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Temperature Dependence of Kinetic Friction: A Handle for Plastics Sorting?



Chad R. Snyder, Kalman Migler


Sortation is a crucial step in mechanical recycling of post-consumer plastics (PCR) whereby properties such as density or spectral signature are used to separate plastics. However it is difficult to sort polyolefin flakes at high throughput by these properties. We ask whether the frictional properties of plastics as a function of temperature may be used as an alternate sorting property, but fundamental studies of friction at elevated temperatures are limited. Here we measure the temperature dependence of kinetic friction for three common polyolefins (high and low density polyethylene and polypropylene) as well as for polyethylene terephthalate (PET), focusing on the softening/melting regime. The results are augmented by differential scanning calorimetry and dynamic modulus temperature scans. For the polyolefins, we find strong increases in the coefficients of kinetic friction during temperature ramps in the softening regime. For the PET, we report a notable peak in the kinetic friction which we associate with the glass transition and cold-crystallization. We discuss the enhanced friction in the context of rubber friction, which exhibits comparable coefficients of kinetic frictions.
Polymer Engineering and Science


plastics, polymers, recycling, circular economy, friction, tribology


Snyder, C. and Migler, K. (2024), Temperature Dependence of Kinetic Friction: A Handle for Plastics Sorting?, Polymer Engineering and Science, [online],, (Accessed May 26, 2024)


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Created February 26, 2024, Updated May 9, 2024