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CHAPTER 7

A STUDY OF PROPERTIES OF KNITTED FABRICS

MADE FROM VARIOUS MICROFIBRES

7.1 INTRODUCTION

This chapter deals with a comparative study of knitted fabrics made

from micro denier polyester and viscose, fibres with those of normal denier

fibre fabrics, besides this low stress mechanical properties of micromodal and

modal cotton blends are also discussed.

7.2 MATERIAL AND METHODS

Details of material and methods have been already discussed in

Chapter 3.

7.3 RESULTS AND DISCUSSION

Table 7.1 gives the physical and mechanical properties of single

jersey knitted fabrics produced from micro and normal denier polyester fibres.

Table 7.1 Physical and mechanical properties

Fabric CPcm WPcm SD/cm² SL (cm) Kc K Ks=Kc*Kw Tf

(Text0.5cm-1) R

Micro Denier 18.5 12.6 233.12 0.3 5.55 3.78 21 16.2 1.4

Normal Denier 18.89 13.78 260.40 0.3 5.67 4.13 23.43 16.2 1.37

CPCm: Courses per centimeter; WPCm: Wales per centimeter; SL: Stitch length in centimeter; SD/cm2 Stitch density per square centimeter and Tf : Tightness Factor (tex/l), where, Tex is yarn linear density and l is loop length in cm, R: Loop shape factor.

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7.3.1 Dimensional Stability

From Table 7.2 it is clearly seen that the change in loop lengths of

the micro denier fabric is much lesser than the normal denier fabric which

contributes to the better dimensional stability of the micro denier fabric.

About 21% change in loop length parameter is indicative of better

dimensional stability when compared to the 23.4% change in normal denier

fabrics. This may be due to the fact that the twist in the micro denier yarns is

much lesser when compared to the normal denier yarns. Due to lesser lint

shedding propensity and hairiness, as previously discussed, the strain

imparted on the yarn for microfibres is lesser which also contributes to the

better dimensional stability.

Table 7.2 Summary of dimensional changes

Particulars Micro Denier

(MD) Normal Denier

(ND)

% change in Micro Denier

=(MD-ND)/MD*100

Change in loop Length (mm)

0.52 0.62 -19.23 %

Areal density (GSM) 190.7 195.4 -2.41 %

Drape coefficient 0.1857 0.2249 -21.11 %

Average corrected bursting strength kg/cm2

11.53 10.75 No Significant

Change

Pilling rating 3.0 3.0 --

After 50,000 cycles at 9 kPa

No Holes No Holes --

Spirality 2◦ 5◦ 60%

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Identical single jersey knitted fabric structures were kept for both

microfibre and normal fibres to study the influence of microfibres on single

jersey knitted structures. Polyester microdenier fabrics have better

drapeability [of about 21%] than the polyester normal denier fabrics, which

may be a result of the basic fibre fineness. Microfibres having significantly

lower fineness and lower resultant stiffness can easily mould into the shape of

the wearer and results in a better fit. There is no significant change in the

thickness, bursting strength, abrasion resistance and pilling resistance values

of both the fabrics. The spirality of the microfibre is lesser by 60% compared

to normal denier yarns. This is a result of the lower TM (Twist multiplier)

employed in the ring spinning process compared to the normal denier.

7.3.2 Comfort Properties

7.3.2.1 Wicking

Table 7.3 indicates that wicking property in the microdenier fabric

is better than the normal denier fabric both in the wale direction as well as the

coarse direction.

Table 7.3 Results of wicking tests

Particulars Micro Denier Normal Denier

Height in cm Time in seconds Time in seconds

Wale Course Wale Course

1 32 32 42 45

2 72 100 91 191

3 167 180 295 316

4 285 310 516 570

5 441 460 710 753

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The packing coefficient of micro denier spun yarns is greater than

that of corresponding normal denier yarns. It is therefore expected that the

average capillary size would be less in microdenier spun yarns. Low capillary

diameter is expected to increase capillary pressure and drive the water faster

into the capillaries of yarn. This has resulted in higher wicking height in

micro denier yarns than the normal denier yarns at any given time.

7.3.3 Fabric Drop Absorbency

Table 7.4 shows that water drop absorbency of the microdenier

fabric is higher than normal denier fabric which may be again due to higher

surface area of microfibres.

