Low smoke and heat release glass fiber/carbon fiber/bisoxazoline resin composites and method of manufacture

The formation of structural composites having low smoke release and low heat release properties by forming a sandwich comprising a non-woven fiber mat between woven glass fiber mats and impregnating said sandwich with a mixture of a bisoxazoline and a polyphenolic compound to form a prepreg which can be formed and molded at elevated temperatures is described.

The present invention relates to structural composites comprising glass 
fibers, carbon fibers and bisoxazoline/polyphenolic resins, to their 
uncured composites or prepregs, the cured products thereof and to a method 
for their preparation. The cured composites exhibit excellent physical 
properties and have exceedingly low smoke and low heat release properties 
which are both desired, and are either presently required or will be 
required in the very near future as materials of construction for use in 
the interiors of commercial aircraft. 
Polymeric compositions prepared by the copolymerization of polyphenolic 
compounds and compounds having at least two 2-oxazoline groups per 
molecule are described and claimed in U.S. Pat. No. 4,430,491 which is 
incorporated herein by reference. Improved processes for preparing these 
compositions are described in U.S. Pat. No. 4,613,662 and in Copending 
U.S. patent applications Ser. No. 880,477, filed 6/30/86; Ser. No. 
022,310, filed 3/5/87 and Ser. No. 030,799, filed 3/27/87 which are all 
commonly assigned. U. S. Pat. No. 4,430,491 also describes the use of 
copolymers of polyphenolics and bisoxazolines in the formation of 
laminates in combination with glass cloth (see Examples XIII and XIV, of 
this patent, for instance). 
We have discovered that prepregs and ultimately cured structural composites 
having unexpectedly low smoke and low heat release properties can be 
prepared by forming a sandwich structure comprised of at least one layer 
of non-woven carbon fibers in the form of a mat having a suitable layer of 
a woven non-combustible fibrous material such as glass fibers, carbon 
fibers, graphite fibers, boron fibers, silicon carbide fibers, asbestos 
fibers, and various metallic fibers (glass fiber is preferred) on each 
side of the carbon fiber layer and impregnating said sandwich structure 
with from about 20 to 40% by weight of the total sandwich structure of a 
resin prepared by the copolymerization of a polyphenolic compound and a 
bisoxazoline. 
The Federal Aviation Administration (FAA) in July of 1986 ruled that 
materials used in the construction of commercial airliner cabins must be 
safer and must pass a 100/100 test from Aug. 21, 1988 until Aug. 21, 1990 
and must pass a 65/65 heat release value as determined by the Ohio State 
University (OSU) test after Aug. 21, 1990. It has been predicted by 
industry authorities that this rule will require that a whole new range of 
materials be developed by the industry because the very few materials 
which showed some promise to date, unfortunately have characteristics that 
make them unacceptable for aircraft interiors. Resins currently used in 
aircraft interiors, such as epoxy resins, polyesters, etc., fail recent 
FAA heat release requirements. Modification of epoxy and polyester resin 
with halogen containing intermediates, provide improved heat flame 
resistance, but cause these materials to give off toxic gases when burned. 
The use of standard phenolic resins, which are attractive profiles for 
heat and flame resistance, is limited due to brittleness and out gassing 
problems. Also, 40% or greater standard phenolic resin is needed to 
provide required or needed strength for composite, causing laminate weight 
increases. Recent modifications on phenolic systems, to improve strength, 
have caused them to fail FAA rules for 1990. 
The cured composites prepared in accordance with this invention readily 
meet all physical property requirements and easily meet the 65/65 FAA 
requirement which is applicable after 1990. 
The tests used to determine whether or not a given material will pass the 
FAA requirements are carried out on an OSU (Ohio State University) heat 
release rate apparatus designed by Dr. Ed Smith which measures the heat 
evolved from a sample exposed to a steady state radiant heat source. The 
test chamber in the OSU test is not completely closed but has one measured 
airflow through it, past the sample. A second measured airflow is 
distributed around the exhaust stack to cool it and joins the first flow 
above the sample. The heat release rate is measured through a thermopile. 
