6,000 milk bottle road in China: How plastic waste found a strange second life in Shanghai

What happens to a plastic milk bottle after the milk is gone? In most cases, it enters a recycling system that may or may not be able to process it. In Shanghai, thousands of such bottles took a very different route. They became part of a road.

More than 6,000 used milk bottles, together with other discarded plastic, were incorporated into a road project at East China University of Science and Technology (ECUST) in 2021. The unusual experiment was designed to demonstrate how plastic that is difficult for conventional recyclers to handle could instead be converted into a material for road construction.

The project was developed by materials science company Dow and dairy brand Shiny Meadow and was unveiled around Earth Day. Rather than treating the discarded bottles simply as waste, the companies explored whether they could be processed and used in polymer-modified asphalt.

Why recyclable milk bottles can still become waste

Plastic being technically recyclable does not necessarily mean it will actually be recycled. Milk bottles present a particular challenge because they can retain traces of milk and other residue after use. That contamination can make collection and processing more difficult, reducing their value to recycling companies.

As a result, some bottles that could theoretically enter a recycling stream may still be rejected. Shiny Meadow had already been working with recyclable packaging, but the company said dealing with packaging that conventional recyclers considered low-value remained a challenge. Lin Rong, the company's director, said the road project provided a practical way to give discarded bottles another purpose instead of allowing them to become waste.

From discarded bottles to asphalt

The Shanghai project used a process in which difficult-to-recycle plastic was recovered and converted into post-consumer recycled material for polymer-modified asphalt. That material was then used during road paving at ECUST's Xuhui Campus. The result was not a road made entirely of plastic bottles. Instead, the recovered plastic became one component of the road material, showing how waste plastic could potentially be absorbed into existing infrastructure projects.

For Dow, the experiment was an example of how materials science could help find applications for waste that traditional recycling systems struggle to process. Bambang Candra, Dow's Asia Pacific commercial vice president for Packaging & Speciality Plastics, said the company wanted to demonstrate that discarded bottles could be given another purpose through technology and collaboration.

Could plastic roads also reduce emissions?

The idea was not simply to find another place to put plastic waste. Dow said the approach could have environmental benefits if it reduces the quantity of conventional bitumen required in road construction. The company also pointed to the possibility of improving road durability, which could potentially mean less frequent maintenance and replacement.

Keeping difficult-to-recycle plastic in productive use could therefore address two problems at once: plastic waste and the environmental cost associated with road construction. However, such projects are best understood as one possible application for recovered plastic rather than a universal answer to the world's recycling problem.

Shanghai project was part of a wider experiment

The ECUST road was not Dow's first attempt to use recycled plastic in infrastructure. The company said it had started working on recycled-plastic road projects in Depok City, Indonesia, in 2017. Similar initiatives later extended to India, including projects in Pune and Bengaluru, while a collaboration was also launched with Thailand's Siam Cement Group.

The broader idea is relatively simple: if some plastic cannot find an economically viable route through conventional recycling, materials engineers can look for another useful application. Road construction is particularly interesting because of the enormous quantities of material used in infrastructure projects.

Why the project attracted attention

The Shanghai experiment offered a different way of thinking about recycling. Instead of asking only whether a discarded plastic bottle can be turned back into another plastic product, the project asked whether that material could serve a completely different purpose.

A milk bottle that once sat on a supermarket shelf eventually became part of a university road. For Shiny Meadow, that fits with the idea of a circular economy, in which products and materials remain useful for as long as possible rather than following a simple "make, use and throw away" cycle.

ECUST also saw the project as more than a road-building exercise. University officials said the collaboration could encourage students to consider unconventional approaches to sustainability and explore whether similar ideas could be scaled up. The experiment ultimately highlights a less obvious problem with recycling: sometimes the technology to recycle a material exists, but the economics and contamination challenges make it difficult to do so at scale.

Finding useful second lives for those materials could become an important part of dealing with the world's growing plastic waste problem.