Patent Publication Number: US-2018029317-A1

Title: Metal-modified, plasma-treated thermoplastics for improved electrical performance

Description:
FIELD 
     The present disclosure relates generally to thermoplastics, and more specifically to thermoplastics modified to improve electrical characteristics. 
     BACKGROUND 
     Components of vehicles and machines, such as aircraft, are designed to tolerate a variety of harsh operational conditions. In some cases, reinforced composite materials are utilized in many aircraft assemblies and systems because the composite materials show resilience against extreme electric-charging such as a lightning strike. The composite materials used in aircraft are typically made to be conductive along the material surface. As a result, the majority of electric current and charging is dissipated along the conductive surface of the composite material. However, some composite materials include interior thermoplastic particles, layers, or other such internal materials, which are not conductive. In some cases, the thermoplastic layers retain and build-up unwanted electric current and/or charge following electric charging. Therefore, a thermoplastic layer is needed with increased conductivity that is capable of dissipating electric current and charge away from the thermoplastic layers following electric charging, while maintaining the structural strength and improved impact resistance provided by the composite material. 
     SUMMARY 
     In accordance with one aspect of the present disclosure, a method of imparting electrical conductivity on an interlayer material is disclosed. In some examples, the method includes forming an interlayer from at least one layer of fabric of thermoplastic fibers. Moreover, the method further includes, treating a surface of the interlayer material using an atmospheric-pressure plasma such that the surface of the interlayer material undergoes a surface activation. Additionally, the method includes depositing a layer of conductive material on the surface of the interlayer material, such that the conductive material increases a conductivity of the interlayer material. 
     In accordance with another aspect of the present disclosure, a method of manufacturing a composite material incorporating an interlayer having electrical conductivity is disclosed. The method includes forming a plurality of interlayers from an interlayer material and treating each interlayer of the plurality of interlayers with an atmospheric-pressure plasma such that a surface of each interlayer of the plurality of interlayers undergoes a surface-activation. Moreover, the method further includes depositing a conductive layer on the surface of each interlayer of the plurality of interlayers such that the conductive layer increases a conductivity of the plurality of interlayers. Additionally, the method includes forming a plurality of reinforcing layers from fibers of reinforcing material and disposing the plurality of interlayers each having the conductive layer on the surface alternately between the plurality of reinforcing layers. Furthermore, the method includes coupling the plurality of reinforcing layers and the plurality of interlayers together. The method further includes infusing the plurality of reinforcing layers and the plurality of interlayers with a matrix material, and curing the matrix material such that the conductivity of the plurality of interlayers improves the electrical conductivity of the composite material. 
     In accordance with yet another aspect of the present disclosure, a composite material having electrical conductivity is disclosed. The composite material includes a plurality of interlayers each formed from a layer of fabric of thermoplastic fibers and a surface of each interlayer of the plurality of interlayers being treated with an atmospheric-pressure plasma such that the surface of each interlayer of the plurality of interlayers undergoes a surface-activation. Moreover, the composite material further includes a conductive layer being deposited on the surface of each interlayer of the plurality of interlayers such that the conductive layer increases a conductivity of each interlayer of the plurality of interlayers. A plurality of reinforcing layers being formed from fibers of reinforcing material, wherein each interlayer of the plurality of interlayers having the conductive layer on the surface is alternately disposed between the plurality of reinforcing layers, wherein the plurality of reinforcing layers are coupled together with the plurality of interlayers. The composite further includes, a matrix material being infused into the plurality of reinforcing layers and the plurality of interlayers, wherein the matrix material is cured such that the conductivity of the plurality of interlayers improves the electrical conductivity of the composite material. 
     The features, functions, and advantages disclosed herein can be achieved independently in various embodiments or may be combined in yet other embodiments, the details of which may be better appreciated with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an exemplary vehicle constructed in accordance with the present disclosure; 
         FIG. 2  is a sectional view of an exemplary composite material in accordance with one embodiment of the present disclosure; 
         FIG. 3A  is a sectional view illustrating one exemplary embodiment of the interlayer fibers of the present disclosure; 
         FIG. 3B  is a sectional view of another exemplary embodiment of the interlayer fibers of the present disclosure; 
         FIG. 3C  is a sectional view of another exemplary embodiment of the interlayer fibers of the present disclosure; 
         FIG. 4  is a perspective view of an exemplary composite material in accordance with one embodiment of the present disclosure; 
         FIG. 5  is a sectional view of a composite laminated structure formed with a preform mold in accordance with one embodiment of the present disclosure; 
         FIG. 6  is a schematic view of the interlayer material being treated in accordance with one embodiment of the present disclosure; 
         FIG. 7  is a schematic view of the interlayer material being treated in accordance with another embodiment of the present disclosure; 
         FIG. 8  is flow diagram illustrating a method for treating the interlayer in accordance with an embodiment of the present disclosure; and 
         FIG. 9  is a flow diagram illustrating a method for forming a composite laminated structure incorporated the treated interlayer of  FIG. 8  in accordance with an embodiment of the present disclosure. 
