Comprehensive Investigation of the Depolymerization Kinetics and Mechanism of Polymers and Blends Originating in Waste Electrical and Electronic Equipment

In the outline of sustainable growth, thermo-chemical recycling appears to be the finest choice for handling the vast waste stream of polymers reaching each year the final recipients. Accordingly, raw materials (monomers) or other secondary value-added products can be obtained. Thus, the existing environment is not charged again and there is no need for additional resources for new polymers production. Thermal depolymerization in an inert atmosphere (also referred as pyrolysis) has long being studied as such technique leading to a variety of products depending on the degradation and process conditions. Among different categories of waste plastics, those coming from electronic and electrical equipment, called WEEE, have recently draw the attention of several researchers worldwide, mainly due to the continuous increasing fraction of these materials in the waste stream. Several papers have been published in literature dealing with the recycling of polymers from WEEE under different experimental conditions. In this project, for the first time, a systematic study is proposed for the depolymerization of the main polymers originating in WEEE. As such, in this study we are focusing on PC, polycarbonate, high impact PS, and the Acrylonitrile-Butadiene-Styrene resin, ABS. These consist of nearly 75% of the whole polymer load in WEEE. The aim is to investigate in detail the depolymerization kinetics of these polymers as well as their degradation mechanism under different experimental conditions. Thus, understanding the reaction mechanism in a molecular level could help as to better design large scale processes for the thermo-chemical recycling of these materials targeting in specific value-added products. In order to fulfill this scope, several process parameters will be investigated and the objectives of the research originate from the following questions: What is the effect of the polymers chemical structure or the existence of polymer blends? What is the effect of the energy source? What is the effect of adding specific catalysts to the system? Depolymerization kinetics will be studied using both thermogravimetric analysis and pyrolysis connected with GC/MS for the identification of the products. Theoretical kinetic models will be developed to evaluate the variation of the activation energy of the reaction with conversion, as well as to identify the reaction mechanism. These experiments will be carried out either to neat polymers reported previously, or to their binary or ternary blends. Thus, possible synergistic effects will be identified. Following, several specific catalysts will be used in the thermal depolymerization of these polymers, aiming in the production of tailored value-added degradation products. The next parameter that will be investigated is the way of providing energy to the system. Thus, either microwave irradiation or UV radiation will be employed for the depolymerization of PC, ABS and HIPS. Reactions will be carried out either in the polymers as such or by adding compounds, such as microwave absorbers. Depolymerization kinetics and degradation mechanism again will be explored. Finally, from the knowledge gained and the optimized process parameters, best depolymerization techniques will be employed to the polymers from several WEEE and the products obtained will be identified.