US20220135846A1

US20220135846A1 - Low thermal expansion film adhesives for multilayer transparent armour and related applications

Info

Publication number: US20220135846A1
Application number: US17/393,457
Authority: US
Inventors: Behnam ASHRAFI; Yadienka Martinez-Rubi; Michael JAKUBINEK
Original assignee: National Research Council of Canada
Current assignee: National Research Council of Canada
Priority date: 2020-08-12
Filing date: 2021-08-04
Publication date: 2022-05-05
Also published as: CA3189142A1; WO2022032377A1; CA3126974A1; US12227681B2; US20230314105A1

Abstract

The present disclosure is directed to a composite material comprising a thermoplastic adhesive and nanotubes oriented in the in-plane orientation. In additional aspects, the disclosure includes a laminated armor material comprising the composite and armor materials.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority from co-pending application U.S. provisional application No. 63/064,595, filed Aug. 12, 2020, the content of which is herein incorporated by reference in its entirety.

FIELD

The present disclosure is directed to a composite material comprising an adhesive and nanotubes oriented in the in-plane orientation, which reduces the coefficient of thermal expansion of the adhesive. In additional aspects, the disclosure includes a laminated armor material comprising the composite and armor materials.

INTRODUCTION

Armor materials, such as transparent amours (bulletproof glass) are often composed of multiple layers of armor material(s) bonded together by adhesives (for example, films of thermoplastic polyurethane). The armor material can include one or more hard layers (glass and/or ceramic) and stiff, ductile backing layers (for example polymethylmethacrylate or polycarbonate such as in FIG. 1). Changes in temperature induce stresses at the interface between armor layers due to the difference (commonly called mismatch) between the thermal expansion of the armor material and that of the adhesive, as well as differences in thermal expansion between different armor materials, when the system is exposed to temperature variations. The mismatch in the coefficient of thermal expansion (CTE) is problematic with transparent armor as in-service temperatures can range between −50° C. and 50° C. causing thermal stresses that can lead to disbonding, which leads to optical degradation (i.e., reduced clarity and transparency) and potentially reduced mechanical performance. Stresses induced by CTE mismatch causes isolated disbonding while a combination of humidity ingression and thermal cycling causes delamination.

SUMMARY

The present disclosure is directed to a composite adhesive material which lessens the CTE mismatch between armor layers and the adhesive, which maintains and/or improves the mechanical and/or optical performance of armour materials.
In particular, the present disclosure is directed to a composite material comprising:

- i) an adhesive; and
- ii) nanotubes;
- wherein the composite material is in a sheet-like formation having x, y and z dimensions, wherein the measurement of the z dimension is less than the x and y dimensions, and wherein a portion of the nanotubes are oriented within the plane in the x and y dimensions of the composite material, and wherein the in-plane orientation of the nanotubes is sufficient to reduce the coefficient of thermal expansion (CTE) of the adhesive.

In one embodiment, the CTE of the composite adhesive in the x and y dimensions (CTE_x,y) is less than the CTE of the composite adhesives in the z dimension (CTE_z).
In another embodiment, the amount of nanotubes in the composite material is about 5 wt % to about 50 wt %, or about 5 wt % to about 25 wt %, or about 5 wt % to about 20 wt %, or 5 wt %.
In one embodiment, about 80% or more, about 85% or more, or about 90% or more of the nanotubes in the composite material have an average angle of about 30°, of about 25°, or about 20° or less relative to the plane of the sheet defined as the x-y plane.
In another embodiment, the adhesive is a thermoplastic adhesive such as thermoplastic polyurethane or polyvinyl butyral. In another embodiment, the adhesive is a thermoset adhesive. In one embodiment, the thermoset adhesive is polyurethane, epoxy or silicone.
In one embodiment, the nanotubes comprise carbon nanotubes, boron-nitride nanotubes, boron-carbon-nitrogen nanotubes, silicon-carbide nanotubes, other nanoparticles, hybrids of any two or more thereof, or a combination of any two or more thereof. In one embodiment, the nanotubes are boron-nitride nanotubes.
In another embodiment, the composite material has a coefficient of thermal expansion of about 3.0×10⁻⁶/° K to about 100.0×10⁻⁶/° K. In another embodiment, the composite material has a coefficient of thermal expansion of about 3.0 10⁻⁶/° K to about 10.0×10⁻⁶/° K, which is advantageous for glass to glass bonding. In a further embodiment, the composite material has a coefficient of thermal expansion of about 50.0 10⁻⁶/° K to about 70.0×10⁻⁶/° K, which is advantageous for polycarbonate and polymethylmethacrylate bonding. In a further embodiment, the composite material has a coefficient of thermal expansion of about 10.0 10⁻⁶/° K to about 50.0×10⁻⁶/° K, which is advantageous for glass to PC/PMMA bonding. In contrast, for an elastomeric thermoplastic alone, the CTE is generally considerably higher (˜250-400 10⁻⁶/° K for example), while for a thermoset based adhesive alone (e.g., epoxy) the CTE is ranges between 55-80 (whereas in combination with the nanotubes described herein it is lowered to a range of 3.0-30.0×10⁻⁶/° K, for example).
In another embodiment of the disclosure, the thickness of the adhesive layer is between about 1 μm to about 1000 μm, or about 10 μm to about 500 μm, or about 100 μm to about 300 μm or about 250 μm.
The present disclosure further includes a laminated armor material, comprising

