The popular bioplastics made of PLA- the polympical acids or polyl acts- have different advantages: they are inexpensive, arise from natural vegetable raw materials such as corn or potato strength and can therefore be CO2-neutral when burning, they can be easily changed for different material requirements and are biological Removable - at least in principle. In fact, the bioplastic, which is often used for packaging, agricultural technology or disposable cutlery, only decreases sufficiently quickly in certain conditions such as higher temperature in industrial composting systems. In contrast, in the bio bin at home, after throwing away into the environment, the plowing in the field or in the ocean, it can take many months or even years until the plastic from polymerized lactants completely disintegrates. However, this can be changed-with specifically built-in chemical breakdown points, reports a team of researchers from Holland, Poland and the Max Planck Institute for Polymer Research in Mainz.
The polymer researchers around Frederik Wurm from the University of Twente have taken a look at the decay of PLA plastic products in sea water. Investigations had previously shown that bio -reduction is not very far here: Pla looks like before in the sea compared to other plastic alternatives even after a year. The scientists searched for ways to make the plastic more susceptible under natural conditions without changing its technically desired material properties too much.
Wurm and colleagues finally tested the incorporation of phosphate ester bridges into PLA – very similar chemical compounds such as those found in natural RNA molecules. Because of these phosphate esters, among other things, RNA decomposes very quickly under natural conditions through hydrolysis, and the enzymes of many microorganisms are also specialized in attacking and breaking down molecular chains here. Wurm's team modified PLA by means of intramolecular transesterification controlled during polymerization – i.e. inserted different numbers of phosphate ester bridges into the polylactide chain at different, defined intervals.
Then the researchers tested how quickly the products decompose in sea water. To do this, they measured the thickness of the plastics and the release of lactic acid, the dismantling product of PLA at regular time intervals. It showed that the more chemical target breakage points, the faster the dismantling process. PLA chains, which consisted of 15 percent of transferred, modified chains, fully fell into lactic acid within two weeks. The less attackable ester in the chain, the longer the breakdown takes: the duration of bio -degradation through hydrolysis could therefore be controlled with this process from days to years, the authors write in their publication in the journal »Journal of the American Chemical Society «. It is also important that the thermal and mechanical material properties of the plastic do not change significantly unless there are too many chemical breakdown points.
The researchers hope that the incorporation of phosphate ester predetermined breaking points could be a universal approach with which the biodegradability of other polymers can also be increased – both in seawater and in soil. This would then be an important step towards less polluting plastic products.
