Patent Publication Number: US-7914635-B2

Title: Fiber-containing composite and method for making the same

Description:
RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 11/441,990, filed May 26, 2006 now U.S. Pat. No. 7,605,097, the contents of which are incorporated herein in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to fiber-containing composites (e.g., natural fiber-containing composites), materials formed therewith, and methods for making the same. 
     BRIEF SUMMARY OF THE INVENTION 
     A unitary, fiber-containing composite is described herein. In a first embodiment, the unitary, fiber-containing composite comprises a first region, a second region disposed above the first region, and a first transitional region disposed between the first region and the second region. The first region comprises a plurality of first thermoplastic binder fibers and a plurality of bast fibers, and the second region comprises a plurality of second binder fibers and a plurality of bast fibers. The first transitional region comprises concentrations of the first binder fiber, the second binder fiber, and the bast fiber. The concentration of the first binder fiber in the first transitional region is greatest proximate to the first region and least proximate to the second region, and the concentration of the second binder fiber in the first transitional region is greatest proximate to the second region and least proximate to the first region. 
     In another embodiment, the composite comprises a third region disposed above the second region, the third region comprising a binder material. In certain embodiments, the binder material in the third region comprises a third binder fiber, and the composite comprises a second transitional region disposed between the second region and the third region. In this embodiment, the second transitional region comprises concentrations of the second binder fiber, the bast fiber, and the third binder fiber. The concentration of the second binder fiber in the second transitional region is greatest proximate to the second region and least proximate to the third region, and the concentration of the third binder fiber in the second transitional region is greatest proximate to the third region and least proximate to the second region. 
     In a further embodiment of the unitary, fiber-containing composite described herein, the composite comprises a fourth region disposed above the third region, a third transitional region disposed between the third region and the fourth region, a fifth region disposed above the fourth region, and a fourth transitional region disposed between the fourth region and the fifth region. The fourth region comprises a plurality of the second binder fibers and a plurality of the bast fibers, and the fifth region comprises the first binder material and a plurality of the bast fibers. The third transitional region comprises concentrations of the second binder fiber, the bast fiber, and the third binder fiber. The concentration of the third binder fiber in the third transitional region is greatest proximate to the third region and least proximate to the fourth region, and the concentration of the second binder fiber in the third transitional region is greatest proximate to the fourth region and least proximate to the third region. The fourth transitional region comprises concentrations of the second binder fiber, the bast fiber, and the first binder fiber. The concentration of the second binder fiber in the fourth transitional region is greatest proximate to the fourth region and least proximate to the fifth region, and the concentration of the first binder fiber in the fourth transitional region is greatest proximate to the fifth region and least proximate to the fourth region. 
     A method for producing a unitary, fiber-containing composite is also described herein. In one embodiment, the method comprises the steps of providing a plurality of first binder fibers having a first linear density, a plurality of second binder fibers having a second linear density, and a plurality of bast fibers. The pluralities of first binder fibers, second binder fibers, and bast fibers are then blended to produce a fiber blend, and the fiber blend is then projected onto a moving belt such that a unitary, fiber-containing composite is formed. In this method, the second linear density can be greater than the first linear density, such that the fibers are deposited onto the moving belt in regions or strata comprising different relative concentrations of the fibers. 
     In a further embodiment of the method described herein, the first step comprises providing a plurality of third binder fibers having a third linear density, and the second step comprises blending the pluralities of first, second, and third binder fibers and the bast fibers to produce the fiber blend. The resulting fiber blend is then projected onto the moving belt in the same or similar manner as that utilized in the first method embodiment. In this embodiment, the third linear density can be greater than the first and second linear densities. 
     In another embodiment of the method described herein, the method further comprises the step of passing heated air through the unitary, fiber-containing composite produced by the above-described embodiments to at least partially melt the first, second, and third binder fibers. 
     In another embodiment of the method described herein, the method further comprises the steps of heating the unitary, fiber-containing composite produced in the above-described embodiments to further melt the first, second, and third binder fibers and compressing the composite to retain the fibers contained therein in a compressed state. 
     In a further embodiment of the method described herein, the method comprises the step of cutting the unitary, fiber-containing composite along a plane that is parallel to the z-direction of the composite to produce at least a first section and a second section. The first section is then placed on top of the second section, and the stacked sections are simultaneously compressed and heated. The first and second sections produced by the cutting step each comprise the first region, first transitional region, second region, second transitional region, and third region of the unitary, fiber-containing composite from which they are cut, and the first section is placed on top of the second section so that the third region of the first section is adjacent to the third region of the second section. Alternatively, the first section can be placed on top of the second section so that the first region of the first section is adjacent to the first region of the second section. In the heating step, the first, second, and third binder fibers contained in the sections are further melted, and the opposing regions of the first and second sections are fused together. The composite is then compressed in order to retain the fibers in the first and second sections in a compressed state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a unitary, fiber-containing composite described in the current specification. 
