MXPA00000203A - Fiber-reinforced composite and method of making same - Google Patents

Abstract

Fiber-reinforced composites prepared from a depolymerizable and repolymerizable polymer have the processing advantages of a thermoset without being brittle. Impregnation of polymer into the fiber bundle can be achieved with ease, while still producing a composite with excellent physical properties and high damage tolerance.

Description

MIXED MATERIAL REINFORCED WITH FIBERS AND METHOD TO FORM THE SAME The invention relates to a mixed material reinforced with fibers. The processes are known to produce a mixed material reinforced with fibers by extracting fibers in a stretch extrusion device, impregnating the fibers with resin and simultaneously forming and curing the structure in a hot die. (See Encyclopedia of Polymer Science and Engineering, 2nd Edition, Vol.4, John Wiley &Sons, New York, pp. 1-28 (1986)). Inasmuch as a low melt viscosity is required for efficient resin impregnation (a necessary requirement for the acceptable properties of the mixed material), the thermosettings have been preferably used for thermoplastic materials. Although thermosetting mixed materials have excellent mechanical properties, they suffer from several disadvantages: Thermosetting matrices have relatively limited elongation, thermofixing precursors are a source of undesirable volatile organic compounds (VOCs), mixed materials they can not be reconfigured or recycled and their production regimes are limited. In recent years, efforts have been directed to form mixed materials using thermoplastic materials. For example, Hawley in the U.S. Patent. 4,439,387 teaches the extrusion of molten thermoplastic resin material through a die that imbibes the fibers. In the patent of E.U.A. No. 4,559,262, to Cogswell et al., Discloses a fiber reinforced composition that is obtained by extracting a plurality of fibers continuously through an impregnation bath, which is a static melt of a thermoplastic polymer of sufficiently low molecular weight (resulting in a low melt viscosity) to adequately wet the fibers. Suitable polymers taught by Cogswell et al. Include thermoplastic polyesters, polyamides, polysulfones, polyoxymethylenes, polypropylene, polyarylene sulfides, mixtures of polyphenylene oxide / polystyrene, polyetheretherketones, and polyetherketones. Cogswell et al. Also teach that in order to achieve acceptable physical properties in the reinforced composition, it is preferred that the melt viscosity be in an excess of 1 Ns / m2. Therefore, if the molecular weight of the thermoplastic resin is sufficiently low to achieve sufficiently low melt viscosity to process the resin, they suffer the properties of the resulting mixed material. The thickness of a single sheet of the sheet (or tape) reinforced with fibers is limited by the prior art process. For example, Cogswell et al. Teaches thicknesses of single-ply tapes about the order of 0.1 mm (col.21, lines 29-31, and col.22, lines 29-30). In order to achieve a thicker belt, several belts and compression molding have been insulated (Col.22, lines 33 to 48).

In principle, mixed thermoplastic materials must solve many of the problems associated with thermoplastics. For example, unlike thermoplastics, thermoplastics can be reconfigured, welded, stacked or thermoformed. In addition, thermoplastics are generally more rigid, more ductile, and have greater elongation than thermoplastics.

