Patent Publication Number: US-2015084228-A1

Title: Reinforced Hollow Profiles

Description:
RELATED APPLICATIONS 
     The present application claims priority as a divisional application of U.S. patent application Ser. No. 13/698,375, filed on Feb. 12, 2013, which is a U.S. national stage filing of International Patent Application No. PCT/US2011/041445, filed on Jun. 22, 2011, which claims priority to Provisional Application Ser. No. 61/357,294, filed on Jun. 22, 2010, all of which are incorporated by reference in their entireties herein. 
    
    
     BACKGROUND OF THE INVENTION 
     Hollow profiles have been formed by pulling (“pultruding”) continuous fibers through a resin and then shaping the fiber-reinforced resin within a pultrusion die. Because the profiles have continuous fibers oriented in the machine direction (longitudinal), they often exhibit a high tensile strength in the machine direction. The transverse strength of such hollow profiles is, however, often poor, which can cause the material to split when a stress is applied in a cross-machine direction (transverse). In this regard, various attempts have been made to strengthen hollow profiles in the transverse direction. For example, U.S. Pat. No. 7,514,135 to Davies, et al. describes a hollow part formed by providing a first layer of reinforcing rovings extending in a longitudinal pultrusion direction and forming a second layer on the first layer, the second layer containing at least some reinforcing fibers that extend in the transverse direction. One problem with this method, however, it is that it relies upon a thermoset resin to help achieve the desired strength properties. Such resins are difficult to use during manufacturing and do not always possess good bonding characteristics for forming layers with other materials. Furthermore, the method described therein is also problematic in that it is difficult to apply the transverse fibers at selective locations (e.g., where they are needed). 
     As such, a need currently exists for a hollow profile that exhibits good transverse strength and that can be made in a relatively efficient and simple manner. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the present invention, a hollow lineal profile is disclosed. The profile comprises a consolidated ribbon that contains a plurality of continuous fibers embedded within a first thermoplastic matrix and substantially oriented in a longitudinal direction. The profile also comprises a plurality of long fibers, at least a portion of which are oriented at an angle relative to the longitudinal direction. The ratio of the weight of the continuous fibers to the ratio of the weight of the long fibers is from about 0.2 to about 10. Further, the ratio of flexural modulus to the maximum flexural strength of the profile is from about 50 to about 2200. 
     In accordance with another embodiment of the present invention, a method for forming a pultruded hollow profile is disclosed. The method comprises impregnating a plurality of continuous fibers with a thermoplastic matrix within an extrusion device; consolidating the impregnated fibers to form a first ribbon in which the continuous fibers are oriented in a longitudinal direction; pultruding the first ribbon and at least a second ribbon through a die to form the hollow profile, wherein the first ribbon, the second ribbon, or both contain long fibers. 
     Other features and aspects of the present invention are set forth in greater detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which: 
         FIG. 1  is a schematic illustration of one embodiment of a pultrusion system that may be employed in the present invention; 
         FIG. 2  is a schematic illustration of one embodiment of an impregnation system for use in the present invention; 
         FIG. 3A  is a cross-sectional view of the impregnation die shown in  FIG. 2 ; 
         FIG. 3B  is an exploded view of one embodiment of a manifold assembly and gate passage for an impregnation die that may be employed in the present invention; 
         FIG. 3C  is a perspective view of one embodiment of a plate at least partially defining an impregnation zone that may be employed in the present invention; 
         FIG. 4  is a side view of one embodiment of pre-shaping and pultrusion dies that may be employed in the present invention, wherein the flow of the continuous and long fiber materials are illustrated as they pass through the dies; 
         FIG. 5  is a perspective view of the dies of  FIG. 4 ; 
         FIG. 6  is a top view of one embodiment of a mandrel that may be employed in the present invention to shape the long fiber layer, wherein the flow of the long fiber material is also illustrated as it passes over the mandrel; 
         FIG. 7  is a perspective view of the mandrel section of  FIG. 6 ; 
         FIG. 8  is an exploded perspective view of one embodiment of a mandrel section that may be employed in the present invention to shape the continuous fiber layer, wherein the flow of the continuous fiber material is also illustrated as it passes over the mandrel; 
         FIG. 9  is a perspective view of the mandrel section of  FIG. 8 ; 
         FIGS. 10A and 10B  are other perspective views of the mandrel section of  FIG. 8 , in which  FIG. 10A  shows a right perspective view and  FIG. 10B  shows a left perspective view of the mandrel section; 
         FIG. 11  is a cross-sectional view of one embodiment of a rectangular, hollow profile of the present invention; 
         FIG. 12  is a cross-sectional view of another embodiment of a rectangular, hollow profile of the present invention; 
         FIG. 13  is side view of one embodiment of a pre-shaping and pultrusion die system that may be employed to form the profile of  FIG. 12 ; 
         FIG. 14  is perspective view of the pre-shaping and pultrusion die system of  FIG. 13 ; 
         FIG. 15  is a cross-sectional view of another embodiment of a rectangular, hollow profile of the present invention; 
         FIG. 16  is a cross-sectional view of one embodiment of an L-shaped, hollow profile of the present invention; and 
         FIG. 17  is yet another embodiment of a rectangular, hollow profile of the present invention. 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention. 
     DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS 
     Definitions 
     As used herein, the term “profile” generally refers to a pultruded part. The profile may possess a wide variety of cross-sectional shapes, such as square, rectangular, circular, elliptical, triangular, I-shaped, C-shaped, U-shaped, J-shaped, L-shaped, slotted, etc. Such profiles may be employed as a structural member for window lineals, decking planks, railings, balusters, roofing tiles, siding, trim boards, pipe, fencing, posts, light posts, highway signage, roadside marker posts, etc. 
     As used herein, the term “hollow” generally means that at least a portion of the interior of the profile is a voided space. The voided space may optionally extend the entire the length of the profile. 
     As used herein, the term “continuous fibers” generally refers to fibers, filaments, yarns, or rovings (e.g., bundles of fibers) having a length that is generally limited only by the length of the part. For example, such fibers may have a length greater than about 25 millimeters, in some embodiments about 50 millimeters or more, and in some embodiments, about 100 millimeters or more. 
     As used herein, the term “long fibers” generally refers to fibers, filaments, yarns, or rovings that are not continuous and typically have a length of from about 0.5 to about 25 millimeters, in some embodiments, from about 0.8 to about 15 millimeters, and in some embodiments, from about 1 to about 12 millimeters. 
     DETAILED DESCRIPTION 
     It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention. 
