Modifying the mechanical properties of inverse vulcanised polymers

The petrochemical industry produces elemental sulfur as a waste product by the process of hydrodesulfurization. As a result, a large quantity of sulfur is produced annually resulting in overground storage of piles of sulfur due to far exceeding its consumption. The abundance of sulfur makes it inexpensive, therefore producing applications to use more sulfur would allow for recycling of a cheap waste product. The process of inverse vulcanisation affords polymers with a high sulfur content with potential applications such as infrared (IR) lenses, Li-S batteries, mercury capture, antibacterial surfaces, and construction. As inverse vulcanised (IV) polymers are relatively new, they still need further development to improve on their mechanical properties to be better suited to applications such as road surfaces, catheters, composites and IR lenses. Road surfaces cannot be too brittle otherwise they would be susceptible to cracks, and they cannot be too soft to cause rutting, hence IV polymers would currently need further modifications to attain properties somewhere in the middle. Catheters require a material that is more flexible as well as tough enough to bend without breaking, while on the other hand, IR lenses require a stiffer material more resistant to bending. The addition of IV polymers in conventional polymers to make composites is another potential application, particularly with IV polymers of lower strength and higher strain that may not be suitable in many applications in their neat form. Current research has mostly explored modifying the mechanical properties of IV polymers through investigating new crosslinkers and adjusting the sulfur content. IV polymer composites have also been explored; however, a few have been for applications in Li-S batteries which often use more expensive fillers and lack data on the mechanical properties. Research on how more conventional fillers and other modifiers affect the mechanical properties of IV polymers could be expanded on. Therefore, increasing toughness was explored by using liquid polybutadiene in hard, brittle IV polymers, which resulted in increasing their flexural strength up to 6 times as well as increasing displacement without softening the polymer, therefore remaining shape persistent. To produce more flexible polymers of higher ductility, the synthesis of an IV polymer that is typically brittle was adjusted through increasing sulfur content and lowering the curing time to produce a flexible polymer of higher strain. The addition of filler additives, carbon black (CB), cellulose microfibres (CMF), and nanoclay (NC) was also explored to further increase the toughness and tensile strength of these materials. The investigation resulted in a 129% increase in tensile strength (CB), 93% increase in toughness (NC), and 634% increase in Young’s modulus (CMF) of the IV polymer, S-DIB. This confirms their compatibility with fillers as well as modifiers like LPBD which would be beneficial in applications such as composites and road surfaces where a highly brittle polymer would fail whereas LPBD, for example, added some flexibility and increased toughness.