WO2019097435A1

WO2019097435A1 - Ultra high strength composite and process for preparation thereof

Info

Publication number: WO2019097435A1
Application number: PCT/IB2018/058980
Authority: WO
Inventors: Ajit Behari Mathur; Satya Srinivasa Rao GANDHAM; Devesh Kumar SHUKLA; Raksh Vir Jasra; Sateesh BONDA; Sandeep Nath TRIPATHI; Gaurang Manilal MEHTA; Abhishek PATATE
Original assignee: Reliance Industries Limited
Priority date: 2017-11-15
Filing date: 2018-11-15
Publication date: 2019-05-23

Abstract

The present disclosure relates to a process for preparation of ultrahigh strength polyethylene composite. The process comprises compacting an oriented polyethylene layer and at least one polymer matrix, followed by fusion to obtain ultrahigh strength polyethylene composite. The composite in accordance with the present disclosure has superior resistance of composites to high speed impact loading and easy dissipation of heat due to high thermal conductivity.

Description

ULTRA HIGH STRENGTH COMPOSITE AND PROCESS FOR PREPARATION THEREOF

FIELD

The present disclosure relates to ultra high strength composite and a process for preparation thereof.

DEFINITIONS

As used in the present disclosure, the following words and phrases are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used to indicate otherwise.

The term“composite” refers to a material made by combining two or more constituent materials with significantly different physical or chemical properties, to produce a material with characteristics different from the individual components.

The term“DPE” relates to disentangled ultra high molecular weight polyethylene used in the context of the present disclosure refers to a homo-polymer or copolymer of ethylene having molar mass in the range of less than 0.3 Million/g mole to 20 Million/g mole, crystallinity greater than 75%; heat of fusion greater than 180 J/g and bulk density ranging from 0.048 to 0.3 g/cc; wherein the polyethylene chains have low entanglement or are completely disentangled. The term‘UHMWPE’ is used for ultra high molecular weight polyethylene.

The term“polymer matrix” used in the context of the present disclosure refers to an organic polymer matrix used to bind reinforcing member like fibers, tape or film. The term“ASTM D4020” used in context to the present disclosure refers to a standard method for measurement of intrinsic viscosity of Ultra-High-Molecular-Weight Polyethylene molding and extrusion materials. The term“Mark-Houwink equation” used in context to the present disclosure refers the relation between intrinsic viscosity and molecular weight. From this equation the viscosity average molecular weight (MW) of a polymer can be determined from data on the intrinsic viscosity and vice versa. The term“RDA-III” used in context to the present disclosure refers to Rheometrics Dynamic Analyser (RDA-III) used for melt rheological analysis of polymers.

BACKGROUND The background information herein below relates to the present disclosure but is not necessarily prior art.

Ultra high strength polymer fibers are known for their applications for making products which can withstand high loading rate and can be used in protecting devices. Articles such as bullet resistant vests, helmets, vehicle panels and structural members of military equipment are typically made from fabrics comprising high strength fibers. In case of impact of a projectile, a compacted sheet made of multiple layers of cloth of such fibers require the fiber property to first catch the projectile and then consume deformational energy (energy dissipation). High strength fibers conventionally used include polyethylene fibers, aramid fibers such as poly (phenylenediamine terephthalamide), graphite fibers, nylon fibers, glass fibers and the like. Aromatic amide (Kevlar) and UHMWPE fiber (Dyneema) are commonly known for such applications. Ballistic -resistant articles as hard or soft armor articles such as helmets, panels and vests are known. Soft-ballistic articles are used in bullet proof vests and hard-ballistic articles (which are molded bodies) are used as shields in another type of bulletproof vests, helmets, etc. Further, ballistic-resistant articles are used in vehicles, buildings, and other objects intended to help protect people, animals, or goods from ballistic impact.

Fibers, such as aramid, or polyethylene is required to be compacted to convert them into ballistic product under compressive load, wherein the fibers fuse into a single object. Depending on the application, the sheets may be pressed together to form a molded article, or bonded together at the edges to form a soft-ballistic article. The process of converting fibers into such products is cumbersome and requires multiple steps for complete fabrication.

Therefore, there is felt a need for a process for preparing ultra high strength composite having improved properties that mitigates the aforestated drawbacks.

OBJECTS

Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:

It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.

An object of the present disclosure is to provide an ultra high strength composite. Another object of the present disclosure is to provide a process for preparing an ultra high strength composite.

