PREPARATION AND PHOTOTHERMAL CHARACTERIZATION OF NANOCOMPOSITES BASED ON HIGH DENSITY POLYETHYLENE FILLED WITH EXPANDED GRAPHITE: PARTICLE SIZE AND SHAPE EFFECTS

摘要

This work aimed at thermal transport characterization of high density polyethylene (HDPE) filled with two sizes (5 and 50μm) of expanded graphite (EG) particles. Sample platelets were produced by melt mixing followed by compression molding. Thermal conductivity k was determined by combining measurements of density, specific heat capacity and thermal diffusivity. For the latter, we used the self-checking, non-contact method of photothermal radiometry (PTR) in back detection configuration. Starting from an effective medium approximation model, we derived a simple linearized expression for the effective k of composites with low particle charge. It explains the unusually high experimental k values (up to four-fold increase) as the effect the strongly non-spherical EG particles (aspect ratio 1/p=110 - 290). Larger particle sizes produce higher k enhancement, while the interfacial thermal resistance (R_(bd) = 2.1×10~(-7) m~2×K/W) has an opposite effect on k. The eventual deviation of experimental k from the model at high particle charge is possibly due to limitation of interparticle free space preventing random orientation of high aspect ratio particles.