The thermopile is composed of thermocouples suspended in the lower air 
stream of the chamber and in the exhaust stack of the chamber to measure 
the temperature of the air/smoke mixture leaving the sample. The 
thermopile output represents the temperature rise of the air passing 
through the chamber. Substracting the baseline radiant heat source 
contribution and using a calibration factor translates to the best release 
rate. 
The heat release rate is recorded at one second intervals to produce a 
graph of the fuel contribution of the sample. In the report the heat 
release rate is stated in two ways: 1. The integral of the heat release 
rate during the first two minutes of the test. 2. The maximum heat release 
rate during the total five minutes of the test. The standard method of 
showing the two values is 2 minute integral/maximum rate (i.e., 100/100). 
The bisoxazolines useful in the practice of this invention include a 
variety of such compounds having at least two 2-oxazoline groups. 
Representative polyfunctional oxazoline compounds useful in this invention 
include 4,4',5,5'-tetrahydro-2,2'-bisoxazole; a 2,2'-(alkanediyl) bis 
[4,5-dihydrooxazole], e.g., 2,2'-(arylene) bis [4,5-dihydrooxazole], e.g., 
2,2'-(1,4-phenylene) bis [4,5-dihydrooxazole], 2,2'-(1,5-naphthalenyl) bis 
[4,5-dihydrooxazole] and 2,2'-(1,8-anthracenyl) bis [4,5-dihydrooxazole]; 
a sulfonyl, oxy, thio or alkylene bis 2-(arylene) [4,5-dihydrooxazole], 
e.g., sulfonyl bis 2-(1,4-phenylene) [4,5-dihydrooxazole], oxy bis 
2-(1,4-phenylene) [4,5-dihydrooxazole], thio bis 2-(1,4-phenylene) 
[4,5-dihydrooxazole] and methylene bis 2-(1,4-phenylene) 
[4,5-dihydrooxazole]; a bis oxazine such as 
2,2'-(1,3-phenylene)-bis[4.5-dihydro-4H-1,3oxazine] and 
2,2'-(1,4-phenylene)-bis[4,5 Dihydro-4H-1,3-oxazine] a 2,2',2"-(arylene 
tris [4,5-dihydrooxazole], e.g., 2,2',2"-(1,3,5-phenylene) tris 
[4,5-dihydrooxazole]; a polymer with aromatic backbone containing pendent 
[2-(4,5-hydrooxazole)], e.g., poly[2-(2-propenyl)-4,5-dihydrooxazole] and 
other oligomeric or polymeric materials with pendent or terminal oxazoline 
or oxazine groups. 
The polyphenolic compounds useful in this invention include those compounds 
having at least two aromatic hydroxyl groups per molecule including the 
bisphenols, the various benzene and fused aromatic ring diols and triols, 
e.g., 1,4-benzene diol (hydroquinone), 1,3-benzenediol (resorcinol), 
1,4-naphthalene diol and 1,3,5-benzene triol; the biphenyl diols, e.g., 
[1,1'-biphenyl]-2,2'-diol; the alkylene and cycloalkylene bisphenols, 
e.g., 2,2'-methylene bisphenol, 4,4'-(1-methylethylidene) bisphenol 
(Bisphenol-A), 4,4'-(phenylmethylene) bisphenol, 4,4'-(cyclohexanediyl) 
bisphenol, 4,4'-1,2-diethyl-1,2-ethenediyl) bisphenol, and 3,4-bis 
(4-hydroxyphenyl)-2,4-hexadiene; the arylene bisphenols, e.g., 
4,4'-phenylene bisphenol; the oxy, thio and sulfonylbisphenols, e.g., 
2,3-oxybisphenol, 4,4'-thiobisphenol and 2,2'-sulfonyl bisphenol; the bis 
(hydroxyaryl alkanones, e.g., bis (4-hydroxyphenyl) methanone, 
1,5-dihydroxy-9,10-anthracenedione and 4-[bis(4-hydroxyphenyl) 
methylene]-2,5-cyclohexadiene-1-one; the various benzamide and benzoate 
derivaties, e.g., 2-hydroxy-N-(4-hydroxyphenyl) benzamide, 
4-hydroxy-4-hydroxyphenyl benzoate, 2-[methyl-2-](4-hydroxybenzoyl) oxy 
[methyl]- 1,3-propanediyl-4-hydroxybenzoate, bis (4-hydroxy 
benzoate)-1,2-ethandiyl; 2-(4-hydroxy benzoate) ethyl ether, bis 
(4-hydroxybenzamide)-1,4-benzenediyl, and the like. 