Another object of the present disclosure is to provide an ultra high strength composite having comparatively superior properties of high speed impact loading.

Still another object of the present disclosure is to provide an ultra high strength composite having easy dissipation of heat due to high thermal conductivity. Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY

The present disclosure provides a process for preparing an ultrahigh strength polyethylene composite. The process comprises stacking at least two layers of disentangled ultrahigh molecular weight polyethylene (DPE) tape having a thickness in the range of 5m to 50m and width to thickness ratio in the range of 50 to 20000, such that the direction of the length of first layer of the DPE tape is perpendicular to the length of the layer stacked above the first layer to obtain a stacked layer. The stacked layer is compacted with a compressing force at a pressure in the range of 1 bar to 700 bar to obtain a compacted layer. The so obtained compacted layer is fused by heating to a temperature below the melt temperature of the DPE to obtain the ultrahigh strength polyethylene (PE) composite.

The present disclosure further provides an ultrahigh strength PE composite comprising a stack of disentangled ultrahigh molecular weight polyethylene (DPE) tape. The stack of DPE tape has a width in the range of 1 - 100 mm and having a thickness in the range of 5m to 50m. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

The ultra high strength composite of the present disclosure will now be described with the help of the accompanying drawing, in which: FIG. 1 illustrates DPE tape/LDPE composite sheet exhibiting resistance to perforation behaviour of the composite sheet in accordance with the present disclosure.

DETAILED DESCRIPTION

Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.

Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.

The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising,"“including,” and“having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.

As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.

The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third, etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.

Although, ultra high strength polymeric fibers have been used in PE application where high resistance to impact load is required, however, conversion of fibers to the composite sheet form is a difficult process and establishing the consistency in the product is even more difficult.

Therefore, the present disclosure provides an ultra high strength composite having superior resistance to high speed impact loading and having easy dissipation of heat due to thermal conductivity of reinforcing member i.e. DPE tape and process for preparation thereof.

The process for preparing an ultrahigh strength PE composite of the present disclosure comprises stacking at least two layers of disentangled ultrahigh molecular weight polyethylene (disentangled UHMWPE) tape having a thickness in the range of 5m to 50m and width to thickness ratio in the range of 50 to 20000 , such that the direction of the length of first layer of the disentangled UHMWE tape is perpendicular to the length of the layer stacked above the first layer to obtain a stacked layer. In one embodiment, the DPE tape has a width to thickness ratio is in the range of 4000 to 6000. In accordance with the present disclosure DPE tape relates to disentangled ultra high molecular weight polyethylene tape used in the context of the present disclosure refers to a homo-polymer or copolymer of ethylene having molar mass in the range of less than 0.3 Million/ gmole to 20 Million/ gmole, crystallinity greater than 75%; heat of fusion greater than 180 J/g and bulk density ranging from 0.048 to 0.3 g/cc; wherein the polyethylene chains have low entanglement or are completely disentangled. The term‘UHMWPE’ is used for entangled ultra high molecular weight polyethylene.

The DPE tape or film has a thickness in the range of 5m to 20m and width to thickness ratio is in the range of 50 to 20000. In one embodiment, the DPE tape has a width to thickness ratio is in the range of 4000 to 6000.

In one embodiment, the DPE tapes having width in the range of 1.0 mm to 100 mm; thickness at least in the range from 5 m to 50 m, more specifically 5 m to 25 m and even more preferably 5m to 20 m, tensile strength in the range from 1.8 GPa to 4.0 GPa and tensile modulus 100 GPa to 200 GPa, and the axial thermal conductivity in the range from 30 W/mK to 200 W/mK, more preferably > 50 W/mK are used. Typically the DPE tapes used are transparent and glossy.

In another embodiment, the process of the present disclosure further comprises subjecting DPE tape or film and optionally at least one other reinforcing matrix to compaction followed by fusion to obtain ultra high strength composite. The reinforcing matrix can be selected from the group consisting of oriented fiber or tape of aromatic imide, carbon fiber, polyester, glass, ceramic, etc. which also forms part with DPE tape in precursor to achieve a balance of resistance to load, energy dissipation, deformation and shear. In an exemplary embodiment a combination of DPE tape and fabric of ultra-high molecular weight fiber can also be arranged in different or same layers of precursor.

In accordance with the present disclosure, the disentangled ultrahigh molecular weight polyethylene (DPE) tape is prepared by using DPE powder, having molecules in disentangled state, a stabilizer, and an additive.

