MIT chemists have developed a way to modify thermoset plastics with a chemical linker that makes the materials much easier to break down, but still allows them to retain the mechanical strength that makes them so useful.Process to Develop Sustainable Thermosets
The researchers showed that they could produce a degradable version of a thermoset plastic called pDCPD, break it down into a powder, and use the powder to create more pDCPD. They also proposed a theoretical model suggesting that their approach could be applicable to a wide range of plastics and other polymers, such as rubber.
The researchers added silyl ether monomers to the liquid precursors that form pDCPD. They found that if the silyl ether monomer made up between 7.5 and 10 percent of the overall material, pDCPD would retain its mechanical strength but could be broken down into a soluble powder upon exposure to fluoride ions.
“That was the first exciting thing we found,” Jeremiah Johnson, a professor of chemistry at MIT says. “We can make pDCPD degradable while not hurting its useful mechanical properties.”
Reusing pDCPD Powder to Form New Material
In the second phase of the study, the researchers tried to reuse the resulting powder to form a new pDCPD material. After dissolving the powder in the precursor solution used to make pDCPD, they were able to make new pDCPD thermosets from the recycled powder.
“That new material has nearly indistinguishable, and in some ways improved, mechanical properties compared to the original material,” Johnson says. “Showing that you can take the degradation products and remake the same thermoset again using the same process is exciting.”
The researchers believe that this general approach could be applied to other types of thermoset chemistry as well. In this study, they showed that using degradable monomers to form the individual strands of the polymers is much more effective than using degradable bonds to “cross-link” the strands together, which has been tried before. They believe that this cleavable strand approach could be used to generate many other kinds of degradable materials.
“This is an exciting advance in engineering thermoset plastics,” says Jeffrey Moore, a professor of chemistry at the University of Illinois, who was not involved in the study. “Chemists have spent most of their effort learning to synthesize better plastics, and far less chemistry research has been invested into the science of polymer deconstruction. Johnson’s work helps to fill this important gap in fundamental knowledge while providing advances of technological significance.”
Licensing and Commercializing the Technology
If the right kinds of degradable monomers can be found for other types of polymerization reactions, this approach could be used to make degradable versions of other thermoset materials such as acrylics, epoxies, silicones, or vulcanized rubber, Johnson says.
The researchers are now hoping to form a company to license and commercialize the technology.
Patrick Casey, a new product consultant at SP Insight and a mentor with MIT’s Deshpande Center for Technological Innovation, has been working with Johnson and Shieh to evaluate the technology, including performing some preliminary economic modeling and secondary market research.
“We have discussed this technology with some leading industry players, who tell us it promises to be good for stakeholders throughout the value chain,” Casey says. “Parts fabricators get a stream of low-cost recycled materials; equipment manufacturers, such as automotive companies, can meet their sustainability objectives; and recyclers get a new revenue stream from thermoset plastics. The consumers see a cost saving, and all of us get a cleaner environment.”