Seams and Sewing Thread Characteristics in Denim Fabric

Seams and Sewing Thread Characteristics

in Denim Fabric

Seams and Sewing Thread Characteristics in Denim Fabric

V.Ramesh Babu, Dr.T.Ramachandaran* and Dr. C.V.Koushik,

M.Senthilkumar

Department of Apparel and Fashion Technology, Sona College of Technology, Salem 05

*Department of Textile Technology, PSG College of Technology, Coimbatore 04.

ABSTRACT

The quality of apparel products depends mainly upon fabric quality, but this alone

may not be the criterion when we deal with quality in terms of garment durability and

comfort. The type of thread used and the selection of seams also play a major role in

garment durability, especially for the fashionable denim garments, even though their

contribution may not be reflected in terms of cost and quantity.

This project focuses on the effect of type of sewing thread and stitch density on seam

properties of denim fabric and the mechanical properties of sewing thread. This

research work has been carried out in to two stages. In the first stage, three types of

commercially available sewing thread were chosen to stitch warpway and weftway

seams in denim fabric, using three different values of stitch density or the SPI

(Stitches per inch).

The seamed denim fabric was subjected to a standard industrial enzyme wash as is

practised commercially for denim jeans. The object was to study the effect of type of

sewing thread and stitch density on warpway and weftway seam properties (seam

strength, seam slippage and seam efficiency) of the denim fabric. In the second stage,

the mechanical properties (breaking load, breaking extension and breaking energy) of

the sewing thread unravelled from the seams in the various denim fabric samples

were compared with those of the parent sewing thread.

The results show that, in general, there is an increase in the strength of the thread

unravelled from the seams in the denim fabric, while the modulus shows a fall. These

are welcome features, as seam durability and flexibility can therefore be expected to

increase during garment use. Also seam strength is dependent upon seam direction,

the weftway seam being stronger than the warpway seam.

• • •

INTRODUCTION

The scope for denim wear is increasing tremendously every year and its worldwide market

share has increased unpredictably in the last few decades. Consumers’ needs and wants are

fine-tuned towards the latest developments and new styles; they are also aware of special

finishes and process treatments given to the garment to make them eco-friendly and user

friendly. So it is of great interest to study the relationship between the major components that

go to make up denim garments, namely denim fabric and the sewing thread that bonds the

components together.

While undergoing special finishes and chemical treatments, there is a considerable loss in the

strength and physical dimensions of the fabric. So it is essential to select the appropriate

sewing thread and seam in order to maintain fabric durability, quality and also to resist wear

and tear.

This project mainly deals with a study of seam properties and sewing thread properties on

denim fabric after the post-garment standard industrial enzyme wash. Three types of threads

and three different stitch densities were used in the study.

MATERIALS AND METHODS

Sewing thread details

The following three commercial sewing threads were used to produce seams in denim fabric.

Core-spun thread PET core – Cotton wrap White coloured

thread 60 Tex (2 ply)

Core-spun thread PET core – PET staple fibre wrap Grey coloured


100% polyester

thread PET Staple Spun

Blue coloured


Denim fabric construction details

Yarn Count: Warp

Weft

8 Ne

14 Ne

Ends per inch 62

Picks per inch 44

Crimp Percentage Warp

Weft

11.4 %

10.5 %

Weave 2 / 1, Right-hand twill

Fabric tensile strength: Warp

Weft

67.3 kgf

23.9 kgf

Weight (oz / yd2) 6.5

Production of seams in the fabric

A Brother-make five-thread overlock machine, Model FBN 310, Stitch Type Class-500 was

used to produce the seams in the denim fabric. The fabric samples were cut to convenient

sizes and warpway and weftway seams (Superimposed Seam Type SSa-1) were produced at a

machine speed of 2860 rpm using three different stitch densities, viz, 6,8,11 SPI. Identical

settings of foot pressure and thread tension were maintained for all the seams produced.

Enzyme wash Treatment

The seamed samples were washed with commercial enzymes using industrial standards. The

following recipe was used.