         FIG. 2  is a cross-sectional view of a unitary, fiber-containing composite described in the current specification. 
         FIG. 3  is a flow diagram depicting the steps of a method for making a unitary, fiber-containing composite. 
         FIG. 4  is an elevation view of an apparatus suitable for performing the method described in the current specification. 
         FIG. 5  is a cross-sectional view of a unitary, fiber-containing composite described in the current specification. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A unitary, fiber-containing composite is described herein. As utilized herein with reference to the fiber-containing composite, the term “unitary” refers to the fact that the enumerated regions of the composite do not form layers having distinct boundaries separating them from the adjacent region(s). Rather, the enumerated regions are used to refer to portions of the composite in which the different fibers are contained in different concentrations. More specifically, the enumerated regions are used to refer to portions of the thickness of the composite in which different fibers predominate or in which the concentration gradient of the fibers (e.g., how the concentration of a particular fiber changes with the thickness of the composite) differs from the adjacent portions (i.e., portions above and/or below) of the composite. Furthermore, while the composite will be described herein as containing particular fibers in specific regions, those of ordinary skill in the art will appreciate that each region of the composite can contain any of the fibers present in the composite. Nevertheless, particular fibers or combinations of fibers will predominate in particular portions of the thickness of the composite, and the enumerated regions described herein are intended to refer to those portions of the composite. 
     Referring now to the drawings, in which like reference numerals represent like parts throughout the several views, one embodiment of the unitary, fiber-containing composite  100  comprises, as depicted in  FIG. 1 , a first region  102 , a second region  106  disposed above the first region  102 , a first transitional region  104  disposed between the first region  102  and the second region  106 , and a third region  110  disposed above the second region  106 . The first region  102  comprises a binder material, which is depicted as a plurality of first binder fibers  114 , and a plurality of bast fibers  118 , the second region  106  comprises a plurality of second binder fibers  116  and a plurality of the bast fibers  118 , and the third region  110  comprises a plurality of third binder fibers  120  and a plurality of the bast fibers  118 . The first transitional region  104  comprises concentrations of the first binder fiber  114 , the second binder fiber  116 , and the bast fiber  118 . The concentration of the first binder fiber  114  in the first transitional region  104  is greatest proximate to the first region  102  and least proximate to the second region  106 , and the concentration of the second binder fiber  116  in the first transitional region  104  is greatest proximate to the second region  106  and least proximate to the first region  102 . 
     As utilized herein, the term “bast fiber” refers to strong woody fibers obtained chiefly from the phloem of plants. Suitable bast fibers include, but are not limited to, jute, kenaf, hemp, flax, ramie, roselle, and combinations thereof. Other suitable bast fibers include, but are not limited to, leaf fibers (e.g., fibers derived from sisal, banana leaves, grasses (e.g., bamboo), or pineapple leaves), straw fibers (e.g., fibers derived from wheat straw, rice straw, barley straw, or sorghum stalks), and husk fibers (e.g., fibers derived from corn husk, bagasse (sugar cane), or coconut husk). In certain embodiments, the bast fiber is jute. The fiber-containing composite can contain any suitable amount of the bast fiber(s). For example, the bast fibers can comprise about 30 to about 70 wt. %, about 30 to about 60 wt. %, or about 60 wt. % of the total weight of the fiber-containing composite. The bast fibers suitable for use in the disclosed fiber-containing composite and method can have any suitable linear density (i.e., denier). For example, the bast fibers can have a linear density of about 8.  8  dtex (8 denier) to about 20 dtex (18 denier). 
     The binders contained in the fiber-containing composite can be any suitable binder material. For example, the binder materials can be a thermoplastic material that is capable of at least partially melting when heated so that the fibers contained within the composite will be bonded together. Suitable thermoplastic binder materials include, but are not limited to, polyesters (e.g., polyethylene terephthalate (PET) or glycol-modified PET (PETG)), polyamides (e.g., nylon 6 or nylon 6,6), polyethylenes (e.g., high density polyethylene (HDPE) or linear low density polyethylene (LLDPE)), polypropylenes, polylactic acid, poly(1,4-cyclohexanedimethylene terephthalate) (PCT), and combinations thereof. 
     As noted above, the binder material contained in the unitary, fiber-containing composite can be provided in the form of binder fibers. The binder fibers contained in the fiber-containing composite can be any suitable binder fibers. For example, the binder fibers can comprise a thermoplastic material that is capable of at least partially melting when heated, thereby providing a means by which the binder fibers and bast fibers can become interconnected within the fiber-containing composite. Suitable thermoplastic binder fibers include polyester fibers (e.g., polyethylene terephthalate (PET) fibers or glycol-modified PET (PETG) fibers), polyamide fibers (e.g., nylon 6 or nylon 6,6), polyethylene fibers (e.g., fibers containing high density polyethylene (HDPE) or linear low density polyethylene (LLDPE)), polypropylene fibers, polylactic acid fibers, fibers containing poly(1,4-cyclohexanedimethylene terephthalate) (PCT), cellulose fibers (e.g., rayon fibers), fibers containing 1,3-propanediol terephthalate, and combinations thereof. Suitable binder fibers also include, but are not limited to, bicomponent binder fibers (e.g., bicomponent binder fibers comprising a thermoplastic sheath) and thermoplastic binder fibers having a relatively low melt flow rate. Suitable bicomponent fibers include bicomponent, sheath-core fibers in which the sheaths have a lower melting point than the cores of the fibers. For example, the bicomponent, sheath-core fiber can have a polyethylene sheath (e.g., a high density polyethylene sheath) and a polypropylene or polyester core. Other suitable bicomponent fibers include fibers having a PET copolymer sheath and a PET core, a PCT sheath and polypropylene core, a PCT sheath