The role of the filler surface chemistry on the dielectric and thermal properties of polypropylene aluminium nitride nanocomposites

Abstract

In nanocomposites, different surface states of nanoparticles can potentially provide different interactions with the base polymer and in turn change the bulk properties. Aluminium nitride (AlN) nanoparticles were surface functionalised with three different silane coupling agents (SCAs) with varying organofunctional and hydrolysable groups. The effects of the filler surface chemistry on the resulting AlN/polypropylene (PP) nanocomposites were examined and compared with an unfilled reference system. It is observed that different organofunctional groups can provide different nucleating effects and the dispersion states of nanoparticles while the hydrolysable group is not the dominant factor. The dielectric spectroscopy results show the hydrolysable group of SCA will also result in a difference of the interphase since the trimethoxy silane treated systems show much higher imaginary permittivity than the triethoxy silane treated systems when the frequency is below 1 Hz. The grafted organofunctional layer on the particle surface can provide a significant improvement of the thermal conductivity of the composite materials, e.g. 15 % improvement in thermal conductivity was observed when adding 10 wt% methacrylate silanes treated nano-AlN into PP, while the untreated counterpart only has 5 % improvement.

Effect of water on the breakdown and dielectric response of polypropylene/nano-aluminium nitride composites

“…This mixture was heated and stirred at 140°C for 4 h, and the resulting slurry was then washed three times with toluene. The treated AlN was vacuum-dried at 80°C for 24 h. Fourier-transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA) verification of the treated AlN can be found in previous work, where it is evident that the silane functionalisation was successful [5,26].…”

“…Investigating samples treated under different humidity conditions is an effective method that can identify the properties of the surface of the nanoparticles. Our previous work also suggests that the potentially different grafting mechanisms related to the different hydrolysable groups of silanes can potentially result in minor differences in the dielectric losses at low frequencies [5]. One possible explanation is the silane functionalised nanoparticles can have a different amount of non-grafted -OH groups from silane, which will result in a different hydrophobicity of corresponding composites (illustrated in Fig.…”

“…A modified form of solution blending was applied in this work, which is expected to give a more consistent dispersion state than the method used previously [5], where a hand mixing step was included. Initially, 4.5-4.95 g of PP was added to 50 ml of xylene and heated at 140°C for 30 min, while stirring at 200 rpm.…”

“…It is reported polar groups like methacrylate could facilitate more nucleating effect than non-polar ones, e.g. octyl (C8) [5]. This may also be the reason why (111) ?…”

“…However, PP cable insulation suffers from a number of drawbacks regarding thermo-mechanical properties; one of them is having a low thermal conductivity, which is 0.14 W m -1 K -1 [4]. This drawback can be overcome by adding fillers with high thermal conductivity, which also can help alleviate the issue of high thermal gradients between the inner and outer of the cable insulation [5][6][7]. This issue can lead to localised regions of higher conductivity/higher dielectric loss which can shorten the lifetime of the cable.…”