Investigation of Degradation Mechanism from Shear Deformation and the Relationship with Mechanical Properties, Lamellar Size, and Morphology of High-Density Polyethylene

Abstract

The degradation of mechanical properties is the most challenging point for the development of plastic mechanical recycling processes. Remelting and shear deformation contained in the mechanical process are a part of degradation in recycled plastics. In this study, virgin high-density polyethylene (HDPE) was simulated to be recycled by remelting and treating with shear deformation being measured at different shear treatment rates (0–100/s) using a cone-plate rheometer. The obtained shear treatment product was remolded as a thin film. The evaluation was performed comparing virgin HDPE (VPE) without any processing with shear-treated HDPE with various shear treatment rates. Tensile property, X-ray crystallography, and morphological observations were performed in order to investigate the relationship between mechanical properties, thickness of lamellar size, and the morphology of shear-treated HDPE as compared to VPE. It can be found that the elongation at break of shear-treated HDPE at a high shear treatment rate (100/s) was significantly decreased from VPE. This degradation mechanism was related to the decreased degree of crystallinity, thickness of the crystalline layer, intermediate layer, and occurrence of crystalline orientation. This study expected to explain the degradation mechanism of HDPE from shear deformation which can be further improved by the processing conditions of the mechanical plastic recycling process.

Revolutionary Plastic Mechanical Recycling Process: Regeneration of Mechanical Properties and Lamellar Structures

“…Kaneyasu et al [25] investigated the mechanism of steady shear deformation of HDPE. Mechanical recycling process was performed by steady shear treatment by using a cone and plate rheometer.…”

“…From this study, it can be evidence that steady shear treatment which was generally detected in the mechanical recycling process affected the degradation of mechanical properties which can be also related to the changes of thickness of lamellar structure and mesoscale surface morphology of HDPE (Figure 9). [25].…”

“…Figure 9.The comparison of tensile properties, morphology, and thickness of lamellar structure of virgin HDPE (VPE) and steady shear-treated HDPE at 100 s −1 . The elongation at break of steady shear-treated HDPE was decreased from its VPE with the creation of crystalline orientation at shear direction and the reduction of thickness of core crystalline layer and intermediate layer[25].…”

Coarse-Grained Simulations on Polyethylene Crystal Network Formation and Microstructure Analysis

“…However, it is evidenced from oscillatory shear deformation studies that lamellar crystal growth can be controlled in plastics by tuning the process conditions, which enhances the mechanical strength of the materials by a thousand-fold [17][18][19]. Additionally, the static shear deformation proved that lamellar crystal axis (C-axis) growth occurs perpendicular to the direction of deformation [20][21][22]. Using such approaches, it could be concluded that processing techniques are crucial in shaping industrial products.…”