HK1128020B - Polyareneazole/thermoset pulp and methods of making same - Google Patents

Description

Polyareneazole/thermoset pulp and method for making same

Background

1. Field of the invention

The present invention relates to thermoset and polyareneazole pulp for use as reinforcement in products including, for example, fluid sealing and friction materials, as processing aids, including its use as a thixotrope and as a filter. The invention also relates to a method for producing such a pulp.

2. Description of the related Art

Fibrous and non-fibrous reinforcement materials have been used for many years in friction products, fluid seal products and other plastic or rubber products. Such reinforcing materials must generally exhibit high wear and heat resistance.

Asbestos fibers have historically been used as reinforcing materials, but because of their health risks, alternatives have been made or proposed. However, many of these alternatives do not perform as well as asbestos in one way or another.

Research publication 74-75, published 2 months 1980, discloses fibrillating KEVLAR from various lengthsA process for making pulp from para-aramid fibers and the use of such pulp as reinforcement in a variety of applications. This publication discloses, by KEVLARPulp made of para-aramid fibers can be used in sheet products alone or with fibers of other materials, such as NOMEXCombinations of m-aramid, wood pulp, cotton and other natural cellulosics, rayon, polyester, polyolefin, nylon, polytetrafluoroethylene, asbestos and other minerals, fiberglass and other ceramics, steel and other metals, and carbon fiber. This publication also discloses a method by KEVLARPara-aramid fiber alone or with KEVLARUse of pulp made with para-aramid staple fibers in friction materials to replace a portion of the asbestos volume, with the remainder of the asbestos volume being replaced with filler or other fibers.

U.S. patent application publication 2003/0022961 (to Kusaka et al) discloses a friction material made from a friction modifier, a binder, and a fiber reinforcement made from a mixture of (a) dry aramid pulp and (b) wet aramid pulp, wood pulp, and acrylic fiber pulp. Dry aramid pulp is defined as aramid pulp obtained from a "dry fibrillation process". The dry fibrillation method is to dry grind aramid fibers between a rotary cutter and a screen to prepare pulp. Wet aramid pulp is defined as aramid pulp obtained by the "wet fibrillation process". The wet fibrillation process is the grinding of short aramid fibers in water between two rotating discs to form fibrillated fibers, followed by dewatering of the fibrillated fibers, i.e., pulp. Kusaka et al also disclose a method of mixing-fibrillating fibers by first mixing a plurality of types of fibrillated organic fibers in a prescribed ratio and then fibrillating the mixture to produce a pulp.

Polypyridobisimidazole polymer is a rigid rod polymer. From such polymers (for example, the composition of which is known as PIPD and is known for the manufacture of M5Polymers of fibers) are known to be useful in protective garments that are both cut and flame resistant. Rigid rod-like polymer fibers having strong hydrogen bonds between polymer chains, such as polypyridobisimidazole, are disclosed in U.S. Pat. No. 5,674,969 to Sikkema et al. An example of a polypyridobisimidazole is poly (1, 4- (2, 5-dihydroxy) phenylene-2, 6-pyrido [2, 3-d: 5, 6-d']Bisimidazoles) which can be prepared by polycondensation of tetraaminopyridines with 2, 5-dihydroxyterephthalic acid in polyphosphoric acid. Sikkema discloses that pulp can be made from these fibers. Sikkema also discloses that in the manufacture of mono-or two-dimensional objects such as fibers, films, tapes and the like, it is desirable for the polypyridobisimidazole to have a high molecular weight corresponding to a relative viscosity ("Vrel" or "hrel") of at least about 3.5, preferably at least about 5, more particularly equal to or greater than about 10, when measured at a polymer concentration of 0.25g/dl in methanesulfonic acid at 25 ℃. Sikkema also discloses that good fiber spinning results can be obtained from poly [ pyridobisimidazole-2, 6-diyl (2, 5-dihydroxyp-phenylene) having a relative viscosity of greater than about 12]Relative viscosities in excess of 50 (corresponding to inherent viscosities greater than about 15.6 dl/g) are achieved, and can be achieved.

There is a continuing need to provide alternative pulps that not only function well in the product, but are also low in cost. Although there are a number of disclosures that suggest alternative reinforcing materials at lower cost, many of these suggested products do not function adequately in use, are significantly more costly than currently marketed products, or have other undesirable characteristics. Thus, there remains a need for reinforcement materials that exhibit high wear and heat resistance at a cost that is comparable to or less expensive than other commercially available reinforcement materials.

Summary of The Invention

One embodiment of the present invention is directed to a pulp comprising:

(a) an irregularly shaped fibrillated thermoset fibrous structure, the structure comprising 60 to 97 wt% of the total solids;

(b) an irregularly shaped fibrillated polyarenazole fiber structure comprising 3-40 wt% of the total solids; and

(c) water accounting for 4-60 wt% of the whole pulp,

the thermoset and polyareneazole fibrous structure has an average largest dimension of no greater than 5mm, a length weighted average length of no greater than 1.3mm, and has stems and fibrils, wherein the thermoset fibrils and/or stems are substantially intertwined with the polyareneazole fibrils and/or stems.

Another embodiment of the present invention is a method of making fibrillated thermoset and polyareneazole pulp, comprising:

(a) combining pulp ingredients comprising:

(1) thermoset fibers capable of being fibrillated and having an average length of no more than 10cm and from 60 to 97 weight percent of the total solids in the ingredients;

(2) a rigid rod aramid fiber having an average length of no more than 10cm and comprising 3 to 40 weight percent of the total solids in the ingredients; and

(3) water accounting for 95-99 wt% of the total components;

(b) mixing the ingredients into a substantially homogeneous slurry;

(c) co-refining the slurry by simultaneously performing:

(1) fibrillating, cutting and masticating the fibrillated thermoset fibers and polyareneazole fibers into irregularly shaped fibrillated fibrous structures having stems and fibrils; and

(2) dispersing all solids so as to render the refined slurry substantially homogeneous; and

(d) the water is removed from the refined slurry,

thereby producing fibrillated thermoset and polyareneazole pulp in which the fibrillated thermoset and polyareneazole fibrous structures have an average largest dimension of no greater than 5mm, a length-weighted average length of no greater than 1.3mm, and the fibrillated thermoset fibrils and/or stems are substantially entangled with the polyareneazole fibrils and/or stems.

