Smart Combinations of Complementary Technologies Are Needed for Recycling Specific Plastics

   According to a recent article published by BASF researchers, multiple recycling technologies must be used in combination to ensure the effective circular utilization of various types of plastics. Unlike commodity plastics used in packaging and other fields, such as polyolefins, specialty plastics often require recycling technologies tailored to their specific properties and application scenarios. For example, modified glass-fiber-reinforced polyolefins, polyurethanes, and polyamides are designed for demanding fields such as automotive, where ordinary plastics generally cannot meet the required performance standards.

To achieve circular utilization of mixed waste plastics with complex compositions, two conditions are required. First, sorting technologies with scale-up capability. Second, the adoption of a suitable combination of recycling technologies. The specific solution adopted depends not only on the characteristics of the material itself, but also on the composition of the waste plastic stream. "There is no one-size-fits-all standardized technology for recycling engineering plastics," emphasized Dr. Bernhard von Vacano, head of BASF's plastics circularity research program. "The key is to intelligently combine multiple complementary technologies for a specific waste plastic stream. Our goal is to produce high-quality recycled materials and achieve closed-loop recycling of engineering plastics."

Multiple Pathways for Plastics Recycling

The most common recycling technology is mechanical recycling, which involves sorting, shredding, and melting plastics. This process has relatively low energy consumption, but it is not suitable for all types of plastics, and it requires that the waste plastic stream be clean and compositionally uniform. Mechanical recycling is particularly suitable for treating packaging waste with high polymer purity and low additive content. However, due to quality and hygiene standards, the application of mechanically recycled materials in new packaging products is subject to certain limitations. For technically demanding application areas, mechanical recycling has limitations because waste plastic streams that meet the requirements are often scarce, and plastic products usually contain complex polymer compositions.

In contrast, dissolution recycling is more suitable for treating waste plastics with more complex compositions. This process uses specific solvents to selectively dissolve, separate, and purify a particular plastic. For example, polyamides can be recovered from end-of-life vehicles and used to manufacture new components.

Another important recycling technology is depolymerization. In this process, plastics are broken down into their basic building blocks, or monomers, and then re-polymerized. BASF researchers have developed the innovative loopamid process, achieving textile-to-textile closed-loop recycling of polyamide 6, or PA6. Waste textiles can thereby be converted into polyamide fibers with quality identical to that of conventional polyamide 6 fibers. BASF has already started up its first loopamid commercial production facility at its Caojing site in Shanghai, China.

Mixed waste plastics with extremely complex compositions can be recycled through thermochemical processes such as pyrolysis or gasification. These technologies have relatively high energy consumption. In the pyrolysis process, the long-chain polymers of plastics are cracked into short-chain hydrocarbons, which can then be used again as feedstock, or pyrolysis oil. The gasification process, meanwhile, produces syngas, which can be used as a chemical feedstock in production.