Flame retarding and fire blocking fiber blends

Flame retarding and fire barrier structure comprising a blend of carbonaceous fibers and natural and/or synthetic fibers. The carbonaceous fibers have a nitrogen content of 5 to 35%, an LOI value of greater than 40 and are derived from stabilized acrylic fibers.

FIELD OF THE INVENTION 
The present invention relates to flame retarding and fire barrier 
structures and fabrics. More particularly, the invention is concerned with 
structures and fabrics comprising a blend of carbonaceous fibers with 
synthetic and/or natural fibers, and a method for using said structures. 
BACKGROUND OF THE INVENTION 
The prior art has used asbestos, carbon and graphite short straight staple 
felts, and various ceramic mateials, particularly ceramic foams as thermal 
insulation having fire blocking properties. The bulk densities of some of 
the well know thermal insulating mateials are in the range of 0.35 to 2 
pounds per cubic foot (5.6-32.04 kg/m.sup.3) for insulating materials 
useful at temperatures not exceeding 120.degree. C., and from 2 to 5 
pounds per cubic foot (32 to 80 kg/m.sup.3) for the high temperature 
(about 3000.degree. F.) insulating materials. Even the newest "light 
weight" insulating material recently disclosed comprising a ceramic from 
which a carbonaceous material has been burned out has a bulk density of 
about 2 to 6 pounds per cubic foot (32 to 96 kg/m.sup.3). In addition, 
with the possible exception of fiberglass which may be used under certain 
conditions as a fire block, the common thermal insulating materials having 
fire block properties, such as carbon or graphite felts and ceramic 
materials, do not have any resiliency, i.e., they do not have the ability 
to recover from compression of the original "loft". Further, these prior 
art materials are not compressible from their original loft to any great 
degree since substantially straight or linear fibers do not have 
substantial distance between the fibers, thus there is very little loft 
between the linear fibers and therefore substantially no compressibility. 
Both government and industry have conducted extensive research into 
developing fabrics that would either be non-flammable or at least retard 
the propagation of a fire. In conjunction with finding an effective 
material to act as a fire barrier, consumer considerations require that 
any such materials to be functional, aesthetically acceptable and 
reasonably priced. 
Unfortunately, past efforts to develop a suitable fire barrier have not 
been very effective. Thus, even fabrics that will not ignite from a 
smoldering cigarete and that are considered to be class 1 fabrics under 
the UFAC upholstery fabric classification test will burn when placed in 
contact with an open flame. Consequently, this leads to the ignition of an 
underlying batting in a cushion or mattress. 
So-called fire retardant foam coatings for draperies, liners and 
backcoatings for upholstery, as well as chemical treatments for apparel 
fabrics that attempt to provide a fire retardant quality to the fabric are 
commercially available. Unfortunately, these materials are, at best, self 
extinguishing only when the source of the flame is removed. If the flame 
source is not removed, these mateials will char, lose their integrity and, 
most importantly, will not prevent the flame from reaching materials 
underneath the fabric covering which act as a major source of fuel for the 
fire. 
Other attempts at solving the flammability problem have centered on the use 
of inherently non-flammable fabrics such as fiberglass which can be used, 
for example in draperies. It has been discovered, however, that the glass 
fibers are self abrasive in that they rub against each other thereby 
becoming self-destructing due to the abrasive action. Thus, hand washing 
and like drying is, out of necessity, the recommended cleaning procedure 
for such fabrics. Moreover, the brittle and broken glass fibers tend to be 
very irritating to the skin thus rendering nay of the applications of the 
fabric unsuitable where there is extensive skin contact. Fiberglass 
fabrics usually contain flammable sizing binders and/or finishes to 
provide an aesthetic appearance. 
Consequently, there is a need for fabrics, battings and the like which not 
only provide fire shielding properties but also are washable, light weight 
and can be fabricated into aesthetically acceptable fabrics for home and 
commercial use. 
U.S. Pat. No. 4,588,635 to James G. Donovan discloses light weight thermal 
insulation material which is a blend of spun and drawn, crimped, staple, 
synthetic polymer microfibers having a diameter of from 3 to 12 microns, 
and synthetic polymeric staple microfibers having a diameter of more than 
12 and up to 50 microns. However, the insulation material is flammable. 
U.S. Pat. No. 4,167,604to William E. Aldrich discloises the use of crimped 
hollow polyester filaments in a blend with fowl down in the form of a 
multiple ply carded web which us treated with a thermosetting resin to 
form a batting having thermal insulating characteristics. The web, 
however, does not have fire retarding characteristics. 