and a PET core, a PETG sheath and a PET core, a HDPE sheath and a PET core, a HDPE sheath and a polypropylene core, a LLDPE sheath and a PET core, a polypropylene sheath and a PET core, or a nylon 6 sheath and a nylon 6,6 core. When such fibers are used in the disclosed composite, the composite can be heated so that the sheaths of the bicomponent fibers are melted to provide links between adjacent fibers within the composite, while the cores of the bicomponent fiber retain their fibrous structure. As noted above, the binder fibers can be thermoplastic binder fibers in which the thermoplastic material has a relatively low melt flow rate. For example, the melt flow rate of the thermoplastic fibers can be about 18 g/10 min. or less (e.g., about 8 g/10 min. or less), as determined in accordance with, for example, ASTM Standard D1238 entitled “Standard Test Method for Melt Flow Rates of Thermoplastics by Extrusion Plastometer.” When such fibers are used in the disclosed composite, the composite can be heated so that the thermoplastic binder fibers are at least partially melted to provide links between adjacent fibers, while the relatively low melt flow rate of the thermoplastic material allows the binder fibers to retain their fibrous structure. 
     Suitable binder materials made from thermoplastic materials, such as a polyolefin, can also contain coupling, compatabilizing, and/or mixing agents. While not wishing to be bound to any particular theory, it is believed that these agents can improve the interaction and/or bonding between the bast fibers and the binder material, thereby yielding a composite having better mechanical properties. Suitable coupling, compatabilizing, and mixing agents include, but are not limited to, titanium alcoholates; esters of phosphoric, phosphorous, phosphonic and silicic acids; metallic salts and esters of aliphatic, aromatic and cycloaliphatic acids; ethylene/acrylic or methacrylic acids; ethylene/esters of acrylic or methacrylic acid; ethylene/vinyl acetate resins; styrene/maleic anhydride resins or esters thereof; acrylonitrilebutadiene styrene resins; methacrylate/butadiene styrene resins (MBS), styrene acrylonitrile resins (SAN); butadieneacrylonitrile copolymers; and polyethylene or polypropylene modified polymers. Such polymers are modified by a reactive group including polar monomers such as maleic anhydride or esters thereof, acrylic or methacrylic acid or esters thereof, vinylacetate, acrylonitrile, and styrene. In certain possibly preferred embodiments, the binder fiber, or at least a portion of the binder fibers contained in the composite, is a polyolefin (e.g., polyethylene or polypropylene) or a copolymer thereof having maleic anhydride (MAH) grafted thereon. 
     The coupling, compatabilizing, and/or mixing agents can be present in the binder fibers in any suitable amount. For example, the agents can be present in the binder fibers in an amount of about 0.01 wt. % or more, about 0.1 wt. % or more, or about 0.2 wt. % or more, based on the total weight of the binder fiber. The agents can also be present in the binder fibers in an amount of about 20 wt. % or less, about 10 wt. % or less, or about 5 wt. % or less, based on the total weight of the binder fiber. In certain possibly preferred embodiments, the binder fibers contain about 0.01 to about 20 wt. % or about 0.1 to about 10 wt. % of the coupling, compatabilizing, and/or mixing agents, based on the total weight of the binder fiber. The amount of coupling, compatabilizing, and/or mixing agents included in the binder fiber can also be expressed in term of the number of moles of the coupling, compatabilizing, and/or mixing agents present per mole of the polymer from which the fiber is made. In certain possibly preferred embodiments, such as when the binder fiber comprises polypropylene and a maleic anhydride coupling agent, the binder fiber can contain about 5 to about 50 moles of maleic anhydride per mole of the polypropylene polymer. 
     The fiber-containing composite of the invention can contain any suitable combination of the binder fibers described above. For example, the binder fibers contained within the composite or a particular region of the composite can all have substantially the same composition or make-up, or the fibers can be a combination of fibers having different compositions. In certain possibly preferred embodiments, the binder fibers contained within the composite or a particular region of the composite can be polypropylene binder fibers having MAH grafted thereon (as described above), with the fibers within each of the region(s) having the linear densities specified below. In certain other embodiments, the binder fibers contained within the composite or a particular region of the composite can be a combination of polypropylene binder fibers having MAH grafted thereon and a second type of thermoplastic binder fibers, such as polyethylene fibers, polyester fibers, or bicomponent binder fibers (as described above). In order to provide a ready visual aid to confirming the appropriate blend of fibers in the composite, the different types of fibers (e.g., binder fibers having different deniers and/or different compositions) used to produce the composite can each be provided in a different color. Therefore, the presence of each fiber in the appropriate region of the composite can be quickly confirmed upon visual inspection of the composite during or after manufacture. 
     The binder fibers contained in the fiber-containing composite can have any suitable linear density or combination of linear densities. In certain embodiments, each of the different binder fiber types contained in the composite can have different linear densities. For example, as depicted in  FIG. 1 , the first binder fiber  114  can have a linear density that is less than the linear density of the second binder fiber  116 . In such an embodiment, the first binder fiber  114  can have a linear density of about 6.  6  dtex (6 denier) or less (e.g., about 0.  5  dtex (0.5 denier) to about 6.  6  dtex (6 denier)), and the second binder fiber  116  can have a linear density of about 6.  6  dtex (6 denier) to about 22.  2  dtex (22 denier). In certain embodiments, the first binder fiber can have a linear density of about 1.  6  dtex (1.5 denier), and the second binder fiber can have a linear density of about 11.  1  dtex (10 denier). The fiber-containing composite described herein can comprise any suitable amount of binder fibers. For example, the binder fibers can comprise about 30 to about 70 wt. %, about 30 to about 60 wt. %, or about 40 wt. % of the total weight of the composite. 