Typically DPE powder is characterized by viscosity average molecular weight and molecular weight distribution in the range from 1.0 million g/mole to 20 million g/mole and 4 - 25, respectively. The intrinsic viscosity is measured as per ASTM D4020-la; and the viscosity average molecular weight is calculated by the Mark-Houwink equation: M = K[h]^a where K and a are constants, K=53700, a = 1.37 and h = intrinsic viscosity and molecular weight distribution measured by melt rheology using RDA -III from TA Instruments employing Orchestrator software. The heat of fusion (AH) of DPE powder, measured by differential scanning calorimeter can be above 180 J/g and the bulk density is 0.3 g/cc or below. DPE powder is further characterized by increase in elastic modulus, represented by a ratio of G’/Go (G’ is the elastic modulus at any point in the curve and Go is the initial elastic modulus) with time above the melt temperature when tested on strain controlled rheometer having a parallel plate assembly (RDA-III), as disentangled polymer chains tend to entangle on application of shearing in sinusoidal tests.

Stabilizers can be mixed with DPE powder for the preparation of the DPE tape for providing thermal and thermo-oxidative stability to DPE powder while processing into DPE tape and during actual usage. The stabilizers used are amongst the common class of stabilizers which includes, but are not limited to, substituted phenols, amines, alkyl, aryl, and mixed alkyl-aryl phosphites/phosphonites, alkyl, aryl, and mixed phosphates, lactone (3-arrylbenzofuran-2- one), thioesters, thio compounds containing oxidizable sulphur and aryl nitroso compounds mainly tetrakis(2,4-di-tert-butylphenyl) 4, 4’-bisphenylene diphosphonite, bis(2,4 di-t- butylphenyl)pentaerythritol diphosphate, tris(2,4-di-t-butylphenyl)phosphate, bis(2, 2,6,6- tetramethyl-4-piperidinyl)sebacate, 2,4,6-tri-t-butylphenyl 2-butyl— 2-ethyl-, 1, 3-propanediol phosphate, octadecyl 3,5 di-tert-butyl-4-hydroxyhydrocinnamate, 5,7-di-tert-butyl-3-(3,4 dimethylphenyl)-3H-benzofuran-2-one, Pentaerythritol tetrakis(3,5-di-ferf-butyl-4- hydroxyhydrocinnamate), 5,7-di-t-butyl-3-(3,4 dimethylphenyl)-3H-benzofuran-2-one, tetrakismethylene (3,5-di-t-butyl-4- hydroxyhydrocinnamate)methane, disterythiodropinate] or mixtures thereof are premixed in the range of 4000 - 8000 ppm in DPE resin. Photo stabilizers such as 2-2’-Hydroxy-3’-tert.butyl-5’-methylphenyl)-5-chloro-benzotrazole, N, N’-(2-ethyl-2’ethoxy-5’-tert.butylphenyl)-oxalamide, bis-2, 2, 6, 6-tetramethyl-4-piperidyl sebacate and mixtures thereof can also be used. The concentration of the photo stabilizer is in the range from 2000 - 5000 ppm, which provides photo-oxidative stability (UV radiation stability) to its final product during outdoor exposure in sunlight. In addition to stabilizers, as per the present disclosure at least one additive can be added in the DPE powder while preparing the DPE tape. The additive is at least one selected from the group consisting of carbon black, graphene, carbon nano tube, colorants, inorganic fillers like calcium carbonate, talc, Ti(¾_. These additives can also be added during conversion of ethylene to DPE (in-situ additivation) or after polymerization, before converting them into tape. In one embodiment, nano sized additives are preferably used. These additives can meet the functional requirements like adhesion with the matrix layer, aesthetics, energy dissipation and high energy absorption, long term mechanical properties, deformational resistance on application of load, electro-magnetic shielding, and the like.

In one embodiment, multilayer DPE tapes having different layers prepared by un-additivated and/or additivated DPE are also used to add such functionalities in the composite product. The stacked layer is compacted with a compressing force at a pressure in the range of 1 bar to 700 bar to obtain compacted layer more preferably 100 bar to 200 bar. The so obtained compacted layer is fused by heating to a temperature below the melt temperature of the disentangled ultrahigh molecular weight polyethylene to obtain the ultrahigh strength polyethylene composite.

The process of DPE composite involves preparation of the DPE tape precursor. In an embodiment DPE tapes are folded while placing them parallel and avoiding any gap between them in such numbers that their assembly attains the required length and width of composite sheet in the nonwoven state.