Table 7.4 Results of water drop test

Particulars Micro Denier Normal Denier

Height of burette tip-10cm

17s 22s

7.3.4 Fabric Drying Rate and Total Absorbency

The high drying rate is, as shown in Table 7.5 due to higher

exposed surface area which facilitates faster drying of the micro denier

fabrics. It is observed that the Micro denier fabric has better water holding

capacity as shown in Table 7.6. This may be due to the fact that the Micro

denier yarns have higher surface area, which allows more moisture

transmission, and also they have more number of fibres in their cross section

to facilitate them in holding the water.

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Table 7.5 Drying rate

Particulars Micro Denier Normal Denier % change in Micro Fabric

Initial Drying Rate (g/ hr/ m²)

414.3* 369.2 12.20 %- better

Table 7.6 Total Absorbency Test

Particulars Micro Denier Normal Denier % change in Micro Fabric

% Initial weight of the fabric

227.7* 219.3 3.86 %- better

* Indicates statistical significance

7.3.5 Scanning Electron Micrographs

Scanning electron micrographs clearly indicate finer and lesser

number of loops for the microfibre knitted fabric (Figures 7.1, 7.2 and 7.3.

The finer denier microfibre being more pliable in nature gets better

incorporated in the yarn resulting in neat surface appearance. The surface thus

develops a smoother look though the same moisture absorption capacity is

retained.

The overall surface as characterised by Figures 7.3 and 7.4 shows

the uniform surface of the microfibre knitted fabric. The surface viewed from

a different angle gave a glimpse of the overall surface appearance of the three

knitted structures under consideration. The lesser number of loops resulted in

a more coherent structure of the microfibre knitted structure. The thicker

protrusions of the normal and cotton knitted structure imparts an overall

rougher appearance.

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Figure 7.1 Scanning electron micrograph of loop formation for normal

fibres on knitted surface

Figure 7.2 Scanning electron micrograph of loop formation for

microfibres on knitted surface

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Figure 7.3 Scanning electron micrograph of surface of normal fibre

knitted material

Figure 7.4 Scanning electron micrograph of surface of microfibre

knitted material

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7.3.6 Viscose Microfibre Fabrics

The results of the single jersey knitted fabrics produced from

viscose fibres are discussed below.

7.3.6.1 Fabric Test Results

From Table 7.7, the stitch density and tightness factor values are

better for microdenier viscose fabrics than normal-denier viscose fabrics,

which due to basic fibre fineness. The better tightness factor values for

microdenier fabrics gives better handle, drape, durability and strength.

Table 7.7 Summary of physical and mechanical properties

Fabric Count Courses Per Cm

Wales per cm

Stitch Density per cm2

Stitch length

cm Kc Kw

Ks= Kc*Kw

Tightness factor

(Text0.5cm-1)

Loop Shape Factor

Micro-Denier

23.62 17.32 11.02 190.86 0.266 4.62 2.93 13.54 18.27 1.58

Normal- Denier

24.6 15.75 11.02 173.5 0.274 4.32 3.02 13.05 17.75 1.43

7.3.6.2 Drape of Knitted Fabrics

Table 7.8 gives the values of drape for micro and normal denier

fabrics. It was found that viscose microdenier knitted fabrics have better

drape-co efficient than normal denier viscose knitted fabrics, which is due to

the basic fibre fineness and the resultant lower bending rigidity of

microfibres. The better drape found in microdenier can also be correlated with

higher tightness factor.

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Table 7.8 Drape of knitted fabrics

Fabric type Drape coefficient

Microdenier 0.2023*

Normaldenier 0.2150 *Indicates statistical significance

7.3.6.3 Spirality

The Spirality values noted in Table 7.9 show better values for

microdenier fabrics than normal denier fabrics which may be due to basic

fibre fineness and lower twist multiplier values compared to microdenier

yarns during spinning. This lower and acceptable level of spirality in

microdenier fabrics reduces the percentage rejection due to that defect.

Table 7.9 Spirality

Fabric Spirality angle

(Degrees)

Microdenier 2*

Normaldenier 8 * Indicates statistical significance

7.3.6.4 Bursting Strength

Table 7.10 gives values of bursting strength for viscose normal

denier and microdenier knitted fabrics. Microdenier fabrics have

comparatively higher bursting strength than normal denier. This may be due

to the fact that more number of fibres can be accommodated in the yarn cross

section for the same yarn diameter in case of microdenier yarns there by

increasing the basic tenacity of yarn and also partly due to higher stitch

density and tightness factor values in microdenier fabrics.

