World Journal Of Engineering
FABRICATION OF A MICROENCAPSULATED n-OCTADECANE
MATERIAL FOR THERMAL ENERGY STORAGE
D. Z. Chen1, C. P. Tsui2, C.Y. Tang2, H. Zhu1, Y.Z. Chen1, G. C. Yang1, Y. Chen1,
L. Chen2
1
College of Materials Science and Engineering, Shenzhen University, Shenzhen, Guangdong, China
2
Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University,
Hung Hom, Kowloon, Hong Kong, China
*Corresponding author: E-mail address: mfgary@inet.polyu.edu.hk (C.P. Tsui)
Introduction
Nowadays, facing upon the energy crisis,
more research attention is being paid to
phase change materials (PCMs) which
possess high enthalpy of fusion. To widen
their applicability and overcome the
problems of leakage and erosion, PCMs
are usually microencapsulated [1]. Several
encapsulation
techniques,
such as
interfacial
polymerization
and
coacervation, were developed. In this
study, an in-situ polymerization method
has been used to synthesize the
microencapsulated n-octadecane material
with urea-formaldehyde (UF) resin as the
shell for energy saving application. The
morphology of the microcapsules and the
effect of core/shell ratios on the formation
of microcapsules have been investigated.
tween-80 (1:1 by weight, Tanjin Damao
Chemical Reagent Co., Ltd.) with a
homogenizer for about 10 min to form the
emulsion. Then, the prepolymer, prepared
through a reaction between urea and
formaldehyde resin (2:1, mole ratio) at 70
o
C for 1.5h, was poured into the previous
emulsion. The pH value of the mixture
was slowly modulated to 2.5 within 1h.
Afterwards, the system was kept stirring at
50 oC for another 1h, followed by filtering,
washing and drying.
Apparatus and Procedures
The morphology of the microcapsules was
observed using a Hitachi SU-70 field
emission scanning electron microscope
(FE-SEM). Thermal properties were
examined using a TA-Q200 differential
scanning calorimeter (DSC) under a N2
atmosphere at a heating rate of 5 oC/min.
Experimental
Materials and Fabrication
n-Octadecane with a purity of 98%
purchased from Shanghai Jingchun
Chemical Reagent Co., Ltd., a kind of
PCMs, was used as the core material. Urea
with a purity above 99.0% and
formaldehyde (37wt.% aqueous solution),
produced by Tianjin Fuchen Chemical
Reagent Company and Tianjin Chemical
Ind., Ltd., respectively, were used as
shell-forming monomers. A certain
amount of n-octadecane was firstly stirred
in the aqueous solution of span-80 and
Fig.1 FE-SEM image of UF resin
/n-octadecane microcapsules.
179
World Journal Of Engineering
100/0
28.97
241.70
-
Results and Discussion
Figure 1 shows the photographs of
urea-formaldehyde resin /n-octadecane
microcapsules. The microcapsules have
smooth and compact surfaces, and have
round spherical profiles.
Figure 2 shows the thermograms of the
Conclusion
The
n-octadecane
was
well
microencapsulated using the proposed
method of in-situ polymerization. The
thermal properties of microcapsules were
dramatically influenced by the core/shell
weight ratios. The microcapsules are
expected to become a potential candidate
for achieving heat energy saving function
in textile and construction industries.
Heat flow (W/g)
0
-2
Acknowledgement
65/35
70/30
75/25
100/0
The authors would like to thank the supports
from the Research Committee of The Hong
Kong Polytechnic University (A-PK50) and
Shenzhen Durability Center for Civil
Engineering (SZDCCE-1003).
Endo
-4
References
15
20
25
30
35
1. Tyagi, V.V., Kaushik, S.C., Tyagi, S.K. and
Akiyama T. Development of phase change
materials
based
microencapsulated
technology for buildings: A review. Renew.
Sust Energ. Rev., 15(2011)1373-1391.
2. Zhang, H. and Wang, X. Fabrication and
performances of microencapsulated phase
change materials based on n-octadecane
core
and
resorcinol
modified
melamine-formaldehyde shell. Colloid Surf.
A., 332(2009) 129-138.
40
o
Temperature ( C)
Fig. 2 DSC thermograms of the microcapsules
with various weight ratios of core/shell
materials.
core material and microcapsules obtained
by DSC. The melting temperature (Tm) and
the latent heat of phase change (ΔHc) are
listed in Table 1. There is a slight
deviation of Tm for the prepared
microcapsules
from that
of
the
n-octadecane (28.97 oC), due to the phase
change behaviors confined by the inner
space of the microcapsules [2]. From Fig.1
and Table 1, it can be seen that the
microcapsule with a weight ratio of
core/shell materials of 70/30 has the highest
latent heat and the PCM content was
determined by the following equation:
PCM content (%) 
H m, MEPCM
 100
H m, PCM
where H m, MEPCM and H m, PCM are the melting
latent heats of the microcapsules and the
core material, respectively. The core/shell
ratio is found to have a great effect on the
microcapsule formation. An appropriate
amount of the shell material is required for
the microencapsulation of PCM.
Table 1 Thermal properties of core
material and microcapsules with various
weight ratios of core/shell materials
Core/shell
Tm
PCM
ΔHc
o
ratio
( C)
(J/g)
content
(wt./wt.)
(%)
65/35
29.07
55.06
22.78
70/30
28.95
92.41
38.23
75/25
30.65
62.25
25.76
180