Evaluation of finishes

Crease ResistanceFlame Resistance Surface property changes

Presented by T. Sri vani,Asst. Prof., DFT.

FLAMMABILITY

Flameproof fabrics are absolutely necessary for protective clothing in many industrial processes where the chances of inflammable fabrics being ignited are high.

Some definitions and terms used relating to flammability

Flammable: A flammable fabric is one which propagates flame, i.e. it continues to burn after the igniting flame has been removed.Flame-resistance rating: the time in seconds necessary for the propagation of flame 100 in, in a vertical strip.Flame-proof: a flame proof fabric is one which does not propagate flame, i.e. any flame goes out quickly when the igniting flame is withdrawn, the material.

Flame-resistant A flame resistant fabric is one whose flame resistant rating is high i.e. above 150.

Inherently flame-proof material: Material which, although not submitted to a flame-proofing process, is flame-proof.

Durably flame-proof material: flame proofed material which after being submitted to a washing treatment, remains flame proof.

Factors affecting flame resistance

Fibre content Type of yarn Fabric structure Fabric weight Fabric surface Finishes applied Type of exposure to flame Temp. flame Flame Exposure time

1. The vertical flame speed is then readily calculated from the rate of loss of weight, the initial weight of the fabric and the weight of the residue.2. The visual timing test in which the rate of flame spread is determined over fabric suspended vertically3. The 45O test in which the time, t, for the flame to travel 5 in. over fabric sloping at an angle of 45O is measured in seconds. The flame resistance rating, M, is then given by 2.5 x T.4. The hoop test in which the rate of flame spread is determined over the fabric mounted on a semicircular frame.

All of these have their merits for special purposes, but research has demonstrated that none of them is valid for all types of fabric.

Method (1) for instance, is impracticable for those which are highly flammable and burn very quickly, but it is very good for slow burning ones;

The results yielded by method (2) do not show good statistical correlation with those of the torsion balance method throughout the whole range of fabrics,

Methods (2) and (3) are not suitable for fabrics which drip while burning.

Method A, basically this method is the vertical strip test in which the rate of propagation of the flame is measured in terms of the distance in millimeters per minute that the base of flame travels up a strip 900mm long and 75mm wide. The time to travel between two markers 500mm apart is observed. The rate of propagation is then given as (500/t) x 60 mm/minute, where t is in seconds.The duration of after flame, i.e. the time in seconds that elapses between the removal of the standard gas lighting flame and the flame extinction.After-glow is also noted the time in seconds between flame extinction and the end of any glowing.

Method B, some fabrics, particularly those made from thermoplastic materials, do not burn in a convenient manner for a satisfactory strip test to be made; they melt, shrink or curl away from the flame. In Method B, the test specimen is hung in sheet form and the igniting flame applied at right-angles to the sheet and near to the bottom edge. The amount of damage and time taken is observed and reported.

Method C, This test is concerned with the transmission of flame across pile fabrics.

Where required these flammability tests may be repeated after washing and dry cleaning, or leaching, in order to determine the durability of any flame-resistant treatments.

Fabrics comprising mixtures of fibres have a flammability inter-mediate between that of the two fibres, and very often characteristic of the more flammable constituents.

Flame-proofing and flame-resistant finishes

Special chemical finishing processes have been developed which reduce the flammability of the treated fabrics. Some recent developments of such finishes are Proban, Antiflamm, and Lifeguard.

In addition to reducing the flammability of the fabric, such finishes should Be permanent and not disappear at the first laundering or cleaningBe non-toxicBe non-irritant to the skinLeave the handle and other desirable fabric properties un-affected

Flammability test:

The scale of evaluation used for apparel:

Class 1: Normal flammability These textiles are generally accepted by the trade as having no unusual burning characteristics.

Class 2: Intermediate flammability These textiles are recognized by the trade as having flammability characteristics between normal and intense burning

3. Class 3: Rapid and intense burning These textiles are considered dangerously flammable and are recognized by the trade as being unsuitable for clothing

Based on the time of flame spread, the test fabric can be classified in to:

For fabrics having no raised surface:

a. If the time of spread is 3.5 seconds or more class 1 flammabilityb. If the flame spread is less than 3.5 seconds- class 3 flammability

For fabrics having raised surface:

a. If the time of spread is 7 seconds or more - class 1 flammabilityb. If the fabric burns with surface flash but the base fabric does not ignite, char, or fuse - class 1 flammability c. If the time of spread is 4 seconds or more but less than7 seconds - class 2 flammability d. If the flame spread is less than 4 seconds and flame intensity is sufficient to ignite, char, or fuse the base fabric - class 3 flammability

Significance of testing flammability of childrens sleep wear:

The standards for flammability of childrens sleepwear were issued to protect young children from death and serious burn injuries associated with ignition of sleep wear garments, such as night gowns and pajamas, by small open flame sources.

These standards cover two size ranges of childrens sleep wear.One standard covers sizes 0-6 and The other standard covers sizes 7-14

The flammability of childrens sleepwear sizes 0 to 14 is evaluated by the Vertical flammability test.

The safety requirements of the two standards are nearly identical.

Test requirements: Specimens of fabrics, Seams and trims of childrenssleep wear garments must self-extinguish after exposureto small open flame.