     Generally speaking, the present invention is directed to a hollow lineal profile formed from a continuous fiber reinforced ribbon (“CFRT”) that contains a plurality of continuous fibers embedded within a first thermoplastic polymer matrix. To enhance the tensile strength and modulus of the profile, the continuous fibers are aligned within the ribbon in a substantially longitudinal direction (e.g., the direction of pultrusion). In addition to continuous fibers, the hollow profile of the present invention also contains a plurality of long fibers that may be optionally embedded within a second thermoplastic matrix to form a long fiber reinforced thermoplastic (“LFRT”). The long fibers may be incorporated into the continuous fiber ribbon or formed as a separate layer of the profile. Regardless, at least a portion of the long fibers are oriented at an angle (e.g., 90°) relative to the longitudinal direction to provide increased transverse strength to the profile. 
     To achieve a good balance between tensile strength and transverse strength, the present inventors have discovered that the relative proportion of the continuous and long fibers may be selectively controlled. Namely, the ratio of the weight of continuous fibers to the weight of long fibers is within the range of from about 0.2 to about 10, in some embodiments from about 0.4 to about 5, and in some embodiments, from about 0.5 to about 4. For instance, continuous fibers may constitute from about 10 wt. % to about 90 wt. %, in some embodiments from about 20 wt. % to about 70 wt. %, and in some embodiments, from about 30 wt. % to about 60 wt. % of the profile. Likewise, long fibers may constitute from about 0.5 wt. % to about 50 wt. %, in some embodiments from about 1 wt. % to about 40 wt. %, and in some embodiments, from about 2 wt. % to about 30 wt. % of the profile. 
     The resulting hollow profiles of the present invention may therefore exhibit a relatively high maximum flexural strength (in the transverse direction) in comparison to profiles having the same shape and size, but lacking the long fiber reinforcement of the present invention. For example, the maximum flexural strength (also known as the modulus of rupture or bend strength) may be about 12 Megapascals (“MPa”) or more, in some embodiments from about 15 to about 50 MPa, and in some embodiments, from about 20 to about 40 MPa. The term “maximum flexural strength” generally refers to the maximum stress reached on a stress-strain curve produced by a “three point flexural” test (such as ASTM D790-10, Procedure A or ISO 178) in the transverse direction at room temperature. It represents the ability of the material to withstand an applied stress in the transverse direction to failure. Likewise, the profile may also exhibit a high flexural modulus. The term “flexural modulus” generally refers to the ratio of stress to strain in flexural deformation (units of force per area), or the tendency for a material to bend. It is determined from the slope of a stress-strain curve produced by a “three point flexural” test (such as ASTM D790-10, Procedure A or ISO 178). For example, the profile of the present invention may exhibit a flexural modulus of about 2 Gigapascals (“GPa) or more, in some embodiments from about 2 to about 25 GPa, in some embodiments from about 4 to about 20 GPa, and in some embodiments, from about 5 to about 15 GPa. 
     The actual values for modulus and strength may of course vary depending on the desired application. Nevertheless, the ratio of the flexural modulus to the maximum flexural strength typically falls within a certain range to achieve a part that exhibits a balance between tensile strength and modulus properties, as well as transverse strength. This ratio, for example, typically ranges from about 50 to about 2200, in some embodiments from about 100 to about 1000, in some embodiments from about 200 to about 800, and in some embodiments, from about 250 to about 600. 
     The profile may also have a very low void fraction, such as about 3% or less, in some embodiments about 2% or less, and in some embodiments, about 1% or less. The void fraction may be determined in the manner described above, such as using a “resin burn off” test in accordance with ASTM D 2584-08. 
     The continuous fibers employed in the hollow profile of the present invention may be formed from any conventional material known in the art, such as metal fibers; glass fibers (e.g., E-glass, A-glass, C-glass, D-glass, AR-glass, R-glass, S1-glass, S2-glass), carbon fibers (e.g., graphite), boron fibers, ceramic fibers (e.g., alumina or silica), aramid fibers (e.g., Kevlar) marketed by E. I. duPont de Nemours, Wilmington, Del.), synthetic organic fibers (e.g., polyamide, polyethylene, paraphenylene, terephthalamide, polyethylene terephthalate and polyphenylene sulfide), and various other natural or synthetic inorganic or organic fibrous materials known for reinforcing thermoplastic compositions. Glass fibers and carbon fibers are particularly desirable for use in the continuous fibers. Such fibers often have a nominal diameter of about 4 to about 35 micrometers, and in some embodiments, from about 9 to about 35 micrometers. The fibers may be twisted or straight. If desired, the fibers may be in the form of rovings (e.g., bundle of fibers) that contain a single fiber type or different types of fibers. Different fibers may be contained in individual rovings or, alternatively, each roving may contain a different fiber type. For example, in one embodiment, certain rovings may contain continuous carbon fibers, while other rovings may contain glass fibers. The number of fibers contained in each roving can be constant or vary from roving to roving. Typically, a roving may contain from about 1,000 fibers to about 50,000 individual fibers, and in some embodiments, from about 2,000 to about 40,000 fibers. 
     Any of a variety of thermoplastic polymers may also be employed to form the first thermoplastic matrix in which the continuous fibers are embedded. Suitable thermoplastic polymers for use in the present invention may include, for instance, polyolefins (e.g., polypropylene, propylene-ethylene copolymers, etc.), polyesters (e.g., polybutylene terephalate (“PBT”)), polycarbonates, polyamides (e.g., Nylon™), polyether ketones (e.g., polyetherether ketone (“PEEK”)), polyetherimides, polyarylene ketones (e.g., polyphenylene diketone (“PPDK”)), liquid crystal polymers, polyarylene sulfides (e.g., polyphenylene sulfide (“PPS”)), fluoropolymers (e.g., polytetrafluoroethylene-perfluoromethylvinylether polymer, perfluoro-alkoxyalkane polymer, petrafluoroethylene polymer, ethylene-tetrafluoroethylene polymer, etc.), polyacetals, polyurethanes, polycarbonates, styrenic polymers (e.g., acrylonitrile butadiene styrene (“ABS”)), and so forth. Polypropylene is a particularly suitable thermoplastic polymer. 
     The continuous fiber ribbon is generally formed in a manner to minimize its void fraction and ensure good impregnation. In this regard, an extrusion device may be employed in the present invention to embed the continuous fibers into a thermoplastic matrix. Among other things, the extrusion device facilitates the ability of the thermoplastic polymer to be applied to the entire surface of the fibers. For instance, the void fraction may be about 3% or less, in some embodiments about 2% or less, and in some embodiments, about 1% or less. The void fraction may be measured using techniques well known to those skilled in the art. For example, the void fraction may be measured using a “resin burn off” test in which samples are placed in an oven (e.g., at 600° C. for 3 hours) to burn out the resin. The mass of the remaining fibers may then be measured to calculate the weight and volume fractions. 
     Such “burn off” testing may be performed in accordance with ASTM D 2584-08 to determine the weights of the fibers and the thermoplastic matrix, which may then be used to calculate the “void fraction” based on the following equations: 
         V   f =100*(ρ t −ρ c )/ρ t  
 
     where, 
     V f  is the void fraction as a percentage; 
     ρ c  is the density of the composite as measured using known techniques, such as with a liquid or gas pycnometer (e.g., helium pycnometer); 
     ρ t  is the theoretical density of the composite as is determined by the following equation: 
       ρ t =1/[ W   f /ρ f   +W   m /ρ m ]
 