Enzyme Tinozyme 150 ml

Water 5 litres

Time 30 min

Machine Drum wash

Dryer 40 min

Temp 80° C

pH 6

The Standard Tests Used

Tests Test Standard Specimen Size

Thread tests

Thread Strength ASTM D - 225602 200 mm

(Instron Tensile Tester)

Fabric tests

Fabric tensile strength ASTM D 5034 - grab test 8-inch × 4-inch

Seam Strength ASTM D 5034 14-inch × 4-inch

RESULTS AND DISCUSSION

The results of the mechanical properties of the parent threads and the threads unravelled from

the warpway and weftway seams of the washed denim fabric are shown in Tables 1 and 2.

Individual thread results are also compared in the bar charts shown in Figures 1 to 3.

Blue Thread - 100% staple spun polyester yarn (2 ply)

White Thread - polyester core spun cotton wrapped yarn (2 ply)

Grey Thread - polyester filament core with polyester spun wrapped yarn (3 ply)

1. White Thread – Polyester filament yarn (PFY) Core, Cotton (C) Wrap

i) The parent yarn is strong. Showing an average breaking load of 2235 grams, it is the

strongest of the three types of thread in this study. The combination of a strong

polyester yarn core and the cohesive inter-fibre grip between the cotton wrapping

fibres provides good resistance to tensile loads. This is an important characteristic

required of a sewing thread.

ii) Its breaking elongation is the lowest at 9.83 per cent. The presence of cotton, which

has a characteristically low extension, lowers the overall extension of the yarn at

break. The wrapping fibres can be expected to straighten under the tensile load and

break even before the polyester core has completely elongated.

iii) As this yarn has a high breaking load, the energy required to rupture it is also

correspondingly high. The energy required to rupture it is 0.38 J.

2. Blue Thread – 100% Polyester (PET) Spun Yarn

i) With a breaking load of 1733 gf, this is the weakest of the three yarns under study.

Though of the same linear density as the other two types of thread, the inadequate

grip between the constituent polyester fibres lowers their cohesion and hence the

overall yarn strength.

ii) The breaking elongation at 15.5 % is intermediate between the other two threads and

is due to the polyester fibre present.

iii) The energy to rupture this 100% spun polyester thread is half that required to rupture

the polyester core-cotton wrapping thread. The low breaking load and the moderate

breaking extension result in the low value of energy of rupture (0.19 J).

3. Grey Thread – Polyester filament yarn PFY Core, Polyester staple fibre (PSF) Wrap

i) This yarn has an intermediate breaking load at 2028 gf. The inter-fibre grip provided

by the smooth polyester sheath fibres cannot be expected to be as strong as that of the

cotton fibres in the White Thread and thus the breaking strength is lower.

ii) The breaking elongation at 19.59% is higher than the other two yarns mainly because

the polyester fibre has an inherently higher extension characteristic.

iii) The energy to rupture this thread is higher than the 100% spun yarn polyester thread.

The fairly high breaking load and the high breaking extension contribute to this value

(0.25 J).

Besides the above points, other aspects like the linear density of the core continuous polyester

filament yarn, the number of filaments it contains, the denier per filament, the level of twist

in the wrapping fibres, the number of plies the thread is composed of, etc would also

influence the mechanical behaviour of the threads.

Effects of the stitching action and the washing treatment on the threads

Effect on tensile modulus

The results of the tensile moduli, the breaking loads and extensions of the threads unravelled

from the seams of the denim samples after the standard industrial wash present some

interesting information on the expected behaviour of the threads in the seams.

Table 2: The Tensile Elastic Moduli of the parent and unravelled threads

WARP MOD1

(G / TEX) MOD2

(G / TEX) WEFT MOD1

(G / TEX) MOD2

(G / TEX)

WHITE - PARENT 274 305.7 WHITE - PARENT 274 305.7

BLUE - PARENT 177.8 265.4 BLUE - PARENT 177.8 265.4

GREY - PARENT 190.4 292.5 GREY - PARENT 190.4 292.5

WH-6-WARP 321.5 121.3 WH-6-WEFT 328.7 123.6

WH-8-WARP 329.5 126.7 WH-8-WEFT 143.3 138.6

WH-11-WARP 146.6 141 WH-11-WEFT 152.4 142.6

BLUE-6-WARP 126.9 124.8 BLUE-6-WEFT 133.7 125.9

BLUE-8-WARP 116 125.7 BLUE-8-WEFT 126.5 128.1

BLUE-11-WARP 121.4 127.9 BLUE-11-WEFT 110.4 128.5

GREY-6-WARP 137.9 108.2 GREY-6-WEFT 138.2 107.2



Table 1: Load, Extension and Energy-to-break of the different threads

WARP DIRECTION WEFT DIRECTION

LOAD [grams]

