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Standardize the widthwise shrinkage and extension recovery in variegated rib with knitted fabrics of 100% cotton with elastane

Abstract

The main aim of knitting and finishing sections of textile industries is to provide fault-free finished fabrics to the garment section. But the knitters and the finishers have to face a lot of problems for the fulfillment of this purpose. They have to face some problems, particularly, whose causes are mostly unknown to them.

The aim of this project is to figure out an international benchmark of standard for the Widthwise shrinkage of variegated wider Rib knitted fabrics with Cotton-Elastane by identifying the most possible causes and remedies of these faults that are encountered due to man, machine, materials and methods.

In comparison with regular Rib construction, the feasibility and the dimensional stability after frequent wash of Variegated wider Rib with Cotton Elastane is remarkable underrated while in case of Polyester or Polyester blend have no issues on that aspect. That’s why this project is done.

Keywords: Lengthwise shrinkage, widthwise shrinkage, tumble drying, line drying, variegated rib.

Introduction:

The ever-increasing demand of knitted apparels has attracted attention in global niche market. Knitted fabrics are used in manufacturing of fashion garments and even it has the potential in the formal wear segments also.

The dimensional stability of knitted fabrics is an important factor of the knitting industry. On the knitted fabric, it is necessary that the wale be perpendicular to the course, but Weft knitted fabrics tend to undergo certain dimensional change after line or tumble drying that causes distortion in which there is a tendency of the knitted loops to bend over.

That causes widthwise or lengthwise shrinkage of fabric. A large number of factors are responsible for causing these dimensional changes in weft knitted fabric structures. And those factors are listed below.

Root causes of Shrinkage:

  • Water absorbing Tendency. (Swelling & Deswelling Effect)
    1. Higher potential relaxation of yarn.
    2. Alteration in the loop shape
    3. Loop length shrinkage
  • Cover Factor of fabric
    1. Gap between Loop
    2. Count of yarn
    3. Loop length
  • Effect of Dyeing and Finishing
    1. Effect of temperature
    2. Effect of Tumbling
    3. Effect of detergent
    4. Effect of moisture content.
  • Knitting factors that have effect in shrinking
    1. GSM
    2. Raw materials
    3. Fabric Structure
    4. Fabric Dia
    5. Machine Gauge

And these root causes are described below.

In this project worked on 100% cotton rib knitted fabric. Cotton are natural fiber. Cotton fiber are hydrophilic. That means cotton loves water.

When cotton absorb water, water molecule act as lubricant between the cellulose molecules, easing the way they get close to each other. Hence length of yarn or length of loop decrease. Detergent used in washing also act as lubricant. Hence detergent is also responsible for shrinkage of yarn.

Absorbing of water is known as swelling. The importance of the swelling mechanism is significant. As the fabric wets out without tension, swelling of the fibers and subsequently the yarns and the fabric results. Upon swelling, the crimp in the yarn loops increases.

In effect, the loops in the knitted structure try to assume their lowest energy state that is a round configuration, which is the lowest energy state for the yarn and therefore for the fabric. The rounding of the loop results in a shortening of the loop and alteration in the loop shape and therefore relaxation and dimensional change.

Loop-after-swelling-deswelling-effect
Figure 1: Loop after swelling and deswelling effect.

Therefore, in drying (deswelling), the loops in a knitted structure are trying to assume a round configuration. Drying shrinkage is normally removed only by large amounts of energy as opposed to low amounts of energy needed to remove elastic shrinkage. It is important to realize that elastic shrinkage occurs in the early stage of drying. And this deswelling is responsible for alteration in the loop shape.

In the case of tumble drying. Tumbling of drying machine causes high yarn tension that’s why alteration of loop shape and shrinkage of yarn occurs more than Line dry.

In the initial stages of tumble drying, the removal of surface or non-bound water is achieved. Other than the simultaneous removal of elastic shrinkage, very little relaxation takes place, because the weight of water trapped in the cotton fabric and its lubricating effect acts as a force working against shrinking.

