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 T echnology, 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. White coloured
Core-spun thread
PET core – Cotton wrap
Core-spun thread
PET core – PET staple fibre wrap
100% polyester
PET Staple Spun
thread
thread Grey coloured thread Blue coloured thread
Denim fabric construction details Yarn Count:
Warp
8 Ne
Weft
14 Ne
Ends per inch
62
Picks per inch
44
Crimp Percentage
Warp
11.4 %
Weft
10.5 %
Weave Fabric tensile strength:
Weight (oz / yd2)
2 / 1, Right-hand twill Warp
67.3 kgf
Weft
23.9 kgf 6.5
60 Tex (2 ply) 60 Tex (3 ply) 60 Tex (2 ply)
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 (Instron Tensile Tester)
ASTM D - 225602
200 mm
Fabric tensile strength
ASTM D 5034 - grab test
8-inch × 4-inch
Seam Strength
ASTM D 5034
14-inch
Fabric tests
×
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 White Thread Grey Thread
- 100% staple spun polyester yarn (2 ply) - polyester core spun cotton wrapped yarn (2 ply) - 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 o f 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 li ke 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.
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
WHITE
BLUE
GREY
WHITE
BLUE
GREY
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
WHITE
BLUE
GREY
WHITE
BLUE
GREY
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
EXTENSION [%]
ENERGY ( J)
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 BLUE - PARENT GREY - PARENT
274 177.8 190.4
305.7 265.4 292.5
WHITE - PARENT BLUE - PARENT GREY - PARENT
274 177.8 190.4
305.7 265.4 292.5
WH-6-WARP WH-8-WARP WH-11-WARP
321.5 329.5 146.6
121.3 126.7 141
WH-6-WEFT WH-8-WEFT WH-11-WEFT
328.7 143.3 152.4
123.6 138.6 142.6
BLUE-6-WARP BLUE-8-WARP BLUE-11-WARP
126.9 116 121.4
124.8 125.7 127.9
BLUE-6-WEFT BLUE-8-WEFT BLUE-11-WEFT
133.7 126.5 110.4
125.9 128.1 128.5
GREY-6-WARP GREY-8-WARP GREY-11-WARP
137.9 141.6 138.2
108.2 107.7 106.2
GREY-6-WEFT GREY-8-WEFT GREY-11-WEFT
138.2 140.7 134.5
107.2 108.5 108.6
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 [gram s]
LOAD [grams] 2500
2500
2000
2000
PARENT
PARENT 1500
6 - WARP
1000
8 - WARP 11 - WARP
500
1500
6 - WEFT
1000
8 - WEFT 11 - WEFT
500 0
0 WHITE
BLUE
WHITE
GREY
BLUE
GREY
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 CoreC 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 %
EXTENSION [%] 25
25
20
20 PARENT 15
6 - WARP
10
8 - WARP 11 - WARP
5
PARENT
15
6 - WEFT
10
8 - WEFT 11 - WEFT
5 0
0 WHITE
BLUE
GREY
WHITE
BLUE
GREY
Figure 2: Breaking extensions of the different sewing threads
Energy [Joules]
ENERGY [J] 0.4
0.4
0.35
0.35
0.3
0.3
PARENT
0.25
6 - WARP 8 - WARP 11 - WARP
0.1
6 - WEFT
0.2
0.2 0.15
PARENT
0.25 0.15
8 - WEFT
0.1
11 - WEFT
0.05
0.05
0
0 WHITE
BLUE
WHITE
GREY
BLUE
GREY
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 PFY Core / Cotton wrap
White Thread - 2 ply 6 SPI 8 SPI 11 SPI PFY Core / PSF wrap Grey Thread – 3 ply 6 SPI 8 SPI
11 SPI 100% PET Spun Yarn Blue Thread – 2 ply 6 SPI 8 SPI 11 SPI
SEAM STRENGTH Warpway Seam (sbf*) kgf
14.4 11.6 8.7
(STB*) (TPO*) (TPO)
Warpway Seam (sbf) kgf 11.6 (TPO) 9.9 (TPO)
9.4
(TPO)
Warpway Seam (sbf) kgf 15.4 (TPO) 12.7 (TPO) 10.0 (TPO)
Weftway Seam (sbf) kgf
28.3 (STB) 40.4 (STB) 43.2 (STB) Weftway Seam (sbf) kgf 33.4 (STB) 44.1 (STB)
41.2 (FTS*) Weftway Seam (sbf) kgf 27.2 (STB) 32.2 (STB) 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 a pplied 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 CorePSF 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
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