This contribution reports on properties of low-density polyethylene-based composites filled with different amounts of graphene nanoplatelets. The studied samples were prepared in the form of films by means of the precoating technique and single screw melt-extrusion, which yields a highly ordered arrangement of graphene flakes and results in a strong anisotropy of composites morphology. The performed tests of gas permeability reveal a drastic decrease of this property with increasing filler content. A clear correlation is found between permeability and free volume fraction in the material, the latter evaluated by means of positron annihilation spectroscopy. A strong anisotropy of the thermal conductivity is also achieved and the thermal conductivity along the extrusion direction for samples filled with 7.5 wt % of GnP (graphene nanoplatelets) reached 2.2 W/m·K. At the same time, when measured through a plane, a slight decrease of thermal conductivity is found. The use of GnP filler leads also to improvements of mechanical properties. The increase of Young's modulus and tensile strength are reached as the composites become more brittle.

The results of thermal conductivity study of epoxy-matrix composites filled with different type of powders are reported. Boron nitride and aluminum nitride micro-powders with different size distribution and surface modification were used. A representative set of samples has been prepared with different contents of the fillers. The microstructure was investigated by SEM observations. Thermal conductivity measurements have been performed at room temperature and for selected samples it was also measured as a function of temperature from 300 K down to liquid helium temperatures. The most spectacular enhancement of the thermal conductivity was obtained for composites filled with hybrid fillers of boron nitride-silica and aluminum nitride-silica. In the case of sample with 31 vol.% of boron nitride-silica hybrid filler it amounts to 114% and for the sample with 45 vol.% of hybrid filler by 65% as compared with the reference composite with silica filler. However, in the case of small aluminum nitride grains application, large interfacial areas were introduced, promoting creation of thermal resistance barriers and causing phonon scattering more effective. As a result, no thermal conductivity improvement was obtained. Different characters of temperature dependencies are observed for hybrid filler composites which allowed identifying the component filler of the dominant contribution to the thermal conductivity in each case. The data show a good agreement with predictions of Agari-Uno model, indicating the importance of conductive paths forming effect already at low filler contents. Figure 3. SEM images of the: a) the composite filled with 45 vol.% hybrid filler Millsil W12 and BN PT100 (90:10), b) filled with 45 vol.% hybrid filler Millsil W12 and BN PT100 (80:20).

An epoxy‐anhydride formulation used for the coating of electrical devices was modified with a commercially available hyperbranched poly(ester‐amide), Hybrane™ S2200, in order to improve the thermal degradability of the resulting thermoset and thus facilitate the recovery of substrate materials after use of the component. The curing kinetics of the unmodified and modified formulations were studied in detail with differential scanning calorimetry, Fourier transform infrared spectroscopy and rheology. The results suggest that S2200 gets incorporated into the network structure and the curing kinetics are accelerated by the presence of hydroxyl groups from S2200. Copyright © 2012 Society of Chemical Industry

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