     The binder material contained in the third region can be any suitable binder material. For example, the binder material can comprise a layer of thermoplastic material that has been laminated to the upper surface of the second region. Such a layer can be formed, for example, by depositing thermoplastic particles onto the upper surface of the second region and at least partially melting the particles to bond them to the fibers contained in the second region. As depicted in  FIG. 1 , the binder material in the third region  110  can comprise a third binder fiber  120 , and the composite  100  can comprise a second transitional region  108  disposed between the second region  106  and the third region  110 . In this embodiment, the second transitional region  108  comprises concentrations of the second binder fiber  116 , the bast fiber  118 , and the third binder fiber  120 . The concentration of the second binder fiber  116  in the second transitional region  108  is greatest proximate to the second region  106  and least proximate to the third region  110 , and the concentration of the third binder fiber  120  in the second transitional region  108  is greatest proximate to the third region  110  and least proximate to the second region  106 . 
     The binder fibers suitable for use in the above-described third region  110  of the composite  100  can be any suitable binder fibers, including those described above as suitable for use as the first and second binder fibers. As with the first and second binder fibers, the third binder fibers can have any suitable linear density. In certain embodiments, the third binder fibers  120  have a linear density that is greater than the linear density of the first and second binder fibers  114 ,  116 . For example, the third binder fibers  120  can have a linear density of about 22.  2  dtex (22 denier) or more (e.g., about 22.  2  dtex (22 denier) to about 72.  2  dtex (65 denier)). In certain embodiments, the third binder fibers can have a linear density of about 35.  5  dtex (32 denier). 
     The unitary, fiber-containing composite described herein can have any suitable weight and density. For example, the composite can have a weight of about 500 to about 2000 g/m 2 , about 500 to about 1500 g/m 2 , or about 600 to about 1200 g/m 2 . In certain embodiments, the unitary, fiber-containing composite can have a density of about 0.08 to about 2 g/cm 3 , about 0.08 to about 1.5 g/cm 3 , about 0.2 to about 1.5 g/cm 3 , about 0.2 to about 0.7 g/cm 3 , or about 0.25 to about 0.6 g/cm 3 . 
     In a further embodiment of the unitary, fiber-containing composite described herein, the composite comprises fourth and fifth regions and third and fourth transitional regions disposed above the third region of the composite. In such an embodiment, the additional layers of the composite (i.e., the fourth and fifth regions and third and fourth transitional regions) can resemble mirror images of the first and second regions and first and second transitional regions of the composite described above. For example, as depicted in  FIG. 2 , such a composite  200  comprises a first region  202 , a first transitional region  204 , a second region  206 , a second transitional region  208 , and a third region  210  similar to those of the embodiment depicted in  FIG. 1 . In particular, the first region  202  comprises a plurality of first binder fibers  220  and a plurality of bast fibers  224 , the second region  206  comprises a plurality of second binder fibers  222  and a plurality of the bast fibers  224 , and the third region  210  comprises a plurality of third binder fibers  226  and a plurality of the bast fibers  224 . The first transitional region  204  comprises concentrations of the first binder fiber  220 , the second binder fiber  222 , and the bast fiber  224 . The concentration of the first binder fiber  220  in the first transitional region  204  is greatest proximate to the first region  202  and least proximate to the second region  206 , and the concentration of the second binder fiber  222  in the first transitional region  204  is greatest proximate to the second region  206  and least proximate to the first region  202 . 
     In addition to these regions, the composite  200  further comprises a fourth region  214  disposed above the third region  210 , a third transitional region  212  disposed between the third region  210  and the fourth region  214 , a fifth region  218  disposed above the fourth region  214 , and a fourth transitional region  216  disposed between the fourth region  214  and the fifth region  218 . As shown in  FIG. 2 , the fourth region  214  comprises a plurality of the second binder fibers  222  and a plurality of the bast fibers  224 , and the fifth region  218  comprises a plurality of the first binder fibers  220  and a plurality of the bast fibers  224 . The third transitional region  212  comprises concentrations of the second binder fiber  222 , the bast fiber  224 , and the third binder fiber  226 . The concentration of the third binder fiber  226  in the third transitional region  212  is greatest proximate to the third region  210  and least proximate to the fourth region  214 , and the concentration of the second binder fiber  222  in the third transitional region  212  is greatest proximate to the fourth region  214  and least proximate to the third region  210 . The fourth transitional region  216  comprises concentrations of the second binder fiber  222 , the bast fiber  224 , and the first binder fiber  220 . The concentration of the second binder fiber  222  in the fourth transitional region  216  is greatest proximate to the fourth region  214  and least proximate to the fifth region  218 , and the concentration of the first binder fiber  220  in the fourth transitional region  216  is greatest proximate to the fifth region  218  and least proximate to the fourth region  214 . 
     The unitary, fiber-containing composite can comprise other fibers in addition to those enumerated above. For example, in order to increase the flame resistance of the resulting composite, the composite can further comprise flame retardant fibers. As utilized herein, the term “flame retardant fibers” refers to fibers having a Limiting Oxygen Index (LOI) value of about 20.95 or greater, as determined by ISO 4589-1. Alternatively, the fibers contained in the composite (e.g., the bast fibers and/or the binder fibers) can be treated with a flame retardant in order to increase the flame resistance of the composite. Also, in certain other embodiments, the composite can comprise fibers derived from animal sources, such as wool, silk, or feathers (e.g., chicken feathers separated from the quill), in addition to or in place of the bast fibers. 
