Composites via in-situ polymerization of composite matrices using a polymerization initiator bound to a fiber coating

This invention is directed to a process of forming composites comprising reinforcing fibers dispersed in a thermoplastic polymer matrix, said process comprising the steps of coating a reinforcing fiber with a curable resin and an initiator for the curing of the resin and for the polymerization of monomer of said polymer; curing said resin to form cured resin coated fiber; coating said resin coated fiber with monomer of said polymer; polymerizing the monomer coating to form a polymer/resin coated fiber; and aligning the polymer/resin coated fiber and molding same into a desired reinforced thermoplastic composite.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to improved thermoplastic composites and to methods 
of preparing same. The improved thermoplastic composition which comprises 
a thermoplastic polymer having fibrous reinforcement dispersed therein. 
The present invention also relates to producing prepregs used in the 
formation of laminates and pultrusions and filament wound articles (all 
forms of composites) having high performance fibers and polymeric 
matrices. 
2. Prior Art 
Prepregs are a well known intermediate form in the preperation of 
composites having high performance fibers and polymeric matrices. In the 
most common form, a prepreg contains a series of parallel fibers (such as 
boron or carbon or glass fibers) held together with a thermosetting 
polymer such as an epoxy resin. One method for forming prepregs is to size 
(impregnate the interstices of) a multifilament bundle of high performance 
fibers with a dilute solution of the resin, and then coat the sized fibers 
with a melt or concentrated solution of the resin. Thereafter, the coated 
fibers are layered up in parallel fashion; and the resultant sheet is 
dried in order to produce a sheet which holds together reasonably well in 
the transverse direction. Subsequently, a series of such sheets are 
stacked with the fiber direction varied in a regular manner, and the 
assemblage is cured either in a closed mold or in an autoclave under 
increased temperature and superatmospheric pressure. 
Pultruded articles are composites prepared by aligning high performance 
fibers coated with a thermosetting resin in a substantially parallel 
linear array and curing the assemblage. Examples include structural parts 
such as I-beams. Filament wound articles are formed by winding similar 
coated fibers in multiple layers on a substrate (e.g., a mandrell or a 
part) and curing the assemblage. Pultrusion and filament winding processes 
may differ from prepreg processes in that in the pultrusion and filament 
winding processes, a prepreg is not isolated and arranged into a desired 
shape before curing. When fibers for pultrusions or filament winding are 
coated from solution, the drying step may overlap both with the aligning 
step and the curing step. 
It has been proposed that fiber filled composites can be formed by passing 
roving that is spread out to expose its multiple filaments through a 
fluidized bed containing resin microparticles of the same diameter as an 
individual filament (8 to 20 microns). The roving, which has been 
pretreated with sizing to temporarily retain the resin particles in place 
is then consolidated and sheathed with an extrusion coating of the same 
resin. This process is claimed to provide a more uniform resin content. 
Several disadvantages flow from this process. For example, air pockets are 
trapped in the rovings which are difficult to remove. The trapped air 
results in voids in the filled composition resulting in a reduction of 
strength. Moreover, the use of the sizing may be detrimental to forming a 
strong interface bond between the resin and the fiber, and precludes any 
tailoring of the sizing to the type of fiber and resin. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is provided a process for 
the manufacture of composites comprising continuous reinforcing fibers 
coated with one or more curable resins dispersed in a continuous phase of 
one or more polymers, said process comprising the steps of: 
(a) impregnating one or more bundles of said continuous reinforcing fibers 
with one or more curable resins which bond to the surface of said fibers 
during the curing of said resins and with one or more initiators for 
promoting the curing of said resins, said initiators bonding to said 
resins forming residues which become a part of said resins during the 
curing thereof, and said initiators being initiators for the 
polymerization of monomers of said polymer and bonding to said polymer 
during the polymerization of said monomers forming residues which become a 
part of said polymer; and 
(b) partially, incompletely or completely curing said resins to form 
bundles of continuous reinforcing fibers impregnated with said partially, 
incompletely or completely cured resins having said resins bonded to the 
surface of said fibers; and 
(c) impregnating said bundle of continuous reinforcing fibers impregnated 
with said partially, completely or incompletely cured resins with one or 
more of said monomers, thereby coating said cured resins bonded to the 
surface of said fibers with said monomers; and 
(d) forming two or more of said bundles into a composite employing a 
procedure selected from the group consisting of: 
(i) polymerizing said monomers impregnating said bundles, and further 
curing said resins if necessary, to form impregnated bundles of fibers 
containing polymer and completely cured resin, said resins coating and 
bonded to said fibers, and said polymers coating and bonded to said 
completely cured resins by said residues of said initiators; 
aligning two or more of said impregnated bundles of fibers containing 
polymer and completely cured resin into a desired shape; and 
molding said aligned bundles into a composite comprising said fibers 
dispersed in a continuous phase of said polymers said completely cured 
resins coating and bonded to said fibers and said polymers coating and 
bonded to said completely cured resins by said residues of said 
initiators; and 
(ii) aligning two or more of said fiber bundles impregnated with monomer 
and completely, incompletely or partially cured resin into a desired 
shape, and 
polymerizing said monomer, and further curing said resin if necessary, to 
form a composite comprising said fibers dispersed in a continuous phase of 
said polymer, said resin coating and being bonded to said fibers and said 
polymer coating and being bonded to said resin by said residues of said 
initiators. 
