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Devulcanization of EPDM-Rubber using Super-Critical CO2

Greevink, W. (2017) Devulcanization of EPDM-Rubber using Super-Critical CO2. Master's Thesis / Essay, Industrial Engineering and Management.

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Waste management is becoming an increasingly important topic. An important facet of waste-management is problems encountered in the recycling of rubbers. Rubbers, as commodity products with interesting and excellent mechanical properties are used in many different applications, most notably tires. The global rubber production (natural and synthetic) equaled 27.000 tons in 2016. Because of the durable character of rubbers, induced by the process of vulcanization, these materials at some point will all become waste which cannot be properly recycled. Vulcanization is generally an irreversible process and thus innovative methods to achieve selective scission of crosslinks within rubber products are desired. Current methods of devulcanization are generally deemed unsatisfactory because most (reclaiming) process, alongside crosslink scission, also cause chain scission thereby reducing the molecular weight and deteriorating mechanical properties. Moreover, these processes require considerable amounts of time and energy and are therefore deemed inefficient. This research investigated an innovative, safe, and promising method to tackle the problem of rubber recycling. The research focusses initially on the devulcanization of EPDM rubber. The method on which the research is based consists of swelling EPDM rubber samples in a supercritical fluid at elevated temperature and pressure. A status of equilibrium swelling, determined by constraining forces of the three dimensional network of crosslinks is reached. The pressure is quickly and momentarily released causing a degassing which will result in a quick expansion of the supercritical fluid within the sample. This expansion is expected to put a further rapid strain on the crosslinks causing them to break, thereby giving the effect of devulcanization. Experimental work was performed on basis of a literature study. EPDM samples were provided by Arlanxeo. According to the research design, multiple sets of samples were exposed to many variances of process variables. Results are presented on basis of the method to generate soluble fraction as a result of crosslink scission and hence a decrease in crosslink density. Eventually the decrease in crosslink density was plotted as a function of soluble fractions on a Horikx plot. No significant decreases of crosslink density as a result of selective scission of crosslinks were observed. In a single case a decrease in crosslink density of 15% with respect to untreated samples was observed, this was however most likely the result of a combination of both crosslink- and main chain scission. Even the addition of a devulcanization agent in the process or the application of huge swelling times did not yield the desired results. It is concluded that most likely EPDM rubber as a complex and highly branched product is not the most suitable starting point for such a research. Additionally, the patent on which the research is based described the method being applied on rubber crumbs rather than compact cubic samples. Moreover, a section on swelling kinetics showed that matching of the solubility parameter is more important than initially recognized, the conditions used in the bulk of the experiments were therefore most likely not appropriate enough to reach significant degrees of swelling. Also, as later on established, the swelling times used in the bulk of the research are most likely not nearly big enough to reach a state of equilibrium swelling. Seeing as in hindsight the methods and process variables used were not always ideal, it is recommended the perform a follow up research. Preferably this follow research should use the section on swelling kinetics as a starting point. Additionally a follow research should comprise more- and maybe better demarcated experiment sets, but also focus on different types of rubber, gum and compound.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Industrial Engineering and Management
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 08:34
Last Modified: 15 Feb 2018 08:34

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