Yet another embodiment of the present invention is a method of making fibrillated thermoset and polyareneazole pulp, comprising:

(a) combining ingredients including water and a first fiber selected from the group consisting of:

(1) the thermosetting fiber capable of being fibrillated accounts for 60-97 wt% of total solids in the pulp;

(2) rigid rod-like polyarenazole fibers accounting for 3-40 wt% of total solids in the pulp;

(b) mixing the combined ingredients into a substantially homogeneous suspension;

(c) refining the suspension in a disc refiner thereby cutting the fibers to an average length of no more than 10cm and fibrillating and masticating at least some of the fibers into irregularly shaped fibrillated fibrous structures;

(d) combining ingredients including the refined suspension, the second fibers of group (a) (1 and 2) having an average length of no greater than 10cm, and water, if necessary, to increase the water content to 95-99 wt% of the total ingredients;

(e) mixing the ingredients, if necessary, to form a substantially homogeneous suspension;

(d) co-refining the mixed suspension by simultaneously performing:

(1) fibrillating, chopping and masticating the solids in the suspension so as to convert all or substantially all of the thermoset and polyareneazole fibers into fibrillated thermoset and polyareneazole fiber structures having irregular shapes of stems and fibrils; and

(2) dispersing all solids so as to render the refined slurry substantially homogeneous; and

(f) the water is removed from the refined slurry,

thereby producing thermoset and polyareneazole pulp in which the fibrillated thermoset and polyareneazole fibrous structure has an average largest dimension of no greater than 5mm, a length weighted average length of no greater than 1.3mm, and thermoset fibrils and/or stems are substantially entangled with polyareneazole fibrils and/or stems.

In certain embodiments, the present invention further relates to a friction material comprising a friction modifier selected from the group consisting of metal powders, abrasives, lubricants, organic friction modifiers, and mixtures thereof; a binder selected from the group consisting of thermosetting resins, melamine resins, epoxy resins, and polyimide resins, and mixtures thereof; and the pulp of the invention. In other embodiments, the present invention relates to a thixotrope or filter comprising the pulp of the present invention.

Additionally, in certain embodiments, the present invention relates to a fluid sealant material comprising a binder and a fiber reinforcement material comprising the pulp of the present invention.

Brief Description of Drawings

The present invention will be more fully understood from the detailed description thereof that follows, taken together with the drawings described below.

FIG. 1 is a block diagram of an apparatus for practicing the wet process for making "wet" pulp of the present invention.

FIG. 2 is a block diagram of an apparatus for carrying out the dry process for making the "dry" pulp of the present invention.

Figure 3 is a digital optical micrograph of a prior art material made when thermoset fibers were refined in the absence of any polyareneazole fibers.

Figure 4 is a digital optical micrograph of fibrillation of the PBO fibers after refining.

Fig. 5 is a digital optical micrograph of fibrillation of PBO and acrylic fibers after co-refining.

Term(s) for

Before describing the present invention, it is useful to define certain terms in the following glossary, which have the same meaning throughout this disclosure unless otherwise indicated.

"fiber" means a relatively flexible unit of matter having a high ratio of length to width across a cross-sectional area perpendicular to its length. The term "fiber" is used herein interchangeably with the terms "filament" or "root (end)". The cross-section of the filaments described herein may be of any shape, but is generally round or bean-shaped. The fibers spun onto the bobbins in the package are called continuous fibers or continuous filaments or continuous filament yarns. The fibers may be cut into short lengths called staple fibers. The fibers may be cut into smaller lengths, known as flock. The yarn, multifilament yarn or tow comprises a plurality of fibers. The yarns may be twisted and/or twisted.

"fibril" means a small fiber with a diameter as small as a fraction of a micron to several microns and a length of about 10 to 100 μm. The fibrils generally extend from a larger fiber trunk having a diameter of 4 to 50 μm. The fibrils act as hooks or anchors to capture and catch adjacent material. Some fibers fibrillate, but others do not fibrillate or effectively fibrillate, and for the purposes defined herein, such fibers do not fibrillate.

"fibrillated fibrous structure" means particles of material having stems and fibrils extending therefrom, wherein the stems are generally cylindrical in shape and have a diameter of about 10 to 50 microns, and the fibrils are hair-like elements, having a diameter of only a fraction of a micron or a few microns, attached to the stems and having a length of about 10 to 100 microns.

"flock" refers to fibers that are shorter in length than staple fibers. The flock has a length of about 0.5 to about 15mm and a diameter of 4 to 50 μm, preferably a length of 1 to 12mm and a diameter of 8 to 40 μm. Flock smaller than about 1mm does not contribute significantly to the strength of the material in which it is used. Fluff or fibers greater than about 15mm generally do not work well because the individual fibers become entangled and therefore not distributed adequately and uniformly throughout the material or slurry. Aramid flock is made by cutting aramid fibers into short lengths without significant or no fibrillation, such as those made according to the methods described in U.S. patent nos.3,063,966, 3,133,138, 3,767,756, and 3,869,430.

"arithmetic" mean length refers to the length calculated by:

"Length weighted average" length refers to a length calculated by:

"weight-weighted average" length refers to the length calculated by the following formula:

the "maximum dimension" of an object refers to the linear distance between the two farthest points in the object.

"staple fibers" can be made by cutting filaments to a length of no more than 15cm, preferably 3 to 15cm, most preferably 3 to 8 cm. The staple fibers may be straight (i.e., not crimped) or crimped to have a saw-tooth crimp along their length, at any crimp (or repeating bend) frequency. The fibers may be in uncoated, coated, or otherwise pre-treated (e.g., pre-stretched or heat treated) form.

Detailed Description

The present invention relates to polyareneazole and thermoset fiber pulp for use as reinforcement materials, friction materials and fluid sealing materials, processing aids and filters, and materials incorporating the pulp. The invention also relates to methods of making polyarenazole and thermoset fiber pulps.

First embodiment of the process of the invention

In a first embodiment, a method of making thermoset fibers and polyareneazole pulp includes the following steps. First, the pulp ingredients are combined, added, or contacted together. Second, the combined pulp ingredients are mixed into a substantially homogeneous slurry. Third, the slurry is simultaneously refined or co-refined. Fourth, water is removed from the refined slurry.

Merging step

In the combining step, the pulp ingredients are preferably added together in a vessel. In a preferred embodiment, the pulp ingredients comprise (1) thermoset fibers, (2) polyareneazole fibers, (3) optional other additives, and (4) water.

Thermosetting fiber

The thermosetting fibers are added to achieve a concentration of 60 to 97 wt% of the total solids in the ingredients, preferably 60 to 75 wt% of the total solids in the ingredients.

The thermoset fibers preferably have an average length of no more than 10cm, more preferably 0.5 to 5cm, most preferably 0.6 to 2 cm. The thermoset fibers also have a linear density of no greater than 10 dtex. Any thermoset fiber in the form of continuous filaments may be cut into shorter fibers, such as staple fibers or flock, before the pulp ingredients are combined together.

