Tuesday, June 29, 2010

TESTING METHOD

When an article is produced, it has to be suitable for its end-uses - it must conform to a set of specifications that have been laid down for it. Quality in textile products can thus be defined as the extent to which an article conforms to its specifications.

For example, a shirt should not only be attractive and fit, but should also possess quality criteria such as shape retention after washing, resistance to colour fading, or lasting wear. A method to evaluate the textile products relative to these quality aspects is to conduct tests that simulate actual wear conditions. This is done by taking a sample of the material and testing it (for example, by extending or tearing it) using various instruments. Experiments are conducted by research organizations, government standards institutions, consumer organizations, and textile buying offices to evaluate the quality of textile articles, and establish minimum performance requirements.

The following section will consider some of the common tests which are performed on textiles (most of the tests discussed are based on British Standards).
 
Abrasion resistance
The abrasion of a fabric is the rubbing away of its fibres and yams. The ability of a fabric to resist abrasion can be tested in a number of ways. One way is by the ‘flexing and abrasion method’ which can be used for all fabrics except floor coverings. Using a flex abrasion tester, a sample of predetermined dimensions is pulled and rubbed in continuous cycles until it breaks. Its abrasion resistance is determined by the load applied by the tester, and the number of cycles taken to break the sample. Visual inspection of the abrasion is also made. The ‘Martindale Tester’ is also well known. In this apparatus, the sample fabric is rubbed against a standard fabric until it wears through.
[International testing standards: Martindale - BS 5690, JIS L-1096, Accelerator - JIS L-1096 (woven), JIS L-1018 (knit). AATCC 93]
 
 Bursting strength
Some fabrics, especially knitted ones, are stressed in many directions at one time. The bursting strength of a knitted fabric is the ability of the material to resist rupture by pressure. To test the bursting strength of such fabrics, a hydraulic bursting strength tester can be used. A fabric sample is clamped over a thin flexible diaphragm, which expands as the pressure increases. The fabric eventually bursts, and the pressure gauge reading gives a measure of the bursting strength of the fabric.
[International testing standards: ASTM D3786, BS 4768, ISO 2360, JIS L-1096]
 
Colour fastness
An important property of fabric is its colour fastness or ability to keep its original colour. To assess the amount of colour change or staining that takes place in a fabric, ‘grey scales’ are used. The grey scale for assessing colour change rates the results of a test from class 1 (poor, substantial change of colour) to class 5 (excellent, no change in original colour). Similarly, the grey scale for assessing staining rates the results from class 1 (heavy staining) to class 5 (no staining).
There are different types of colour fastness which need to be tested as the colour of a fabric can be affected by a variety of factors.

1 . Colour fastness to washing/dry-cleaning
The apparatus used for this test is known as a launderometer. Specific sizes for fabric swatches are prepare for laundering, one being retained for colour change comparison. The colour change is assessed by using the grey scales under standard lighting conditions. Any staining is measured in the same way.
[International testing standard, AATCC 61, BS 1006, DIN 54014, DIN 54011, ISO 105, JIS L-0844]
 
2. Colour fastness to dry and wet crocking
The crockmeter test determines the degree of colour which is transferred from one surface to another by rubbing. The test reveals the presence of surface dyes that have not been removed properly by rinsing, or a failure of the dye class to give good dye affinity and fixation. The test, which can be done under either wet or dry conditions, involves mounting the fabric sample in a crockmeter, which rubs it in continuous cycles against a standard white test fabric. A fixed pressure is applied for a set number of cycles, and the amount of colour which is stained onto the white test fabric is then assessed by comparing it with the grey scale for assessing staining.
[International testing standards: AATCC 8, BS 1006 X12, ISO 105 X12, JIS L-0849, IWS TM 165, AS 2001.4.3]
 
