electrical & electronic | Thermal management
Thermal conductivities of various additives for plastics
market and it is exploring the potential for graphenes in plastics. Dr Angelos Kyrlidis, principal scientist at the company, discussed initial fi ndings during his presenta- tion on thermally and electrically conductive additives at the Compounding World Forum 2014 in Philadelphia last December. He said “breakthrough” performance – not only in conductivity values but also in mechanical properties – is possible with graphenes at loadings of under 1%. Data was presented that showed graphene increased the thermal conductivity of polypropylene more than carbon black.
Source: HPF/ Quarzwerke
“In-house testing has confi rmed the performance benefi ts of graphenes but also identifi ed the importance of delivering them in the appropriate form,” he said. Electrical conductivity of compounds is highly depend- ent on additive morphology and the quality of disper- sion. Cabot is developing materials that can be processed easily in conventional equipment.
Movement in minerals
Not all graphites are the same; particle size, fl ake morphology and the intrinsic anisotropic thermal conductivity of graphite introduce a strong anisotropy in the thermal conductivity of a material. Bar chart shows in-plane and through-plane thermal conductivity of injection moulded HDPE plaques loaded with different Imerys graphite grades
dispersion in the polymer matrix, an essential property in pipe applications, for example, because carbon black that is not well-dispersed is known to act as a mechanical weak point. While thermally conductive plastic is gaining
increasing attention, the development of new markets means developing new specifi cations and makes understanding the potential benefi ts and pitfalls of new additives of great importance. Graphite is used when high thermal conductivity is needed, although it has the drawback of decreasing the mechanical properties. Conductive carbon black is used only in applications that require moderate increase of thermal conductivity, such as geothermal pipes, as it is very effective in preserving the mechanical properties of the fi nal material. Conductive additives from Imerys are priced between €2 and €20 per kg, depending on purity and grade. Cabot is also active in the conductive carbon black
34 INJECTION WORLD | March 2015
HPF - The Mineral Engineers, a division of Quarzwerke, began marketing a range of Silatherm aluminosilicate fi llers two years ago. It says they generate a signifi cant increase in the thermal conductivity of thermoplastics and thermosets. “The values measured in polyamide show that through the use of our Silatherm alumino- silicate grades thermal conductivities of up to 2.3 W/mK can be achieved and that the mechanical properties remain at a very good level for these high fi ller propor- tions,” the company claims. By comparison, unfi lled PA 6 has a thermal conductivity of 0.3 W/mK.
Market development manager Klaus Berger says that HPF has very fl exible production that enables it to obtain precise particle sizes and particle size distribu- tion. The larger the grain size, the greater the abrasion during processing. HPF grades have a Mohs hardness of 5-6, which is similar to that of glass fi bres. This compares with 9-10 for aluminium oxide, which is another contender in this market.
HPF applies different surface coatings according to
the host polymer. Berger says the strongest demand from compounders is for Silatherm grades compatible with polyamides, but recently there has been a growth in interest from companies producing polypropylene compounds. HPF is currently carrying out trials on grades compatible with PP. Silatherm provides approximately the same level of
thermal conductivity along all three axes; in-plane conductivity is similar to that obtained with boron nitride, but through-plane conductivity is lower. So if higher through-plane conductivity is required, the two additives can be blended together. Compounders will probably want to try and use as little boron nitride as
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