Heat and Microbes combine Plastics to create useful Chemicals

Plastic Mixtures (source: Wikimedia)

         

           Plastic mixtures are transformed into small molecules using a two-step method, although it may be difficult to scale up.

 

Plastic mixtures, which are typically difficult to recycle, have been broken down into useable, smaller chemical components using a two-step procedure, according to a paper published in Science on October 13.

 

The planet's plastics dilemma is made worse by how challenging it is to recycle these durable materials. Although there are chemical ways to break up their lengthy polymer chains, these procedures have been challenging to scale up, in part because recycling must deal with mixes of plastics.

 

High-density polyethylene (HDPE), a soft plastic frequently used in food packaging; polystyrene, which includes styrofoam; and polyethylene terephthalate (PET), a strong, light-weight plastic used to make plastic bags, have all been combined in a process that first uses chemistry and then biology to break down a mixture of the most typical plastics that make it into recycling plants.

 

According to Ning Yan, a chemist at the National University of Singapore and one of the few researchers to have created a system capable of that, "just a few works have described chemical recycling of plastic mixtures before." Even more unusual, he continues, is combining chemical and biological mechanisms to change plastic combination.

 

Two-Stage Procedure

Polymer chain (source: Wikimedia)

The scientists initially converted the challenging polymer chains into oxygen-containing organic acid molecules using a catalysed oxygenation process with a cobalt- or manganese-based catalyst. The method was developed in response to a 2003 study headed by Walter Partenheimer, a chemist at DuPont in Wilmington, Delaware, who used it to disintegrate single polymers into compounds like acetone and benzoic acid.

 

Beckham, however, sought to transform organic acid molecules into something that could be more easily commoditized. The scientists used bacteria to accomplish that, particularly the bacterium Pseudomonas putida, which can be modified to use various tiny chemical compounds as a source of carbon. It's a really fascinating organism, according to Beckham. The researchers created dicarboxylic acids from polyethylene, teraphthalic acids from PET, and benzoic acids from polystyrene using their "autoxidation" technique. The scientists built the microorganisms to digest these oxygenated organic compounds.

 

Two chemical components that the bacteria created are each employed to create superior performance-enhanced polymers or biopolymers. According to Susannah Scott, a chemist at the University of California, Santa Barbara, "biology can take many carbon sources and funnel them into a single product, in this case, a molecule that can be utilised to produce a highly biodegradable polymer."

 

The procedure was tested on a variety of plastics present in commonplace products in addition to being produced utilising a mixture of pure polymer pellets. "We bought PET from the vending machine outside my office in single-use beverage bottles and HDPE in milk containers. Then there are cups made of plastic or styrofoam", explains Beckham.

 

Limitations on Temperature

But Shannon Stahl, a chemist at the University of Wisconsin-Madison, a co-author, warns that expanding the method will be difficult. The temperature at which the process of autoxidation is carried out is one problem. Currently, each plastic reacts best at a different temperature, and the temperature the team chooses for the mixture corresponds to the reaction that is the most difficult to carry out. To determine the precise mechanism of this reaction and raise reaction yields, more fundamental chemistry is required, according to Stahl.

 

However, he points out that many businesses currently use autoxidation techniques to convert xylene into terapthalic acid, a chemical that serves as a precursor to PET. There is a tonne of internal information present, and Stahl believes that if one or more of these businesses choose to investigate it, they might provide a tonne of technological know-how. According to Beckham, the group is putting the team's method through economic analysis and life-cycle review.

 

Selling the smaller chemicals that the bacteria create will also be challenging since, according to Yan, there is considerably less of a market for them than there is for waste plastic. Economic competitiveness will determine whether the method is scaled up, he believes.