Serviceability, Wear,Abrasion and Abrasion Resistance

 

Serviceability, Wear,Abrasion and Abrasion Resistance

Serviceability: Serviceability of a fabric is it’s length of life upto it’s end of usefulness which occurs when it becomes deficient in one necessary property. In clothing for example, the end of service generally is reached when, due to color fading, shrinkage in laundering or bagging at knees or elbows the garment no longer has a presentable appearance.

Wear: Wear is the net result of a number of agencies which reduce the serviceability of an article. Some of the more important of these are bending and stretching, tearing, abrasion, laundering and cleaning.

Factors causing wear:

Ø  Direct force on the fabric. This never occurs in normal wear but only under abnormal stress.

Ø  Impact effects. These are important only in floor coverings.

Ø  Flexing or friction between fiber and fiber and between yarn and yarn due to bending of the fabric.

Ø  Abrasion.

Abrasion:

Abrasion is one aspect of wear and is the rubbing away of the component fibers and yarns of the fabric.

Abrasion may be classified as follows-

1.      Plane or flat abrasion-A flat area of material is abraded.

2.      Edge abrasion-This kind of abrasion occurs at collars and folds.

3.      Flex abrasion-In this case, rubbing is accompanied by flexing and bending.            

Abrasion Resistance:

The resistance power against damage due to abrasion of a fabric known as abrasion resistance.

Factors affecting abrasion resistance:

1. Fibre type:

Nylon is generally considered to have the best abrasion resistance. Polyester and polypropylene also have good abrasion resistance. Blending either nylon or polyester with wool and cotton is found to increase their abrasion resistance.

Viscose and acetates have the lowest abrasion resistance.

2. Fibre properties:

A fabric made up with longer fibres gives better abrasion resistance than short fibres because they are harder to remove from the yarn. For the same reason filament yarns are more abrasion resistant than staple yarns made from the same fibre. Increasing fibre diameter up to a limit improves abrasion resistance.

3. Yarn twist:

An optimum amount of twist in a yarn gives the best abrasion resistance. At low-twist factors, fibres can easily be removed from the yarn so that it is gradually reduced in diameter. At high twist levels, the fibres are held more tightly but the yarn is stiffer so it is hard abrade under pressure.

4. Fabric structure:

Fabrics with the crimp evenly distributed between warp and weft give the best wear because the damage is spread evenly between them.

Martindale Abrasion Tester:

Description of the machine:

1. This apparatus gives a controlled amount of abrasion between fabric surfaces.
2.  Abrasion is given at comparatively low pressures in continuously changing directions.

3.      In this test, circular specimens are abraded under known pressure.

4.      This abrasion is given by a motion that is the resultant of two simple harmonic motions at right angles to one another.

5.   The fabric is abraded against a standard fabric called abradant.

6. Abrasion resistance is estimated by visual appearance or by loss in mass of the specimen.

Method:

1.      Four specimens, each of 38mm in diameter are cut by using the appropriate cutter.

2.      Then they are mounted in the specimen holders with a circle of standard foam backing behind the fabric. The specimens must be placed flat against the mounting block.

3. The test specimen holders with the specimens are placed on the abradant.
4. A spindle is inserted through the top plate and the correct weight (usually of a size to give a pressure of 12kPa but a lower pressure of 9kPa may be used if specified) is placed on top of this.
5. The standard abradant should be replaced at the start of each test and also replaced after each 50,000 cycles if the test is continued beyond this number.
6. While the abradant is replaced it is held flat by a weight and the retaining ring is tightened.
7. Behind the abradant, there is a standard backing felt which is replaced at longer intervals.
8. After appropriate clamping of specimen on the holders, required numbers of cycles of abrasion is applied. 

Assessment of abrasion damage:

Several methods are used to judge the amount of damage. Some are mentioned below:

     i.               The difference in appearance between an abraded and unabraded specimen.

   ii.               The number of cycles required to produce a hole, broken threads or broken strip.

iii.               Loss in weight often plotted against the number of cycle.

 iv.               Change in thickness e.g. loss of pile height.

   v.               Loss in strength, e.g. tensile, bursting or tearing strength, expressed in percentage of unabraded strength.

 vi.               Change in some other properties like lustre, air permeability etc.

vii.               Microscopic examination of damage of yarns and fibres.

The specimen is examined at suitable intervals without removing it from its holder. In the Table, the time intervals between examinations are shown.

All four specimens should be judged individually. The individual values of cycles to breakdown of all four specimens are reported and also the average of these.

Points to be consider before abrasion testing / Factors affecting abrasion tests:

1.          Condition of specimen: The fabric should be conditioned and tested in a standard testing atmosphere.

2.          Choice of testing instrument: The choice of testing instrument may be dependent upon the character of the testing desired, e .g-flat abrasion, flexing abrasion, etc.