Unfortunately, mixed materials prepared by embedding the fibers in a typical thermoplastic resin suffer from a number of disadvantages. First, as previously noted, low molecular weight resins are required in order to achieve the low viscosities necessary for processing. Second, complete impregnation requires slow traction regimes. Third, the static impregnation bath can cause the polymer to melt to be hot unduly for a long time, ultimately resulting in degradation of the polymer. Fourth, the shape and size of the final mixed material is limited. For example, the thickness of a single sheet of a ribbon of thermoplastic mixed material is generally not greater than about 0.1 mm and the length of the mixed material is limited to no more than about 100 mm. There is a need to balance the processability of the thermoplastic resin with the final physical properties of the mixed material. It should be convenient, therefore, to have a fiber-reinforced mixed material prepared using a thermoplastic resin having sufficiently low melt viscosity to adequately wet the fiber. At the same time, it would be convenient that the resin is not limited by the molecular weight restrictions as a means to achieve low melt viscosity, so that the mixed material prepared using said resin exhibits improved physical properties compared to the mixed thermoplastic materials prepared as described in the matter. It would also be an advantage in the matter to remove the static impregnation bath with an impregnation means that does not require that the melt be exposed to advanced temperatures for an unduly long time. Finally, it would be convenient to prepare longer mixed material tapes or articles having single sheet thicknesses greater than 0.2 mm, preferably greater than 0.5 mm, thus eliminating the need for a compression molding step to constitute the thickness. The present invention addresses a need in the art by providing a thermoplastic composite material reinforced with fibers comprising a depolymerizable and repolymerizable thermoplastic polymer resin and at least 30 volume percent reinforcing fibers that are impregnated by the polymer resin and They extend through the length thereof with the condition that the fibers are greater than 100 mm in length and have a thickness of a single sheet of at least 0.2 mm. In a second aspect, the present invention is a process for preparing a fiber reinforced rigid thermoplastic polyurethane mixed material by the steps of extracting a fiber bundle continuously through a melt obtained by heating a rigid thermoplastic polyurethane containing a hydrolytic catalyst and Thermally stable at a sufficient temperature to depolymerize the thermoplastic polyurethane; impregnating the extraction fiber bundle with the depolymerized thermoplastic polyurethane to form a mixed material melt, forming the fusion of mixed material in an article having a thickness of at least 0.2 mm; then cooling the fusion of mixed materials to repolymerize the thermoplastic polyurethane, wherein the fiber constitutes at least 50 percent of the volume of the total volume of the mixed material. In a third aspect, the present invention is an improved method for preparing a mixed material reinforced with fibers by stretch extraction, which method includes a step of impregnating a fiber bundle with a melt of a polymer, the improvement comprising flowing the melting through a heated conduit having a substantially longitudinal groove suitable for the passage of the fiber bundle in a transverse direction of the melt flow and passing the fiber bundle through the groove so that the melt impregnates completely in a manner Substantial fiber bundle. The present invention addresses a problem in the art by providing a thermoplastic having sufficiently low melt viscosity at advanced temperatures to effectively impregnate the fiber bundle, without limiting the molecular weight of the thermoplastic. In a preferred aspect of the present invention, the need for a hot polymer melt deposit by contacting the fiber with a flow stream of the hot melt is eliminated. Therefore, undesirable degradation of the polymer is reduced. Figure 1 is a schematic of a preferred stretch extrusion / extruder apparatus that is used to prepare a reinforced thermoplastic composite material. Figure 2 is a developed view of an impregnation unit and a consolidation unit of the stretch extrusion / extruder apparatus. Figure 3 is a side view of an impregnation bolt. Figure 4 is a preferred design of a disposal plate. The depolymerizable and repolymerizable thermoplastic polymer (DRTP) can be impregnated into a fiber bundle to form a mixed material reinforced with fibers by some suitable means, preferably, by extrusion process by stretching which are well known in the art. Preferably, the impregnation process is carried out using a combination of fiber extrusion and extrusion of a polymer resin melt according to the process illustrated in Figure 1. It should be understood that the process can be used for the impregnation of a fiber bundle with any flowable resin, not just the DRTP.

Referring now to Figure 1, the fiber bundle (10) of a fiber storage grid (12) is pulled through a fiber preheating station (14), which contains infrared ceramic heaters. The fiber bundle (10) can be composed of a number of different types of materials including glass, carbon, aramid fibers, ceramics and various metals. The preheating station is hot enough to remove any water present in the fibers and to preheat the fibers to a temperature above the solidification point of the resin melt. The fiber bundle (10) is then pulled through a fiber pretensioning unit (16) which is a bolt arrangement that disseminates the individual fibers and places them under tension, then pulling them through an impregnation unit (18). ), wherein the fiber bundle is wetted with the resin melt. The resin melt is preferably prepared in the following manner. The solid resin is granulated, then dried in a dehumidifier (24) to no more than 200 ppm water, more preferably no more than 100 ppm water. The dehumidified granular resin is then extruded advantageously through a single hot screw extruder (26), which melts the resin by shear and heat. The resin melt is then transported through a hot resin channel (28) to the impregnation unit (18).

