Date of Award
Doctor of Philosophy (PhD)
Rhett C Smith
Plastic consumption has increased at a shocking rate over the past 20 years, consequently the accumulation of plastic waste has followed. The majority of plastic waste tends to get disposed of in landfills or incinerated for energy recovery, however the efficiency of the aforementioned processes is fairly poor. Only 9% of all plastic waste produced is successfully recycled. The miniscule amount of plastic waste that is recycled is either melted and recast into materials or ground up and used for other applications. However, recycling conventional plastics tend to degrade the plastic material and render it useless after repeated melt-casting cycles. Thus, the current recycling processes are severely limited. One solution to the current recycling process is to synthesize new polymers that can withstand repeated melt processing cycles without loss in mechanical properties or degradation.
In the current contribution, new polymers that have high sulfur-content are studied for durable applications. High sulfur-content polymers are synthesized utilizing a variety of different monomers. The thermal and mechanical properties and recyclability of the materials are considered.
Chapter 2 focuses on the use of a modified commercially available polystyrene derivative as a starting material for reaction with sulfur. It was found that varying the amount of sulfur in the polymer formulation achieved materials with drastically different thermal and mechanical properties. The recycling/thermal healability of higher content sulfur materials were assessed through dynamic mechanical analysis (DMA). The average crosslink length was determined by fractionation studies.
Chapter 3 presents work on utilizing an amino acid produced from bacteria as a starting material to react with sulfur. The sulfur content was either 30 or 50 weight percent by mass and the thermal and mechanical properties were analyzed. In both cases the polymers showed to be thermosets and could not be reprocessed through simple melt- processing techniques. The flexural strengths and modulus were shown to be quite high and comparable to that of Portland cement. Additionally, the acid stability of the polymers were also tested and compared to that of Portland cement.
The work presented in Chapter 4 shows a new method to synthesize high sulfur-content materials. A bisphenol A derivative without the presence of any alkene moieties was reacted with elemental sulfur. The following method focuses on using Radical-induced Aryl halide-Sulfur Polymerization (RASP) to synthesize high sulfur-content materials as opposed to inverse vulcanization. The mechanical properties, acid stability, and recyclability/thermal healability of the polymers were analyzed and discussed.
Chapter 5 presents work that combines the inverse vulcanization and RASP process. A modified bisphenol A derivative was synthesized and shown to undergo inverse vulcanization with 80 wt% sulfur. The sample was then subsequently reacted to undergo RASP. The thermal and mechanical properties of the inverse vulcanized and RASP material were compared to each other.
Thiounn, Timmy, "Synthesis and Characterization of High Sulfur-Content Polymers with Petrochemical and Microbial Comonomers" (2020). All Dissertations. 2607.