3.          Choice of abrasive motion: The rubbing movement may be reciprocating, rotary or multi-directional.

4.          Direction of abrasion: The direction of abrasion can be at angles to the warp and weft directions.

5.          Choice of abradant: The severity of the abrasion will vary with the nature of abradant. For example: steel and silicon carbide give constant abrasive qualities. A standard worsted or canvas fabric, emery cloth of various grade are also used as abradant.

6.          Backing the specimen: The hardness of the backing of the specimen may affect the results. In some testes a hard backing is used, in others a felt or foam rubber.

7.          Cleanliness of the specimen and instrument: The region to be abraded should be handled as little as possible and be free from foreign matter such as graphite of pencils. The accessories of the instrument which may rub the fabric must be spotlessly clean and free from grease.

8.          Tension on the specimen: Standard method of mounting the specimen should be used to avoid errors due to variation in the tension used.

9.          The pressure between abradant and specimen: The severity of the abrasion will be affected by the pressure applied. So suitable standard must be set up.

10.      The end point of the test: The test should be frequently stopped as soon as the hole appeases or the specimen breaks by automatic stop motion.

YARN GEOMETRY

 

YARN GEOMETRY

                                                                                                              

Molecular properties and fiber structure determines fiber properties, which along with yarn structure determines yarn properties, which along with fabric structure determines fabric properties and end use behavior.

Yarn and It’s Classification

Yarn is a product of substantial length and relatively small cross section consisting of fibers or filaments with or without twist. It is the long fine structures capable of being assembled or interlaced into such textile products as woven and knitted fabrics, braids, ropes and cords.

Classification of yarns

A. Single yarn

It is the simplest continuous strand of textile material composed of one of the following: 

i) Continuous filament 

   Continuous filament yarns are the simplest in the structure but can be subjected to many modifying process for changing their texture, extensibility, bulk and other properties. They are of two types-monofilament contains only one filament and multifilament contains two or more filaments.

ii) Spun yarn

Yarn in which a number of discontinuous fibers are held together, generally by twist is called spun yarn. It is of two types-homogeneous, which are spun from only one type of fiber and blended, which are spun from more than one types of fiber.

iii) Modified continuous filament

The continuous filament yarns which are textured or modified to change their appearance and other properties are called modified continuous filament.

B. Multifold yarn

Multifold yarns (formerly called ply yarns) are made by twisting together two or more single yarns.

C. Cabled yarn

Cabled yarns are made by twisting together two or more multifold yarns. Example-cords.

D. Complex yarn

In a complex yarn either a continuous filament core is surrounded by staple fiber or a spun yarn core is surrounded by continuous filaments. It is a special type yarn. Example-core spun yarn.

E. Fancy yarn

Fancy yarns are of decorative interest. They are made by introducing spiral forms of irregularity or hairiness into either spun or continuous filament yarns. Example-slub yarns, snarl yarn, loop yarn etc.

Yarn Designation

           

The factors or parameters which are required to express the yarn structure and properties are called yarn designation. The factors are-

v  Yarn count

v  No. of filaments

v  No. of components in folding

v  Direction and amount of twist

v  No. of components in cabling

v  Fibre components

By yarn designation it is possible to express the identities of single, folded and cabled yarn.

Yarn Twist

Twist is the measure of the spiral turns given to a yarn in order to hold the constituent fibers or threads together. According to Textile Institute “Twist is the spiral disposition of the components of a thread which is usually the result of the relative rotation of the two ends”

Types of twist

According to the direction of twist, it is of two types: S-twist and Z-twist.

S-twist

A single yarn has S – Twist if, when it is held in the vertical position, the fibers inclined to the axis of the yarn conform in the direction of the slope to the central portion of the letter “S”.

Z-twist

A single yarn has Z – Twist if, when it is held in the vertical position, the fibers inclined to the axis of the yarn conform in the direction of the slope to the central portion of the letter “Z”.

Amount of twist

The amount of twist in a thread means the number of turns of twist per unit length in the twisted condition.

If N be the number of turns of twist in L (inch) length of yarn, then the amount of twist,

                                        

Amount of twist in yarn is expressed as TPI, TPCm etc.

Twist contraction

Normally before twisting, yarn contains fiber individually in extended state. By twisting yarn is contracted and mass per unit length increased because when yarns are twisted, the fibers in the yarn have to follow a longer path. For staple yarn, this phenomenon is called contraction. For filament yarn this is called retraction.

Contraction factor

Contraction factor indicates the factor by which the draft must be adjusted to prevent the twist contraction from decreasing the size or count of staple spun yarn. Contraction factor may be expressed as,

                  

Retraction factor

It represents the fractional decrease in length or increase in the linear density on twisting continuous filament yarns. Retraction factor may be expressed as,

                   

                        

                

Its value ranges from 0 to 1.

