Government Interest This work is in part supported by National Textile Center grant no. 5- 33540. Thus, the United States government has certain rights in the invention.

Field of the Invention The present invention relates to the field of textile components for use in the manufacture of composite materials. More particularly, the present invention relates to an air-jet textured high modulus yarn and reinforcement layers formed therefrom for composite materials. The composite materials possess high strength and high resistance to delamination.

Related Art It is well known that composite materials can be formed from a combination of reinforcing textile structures and impregnating resins or matrices such as apoxy resin. Such materials are widely used in fields ranging from aeronautics to industrial applications. In order to obtain materials having the desired properties, it has been necessary to use a relatively high proportion of textile structures in particular by building up various reinforcing layers of the textile structures. It is further known, however, that the impregnation of such reinforcing textile layers by the resins is not achieved optimally and that owing to the effect of mechanical stresses, this can result in damage to the composite material due to separation of certain layers of the textile reinforcement layers.

This is known to those skilled in the art as"delamination", and it is a

shortcoming of composite materials for which there has been a longfelt need to overcome as recognized by those skilled in the art.

One of the means proposed in the prior art to overcome such disadvantage consists of the use of a multi-dimensional (for example, three dimensional) structures as a reinforcement in the composite material. Such structures have been found to be satisfactory in many cases, but they are expensive and take a long time to fabricate.

Applicants have overcome this well-known shortcoming of conventional composite materials through the use of an air-jet textured high modulus yarn in the formation of the reinforcement layers from which the composite material is fabricated. The composite materials produced in accordance with the invention provide increased resistance to delamination and yarn pullout by increasing the cohesion between adjacent yarns. The increased cohesion is achieved by using air-jet textured high modulus yarns in the formation of the textile reinforcement layers incorporated into the composite material. The greater bulk provided by the air-jet textured high modulus yarns provides cohesion so as to better prevent delamination as well as to provide greater bulk so as to reduce the number of textile reinforcement layers required in a composite material without significantly effecting the desired end properties of the composite material. Moreover, the air-jet textured high modulus yarns serve not only to increase resistance to delamination of the composite material but also serve to provide high tensile strength to the composite material.

Summary of the Invention A delamination resistant high strength composite material is provided comprising a plurality of textile reinforcement layers formed from air-jet textured high modulus yarns between about 400-4000 denier and 300-3000 filaments, and wherein the yarns are overfed between about 20%-40%. An impregnating resin such as apoxy resin is used to permeate the textile reinforcement layers formed by the air-jet textured high modulus yarns and to thereby fabricate the high strength and delamination resistant composite material.

Also, the invention provides a high strength delamination resistant composite material comprising a plurality of textile reinforcement layers formed from sheaths/core air-jet texture high modulus yarns wherein the yarns comprise a high modulus core yarn between 400-1200 denier and 600-1300 filaments and one or more high modulus sheath yarns between about 300-900 denier and 400-700 filaments, wherein the core yarn is overfed between about 2%-10% and the sheath yarn is overfed between about 30%-70%. An impregnating resin such as apoxy resin is used to permeate the textile reinforcement layers in order to form the high strength and delamination resistant composite material.

Also, in addition to the high strength delamination resistant composite material of the invention described hereinabove, the invention further provides the novel textile reinforcement layer and the novel air-jet textured high modulus yarn utilized in the fabrication of the composite materials of the present invention.

It is therefore an object of the present invention to provide textile reinforcement layers and yarns for forming the textile reinforcement layers, the configuration of which renders the reinforcement layers and the yarns forming same well suited for use in the fabrication of high strength delamination resistant composite materials.

Another object of the present invention is to provide a high strength delamination resistant composite material formed from novel textile reinforcement layers and yarns so as to provide for both high strength and enhanced resistance to delamination of the textile reinforcement layers of the composite material.

It is another object of the present invention to provide for a novel air-jet textured high modulus yarn which is particularly well adapted for use in forming reinforcement layers that are in turn used to fabricate high strength and delamination resistant composite materials.

Some of the objects of the invention having been stated hereinabove, other objects will become apparent as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow.

Some of the objects of the invention having been stated hereinabove, other objects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow.

Brief Description of the Drawings Figure 1 is a front elevation view of the EMAD air-jet texturing machine; Figure 2 is a graph of spin finish extract on dry and wet air-jet textured Dacron and Nylon ; Figure 3 is a graph of yarn-to-yarn friction test of dry and wet air-jet textured Dacron and Nylon ; Figure 4 is a graph of on-line tension testing measurements for dry and wet air-jet textured Dacron and Nylon ; Figure 5 is a graph of a yarn tensile strength test for dry and wet air-jet textured Dacron and Nylon ; Figure 6 is a graph of individual filament tensile strength tests for dry and wet air-jet textured Dacron and Nylon ; Figure 7 is a graph of yarn diameter measurements for dry and wet air- jet textured Dacron and Nylon ; Figure 8 is a graph of spin finish extract on air-jet textured high modulus Kevlar and Spectra yarns; Figure 9 is a graph of friction tests for air-jet textured high modulus Kevlar and Spectra yarns ; Figure 10 is a graph of yarn tensile strength test for air-jet textured high modulus Kevlar and Spectra yarns; Figure 11 A is a scanning electron microscope photograph of supply high modulus Kevlar textile yarn; Figure 11 B is a scanning electron microscope photograph of dry textured high modulus Kevlar yarn; Figure 11C is a scanning electron microscope photograph of wet textured high modulus Kevlar yarn; Figure 11D is a scanning electron microscope photograph of wet textured high modulus Kevlar yarn ;