     
    
    
     It should be understood that the drawings are not necessarily to scale, and that the disclosed embodiments are illustrated diagrammatically, schematically, and in some cases in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and apparatuses or which render other details difficult to perceive may have been omitted. It should be further understood that the following detailed description is merely exemplary and not intended to be limiting in its application or uses. As such, although the present disclosure is for purposes of explanatory convenience only depicted and described in illustrative embodiments, the disclosure may be implemented in numerous other embodiments, and within various systems and environments not shown or described herein. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a vehicle  20 , is illustrated. While one non-limiting example of the vehicle  20  is that of an aircraft, it will be appreciated that the present disclosure applies to other types of vehicles and machines as well, such as but not limited to, marine vessels, construction equipment, and power generators. In some embodiments, the vehicle  20 , or aircraft, is configured with an airframe  22 , including a fuselage  24 , a plurality of wings  26 , a tail section  28 , and other such assemblies and systems of the vehicle  20 . Additionally, one or more propulsion units  30  are coupled to the underside of each of the wings  26  in order to propel the vehicle  20  in a direction of travel. However, other attachment locations and configurations of the propulsion units  30  are possible. Furthermore, each of the wings  26  are attached along an approximately central portion of the fuselage  24 , and the wings  26  are swept back towards the tail section  28  or aft portion of the vehicle  20 . Moreover, in some embodiments, the assemblies, systems and other components of the vehicle  20 , are exposed to environmental conditions such as but not limited to, extreme temperature variations, high and/or low humidity, electrical charging and/or discharging, mechanical vibration, airborne particles, debris, and other such conditions encountered during operation. As a result, in some embodiments, the materials and other components used to fabricate the fuselage  24 , wings  26 , tail section  28 , propulsion units  30  and other such assemblies and systems, are configured such that they are capable of withstanding thermal expansion and/or contraction, increased moisture levels, electrical charging, mechanical shocks, and other such conditions. 
     Moving on to  FIGS. 2 and 4 , one embodiment of a composite material  32  used to fabricate, or otherwise construct, assemblies and systems of the vehicle  20  is illustrated. In one non-limiting example, the composite material  32  is a fabric built up from a plurality of alternating layers composed of one or more reinforcing layers  34  and one or more interlayers  36 . In an embodiment, the reinforcing layers  34  and the interlayers  36  are stacked or otherwise arranged such that one layer of the interlayer  36  is positioned (i.e., sandwiched) between two of the reinforcing layers  34 . For example, the composite material  32  is formed as a stack of material starting with a reinforcing layer  34  placed at the bottom. An interlayer  36  is placed on top of the bottom reinforcing layer  34  and another reinforcing layer  34  is placed on top of the interlayer  36 . As a result, some embodiments repeat this stacking pattern to create the desired thickness of the composite material  32 . Moreover, in some embodiments, following the build-up of the composite material  32 , a stitching  38 , or other fastening mechanism, is used to couple, or otherwise connect and hold the alternating reinforcing layers  34  and interlayers  36  in place. 
     In some embodiments, the reinforcing layers  34  are composed of carbon-fiber, glass-fiber, mineral-fiber, or other such reinforcing material. Moreover, in one non-limiting example, the reinforcing layers  34  are formed such that a plurality of carbon-fibers, glass-fibers, mineral-fibers, or other such fibers are arranged to create layers of fibers having a unidirectional pattern. Such an arrangement of the fibers provides a tough, durable and lightweight structural material for use in fiber reinforced composite materials and other such reinforcing materials. 
     Moreover, the interlayers  36  are formed from a fabric of one or more different type of continuous fibers, and in one non-limiting example, the interlayers  36  are formed from a layer of non-woven fabric of thermoplastic fibers having at least two different types of thermoplastic fibers. In some embodiments, the interlayers  36  are non-woven layers of material such as but not limited to, spunbonded fabric, spunlaced fabric, mesh fabric, or other such fabric. For example, a spunbonded fabric is produced from continuous filaments or fibers that are continuously spun and thermally bonded to form a layer of non-woven fabric. Alternatively, a spunlaced fabric is prepared from continuous filaments or fibers which are continuously spun and bonded mechanically. In some exemplary embodiments, the interlayers  36  are formed using the above mentioned methods from one or more different types of thermoplastic filaments or fibers such as but not limited to, polyamide, polyimide, polyamide-imide, polyester, polybutadiene, polyurethane, polypropylene, polyetherimide, polysulfone, polyethersulfone, polyphenylsulfone, polyphenylene sulfide, polyaryletherketone, polyetherketoneketone, polyetheretherketone, polyacrylamide, polyketone, polyphthalamide, polyphenylene ether, polybutylene terephthalate, polyethylene terephthalate, polyester-polyarylate (e.g., Vectran®). 
