Sustainable new materials from waste

Challenge

Modern plastics, rubbers and ceramics are ubiquitous in our everyday lives. Unfortunately, many of these materials cannot be recycled and often accumulate in waste streams and the environment.

There is a need for next-generation recyclable plastic, rubber, and ceramics designed with controllable properties, such as hardness, flexibility, colour, and transparency.

RESEARCH

We have previously covered A/Prof. Justin Chalker’s (from Flinders University) work on polymers for environmental remediation and here he is extending that work into new application areas. He has co-led a team in a collaboration with Dr Tom Hasell at the University of Liverpool, providing precise new design principles for controlling the properties of plastic, rubber, and glass made from sulfur – an abundant waste product of the petrochemical industry. For instance, making a polymer from sulfur, canola oil and dicyclopentadiene (DCPD) provides several different types of materials. Add more canola oil, it is a soft rubber; add more of the rigid dicyclopentadiene and the material becomes harder and more durable.

Reacting sulfur, limonene (waste product of the citrus industry) and dicyclopentadiene at various ratios can provide materials from soft waxes to hard glass.

In yet another example, terpinolene (an essential oil found in allspice and other plant products) was reacted with sulfur to form an orange transparent film. By adding in dicyclopentadiene during the reaction, the colour could be tuned from orange to red to black (image below). The dicyclopentadiene also made the film retain its shape better at higher temperatures.

Sulfur has very different properties to carbon, and this may lead to many interesting new applications for these polymers.

Left: Sulfur crystals form on the cut surface of the polymer made with lower levels of DCPD. Centre: A high level of DCPD prevents these crystals from forming.  Right: Polymer deposited around nanoscale salt crystals, which are then removed. This creates a porous ‘sponge’ with high absorbency.

Impact

As most polymers are made directly from our limited reservoir of petrochemicals, every kilogram of sulfur (we generate 100M tons each year) we use to make polymers, saves petrochemical resources and reduces its waste.

As well as environmental remediation, sulfur polymers have potential in:

• construction, especially where thermal insulation, electrical insulation, and chemical resistance are important
• high capacity batteries that are more stable to repeated charge/discharge cycles
• lenses and optical filters in IR thermal imaging, night-vision lenses, and LIDAR
• agriculture.