Both standards require - Manufacturers to test prototypes of sleep wear garments with acceptable results before productionTo sample and test garments from regular production

Failure to comply with the sampling and testing requirements of the standards is a violation of law.

Vertical flammability test

Exclusively used for testing childrens sleep wear.

Test method: A sample consists of 5 test specimens, eachmeasuring 3.5 in x 10 in. Each specimen is mounted in a Special U shaped holder.

Oven dry the sample for 30 min at 105 C and cooling for 30min in a desiccator

The samples are suspended vertically in the chamber one at a time and subjected to flame impingement along the center bottom edge for 3 seconds and allowed to burn

The char length for each specimen is measured and recorded

Char length: the distance from the original lower edge of a specimen to the end of the tear or void in the charred, burned, or damaged area of the specimen.

Test criteria: Three samples consisting of five specimens each are tested. An item is considered acceptable if

The average char length of the five specimens that make up a sample does not exceed 7.0 inches andThe full specimen burn of any individual specimen is not its full length, i.e., 10.0 inches

Flammability testing is done at any one of the stages likeFabric, Garment prototype and production sample

Fabric sampling: 3 sampling plansNormal A fabric sampling unit is any length of fabric upto 5,000 yards- A sample of 5 specimens is taken from the beginning and end of the roll of fabric

Reduced A fabric sampling unit is increases upto 10,000 yards. A sample of 5 specimens is taken from the beginning and end of the roll of fabric

3. Tightened - A fabric sampling unit is same as normal sampling. An additional sample is taken from the middle of the fabric roll

Normal sampling 15 samples acceptedreduced sampling

Reduced sampling 1 sample rejectedNormal sampling

Normal sampling 1 sample rejectedTightened sampling

Tightened sampling 5 consecutiveNormal sampling samples accepted

Tightened samplingremains in effect Production must be for 15 consecutive discontinued until fabric units,the flammability of the fabric improved

Measurement of crease recovery or crease resistance:

The test must however be carried out in a standard testing atmosphere and on a pre conditioned fabric

Warp and weft way recovery are reported separately to the nearest degree from the mean values of ten tests in each direction.

A random sample should be taken but the selvedges, piece ends and creased or folded regions should be avoided.

THE TOOTAL TEST

Test specimens are cut from the fabric in both warp and weft directions, 4cm long by 1cm wide.

The specimen is folded over and creased by placing It under a strip of spring steel with a 500 g weight to to supply the pressure for creasing.

After 5 min, the specimen is removed and suspended over a wire and allowed for recovery for 3 min ,after which the distance between the ends of the inverted Vis read from a scale engraved ona mirror below the wire To avoid touching of the specimen.

The Shirley crease recovery test: The combined stiffness and crease recovery tester.

The instrument consists of a circular dial which carries the clamp for holding the specimen

Directly under the center of the dial is a knife edge and an index line for measuring the recovery angle.

The scale of the instrument is engraved on the dial

The load time of creasing and recovery time may be altered to suit particular cases.

The Shirley crease recovery tester

A specimen is cut from the fabric with a template, 2in long by 1in wide.

It is carefully creased by folding in half, placing it between two glass plates, and adding a 2kg weight.

After 1 min, the weight is removed and the specimen is transferred to the fabric clamp on the instrument and allowed to recover from crease.

As it recovers, the dial of the instrument is rotated to keep the free edge of the specimen in line with the knife edge.

After I min, the recovery angle in degrees is read on the engraved scale.

Continental method:

A strip of fabric is folded over at one end, loaded by 1 kg for 1 hr and allowed to recover.

The specimen lies in a horizontal position and the foldedPiece recovers in an upward direction.

The angle of recovery is then measured after 5 min and again after 1 hr.

A time schedule for measurement of 10 warp way and 10 weft way specimens is set, so that testing proceeds without undue delays.

The L.I.N.R.A. Sunray crease evaluator:

It is a quick test of crease recovery in which the clenchedFist test is done by crushing the fabric in the hand and then allowing for recovery for visual appraisal of crease recovery.

A circle of fabric 4in in diameter is cut along one radius folded fanwise and inserted in a specially designed loading device.

The folded specimen is loaded with a 10 lb weight for 3 min and later the specimen is removed and placed in a polished glass Petri dish. A standardized method of shaking the specimen is employed to assist recovery.

The sample is then scanned whilst rotating on a turn table by a beam of light at right angles to the radial creases and at an angle of 20 degrees to the horizontal.

The varying amount of light reflected vertically upwards is picked up by a photo cell and the fluctuations in the voltage output are fed in to a circuit which enables the degree of crease recovery to be derived.

A correction is made to the value obtained, since even flat fabric would reflect some light vertically.

Visual comparison against standards:

The fabric is creased in a random manner and then assessed against either photographic standards or against three dimensional replicas of creased fabrics.

Celanese wrinkle tester is used to test with the replicas of creased fabrics

This tester causes creasing by suspending the fabric specimens in a rubber tube and then partially exhausting the air, causing the tube to collapse and thus crease the fabric.

Surface properties of fabricsAbrasion resistancePillingThick nessAir permeability andWater resistanceSoil releaseMartindale abrasion resistance and pilling testers

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