There is plastic waste that can be processed into soap

Plastics and soaps often have little in common in terms of their texture, their appearance and, above all, their texture utility. But there is one strange connection Between the two at the molecular level: The chemical structure of polyethylene – one of the most commonly used plastics – resembles that of a fatty acid, which is used as a chemical soap precursor.

Both materials are made of long carbon chainsAlthough fatty acids You have an extra group of atoms at the end of the chain.

Therefore, a team led by researchers from Virginia Tech (USA) has now succeeded in developing a new method to recycle plastic and turn it into plastic substances of high value, known as surfactants (also called surfactants) used in soaps, detergents and other products. The results of the study will be published in this week Science.

The key: shorten carbon chains

For Guoliang “Greg” Liu, associate professor of chemistry at Virginia Tech’s College of Science, this similarity in materials meant it had to be possible to convert polyethylene into fatty acids. Although the dilemma was how to efficiently break a long polyethylene chain into many short chains, Liu hoped to find a way to do it upcycling (Reusing materials for a second life) to recycle low quality plastic waste.

The answer came from considerations of fire and incineration, as Liu began to wonder what would happen if polyethylene could be incinerated in a safe lab.

Incomplete combustion of polyethylene would produce smoke which, if someone could catch it, might be contained “broken” polymers into short chainswhich would then “turn into small gaseous molecules before fully oxidizing to carbon dioxide (CO2),” according to Liu’s reasoning.

At the bottom, the furnace-shaped reactor is hot enough to break polymer chains, and at the top it cools to stop decomposition

“If we break down the synthetic polyethylene molecules in this way, but stop the process before they completely break down into small gaseous molecules, we should get short-chain polyethylene-like molecules,” he adds.

With the help of Zhen Xu and Eric Munyaneza, two graduate students in his lab, the chemist built a small reactor shaped like a Oven in which they could heat polyethylene in a so-called process thermolysis of the thermal gradient. Below is the oven one sufficiently high temperature to break that polymer chains and at the top cools at a temperature low enough to stop decomposition.

Guoliang Liu holds a jug of water in his laboratory in Hahn Hall South. /Steven Mackay, Virginia Tech.

After thermolysis, they collected the remains – sort of like cleaning soot out of a chimney – and found that those residues were actually soot short chain polyethylene or more precisely: from waxes.

That was the first step to which some more procedures were added, such as saponificationto make the first soap out of plastic.

Therefore, to continue the process, the team enlisted the help of experts computer modelling And economic analysisamong other things, to improve the recycling process and to be able to share it with the scientific community.

“Our research shows a new way to recycle plastics without the use of catalysts novel or complex processes. “In this work, we have shown the potential of a common strategy for recycling plastics,” points out Xu, co-author of the article.

“This will help people to come up with more creative processes upcycling in the future,” he says.

cheap war on pollution

Although polyethylene was the plastic that inspired this project, the method of upcycling can work with it too polypropylene. And together, these two materials make up much of the plastic that consumers encounter every day in food packaging or fabrics.

In this sense, another interesting feature of this type of reuse is that it can be done with these two plastics at the same time You don’t have to separate them.

For a large-scale recycling method to be effective, the end product must be valuable enough to cover the cost of the process.

This is a major benefit compared to some current recycling methods that require careful classification of plastics (even some very similar ones) to avoid contamination.

It’s actually a technique very simple requirementssuch as the availability of plastic and heat.

While later steps in the process require some additional conditions to convert the wax molecules into fatty acids and soap, the initial conversion of the plastic is a straightforward reaction. This contributes to the economy of the process, as well as to a Ecological damage comparatively low, according to those responsible for the article.

A vial filled with waxes made from waste polyethylene and polypropylene is heated in an oil bath and the waxes are oxidized by a stream of air to produce fatty acids through catalytic oxidation. /Steven Mackay, Virginia Tech.

Otherwise, the final product must be like this for the transformation method to be effective on a large scale valuable enough as for cover cost of the process and make it economically attractive. And while soaps may not seem like a particularly expensive product at first glance, they can actually be worth double or triple the weight of plastics.

According to Liu, this research lays the groundwork for a new way to reduce waste by channeling used plastics into others’ production useful materials.

For his part, Xu points out that “plastic pollution is a global challenge and not the problem of a few dominant countries,” so “a simple process can be more accessible to many other countries around the world.”

In conclusion, he assumes that this is a “good start for the fight against plastic pollution”.

Reference:

Liu, G et al. “Chemical upcycling of polyethylene, polypropylene and mixtures to high-quality surfactants”. Science (2023).

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