As used herein "completely cured" resins are those in which less than about 
20 mole percent of the original curable groups remain unreacted as 
determined by the method of infrared spectrophotometry; "partially cured" 
resins are those in which from about 40 to about 80 mole percent of the 
original curable groups remain unreacted determined by the method of 
infrared spectrophotometry; and "incompletely cured" compositions are 
those in which less than about 40 mole percent of the original curable 
groups are unreacted as determined by the method of infrared 
spectrophotometry. 
The composite formed by the process of this invention are superior to those 
formed by other conventional methods such as solution impregnation, film 
stacking, hot melt impregnation or fluidized bed coating because among 
other advantages the process allows for good fiber wetting, higher fiber 
loading, and a relatively superior fiber/matrix interface. The resulting 
composite exhibits superior flexural properties. 
DETAILED DESCRIPTION OF THE INVENTION 
The first step of the process of this invention comprises impregnating 
bundles of continuous reinforcing fibers with one or more curable resins 
and one or more initiators for curing said resins and polymerizing said 
monomers. These initiators bond to the cured resin and polymer during the 
curing and polymerization steps respectively. The types of impregnation 
procedures which may be used will vary widely and any conventional bundle 
impregnation techniques can be used. For example, in the preferred 
embodiments of the invention, the bundles are first impregnated with the 
curable resins and the initiators prior to impregnation with the monomer 
and thereafter the resins are partially cured, incompletely cured or 
completely cured to ensure that curable resin will be able to coat and 
effect a bond with the fiber so that the resins remain on the fiber and do 
not dissolve in the liquid monomer when same is used to impregnate the 
bundle of fiber. Coating the fiber with resin and curing the resin before 
impregnation with the monomer also allows for bonding of the initiators to 
the resins. 
The types of impregnation procedures which may be used in the practice of 
this invention may vary widely, and any conventional bundle impregnation 
technique can be used. For example, one preferred and convenient method 
for impregnating the bundles of fibers, and coating individual fibers with 
the various components is to first pass the bundles of continuous fibers 
through a liquid containing the curable resin and an effective amount of 
initiator, and thereafter curing the resin to form a partially cured, 
incompletely cured or completely cured resin bonded to the surface of the 
fibers and bonded to said initiator. The bundles of continuous fibers are 
then passed through liquid monomer or a solution containing the monomer. 
Thereafter, the bundles of continuous fiber can be conducted to the next 
process steps, as for example further curing to complete curing of the 
resin, if necessary, and the polymerizing step. Useful bundle impregnation 
techniques are described in more detail in Handbook of Composites (George 
Lubin ed., Van Nostrand published 1982) which is hereby incorporated by 
reference. 
The continuous reinforcing fibers used in the process of the present 
invention may be any of a variety of conventional materials used as 
continuous reinforcement in both thermoplastic and thermoset compositions, 
the only requirement being that the fiber has a surface which has a strong 
affinity for the particular curable resin employed, such as forming 
covalent bonds or ionic bonds with the curable resin, or having strong van 
der waals interactions therewith. For example, suitable fibers are those 
which contain surface functional groups, such as hydroxyl, carboxylic 
acid, thiol, amino, olefin, cyanate, ester, amide, and like reactive 
functional groups. Such functional groups may naturally exist on the 
surface of some fibers. Alternatively, fibers can be treated by reagents 
to introduce such functional groups. For example, organic fibers may be 
treated with chemical oxidisers such as chromic acid, nitric acid, and the 
like; or exposed to corona discharge in air or an oxygen plasma; or 
subjected to electro-chemical oxidation to introduce functional groups 
such as hydroxyl and carboxylic acid on to the surface of the fiber. 
Reinforcing fibers useful in the practice of this invention may vary 
widely. Useful reinforcing fibers include inorganic fibers such as carbon 
fibers (including graphite fibers), glass fibers (E-S, high silica, or 
quartz types), boron fibers, a variety of ceramic fibers derived from 
alumina, and silicon carbide fibres, and organic fibers having high 
strength and modulus such as Kevlar type aramids, polyethylene, 
poly(benzimidazole), aromatic polyesters, and the like. Various 
reinforcing fibers which are useful in the conduct of this invention are 
well known in the art and will not be described herein in great detail. 
Preferred carbon fibers are well known in the prepreg art, as indicated 
for example, by Handbook of Composite, (George Lubin ed, Van Nostrand pub. 
1982). 
