Flame evaluatio

FLAMMABILITY OF FABRICS• The term inflammability refers to the ease of ignition and

burning rate of fabrics.

• The flammability of fabrics (particularly drapery, textile covering and clothing fabrics) constitutes a danger in ordinary conditions of use.

• The flame response of textile fibres is linked to their L.O.I. (limit oxygen index), which indicates the minimum quantity of oxygen a fibre needs in order to burn.

• Given that the percentage of oxygen in the air is around 21%, it is clear that all fibres with an L.O.I. lower than this level will burn easily, while those with a higher L.O.I. will tend not to burn.

• From the table it can be seen that polyester, polyamide both of these melt and form viscous masses and cellulosic fibres are highly flammable.

Principles of Textile Testing – J.E. BOOTH

• Some general conclusions on the factors which affect the flame-resistance of fabrics are included in a report published by the British Standards Institution, The Flammability of Apparel Fabrics in Relation to Domestic Burning Accident.

Fibre Content • The flame-resistance of a fabric is partly dependent on the

fibre from which it is made. Cellulosic fibres such as cotton, flax and viscose rayon give fabrics of low flame-resistance;

• Wool fabrics are usually difficult to ignite;

• Nylon and Terylene both thermoplastic fibres, shrink from the flame and tend not to ignite, although special stiffening treatments and certain dyes may result in the flammability of nylons and Terylene.

Factors affecting flame-resistance


Type of Yarn• It has been found that for all practical purposes yarn structure in

itself does not affect the flame-resistance of a fabric.

Fabric Structure• The flame-resistance of a fabric appears to be largely

independent of the manufacturing process by which it has been made, e.g. weaving, knitting , twisting, lace making fibre bonding, felting.

Fabric Weight• For fabrics which propagate flame it has been found that flame-

resistance is related to their weight as well as to their fibre content; for any given fibre, the heavier the fabric the higher will be its flame resistance.

• For a given fibre the flame resistance rating of a fabric has been found to be directly proportional to its weight in ounces per square yard;


How fire retardants work

• Most all of the FR compounds have a few elements in common that provide the necessary protection - namely boron, phosphorous, nitrogen and halogens

1. Boron

• Boric acid (H3BO3) and borax (Na2B4O7) are often used as non-durable flame retardants in applications such as cellulose batting and shredded newspaper for insulation.

• Boron functions in the condensed phase as a lewis acid and coats the fiber with a glassy polymer to insulate the polymer


2. Phosphorus and Nitrogen

• Phosphorus and nitrogen also work in the condensed phase. Phosphorus compounds react with the C(6) hydroxyl of the anhydroglucose unit.

• This reduces the amount of fuel to the flame. Additionally, phosphorous promotes char formation. The acidity associated with certain phosphorous analogues and its electrophilic nature lowers the activation energy for dehydrating cellulose.

• Nitrogen alone is not an effective flame retardant, however it acts synergistically with phosphorous.

• It is thought that nitrogen reacts with phosphorous to form polymeric species containing P-N bonds.


• Special chemical finishing processes have been developed which reduce the flammability of the treated fabrics.

• Marsh discusses some of these processes in An

Introduction to Textile Finishing.

• Some recent developments have led to the introduction of such finishes as ‘Proban’, ‘Antiflamm’, and ‘Lifeguard’ and are mentioned in the B.S.I. publications P.D. 2777:1957.

Flame-Proofing and Flame-resistant finishes


Methods of test for evaluationMethods of test for evaluation• It is not easy to measure directly the vertical flame

speed over rapidly burning fabrics as the flame front is not well defined. It is, however, possible to measure the vertical flame speed indirectly by weighing the fabric continuously on a torsion balance while it is burning.

• The vertical flame speed in then readily calculated from the rate of loss of weight, the initial weight of the fabric, and the weight of the residue.

• Although the torsion balance procedure is considered valid for all types of fabric, it is unsuitable for practical purposes in industrial conditions. This fact has led to the development of alternative procedures which are specified in detail in various British Standards.


Evaluation of the flame retarding performance and stiffness of the fabric The vertical flammability of the fabrics was measured according to ASTM Standard Method D6413.

The limiting oxygen index (LOI) of the fabrics was measured according to ASTM Standard Method D2863.

The fabric stiffness was measured according to ASTM Standard Method D6828 using a “Handle-O-Meter” tester (Model 211-300) manufactured by Thwing-Albert, Philadelphia.

The slot width was 5 mm, and the beam size was 1000 grams. The fabric stiffness presented in this paper was the mean of measurements of 5 specimens.


Among these alternatives are as follows : 1. The visual timing test – in which the rate of flame spread is determined over fabric suspended vertically.

2. The 45° test – in which the time t, the flame to travel 5 in. over fabric sloping at an angle of 45° is measured in seconds. The flame resistance rating, M, is then given by 2.5 x t.

