2. F AM AB IT OF F RICS
L M IL Y
AB
• 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
3. Factors affecting flame-resistance
• 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.
Principles of Textile Testing – J.E. BOOTH
4. 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;
Principles of Textile Testing – J.E. BOOTH
5. 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
Principles of Textile Testing – J.E. BOOTH
6. 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.
Principles of Textile Testing – J.E. BOOTH
7. Flame-Proofing and Flame-resistant finishes
• 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.
Principles of Textile Testing – J.E. BOOTH
8. Methods 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.
• T vertical flame speed in then readily calculated
he
from the rate of loss of weight, the initial weight of
the fabric, and the weight of the residue.
• Although
considered
unsuitable
conditions.
the torsion balance procedure is
valid for all types of fabric, it is
for practical purposes in industrial
T fact has led to the development of
his
Principles of Textile Testing – J.E. BOOTH
9. 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 ThwingAlbert, 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.
Principles of Textile Testing – J.E. BOOTH
10. 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
Principles of Textile Testing – J.E. BOOTH
11.
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.
M
ethod 2 & 3 are not suitable for fabrics which drip while
burning.
T results of the test using the torsion balance procedure
he
Principles of Textile Testing – J.E. BOOTH
13. 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.
Principles of Textile Testing – J.E. BOOTH
15. Progress in Flammability Testing
• 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.
Principles of Textile Testing – J.E. BOOTH
16. Method 1.
• 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 ‘afterflame’ 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.
Principles of Textile Testing – J.E. BOOTH
17. Method 2.
• 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.
Principles of Textile Testing – J.E. BOOTH
18. Conclusions from available date
• 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 = 9.3
where 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
Principles of Textile Testing – J.E. BOOTH
19. • 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)
Principles of Textile Testing – J.E. BOOTH
21. • 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.
Principles of Textile Testing – J.E. BOOTH
22. •
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 unaffected.
Principles of Textile Testing – J.E. BOOTH
23. 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
.
Principles of Textile Testing – J.E. BOOTH
24. 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
Principles of Textile Testing – J.E. BOOTH