Figure 12A is a scanning electron microscope photograph of high modulus supply Spectra yarn ; Figure 12B is a scanning electron microscope photograph of dry textured high modulus Spectra yarn; Figure 12C is a scanning electron microscope photograph of wet textured high modulus Spectra yarn; Figure 13 is a graph of load versus extension for sheath core Kevlar yarn at 2% core overfeed and 70% effect overfeed ; Figure 14 is a graph of load versus extension for sheath core Kevlar yarn at 2% core overfeed and 100% effect overfeed; Figure 15 is a graph of load versus extension for sheath core Kevlar yam at 7% core overfeed and 30% effect overfeed ; Figure 16 is a graph of load versus extension for sheath core Kevlar yarn at 3% core overfeed and 30% effect overfeed; Figure 17 is a graph of load versus extension for sheath core Kevlar yarn at 4% core overfeed and 30% effect overfeed ; Figure 18 is a graph of load versus extension for sheath core Kevlar yarn at 5% core overfeed and 30% effect overfeed; Figure 19 is a graph of load versus extension for sheath core Kevlar yarn at 6% core overfeed and 30% effect overfeed; Figure 20 is a graph of load versus extension for sheath core Kevlar yarn at 5% core overfeed and 30% effect overfeed ; Figures 21-33 show graphs of load versus strength on selected samples of sheath core air-jet textured Kevlar that depict the effect of core overfeed on peak load wherein the break was recorded at 75% of the peak load and most yarns were not fully broken (Figures 21-26) and where several yarns were allowed to break fully to exhibit the dual break characteristic (Figures 27-33).

Detailed Description of the Invention Principles of Air-Jet Texturing Air-jet texturing is a unique process whereby flat synthetic multifilament yarns are give spun-like structure with a compact core and surface loops occurring frequently at"irregular"intervals along its length.

The process for air-jet texturing is well known. When the overfed filaments enter the texturing nozzle, they are carried along through the nozzle, blown out from the texturing end, and are formed into loops which are mutually trapped in the yarn structure by the effect of the supersonic and turbulent air stream and forms a textured yarn structure. The supplyyarn is normallywetted just before it is fed into the texturing nozzle by passing it through a wetting unit.

Wet texturing improves the quality of textured yarn produced.

Textured yarn is taken up at right angles to the nozzle axis by the delivery rollers located after the nozzle. Another set of takeup rollers, running at slightly higher speeds than the delivery rollers, may be used before the high- speed winders to apply tension to the textured yarn in order to stabilize the loops formed during the process. The textured yarn is then wound up by means of a high-speed winding unit. Heaters can optionally be used to impart further desired properties to thermoplastic yarns, but this is not essential for the process.

Texturing nozzles are usually enclosed in a chamber not only to reduce the noise created by the air jets, but also to collect the used water and the spin- finish washed off from the filaments during the process. Some texturing nozzles have an impact element at the nozzle exit, to be used in certain cases as recommended by the supplier. These impact elements, which can be of different shapes, e. g., cylindrical, flat, or spherical, are believed to improve the process stability and yarn quality in texturing finer yarn. Others suggest that these baffles seek to utilize the air energy exhausting from the venturi and have contributed significantly in raising of the throughput speed potential of the jets.

As well as single supply yarn, two or more yarns of the same or different types can be textured at the same speed (parallel end texturing), or can be co- textured at different speeds (core and effect texturing or core/sheath texturing)

by use of separate feed rollers, hence facilitating blending different types of yarns during process. This process is by far the most versatile continuous yarn texturing method in that it can blend filaments together during processing, and supply yarns need not be restricted to the thermoplastics. This permits the texturing of non-thermoplastic materials, which react very differently to heat treatment. This greater versatility offers the texturiser a potential of developing numerous types of yarns.

Applications of Air-Jet Textured Yarns Yarns produced by air-jet technique are unique in that they more closely simulate spun staple fiber yarn structure, both in appearance and physical characteristics, whereas the bulkiness of false-twist textured stretch yarn decreases with the degree of imposed tension, the geometric form of air-jet textured yarns can be made to remain virtually unchanged at loads corresponding to those normally imposed in fabric production and during wear.

This is due to the'locked in'entangled core and loop structure attributed to air- jet textured yarns.

Air-jet textured yarns also more closely resemble conventionally spun yarns in that the yarn surface is covered with fixed resilient loops, and these serve the same purpose as the protruding hairs in spun yarns by forming an insulating layer of entrapped, still air between neighboring garments. Table 1 below shows a brief overview of prevalent air-jet textured yarn applications known today.

Table 1 Air Jet Textured Yarn Applications Application Feeder Yarn Yarn Construction Sportswear Nylon, Polyester, low Core/effect Leisurewear dpf and sub-denier Single Anti-gliss yarns Parallel Ski Clothing Parkas, Jackets, Pants Jogging Suits Rainwear Coating Fabrics Automotive Textiles Polyester dtex Flat Weaves 800-3000 Core/effect Velours approximately 400 Core/effect +Parallel Circular Knit Velours approximately 190 Single Apparel Nylon, Polyester Single + core/effect Slacks Texspun Shirts Blouses Women's apparel Decorator Fabrics Polypropylene, Core/effect + Parallel Draperies Polyester Upholstery Table linen Coating (reinforcement) Polyester, Nylon Core/effect + Parallel fabrics, Scheffer fabrics for automobile tires etc. from high-tenacity yarns Sewing Thread Polyester, Nylon Core/effect, Texspun Texturing Nozzles The heart of the air-jet texturing process is the texturing nozzle. This may vary in design and details, but it serves the same purpose of creating a supersonic, turbulent and non-uniform flow to entangle the filaments and form them into loops to generate stable textured yarns.

Since the development of the first nozzle in 1952 to the present day, the air-jet texturing process has experienced many developments and improvements and seen many variations in the detailed nozzle design. In contrast with earlier days of the process, presently a great number of texturing nozzles are available to be fitted to modern texturing machines. The industrial jets for air-jet texturing can be categorized into two main groups, converging- diverging type in which a converging-diverging nozzle is used in the jet

assembly and the cylindrical type, in which one or more air holes open at an angle to the cylindrical, straight, and uniform main flow duct of the nozzle.