Thermosetting fiber polymers

By thermoset fibers is meant that the fibers are made of a thermoset polymer. Thermoset polymers generally have precursors that are heated to a suitable temperature in a short period of time so that they will flow as a viscous liquid and can be formed into fibers and other shaped structures. Subsequently, the liquid polymer typically undergoes a chemical crosslinking reaction, which subsequently causes the liquid to solidify or "set" to form an infusible mass that is no longer thermally reversible.

In a most preferred embodiment, the thermoset fibers that can be used with the present invention include acrylic fibers. For the purposes of the present invention, acrylonitrile-based refers to polymers in which at least 85% by weight of the polymer is acrylonitrile units. The acrylonitrile unit is- (CH2-CHCN) -. In certain embodiments, the acrylic fiber can be made from an acrylic fiber polymer consisting of up to 85 wt% or more acrylonitrile and 15 wt% or less of an ethylenic monomer copolymerizable with acrylonitrile, and mixtures of two or more such acrylic fiber polymers. Examples of the ethylenic monomer copolymerizable with acrylonitrile include acrylic acid, methyl methacrylate and esters thereof (methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, etc.), vinyl acetate, vinyl chloride, vinylidene chloride, acrylamide, methacrylamide, methacrylonitrile, allylsulfonic acid, methanesulfonic acid and styrenesulfonic acid.

Other thermoset fibers useful in the present invention include melamine resin based fibers (as BASOFIL)Fibers supplied by Basofil Fibers, LLC) and Fibers based on other thermosetting resins.

Polyarenazole fibers

Polyareneazole fibers are added to achieve a concentration of 3 to 40 wt% of the total solids in the ingredients, preferably 25 to 40 wt% of the total solids in the ingredients. The polyareneazole fibers preferably have a linear density of no greater than 10 dtex, more preferably 0.8 to 2.5 dtex. The polyareneazole fibers also preferably have an average length along their longitudinal axis of no more than 10cm, more preferably an average length of 0.65 to 2.5cm, most preferably an average length of 0.65 to 1.25 cm.

Polyarenazole polymers

Polymers suitable for making polyareneazole fibers must have a fiber-forming molecular weight in order to be formed into fibers. The polymers may include homopolymers, copolymers, and mixtures thereof.

As defined herein, "polyareneazole" refers to a polymer that has either: a heteroaromatic ring fused to an adjacent aryl (Ar) of the repeating unit structure (a):

wherein N is a nitrogen atom, Z is a sulfur, oxygen, or NR group, wherein R is hydrogen or a substituted or unsubstituted alkyl or aryl group attached to N; or two heteroaromatic rings, each fused to a common aryl (Ar) of any of the repeating unit structures (b1 or b2)¹) The method comprises the following steps:

or

Wherein N is a nitrogen atom and B is an oxygen, sulfur or NR group wherein R is hydrogen or a substituted or unsubstituted alkyl or aryl group attached to N. The number of repeat unit structures represented by structures (a), (b1), and (b2) is not critical. Each polymer chain typically has from about 10 to about 25,000 repeating units. Polyareneazole polymers include polybenzazole polymers and/or polypyridazole polymers. In certain embodiments, the polybenzazole polymer comprises a polybenzimidazole or polybenzobisimidazole polymer. In certain other embodiments, the polypyridazole polymer comprises a polypyridobisimidazole or polypyridoimidazole polymer. In certain preferred embodiments, the polymer is of the polybenzobisimidazole or polypyridobisimidazole type.

In structures (b1) and (b2), Y is an aromatic, heteroaromatic, aliphatic group, or zero; preferably an aromatic group; more preferably a 6-membered aromatic group of carbon atoms. More preferably, the 6-membered aromatic group of carbon atoms (Y) has a bond oriented para, having two substituted hydroxyl groups; even more preferably 2, 5-dihydroxyp-phenylene.

In the structural formula (a), (b1) or (b2), Ar and Ar¹Each represents any aromatic or heteroaromatic group. The aromatic or heteroaromatic group may be a fused or non-fused polycyclic ring system, but is preferably a single 6-membered ring. More preferably, Ar or Ar¹The radicals are preferably heteroaromatic in which a nitrogen atom is substituted for one of the carbon atoms of the ring system or Ar¹May contain only carbon ring atoms. Further preferably, Ar or Ar¹The radical is heteroaromatic.

As defined herein, "polybenzazole" refers to polyareneazole polymers having the repeating structure (a), (b1) or (b2) wherein Ar or Ar¹The group is a single 6-membered carbon atom aromatic ring. Preferably, the polybenzazole comprises a class of rigid rod polybenzazoles having the structure (b1) or (b 2); more preferably, the rigid rod-shaped polybenzoxazole having the structure (b1) or (b2) has a 6-membered carbocyclic aromatic ring Ar¹. Such preferred polybenzazoles include, but are not limited to, poly (phenylene terephthalamide)Benzimidazole (B ═ NR), polybenzothiazole (B ═ S), polybenzoxazole (B ═ O), and mixtures or copolymers thereof. When the polybenzazole is polybenzimidazole, it is preferably poly (benzo [1, 2-d: 4, 5-d']Bis-imidazole-2, 6-diyl-1, 4-phenylene). When the polybenzazole is polybenzothiazole, it is preferably poly (benzo [1, 2-d: 4, 5-d']Bis-thiazole-2, 6-diyl-1, 4-phenylene). When the polybenzazole is a polybenzoxazole, it is preferably poly (benzo [1, 2-d: 4, 5-d']Bisoxazole-2, 6-diyl-1, 4-phenylene).

As defined herein, "polypyridazoles" refers to polyareneazole polymers having the repeating structure (a), (b1), or (b2), wherein Ar or Ar¹The group is a single 6-membered aromatic ring of 5 carbon atoms and 1 nitrogen atom. Preferably, the polypyridazoles comprise a class of rigid rod polypyridazoles having structure (b1) or (b2), more preferably, the rigid rod polypyridazoles having structure (b1) or (b2) have a 6-membered heterocyclic aromatic ring Ar¹. Such more preferred polypyridazoles include, but are not limited to, polypyridobisimidazole (B ═ NR), polypyridobisthiazole (B ═ S), polypyridobisoxazole (B ═ O), and mixtures or copolymers thereof. More preferably, the polypyridazole is a polypyridobisimidazole (B ═ NR) of the following structure:

or

Wherein N is a nitrogen atom and R is hydrogen or a substituted or unsubstituted alkyl or aryl group attached to N, preferably wherein R is hydrogen. The average number of repeating units of the polymer chain is generally from about 10 to about 25,000, more typically from about 100 to about 1,000, even more typically from about 125 to about 500, and even more typically from about 150 to about 300.