In the preferred embodiments of the invention, the continuous reinforcing 
fibers of choice are carbon, boron, glass, aramid, poly(benzimidazole), 
aromatic polyesters, and polyethylene, and in the particularly preferred 
embodiments are S-glass, E-glass, boron, aramid, polyethylene, and carbon 
fibers. Amongst these particularly preferred embodiments, most preferred 
are those embodiments of the invention in which the continuous reinforcing 
fibers are glass fibers, aramid fibers such as Kevlar, polyethylene fibers 
and carbon fibers, with carbon fibers and glass fibers being the fiber 
reinforcements of choice. In the case of the especially preferred carbon 
fibers, multi-filament fibers, and especially fibers with 1,000 or more 
filaments, are preferred. Such multi-filament carbon fibers are available 
either in sized or unsized form, in a variety of thicknesses per filament, 
total thicknesses, filament numbers, tensile strength and modulus. 
Included within the carbon fibers useful in the present invention are 
those sold under the following trademarks of the following companies: 
CELION.RTM. 6000, 3000, 12000 (Celanese Corporation); FORTAFIL.RTM. 3 
(Great Lakes Carbon); HI-TEX.RTM. 3000, 2000, 12000 (HITCO Corporation); 
AS, NTS, NMS (Hrecules Incorporated); THORNEL.RTM. 50, 300; P55 BS, P75, 
P100 (Union Carbide Corporation). Properties of these fibers are 
summarized in Table 11.1 on pages 225-26 of Lubin's Handbook of 
Composites, cited above. 
Fibers for use in the practice of this invention may be unsized or such 
fibers may be sized with suitable sizing agents. As will be appreciated in 
the art, sizing is normally conducted by passing a multifilament fiber 
through the material to be applied as a solution thereof in a volatile 
solvent in which the continuous reinforcing fibers are substantially 
insoluble. 
The type of curable resin employed in the conduct of this invention may 
vary widely. In each particular instance, the choice of resin will depend 
on a number of factors including the desired properties of the composite, 
on the type of fiber employed, and the like. In general, resins which are 
used in any particular instance are those which have high affinities for 
the fiber of choice, due to forming bonds, as for example covalent bonds 
or ionic bonds with functional groups on the surface of the fiber, or due 
to strong van der Waals or other physical interactions with the surface of 
the fiber. For example, when the fiber of choice is carbon, often the 
surface of the carbon fiber is oxidized to introduce hydroxyl and 
carboxylic functional groups on the surface of the fiber. Such functional 
groups will react with and form bonds with certain curable resins, such as 
epoxy resins, during the curing process. Other organic fibers may react in 
a similar fashion with such curable resins when hydroxyl and carboxylic 
acid functionalities are present on the fiber surface. Such 
functionalities may be introduced by chemical oxidisers such as nitric 
acid or chromic acid, or by exposing the fibers to a corona discharge in 
air or an oxygen plasma, or by subjecting the fiber to electrochemical 
oxidation. 
Curable resins useful in the practice of this invention may vary widely. 
The only requirement is that the curing of the resins be promoted by an 
initiator which becomes a part of the cured resin during the curing 
process. Illustrative of suitable curable resins are thermoset resins such 
as phenolic resins, epoxy resins, allylic resins, alkyd resins, urethane 
resins, unsaturated polester resins, amino (melamine and urea) resins, and 
like curable resins. Preferred for use in the practice of this invention 
are epoxy resins. These preferred epoxy resins are those prepared by 
reaction between an aliphatic or cycloaliphatic epoxide, or a halo 
epihydrin, and an aliphatic, cycloaliphatic or aromatic polyol in the 
presence of a catalyst. Illustrative of such preferred epoxy resins are 
those formed by reaction of epichlorohydrin with a polyhydroxy compound 
such as bisphenol A. These epoxy resins are known as diglycidyl ethers of 
bisphenol A. Also illustrative of the preferred epoxy resins are epoxy 
phenol novolac resins which are basically novolac resins in which all or a 
portion of the phenolic hydroxyl groups have been converted to glycidyl 
ethers. Some commercially available epoxy resins which may be used in the 
practice of this invention include Epon resins from Shell Chemical, such 
as Epon 826 and Epon 828; Araldite resins from Ciba Geigy including 
epoxy-novolac (such as EPN 1139), epoxy phenol novolac (such as XB 3337), 
and epoxy cresol novolac (such as ECN 1235), and DER resins from Dow 
Chemical such as DER 330 and DEN 485. 
Monomers selected for use in the practice of this invention are not 
critical, the only requirement being that the monomers form a 
thermoplastic polymer and that the polymerization of the resin be 
initiated by an initiator which becomes a part of the polymer chain. 
Illustrative of such monomers are those which polymerize by ring-opening 
or by addition. Illustrative of such monomers which polymerize by 
ring-opening are those which form polymers such as polylactones, such as 
poly(2,2-diethyl .beta.-propio-lactone), poly(2,2-bis(chloro-methyl) 
.beta.-propio-lactone), poly(2,2-diphenyl .beta.-propio-lactone) 
poly(6-oxa-bicyclo(2.2.2) octan-5-one), poly(.delta.-valerolactone), 
poly(1,4-dioxane-2-one), poly(.alpha.,.alpha.-dimethyl .beta. 
propiolactone), polylactide, poly(.epsilon.-caprolactone), 
poly(3-oxa-.epsilon.-caprolactone), and the like; and polylactams such as 
poly(caprolactam), poly(laurolactam), poly(caprylactam), 
poly(pivlolactam), poly(6-azabicyclo (2.2.2) octan-5-one), 
poly(7-azabicyclo (3.2.1) octan-6-one), and the like. 