     In some embodiments, the interlayers  36  are made up of filaments or fibers which incorporate two or more different thermoplastic materials.  FIGS. 3A-C  illustrate several different non-limiting configurations of a thermoplastic fiber  44  formed using two different thermoplastic materials. While  FIGS. 3A-C  show thermoplastic fibers  40  which are constructed of two different materials, other embodiments of thermoplastic fibers  44  composed of a different number of thermoplastic materials is possible.  FIG. 3A  provides one exemplary cross-sectional illustration of the thermoplastic fiber  44  being made from substantially equal amounts of a first material  46  and a second material  48 . In such a configuration, the first material  46  and the second material  48  are extruded, or otherwise forced through a fixture with two openings to produce the thermoplastic fiber  44  such that the first material  46  is stacked on top of the second material  48 . Moreover,  FIG. 3B  illustrates another non-limiting example of the thermoplastic fiber  44  being formed by the extrusion of the first material  46  and the second material  48  through a fixture with four openings. As a result, the thermoplastic fiber  44  illustrated in  FIG. 3B  is composed of alternating regions of first and second materials  46 ,  48 . In an additional embodiment illustrated in  FIG. 3C , the thermoplastic fiber  44  is formed using a coaxial arrangement of the first and second materials  46 ,  48 . For example, the first material  46  defines a sheath region and the second material  48  defines a core region of the thermoplastic fiber  44 . The thermoplastic fiber  44  configurations illustrated in  FIGS. 3A-3C  show the fibers having a circular or thread-like cross-section. It will be appreciated that the thermoplastic fibers  44  are capable of being extruded, or otherwise formed into other shapes and structures, such as but not limited to, rectangular shaped ribbons, oval-shaped filaments or fibers, or any other suitable shape or structure. 
     Referring now to  FIG. 5 , and with continued reference to  FIGS. 2-4 , one non-limiting example of the stack of composite material  32  being formed into a fiber-reinforced composite laminate structure  50  is illustrated. In some embodiments, the composite laminate structure  50  is formed by vacuum-assisted resin transfer molding (i.e., preform molding), however other molding processes are possible. In vacuum-assisted resin transfer molding, the composite material  32  is positioned onto a mold  52  or other such template, which is used to impart a shape to the composite material  32 . As a result, depending on the intended application, different molds  52  are used to size, shape, and otherwise form the composite laminate structure  50 . Moreover, a matrix material, such as but not limited to a resin, an epoxy, or other such hardening material, is introduced into the mold  52 , and the matrix material infuses through the composite material  32  being supported by the mold  52 . In some embodiments, the matrix material permeates through the entire composite material  32  and saturates the reinforcing layers  34  and the interlayers  36  which are disposed in between the reinforcing layers  34 . Alternatively, in some embodiments the matrix material is directed or controlled to permeate through a portion of composite material  32 . Moreover, the interlayers  36  are configured to facilitate the permeation of the matrix material through the interlayers  36  to ensure that all of the layers of the composite material  32  are sufficiently saturated (i.e., wet-out) with the matrix material such that the matrix material covers the interlayers  36  to maximize the contact area between the interlayers  36  and the reinforcing layers  34 . Furthermore, the stitching  38  inserted between the reinforcing layers  34  and the interlayers  36  helps to hold the stack of composite material  32  in place during the infusion of the matrix material. 
     While one non-limiting example of forming the composite laminate structure  50 , such as but not limited above, preform molding, is discussed above, it should be known that other methods are possible. For example, in another embodiment, the interlayers  36  are alternately disposed in between the reinforcing layers  34  to build-up the stack of composite material  32 . Furthermore, prior to placing the composite material  32  onto the mold surface the composite material  32  is pre-impregnated (i.e., prepreg), or otherwise infused, with matrix material, such as resin, epoxy, or other such hardening material. In some embodiments, the composite material  32  prepreg is partially cured following the infusion with matrix material. In some cases, this partial curing allows for easier handling of the composite material  32  and matrix material. Moreover, when the composite laminate structure  50  is ready to be formed the composite material  32 , with the pre-impregnated matrix material, is placed onto the mold surface and fully cured at an elevated temperature and/or pressure. As a result, the composite laminate structure  50  is formed and shaped according to the size and shape of the mold surface. 
     In some embodiments, either during or after the infusion of the matrix material, the mold  52  holding the stack of composite material  32  is enclosed within a vacuum chamber, or other pressure controlled environment, to further facilitate the transport and infusion of the matrix material throughout the stack of composite material  32 . Moreover, in some embodiments, after the stack of composite material  32  is saturated with the matrix material, the mold  52  is heated to a temperature which cures or otherwise hardens the matrix material. As a result, as the matrix material begins to harden reinforcing layers  34  and the interlayers  36  are bound together. When the matrix material is fully cured, the composite laminate structure  50  will be formed into the shape of the supporting mold  52 . In some embodiments, during the curing of the matrix material the temperature is steadily increased such that during the initial phase of the temperature increase the matrix material continues to flow in between the reinforcing layers  34  and the interlayers  36 . Moreover, as the temperature continues to rise the matrix material begins to at least partially solidify and once the cure temperature is reached, the mold  52  and the stack of composite material  32  is held at the cure temperature for a pre-determined period of time. In one non-limiting example, the cure temperature of the matrix material is between a range of 150° to 200° C. and the cure time is between 1 to 6 hours. However, the cure temperature and time will vary depending on the stack of composite material  32  and the matrix material used to form the composite laminate structure  50 . 
