Influence of loop length on microcapsule distribution in cotton interlock knitted fabric

Journal of Science & Technology 143 (2020) 056-060 
56 
Influence of Loop Length on Microcapsule Distribution 
in Cotton Interlock Knitted Fabric 
Dao Thi Chinh Thuy, Chu Dieu Huong* 
Hanoi University of Science and Technology - No.1 Dai Co Viet, Hai Ba Trung, Hanoi, Viet Nam 
Received: February 28, 2020; Accepted: June 22, 2020 
Abstract 
Functional textile using microcapsules has been taken lots of interest all over the world. Along with 
microcapsules, the textile substrate contributes important part to the performance of end use products. This 
study was to investigate the effect of loop length on the microcapsule distribution in cotton interlock knitted 
fabric. Four levels of loop length studied were 2.83, 2.87, 2.96 and 3.05mm. Microcapsules were applied to 
fabrics by coating technique. The microcapsule distribution in the treated fabric was expressed by the 
average area of microcapsule aggregates on the fabric surface, which was determined by Meander 3.1.2 
software of Peacock Media on the SEM images. The results showed an increase of microcapsule aggregate 
area in the order of 7537, 8600, 13379 and 16020 µm2 for the loop length of 2.83, 2.87, 2.96 and 3.05 mm, 
respectively. This revealed the less even distribution of microcapsules at the higher loop length. The 
principle of coating technique, as well as the higher porosity of the fabric at higher loop length, were thought 
to account for this trend. 
Keywords: loop length, knitted loop model, microcapsule, functional textile. 
1. Introduction 
The functional textile using microcapsules has 
been researched and applied widely in the recent 
years. Microcapsules are microparticles in which 
solid, liquid or gaseous active ingredients (the core) 
are packaged within the second materials (the shells 
or the membranes). The main advantage of them is to 
control the release of active ingredients and to protect 
the active ingredients from surrounding environment 
[1], [2]. Due to their advantages, microcapsules have 
been used in many fields of functional textile such as 
medical textile, fragrant textile, cosmetic textile, 
flame retardant textile and thermo-regulating 
textile [3]–[7]. 
In the functional textile using microcapsules, the 
fabric substrate plays a very important role because 
the change in fabric structural parameters will alter 
the properties and then the performance of the end 
product. 
N. Carreras et al. [3] studied the influence of 
textile material on the microcapsule loading 
capability of four kinds of woven fabrics that were 
cotton, polyamide, acrylic and polyester. Those 
fabrics were padded with PCL microspheres 
containing ibuprofen, the microcapsule loading 
capability of them were 4.30, 4.36, 4.64 and 5.65%, 
respectively. According to the authors, with the same 
* Corresponding author: Tel.: (+84) 3868.1997 
Email: huong.chudieu@hust.edu.vn 
pick-up value, the microcapsule loading capability of 
polyester fabric (5.65%) was higher than that of 
cotton fabric (4.30%) because the crystalline structure 
and the hydrophobicity of polyester fabric made it 
have higher affinity with microcapsules than cotton 
fabric. The yarn count, the weft yarn density and the 
woven structure were also reported to affect the 
microcapsule loading capability of woven fabrics [4]. 
According to F. Salaun et al. [6], the distribution 
of melamine formaldehyde microcapsules, which 
were padded to fabrics, depended on the textile 
materials with all three types of binders (Alcoprint 
PB-66, Dicrylan PMC and Airflex EN428). Due to 
the high wetting ability of polyester with the binder 
solutions, the binders wrapped the fibers 
homogenously throughout the fabric, so the 
microcapsules could enter the inner structure of the 
fabrics. Contrarily, the low wetting ability of cotton 
with the binder solutions made the binders form a 
thin film over the fabric surface and could not 
penetrate the pores of the fabrics, therefore the 
microcapsules were only distributed on the surface of 
the fabrics. Beside the textile material, the method of 
fabric construction also affected the microcapsule 
distribution on the fabrics. In the research of B. Golja 
et al. [5], the melamine formaldehyde microcapsules 
containing flame - retardant agent were coated to 
nonwoven polyester and woven cotton fabric. The 
woven cotton fabric was almost completely covered 
with microcapsules while on the nonwoven polyester 
fabric, most microcapsules were captured in the 
Journal of Science & Technology 143 (2020) 056-060 
57 
nooks among the fibers and only a few microcapsules 
were located on the fibers. 