In another embodiment, the required lengths of the DPE tape are cut and placed to make layers of required width and length of composite precursor.

In yet another embodiment a wide width of the continuous fabric form is prepared by aligning the DPE tapes parallel to each other and stacking the alternate layers in a position other than parallel with or without the use of the matrix material.

Every alternate layer of the tape is preferably placed perpendicular to the adjoining layer i.e. 90°. Some of the layers of tape are placed at other angles between 1° and 90°. As per the required thickness of the composite, the number of layers is aligned one over the other preferably keeping each following layer at >10° angle than the nearest neighbour (adjoining layer) and more specifically at 90°.

The DPE tape of the same thickness and same width are used to prepare DPE tape precursor of composite. In one embodiment DPE tapes of different thickness and different width can also be used in the preparation of composite precursor so that the possible gaps between the parallel aligned tapes in the other layers are fully covered. DPE tapes of the same thickness are preferably used to prepare each layer of reinforcing component of composite.

In an embodiment the DPE tape can also be woven wherein weft moves in warp member in a uniform or random fashion, alternately or at different regular intervals providing a good physical entanglement of tapes in the precursor.

The stack of layers (woven or non-woven) in the precursor, as per the required thickness of the composite, can also be prepared by folding continuous length of tapes such that each member of the tape is a continuous piece in the product in the final composite which can provide high resistance to deformation on the application of different types of load. Conventionally, the reinforcing member of the composite generally used are cut pieces of high strength tape or fabric made of high strength fiber or film, according to the shape and size of each layer as per composite design and stacked in typical order. In accordance with the present disclosure a long and continuous length of DPE tape are folded to prepare the layers of precursor used to fabricate composite. This continuous or long length DPE tape used for composite can help in providing high deformation resistance on high impact loading or sudden loading as compared to cut pieces used as per the size of the tape. The superior performance of composite prepared by continuous length of tape can be suitable in fabricating composite with lower areal weight than conventional product of similar application.

The combination of woven or non-woven layers of tape in the precursor can also be stacked depending of the functional requirement of the composite and magnitude of load, type of load and energy dissipation which it should resist, wherein woven part in the final composite may range up to 75% of the reinforcing material. In accordance with the present disclosure the DPE film or tape of length as per required width of the composite sheet can also be cut wherein the width of the film can be as wide as 500 mm. The film can be uniaxially or biaxially oriented and can form a member of composite sheet.

In an embodiment a combination of DPE tape and polymer matrix is arranged in different or same layer to form a precursor. Precursor is basically assembly of tapes where matrix can be inserted like a polyethylene film or resin like epoxy is impregnated. Precursor can also be a combined piece having tape layers and matrix. In another embodiment oriented fiber or tape of aromatic imide, carbon fiber, polyester, glass, ceramic, etc. is used along with DPE tape in the preparation of the precursor to achieve a balance of resistance to load, energy dissipation, deformation and shear. The fabric of DPE fiber, tape and fiber of other materials can also add to better binding strength of each member in the composite layers. The concentration of the fiber, fabric or tape of the reinforcing material other than DPE tape can vary up to 75% of the total reinforcing material in the composite.

The matrix materials used for binding the tape/fiber layers of precursor to prepare composite sheet include low density polyethylene, linear low density polyethylene, ethylene vinyl acetate copolymer (vinyl acetate concentration from 5 - 30%), polyethylene wax and other ethylene polymers (with or without halogenation), polyurethanes (thermoplastic polyurethane, long aliphatic chain containing thermoset polyurethane with and without chemically bonded flame retardants), ethylene acrylic acid copolymer, hyper branched polymers including polyesters, polyamides, polyimides, polyurethanes, epoxy resin, polyester resin, cyanoacrylate, latex, elastomers, polyisobutylene, etc. The matrix or mixture thereof can be applied on the reinforcing material in the form of powder, low viscosity fluid, solution or thin film while shaping the precursor into the required shape of composite.

The precursor with or without matrix so obtained can be shaped into the required form by compression at a pressure in the range from 1 bar to 700 bar and more specifically 100 bar to 200 bar and temperature in the range from 10 °C to 130 °C, depending on the required physical strength of the composite and curing efficiency or shaping characteristics of the matrix. In one embodiment, the DPE tape is surface pre-treated for functionalization by the method selected from surface oxidation by corona or plasma treatment, grafting of polar monomers, sulfonation and the like, before fabrication of precursor to achieve good surface adhesion with the matrix. It is ensured that any of the required properties of DPE tape do not drop by >10% during surface pre-treatment.