U.S. Pat. No. 4,321,154 to Francois Ledru relates to high temperature 
thermal insulation material comprising insulating material fibers and 
pyrolytic carbon. To make the insulation light weight, an expanding agent 
is utilized that is composed of a hollow particles such as microspheres. 
European Patent Application 0199567 of McCullough, et al discloses 
non-linear carbonaceous fibers which are used in the structures and 
fabrics of the present invention. 
The carbonaceous fibers of the invention according to the test method of 
ASTM D 2863-77 have a LOI value greater than 40. The test method is also 
known as "oxygen index" or "limited oxygen index" (LOI). With this 
procedure the concentration of oxygen in O.sub.2 /N.sub.2 mixtures is 
determined at which a vertically mounted specimen is ignited at its upper 
end and just continues to burn. The size of the specimen in 0.65 
.times.0.3 cm with a length from 7 to 15 cm. The LOI value is calculated 
according to the equation: 
##EQU1## 
The LOI values of different fibers are as follows: 
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polypropylene 17.4 
polyethylene 17.4 
polystyrene 18.1 
rayon 18.6 
cotton 20.1 
nylon 20.0 
polycarbonate 22 
rigid polyvinyl chloride 
40 
stabilized polyacrylonitrile 
greater than 40 
graphite 55 
______________________________________ 
The term "stabilized" herein applies to fibers or tows which have been 
oxidized at a specific temperature, typically less than about 250.degree. 
C. for PAN fibers, provided it is understood that in some instances the 
filaments or fibers are oxidized by chemical oxidants at lower 
temperatures. 
The term "Reversible Deflection" as used herein applies to a helical or 
sinusoidal compression spring. Particular reference is made to the 
publication "Mechanical Design--Theory and Practice", MacMillan Publ. Co., 
1975, pp 719 to 748; particularly Section 14-2, pages 721-24. 
SUMMARY OF THE INVENTION 
In accordance with the present invention there is provided flame retarding 
and flame shielding or blocking structures comprising at least about 7.5% 
by weight of linear and/or non-linear carbonaceous fibers having a carbon 
content of at least 65%, derived from heat set stabilized acrylic fibers 
or a pitch based fiber. The structure comprises synthetic and/or natural 
fibers in an intimate blend with the carbonaceous fibers. Advantageously, 
the carbonaceous fibers of the structures comprise non-flamable non-linear 
carbonaceous filaments having a reversible reflection ratio of greater 
than 1.2:1, preferably greater than 2.0:1, and an aspect ratio (1/d) 
greater than 10:1. The non-linear fibers have been found to provide 
considerable loft and improved thermal insulating properties to structures 
and/or fabrics utilizing them. The non-linear fibers also provides a 
porosity which inhibits the spread of fire. Both linear and non-linear 
carbonaceous fibers have a LOI value greater than 40. 
Furthermore, it has been surprisingly found that the carbonaceous fibers 
when intimately blended in an amount of at least 7.5% together with, 
synthetic and/or natural fibes into a structure, such as a batting, 
fabric, tow or the like, results in a synergistic effect with respect to 
fire blocking and fire retarding properties to the blend. It is understood 
that when the structure is densified for a particular use, it is 
preferably to use a higher amount of carbonaceous fibers. 
The invention further contemplates a method for providing flame retarding 
and fire shielding structures with respect to a structural part or a pair 
of adjacent structural parts. 
It is therefore an object of the invention to provide a structure such as a 
tow, fabric or batting which is both fire retarding and provides a fire 
barrier. 
It is another object of the invention to provide a fire shielding structure 
comprising an intimate blend of carbonaceous fibers with other synthetic 
and/or natural fibers which possesses good handling and washing 
characteristics. 
It is yet another object of the invention to provide a method for forming a 
fire shield for a structural part or a pair of adjacent structural parts. 
It is still a further object of the invention to provide a fabric which is 
aesthetically acceptable and possesses fire blocking characteristics.

DETAILED DESCRIPTION OF THE INVENTION 
In accordance with the invention, it has ben surprisingly discovered that a 
fibrous structure comprising at least 7.5% of heat set carbonaceous fibers 
having an LOI value of greater than 40 and which are derived from an 
acrylic fiber or a pitch based fiber, when intimately blended with natural 
and/or synthetic fibers provides a synergistic improvement in the fire 
retarding and fire blocking characteristics of the resulting composition. 
Even more significant results are achieved when the carbonaceous fibers 
are non-linear fibers, have a reversible deflection ratio of greater than 
1.2:1 and an aspect ratio (1/d) greater than 10:1. Both the linear and 
non-linear fibers can be utilized in connection with the present 
invention. When the carbonaceous fibers are non-linear the loft and the 
reforming characteristics of the structure, fabric or tow, which contains 
the blend of fibers, is maintained even after long periods of compression. 
