Researchers from the FAMU-FSU College of Engineering have made new discoveries on the effects of temperature on sustainable polymers. Their findings could help the industry produce better plastics for the environment.
“Plastic produced from petroleum, a non-renewable resource, stays too long in our land and water when it is discarded,”
Alamo and former doctoral candidate Xiaoshi Zhang, now a postdoctoral researcher at Penn State, recently published the work in a series of articles focusing on the crystallization of “green” polymers. The last article appears as a cover article in Macromolecules, a leading polymer science journal.
“There is a worldwide motivation for transforming the way the largest volume of plastic is produced,” Alamo said. “Polymer chemists and physicists are working hard to produce substitute materials to end problematic plastic waste.”
Determining the correct temperature for processing is critical to producing better materials that will help scientists replace cheap petroleum-based polymers with economically viable sustainable polymers.
“How the polymer is melted and cooled to get the desired shape is important,” Alamo said. “We are trying to understand the intricacies of crystallization to further understand the transformation process.”
The team is studying a type of polymer called ‘long-spaced polyacetal’, which is used in plastics. Synthesized in a laboratory at the University of Konstanz in Germany, the long-distance polyacetals used by the Alamo team come from sustainable biomass. They contain a polyethylene backbone connected to acetal groups at precise equal distances. The structure combines the toughness of polyethylene with the hydrolytic degradability of the acetal group. This type of polymer is strong but breaks down more easily with water than traditional polymers.
“What we found is that these types of polymers crystallize in an unusual way when cooled after melting,” Alamo said.
During the cooling process, molecules that look like curly strands of molten plastic spaghetti untangle to form crystals and are responsible for the hardness of the final material. Alamo’s group demonstrated that polymer crystallization is controlled by molecular events occurring on the crystal growth front.
The researchers found that when cooled rapidly, these polyacetals become hard and crystalline and the molecules self-assemble into a type of crystal called “Form I.” When cooled slowly, the material is also very crystalline, but the crystals formed are quite different and are called “Form II”. When cooled to intermediate temperatures, the material does not solidify at all. This phenomenon has never been observed in any other crystalline polymer, according to the researchers.
“For the crystals to form, an energy barrier must first be overcome,” Alamo said. “At low temperatures, crystals form easily. At high temperatures, crystals are more stable, and at intermediate temperatures, crystals compete to form and the material cannot solidify.”
“This is a significant discovery because it is an important key to understanding how the plastic we use becomes solid,” he said. “We want to provide industry with the best possible transformation processes. We want sustainable plastics that do not warp or have difficulty solidifying.”
Research could provide new ways of producing plastics that will be cheaper to produce and sustainable.
Interesting new developments for waste sulfur-based polymers
Xiaoshi Zhang et al, Crystallization of precision long-spaced polyacetals II: effect of polymorphism on isothermal crystallization kinetics, Macromolecules (2020). DOI: 10.1021 / acs.macromol.0c01443
Researchers Help Develop Sustainable Polymers (2020, September 25)
recovered September 27, 2020
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