Challenges and solutions on identification of high-performance black plastics for closed-loop car recycling

Plastics represent, in volume, up to 50% of materials present in modern vehicles with most of them being black. Consequently, black plastics are a key material stream to be managed in end-of-life vehicles (ELV) waste. The EU directive on ELV, updated in 2023, introduces new rules covering all aspects of a vehicle life cycle, from its design and market placement until its final treatment as ELV. These new specific criteria now put pressure on car manufacturers and black plastic recyclers to boost circularity in the production and recycling chains, including:

• Improving circular design of vehicles to facilitate removal of materials, parts and components for reuse and recycling;
• Ensuring that at least 25% of the plastics used to build a new vehicle comes from recycling (of which 25% from recycled ELVs).

The first step required to improve the circularity of ELV polymers is to identify the main polymer types present in the stream with optical sensing. Current identification workflows are successfully employed by the plastic-waste recycling industry, based on material-specific signals present in the visible-to-near infrared (VNIR) and short-wave infrared (SWIR) ranges (400–2500 nm). Nevertheless, VNIR/SWIR sensors are unsuitable for identification of black plastics due to the strong signal absorption by dark pigments in this spectral region. In recent years, novel hyperspectral sensors operating in mid-wave infrared (MWIR, 2700–5300 nm) have been successfully employed for identification of black plastics. Yet, the automotive industry requires high-performance materials which led to the development and use of very specific polymer variants, including multi-polymer blends (e.g. ABS/PC), polymer subtypes (e.g. PA6 and PA6.6), and functional additives (e.g. glass fiber, talc, carbon black). Consequently, the identification of the usual polymer classes is not adapted to meet the minimum quality requirements for recycling and, hence, not adequate for future use for car material streams (closed loop). 

Such complexity is justified by the need for high performance and functionality of materials in automotive applications, but impacts recyclability and ultimately leads to downcycling. In order to ensure that high-purity black plastics are obtained at the end of the recycling operation, at the standards needed by the automotive industry, it is necessary to go beyond the identification of main polymer types. 

In this contribution, we address the current challenges and propose solutions to identify the important high-performance polymers used by the automotive industry that could be recycled. Further, we evaluate the suitability of current industrial optical sensing techniques for identification of black plastics originated from ELV waste. We also propose solutions for the identification of plastics with highly-complex composition present in ELVs such as multi-polymer blends (e.g. ABS/PC), polymer subtypes (e.g. PA6 and PA6.6), and functional additives (e.g. glass fiber, talc, carbon black).