For the purposes of the present invention, the relative molecular weights of the polyareneazole polymers are conveniently characterized by diluting the polymer product with a suitable solvent, such as methanesulfonic acid, to a polymer concentration of 0.05g/dl and measuring one or more dilute solution viscosity values at 30 ℃. The molecular weight growth of the polyareneazole polymer of the invention is suitably monitored and correlated by one or more dilute solution viscosity measurements. Thus, dilute solution measurements of relative viscosity ("Vrel" or "hrel" or "nrel") and inherent viscosity ("Vinh" or "hinh" or "ninh") are commonly used to monitor polymer molecular weight. The relative and inherent viscosities of dilute polymer solutions are related according to the following formula:

Vinh＝ln(Vrel)/C，

where ln is a natural logarithmic function and C is the concentration of the polymer solution. Vrel is a dimensionless ratio of the viscosity of the polymer solution to the viscosity of the solvent without polymer, and Vinh is then expressed as a number in reciprocal concentrations, typically decimeters per gram (dl/g). Thus, in certain aspects of the invention, the formation of a polypyridoimidazole polymer can be characterized in that it provides a polymer solution having an inherent viscosity of at least about 20dl/g, as measured at a polymer concentration of 0.05g/dl in methanesulfonic acid at 30 ℃. Because the invention disclosed herein gives polymers of higher molecular weight, resulting in viscous polymer solutions, a concentration of about 0.05g/dl polymer in methanesulfonic acid is useful for determining inherent viscosity over a reasonable period of time.

In certain embodiments, the invention employs polyareneazole fibers having an inherent viscosity of at least 20 dl/g; in other more preferred embodiments, the inherent viscosity is at least 25 dl/g; in some most preferred embodiments, the inherent viscosity is at least 28 dl/g.

Optionally other additives

Other additives may optionally be added so long as they remain suspended in the slurry during the mixing step and do not significantly alter the refining step performed on the specified solid components listed above. Suitable additives include pigments, dyes, antioxidants, flame retardant compounds and other processing and dispersing aids. Preferably, the pulp ingredients do not include asbestos. In other words, the pulp produced is asbestos-free or asbestos-free.

Water (W)

The water is added in an amount of 95 to 99 wt% of the total components, preferably 97 to 99 wt% of the total components. Alternatively, water may be added first. Subsequently, the other ingredients can be added at a rate that optimizes dispersion in water while mixing the combined ingredients.

Mixing step

In the mixing step, the ingredients are mixed into a substantially homogeneous slurry. By "substantially homogeneous" it is meant that a random sample of the slurry contains the same concentration wt% of each of the starting components as the value for all components in the combining step in the range of + -10 wt%, preferably + -5 wt%, most preferably + -2 wt%. For example, if the concentration of solids in the total mixture is 50 wt% thermoset fibers plus 50 wt% polyareneazole fibers, then a substantially homogeneous mixture in the mixing step means that each random sample of slurry has (1) a concentration of 50 wt% ± 10 wt%, preferably ± 5 wt%, most preferably ± 2 wt% thermoset fibers and (2) a concentration of 50 wt% ± 10 wt%, preferably ± 5 wt%, most preferably ± 2 wt% polyareneazole fibers. Mixing can be accomplished in any vessel equipped with a rotating paddle or some other agitator. Mixing can occur after the ingredients are added or during the addition or combination of the ingredients.

Refining step

In the refining step, the pulp ingredients are simultaneously co-refined, converted or modified as described below. Thermoset and polyareneazole fibers are fibrillated, cut and masticated into irregularly shaped fibrous structures having stems and fibrils. All solids are dispersed to render the refined slurry substantially homogeneous. "substantially uniform" is as defined above. The refining step preferably comprises passing the mixed slurry through one or more disc grinders, or circulating the slurry back through a single refiner. The term "disc refiner" refers to a refiner comprising one or more pairs of discs held in relative rotation so as to refine the constituents by virtue of shear between the discs. In one suitable type of disc mill, the refined slurry is pumped between closely spaced circular rotor and stator discs that rotate relative to each other. Each disk has a surface facing the other disk with at least partially radially extending surface grooves. A preferred disc mill that can be used is disclosed in us patent 4,472,421. In a preferred embodiment, the plate gap setting for the disc refiner is at most 0.18mm, preferably 0.13mm or less, to an actual minimum setting of about 0.05 mm.

If uniform dispersion and sufficient refining is desired, the mixed slurry may be passed through a disc mill more than once or through a series of at least 2 disc mills. When the mixed slurry is refined in only one refiner, the resulting slurry tends to be insufficiently refined and unevenly dispersed. Instead of dispersing to form a substantially homogeneous dispersion, agglomerates or aggregates may be formed which are composed entirely or substantially of one or the other solid component, or both. Such agglomerates or aggregates have a greater tendency to break up and disperse into the slurry when the mixed slurry is passed through the refiner more than once or through more than one refiner. Optionally, the refined slurry may be passed through a screen to separate out long fibers or lumps which are to be recycled through one or more refiners until cut to an acceptable length or consistency.

Since the substantially homogeneous slurry containing the multiple components is co-refined in this processing step, any one type of pulp component (e.g., polyareneazole fiber) is refined in the presence of all other types of pulp components (e.g., thermoset fibers), while those other components are being refined. This co-refining of the pulp ingredients results in a pulp that is superior to a pulp blend produced by merely mixing the two pulps together. The addition of the two pulps, followed by merely mixing them together, does not result in a substantially uniform and tightly connected fiber component of the pulp produced by co-refining the pulp components into pulp in accordance with the present invention.

Removing step

Water is then removed from the refined slurry. The water can be removed by collecting the pulp in a dewatering device, such as a horizontal filter, and if desired, the water can be further removed by pressurizing or pressing the pulp cake. The dewatered pulp may then optionally be dried to a desired moisture content and/or baled or wound onto rolls. In certain preferred embodiments, the water is removed to the extent that the resulting pulp can be collected on a screen and wound onto a roll. In certain embodiments, the presence of no more than about 60 wt% total water content is the desired water content, and preferably from 4 to 60 wt% total water content. However, in certain embodiments, the pulp may leave more water so that there is a higher total water content, up to 75 wt% total water content.

FIGS. 1 and 2 of the drawings

The method will now be described with reference to fig. 1 and 2. Throughout the detailed description, like reference characters refer to like elements throughout the various figures.

