Page 105 - Polymer-based Nanocomposites for Energy and Environmental Applications

Nanoclay and polymer-based nanocomposites: Materials for energy efficiency 81

operation methods, but they both incorporate PCMs directly in conventional construc-
tion materials, which generate surly the incompatibility problems [7].

3.3.3 Encapsulation techniques
In this technique, PCMs have to be encapsulated before being used into building mate-
rials to prevent their interaction with the outside environment, increase the surface
area available for heat transfer, and eliminate leakage problems. Generally, two
PCM encapsulation methods are reported: macroencapsulation and microencapsula-
tion [6-8].

3.3.3.1 Macro-encapsulation
PCMs can be packed in a container, such us shells, tube spheres, and panels. This tech-
nique called macroencapsulation allows easy incorporation of PCMs in the building
elements and provides a volume control and protection against environmental degra-
dation. However, this form of containments suffers from leakage problems, poor heat
transfer characteristics, tendency of solidification at the edges, and complicated inte-
gration into building materials [6-8].

3.3.3.2 Micro-encapsulation
The principle of this technique is forming capsules of micrometer size by coating the
PCM particles with a thin shell usually made from polymers [6]. It’s done to prevent
PCMs from leakage and to tackle the issues of volumetric changes during the phase-
change process, reactivity to the environment, compatibility, and strength with the
construction materials [6-8]. Microencapsulation techniques are usually categorized
as physical and chemical techniques [23]. Physical methods include spray drying,
pan coating, air-suspension coating, centrifugal extrusion, and fluidized-bed pro-
cesses, while the chemical methods include interfacial polymerization, suspension
polymerization, phase separation, and simple or complex coacervation methods
[23]. The mean advantages and disadvantages of encapsulation techniques are listed
in Table 3.3.

3.3.4 Shape-stabilized PCM
The PCM material is dispersed in another phase of a support material such as high-
density polyethylene (HDPE), styrene, and butadiene to fabricate shape-stabilized
PCMs [7]. These materials are a promising solution for PCM leakage issues. They
show increased specific heat capacity, appropriate thermal conductivity, and
maintaining the shape of the PCM stabilized during the phase-change process as well
as a good thermal reliability melt/freeze cycles over a long period [6-8]. Inaba and
Tu [24] studied the thermophysical properties of shape-stabilized PCMs made of par-
affin as a dispersed material and a high-density polyethylene (HDPE) as a supporting
material. Furthermore, little amount of ethylene/α-olefin was added to the paraffin