     Additionally, it should be noted that generally, the gel temperature of the matrix material will be at or below the melting temperature of the reinforcing layers  34  and interlayers  36 . As such, the melting temperature of the reinforcing layers  34  and interlayers is above 200° C., however other melting temperatures are possible. Moreover, in some embodiments, the gel and cure temperatures of the matrix material will be above the glass-transition temperature and below the melting temperature of the reinforcing layers  34  and the interlayers  36 . In such embodiments, a cure temperature between the glass-transition temperature and the melting temperature will facilitate the shaping and molding of the reinforcing layers  34  and the interlayers  36  without changing the structural integrity of the materials. Alternatively, it is possible that some embodiments will use a cure temperature which is slightly above the melting temperature of the reinforcing layers  34  and the interlayers  36  to facilitate an interdiffusion between the matrix material and the reinforcing layers  34  and/or interlayers  36 . 
     Once the matrix material is fully cured, the formation of the composite laminate structure  50  is complete. Moreover, the finished composite laminate structure  50  will take the form of the mold  52  which held the composite material  32  and matrix material during molding. Differently shaped molds  52  are used depending on the desired shape for the composite laminate structure  50 . As a result, a plurality of differently shaped molds  52  are used to produce differently shaped composite laminate structures  50  which are used in various assemblies and systems of the vehicle  20  shown in  FIG. 1 . 
     As further shown in  FIG. 5 , with continued reference to  FIGS. 2-4 , in some cases the reinforcing layers,  34 , the interlayers  36 , the stitching  38  and the matrix material are arranged to produce a composite laminate structure  50  that exhibits certain properties. For example, in some cases the composite laminate structure  50  is incorporated into structural assemblies and systems which require certain structural properties, such as but not limited to, high compressive strength, high tensile strength, increased fracture toughness, and other such properties. Moreover, in some embodiments the addition of the interlayer  36  provides an improved impact resistance to composite laminate structure  50 . Additionally, the composite laminate structure  50  will generally be required to exhibit good chemical resistance to solvents including but not limited to, aviation fuel, hydraulic fluid, brake fluid, ketones, water, and other chemicals the composite laminate structure  50  will come into contact with. Moreover, the composite laminate structure  50  must be able to withstand a host of environmental conditions it will be exposed to during use. For example, in some embodiments, the composite laminate structure  50  is exposed to extreme temperature variations, high and/or low humidity, electrical charging and/or discharging, mechanical vibration and shock, airborne particles and debris, and other such environmental conditions encountered during use and/or operation. 
     Generally, the thermoplastic material which forms the interlayer  36  has inherent electrically insulating properties. As a result, when the interlayer is exposed to electrical current or charge some embodiments of the interlayer  36  will behave like an electrical storage device (i.e., a capacitor). In some situations, the composite laminate structures  50  formed with the reinforcing layers  34  and the interlayers  36 , are capable of holding onto or storing an electrical charge for a prolonged period of time. During operation, the vehicle  20  in  FIG. 1 , is exposed to several potential electrical events, such as but not limited to a lightning strike, electromagnetic interference (EMI), electric current, and other such events, which interferes with portions of the vehicle  20 . For example, during a lighting strike, the airframe  22  of the vehicle ( FIG. 1 ) is exposed to high electric current which must be dissipated. However, in some embodiments, the composite laminate structures  50 , incorporated into a portion of the assemblies and systems of the airframe  22  ( FIG. 1 ), have a high electrical resistance and are unable to dissipate the electric current or charge. As a result, some embodiments of the composite laminate structure  50  include methods and materials to improve the electrical conductivity of the composite laminate structures  50 . 
     Referring to  FIG. 5 , and in continued reference to  FIGS. 2-4 , some applications of the composite laminate structures  50  incorporate an conductive mesh  54  formed out of nickel, copper, aluminum, or other such conductive material, to provide a conductive path for the electric current or charge produced by electrical charging and/or discharging. The conductive mesh  54  is configured to provide a conductive pathway which carries the electric current imparted into the composite laminate structure  50  away from the bulk of the structure. In some embodiments, the conductive mesh  54  is positioned along both a top side  56  and a bottom side  58  of the composite laminate structure  50 . Alternatively, in some embodiments, the conductive mesh  54  is positioned on only one of the top side  56  or bottom side  58  of the composite laminate structure  50 . 