It is understood that the greater the amount of non-linear carbonaceous 
fibers which are utilized, the better will be the reforming and fire 
retarding characteristics of the structure. Preferably, when only linear 
carbonaceous fibers are being utilized, they are present in the blend in 
an amount of at least 17%. 
The natural or other synthetic fibers may also be linear or non-linear. 
However, the non-linear carbonaceous fibes of the invention are 
substantially permanently non-linearly set so that the structure 
permanently maintains a degree of loft and porosity to provide good hand 
even when the other fibers lose their non-linearity. 
The non-linear carbonaceous fibers which are utilized may have a sinusoidal 
and/or a coil-like configuration depending upon the ultimate use of the 
fibers. The acrylic derived fibers have a nitrogen content between 5 amd 
35%, preferably from 18 to 25%. The terpolymers with acrylic units may 
contain the higher nitrogen content. 
In accordance with one embodiment of the invention, the carbonaceous fibers 
are opened and is then blended with either synthetic fiber or natural 
fiber or both to form a mixture. Although the relative amount of 
carbonaceous fibers and other fibers may be varied over substantially 
broad limits, it has been found that at least 7.5% carbonaceous fibers, 
preferably non-linear fibers, must be employed in order to achieve the 
flame retarding characteristics of the material of the invention. 
Preferably, 7.5% of the carbonaceous fiber is used in a batting having a 
density of 0.4 to 0.6 lb/ft.sup.3 (6.4 to 9.6 kg/m.sup.3). 
The blend of carbonaceous fibers and other fibers may be then formed into a 
carded web employing conventional carding equipment which is well known to 
persons of ordinary skill in the art. The carding operation serves to 
uniformly blend the carbonaceous fibers and other staple fibers. The 
carded web will ordinarily have a thickness in the range of up to 2 inches 
(5.0cm), but may be built-up in multiple plies to produce a web having a 
thickness of one inch or more depending upon the desired end use of the 
material. 
The blend of fibers may be utilized in order to form fabrics having fire 
retarding characteristics. For example, a blend of fibers which contains 
from 7.5 to about 20% of the carbonaceous fibers of the invention may be 
utilized for manufacture fire retardant articles such as clothing, 
blankets, sheets, and the like because of the excellent washability and 
shape retaining quality especially when a large portion (about 30-50%) of 
non-linear fibers are employed. Carbonaceous fibers in which the nitrogen 
content is between 18 and 20% are especially useful for fabrics making 
skin contact with the wearer. 
Fabric structures which contain the carbonaceous fibers of the invention in 
amounts from about 20 to about 40% may advantageously be used for seat 
coverings in aircrafts upholstery, battings in seat covers, curtains and 
the like. 
Use of greater amounts of carbonaceous fibers in the blends improves the 
fire blocking and fire shielding characteristics of the structures. The 
structures having greater amounts of carbonaceous fibers also have greater 
chemical resistance. The structures may be used as fiber filter, hose 
coverings, static precipitators and the like. However, it is desirable to 
try to maintain a fabric characteristic close to conventional structures 
so as to have an aesthetic appearance and feel. 
The fabrics may comprise a blend of all natural, all synthetic or a 
combination of both together with the carbonaceous fibers. 
The natural fibers wherein the synergistic effect is found when used in a 
blend with the carbonaceous fibers of the invention include cotton, wool, 
flax and silk. 
The synthetic fibers which can be utilized to form a blend with the 
carbonaceous fibers to the present invention includes polyolefins, for 
example polyethylene, polypropylene and the like, polyvinyl chloride, 
polyvinyl alcohol, polyesters, polyacrylonitrile, polyacrylates, 
polycarbonate, cellulosic products, ionomers, DACRON (Trademark), KEVLAR 
(Trademark), and the like. It is to be understood of course, that a blend 
of natural and/or synthetic fibers with the carbonaceous fibers may be 
used. 
The precursor stabilized acrylic filaments which are advantageously 
utilized in preparing the carbonaceous fibers of the invention are 
selected from the group consisting of acrylonitrile homopolymers, 
acrylonitrile copolymers and acrylonitrile terpolymers. 
The copolymers and terpolymers preferably contain at least about 85 mole 
percent of acrylic units, preferably acrylonitrile units, and up to 15 
mole percent of one or more monovinyl units copolymerized with styrene, 
methylacrylate, methyl methacrylate, vinyl chloride, vinylidene chloride, 
vinyl pyridene, and the like. 