In the previous study [7], we investigated the 
change in microcapsule distribution and active release 
capability of three kinds of interlock knitted fabric 
that were cotton, peco 65/35 and polyester. The 
eudragit RSPO microcapsules containing ibuprofen 
were applied to the fabrics by impregnating 
technique. The surfaces of the treated-fabrics were 
captured by SEM. The SEM images showed many 
microcapsule aggregates in all three kinds of fabric. 
The microcapsule aggregate is a big disadvantage for 
the targeted application since it reduces the total 
surface area of microcapsules and may prevent the 
release of ibuprofen from the microcapsules deep 
inside the aggregate. The software Meander 3.1.2 of 
Peacock Media was used to determine the area of the 
microcapsule aggregates. The average area was 
78891, 49408 and 38850 m2 for cotton, peco 65/35 
and polyester, respectively. Due to the decrease in the 
size of microcapsule aggregates, the weight 
percentage of ibuprofen released from the treated 
fabric after 24 hours increased. It was 37.3, 42.2 and 
50.9% from cotton, peco 65/35 and polyester. 
In the interlock knitted fabric, loop length is the 
most important structural parameter because it affects 
many properties of the fabric such as the elongation, 
the strength, the air permeability  Another our 
previous study [8] has shown the effect of loop length 
on the microcapsule loading capability of interlock 
knitted fabric. For the cotton interlock fabric, the loop 
length varied over five levels of 2.81, 2.83, 2.87, 2.96 
and 3.05 mm. For the CVC interlock fabric, the loop 
length was 2.65, 2.80 and 2.95 mm. The eudragit 
RSPO microcapsules containing ibuprofen were 
applied to the fabrics by coating technique. The 
results showed that in both the cotton and the CVC 
fabrics, increasing the loop length made the surface 
density of fabric lower and the porosity of fabric 
higher, resulting in higher microcapsule loading 
capability. 
To continue revealing the influence of loop 
length on the characteristics of microcapsule-treated 
fabric, in this research we will study the influence of 
loop length on the microcapsule distribution in the 
cotton interlock knitted fabric. 
2. Material and Experimental method 
2.1. Material 
2.1.1. Cotton interlock knitted fabric 
 Five lots of interlock fabric were knitted from 
cotton yarn Ne40. The knitting process was 
conducted on circular knitting machine Fukahara 
(knitting gauge E18) with the loop length of 2.83, 
2.87, 2.96 and 3.05 mm. These values of loop length 
are chosen according to the dimensional stability of 
the fabric. The grey fabrics were then scoured and 
bleached under similar conditions. All the knitting, 
scouring and bleaching processes were carried out at 
Doximex Knitting Company. 
Table 1. Structural parameters of cotton interlock 
knitted fabrics 
Code of fabric lot B1 B2 B3 B4 
Yarn count Ne40 Ne40 Ne40 Ne40 
Loop length (mm) 2.83 2.87 2.96 3.05 
Course density 
(number of 
courses/10cm) 
188 186 178 173 
Wale density 
(number of 
wales/10cm) 
152 150 148 143 
Area density 
(number of 
loops/cm2) 
286 279 263 247 
Mass per unit area 
(mg/mm2) 
0.240 0.230 0.230 0.220 
Porosity (%) 81.0 81.6 81.8 82.6 
2.1.2. Ibuprofen - loaded microcapsules 
 The ibuprofen - loaded microcapsules were 
elaborated by solvent evaporation method. Eudragit 
RSPO was used as the polymer shell, quillaja saponin 
was used as the natural surfactant and ethyl acetate 
was used as the non - halogenated solvent. The 
microcapsules exhibited spherical shapes with the 
mean diameter of around 21.5 µm (Fig. 1). 