One of the earliest air-jet texturing nozzles was used on a standard ring- twisting machine Czechoslovakia. However, it is not certain whether the Czechoslovak jet appeared earlier than the similar nozzle developed by Du Pont in 1922. The jet was aimed at producing continuous filament yarn having bulkiness at least as high as that of staple yarn spun from comparable fibers. It seems that the apparent simplicity of this early nozzle did not help much to accomplish the desired textured yarns and, therefore, modifications had to be made, which resulted in the Taslan line of nozzles types Vil, Vlil, IX, XIV, and XV.

Contemporary Taslan nozzles allow the supply yarn to enter a needle with the airflow passing through a uniform gap around the needle circumference through an inlet hole displaced to one side. These nozzles may have impact elements as mentioned previously. These Du Pont nozzles are basically made with a"venturi", which is a converging-diverging nozzle to create the required, highly turbulent, supersonic flow, and the"needle"to guide the supply yarn into this violent air flow. Both parts are assembled in a nozzle housing. The annular gap between the needle and the venturi is required to be adjusted precisely to obtain the optimum nozzle efficiency and to maintain the nozzle to nozzle consistency. The precise setting requirement has been a major disadvantage of such types of nozzles.

In the late 1970s, the Heberlein Company of Switzerland introduced a texturing nozzle under the trade name of HemaJet. The air is fed into the main duct of this"standard core"nozzle by means of three small inlet bores where it impinged upon the overfed supply yarn from three sides. The HemaJet nozzles are made of one solid piece and require no adjustment during operation, which reduces the attention and maintenance required. Nozzle to nozzle consistency, which relies on manufacturing tolerances are also improved. A spherical impact element (baffle ball) is provided to be used optionally. This is particularly recommended by the manufacturer for yarns in the low dtex regions.

In recent years the Heberlein Company has announced several-other nozzles, known as T-series, having the same basic design features but covering a wider supply yarn range of from 30 dtex to 5000 dtex. The trump- shaped diverging exit of the standard core was widened, and this became a common feature of all the T-series nozzles. Some of these recent nozzles have reduced the compressed air consumption considerably.

Another player in the nozzle arena is The Enterprise Machine and Development Corporation (EMAD) nozzle. This nozzle is very similar to the later Tasfan nozzles in its internal nozzle configuration but there are some additional features at the exit regions where a very complex yarn guiding system at the nozzle exit together with a cylindrical baffle element are incorporated in the design. EMAD nozzles have found application in the textile industry, mainly in the coarse linear density range for carpet and drapery yarns.

Yarn Wetting During Texturing Modern industrial practice often involves wetting of the filament yarns during the air-jet texturing process by passing the supply yarn through a water bath, wetting head or spray unit. Regardless of application technique, wetting of the yarns results in improved process stability and consequently in improved loop stability and hence in better quality yarns. It should however be noted that, although wetting improves texturing, it removes most of the spin finish on the supply yarn and causes clogging of the nozzle due to the removed spin finish. Impurities in the water used could also contribute to the nozzle contamination. This reduces the nozzle efficiency, and causes stoppages of the process for cleaning the clogged nozzles. The use of water, in certain applications, may also result in undesirable high moisture content in the final textured yarn. But, since these applications don't constitute a big part of the air jet texturing applications, this issue is not considered critical.

Choosing Suitable Supply Yarn Understanding the requirements of the supply yarn has contributed greatly towards the development of the process. The most important factors in texturing filament yarn by air-jets are the fluid (drag) and the frictional forces acting on the filaments. These determine the resultant forces acting on the

filaments, which transport them through the texturing nozzle and facilitate the entanglement and loop formation process by bending, buckling and twisting the filaments. Filaments with varying fineness, different cross-sectional shapes and different filament numbers within the yarn bundle may behave differently in the airflow.

The frictional and pressure drag forces acting on a filament under any given flow conditions are functions of the local air velocity, and of the filament surface and projected areas exposed to the flow. The air supply pressure primarily determines the air velocity, whereas the jet velocity profile is affected by the design of the nozzle. The surface and projected areas exposed to the flow are determined by the width (diameter for a circular filament) and length of the filament exposed to the airflow, and also by the location of the filament across the nozzle and its orientation. Therefore, forces acting on the individual filaments at different locations in the nozzle may vary and such varying fluid forces acting on the filaments at any instant cause them to travel at different speeds and hence cause them to be displaced longitudinally relative to each other.

Increasing the diameter of a circular filament of certain lengths gives rise to a greater drag force acting on it owing to its greater projected and surface areas. On the other hand, its inertia resistance to the fluid forces, which transport filament, is a function of the filament's cross-sectional area. An increase in filament diameter thus causes the fluid forces to increase proportional to the filament diameter, but the force required to overcome the inertia and to transport this coarser filament will increase with the square of the filament diameter. Consequently coarser filaments will require greater forces than the finer filaments to overcome their inertial resistance. Furthermore, filaments with larger diameters have higher bending and torsional stiffnesses, hence requiring increased forces and torques to bend and twist the filaments to facilitate the loop formation process.

This leads to the generalization that supply yarns that are composed of finer filaments should texture more satisfactorily than coarser filament yarns.

However, when"ultrafine"filament yarns with linear densities about 1 dtex per

filament are used in air-jet texturing there may be further complications such as pre-mingling of the filaments as they enter the nozzle, which affects the texturing conditions adversely. Hence, it can be argued that there is a limit to the filament fineness and the optimum range of linear density per filament that is approximately 1-2 dtex for the supply yarns for the current texturing nozzles used for producing apparel yarns.

Factors Affecting Loop Formation Effects of Air Pressure: As the air pressure increases: (1) the air velocity at the exit increases; (2) the degree of non-uniformity in the velocity distribution increases; and (3) the turbulence increases.

Due to the above, the filament separation and the longitudinal displacements of the filaments with respect to each other become more effective, and filaments travel and change their positions at a greater rate.

Hence a better loop formation and texturing quality can be achieved, this resulting in lower tenacities and breaking elongation. Also, the linear density of the textured yarn will be increased more. There is not much written about this in the air-jet texturing literature and what is proposed has been widely accepted.

