MATERIALS | NANOCOMPOSITES
“For high-aspect ratio flakes (for example, 300
micron flakes), the shear forces are enough to tear graphene apart, creating primary covalent bonding opportunities at graphene edges. These dangling bonds are satisfied by the molten polymer itself, resulting in strong effective bonding between graphene and the host polymer,” he explains. TLC has recently commenced an upgrade of its
process that includes a new way of feeding raw materials into the proprietary exfoliator that will allow loadings of 35% by weight. In some cases this has allowed the throughput to be tripled, Mazar says. It will also allow higher speeds and larger scale. To date, TLC says it has successfully scaled a
This SEM image of a cryogenic fracture surface for a PEEK compound with 20 wt% of TLC Products’ exfoliated graphite graphene nanoparticles shows an even dispersion. The red markers show the dimensions of several graphene nano-flakes. Image: TLC Products
tion but that they see a challenge in building a solid industrial value chain to shorten time to market.
Tackling exfoliation US-based TLC Products offers graphene polymer matrix composites (G-PMCs) using a patented technology, licensed from Rutgers, the State University of New Jersey, claimed to enable in-situ exfoliation of graphite into graphene in a single- step process. In addition to supplying custom pelletised compounds and masterbatches, TLC plans to license its technology. It says it currently has one licensee and is negotiating with another. TLC claims its process is low-cost, suitable for
large-volumes, and is scalable. It says starting with graphite as a raw material and exfoliating it into graphene in situ provides a cost benefit. Its process is also said to provide more intimate bonding, create more even dispersion, and prevent reagglomeration. The extent of bonding with the polymer matrix and the property improvement achievable depends on the polymer type, the company says. Improve- ments have been seen with a wide range of polymers tested to date, with the largest increases in more polar polymers such as PET and PEEK. “When a continuous material (for example,
graphite) is split in two, bonding opportunities are created on both sides of the fracture. Through multiple high-shear events, graphite is successively reduced down to few-layer graphene, exposing secondary π bonding opportunities at graphene faces,” says Mark Mazar, Technical Director at TLC Products.
20 COMPOUNDING WORLD | October 2023
batchwise laboratory process to larger continuous processes. “We have gone through two scale-ups, [each with] about an order of magnitude increase in throughput. We are currently designing the next scale-up, which will have a throughput of about 2,500 lb/hr [around 1,100 kg/hr],” Mazar says. Graphene-enhanced polymers may find use in a
wide range of applications. TLC says G-PMCs are currently being considered for automotive parts such as car body panels, bumpers, housings and electron- ics where, in many cases, they can replace carbon fibre composites. “Graphite is less expensive and more environmentally friendly compared to carbon fibres and G-PMCs dramatically improve stiffness and strength. G-PMCs also absorb a wide range of radiation, from radio waves to UV,” Mazar says.
Moving in CNTs Carbon nanotubes (CNTs) also offer the opportu- nity to significantly improve electrical conductivity and/or mechanical properties, but dispersing CNTs is a challenge due to the strong intermolecular attraction (caused by van der Waals forces) that entangles the structure and causes clustering or agglomeration, says Nadav Goldstein, Vice-Presi- dent of Business Development and Innovation at Israel-headquartered compounder Kafrit Group. In the agglomerated state, CNTs tend to lose their beneficial properties, the company says, so exfoliating the CNTs and dispersing them in the matrix is key to unlocking the material benefits. Kafrit recently invested in an Israeli start-up, Nemo Nanomaterials, which claims to have developed a proprietary process to break down agglomerates and produce a masterbatch contain- ing well-dispersed CNTs. This masterbatch can then be used with standard processes to produce plastic parts with dispersed CNTs. Property improvements include enhanced
strength, high Young’s modulus, and high electrical conductivity. Goldstein reports that in EMI shield-
www.compoundingworld.com
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