WHITE BLUE GREY WHITE BLUE GREY

PARENT 2235 1733 2028 2235 1733 2028

6 - WARP 2127.7 1747 2153 2005 2013 2318

8 - WARP 2236 1867 2206 1726 1972 2180

11 - WARP 2113 1974 2319 2129 1728 2146

EXTENSION [%]


PARENT 9.83 15.5 19.59 9.83 15.5 19.59

6 - WARP 21.56 16.39 20.76 18.89 16.75 21.93

8 - WARP 20.03 17.02 21.11 15.9 17.55 21

11 - WARP 19.57 17.23 22.09 19.26 16.99 21.11

ENERGY ( J)


PARENT 0.38 0.19 0.25 0.38 0.19 0.25

6 - WARP 0.38 0.18 0.3 0.335 0.22 0.34

8 - WARP 0.373 0.2 0.31 0.2529 0.22 0.31

11 - WARP 0.325 0.22 0.34 0.32 0.18 0.3

The general observation is that there is a fall in the tensile modulus at loads of 100 g

(MOD 1) and 250 g (MOD 2) for all the three types of thread. Only for the PFY Core-C

Wrap White Thread is there an apparent and inexplicable increase in the moduli at 100 g

load, in three cases, the 6-spi seam in the warpway and weftway directions and the warpway

8-spi seam. This effect may be due to particular specimen effects and cannot be

representative of the sample as a whole.

Ignoring these three cases, the average modulus of the PFY Core-C Wrap White Thread after

stitching and washing is 47% of that of the parent yarn at 100-g load. Similarly, the moduli of

the 100% PSF Blue Thread and the PFY Core-PSF Wrap Grey Thread are respectively 31%

and 27% of the modulus of original parent yarn values at 100-g load. The moduli at the 250-g

load are still lower in all the three cases.

There is no discernable effect of the direction of the seam, warpway or weftway, on the

modulus values. There is also no particular trend by which the stitch density influences the

thread moduli.

It may be thus concluded that the effect of the standard enzyme wash is to lower the moduli

of the threads in the seams. Added to the effect of washing, is the effect of the mechanical

action of stitching and stitch formation. The speed at which the thread is stitched (2860

stitches /min) and the bending and twisting strains imposed as a result of thread formation

cause the threads to be in a state of mechanical stress, whereby it suffers a lowering of its

tensile modulus.

The advantage of the combined effect is that the flexibility of the seam and hence its

contribution to the drape of the garment will be improved. The disadvantage is that the thread

is susceptible to strains in regular garment use to a greater extent. Of course, the extent of

such increased strains would depend on the type of denim garment and its tightness of fit on

the users. In any case, it is not likely that the 100-g load would be equalled or exceeded in the

strains of normal garment use.

Effect on other mechanical properties

Breaking Strength

The PFY Core-C Wrap White Thread shows a drop in breaking load, about 3.5% for the

thread from the warpway seam and nearly 13% for that unravelled from the weftway seam.

The blue and grey threads, on the other hand, show a fairly uniform increase of about 10%

for both the warpway and weftway seams. There is little effect of the stitch density on the

strength results.

LOAD [grams]

0

500

1000

1500

2000

2500

WHITE BLUE GREY

PARENT

6 - WARP

8 - WARP

11 - WARP

LOAD [grams]

0

500

1000

1500

2000

2500

WHITE BLUE GREY

PARENT

6 - WEFT

8 - WEFT

11 - WEFT

Figure 1: Breaking loads of the different sewing threads

The change in strength values after washing could reflect a differential change in the linear

density of the three types of threads. It is likely that the blue and grey threads have suffered a

greater degree of shrinkage than the white thread. The PET sf in the blue thread and the PET

yarn and wrapping PET sf in the case of the grey thread are bound to relax and shrink due to

the washing treatment. Such shrinkage would cause an increase in the linear density of the

threads and this in turn would result in a corresponding increase in the thread strength.