3. 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 type 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 burnings once.

Method 2- do not show good statistical correlation with those of the torsion balance met.

Method 2 & 3 are not suitable for fabrics which drip while burning.

The results of the test using the torsion balance procedure have accordingly been preferred as the basis of consideration by the BSI committee hod throughout the whole range of fabrics


Instrument

45 Degree tester

45 degree tester vertical tester


PEKOFLAM• PEKOFLAM is applied to cotton fabric in the form of flame

retardant finish. The starting materials were dress materials with GSM in the range 80-260.

• Along with commercial dress material, a grey fabric was included in the experiment and was subjected to finishing in stages. The finishing agent was applied from 300-500gpl and products were characterized for mechanical properties.

• An improvement in tearing strength following finishing was the highlight of the present investigation.

• It is desired for a technical textile to exhibit higher tearing strength depending on the conditions of use. The results also confirm increase in drape coefficient value which is necessary for a protective textile.


• An interim report on flammability testing was published in 1965. Both the vertical strip test and the 45° test were examined critically and several recommendations on further work to be done were made.

• In February, 1967 the Flammability Working Party was established and in January, 1968 a revised Draft British Standard for the testing of the flammability of fabrics was publihsed.

Progress in Flammability Testing


• 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 900 mm long and 75 mm wide.

• The time to travel between two markers 500 mm apart is observed. The rate of propagation is then given as (500 / t) x 60 mm / minute, where t is in seconds.

• Other information derived and reported includes 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.

• The extent of charring is given by ‘char length’. This is the difference in millimeters between the original specimen length and the undamaged length of the specimen.

Method 1.


• Some fabrics, particularly those made from thermoplastic materials, do not burn in a convenient manner for a satisfactory strip test to be made; then melt, shrink or curl away from the flame.

• The test specimen is hung in sheet from 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 3.• 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 bleaching, in order to determine the durability of any flame-resistance treatments.

Method 2.


• All cellulosic materials, wood, paper and textiles propagate flame at a rate which is inversely proportional to their weight per unit area.

• In fact, a useful formula to have in mind for cotton and viscose rayon fabrics is

WV = 9.3where W is the weight in ounces per square yard, and

V is the vertical flame speed in inches per second.

Since the flame resistance index M is the time taken for flame to be propagated vertically 100 in., the above result may be written

M = 10.8W

Conclusions from available date


• The corresponding expressions for other fibres have been determined with less precision because up to the present it has not been possible to test such a wide range of materials as for cellulosic fabrics, and because of the variations in the results for various thermoplastic fibres.

• The following relations are put forward tentatively;

WV = 8 or M = 12.5 W (60% wool & 40%Cotton )

WV = 2.9 or M = 35 W (wool)


Description Weight per unit area oz/yd2 Rating

20% wool 80% cotton 3.7 56

20% wool 80% cotton 4.0 48

40% wool 60% cotton 3.5 45

40% wool 60% cotton 4.4 50

50% wool 50% viscose 7.7 149

55% wool 45% cotton 3.9 50

60% wool 40% cotton 3.7 44

60% wool 40% cotton 4.1 59

50% wool 50% nylon 8.5 ∞

50% wool 33% viscose 17% nylon 7.7 213

50% wool 33% nylon 17% viscose 8.6 ∞

67% viscose 33% fibrolane 5.4 56



67% viscose 33% fibrolane 9.1 71Principles of Textile Testing – J.E. BOOTH

• These figures would indicate that for fabrics of comparable weights, wool – cotton mixtures are about as flammable as cotton and viscose.

• The lower speed of propagation of flame over acetate,

silk and wool fabrics is due to the fact that they melt and drip during burning, and as each burning drip falls the flame front is momentarily checked, some of the heat from combustion have been removed.

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

• Pure nylon and Terylene do not propagate flame continuously in a vertical direction.


• Generally in addition to reducing the flammability of the fabric, such finishes should be

1. permanent and not disappear at the first laundering or cleaning.

2. non-toxic.

3. non-irritant to the skin.

4. Leave the handle and other desirable fabric properties un- affected.


RISK EVALUATION

• Although the inherent toxicological hazard of each flame retarding chemical is invariable, the risk evaluations are not performed for the chemical itself but for each flame retardant-textile-system separately because the exposure scenarios and the estimated human exposures are variable.

• A second reason is the necessity to demonstrate the need and benefit for the specific application of a flame retardant to enable a risk management by evaluating the risk to benefit relation.

• Quantitative risk evaluations are performed for effects

where a NOAEL could be determined.


REFERENCES

• Principles of Textile Testing – J.E. BOOTH

• FIBRE TO FABRIC- B.P. Copman

• Textile Progress – P.W.Harrison

• Introduction to Textile Finish – J.V.MARSH


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Flame evaluatio

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