MX2008007927A - Polyareneazole/wood pulp and methods of making same - Google Patents

Abstract

The present invention relates to wood pulp and polyareneazole pulp for use as reinforcement material in products including for example friction materials, fluid sealing materials, and papers. The pulp comprises (a) irregularly shaped, wood pulp fibrous structures, (b) irregularly shaped, polyareneazole fibrous structures, and (c) water, whereby wood pulp fibrils and/or stalks are substantially entangled with polyareneazole fibrils and/or stalks. The invention further relates to processes for making such wood pulp and polyareneazole pulp.

Description

POLYARENOAZOLE / WOOD PULP AND METHODS TO PREPARE THE SAME Field of the Invention This invention relates to wood pulp and polyarenoazole pulp for use as a reinforcing material in products including, for example, friction materials, fluid sealing materials and papers. The invention also relates to processes for making this pulp.

BACKGROUND OF THE INVENTION Fibrous and non-fibrous reinforcing materials have been used for many years in friction products, fluid sealing products and other plastic or rubber products. These reinforcement materials should typically exhibit high resistance to wear and heat. Historically, asbestos fibers have been used as reinforcement materials, but due to their health risks, replacements have been made or proposed. However, many of these replacements do not perform as well as asbestos in one way or another. Research Disclosure 74-75, published in February 1980, describes the elaboration of pulped elaborated fibers of para-aramid of the brand KEVLARMR fibrillated of variable lengths and the use of this pulp as a reinforcement material in several applications. This publication describes that the pulp Ref .: 193379 made of fibers of para-aramid of KEVLAR1 mark ^ can be used in single-rolled products, or in combination with fibers of other materials, such as meta-aramid of NOMEXMR brand wood pulp, cotton and other natural cellulosics, rayon, polyester, polyolefin, nylon, polytetrafluoroethylene, asbestos and other materials, fiberglass and others, ceramics, steel and other metals, and coal. The publication also discloses the use of pulp para-aramid fiber of KEVLARMR brand, alone, or short cut fiber of para-aramid of KEVLARMR mark, in friction materials to replace a fraction of the volume of asbestos, with rest of the volume of the asbestos that is replaced by fillers or other fibers. Publication of patent application US 2003/0022961 number (Kusaka et al.) Discloses friction materials made from a friction modifier, a binder and a fibrous reinforcement made of a fiber of (a) a dry pulp of aramid and (b) wet aramid pulp, wood pulp or acrylic fiber pulp. Dry aramid pulp is defined as an aramid pulp obtained by "the dry fibrillation method". The method of dry fibrillation is moles dry the aramid fibers between a rotary cutter and a screen to prepare the pulp. Wet aramid pulp is defined as an aramid pulp obtained by "the wet fibrillation method". The method of wet fibrillation is to grind short aramid fibers in water between two rotating discs to form fibrillated fibers and then dehydrate the fibrillated fibers, i.e., the pulp. Kusaka et al., Further discloses a method for fibrillating by mixing fibers by first mixing plural types of organic fibers that fibrillate in a defined ratio, and then fibrillating the mixture to produce a pulp. The polypyridobisimidazole polymer is a polymer of rigid rods. The fiber made from this polymer (such as the polymer composition, which is referred to as PIPD and is known as the polymer used to make the MS1 fiber) is known to be useful in both flame-resistant and cut-resistant protective clothing. Rigid rod polymer fibers having strong hydrogen bonds between polymer chains, for example, polypyridobisimidazoles, have been described in U.S. Patent No. 5,674,969 to Sikkema et al. An example of a polipiridobisimidazol is poly (1, 4- (2, 5-dihydroxy) phenylene-2, 6-pyrido [2, 3-d: 5, 6-d 'jbisimidazol), which may be prepared by polymerization condensation of tetraaminopyridine and 2,5-dihydroxyterephthalic acid in polyphosphoric acid. Sikkema describes that the pulp can be made from these fibers. Sikkema also discloses that in the production of single- or two-dimensional objects such as fibers, films, tapes and the like, it is desired that the polypyrrobisimidazoles have a high weight molecular which corresponds to a relative viscosity ("Vrel" or "hrel") of at least about 3.5, preferably at least about 5, and more particularly equal to or greater than about 10, when measured at a polymer concentration 0.25 g / dl in methanesulfonic acid at 25 ° C. Sikkema also discloses that good fiber spinning results are obtained with poly [pyridobisimidazole-2,6-diyl (2,5-dihydroxy-p-phenylene)] having relative viscosities greater than about 12, and that relative viscosities can be achieved of more than 50 (corresponding to inherent viscosities greater than about 15.6 dl / g). There is a current need to provide alternative pulps that perform well in products and that are inexpensive. Despite the numerous descriptions that propose alternative low-cost reinforcement materials, many of these proposed products do not perform adequately in use, cost significantly more than currently commercial products, or have other negative attributes. As such, the need remains for reinforcing materials that exhibit high wear and heat resistance, and that are comparable or less expensive than other commercially available reinforcing materials.

Brief Description of the Invention One embodiment of this invention relates to a pulp for use as a reinforcing or processing material, comprising: (a) fibrillated, fibrillated, irregularly shaped fibrous wood pulp structures, structures that are to 97 weight percent of the total solids; (b) fibrillated, irregularly formed polyarenoazole fibrous structures that are from 3 to 40 weight percent of the total solids; and (c) water, wood pulp and fibrous polyarenoazole structures having a maximum average dimension of no more than 5 mm, a weighted average length in length of no more than 1.3 mm, and stems and fibrils where the fibrils and / or stems of the wood pulp are substantially entangled with the fibrils and / or stems of polyarenoazole. Another embodiment of this invention is a process for making a pulp of fibrillated wood and polyarenoazole pulp for use as a reinforcing material, comprising: (a) combining pulp ingredients, including: (1) wood pulp fiber which has an average length of no more than 1 cm and which is 60 to 97 weight percent of the total solids in the ingredients; (2) rigid rod polyarenoazole fiber having an average length of no more than 10 cm and which is from 3 to 40 weight percent of the total solids in the ingredients; and (3) water which is 95 to 99 weight percent of the total ingredients; (b) mixing the ingredients to a substantially uniform slurry; (c) co-refine the slurry to simultaneously: (1) fibrillate, cut and chew fiber from fibrillated wood pulp and polyarenoazole fiber to fibrillated, fibrillated structures, irregularly formed with stems and fibrils; and (2) dispersing all solids such that the refined slurry is substantially uniform; and (d) removing water from the refined slurry, thereby producing a pulp of fibrillated wood and polyarenoazole pulp with the fibrillated wood pulp and fibrous structures of polyarenoazole having a maximum average dimension of no more than 5 mm, a weighted average length in length of not more than 1.3 mm, and the fibrils and / or stems of the fibrillated wood pulp are substantially entangled with the fibrils and / or stems of polyarenoazole.