- i) a first armor material;
- ii) a second armor material; and
  an adhesive layer between the first and second armor materials which bonds the first armor material to the second armor material, wherein the adhesive layer comprises the composite material as defined above.

The present disclosure further includes a laminated armor panel comprising two or more layers of armor material and adhesive layers between each layer of armor material, which bonds the armor materials, wherein the adhesive layer comprises the composite material as defined above.
In one embodiment, about 80% or more, about 85% or more, or about 90% or more of the nanotubes in the composite material have an average angle of about 30°, of about 25°, or about 20° or less relative to the plane of the sheet defined as the x-y plane.
In another embodiment, the first and second armor material (or additional layers of armor materials) are the same or different and each are independently selected from ceramic, metal, glass, a polymeric material and fibre reinforced polymer composites.
In a further embodiment, the first and second armor materials (or additional layers of armor materials) are transparent.
In another embodiment, the first and second transparent armor material (or additional layers of armor materials) is glass or ceramic.
In another embodiment, the polymeric armor material is a thermoplastic material. In another embodiment, the thermoplastic material is polycarbonate or polymethylmethacrylate.
In another embodiment, the nanotubes comprise carbon nanotubes, boron-nitride nanotubes, boron-carbon-nitrogen nanotubes, silicon-carbide nanotubes, other nanoparticles (such as graphene nanoplatelets, or h-BN), hybrids of any two or more thereof, or a combination of any two or more thereof.
In a further embodiment, the nanotubes comprise boron nitride nanotubes, or other reinforcing particles that do not absorb visible light.
In a further embodiment, the amount of nanotubes in the composite material is about 5 wt % to about 50 wt %. In another embodiment, the first and second armor materials have a coefficient of thermal expansion of about 1.0 10⁻⁶/° K to about 10.0×10⁻⁶/° K, and the composite material has a coefficient of thermal expansion of about 3.0 10⁻⁶/° K to about 100.0×10⁻⁶/° K.
In another embodiment, the composite material has a coefficient of thermal expansion of about 3.0 10⁻⁶/° K to about 100.0×10⁻⁶/° K. In another embodiment, the composite material has a coefficient of thermal expansion of about 3.0 10⁻⁶/° K to about 10.0×10⁻⁶/° K, which is advantageous for glass to glass bonding (as armor materials). In a further embodiment, the composite material has a coefficient of thermal expansion of about 50.0 10⁻⁶/° K to about 70.0×10⁻⁶/° K, which is advantageous for polycarbonate and/or polymethylmethacrylate bonding (as armor materials). In a further embodiment, the composite material has a coefficient of thermal expansion of about 10.0 10⁻⁶/° K to about 50.0×10⁻⁶/° K, which is advantageous for glass to PC/PMMA bonding (as armor materials).
In another embodiment, the composite adhesive layer has a graded composition (i.e., varying content of nanotubes) in the thickness (z) direction.
In another embodiment, the laminated armor material is transparent wherein:

- the first armor material is glass;
- the second armor material is polycarbonate or polymethylmethacrylate; and
- the composite material comprises thermoplastic polyurethane and boron nitride nanotubes.

In another embodiment, the laminated armor material is transparent wherein (such as in FIG. 1):

- two or more armour material layers (for example, three layers, four layers, or five layers, or more) which are glass or ceramic layers bonded to each other using the composite materials of the disclosure;
- a backing layer of polycarbonate or polymethylmethacrylate is bonded to the multi-layer using the composite of the disclosure;
- wherein the composite material comprises thermoplastic polyurethane and boron nitride nanotubes.