In the case of the white thread, the restraining effect of the relatively rough-surfaced cotton

wrapping fibres has probably given rise to a negative effect and hence the strength has

dropped. The different behaviour of the warpway and weftway seams is not clear at the

moment, but could be ascribed to the 2/1-twill structure of the denim fabric.

Breaking extension and energy of rupture:

The extensions-at-break of the three types of thread are all greater than the breaking

extensions of the respective parent threads. The greatest increase is shown by the PFY Core-

C Wrap White Thread and this is observed for both the warpway and weftway seams. The

other two types of thread show a uniform 9-10% increase in extension.

EXTENSION [%]

0

5

10

15

20

25

WHITE BLUE GREY

PARENT

6 - WARP

8 - WARP

11 - WARP

Extension %

0

5

10

15

20

25

WHITE BLUE GREY

PARENT

6 - WEFT

8 - WEFT

11 - WEFT

Figure 2: Breaking extensions of the different sewing threads

ENERGY [J]

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

WHITE BLUE GREY

PARENT

6 - WARP

8 - WARP

11 - WARP

Energy [Joules]

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

WHITE BLUE GREY

PARENT

6 - WEFT

8 - WEFT

11 - WEFT

Figure 3: Breaking energies of the different sewing threads

The PFY Core-C Wrap White Thread shows a fall in the energy to rupture the threads, the

weftway thread showing a 20% fall. The other threads show increases in the energy of

rupture that correspond with the changes in the breaking load and extension values.

The above changes in the mechanical properties are welcome changes that would contribute

to better sewing thread and seam performance in garments.

Effects on Seam Properties on denim fabric

The results of tests on the seams are shown in Table 2 below.

Table 3: Seam strengths at varying stitch densities

THREAD SEAM STRENGTH

PFY Core / Cotton wrap

White Thread - 2 ply

Warpway Seam (sbf*) kgf

Weftway Seam (sbf) kgf

6 SPI 14.4 (STB*) 28.3 (STB)

8 SPI 11.6 (TPO*) 40.4 (STB)

11 SPI 8.7 (TPO) 43.2 (STB)

PFY Core / PSF wrap

Grey Thread – 3 ply Warpway Seam

(sbf) kgf Weftway Seam

(sbf) kgf

6 SPI 11.6 (TPO) 33.4 (STB)

8 SPI 9.9 (TPO) 44.1 (STB)

11 SPI 9.4 (TPO) 41.2 (FTS*)

100% PET Spun Yarn

Blue Thread – 2 ply Warpway Seam

(sbf) kgf Weftway Seam

(sbf) kgf

6 SPI 15.4 (TPO) 27.2 (STB)

8 SPI 12.7 (TPO) 32.2 (STB)

11 SPI 10.0 (TPO) 37.8 (STB)

*Sbf – Seam Breaking Force; TPO – Thread Pullout; STB – Sewing Thread Breaks; FTS –

Fabric Tear at Seam

Effect of Seam Direction and SPI on Seam Strength

The first observation is that in the case of all of the threads, the warpway seams decrease in

strength as the stitch density increases. The strength of the weftway seams, on the other hand,

shows an increasing trend with increase in the SPI of the seams.

Warpway Seams: In all of the types of thread investigated, the warpway seam strengths

are lower than those of the weftway seams. When a warpway seam is tested for its strength, it

is the weft threads in the fabric that are loaded along with the sewing thread composing the

seam. The weft yarn in a fabric is also generally not as strong as the warp yarn. Though the

weft yarn in the denim fabric under test is coarser than the warp yarn, the picks per inch are

much lower than the ends per inch.

As the stitch density increases, fewer weft threads are included inside a single stitch, so there

are fewer threads to break as every stitch of the sewing thread takes on the applied load. This

is why the seam strength decreases with increase in stitch density. In most of the cases, the

effect of sewing thread pullout is more pronounced as there are fewer picks per inch that offer

greater space for the sewing thread to slip through.

Weftway Seams: Due to the twill weave structure of the fabric, a greater number of warp ends

are available to take the load with every stitch and this results in higher seam strength in this

case. This is also the reason for the increase in seam strength with increase in stitch density.

Though there are fewer ends to share the load per stitch as the SPI increases, the longer floats

of the twill weave offer greater collective resistance to the applied load.