In still another embodiment of the invention is a process for making a pulp of fibrillated wood and polyarenoazole pulp for use as a reinforcing and processing material, comprising: (a) combining ingredients including water and a first fiber of the group that consists of: (1) wood pulp fiber that is 60 to 97 weight percent of the total solids in the pulp; (2) rigid rod polyarenoazole fiber which is from 3 to 40 weight percent of the total solids in the pulp; and (b) mixing the combined ingredients to a substantially uniform suspension; (c) refining the suspension in a disk refiner, thereby cutting the fiber to have an average length of no more than 10 cm, and fibrillating and chewing at least some of the fiber to fibrillated, fibrillated, irregularly formed structures; (d) combine the ingredients that include the refined suspension, the second fiber of the group of (a) (1 and 2) that has an average length of no more than 10 cm, and water, if necessary, to increase the concentration of water at 95-99 percent by weight of the total ingredients; (e) mixing the ingredients, if necessary, to form a substantially uniform suspension; (d) co-refining the mixed slurry to, simultaneously: (1) fibrillate, cut and chew solids in the suspension such that all or substantially all of the wood pulp and polyarenoazole fiber is converted to irregularly shaped fibrillated wood pulp and fibrous polyarenoazole structures with stems and fibrils; and (2) dispersing all solids such that the refined slurry is substantially uniform; and (f) removing water from the refined slurry, thereby producing a pulp of fibrillated wood and polyarenoazole pulp with fibrillated wood pulp and fibrous structures of polyarenoazole having a maximum average dimension of no more than 5 mm, a weighted average length in length of not more than 1.3 mm, and the fibrils and / or stems of the wood pulp are substantially entangled with the fibrils and / or stems of polyarenoazole. In some embodiments, this invention additionally relates to friction materials, fluid sealing materials, and papers comprising the pulp of the present invention.

Brief Description of the Figures The invention can be understood more fully by from the following detailed description thereof in conjunction with the accompanying figures described as follows. Figure 1 is a block diagram of the apparatus for performing a wet process to make "wet" pulp according to the present invention. Figure 2 is a block diagram of the apparatus for performing a dry process for making "dry" pulp according to the present invention. Figure 3 is a digital optical micrograph of the prior art material that is made when the wood pulp is refined without any polyarenoazole fiber that is present. Figure 4 is a digital optical micrograph of the fibrillation of the PBO fiber after refining. Figure 5 is a digital optical micrograph of the fibrillation of PBO and wood pulp after co-refining.

Detailed Description of the Invention Glossary Before the invention is described, it is useful to define certain terms in the following glossary which will have the same meaning throughout this description unless otherwise indicated. "Fiber" means a unit of matter, relatively flexible, that has a high ratio of length to width through its cross sectional area perpendicular to its length. Here, the term "fiber" is used interchangeably with the term "filament" or "end". The cross section of the filaments described herein may be of any shape, but is typically circular or bean type. Fiber spun in a package reel is referred to as continuous fiber or continuous filament or continuous filament yarns. The fiber can be cut into short lengths called cut fiber. The fiber can be cut into even smaller lengths called flocculent fiber. The yarns, multi-filament yarns or tows comprise a plurality of fibers. The thread can be twisted and / or twisted. "Fibrilla" means a small fiber having a diameter as small as a fraction of a micrometer or a few micrometers and having a length of about 10 to 100 micrometers. The fibrils generally extend from the main trunk of a longer fiber having a diameter of 4 to 50 microns. The fibrils act as hooks or fasteners to secure and capture adjacent material. Some fibers fibrillate, but others do not or do not fibrillate effectively and for the purposes of this invention these fibers do not fibrillate. "Fibrillated fibrous structures" means material particles that have a stem and fibrils that are extend from the same where the stem is generally columnar and approximately 10 to 50 microns in diameter and the fibrils are hair-like members, of only a fraction of a micron or a few microns in diameter attached to the stem and approximately 10 to 100 microns long. "Flocculent fiber" means short fiber lengths, shorter than the cut fiber. The length of the flocculent fiber is from about 0.5 to about 15 mm and a diameter from 4 to 50 microns, which preferably has a length of 1 to 12 mm and a diameter of 8 to 40 microns. The flocculent fiber that is less than about 1 mm does not add significantly to the strength of the material in which it is used. The flocculent fiber or fiber that is more than about 15 mm often does not work well because the individual fibers can become entangled and can not be distributed properly and uniformly throughout the length of the thick material or suspension. The aramid flocculent fiber is made by cutting aramid fibers in short lengths without significant fibrillation or any fibrillation, such as those prepared by the processes described in U.S. Patent Nos. 3,063,966, 3,133,138, 3,767,756, and 3,869,430. "Arithmetic" length means the calculated length of the following formula: ? [(Each individual pulp length)] Arithmetic length =? [Individual pulp account] Length "weighted average in length" means the calculated length of the following formula: 2? [Each length of individual pulp] Average length weighted in length -? [Each length of individual pulp] "Weight-weighted average" length means the calculated length of the following formula: ? [Each length of individual pulp 3] Weighted average length in weight =? [Each individual pulp length2] "Maximum dimension" of an object means the straight distance between the two points most distant from each other in the object. "Fiber cut" can be made to cut filaments to lengths of no more than 15 cm, preferably 3 to 15 cm; and more preferably from 3 to 8 cm. The cut fiber can be straight (ie not curly) or crimped to have a sawtooth-shaped curl along its length, with any frequency of curls (or repetitive bending). The fibers may be presented in an uncoated, or coated, or pre-treated form (eg, pre-stretched or heat-treated).

This invention relates to polyarenoazole pulp fiber and wood having use in friction materials, fluid sealing materials, and papers, and other materials that incorporate this pulp. The invention also relates to processes for making a pulp of polyarenoazole pulp fibers and wood pulp.

