Graphene/polymer composites

A European project in which Sirris participated has led to the conclusion that the poor dispersion of graphene in the plastic matrix prevents significant improvement in its properties.

For many years, the plastics industry has been using fillers to alter the characteristics of its products, most often, seeking to improve mechanical, thermal or electrical properties.

Various laboratory-based studies have already been conducted on graphene and have demonstrated that this material, presented in the form of a nanometric single-layer carbon network, could well be the nanofiller of the future for, thanks to its 2D structure, it could significantly improve a certain number of properties.

The aim of Graphpol, a European project jointly led by TU Chemnitz, IKV, TU Hasselt, Fraunhofer IWU and Sirris, and completed in May 2017, was to evaluate the complete graphene/polymer nanocomposite production chain at pre-industrial level.

The first phase of the project consisted in identifying suppliers capable of distributing graphene throughout Europe. It very rapidly transpired that graphene prices vary considerably. The project's partners called upon five different suppliers: four of them offered 'low cost' products (from €100 to €2,000/kg), whilst the last applied a far higher price (€100/g).

Different analyses demonstrated that, despite the 'graphene' designation, the least expensive materials were more analogous to graphite and were not in the form of single-layer carbon. Despite this observation, the investigations undertaken were continued for it was inconceivable to proceed to more in-depth study making exclusive use of highly expensive graphene (single-layer in this case).

A twin-screw extruder set in various configurations was used to prepare PA6, ABS, PP and PE-based composites, in order to simulate a real industrial process. The resulting granules were then injected to assess the mechanical, electrical and thermal properties of obtained materials. The same pieces were injected with a virgin material, but also with polymer / carbon nanotube composites, in order to compare results.

The different tests conducted led to several conclusions. First of all, it is particularly difficult to homogeneously integrate graphene within a polymer without creating agglomerates which have a negative impact on the expected improvements in properties. As such, mechanical properties were barely modified through the addition of graphene. The same applies to thermal and electrical properties since the dispersion of graphene in composites is insufficient to enable the creation of a conductive network. Furthermore, results obtained on parts filled with graphene did not equal those obtained on samples filled with carbon nanotubes.

In order to resolve the problem of graphene agglomeration in composites, a parallel study was conducted, aimed at functionalising graphene to improve its dispersion in the polymer. Functionalisation yielded interesting results, however, did not enable the measured mechanical properties to be improved.

Thanks to the Graphpol project, we are now able to confirm that despite the great theoretical potential of commercial graphene, it does not offer significant improvement of the mechanical, electrical and thermal properties in polymers. Improved dispersion of the nanofiller in the matrix warrants more in-depth study in order to overcome the problems encountered.