Development of thermoregulating textile materials with microencapsulated Phase Change Materials (PGM). IV. Performance properties and hand of fabrics treated with PCM microcapsules

Abstract

Polyester knit fabrics were treated with phase-change-material microcapsules by a pad–dry–cure method with a polyurethane binder. The treated fabrics were evaluated in terms of the thermal properties, air permeability, moisture vapor permeability, moisture regain, low-stress mechanical properties, and hand, with respect to the add-on of microcapsules. The surface morphology of the treated fabrics was investigated with scanning electron microscopy. The low-stress mechanical properties of the treated fabrics, including the tensile, shear, bending, surface, and compression properties, were measured with the Kawabata evaluation system for fabrics (KES-FB). As the add-on increased, the heat storage capacity of the treated fabrics increased. The treated fabric with 22.9% add-on was capable of absorbing 4.44 J/g of heat. The air permeability and moisture vapor permeability decreased, whereas the moisture regain increased, with an increase in the add-on. The tensile linearity and geographical roughness increased, whereas the resilience, bending, and shear properties decreased with an increase in the add-on. The fabrics became stiffer, less smooth, and less full as the add-on increased, and thus the total hand value decreased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 910–915, 2005

Full text

Development of Thermoregulating Textile Materials with
Microencapsulated Phase Change Materials (PCM). IV.
Performance Properties and Hand of Fabrics Treated with
PCM Microcapsules
Younsook Shin,
1
Dong-Il Yoo,
2
Kyunghee Son
1
1
Department of Clothing and Textiles, Chonnam National University, Gwangju 500-757, Korea
2
Department of Textile Engineering, Chonnam National University, Gwangju 500-757, Korea
Received 16 September 2004; accepted 14 December 2004
DOI 10.1002/app.21846
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: Polyester knit fabrics were treated with
phase-change-material microcapsules by a pad–dry–cure
method with a polyurethane binder. The treated fabrics
were evaluated in terms of the thermal properties, air per-
meability, moisture vapor permeability, moisture regain,
low-stress mechanical properties, and hand, with respect to
the add-on of microcapsules. The surface morphology of the
treated fabrics was investigated with scanning electron mi-
croscopy. The low-stress mechanical properties of the
treated fabrics, including the tensile, shear, bending, surface,
and compression properties, were measured with the Kawa-
bata evaluation system for fabrics (KES-FB). As the add-on
increased, the heat storage capacity of the treated fabrics
increased. The treated fabric with 22.9% add-on was capable
of absorbing 4.44 J/g of heat. The air permeability and
moisture vapor permeability decreased, whereas the mois-
ture regain increased, with an increase in the add-on. The
tensile linearity and geographical roughness increased,
whereas the resilience, bending, and shear properties de-
creased with an increase in the add-on. The fabrics became
stiffer, less smooth, and less full as the add-on increased, and
thus the total hand value decreased. © 2005 Wiley Periodicals,
Inc. J Appl Polym Sci 97: 910–915, 2005
Key words: mechanical properties; stress; thermal proper-
ties
INTRODUCTION
Phase-change materials (PCMs) have been used as
thermal storage and control materials because of the
heat absorption and release that occur upon a change
of phase.
1,2
In 1987, the microencapsulation technol-
ogy of PCMs was developed and incorporated with
textile materials.
3
Currently, for garments and home
furnishing products, microencapsulated PCMs are in-
corporated into acrylic fibers or polyurethane foams
or are embedded into a coating compound and topi-
cally applied to a fabric or foam.
4
Some researchers
have tried to apply PCM technology to protective
garments worn in extreme environments, from cold
water to hot deserts.
4–6
Many studies have been done on PCM fabrics and
garments. Pause
7
developed the concept of dynamic
thermal insulation with the insulation value of PCM
fabrics. Hittle and Andre
8
used the index of the tem-
perature regulation factor to measure the tempera-
ture-regulating ability of PCM fabrics. An evaluation
for PCM garments was conducted by Shim et al.
9
to
measure PCM effects during environmental tran-
sients. Kim and Cho
10
carried out wear trials of PCM
garments and found that the changes in the mean skin
and microclimate temperature with PCM garments
were less than the changes with non-PCM garments.
Yin et al.
11
also found that the rate of temperature
increase of a garment with a higher PCM add-on level
was lower than that of a garment with less PCM. Most
research has concerned the effects of thermal proper-
ties of PCM materials on wearing comfort.
In addition to the thermal properties, the air perme-
ability, moisture vapor permeability, and moisture re-
gain of materials also influence the heat balance of the
body and, consequently, affect clothing comfort.
12
Fabric hand determines the tactile comfort perceived
by humans and is incorporated with mechanical prop-
erty (tensile, bending, shear, compression, and sur-
face) measurements by the Kawabata evaluation sys-
tem. Although PCM microcapsules impart thermo-
regulating properties to materials and thus improve
the thermal comfort of clothing, they can affect other
comfort-related properties and hand of the materials
adversely, especially when the topical application of
microcapsules results in drastic changes in the surface
Correspondence to: Y. Shin (yshin@chonnam.ac.kr).
Contract grant sponsor: Korea Science and Engineering
Foundation; contract grant number: R04-2000-000-00090-0.
Journal of Applied Polymer Science, Vol. 97, 910–915 (2005)
© 2005 Wiley Periodicals, Inc.