The behaviour of the sewing thread in the majority of the cases here is to break due to the

applied tensile forces. The stronger and greater number of warp ends that it has to pass

through during the test offers too much of a resistance and hardly any chance of slipping

through. The net result is that the sewing thread breaks. Only in the case of the PFY Core-

PSF Wrap Blue Thread, at 11 SPI, does the fabric itself tear.

Effect of Sewing Threads Type on Seam Strength

The warpway seam strengths are more or less in conformation with the breaking loads of the

respective parent threads. The PFY Core-Cotton Wrap - White Thread and the 100% PET

Spun Yarn - Blue Thread show a roughly 10 % difference in strength for all the SPI values.

However, the blue thread appears to be the stronger in the seam than the white thread. The

PFY Core-PSF Wrap Grey Thread appears to be the weakest of the three types of thread.

When the threads form the weftway seams the behaviour shows a dramatic change. The grey

thread is the strongest, next comes the white thread and the weakest is the blue thread! The

reason for this turn of events is not clear at the present moment.

Further studies with different kinds of fabric are underway and the findings will be reported

in due course. It is hoped that this subsequent work will throw more light on the behaviour of

threads and seams.

Conclusions

The following points on the behaviour of sewing threads and seams emerge as a result of this study.

1. The tensile modulus, at loads of 100 g and 250 g, of threads unravelled from the denim fabric

seams after the standard industrial wash shows a fall for all the three types of thread

investigated. The modulus is not affected by the direction of the seam nor its stitch density.

The threads and therefore the seams they constitute can be expected to be more flexible and

add to fabric drape.

2. The threads unravelled from the seams show a general increase in breaking load. This is attributed to a change in the linear density that can be expected from the elaborate industrial

wash given to the test fabric after seaming. There is little influence of the stitch density on the

breaking strength.

3. The breaking extension of the unravelled also increases in the case of two of the threads

studied. The PFY Core-Cotton Wrap White Thread alone shows a fall in this parameter.

4. The work of rupture of the unravelled threads shows changes that are in keeping with the

changes in the thread breaking strengths and extensions.

5. Seam strength is dependent upon the direction of the seam. The weftway seam is appreciably

stronger than the warpway seam in all of the cases. Also, the weftway seam strength increases

with stitches per inch while the warpway seam strength decreases with increase in the stitch density.

6. The relationship between sewing thread strength and seam strength seems to be complex, but

more elaborate studies would have to be done to get a clearer picture.

Acknowledgement

Our sincere thanks are due to our management, the AFT department students and faculty, Sona

College of Technology, Salem. Thanks are also due to the sponsorship given by KG Denim Ltd,

Coimbatore, Madura Coats Ltd, Tirupur and Sundarsons (India) Exports, Salem. The testing services

provided by M/s TexanLab, Salem and SITRA, Coimbatore are gratefully acknowledged.

Reference

1) Morris, P. A. and Brain, D. H., Seam Slippage, Clothing Res. J. 3, 135-144 (1975)

2) Shimazaki, K. and Lloyd, D. W., Opening Behavior of Lockstitch Seams in Woven Fabrics

Under Cyclic Loading Conditions, Textile Res. J. 60, 654-662 (1990)

3) Annual Book of ASTM Standards, ASTM D 6193-97: Standard Practice for Stitches and

Seams, pp. 909-1049; ASTM D 1682-64: Breaking Load and Elongation of Textile Fabrics, pp. 347-354; ASTM D 1683-81: Failure in Sewn Seams of Woven Fabrics, pp. 355-361;

American Society for Textile and Materials, Easton, PA, 1985

4) Dorkin, C. M. C. and Chamberlain, N. H., Lockstitch Seams in Knitted Fabrics, Technical

Report 11, The Clothing Institute, London, 1962

5) Galuszynski, S., Some Aspects of the Mechanism of Seam Slippage in Woven Fabrics, J.

Textile Inst. 76, 425-433 (1985)

6) Ezekiel, M., Methods of Correlation Analysis, John Wiley & Sons, NY, 1953

7) International Journal of Clothing Science and Technology, Volume 17, Numbers 3-4,

March 2005, pp. 225-231

Documents

Seams and Sewing Thread Characteristics in Denim Fabric