     In certain possibly preferred embodiments, the fiber-containing composite can comprise a scrim disposed on one or more surfaces of the composite. As depicted in  FIG. 5 , the fiber-containing composite  500  comprises a scrim  530  disposed on the surface of the composite adjacent the first region  102 . The scrim  530  can be attached to the surface adjacent the first region  102  of the composite  500  using any suitable adhesive (not shown) or the scrim  530  can be attached to the surface adjacent the first region  102  of the composite  500  via the partially melted binder fibers  114  in the first region  102  of the composite  500 . While the composite has been depicted in  FIG. 5  with the scrim  530  disposed on the surface adjacent the first region  102 , the scrim can be, in certain other embodiments, disposed on the surface of the composite that is adjacent the third region of the composite. In certain other embodiments, a first scrim can be disposed on the surface of the composite that is adjacent the first region of the composite, and a second scrim can be disposed on the surface of the composite that is adjacent the third region of the composite. 
     The scrim used in the fiber-containing composite can be any suitable material. For example, the scrim can be a woven, knit, or nonwoven textile material comprising natural fibers, synthetic fibers, or combinations thereof. In certain possibly preferred embodiments, the fibers  532  in the scrim  530  are thermoplastic fibers having a melting temperature that is higher than the binder fibers contained in the composite. For example, suitable thermoplastic fibers for the scrim can have a melting temperature of about 200° C. or higher, as well as high thermal stability and low heat deflection at elevated temperatures. In certain possibly preferred embodiments, the scrim is a nonwoven textile material comprising a plurality of thermoplastic fibers, such as polyester fibers. More particularly, the scrim can be a nonwoven textile material comprising a plurality of spunbond thermoplastic (e.g., polyester) fibers. Scrims suitable for the composite can have any suitable weight. For example, the scrim can have a weight of about 15 to about 35 g/m 2  or about 17 to about 34 g/m 2 . 
     The unitary, fiber-containing composite described above can be utilized in a variety of applications. For example, the composite can be used as the substrate for an automobile headliner, an automobile door panel, a panel used in office furniture, etc. In one embodiment, the composite comprises the structural support for an automobile headliner. In such an embodiment, the composite can have a fabric layer adhered to one surface with or without the use of an additional adhesive. For example, in certain embodiments, the binder material disposed on the surface of the composite can provide sufficient tack for the fabric to adhere to the surface of the composite. Such an automobile headliner can also comprise a layer of foam or other suitable material (e.g., batting) disposed between the composite and the fabric layer. 
     A method for producing a unitary, fiber-containing composite is also described herein. In one embodiment, the method comprises the steps of providing a plurality of first binder fibers having a first linear density, a plurality of second binder fibers having a second linear density, and a plurality of bast fibers. The pluralities of first binder fibers, second binder fibers, and bast fibers are then blended to produce a fiber blend, and the fiber blend is then projected onto a moving belt such that a unitary, fiber-containing composite is formed. In this method, the second linear density can be substantially equal to the third linear density and greater than the first linear density, such that the fibers are deposited onto the moving belt in regions or strata comprising different relative concentrations of the fibers. 
     An apparatus suitable for performing the above-described method is depicted in  FIG. 4 . A commercially available piece of equipment that has been found to be suitable for carrying out the above-described method is the “K-12 HIGH-LOFT RANDOM CARD” by Fehrer AG (Linz, Austria). In the apparatus  400  depicted in  FIG. 4 , the binder fibers and bast fibers are blended in the appropriate proportions and introduced into a feed chute  410 . The feed chute  410  delivers the blended fibers to a transverse belt  440  that delivers a uniform thickness or batt of fibers to an air lay machine comprising a cylinder  420 . The cylinder  420  rotates and slings the blended fibers towards a collection belt  430 . The collection belt  430  typically comprises a plurality of perforations in its surface (not shown) so that a vacuum can be drawn across the belt which helps the fibers to properly settle on the collection belt  430 . The rotation of the cylinder  420  slings the fibers having a higher linear density a further distance along the collection belt  430  than it slings the fibers having a lower linear density. As a result, the unitary, fiber-containing composite  100  collected on the collection belt  430  will have a greater concentration of the fibers with a lower linear density adjacent to the collection belt  430 , and a greater concentration of the fibers with a higher linear density further away from the collection belt  430 . In general, the larger the difference in linear density between the fibers, the greater the gradient will be in the distribution of the fibers. 
     In a further embodiment of the method described herein, the first step comprises providing a plurality of third binder fibers having a third linear density, and the second step comprises blending the pluralities of first, second, and third binder fibers and the bast fibers to produce the fiber blend. The resulting fiber blend is then projected onto the moving belt in the same or similar manner as that utilized in the first method embodiment. In this embodiment, the third linear density can be greater than the first and second linear densities. 
     The fibers suitable for use in the above-described methods can be any suitable binder fibers and bast fibers. For example, the first, second, third, and bast fibers suitable for use in the described methods can be the same as those discussed above with respect to the various embodiments of the unitary, fiber-containing composite. 
     In certain embodiments of the described methods, such as when at least one of the binder fibers is a thermoplastic binder fiber, the unitary, fiber-containing composite produced by the above-described steps can be heated to at least partially melt the thermoplastic binder fiber and bond together at least a portion of the fibers contained in the composite. For example, the method can further comprise the step of passing heated air through the unitary fiber-containing composite produced by the above-described embodiments to partially melt all or a portion of the binder fibers. As will be understood by those of ordinary skill in the art, the unitary fiber-containing composite can be heated by other means, such as infrared radiation. This step serves to set an initial thickness for the composite of, for example, about 5 to about 50 mm or about 10 to about 50 mm. 
