Flow-induced demixing for mechanical recycling of degradable polymers

Overview

This research explores a novel mechanical recycling strategy for degradable polymers using flow-induced demixing during extrusion. By tuning processing parameters, the resulting extrudate develops a molecular weight gradient (for single polymers) or a compositional gradient (for polymer blends) in the radial direction. This fractionation enables recovery of desired material fractions, offering a pathway to higher-value recycled outputs from biodegradable polymer waste streams such as PLA and PHA blends.

Technical specifications

• Core mechanism: Flow-induced demixing exploits shear rate gradients and radial pressure differences during extrusion to drive molecular segregation within the polymer melt
• Single polymer feedstock: Produces a molecular weight gradient across the radius of a cylindrical extrudate, with higher molecular weight species concentrating toward the center
• Polymer blend feedstock: Produces a compositional gradient, enabling enrichment of one blend component in the center of the extrudate
• Influencing factors: Blend component viscosity ratios and post-processing heat treatment affect the degree of demixing and fractionation outcomes
• Auxiliary processing: Physical and chemical approaches can be used to remove heavily degraded or lower-value materials from the exterior of the extrudate
• Model feedstocks: Validation will examine neat PLA, neat PHA, and PLA/PHA blends as representative biodegradable polymer systems

Technology readiness level

This research is at an early-to-mid stage of development. Initial studies in the lab have demonstrated flow-induced demixing as a viable approach for separating polyolefin blends, with enrichment of one component observed in the center of the extrudate. Future validation will systematically assess three model biodegradable polymer feedstocks through simulated mechanical recycling at a common processing temperature, characterizing molecular weight and compositional gradients via radial sectioning of extrudates. The degree of degradation introduced by this method will also be measured to determine practical feasibility for industrial recycling applications.