Engineering with Graphene for Multi-functional Coatings and Fibre-Composites

Lead Research Organisation: Imperial College London
Department Name: Dept of Mechanical Engineering

Abstract

Graphene is a material comprising a single layer of carbon atoms, yet particles can have linear dimensions potentially in the millimetre range. It has a remarkable set of properties that offer potential benefits when added to polymer materials, including toughening, electrical conductivity, self-lubrication and fire retardance. The intrinsic two-dimensional geometry of graphene has pros and cons; specifically, it directs us towards applications in thin layers, such as for coatings where its geometry can best be utilised. These applications also intrinsically require relatively small quantities of filler for a significant impact, thus making efficient use of relatively small quantities of graphene that are likely to be available initially. The combination of graphene with existing state-of-the-art commercial systems is a particularly promising route to rapid commercialisation through the enhancement of current materials.

The overall aim of the proposed research is to show how graphene can be used in a composite engineering context, to improve the properties of current polymer-based materials. The key challenges are the dispersion and functionalisation of well-defined graphene material, and the development of processing routes to combine it with the selected polymer systems. It is essential to avoid agglomerates that act as defects, and to maximise the chemical interaction with the matrix to avoid unwanted delamination. Measurement of stress transfer in native graphene flakes indicate that they must remain flat over many tens of microns for efficient reinforcement; but the judicious use of non-damaging functionalisation routes should relax this requirement by at least an order of magnitude.

Optimised surface chemistry is the key both to interaction with the matrix in-service and to effective processing of truly exfoliated graphite. We will exploit our specific, scalable, in-house routes to functionalised, dispersed graphenes with minimised framework damage. Thus the first challenge is to produce graphene in a scalable manner with the correct functionality to ensure good compatibility with the matrices used and optimum property improvement. The team have identified two potential routes, and as we do not know a priori which will be the most effective we will investigate both. These modified graphenes will be combined with matrices at modest loadings of a few percent, to create optimised composite systems sufficient to offer benefits to functional coatings in the applications described below. A further, fundamental aspect is the opportunity to create high graphene content composites and to control the graphene distribution in the formation of structures designed to take advantage of its unique intrinsic properties. To meet this challenge, we will develop three alternative routes for the creation of large area graphene-based films; these systems offer a more radical approach to even greater potential improvements.

The basic mechanical and physical properties of the modified graphene and polymer blends will be measured to identify the most promising materials. We will combine these graphene materials with relevant matrices, especially epoxy/polyester resins for the following applications: mould release and functional coatings for composite parts, lightning-strike protection and improved barrier properties for fibre-composite aircraft and wind-turbine blades; tough, low permeability, scratch resistant, and self-lubricating functional coatings for applications in pipe networks (including valves) and mechanical systems; and fire-resistant coatings by virtue of enhanced barrier properties and char formation.

Planned Impact

The intrinsic two-dimensional geometry of graphene directs us towards applications in thin layers such as coatings, where its combination with state-of-the-art commercial systems is a particularly promising route to rapid and effective impact. This can be achieved because the UK is a major producer and exporter of coatings, adhesives and composite materials. The UK also has a significant manufacturing sector which uses these materials in applications from pipes to aircraft. The use of fibre composites is accelerating, and improved materials represent a significant opportunity for UK industry, society and the economy as a whole. These novel materials will increase the competitiveness of the UK within the world markets.

The materials developed in this programme will increase the lifetime of pipeline networks and of wind-turbine blades. This will help maintain a good balance of energy generation and help ensure continuity of supply of water, fuel and electricity. This has additional economic and social benefits, by reducing the cost and disruption due to the reduced need for both planned and emergency maintenance. The reduction in corrosion and leaks will benefit the environment by reducing instances of pollution in the case of pipelines for oil, gas or chemicals. There are also benefits to health by the reduction of the risk of contamination of water supplies due to corroded or fractured pipes. Conservation of water is an increasingly important topic, and one which society feels very strongly about, so reducing leakage plays a big part in this. The fire-retardant coatings developed will increase safety, hence reducing the likelihood and severity of damage to facilities and injury to people. This has both economic and social benefits.

The use of improved materials, such as using graphene instead of copper in passenger aircraft for lightning strike protection offers a weight saving in transport applications. This will lead to improvements in fuel consumption and safety, with noise reduction due to improved performance, with consequent benefits to society of improved quality of life. Reducing the severity of a lightning strike also preserves life. There is a concurrent reduction in the economic damage to an aircraft, reducing the time and expense of any repair, also ensuring that the aircraft spends less time out of service.

We anticipate these benefits being realised relatively soon after the end of the programme, as we have strong links with material producers and users which will ensure timely exploitation. It is our intention to ensure that the processes developed in this programme can be scaled up readily, and that the materials are industrially relevant. Therefore we estimate a timescale of five years being relevant for the benefits to be seen.

For the RAs, and particularly for the PhD students, the close collaboration between the research teams and the interdisciplinary nature of the project will lead to excellent training opportunities for the RAs. The researchers will be able to demonstrate flexible working, good time management and the ability to work within varied environments. The students will work closely with the RAs, making this an unusually strong training opportunity and developing a wider range of skills. The students will benefit greatly from working closely with a more experienced RA. The researchers will be encouraged to attend the College's excellent transferrable skills courses. They will be encouraged to present their findings at UK and international conferences, and to write up their work for leading journals. The RAs will also have the opportunity to co-supervise the PhD students. They will be encouraged to develop and supervise small projects of their own, in association with undergraduate or MSc project students, to develop their own management and leadership skills.

Publications

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Description Various thermal and mechanical properties of the epoxy nanocomposites were measured and the most noteworthy finding was a remarkable increase in the thermal conductivity when relatively very low contents of rGO were present. For example, a value of 0.25 W/mK was measured at 30 °C for the nanocomposite with merely 0.06 weight percentage (wt%) of rGO present, which represents an increase of ~40% compared with that of the unmodified epoxy polymer. This value represents one of the largest increases in the thermal conductivity per wt% of added rGO yet reported.
Exploitation Route To improve the thermal properties of such nanocomposites produced by such a facile method.
Sectors Aerospace, Defence and Marine,Construction,Electronics