     ρ m  is the density of the thermoplastic matrix (e.g., at the appropriate crystallinity); 
     ρ f  is the density of the fibers; 
     W f  is the weight fraction of the fibers; and 
     W m  is the weight fraction of the thermoplastic matrix. 
     Alternatively, the void fraction may be determined by chemically dissolving the resin in accordance with ASTM D 3171-09. The “burn off” and “dissolution” methods are particularly suitable for glass fibers, which are generally resistant to melting and chemical dissolution. In other cases, however, the void fraction may be indirectly calculated based on the densities of the thermoplastic polymer, fibers, and ribbon in accordance with ASTM D 2734-09 (Method A), where the densities may be determined ASTM D792-08 Method A. Of course, the void fraction can also be estimated using conventional microscopy equipment. 
     Referring to  FIG. 2 , one embodiment of an extrusion device is shown that may be employed for impregnating the fibers with a thermoplastic polymer. More particularly, the apparatus includes an extruder  120  containing a screw shaft  124  mounted inside a barrel  122 . A heater  130  (e.g., electrical resistance heater) is mounted outside the barrel  122 . During use, a thermoplastic polymer feedstock  127  is supplied to the extruder  120  through a hopper  126 . The thermoplastic feedstock  127  is conveyed inside the barrel  122  by the screw shaft  124  and heated by frictional forces inside the barrel  122  and by the heater  130 . Upon being heated, the feedstock  127  exits the barrel  122  through a barrel flange  128  and enters a die flange  132  of an impregnation die  150 . 
     A continuous fiber roving  142  or a plurality of continuous fiber rovings  142  are supplied from a reel or reels  144  to die  150 . The rovings  142  are generally kept apart a certain distance before impregnation, such as at least about 4 millimeters, and in some embodiments, at least about 5 millimeters. The feedstock  127  may further be heated inside the die by heaters  133  mounted in or around the die  150 . The die is generally operated at temperatures that are sufficient to cause melting and impregnation of the thermoplastic polymer. Typically, the operation temperatures of the die is higher than the melt temperature of the thermoplastic polymer, such as at temperatures from about 200° C. to about 450° C. When processed in this manner, the continuous fiber rovings  142  become embedded in the polymer matrix, which may be a resin  214  ( FIG. 3A ) processed from the feedstock  127 . The mixture is then extruded from the impregnation die  150  to create an extrudate  152 . 
     A pressure sensor  137  ( FIG. 3A ) senses the pressure near the impregnation die  150  to allow control to be exerted over the rate of extrusion by controlling the rotational speed of the screw shaft  124 , or the federate of the feeder. That is, the pressure sensor  137  is positioned near the impregnation die  150  so that the extruder  120  can be operated to deliver a correct amount of resin  214  for interaction with the fiber rovings  142 . After leaving the impregnation die  150 , the extrudate  152 , or impregnated fiber rovings  142 , may enter an optional pre-shaping, or guiding section (not shown) before entering a nip formed between two adjacent rollers  190 . Although optional, the rollers  190  can help to consolidate the extrudate  152  into the form of a ribbon (or tape), as well as enhance fiber impregnation and squeeze out any excess voids. In addition to the rollers  190 , other shaping devices may also be employed, such as a die system. The resulting consolidated ribbon  156  is pulled by tracks  162  and  164  mounted on rollers. The tracks  162  and  164  also pull the extrudate  152  from the impregnation die  150  and through the rollers  190 . If desired, the consolidated ribbon  156  may be wound up at a section  171 . Generally speaking, the ribbons are relatively thin and typically have a thickness of from about 0.05 to about 1 millimeter, in some embodiments from about 0.1 to about 0.8 millimeters, and in some embodiments, from about 0.2 to about 0.4 millimeters. 
     Within the impregnation die, it is generally desired that the rovings  142  are traversed through an impregnation zone  250  to impregnate the rovings with the polymer resin  214 . In the impregnation zone  250 , the polymer resin may be forced generally transversely through the rovings by shear and pressure created in the impregnation zone  250 , which significantly enhances the degree of impregnation. This is particularly useful when forming a composite from ribbons of a high fiber content, such as about 35% weight fraction (“Wf”) or more, and in some embodiments, from about 40% Wf or more. Typically, the die  150  will include a plurality of contact surfaces  252 , such as for example at least 2, at least 3, from 4 to 7, from 2 to 20, from 2 to 30, from 2 to 40, from 2 to 50, or more contact surfaces  252 , to create a sufficient degree of penetration and pressure on the rovings  142 . Although their particular form may vary, the contact surfaces  252  typically possess a curvilinear surface, such as a curved lobe, rod, etc. The contact surfaces  252  are also typically made of a metal material. 
       FIG. 3A  shows a cross-sectional view of an impregnation die  150 . As shown, the impregnation die  150  includes a manifold assembly  220 , a gate passage  270 , and an impregnation zone  250 . The manifold assembly  220  is provided for flowing the polymer resin  214  therethrough. For example, the manifold assembly  220  may include a channel  222  or a plurality of channels  222 . The resin  214  provided to the impregnation die  150  may flow through the channels  222 . 
     As shown in  FIG. 3B , some portions of the channels  222  may be curvilinear, and in exemplary embodiments, the channels  222  have a symmetrical orientation along a central axis  224 . Further, in some embodiments, the channels may be a plurality of branched runners  222 , which may include first branched runner group  232 , second group  234 , third group  236 , and, if desired, more branched runner groups. Each group may include 2, 3, 4 or more runners  222  branching off from runners  222  in the preceding group, or from an initial channel  222 . 
     The branched runners  222  and the symmetrical orientation thereof generally evenly distribute the resin  214 , such that the flow of resin  214  exiting the manifold assembly  220  and coating the rovings  142  is substantially uniformly distributed on the rovings  142 . This desirably allows for generally uniform impregnation of the rovings  142 . 
     Further, the manifold assembly  220  may in some embodiments define an outlet region  242 , which generally encompasses at least a downstream portion of the channels or runners  222  from which the resin  214  exits. In some embodiments, at least a portion of the channels or runners  222  disposed in the outlet region  242  have an increasing area in a flow direction  244  of the resin  214 . The increasing area allows for diffusion and further distribution of the resin  214  as the resin  214  flows through the manifold assembly  220 , which further allows for substantially uniform distribution of the resin  214  on the rovings  142 . 
     As further illustrated in  FIGS. 3A and 3B , after flowing through the manifold assembly  220 , the resin  214  may flow through gate passage  270 . Gate passage  270  is positioned between the manifold assembly  220  and the impregnation zone  250 , and is provided for flowing the resin  214  from the manifold assembly  220  such that the resin  214  coats the rovings  142 . Thus, resin  214  exiting the manifold assembly  220 , such as through outlet region  242 , may enter gate passage  270  and flow therethrough, as shown. 
     Upon exiting the manifold assembly  220  and the gate passage  270  of the die  150  as shown in  FIG. 3A , the resin  214  contacts the rovings  142  being traversed through the die  150 . As discussed above, the resin  214  may substantially uniformly coat the rovings  142 , due to distribution of the resin  214  in the manifold assembly  220  and the gate passage  270 . Further, in some embodiments, the resin  214  may impinge on an upper surface of each of the rovings  142 , or on a lower surface of each of the rovings  142 , or on both an upper and lower surface of each of the rovings  142 . Initial impingement on the rovings  142  provides for further impregnation of the rovings  142  with the resin  214 . 
     As shown in  FIG. 3A , the coated rovings  142  are traversed in run direction  282  through impregnation zone  250 , which is configured to impregnate the rovings  142  with the resin  214 . For example, as shown in  FIGS. 3A and 3C , the rovings  142  are traversed over contact surfaces  252  in the impregnation zone. 
     Impingement of the rovings  142  on the contact surface  252  creates shear and pressure sufficient to impregnate the rovings  142  with the resin  214  coating the rovings  142 . 