I. First Modality of the Inventive Process In a first embodiment, the process for making a fiber of wood pulp and polyarenoazole pulp comprises the following steps. First, the pulp ingredients are combined, added or contacted together. Second, the combined pulp ingredients are mixed to a substantially uniform slurry. Third, the slurry is refined or co-refined simultaneously. Fourth, water is removed from the refined slurry.

Combination Step In the combination step, the ingredients of the pulp are preferably added together in a container. In a preferred embodiment, the ingredients of the pulp include (1) wood pulp fiber, (2) polyarenoazole fiber, (3) optionally other additives, and (4) water.

Wood Pulp Fiber The wood pulp fiber is added at a concentration of 60 to 97% by weight of the total solids in the ingredients and preferably 60 to 75% by weight of the total solids in the ingredients. The wood pulp fiber preferably has a roughness of not more than 50 mg per 100 meters in length. In a preferred embodiment, the roughness is about 12 to 25 mg per 100 meters in length. Fiber roughness is defined as the pulp-dried mass of weight in mg divided by the fiber length of the total contour of all fibers as measured using a FQA table analyzer, Fiber Quality Analyzer (sold by Op Test Equipment Inc., 900 Tupper St., Hawkesbury, ON, K6A 3S3 Canada). In some embodiments, wood pulp fiber has an average length of no more than 1 cm. The wood pulp fiber also preferably has an average length of no more than about 5 mm. "Wood pulp" as used herein refers to the product of the boiling of wood chips with alkaline liquors or solutions of acidic or neutral salts followed by bleaching with chlorine compounds, the object being to remove more or less completely the hemicelluloses and wood lignin incrustations. The Kraft pulp is a type of wood pulp and the method to make it includes cooking (digestion) of the wood chips in an alkaline solution for several hours during which the typical products attack the lignin in the wood. The dissolved lignin is removed later leaving behind the cellulose fibers. The unbleached kraft pulp is dark brown in color, so before it can be used in many papermaking applications, it is typically bleached to lighten the color. In some embodiments, the wood pulp of this invention includes lyocell fibers and other fibers or fibrous structures that are obtained from cellulose with additional or different processing as described above.

Polyarenoazole fiber The polyarenoazole fiber is added at a concentration of 3 to 40% by weight of the total solids in the ingredients, and preferably 25 to 40% by weight of the total solids in the ingredients. The polyarenoazole fiber preferably has a linear density of not more than 10 dtex and more preferably from 0.8 to 2.5 dtex. The polyarenoazole fiber also preferably has an average length along its longitudinal axis of no more than 10 cm, more preferably a average length of 0.65 to 2.5 cm, and more preferably an average length of 0.65 to 1.25 xcm.

Polyarenoazole Polymer Polymers suitable for use in the manufacture of the polyarenoazole fiber must be of fiber-forming molecular weight so that they are formed into fibers. The polymers may include homopolymers, copolymers, and mixtures thereof. As defined herein, "polyarenoazole" refers to polymers having either: a heteroaromatic ring fused to an adjacent aromatic group (Ar) of the repeating unit structure (a): (a) with N which is a nitrogen atom and Z which is a sulfur atom, oxygen or an NR group with R which is hydrogen or a substituted or unsubstituted alkyl or aryl attached to N; or two heteroaromatic rings each fused to a common aromatic group (Ar1) of any of the structures (bl or b2) of the repeating unit: b1 b2 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 bonded to N. The number of repeating unit structures represented by the structures (a ), (bl), and (b2) is not critical. Each polymer chain typically has from about 10 to about 25,000 repeating units. Polyarenoazole polymers include polybenzazole polymers and / or polyprimidazole polymers. In certain embodiments, the polybenzazole polymers comprise polybenzimidazole or polybenzobisimidazole polymers. In certain different embodiments, the polypyridazole polymers comprise polypyridobisimidazole or polypyridoimidazole polymers. In certain preferred embodiments, the polymers are of one type of polybenzobisimidazole or polypyridobisimidazole. In structure (bl) and (b2), Y is an aromatic, heteroaromatic, aliphatic, or zero group; preferably an aromatic group; more preferably an aromatic group of six members of carbon atoms. From Even more preferably, the aromatic group of six carbon atom members (Y) has para-oriented bonds with two substituted hydroxyl groups; more preferably 2, 5-dihydroxy-para-phenylene. In structures (a), (bl), or (b2), Ar and Ar1 each represent any aromatic or heteroaromatic group. The aromatic or heteroaromatic group can be a fused or non-fused polycyclic system, but preferably it is a single six-membered ring. More preferably, the group Ar or Ar1 is preferably heteroaromatic, wherein one nitrogen atom is replaced by one of the carbon atoms of the ring system or Ar or Ar1 may contain only carbon ring atoms. Even more preferably, the group Ar or Ar1 is heteroaromatic. As defined herein, "polybenzazole" refers to polyarenoazole polymer having the structure (a), (bl), or (b2), where the group Ar or Ar1 is a six-membered aromatic ring of carbon atoms. Preferably, the polybenzoles include a class of rigid rod polybenzezoles having the structure (bl), or (b2); more preferably rigid rod polybenzezoles having the structure (bl), or (b2) with a six-membered aromatic carbocyclic Ar1 ring. These preferred polybenzazoles include, but are not limited to polybenzimidazoles (B = NR), polybenzthiazoles (B = S), polybenzoxazoles (B = 0), and mixtures or copolymers thereof. When the polybenzozazole is a polybenzimidazole, it is preferably poly (benzo [1,2-d, 4,5-d '] bisimidazol-2,6-diyl-1,4-phenylene). When the polybenzazole is a polybenzthiazole it is preferably poly (benzo [1,2-d: 4,5-d '] bisimidazol-2,6-diyl-1,4-phenylene). When the polybenzazole is a polybenzoxazole, it is preferably poly (benzo [1,2-d: 4, 5-d '] bisimidazole-2,6-diyl-1,4-phenylene) as defined herein, " polypyridazole "refers to the polyarenoazole polymer that has the structure (a), (bl), or (b2), where the group Ar or Ar1 is an iidual aromatic ring with six members of five carbon atoms and one nitrogen atom. Preferably, these polypyridazoles include a class of rigid rod polypyridazoles having the structure (bl), or (b2); more preferably rigid rod polypyridazoles having the structure (bl), or (b2) with a six-membered heterocyclic aromatic Ar1 ring. These more preferred polypyridazoles include, but are not limited to, polypyridobisimidazole (B = NR), polypyridobisthiazole (B = S), polypyridobisoxazole (B = 0), and mixtures or copolymers thereof. Even more preferred, the polypyridazole is a polypyridobisimidazole (B = NR) of the structure: or wherein N is a nitrogen atom and R is hydrogen or an N-linked substituted or unsubstituted alkyl or aryl, preferably where R is H. The average number of repeat units of the polymer chains is typically in the range of about 10 to about 25,000, more typically in the range of about 100 to 1,000, still more typically in the range of about 125 to 500, and additionally typically in the range of about 150 to 300. For the purposes of this invention, the relative molecular weights of the polyarynazole polymers are suitably characterized by diluting the polymer products with a suitable solvent , such as methanesulfonic acid, at a polymer concentration of 0.05 g / dl, and by measuring one or more viscosity values of diluted solution at 30 ° C. The molecular weight development of the polyarenoazole polymers of the present invention is suitably monitored by, or correlated to, one or more viscosity measurements in dilute solution. Accordingly, measurements of diluted solution of relative viscosity ("Vrel" or "hrel" or "nrel") and inherent viscosity ("Vinh" or "hinh" or "ninh") are typically used to monitor the molecular weight of the polymer. The relative and inherent viscosities of diluted polymer solutions are related according to the expression Vinh = In (Vrel) / C, where ln is the natural logarithmic function and C is the concentration of the polymer solution. Vrel is a non-unit ratio of the viscosity of the polymer solution to that of the polymer-free solvent, thus Vinh is expressed in units of inverse concentration, typically as deciliters per gram ("dl / g"). Therefore, in certain Aspects of the present invention, polypyridoimidazole polymers are produced which are characterized as providing a polymer solution having an inherent viscosity of at least about 20 dl / g at 30 ° C at a polymer concentration of 0.05 g / dl in acid methanesulfonic Because the higher molecular weight polymers resulting from the invention described herein give viscous polymer solutions, a concentration of about 0.05 g / dl of polymer in methanesulfonic acid is useful to measure the inherent viscosities in a reasonable amount of time. . In some embodiments, this invention utilizes polyarenoazole fiber having an inherent viscosity of at least 20 dl / g; in other more preferred embodiments, the inherent viscosity is at least 25 dl / g; and in some more preferred embodiments, the inherent viscosity is at least 28 dl / g.