After the surface water on the fibers in the structure has evaporated, deswelling occurs. It has been shown that at moisture levels below 20%, the greatest levels of relaxation occur.

How to reduce widthwise shrinkage? (Methods)

For this study three types of methods have been chosen to improve widthwise shrinkage. Those methods are described below.

Methods-01: Using blended cotton-synthetic yarn for better shrinkage control

In the case of synthetic fiber swelling does not occur because, Generally synthetic fibers are very strong which conveys a sense that they have very strong intermolecular force of attraction which means that it has very small intermolecular gap and for absorption of water the gap is not large …so generally synthetic fibers do not absorb water. Hence, synthetic fiber does not swell.as a result yarn does not shrink.

So, it’s possible of improving shrinkage by using blended yarn in the case of variegated knit fabric.

Blended yarn improve shrinkage in another way. Described below.

Heat-setting is a heat treatment by which shape retention, crease-resistance, resilience and elasticity are imparted to the fibers. Another big reason of giving heat into fabric for Dimensional stability.

Fiber-after-swelling-deswelling-effect
Figure 2: Fiber after swelling and deswelling effect.

When heat apply on crystalline region of fiber it’s become parallel to each other. The more parallel become the more dimensional stability. Hence, less shrinkage occurs. The cotton polymer is a linear, cellulose polymer. Cotton is a crystalline fiber.

Its polymer system is about 65 to 70 percent crystalline and, correspondingly, about 35-30 percent amorphous. Where synthetic fiber is almost 100% crystalline. So, during heat-set synthetic fiber get more dimensional stability then cotton fiber. Hence, blended yarn has less shrinkage tendency over 100% cotton yarn.

It’s possible of improving shrinkage by using blended yarn in the case of variegated knit fabric.

Methods-02: Construction Reshaping

Alteration in rib fabric construction will also reduce great percentage of shrinkage. If buyer agree to change structure then a stable structure which have less shrinkage can be given. Why alteration in structure will improve shrinkage? The answer is given below.

Cover factor is a scientific measurement of the percentage area of the fabric covered by the yarns and fiber. If cover factor in a fabric is more that means loop to loop distance of fabric is less. Hence, chance of shrinkage due to swelling is less. And vice versa.

I gave looping diagram of some rib knitted fabric for better understanding.

strong-bond-small-gap-Looping-diagram-normal-rib-knitted-fabric

very-small-gap-strong-bond-Looping-diagram-normal-rib-knitted-fabric

very-small-gap-Looping-diagram-normal-rib-knitted-fabric
Figure 3: Looping diagram of normal rib knitted fabric.

These are the looping diagram of normal rib knitted fabric. As we see in these fabric structure, there is no or very little Gap between Loop or can be said Cover factor of this fabric is high.

Hence, In the case of swelling and deswelling, yarn does not get enough free space for shrinkage. That’s why shrinkage percentage of Normal rib knitted fabric is less.

But in the Case of variegated rib

gap-bond-gap-Looping-diagram-variegated-rib-knitted-fabric

5-2-Looping-diagram-variegated-rib-knitted-fabric

8-4-Looping-diagram-variegated-rib-knitted-fabric
Figure 4: Looping diagram of variegated rib knitted fabric.

These are the looping diagram of variegated fabric. As we see in these fabric structure, there is huge Gap between Loop or can be said Cover factor of this fabric is less. Hence, In the case of swelling and deswelling, yarn gets enough free space for shrinkage. That’s why shrinkage percentage of variegated rib knitted fabric is high.

So, if we minimize the space between loops then shrinkage will be improved. And space between loops can be reduced by changing fabric structure. So, construction reshaping will give better control in shrinkage.

Methods-03: Alteration in raw materials

The smaller the stitch length, the less yarn length per stitch, the tighter the stitch, and the shorter the loop. Tighter knitting as compared to looser knitting yields less shrinkage in the length and more in the width and a heavier fabric.