Fig. 1. SEM image of the ibuprofen - loaded 
microcapsules 
2.2. Experimental method 
2.2.1. Apply microcapsules to the fabric 
 Microcapsules were applied to the fabric by 
coating technique, using the experimental coating 
equipment Mini Coater (DaeLim Starlet Co.,Ltd - 
Korea). 
The main coating parameters: 
Journal of Science & Technology 143 (2020) 056-060 
58 
- Type of coating formulation: dispersion of 
microcapsule in distilled water 
- Microcapsule concentration: 14 mg/ml 
- Coating rate: 40 mm/second 
- Fabric sample dimensions: 20 x 20 cm 
- Coating distance: 15 cm 
Microcapsule-coated fabric was vacuum dried at 
45oC in the vacuum drier OV-11 of Jeio Tech Co., 
Inc (Korea) until completely dried. 
2.2.2. Evaluate the microcapsule distribution on the 
fabric 
The microcapsule - treated fabric was observed 
by scanning electron microscope (SEM) JEOL JSM-
7600F (USA) under the low magnification mode at 2 
kV with the working distance of 8.0 mm. 
Both the lower side and the upper side of the 
fabrics were captured. The upper side is the fabric 
surface just under the coating blade and the lower 
side is the other. 
The microcapsule distribution was evaluated 
according to the area of the microcapsule aggregates 
on SEM image, which was determined by the 
software Meander 3.1.2 of Peacock Media. For each 
level of loop length, the average area of microcapsule 
aggregates was deduced from the values obtained by 
three SEM images. The SEM images were taken at 
the center (dimension of 3 mm x 3 mm) of each 
treated fabric sample. In the SEM images, only the 
aggregates bigger than 2000 µm2 were taken into 
consideration. 
2.2.3. Determine the content of microcapsule per 
fabric area 
The microcapsule content per fabric area, 
abbreviated by M (mg/cm2), was used to explain the 
influence of loop length on the microcapsule 
distribution in the fabric. It was calculated by the 
calculation (1) as below: 
 =
 
15 × 20
(1) 
In which: 
- M1 (mg): the weight of fabric sample before 
the microcapsule treatment 
- M2 (mg): the weight of fabric sample after the 
microcapsule treatment 
- 15 (cm) was the coating distance or the length 
of fabric sample coated with microcapsules. 
- 20 (cm) was the width of fabric sample coated 
with microcapsules. 
A 
B 
C 
D 
Fig. 2. SEM images of the upper side of 
microcapsule-treated fabrics B1 (A), B2 (B), B3 (C), 
B4 (D) 
 : microcapsule aggregates 
Journal of Science & Technology 143 (2020) 056-060 
59 
The measurement was triplicated for each level 
of loop length. 
3. Result and discussion 
 The SEM images of fabric upper side are shown 
in Fig. 2A-D. The images reveal a lot of individual 
microcapsules as well as microcapsule aggregates on 
the fabric upper surface. 
The SEM images of the lower side of B1 fabric 
(the lowest loop length at 2.83 mm) and B4 fabric 
(the highest loop length of 3.05 mm) are presented at 
Fig. 3A, B: 
A 
B 
Fig. 3. SEM images of the lower side of the fabrics 
B1 (A) and B4 (B) 
 : microcapsules 
Comparing Fig. 2 to Fig. 3, it could be seen that 
most microcapsules located at the upper side of the 
fabrics. In the area of 318 x 424 µm, only few 
microcapsules with very small size (below 5 µm) 
were observed on the lower surface of the fabric B1 
(lowest loop length at 2.83 mm). It was only 60 
microcapsules with diameter below 10 µm for the 
fabric B4 (highest loop length at 3.05 mm). In 
contrast, in the same area of fabric, there were 
hundreds of microcapsules on the upper side of all 
fabrics from B1 to B4. Because the microcapsules 
were applied to the fabrics by coating technique, 
which exerted no force to the fabric surface, it was 
difficult for the microcapsules to go inside the fabric 
structure. Instead, most of them were kept just on the 
fabric upper surface. Therefore, in the following 
parts, just the microcapsule distribution on the upper 
side of the fabrics will be considered. The term 
“fabric surface” hereinafter can be understood as the 
upper side of the fabric. 