Packing of fibers in yarn

The idealized packing of circular fibers in the yarn can be described by two basic forms-open packing and close packing.

Open packing

Open packing is that, in which the fibers lie in layers between successive concentric circles. At the center of the open packed assembly of circular fibers, there is a single fiber. Around this, six fibers can be packed, to that all seven fibers are touching. The third layer is added so that the fibers just touch the circles which circumscribe the second layer of six fibers.

 

                                       

Close packing 

Close packing is that, in which the fibers fit into a hexagonal pattern. Here with a single fiber core, close packing of circular fibers give a yarn with a hexagonal outline in which all are touching each other.

 

  

                                                                    

       

Packing fraction or packing density 

The yarn specific volume is always more than that of fiber themselves. This relation can be analytically expressed in terms of a parameter called packing fraction.

Packing fraction is the ratio of specific volume of fibers in yarn to specific volume of yarn after packing.

For filament yarn, φ = 1

For staple fiber yarn φ = 0.6

THERMAL PROPERTIES

 

THERMAL PROPERTIES

Thermal Properties:

The behaviour shown by a textile material when it is subjected to heat is known as thermal property. Followings are the thermal properties of a textile material-

v  Thermal conductivity

v  Glass transition temperature

v  Melting temperature

v  Thermal expansion

v  Heat of wetting or heat of absorption

v  Heat setting

v  Thermal conductivity:

Thermal conductivity is the rate of transfer of heat in calorie along the body of a textile material by conduction. Higher conductivity of a material indicates that the heat will pass through the material very easily.

Woolen dresses are comfortable to wear during winter season due to its lower conductivity and cotton dresses are comfortable to wear in summer season because of its higher conductivity.

Typical values of thermal conductivity for some fibres:

Fibre                                      Thermal conductivity (mWm^-1K^-1)

Cotton                                      71

Wool                                        54

Silk                                           50

(Above thermal conductivity of fibres with a bulk density of 0.5 gm/cm³)

PVC                                          160

Cellulose acetate                    230

Nylon                                       250

Polyester                                 140

Polyethylene                           340

Polypropylene                          120

v  Glass transition temperature:

The temperature up to which a textile material behaves hard as like glass and after which it behaves soft as like rubber is known as glass transition temperature and it is expressed by Tg. The range of Tg lies between -100⁰ C to 300⁰ C.

Factors influence the Tg value of polymers:

v  Higher the flexibility of chain bond, lower will be the Tg value.

v  Composition of ring structure in molecular chain raises the value of Tg.

v  Bulky side groups raise the value of Tg.

v  Flexibility of side groups decreases the value of Tg.

v  Tg increases with molecular weight upto 20,000.

v  Polarity of side groups increases the value of Tg.

v  Co-polymers have lower value of Tg than homo-polymers.

v  Increase of orientation restrict the chain movement and increase the value of Tg. (Tg of undrawn polymer fibre is 110⁰C whereas Tg of fully drawn polymer fibre is 150⁰C)

v  Melting temperature:

The temperature at which a textile material melts is known as melting temperature and it is expressed by Tm. At melting temperature a polymer losses its identity and change into viscous liquid. It losses its strength and some molecular weight at melting temperature. Cellulose and protein fibres decompose before melting.

Typical values of T_g and T_m for some MMF:

Fibre                                                      Tg (⁰C)                                                     Tm (⁰C)

Nylon-6                                        50                                             215

Nylon-6.6                                     50                                             260

Polyester                                     69                                             260

PVC                                              81                                             310

PAN                                             97                                             314

Rubber                                                  -73                                             36

Cellulose tri-acetate                     -                                              300

v Thermal expansion:

Thermal expansion is the increment of length of a textile material after heating. Thermal expansion is measured by co- efficient of thermal expansion. Co-efficient of thermal expansion can be defined as the fractional increase in length of a material due to rise in temperature by 1⁰ C.

Co-efficient of thermal expansion = Increase in length x100             

                        Initial length of a textile material

v Heat of wetting or heat of absorption:

When textile materials absorb water they show their ability to leave off small amount of heat which is known as heat of wetting or heat of absorption.

If 1 gm dried material is completely wetted, then heat in calorie/gm involved in that material is known as heat of wetting.

v Heat setting:

                   

Heat setting is the process of stabilizing the form, size and dimension of the material by drying and cooling in successive dry and wet condition.

For manmade fibre, heat setting process must be done to keep the dimension of fabric during further heat treatment. Usually, spandex or elastane is heat set at 180-200⁰C based on different brands. After heat setting material becomes able to keep its dimensions up to setting temperature. Heat setting is usually done by hot air or steam flow treatment.