characteristics of materials. The extent of change in
these properties depends on the loading amount of
PCM microcapsules. Therefore, the performance prop-
erties of fabrics treated with PCM microcapsules need
to be measured and considered before use in a gar-
ment.
In our laboratory, PCM microcapsules were synthe-
sized and applied to polyester knit fabrics topically to
develop thermoregulating textile materials. In a pre-
vious study,
13
the PCM microcapsules were character-
ized with respect to the structure, morphology, size
distribution, thermal properties, and stability. The
laundering durability of the treated fabrics was also
evaluated. This report focuses on the effects of the
PCM microcapsule add-on level on the air permeabil-
ity, moisture vapor permeability, moisture regain,
low-stress mechanical properties, hand, and thermal
properties of the treated fabrics.
EXPERIMENTAL
Materials
The fabric was a scoured and bleached 100% polyester
knit (68 ⫻58/in.
2
) with a weight of 195 g/m
2
and a
thickness of 1.47 mm. Melamine–formaldehyde micro-
capsules containing eicosane were manufactured by in
situ polymerization according to a previous study.
13
The characteristics of the prepared microcapsule are
summarized in Table I. All the chemicals were re-
agent-grade.
Application of the microcapsules to the fabrics
The manufactured microcapsules, mixed with a poly-
urethane binder (Snotex P110, Dae Young Chemical
Co, Ltd., Seoul, South Korea), were applied topically
to the polyester knit fabric with a pad–dry– cure
method. The procedures are described in detail else-
where.
13
Evaluation of the treated fabrics
The surface of the microcapsule-treated fabrics was
observed with a scanning electron microscope (JSM-
5400, JEOL, Inc., Tokyo, Japan). The heat storage ca-
pacity and phase-change temperatures were mea-
sured with differential scanning calorimetry. The heat-
ing and cooling rate was 2°C/min up to 50°C under an
atmosphere of N
2
. The air permeability (Frazier meth-
od; ASTM test method D737-96), moisture vapor per-
meability (ASTM test method E96-95), and moisture
regain (ASTM test method D885-98) were measured
with standard procedures. The low-stress mechanical
properties of the treated fabrics, including the tensile,
shear, bending, surface, and compression properties,
were measured with the Kawabata evaluation system
for fabrics (KES-FB). Primary hand values (HVs), in-
cluding Koshi (stiffness), Numeri (smoothness), and
Fukurami (fullness), and the total hand values (THVs)
were calculated from the mechanical properties with
the KN-203-LDY and KN-302-WINTER equations, re-
spectively.
14
RESULTS AND DISCUSSION
Thermal properties of the treated fabrics
Table II shows the melting temperature and heat stor-
age capacity versus the add-on of the microcapsules.
As the add-on increases, the heat storage capacity of
the treated fabric increases. Therefore, during the
phase-change process, the rate of the temperature rise
of the treated fabrics with a higher microcapsule add-
on level is expected to be lower than that with fewer
microcapsules.
10,11
The treated fabric with 22.9% add-
on is capable of absorbing 4.44 J/g of heat if the
microcapsules on the fabric undergo a melting pro-
cess. The heat of absorption by the microcapsules
delays the microclimate temperature increase of cloth-
ing and results in a decrease of the sweat release from
skin.
4
This leads to enhanced thermophysiological
comfort and prevents heat stress.
The selection of a PCM should take into account the
end use of the textile material. For example, if the
textiles are used for underwear, a PCM with a phase
change occurring in the range of skin temperatures
should be selected. On the other hand, for the lining
material of a ski suit, a PCM needs to phase-change at
a much lower temperature.
15
The melting temperature
of the treated fabric, 35°C, is slightly lower than that of
the microcapsules. It can be speculated that a trace
amount of impurities, possibly from the shells of mi-
crocapsules, may transfer into eicosane when the
treated fabrics are cured at 150°C. This would cause
TABLE I
Characteristics of Eicosane-Containing Microcapsules
Size (
␮
m) T
m
(°C) T
c
(°C) ⌬H
f
(J/g) ⌬H
c
(J/g)
1.89 36.9 31.7 134.3 132.9
Eicosane ⌬H
f
⫽263.7 J/g. T
m
⫽melting temperature; T
c
⫽
crystallization temperature; ⌬H
f
⫽heat of fusion; ⌬H
c
⫽
heat of crystallization
TABLE II
Heat Capacity (⌬H
f
) and Melting Temperature (T
m
)of
the Treated Fabrics Depending on the Add-On
Add-on (%) T
m
(°C) ⌬H
f
(J/g)
5.3 35.31 0.91
11.1 34.85 2.15
18.1 35.33 4.10
22.9 34.91 4.44
THERMOREGULATING TEXTILE MATERIALS. IV 911