Referring to fig. 1, there is a block diagram of an embodiment of a wet process for making "wet" pulp according to the present invention. The pulp ingredients 1 are added to vessel 2. The container 2 is provided with an internal agitator, similar to the agitator in a washing machine. The agitator disperses the ingredients into the water to form a substantially homogeneous slurry. The mixed slurry is transferred to the primary refiner 3 refining the slurry. Subsequently, the refined slurry may be transferred, optionally, to a second refiner 4, and optionally subsequently to a third refiner 5. Although only 3 refiners are shown, any number of refiners may be used depending on the degree of homogenization and refining desired. After the last refiner in the series, the refined slurry is optionally transferred to a filter or analyzer 6 which allows passage of slurry with dispersed solids below a selected screen size, while dispersed solids larger than the selected screen size are recycled back to one or more refiners, such as through line 7, or to a refiner 8 which specially refines such recycled slurry, whereby the refined slurry is again passed through the filter or analyzer 6. From the filter or analyzer 6, the properly refined slurry is sent to a horizontal water vacuum filter 9 which removes water so that the water content of the pulp does not exceed 75 wt% of the total composition. The transfer of slurry from one point to another can be accomplished by any conventional method and apparatus, such as by one or more pumps 10. The pulp is then transported to a dryer 11, which removes more water until the pulp has the desired water content. The refined pulp is then packaged in a baling machine 12.

Referring to fig. 2, there is a block diagram of an embodiment of the dry process for making "dry" pulp according to the present invention. The dry method is the same as the wet method except for the portion after the horizontal water vacuum filter 9. After the filter, the pulp is passed through a press 13 from which more water is removed until the pulp reaches the desired water content. The pulp then passes to a fluffer 14 to loosen the pulp and then to the dryer 11 where more water is removed. The pulp is then fed through rotor 15 and baled in baler 12.

Second embodiment of the process of the invention

In a second embodiment, the process for making thermoset and polyareneazole pulp is the same as the first embodiment of the process described above except for the following differences.

It may be necessary to cut the thermoset or polyareneazole fibers or both the thermoset and polyareneazole fibers short before combining all of the ingredients together. This is accomplished by combining water with the fiber components. Subsequently, the water is mixed with the fibers to form a first suspension and processed through a first disc mill to cut the fibers into short pieces. The disc refiner cuts the fibers to an average length of no more than 10 cm. The disc refiner will also partially fibrillate and partially masticate the fibers. Other fibers not previously added can also be cut in this manner to form a second processed suspension. Subsequently, the other fibers (or second suspension if processed in water) are combined with the first suspension.

Before or after or during the addition of the other ingredients, if necessary, more water is added to increase the water content to 95 to 99 wt% of the total ingredients. After all the ingredients have been combined, they may be mixed, if necessary, to make a substantially homogeneous slurry.

The components of the slurry are then co-refined together, i.e., refined simultaneously. The refining step includes fibrillating, chopping and masticating the solids in the suspension so as to convert all or substantially all of the thermoset fibers and polyareneazole fibers into irregularly shaped fibrillated fibrous structures. This refining step also disperses all solids so that the refined slurry is substantially homogeneous. Subsequently, water is removed as in the first embodiment of the process. Both processes produce identical or substantially identical thermoset fibers and polyareneazole pulp.

Pulp of the invention

The resulting product produced by the process of the present invention is a thermoset fiber and polyareneazole pulp for use as a reinforcement in the product. The pulp comprises (a) a fibrous structure of irregularly shaped thermoset fibers, (b) an irregularly shaped polyareneazole fibrous structure, (c) optionally other minor additives, and (d) water.

The concentration of the individual constituent components in the pulp corresponds, of course, to the concentration of the corresponding constituents described above for the production of the pulp.

Irregularly shaped thermoset fibers and polyareneazole fibrillated fibrous structures have stems and fibrils. The thermoset fiber fibrils and/or stems are substantially intertwined with the polyareneazole fibrils and/or stems. The fibrils are important and function as hooks or anchors or antennae that attach and hold onto the pulp and adjacent particles in the final product, thereby providing integrity to the final product.

The thermoset fibers and polyareneazole fibrillated fibrous structures preferably have an average largest dimension of no greater than 5mm, more preferably 0.1 to 4mm, most preferably 0.1 to 3 mm. The thermoset fibers and polyareneazole fibrillated fibrous structures preferably have a length weighted average length of no more than 1.3mm, more preferably 0.7 to 1.2mm, most preferably 0.75 to 1.1 mm.

Thermoset fibers and polyareneazole pulp do not contain a large number of aggregates or clumps of the same material. Furthermore, the pulps have a Canadian Standard Freeness (CSF), measured according to TAPPI test T227 om-92, of 100 to 700ml, preferably 250 to 450ml, which is a measure of their drainability.

The surface area of a pulp is a measure of the degree of fibrillation and affects the porosity of a product made from the pulp. In some embodiments of the invention, the pulp has a surface area of 7 to 11m²/g。

It is believed that the fibrillated fibrous structures, when substantially uniformly dispersed throughout the reinforcement and friction and fluid sealing materials, will provide a large number of reinforcing sites and increased abrasion resistance by virtue of the high temperature characteristics of the polyareneazole polymer and the fibrillation tendency of the polyareneazole fibers. When co-refined, the blend of thermoset and polyareneazole materials is so intimate that in friction or fluid seal materials there is always some polyareneazole fibrous structure in close proximity to the thermoset fibrous structure and therefore stress and wear in service is always shared. Thus, when co-refined, the thermoset and polyareneazole materials are in such intimate contact that in a friction or fluid seal material there is always some polyareneazole fibrous structure in close proximity to the thermoset fibrous structure and therefore stress and wear in service is always shared.

Fluid sealing material

The invention also relates to a fluid sealing material and a method for manufacturing the fluid sealing material. Fluid sealing materials are used or utilized as barriers to prevent the egress of fluids and/or gases and to prevent the ingress of contaminants in the event that two objects come close together. One exemplary application of fluid sealing materials is in gaskets. The fluid sealant comprises a binder; optionally at least one filler; and fibrous reinforcement comprising the thermoset and polyareneazole pulp of the present invention. Suitable binders include, but are not limited to, nitrile rubber (nitrile rubber), butadiene rubber, neoprene rubber, styrene butadiene rubber, nitrile-butadiene rubber (nitrile-butadiene rubber), and mixtures thereof. The binder can be added with all other raw materials. The binder is typically added in the first step of the liner manufacturing process, where the dry ingredients are mixed together. Other ingredients optionally include uncured rubber particles and rubber solvent, or a solution of rubber in a solvent, to cause the binder to coat the surfaces of the filler and pulp. Suitable fillers include, but are not limited to, barium sulfate, clay, talc, and mixtures thereof.

Suitable methods for manufacturing the fluid sealing material are, for example, beater-add methods or wet methods, wherein the gasket is made of a slurry of materials; or by so-called calendering or dry manufacturing, in which the ingredients are incorporated into an elastomer or rubber solution.

