Bicomponent sheath-core fibers, acquisition distribution layer, hygiene product, through-air bonded nonwovens

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https://doi.org/10.1177/1558925019885497
Journal of Engineered Fibers and Fabrics
Volume 14: 1­
–8
© The Author(s) 2019
DOI: 10.1177/1558925019885497
journals.sagepub.com/home/jef
Introduction
Nonwoven fabrics are specific types of porous structure
composed of fibers that are bonded together by mechani-
cal, thermal, or chemical agents. Nonwovens occupy the
critical status in the whole textile industry because of their
short processing, massive products, low cost, and wide
raw material.1–3 Thermal bonding is a method of bonding
the web using thermal energy. The principle of through-air
bonded nonwoven material is that most of the high-molec-
ular polymers are thermoplastic, they will soften and melt
when heated to a certain temperature, become viscous flu-
ids with certain flow properties, and then re-solidified after
cooling.4 Bicomponent fibers consist of core and sheath
part with two different melting points. They are widely
used in the through-air bonding process for bonded
nonwoven production. The core part of the bicomponent
fiber has a high melting point and provides structural rigid-
ity of the web, and the sheath of the fiber has a low melting
point and easily melts and bonds the fibers together.5,6
Increased use of diapers in consumer applications as a
result of modernization and increased consumer awareness
has led to a big market among personal hygienic products.7
Figure 1 shows the basic structure of a diaper. Constant
Preparation and properties of eccentric
hollow fiber nonwovens for acquisition
distribution layer
Huan Liu, Yan Feng and Xiaoming Qian
Abstract
Through-air bonding is one of the thermal methods of bonding fibers in the production of nonwoven webs, and they
are widely used in disposable sanitary products, especially in the acquisition distribution layer of diapers. In this article,
the through-air bonded nonwoven fabrics were successfully prepared by ethylene–propylene fibers (polyethylene and
polyethylene terephthalate (PE/PET)) and eccentric hollow fibers (PE/PET). The influence of process parameters such as
the ratio of fibers was discussed for performance of through-air bonded nonwoven. Besides, the surface morphology,
physical characteristics (thickness and breaking strength), air permeability, moisture permeation, liquid permeability, and
absorption properties test of the nonwoven fabrics were investigated. The results demonstrated that the addition of
eccentric hollow fiber increased the permeability, mechanical property, and the core absorption effect of the through-
air bonded nonwovens. According to the results, the fabrics made of eccentric hollow fibers have good absorption and
liquid transfer characteristics; the permeation time and wetback were found to be 0.85 s and 0.03 g, respectively.
Keywords
Bicomponent sheath-core fibers, acquisition distribution layer, hygiene product, through-air bonded nonwovens
Date received: 4 July 2019; accepted: 9 October 2019
School of Textile Science and Engineering, Tianjin Polytechnic
University, Tianjin, China
Corresponding author:
Yan Feng, School of Textile Science and Engineering, Tianjin Polytechnic
University, Tianjin 300387, China.
Email: fengyan@tjpu.edu.cn
885497JEF0010.1177/1558925019885497Journal of Engineered Fibers and FabricsLiu et al.
research-article2019
Original Article

2. 2 Journal of Engineered Fibers and Fabrics 
rise in disposable income and various initiatives taken by
the manufacturers to increase awareness among parents
for baby hygiene in the emerging economies have fueled
the growth of the global baby diaper industry.8,9
Qualifications necessary for a baby diaper determined by
subjective panel tests are softness, elasticity, thickness,
and necessary wet strength in the cross direction (CD).