Illustrative of such monomers which polymerize by addition are those which 
form polymers such as polystyrene, poly(1,3-butadiene) 
poly(.alpha.-methylstyrene), poly(.alpha.-chlorostyrene), poly(4-methoxy 
styrene), poly(vinyl chloride), poly(vinyl acetate), poly(vinyl methyl 
ether), poly(vinyl butylether), poly(vinyl methyl ketone), poly(vinyl 
formate), poly(vinyl pyrrolidone), poly(vinyl carbazole), 
poly(methylpentene), poly(acrylonitrile), poly(methyl acrylate), 
poly(acrylic acid), poly(butyl acrylate), poly(methacrylic acid), 
poly(methylmethacrylate) poly(acrylamide), and the like. 
Preferred for use as monomers in the practice of this invention are cyclic 
monomers such as lactones and lactams which polymerize by ring opening. 
Illustrative of such preferred monomers are caprolactam, laurolactam, 
caapryllactam, pivalolactam, bicyclic lactams (such as 
6-azabicyclo(2.2.2)octan-5-one, 7-azabicyclo(3.2.1) octan-6-one, bicyclic 
lactones such as 6-oxabicyclo(2.2.2) octan-5-one; and 
.alpha.,.alpha.-disubstituted .beta.-propiolactones such as pivalolactone, 
.alpha.,.alpha.-diethyl .beta.-propiolactone, 
.alpha.,.alpha.-bis-(chloromethyl) .beta.-propiolactone, 
.alpha.,.alpha.-diphenyl .beta.-propiolactone, and the like. 
Of the preferred lactam and lactone monomers, preferred for use in the 
practice of this invention are monomers selected from the group consisting 
of lactams such as caprolactam, laurolactam, capryllactam, pivalolactam; 
and lactones such as pivalolactone, 
.alpha.,.alpha.-diethyl-.beta.propiolactone, and 
.alpha.,.alpha.-diphenyl-.beta.propiolactone. Particularly preferred for 
use as monomers in the practice of this invention are caprolactam and 
pivalolactone, and most preferred is pivalolactone. 
Initiators used in the practice of this invention may vary widely. Useful 
initiators are those which contain functionalities which can promote the 
curing of the curable resin and initiate the polymerization of the 
monomer, which funcationalities are or become a structural part of the 
resin and the polymer. As a result, the residue of the initiator functions 
as a linking group bonding the cured resin to the polymer. The initiators 
may be compounds which are separate and distinct from the resin, and which 
are multifunctional and which contain functionalities which promote the 
cure of the curable resin and which initiates the polymerization of the 
monomer as described above. The initiators may also be mixtures of 
materials, one class of materials having functionalities for promoting the 
cure of the resins, and the other class of materials being a curable resin 
or other materials capable of cocuring with said resin and having 
functionalities for initiating the polymerization of the monomer. Useful 
initiators will depend on the particular resin and monomers employed. For 
example, when the resin is an epoxy and the monomer is a lactone, useful 
initiators will include functionalities which act as curing agents for the 
curing of the epoxy resins, such as polyamine, anhydride, thiol and 
polybasic acid functions and functionalities which initiate the 
polymerization of lactones such as phosphine functions and carboxylate 
functions. Illustrative of such materials are compounds which include an 
amine function (preferably a primary amine function) and a phosphine 
function such as bis(3-aminopropyl) phenyl phosphine, and compounds which 
include both an amine function (preferably a primary amine) and carboxylic 
acid salts such as the tetramethyl ammonium salt of p-aminobenzoic acid. 
Similarly, when the resin is an epoxy resin and the monomer is a lactam, 
useful initiators will include one or more functionalities which initiate 
the curing of an epoxy resin such as those listed above, and one or more 
functionalities for initiating the polymerization of the lactam, such as 
alcoholate functions, organic acid salt functions and amide salt 
functions. In some cases, functional groups capable of promoting cure of 
the resin may also be capable of initiating polymerization of the monomer. 
In these cases a sufficient amount of the multifunctional initiator should 
be added to permit full curing of the resin and initiation of 
polymerization. Useful initators and the amounts thereof, and other 
reaction parameters required in the curing and polymerization step are 
well known in the art and will not be described herein in great detail. 
Illustrative of such useful initiators and reaction parameters are those 
described in "Preparative Methods of Polymer Chemistry", Sorenson & 
Campbell, Interscience Publishers (1978) which is incorporated herein by 
reference. 
