Page 106 - Polymer-based Nanocomposites for Energy and Environmental Applications

82 Polymer-based Nanocomposites for Energy and Environmental Applications

Table 3.3 Advantages and disadvantages of different encapsulation
techniques [6]

Encapsulation
techniques Advantages Disadvantages
Macroencapsulation l Improved material compatible l Solidification at the
with surrounding material edges
Improves PCM handling during Poor thermal
l l
production conductivity or heat
l External volume change effects transfer characteristics
are mitigated
l Preventing changes of its
composition through contact
with environment
l Can serve directly as heat
exchangers
Microencapsulation l Good control of volume change l Costly process
during the phase-change process l Can affect the strength
Easily incorporable into of material
l
conventional building materials l Lead to supercooling
l Enhancing conductive heat effects
transfer between PCM and the
surrounding material
l Thermal reliability is
considerably improved
l Chemical stability is improved
l Prevent PCM leakage by acting
as a barrier

to reduce oozing rate of the paraffin from the shape-stabilized PCM when melting/
freezing cycles are repeated. It was found that the prepared shape-stabilized PCM
(74 wt% of paraffin and 26 w% of HDPE) had a heat of fusion of 121.4 kJ/kg and
a melting temperature of 54.15°C. The micrograph in Fig. 3.3 showed that the paraffin
as seen in the black part was dispersed in three-dimensional netted texture of HDPE as
indicated at the white part and there was no leakage of the melted paraffin during the
heat storage process.
Xiao et al. [6] found that a maximum of about 80% of the paraffin can be encap-
sulated into styrene-butadiene-styrene (SBS) without any infiltration of the molten
paraffin. The heat of fusion and the melting temperature were determined as
165.21 kJ/kg and 56–58°C, respectively.
In order to overcome the problem of low thermal conductivity and in order to con-
trol the encapsulation, the shape-stabilized PCM was mixed with exfoliated graphite.
However, according to Zhang et al. [25], the product made of SBS/paraffin has the
defect of rigidity, and if it has a large volume, it cannot be able to sustain its own