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Table 7.10 Bursting strength

Parameters Micro Denier

kg/cm2 Normal Denier

kg/cm2

Mean 6.80(0.16) 5.60(0.14) Values in parantheses indicate standard deviation

7.3.6.5 Moisture Transmission Properties of Viscose Microfibres

Viscose being a regenerated cellulose fibre in nature the moisture

transport properties in particular wicking are different compared to synthetic

fibres and this aspect created considerable interest for the study. Moisture

transport in textile materials is quite similar to wicking of water in capillaries.

As capillary wicking is determined by two fundamental properties of capillary

such as its effective diameter, and the surface energy of its inside face. The

smaller the diameter or the higher the surface energy, the more readily water

moves up the capillary. In textile structures, the spaces between fibres

effectively form capillaries, the closer fibres are packed together in yarn, the

smaller the apparent capillary diameter and more readily wicking can

occur. Fibre properties such as diameter, cross section, crimp and stiffness all

play a role in capillary formation. For eg., microfibres packed together very

tightly and form narrow capillaries enabling a faster wicking.

Similarly, surface energy is a measure of attraction between water

and internal surface of the capillary, which largely depends on the chemical

structures of the exposed surface. Fibres with high surface energy are often

referred to as hydrophilic (as in our case viscose being hydrophilic, it has high

surface energy). For two fabrics comprised of fibres of identical diameter and

textures but different surface energy, the fabric with higher fibre surface

energy will wick faster. Also hydrophilic fibres swell and thus reduce the

capillary size thereby increasing the pressure for faster wicking. Thus viscose

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microfibres behave differently in the moisture transport properties compared

to other synthetic microfibres such as polyester, polyamide etc.

7.3.6.6 Wicking

From Table 7.11, it can be inferred that wicking values which are

better for microdenier fabrics due to better packing coefficient of microdenier

spun yarns than that of corresponding normal denier yarns. It is therefore

expected that average capillary size would be less in microdenier spun yarns.

Low capillary diameter is expected to increase capillary pressure and drive

water faster into the capillaries of yarn. This has resulted in higher wicking

height in micro-denier yarns than normal denier yarns at any given time.

Table 7.11 Wicking Tests

Wale wise (Time in Seconds)

Height in cm 1 2 3 4 5 6 7 8 9 10

Normal Denier 2 6 11 22 54 107 155 252 384 590

Micro Denier 1 4 9 20 35 62 105 185 273 391

Course wise (Time in Seconds)

Height in cm 1 2 3 4 5 6 7 8 9 10

Normal Denier 2 8 20 48 78 155 213 282 401 556

Micro Denier 1 4 12 25 53 112 184 257 360 481

7.3.6.7 Water Drop Test

From Table 7.12, it can be inferred that drops of water on

microdenier fabrics, spread quickly than fabrics of normal denier yarns, which

is due to higher surface area of microdenier fibres.

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Table 7.12 Water drop test

Particulars Micro Denier Normal Denier

Height of burette tip – 10cm 15* s 21.3 s

7.3.7 Low Stress Mechanical Properties of Micromodal Knitted

Fabrics and Cotton Blends

The geometrical properties of knitted fabrics made from micro

modal and micromodal cotton blends are given in Table 7.13

Table 7.13 Geometrical properties of knitted fabrics

Property Micromodal Micromodal / cotton blend

CPcm 22.04 21.98 WPcm 18.11 18.0

Stitch density, cm2 399.3 395.6 Loop length (cm) 0.233 0.233

GSM 164.3 159.8 Thickness (mm) 0.865 0.871

7.3.8 Tensile Properties

Table 7.14 gives the various low stress mechanical properties

measured by the Kawabata evaluation system-F and asterisk put above the

values indicates the significance level. The initial modulus of micro modal

fabrics is significantly lower than micro modal – cotton blend. A lower value

of initial modulus indicates higher flexibility.

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Tensile values of LT, linearity counts are almost similar in both the

fabrics. WT (Tensile energy) and EMT (elongation) show a significantly

higher value for micro modal weft knitted fabrics. An increase in the tensile

properties implies better comfort. The micro modal fabrics on this basis are

found to be more comfortable.