In the preferred embodiments of this invention, useful initiators will 
include functionalities which promote the curing of epoxy resins and which 
initiate the polymerization of lactones and lactams. Such preferred 
initiators contain functionalities which initiate the polymerization of 
.beta.-lactones such as amino functions (prefrably tertiary) as for 
example methylphenylamino, diphenylamino, dimethylamino and like amino 
functions; phosphino functions (preferably tertiary) such dimethyl 
phosphino, diethylphosphino, methylethylphosphino, diphenylphosphino, and 
the like phosphino functions; functionalities which can polymerize .beta. 
and larger ring lactones as well as lactams such as metal carboxylate 
functions as for example alkali metal carboxylic salt functions such as 
lithium, sodium and potassium carboxylate salt functions, quaternary 
ammonium carboxylate salt functions and the like; alcoholate functions 
such as sodium alcoholate functions derived from an alcohol by replacing 
the hydroxyl function with a base such as sodium; functionalities which 
can polymerize lactams such as amide salts as for example magnesium bromo 
caprolactam and which include functionalities for the curing of epoxy 
resins such as poly primary amino functions, polybasic acid functions, 
anhydride functions, polyhydroxy functions, poly thiol functions, and like 
functions. A difunctional compound which is representative of those which 
can be used in the practice of this invention to initiate curing of epoxy 
resins and the polymerization of .beta.-lactones is 
bis-(3-aminopropyl)phenyl phosphine in which the two amino functions 
initiate curing of the epoxy and the phospine function initiates 
polymerization of the polymer. 
Although not essential, nucleating agents may be added to the monomer to 
provide maximum toughness. A variety of materials known to be effective as 
nucleating agents for other crystalline polymers can be used such as metal 
salts of aromatic or alicyclic carboxylic or sulfonic acids (e.g., lithium 
benzoate, sodium, .alpha.-naphthalene sulfonate, sodium cyclohexane 
carboxylate), salts of aliphatic mono or dibasic carboxylic or sulfonic 
acids (e.g., sodium caproate, sodium succinate), salts of arylalkyl 
carboxylic or sulfonic acids (e.g., aluminum phenylacetate), or 
particulate inorganic materials (clays, silica, titanium dioxide, and the 
like). The amount of the nucleating agent can range from about 0.01 to 
about 3 weight percent based on the total weight of the molding 
composition. More preferably, the nucleating agent ranges from about 0.1 
to about 1 weight percent based on the total weight of the molding 
composition. 
Other additives for appearance and property improvement can be incorporated 
into the molding compounds of the present invention such as colorants, 
antioxidants, stabilizers, and the like. Examples of suitable antioxidants 
are 1,3,5-trimethyl-2,4-bis(3,5-ditert-butyl-4-hydroxybenzyl)benzene and 
N-phenyl-.beta.-naphthylamine. Examples of suitable stabilizers are 
dialkyl sulfides such as dilauryl sulfide or dicetyl sulfide. 
The contact times for the impregnating steps are not critical and are 
usually not very long. For example, contact times of from a few seconds to 
a few minutes are generally suitable. Moreover, the temperature and 
pressure at which the impregnating step is carried out is not critical. 
For convenience, the impregnating step is usually carried out at about 
room temperature (20.degree. C. to about 30.degree. C.) and at atmospheric 
pressures if the monomer is a liquid at room temperature. If not, the 
monomer may be applied at elevated temperature or in solution. 
In the second step of the process of this invention, the impregnated 
bundles of continuous fiber are formed into the desired composite 
comprising the fiber dispersed in a continuous phase of the thermoplastic 
polymer. Several methods may be employed, differing only as to when 
polymerization is carried out and when curing is completed. In one of 
these preferred procedures, the bundles are impregnated with the curable 
resin and initiator and the resin is partially, completely or incompletely 
cured to form a resin impregnated bundle where the partially, completely 
or incompletely cured resin is bonded to the surface of the fibers. 
Thereafter, the bundles are impregnated with the monomer which is 
polymerized, the resin is further cured (if necessary), and the fiber 
bundles impregnated with polymer/completely cured resin are aligned and 
consolidated or molded into a desired composite shape. In the other 
embodiment, the bundles are impregnated with resin and initiator and the 
resin is partially, completely or incompletely cured to form a resin 
impregnated fiber bundle in which the resin is bonded to the surface of 
the fiber. The bundle is then impregnated with monomer and the monomer 
impregnated bundles are aligned in a desired shape. The monomer is then 
polymerized and the resin further cured (if necessary) to form the desired 
shaped composite. Each of these methods for forming the fiber bundles 
impregnated with polymer/completely cured resin into the composite is 
equally desirable and represent the preferred embodiments of carrying out 
the forming step. 
