.
For plastics processors such as masterbatchers and compounders Transpec can identify and qualify incoming material and then be used for near-line quality analysis, to check formulations through identity and concentration measurements as well as making property predictions.
For research and development, the ability to look for trends and correlations in formulation-property relationships and through the building of databases--with high legacy value speeds up the learning curve while increasing knowledge.
For sectors such as the power and aerospace industry it is not just virgin material that is of interest - qualifying material in actual use, tracking of degradation and lifetime predictions are vital for asset management. There are similar needs in the recycling sector to identify and further qualify material streams.
The following is an example of Transpec-Raman application with PC/ABS blends with various phosphorus-based flame retardants. The illustrations show the high quality Raman spectra obtained, which, although appearing similar to the eye, contain differences related to the molecular bonds and environment of each compound. In this example, a calibration set with known concentration of the flame retardants in PC/ABS was scanned (figure 2) and the properties used to start the database. The set-up software then took these spectra and used MVSA to correlate them to FR type and concentrations, limiting oxygen index (LOI) scores and PC/ABS blend ratio.
The model built from this relationship can be used as a routine QA method to rapidly test samples to determine the PC/ABS ratio, FR type and FR concentration and predict LOI score all in one simple and rapid measurement. Figure 3 compares predicted against measured properties.
When colour or material degradation are important, WideWavelength Transpec provides a complementary solution. The spectra in figure 4 show lab-aged epoxy resin/glass mat composites which have been correlated to thermal endurance time-temperature ageing tests. Simple rapid examination reveals the spectral shifts in the visible region as discoloration occurs but the WideWavelength method picks up both this and also molecular degradation in the NIR region.
On board analysis distills the raw data and information on a composite ageing metric which relates to a master ageing curve and a prediction is then obtained of the ageing temperature and time. The multi-variate regression coefficient information shows the dominant spectral regions that feed the model prediction below it (figure 5). This model can now be used to predict the temperature and exposure time and in this case provide information on the quality of this electrical insulating material.
The Transpec concept means that there are many opportunities for the plastics and rubber industry to use a rapid, portable analytical tool to tackle a wide range of measurements from ID and concentration to hard-to-measure property predictions. The beauty of the technique is that it uses information already to hand as well as new information to address the real needs of the material producer and user.
Dr William Mortimore of GnoSys UK, a research and technology company with its roots in the University of Surrey's polymer research centre, describes a new spectrographic testing system which extends what can be learned from two established forms of spectrometer.
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|Title Annotation:||testing & inspection|
|Comment:||Spectroscopy is adapted to meet more demanding materials characterisation.(testing & inspection)|
|Publication:||British Plastics & Rubber|
|Date:||Feb 1, 2011|
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