Other Optional Additives Other additives may optionally be added, as long as they are suspended in the slurry in the mixing step and do not significantly change the effect of the refining step in the mandatory solid ingredients listed above. Suitable additives include pigments, dyes, antioxidants, compounds Flame retardants, and other processing and dispersion aids. Preferably, the ingredients of the pulp do not include asbestos. In other words, the resulting pulp is free of asbestos or without asbestos.

Water Water is added at a concentration of 95 to 99% by weight of the total ingredients, and preferably 97 to 99% by weight of the total ingredients. In addition, water can be added first. Then the other ingredients can be added at a ratio to optimize the dispersion in the water while the combined ingredients are mixed simultaneously.

Mixing Step In the mixing step, the ingredients are mixed to a substantially uniform slurry. By "substantially uniform" it is meant that the random samples of the slurry contain the same weight percent of the concentration of each of the starting ingredients as in the total ingredients in the combination step plus or minus 10% by weight. weight, preferably 5% by weight, and more preferably 2% by weight. For example, if the concentration of the solids in the total mixture is 50% by weight of wood pulp fiber more 50% by weight of polyarenoazole fiber, then a substantially uniform mixture in the mixing step means that each random sample of the slurry has (1) a concentration of wood pulp fiber of 50% plus or minus 10% in weight, preferably 5% by weight, and more preferably 2% by weight and (2) a concentration of polyarenoazole fiber of 50% plus or minus 10% by weight, preferably 5% by weight, and more preferably 2% by weight. Mixing can be achieved in any container that contains rotating knives or some other agitator. Mixing may occur after the ingredients are added as long as the ingredients are added or combined.

Refining Step In the refining step, the ingredients of the pulp are co-refined, converted or modified simultaneously, as follows. The wood pulp fibers and the polyarenoazole fiber are fibrillated, cut and chewed to irregularly formed fibrous structures having stems and fibrils. All solids are dispersed such that the refined slurry is substantially uniform. "Substantially uniform" is as defined above. The refining step preferably comprises passing the mixed slurry through one or more refiners discs, or recycle the slurry back through an individual refiner. By the term "disk refiner" is meant a refiner containing one or more pairs of disks that rotate relative to one another, thereby refining the ingredients by a cutting action between the disks. In a suitable type of disc refiner, the refined slurry that is refined is pumped between rotating discs and closely spaced circular stators, which can rotate with respect to each other. Each disk has a surface, which faces the other disk, with at least surface slots that extend partially radially. A preferred disk refiner that can be used is described in U.S. Patent No. 4,472,241. In a preferred embodiment, the plate spacing adjustment for the disc refiner is a maximum of 0.18 mm and preferably the spacing adjustment is 0.13 mm or smaller, at a practical minimum setting of approximately 0.05 mm. If necessary for uniform dispersion and proper refining, the mixed slurry is passed through the disk refiner more than once or through a series of at least two disk refiners. When the mixed slurry is refined in only one refiner, there is a tendency for the resulting slurry to be improperly refined and not evenly dispersed. Conglomerates or aggregates can be formed completely or substantially of one solid ingredient, or the other, or both, instead of being dispersed to form a substantially uniform dispersion. These conglomerates or aggregates have a greater tendency to separate and disperse in the slurry when the mixed slurry is passed through the refiner more than once or is passed through more than one refiner. Optionally, the refined slurry can be passed through a screen to segregate the long fibers or agglomerates, which can be recycled through one or more refiners until cut to acceptable lengths or acceptable concentration. Because a substantially uniform thick slurry containing multiple ingredients is co-refined in this step of the process, any type of pulp ingredient (eg, polyarenoazole fiber) is refined into a pulp in the presence of all other types of pulp. pulp ingredients (eg, wood pulp fiber) while these other ingredients are also being refined. This co-refining of pulp ingredients forms a pulp that is superior to a mixture of pulp generated by mixing only two pulps together. The addition of two pulps and then only mixing together does not form the fibrous components substantially uniformly and intimately connected pulp generated by co-refining the ingredients of the pulp in the pulp according to the present invention.

