Chemical companies are developing new grades of plastics that will meet the specialized demands that electric vehicles are placing on materials. BEVs present new challenges that are absent from vehicles powered by internal-combustion engines (ICEs).
Vehicles with ICEs typically run just 5% of the time. By contrast, BEV batteries need to be charged, so their systems can be running even when they are stationary, says Ian van Duijvenboode, senior global director, mobility, at nylon producer Ascend Performance Materials. That creates challenges for materials because they have to maintain their properties and performance for much longer periods.
Some materials that were tested for 3,000 hours for ICE vehicles are being tested for 5,000-10,000 hours for BEVs, he says. “It’s a completely different level of aging performance that we need to deliver.”
BEVs require auxiliary heat systems because they lack the waste heat generated by ICEs. By their nature, these systems will generate heat, and materials will need to tolerate that heat without sacrificing performance.
The temperature of the BEV’s battery needs to be moderated to keep it within optimal ranges. Coolants can be used, but these need to be circulated in tubes made of chemically resistant materials, van Duijvenboode says. Ascend developed a line of long-chained nylons, called HiDura, that have the proper chemical resistance.
Thermal Runaway and Flame Retardancy
Materials used in battery packs and the charging equipment need to have flame retardancy to prevent thermal runaway.
Polycarbonate (PC), polyesters and acrylonitrile butadiene styrene (ABS) are relatively easy to make flame-resistant, says Ramesh Iyer, director, engineering plastics at Independent Commodity Intelligence Services (ICIS). Nylon can achieve this, although at a cost.
Polypropylene (PP) flame-retardant grades are available, but the amount of modification required compromises on mechanical properties, Iyer says. To achieve a balance of properties and flame retardancy, some companies have developed long glass fiber-filled grades.
Thermal runaway can put incredible demands on materials. An Ascend polyamide, Starflam X-Protect, can withstand direct flame exposure at 1,100° C (2,012° F) for 15 minutes, van Duijvenboode says. Those 15 minutes should provide passengers with enough time to escape a BEV in the case of a fire.
BEV producers are developing automobiles with faster charging times, which require higher voltages.
Materials need to tolerate those higher voltages, so companies are developing polymers with high comparative tracking indexes (CTI). For many materials, the benchmark is a CTI of 600V.
Solvay recently launched a new grade of polyphenyl sulfide (PPS), Ryton Supreme HV, that meets this CTI benchmark.
Similarly, Covestro has introduced PC products that have a CTI of 600V.
BEVs have many sensors, which require shielding from electromagnetic interference (EMI) and radio frequency interference (RFI), Iyer says. Such shielding is typically made of static dissipative or conductive materials such as metal.
The problem with metal is weight, which will reduce how far BEVs can go on a battery charge. Companies are eager to develop plastics that can replace metals in shielding.
BEVs require different materials to mask noises because they no longer are hidden by the rumbling from an ICE.
In addition, the noises generated by BEV motors can be 4,000 hertz, 10 times higher than those from ICEs, according to Ascend.
Different frequencies require different materials, and rubber gaskets and grommets may not mask those higher frequencies, says Kai Becker, principal applications technology engineer at Ascend Performance Materials. “We found a way to formulate our materials such that they act even on those high frequencies.”
Other sources of noise can come from the motors and compressors that are individually mounted onto the chassis of an electric vehicle. Ascend developed a nylon, Vydyne AVS, that can be used to make the brackets and greatly dampen the noise associated with vibration.
Other companies also are developing polyurethane foams that can mask the different frequencies generated by BEVs.
Al Greenwood (pictured, left) is deputy news editor for Independent Commodity Intelligence Services (ICIS).