The reinforcing tape and / or fiber layers of the precursor are stacked such that the composite

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thickness of 1 mm to 30 mm is achieved with areal weight from 1 to 15 Kg/m .

The composite sheet made up of woven or non-woven tape and / or fiber and / or fabric / or film, with or without matrix and can be prepared under high pressure and temperature. The temperature for compression of the precursor remains at least 10 °C below the melt temperature of DPE tape and other reinforcing members and close to the curing or softening temperature of matrix and the pressure can be as high as 500 bar. The composite can be considered as soft and flexible composite wherein the matrix after curing remains rubbery or soft. Such composite layers can also be stacked and / or stitched to form a final finished form for load resistant product (soft ballistic resistant product). The number of reinforcing member layers can be selected as per the functional requirements of the product. The areal weight of the product remains below 5 kg/m . A rigid composite can be obtained by having DPE layers in the precursor for a soft composite product and matrix which on curing or cooling becomes hard and rigid (hard ballistic resistant products). The aerial weight of such product can be lower than 15 Kg/m .

Further, in accordance with the present disclosure the number of layers of tape required to build a specific thickness of composite are more for thin tapes as compared to the number of layers of relatively thicker tape as this provide stronger reinforcing effect even if the strength of both is in close range. Typically in the present disclosure the tapes of thickness < 20 microns (more specifically 10 to 15 microns) are used as compared to commonly used tape or fiber (thickness >20 microns). This is also helpful in achieving low areal weight of composite.

In accordance with the present disclosure the direct compression of the precursor made of surface treated DPE tape into a composite without or with very little use of matrix can be useful in achieving a better balance of high shear, bending and impact strength as compared to DPE tape without surface treatment. In accordance with the present disclosure the high axial thermal conductivity of DPE tape can make it suitable for faster dissipation of heat on impaction of a projectile on the composite which improves the performance of the product like bullet proof article. DPE tape having flat surface provides an advantage of easy compaction while preparing composite sheet by using the same. The crystallinity of the DPE tape material is high, as it is prepared below the melt temperature, the compaction /fusion is superior to fiber, which is prepared by the gel spinning process. The energy dissipation and resistance to break is reflected by the mechanical strength of the tape.

The close compaction of wide tape as compared to fiber can provide high projectile capturing capability and better energy dissipation than fiber and narrow width tapes. Fast removal of heat generated due to friction of the projectile on the composite made of tape due to high thermal conductivity is also advantageous.

Wide width tape of very low thickness can perform better in achieving the required load bearing properties as well as converting the tape form to composite sheet form.

Use of such tape / film facilitates the process of compaction and fusion of oriented polyethylene layers and thereby improves the performance of catching the projectile and energy dissipation due to the higher compact density of fibers being closely embedded in the tape/fiber. High thermal conductivity of the tape also improves the energy dissipation. The close packing of the oriented fibers in the tape can also support the creep resistance as needed for long term usage of composites. The required quantity of resin for binding the tape as against fibers is less. Alternatively, resin free compacting can be more effective in tape as compared to fibers. Composites prepared by using DPE tapes have better properties as compared to the fiber and tapes for similar applications and is useful in speciality application areas like protective clothing, shields, automotive parts /body etc. The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.

The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.

EXPERIMENTAL DETAILS:

Experiment 1:

Continuous tapes of DPE (MW: 4.83 million g/mole, MWD: 8.3, enthalpy of fusion (DH): 227 J/g, prepared by hot stretching was used for preparing composite precursor. These continuous tapes having see-through clarity, width about 30 mm, width to thickness ratio 1200 to 1360, tensile strength as 1.95- 2.53 GPa and tensile modulus as 110- 150 GPa were arranged in a square form of 21 cm x 21 cm. The tapes were aligned parallel to each other without any gap between them as a first layer. The second layer of tape in a similar fashion was prepared and placed over the first layer at right angle. Likewise a stack of tape layers were prepared while every alternate layer was having alignment 90° w.r.t. adjoining layer. The number of layers arranged was such that the thickness of the final composite is 3.2 mm. The length of the tapes was taken such that the extra length of tape used for the first layer is used to prepare the alternate layer, whereas the extra length of the second layer is used for preparing the fourth layer and so on. Thus forming a folded assembly of 10 layers from a single length of the tapes, which can be stacked to build a thickness of about 3 mm in the final composite precursor. LDPE layers of 10 micron thickness were used to wrap the stacked layers and 3 such layers were placed in between the tape layers, as matrix, such that in the final composite they are at a gap of about 1 mm from each other thus forming about 2.5% (by weight) of the final composite precursor.