The above enumerations of oxazoline and phenolic compounds are illustrative 
of the respective types of compounds useful in the preparation of the 
polymers embodied in the present invention. In addition to the various 
isomers of these representative compounds, a broad variety of substituted 
compounds are likewise applicable, the sole requirement being that the 
substituent group is not reactive with either the oxazoline or the 
aromatic hydroxyl group. Examples of substituent groups included are 
alkyl, aryl, halo, cyano, nitro, alkoxy, aryloxy, alkyl and aryl sulfides, 
amine and alkyl or aryl substituted amine, amide, ester and the like 
groups. 
In addition to the polyphenolic compounds noted above a variety of 
oligomers containing a plurality of phenolic groups constitute an 
important class of materials useful for reaction with the oxazolines or 
oxazines in this invention. Particularly representative of such oligomers 
are the base or acid catalyzed phenol-formaldehyde condensation resoles, 
the phenolic resins characterized in having benzylic ether linkages 
prepared by metal ion catalysts such as disclosed in U.S. Pat. No. 
3,485,797 are also useful in this invention. Other suitable polyphenolic 
oligomers include aromatic polyethers, polysulfones, polyarylates, etc 
containing pendent and/or terminal phenolic hydroxyl residues. 
The carbon fibers useful in this invention can be described as those carbon 
fibers obtainable from the processing of mesophase or nonmesophase 
petroleum pitch, carbon fibers and from coal tar pitch or similar carbon 
containing materials may also be used. Furthermore, carbon fibers made 
using PAN, acrylic or rayon precursors may also be used. The carbon fiber 
forms useful in this invention consist of paper, felt or mat (woven or 
nonwoven) structures. 
Glass fibers, preferably in the form of woven glass cloth which are useful 
in the present invention include those described in "Modern Plastics 
Encyclopedia", 1986-87, page 136 and in U.S. Pat. No. 4,061,8129 for 
instance. 
In the practice of this invention it is essental that the composite be made 
from a mat of carbon fibers which is preferably in the form of a non-woven 
mat or needle punched mat an the mat can be of various weights (6-12 
ounces/square yard or multiples thereof) Although the carbon fiber mat may 
be used, per se, it is preferred that a sandwich of the carbon fiber mat 
between layers of glass fiber mats and preferably the glass fiber mats are 
woven glass cloth mats. 
In practice, the carbon fiber mat or glass fiber-carbon fiber mat sandwich 
is generally impregnated with a solution of the bisoxazoline-polyphenolic 
resin using a solvent for the resin such as acetone, methanol, Isopropanol 
and mixtures thereof. Impregnation techniques include dipping, brushing, 
spraying, etc. and the like. The thus impregnated mat or sandwich is 
allowed to dry forming a prepreg (20-40% by weight resin content) which 
can then be cured by either vacuum bagging in an autoclave or by hot press 
curing at 150.degree.-225.degree. C. for from 1-2 hours to produce a 
laminate which has excellent physical properties and easily meets the 
flammability parameters which are now and in the immediate future required 
for commercial aircraft interior use set forth by the FAA. 
This invention is further illustrated in the following representative 
examples.