     In some embodiments, as shown in  FIG. 3A , the impregnation zone  250  is defined between two spaced apart opposing plates  256  and  258 . First plate  256  defines a first inner surface  257 , while second plate  258  defines a second inner surface  259 . The contact surfaces  252  may be defined on or extend from both the first and second inner surfaces  257  and  259 , or only one of the first and second inner surfaces  257  and  259 .  FIG. 3C  illustrates the second plate  258  and the various contact surfaces thereon that form at least a portion of the impregnation zone  250  according to these embodiments. In exemplary embodiments, as shown in  FIG. 3A , the contact surfaces  252  may be defined alternately on the first and second surfaces  257  and  259  such that the rovings alternately impinge on contact surfaces  252  on the first and second surfaces  257  and  259 . Thus, the rovings  142  may pass contact surfaces  252  in a waveform, tortuous or sinusoidual-type pathway, which enhances shear. 
     The angle  254  at which the rovings  142  traverse the contact surfaces  252  may be generally high enough to enhance shear, but not so high to cause excessive forces that will break the fibers. Thus, for example, the angle  254  may be in the range between approximately 1° and approximately 30°, and in some embodiments, between approximately 5° and approximately 25°. 
     In alternative embodiments, the impregnation zone  250  may include a plurality of pins (not shown), each pin having a contact surface  252 . The pins may be static, freely rotational, or rotationally driven. In further alternative embodiments, the contact surfaces  252  and impregnation zone  250  may comprise any suitable shapes and/or structures for impregnating the rovings  142  with the resin  214  as desired or required. 
     To further facilitate impregnation of the rovings  142 , they may also be kept under tension while present within the impregnation die. The tension may, for example, range from about 5 to about 300 Newtons, in some embodiments from about 50 to about 250 Newtons, and in some embodiments, from about 100 to about 200 Newtons per roving  142  or tow of fibers. 
     As shown in  FIG. 3A , in some embodiments, a land zone  280  may be positioned downstream of the impregnation zone  250  in run direction  282  of the rovings  142 . The rovings  142  may traverse through the land zone  280  before exiting the die  150 . As further shown in  FIG. 3A , in some embodiments, a faceplate  290  may adjoin the impregnation zone  250 . Faceplate  290  is generally configured to meter excess resin  214  from the rovings  142 . Thus, apertures in the faceplate  290 , through which the rovings  142  traverse, may be sized such that when the rovings  142  are traversed therethrough, the size of the apertures causes excess resin  214  to be removed from the rovings  142 . 
     The impregnation die shown and described above is but one of various possible configurations that may be employed in the present invention. In alternative embodiments, for example, the fibers may be introduced into a crosshead die that is positioned at an angle relative to the direction of flow of the polymer melt. As the fibers move through the crosshead die and reach the point where the polymer exits from an extruder barrel, the polymer is forced into contact with the fibers. It should also be understood that any other extruder design may also be employed, such as a twin screw extruder. Still further, other components may also be optionally employed to assist in the impregnation of the fibers. For example, a “gas jet” assembly may be employed in certain embodiments to help uniformly spread a bundle or tow of individual fibers, which may each contain up to as many as 24,000 fibers, across the entire width of the merged tow. This helps achieve uniform distribution of strength properties in the ribbon. Such an assembly may include a supply of compressed air or another gas that impinges in a generally perpendicular fashion on the moving fiber tows that pass across the exit ports. The spread fiber bundles may then be introduced into a die for impregnation, such as described above. 
     Regardless of the technique employed, the continuous fibers are oriented in the longitudinal direction (the machine direction “A” of the system of  FIG. 1 ) to enhance tensile strength. Besides fiber orientation, other aspects of the ribbon and pultrusion process are also controlled to achieve the desired strength. For example, a relatively high percentage of continuous fibers may be employed in the ribbon to provide enhanced strength properties. For instance, continuous fibers typically constitute from about 40 wt. % to about 90 wt. %, in some embodiments from about 50 wt. % to about 85 wt. %, and in some embodiments, from about 55 wt. % to about 75 wt. % of the ribbon. Likewise, thermoplastic polymer(s) typically constitute from about 10 wt. % to about 60 wt. %, in some embodiments from about 15 wt. % to about 50 wt. %, and in some embodiments, from about 25 wt. % to about 45 wt. % of the ribbon. 
     Furthermore, a combination of multiple continuous fibers ribbons may be employed that are laminated together to form a strong, integrated structure having the desired thickness. The number of ribbons employed may vary based on the desired thickness and strength of the profile, as well as the nature of the ribbons themselves. In most cases, however, the number of ribbons is from 2 to 40, in some embodiments from 3 to 30, and in some embodiments, from 4 to 25. 
     As stated above, the hollow profile also contains a plurality of long fibers optionally embedded within a second thermoplastic matrix. The long fibers may be formed from any of the material, shape, and/or size as described above with respect to the continuous fibers. Glass fibers and carbon fibers are particularly desirable for use as the long fibers. Furthermore, the second thermoplastic matrix in which the long fibers may optionally be embedded may include a thermoplastic polymer, such as described above. It should be understood that the first thermoplastic matrix employed for the continuous fibers may be the same or different than the second thermoplastic matrix employed for the long fibers. In one embodiment, for example, the long fibers are separately impregnated with a thermoplastic polymer, such as in a manner described below, and thereafter cooled and chopped into to pellets having a length of about 25 millimeters or less. These pellets may be subsequently combined with a continuous fiber ribbon. Regardless, at least a portion of the long fibers in the hollow profile are oriented at an angle relative to the longitudinal direction (i.e., pultrusion direction) to provide increased transverse strength. For example, about 10% or more, in some embodiments about 20% or more, and in some embodiments, about 30% or more of the fibers may be oriented at an angle relative to the longitudinal direction. This angle may, for instance, be about 10° to about 120°, in some embodiments from about 20° to about 110° C., and in one embodiment, about 90°. This may be accomplished by intentionally orienting the fibers in the desired direction, or by random distribution. 
     The manner in which the long fibers and the continuous fiber ribbon are combined together to form the hollow profile of the present invention may vary depending on the intended application and the locations of the profile in which increased strength is required. In one embodiment, for example, the long fiber material is formed as a separate layer from the continuous fiber ribbon. Among other things, this allows the long fiber material to be selectively added at only those locations where increased transverse strength is most needed. 
     Referring to  FIG. 1 , one particular embodiment of a system is shown in which one or more continuous fiber ribbons  12  are initially provided in a wound package on a creel  20 . The creel  20  may be an unreeling creel that includes a frame provided with horizontal rotating spindles  22 , each supporting a package. A pay-out creel may also be employed, particularly if desired to induce a twist into the fibers. It should also be understood that the ribbons may also be formed in-line with the formation of the profile. In one embodiment, for example, the extrudate  152  exiting the impregnation die  150  from  FIG. 2  may be directly supplied to the system used to form a profile. A tension-regulating device  40  may also be employed to help control the degree of tension in the ribbons  12 . The device  40  may include inlet plate  30  that lies in a vertical plane parallel to the rotating spindles  22  of the creel  20 . The tension-regulating device  40  may contain cylindrical bars  41  arranged in a staggered configuration so that the ribbons  12  passes over and under these bars to define a wave pattern. The height of the bars can be adjusted to modify the amplitude of the wave pattern and control tension. 