Friction material

The pulp of the present invention can be used as a reinforcing material in friction materials. By "friction material" is meant a material used for its friction characteristics such as coefficient of friction to stop or transmit kinetic energy, high temperature stability, wear resistance, noise and vibration damping properties, and the like. Exemplary uses for friction materials include brake pads, dry clutch facings, clutch facing segments, brake pad backing/insulation layers, automatic transmission paper, wet brakes, and other industrial friction paper.

With respect to this new use, the invention also relates to a friction material and a method for manufacturing the friction material. Specifically, the friction material comprises a friction modifier; optionally at least one filler; a binder; and a fibrous reinforcement comprising the thermosetting fiber of the present invention and polyareneazole pulp. Suitable friction modifiers are metal powders such as iron, copper and zinc; abrasives such as oxides of magnesium and aluminum; lubricants such as synthetic and natural graphite, and sulfides of molybdenum and zirconium; and organic friction modifiers such as synthetic rubber and cashew nut shell resin particles. Suitable binders are thermosetting resins such as phenolic resins (i.e. pure (100%) phenolic resins and various phenolic resins modified with rubber or epoxy), melamine resins, epoxy resins and polyimide resins and mixtures thereof. Suitable fillers include barite, whiting, limestone, clay, talc, various other magnesium-aluminum-silicate powders, wollastonite, stevensite, and mixtures thereof.

The actual steps for making the friction material may vary depending on the type of friction material desired. For example, methods of making molded friction parts typically involve incorporating the required ingredients into a mold, curing the part and forming, heat treating and grinding the part, if required. Automatic transmissions and friction paper can generally be made by combining the required ingredients in a slurry and using conventional paper making processes on a paper machine.

Many other uses for the pulp are possible, including its use as a processing aid such as a thixotrope or as a filter. When used as a filter, the pulp of the present invention is generally combined with a binder and formed into a sheet or paper product in a molded shape by a conventional method.

Test method

The following test methods were used in the following examples.

Canadian Standard Freeness (CSF) was tested in conjunction with optical microscopy as described in TAPPI method T227. CSF measures the drainage rate of the diluted pulp suspension. It is a useful test to evaluate the degree of fibrillation. The data obtained from carrying out this test are expressed as canadian freeness values, which represent the number of milliliters of water that is expelled from the water slurry under specified conditions. This value is large, indicating a high freeness and a high tendency to drain. The low value indicates a slow tendency of the dispersion to drain. Freeness is inversely related to the degree of fibrillation of the pulp, as a greater number of fibrils will reduce the rate at which water drains through the forming paper mat.

The average fiber length, including the length weighted average length, was determined using a fiber quality Analyzer (sold by OpTest Equipment Inc., 900Tupper St., Hawkesbury, ON, K6A 3S3 Canada) according to TAPPI test method T271.

Temperature: all temperatures are measured in degrees Celsius (. degree. C.).

Denier is determined according to ASTM D1577 and is the linear density of the fiber in grams of weight of 9000m of the fiber. Denier is determined on a Vibroscope from Textech, Munich, Germany. Denier multiplied by (10/9) equals decitex (dtex).

Examples

The invention will now be illustrated by the following specific examples. All parts and percentages are by weight unless otherwise indicated. Examples prepared according to the process of the invention are indicated numerically. Comparative examples are indicated by letters.

The following examples show that the degree of fibrillation of thermoset fibers is surprisingly increased by co-refining a small amount of polyareneazole fiber in the presence of thermoset fibers. The degree of fibrillation is an important characteristic of the pulp product. There is a direct relationship between the degree of fibrillation and the retention of the filler. In addition, fibrillation can be used to achieve uniform dispersion of the pulp product in a variety of different materials. By physical entanglement, highly fibrillated fibers will also be able to bond more strongly to the matrix than non-fibrillated fibers. In the examples below, poly (p-Phenylene Benzobisoxazole) (PBO) fibers are used as a representative of the polyareneazole fiber family, while acrylic fibers are used to represent thermoset fibers.

Comparative example A

This example shows a prior art material made when thermoset fibers were refined without any polyareneazole fibers. 68.1g of 1.9 dtex acrylic fiber (sold by Sterling Fibers, Inc., 5005Sterling Way, Pace, FL 32571) having a 9.5mm cut length was dispersed in 2.7L of water. The dispersion was passed through a Sprout-Wadron single speed, 30cm single disc refiner (sold by Andritz, Inc., Sprout-Bauer Equipment, Muncy, Pa 17756) 5 times with a disc gap set at 0.26mm, followed by 12 passes through the refiner with a disc gap set at 0.13 mm. The properties of the 100% acrylonitrile-based refined material thus produced are shown in table 1; fig. 3 is a digital optical micrograph of the material showing the limited fibrillation that such material undergoes after refining.

Subsequently, paper is made from the refined material by: 6.7g of material (on a dry basis) was dispersed in 1.5L of water for 3min using a standard pulp disintegrator (as described in appendix A of TAPPI 205) and the dispersion was added to a wet-laid paper mold with a 21cm x 21cm size screen. Subsequently, the dispersion was diluted with 5L of water and formed a wet laid paper on a screen, and excess water was removed with a plunger. Subsequently, the paper was dried in a paper dryer at 100 ℃ for 10 min. The properties of the paper so produced are shown in table 1.

Comparative example B

This example shows a 100% polyareneazole pulp. A100% PBO pulp was produced in the same manner as in comparative example A, except that 68.1g of 1.7 dtex PBO fiber (sold by Toyobo Co., Ltd., Zylon Department, 2-2-8Dojima-Hama, Kita-Ku Osaka) having a 12.7mm cut length was used instead of the acrylic fiber. The properties of the 100% PBO refined material thus produced are shown in table 1; fig. 4 is a digital optical micrograph of the pulp showing fibrillation of the PBO fibers after refining. Subsequently, paper was made from the PBO refined material (as described in comparative example a) and the properties of the paper so produced are shown in table 2.

Example 1

The pulp of the present invention was produced in the same manner as in comparative example A, except that a dispersion comprising a mixture of the starting unrefined staple fibers of comparative example A and the starting unrefined staple fibers of comparative example B was refined and passed through a disc refiner 17 times to form a co-refined pulp. The fiber mixture comprised 61.7g of 1.9 dtex acrylic fiber (sold by Sterling Fibers, Inc., 5005Sterling Way, Pace, FL 32571) having a 9.5mm cut length and 6.4g of 1.7 dtex PBO fiber (sold by Toyobo Co., Ltd., Zylon department, 2-2-8Dojima-Hama, Kita-Ku Osaka) having a 12.7mm cut length. The co-refined pulp had about 9 wt% PBO and 91 wt% acrylonitrile, and the properties of the pulp so produced are shown in table 1. Subsequently, paper was made from this pulp (as described in comparative example a), and the properties of the paper so produced are shown in table 2.