Removal Step The 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, additional water can be removed by applying pressure or squeezing the filter cake from the pulp. The dewatered water can then be further dried to a desired moisture content, and / or can be packed or rolled into rolls. In some preferred embodiments, the water is removed to a degree that the resulting pulp can be collected to a screen and rolled into rolls. In some embodiments, no more than about 60% by total weight of water that is present is a desired amount of water and preferably from 4 to 60% by total weight of water. However, in some embodiments, the pulp may retain more water, so that greater amounts of total water will be present, such as 75% by total weight of water.

Figures 1 and 2 This process will now be described with reference to Figures 1 and 2. Throughout this detailed description, similar reference characters refer to to similar elements in all the figures. With reference to Figure 1, a block diagram of one embodiment of a wet process for making "wet" pulp according to the present invention is presented. The pulp ingredients 1 are added to the container 2. The container 2 is provided with an internal mixer, similar to a mixer in a washing machine. The mixer disperses the ingredients in the water creating the substantially uniform thick suspension. The mixed slurry is transferred to a first refiner 3 which refines the slurry. Then, optionally, the refined slurry may be transferred to a second refiner 4, and optionally to a third refiner 5. Three refiners are illustrated but any number of refiners may be used depending on the degree of uniformity and refinement desired. After the last refiner in the series of refiners, the refined slurry is optionally transferred to a filter or classifier 6 which allows the slurry to thicken with the solids dispersed below a chosen mesh size or sieve, pass and re-circulate the dispersed solids larger than a chosen size of screen or mesh back to one or more of the refiners such as the line 7 of passage or a refiner 8 dedicated to refine this recirculated slurry from which the refined slurry is passed again to the filter or classifier 6. The suspension thickens properly refined passes from the filter or classifier 6 to a horizontal water vacuum filter 9 that removes water. The slurry can be transferred from point to point by any conventional method and apparatus such as with the aid of one or more pumps 10. Then, the pulp is transported in a dryer 11 that removes more water until the pulp has the desired concentration of water. Then, the refined pulp is packed in a packer 12. With reference to Figure 2, a block diagram of a dry process embodiment for making "dry" pulp according to the present invention is shown. This dry process is the same as the humerus process except after the horizontal water vacuum filter 9. After that filter, the pulp goes through a press 13 that removes more water. The pulp then goes through a softener 14 to soften the pulp and then a dryer 11 to remove more water at the desired concentration. The pulp is then passed through a rotor 15 and packed into a packer 12.

II. Second Modality of the Inventive Process In a second modality, the process to elaborate the wood pulp and polyarenoazole pulp is the same as the first modality of the process described above with the following differences. Before combining together all the Ingredients, either wood pulp fiber or polyarenoazole fiber, or both wood pulp fiber and polyarenoazole fiber, may need to be shortened. This is done by combining water with the fiber ingredient. Then, the water and fiber are mixed to form a first suspension and processed through a first disk refiner to shorten the fiber. The disc refiner cuts the fiber to an average length of no more than 10 cm. The disc refiner will also partially fibrillate and partially chew the fiber. The other fiber, which was not previously added, can be shortened in a short manner by forming a second processed suspension. Then, the other fiber (or the second suspension, if processed in water) is combined with the first suspension. More water is added before or after, or when, the other ingredients are added, if necessary, to increase the water concentration to 95-99% by weight of the total ingredients. After all the ingredients are combined, they can be mixed, if necessary, to achieve a substantially uniform thick suspension. The ingredients in the slurry are then co-refined together, that is, simultaneously. This step of refining includes fibrillating, cutting and chewing solids in the suspension such that all or substantially all of the wood pulp fiber and the polyarenoazole fiber are converted to fibrous structures, fibrillated, irregularly formed. This refining step also disperses all solids such that the refined slurry is substantially uniform. Then, water is removed as in the first mode of the process. Both processes produce the same or substantially the same wood pulp fiber and polyarenoazole pulp.

The Inventive Pulp The resulting product produced by the process of this invention is a wood pulp and polyarenoazole pulp for use as a friction reinforcement material and fluid and paper sealing products. The pulp comprises (a) fibrous structures, wood pulp, irregularly formed, (b) fibrous polyarenoazole structures, irregularly formed, (c) optionally other minor additives, and (d) water. The concentration of the separate ingredients components in the pulp correspond, of course, to the concentrations described in advance of the corresponding ingredients used in the pulping. Fibrous, fibrillated structures of polyarenoazole and wood pulp, irregularly formed have stems and fibrils. The fibrils and / or stems of the wood pulp are substantially entangled with the fibrils and / or stems of polyarenoazole. The fibrils are important and act as hooks or fasteners or tentacles that adhere to and retain adjacent particles in the pulp and final product, thereby providing integrity to the final product. The fibrous, fibrillated, polyarenoazole and wood pulp structures preferably have a maximum average dimension of no more than 5 mm, preferably 0.1 to 4 mm, and more preferably 0.1 to 3 mm. The fibrous, fibrillated, polyarenoazole and wood pulp structures preferably have a length-weighted length of no more than 1.3 mm, more preferably 0.7 to 1.2 mm, and more preferably 0.75 to 1.1 mm. In a preferred embodiment, the wood pulp and the polyarenoazole pulp are without aggregates or substantial conglomerates of the same material. In addition, the pulp has a refined Canadian standard (CSF) as measured by the TAPPI test 227 om-92, which is a measure of its drainage characteristics, from 100 to 700 ml, and preferably from 250 to 450 ml. The surface area of the pulp is a measure of the degree of fibrillation and influences the porosity of the product made from the pulp. In some embodiments of this invention, the surface area of the pulp is 7 to 11 square meters per gram.

It is believed that fibrillated fibrous structures, dispersed in a substantially homogeneous manner throughout the length of the reinforcing material, and friction and fluid sealing materials, provide, by virtue of the high temperature characteristics of the polyarenoazole polymers and the propensity for fibrillation of polyarenoazole fibers, many sites of reinforcement and increased resistance to wear. When co-refined, the mixture of the wood pulp and polyarenoazole materials is in intimate contact so that in a friction or fluid sealing material there are always some fibrous polyarenoazole structures near the pulp fiber structures of wood, so that the efforts and abrasion of service are shared. Therefore, when co-refined, the polyarenoazole materials and the wood pulp are in intimate contact such that in a friction or fluid sealing material there are always some fibrous polyarenoazole structures near the pulp fiber structures. of wood so that the efforts and abrasion of the service are always shared.