The present disclosure further includes a process for preparing the composite material of the disclosure, the process comprising:

- i) obtaining a solution of a polymeric adhesive in a first solvent;
- ii) obtaining a suspension of nanotubes in a second solvent;
- iii) mixing the solution of the polymeric adhesive and the suspension of nanotubes together to form a mixture; and
- iv) filtering or spraying the mixture onto a substrate to obtain the composite material of the disclosure.

Other features and advantages of the present application will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples while indicating preferred embodiments of the application are given by way of illustration only, since various changes and modifications within the spirit and scope of the application will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will now be described in greater detail with reference to the drawings in which:

FIG. 1 is a schematic representation of a laminated armor material;

FIG. 2 is a graph of tensile curves for various composites of the disclosure.

FIGS. 3 (A and B) shows SEM images of the surface of BNNT-TPU composites of in embodiments of the disclosure.

FIG. 4(A) shows a representative nanotube (NT) in the composite adhesive sheet in an embodiment of the disclosure, while 4(B) is a graph showing the axes of the nanotube.

DESCRIPTION OF VARIOUS EMBODIMENTS

Definitions

Unless otherwise indicated, the definitions and embodiments described in this and other sections are intended to be applicable to all embodiments and aspects of the present disclosure herein described for which they are suitable as would be understood by a person skilled in the art.
The term “and/or” as used herein means that the listed items are present, or used, individually or in combination. In effect, this term means that “at least one of” or “one or more” of the listed items is used or present.
As used in the present disclosure, the singular forms “a”, “an” and “the” include plural references unless the content clearly dictates otherwise. For example, an embodiment including “a compound” should be understood to present certain aspects with one compound, or two or more additional compounds.
In embodiments comprising an “additional” or “second” component, such as an additional or second compound, the second component as used herein may be chemically different from the other components or first component. A “third” component may be different from the other, first, and second components, and further enumerated or “additional” components are similarly different. It is also contemplated that in some embodiments, the first, second, third, and/or additional components may be chemically the same. For example, the first armor material and the second armor material may be the same chemical material. For example, the first thermoplastic or thermosetting adhesive and the second thermoplastic or thermosetting adhesive may be the same thermoplastic or thermosetting adhesive. For example, the first nanomaterial filler and the second nanomaterial filler may be the same nanomaterial filler.
As used in this disclosure and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “include” and “includes”) or “containing” (and any form of containing, such as “contain” and “contains”), are inclusive or open-ended and do not exclude additional, unrecited elements or process steps.
The term “consisting” and its derivatives as used herein are intended to be closed terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, and also exclude the presence of other unstated features, elements, components, groups, integers and/or steps.
The term “consisting essentially of”, as used herein, is intended to specify the presence of the stated features, elements, components, groups, integers, and/or steps as well as those that do not materially affect the basic and novel characteristic(s) of these features, elements, components, groups, integers, and/or steps.
The terms “about”, “substantially” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies or unless the context suggests otherwise to a person skilled in the art.
The term “TPU” as used herein refers to thermoplastic polyurethane.
The term “CNT” as used here in refers to carbon nanotube.
The term “BNNT” as used herein refers to boron-nitride nanotubes.
The term “CTE” as used herein refers to the coefficient of thermal expansion.
The term “composite material” as used herein refers to a material in which two or more distinct substances combine to produce structural or functional properties not present in any individual component.
The term “sheet-like formation” as used herein refers to the shape of the composite material having x, y and z dimensions (or axis), and wherein the z dimension is significantly less than both the x and y dimensions. For example, the x and y dimensions can be measured in the centimeter or meter range (but not limited to such), while the z dimension can be measured in the micrometer or millimeter range (but not limited to such).
The phrase “oriented within the plane” or “in-plane orientation” as used herein refers to the orientation or direction of the central axis of each nanotube in the composite material relative to the plane defined by the surface of the composite material, wherein the composite material is defined as being parallel to the xy plane and the nanotubes have an orientation in the x and/or y dimension.
The term “laminated” as used herein means that the armor materials are constructed by stacking the materials or plies in layers to form the laminated material.
The term “armor material” as used herein refers to a material that can slow down, stop, neutralize, or lessen the impact of ballistic projectiles such as bullets, shells, shrapnel or fragments.
The term “thermoplastic adhesive” as used herein refers to polymer materials that melt at an elevated temperature and solidify on cooling to form strong bonds between a wide range of materials.
(I) Composites
The present disclosure is directed to a composite adhesive material which lessens the CTE mismatch between armor layers and the adhesive. In one embodiment, generally mixing components, such as nanotubes or other binders, into adhesives reduces the toughness (for example, tensile properties) of the adhesive. In the present disclosure, the process of preparing the composite material does not significantly impact the toughness of the adhesive material, and therefore maintains its adhesive properties while controlling the CTE. Accordingly, the present disclosure is directed to a composite material comprising:

In one embodiment, the portion of the nanotubes are preferentially oriented within the plane (i.e., x and y directions) of the composite material, and wherein the content and in-plane orientation of the nanotubes is sufficient to reduce the coefficient of thermal expansion (CTE) of the thermoplastic elastomer.
In one embodiment, nanotubes which lie completely flat only have orientation in the x and/or y dimensions and are in-plane, while nanotubes which stand completely erect only have orientation in the z dimension and are not in-plane. Nanotubes which lie on an angle and have, for example, orientation in the x, y and z dimensions also lie in-plane. In one embodiment, about 80% or more, about 85% or more, or about 90% or more of the nanotubes in the composite material have an average angle of less than about 30°, of less than about 25°, or less than about 20° relative to the plane of the sheet defined as the x-y plane.
In one embodiment, the CTE of the adhesive having nanotubes oriented in the x and y dimensions is anisotropic such that the CTE in the x and y directions (CTE_x,y) is less than the CTE in the z direction (CTE_z). Accordingly, in one embodiment, the nanotubes lying in the in-plane direction (x and y dimensions) of the sheet-like formation further reduces the thermal stress relative to the case of nanotubes randomly distributed and oriented in all directions.
In another embodiment, the amount of nanotubes in the composite material is about 5 wt % to about 50 wt %, or about 5 wt % to about 25 wt %, or about 5 wt % to about 20 wt %, or 5 wt %. In one embodiment, the amount of nanotubes in the composite material is at least 5 wt %.
In another embodiment, the adhesive is a thermoplastic adhesive or a thermoset. In one embodiment, the thermoplastic is thermoplastic polyurethane or polyvinyl butyral. In one embodiment, the thermoset is polyurethane, epoxy or silicone.
In one embodiment, the nanotubes comprise carbon nanotubes, boron-nitride nanotubes, boron-carbon-nitrogen nanotubes, silicon-carbide nanotubes, other nanoparticles, hybrids of any two or more thereof, or a combination of any two or more thereof. In one embodiment, the nanotubes are boron-nitride nanotubes.
In another embodiment, the composite material has a coefficient of thermal expansion of about 3.0 10⁻⁶/° K to about 100.0×10⁻⁶/° K. In another embodiment, the composite material has a coefficient of thermal expansion of about 3.0 10⁻⁶/° K to about 10.0×10⁻⁶/° K, which is advantageous for glass to glass bonding. In a further embodiment, the composite material has a coefficient of thermal expansion of about 50.0 10⁻⁶/° K to about 70.0×10⁻⁶/° K, which is advantageous for polycarbonate and polymethylmethacrylate bonding. In a further embodiment, the composite material has a coefficient of thermal expansion of about 10.0 10⁻⁶/° K to about 50.0×10⁻⁶/° K, which is advantageous for glass to PC/PMMA bonding.
In another embodiment of the disclosure, the thickness of the adhesive layer is between about 1 μm to about 1000 μm, or about 10 μm to about 500 μm, or about 100 μm to about 300 μm or about 250 μm.
(II) Laminated Armor Materials
The present disclosure also includes laminated armor materials comprising armor material which are bonded to each other using the composite material of the disclosure. In particular, the composite material lessens the mismatch of the CTEs between the armor materials and the adhesive layer, resulting in less delamination of the armor materials.
Accordingly, in one embodiment of the disclosure, there is included a laminated armor material, comprising