The precursor so prepared was compression molded at 95 °C using three plate positive molds. The compression pressure up to 100 bar was applied for 30 min (built up in four stages progressively at equal interval). This was subsequently cooled to room temperature in 3 hours while under pressure at 100 bar. The composite sheet so obtained was having areal weight of 2.798 Kg/m².

Experiment 2:

Tape of DPE of MW: 4.99 million g/mole, MWD: 10.6 and DH 201 J/g, having see-through clarity, width 16 + 2mm, thickness 10+1 micron and tensile strength and tensile modulus as 2.5 - 2.9 GPa and 130 - 150 GPa, respectively was used to prepare composite precursor. The layers of tape were aligned such that each alternate layer was aligned at 90° w.r.t. the nearest neighbouring layer. Stacks of 10 layers were prepared with a continuous length of tape to obtain a final thickness of composite precursor of about 3.0 mm.

LDPE film of thickness 10 micron was wrapped around the composite precursor while 12 such layers were placed (one each at regular interval) in between the DPE tape layers forming about 7% (by weight) of the total weight of the composite.

The precursor as prepared was compressed in a preheated three plate positive mold at a temperature of 95 °C while increasing the pressure at a regular interval (two stages) to attain 100 bar. The applied pressure and temperature was maintained for 10 min and then allowed to cool under the same pressure (100 bar) for 3 hrs. Thus a composite sheet of 2lcm x 21 cm

2

was obtained having areal weight of 2.63 Kg/m .

Experiment 3:

DPE tape and the process of preparing composite precursor were used as per experiment 2 except the tensile strength and tensile modulus of the DPE tape used were in the range of 2.5 to 3.15 GPa and 135 - 146 GPa. The numbers of layers of tape stacked were such that the composite thickness of 5.8 mm is achieved. 20 layers of 10 micron thick LDPE film were placed in the precursor (one each at regular interval) between the tape layers forming about 2.25 wt% (by weight) of the total weight of the composite precursor.

The process of preparing the composite sheet using the composite precursor was carried out at similar conditions as per experiment 2. The areal weight of the composite sheet as prepared was 5.1 Kg/m². Experiment 4:

A combination of DPE tapes, prepared by using DPE of MW: 5.4 million g/mole, MWD: 14.3 and DH: >195 J/g, of width 8 to 35 mm, thickness 10 - 20 micron, tensile strength 2.5 + 0.2 GPa and tensile modulus 130 + 5 GPa were used to prepare a composite precursor. A 10 micron thick LDPE film layers were placed one each at regular intervals between the tape layers (forming about 8.25 wt% of total weight of the composite).

The process of preparing the composite sheet was the same as per experiment 2. The areal weight of the composite sheet so prepared was 6.8 Kg/m .

Experiment 5: Ballistic evaluation of the samples, prepared as per experiments 1 - 4 was carried out with 9 x 19 mm ammunitions with a velocity of about 400 m/s as per standard test method. No perforation was observed in the samples as illustrated in Figure 1. The back face signature was measured and it was found to be < 25 mm.

Experiment 6:

The layers of corona treated DPE tape of width 45mm, thickness 18 micron having tensile strength 2.30 GPa and tensile modulus 135 GPa were stacked after applying epoxy: hardener mixture of 3:1 on each layer. A 4 mm thick composite sheet was prepared after removal of excess epoxy resin by squeezing/compression. Hard sheet of thickness ~ 4 mm was successfully prepared.