Table 7.14 Tensile properties

Property Micromodal Micromodal / cotton blend

LT 0.627 0.610

WT (g.cm/cm² ) 67.18* 51.25

RT (% ) 14.63* 18.44

EMT (%) 43.55* 33.78

Initial modulus (g/cm) 140 144 *-Indicates statistical significant difference at 95% confidence level when TAct > T95%

Figure 7.5 Load-extension curve-micromodal and micromodal-cotton

blend (Courseway)

Figure 7.5 compares the tensile properties of modal cotton and

micromodal knitted fabrics.

F - g

f/cm

E (Strain) %

(a) (b)

(a) Blend, (b) Modal

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7.3.9 Bending

The bending properties namely, B (bending rigidity), given in

Table 7.15 show a lower value for micromodal fabrics. Bending hysteresis

also follow the same trend. The ratio of 2HB/B, residual curvature shows a

decrease for micro modal knitted fabrics, which is an indication that this

fabric has a better handle. Figure 7.16 compares the bending property of

micromodal and micromodal cotton blends in the wale way.

Table 7.15 Bending properties

Property Micromodal Micromodal / cotton blend

B ( g.cm²/cm ) 0.0162 0.0196

2 HB (g.cm/cm) 0.0148 0.0276

2HB /B 0.9135 1.4

Figure 7.6 Bending curves of micromodal and micromodal-cotton

blends-wale way

K c

m-1

M gf.cm/cm

(a)

(b)

(a) Modal, (b) Blend

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7.3.10 Shear Rigidity (G)

Shear rigidity given in Table 7.16 shows a significantly lower value of micro modal fabric in comparison with a fabric knitted from micro modal-cotton blend. Shear hysteresis (2HG and 2HG5) follow the same trend. The ratios of 2HG/G and 2HG5/G, which represent residual curvature, also follow a similar trend. The lower the value, better the recovery and vice versa. The shear recovery values are almost similar for both the fabrics.

Figures 7.7 and 7.8 compare the shear properties of micromodal and micromodal cotton blended knitted fabrics in wale and course ways.

Table 7.16 Shear properties

Property Micromodal Micromodal / cotton blend

G (g/cm.deg) 0.38 0.48 2HG ( g/cm) 2.57 2.19

2HG5 ( g/cm) 2.43 2.29 2HG/G 6.763 4.562

2HG5/G 6.394 4.770

Figure 7.7 Shear strain curves of micromodal and micromodal-cotton

blends-wale way

D

egre

e

F gf/cm

(a)

(b)

(a) Modal, (b) Blendl

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Figure 7.8 Shear strain curves of micromodal and micromodal-cotton

blends- course way

7.3.11 Compression

WC (compressional energy) shown in Table 7.17 for the micro

modal fabrics is significantly higher than that of the micro modal-cotton

blend. Higher value of WC is an indication of greater compression and on this

basis, the compressibility of micro modal fabrics is better. RC (compress

ional resilience) values are almost similar for both the fabrics. Interestingly,

the percentage of compression which is a non-standard parameter shows an

increase for micro modal fabrics. Kothari and Das (1993) have suggested the

following model T/To= 1-α logP/Po for needle punched, spun bonded non

woven fabrics. In this equation α represents a measure of compression and

higher the value, greater the compression. Values of α from the compression

curves of the two fabrics were computed and are given in table. It is apparent

that micro modal weft knit is significantly higher than blend. This is another

proof that micro modal weft knit fabric exhibit higher compressability.

D

egre

e

F gf/cm

(a)

(b)

(a) Modal, (b) Blend

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Figure 7.9 compares the compressional properties of the knitted fabrics made

from micromodal and micromodal cotton blends.

Table 7.17 Compression properties

Property Micromodal Micromodal / cotton blend

LC 0.381* 0.328

WC (gf.cm/cm²)

0.385* 0.306

RC (%) 29.52 31.45

% Compression

46 40

α 0.22 0.20 *-Indicates statistical significant difference at 95% confidence level when TAct > T95%

Figure 7.9 Compression curves of micromodal and micromodal-cotton

blend

P –

gf/c

m2

Thickness, mm

(a) (b)

(a) Blend, (b) Modal

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7.3.12 Surface Property

Surface properties MMU (coefficient of friction),and SMD (surface

roughness) shown in Table 7.18 are similar for both the fabrics. The total

handle value calculated on the basis of the equation meant for winter fabrics

shows a higher value for micro modal fabrics. The micro modal has been

found to be exhibit higher value of tensile properties, lower bending and

shear, higher value of compression better wicking, higher shrinkage lower air

permeability, better drapeability.