The present disclosure further includes a laminated armor panel comprising two or more layers of armor material and adhesive layers between each layer of armor material, which bonds the armor materials, wherein the adhesive layer comprises the composite material as defined above.
In one embodiment, nanotubes which lie completely flat only have orientation in the x and/or y dimensions and are in-plane, while nanotubes which stand completely erect only have orientation in the z dimension and are not in-plane. Nanotubes which lie on an angle and have, for example, orientation in the x, y and z dimensions also lie in-plane. In one embodiment, about 80% or more, about 85% or more, or about 90% or more of the nanotubes in the composite material have an average angle of about 30°, of about 25°, or about 20° or less relative to the plane of the sheet defined as the x-y plane.
In one embodiment, nanotubes lying in the in-plane direction (x and y dimensions) of the sheet-like formation reduces the in plane coefficient of thermal expansion (CTExy) of the thermoplastic adhesive relative to that in the z direction or of a similar composite with nanotubes randomly oriented in all directions. In one embodiment, the CTE of the adhesive having nanotubes oriented in the x and y dimensions is anisotropic such that the CTE in the x and y directions (CTE_x,y) is less than the CTE in the z direction (CTE_z). Accordingly, in one embodiment, the nanotubes lying in the in-plane direction (x and y dimensions) of the sheet-like formation further reduces the thermal stress relative to the case of nanotubes randomly distributed and oriented in all directions.
In another embodiment, the first and second armor material are the same or different and each are independently selected from ceramic, metal, glass, a polymeric material and fibre reinforced polymer composites.
In a further embodiment, the first and second armor materials are transparent. For example, the first and second transparent armor material is glass or ceramic.
In another embodiment, the polymeric armor material is a thermoplastic material. In another embodiment, the thermoplastic material is polycarbonate or polymethylmethacrylate.
In another embodiment, the laminated armor material is a multi-layer structure having two or more layers of glass or ceramic armor materials each bound to each other using the composite material of the disclosure, and a backing layer of a polymeric armor material (such as polycarbonate or polymethylmethacrylate) bound to the multi-layer glass and/or ceramic layers using the composite material.
In another embodiment, the nanotubes comprise carbon nanotubes, boron-nitride nanotubes, boron-carbon-nitrogen nanotubes, silicon-carbide nanotubes, other nanoparticles, hybrids of any two or more thereof, or a combination of any two or more thereof.
In a further embodiment, the nanotubes comprise boron nitride nanotubes, or other transparent reinforcing particles. In another embodiment, the nanotubes are transparent and are boron nitride nanotubes.
In a further embodiment, the amount of nanotubes in the composite material is about 5 wt % to about 50 wt %, or about 5 wt % to about 25 wt %, or about 5 wt % to about 20 wt %, or 5 wt %. In one embodiment, the amount of nanotubes in the composite material is at least 5 wt %.
In one embodiment, the portion of the nanotubes in the in-plane orientation in the x and y dimension is sufficient to reduce the coefficient of thermal expansion of the thermoplastic adhesive.
In another embodiment, the composite material has a coefficient of thermal expansion of about 3.0×10⁻⁶/° K to about 100.0×10⁻⁶/° K.
In another embodiment, the first and second armor materials (or additional layers of armor materials) have a coefficient of thermal expansion of about 1.0×10⁻⁶/° K to about 10.0×10⁻⁶/° K, and the composite material has a coefficient of thermal expansion of about 3.0×10⁻⁶/° K to about 100.0×10⁻⁶/° K.
In another embodiment, the first and second armor materials (or additional layers of armor materials) are transparent (for example, glass or ceramic) and have a coefficient of thermal expansion of about 1.0×10⁻⁶/° K to about 10.0×10⁻⁶/° K, and the composite material has a coefficient of thermal expansion of about 3.0×10⁻⁶/° K to about 10.0×10⁻⁶/° K.
In one embodiment, the first armor material has a coefficient of thermal expansion of about 1.0×10⁻⁶/° K to about 10.0×10⁻⁶/° K, the second armor material has a coefficient of thermal expansion of about 50.0×10⁻⁶/° K to about 70.0×10⁻⁶/° K, and the composite material has a coefficient of thermal expansion of about 10.×0 10⁻⁶/° K to about 50.0×10⁻⁶/° K.
In another embodiment, the laminated armor material is transparent wherein:

In another embodiment, the composite adhesive layer has a graded composition (i.e., varying content of nanotubes) in the thickness (z) direction between the first and second armor materials. In such an embodiment, the amount of nanotubes in the composite material varies in the z direction of the layer and this variation can be in discrete steps, such as can be achieved by combining multiple composite material layers of different composition, or continuous, such as achieved by varying the composition during preparation of a single composite layer. In another embodiment, the laminated armor material is a multi-layer material having more than two armor materials, in which each subsequent armor material is bonded to the adjacent armor material using the composite material of the disclosure. For example, a three-layer laminated armor material comprises a first armor material, a first adhesive layer which is the composite material, a second armor material, a second adhesive layer which is the composite material, and a third armor material. In one embodiment, the first, second and third armor materials are the same or different, and can be, for example, glass as a transparent armor material, and wherein the composite material comprises a thermoplastic adhesive and BNNT. In another embodiment, a fourth armor material, a fifth armor material, etc., can be added to the laminated material.
In one embodiment, FIG. 1 is a schematic representation of a laminated armor material 10 having four armor layers. The armor layers 12 and the backing armor layer 14 are bonded together through adhesive layers 16. The arrow 18 shows the direction of a projectile, such as a bullet.
In another embodiment, the CTE of the various layers of the laminated armor material is controlled and selected such that the thermal stresses remain sufficiently low as to reduce disbanding.
(III) Process for Preparing the Composite
The present disclosure further includes a process for preparing the composite material of the disclosure, the process comprising:

- i) obtaining a solution of a polymeric adhesive in a first solvent;
- ii) obtaining a suspension of nanotubes in a second solvent;
- iii) mixing the solution of the polymeric adhesive and the suspension of nanotubes together to form a mixture; and
- iv) filtering, spraying, or casting the mixture onto a substrate to obtain the composite material of the disclosure.

In one embodiment, the first solvent is THF, acetone, DMF or other suitable solvent for dissolving the adhesive.
In another embodiment, the second solvent is THF, acetone, DMF, methanol or ethanol.
In another embodiment, when the mixture is filtered as in step iv), the polymeric adhesive is substantially not soluble in the second solvent, and the first and second solvents are miscible in one another.
In another embodiment, when the mixture is sprayed in step iv), the first solvent and the second solvent are the same.
Although the disclosure has been described in conjunction with specific embodiments thereof, if is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present disclosure.

EXAMPLES

The operation of the disclosure is illustrated by the following representative examples. As is apparent to those skilled in the art, many of the details of the examples may be changed while still practicing the disclosure described herein.

Example 1—Preparation of NT-TPU Sheets

The process reported in Martinez-Rubi et al. [Fabrication of high content carbon nanotube-polyurethane sheets with tailorable properties, ACS Appl. Mater. Interfaces (2017) 9, 36, 30840-30849.] was used for producing CNT-TPU sheets and it was adapted for producing BNNT-TPU sheets. The method makes use of a TPU solvent/non-solvent combination to control adsorption of TPU on the high aspect ratio and high surface area nanomaterials creating strong interfacial associations between TPU and NTs. The compositions are controlled by adjusting the ratio of NTs to TPU in solution (Table 1). By changing the TPU concentration in solution a broad range of compositions (i.e., NT:TPU weight ratios) was obtained. Nonwoven sheets/fabrics of TPU-coated NTs, where a network of nanotubes is randomly oriented in plane, are recovered by vacuum filtration of the above suspensions. Briefly, for CNT-TPU nanocomposites, CNTs were first dispersed in methanol (0.4 mg/m L) by sonication and, separately, TPU was dissolved in acetone. For BNNT-TPU nanocomposite, BNNTs were first dispersed in methanol (0.6 mg/mL) by sonication and, separately, TPU was dissolved in THF. The dispersed NTs were subsequently combined with the TPU solution, followed by additional sonication cycles. Nonwoven NT-TPU sheet were then recovered by vacuum filtration, dried flat at room temperature and at 75° C. for 5 hours.

TABLE 1

Composition and properties of NT-TPU composite
sheets at different NT:TPU weight ratios

NT/TPU

Density

Thickness

Volume fraction (vol. %)

Sample	wt. ratio	wt. ratio	(g/cm³)	(μm)	NT	TPU	Void

In solution¹

CNT-TPU Sheets

CNPU-55	1:1.5	45:55	0.70	98	19	31	50
CNPU-65	1:2.5	35:65	0.94	97	19	51	29
CNPU-80	1:5	20:80	1.12	139	13	75	12

In solution²

BNNT-TPU Sheets

BNPU-55	1:1	55:45	0.809	72	23	31	46
BNPU-45	1:1.5	45:55	0.883	80	21	41	38
BNPU-40	1:2	40:60	1.146	71	23	59	18
BNPU-30	1:3	30:70	1.194	91	18	71	11
BNPU-20	1:4	20:80	1.109	123	14	71	15

¹methanol/acetone and
²methanol/THF solvent/non-solvent mixtures

To enable measurement of thermal expansion with high BNNT content, 30 cm×30 cm sheets were produced by the filtration process.
These sheets were cut to 2.5 cm squares, and squares were stacked and consolidated/densified by hot press lamination to produce thick specimens (˜4-5 mm thick) with similar in-plane orientation.
Specimens were cut for both in-plane and through thickness CTE measurements using thermomechanical analysis (TA Instruments Q400). Each specimen was exposed to 3 thermal cycles (from 25° C. to 60° C. and vice versa; temperature rate: 2° C./min) while dimensional changes were measured (static load: 2 mN). Table 2 summarizes CTE of TPU and several CNT-based and BNNT-based nanocomposites).

