Estudo do potencial de reuso de aparas oriundas do processamento de malhas de sombreamento baseadas em polietileno

Abstract

The increasingly frequent use of plastic has brought various benefits to humanity due to its wide versatility. However, problems arising from the disposal of these wastes in landfills and the environment have raised significant concerns. This study focuses on High Density Polyethylene (HDPE), a polymer widely used due to its remarkable properties, such as chemical and biological resistance and high molding capacity, which hinders the action of natural agents during the degradation process, making it necessary to propose ways to reuse this material. This requires considering economic (resources and profitability), social and environmental objectives. In this context, the central objective of the study was to evaluate the potential for reusing scraps from the processing of shading nets for agricultural use made with polyethylene (PE), in order to validate the use of the sustainable option. The analysis covered the structural, rheological, thermal and mechanical characterization of the test specimens produced with virgin polyethylene (coming directly from petrochemicals), with black recycled polyethylene (obtained from the recycling of black HDPE shading nets) and with gray recycled polyethylene (obtained by recycling a mixture of shade nets). The results indicate that the materials are chemically similar as they have characteristic polyethylene bands. Regarding density, black recycled PE presented typical HDPE values (0.959 g/cm3 ), while gray recycled PE presented typical LLDPE values (0.932 g/cm3 ), reinforcing the mix of grade materials other than PE. As for thermal properties, there was a reduction in the melting temperature for recycled materials (Tm = 125 to 128ºC), as well as a ΔH indicating lower absorption and release of energy comparable to virgin (Tm = 137ºC). Finally, significant differences were observed in the mechanical properties, with the virgin polyethylene sample having higher tensile strength and Young's modulus than the black and gray recycled ones, with values of 23.6 MPa, 19.9 MPa and 16.0 Mpa and 1109.5 MPa; 878.2 MPa and 390.7 Mpa, respectively, indicating a greater capacity to support loads and maintain the structural integrity. However, there were inferior results of virgin polyethylene in relation to elongation when compared to recycled materials, whose results were 35.6%; 126.2% and 374.1%, suggesting greater capacity for plastic deformation before failure. In this context, black recycled material showed potential for reuse in the manufacture of shading nets, although it requires improvements in mechanical properties to meet the required quality standards. On the other hand, the gray recycled material was shown to come from linear low-density polyethylene due to the mixture of materials and has no potential for reuse in the shading nets object of the study. Finally, this study emphasizes the importance of considering sustainability in the life cycle of polymers resulting from industrial scraps, highlighting the potential for reusing these through primary recycling, contributing both to the circular economy and to the reduction of environmental impact.