     The conductive mesh  54  provides adequate conductivity to conduct or otherwise redirect the electric current away from the bulk of the composite laminate structure  50 . However, in some embodiments, the interlayers  36  that are incorporated within the composite laminate structure  50  retain the inherently insulating properties of thermoplastic material. As a result, the interlayers  36  are capable of storing residual electrical current or charge which is generated from electrical charging and/or discharging. In one non-limiting example, For example, following an electrical charging and/or discharging event, such as but not limited to a lightning strike, the conductive mesh  54  may not be completely effective in dissipating the electric current from the composite laminate structures  50 , and the interlayers  36  retain some of the electric current or charge (i.e., edge-glow). 
     As a result, in some embodiments, increasing the conductivity of the interlayers  36  will provide improvement against charge build-up on the interlayers  36  and within the composite laminate structures  50 . As discussed above, in some embodiments the interlayer  36  is formed from a thermoplastic material, such as but not limited to, polyamide, polyimide, polyamide-imide, polyester, polybutadiene, polyurethane, polypropylene, polyetherimide, polysulfone, polyethersulfone, polyphenylsulfone, polyphenylene sulfide, polyaryletherketone, polyetherketoneketone, polyetheretherketone, polyacrylamide, polyketone, polyphthalamide, polyphenylene ether, polybutylene terephthalate, polyethylene terephthalate, polyester-polyarylate (e.g., Vectran®). However, the thermoplastic material of the interlayer  36  is generally not conductive, and therefore should be modified or otherwise treated to help improve its conductivity and other surface electrical properties. 
     Referring to  FIGS. 6 and 7 , with continued reference to  FIGS. 2-5 , one embodiment of the interlayer  36  having increased conductivity is illustrated. In one non-limiting example, the interlayer  36  is made to be more conductive by adding a conductive material  60  onto the surface of the interlayer  36 . In some embodiments, the conductive material  60  is deposited as a continuous layer onto the top side  62  and the bottom side  64  of the interlayer  36  surface. Alternatively, in other embodiments, a discontinuous layer (i.e., decorating the surface) of conductive material  60  is deposited onto top and bottom side  62 ,  64  of the interlayer  36  surface. Furthermore, in other embodiments, the conductive material  60  is deposited on one of the top and bottom sides  62 ,  64  of the interlayer  36  surface. 
     In some embodiments, depositing the conductive material  60  on at least one of the top and bottom sides  62 ,  64  of the interlayer  36  surface will help improve the conductivity of the material. Moreover, in some embodiments, the interlayers  36  in the composite laminate structure  50  are electrically coupled to each other such that the electric current or charge is dissipated from each of the interlayers  36  which are dispersed throughout the composite laminate structure  50 . In one non-limiting example, the stitching  38  provides an electric coupling between the interlayers  36  of the composite structure, however, other methods of electrically coupling the interlayers  36  together are possible. As a result, in some embodiments, the enhanced conductive properties of the interlayers  36  facilitates the removal or dissipation of the electric current or charge from the interlayers  36  following electrical charging/discharging. 
     In some embodiments, the thermoplastic material used to fabricate the interlayer  36  has a lack of robust bonding or attachment sites (i.e., covalent bonding sites) along the top and bottom sides  62 ,  64  of the interlayer  36  surface. The lack of available bonding sites creates poor adhesion or bonding, and as a result, make it difficult to deposit the conductive material  60  along the top and bottom sides  62 ,  64  of the interlayer  36 . As illustrated in  FIG. 6 , one embodiment imparts the interlayer  36  is treated with, such as but not limited to, an atmospheric-pressure plasma  66  on the top and bottom sides  62 ,  64  of interlayer  36  surface to provide improved bonding or attachment sites. For example, the atmospheric-pressure plasma  66  produces ionized gas at atmospheric pressure. The ionized gas is directed towards and bombards or collides with the top and bottom sides  62 ,  64  of the interlayer  36  surface. Moreover, the atmospheric-pressure plasma  66  is configured to only interact with the surface of the top and bottom sides  62 ,  64  of the interlayer  36 . As a result, adhesion and bonding along the interlayer  36  surface is improved while the bulk properties of interlayer  36  are left unchanged. 
     In some embodiments, the improvement in the adhesion and bonding to the interlayer  36  surface is caused by an increase in the surface activation energy produced by the treatment with the atmospheric-pressure plasma  66 . During treatment, the top and bottom sides  62 ,  64  of the interlayer  36  are bombarded with the ionized gas  68 . This surface bombardment results in producing a plurality of available bonding and attachment sites  70  (i.e., available functional groups on the surface) along the top and bottom sides  62 ,  64  of the interlayer  36  surface. While the use of atmospheric-pressure plasma  66  is illustrated in FIG.  6 , the plurality of bonding and attachment sites  70  can be formed from other types of surface treatment, such as but not limited to, corona discharge, flame plasma, wet chemical treatment and other known surface treatments. 