Example 2

Another pulp of the invention was produced in the same manner as in example 1, except that the mixture contained 50.8g of 1.9 dtex acrylic fiber and 17.3g of 1.7 dtex PBO fiber. The co-refined pulp had about 25 wt% PBO and 75 wt% acrylonitrile. The properties of the pulp thus produced are shown in table 1; fig. 5 is a digital optical micrograph of the pulp showing fibrillation of both PBO and acrylic fibers after refining. Subsequently, paper was made from this pulp (as described in comparative example a), and the properties of the paper so produced are shown in table 2.

Comparative example C

This example demonstrates that a pulp obtained by refining thermoset fibers and polyareneazole fibers separately from each other and then mixing them together provides a paper having lower tensile strength (and therefore lower degree of fibrillation) than a paper made from a co-refined pulp of the present invention.

The refined material sample made in comparative example a was mixed with the refined material sample of comparative example B in an amount of 75 wt% acrylonitrile-based material to 25 wt% PBO material (dry basis) using a standard pulp disintegrator as described in appendix a of TAPPI205 for 5 minutes. The TAPPI disintegrator was used to mix the two refined pulps of comparative examples A and B because the agitation was vigorous enough to mix and disperse the previously refined pulp well without changing its length or fibrillation. The properties of the pulp thus produced are shown in table 1. Subsequently, paper was made from the pulp (as described in comparative example a), and the properties of the paper so produced are shown in table 2. Comparison of the strength of both the paper made from example 2 and the paper made from this example shows that the paper made from the co-refined pulp has significantly improved physical properties (e.g., tensile strength is 0.18N/cm for the paper made from the co-refined pulp, while the paper made from the pulp of this example is 0.07N/cm).

The refined thermoset material had no significant fibrillated fibers as described in comparative example a. By adding polyareneazole fibers to the thermoset fibers and then refining the two fibers together as in examples 1 and 2, the thermoset fibers obtained exhibited a higher degree of fibrillation. This effect is clearly seen in the 25/75 PBO/acrylonitrile-based co-refined pulp product shown in FIG. 3. Notably, the pulp of example 2 had a Canadian Standard Freeness (CSF) comparable to the CSF obtained by mixing 100% acrylonitrile-based pulp and 100% PBO pulp in a dry weight ratio of 75/25 as described in comparative example C. The results of optical microscopy combined with CSF show that polyareneazole materials can induce fibrillation in thermosets.

The average fiber length of the pulp products produced in the examples is shown in table 1, and it is noted that the co-refined samples have shorter fiber lengths than the samples containing only one type of fiber. This indicates that by co-refining with polyareneazole fibers, a very different type of pulp product is produced, which cannot be achieved by simply mixing polyareneazole pulp with other pulps.

Table 2 summarizes the modulus and tenacity results obtained from the handsheets made in the examples. The handsheet data of example 2 shows that paper with surprisingly high modulus can be made from certain pulps of the present invention. Its modulus is several times higher than that of single material paper and is only achieved when polyarenazoles are processed with thermosets.

Table 1:

pulp and method for producing the same	Wt% acrylonitrile system	Wt％PBO	CSF[ml]	Arithmetic mean length [ mm ]]	Length weighted average length [ mm]	Weight weighted average length [ mm]
							Comparative example A	100	0	748	0.504	2.445	4.266
Comparative example B	0	100	670	0.209	1.174	2.691
							Example 1	91	9	722	0.215	0.722	1.753
Example 2	75	25	732	0.213	0.680	1.668
							Comparative example C	75	25	763	0.340	2.219	4.340

Table 2:

pulp from the following examples	Wt% acrylonitrile system	Wt％PBO	Tensile Strength [ N/cm]	Young's modulus [ MPa ]]	Density [ g/cc ]]	Basis weight [ g/m ]2]
							Comparative example A	100	0	0.07	1.87	0.19	142.26
Comparative example B	0	100	0.23	1.18	0.23	138.98
							Example 1	91	9	0.05	1.71	0.17	147.43
Example 2	75	25	0.18	5.44	0.22	139.38
							Comparative example C	75	25	0.07	0.63	0.18	144.55

Example 3

The brake pad incorporating the pulp of the present invention was manufactured as follows. About 20kg of an asbestos-free base compound powder comprising a mixture of 7 wt% cashew nut shell resin, 17 wt% inorganic filler, 21 wt% graphite, coke and lubricant, 18 wt% inorganic abrasive and 16 wt% soft metal was mixed together in a 50Littleford mixer for 10-20 min. The mixer has two high speed cutoff knives with blades of "star and bar" configuration and a slower rotating plow.

Subsequently, 5kg of the fully blended base compound powder was blended with the pulp of the present invention (co-refined pulp 50 wt% polyarenazole and 50 wt% thermoset), with the amount of pulp being 3.8 wt%, based on the combined weight of the compound powder and pulp. Subsequently, the pulp is dispersed into the base compound powder by further mixing for 5-10 min. Once mixed, the resulting brake pad composition had a normal visual appearance in which the fibers were well dispersed in and completely coated by the base compound powder, with substantially no detectable pilling of the pulp or separation of any of the components.

The brake pad composition was then poured into a single cavity steel mold for the front disc brake pad and cold pressed to a gauge thickness of about 5/8 inches (16mm) and removed from the mold to form a pre-formed brake pad weighing approximately 200 g. A total of 12 replicated preforms were fabricated. The preform was then placed into a two-cavity mold, placed in an industrial press, and pressure cured (binder phenolic resin crosslinked and reacted) at 300 ° F (149 ℃) for about 15 minutes, with timed venting to allow escape of phenolic reaction gases, followed by heat curing with slight restraint at 340 ° F (171 ℃) for 4 hours to complete phenolic binder crosslinking. The cured, molded brake pad was then ground to the desired thickness of about one-half inch (13 mm).

Example 4

This example shows how the pulp of the present invention can be incorporated into a beater-add pad for fluid sealing applications. Water, rubber, latex, fillers, chemicals and pulp of the present invention are combined in the desired amounts to form a slurry. On an endless wire screen (e.g., a paper machine screen), the slurry essentially drains its moisture content, is dried in a heated tunnel, and is vulcanized on heated calender rolls to form a material having a maximum thickness of about 2.0 mm. The material is pressed in a hydraulic press or twin roll calender which increases density and improves sealability.

