Mechanical and Thermal Properties of Mixed PE Fractions from Post-Consumer Plastic Packaging Waste

The functional properties of recycled post-consumer flexible polyethylene packaging waste have been studied using materials collected and sorted at a large-scale facility in Sweden. The studied fraction was used both as received and after simple laboratory washing in water with added sodium hydroxide at 40 °C. The materials were melt-compounded with a twin-screw extruder using two different temperature profiles and two screw configurations and injection-molded into slabs, whose thermal and mechanical properties were assessed. The results showed that the mechanical properties of injection-molded samples were not changed significantly either by the washing or by the temperature or screw configuration used in the compounding. Washing reduced the viscosity and molecular mass to a minor extent. As expected, the ash content of the compounded pellets was reduced by washing. The thermo-oxidative stability decreased with increasing compounding temperature and with washing.

Soil quality of simulated landfill exposure to plastics in context of heavy metal analysis

It is imperative to have soil guidelines that consider commodities on the market especially biodegradable plastics that are increasing in popularity nowadays. In this short communication, heavy metal in soil was investigated after degrading plastics commonly used on the market. The plastic materials included virgin linear low-density polyethylene, plastic waste of polyolefin origin, and biodegradables of oxo- and hydro-based types. Soil/water matrix that simulates arid land conditions was used. Metals including cobalt, chromium, cadmium, and nickel, among others, were studied after exposure of three continuous months. It was noted that background concentrations reduced with water indicating that leachate might contain the majority of the transferred metals from plastics. In particular, the concentration of nickel in soil was detected to be 84 ppm after exposure to type I of the oxo-biodegradable commercial plastics. Furthermore, the material of similar source started to retain nickel by day 74 of exposure. This surpasses both Canadian and Australian guidelines discussed herein. Furthermore, nickel concentrations exceeded international guidelines and point towards the need for remediation. Mean values of chromium exceeded soil control results and the USA remediation values in the case of single screw compounded plastics. It should also be noted that the work conducted points towards metal trace detection limits that are tied to waste and sludge disposal in an improper manner with time.

Insights into the evaluation of the abiotic and biotic degradation rate of commercial pro-oxidant filled polyethylene (PE) thin films

In this study, commercial products formulated from polyethylene (PE) with pro-oxidant additives, were subjected to abiotic and biotic environments. The materials were presumed to be oxo-biodegradable plastics with thicknesses varying between 30 and 70 μm, and calcium carbonate (CaCO₃) filler content reaching up to 11 wt%. Accelerated (aging) weathering tests conducted revealed that UV radiation triggered the biodegradation mechanism. Weight loss reached 50% after exposure to weathering which was attributed to triggering the fragmentation of the plastic films. Furthermore, some 83% of weight loss was estimated after 12 months of soil burial. Fluctuation of weight in mid exposure time spans was related to the cross-linking reaction within the polymeric matrix. The mechanical properties investigated along with the thermal stability profile determined for the materials showed that weathering was more severe than soil burial. Thermogravimetry revealed that onset temperature (T_os) was lower than conventional PO products by 25 °C. This could be attributed to the thermal response of the materials due to presence of ion salts and sterates within their composition. The claims by the manufacturing companies which provided the original specimens under an environmentally friendly pretence is disputed due to the fact that none of the products actually showed evidence of major fragmentation or deterioration after exposure to harsh environments. The work also paves the way in standardising assessment methodology for examining biodegradable plastics.

On the Kinetics of Degradation Reaction Determined Post Accelerated Weathering of Polyolefin Plastic Waste Blends

Polyolefin (PO) polymers constitute the majority of consumer plastic commodities. The reliance on such materials make it near imposable to avoid touching one in any given day. Therefore, the accumulation of plastic solid waste (PSW) in developed and developing societies alike requires immediate attention to manage and valorize this type of waste. In this work, PSW originating from real life sources and virgin linear low-density polyethylene (LLDPE) films were compounded in a mechanical recycling effort. The recycled blends constituted up to 100% (by weight) of the waste material. Accelerated weathering (aging) was conducted on the blends, reaching threshold limit of exposure to study the major changes occurring on the recycled blends. Thermogravimetry and differential scanning calorimetry (DSC) were used to determine their characteristics and applicability for future recycling using thermo-chemical treatment (TCT) methods. Analytical solution methods following the international committee of thermal analysis and calorimetry (ICTAC) were followed in conducting the measurements and kinetic calculations alike. A novel analytical mathematical solution model is also introduced to determine both the pre-exponential factor (A_o) and apparent activation energy (E_a) of the degradation reaction. The model proved to be a more accurate analysis tool, and the work in whole enabled the determination of future plans for using such waste components as a feedstock to thermal units.

Influential parameters on natural weathering under harsh climatic conditions of mechanically recycled plastic film specimens

In this work, real life reclaimed plastic solid waste (PSW) secured from the municipal sector was mechanically recycled and compounded with virgin linear low density polyethylene (LLDPE). The compounding of the plastic film samples utilised the means of extrusion and blown filming to produce various formulations of the blends containing up to 100% (by weight) of the PSW in the examined specimens. The film samples were compared to market products used in the State of Kuwait where PSW accumulation presents a major obstacle. Natural weathering under arid and harsh climatic conditions was also performed to determine the degradation extent of the film samples. Haze (%), light transmission (%) and the total change in colour (ΔE) were measured as indicators to the degradation profile of the polymeric materials, in addition to tensile pull mechanical properties. Properties were noted to deteriorate as a function of weathering time and waste content. Statistical analysis was also performed on the properties measured and climatic conditions including airborne pollutants levels. The abundance of the secondary airborne pollutant (ozone) was determined to be a significant variable on the studied properties. This can be attributed to induced photo-oxidation the polymeric matrix is subjected to under such climatic conditions which increases oxygen diffusion throughout the polymeric matrix. Future development of the recycled blends studied in this work can be a route for the decrease of associated environmental stressors with virgin plastic resin conversion.