A polymer nanocomposite is simply a composite in which we combine a polymer matrix (which could be thermosetting or thermoplastic) with some kind of nanomaterial. In keeping with conventional polymer composites, there may also be some other form of conventional fibre reinforcement (such as woven carbon fibre) included.
Essentially any material in which a majority of the particles have at least one external dimension which is less than 1 nanometre. Broadly speaking, we can group these materials as follows:
A number of materials have been found to exhibit exceptional and/or unique properties – e.g. strength, stiffness, electrical and/or thermal conductivity – when present in their nano form. Graphene is perhaps the best-known example.
In making polymer nanocomposites, the aim is to take these exceptional properties and impart them on to a “standard” material. More specifically, we want to take a very small amount of the nanomaterial (because it will typically be expensive, and because adding large amounts may cause processing difficulties) and use it to significantly enhance the properties of a bulk material without a significant increase in weight. In doing so, there is the opportunity to open up new, more demanding applications for polymer composites with significantly enhanced functionality… or to match existing performance with thinner, lighter structures.
Increases in mechanical properties are generally attributed to the large surface area interface between the nanomaterial and the bulk polymer, when compared with a regular, micron-sized additive. This means that, gram-for-gram, a nanomaterial has the potential to provide much greater enhancements in properties. However, this only applies if there is good compatibility between the nanomaterial and the polymer, in order to allow efficient stress transfer between the two.
More specifically, certain nanomaterials are thought to improve fracture toughness by either deflecting or bridging cracks within the composite.
When it comes to electrical and thermal properties, the theory goes that conductive nanomaterials – if adequately dispersed – are able to provide a continuous conductive pathway through a bulk material.
Improvements in gas barrier properties are thought to be due to the nanomaterials forming a “tortuous path”, which any small molecule must traverse in order the permeate the bulk material.
The ability of nanomaterials to improve the fire performance of composites is a little harder to explain, however the favoured hypothesis appears to be that they contribute to the formation of a more robust char layer. This char layer provides a physical barrier which helps protect the unburnt polymer beneath and also prevents flammable volatiles from being released from the bulk material.
Despite a large amount of excitement and no little research effort over a number of years, the number of real-world applications for polymer nanocomposites (as opposed to prototypes and demonstrators) remains rather limited.
By and large, this comes down to the fact that making a polymer nanocomposite remains far from straightforward, with a number of factors potentially influencing the final properties, such as:
If these things are not optimised, what you end up with is a material that offers – at best – only marginal performance improvements… whereupon the only thing which distinguishes the nanocomposite from a more conventional alternative is the hefty price tag.
We work with nanomaterial producers to help them evaluate the performance of their materials in composites, in order to understand which applications they may wish to target. We also work with component manufacturers, to help them understand the potential – and limitations – of nanocomposites in their applications and processes.
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