TABLE 2

Measurement of Coefficient of Thermal Expansion of Various Composites

		INITIAL	DISPLACEMENT	CTE
	DIRECTION OF	DIMENSION	CHANGE	(μm/
SPECIMEN	MEASUREMENT	(mm)	(μm/° C.)	° C.)

TPU	In-plane	8.02	2.26	282
BASELINE
TPU	In-plane	9.40	2.88	306
BASELINE
(REPEAT)
TPU	Through-	5.09	1.75	344
BASELINE	thickness
TPU	Through-	4.70	1.34	286
BASELINE	thickness
(REPEAT)
BNPU-40	In-plane	9.64	0.53	54
	Through-	4.71	1.91	405
	thickness
CNPU-80	In-plane	8.03	0.38	47
	Through-	6.42	0.66	103
	thickness
CNPU-65	In-plane	9.58	0.27	28
	Through-	4.56	0.23	50
	thickness
CNPU-55	In-plane	8.11	0.10	12
	Through-	4.97	0.084	17
	thickness

Tensile testing was performed on a single layer sheet using a tensile test frame (a Criterion Model 41). A minimum of five strips (˜30 mm×2 mm) of each material were tested at a displacement rate of 5 mm/min and initial gauge length of ˜20 mm. Table 3 reports tensile properties of composite adhesive sheets as compared to the baseline TPU. A representative strain-strain curves for each composite adhesive sheet is displayed in FIG. 2.

TABLE 3

Summary of tensile mechanical properties of BNNT-TPU nanocomposite sheets

	BNNT-TPU
	wt. ratio	E	σ_fail	σ_ε=30%	ε_fail	G_t
Sample	(%)	(MPa)	(MPa)	(MPa)	(%)	(MJ/m³)

BNPU-55	55:45	942 ± 140	12 ± 0.4		11 ± 2	1.1 ± 0.2
BNPU-45	45:55	1152 ± 147	15 ± 1		9 ± 1	1.2 ± 0.2
BNPU-40	40:60	1458 ± 98	22 ± 0.5	18.9 ± 0.5	94 ± 24	21 ± 5
BNPU-30	30:70	995 ± 122	18 ± 1	14.5 ± 0.5	212 ± 28	37 ± 5
BNPU-20	20:80	694 ± 68	18 ± 1	13.0 ± 0.5	336 ± 64	55 ± 11
TPU	0:100	120 ± 8	34b	5.3 ± 0.3	580^a	35^a

^aFrom the manufacturer data sheet.

FIG. 3 shows SEM images of the surface of BNNT-TPU composites sheets fabricated by the one-step filtration method at different BNNT/TPU weight rations. BNNTs can be seen randomly oriented in-plane, together with some non-tubular impurities, forming nonwoven BNNT-TPU sheets.

Example 2—Nanotube Partial Alignment with Respect to x, y Plane

FIG. 4(A) shows a representative nanotube (NT) in the composite adhesive sheet in an embodiment of the disclosure, while 3(B) is a graph showing the axes of the nanotube. The L_NTrepresents a linear regression of nanotube, and defined in such a way that the summation of distances between each point on NT and L_NTis minimized. Θ is the angle between L_NTand x and y plane (z=0).
While the present disclosure has been described with reference to what are presently considered to be the preferred examples, it is to be understood that the application is not limited to the examples described herein. To the contrary, the present disclosure is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
All publications, patents and patent applications are herein incorporated by reference in their entirety to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference in its entirety. Where a term in the present disclosure is found to be defined differently in a document incorporated herein by reference, the definition provided herein is to serve as the definition for the term.

Claims

1. A composite material comprising:

a) an adhesive; and

b) nanotubes;

wherein the composite material is in a sheet-like formation having x, y and z dimensions, wherein the measurement of the z dimension is less than the x and y dimensions, and wherein a portion of the nanotubes are oriented within the plane in the x and y dimensions of the composite material, and wherein the in-plane orientation of the nanotubes is sufficient to reduce the coefficient of thermal expansion (CTE) of the adhesive.

2. The composite material of claim 1, wherein the CTE of the composite adhesive in the x and y dimensions (CTE_x,y) is less than the CTE of the composite adhesive in the z dimension (CTE_z).

3. The composite material according to claim 1, wherein the amount of nanotubes in the composite material is about 5 wt % to about 50 wt %.

4. The composite material according to claim 3, wherein the amount of nanotubes in the composite material is about 5 wt % to about 25 wt %.

