Researchers at Wageningen University & Research have developed a new type of plastic that could not exist according to materials theory. Its properties lie between glass and plastic: it is easy to shape and resists impact. This combination arises because the building blocks are not chemically attached to each other, but are held together by physical forces. The resulting material is easier to shape and repair than traditional plastic. The researchers published their results in the scientific journal Nature Communications.
A drinking glass shatters if you drop it. A plastic cup bounces slightly off the ground and remains unharmed.Plastic needs a mould to be pressed into the right shape. Glass you can blow and mould at high temperature. Wageningen researchers have now combined the best of both worlds in an innovative material. For now, only a few grams are involved, but the effect is clear. After heating, the amber-coloured plastic can be moulded and blown like glass and is impact-resistant like plastic. The researchers call this new type of material a compleximer.
New type of plastic is complex
The research initially caused surprise. "It threw a completely different light on something scientists have been trying to understand for decades," says Jasper van der Gucht, professor of Physical Chemistry and Soft Matter. For years, the rule of thumb for glassy materials that include plastics and glass has been: the slower the material melts and the easier it is to work with, the more brittle it is. But now we have something completely different from that: a material that melts slowly and can take a beating."
Breaking through material theory
For Van der Gucht, the excitement really lies in the new fundamental discovery, defying the laws of materials science. But if he gives his imagination free rein, he sees possibilities for the new material in the future. Because compleximers are impact-resistant and easily machined, they are also quick and easy to repair. Think, for example, of roof panels, garden furniture or a body made of compleximers. "Do they have a big crack? Then just put the hairdryer on it, press, and the hole is closed again."
Building blocks of a new type of plastic
The difference with traditional plastics is the way the building blocks of the new type of plastic are connected. On a molecular scale, plastics consist of long chains. Normally, these are 'glued' together with chemical cross-links. The new variant connects the chains with physical forces of attraction. One half is positively charged, the other half has a negative charge. These opposites attract each other, just like magnets, "This is how the chains stay together, without being chemically stuck," Sophie van Lange, first author of the publication, explains.
Space between chains
The researchers compared their material with substances in the literature that also contain charges, such as ionic liquids that conduct electricity and are used in solar panels and batteries, among other things. They found that other charged substances also seemed to behave differently, although scientists had not previously considered this. "That was crazy, but exciting at the same time," Van der Gucht says. So substances with charges show a whole new kind of behaviour.
Hypothesis
The researchers are not sure exactly why this works. They suspect it has to do with the distance between the molecular chains that make up the plastic. The chemical cross-links in traditional plastics pull the long chains tight and close together. The attraction of negative and positive chains works at greater distances, creating more space between the chains. At the molecular scale, this makes the material look different, possibly leading to different behaviour of the material. "But," Van Lange stresses, "that is just a hypothesis for now."
What I find most exciting at the moment is that we have shown that loaded materials can behave in fundamentally different ways than we thoughtJasper van der Gucht, professor of Physical Chemistry and Soft Matter
Bio-based version
In follow-up research, two researchers will delve deeper into the underlying physics to better understand these mysterious materials. They will also study how to modify the properties of these compleximers to make them applicable for different purposes. In addition, durability is on the agenda. For now, the scientists are making the compleximers from fossil raw materials, but Van der Gucht does not want to stop there. "We have a number of ideas for a biobased version that we want to apply in the coming years," the professor said.
More research into new type of plastic
For the time being, (bio-based) compleximers will not yet appear on the market, but within WUR applied plastics researchers are already eager to start working on them. "I am very excited about our colleagues' research," says Wouter Post, senior researcher Sustainable Plastic Technology. "Their research contributes to a fundamentally better understanding of materials and plastics in particular. That is essential for the transition to their more sustainable use." According to Post, the research also highlights a blind spot in current plastics research: "Most applied research in this field focuses on better recycling, while this study actually opens doors to plastics that are easy to repair or even biodegrade at lightning speed.
New questions
Van der Gucht and Van Lange are not yet working on practical applications. For them, the biggest gains now lie elsewhere. "The fact that we have shown that loaded materials can behave fundamentally differently from what we thought is the most exciting thing at the moment," says Van der Gucht. "We started with a material that could not exist according to current knowledge and end up with new questions about how materials behave. That's where the real work starts now."
Opening photo and source: WUR,
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