Although there are many advantages on the use of dia-
pers, it may also form a moist environment after wearing
for a long time, causing skin diseases or diaper rash.10–12
Therefore, the usability of diaper needs to be improved to
get a product having quick penetration of liquid and a low
infiltration rate. Acquisition distribution layer (ADL) is
the nonwoven material sandwiched between the top sheet
and the absorbent core layer, and its function is to acceler-
ate the penetration and diffusion of liquid and reduce the
liquid infiltration.13 As shown in Figure 2, the liquid pen-
etrates from the top sheet to the ADL and is diffused uni-
formly by the wicking effect of the ADL. Then, it is
absorbed and stored by the absorbent core under pressure
and gravity. In use process, the ADL provides a temporary
reservoir for each liquid occurring in the sheet layer, and it
leads to a complete release and movement of the liquid
into the absorption core layer. This prevents the pooling of
the liquid against the wearer’s skin, reduces the leakage of
liquid from the absorbent structure, and provides improved
dryness and comfort to the wearer.14–16 Nonwoven fabric
with the ADL should have the characteristics of fast liquid
penetration and excellent liquid diffusion. In the early
days, spunbonded nonwovens or perforated films were
mainly used as the ADL, but in recent years, through-air
bonding nonwoven was mainly used. In order to improve
the visual effect, nonwovens of different colors were also
used as the ADL. It is the developing trend to increase the
velocity, enlarge the area, and distribute the liquid evenly.17
In this article, the properties of through-air bonded non-
woven fabric made of eccentric hollow fiber and ethylene–
propylene (ES) fiber are studied. In addition, the effect of
the eccentric hollow fiber ratio on the thickness, air perme-
ability, solution absorption performance, and liquid per-
meability of nonwoven was discussed.
Experimental
Materials
Thermoplastic synthetic fibers are usually used as raw
materials for through-air bonded nonwoven materials.
When selecting the fibers, the thermal properties of the
main structure of the fiber and the bonding components
should be considered. In order to reduce the thermal
shrinkage of the main fiber as much as possible, the
original performance of the fiber was maintained.
Figure 1. The structure of a diaper.
Figure 2. The sketch diagram of ADL working principles in a
diaper.

3. Liu et al. 3
Therefore, the performances of fibers were tested to
provide a theoretical basis for the processes. The main
fibers were provided by Beijing Jinglan nonwoven fab-
rics Co., Ltd, and the detailed information of the fibers
was shown in Table 1.
Preparation of through-air bonded nonwovens
The current investigation involved a series of seven non-
woven fabrics including different fiber sizes, cross-
sectional shapes, and their percentages to measure their
basic physical properties, liquid permeability, absorption
properties, and so on. Figure 3 shows the process of
through-air bonded nonwovens. Fibers were passed
through the opening machine before being fed manually to
the feed belt on the carding machine, where the openers
ensure the raw material opening, cleaning, and blending.
All the fabrics were carded by AS181A carding machine
and bonded through the hot air. Seven samples were pre-
pared in this experiment, and the ratios of ES fiber/eccen-
tric hollow fiber were varied with 100:0, 80:20, 60:40,
50:50, 40:60, 20:80, and 0:100 wt% (Table 2). The density
of the samples was 30 g/m2. The temperature of the hot air
was set at 135°C with a motor frequency 25 Hz and heating
time of 3 mins.
Testing and characterization
ES fibers, eccentric hollow fibers, and nonwoven webs
were characterized by different tests. Almost all the tex-
tile testing was carried out at standard atmosphere, with
temperature of 21
±
2°C and relative humidity of
65 ± 3%.
Differential scanning calorimetry. The differential scanning
calorimetry (DSC) was used to evaluate the thermal prop-
erties of the raw materials. The testing was carried out
using the DSC 200F3 (NETZSCH Co., Ltd., Selb, Ger-
many) thermal analysis system, and the thermogram signal
was derived from the temperature difference between the
sample and the reference. Samples were heated at a heat-
ing rate of 10°C/min in nitrogen supply of 100
mL/min.
Polymer bonding temperature ranges were selected based
on the melting information of polymers.
Scanning electron microscopy. Scanning electron micros-
copy (SEM) images of the fiber surface and the webs after
bonding were taken using the TM3030 scanning electron
microscope (Hitachi Co., Ltd., Japan). The sample is glued
to the sample table with conductive adhesive and coated
with a layer of gold for easy observation.