Friction Material The pulp of the present invention can be used as a reinforcement material in friction materials. By "friction materials" is meant material that is used for its friction characteristics, such as coefficient of friction, to stop or transfer movement energy, stability at high temperatures, wear resistance, noise and vibration damping properties, etc. Illustrative uses for friction materials include brake pads, brake blocks, dry clutch linings, clutch liner segments, brake pad insulator / backing layers, automatic transmission papers, wet brake, and other paper industrial friction In view of this new use, the invention also relates to friction material and processes for making the friction material. Specifically, the friction material comprises a friction modifier; optionally at least one filling agent; a binder; and a reinforcing fibrous material comprising the wood pulp and the polyarenoazole pulp of this invention. Suitable friction modifiers are metal powders such as iron, copper and zinc; abrasives such as magnesium and aluminum oxides; lubricants, such as natural and synthetic graffiti, and molybdenum and zirconium sulphides; and organic friction modifiers such as synthetic rubbers and cashew nut resin particles. Suitable binders are thermosetting resins such as phenolic resins (ie, straight phenolic resin (100 %) and various phenolic resins modified with rubber or epoxy), melamine resins, epoxy resins and polyimide resins, and mixtures thereof. Suitable fillers include barite, gypsum white, limestone, clay, talc, various other magnesium-aluminum-silicate powders, wollastonite, attapulgite, and mixtures thereof. The actual steps for making the friction material may vary, depending on the type of friction material desired. For example, methods for making molded friction parts generally comprise combining the desired ingredients in a mold, curing the part, and forming, heat treating and grinding the part, if desired. The friction and automotive transmission papers can be made in general by combining the desired ingredients in a slurry and by making a paper in a paper machine using conventional papermaking processes.

Fluid Sealing Material The invention further relates to fluid sealing material, and to processes for making fluid sealing materials. The fluid sealing materials are used in or as a barrier to prevent the discharge of fluids and / or gases and are used to prevent the entry of contaminants where these items are joined together. An illustrative use for the sealing material of fluids is in packaging. The fluid sealing material comprises a binder; optionally at least one filling agent; and a fibrous reinforcement material comprising the wood pulp and polyarenoazole pulp of this invention. Suitable binders include nitrile rubber, butadiene rubber, neoprene, styrene-butadiene rubber, nitrile-butadiene rubber, and mixtures thereof. The binder can be added with all the other starting materials. The binder is typically added in the first step of the packaging production process, in which the dry ingredients are mixed together. Other ingredients optionally include uncured rubber particles and a rubber solvent, or a solution of rubber in solvent, to cause the binder to scan surfaces of fillers and pulp. Suitable fillers include barium sulfates, clays, talc, and mixtures thereof. Suitable processes for preparing the fluid sealing materials are, for example, an addition process in a blender or wet process where the packaging is made from a thick suspension of materials, or by what is called a calendering or dry process where the materials are combined in an elastomeric or rubber solution. Many other applications of the pulp are possible, including its use as a component in papers, or its use as a filter material. When used as a material of filter or paper, typically the pulp of this invention is combined with a binder and a molded part or paper product or sheet that is made by conventional methods.

Test Methods The following test methods were used in the following examples. Canadian standard refining (CSF) was measured as described in the TAPPI T 227 method in conjunction with optical microscopy. The CSF measures the rate of drainage of a diluted suspension of pulp. It is a useful test to assess the degree of fibrillation. The data obtained from the conduction of this test are expressed as Canadian freedom numbers, which represent the millimeters of water that are drained from an aqueous slurry under specific conditions. A large number indicates a high freedom and a high tendency of water to drain. A low number indicates a tendency for the dispersion to slowly drain. Freedom is inversely related to the degree of fibrillation of the pulp, since large numbers of fibrils reduce the rate at which water drains through a forming paper mat. The average fiber lengths, which include a weighted average length in length, were determined using a fiber quality analyzer (sold by OpTest Equipment Inc., 900 Tupper ST., Hawkesbury, ON, K6A 3S3 Canada) following the TAPPI T 271 test method. Temperature: All temperatures were measured in degrees Celsius (° C). The denier is measured according to ASTM D 1577 and is the linear density of a fiber as expressed as the weight in grams of 9000 meters of fiber. The denier is measured in a Vibroscope from Textechno in Munich, Germany. Denier times (10/9) are equal to decitex (dtex).

Examples This invention will now be illustrated by the following specific examples. All parts and percentages are by weight unless otherwise indicated. The examples prepared according to the process or processes of the present invention are indicated by numerical values. The comparative examples are indicated by letters. The following examples illustrate the surprising increase in the degree of fibrillation of a wood pulp fiber by co-refining a small amount of polyarenoazole fiber in the presence of the wood pulp fiber. The degree of fibrillation is an important characteristic of a pulp product. There is a direct relationship between the degree of fibrillation and retention of the filler. In addition, fibrillation is useful to achieve uniform dispersion of Pulp products in a variety of materials. A highly fibrillated fiber will also be able to bind to a matrix more intensely through physical entanglement than a non-fibrillated fiber. In the examples that follow, poly (paraphenylene-benzobisoxazole) (PBO) fiber was used as a representative of the polyarenoazole fiber family and kraft pulp was used to represent the fibers of wood pulp.

Comparative Example A This example illustrates the prior art material that is made when refining wood pulp fiber without any polyarenoazole fiber that is present. 68.1 grams of a hardwood pulp (Hawesville hardwood, bleached kraft pulp, sold by Weyerhaeuser Company PO Box 9777 Federal Way, WA 98063-9777) were dispersed in 2.7 L of water. The dispersion was passed 5 times through a single disc refiner of 30 cm. , single speed, Sprout-Wadron (sold by Andritz, Inc., Sprout-Bauer Equipment, Muncy, PA 17756) with disc spacing adjusted to 0.13 mm. The properties of the 100% refined wood pulp as produced this way are shown in Table 1; Figure 3 is a digital optical micrograph of the material showing the limited fibrillation experienced by this material after refining.

