Morphology and toughness enhancements in recycled high‐density polyethylene (rHDPE) via solid‐state shear pulverization (SSSP) and solid‐state/melt extrusion (SSME)

Abstract

Solid-state, mechanochemical polymer processing techniques are explored as an effective and sustainable solution to appearance and performance issues commonly associated with recycled plastic products. Post-consumer high-density polyethylene (HDPE) from milk jugs is processed via conventional twin screw extrusion (TSE), solid-state shear pulverization (SSSP), and solidstate/melt extrusion (SSME), and compared to the as-received and virgin forms regarding output attributes and mechanical properties, as well as morphology. Solid-state processing methods, particularly SSME with a harsh screw configuration, produce samples with consistent appearance and melt flow characteristics. Tensile ductility/toughness and impact toughness are enhanced by up to 11-fold as compared to the as-received sample, to a level near and above those of an equivalent virgin HDPE. Calorimetry, optical microscopy, X-ray scattering, and rheology characterization reveal that the mechanical improvements result from a favorable combination of physical and molecular changes in rHDPE, such as impurity size reduction, spherulite size enlargement, and chain branching.

Crystallinity and Property Enhancements in Neat Polylactic Acid by Chilled Extrusion: Solid‐State Shear Pulverization and Solid‐State/Melt Extrusion

“…A chilled extruder-based technique called solid-state shear pulverization (SSSP) [26][27][28][29][30][31][32][33][34][35][36][37][38], along with a hybrid SSSP-TSE technique called solid-state/ melt extrusion (SSME) [39,40], is an alternative processing technique that can tailor material properties to practical applications, while fully retaining the environmental benefit.…”

Residence Time Distribution and Specific Mechanical Energy in Solid‐State Shear Pulverization: Processing‐Structure‐Property Relationships in a Chilled Extruder

“…Solid‐state shear pulverization (SSSP) is a case of fundamental and distinctly unconventional modification of TSE; SSSP is geometrically identical to TSE, but operates under low processing temperatures . In SSSP, materials are intentionally retained in the solid state via active heat removal through chilled barrels, and consequently subjected to high shear and compressive forces from the pulverization mechanism.…”

“…Over the last three decades, SSSP has been studied extensively, for modifying homopolymers , dispersing additives , compatibilizing polymer blends , and creating polymer composites and nanocomposites . A hybrid process that combines aspects of SSSP and TSE in one instrumentation, known as solid‐state/melt extrusion, has been also developed .…”

Low‐temperature compounding of flax fibers with polyamide 6 via solid‐state shear pulverization: Towards viable natural fiber composites with engineering thermoplastics

“…There is a need for a robust processing technique that can compound natural fibers with a wide range of thermoplastic matrix options, and yield a composite morphology with highly debundled and distributed natural fibers, preferably at the level of elementary fibers. Solid‐state shear pulverization (SSSP) is a developing technique for processing homopolymers, polymer blends, and polymer composites and nanocomposites that uses a modified TSE in a chilled, solid‐state setting . It applies shear and compression at temperatures well below T m , T g , and T deg of the materials.…”

“…The continuous, scalable process does not require monomers or solvents, and thus is environmentally benign. In sustainable materials research, SSSP has been applied to the processing of recycled plastics and bioderived polymers for two decades , and its use in biocomposites with lignocellulosic fillers have recently been reported . The distinguished advantage of the SSSP process highlighted in prior polymer nanocomposites work is the ability to achieve prominent levels of filler exfoliation and dispersion in situ .…”