Thickness. The thickness of a nonwoven fabric can be
defined as the distance between the front and back of the
material measured as the distance between a reference plate
on which the nonwoven rests and a parallel presser-foot that
applies a pressure to the fabric. The thickness of the through-
air bonded nonwoven was determined according to the GB/
Table 1. Characteristics of the raw fibers.
Fibers properties Concentric sheath/core
bicomponent fibers
Eccentric hollow sheath/
core bicomponent fibers
Ingredient PE/PET PE/PET
Fineness (dtex) 1.35 2.52
Mean length (mm) 51 51
Eccentricity (%) 0 54.9
Hollow ratio (%) 0 9.5
Fiber tenacity (cN/dtex) 3.46 2.23
Fiber elongation (%) 28.25 57.23
PE: polyethylene; PET: polyethylene terephthalate.
Figure 3. The process of through-air bonded nonwoven.
Table 2. Samples with different fiber mixing ratios.
The serial number of samples 1 2 3 4 5 6 7
The ratios of ES fiber (%) 100 80 60 50 40 20 0
The ratios of eccentric
hollow fiber (%)
0 20 40 50 60 80 100
ES: ethylene–propylene.

4. 4 Journal of Engineered Fibers and Fabrics 
T3820-1997 using a fabric thickness tester (YG 414LA; Lai
Zhou electronic instrument Co., Ltd).
Tensile strength. The tensile strength and elongation at
break of the through-air bonded nonwoven were deter-
mined according to QB/T 2710–2005 using a Tensile
Tester (Instron 3369; America Instron Co., Ltd).
Air permeability. Air permeability is described as the rate of
air flow passing perpendicularly through a known area,
under a prescribed air pressure differential between the
two surfaces of a material. Tests were performed according
to the standard GB/T5453-1997 using a YG461H air per-
meability tester (Ningbo Textile Instrument Factory,
Ningbo, China). The air pressure differential between the
two surfaces of the material was 100 Pa.
Water vapor permeability. The water vapor permeability
was determined on the Water Vapor Permeability Tester
YG216-II (Wenzhou Darong Textile Instrument Co., Ltd.,
Wenzhou, China), according to GB/T12704. The cup
method is a very common method for testing the moisture
transfer ability of nonwovens.18 When vapor passes through
a textile layer, two processes are involved: diffusion and
sorption–desorption. Water vapor diffuses through a textile
structure in two ways, simple diffusion through the air
spaces between fibers and yarns and along the fiber itself.19
The liquid absorption rate. The liquid absorption ratio refers to
the ratio of the amount of liquid absorbed by the sample to its
own weight after it is completely immersed in the liquid for a
certain period. It was performed in accordance with the GB/T
6529. The liquid absorption rate is expressed as follows
La
M M
M
=
−
×
2 1
1
100%
whereLa(%) = Liquidabsorptionrate(%),M1 = Average
dry weight of samples (g), and M2 = Average wet weight of
samples (g).
The liquid holdup rate. The liquid holdup is the ratio of wet
weight to dry weight of the sample under the action of 1.2-
kg standard compaction after a period of complete wetting.
It was performed in accordance with the GB/T 6529. The
liquid holdup rate is expressed as follows
Lh
M M
M
=
−
×
3 1
1
100%
where Lh (%) = Liquid holdup rate (%), M1 = Average dry
weight of samples (g), and M3
=
Average wet weight of
samples after pressure action (g).
Liquid strike-through time and rewet. Under specified condi-
tions, 5
mL of simulated urine flows to the nonwoven
fabric sample, which is placed on the standard absorber
pad. The liquid flow rate is 5 mL/s (blank experiment). The
liquid strike-through time (STT) and rewet of the ADL
materials were determined according to GB/T 24218.8-
2010 using an instrument for measurement of liquid STT
and rewet. (Lister AC Model: L6141; Austria Lan Jing
Testing Instrument Co., Ltd).
Results and discussion
The thermal performance of raw fiber
Thermal stability of the ES fiber and eccentric hollow fiber
were studied by DSC, and the results are shown in Figure 4.
