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What are Polymer Nanocomposites?

  • 9th September 2020
  • Ben Hargreaves
  • Reading time: about 6 minutes

In a nutshell…

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.

…and a nanomaterial is…?

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:

Spherical nanoparticles (which have all three dimensions in the nano-scale)

  • Spherical nanoparticles; which have all three dimensions in the nanoscale (e.g. nano-TiO2 or nano-SiO2).

Nanotubes (or nanowires) (which have 2 dimensions in the nano-scale)

  • Nanotubes; which have two dimensions in the nanoscale (e.g. carbon nanotubes, halloysite clays or nanofibrillated cellulose).

Nanoplatelets (which have one dimension in the nano-scale)

  • Nanoplatelets; which have just one dimension in the nanoscale (e.g. graphene, hexagonal boron nitride or bentonite clays).

Why are people interested in polymer nanocomposites?

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.

How do nanocomposites work?

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.

Micro filler dispersed in polymer resin
Micro filler dispersed in polymer resin
Equivalent amount of nano filler dispersed in resin
Equivalent amount of nano filler dispersed in resin

More specifically, certain nanomaterials are thought to improve fracture toughness by either deflecting or bridging cracks within the composite.

Nanofiller deflecting a crack
Crack Deflection
  • Large platelet-like nanomaterials can be effective at deflecting cracks.
  • As a result, the total crack area is increased and energy absorption is increased.
Nanofiller bridging crack
Crack bridging
  • Nanotubes can be effective at bridging the gap created as a crack front progresses.
  • Energy is dissipated due to frictional pull-out of the bridging nanotubes.
  • As a result, the crack propagation speed is reduced.

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.

Nanomaterials - if adequately dispersed - are able to provide a continuous conductive pathway through a bulk material
For electrical conductivity, it may not be necessary to aim for perfect, uniform distribution. At low nanoparticle loadings, the presence of some agglomerates can actually be favourable.

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.

Nanofillers act as a gas diffusion barrier

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.

Enhanced fire performance of nanocomposites

That’s the theory, however…

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:

  • the specific grade of nanomaterial being used (for example, if it is graphene; how many layers does it have? what are the lateral dimensions? has it been functionalised in any way? etc);
  • the amount of nanomaterial being used;
  • the way in which the nanomaterial is incorporated into the bulk polymer and;
  • the way in which components are manufactured.

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.

At Coventive…

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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About the author

Ben Hargreaves

Ben is the Business Manager at Coventive Composites.

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