With the potential for huge energy and cost savings, a number of manufacturers now favour recycled materials over virgin materials for their products. However, using recycled materials can present a number of problems, with undetected contaminants decreasing the quality and value of recyclate, and even a small amount of moisture having a negative impact on mechanical properties. The impact this has is not just economic and environmental – it can also have health and safety implications. For instance, where recycled PET is used for bale strapping, it is crucial that the tensile strength is retained to ensure the strapping does not loosen, presenting a potential hazard.
One of the most efficient tools for process and quality control is in-line near infrared spectroscopy (ILNIRS), a high speed, continual process that can identify materials and ascertain their purity. ILNIRS analyses polymer melt by monitoring changes in near-infrared light which is shone through the melt during processing. This provides information about the state of the polymer, such as the extent of degradation, additive concentration and details of process conditions, including temperature and pressure. It can also be used to detect colour, which can be due to either a desired additive or contamination. The technique can also work with visible, mid-infrared and UV light, depending on the materials involved and the processor’s needs.
While spectroscopy is used in current recycling processes to identify the composition of solid materials, ILNIRS could be utilised in a revolutionary way, to evaluate the quality, and segregate polymer recyclate at the point of production, during the melt stage. Used in this way, ILNIRS makes it much easier to spot and remove undesirable contaminants at the melt stage, before the processed recycled plastic is despatched to clients.
For instance, currently, optical and other sorting techniques used in bottling and materials recovery facilities (MRFs) cannot be used for high volume Polyethylene (PE) recycling. Any limited sorting that can be done is by hand and low quality, as the feedstock is baled and multilayered (approx 100mm depth), which current optical techniques cannot penetrate. For example, when running polyethylene (PE) film through an extruder to determine the quality of the melt, contamination of the PE by polypropylene (PP) may not be visible to the naked eye. However, if using ILNIRS, any contaminants in the polymer melt would be detected by the infrared and could then be separated at the pelletising stage rather than the initial feedstock. Analysing the melt will give the opportunity to remove contaminant that is otherwise missed and can cause product failure or downtime.
It is not just recyclers and polymer manufacturers who could benefit from this advanced technique, which is used in a number of applications, including pharmaceutical, medical diagnostics (including blood sugar and pulse oximetry), food and agrochemical quality control, and combustion research. It is also utilised in research in functional neuroimaging, sports medicine and science, elite sports training, ergonomics, rehabilitation, neonatal research, brain computer interface, urology (bladder contraction), and neurology (neurovascular coupling).
ILNIRS is just one of the techniques being demonstrated at a free workshop taking place at the University of Exeter. Attendees will get the chance to tour the facilities of the University’s Exeter Technologies Group, including near infrared spectroscopy and thermal characterisation equipment, as well as the additive layer manufacturing facilities.
The workshop will cover identifying and knowing materials, quality control and changes in industry, and is designed to give businesses an advantage by showing delegates how to identify failures, establish information about competitor products and manage suppliers, as well as improving quality and performance and reducing waste. The aim is to encourage discussions on how to improve recycling; by increasing your knowledge of materials, allowing validation of material constituents and improving the overall quality of recyclate.
The workshop is being hosted by the Centre for Alternative Materials and Remanufacturing Technologies (CALMARE), a centre part funded until mid 2015 by the European Regional Development Fund (ERDF). The centre is based within the Exeter Technologies Group, which has worked with partners to use the technique for a range of project applications – as an in-line monitoring tool for scrap reduction and re-use in the plastics industry, in spectroscopic instrumentation for injection moulding and to detect polylactic acid (a thermoplastic polyester), which can contaminate PET plastic bottles, if not detected and removed.
For more information about the workshop, and to book a space, please visit http://bit.ly/1AgM7mE