Scientists began to evaluate the potential of graphene in polymers soon after the complete characterization of graphene. A first research objective focused on how to increase the electrical conductivity of graphene; this was soon followed by investigations into its mechanical properties.
There were then descriptions of the improved flame retardancy and thermal conductivity of graphene due to its excellent barrier properties. Many articles on the properties of graphene have been published.
Different industries have been drawn to using graphene after seeing the positive results of the material to improve different properties of polymers. The value of graphene for polymer composites for industrial applications has been established with graphene manufacturers working with partners.
One of the world’s leading manufacturers of graphene, The Sixth Element (Changzhou) Materials Technology, has a production capacity of 1000 t / a and substances registered in the EU, has combined its own expertise with the expertise of industrial partners focusing on rubber, plastics and coatings to focus on the application of graphene in different polymer systems.
The partnership has developed natural rubber graphene composites that increase electrical conductivity, coatings that improve corrosion protection and / or electrical conductivity, and graphene epoxy composites.
They also developed abrasion resistant plastic composites that exhibit significantly better electrical and mechanical properties which, in some cases, could also demonstrate antibacterial effects.
The incredible properties of graphene oxide, reduced graphene oxide and graphene only become evident when they are integrated as primary particles in the polymer matrix.
This is the main challenge both for the production of a graphene polymer composite and for the production of the final article.
Different methods of dispersing primary particles in polymer composites have been widely studied by The Sixth Element. One method that can be used is the dispersion of graphene already in the monomer before polymerization.
For this to be possible, the monomers must be liquid at room temperature or slightly warmer. Bead 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 type of graphene.
If the resin is liquid at room temperature, a 3-roller mill is the best graphene dispersion equipment for polymerized resins. This technique for thermosetting resins is used by The Sixth Element when it focuses on coating systems.
A different processing technique for incorporating primary graphene particles is required for polymers which are solid at room temperature. Extrusion systems are standard for this type of polymers.
Aqueous graphene suspensions can be added during the extrusion process if the systems are equipped with highly efficient evaporation and ventilation systems.
The distribution of primary particles is supported by the high shear forces of the extrusion system. If the suspension matrix is ââalready part of the formulation, it is possible to add graphene suspensions based on oils, plasticizers or similar liquid additives in case the polymer is sensitive to water.
In cases where the above dispersion 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 the liquefied resin at high temperature is not too short and if the shear forces are very high.
The Sixth Element has established relationships with companies experienced in processing polymers with nanoscale additives and its associated challenges to further process thermoplastic materials with injection molding and similar processing techniques.
Technology that prevents re-agglomeration of primary particles is provided by these companies, which prevents 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, together with their partner, found that they could demonstrate that adding about 10-12% by weight of The Sixth Element SE1233 reduced electrical resistivity by the order of 10.5 Î© in a polymer system with an electrical resistance significantly greater than 1030 .
In another example, The Sixth Element used a silane-modified graphene oxide in an in situ polymerization of polyurethane.
Even though graphene oxide is a poor electrical conductor, the combination of a specific polyurethane with an electrical resistivity of about 108Î© / mÂ² and 0.4 weight -% graphene oxide leads to an electrical resistivity of 105/ mÂ². This is mainly due to the large amount of sp2-orbitals available in polyurethane resin and graphene oxide structure.
While the focus is on using graphene to improve mechanical properties, the way in which graphene is incorporated into the polymer matrix plays an important role. When adding graphene to the in situ polymerization of PA6, which is then used to produce fibers, the tensile strength and other mechanical properties of this fiber are improved by 40% and more, while the elongation at break is unchanged. In a specific embodiment, instead of graphene, graphene oxide is used.
PA6 / Graphene fibers – compared to PA6 fibers. Image Credit: The Sixth Element (Changzhou) Materials Technology Co., Ltd.
When graphene is added to the polymer using extrusion technology, graphene acts in the same way as, for example, glass fibers or carbon fibers.
The relationship between the volume of the matrix system and graphene will define the increase in mechanical properties. Graphene, as a material with a very high aspect ratio, will fill a higher volume with the same addition of weight as materials with a low aspect ratio.
This is the reason why the addition of less than 1% by weight, normally something around 0.5% by weight, leads to an increase in tensile strength, flexural modulus or modulus of Young by 20% or more.
Antistatic flame retardant PE graphene 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 carried out extensive work to improve the mechanical and electrical properties of PE compounds used in PE pipes for the oil and gas industry. Piping systems require high electrical conductivity, exceptional flame retardant properties and high mechanical strength with excellent elongation properties to compensate for dimensional variations due to temperature fluctuations.
In order to achieve the best balance between electrical conductivity, flame retardancy, increased mechanical strength while maintaining the elongation properties of pure PE, The Sixth Element tested different graphene-based formulations. Using only highly conductive types of graphene with an amount of 1 to 3% by weight of flame retardant obtained V0 with an electrical resistivity of less than 105/ mÂ².
A large increase in tensile strength and flexural strength was observed, but the elongation at break was significantly reduced. This is due to the stiffening characteristics of graphene as a reinforcing material. With a combination of carbon black and a type of graphene specially designed to improve mechanical properties, the required amount of fillers is reduced and the elongation at break has almost the same level as net PE resin. In a specific embodiment, the electrical resistivity is much less than 105Î© / mÂ², the flame retardancy is V0, and the wall thickness may be reduced due to exceptional tensile strength and bending strength.
The Sixth Element continuously invests in R&D to create new formulations to improve the electrical, mechanical and thermal properties of different plastic polymer composites (thermosetting systems, thermoplastic systems, elastomers).
This information has been obtained, reviewed and adapted from material 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.