The methods employed to polymerize monomers into the corresponding polymer 
and to cure epoxy resins respectively are well known in the art and will 
not be described in great detail. For example, useful procedures are 
described in "Preparation Methods in Polymer Chemistry," Sorenson & 
Campbell Interscience Publishers (1968). Briefly stated, to polymerize the 
monomer and to cure the resin, the coated fiber formed as described below 
either as individual fibers or as a bundle of fibers, or as bundles of 
fibers which have been aligned into a desired shape are heated to a 
temperature which is at least sufficient to promote the initiation of the 
polymerization and curing reaction and which is less than the degradation 
temperature of the monomers, cured resins, precured resins, polymers 
and/or continuous fibers. As indicated, the temperature will depend on 
monomers, initiator, precured resin and/or fibers, and can vary widely. In 
general, the polymerization temperature is from about room temperature to 
about the melting point of the polymer being prepared or at a temperature 
above the glass transition temperature of said polymer. In the preferred 
embodiments of the invention, the polymerization temperature is from about 
50.degree. C. to about 280.degree. C., and in the particularly preferred 
embodiments of the invention the polymerization temperature is from about 
90.degree. C. to about 160.degree. C. 
The methods of aligning the monomer, partially, completely or incompletely 
cured resin and initiator impregnated bundles, or polymer and partially, 
completely of incompletely cured resin impregnated bundles into the 
desired shape are not critical and may differ widely depending upon the 
nature of the composite being formed. For example, such step will vary 
depending upon whether a prepreg, pultrusion or filament-wound article is 
being made. The following discussion will deal with prepregs first, and 
thereafter with the other two. It should be understood that anything said 
about prepregs would apply, with modifications apparent to one skilled in 
the composite field, to the other two. 
For the prepregs, the polymer and partially, completely or incompletely 
cured resin, or monomer, and partially, completely or incompletely cured 
resin, impregnated bundles of fibers are aligned in a conventional 
fashion, with one convenient means of doing so involving the use of large 
rollers. By winding a monolayer of polymer and partially, completely or 
incompletely cured resin, or monomer and partially, completely or 
incompletely cured resin impregnated bundles of fibers on a large roller, 
a cylindrical sheet of aligned and impregnated bundles of fibers can be 
formed. The circumference and height of such a large roller can be varied 
depending upon what size prepregs are desired, with typical dimensions 
being between about 0.5 and about 3 meters in height. In those embodiments 
in which the monomer and partially, completely or incompletely cured resin 
impregnated bundles have been aligned, the monomer is polymerized and the 
resin is further cured, if necessary, using conventional techniques for 
polymerizing monomers and curing resins to form a continuous cylinder of a 
composite comprising a continuous polymer phase having dispersed therein 
fiber having the cured resin bonded to the surface thereof and having the 
polymer phase bonded to the cured resin by way of the residues of the 
initiators. It should be appreciated that aligning, polymerization and 
further curing can be carried out simultaneously. In those embodiments of 
the invention in which the polymer and partially, completely or 
incompletely cured resin impregnated bundles are aligned, the aligned 
bundles are moulded into a composite containing a continuous polymer phase 
containing dispersed continuous fibers having the cured resin bonded to 
the surface thereof, and in which the polymer phase is bonded to the cured 
resin by residues of the initiator. It will be appreciated that, once the 
aligned bundles of fibers are consolidated, a sheet can be cut off of the 
roll with the circumference of the roll providing the maximum height of 
the sheet and the width of the roll providing the width of the sheet. 
Although the use of a roll is a preferred means of aligning the coated 
fibers, other techniques such as pick-up on a conveyer or release paper 
may be used. In any case, it is desirable, in order to achieve a prepreg 
of uniform geometric arrangement, that the fibers be carefully aligned in 
a generally parallel fashion with the coating of adjacent coated fibers 
touching (in sufficient contact to have a continuous sheet without voids). 
Once the aligned polymer/partially, completely or incompletely cured 
resin/initiator, or monomer/partially, completely or incompletely cured 
resin/initiator impregnated bundles fibers have been formed (e.g., on the 
roll) they would normally be stacked in any conventional fashion such as 
(0.degree., +45.degree., -45.degree., 90.degree.).sub.ns to form a 
multilayer and then heated to form the consolidated shape. Heating of the 
assemblage may be conducted in a mold with pressures (e.g., from about 0.2 
to about 10 MPa) and temperatures (e.g., from about 180.degree. to about 
310.degree. C.) or in an autoclave. The bagging used for curing epoxy 
composites in an autoclave is preferably used (but is not required) in 
heating an assemblage of the present prepregs in an autoclave. To reduce 
loss of geometrical configuration in an autoclave or a mold, some staging 
of temperatures and/or pressures may be desirable, but shorter overall 
heating times and less complex staging requirements should be present 
compared to those required for high temperature epoxy composites. 
The total fiber content (by volume) of the prepregs of the present 
invention may be varied, by modifying the quantity of the impregnating 
monomer, employed along a broad range as for example from about 25 volume 
percent fibers to about 80 volume percent fibers in the prepreg based on 
the total weight of the prepreg. The fiber content of the final molded or 
cured composite will generally be only slightly more than that of the 
prepreg. In addition, however, if a lower fiber content is desired, it is 
permissible to coat the same bundle of fibers with multiple passes prior 
to the aligning and polymerizing curing steps. In such instance, it is 
preferred to polymerize monomer and cure the resin impregnating the 
bundles of fibers at least partially, between successive passes. 