Through the DSC testing, the physical properties such as
the melting point and the crystallization temperature of the
raw fibers were obtained. As can be seen from the figure,
the two melting peaks correspond to the sheath and core
structure of the fiber, respectively. The raw fibers were
made up of the sheath part (PE) whose melting point is
about 127°C and core part (PET) whose melting point is
about 262°C. Through the DSC analysis, the basis for hot
air process could be provided.
SEM analysis
SEM has been proved to be a useful tool for studying fiber
morphology features including cross-sectional and surface
features. Figure 5(a) and (c) showed the surface of eccen-
tric hollow fiber and ES fiber. Both ES fiber and eccentric
hollow fiber have smooth and flat longitudinal structure.
Figure 5(b) and (d) showed the cross-section of the eccen-
tric hollow fiber and ES fiber. Both are composed of two
kinds of polymers; the difference is that the two compo-
nents of ES fiber are symmetrically distributed, while the
eccentric hollow fiber is asymmetrically distributed, and
there is a cavity structure in the core part.
The surface morphologies ofADL materials are shown in
Figure 6. It can be observed that the fiber overlapped parts in
the web form a “point bonding” state through hot-melt bond-
ing. Moreover, the unconnected parts still maintain the origi-
nal structural state. The fibers have a certain crimp structure,
enabling the fibers to cross-link with each other.
Effects of the fiber blending ratio on
performance of the hot-air through nonwoven
The influence of different blending ratios on the performance
of the hot-air through nonwoven is examined in this section.
Figure 7 shows the flow of liquids in the ADL and illustrates
the advantages, and then, following is a detailed analysis.
Thickness of ADL. The results of the thickness test demon-
strated that there is a good correlation between thickness
and the content of eccentric hollow fiber of the fabrics. As
shown in Figure 8, with the increase of the content of the

5. Liu et al. 5
eccentric hollow fiber, the thickness and fluidity of the
ADL material increase gradually, which is beneficial to
absorb and store liquid. The reason is that the asymmetric
structure of the eccentric hollow fiber causes the fiber to
crimp when it was heated, which makes the thickness of
the ADL material to increase.
Figure 4. DSC curve of ES fiber and eccentric hollow fiber.
Figure 5. SEM images of fiber for (a) surface and (c) cross-section of eccentric hollow fiber, (b) surface and (d) cross-section of ES
fiber.

6. 6 Journal of Engineered Fibers and Fabrics 
Strength of ADL. Figure 9 shows the tensile strength of a
series of diversion layer materials. The results indicate that
the maximum tensile strength of through-air bonded non-
woven occurs when the fiber ratio is composed of
0/100
wt%. Most fibers in through-air bonded nonwoven
have been arranged along the machine direction (MD);
therefore, the tensile strength along the MD is higher than
that along the CD.
Air permeability and water vapor transmission rate ofADL. Air
permeability is a very important parameter for ADL mate-
rials. As may be seen in Figure 10, the air permeability was
higher for samples with higher content of the eccentric
hollow fiber. Highest air permeability makes the sample
preferable for hygiene products. The highest air permea-
bility result was obtained by using sample 7 due to its
highest thickness and bulkiness. The water vapor transmis-
sion rate and air permeability have the same trend; both
Figure 7. The advantages of eccentric hollow fiber in ADL.
Figure 8. The thickness of ADL for various fiber sizes at
different ratios.
Figure 9. The strength of ADL for various fiber sizes at
different ratios.
Figure 6. SEM image of the ADL material made of (a) ES fiber and (b) eccentric hollow fiber.

7. Liu et al. 7
became better with the increase of the eccentric hollow
fiber content in the samples.
Liquid STT and wetback of ADL. The liquid absorption and
holding behaviors of ADL materials play a very substantial
role in the functional properties of diapers. This part mainly
compares the liquid penetration performance of different
samples, mainly including liquid STT and wetback. The
ADL of diapers needs to have excellent liquid penetration
performance to ensure the dry skin of infants. Eccentric hol-
low fiber is a kind of irregular cross-sectional fiber, and the
core layer has a cavity structure, which increases the surface
area of the fiber and has good effect on water absorption, and
at the same time, liquid is locked up by the absorption core.