     In another embodiment of the method described herein, the unitary, fiber containing composite can be compressed to produce a composite having a density and/or a rigidity that are high enough for the composite to act as a structural support, for example, for an automobile headliner. In such an embodiment, the method can further comprise the step of heating the unitary, fiber-containing composite produced in the above-described embodiments using, for example, a hot belt laminator, which concentrates heat on the surfaces of the composite. Such heating further melts the first, second, and third binder fibers, and the compressive forces exerted on the composite by the laminator serve to retain the fibers in a compressed state. 
     The unitary, fiber-containing composite can be further processed using convention “cold mold” thermoforming equipment in which the composite is first heated and then pressed to the appropriate shape and thickness using an unheated mold. In such an embodiment of the method, the composite can be heated to a temperature of about 170 to about 215° C. during a heating cycle of about 30 to about 120 seconds using, for example, infrared radiation. The heated composite is then placed inside a mold, which typically is maintained at a temperature of about 10 to about 30° C., and compressed to the appropriate shape and thickness. The compression step typically is about 1 minute in length, during which time the thermoplastic binder fibers will cool to such an extent that the composite will maintain substantially the compressed configuration upon removal from the mold. As will be understood those of ordinary skill in the art, owing at least partially to the rigidity of the bast fibers, the composite may expand (for example, in the z-direction) upon heating and before being placed in the mold. 
     In a further embodiment of the method described herein, the method comprises the step of cutting the unitary, fiber-containing composite along a plane that is parallel to the z-direction of the composite (i.e., the thickness of the composite) to produce at least a first section and a second section. The first section is then placed on top of the second section, and the stacked sections are heated and compressed. The first and second sections produced by the cutting step each comprise the first region, first transitional region, second region, second transitional region, and third region of the unitary, fiber-containing composite from which they are cut, and the first section is placed on top of the second section so that the third region of the first section is adjacent the third region of the second section. Alternatively, the first section is placed on top of the second section so that the first region of the first section is adjacent to the first region of the second section. In the heating and compression step, the first, second, and third binder fibers contained in the sections are further melted, and the opposing regions of the first and second sections are fused together. The step of heating and then compressing the composite also serves to retain the fibers in the first and second sections in a compressed state. 
     The following example further illustrates the invention but, of course, should not be construed as in any way limiting its scope. 
     EXAMPLE 1 
     This example demonstrates a method for producing a unitary, fiber-containing composite as described above and the properties of a unitary, fiber-containing composite as described above. Three similar unitary, fiber-containing composites (Samples 1A-1C) were produced by air laying a fiber blend using a K-12 HIGH-LOFT RANDOM CARD by Fehrer AG (Linz, Austria). In particular, the composites were produced from a fiber blend containing approximately 40 wt. % (based on the total weight of the fiber blend) of bicomponent binder fibers and approximately 60 wt. % of jute fibers, which had a linear density of approximately 8.  8 -2 dtex (8-18 denier). The binder fibers had a high-density polyethylene sheath (melting point of approximately 128° C.) and a polypropylene core (melting point of approximately 149° C.). The binder fiber content was comprised of three bicomponent binder fibers having three different linear densities. The first binder fibers, which comprised approximately 10 wt. % of the total weight of the fiber blend, had a linear density of approximately 1.  6  dtex (1.5 denier). The second binder fibers, which comprised approximately 20 wt. % of the total weight of the fiber blend, had a linear density of approximately 11.  1  dtex (10 denier). The third binder fibers, which comprised approximately 10 wt. % of the total weight of the fiber blend, had a linear density of approximately 35.  5  dtex (32 denier). 
     As noted above, the above-described fiber blend was air laid using the K-12 HIGH-LOFT RANDOM CARD by projecting the fibers onto a moving belt. Due to the difference in denier between the fibers contained in the fiber blend, the composites produced by the air laying step contained a greater concentration of the 1.  6  dtex (1.5 denier) binder fiber in a first region closest to the collection belt, a greater concentration of the 11.  1  dtex (10 denier) binder fiber in a middle region, and a greater concentration of the 35.  5  dtex (32 denier) binder fiber in an upper region. Following the air laying step, the resulting composites were passed through a through-air oven in which air heated to a temperature of approximately 175° C. (347° F.) was passed through the composite to partially melt the binder fibers. 
     Sample 1A was then produced by passing a composite, which had been laid so that it had a weight of approximately 1100 g/m 2 , through a compression oven in which the belts were heated to a temperature of approximately 204° C. (400° F.). After passing through the compression oven, Sample 1A had a thickness of approximately 3.3 mm. 
     Samples 1B and 1C were produced by cutting two composites, which had been laid so that the composites had weights of approximately 537 g/m 2  and approximately 412 g/m 2 , respectively, in the z-direction (i.e., along a plane parallel to the thickness of the composite) and stacking the resulting sections on top of each other so that the regions containing the greatest concentration of the 35.  5  dtex (32 denier) binder fiber were adjacent to each other. The stacked sections were then passed through a compression oven in which the belts were heated to a temperature of approximately 204° C. (400° F.). After passing through the compression oven, Sample 1B had a thickness of approximately 3.3 mm, and Sample 1C had a thickness of approximately 2.3 mm. Due to the stacking of the sections, Sample 1B had a weight of approximately 1075 g/m 2 , and Sample 1C had a weight of approximately 825 g/m 2 . 
     Samples 1A-1C were then tested to determine their physical properties, such as the stiffness, strength, toughness, flammability, and sound absorption at different frequencies. The results of these measurements, including the test methods used to determine the properties, are set forth in Table 1 below. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Physical properties of Samples 1A-1C. 
               