Finer yarns can be knitted more tightly to give the same yield as a heavier, coarse yarn. Finer yarns cost more, but knitting them tightly gives better control of length shrinkage and still meets the desired fabric yield. So, to obtain less shrinkage stitch length should be as minimum as possible. And finer yarn should be used for less shrinkage.

Piloting/Testing of these described methods: (Experimentation or procedures)

Four methods have been tested to find results.  Among four three methods mentioned earlier. Another method is factory practice which has been piloted to compare our study.

Piloting/testing of method-1: Using blended cotton-synthetic yarn for better shrinkage control

In this method yarn is considered as independent variables that means yarns fiber can be changed during processing. Yarn fibers are changed in two way. These are mentioned below.

  1. CVC (60% cotton +40% polyester)
  2. PC (65% polyester + 35% cotton)

CVC (60% cotton + 40% polyester)

In this method fabric is knitted by following given instructions.

Fabric structure: FFLY (4*4) Rib

Yarn composition: 30CVC 60%40%+30Dly Here, 30 CVC means 30 count yarn consist of 60% cotton and 40% polyester and 30Dly means 30 deniers of lycra yarn.

  • Stitch length: 3.00 mm
  • Machine gauge: 42*18
  • Gray fabric DIA: 36/54 inch
  • Gray fabric GSM: 452
  • Finished fabric DIA: 54 inches
  • Finished fabric GSM: 220

Fabric is knitted by following given instruction. The fabric went through dyeing and finishing process then fabric sample send to Lab to find out shrinkage.

PC (65% polyester + 35% cotton):

In this method fabric is knitted by following given instructions.

Fabric structure: FFLY (4*4) Rib

Yarn composition: 30PC 65%35%+30Dly Here, 30 PC means 30 count yarn consist of 65% Polyester and 45% Cotton and 30Dly means 30 deniers of lycra yarn.

  • Stitch length: 3.05 mm
  • Machine gauge: 42*18
  • Gray fabric DIA: 30/45 inch
  • Gray fabric GSM: 491
  • Finished fabric DIA: 54 inches
  • Finished fabric GSM: 227

Fabric is knitted by following given instruction. The fabric went through dyeing and finishing process then fabric sample send to Lab to find out shrinkage.

Piloting/testing of method-2: Construction reshaping

In this method structure of fabric has been changed for better stability. Fabric will be knitted as given instruction.

Fabric structure: FFLY (4*4) Rib (1 put design another side will be plain)

Yarn composition: 30Comb+30Dly. Here, 30Comb means 30 count yarn consist of 100% combed Cotton and 30Dly means 30 deniers of lycra yarn.

  • Stitch length: 2.95 mm
  • Machine gauge: 42*18
  • Gray fabric DIA: 66 inches
  • Gray fabric GSM: 310
  • Finished fabric DIA: 61 inches
  • Finished fabric GSM:250

Fabric is knitted by following given instruction. The fabric went through dyeing and finishing process then fabric sample send to Lab to find out shrinkage.

Piloting/testing of method-3: Alteration in raw materials

In this method independent variable is properties of raw materials. Finer yarn has been inputted and specification has been changed as mentioned below.

Fabric structure: FFLY (4*4) Rib

Yarn composition: 34comb+30Dly. Here, 34comb means 34 count yarn (finer than previous used yam) consist of 100% combed Cotton and 30Dly means 30 deniers of lycra yarn.

  • Stitch length: 2.85mm (shorter than previous)
  • Machine gauge: 42*18
  • Gray fabric DIA: 43 inches
  • Gray fabric GSM: 286
  • Finished fabric DIA: 47 inches
  • Finished fabric GSM:194

Fabric is knitted by following given instruction. The fabric went through dyeing and finishing process then fabric sample send to Lab to find out shrinkage.