Then a paper of the refined material was made by dispersing with a normal pulp blaster (as described in Annex A of TAPPI 205), 6.7 grams of the material (on a dry weight basis) in 1.5 L of water for 3 minutes, adding the dispersion to a wet setting paper mold having a screen with the dimensions of 21 cm x 21 cm. The dispersion was then diluted with 5 L of water and a wet laying paper was formed on the screen and the excess water was removed with a rotating pin. The paper was then dried at 100 ° C for 10 minutes in a paper dryer. The properties of the paper as it is produced are shown in Table 2.

Comparative Example B This example illustrates a polyarenoazole pulp at 100% A 100% PBO pulp was produced using the same procedure as in Comparative Example A with the exception of using 68.1 grams of a PBO fiber of 1.7 dtex having a cut length of 12.7 mm (sold by Toyobo Co., Ltd ., Zylon Department, 2-2-8 Dojima-Hama, Kita-Ku Osaka) instead of wood pulp. The properties of the 100% PBO refined material as produced are shown in Table 1; Figure 4 is a digital optical micrograph of the pulp showing the fibrillation of the PBO fiber after refining. Then a paper was prepared (as described in Comparative Example A) of the refined PBO material and in Table 2 the properties of the paper as produced is shown.

EXAMPLE 1 A pulp of this invention was produced using the same procedure as in Comparative Example A with the exception of a dispersion containing a mixture of the unrefined chopped staple fibers from Comparative Example A and the unrefined staple fibers from the start of the Comparative Example B was refined by passing 17 times through the disk refiner to form a co-refined pulp. The fiber mixture contained 61.7 grams of a hardwood pulp (Hawesville hardwood, bleached kraft pulp, sold by Weyerhaeuser Company PO Box 9777 Federal Way, WA 98063-9777) and 6.4 grams of 1.7 dtex PBO fiber having a cut length of 12.7 mm (sold by Toyobo Co., Ltd., Zylon Department, 2-2-8 Dojima-Hama, Kita-Ku Osaka). In Table 1 the properties of the pulp are shown as it is produced. A paper was then made (as described in Comparative Example A) of the pulp and the properties of the paper as produced are shown in Table 2.

Example 2 Another pulp of this invention was produced using the same procedure as in Example 1 with the exception that the mixture contained 50.8 grams of the hardwood pulp and 17.3 grams of the PBO fiber of 1.7 dtex. The co-refined pulp has approximately 25 weight percent PBO and 75 weight percent wood pulp. The properties of the pulp as they are produced are shown in Table 1; Figure 5 is a digital optical micrograph of the pulp showing the fibrillation of both the PBO fiber and the wood pulp after refining. A paper was then made (as described in Comparative Example A) of the pulp and Table 2 shows the properties of the paper as it is produced.

Comparative Example C This example demonstrates that refining wood pulp fibers separately from polyarenoazole fibers and then blending them together results in a pulp providing a paper having lower tensile strength (and thus less fibrillation) than an elaborate paper of the co-refined pulp of this invention. A sample of the refined material made in Comparative Example A was mixed with a sample of the refined material of Comparative Example B in an amount of 75% by weight of the wood pulp material to 25% by weight of the PBO material (dry weight basis) using a normal disintegrator as described in Annex A of TAPI 205 during 5 minutes. The TAPPI disintegrator was used to mix the two refined pulps of Comparative Examples A and B because the agitation is vigorous enough to thoroughly mix and disperse the previously refined pulps, but will not change their length or fibrillation. In Table 1 the properties of the pulp are shown as it is produced. A paper was then made (as described in Comparative Example A) of the pulp and the paper properties as produced are shown in Table 2. The 100% refined wood pulp material as described in Example A Comparative results in high levels of CSF. With the addition of PBO to the wood pulp and co-refining, the resulting pulp shows a drop in CSF values. This effect is clearly observable in Example 2, where co-refined pulp of PBO / wood pulp was produced 25/75 and shown in the optical micrograph that is Figure 6. The CSF value obtained with this sample is dramatically different of the CSF value obtained by mixing the pulp of Comparative Example A (100% PBO) and B (100% wood pulp) in a ratio based on weight dry 75/25 as described in Example 2. These examples demonstrate the beneficial effect of co-refining wood pulp with PBO versus mixing pulp products in conventional mixing equipment. The averages of the fiber lengths of the pulp products produced in the examples are listed in Table 1. It is interesting to note that the co-refined samples of this invention (Examples 1 and 2) have a shorter fiber length than the pulp produced in Comparative Example C. This shows that when co-refining PBO with wood pulp, very different types of pulp products are produced that can not be achieved by mixing only PBO pulp or wood pulp. Table 2 summarizes the results of the modulus and tenacity obtained from the hand-rolled papers elaborated in the examples. Examples 1 and 2 show more impressive and surprising data; the papers formed exceeded the modulus and tenacity properties of a pulp made by simply mixing the pulps in a 75/25 ratio (Comparative Example C) and in some cases even exceeded the single material papers of Comparative Examples A and B. As demonstrated in Comparative Example C, these results can only be achieved when PBO pulp and wood are processed together. The simple mixing of wood pulp and PBO does not solve any benefit with regarding 100% wood pulp paper Table 1 Table 2 EXAMPLE 3 This example illustrates how the pulp of this invention can be incorporated into an addition to blender packaging for fluid sealing applications. Water, rubber, latex, fillers, chemicals, and the pulp of this invention are combined in the desired amounts to form a slurry. In a circulation wire screen (such as a screen or wire of a paper machine), the slurry is mostly drained of its water content, dried in a heating tunnel, and vulcanized in rolls of calendering heated to form a material having a maximum thickness of about 2.0 mm. This material is compressed in a hydraulic press or a two-roll calender, which increases density and improves sealability. These blender-to-blender packaging materials generally do not have as good sealability as equivalent compressed fiber materials and are more suitable for high temperature applications at moderate pressure. The blender addition packages find applicability in the elaboration of auxiliary machine packages, or after further processing, the cylinder head gaskets. For this purpose, the semi-finished product is laminated on both sides of a spiked metal sheet and physically fixed in place by the tines.

