“Green” recyclable rubber gives new life to single-use building materials

Australian scientists have created a new kind of rubber polymer that could make for more sustainable building materials. This versatile new material can be used on its own like regular rubber, or mixed with filler materials to create brand new composites. Then when the useful life of the product is over, the material can be recycled in an almost endless loop.

The rubber polymer is made of sulfur and canola oil, and it has a unique chemical structure. The rubber doesn’t melt – instead, its sulfur bonds can be broken and reformed by applying pressure and gentle heat of about 100 °C (212 °F). This reaction is triggered while a powdered form of the polymer is in a mold. The team calls this process “reactive compression molding.”

This allows the material to be shaped into tubing, coatings, bumpers, insulation, and many other things you’d normally find made of rubber. But the important thing is that this isn’t the end of the story. Once these products have worn out or are no longer needed, they aren’t just thrown away – the rubber can be ground up into powder, placed back into a mold, and recycled into something new.

A diagram showing how reactive compression molding works
A diagram showing how reactive compression molding works

Flinders University

Not only does that save discarded things from going to waste after one use, but the team says that other filler materials can be mixed in with it to create new composites. And best of all, these can also be recycled down the track.

The filler can be almost anything, the team says, but certain things will make the final material stronger or more durable. And importantly, it’s still recyclable with the filler, which can give materials such agricultural waste, carbon fiber, PVC and other plastics a new lease on life.

The team tested a few different mixtures and found some intriguing use cases were possible.

“We made one composite where 70 percent of its mass was coconut coir and 30 percent of the mass was the rubber polymer,” Justin Chalker, lead author of the study, tells New Atlas. “The material is very rigid and could be used potentially in construction or insulation. If more polymer is used in that composite, it gives it more flexibility. In another example, we made a composite that was 80 percent sand by mass and 20 percent polymer. The polymer binds the sand together in a very hard and durable material. We envision this could potentially be used as a concrete replacement.

“Finally, we made a composite from a blend of milled carbon fiber and the polymer. There are not too many applications for recycled carbon fiber so this is an exciting result. At just 20 percent mass carbon fiber, the mat that was formed is quite durable. It could find potential use in construction applications such as concrete components, asphalt additives, tiling, insulation and more.”

Other repurposing efforts are possible too, For example, Chalker explains, the rubber polymer can first be used to purify water. Since it has a high sulfur content, the material can bind to metals like iron, removing it from water. After capture, the iron-laden rubber can then be put through reactive compression molding to make mats or other construction materials.

This isn’t the only novel form of rubber that the team has come up with. Just last week, some of the same researchers unveiled another new type of rubber that can heal damage at room temperature, when a catalyst is applied. Together, these kinds of advances could help make construction a more sustainable industry.

The new research was published in Chemistry – A European Journal.

Source: Flinders University

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