Effects of Texturing Speed: The texturing speed affects the bulkiness of the yarn, and its structure becomes more closely packed at low speeds. It is reasonable to expect that the inter-filament friction in the core of such yarns becomes higher than that of less compact yarns. The increased inter-filament friction would contribute to the strength of the yarn in a manner analogous to that of the inter-fiber friction in spun yarns and could account for the higher strength and extensibility of the yarns textured at low texturing speeds. As the texturing speed is increased the yarn structure becomes less compact and consequently inter-filament friction is expected to reduce and so cause the yarn strength to drop. It has been found that as the texturing speed continues to increase beyond the critical speed at which both strength and extensibility are at a minimum, then texturing becomes less effective and causes less compact structure and to increase number of

relatively straight filaments that are available to carry the applied load. Also, with increased texturing speeds, for a fixed overfeed, the linear density of the textured yarn reduces because of the poor loop formation.

Effects of Impact Elements: Impact elements are unlikely to have any significant effect on the flow inside the texturing nozzle, since any such element is usually situated at a distance of about one nozzle diameter from the exit. It is thus remote from the immediate nozzle exit region where loop formation actually occurs. One possible minor role of impact element is to act as a physical barrier to those filaments that are blown well away from the nozzle. This is more likely to occur with finer filaments. There is little experimental evidence present in the literature which suggests that the impact elements are a critical component of the air-jet texturing process.

EXPERIMENTAL TESTING A. Nylon and Polyester Yarns Processing The experimental setup used at North Carolina State University, College of Textiles is as shown in Figure 1. The supply yarn is passed through the ceramic yarn guide on to the first roller. The yarn is held into place by the use of a roller and belt system, which is used to secure a positive grip of the yarn, which in turn prevents any slippage from occurring. The yarn is then fed into the texturing box. The texturing box is composed of the texturing nozzle, a baffle ball, a wetting unit and a guide which helps guide the yarn out of the texturing box at ninety degrees. Just before the yarn enters the nozzle, it is wetted with water using a water spray. The region between the input roller and the texturing box is known at the overfeed zone. The overfeed is achieved by running the take up roller at a slower speed compared to the let off roller. The overfeed used for the preliminary trials using Nylon and Polyester was 20%.

The yarn is then passed through a delivery roller with roller and belt arrangement and finally is taken up by suction and collected in the collecting basket. The region between the texturing box and the delivery roller is termed the mechanical stretch region. The mechanical stretch is achieved by running

the delivery roller at a higher speed than the take-up roller. The mechanical stretch used for the preliminary trials using Nylon and Polyester was 6%.

The final output speed on the machine is equal to the speed of the delivery roller. The speed of the machine for the preliminary trials was 300 m/min. The air pressure used was 80 PSI for the preliminary trials, while for the high modulus texturing, 140 PSI was used. The amount of water consumed was 1 liter/hour/jet.

Testing and Evaluation SOXHLETT APPARATUS: (Spin Finish Tests) Ten-gram samples of each yarn type were used for the tests. The samples were then put in cardboard tubes of known weight. Then, they were put in uncovered glass flasks (of known weight) and kept in a"heating oven"at 125°C for two and half-hours. The samples were then covered and put in a "Desicator"for a further 30 minutes. This was done in order to remove any moisture content that may be present in the samples. There after their bone- dry weight was obtained using precision weight scale. This weight was noted as the"before extraction"weight. The cardboard tubes containing the samples were then taken out of the glass flasks and placed in the Soxhlet apparatus for six hours, wherein the extraction of spin finish was obtained by use of hexane gas and water. They were then taken out kept back in the glass flask and put in the heating oven at 125°C for two and half hours. The samples were then put in a desicator for a further 30 minutes, after which their bone-dry weight was measured using a precision weight scale. This weight was noted as"after extraction"weight.

The same procedure was repeated for wet textured yarn, dry textured yarns, dry straight filament yarns and wet straight filament yarns. In order to understand the filament-to-filament frictional behavior, it was necessary to prevent the formation of loops. There are no test procedures available to accurately measure friction of one looped surface over another looped or crimped surface. In order to correlate the frictional behavior with the amount of spin finish removed, it became necessary to measure the spin finish percentage in the straight yarns. Here the straight yarns refer to yarns

produced without any overfeed. The yarns are just blown apart using the nozzle under dry and wet conditions.

LAWSON-HEMPHfLL CONSTANT TENSION TESTER (For Friction Tests) The yarn passes through the guide and is then wrapped around the godet rollers five times in order to prevent any slippage from occurring. From here the yarn then passes through the tension arm, which maintains a constant input tension in the yarn. There are different tensions arms for different linear densities of yarns. The yarn then passes through the testing arrangement either a yarn to yarn/yarn to metal, based on the test being conducted as shown in the figure. From here the yarn passes through the sensor and then finally on to the pair of godet rollers leading up to the suction unit. It is wound five times around this pair too to prevent any slippage from occurring. The tensiometer, reads the output tension fluctuations. The speed of the rollers can be set by the PLC unit.

The sensor was first calibrated using known dead weight. The machine speed for the yarn to yarn test was set at the recommended 20 m/min. The speed was changed to recommended 100 m/min for the yarn to metal tests.

The input tension (TI) was set according to the recommended convention of 1 gm/tex. The output tension (T2) was obtained directly from the tensiometer.

The Coefficient of Friction was then calculated using the below equations for the particular tests conducted.

Yarn to yarn: The coefficient of friction was calculated using the following recommended equation: Where n is set at 3 wraps as recommended and A is the angle of wrap.

Yarn to Metal : The coefficient of friction was calculated using the following recommended equation:

WhereS = Degrees x 3.14. 1 80 (radians) Degrees = 180 ON-LINE TENSION MEASUREMENTS The yarns were textured on the EMAD machine using the yarn path.

The tension measurements were taken at the overfeed zone and the mechanical stretch region. Five reading for each yarn were taken for statistical accuracy. The tension reading was taken using precision tension meter.