Example 4 This example illustrates how the pulp of this invention can be incorporated into a package made by a calendering process. The same ingredients as in Example 3, minus water, are completely dry mixed together and then mixed with a rubber solution prepared using an appropriate solvent. After mixing, the compound is then generally transported in batches to a roller calender. The calender consists of a small roller that is cold and a large roller that is hot. The compound is fed and pulled in the separation of the rollers of the calender by the rotary movement of the two rollers. The composite will adhere and coil itself around the heated bottom roll in generally approximately 0.02 mm thick layers, depending on the pressure, to form an elaborate packing material of the accumulated composite layers. By doing so, the solvent evaporates and the vulcanization of the elastomer begins. Once the desired thickness of the packing material is reached, the rollers are stopped and the packing material is cut from the hot roll and cut and / or perforated to the desired size. No further pressing or heating is required, and the material is ready to perform as a gasket or gasket. In this way, packaging can be made up to approximately 7 mm thick. However, many packages made in this way are much thinner, usually about 3 mm or less thick. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (17)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. Pulp for use as reinforcement or processing material, characterized in that it comprises: (a) fibrous structures of fibrillated wood pulp, the structures that they are from 60 to 97 weight percent of the total solids; (b) fibrillated polyarenoazole fibrous structures which are from 3 to 40 weight percent of the total solids; the fibrous structures of wood pulp and polyarenoazole having a maximum average dimension of no more than 5 mm, a weighted average length in length of no more than 1.3 mm, and stems and fibrils where the fibrils and / or stems of the pulp of wood are substantially entangled with the fibrils and / or stems of polyarenoazole.
2. 2. Pulp according to claim 1, characterized in that the fibrous structures of wood pulp are approximately 60 to 75 weight percent of the total solids.
3. 3. Pulp according to claim 1, characterized in that the fibrous polyarenoazole structures are approximately 25 to 40 weight percent of the total solids.
4. 4. Pulp according to claim 1, characterized in that it has a Canadian standard refinement (CSF) of 100 to 700 ml.
5. 5. Pulp according to claim 1, characterized in that the polyarenoazole is a polybenzazole polymer of rigid rods or polypyridazole polymer of rigid rods.
6. 6. Pulp according to claim 5, characterized in that the polybenzazole is a polybenzobisoxazole.
7. 7. Pulp according to claim 5, characterized in that the polypyridazole is a polypyridobisimidazole.
8. 8. Friction material, characterized in that it comprises: a friction modifier; a binder; and a fibrous reinforcement material comprising the pulp of claim 1.
9. 9. Friction material according to claim 8, characterized in that the friction modifier is selected from the group consisting of metal powders, abrasives, lubricants, organic modifiers of friction, and mixtures thereof; and the binder is selected from the group consisting of wood defibering resins, melamine resins, epoxy resins and polyimide resins, and mixtures thereof.
10. 10. Fluid sealing material, characterized in that it comprises: a binder; and a reinforcing fibrous material comprising the pulp of claim 1.
11. 11. A fluid sealing material according to claim 10, characterized in that the binder is selected from the group consisting of nitrile rubber, butadiene rubber, neoprene, styrene-butadiene rubber, nitrile-butadiene rubber, and mixtures thereof.
12. 12. Paper, characterized in that it comprises the pulp of claim 1 and a binder.
13. 13. A process for making a fibrillated wood pulp and fibrillated polyarenoazole pulp for use as a reinforcement material, characterized in that it comprises: (a) combining the pulp ingredients including: (1) wood pulp fiber having a average length of no more than 1 cm and which is 60 to 97 weight percent of the total solids in the ingredients; (2) polyarenoazole fiber of rigid rods having an average length of no more than 10 cm and which is from 3 to 40 weight percent of the total solids in the ingredients; Y (3) water that is 95 to 99 weight percent of the total ingredients; (b) mixing the ingredients to a substantially uniform slurry; (c) co-refine the slurry to, simultaneously: (1) fibrillate, cut and chew fiber from fibrillated wood pulp and polyarenoazole fiber to fibrous and thin structures irregularly formed with stems and fibrils; and (2) dispersing all solids such that the refined slurry is substantially uniform; and (d) removing the water from the refined slurry, thereby producing a pulp of fibrillated wood and polyarenoazole pulp with the fibrous structures of fibrillated pulp and polyarenoazole having a maximum average dimension of no more than 5 mm, a weighted average length in length of not more than 1.3 mm, and the fibrils and / or stems of fibrillated wood pulp are substantially entangled with the fibrils and / or stems of polyarenoazole. Process according to claim 13, characterized in that the wood pulp fiber having a roughness of not more than 50 mg / 100 m; and the polyarenoazole fiber It has a linear density of no more than 2.5 dtex. 15. Process according to claim 13, characterized in that the pulp is without substantial addition of the same material. Process according to claim 13, characterized in that the refining step comprises passing the mixed slurry through a series of disk refiners. Process for making a pulp of fibrillated wood and polyarenoazole pulp for use as a reinforcing and processing material, characterized in that it comprises: (a) combining the ingredients with water and a first fiber of the group consisting of: (1) ) wood pulp fibers that are 60 to 97 weight percent of the total solids in the pulp; and (2) polyarenoazole fibers of rigid rods which are from 3 to 40 weight percent of the total solids in the pulp; (b) mixing the combined ingredients to a substantially uniform slurry; (c) retinating the suspension in a disk refiner, thereby cutting the fiber to have an average length of no more than 10 cm, and fibrillating and chewing at least some of the fiber to fibrillated fibrous structures irregularly formed; (d) combine the ingredients that include the refined suspension, the second fiber of the group of (a) (1 and 2) that has an average length of no more than 10 cm, and water, if necessary, to increase the concentration of water at 95-99 percent by weight of the total ingredients; (e) mixing the ingredients, if necessary, to form a substantially uniform suspension; (d) co-refining the mixed slurry to, simultaneously: (1) fibrillate, cut and chew solids in the suspension such that all or substantially all of the wood pulp and polyarenoazole fiber is converted to fibrous structures of fibrillated wood pulp and polyarenoazole, irregularly formed, with stems and fibrils; and (2) dispersing all solids such that the refined slurry is substantially uniform; and (f) removing the water from the refined slurry, thereby producing a pulp of wood and polyarenoazole pulp with the fibrillated wood pulp and fibrous structures of polyarenoazole having a maximum average dimension of no more than 5 mm, a weighted average length in length of not more than 1.3 mm, and the fibrils and / or stems of wood pulp are substantially entangled with the fibrils and / or stems of polyarenoazole.