     If desired, the ribbons  12  may be heated in an oven  45  having any of a variety of known configuration, such as an infrared oven, convection oven, etc. During heating, the fibers are unidirectionally oriented to optimize the exposure to the heat and maintain even heat across the entire profile. The temperature to which the ribbons  12  are heated is generally high enough to soften the thermoplastic polymer to an extent that the ribbons can bond together. However, the temperature is not so high as to destroy the integrity of the material. The temperature may, for example, range from about 100° C. to about 300° C., in some embodiments from about 110° C. to about 275° C., and in some embodiments, from about 120° C. to about 250° C. In one particular embodiment, for example, acrylonitrile-butadiene-styrene (ABS) is used as the polymer, and the ribbons are heated to or above the melting point of ABS, which is about 105° C. In another embodiment, polybutylene terephalate (PBT) is used as the polymer, and the ribbons are heated to or above the melting point of PBT, which is about 224° C. 
     Upon being heated, the continuous fiber ribbons  12  may be provided to a consolidation die to help bond together different ribbon layers, as well as for alignment and formation of the initial shape of the profile. Referring to  FIGS. 1 ,  4 , and  5 , for example, one embodiment of a consolidation die  50  for use in forming a “hollow” profile is shown in more detail. Although referred to herein as a single die, it should be understood that the consolidation die  50  may in fact be formed from multiple individual dies (e.g., face plate dies). In this particular embodiment, the consolidation die  50  receives a first layer (or laminate)  12   a  of continuous fiber ribbons and a second layer (or laminate)  12   b  of continuous fiber ribbons at an inlet end  56 . The ribbons within each layer are bonded together and guided through channels (not shown) of the die  50  in a direction “A”. The channels may be provided in any of a variety of orientations and arrangements to result in the desired reinforcement scheme. In the illustrated embodiment, for example, the layers  12   a  and  12   b  are initially spaced apart from each other in the vertical direction. As they pass through the channels of the die  50 , the widths of the layers  12   a  and/or  12   b  are optionally ribbonred to help prevent pressure wedges, and to keep the continuous fibers aligned and twist-free. Within the die  50 , the ribbons are generally maintained at a temperature at or above the melting point of the thermoplastic matrix used in the ribbon to ensure adequate consolidation. 
     Although not specifically shown in  FIGS. 1 ,  4 , and  5 , a mandrel may also be provided in the interior of the consolidation die  50  to help guide the laminates  12   a  and  12   b  into contact with each other on at least one side of the profile. In the illustrated embodiment, for example, a side portion  57  of the first layer  12   a  and a side portion  53  of the second layer  12   b  are angled so that they contact each other and form a side of the hollow profile. The other side of the profile is, however, typically left open within the consolidation die  50  so that the discontinuous fiber material can be subsequently applied to the interior of the profile in the pultrusion die. Of course, for those embodiments in which the discontinuous fiber material is not applied to the interior of the hollow profile, the consolidation die  50  may not be employed at all as the entire profile can be optionally shaped within the pultrusion die. 
     When in the desired position, the layers  12   a  and  12   b  of continuous fiber material are pulled into a pultrusion die  60 . It is generally desired that the layers are allowed to cool briefly after exiting the consolidation die  50  and before entering the pultrusion die  60 . This allows the consolidated laminate to retain its initial shape before progressing further through the system. Such cooling may be accomplished by simply exposing the layers to the ambient atmosphere (e.g., room temperature) or through the use of active cooling techniques (e.g., water bath or air cooling) as is known in the art. In one embodiment, for example, air is blown onto the layers (e.g., with an air ring). The cooling between these stages, however, generally occurs over a small period of time to ensure that the layers are still soft enough to be further shaped. For example, after exiting the consolidation die  50 , the layers may be exposed to the ambient environment for only from about 1 to about 20 seconds, and in some embodiments, from about 2 to about 10 seconds, before entering the second die  60 . 
     The configuration of the pultrusion die  60  depends in part on the desired shape and properties for the resulting profile. For hollow profiles, for example, the pultrusion die often contains a mandrel within its interior so that the fiber material flows between the interior surface of the die and the external surface of the mandrel to form the desired shape. Solid profiles, however, are typically formed without a mandrel. Further, although referred to herein as a single die, it should be understood that the pultrusion die  60  may be formed from multiple individual dies. In fact, the pultrusion die may preferably employ a first die section in which the discontinuous material is supplied and shaped a second die section in which the continuous fiber material is shaped. In  FIGS. 4-5 , for example, a first die section  62  is employed that supplies and shapes discontinuous fiber material  61  and a second die section  64  is employed that shapes the continuous fiber layers  12   a  and  12   b.    
     The particular manner in which the long fiber material  61  is supplied to the first die section  62  is shown in more detail in  FIGS. 6-8 . As shown, a long fiber material  61  enters the first die section  62  and is curved into its interior cavity. Although not required, such a curved inlet allows the long fiber material  61  to gradually flow into in the direction “A” and toward a die outlet  67 . In such embodiments, the angle β at which the long fiber material is provided relative to the flow direction “A” of the continuous fiber layers  12   a  and  12   b  may generally vary, but is typically about 45° or more, in some embodiments about 60° or more, and in some embodiments, from about 75° to about 90°. In certain cases, a non-perpendicular flow angle may be advantageous because it minimizes or overcomes backpressure in the die that may be caused by the high pressure flow of the long fiber material, which can sometimes lead to an undesirable backflow. The angled input orientation of the long fiber material, in combination with its curved configuration, may also reduce the likelihood that static spots (dead spots) may form inside the die, which may cause resin degradation, fiber hang-up, or breakage. 
     Upon entering the first die section  62 , the discontinuous material  61  also flows over a mandrel  68 . The mandrel  68  may be supported in a cantilever manner so that it resists the forward force of the continuous material being pulled around and over the mandrel. Further, although the entire mandrel is not shown herein, it should be understood that it may nevertheless extend into the aforementioned consolidation die  50  to help “pre-shape” the continuous fiber material in the manner described above. Regardless, the mandrel  68  shown in  FIGS. 6-8  possesses multiple sections for accomplishing the desired shaping of the profile. More particularly, the mandrel  68  contains a first mandrel section  69  that is solid and generally rectangular in cross-section. Thus, the discontinuous material  61  passes over and around the mandrel section  69  from its proximal end  71  to its distal end  73 . In doing so, the material  61  assumes the shape defined between the interior surface of the first die section  62  and an external surface  75  of the mandrel section  69 , which in this embodiment, is a hollow rectangular shape. 
     The final shape of the continuous fiber layer is formed in the second die section  64  of the pultrusion die  60 , over and around a second section  79  of the mandrel  68  as shown in  FIGS. 9-10 . The second mandrel section  79  contains a U-shaped recess  103  that engages a protrusion  77  of the first mandrel section  69  for connecting thereto. In this embodiment, the second mandrel section  79  also contains an upper wall  83  and lower wall  85  that are generally perpendicular to the direction “A” of material flow. An upwardly facing surface  91  intersects a curved edge  93  of the upper wall  83  and slopes axially in the direction “A”. Similarly, a downwardly facing surface  95  intersects a curved edge of the lower wall  85  and slopes axially in the direction “A”. The surfaces  91  and  95  both converge at an edge  97 . During formation of the profile, the first layer  12   a  of continuous fiber material is pulled over the surface  91  and assumes the shape defined between an interior surface of the pultrusion die  60  and the upper wall  83 . The second layer  12   b  of continuous fiber material is pulled over the surface  95  and likewise assumes the shape defined between an interior surface of the pultrusion die  60  and the lower wall  85 . The layer  12   a  and  12   b  are also gradually pulled into contact with each other at the edge  97  to form one side of the resulting profile. If necessary, the materials may be subjected to a subsequent compression step, such as in a land die section (not shown), to further increase the degree of adhesion between the layers at their edges. 
