Solid‐state shear pulverization of post‐industrial ultra‐high molecular weight polyethylene: Particle morphology and molecular structure modifications toward conventional mechanical recycling

Abstract

Ultra-high molecular weight polyethylene (UHMWPE) is one of the most prominent high-performance thermoplastics for biomedical, leisure, and coating applications. Large-scale recycling of UHMWPE is extremely difficult due to the high melt viscosity of the material as well as its exceptional chemical resistance and impact strength. There is a need for a commercially scalable methodology that can process the waste feedstock for mechanical recycling while sustaining the outstanding physical properties of the material. Solid-state shear pulverization (SSSP) is a continuous, twin-screw extruder-based processing technique in which the low-temperature application of shear and compressive forces impart changes in structure at different length scales to overcome the challenges of difficult-torecycle polymers. This paper investigates the use of SSSP in mechanically recycling post-industrial scrap UHMWPE (rUHMWPE) material from a local ski and snowboard manufacturer. The SSSP-processed particles are flat, micron-scale flakes with enhanced surface area, which can sinter very quickly when compression molded. The molded rUHMWPE samples in turn exhibit enhanced ductility and toughness compared to the as-received scrap material, based on the tunable mechanochemical modification of the ethylene chains.

Effects of Polymer Properties on Solid-State Shear Pulverization: Thermoplastic Processability and Nanofiller Dispersibility

“…A full understanding of the deformation mechanism in SSSP would result from detailed fractional and multiple pass analysis on an individual polymer basis. 28 …”

“…A full understanding of the deformation mechanism in SSSP would result from detailed fractional and multiple pass analysis on an individual polymer basis. 28 The SEM and photographic images of the SSSP output are compiled in Figure 3, all taken under equal magnifications. The particle size and shape, as well as the texture of the pulverized polymer surface, differ considerably.…”

“… 9 Solid-state shear pulverization (SSSP) is one alternative TSE-based technique that can tailor the macro-, micro-, and nanoscale structures of polymeric materials to achieve specific properties and performance. 10 − 28 High compressive and shearing forces are applied at low temperatures, which results in the repeated fragmentation and fusion of the material. The associated mechanochemistry leads to the modification of the macromolecular structure and promotes the intimate mixing and homogeneous dispersion of multicomponent systems.…”

“… 4 , 29 The mechanochemical process results in not only macroscopic morphological changes like size reduction, but also permanent molecular changes, such as free-radical formation, chain scission, and branch formation. 21 , 22 , 26 , 28 …”

“…4,29 The mechanochemical process results in not only macroscopic morphological changes like size reduction, but also permanent molecular changes, such as free-radical formation, chain scission, and branch formation. 21,22,26,28 This 10-polymer comparison report is divided into two sections. In the first part, thermal, mechanical, and rheological properties of as-received neat polymers were evaluated and correlated to SSSP output and processing characteristics; polymers were individually processed, and identical pulverization parameters were used for each material.…”