For pultrusions, a multitude of the impregnated bundles of high performance 
fibers will be aligned generally in a continuous operation, so that the 
fibers are each generally linear, and collectively in a substantially 
parallel array. Unlike prepregs, this array will not normally be a 
monolayer, but instead be an array with significant thickness (in numbers 
of fibers) in all directions transverse to the individual fibers. The 
heating operation for consolidation of the bundles into the composite 
normally proceeds directly after alignment in those instances where 
monomer/precured resin impregnated bundles are aligned, the monomers are 
polymerized and the resin cured and the polymer/cured resin impregnated 
bundles consolidated into the desired shape in the heating step. The fiber 
content of the part at the heating stage is generally about 40 to about 
80% fibers. 
For filament winding, the impregnated bundle of high performance fibers 
will be aligned on a substrate, which may either be a mandrel to impart a 
shape for the interior of a composite or an object or part which the 
composite is to cover in the final application. Examples of such 
substrates are wheel rims, pipes, pressure vessels and shafts. The winding 
may be similar to that used for winding a roller in making prepregs except 
that multiple layers are formed, generally with the fibers angled away 
from a direct circumferential direction in a crossing arrangement between 
layers. As with pultrusions, the heating step for either consolidation or 
polymerization/curing and consolidation usually immediately follows 
aligning. 
The composites of this invention have many uses. For example, these 
composites can be used as replacements for metals in aircraft, automotive 
and a variety of other applications. 
Through use of the process of this invention, the bundles of continuous 
fibers are thoroughly and uniformly impregnated thus forming thoroughly 
and uniformly coated fibers. The result is composites having maximized 
fiber content and minimized voids. 
Moreover, because the cured resin is bonded to the surface of the fibers 
and the polymer is bonded to the surface of the resin by way of the 
initiator linkages. The result is that the composite exhibit greater 
flexural strength than composites formed by conventional procedures.

The following examples are presented to more particularly illustrate the 
invention, and are not to be construed as limitations thereon. 
COMATIVE EXAMPLE 1 
A tow of carbon fibers (AS4-12K from Hercules) was pulled through a nozzle 
where it was impregnated with pivalolactone monomer. The monomer contained 
1.times.10.sup.-3 ml/g of tri-n-butyl phosphine (Bu.sub. 3P) as a 
polymerization initiator and 1.times.10.sup.3 g/g of 
N-phenyl-2-naphthylamine as an antioxidant for the subsequent polymer. The 
monomer-impregnated tow was then wound onto a heated drum at 140.degree. 
C. Polymerization was complete in about 1/2 minute. After the entire drum 
was wound with fiber/polymer it was cut off the drum and pieces were then 
cut from this sheet of prepreg material. Several pieces of prepreg were 
stacked and then fused by vacuum/compression molding into a unidirectional 
laminate. 
COMATIVE EXAMPLE 2 
A tow of carbon fibers (AS4-12K from Hercules) was coated with an epoxy 
resin by pulling the tow through a nozzle where it was coated with a 1.1% 
g/ml solution of DER 330 (a diglycidyl ether of bisphenol A based epoxy 
from Dow Chemical) in acetone. The two was then wound onto a drum where 
the acteone was allowed to evaporate away for several hours. The fiber was 
then rewound onto a 3 inch spool once all the acetone was removed. 
These fibers were then used to form a prepreg in the same manner described 
in Comparative Example 1 except that the drum temperature was 130.degree. 
C. 
COMATIVE EXAMPLE 3 
A tow of carbon fibers (AS4-12K from Hercules) was coated with an epoxy 
resin and an aliphatic amine curing agent by pulling the tow through a 
nozzle where it was impregnated with a solution containing 1.2% g/ml DER 
330 and 0.15% of HMDA (1,6-hexane diamine) in methylene chloride. The tow 
was then wound onto a drum where the methylene chloride was allowed to 
evaporate for several hours. The fiber was then rewound onto a 3 inch 
spool. The relative amounts of epoxy and amine were chosen such that their 
weight ratio was slightly less (100/12.5) than stoichiometric (100/15.9). 
The fibers were allowed to stand so that the epoxy/amine coating could 
cure. After about 24 hours had elapsed from the time the fibers were 
coated, they were used to form a polypivalolactone (PPL)/carbon fiber 
prepreg using the procedures described in Comparative Example 1, but with 
a drum temperature of 130.degree. C. 
