Researchers Develop Plastic Catalysts for Coatings
A group of chemists from the University of Konstanz in Germany have reportedly developed a new class of catalysts that enable the manufacturing of polyethylene (PE) dispersions directly in water, providing potential for environmentally friendly, solvent-free plastic coatings.
Professor of Chemical Materials Science Stefan Mecking and Dr. Fei Lin from the university’s Department of Chemistry recently had their article, “Hydrophilic Catalysts with High Activity and Stability in Aqueous Polymerization to High Molecular Weight Polyethylene,” published in the journal Angewandte Chemie.
Polymerization Building Blocks
According to the release, polyethylene is one of the most important types of plastic used in a wide range of everyday objects, including plastic bottles, pipes, ski coatings and toys. Additionally, the technical characteristics and low production costs of plastics make it an “essential” industrial material.
These plastics are reportedly comprised of large, long-chain molecules that can be branched polymers, and are comprised of many repeat units formed from basic building blocks. For PE, the building block is ethylene, a gaseous hydrocarbon compound.
In the form of a dispersion, PE can also form a basis for different coatings and adhesives. The chemists report that suitable chemical catalysts are used to promote and speed up the polymerization process, with the individual building blocks connecting to form larger polymer molecules.
For PE dispersions in coatings, polymerization is carried out in organic solvents that are gradually replaced by water, reportedly requiring additional steps that are both technically complex and energy intensive.
As a result, the Konstanz team set out to develop options to produce PE during polymerization in the form of an aqueous dispersion, serving as a basis for solvent-free and emission-free coatings in which only water evaporates during the film formation. However, they report this proved to be a challenge.
“This requires catalysts that are active in water but, at the same time, are not destroyed by water. Most of the traditional catalysts decompose once they come into contact with water,” explained Mecking.
“We developed water-soluble catalysts for the polymerization of ethylene that not only remained stable but also highly active, although they were in direct contact with water during the entire chemical reaction,” stated Lin, a postdoctoral researcher in Mecking's research team and a Humboldt Fellowship Awardee.
The chemists used laboratory scale studies to demonstrate that their novel catalysts polymerize ethylene in water to form a large number of small PE particles with a high molecular weight and linearity. This is also called a high-density polyethylene, or HDPE.
“This is decisive for the final characteristics of coatings produced on the basis of PE dispersions, and thus for the applicability of our method,” said Mecking.
According to the report, the findings from the research provide possibilities for an environmentally friendly polymerization processes and for the efficient production of solvent-free and emission-free PE coatings.
The study was performed as part of Mecking’s Degradable Polyolefin Materials Enabled by Catalytic Methods (DEEPCAT) project and was supported by an Advanced Grant by the European Research Council. Since 2019, the project has looked at the development of plastics that can be degraded in an environmentally friendly way.