YARN AND INDIVIDUAL FILAMENT STRENGTH TESTS: (SINTECH) As per ASTM test method D3882 recommendations, twenty-five filament samples were taken for each type of yarn. They were placed on a"C"shaped cardboard. The specimen length used for individual filament strength tests was 25.4 mm. The samples were then tested using the fiber tensile/slack compensation method.

For yarn strength tests, ten samples were prepared as per the recommendations. The specimen length used for these tests was 254 mm, again, as per recommendations. The samples were then tested using the yarn tensile/slack compensation method.

FILAMENT DIAMETER MEASUREMENTS (OPTICAL MICROSCOPE) An optical microscope was used to measure the filament diameters.

The filament was mounted on the slide by using the mineral oil. The yarn was cut to a very short length using a blade. A drop of mineral oil was then put on the yarn and filaments were separated using a needle. The cover slip was then mounted on the slide. The prepared slide was then put under the 10X- magnification lens. The lens was then turned on to the 40X-magnification lens.

A number of filaments are then brought into the view by moving the slide table around. The refractive index of the medium (mineral oil) being different from that of the filament, one could see the filaments clearly. Here mineral oil is just a convenient medium of suspension rather than air. The filaments were then viewed and their diameter was measured using the method described below.

The filament is aligned to one of the marks. The number of marks that the filament width covers is equal to the diameter, where one mark is equal to 2.5 micrometers.

Test Results For Nylon and Polyester Yarn Preliminary Trials The work reported herein was carried out to establish operating conditions with the process of air-jet texturing. This was done by studying important aspects of the process. The role of water, spin-finish content, effect of the texturing process on the filament yarn diameter and frictional behavior of the yarn after wet texturing and dry texturing was considered for the purpose of the study.

Below is presented a detailed account of the experimental work carried out to achieve the objectives, along with results and discussion. The study was carried out based on the following hypotheses: A. Water acts as a lubricant in wet texturing process.

B. Spin finish is partly removed from the yarns in wet texturing and dry texturing removing insignificant amounts of spin finish.

C. The co-efficient of friction increases with wet texturing for nylon yarns. The coefficient of friction decreases for polyester yarn with wet texturing.

D. The Process does not affect the individual filament shape and modulus.

The objective of proving the above hypotheses was achieved by using the following test methods: 1. Friction tests: Lawson Hemphill CTT 2. Take up tension tests: Precision Tension Meter.

3. Spin finish tests: Soxhlet apparatus.

4. Individual filament strength tests: SINTECH 5. Filament diameter: Optical Microscope Experimental Nylon and Polyester yarns of different linear densities (see Table 2 below) were textured using a HEBERLIEN T100 W nozzle on an EMAD machine at 300 m/min. An overfeed of 20%, air pressure of 80 PSI and mechanical stretch of 6% were used, during both dry and wet texturing. Yarns were wet during texturing with a water consumption rate of 1 liter/hour/jet. YARN LINEAR NUMBER CROSS MOISTURE TENACITY (gpd) SHEAR TYPE DENSITY OF SECTIONAL REGAIN (%) MODULUS (dtex) FILAMENTS SHAPE (Gpa) 1 140/50 140 50 TriLobal 0. 4 6 0. 8 Dacron 2 150134 150 34 Circular 0. 4 6 0. 8 Dacron 3 240/54 240 54 Circular 0. 4 6 0. 8 Dacron 4 156/102 156 102 TriLobal 4. 1 5. 5 0. 4 Nylon 5 100134 100 34 Circular 4. 1 5. 5 0. 4 Nylon 6 Kevlar 888 Square-35 1. 2 149 rounded 7 M5 Circular 8 Spectra 687 Circular 0.18 Table 2: Yarns used in experimental work In order to prove the suggested hypothesis (see above) several different tests were conducted as a part of the tests. The test results and a brief analysis of the findings are set forth below.

Spin Finish The objective of this test was to compare the spin finish content of supply yarn and after wet and dry texturing and to use these results to show the difference in the spin finish contents between supply yarn and textured, and thus prove hypotheses B.

The results shown in Figure 2 in conjunction with tension readings clearly show that wet textured yarns have a lower spin finish percentage, yet better texturing quality. This clearly indicates that water acts as a lubricating agent and helps in the displacement of filaments relative to each other thus facilitating loop formation.

Friction The objective of the friction tests was to evaluate the yarn to yarn frictional coefficients of the selected supply yarns before and after wet texturing. To use these results to confirm hypotheses A and C.

From Figure 3 it may be observed that for the Dacron yarn the coefficient of friction increased very slightly from dry textured yarn to wet textured yarn. This primarily due to the fact that more amount of spin finish was removed during wet texturing which in turn decreases the lubricating effect and hence increases the friction between the filaments. There was no significant difference in the friction coefficients of supply yarns and dry textured yarns.

For Nylon yarns, the friction coefficient increased very slightly from supply yarn to dry textured yarns and then again decreased from dry textured yarn to wet textured yarn. This again proved the fact that many authors have advocated that the behavior of Nylon in texturing process is different compared to other yarns. Another interesting fact that was noted here was that the trilobal shaped filament yarns had a higher coefficient of friction value than circular ones. This was true for both Nylon and Dacron yarns. This may be due to better packaging of the trilobal filaments than the circular filaments, which may cause higher frictional values.

Stabilizing Zone Tension The objective of this action was to measure the take up tensions during wet and dry texturing and to use the comparative values to indicate the superiority of wet texturing over dry. Further, this data would be used as . supporting evidence to prove the role of water as a lubricant.

Previous findings have proved that the higher the takeup tension in the mechanical stretch region, the better is the quality of the textured yarn. Test results shown in Figure 4 clearly indicate the increased tension values in wet texturing compared to dry texturing, under identical conditions of relative humidity, water pressure, air pressure and overfeed. Also, the constant tension in the overfeed region indicates that no fluid forces are active in that region.

Tensile Strength The objective of this test was to compare the single fiber strengths of supply yarn with the wet and dry textured yarns of each type and use these results to prove hypothesis D.