Preferred precursor materials are prepared by melt spinning or wet spinning 
the precursor materials in a known manner to yield a monofilament or 
multi-filament fiber tow. The fibers or filaments are formed into a yarn, 
woven cloth, fabric knitted cloth and the like by any of a number of 
commercially available techniques, heated, preferably to a temperature 
above about 525 degrees C in a non-oxidizing atmosphere and thereafter 
deknitting and carded to produce a wool-like fluff which may be laid up in 
batting-like form. 
Examplary of the products which can be structures of the present invention 
are set forth in the following examples. It is understood that the 
percentages referred to herein relates to percent by weight. 
EXAMPLE I A. Battings were made by blending an appropriate weight percent 
of each respective opened fiber in an blender/feed section of a sample 
size 12" Rando Webber Model B manufactured by Rando Machine Corp. of 
Macedon, NY. The battings produced typically were 1 inch (2.54 cm) thick 
and had bulk densities in a range of from 0.4 to 6 lb/cc (6.4 cm to 96 
kg/cc m.sup.3). The battings were thermally bonded by passing the Rando 
batting on a conveyor belt through a thermal bonding oven at a temperature 
of about 300.degree. C. 
Flammability tests were run in a standard apparatus as cited in FTM 5903 
according to the procedure of FAR 25.853b which references FTM 5903. The 
results are shown in the following Table I: 
TABLE I 
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Sample 
Sample Burn After Flame Drop 
Pass 
No. Composition 
% Wt. Length (in.) 
Flame (Sec.) 
Time (sec.) 
or Fail 
__________________________________________________________________________ 
1 NCF/PEB/PE 10/20/70 
2/1/1 0/0/0 0/0/0 passed 
2 NCF/PEB/PE 20/20/60 
.75/.75/.75 
0/0/0 0/0/0 passed 
3 NCF/PEB/PE 25/20/55 
.75/.75/.75 
0/0/0 0/0/0 passed 
4 NCF/PEB/PE 30/20/50 
.5/.5/.5 0/0/0 0/0/0 passed 
5 NCF/PEB/PE 40/20/40 
&lt;.5/&lt;.5/0 
0/0/0 0/0/0 passed 
6 NCF/PEB/PE 5/20/75 
complete &gt;20 sec. 
0/0/0 failed 
7 NCF/PEB/PE 50/20/30 
0/0/0 0/0/0 0/0/0 passed 
8 OPF/PEB/PE 10/20/70 
complete &gt;20 sec. 
0/0/0 failed 
9 LCF/PEB/PE 50/20/30 
&lt;.25/&lt;.25/&lt;.25 
0/0/0 0/0/0 passed 
10 NCF/PEB/cotton 
10/10/80 
.5/.25/.5 
0/0/0 0/0/0 passed 
11 Nomex .TM./PEB/PE 
20/20/60 
complete &gt;38 sec. 
0/0/0 failed 
12 Nomex .TM./PEB/PE 
50/20/30 
complete &gt;30 sec. 
0/0/0 failed 
13 NCF/PEB/Cotton 
10/15/75 
.75/.75/.5 
0/0/0 0/0/0 passed 
14 NCF/PEB/Cotton 
5/15/80 
&gt;12 &gt;14 -- failed 
15 NCF/PEB/PE 5/20/75 
&gt;12 &gt;195 0/0/0 failed 
16 NCF/PEB/PE 7.5/20/72.5 
2/10/2 0/7/0 0/0/0 borderline 
17 LFC/PEB/Cotton 
25/15/60 
1/1.25/1 0/0/0 0/0/0 passed 
18 OPF/PEB/Cotton 
50/15/35 
&gt;14 3 sec. 0/0/0 failed 
19 NCF/PEB/Cotton 
20/15/65 
.75/.75/.75 
0/0/0 0/0/0 passed 
20 NCF/PEB/Wool 
5/15/80 
&gt; 10 &gt;5 0/0/0 failed 
21 NCF/PEB/Wool 
10/15/75 
1.25/1/1 0/0/0 0/0/0 passed 
22 NCF(sc)/PEB/Cotton 
20/15/65 
1/1/.75 1/.5/0 0/0/0 passed 
23 OPF/PEB/PE 50/20/30 
&gt;12 8/8 0/0/0 failed 
__________________________________________________________________________ 
NCF = nonlinear carbonaceous fiber 
LCF = linear carbonaceous fiber 
LCF(SC) = linear carbonaceous fiber with small amplitude crimp 
PEB = 8 denier polyester binder fiber of 410 KODEL(Trademark) 
PP = polypropylene 
PE = 6 denier 2" staple Dupont DACRON (Trademark) 164 FOB polyester 
Cotton = nontreated 11/2" cotton 
OPF = stablized polyacrylonitrile fiber 
NOMEX = trademark of an aramid fiber available from E.I. du Pont & Co. 
