PVC from pipes, coatings and cables could have an unexpected second life: becoming a lubricating oil for machines. An international team has obtained liquids similar to polyalphaolefins, used as bases in many synthetic lubricants.
This achievement targets a plastic that is particularly difficult to recycle. Polyvinyl chloride, or PVC, contains a lot of chlorine. During conventional treatments, this element can damage catalysts, corrode equipment or form undesirable by-products. Around 60 million tonnes of PVC are produced every year worldwide.
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The process relies on aluminium chloride, denoted AlCl3, used at 70 °C. At this moderate temperature, PVC loses part of its chlorine. Its carbon chain then takes part in several reactions with alpha-olefins, molecules already used to make synthetic oils.
In other words, the plastic is not just a material to be broken down. Its structure guides the formation of new lubricating chains. The researchers thus obtain PVC-derived polyalphaolefins, called vPAO, without relying on the catalysts used in some current production processes.
The measured properties match those sought to limit friction. At 100 °C, the kinematic viscosity of the products ranges from about 14.9 to 26.3 mm²/s. Their friction coefficient is between 0.08 and 0.15 in the tests carried out by the team.
Viscosity can also remain relatively stable when temperature changes. The best viscosity index reaches 130. This value describes an oil's ability to maintain consistent behaviour between cold start and hot operation of a mechanism.
The experiments included real PVC objects, making it possible to check that additives and commercial formulations do not immediately block the reaction.
It now remains to determine the cost, reagent consumption and chlorine management in larger-scale production. A provisional patent application has been filed. The next steps will above all have to show that this transformation works with heterogeneous waste, without shifting its impact to other chemical residues.