Yarn Tensile Strength: The tensile strength of supply yarn was found to be the highest, then the dry textured yarn and then the wet textured yarns.

This can be taken as a very good indication of the quality of texturing. The better the texturing, the more the number of loops that are formed. Due to this load bearing straight length of the yarn decreases and hence the yarn becomes weaker.

The findings shown in Figure 5 clearly indicate that wet textured yarns have the highest number of loops and that the presence of water helps lubricate the filaments and hence assist in the formation of loops.

Individual Filament Tensile Strength: The results shown in Figure 6 show that the trilobal filaments are much weaker compared to their circular counterpart. This could very well indicate that they could be better textured than the circular yarns. But there was no significant difference between the individual filament strength test results of supply, dry and wet textured yarns, which proves the hypothesis D.

Yarn Diameter The objective of this test was to get accurate individual filament diameter for supply yarn to repeat the process for filaments for wet texturing and use this data to prove hypothesis D.

The diameters in all cases (as shown in Figure 7) appear to have NOT changed. These indicate that there is no damage to the filaments due to the texturing process.

B. KEVLAR° AND SPECTRATM High Modulus Yarns The work reported herein was carried out to answer four fundamental questions regarding the texturing of high modulus yarns: 1. What are the optimum conditions required to air texture high modulus yarns.

2. What structural changes take place in the yarn as a result of the air texturing process and how do they affect the final properties of the yarn.

3. How different are the texturing conditions for air texturing high modulus yarns compared to commonly air textured yarns like nylon and polyester.

4. What are the most important processing parameters influencing the end quality of high modulus air textured yarns.

The following apparatus were used to understand and answer the above four queries: 1. EMAD Double Head Air Jet Texturing Machine: Used for producing air textured yarns 2. Lawson Hemphill CTT: For friction tests 3. Precision Tension Meter: For takeup tension tests 4. Soxhlet apparatus: Spin finish tests 5. SINTECH : Individual filament strength tests Experimental Kevlar (888/660) and Spectra (687/450) yarns were air textured using a HEBERLIEN T331 nozzle on an EMAD machine at 147 m/min. An overfeed of 20%, air pressure of 140 PSI and mechanical stretch of 6% were used, during both dry and wet texturing. Yarns were wet during texturing with a water consumption rate of 1 liter/hour/jet.

The following tests were conducted as a part of the procedure to understand the air texturing of high modulus yarns. The guidelines for the tests were taken keeping in mind the preliminary trials.

Spin Finish The objective of this test was to compare the spin finish content of supply yarn and after wet and dry texturing and to use these results to show the difference in the spin finish contents between supply and textured yarns. This information may be used to explain the difference in texturing quality of the dry textured and wet textured high modulus yarns. It may also be used to identify the role of water in texturing high modulus yarns and also give insights into the

optimum quantity of water than required for the best output yarns. These results along with the friction results may also help in explaining the difference in the texturing behaviors of Kevlar and Spectra.

The results form the spin finish tests shown in Figure 8 reveal the following : 1. Wet textured yarns have a lower spin finish percentage, yet better texturing quality. This clearly indicates that water acts as a lubricating agent and helps in the displacement of filaments relative to each other thus facilitating loop formation. This observation is in conformance with what was observed during the preliminary trials with Polyester and Nylon yarns.

2. The spin finish content of supply Kevlar yarn being was found to be higher compared to Spectra supply yarn. This information along in conjunction with other structural differences between the two yarns may be helpful in explaining the better texturing quality obtained with Kevlar, under the same operating conditions.

3. The spin finish content percent will also indicate the speed at which the texturing box may get contaminated while texturing with different high modulus yarns. In the above case, the Kevlar yarn texturing process will contaminate the nozzle much faster than Spectra yarn process. This information may be used in the for maintenance purposes.

Friction The objective of the friction tests was to evaluate the yarn to yarn frictional coefficients of the supply yarns before and after wet texturing. The information generated from these tests and shown in Figure 9 in conjunction with the spin finish tests may help to: 1. Reaffirm the role of water acting as a lubricant. This is proved by the results below, which clearly indicate that wet textured yarn has a higher coefficient of friction compared to dry textured yarns.

2. Higher coefficient of friction values may point towards the need

for use of surfactants in order to improve the final yarn quality.

The use of surfactants may help the filaments slide by each other better and hence increase the loop heights resulting in better quality air textured yarns.

Tensile Strength The tensile strength tests were carried out in order to understand the following : 1. What percentage reduction in yarn tenacity occurs as a result of air texturing high modulus yarns. This information may prove to be very essential when it comes down to finding end uses for the product.

2. The tenacity results shown in Figure 10 are also a very good indicator of the quality of air textured yarns. The better the quality the lower the tenacity. This can be explained as follows.

The better the texturing, the more the number of loops that are formed. Due to this the load bearing straight length of the yarn decreases and hence the yarn becomes weaker. The results show us that wet textured Kevlar and Spectra are much better textured than their dry counterparts.

3. Comparing the fall in tenacities in Kevlar and Spectra Yarns it may also be observed that the fall in tenacity is variable for different high modulus yarns. More experimental work in the future might show that certain types of high modulus yarns are more suitable for the process than others.

Scanning Electron Microscopy Scanning electron microscopy pictures were taken as shown in Figures 11 A-11 D in order to observe the structural changes that the Kevlar and Spectra yarns may have undergone as a result of the process. The scope of the research did not permit for deep evaluation, but they can be utilized for future study in this area. The pictures above depict the structural changes occurring in Kevlar. Figures 12A-12D next depict the structural changes in Spectra yarn.

The difference in the texturing quality of the two yarns can be seen clearly.

The Kevlar yarn is textured far better compared to Spectra yarn. This may be due the fact that Kevlar has got many more filaments and hence the surface area on which the air can act on is that much more.

TESTING EXAMPLE 1 (KEVLARe and Spectra Yarn) The study found that high modulus yarns can be textured very effectively. Due to limitations of available equipment, some of the other possibilities, such as extremely high machine speeds, could not be tried out.

