Sunday, May 29, 2022

Making polyurethane degradable gives its components a second life

A method to make polyurethane degradable.

Scientists now have found a method to make polyurethane degradable. According to them, when the original product’s valuable life is finished, the polymer can be dissolved into ingredients to create new products such as superglue.

These polyurethanes could likewise be utilized in microscopic capsules that break open to release cargo, for example, biocides.

Ephraim Morado, a doctoral student who is presenting the work at the meeting said, “Millions of tons of polyurethanes are produced every day, and they’re widely used in foams, plastics, sneakers, insulation and other products. But when people finish using them, these materials are usually discarded. Waste polyurethane either ends up in landfills, or it’s incinerated, which requires a lot of energy and generates toxic byproducts. As an alternative, we want to develop the next generation of polyurethane that can degrade easily and be reprocessed into a new material that can then be commercialized, such as adhesives or paint.”

Steven Zimmerman, Ph.D., the project’s principal investigator said, “A lot of people interested in recycling are trying to make polymers that will break down into their original starting materials and then remake the same polymer. We’re taking a very different, intermediate approach, which industry might be more interested in pursuing in the short term because it would be easier and cheaper. We’re trying to break our polymers down into some other starting materials that are familiar to the industry.”

The key distinction between standard polyurethane and Morado’s version is the insertion of a hydroxy acetal as one of the monomers, close by the traditional monomers. Zimmerman’s team had first utilized a special iodine-containing acetal to make degradable polymers and polyacrylamide gels. In that previous work, the polymer could be disintegrated in marginally acidic water.

Morado created a ney kind of acetal to dissolve the unconventional polyurethane with no presence of water. Investigating for over a month, he found that a solution of trichloroacetic acid in dichloromethane, an organic solvent, could dissolve the polyurethane at room temperature in just three hours.

That is in contrast to the harsher conditions of the typical incineration technique, which requires an excess of 1,400 F to avoid toxic gas formation. In contrast to water, dichloromethane makes the material swell and that swelling empowers the acid to arrive at the backbone of polyurethane’s molecular chains, which it can break at positions where the acetal groups are found. Degradation discharges liquor monomers that would then be able to be utilized to make new items, for example, adhesives whose performance rivals superglue.

Morado also created other acetal-containing polyurethanes that can be triggered to degrade when exposed to light. He used these materials to make microcapsules that could contain herbicides or even biocides for killing barnacles and other creatures that stick to ship hulls.

He along with with Zimmerman, now developing adhesives that dissolve when treated with a few drops of acid in dichloromethane solvent. One potential application is on circuit boards, where a chip that had been securely glued to the board could be swapped out for a replacement if the original chip had failed.

Scientists also working on polyurethanes that can degrade under even milder conditions, such as exposure to vinegar. That would be particularly useful for, say, degradable sutures or household applications such as removable picture hangers.

The researchers will present their results today at the American Chemical Society (ACS) Fall 2019 National Meeting & Exposition.


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