the melting temperature of the microcapsule-treated
fabrics to decrease. Because of the melting tempera-
ture of the fabrics treated with the microcapsules, the
treated fabrics would be appropriate for outwear use
in a warm environment.
Scanning electron microscopy (SEM) observation
of the treated fabrics
Figure 1 shows the micrographs of the surfaces of
treated fabrics obtained from SEM observations. With
5.35% add-on, microcapsules with a binder fill up
some of the interstices between fibers. As the add-on
increases, more and more interstices are filled, and the
microcapsule–binder layer covers most of the fabric
surface at 22.9% add-on. Small cracks can be observed
on the layer at 22.9% add-on. The surface morphology
of the fabric is extensively changed by the microcap-
sule treatment, and this change affects the overall
properties of the fabric.
Air permeability and hygroscopic properties
Figures 2–4 show the air permeability, moisture vapor
permeability, and moisture regain as functions of the
microcapsule add-on, respectively. As the add-on in-
creases, the air permeability and moisture vapor per-
meability decrease. The air permeability and moisture
vapor permeability decrease by 28 and 20% at 22.9%
add-on, respectively, in comparison with those of the
untreated sample. There are some factors affecting the
air permeability and moisture vapor permeability of
the fabric, such as the fabric structure, thickness, and
Figure 1 SEM photographs of an untreated sample at (A) 500⫻and (B) 2000⫻, a sample with 5.3% add-on at (C) 500⫻and
(D) 2000⫻, and (c) a sample with 22.9% add-on at (E) 500⫻and (F) 2000⫻.
912 SHIN, YOO, AND SON