Referring now to Figure 2, the impregnation unit (18) contains at least one impregnation bolt (20) and a series of rods (22). The impregnation bolt (20) comprises a substantially cylindrical member (30), which contains: a) two longitudinal channels, a first channel for resin transfer (32), and a second channel for a cartridge heater (34), which keeps the impregnation bolt (20) hot at a temperature above the melting point of the resin, or in the case of the DRTP, above the temperature at which the depolymerization occurs, preferably on the scale of approximately 200 ° C to around 300 ° C; and b) a groove formed by mounting an elongate member (36) above a longitudinal opening in the impregnation bolt (20) coincident with the first channel (32). The longitudinal opening in the upper part of the impregnation bolt (20), provides a means for the resin melt to come into contact with the fiber bundle (10), which is pulled through the groove in a substantially direction transverse to the flow of the resin melt through the first channel. The contact of the melt and the beam are described as 38 in Figure 2. It should be understood that the term "top opening" is used for convenience and not for the purpose of limiting the design of the impregnation bolt. In addition, the creation of a groove through which the fiber bundle 10 can pass and contact the resin can be made in a variety of ways, such as grinding a hollow cylinder longitudinally. After the fiber bundle 819 is pulled through the slot of the impregnation bolt (20) and wetted with the resin melt, the moistened fiber bundle (10a) is wound through a series of dry rods ( 20) to facilitate the impregnation of the resin. The bundle of impregnated fibers (10a) is pulled through the consolidation unit (40), which contains the die (42) which initially forms the fiber bundle (10a) and a plurality of washing plates (40), which further configure the bundle (10a) in the desired article and which removes the excess melting. and consequently improves the impregnation. Each washing plate (44) has an opening in the shape of the part to be formed. The dimensions of the opening also become smaller below the impregnation unit (18) until the desired dimensions of the section to be formed are achieved. Figure 4 illustrates a preferred design of the wash plates (44). Referring again to Figure 1, the mixed materials section is pulled through a cooling die (46) which solidifies the melt and provides a uniform surface. The cooling die (46) is designed to have the dimensions of the article that will be formed. The entire article is preferably pulled by a caterpillar type evacuation machine (48). The fibers, which are preferably aligned substantially in parallel with one another, constitute at least about 30 percent of the volume, preferably at least about 50 percent of the volume and more preferably at least about 65 percent of the volume. volume, of the total volume of the mixed-material article reinforced with finished fibers and the reinforcing fibers extend substantially through the length of the mixed material. The stretch-extruded sections can be cut to a desired length from millimeters to kilometers and further be shaped, formed or joined using techniques well known in the art, including thermoforming, hot stamping and welding. Surprisingly, the preferred process of the present invention provides a means for preparing a mixed material having a sheet thickness of at least 0.2 mm, preferably at least 1 mm, more preferably at least 2 mm and even more preferably at least 5 mm. The preferred class of polymers for the fiber reinforced composite material are thermoplastic polymers which depolymerize upon heating and re-polymerize upon cooling. Examples of thermoplastic polymers include polymers having the following structural unit: Z II - Z * - C-NH - where Z is S or O, preferably O, u Z 'is S, O, N-alkyl and NH, preferably O or NH, more preferably O. The preferred DRTPs are thermoplastic polyurethanes and thermoplastic polyureas, preferably thermoplastic polyurethanes. DRTP is a one or two phase polymer that can be prepared by reacting approximately stoichiometric amounts of: a) a diisocyanate or a diisothiocyanate, preferably a diisocyanate; b) a low molecular weight compound (not greater than 300 Daltons) having two active hydrogen groups and c) optionally, a high molecular weight compound (that molecular generally on the scale of about 500 to about 8,000 Daltons) with two groups active hydrogen The low molecular weight compound, in combination with the diisocyanate or diisothiocyanate contributes to what is known as the "hard segment content" and the high molecular weight compound, in combination with the diisocyanate or diisothiocyanate, contributes to what is known as the "content of soft segments". As used herein, the term "active hydrogen group" refers to a group that reacts with an isocyanate or isothiocyanate group as shown: II R '- Z'H + R - NCZ? R '- - C- NH wherein Z and Z 'are as previously defined and R and R' are connection groups, which may be aliphatic, aromatic or cycloaliphatic or combinations thereof.