There was a large drop in yarn tenacity for Kevlar after the yarn was air jet textured. However the drop in yarn tenacity for Spectra was much less. The yarn tenacity can be controlled by controlling the number of loops that are allowed to be formed on the surface. This can be done by controlling the overfeed.

Due to the very high content of spin finish on high modulus yarns, the problem of nozzle contamination is very prominent while air texturing high modulus yarns.

The most important property that is obtained by air texturing high modulus yarns can be attributed to the crimped surface of the output yarns. In composites this structure could impart greater cohesion. This can be especially beneficial for Spectra yarn applications. Spectra yarn does not stick to any surface easily, the looped structure may help it better adhere to the resin in a composite. Due to non-availability of time, tests could not be performed to confirm this.

TESTING EXAMPLE 2 (KEVLARe Yarn) Input Yarn Parameters Linear Density 600 Denier Filaments 666 SAMPLE ID AIR SPEED OVERFEED STRETCH PRESSURE (MTS/MIN) (PSI) S1 140 100 40 18 S2 140 100 30 8 S3 140 100 50 28 S4 140 200 40 18 S5 140 200 30 8 S6 140 200 50 28 S7 140 300 40 18 S8 140 300 30 8 S9 140 300 50 28 S10 120 100 30 8 S11 120 100 40 18 S12 120 100 50 28 S13 120 200 30 8 S14 120 200 40 18 S15 120 200 50 28 S16 120 300 30 8 S17 120 300 40 18 S18 120 300 50 28 S19 160 100 30 8 S20 160 100 40 18 S21 160 100 50 28 S22 160 200 30 8 S23 160 200 40 18 S24 160 200 50 28 S25 160 300 30 8 S26 160 300 40 18 S27 160 300 50 28 Table 3 The tests (see Table 3 above) conducted confirm that there is a significant reduction in strength due to the disorientation of filaments in the textured yarn structure. The tests indicate that there is a marginal difference in the tensile strength among the yarns textured with parameters selected in the tests. There is probably a threshold condition at which there is a sharp decline in strength after which there is relatively little difference in the tensile strength.

If one assumes the strength to be directly related to the extent of disorientation in the filaments then is it possible to state that there might be a limit to the degree of disorientation that can be caused by the texturing process.

The ratio of overfeed of the parent yarn to the stretch in the resultant textured yarn determines, to a large extent, the creep in the resultant textured yarn. The jet breaks open the bundle of filaments that are overfed into it and loops are formed at the exit of the jet. The stretch in the post texturing zone helps to set the loops formed at the exit of the nozzle. There is a limit to the volume of filaments that the jet can handle and so there is a limit to the maximum overfeed in the yarn. The overfed yarn has to be incorporated to the body of yarn in the form of loops that are then stretched. The greater the difference between overfeed and the stretch the more is the creep. However it is not possible to indefinitely increase the creep beyond a certain extent. The stability of the process deteriorates, and it is not possible to increase overfeed beyond 50%, even at high pressures and low speed. There is probably a minimal difference between the stretch and the overfeed beyond which there is a proportional increase in the creep. It might therefore be possible to control the exact amount of creep in the yarn. The control of creep might be useful when it is essential to record the first time deformation in the fabrics.

Visual inspection is not a sound technique to assess the quality of textured yarns. There is a need to further explore methods of evaluation of the quality of these yarns. A visual inspection does not reveal the entanglements that are well within the body of the yarn. It is possible to produce a yarn that has very few surface loops that is highly disoriented internally. Conversely, it is possible to produce a yarn with large surface loops that is better oriented.

However visual inspection does reveal if texturing has taken place and stretching the yarn by hand gives an estimation of the creep. This is useful while setting overfeed/stretch. The loops can be characterized during a visual inspection. The feel of the loops also reveals if there is intense entanglement as opposed to loops that are loosely bound into the core of the yarn.

Summary of Preliminary Findings 1. There is probably a threshold condition at which there is a sharp decline in strength.

2. The creep in the textured yarn depends on the ratio of overfeed to the stretch when all other processing parameters are constant. A 22% differential was found to have a creep of about 4-5%.

TESTING EXAMPLE 3 (Sheath/Core KEVLAR@5 Yarn) YARN CONSTRUCTION DETAILS AIR JET TE-370 CORE: Kevlar 850/1000 Denier EFFECT: Kevlar 600/670 Denier It should be possible to vary the linear density of the core yarn from 400-1200 Denier and filaments from 600-1300 and effect yarns from 300-900 Denier and effect filaments form 400-700 filaments and still produce yarns that will show similar behavior if other processing parameters are adjusted accordingly. It should also be possible to use other yarns like spectra and high tenacity polyester to produce similar core effect yarns.

WINDING TENSION 2% TENSION IN THE DRAW ZONE 2% SAMPLE ID CORE EFFECT STRETCH SPEED AIR OVERFEED OVERFEED (m/min) (psi) FIG. 13 T4 2% 70% 3% 100 140 FIG. 14 T5 2% 100% 3% 150 140 T6 T7 T8 FIG. 15 T9 7% 30% 3% 100 170 T10 Single yarn (1110/1000 Dn) FIG. 16T11 3% 30% 1% 100 170 FIG. 17 T12 4% 30% 2% 100 170 FIG. 18 T13 5% 30% 3% 100 170 FIG. 19 T14 6% 30% 3% 100 170 FIG. 20 T15 5% 30% 3% 100 140 1 Ib=40448 N Table 4 Discussion of Graphs Figure 13: At an overfeed of 70% the tail is flat and extended. Toward the end of the tail there is a slight increase in the loading, this is due to the complete extension of the effect filaments. The low overfeed of the core yarn at 2% accounts in part of the disjoint appearance of the tail.

Figure 14: At an overfeed of 100% the tail is flat and extended. Toward the end of the tail there is a slight increase in the loading, this is due to the complete extension of the effect filaments. At this overfeed the loops were very large and the process did not seem very stable. The low overfeed of the core yarn 2% accounts in part for the disjoint appearance of the tail.