     In some embodiments, the interlayer  36  is configured into a pre-treatment roll  72  and a post-treatment roll  74  to help improve throughput of the interlayer  36  as it is fed through the atmospheric-pressure plasma  66 . In some embodiments, the atmospheric-pressure plasma  66  is configured to simultaneously treat the top and bottom sides  62 ,  64  of the interlayer  36 , however other configurations are possible. Alternatively, in other embodiments, instead of forming pre-treatment and post-treatment rolls  72 ,  74 , the interlayer  36  is configured in flat sheets or other such configuration, while undergoing treatment with the atmospheric-pressure plasma  66 . In one non-limiting example, the atmospheric-pressure plasma  66  is an atmospheric-pressure oxygen plasma, which is comprised of ionized oxygen gas to oxidize the top and bottom sides  62 ,  64  of the interlayer  36 . As a result, the atmospheric-pressure plasma  66  (i.e., atmospheric-pressure oxygen plasma) produces an increased oxygen content along the top and bottom sides  62 ,  64  of the interlayer  36  which creates and/or increases the available (i.e., unbound) oxygen sites at the bonding and attachment sites  70  along the top and bottom sides  62 ,  64  of the interlayer  36 . In some embodiments, these available oxygen sites are then capable of bonding to or otherwise attaching with the conductive material  60  ( FIG. 6 ) such that the conductive material  60  adheres to the top and bottom sides  62 ,  64  of the interlayer  36  surface. 
     In addition to oxygen, the atmospheric-pressure plasma  66  can be formed using other gases or mixture of gases, such as but not limited to, nitrogen, argon, helium, nitrous oxide, ambient air, water vapor, carbon dioxide, methane, ammonia, and other such gases. Moreover, in some embodiments, treatment with the atmospheric-pressure plasma  66  provides other improvements in addition to creating additional bonding or attachment sites  70 . For example, in some embodiments, the increase in surface activation energy caused by the atmospheric-pressure plasma  66  can improve the wettability of liquids along the interlayer  36 , such as but not limited to the matrix material as it is infused into stack of composite material  32  during the composite laminated structure  50  formation. Moreover, in some embodiments, bombarding the interlayer  36  with atmospheric-pressure plasma  66  helps to remove any contaminants that are present along the top and bottom sides  62 ,  64  of the interlayer. A cleaner surface will generally show better adhesion and bonding properties. As a result, in some embodiments, the atmospheric-pressure plasma  66  will provide a cleaner surface and an increased number of bonding or attachment sites  70  such that the conductive material  60  ( FIG. 7 ) will have improved adhesion to the top and bottom sides  62 ,  64  of the interlayer  36 . 
     Referring now to  FIG. 7 , and with continued reference to  FIG. 6 , one non-limiting example of depositing the conductive material  60  on the interlayer  36  is illustrated. In some embodiments, following the treatment with the atmospheric-pressure plasma  66 , the interlayer  36  is further treated by depositing a layer of conductive material  60  along the top and bottom sides  62 ,  64  of the interlayer  36 . Moreover, in some embodiments, the conductive material  60  is deposited as either a continuous layer or a discontinuous layer along the top and bottom sides  62 ,  64  of the interlayer  36  surface. As such, the continuous and/or discontinuous layer of conductive material  60  is capable of providing improved electrical surface properties of the interlayer  36 , such as but not limited to, an increase in the conductivity, improved EMI shielding, and other such electrical properties. Moreover, in some embodiments, depending on the planned application of the interlayer  36 , the conductive layer  60  is deposited on only one of the top or bottom sides  62 ,  64  of the interlayer  36  surface. 
     In one non-limiting example the conductive layer  60  is a metal, including but not limited to, nickel, copper, silver, or other such metal, which provides improved electrical surface properties of the interlayer  36 . Moreover, in some embodiments, to improve the throughput of interlayer  36  treatment, the post-treatment roll  74  of the interlayer  36  is exposed to chemical vapor deposition (CVD) deposition  76  to produce a conductive interlayer roll  78 . In some embodiments, CVD deposition  76  is configured to simultaneously deposit the conductive layer  60  on the top and bottom sides  62 ,  64  of the interlayer  36  as it is fed through CVD deposition  76 . Furthermore, while  FIG. 7  illustrates the use of CVD deposition  76  for the deposition of the conductive material  60 , other deposition methods such as but not limited to, electrodeposition, sputtering, electron beam evaporation, or other such methods are possible. Similarly to curing of the composite laminate structure  50  described above, CVD deposition  76  is generally configured to deposit the conductive material  60  at a temperature which is below the glass transition temperature and/or the melting point of the interlayer  36 . In one non-limiting example, the specified melting temperature of the interlayer  36  will be greater than 200° C. However, other melting temperatures are possible depending on which thermoplastic material is used to fabricate the interlayer  36 . 