            
           
           
               
               
            
               
                   
                 Sample 
               
            
           
           
               
               
               
               
               
            
               
                 Property 
                 Test Method 
                 1A 
                 1B 
                 1C 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Thickness (mm) 
                 — 
                 3.3 
                 3.3 
                 2.3 
               
               
                 Weight g/m 2   
                 FLTM BN 106-01 
                 1100 
                 1075 
                 825 
               
               
                 Stiffness (N/mm) 
                 ASTM D790 
                 7.2 
                 7.6 
                 7.4 
               
               
                 Strength (N) 
                 ASTM D790 
                 19 
                 18 
                 9.9 
               
               
                 Toughness (%) 
                 ASTM D790 
                 130 
                 106 
                 120.7 
               
               
                 Flammability 
                 ISO 3795/SAE J369 
                 0.68 
                 0.50 
                 0.8 
               
               
                 Fogging 
                 SAE J1756 
                 99.5 
                 100 
                 100 
               
               
                 Odor 
                 SAE J1341 
                 Pass 
                 Pass 
                 Pass 
               
               
                   
                 (1 L jar) 
               
               
                 Sound absorption 
                 ASTM E1050-98 
                 28.1 
                 23.1 
                 18.3 
               
               
                 at 1000 Hz (%) 
                 (10 mm air gap) 
               
               
                 Sound absorption 
                 ASTM E1050-98 
                 43.1 
                 35.8 
                 23.4 
               
               
                 at 1500 Hz (%) 
                 (10 mm air gap) 
               
               
                 Sound absorption 
                 ASTM E1050-98 
                 51.6 
                 51.0 
                 40.5 
               
               
                 at 2000 Hz (%) 
                 (10 mm air gap) 
               
               
                 Sound absorption 
                 ASTM E1050-98 
                 84.7 
                 81.3 
                 68.9 
               
               
                 at 2500 Hz (%) 
                 (10 mm air gap) 
               
               
                 Sound absorption 
                 ASTM E1050-98 
                 98.4 
                 97.3 
                 89.0 
               
               
                 at 3000 Hz (%) 
                 (10 mm air gap) 
               
               
                   
               
            
           
         
       
     
     As can be seen from the results set forth in Table 1 above, Samples 1A-1C exhibited physical properties which should render the composites suitable for use as, for example, the substrate for an automobile headliner, an automobile door panel, or a panel used in office furniture. In particular, the stiffness, strength, and toughness of the composites indicate that they should be able to span the width and/or length of a typical automobile passenger compartment without significant or observable sagging. In particular, the composites should be able to pass the climatic sag requirements of most automobile manufacturers. Furthermore, the sound absorption measurements demonstrate that the composites should be able to provide an amount of sound absorption that is desirable for certain applications, such as the substrate for an automobile headliner. 
     EXAMPLE 2 
     This example demonstrates a method for producing a unitary, fiber-containing composite as described above and the properties of a unitary, fiber-containing composite as described above. Two similar, unitary fiber-containing composites (Samples 2A and 2B) were produced using substantially the same procedure as that described above and used to produce Sample 1A. 
     Sample 2A was produced from a fiber blend containing approximately 40 wt. % (based on the total weight of the fiber blend) of bicomponent binder fibers and approximately 60 wt. % of jute fibers, which had a linear density of approximately 8.  8 -20 dtex (8-18 denier). The binder fibers had a high-density polyethylene sheath (melting point of approximately 128° C.) and a polypropylene core (melting point of approximately 149° C.). The binder fiber content was comprised of three bicomponent binder fibers having three different linear densities. The first binder fibers, which comprised approximately 15 wt. % of the total weight of the fiber blend, had a linear density of approximately 1.  6  dtex (1.5 denier). The second binder fibers, which comprised approximately 10 wt. % of the total weight of the fiber blend, had a linear density of approximately 11.  1  dtex (10 denier). The third binder fibers, which comprised approximately 15 wt. % of the total weight of the fiber blend, had a linear density of approximately 35.  5  dtex (32 denier). 
     Sample 2B was produced from a fiber blend containing approximately 40 wt. % (based on the total weight of the fiber blend) of binder fibers and approximately 60 wt. % of jute fibers, which had a linear density of approximately 8.  8 -2 dtex (8-18 denier). The binder fibers were polypropylene binder fibers containing polypropylene that had been grafted with approximately 10 wt. % maleic anhydride (MAH). The binder fiber content was comprised of three binder fibers having three different linear densities. The first binder fibers, which comprised approximately 15 wt. % of the total weight of the fiber blend, had a linear density of approximately 1.  6  dtex (1.5 denier). The second binder fibers, which comprised approximately 10 wt. % of the total weight of the fiber blend, had a linear density of approximately 11.  1  dtex (10 denier). The third binder fibers, which comprised approximately 15 wt. % of the total weight of the fiber blend, had a linear density of approximately 35.  5  dtex (32 denier). 
     After production, Samples 2A and 2B were then tested to determine their physical properties, such as the stiffness, strength, and toughness. The results of these measurements, including the test methods used to determine the properties, are set forth in Table 2 below. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Physical properties of Samples 2A and 2B. 
               