5. The composite material according to claim 4, wherein the amount of nanotubes in the composite material is about 5 wt % to about 20 wt %.

6. The composite material according to claim 1, wherein the amount of nanotubes in the composite material is at least 5 wt %.

7. The composite material according to claim 1, wherein about 80% or more of the nanotubes in the composite material have an average angle of about 30° or less relative to the plane of the sheet defined as the x-y plane.

8. The composite material according to claim 1, wherein the adhesive is a thermoplastic or a thermoset polyurethane.

9. The composite material according to claim 1, wherein the nanotubes comprise carbon nanotubes, boron-nitride nanotubes, boron-carbon-nitrogen nanotubes, silicon-carbide nanotubes, other nanoparticles, hybrids of any two or more thereof, or a combination of any two or more thereof.

10. The composite material according to claim 9, wherein the nanotubes are boron-nitride nanotubes.

11. The composite material according to claim 1, wherein the composite material has a coefficient of thermal expansion of about 3.0 10⁻⁶/° K to about 100.0×10⁻⁶/° K.

12. The composite material of claim 11, wherein the composite material has a coefficient of thermal expansion of about 3.0 10⁻⁶/° K to about 10.0×10⁻⁶/° K.

13. The composite material of claim 11, wherein the composite material has a coefficient of thermal expansion of about 50.0 10⁻⁶/° K to about 70.0×10⁻⁶/° K.

14. The composite material according to claim 1, wherein the z dimension of the composite material is between about 1 μm to about 1000 μm.

15. A laminated armor material, comprising

a) two or more armor materials; and

b) an adhesive layer between the armor materials which bonds the armor materials together, wherein the adhesive layer comprises the composite material as defined in claim 1.

16. The laminated armor material according to claim 15, wherein about 90% or more of the nanotubes in the composite material have an average angle of about 20° or less relative to the plane of the sheet defined as the x-y plane.

17. The laminated armor material according to claim 15, wherein the armor materials are the same or different and each are independently selected from ceramic, metal, glass, a polymeric material and fibre reinforced polymer composites.

18. The laminated armor material according to claim 15, wherein the armor materials are transparent.

19. The laminated armor material according to claim 18, wherein the transparent armor material is glass or ceramic.

20. The laminated armor material according to claim 17, wherein the polymeric armor material is a thermoplastic material.

21. The laminated armor material according to claim 20, wherein the thermoplastic material is polycarbonate or polymethylmethacrylate.

22. The laminated armor material according to claim 15, wherein the nanotubes comprise carbon nanotubes, boron-nitride nanotubes, boron-carbon-nitrogen nanotubes, silicon-carbide nanotubes, other nanoparticles, hybrids of any two or more thereof, or a combination of any two or more thereof.

23. The laminated armor material according to claim 22, wherein the nanotubes comprise boron nitride nanotubes, or other transparent reinforcing particles.

24. The laminated armor material according to claim 15, wherein the amount of nanotubes in the composite material is about 5 wt % to about 50 wt %.

25. The laminated armor material according to claim 15, wherein the armor materials have a coefficient of thermal expansion of about 1.0 10⁻⁶/° K to about 10.0×10⁻⁶/° K, and the composite material has a coefficient of thermal expansion of about 3.0 10⁻⁶/° K to about 10.0×10⁻⁶/° K

26. The laminated armor material according to claim 15, wherein a first armor material has a coefficient of thermal expansion of about 1.0 10⁻⁶/° K to about 10.0×10⁻⁶/° K, a second armor material has a coefficient of thermal expansion of about 50.0 10⁻⁶/° K to about 70.0×10⁻⁶/° K, and the composite material has a coefficient of thermal expansion of about 10.0 10⁻⁶/° K to about 50.0×10⁻⁶/° K.

27. The laminated amor material according to claim 15, wherein the composite adhesive layer has a graded composition in the thickness (z) direction.

28. The laminated armor material according to claim 15, wherein the laminated armor material is transparent and comprises a first and second armor material wherein:

a) the first armor material is glass;

b) the second armor material is polycarbonate or polymethylmethacrylate; and

c) the composite material comprises thermoplastic polyurethane and boron nitride nanotubes.

29. A process for preparing the composite material of claim 1, the process comprising:

a) obtaining a solution of an polymeric adhesive in a first solvent;

b) obtaining a suspension of nanotubes in a second solvent;

c) mixing the solution of the polymeric adhesive and the suspension of nanotubes together to form a mixture;

d) filtering or spraying the mixture onto a substrate to obtain the composite material of claim 1.