Chemistry, Materials & Packaging
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Enter Plastic Waste; Exit Stronger, Safer Materials

This week, we examine two innovations that not only divert plastic waste but turn it into stronger, more beneficial materials: IBM has discovered a way to convert polycarbonates into plastics safe for water purification, fiber optics and medical equipment; while shredded plastic waste is helping to create more durable, weather-resistant roads in Chennai, India.

“Polycarbonates are common plastics in our society – especially in consumer electronics in the form of LED screens, smartphones and Blu-rays, as well as everyday eyeglass lenses, kitchen utensils and household storage gear,” explained Gavin O. Jones, a research staff member at IBM Research – Almaden in San Jose, California. “We now have a new way of recycling to improve how this prominent substance impacts the world’s health and environment.”

Citing the American Chemical Society, IBM says that the world generates more than 2.7 million tons of polycarbonates every year. Over time, polycarbonates decompose and leach BPA, a chemical that, in 2008, caused retailers to pull plastic baby bottles from store shelves due to concerns about the potential effects of BPA on the brain. Since then, BPA has continued to be a cause for concern in materials such as cash register receipts and food can linings.

IBM research scientists added a fluoride reactant, a base and heat to old CDs to produce a new plastic with temperature and chemical resistance superior to the original material. The company claims that when the powder is reconstructed into new forms, its strength prevents the decomposition process that causes BPA leaching. Thus, the new, one-step chemical process can convert polycarbonates into plastics safe for water purification, fiber optics and medical equipment.

“While preventing these plastics from entering landfills, we simultaneously recycle the substance into a new type of plastic -- safe and strong enough for purifying our water and producing medical equipment,” said Jeannette Garcia, who is also a research staff member at IBM Research – Almaden. “It’s an environmental win on many fronts.”

The team published a paper, One-step Conversion of Polycarbonates into Value-added Polyaryl ether sulfones, detailing their findings in the peer-reviewed journal, Proceedings of the National Academy of Sciences of the United States of America. The work was part of IBM’s larger efforts to use informatics in materials science and other research, in the hopes that leveraging existing knowledge from the world’s scientific databases and accelerating computations used in these types of experiments could help identify patterns and to bring new discoveries to realization faster.

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Meanwhile, in response to the growing problem of plastic litter, a chemistry professor in India invented a cheap way to use discarded, low-grade polymer to make some of the most durable roads in the world. He made the discovery 15 years ago, and the roads have stood the test of time.

Built in 2002, Jambulingam Street in the bustling Nungambakkam area of Chennai was one of the first to have a plastic tar road. It has weathered a major flood, several monsoons, recurring heat waves and a steady stream of cars, trucks and auto rickshaws without showing the usual plethora of cracks, potholes and other usual wear and tear.

Dr. R. Vasudevan, the professor behind the solution and the dean at the Thiagarajar College of Engineering in Madurai, made the discovery through trial and error by sprinkling shredded plastic over hot gravel to coat the stones in a thin film of plastic. He then added the plastic-coated stones to molten tar, or asphalt, and found that the petroleum-based products (plastic and tar) bonded well together. The process was patented in 2006.

The idea for polymer-modified asphalts, though, is even older. Such commercial products first became popular in Europe in the 1970s, but now they are frequently used in the Middle East due to their higher melting point compared to ordinary roads, and North America claims over a third of the global market. (Vancouver, British Columbia in Canada, for example, began experimenting with an asphalt mix containing wax derived from plastic trash in 2012.) Polymer-modified asphalts are highly versatile and are typically made from virgin plastics or sometimes crumb rubber from ground tires, but ultimately, they remain more costly than conventional roads. The most widely-used polymer, styrene-butadiene-styrene, can increase the price of a road by 30 to 50 percent.

The plastic tar roads, on the other hand, are much more frugal: they cost roughly 8 percent less than a conventional road, because they save around one metric tonne of asphalt for every kilometer. And they use the equivalent of 1 million plastic bags, to boot.

Flimsy, single-use items such as shopping bags and foam packaging are the ideal raw material, since they are impossible to recycle and can be problematic for city drains and the environment. Whichever plastics are used, they must be collected and shredded, which means job creation for waste pickers and small entrepreneurs (typically women who buy subsidized shredding machines and sell their finished product) is an added benefit.

This year, a modified version is being used for a national highway for the first time. Adding road scrap alongside the plastic-coated gravel, the highway will connect Chennai with Villupuram and is expected to reduce construction costs by 50 percent.

Urban plastic roads are still a rarity in India – Chennai was an early adopter of the technology – but many more can be expected over the coming years. Last November, the Indian government announced that they would be the default method of construction for most city streets as part of a multi-billion-dollar overhaul of the country’s roads and highways. Urban areas with more than 500,000 people are now required to construct roads using waste plastic.