     In some embodiments, CVD deposition  76  is configured for a specific material deposition amount. For example, as further illustrated in  FIG. 7 , CVD deposition  76  is capable of depositing a continuous, uniform layer of the conductive material  60  on both the top and bottom sides  62 ,  64  of the interlayer  36 . Moreover, in another embodiment, CVD deposition  76  is capable of being configured to deposit a non-uniform, continuous layer of conductive material  60  such that the thickness of the conductive material  60  is deposited with a varying thickness along the top and bottom sides  62 ,  64  of the interlayer  36 . In still other embodiments, the uniform and non-uniform continuous layer of conductive material  60  is deposited along one of the top or bottom sides  62 ,  64  of the interlayer  36 . Additionally, in some alternative embodiments, a lower amount of conductive material  60  is needed such that a discontinuous layer (i.e., decorating the surface) is deposited along the top and bottom sides  62 ,  64  of the interlayer  36 . Moreover, in some embodiments, the discontinuous layer of conductive material  60  is configured such that it is deposited on one of the top and bottom sides  62 ,  64  of the interlayer  36 . 
     Alternatively, CVD deposition  76  is capable of depositing a plurality of different conductive layers  60  along the top and bottom sides  62 ,  64  of the interlayer  36 . In some embodiments, the plurality of different conductive layers  60  are deposited directly on top of one another, therefore forming a stack of conductive material  60 . For example, a multiple metal layer stack including, but not limited to, nickel, copper, silver, or other such metal is deposited along the top and bottom sides  62 ,  64  of the interlayer  36 . As described above, CVD deposition  76  is capable of being used for depositing the plurality of different layers of metal along the top and bottom sides  62 ,  64  of the interlayer  36 . In some embodiments, the interlayer  36  will be fed through CVD deposition  76  multiple times, with each pass depositing a different metal layer. Moreover, in some embodiments the plurality of different metals forming the conductive layer  60  can be deposited on both the top and bottom sides  62 ,  64  of the interlayer  36 , deposited on one of the top and bottom sides  62 ,  64  of the interlayer  36 , deposited as continuous uniformly and/or non-uniformly thick layers of conductive material. Alternatively, the plurality of different metals is deposited to form discontinuous uniformly, and/or non-uniformly thick layers of conductive material, however other deposition variations are possible depending on the planned interlayer  36  application. In some embodiments, the deposition of multiple different metal layers to form the conductive layer  60  to improve the electrical surface properties of the interlayer  36  such as, but not limited, to increased conductivity, improved EMI shielding, and other such electrical properties. In one non-limiting example, the deposition of different metal layers provides a broader spectrum of electromagnetic frequencies which are dampened or otherwise blocked by the conductive layer  60  deposited along the top and bottom sides  62 ,  64  of the interlayer  36 . 
     INDUSTRIAL APPLICABILITY 
     In general, the foregoing disclosure finds utility in various applications such as in transportation, mining, construction, industrial, and power generation machines and/or equipment. In particular, the disclosed composite material incorporating a modified thermoplastic layer is applied to vehicles and machines such as aircraft, hauling machines, marine vessels, power generators, and the like. Through the novel teachings outlined above, the composite laminate structure  50  is fabricated using a plurality of reinforcing layers  34  and interlayers  36 . Moreover, in some embodiments, the interlayers  36  are modified to provide enhanced electrical surface properties, such as but not limited to increased conductivity, improved EMI shielding, and other such electrical properties. As a result, in some embodiments, the interlayers  36  with enhanced electrical surface properties provide improved dissipation of electrical current or charging of the composite laminate structure  50  while also maintaining improved impact resistance to the composite laminate structure  50 . 
       FIG. 8 , with continued reference to  FIGS. 1-7 , illustrates an exemplary method  80  of modifying the interlayer  36  to impart improved electrical surface properties. In a first block  82  of method  80 , the interlayer  36  is formed from a thermoplastic material, such as but not limited to polyamide, polyimide, polyamide-imide, polyester, polybutadiene, polyurethane, polypropylene, polyetherimide, polysulfone, polyethersulfone, polyphenylsulfone, polyphenylene sulfide, polyaryletherketone, polyetherketoneketone, polyetheretherketone, polyacrylamide, polyketone, polyphthalamide, polyphenylene ether, polybutylene terephthalate, polyethylene terephthalate, polyester-polyarylate (e.g., Vectran®). Moreover, in some embodiments, the interlayer  36  is configured to form a non-woven fabric layer of thermoplastic material, however other configurations of the interlayer  36  are possible. 
     In a next block  84 , the interlayer  36  is treated such that the top and bottom sides  62 ,  64  of the interlayer  36  are modified to create a plurality of bonding or attachment sites  70 . In some embodiments, the interlayer  36  is modified or otherwise treated using an atmospheric-pressure plasma  66  which bombards the top and bottom sides  62 ,  64  of the interlayer  36 . Moreover, in one non-limiting example, the atmospheric-pressure plasma  66  is an atmospheric-pressure oxygen plasma and uses ionized oxygen gas to create the plasma that treats the surface of the interlayer  36 . In some cases, the atmospheric-pressure oxygen plasma helps to increase the surface energy along the top and bottom sides  62 ,  64  of the interlayer  36 , as well as provide a plurality of bonding and/or attachment sites  70 . In a next block  86  of the method  80 , a conductive layer  60  is deposited along the top and bottom sides  62 ,  64  of the interlayer  36 . In some embodiments, the increased surface energy and plurality of bonding and attachment sites  70  produced by the atmospheric-pressure plasma  66  enhance the adhesion of the conductive layer  60  to the top and bottom sides  62 ,  64  of the interlayer  36 . Moreover, in some embodiments, the addition of the conductive layer  60  to the interlayer  36  provides improved electrical surface properties, such as but not limited to increased conductivity and improved EMI shielding. 
