| Summary: | Phase change materials based on polyethylene (LDPE, LLDPE and HDPE) and copper (micro
and nano) blended with soft paraffin wax were studied in this work. The purpose of this study
was to form composites that can store energy as well as conduct heat. The influence of wax
content, as well as copper content and copper particle size, on the morphology and thermal,
mechanical and conductivity properties was investigated. The scanning electron microscopy
results show that both the Cu micro-and nano-particles were well dispersed in the matrix. The
nano-particles, did, however, also form agglomerates. The results also show that the Cu
micro-particles have a greater affinity for the wax than for the polyethylenes, giving rise to
preferable crystallization of the wax around the Cu particles. The differential scanning
calorimetry results show that the Cu micro- and nano-particles influence the crystallization
behaviour of the polyethylenes in different ways. The extent to which the copper particles
influence the crystallization behaviour of the polyethylenes also depends on the respective
morphologies of the different polyethylenes. All the polyethylene/wax blends are immiscible
or only partially miscible at wax contents of 30, 40 and 50%. The presence of wax in the
polyethylene/wax blends reduces the melting temperatures of all three polyethylenes,
indicating the plasticizing effect of the molten wax in the polyethylene matrix. The
thermogravimetric analysis results show observable influence of both the presence of copper
and the sizes of the copper particles, as well as the presence and amount of wax, on the
thermal stabilities of the blends and composites. The thermal conductivities of the composites
show a non-linear increase with an increase in Cu particle content. The presence of wax
slightly decreases these values, confirming the preferable crystallization of wax around the Cu
particles. The thermal conductivities of the Cu nano-particle containing composites, at the
same copper contents, are almost the same as those of the micro-particle containing
composites. Youngâs moduli increased with an increase in copper content in both the
polyethylene composites and the polyethylene/wax blend composites, except in the case of
HDPE where a decrease was observed. The dynamic mechanical analysis storage moduli
determined through dynamic mechanical analysis show the same trends as the Youngâs
moduli. The tensile strengths show variable behaviour, but mostly these values decrease with
increasing Cu and wax contents. The energy storage results show that the heat transport is
faster in the case of the blend composites compared to the polyethylene/wax blends, and the
heat transport in the polyethylene/wax blends is also faster than in the neat polyethylene
|
|---|
