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Graphene nanotubes are newly-developed additives that add electrical conductivity to silicone formulations. They can be used in many types of silicones including liquid silicone rubber (LSR), heat cured rubber (HCR), and room temp vulcanizing (RTV).
Nanotubes are made of carbon atoms. When an ultra-low percentage of nanotubes are dispursed in silicone, the parts remain flexible and free of the negative properties that occur when using conventional additives.
Conventional Additive Options for Elastomer Conductivity
Conventional silicone additives are carbon black, carbon fiber, metal fillers and graphene. To achieve conductivity, the formulation must use between .5 and 40% of these additives, which negatively impacts the performance properties of the silicone.
The most common negative side-effects of standard conductive additives are hardening, loss of elasticity and color change.
Graphene Nanotube Advantages
Graphene nanotube technology was developed by Luxembourg-based OCSiAl under the brand name TUBALL™. Nanotubes are one-atom-thick graphene sheets rolled in a tube more than 5 µm long. These tiny tubes, commonly called single wall carbon nanotubes, are 100 times stronger than steel.
When embedded into a material’s matrix, graphene nanotubes create a 3D conductive network that enables conductivity without negative trade-offs. Even low dosages of 0.05 wt.% can provide the desired electrical conductivity and/or antistatic properties. There is minimal impact on compound elasticity, tensile parameters, viscosity and rheological properties.
TUBALL graphene nanotubes are available in diameters from 1.6+0.4 nm, lengths > 5 nm and wall thickness of 1 atom. This relationship of length to diameter provides the highest possible surface area and ensures permanent and uniform conductivity without “hot spots.”
In fact, to get the same conductivity as .01 – 0.1% graphene nanotubes would require the following additive concentrations:
- Carbon Black: 20-40%
- Caron Fiber: 3-12%
- Metal fillers: 15-35%
- Graphene: 1-6%
- MWCNT: 0.5-5%
Compared to using antistatic polymers, graphene nanotubes provide permanent conductivity and longer cycle life of the final parts.
Applications for Graphene Nanotubes
High performance is critical for conductive vehicle components made from flexible silicone. It is also extremely important for other products such as flexible silicone electrodes and sensors, cable connectors and sleeves, printing rollers and pads, conveyor belts, and car tires.
Graphene nanotubes are rapidly being selected for use in automotive, transportation, electronics, construction, mining, healthcare and consumer wearable products and components. They are also ideal for wearables such as FitBit and AppleWatch because they conduct electrical pulses better.
Processing silicones using graphene nanotubes
To simplify nanotube handling, OCSiAl offers a pre-disbersed form of graphene nanotubes called TUBALL MATRIX. Since the TUBALL powder is already disbursed in a polymer, it adds much better to the silicone without any color loss.
The MATRIX solution can be dropped into any standard processing and mixing equipment. This saves on production costs and reduces replacement costs for defective parts.
TUBALL MATRIX 601 and 602 are for use in LSR and RTV, while TUBALL MATRIX 605 is formulated for HCR.
Test Case Examples using Graphene Nanotubes
Graphene nanotubes have been extensively tested for use with antistatic compounds, ESD compounds and electrostatic paintings and EMI shielding compounds. Following are some specific test cases.
- Connecting cable sleeve:
5% TUBAL Matrix 605 replaced 15-25% carbon black for the inner layer of the sleeve. Volume resistivity was less than 100 Ω∙cm, elasticity was not impacted, viscosity remained low, processing and mechanical properties were superior and cycle life improved.
- Conductive LSR with TUBALL MATRIX:
LSR 6360 with 4% TUBALL Matrix 601 produced 80 Ω∙cm vs. 10^4 Ω∙cm for LSR 6360 without. Tensile strength increased 5%, elongation at break decreased 6%, tear strength increased 80% and hardness was not affected.
- Conductive HCR with TUBALL vs. Carbon Black:
For high dynamic pressure applications, TUBALL samples lasted to 300% deformation, versus sample broken at 100% deformation with 25% carbon black. Samples broke at 50% deformation with ELASTOSIL R 570/70.
- Printing rollers, plates, hoses, cable jackets:
1-2% TUBALL MATRIX 601 used for LSR, TRV (or MATRIX 605 used for HCR) increased volume resistivity 10^5 Ω∙cm maintaining mechanical properties, enabling coloration, with better processing and longer cycle life. More cost-effective.
OCSiAl recently partnered with HM Royal because of growing demand for high-performance sustainable elastomers by the American market. They have also opened a new office in Gahanna, Ohio to expand their market presence. For more information on this technology, watch this video: visit the OCSiAl page or contact an H.M. Royal representative.