     Within the die  60 , the ribbons are generally maintained at a temperature well above the melting point of the thermoplastic matrix used in the ribbon to facilitate the ability to shape the part and intermix together the discontinuous fiber material. However, the temperature is not so high as to destroy the integrity of the material. The temperature may, for example, range from about 100° C. to about 350° C., in some embodiments from about 120° C. to about 320° C., and in some embodiments, from about 150° C. to about 300° C. 
     If desired, the resulting profile may also be applied with a capping layer to enhance the aesthetic appeal of the profile and/or protect it from environmental conditions. Referring to  FIG. 1 , for example, such a capping layer may be applied via an extruder oriented at any desired angle to introduce a thermoplastic resin into a capping die  72 . The resin may contain any suitable thermoplastic polymer known in the art that is generally compatible with the thermoplastic polymer used to form the profile. Suitable capping polymers may include, for instance, acrylic polymers, polyvinyl chloride (PVC), polybutylene terephthalate (PBT), ABS, polyolefins, polyesters, polyacetals, polyamids, polyurethanes, etc. Although the capping resin is generally free of fibers, it may nevertheless contain other additives for improving the final properties of the profile. Additive materials employed at this stage may include those that are not suitable for incorporating into the continuous fiber or long fiber layers. For instance, it may be desirable to add pigments to the composite structure to reduce finishing labor of shaped articles, or it may be desirable to add flame retardant agents to the composite structure to enhance the flame retarding features of the shaped article. Because many additive materials are heat sensitive, an excessive amount of heat may cause them to decompose and produce volatile gases. Therefore, if a heat sensitive additive material is extruded with an impregnation resin under high heating conditions, the result may be a complete degradation of the additive material. Additive materials may include, for instance, mineral reinforcing agents, lubricants, flame retardants, blowing agents, foaming agents, ultraviolet light resistant agents, thermal stabilizers, pigments, and combinations thereof. Suitable mineral reinforcing agents may include, for instance, calcium carbonate, silica, mica, clays, talc, calcium silicate, graphite, calcium silicate, alumina trihydrate, barium ferrite, and combinations thereof. 
     While not shown in detail herein, the capping die  72  may include various features known in the art to help achieve the desired application of the capping layer. For instance, the capping die  72  may include an entrance guide that aligns the incoming profile. The capping die may also include a heating mechanism (e.g., heated plate) that pre-heats the profile before application of the capping layer to help ensure adequate bonding. 
     Following optional capping, the shaped part  15  is then finally cooled using a cooling system  80  as is known in the art. The cooling system  80  may, for instance, be a vacuum sizer that includes one or more blocks (e.g., aluminum blocks) that completely encapsulate the profile while a vacuum pulls the hot shape out against its walls as it cools. A cooling medium may be supplied to the sizer, such as air or water, to solidify the profile in the correct shape. 
     Vacuum sizers are typically employed when forming the profile. Even if a vacuum sizer is not employed, however, it is generally desired to cool the profile after it exits the capping die (or the consolidation or calibration die if capping is not applied). Cooling may occur using any technique known in the art, such a vacuum water tank, cool air stream or air jet, cooling jacket, an internal cooling channel, cooling fluid circulation channels, etc. Regardless, the temperature at which the material is cooled is usually controlled to achieve optimal mechanical properties, part dimensional tolerances, good processing, and an aesthetically pleasing composite. For instance, if the temperature of the cooling station is too high, the material might swell in the tool and interrupt the process. For semi-crystalline materials, too low of a temperature can likewise cause the material to cool down too rapidly and not allow complete crystallization, thereby jeopardizing the mechanical and chemical resistance properties of the composite. Multiple cooling die sections with independent temperature control can be utilized to impart the optimal balance of processing and performance attributes. In one particular embodiment, for example, a vacuum water tank is employed that is kept at a temperature of from about 10° C. to about 50° C., and in some embodiments, from about 15° C. to about 35° C. 
     As will be appreciated, the temperature of the profile as it advances through any section of the system of the present invention may be controlled to yield optimal manufacturing and desired final composite properties. Any or all of the assembly sections may be temperature controlled utilizing electrical cartridge heaters, circulated fluid cooling, etc., or any other temperature controlling device known to those skilled in the art. 
     Referring again to  FIG. 1 , a pulling device  82  is positioned downstream from the cooling system  80  that pulls the finished profile  16  through the system for final sizing of the composite. The pulling device  82  may be any device capable of pulling the profile through the process system at a desired rate. Typical pulling devices include, for example, caterpillar pullers and reciprocating pullers. If desired, one or more calibration dies (not shown) may also be employed. Such dies contain openings that are cut to the exact profile shape, graduated from oversized at first to the final profile shape. As the profile passes therethrough, any tendency for it to move or sag is counteracted, and it is pushed back (repeatedly) to its correct shape. Once sized, the profile may be cut to the desired length at a cutting station (not shown), such as with a cut-off saw capable of performing cross-sectional cuts. 
     One embodiment of the hollow profile formed from the method described above is shown in more detail in  FIG. 11  as element  16 . As illustrated, the hollow profile  16  has a generally rectangular shape. An inner layer  4  is formed by the LFRT material that extends around the entire profile and defines an interior surface  5 . An outer layer  6  is likewise formed by the CFRT material that extends around the perimeter of the inner layer  4  and positioned adjacent thereto. The thickness of these layers and the relative proportion of the LFRT and CFRT materials may be strategically selected to help achieve a particular tensile strength and transverse strength (e.g., flexural modulus) for the profile. For example, higher percentages of LFRT material (and/or thickness) generally result in higher transverse strength, while higher percentages of CFRT material (and/or thickness) generally result in higher tensile strength. To optimize these properties, the ratio of the weight of the CFRT layer to the weight of the LFRT layer is typically from about 0.2 to about 10, in some embodiments from about 0.4 to about 5, and in some embodiments, from about 0.5 to about 4. In this regard, the thickness of the inner layer  4  may be from about 0.1 to about 2.0 millimeters, in some embodiments from about 0.5 to about 1.5 millimeters, and in some embodiments, from about 0.6 to about 1.2 millimeters, and the thickness of the outer layer  6  may be from about 0.2 to about 4.0 millimeters, in some embodiments from about 0.5 to about 3.0 millimeters, and in some embodiments, from about 1.0 to about 2.0 millimeters. The total thickness of the layers  4  and  6  may likewise be from about 1.0 to about 4.0 millimeters, and in some embodiments, from about 2.0 to about 3.0 millimeters. 
     The profile  16  of  FIG. 11  also includes a capping layer  7  that extends around the perimeter of the outer layer  6  and defines an external surface  8  of the profile  16 . The thickness of the capping layer  7  depends on the intended function of the part, but is typically from about 0.1 to about 5 millimeters, and in some embodiments, from about 0.2 to about 3 millimeters. 
     In the embodiments described and shown above, the LFRT material is positioned around substantially the entire interior perimeter of the profile. However, it should be understood that this is not required, and that it may be desired in certain applications to apply the material only to specific locations that are advantageous according to a particular design. One example of such a profile is shown in more detail in  FIG. 12 . As illustrated, the profile  216  generally has a hollow, rectangular shape. In this embodiment, an inner layer  206  is formed by the CFRT material that extends around the entire profile and defines an interior surface  205 . The thickness of the layer  206  may be similar to the CFRT layer described above with reference to  FIG. 11 . Contrary to the embodiment of  FIG. 11 , however, the profile  216  does not contain a continuous LFRT layer. Instead, LFRT material is located at discrete layers  204  at upper and lower surfaces  208  and  209  of the profile  216 . Such discrete placement of the LFRT material may provide enhanced transverse strength at only those locations where it is needed for a particular application. A capping layer  207  may cover the periphery of the profile  216 . 