The compound with two active hydrogens can be a diol, a diamine, a titriol, a hydroxyamine, a thiol-amine or a hydroxythiol, preferably a diol. The DRTP can be rigid or white. The soft DRTP, preferably thermoplastic polyurethanes (STPUs) are characterized by having a Shore A hardness of no more than 95 or a Tg not higher than 20 ° C. Rigid DRTPs, preferably rigid thermoplastic polyurethanes (RTPUs), have a glass transition temperature (Tg) of not more than 50 ° C and normally have a hard segment content of at least 75 percent . The description and preparation of RTPU is described, for example, by Goldwasser et al. In the U.S. Patent. 4,376,834. RTPUs are preferred thermoplastic polymers for the mixed materials of the present invention. Examples of commercially available TRPUs include treated thermoplastic polyurethanes of ISOPLAST ™ (a trademark of the Dow Chemical Company). Preferred diisocyanates include aromatic, aliphatic and cycloaliphatic diisocyanates and combinations thereof. Representative examples of these preferred diisocyanates can be found in U.S. Pat. 4,385,133; 4,522,975; and 5,167,899. Preferred diisocyanates include 4,4'-diisocyanatodiphenylmethane, p-phenylene diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, 1,4-diisocyanatocyclohexane, hexamethylene diisocyanate, 1,5-naphthalene diisocyanate, 3,3-diisocyanate. '-dimethyl-4,4'-biphenyl, 4,4'-diisocyanatodicyclohexylmethane and 2,4-toluene diisocyanate. Most preferred are 4,4'-diisocyanatodicyclohexylmethane and 4,4'-diisocyanatodiphenylmethane. The most preferred is 4,4'-diisocyanatodiphenylmethane. Preferred low molecular weight compounds having two active hydrogen groups are ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, tripropylene glycol, tetraethylene glycol, neopental glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4- (bishydroxyethyl) hydroquinone, 2,2-bis (β-hydroxy-4-ethoxyphenylpropane (ie, ethoxylated bisphenol A) and mixtures thereof The most preferred chain extenders are 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, tripropylene glycol, and mixtures thereof The DRTPs may optionally contain structural units formed of a high molecular weight compound having two active hydrogen groups which preferably is a glycol having a molecular weight on the scale of preferably not less than about 750, more preferably not less than about 100, and still m most preferably not less than about 15,000; and preferably not more than about 6000, and more preferably not more than about 5000. These high molecular weight glycol units constitute a sufficiently low fraction of DRTP, preferably the RTPU, so that the T2 of the DRTP is by above 50 ° C. Preferably, the high molecular weight glycol units constitute no more than about 25, more preferably no more than about 10, and even more preferably no more than about 5 weight percent of the RTPU, at about 0. percent by weight of the RTPU. The high molecular weight glycol is preferably a polyester glycol or a polyether glycol or a combination thereof. Examples of preferred polyester glycols and polyether glycols include polycaprolactone glycol, polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol, polyethylene adipate, polybutylene adipate glycol, polyethylene-butylene adipate glycol, and polyhexamethylene carbonate glycol , or their combinations. The isocyanate to XH ratio of the reactants, preferably OH, ranges from about 0.9: 1, preferably from about 0.975: 1, and more preferably from about 0.985: 1 to about 1.05: 1, preferably to about 1025: 1 and more preferably at about 1015: 1. The DRTP, preferably the RTPU, was advantageously prepared in the presence of an effective amount of a hydrolytically and thermally stable catalyst, which catalyzes the reaction between the isocyanate groups and the active hydrogen groups, preferably the hydroxyl groups, to form urethane linkages, urea or thiourea, preferably urethane ligatures, and remains active during depolymerization of the polymer to catalyze the reforming of urethane, urea or thiourea linkages, preferably urethane linkages, and molecular weight reconstitution. Examples of said catalysts are Sn + 2 such as stannous octoate; and Sn "2 catalysts such as dialkyltin dimercaptides, preferably dimethyltin dimercaptide (available as FOMREZ ™ UL-22, a trademark of Witco Chemical) and dialkyltin dicarboxylates, such as those described in detail in US Patent 3,661,887. Preferably, the catalyst is present in an amount of about 0.001 to about 5 weight percent, based on the weight of the reactants.The non-DRTP thermoplastic resins may be used in combination with DRTP to form the mixed materials herein invention, provided that DRTP is not used at sufficiently low levels so that the melt viscosity of the resin remains low enough to efficiently impregnate the fiber bundle.The non-DRTP examples include copolymers of acrylonitrile-butadiene-styrene, polystyrenes, polyphenylene oxide, mixtures of polyphenylene oxide-polystyrene, polyoxymethylene , polypropylene, polyamides, poly (butylene terephthalate), poly (ethylene terephthalate), polyester copolymers of poly (butylene terephthalate) and poly (ethylene terephthalate), styrene-acrylonitrile copolymers and ethylene-propylene-diene terpolymers .

