MATERIALS | RECYCLED COMPOUNDS
FTIR analysis of recycled material: the spectra suggest that the material is dominated by PE
Source: Intertek
to products and processes. Data mining and Statistical Process Control (SPC) helps to ensure the quality of production, processes and increases productivity. Furthermore, the insight that can be obtained from SPC can help to standardise processes, minimise waste and help optimise the recycled material value. It is important in any evaluation programme that methods are validated against the set criteria for reproducibility and repeatability (independent of user) and the SPC data builds as performance tests are repeated. The insight from a materials evaluation programme benefits all stakeholders from waste collectors, sorters and recyclers, materials producers, and converters through to brand owners and retailers. Triepels says a typical approach to materials evalu-
ation which is applicable to both virgin and recycled materials, includes initial characterisation through a small selection of analytical techniques to provide insight into the materials involved. This is followed by a processing step involving common methods – in- jection moulding, cast film extrusion and blow film extrusion – followed by a range of tests to determine physical and mechanical properties. This approach can be applied to the recycled material only or on mixes of recycled and virgin materials. For initial characterisation and a first step towards understanding the nature of recycled material, Triepels adds that a set of analytical techniques including FTIR Spectroscopy, and thermal analysis such as Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA), can be conduct- ed. These tests help to identify the main polymer present and provide an indication of potential challenges that the material presents, as well as help indicate which processing options could work.
34 INJECTION WORLD | April 2022
FTIR provides a rapid means of achieving a chemical “fingerprint” of the bulk material. The speed and chemical information provided are ideal for monitoring the major polymer present and can be used to compare batches of recycled materials. The spectra peaks are attributed to the vibrational behaviour of different functional groups within the polymer/additive formulation (see chart above). In thermal analysis, melting points obtained by DSC techniques can be used to confirm the FTIR spectra suggestions and TGA techniques provide more information about the moisture content, as well as additives present in the compound, such as carbon black and minerals like calcium carbonate and talc. Common processing approaches are used to
produce test materials for evaluation of physical properties. The behaviour of these materials during these processes can contribute valuable informa- tion on how stable the process is for the uniformity and quality of the extruded material, and assess- ment of impurities can be made through a melt extrusion filtration test, says Triepels. The processed materials are then subjected to a
range of tests to determine their physical, thermal, and mechanical properties, following conditioning. ISO 291:2008 sets out specifications relating to the conditioning and testing of all plastics and all types of test specimen at constant atmospheric condi- tions. Conditioning brings the material into equilibrium with normal room conditions, and this enables more reproducible results that allow a better understanding of a material’s performance. Typical conditions include 23°C ± 2°C and 50% ± 10% relative humidity for over 16 hours. Standard- ised tests that can be included in a materials
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