       FIGS. 13-14  illustrate one embodiment of the consolidation die  250  and pultrusion die  260  that may be employed to form the profile  216 . Similar to the embodiments described above, the consolidation die  250  in this embodiment receives a first layer  212   a  and second layer  212   b  of continuous fiber material at an inlet end  256 . The layers  212   a  and  212   b  are guided through channels (not shown) of the die  250  in a direction “A”. As they pass through the channels, the widths of the layers  212   a  and/or  212   b  are optionally ribbonred and connected at one side as described above. When in the desired position, the layers  212   a  and  212   b  are pulled into the pultrusion die  260 , which employs a first die section  262 , a second die section  264 , and a mandrel  268  that extends therethrough. Together, each of these components helps shape the continuous fiber material. More particularly, as the continuous fiber layers pass over and around the mandrel  268  from its proximal to distal end, they assume the shape defined between the interior surface of the die  260  and an external surface of the mandrel, which in this embodiment, is a hollow rectangular shape. The long fiber material  281  is then introduced into a third die section  280  via an inlet portion, which is typically in the form of a cross-head die that extrudes the material at an input angle as mentioned above. In this particular embodiment, however, the long fiber material  281  is split into an upper stream  240  and a lower stream  242  within the third die section  280 . As the streams  240  and  242  converge in the direction “A” of the material flow and are pulled through the die system, they form the upper and lower discrete layers  204 , respectively, of the profile  216 . A capping layer  207  may then be applied using a capping die  272  as shown. 
     Of course, other hollow profiles may be formed in the present invention. Referring to  FIG. 15 , for example, another embodiment of a generally rectangular, hollow profile  316  is shown in more detail. In this particular embodiment, an inner layer  304  is formed by the LFRT material that extends around the entire profile and defines an interior surface  305 . The thickness of the layer  304  may be similar to the long fiber layer described above with reference to  FIG. 11 . Contrary to the embodiment of  FIG. 11 , however, the profile  316  does not contain a CFRT layer around the entire periphery of the profile. Instead, the CFRT material is provided as a discrete vertical layer  306   a  and horizontal layer  306   b  within the interior of the profile  316 . A capping layer  307  is likewise provided that extends around the periphery of the inner layer  304  and defines an external surface  308  of the profile  316 . 
     Still another embodiment of a hollow profile is shown in  FIG. 16 . In this embodiment, the profile  416  has a generally L-shaped cross-section. An inner layer  406  of the L-shaped profile  416  may include the CFRT material and an outer layer  404  may include the LFRT material. Discrete layers  409  of CFRT material may also be employed. Further, a capping layer  407  may extend around the entire periphery of the profile  416  and define an external surface  408  thereof. 
     The embodiments described above contain the LFRT and CFRT materials in separate layers so that selective reinforcement may be provided to the profile. However, this is by no means required. In fact, in certain embodiments of the present invention, the long fiber material is integrated into the continuous fiber ribbon so that the materials are not provided as separate layers. This may be accomplished, for instance, by incorporating the long fiber material into the continuous ribbon during impregnation. 
     Referring again to  FIGS. 2-3 , for example, long fiber pellets (not shown) containing a plurality of long fibers randomly distributed within a second thermoplastic matrix may be supplied to the hopper  126  and combined with the first thermoplastic matrix  127 . In this manner, the long fiber pellets are melt-blended with the first thermoplastic matrix used to impregnate the continuous fiber strands and create an extrudate  152  that contains continuous fibers, long fibers, and two different thermoplastic matrices, which may include the same or different polymers. In the alternative, the long fibers may be added directly to the hopper  126  without being pre-embedded with a thermoplastic matrix. In such embodiments, the first thermoplastic matrix will encapsulate both the continuous and long fibers. Regardless of the technique employed, however, the long fiber material may be distributed in a substantially homogeneous manner throughout the profile. One example of such a profile is shown in  FIG. 17  as element  516 . In this embodiment, the profile  516  is generally rectangular in shape and contains a continuous fiber ribbon  514  within which is distributed a plurality of long fibers  518 . A capping layer  519  also extends around the perimeter of the ribbon  514  and defines an external surface of the profile  516 . It should also be understood that such “hybrid” ribbons, which contain both continuous and long fibers, may also be combined with one or more additional ribbons as described above. These additional ribbons may contain continuous fibers, long fibers, or combinations thereof, and may be pre-manufactured or made in line. 
     As will be appreciated, the particular profile embodiments described above are merely exemplary of the numerous designs that are made possible by the present invention. Among the various possible profile designs, it should be understood that additional layers of continuous and/or long fiber material may be employed in addition to those described above. Further, the embodiments described above are generally considered “lineal” profiles to the extent that they possess a cross-sectional shape that is substantially the same along the entire length of the profile. It should be understood, however, that profiles may also be formed in the present invention that have a varying cross-sectional shape, such as curved, twisted, etc. 
     The present disclosure may be better understood with reference to the following example. 
     Example 
     Continuous fiber ribbons were initially formed using an extrusion system as substantially described above and shown in  FIGS. 2-3 . Glass fiber rovings (E-glass, 2200 tex) were employed for the continuous fibers with each individual ribbon containing three (3) fiber rovings. The thermoplastic polymer used to impregnate the fibers was acrylonitrile butadiene styrene (ABS), which has a melting point of about 105° C. Each ribbon contained 60 wt. % glass fibers and 40 wt. % ABS. The resulting ribbons had a thickness of between 0.2 to 0.4 millimeters and a void fraction of less than 1%. Once formed, the ribbons were then fed to an extrusion/pultrusion line operating at a speed of 5 feet per minute. Prior to consolidation, the ribbons were heated within an infrared oven (power setting of 160). The heated ribbons were then supplied to a consolidation die having a U-shaped channel that received the ribbons and consolidated them together while forming the initial shape of the profile. Within the die, the ribbons remained at a temperature of about 121° C., just above the melting point of the ABS matrix. Upon consolidation, the resulting laminate was then briefly cooled with ambient air. The laminate was then passed through the pultrusion die as shown in  FIG. 1 . Long fiber pellets were applied to the interior section of the U-shaped profile at 246° C. 
     The resulting part was then supplied to a 1-inch land section to impart the final “U shape” and cooled using an oil cooled sizing unit set at a temperature of about 26° C. Air cooling was then employed to complete the cooling process. The profile had a thickness of approximately 3.2 millimeters and a width of approximately 40 millimeters. While this particular part formed had a U-shape, it should be understood that a substantially rectangular hollow profile may simply be formed from two different U-shaped laminates in the manner described above and shown herein. 
     Ten (10) different U-shaped profile samples were formed as described above with different amounts of continuous fibers and long fibers. The amount of long fibers was varied by using different percentages of long fibers in the pellets, ranging from 0 wt. % to 40.%, and the amount of continuous fibers was varied by using different numbers of ribbons, ranging from 2 to 7. The manner in which each of the samples was formed is reflected below in Table 1. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                   
                 Wt Ratio of 
               
