Russian chemical physicists developed a new composite material, which looks like polyethylene, but has improved properties. New composite is much more rigid and better resists high temperatures. These remarkable properties said material owes to the layer mineral with exotic name “montmorillonite”, which origins from Montmorillon settlement in France. The composite has only traces of montmorillonite, however, authors worked very hard to insert these traces into polymer matrix. Scientists developed an elegant synthesis technique, which solves previously unmanageable problem – keeping mineral structure intact, while introducing it into a polymer with absolutely different chemical nature.

There’s no need to dedicate much time to explaining why polyethylene properties should be improved. Polyethylene is very sensitive to heating – it deforms, quickly get fire and burns almost entirely. Polar polymers, such as polyesters and polyvinyl chloride, are a grateful material – they accept up to 90% of mineral additives, resulting in rigid non-combustible materials. Well, this does not work with polyethylene – his chemical nature prevents its matrix from binding with mineral particles. I’d rather say – “prevented”, because Russian scientists found a “back-door entrance”, which is described below.

Authors of the technique used unusual filling agent – a mineral, which consists of numerous layers like a large book – however, these layers are not bonded. We should be thoroughly honest – authors used non-natural mineral, but slightly modified. This modified montmorillonite had expanded space between the layers, and layer surface contained organic (more hydrophobic) cations instead of part of original sodium. The question is – what is the way of introducing this filling agent into the polymer matrix to keep mineral’s layer structure and to make the mineral uniformly distributed? It is not just heating and mixing. Authors found out that the mineral should first be saturated with a catalytic agent (this can be done by adsorption into interlayer space), and only after that ethylene should be polymerized.

 

 

Since the catalytic agent is located both inside and outside mineral layers, polyethylene forms inside and outside mineral layers as well – thus multilayer “filling” becomes tightly bonded with polyethylene matrix. The result is new composite material, with evenly distributed nanolayers of montmorillonite (which as any clay doesn’t burn and doesn’t stretch under heating) in the total volume of polyethylene.

Scientists thoroughly studied the structure of the new material and its properties. They used many techniques and, what is notable, were the first, who used the technique of very cold (it means – very slow) neutron scattering. Researchers found out that they can synthesize the material with predetermined structure and properties by varying synthesis parameters and mineral modifications. Introduction of as little as 1-3 volume percent of montmorillonite significantly reduces (compared to polyethylene) flammability and gas permeability of the new composite, as well as increases its thermal stability. If you imagine that your composite gets on fire, it would burn slowly, turning into a small laminated coal – nothing to do with a flame. Russian scientists claim they understand the mechanism of this phenomenon, which is very important for science and technology. And what makes sense for users (ordinary people), is non-flammable and thermostable composite polyethylene – this means safe and universal.

Source: Russian Science News

Kizilova Anna