Plastics are everywhere, in food packaging and clothing, in fridges, ovens and laptops, in hospital equipment and cars. Plastics make our lives easy and we are addicted to them. But this dependence of ours comes with serious environmental consequences and creates a global waste disposal problem. The solution is biodegradable plastics.
Polylactide plastics (PLA) are a promising alternative to the common PET-plastics (used for example in soft drink bottles). PLAs are not a by-product of the petrochemical industry and they can be produced from inexpensive raw materials such as corn, beets, agricultural waste. They can be produced in normal industrial facilities, have many applications and are biodegradable. Their production, however, is relatively expensive and has cornered PLAs to niche markets, such as biomedical implants and packaging for the organic food industry. To turn PLAs into a feasible, greener alternative to PETs, the production method needs to improve.
New catalysts for better plastics
One of the ways to produce PLA plastics is via a process called ring-opening polymerisation, where small ring-like molecules called lactides (the monomers) are opened and knitted together to form long polylactide chains (the polymers). The effectiveness of the production method depends on the properties of the catalysts - the molecule used to kick-start the reaction.
Sonja Herres-Pawlis, a chemist from the Ludwig-Maximilians-University in Munich, Germany, has been working on the lactide polymerisation reaction, investigating new ways to make PLA production more efficient. The approach followed by her team is to look for an alternative catalyst for the reaction.
The right catalyst to make PLA plastics less expensive than petrochemical compounds has to be cheap, odourless, colourless and nontoxic. This excludes most of the heavy metals (e.g. copper, lead), that are chemically interesting, but known to be highly toxic to the environment. The catalyst also has to chemically tolerate the lactide ring molecules which are the precursor to PLA plastics.
Herres-Pawlis's team has been testing alternative catalysts in different polymerization experiments, to see how polymer chains develop using a technique called gelpermeation chromatography. "We test numerous of our potential catalysts, so we actually polymerise lactide, then weigh the polymer yield and determine the whole polymerization performance," she explains. "By doing this with a lot of catalysts at various polymerization conditions, you get an idea what is going on a molecular level."
On top of the experimental work, Herres-Pawlis's colleague Ines dos Santos Vieira calculated the whole reaction mechanism to understand its working principles using the Molecular Simulation Grid (MoSGrid) portal.
MoSGrid is a web-based portal that offers access to molecular simulation codes for use in quantum chemistry and molecular dynamics research. The portal allows scientists to submit and monitor computing jobs, and retrieve processed results for analysis. MoSGrid is user-friendly and enables both experienced users and beginners to perform experiments in computational chemistry on remote grid resources provided by several academic computing centres. The advantage for the researcher is that local installation of computational chemistry suites or additional software is no longer necessary for their work.
For Herres-Pawlis, the main benefit of processing the calculations via the portal is that "MoSGrid offers a nice way of handling the data and organizing the mass of calculations through workflows," she says.
The results, published on the Chemistry - A European Journal, suggest that zinc guanidine complexes are a good candidate. They are able to polymerise PLA under difficult conditions, at high temperatures and without purification. "Very importantly," stresses Herres-Pawlis, "our catalyst is non-toxic."
This opens the way to turn biodegradable PLA plastics into competitive alternatives to petrochemical-based PET plastics. The next step will be join forces with industry partners: "We just started a collaboration with a polymer company and they will test the catalyst on large scale," says Herres-Pawlis.
The original verison of this article appeared on the European Grid Infrastructure website.