Western researchers are developing processes for recycling thermosetting plastics
Case Western Reserve University researchers are working on a simple method of converting waste thermoset plastic into new thermosetting plastics with similar properties.
Their process involves mixing thermoset with a catalyst and then pulverizing the mixture. The catalyst binds to the crosslinking points, where it can break the crosslinking bonds and then shape new ones into a new thermoset. You call the technology vitrimization.
Researcher Liang Yue said in a telephone interview that the research was born out of a desire to recycle tough thermoset scrap instead of dumping it.
“These are strong materials and are impact resistant, but until now they were for single use. We’re trying to change that, ”said Yue.
Wind turbine blades, auto parts, and a host of other industrial and commercial products are made from tough thermosetting plastics such as epoxies, polyurethanes, and reinforced unsaturated polyesters. These products can land in landfills or be incinerated, which has undesirable consequences at the end of the life of the products.
Much work has been done to grind thermosetting scrap and add the resulting powder as a filler in virgin thermosetting resin, but this approach is thwarted by a poor bond between the filler and virgin resin.
Yue and others began working on the concept two years ago in the laboratory at the Case Western School of Engineering in Cleveland when he worked with lead researcher Ica Manas-Zloczower, professor of advanced materials and energy. Her team, which included several other Case Western researchers, recently announced their discovery in ACS Macro Letters.
The team reported on recent work with thermoset epoxy materials and a zinc-based catalyst. A material with so-called dynamic cross-links was created. The “permanent” cross-links in the scrap combine with zinc ions which, under heat and pressure, catalyze the formation of new cross-links.
The powder they make can be compression molded into a new thermoset part. The process does not rely on solvents and in theory such scrap could be recycled indefinitely. These advantages are reminiscent of the ability to recycle thermoplastics over many cycles.
Yue said the researchers want to expand their work with more thermoset polymers. He said it should be applicable to elastomeric thermosetting plastics, such as rubber, which could then be injection molded. In the future, even polyolefins for recycling based on vitrification may be applicable.
Various approaches to vitrimization have been studied by several research groups for more than a decade. Case Western’s work appears to be more promising and more economical than other approaches that have been tried to date, Yue said.
According to Yue, the team’s paper sparked interest in the industry. He and Manas-Zloczower are negotiating with potential industrial partners to scale their process by mechanical-chemical ball milling of scrap and produce thousands of pounds of reusable powder resin.
“We can recycle tons of epoxy waste in a matter of hours,” he said.