               
                   
                   
                 Long Fibers  
                 Number of  
                 Continuous Fiber 
               
               
                   
                   
                 in Pellets 
                 Continuous 
                 Material to Long  
               
               
                   
                 Sample 
                 (wt. %) 
                 Fiber Ribbons 
                 Fiber Material 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 1 
                 0 
                 7 
                 — 
               
               
                   
                 2 
                 20 
                 2 
                 1.21 
               
               
                   
                 3 
                 20 
                 3 
                 1.99 
               
               
                   
                 4 
                 20 
                 4 
                 3.20 
               
               
                   
                 5 
                 30 
                 2 
                 0.72 
               
               
                   
                 6 
                 30 
                 3 
                 1.54 
               
               
                   
                 7 
                 30 
                 4 
                 2.34 
               
               
                   
                 8 
                 40 
                 2 
                 0.57 
               
               
                   
                 9 
                 40 
                 3 
                 0.95 
               
               
                   
                 10 
                 40 
                 4 
                 1.52 
               
               
                   
                   
               
            
           
         
       
     
     To determine the strength properties of the U-shaped profile, three-point flexural testing was performed in accordance with ASTM D790-10, Procedure A. One transverse edge of the profile was supported with a fixture, and the load from the Instron meter was applied to the free edge of the U profile. The following equation was used to calculate the maximum stress load on the part: Maximum stress load=(6*P max *L)/w*t 2  where P max =maximum load, L=length of lever arm, w=sample width, t=sample thickness. The strength properties of the samples are set forth below in Table 2. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                   
                   
                 Ratio of  
               
               
                   
                   
                 Maximum 
                   
                 Flexural 
               
               
                   
                   
                 Flexural 
                 Flexural 
                 Modulus  
               
               
                   
                   
                 Strength  
                 Modulus 
                 to Flexural 
               
               
                   
                 Sample 
                 (MPa) 
                 (GPa) 
                 Strength 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 1 
                 11.73 
                 26.6 
                 2268 
               
               
                   
                 2 
                 35.39 
                 6.2 
                 175 
               
               
                   
                 3 
                 32.36 
                 8.7 
                 269 
               
               
                   
                 4 
                 32.76 
                 13.7 
                 418 
               
               
                   
                 5 
                 30.94 
                 7.87 
                 254 
               
               
                   
                 6 
                 27.17 
                 13.55 
                 499 
               
               
                   
                 7 
                 26.57 
                 14.87 
                 560 
               
               
                   
                 8 
                 27.93  
                 11.82 
                 423 
               
               
                   
                 9 
                 26.57  
                 13.75 
                 518 
               
               
                   
                 10 
                 29.66 
                 14.75 
                 497 
               
               
                   
                   
               
            
           
         
       
     
     It should be understood that the strength properties of the U-shaped parts referenced above would be substantially equivalent to a substantially rectangular hollow profile part due to the fact that such a profile is a combination of two U-shaped parts, and that the strength properties would be determined by cross-sectioning the hollow profile into a U-shaped part for testing purposes. 
     These and other modifications and variations of the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in such appended claims.