COMATIVE EXAMPLE 4 
A tow of carbon fibers (AS4-12K from Hercules) was coated with an epoxy 
resin and an aromatic amine curin agent by pulling the tow through a 
nozzle where it was impregnated with a solution containing 1.2% g/ml DER 
330, 0.27% DDS (4,4'diamino diphenyl sulfone), and 0.01% BF.sub. 3-MEA 
(boron trifluoride monoethylamine) in acetone. The BF.sub. 3-MEA serves to 
accelerate the reaction of the epoxy and amine. After the evaporation of 
the acetone, the fibers were heated for 2 hours at 125.degree. C. to 
provide for a partial cure of the epoxy/amine coating (this system 
requires an elevated temperature cure). The weight ratio of epoxy to amine 
chosen was slightly less (100/23) than stoichiometric (100/34), but within 
usual recommended ranges (see Epon Resin Structural Reference Manual from 
Shell Chemical Co.). Twenty-four hours after coating the fibers, they were 
used to form a PPL/carbon fiber prepreg using the procedures described in 
Comparative Example 1, but with a drum temperature of 130.degree. C. 
EXAMPLE 1 
A tow of carbon fibers (AS4-12K from Hercules) was coated with an epoxy 
resin and an amine-phosphine compound (curing agent - polymerization 
initiator) by pulling the tow through a nozzle where it was impregnated 
with a solution containing 1.1% g/ml DER 330 and 0.28% bis(3-aminopropyl) 
phenyl phosphine (aminephosphine) in methylene chloride. The weight ratio 
of epoxy to amine-phosphine chosen was slightly less (100/25) than 
stoichiometric (100/31). The methylene chloride was allowed to evaporate 
and then the fibers were rewound onto a 3-inch spool. About 24 hours after 
the fibers were coated, they were used to form a PPL/carbon prepreg using 
the procedures described in Comparative Example 1, with two differences. 
First, the drum temperature was 130.degree. C. and more importantly, no 
initiator (Bu.sub.3 P) was added to the monomer, allowing the coating on 
the fibers to initiate polymerization. 
EXAMPLE 2 
Identical procedures to those in Example 1 were used except that the fibers 
were coated with a solution containing 1% g/ml DER 330 and 0.37% 
amine-phosphine in methylene chloride. Also, the amount of pivalolactone 
monomer added to the fibers was reduced by 20%. 
COMATIVE EXAMPLE 5 
A series of experiments were carried out to compare the flexural properties 
of the laminates of Comparative Examples 1 to 4 with the flexural 
properties of the laminates of Examples 1 and 2 prepared in accordance 
with the process of this invention. The properties were determined by ASTM 
D790 and are set forth in the following Table 1. 
TABLE 1 
______________________________________ 
Properties of Unidirectional 
PPL/Carbon-Fiber Laminates With 
Different Fiber Coatings 
Flexural Strength 
Percent of 
Ex- Wt % Absolute 
Theoretical 
ample PPL Wt % Coating on Fibers 
(ksi) Maximum.sup.a 
______________________________________ 
.sup. C1.sup.c 
26 0 140 .+-. 12 
41 
C2 31.5 0.92 epoxy.sup.b 
108 .+-. 8 
35 
C3 27 0.94 epoxy 171 .+-. 6 
51 
0.12 HMDA 
C4 24.3 0.94 epoxy 169 .+-. 8 
48 
0.21 DDS 
1 25.5 0.80 epoxy 204 .+-. 10 
60 
0.21 amine-phosphine 
2 22.9 0.75 epoxy 242 .+-. 19 
67 
0.27 amine-phosphine 
______________________________________ 
.sup.a Theoretical maximum = (volume % fibers) (fiber tensile strength). 
.sup.b Dow epoxy resin DER 330 
.sup.c Comparative Example. 
COMATIVE EXAMPLE 6 
A series of experiments were carried out to verify that the amine-phosphine 
coating on the fibers was actually responsible for initiating 
polymerization in Examples 1 and 2. In these experiments, pivalolactone 
monomer was added to a stainless steel pan which was then sealed to 
prevent evaporation. This pan was placed in a Dupont Instruments 9900 DSC 
and the temperature raised from 0.degree. C. to 225.degree. C. at a rate 
of 5.degree. C./minute. 
About 18 mg of pivalolactone was added to a DSC pan as described above. The 
center of the exotherm peak due to the thermal polymerization of 
pivalolactone was 177.degree. C. 
About 10 mg of pivalolactone and 10 mg of AS4-12K carbon fibers were added 
to a DSC pan and tested as described above. The exotherm peak was at 
181.degree. C. 
About 19 mg of pivalolactone and 17 mg of the fiber coated as described in 
Example 1 was added to a DSC pan and tested as described above. The 
exotherm peak was at 125.degree. C. This experiment was conducted about 19 
hours after the fibers were coated and 5 hours before they were used in 
forming a PPL/carbon prepreg. 
The results of these experiments are set forth in the following Table 2. 
TABLE 2 
______________________________________ 
DSC Scan Results 
Peak 
Weight of Weight Exotherm 
Exp pivalolactone 
of Fiber Wt % Temperature 
No (mg) (mg) Coating on Fibers 
(.degree.C.) 
______________________________________ 
1 17.5 0 0 177 
2 10 10 0 181 
3 19 17 0.80 epoxy 125 
0.21 amine- 
phosphine 
______________________________________ 
The downward shift in the peak exotherm temperature in the presence of 
coated fibers proves that this coating is responsible for initiation of 
polymerization.