       FIG. 9 , with continued reference to  FIGS. 1-8 , illustrates a method  88  for forming a composite laminate structure  50  which incorporates the interlayer  36  having improved electrical surface properties. In a first block  90 , the interlayer  36  is treated to provide enhanced and improved electrical properties. In one embodiment, the top and bottom sides  62 ,  64  of the interlayer  36  are treated to improve the adhesion between the interlayer  36  and a conductive material  60  which is deposited on the top and/or bottom sides  62 ,  64  of the interlayer  36 . In some embodiments, following treatment of the interlayer  36 , a determination is made whether to deposit the conductive material  60  on one of or on both the top and bottom sides  62 ,  64  of the interlayer  36 . If the determination is made to deposit the conductive material  60  on both the top and bottom side  62 ,  64  is made, then in a next block  92  the conductive material  60  is subsequently deposited on the top and bottom sides  62 ,  64  of the interlayer  36 . Alternatively, if the determination to deposit the conductive material  60  on only one of the top and bottom sides  62 ,  64  of the interlayer is made, then in a next block  94  the conductive material  60  is deposited along the top or bottom sides  62 ,  64  of the interlayer. 
     Following the deposition of the conductive material  60 , in a next block  96 , it is determined whether the interlayer  36  will be used in a preform composite assembly or other type of assembly. If a preform composite assembly is to be made, then in a next block  98  one or more of the treated interlayers  36  are alternately disposed in between the reinforcing layers  34 . In some embodiments, the treated interlayers  36  and reinforcing layers  34  are built-up to form a stack of composite material  32  which is placed on the preform mold  52 . In a next block  100 , the preform mold  52  is infused with a matrix material such as resin, epoxy, or other such hardening material. The matrix material saturates each of the layers of the interlayer  36  and reinforcing layer  34 . Moreover, in a next block  102 , once the stack of composite material  32  is infused with the matrix material the preform mold  52  is placed into a vacuum chamber or other pressure vessel and heated to the cure temperature of the matrix material. The matrix material binds the reinforcing layers  34  and interlayers  36  to form the preform composite laminate structure  50 . Moreover, during curing the composite laminate structure  50  is formed into the shape of the supporting mold  52 . In some embodiments, the treated interlayers  36  are incorporated within the composite laminate structure  50  to provide improved electrical properties and characteristics, such as increased conductivity, improved EMI shielding, and other such electrical properties. In one non-limiting example, the composite laminate structure  50  with the treated interlayers  36  is capable of dissipating any electric current or charging which results from electric charging or discharging such as, but not limited to, a lightning strike. 
     Referring back to block  96 , if a preform composite is not to be formed using the treated interlayers  36 , then in block  104  preparations are made to incorporate the treated interlayer  36  into the composite laminate structure  50  using a different fabrication process, such as a prepreg composite assembly. In prepregging, the treated interlayer  36  is alternately disposed between reinforcing layers  34  to build-up the composite material  32  and the composite material is infused with a matrix material, such as but not limited to a resin, epoxy, or other hardening material. Alternatively, in some embodiments, the interlayer  36  is melt-bonded, to the reinforcing layers  34  prior to infusing the interlayers  36  and reinforcing layers  34  with the matrix material. During melt-bonding, an interlayer  36  is spread out on each side of the reinforcing layers  34 . Heat and pressure are introduced such that the interlayers  36  and reinforcing layers  34  are melted, bonded or otherwise attached, such that the interlayers  36  and reinforcing layers  34  do not move with respect to each other. 
     In a next block  106 , the composite material  32  is arranged onto the mold surface and prepared to form a composite laminated structure  50 . In a next block  108 , the composite material  32  and the prepreg mold are placed under vacuum and heated to a cure temperature of the matrix material such that the composite laminate structure  50  is formed incorporating the one or more of the treated interlayers  36 . Similar to the preform composite assembly formed in block  102 , the prepreg composite assembly with the treated interlayer  36  provides a composite laminate structure  50  having improved electrical properties, such as increased conductivity, improved EMI shielding and other such electrical properties. 
     While the foregoing detailed description has been given and provided with respect to certain specific embodiments, it is to be understood that the scope of the disclosure should not be limited to such embodiments, but that the same are provided simply for enablement and best mode purposes. The breadth and spirit of the present disclosure is broader than the embodiments specifically disclosed and encompassed within the claims appended hereto. Moreover, while some features are described in conjunction with certain specific embodiments, these features are not limited to use with only the embodiment with which they are described, but instead may be used together with or separate from, other features disclosed in conjunction with alternate embodiments.