TECHNOLOGY | THERMALLY CONDUCTIVE COMPOUNDS
brittleness, Peréz claims. “The quantity needed of AvanThermal Conductive NCC-1701-A to obtain 2.5 W/m.K through-thickness (Guarded Heat Flow Meter Technique ASTM E1530) is at least 80% lower than that needed for other solutions such as aluminium oxide, boron nitride, or graphite,” he says.
Figure 2: The high aspect ratio of AvanThermal Conductive NCC-1701-A multilayer graphene makes it possible to obtain a percolative network at moderate filler loadings to obtain high thermal conductivity values Source, Avanzare
matrix requires a balance of a well-organised percolating network and a low number of defects, due to the drop in conductivity associated to defects in the sp2
structure of graphene materials,
he says. “AvanThermal Conductive NCC-1701-A produces a high dispersion degree of the polymer matrix and a good interfacial interaction between the matrix and the nanoflakes. The very low defect content in the graphene plane also allows an easy transport of phonons, responsible for the thermal conductivity. The combination of both properties allows a drastic improvement in thermal conductivity.” A phonon is a quantum of vibrational mechanical energy, just as a photon is a quantum of electromagnetic energy.
Graphene performance AvanThermal Conductive NCC-1701-A can be used in diverse thermoplastic matrixes, as well as thermosets and elastomers. It works at very low addition rates (Figure 2) allowing lower densities to be obtained than with other additives, and also improved mechanical properties due to the lower
While graphites and graphenes are aimed at high-end applications, there is room in the market for alternative additives that may not offer such high performance but that some compounders may be more comfortable working with, according to Huber Engineered Materials. The company plans to launch a line of thermally conductive Martinal TM additives in the not-too-distant future that it says will build on the Martoxid TM aluminium oxide-based thermally conductive additives it introduced back in 2016. Martinal is a trade name Huber currently uses for aluminium hydroxide additives (it also markets magnesium hydroxides under the Magnifin name) but the company does not disclose the composition of Martinal TM grades. It says they will be offered where high thermal conductivity is not required, typically providing thermal conductivity in compounds of up to 2W/m.K. Martinal and Martoxid products are both inert
white materials, which enable them to be used in any type of polymer system, including water- sensitive applications. Some Martoxid grades enable conductivities of up to 3W/m.K at loadings of up to 90 wt%. Despite the high addition levels, mechanical strength properties of such compounds are said to be excellent and processability is good. There are four series of Martoxid TM products, with varying chemical properties. Key characteristics of the Martoxid products are said to include isotropic thermal conductivity, high electric insulation, high thermal stability, high chemical stability, and low thermal expansion.
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Thermal imaging results showing how samples with different TC values dissipate spot heat (the images are overlaid). A circular heat source at 60°C was placed on each sample for 20 seconds, then removed (time= 0) and the samples allowed to cool to room temperature
28 COMPOUNDING WORLD | August 2020
Source: Huber
www.compoundingworld.com
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