Effects of mechanical recycling on optical properties and microstructure of recycled high‐density polyethylene pellets and bottles

Abstract

The demand for recycling high-density polyethylene (HDPE) utilizing mechanical recycling technologies is currently felt strongly by both society and industry. However, thermal oxidation of the polymer during the recycling process may lead to irreversible changes in the material properties of recycled high-density polyethylene (rHDPE). The effects of mechanical recycling on the optical characteristics and microstructure of rHDPE pellets and bottles were investigated in this study. The results revealed that the apparent color of the rHDPE became more yellow and gray compared to the virgin HDPE (vHDPE), and showed a signal at 670-680 nm in the solar reflectance spectrum. The thermal oxidation of rHDPE considerably raised the absorption intensities of carbonyl, ester, and hydroxyl groups in attenuated total reflection Fourier transform infrared spectrum. In addition, the presence of carbonyl and hydroxyl unsaturated chemicals might make it challenging to recognize the distinctive peaks of vHDPE in the ultraviolet-visible diffuse reflectance (UV-Vis-DIR) spectra at wavelengths less than 400 nm. Thermal oxidation of rHDPE was also confirmed in the C OH, C O, and O C O valence structures of C1s and O1s. A characteristic valence band (VB) profile at 25 eV can be used as the recognizable information for the oxidation of rHDPE. The microstructure of the surface of rHDPE pellets exhibited rough and uneven morphological defects. The higher recycled content made rHDPE bottles' surface morphology rougher and their cross-section microstructure thinner and more porous than vHDPE bottles.

Practicality of physical recycling method for waste polymer composites exampled via high density polyethylene/automobile shredder residue composites

“…29,30 Mechanochemistry can induce chemical reactions through the action of a force field, promote the formation of a stable compatible interface between incompatible systems, and at the same time reduce the size of phase domains to achieve homogenization. 22,23,31,32 Solid state shearing milling (S 3 M) technology is a typical mechanochemical method which realizes processing through the three-dimensional shearing via disc rotation. Three-dimensional shearing structure can not only provide strong friction, extrusion, but also provide strong shear and circumferential stress field effects, realizing physical recycling of tough and viscoelastic polymer materials.…”

“…Fortunately, with the merging of mechanochemistry, the physical recycling method can retain the performance of waste polymers without degradation and deterioration 29,30 . Mechanochemistry can induce chemical reactions through the action of a force field, promote the formation of a stable compatible interface between incompatible systems, and at the same time reduce the size of phase domains to achieve homogenization 22,23,31,32 …”