surface characteristics (pore size and porosity).
12
As
shown in the SEM pictures of Figure 1, the microcap-
sules and binder fill up pores of the treated fabric and,
consequently, change the surface morphology and in-
crease the thickness of the fabric. These changes lead
to a decrease in the air permeability and moisture
vapor permeability. The moisture vapor permeability
determines heat released by means of evaporative
heat reflux
15
and affects the formation of condensation
in a garment system.
12
Therefore, the reduction of the
moisture vapor permeability affects the thermal com-
fort of a garment adversely. For better comfort prop-
erties, we need to explore fabric treatment methods
that do not block pores of the fabric too much. On the
other hand, the treated fabrics become more hygro-
scopic with increasing add-on. The moisture regain of
the treated fabric with 22.9% add-on increases up to
228% in comparison with that of the untreated sample.
More hygroscopic material removes sweat more effec-
tively from the skin or adjacent environment and
helps with more effective wet heat loss through evap-
oration, leading to a pleasant microclimate in cloth-
ing.
16
It has been speculated that the hydrophilicity of
the treated fabrics increases because of methylol
groups in the shell material (melamine–formalde-
hyde) of the microcapsules
17
and hydrophilic binder.
Low-stress mechanical properties and hand
Table III shows the low-stress mechanical properties
of the treated fabrics versus the add-on of microcap-
sules. The tendency of curling on the edge of the
control knit fabric prevented us from measuring its
tensile energy (WT) low-stress mechanical properties.
Therefore, comparisons are made between the treated
fabrics with different levels of add-on.
The tensile properties indicate the extensibility and
recoverability of fabric from external stress.
14
As the
add-on increases, the tensile linearity (LT) increases,
and this results in a stiffer feel at a higher add-on. The
tensile resilience (RT) decreases as the add-on in-
creases up to 18.1%, and this indicates the reduction of
recoverability from tensile deformation.
The bending properties are related to the wear per-
formance of clothing, including wrinkle properties
and drapability. The bending stiffness (B) and bending
hysteresis (2HB) increase as the add-on increases. The
treated fabrics become stiffer and more inelastic in
bending with the increase of add-on.
The shear properties are accompanied by biaxial
tensile properties and also are related to the drapabil-
ity and shape of clothing.
14
The shear rigidity (G),
shear hysteresis (2HG), and shear hysteresis at a 5°
shear angle (2HG
5
) also increase with the increase of
add-on. A larger Gvalue makes the fabric stiff, and a
larger 2HG value causes inelastic behavior in shear-
ing. A larger 2HG
5
value causes inelastic properties in
Figure 2 Air permeability of the treated fabrics versus the
microcapsule add-on.
Figure 3 Moisture vapor permeability of the treated fabrics
versus the microcapsule add-on.
Figure 4 Moisture regain of the treated fabrics versus the
microcapsule add-on.
THERMOREGULATING TEXTILE MATERIALS. IV 913

