Understanding Graphene: Part 5 – Polymer nanocomposites
Graphene polymer nanocomposites. It sounds a bit of a mouthful doesn’t it? This term basically means adding lots of little pieces of graphene to various plastics to create better materials. Interested? Then read on…
Composites are nothing new; think of glass fibre reinforced plastics (GRP) used to make everything from boats, pipes and containers. Carbon fibre technology is used for formula one cars and aerospace applications. Over half of the Airbus A350 passenger jet is made from carbon fibre composites. These materials are used because they are better than traditional alternatives and so can make lighter structures for the same or improved strength. The commercial implications are obvious; there is a big market out there for composite products.
Nanocomposites are similar in principle except that the materials used have very small dimensions, of less than 100 nanometers. This brings us to graphene. Having excellent thermal and electrical conductivity as well as high tensile strength, it is a natural choice as an additive to various polymers (plastics). It is also available as nanoscale powders and suspension in various liquids.
At InvestorIntel we have produced a report that analyses the global market for graphene production. We found that while no one can currently produce sheet graphene at scale, there are many organisations producing nanoscale graphene as powders or suspensions of nanoplatelets. At least four producers are specifically making graphene additives for polymer composites at present.
At this point, dear InvestorIntel reader, you’ll be asking ‘Why not more?’ Setting patent barriers aside, part of the reason is that when one works at the nanoscale, making sure the additives and polymer matrix are intimately mixed is harder to achieve than would seem a first sight.
Part of the problem is that graphene is very hydrophobic (it repels water), many polymers are hydrophilic (water loving) such as polyvinyl alcohol (PVA). Think about mixing oil and water and you’ll get the idea that graphene and hydrophilic polymers do not mix well. One way round this is to modify the graphene to change its physical properties by reacting it with oxygen to create graphene oxide. This material mixes better with hydrophilic polymers but at the cost of a loss of its electrical conductivity because graphene oxide does not conduct electricity anywhere near as well as graphene.
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There are lots of hydrophobic polymers that graphene will mix with and the addition of graphene improves the electrical and thermal conductivity as well as strength and gas barrier properties.
There are many methods such as electro deposition, electro spinning and atom transfer radical polymerization for making modified graphene nanocomposites and the dedicated reader can find more at this link. We will look at the two main methods for making polymer nanocomposites with graphene; solution casting and melt blending.
The solution cast technique is one way to form graphene nanocomposite films. The process starts with finding a common solvent that is compatible with both graphene and the chosen polymer. For example one commonly used solvent is chloroform.
The graphene nanoplatelets are dispersed in the solvent with the polymer using ultrasound mixing. This intimately mixes the graphene, solvent and polymer. The resulting liquid is then spread on a suitable surface and the solvent evaporated off leaving the graphene polymer composite film that can be washed and dried to remove any remaining solvent.
Melt blending involves adding the polymer and graphene powder to a heated screw mixer. The heat causes the polymer to form a liquid melt into which the graphene is dispersed with mixing. The melt is extruded and cooled to leave a nanocomposite of polymer and graphene.
So we now know that producing graphene nanocomposite materials is possible. The next question is are they any good? A team in Malaysia has reviewed graphene nanocomposite materials made by various methods.
They have found that graphene nanoplatelets do indeed improve the physical properties of the polymers they are mixed with. The improvements appear to be best at an addition of 1-5% by weight of graphene. For example a polymer called Polythyleneoxide (PEO) can have its tensile strength improved by as much as 189% by the solution casting approach and 104% by melt blending. The thermal stability and electrical conductivity of polymers has also been improved.
I was initially sceptical of claims for graphene-enhanced products such as tennis racquets, bicycle wheels and parts for racing cars. I’m becoming less sceptical with time. These niche applications will take time to cascade to everyday products, however the commercialization of graphene seems well underway.
Publisher’s Note: To buy the Global Graphene Report, please email mailto:Fred@Wescow.com or +1 416 707 7276.
Adrian Nixon began his career as a scientist and is a Chartered Chemist and Member of the Royal Society of Chemistry. As a scientist and ... <Read more about Adrian Nixon>