Scientists began evaluating graphene’s potential in polymers soon after the full characterization of graphene. An initial research objective focused on how to increase graphene’s electrical conductivity; this was soon followed by investigations into its mechanical properties.
There were then descriptions of graphene’s enhanced flame retardancy and thermal conductivity because of its excellent barrier properties. Many papers on graphene’s properties have been published.
Different industries became attracted to using graphene after seeing the material’s positive results for enhancing different polymer properties. The value of graphene for polymer composites for industrial applications was established with graphene manufacturers working with partners.
One of the leading global graphene manufacturers, The Sixth Element (Changzhou) Materials Technology, has a production capacity of 1000 t/a and EU registered substances, combined their own expertise with the expertise of industrial partners focusing on rubber, plastics and coating to focus on the application of graphene in different polymer systems.
The partnership developed natural rubber graphene composites that increase electrical conductivity, coatings that enhance corrosion protection and/or electrical conductivity and graphene epoxy composites.
They also developed abrasion resistant plastic composites that show markedly better electrical and mechanical properties that, in some cases, could also demonstrate anti-bacterial effects.
The incredible properties of graphene oxide, reduced graphene oxide and graphene only become evident when embedded as primary particles within the polymer matrix.
This is the primary challenge for both producing a graphene polymer composite and also for producing the final article.
Different methods for dispersing primary particles in polymer composites well has been extensively studied by The Sixth Element. Dispersing graphene already in the monomer prior to polymerization is one method that can be used.
In order for this to be possible, the monomers must be liquid had room temperature or slightly warmer. Pearl mills, which are grinding equipment used in the coating industry, or ultrasonic means can be used for this process.
A chemical bond between the polymer and graphene can be created depending on the graphene type.
If the resin is liquid at room temperature, a 3-roll mill is the best graphene dispersing equipment for polymerized resins. This technique for thermoset resins is used by The Sixth Element when focusing on coating systems.
A different processing technique to incorporate primary particles of graphene is needed for polymers that are solid at room temperature. Extrusion systems are standard for this kind of polymers.
Water-based suspensions of graphene are able to be added during the extrusion process if systems are equipped with very effective evaporation and ventilation systems.
The distribution of the primary particles is supported by the extrusion system’s high shear forces. If the suspension matrix is already part of the formulation, it is possible to add graphene suspensions based on oils, plasticizers, or similar liquid additives in case the polymer is water sensitive.
In cases where the above dispersing methods are not suitable, a reasonable number of primary particles can be obtained by adding dry graphene powders to the polymer prior to extrusion. This is possible if the retention time of liquified resin at high temperatures is not too short and if shear forces are very high.
The Sixth Element has built relationships with companies experienced with processing polymers with nano-scaled additives and its associated challenges in order to further process thermoplastic materials with injection moulding and similar processing techniques.
A technology that avoids re-agglomeration of primary particles is provided by these companies, which avoids a loss of the superior properties of graphene.
The electrical characteristics of the polymer dictate the amount of graphene to be added to the polymer to achieve the required electrical properties.
The Sixth Element, working with their partner, found that they could demonstrate that the addition of around 10 – 12 weight % of The Sixth Element SE1233 reduced the electrical resistivity in the range of 105 Ω in a polymer system with an electrical resistance of significantly more than 1030 Ω.
In another example The Sixth Element used a silane-modified graphene oxide in an in-situ polymerisation of polyurethane.
Even though graphene oxide is a poor electrical conductor, the combination of a specific polyurethane with an electrical resistivity of around 108Ω/m² and 0.4 weight - % graphene oxide led to electrical resistivity of 105Ω/m². This is mainly due to the high amount of sp2-orbitals available in the polyurethane resin and the graphene oxide structure.
If the focus of using graphene for enhancing mechanical properties, the way of how graphene is incorporated in polymer matrix plays in important role. When adding graphene to the in-situ polymerization of PA6, which is then used for producing fibres, tensile strength and other mechanical properties of this fibre is enhanced by 40 % and more, while elongation to break is unchanged. In a specific embodiment instead of graphene, graphene oxide is used.
PA6/graphene fibres – in comparison with PA6 fibres. Image Credit: The Sixth Element (Changzhou) Materials Technology Co.,Ltd.
When graphene is added to the polymer using extrusion technology, graphene acts in a similar way than e.g. glass fibres or carbon fibres.
The relation between the volume of the matrix system and graphene will define the increase of the mechanical properties. Graphene as a material with a very high aspect ratio, will fill a higher volume with the same weight addition than materials with low aspect ratio.
This is the reason why the addition of less than 1 weight %, normally something around 0. 5 weight %, leads to an increase of tensile strength, bending modulus, or Youngs modulus of 20 % or more.
Antistatic flame-retardant graphene PE pipe. Image Credit: The Sixth Element (Changzhou) Materials Technology Co.,Ltd.
Antistatic Graphene PE Pipe. Image Credit: The Sixth Element (Changzhou) Materials Technology Co.,Ltd.
The Sixth Element has done extensive work to enhance the mechanical and electrical properties of PE compounds used in PE pipes for oil and gas industry. The piping systems require, high electrical conductivity, outstanding flame-retardant properties and high mechanical resistance with excellent elongation properties to compensate dimension variations due to temperature fluctuations.
In order to get the best balance of electrical conductivity, flame retardancy, increasing mechanical resistance with keeping elongation properties of neat PE, The Sixth Element has tested different graphene-based formulations. Using only highly conductive graphene types with an amount of 1 – 3 weight % flame retardance achieved V0 with an electrical resistivity of lower than 105Ω/m².
A strong increase in tensile strength and bending strength was observed, but elongation to break was drastically reduced. This is due to the stiffening characteristics of graphene as a reinforcing material. With a combination of carbon black and a specially designed graphene type for improving mechanical properties the necessary amount of fillers is reduced and elongation to break has almost the same level than the net PE resin. In a specific embodiment the electrical resistivity is far below 105Ω/m², flame retardancy is V0 and wall thickness can be reduced to due outstanding tensile strength and bending strength.
The Sixth Element is continuously investing in R&D to create new formulations to boost electrical, mechanical and thermal properties for different plastic polymer composites (thermoset systems, thermoplastic systems, elastomers).
This information has been sourced, reviewed and adapted from materials provided by The Sixth Element (Changzhou) Materials Technology Co.,Ltd.
For more information on this source, please visit The Sixth Element (Changzhou) Materials Technology Co.,Ltd.