shearing and wrinkling problems. Both the bending
and shear properties increase with the increase of
add-on, and this indicates a decrease in the recovery
from deformation and elasticity.
The compression properties are related to the full-
ness and bulkiness of the fabric. The linearity in com-
pression (LC) increases as the add-on increases. A
larger LC value causes a hard feeling in compression.
The compression energy (WC) is similar, regardless of
the add-on. The compressional resilience (RC) de-
creases with an increase in the add-on. This means
that recoverability from compressional deformation
decreases as the add-on increases, so the treated fab-
rics show inelastic compression properties. It is
thought that the bulkiness of the treated fabrics de-
creases because of the reduction of recovery from
compressional deformation as the add-on increases.
The surface properties are related to the smoothness
of the fabric. As the add-on increases, the frictional
smoothness (MIU) decreases and then increases at
22.9% add-on, whereas the geometrical roughness
(SMD) increases and then decreases at 22.9% add-on.
The surface frictional roughness (MMD) increases
with the increase of the add-on. As shown in Figure 1,
at a lower add-on, the microcapsules exist sparsely in
the intersection of yarns, and this results in a rough-
ening effect on the fabric surface. This roughening
surface might impart more contact points between the
fibers and yarns and thus enhance the fiber-to-fiber
and yarn-to-yarn interfriction.
18
On the other hand, at
a higher add-on (22.9%), the microcapsules and binder
fill up more interstices between fibers or yarns and
spread into a more continuous form on the fabric
surface; this reduces SMD. Kim and Cho
10
found that
the surfactant treatment made fabrics smoother and
softer even though the add-on was increased, and a
better THV resulted.
Figure 5 shows the effects of the add-on on primary
HVs. Koshi is a feeling combined mainly with Band is
influenced by bending and shear properties. It is re-
lated to a moderate space between the human body
and the outer garment that allows freer body move-
ments.
15
Numeri indicates smoothness and softness,
which are influenced by the surface properties. Fuku-
rami indicates bulkiness and resilience and is related
to the compression properties. As the add-on in-
creases, Koshi increases because of the increase in the
bending and shearing properties. The reduction of
MIU and the increase in the roughness can be attrib-
uted to the reduction of Numeri. On the other hand,
Fukurami decreases because of the increase in LC and
the decrease in RC with an increase in the add-on.
Overall, THV decreases with an increase in the add-
on, as shown in Figure 6. THV of the treated fabrics
TABLE III
Low-Stress Mechanical Properties of the Treated Fabrics
Mechanical properties
Add-on (%)
5.3 11.1 18.1 22.9
Tensile LT 0.590 0.697 0.723 0.746
WT (gf cm/cm
2
)22.29 26.43 26.26 22.45
RT 44.08 35.68 33.96 35.43
Bending B(gf cm
2
/cm) 0.175 0.187 0.189 0.255
2HB (gf cm
2
/cm) 0.1726 0.1909 0.1920 0.2051
Shear G(gf/cm deg) 1.08 1.09 1.20 1.36
2HG (gf/cm) 3.03 3.11 3.70 3.97
2HG5 (gf/cm) 3.14 3.28 3.86 4.25
Compression LC 0.498 0.447 0.495 0.501
WC (gf cm/cm
2
)0.277 0.281 0.278 0.281
RC 52.77 52.01 49.60 47.21
Surface MIU 0.322 0.316 0.239 0.297
MMD 0.0272 0.0303 0.0420 0.0529
SMD (
␮
) 6.93 7.35 7.93 7.66
WT ⫽tensile energy
Figure 5 Primary HV of the treated fabrics versus the
microcapsule add-on: (F) Koshi, (E) Numeri, and (Œ) Fuku-
rami.
914 SHIN, YOO, AND SON

ranges from 3.91 to 2.90, being above average (3.0) and
slightly below average on Kawabata’s scale from 0
(not useful) to 5 (excellent). For better hand of the
treated fabric, the inclusion of a softener in the treat-
ment bath formulation might be considered as for
durable-press and flame-retardant finishes.
CONCLUSIONS
The heat storage capacity of treated fabrics increases
with an increase in the microcapsule add-on. A treated
fabric with 22.9% add-on is capable of absorbing 4.44
J/g of heat if the microcapsules on the fabric undergo
a melting process. The air permeability and moisture
vapor permeability decrease by 28 and 20%, respec-
tively, at 22.9% add-on. The moisture regain of the
treated fabrics increases progressively up to 228% in
comparison with that of the control fabric. As the
add-on increases, Koshi increases, whereas Numeri
and Fukurami decrease. Overall, THV decreases.
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Figure 6 THV of the treated fabrics versus the microcap-
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THERMOREGULATING TEXTILE MATERIALS. IV 915