The mixed materials may also include additives such as flame retardants, UV stabilizers, pigments, dyes, antistatic agents, antimicrobials, fungicides, mold release agents and flow promoters. Reinforced thermoplastic composite materials can be prepared from DRTP which have surprisingly superior physical properties compared to mixed prepared thermoplastic materials that are not depolymerizable and depolymerizable. In addition, the use of DRTP, particularly with the preferred apparatus, allows fast traction regimes, preferably at least 1 m / minute, more preferably at least 2 m / minute, more preferably at least 5 m / minute. and even more preferably at least 10 m / minute, without sacrificing the degree of impregnation. The preferred mixed material has a flexural strength of at least 500 MPa, more preferably at least 750 MPa and even more preferably at least 1200 MPa, even when glass fibers are used. Much higher resistances can be achieved by using aramid or carbon fibers.

The reinforced composite materials of the present invention can be used in a wide array of applications requiring very high rigidity and hardness and exceptional impact, such as skis, ski poles, mast brackets, tent poles, concrete, crash barriers , window frames or doors, trays for cables and cable for optical fibers.

The following example is for illustrative purposes only and is not intended to limit the scope of this invention. Example - Preparation of Impregnated Glass Fibers with a Rigid Thermoplastic Polyurethane Twenty-four fiber bundles (Owens Corning, R43S, 2400 tex) arranged in 3 layers, were pulled through the preheat station at 240 ° C. The ISOPLAST ™ 2530 polyurethane treated thermoplastic resin (a trademark of The Dow Chemical Company) which was previously dried at 95 ° C for 8 hours in a Piovan dehumidification dryer and processed in a Collins single screw extruder (speed of screw 25 rpm, barrel zone temperatures 250 ° C (hopper), 260 ° C, and 70 ° C). The connector was set at 280 ° C. Each layer of fibers was pulled through an impregnation bolt, where the fibers were saturated with the polyurethane melt, then were woven through several hot rod rows. The impregnation bolts each had a slot dimension that is 0.8 mm high and 60 mm wide, and a first channel length of 120 mm and an anal diameter of 30 mm. The impregnation bolts were maintained at 285 ° C and the other rods were maintained at 260 ° C. The fibers were pulled at a rate of 2 m / minute. Strips having a dimension of 2 cm in width by 2 mm in thickness (and of variable length) were produced. The flexural strength of the fiber-reinforced composite material was 1300 MPa, and the flexural modulus was 41 GPa (tested in accordance with BS 2787).

Claims (6)

1. CLAIMS 1. A mixed fiber reinforced thermoplastic material comprising a depolymerizable and repolymerizable polymer resin having a Tg of at least 50 ° C and at least 30 volume percent of reinforcing fibers that have been impregnated by the resin and extended to through the length of the mixed material, provided that the mixed material is more than 10 mm long and has a thickness of a single sheet of at least 0.2 mm, and where the polymerizable, repolymerizable polymer resin is a rigid thermoplastic polyurethane or a rigid thermoplastic polyurea or a combination of both.
2. 2. The thermoplastic composite material of claim 1, wherein the mixed material has a thickness of a single sheet of at least 0.5 mm.
3. 3. The thermoplastic composite material of any of claims 1 or 2, wherein the polymerizable and repolymerizable polymer resin is a thermoplastic polyurethane and is a stretch extruded product.
4. 4. The thermoplastic composite material of any of claims 1 to 3, wherein the fiber constitutes at least 50 volume percent of the resin and the mixed material has a thickness of at least 1 mm. A process for preparing an article of fiber reinforced rigid thermoplastic polyurethane material by the steps of: a) extracting a bundle of fibers continuously through a melt obtained by heating a rigid thermoplastic polyurethane containing a hydrolytically and thermally stable catalyst , at a temperature sufficient to depolymerize the thermoplastic polyurethane; b) impregnating the extracted fiber bundle with the depolymerized thermoplastic polyurethane to form a fusion of mixed materials; c) forming the fusion of mixed materials in an article having a thickness of at least 0.2 mm; then d) cooling the melting of mixed materials to repolymerize the thermoplastic polyurethane; wherein the fiber constitutes at least 50 percent of the volume of the total volume of the mixed material. The method of claim 4, wherein in step (b), the fibers are impregnated by the flow of the polyurethane through a hot conduit having a substantially longitudinal groove suitable for the passage of the fiber bundle in one direction Transverse flow of the resin; and passing the fiber bundle through the slot so that the resin impregnates the fiber bundle.