Experiment 7:

DPE Tape/Epoxy composite: Corona treated tape prepared by using DPE of MW: 6.25 million g/mole, MWD: 10.3, DH: 195 J/g was used to prepare composite precursor. This tape (width: 15+1 mm, thickness 16±2m) having see-through clarity and tensile strength 2.7+1 GPa and tensile modulus 135+2 GPa. The tape was folded 0 and 90°, alternately to form 11 cm x 11 cm precursor sheets. The tapes were aligned parallel to each other without any gap between them as a first layer. The second layer of tape in a similar fashion was prepared and placed over the first layer at right angle. The length of the tapes was taken such that the extra length of tape used for the first layer is used to prepare the third layer and so on, whereas the extra length of the second layer is used for preparing the fourth layer and so on, thus forming a 20 DPE tape layers as single precursor sheet . 10 no’s of precursor sheets of having 20 layers were stacked by maintaining the 0° & 90° pattern such that the thickness of the final composite is more than 3 mm. The pre-mixed & degassed Epoxy resin (epoxy/hardener ratio of 3:1) was impregnated in the precursor composite sheets of l lcm x l lcm and complete wetting was ensured. The excess resin was squeezed out with an external pressure and subsequently cured under pressure. Thereby, the composite sheet of l lcm x l lcm made was having DPE tape & Epoxy volume fraction ratio’s 91.4% & 8.6%. The final DPE/Epoxy composite sheet obtained was having 3.5 mm thickness and areal weight of 3 kg/m .

TECHNICAL ADVANCEMENTS The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for preparing ultra high strength tape/film based composite.

• easy compaction of tape in the form of composite;

• comparatively superior resistance of composites to high speed impact loading; and · easy dissipation of heat due to high thermal conductivity.

Throughout this specification the word“comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

The use of the expression“at least” or“at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.

The numerical values given for various physical parameters, dimensions, and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.

While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

Claims

CLAIMS:

1. A process for preparing a ultrahigh strength polyethylene composite, said process comprising the following steps:

a. stacking at least two layers of disentangled ultrahigh molecular weight polyethylene (DPE ) tape having a thickness in the range of 5m to 50m and width to thickness ratio in the range of 50 to 20000, such that the direction of the length of first layer of said tape is perpendicular to the length of the layer stacked above said first layer to obtain a stacked layer;

b. compacting said stacked layer with a compressing force at a pressure in the range of 1 bar to 700 bar to obtain compacted layer; and

c. fusing said compacted layer by heating to a temperature below the melt temperature of said disentangled ultrahigh molecular weight polyethylene to obtain said ultrahigh strength PE composite.

2. The process as claimed in claim 1, wherein said DPE tape in step a) has a width to thickness ratio in the range of 4000 to 6000.

3. The process as claimed in claim 1, wherein at least ten layers of said DPE tapes are stacked one over the other.

4. The process as claimed in claim 1, wherein said step of stacking is carried out in the presence of at least one polymer matrix.

5. The process as claimed in claim 4, wherein said polymer matrix is selected from the group consisting of low density polyethylene, linear low density polyethylene, polyethylene wax, chlorinated polyethylene, ethylene vinyl acetate copolymers, polyurethanes, polyamides / imides, epoxy resin, polyester resin, cyanoacrylate, elastomers, and polyisobutylene.

6. The process as claimed in claim 1, wherein said stack of layers of DPE tapes is prepared by aligning alternate layers having an alignment 90 ° with respect to the adjoining layer.

7. The process as claimed in claim 1, wherein said DPE tapes are aligned parallel to each other without any gap between them.

8. The process as claimed in claim 1, wherein said layers of DPE are formed by continuous tape.

9. The process as claimed in claim 1, wherein said layers of DPE tape are surface functionalized.

10. The process as claimed in claim 1, wherein said surface functionalization is carried out by pre-treating said tape using at least one method selected from surface oxidation by corona or plasm treatment, grafting of polar monomers, and sulfonation.

11. The process as claimed in claim 1, wherein said DPE tape is prepared by using disentangled ultrahigh molecular weight polyethylene (DPE) powder, a stabilizer, and an additive.

12. The process as claimed in claim 11, wherein said stabilizer is selected from the group consisting of substituted phenols, amines, alkyl, aryl, and mixed alkyl-aryl phosphites/phosphonites, alkyl, aryl, and mixed phosphates, lactone (3- arrylbenzofuran-2-one), thioesters, thio compounds containing oxidizable sulphur and aryl nitroso compounds and photo stabilizers.

13. The process as claimed in claim 11, wherein said additive is selected from the group consisting of carbon black, graphene, carbon nanotube, colorants, inorganic fillers like calcium carbonate, talc, and Ti(¾.

14. The process as claimed in claim 1, wherein said compaction is carried out at a temperature in the range of 10 °C to 130 °C.

15. An ultrahigh strength PE composite comprises a stack of DPE tape having width in the range of 1-100 mm and having a thickness in the range of 5m to 50m.