32 to their higher resilience and fatigue resistance, and greater resistance to corrosion. A test laboratory uses new infrared (IR) thermography techniques to obtain accurate and non-intrusive measurements of the actual temperature of materials during fire tests. The ultimate aim is to conduct virtual tests on thermoplastics and compare their performance in real applications with those of conventional thermosetting composites. The project aims to establish a methodology that allows the characterisation of thermoplastics to improve the prediction of their behaviour and resistance when subjected to mechanical loads or fire and high temperatures. The measurements obtained by infrared thermography allow computer simulations to be carried out, which virtualise testing to select this type of material in the aeronautical industry. This can significantly reduce the number of validation tests. Biodegradability A team of researchers has developed a plastic that has similar thermoplastic properties to polyethylene but is also biodegradable. The material is a semicrystalline polyester, which breaks down fully to its starting materials using mild chemical or biological processes. High-density polyethylene (HDPE) is particularly strong and durable. It owes its thermoplastic properties to the internal structure of its molecular chains, which are arranged in a crystalline manner with added attraction due to van der Waals forces. The molecular chains are also pure hydrocarbons. The combination of crystallinity and hydrocarbon content means that microorganisms, which might be able to degrade the plastic, cannot access the chains to break them up. The polyester has similar crystallinity to HDPE and retains its mechanical properties, but unlike polyethylene it also contains functional groups that could theoretically be degraded chemically or enzymatically. However, under normal circumstances, the more crystalline a polyester is (i.e. the more similar to HDPE), the less readily it can be biodegraded. Adding ethylene glycol, one of the building blocks of polyester, gives a high melting point, but it also increases degradability in these polyethylene-like materials. The end goal is closed-loop chemical recycling in a process that breaks the plastic down into its raw materials and March/April 2024 | E-Mobility Engineering Thermoplastic types Thermoplastics are the most commonly used type of plastic, with the top three being polyethylene (including high-density HDPE and low-density LLDPE/LDPE), polypropylene (PP), polyvinyl chloride (PVC) and polyethylene terephthalate (PET). Within each group are many different types of material, from solids to films, and many variants with differing properties. Acrylonitrile butadiene styrene (ABS), among other specialist styrenic materials, is rigid, opaque, glossy and tough, with good low-temperature properties, good dimensional stability and low creep. ABS is easily electroplated, and sometimes parts require this for shielding purposes, for example. Aramids PI aromatic polyamide is becoming an increasingly popular choice for e-mobility, particularly electric aircraft, due to its high strength, exceptional thermal and electrical properties up to 480 C, and resistance to ionising radiation. PEEK (Polyether ether ketone) is a rigid, opaque (grey) material with a unique combination of properties, which include exceptional chemical, wear, electrical and temperature resistance, as well as dimensional stability and numerous processing capabilities. It is increasingly being used as a replacement for machined metals in a wide variety of high-performance end-use applications, ranging from components for cars and aircraft to the pumps, valves and seals in a powertrain. Polycarbonates are strong, stiff, hard, tough and transparent engineering thermoplastics that can maintain rigidity up to 140 C and toughness down to -20 C, and special grades even lower. Polyesters (thermoplastic) PETP, PBT and PET are engineered polymers that are used in the manufacture of a wide range of components, including under-bonnet parts and exterior parts such as window-wiper holders and exterior-mirror housings. Polyetherimide (PEI) resins have long-term, high heat capability with dimensional stability from -40 C to 130 C for onboard chargers and DC-to-DC converters, as well as fast charger handles and connectors with inherent low flame, smoke and toxicity (FST). Other amorphous, thermoplastic polyimides (TPI) have extreme high-temperature performance for aerospace applications, and they can withstand the higher temperatures required for lead-free, solder-reflow manufacturing processes for connectors. Many materials are a trade-off of different performance points (Image courtesy of SABIC)
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