            
           
           
               
               
               
               
            
               
                 Property 
                 Test Method 
                 Sample 2A 
                 Sample 2B 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 Stiffness (N/mm) 
                 ASTM D790 
                 2.28 
                 4.05 
               
               
                 Strength (N) 
                 ASTM D790 
                 22.16 
                 32.62 
               
               
                 Toughness (%) 
                 ASTM D790 
                 122.56 
                 126.70 
               
               
                   
               
            
           
         
       
     
     As can be seen from the results above, the composite produced using the binder fibers containing a coupling agent (i.e., Sample 2B) exhibited improved mechanical properties relative to the composite produced using binder fibers that do not contain a coupling, compatabilizing, and/or mixing agent (i.e., Sample 2A). Sample 2B also exhibited substantially reduced sagging compared to Sample 2A when the composites were tested to determine if they meet the climatic sag requirements of most automobile manufacturers. While not wishing to be bound to any particular theory, it is believed that the improved mechanical properties are due to the improved interaction and/or bonding between the bast fibers and the binder fibers. 
     EXAMPLE 3 
     This example demonstrates a method for producing a unitary, fiber-containing composite as described above and the properties of a unitary, fiber-containing composite as described above. Two similar, unitary fiber-containing composites (Samples 3A and 3B) were produced using substantially the same procedure as that described above and used to produce Sample 1A. 
     Both samples were produced from a fiber blend containing approximately 45 wt. % (based on the total weight of the fiber blend) of binder fibers and approximately 55 wt. % of jute fibers, which had a linear density of approximately 8.  8 -2 dtex (8-18 denier). The binder fibers were polypropylene binder fibers containing polypropylene that had been grafted with approximately 10 wt. % maleic anhydride (MAH). The binder fiber content was comprised of four binder fibers having four different linear densities. The first binder fibers, which comprised approximately 15 wt. % of the total weight of the fiber blend, had a linear density of approximately 1.7 dtex. The second binder fibers, which comprised approximately 10 wt. % of the total weight of the fiber blend, had a linear density of approximately 11 dtex. The third binder fibers, which comprised approximately 10 wt. % of the total weight of the fiber blend, had a linear density of approximately 30 dtex. The fourth binder fibers, which comprised approximately 10 wt. % of the total weight of the fiber blend, had a linear density of approximately 70 dtex. 
     Sample 3B further comprised a spunbond, nonwoven polyester (i.e., polyethylene terephthalate) scrim having a weight of approximately 17 g/m 2 . The scrim was disposed on the surface of the composite that was proximate to the region containing the greatest concentration of the first binder fibers (i.e., the binder fibers having a linear density of approximately 1.7 dtex). The scrim was attached to the composite by placing the scrim onto the surface of the composite and then passing the composite through the compression oven, as described above. 
     Samples 3A and 3B were then tested to determine their physical properties, such as the stiffness, strength, toughness, and sound absorption. The results of these measurements, including the test methods used to determine the properties, are set forth in Table 3 below. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Physical properties of Samples 3A and 3B. 
               
            
           
           
               
               
               
               
            
               
                 Property 
                 Test Method 
                 Sample 3A 
                 Sample 3B 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 Stiffness (N/mm) 
                 ASTM D790 
                 2.21 
                 2.28 
               
               
                 Strength (N) 
                 ASTM D790 
                 27.99 
                 29.55 
               
               
                 Toughness (%) 
                 ASTM D790 
                 122.56 
                 123.65 
               
               
                 Sound absorption at 
                 ASTM E1050-98 
                 12 
                 41 
               
               
                 1000 Hz (%) 
                 (10 mm air gap) 
               
               
                 Sound absorption at 
                 ASTM E1050-98 
                 32 
                 58 
               
               
                 2000 Hz (%) 
                 (10 mm air gap) 
               
               
                 Sound absorption at 
                 ASTM E1050-98 
                 70 
                 75 
               
               
                 3000 Hz (%) 
                 (10 mm air gap) 
               
               
                   
               
            
           
         
       
     
     As can be seen from the results above, the composite produced using the nonwoven scrim (i.e., Sample 3B) exhibited improved mechanical properties relative to the composite produced without the scrim (i.e., Sample 3A). Sample 3B also exhibited substantially reduced sagging compared to Sample 3A when the composites were tested to determine if they meet the climatic sag requirements of most automobile manufacturers. 
     All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.