The STT and wetback capacity of the samples with dif-
ferent fiber cross-sections and blending ratios was shown
in Figure 11. It can be observed in the figure that with the
increase of the content of eccentric hollow fibers in the
sample, the liquid STT becomes shorter. There are many
factors that may account for this result, and the following
are the typical ones. When the samples have the same sur-
face density, samples made from coarse denier fibers have
large aperture. In terms of fast wicking process, the coarse
capillaries are decisive. So, the liquid penetration time is
shorter. The samples made with eccentric hollow fiber are
fluffy because of the three-dimensional crimp structure.
The distribution of fibers in the vertical direction is rela-
tively increased, which is conducive to liquid permeabil-
ity.20,21 The liquid holdup rate of several samples is similar,
and the minimum wetback reaches 0.03 g.
Liquid absorptive capacity of ADL. The general purpose of
the liquid absorptive capacity test was to study the influ-
ence of fiber materials on the absorbency behavior of the
through-air bonded nonwoven. In this study, the liquid
absorption rate and liquid holdup rate of the samples were
measured, and the results were shown in the Figure 12. It
can be observed that sample 1 has the lowest
liquid absorption rate (2468%), and with the increase of
the content of eccentric hollow fiber, the liquid absorption
rate of the sample increases gradually. Then, the highest
liquid absorption rate of sample 6 was 3712%. Fiber cross-
sectional shape is one of the determining factors of the
geometric configuration of nonwoven’s pore structure.
These attention-grabbing fibers have typically focused on
providing high surface area and surface capillary which
are beneficial to the liquid absorbency of the material.18,19
The liquid-holding capacity of the samples with differ-
ent fiber cross-sections and fiber mixed percentages was
shown in Figure 12. It can be observed in the figure that the
sample 1 has the highest liquid holdup rate (58.6%). We
can see that with the increase of the content of eccentric
hollow fiber, the liquid holdup rate of the sample reduced
gradually. Then, the minimum liquid holdup rate of sample
7 was 38.1%. There are many causes of this phenomenon;
ES fiber acts as a smaller pore size with higher capillary
pressure; therefore, they can retain the liquid. As a material
for theADL, a smaller liquid holdup rate after being pressed
Figure 10. The air permeability and water vapor transmission
rate of ADL for various fiber sizes at different ratios.
Figure 11. The liquid strike-through time and wetback of
ADL for various fiber sizes at different ratios.
Figure 12. The liquid absorptive capacity of ADL for various
fiber sizes at different ratios.

8. 8 Journal of Engineered Fibers and Fabrics 
was expected, which can prevent the liquid back to the sur-
face layer, thus ensuring the dryness of the baby’s skin.
Conclusion
The main objective of this study was to improve the perfor-
mance of ADL materials made by ES fiber (polyethylene
and polyethylene terephthalate (PE/PET)) and eccentric
hollow fiber (PE/PET) bonded by hot air. Exploring the
effect of the ratio of two fiber blends on the properties of
ADL materials, the liquid permeability, liquid absorption
and other properties of ADL materials were tested, respec-
tively. From the results, it was found that the absorption and
penetration performances of ADL were greatly improved
by the permanent crimp eccentric hollow fiber structure. In
terms of performance, the ADL materials made of eccentric
hollow fiber are superior to ES fiber. According to our
study, the shortest liquid STT of samples was 0.85
s, the
rewet was 0.03 g, the fluid absorption rate was 3712%, and
the liquid holdup rate was 38.1%. Eccentric hollow fiber
can promote the level of the hygiene nonwoven products
and enrich the variety of hygiene products.
Acknowledgements
The authors gratefully acknowledge the support by the Beijing
Jinglan nonwoven fabrics Co., Ltd for experiment.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of this
article.
Funding
The author(s) received no financial support for the research,
authorship, and/or publication of this article.
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