The formation of microcapsule aggregates on the 
fabric surface was explained in our previous study 
[7]. Since the microstructure of the fabric surface is 
always bumpy, the microcapsules can certainly not be 
distributed evenly on the fabric, resulting in a number 
of microcapsules laying closely to each other after the 
coating process. Furthermore, the high hydration rate 
of wet microcapsules (40%) favors the deformation 
of the microcapsules. Hence, the microcapsules lying 
closely to each other after the coating process could 
stick together to create large microcapsule aggregates, 
which are even weaker and easier to be deformed by 
drying than the smaller individual ones. Also, as be 
mentioned, the microcapsule aggregate is an obstacle 
for the release of active ingredient from the end 
product. 
The microcapsule distribution on the fabric 
surface was expressed by the average size of the 
microcapsule aggregates, which altered by the change 
in loop length as in the chart at Fig. 4 below: 
Fig. 4. Average area of microcapsule aggregates 
according to the loop length 
Fig. 5. Microcapsule content per fabric area 
according to the loop length 
7537
8600
13379
16020
0
2.000
4.000
6.000
8.000
10.000
12.000
14.000
16.000
18.000
2,83 2,87 2,96 3,05
A
v
er
ag
e 
ar
ea
 o
f 
m
ic
ro
ca
p
su
le
 a
gg
re
ga
te
s 
(µ
m
2
 )
Loop length (mm)
2,28
2,33
2,38
2,42
2,10
2,15
2,20
2,25
2,30
2,35
2,40
2,45
2,83 2,87 2,96 3,05
M
ic
ro
ca
p
su
le
 c
o
n
te
n
t 
p
er
fa
b
ri
c 
ar
ea
 (
m
g/
cm
2
)
Loop length (mm)
Journal of Science & Technology 143 (2020) 056-060 
60 
 The chart at Fig. 4 expresses the higher average 
area of microcapsule aggregates when the loop length 
increase. It was 7537, 8600, 13379 and 16020 µm2 on 
the fabric with loop length of 2.83, 2.87, 2.96 and 
3.05 mm, respectively. That means the microcapsule 
distribution becomes less even at the higher loop 
length. In order to give reason for this, the 
microcapsule content per fabric area was determined 
as mentioned at part 2.2.3. The results were as at the 
chart below: 
The data at the chart in Fig. 5 shows that the 
increase of loop length helps to retain more 
microcapsules in 1cm2 of the fabric: the microcapsule 
content per fabric area was 2.28, 2.33, 2.38 and 2.42 
at the loop length of 2.83, 2.87, 2.96 and 3.05 mm, 
respectively. 
As presented at Table 1, when the loop length 
went up gradually over four levels from 2.83 to 3.05 
mm, the porosity of the fabric increased in the order 
of 81.0, 81.6, 81.8 and 82.6%. It should be noted that 
the coating formulation was in type of microcapsule 
dispersion in water only. Therefore, the fabric with 
higher porosity could absorb more coating 
formulation, resulting in a higher microcapsule 
content per fabric area. Because most microcapsules 
were kept on the fabric surface, the higher 
microcapsule content per fabric area will induce a 
denser distribution of them on the fabric surface. 
Subsequently, it could be the denser distribution that 
increased the risk of bigger microcapsule aggregates 
on the fabric. 
4. Conclusion 
 In the study, the effect of loop length on the 
microcapsule distribution in cotton interlock knitted 
fabric was investigated. By the coating technique, 
most microcapsules deposited on the upper side of the 
fabric. When the loop length increased in the order of 
2.83, 2.87, 2.96 and 3.05 mm, the porosity of the 
fabric increased, inducing the rise of microcapsule 
content per fabric area, which subsequently increased 
the risk of forming microcapsule aggregates on fabric 
surface. The average size of microcapsule aggregates 
on the fabric surface was 7537, 8600, 13379 and 
16020 µm2 at the loop length of 2.83, 2.87, 2.96 and 
3.05 mm, respectively. That meant, in the scope of 
investigation, the microcapsule distribution became 
less even at higher loop length. 
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