Carbon nanofiber reinforced Co-continuous HDPE/PMMA composites: Exploring the role of viscosity ratio on filler distribution and electrical/thermal properties

Double percolation threshold method was used in this work to fabricate conductive polymer blend composites comprising of high density polyethylene (HDPE), poly (methyl methacrylate) (PMMA), and carbon nanofibers (CNFs). Distribution of fillers and their consequent effect on electrical conductivity (EC) and thermal conductivity (TC) is a function of many parameters including viscosity ratio (VR) of polymeric components, which varies with processing temperatures. Here, the effect of VR on the ultimate TC and EC of this polymer blend composite was investigated by blending the components at two processing temperatures of 150 and 230 °C with VR of 3.5 and 0.9, respectively. The obtained results demonstrated more homogeneous distribution of CNFs in the blend with VR of 0.9 while it was mostly aggregated in the blend with VR of 3.5 leading to different TC and EC properties at the same loading of CNFs. This means that the composite with higher EC showed lower TC and vice-versa. These phenomena can be explained due to passage of electrons through the filler-matrix interface with tunneling effect, whereas phonons will be scattered at the interfaces. Therefore, although more homogenous distribution of fillers results in improved EC, it is accompanied with formation of more interfacial area and phonon scattering, and less enhancement of TC. This study provides a better understanding of the TC and EC mechanisms, and also the importance of VR in optimization of these properties, which can be applied for fabrication of the desired composites based on their targeted applications.