Waste Management Pathways for Cross-linked Polyethylene via Remolding & Pyrolysis

Abstract

Plastic is used for manufacturing an increasingly wide range of commodities, to the extent that it currently displaces metal and glass is becoming the material of choice for most disposable items. On the average 12% of our municipal solid waste are plastics (LDPE, Polypropylene, PET, and Polystyrene). These are characterized with a high value waste stream and are slowly degradable. Efforts in reprocessing and reducing plastic's negative environmental impact are increasing. Polymerization of methane draws a paramount amount of fossil fuel. In attempting to recycle LDPE that is mildly cross-linked for cable manufacturing, two pathways have been adopted; mechanical & chemical recycling of waste XLPE generated from major cable company Ducab Inc., in Abu Dhabi. The mechanical recycling conducted by exploring the changes of material properties following remolding, re-extruding/calendaring and injection it also undertakes the shredding, sieving, and infusion/mixing ratio of the cross-link polyethylene waste with virgin polyethylene. In the chemical recycling, a chemical kinetics of cross-linked polyethylene under pyrolysis is carried. The thermal degradation of the cross-linked LDPE/Si-XLPE was investigated under two different conditions: dynamic and isothermal heating. Also a nitrogen pyrolysis of Silane Cross-linked Polyethylene waste (Si-XLPE) conducted for producing pyro-oil, which later is distilled and its properties were assessed. In mechanical recycling it was observed that as the amount of waste infusion is increased the sample ductility and strength is mildly reduced. Dynamic tests showed that the molded XLPE has a higher viscosity than LDPE at phase shift of 10.75°for XLPE compared to 9.88° for LDPE. Finally, in the view of these results a visco-elastic material model is inferred for the reproduction of experimental results in static and dynamic loading conditions. Thermogravimetric results in chemical recycling showed the main region of weight loss occurs between 450 and 480 °C and it corresponds to highest conversion rate. The dynamic heating concluded slightly different values than the one obtained from isothermal since the kinetic parameters are highly dependent on the reaction time. These results suggest that Si-XLPE that commonly used in the cable industry follows a similar behavior to the LDPE shown by diligent analysis of the composition, melting point, thermal stability and thermal degradation. The produced pyro-oil consists mainly of alkanes and alkenes and possesses high calorific value. It can be concluded that only small variation in this oil is present when compared to petro diesel. This may suggest using it as substitute for petroleum-based feedstock in the petrochemical industry.

Date of Award	Jun 2013
Original language	American English
Supervisor	Isam Janajreh (Supervisor)