Result discussion

Lab report of every methods are given below to compare (Tumble drying)

Methods Name Lengthwise shrinkage Widthwise shrinkage
00 Factory Practice -9% -41%
1st method

 

 

(Using blended cotton-synthetic yarn for better shrinkage control.)

 

CVC (60% cotton + 40% polyester)

 

 

-3.3% -12%
PC (65% polyester + 35% cotton) -2% -5%
2nd method Construction Reshaping of fabric -7.5% -2%
3rd Method Alteration in raw materials -4% -23.8%
  • Table 1: Lab report
Shrinkage-variegated-Rib-fabric
Table 2: Chart of shrinkage

Factory practice/baseline has -41% widthwise shrinkage. This is huge. As all methods are tested, we can see all of my knitting method (options) has positive impact in the case of widthwise shrinkage compare to factory practice.

Factory-Practice-30cb+30dl
Figure 5: Factory Practice (30cb+30dl)

Though there are difference between percentages. Lowest widthwise shrinkage can obtain by following my 2nd method by construction reshaping of fabric. It’s only -2% where factory practice is -41%.

Method-2-30CVC +30DL
Figure 7: Method 02 (30CVC +30DL)

A great percentage of widthwise shrinkage can be improved by following another method which is method no 1 (Using PC blended cotton). In this case widthwise shrinkage is only -5% way much better than factory practice.

Method-2-30cB+30dL-One-Faced-Rib
Figure 8: Method 02 (30cB+30dL) One Faced Rib

Using CVC blended yarn also improved widthwise shrinkage which is -12% in mathematical term. Though it is less effective than PC blended yarn.

Method-3-34CB+30Dl
Figure 9: Method 03 ( 34CB+30Dl)

My third method (alteration in raw materials) is also capable to improve shrinkage but less effective rather than other options its only -23.8% but much better than factor practice.

Summary of results:

By analyzing the lab report it’s proven that all methods are effective.

Below methods are listed as order of Effectiveness.

  1. 2nd method (Construction Reshaping of fabric): (-2%)
  2. 1st method (Using PC 65% polyester + 35% cotton for better shrinkage control) :(-5%)
  3. 1st method(Using CVC (60% cotton + 40% polyester) for better shrinkage control): (-12%)
  4. 3rd method (Alteration in raw materials): (-23%)

Any factory can follow these method for improving widthwise shrinkge. These methods are proven in the HAMS GARMENTS LTD lab.

Fake shrinkage

Another short study has been done along with this projet. Its calles Fake shrinkage. There is a properties that show fake shrinkage of fabric. Means fabric shows more widthwise shrinkage in Fabric state rather than Garments state. A great number of perchantage widthwise shrinkage reduce in Garments due to dimensional stability. Several data are collected from HAMS GARMENTS LTD lab to show fake shrinkage.

Those data has been given below.(Tumble drying)

Fabric types In fabric state In garments state
Lengthwise shrinkage Widthwise shrinkage Lengthwise shrinkage Widthwise shrinkage
12*4 -0.6% -15.00% 0.16% -4.5%
5*2 -2.80% -11.50% 0.3% -5.5%
4*4 -3.7% -24.2% -2.5% -6.30%

So, it can be said that widthwise shrinkage in fabric state does not matter so much. Cause in the garments state widthwise shrinkage is very few. Does not affect at wear ability at all.

Conclusion

This study illustrated that the effect of drying in weft knitted fabric made of different structure.

The importance of understanding shrinkage and it causes is key to its control. In summary, a partnership between a mill and an apparel firm is a necessity for success in the marketplace. This is true whether the product is a national or store brand at retail.

Mutual planning and engineering of a product is the only recipe for success. In order to meet product specifications, the correct yarn, fabric structure, using blended yarn, alteration in raw materials, machine set-up, and dyeing and finishing processes must be chosen.

Arbitrary specifications and improper choices of processing routes are a guarantee for failure in the battle to control shrinkage for cotton fabrics.

If anyone has any feedback or input regarding the published news, please contact: info@textiletoday.com.bd

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