Such a spacer material added to the beater typically does not have as good a seal as a comparable pressed-fibre material and is most suitable for medium pressure, high temperature applications. The gasket added to the beater can be used for manufacturing auxiliary engine gaskets or after further processing, for cylinder head gaskets. For this purpose, the semi-finished product is laminated to both sides of the needled metal sheet and is physically held in place by the needling.

Example 5

This example demonstrates how the pulp of the present invention can be incorporated into a liner by calendering. The same ingredients as in example 4, excluding water, were thoroughly dry blended together and then blended with a rubber solution prepared using an appropriate solvent.

After mixing, the compound is typically fed intermittently to a roll calender. The calender consists of a cooled small roll and a heated large roll. The compound is fed and drawn into the calender nip by the rotary motion of the two rolls. The compound itself adheres and wraps in multiple layers, typically about 0.02mm thick, around the underlying hot roll, depending on the pressure, to form a liner material formed by the build-up of layers of the compound. During this process, the solvent evaporates and the elastomer begins to vulcanize.

Once the desired thickness of the liner material is achieved, the calender rolls are stopped and the liner material is cut from the heated rolls and cut and/or die-cut to the desired dimensions. No additional pressing or heating is required and the material can already be used as a gasket. In this way, a gasket of up to about 7mm thickness can be manufactured. However, most gaskets made in this way are much thinner, typically about 3mm or less in thickness.

Claims (19)

1. A pulp for use as a reinforcement or processing material comprising:

(a) a fibrillated thermoset fiber structure, the structure comprising 60 to 97 wt% of the total solids;

(b) a fibrillated polyareneazole fiber structure, which accounts for 3-40 wt% of the total solids;

the thermoset and polyareneazole fibrous structure has an average largest dimension of no greater than 5mm, a length weighted average length of from 0.7 mm to 1.3mm, and has stems and fibrils, wherein the thermoset fibrils and/or stems are substantially intertwined with the polyareneazole fibrils and/or stems.

2. The pulp of claim 1, wherein the thermoset fiber structure comprises from about 60 to 75 weight percent of the total solids.

3. The pulp of claim 1, wherein the polyareneazole fibrous structure comprises about 25 to 40 wt% of the total solids.

4. The pulp of claim 1 having a canadian standard freeness of 100 to 700 ml.

5. The pulp of claim 1, wherein the thermoset fibrous structure is a thermoset fiber.

6. The pulp of claim 1 wherein the polyareneazole is a rigid rod polybenzazole or a rigid rod polypyridazole polymer.

7. The pulp of claim 6, wherein the polybenzazole is a polybenzobisoxazole.

8. The pulp of claim 6, wherein the polypyridazole is polypyridobisimidazole.

9. A friction material comprising:

a friction modifier selected from the group consisting of metal powders, abrasives, lubricants, organic friction modifiers, and mixtures thereof;

a binder selected from the group consisting of thermosetting resins, melamine resins, epoxy resins, and polyimide resins, and mixtures thereof;

and

the pulp of claim 1.

10. A thixotrope comprising the pulp of claim 1.

11. A fluid sealant material comprising:

a binder; and

a fiber reinforcement comprising the pulp of claim 1.

12. The fluid sealant material of claim 11 wherein the binder is selected from the group consisting of nitrile rubber, butadiene rubber, neoprene rubber, styrene butadiene rubber, nitrile rubber, and mixtures thereof.

13. A filter comprising the pulp of claim 1 and a binder.

14. A method of making fibrillated thermoset and polyareneazole pulp for use as a reinforcement material, comprising:

(a) combining pulp ingredients comprising:

(1) thermoset fibers capable of being fibrillated and having an average length of no more than 10cm and from 60 to 97 weight percent of the total solids in the ingredients;

(2) a rigid rod aramid fiber having an average length of no more than 10cm and comprising 3 to 40 weight percent of the total solids in the ingredients; and

(3) water accounting for 95-99 wt% of the total components;

(b) mixing the ingredients into a substantially homogeneous slurry;

(c) co-refining the slurry by simultaneously performing:

(1) fibrillating, cutting and masticating the fibrillated thermoset fibers and polyareneazole fibers into irregularly shaped fibrillated fibrous structures having stems and fibrils; and

(2) dispersing all solids so as to render the refined slurry substantially homogeneous; and

(d) the water is removed from the refined slurry,

thereby producing fibrillated thermoset and polyareneazole pulp in which the fibrillated thermoset and polyareneazole fibrous structures have an average largest dimension of no greater than 5mm, a length-weighted average length of no greater than 1.3mm, and the fibrillated thermoset fibrils and/or stems are substantially entangled with the polyareneazole fibrils and/or stems.

15. The method of claim 14, wherein the thermoset fibers have a linear density of no greater than 10 dtex; and the polyareneazole fibers have a linear density of no greater than 2.5 dtex.

16. The method of claim 14, wherein the thermoset fibrous structure is a thermoset fiber.

17. The method of claim 14, wherein the refining step comprises passing the mixed slurry through a series of disc grinders.

18. A method of making fibrillated thermoset and polyareneazole pulp for use as a reinforcing and processing material, comprising:

(a) combining ingredients including water and a first fiber from the group:

(1) thermosetting fibers capable of being fibrillated and comprising 60 to 97 wt% of the total solids in the pulp; and

(2) rigid rod-like polyarenazole fibers accounting for 3-40 wt% of total solids in the pulp;

(b) mixing the combined ingredients into a substantially homogeneous suspension;

(c) refining the suspension in a disc refiner thereby cutting the fibers to an average length of no more than 10cm and fibrillating and masticating at least some of the fibers into irregularly shaped fibrillated fibrous structures;

(d) combining ingredients including the refined suspension, the second fibers of group (a) (1 and 2) having an average length of no greater than 10cm, and water, if necessary, to increase the water content to 95-99 wt% of the total ingredients;

(e) mixing the ingredients, if necessary, to form a substantially homogeneous suspension;

(d) co-refining the mixed suspension by simultaneously performing:

(1) fibrillating, chopping and masticating the solids in the suspension so as to convert all or substantially all of the thermoset and polyareneazole fibers into fibrillated thermoset and polyareneazole fiber structures having irregular shapes of stems and fibrils; and

(2) dispersing all solids so as to render the refined slurry substantially homogeneous; and

(f) the water is removed from the refined slurry,

thereby producing thermoset and polyareneazole pulp in which the fibrillated thermoset and polyareneazole fibrous structure has an average largest dimension of no greater than 5mm, a length weighted average length of no greater than 1.3mm, and thermoset fibrils and/or stems are substantially entangled with polyareneazole fibrils and/or stems.

19. The method of claim 18, wherein the thermoset fibrous structure is a thermoset fiber.