Table 7.18 Surface properties

Property Micromodal Micromodal / cotton blend

MIU 0.205 0.208

MMD 0.0114* 0.0181

SMD (µ m) 4.645 4.654 *-Indicates statistical significant difference at 95% confidence level when TAct > T95%

Figure 7.10 Surface roughness of micromodal knitted fabrics

Coe

ff. o

f fric

tion

SMD

m

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Figures 7.10 and 7.11 show the surface roughness of the fabrics

from which it is apparent that the undulations are less for micromodal fabrics

showing better smoothness.

Figure 7.11 Surface roughness of micromodal-cotton knitted fabrics

7.3.13 Handle of Fabrics

Table 7.19 shows the results of primary handle values namely

koshi, fukurami, shari, numeri and the total hand values (THV) for the two

fabrics. It is clear that the micromodal fabrics exhibits a higher modal value in

comparison with micromodal–cotton blend. In terms of the summer category,

the total handle value of fabrics show an opposite effect.

7.3.14 Comfort Characteristics

The results of qmax (warm-cool feeling), thermal conductivity, water

vapour transmission rate for micro modal are given in Table 7.19. It is

apparent that the values of Qmax (warm-cool feeling) are almost similar for all

fabrics. Thermal conductivity values also show not much variation. Similar

Coe

ff. o

f fric

tion

SMD

m

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trend is noticed for the moisture vapour transmission rate (MVTR). In view of

this, the use of micro modal in blends of cotton (50-50) is recommended. The

comfort properties of the micro modal and micromodal cotton blend are found

to be similar.

Table 7.19 Handle values of micromodal and micromodal-cotton blend

fabrics

Property Micromodal Micromodal / cotton blend

HV Summer Winter Summer Winter Koshi 4.79 4.79 4.01 4.01 Fukurami 10.95 10.95 12.55 12.55 Shari / Numeri 10.4 6.45 6.97 0.18 Thermal conductivity (q max) W/cmC

0.11 0.11 0.11 0.11

K×10 ² 0.51 0.49 0.49 0.51 Water vapour transmission (qw×10²)

0.33 0.33 0.33 0.33

Total Hand Value 1.92 3.29 3.07 2.37

Table 7.20 gives details of initial modulus, elastic recovery and

shear recovery from which it is apparent micro modal fabrics have better

recovery.

.

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Table 7.20 Recovery properties of knitted fabrics

Property Micromodal

Micromodal / cotton blend

Course Wale Course Wale Initial modulus (p) 272 244 227 610

Overall 1311 1724 833 1786

Elastic recovery (%) 26.3

(18.55) 37.6

(18.32) 26.78

(14.14) 33.7

(15.15)

Shear recovery (%) 40

47.5

35

41

7.4 CONCLUSION

The following conclusions may be drawn from the study.

1. Micro denier fabrics have shown superior properties when

compared to normal denier fabrics in various aspects of

physical and dimensional behaviour. The microfibre fabrics

are characterised by high drapeability, acceptable spirality,

excellent moisture transmission properties such as drying rate,

total absorbency, wicking rate, drop absorbency and water

absorbency.

2. Microfibre knitted fabric is dimensionally more stable when

compared to that of normal denier knitted fabric because of

less loop shape deformation and characterised by lesser lint

shedding propensity. The superior properties of microfibre

fabric can be conveniently utilized to explore and optimize

new products for apparel and sports wear.

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The results from Kawabata evaluation systems clearly indicate

the superiority of micro modal fabrics over blend with cotton.

3. A comparison of micro modal knitted fabrics with those of

micromodal-cotton blends shows that the former has a higher

extension, lower initial modulus, lower bending rigidity ,

lower shear rigidity, higher compression, lower friction and

better handle. Elastic recovery also has been found to be good

for micromodal knitted fabrics.

4. Comfort properties such as qmax, and thermal conductivity for

both the fabrics are found to be similar. In view of this, the use

of microdenier modal fibers with blends of cotton is

recommended.