The above table shows surprisingly that use of as little as 7.5% by weight 
of carbonaceous fibers in the blends resulted in substantially no after 
flame when the flame source was removed and no flame drippings 
TABLEII 
__________________________________________________________________________ 
Example II: 
Following the procedure of Example I similar tests were performed and the 
results are shown in the 
following Table II. 
Sample 
Sample Densification 
Burn After Flame Pass 
No. Comp. Composition 
Method Length (in) 
Flame (sec) 
Drop (sec) 
or Fail 
__________________________________________________________________________ 
1 NCF/PEB/PE 30/20/51 
NP 1.5/1.5/1 
0/0/0 0/0/0 passed 
2 NCF/PEB/PE 30/20/50 
PS .5/.75.5 
0/0/0 0/0/0 passed 
3 Nomex .TM./PEB/PE 
20/20/60 
NP total 30 sec. 2 sec. 
failed 
4 Nomex .TM./PEB/PE 
50/20/30 
NP total 40 sec. -- failed 
5 NCF/PEB/PE 20/20/60 
NP 2/2/2 0/0/0 0/0/0 passed 
6 NCF/PEB/PE 20/20/60 
PS 1.5/1.5/1.5 
0/0/0 0/0/0 passed 
7 NCF/PEB/Cotton 
30/15/55 
NP 1/1/1 0/0/0 0/0/0 passed 
8 NCF/PEB/Cotton 
30/5/55 
-- .5/.5/.5 
0/0/0 0/0/0 passed 
9 NCF/PEB Cotton 
30/15/55 
NP .75/.75/.75 
0/0/0 0/0/0 passed 
10 NCF/PEB/Cotton 
30/15/15 
PS 1.25/1.5/1.25 
0/0/0 0/0/0 passed 
11 Kevlar .TM./PEB/PE 
50/20/30 
-- .5/.5/.5 
0/0/0 0/0/0 passed 
12 Kevlar .TM./PEB/PE 
50/20/30 
NP 3.5/3/3.5 
0/0/0 0/0/0 passed 
13 Kevlar .TM./PEB/PE 
50/20/30 
PS 1.25/1.5/1.5 
0/0/0/ 0/0/0 passed 
14 Kevlar .TM./PEB/PE 
20/20/60 
-- &gt;12 complete burn failed 
15 Kevlar .TM. /PEB/cotton 
50/15/35 
-- 15/.5/.5 
0/0/0 0/0/0 passed 
16 Kevlar .TM./PEB/cotton 
50/15/35 
NP .5/.5/.5 
0/0/0 0/0/0 passed 
17 Kevlar .TM./PEB/cotton 
50/15/35 
PS .75/.75/.75 
0/0/0 0/0/0 passed 
__________________________________________________________________________ 
NP = needle punched at 100 punches/in.sup.2 
PS Pin Sonic Thermally Bonded in diamond pattern 
EXAMPLE III 
Non-Flammability Test 
The non-flammability of the fabric of the invention has been determined 
following the test procedure set forth in 14 CFR 25.853(b), which is 
herewith incorporated by reference. The test was performed as follows: 
A minimum of three 1".times.6".times.12" (2.54 cm.times.15.24 
cm.times.30.48 cm) specimens comprised of 10% carbonaceous fiber--10% 
polyethylene--80% cotton were conditioned by maintaining the specimens in 
a conditioning rom maintained at 70 degrees .+-.5 degrees F temperature 
and 50%.+-.5% relative humidity for 24 hours preceding the test. 
Each specimen was supported vertically and exposed to a Bunsen or Turill 
burner with a nominal I.D. tube adjusted to give a flame of 11/2 inches 
(3.81cm) in height by a calibrated thermocouple pyrometer in the center of 
the flame was 1550 degrees F. The lower edge of the specimen was 3/4 inch 
(1.91cm) above the top edge of the burner. The flame was applied to the 
center line of the lower edge of the specimens for 12 seconds and then 
removed. 
Pursuant to the test, the material was self-extinguishing. The average burn 
length did not exceed 8 inches (20.32 cm). The average after flame did not 
exceed 15 seconds and there were no flame drippings. 
Similar results may be achieved if the carbonaceous fiber is either derived 
from an acrylic precursor or a pitch based fiber.