3. Colourfastness to bleaching
In this test, after the sample is bleached, grey scales are used to evaluate the colour change, and the result is compared with commercially accepted standards.
[International testing standards: Hypochlorite - AATCC 3, ISO 105 NO1, BS 1006 NO1, JIS L0856. Peroxide - AATCC 101, BS 1006 N02, ISO 105 N02]
 
4. Colour fastness to perspiration
In this test, a fabric sample is soaked with a simulated perspiration solution. It is then subjected to mechanical pressure and allowed to dry slowly in certain atmospheric conditions for a period of time (as specified by testing standard). Changes in colour and staining are assessed by the appropriate grey scales.
[International testing standards: AATCC 15, BS 1006 E04, ISO 105 E04, JIS L-0848]
 
5. Colour fastness to light
It is important for fabrics such as curtains and upholstery to have good light fastness properties. In the test, a fabric sample is exposed to daylight under given conditions, including protection from rain, together with eight dyed wool standards. Its colour fastness is assessed by comparing the colour change of the sample with that of the standards. Results range from class I (substantial colour fading) to class 8 (no colour fading).
[International testing standards: BS 1006 B02, JIS L-0843, ISO 105 B02, AATCC 16E] 

Dimensional stability
The dimensional stability test is designed to show how well a fabric keeps its shape after washing, Washing usually results in shrinkage, although some fabrics can expand, or gain, after washing, For this test, the washing time and temperature, drying procedure and restoration technique (such as ironing) are all specified, and options are available. The sample is measured in both the warp and weft directions (or wales and courses for knitted fabrics). The percentage of shrinkage (gain) is calculated and the results compared with commercially accepted standards.
[International testing standards: BS EN 25077, BS 4923, ISO 5077, ISO 6330, AATCC 135, AATCC 150] 

Flammability
It is important to know both whether a fabric will bum or not, and, if it does, how quickly the flame will spread through it. The flammability testing procedure therefore determines both whether a fabric will ignite and the time that it takes to bum. Standardized conditions are applied including the size of the sample, the flame length used, and the timing of the test. The fabric sample is first placed in an oven at about 105° C for 30 minutes, then put in a flammability tester where a flame is applied and the result observed. The fabric is then classified according to whether it burned, and if so, how long the flame took to spread.
[International testing standards: General Clothing Textiles - ASTM D1230, US CPSC CFR 16 Part 1610, Canadian Hazardous Products Act, UK Flammability BS 5438]
 
Seam strength/slippage
The seam slippage of a woven fabric refers to the ability of a seam to withstand forces trying to pull it apart. A strip of fabric is folded and stitched across the width of the seam. A load is then applied to the strip at right angles to the seam using ‘grab-test’ jaws, and the extent to which the seam opens is measured. The seam strength is recorded as the seam breaks under test conditions. The measuring equipment gradually increases the axial load on the sample (the load applied depends on the testing requirements) and the width of the seam opening at its widest place is measured to determine the seam slippage.
[International testing standard: ASTM D1683, ASTM D434, JIS L-1093/ 1096, BS 3320]

Tear strength
This term means the force required expressed in units of weight to tear a fabric. A fabric sample of standard dimensions (according to the testing requirements) has a slit cut into it. The testing apparatus then measures the work done in tearing a fixed distance through the cloth. The ‘Elmendorf’ is a popular tearing tester.
[International testing standards: Elmendorf - ASTM D1424, JIS L-1096 Tongue Tear (single/ double) - ASTM D226 1, JIS L- 1096, Wing-Rip - BS 4303]
 
Tensile strength
This term refers to the breaking load or force, expressed in units of weight, required to break or rupture a specimen. A number of methods can be used to test the tensile strength of a textile sample such as fibre, yarn or cloth. The sample is clamped between two sets of jaws, a force or load is applied to it until it ruptures and the average breaking load is recorded in the 'Strip Test', and the ‘Grab Test’.
[International testing standards: One-inch Grab - ASTM C5034, ISO 5082, JIS L-1096, Strip Test - ASTM D1682, ISO 5081, BS 2576, JIS L- 1096]

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