EXAMPLE 1 
A solution (35% solids) of 300 g of 
2,2'-(1,3-phenylene)-bis[4,5-dihydrooxazole], 700 g of Alnovol PN320 (a 
phenol-free phenol-formaldehyde condensation novolac having a molecular 
weight of 3000-4000, acid No. 0-1, M.P. 83.degree.-88.degree. C. obtained 
from American Hoechst Co.), 20 g of diphenylphosphite and 10 g of 
dichloro-p-xylene in 1 kg of acetone was prepared having a weight ratio of 
Alnovol: 2,2'-(1,3-phenylene)-bis[4,5-dihydrooxazole] of 80:20. A sandwich 
was prepared from one square foot of a carbon fiber mat (Carboflex from 
Ashland Oil Company) which had a weight of 6 ounces per square yard which 
was placed between two plies (one on each side) of a woven glass fiber 
cloth (7781 glass from J. P. Stevens, 9 oz./yard.sup.2. The sandwich was 
stitched together with glass threads to give a single pad weighing 88 g. 
The pad was then treated with the foregoing solution to form a prepreg 
which was drawn between two rollers and squeezed to a thickness of 0.09 
inches. 
The resulting prepreg was then dried in an oven at 200.degree. F. for seven 
minutes. The dried prepreg sandwich, which weighed 147 g and was composed 
of about 60% by weight of fiber and 40% by weight of resin, was then press 
molded at 100 psi and 150.degree. C. for 2 hours. The resulting cured 
sample was then cut into coupons for physical testing and the test results 
are given in the following Table. 
EXAMPLE 2 
The procedure of Example 1 was followed except that the non-woven carbon 
fiber mat was one having a weight of 12 ounces per square yard and the 
resulting prepreg contained 22% by weight of resin. The test data for the 
final cured composite are given in the following Table. 
EXAMPLE 3 
The procedure of Example 1 was followed except that the resin was a 70:30 
Alnovol 320:2,2'-(1,3-phenylene) bis[4,5-dihydrooxazole]. The properties 
of the resulting cured and formed composite are given in the following 
Table. 
EXAMPLE 4 
The procedure of Example 1 was followed using a 40:60 weight ratio of 
Alnovol 320:2,2'-(1,3-phenylene)bis[4,5-dihydrooxazole]. The properties 
for the final cured composite are given in the following Table. 
EXAMPLE 5 
The procedure of Example I was followed using a 80:20 weight ratio of 
Alnovol 320:2,2'-(1,4-phenylene) bis[4,5-dihydrooxazole]. The properties 
for the final cured composite are given in the following Table. 
TABLE 
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COMPOSITE PROPERTIES 
Property Example 1 
Example 2 
Example 3 
Example 4 
Example 5 
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Tensile Strength (PSI) 
20,500 
14,500 
19,800 
18,200 
19,800 
Tensile Modulus (PSI) 
1,799,000 
1,232,000 
1,539,000 
1,981,000 
2,450,800 
Elongation (%) 
1.7 1.4 1.7 1.3 1.2 
Flexural Strength (PSI) 
32,800 
4,600 11,700 
26,600 
49,200 
Flexural Modulus (PSI) 
3,394,000 
574,000 
1,543,000 
2,584,000 
3,208,300 
Barcol Hardness 
26.7 -- -- 35 
OSU Test: 
Heat released in 2 min. 
34 17 47 32 36 
(KW .times. Min. .times. M.sup.-2) 
Maximum Rate of Heat 
38 22 59 43 39 
Released (KW .times. M.sup.-2) 
2 min. integral/max. rate 
34/38 17/22 47/59 32/43 36/39 
Smoke Optical Density Test: 
D.sub.s (4 min.) 
Flaming 25 22 25 21 
Non-Flaming 5 6 3 5 
D.sub.max : 
Flaming 38 22 39 34 
Non-Flaming 7 8 6 11 
Carbon Fiber Mat (Oz./yd.sup.2) 
6 12 6 6 
Phenolic Resin/Bisoxazoline 
80/20 80/20 70/30 40/60 80/20 
Ratio 
Resin Conc. in Solution (%) 
35.0 25.0 35.0 35.0 30.0 
Resin Conc. in Prepreg (%) 
31.6 22.0 31.6 32.5 27.8 
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