Figure 15: The higher overfeed of the core at 7% causes the effect filaments to take up the load before the load reaches zero. It should therefore be possible to control the recovery load of sheath-core yarns.

Figure 16: The low overfed of the core results in the separation of the tail from the initial part of the curve.

Figure 17 (no comment).

Figure 18 (no comment).

Figure 19 (no comment).

Figure 20: The effect of lower air pressure as compared to Figure 18 is that there are fewer entanglements between the core and the sheath structure.

This paucity of entanglements results in the separation of the tail from the load extension curve of core region.

The distinction of the invention is that there is an effort to maximize the area under the entire curve as shown in Figures 13-20. In previous research

the objective has been to maintain the orientation (hence strength) of the core filament while using the effect filaments to generate loops.

NOVELTY OF YARN IN TESTING EXAMPLE 3 1. The objective is to maximize the area under the entire curve along with retaining a high peak load.

2. The energy that is needed to overcome the frictional forces during the slippage is of significance in increasing the area under the curve.

3. Maximizing the slippage friction is achieved by adjusting the overfeeds of the core and effect yarns and is determined to a lesser extent by other parameters.

4. There is an ability to exercise limited control over the shape of the curve.

5. The size of the surface loops can be controlled.

USE IN COMPOSITES Sheath-Core yarns can be used to make composites that will have high strength due to the high volume fraction of the core filaments and also have good resistance to delimination due to the relatively low volume fraction of the effect filaments.

A lower volume fraction is present on the surface due to the loops on the suface. De-lamination is a surface phemenon and thus the low volume fraction of filaments on the surface should help to reduce the risk of delamination. The relatively parallel core filament result in a high volume fraction at the center of the composite structure this will contribute to the strength of the composite structure.

The dual break characteristic can be made use of in a composite that will have a high initial resistance to a impact force due to the core filaments.

The sheath core structure will hold the composite together even after the composite breaks as the sheath yarn will still retain the ability to absorb more energy. In this manner it should help to prevent or reduce the chances of a catastrophic break of the composite.

These yarns can be used to make 3d or 2d woven performs that are then impregnated with epoxy resin using the vacuum transfer resin molding or any other applicable technique.

The same is also true with respect to the single high modulus KEVLAR and Spectra yarns described in Texturing Examples 1 and 2. The sheath- core yarns are believed, however, to process even greater application to use in composite materials.

TESTING EXAMPLE 4 (Sheath-Core KEVLAR Yarns) The texturing process results in variable reduction of the tensile strength.

The very purpose of using high tenacity yarns on most of their applications is the high tensile strength. To compromise 70% of that strength is not acceptable. In the making of composite however the loops caused by texturing greatly increase the surface area exposed to the resin and are thus more suited to this application as compared to a yarn composed of straight filaments.

There is thus a necessity to bring together the seemingly conflicting requirements of high strength and surface loops. A useful fact to keep in mind is that a composite material that has a low volume fraction of fibers is more resistant to delamination where as a composite that has a high volume fraction has higher strength.

The Sheath-Core yarns described here are composed of sheath filaments that form surface loops while the core filaments retain their orientation and thus the high tenacity. The sheath filaments that bind the parallel core filaments together. The low overfeed of the core is a distinguishing factor between the Sheath Core and yarns and other Co-textured yarns. The most interesting feature of Sheath-Core yarns is its characteristic"dual break" (described in detail herein before). The initial loading is almost entirely taken up by the parallel core filaments, due to their low extension, however at peak load there is catastrophic break of the core filaments this is followed by a steep decline in the stress. This is followed by a period of extension where the stress is almost constant, the stress is this region is due to the slippage of the effect yarns from the core. Once the yarn has extended sufficiently the remaining sheath yarns then begin to take up the load and there is a slight increase in the

stress. Ultimately the effect filaments break.

Overfeed of the core filament plays a very critical role in the texturing of Sheath-Core yarns. Increasing overfeed of the core filament leads to a reduction in the alignment of the core filaments. Thus to maximize the tenacity it is important to minimize overfeed of the core filaments. However there is a minimal overfeed that is necessary to allow good binding between the sheath and the Core filaments. Increasing overfeed tends to produce a more cohesive yarn structure. The preliminary tensile tests were conducted at 5,10 and 15%, overfeed of the core while the effect overfeed was kept at a constant 30%. The higher overfeed of the core filaments the lesser their orientation or there is more room for them to be disoriented. Therefore it is possible that the Sheath and the Core filaments have similar levels of disorientation and hence similar peak loading capacity. This might result in the second break being close to the first. It is important to determine the overfeed to which the Sheath-Core yarns exhibit the dual break. This"Dual Break"property of the yarn, and the ability to control it might have special applications. To better understand the effect of the extent of core overfeed it is necessary to produce Sheath-Core yarns by gradually increasing the core overfeed starting with a minimum of 1% and increasing it by one percent at a time to 8%.

As compared to the single yarns of Examples 1 and 2 higher air pressure is needed to produce good loop formation in Sheath-Core yarns.

Influence of the Nozzle The T370 is used in the texturing of Sheath-Core yarns. It is understood that loop formation takes place at the exit of the nozzle. The initial results show that a more cohesive Sheath-Core yarn, with larger surface loops, is formed by the use of a nozzle of larger orifice size. The large nozzle diameter probably allows more room for the sheath filaments to wrap around the parallel core filaments and form a cohesive structure. It could also be possible that the Heberline T341 is inappropriate for the production of core effect yarn. It will be of interest to texture sheath-core yarns using a nozzle of intermediate diameter and observe the reduction in the surface loop size. The large size of surface loops, which is attributed to the large nozzle diameter, might entangle with each

other or machine parts while processing downstream. From current observation loop sizes almost entirely depend on the size of the nozzle diameter and on overfeed. The use of the Heberline T351 will further understand the influence of nozzle diameter on the loop size.

Testing While the initial tests were begin conducted there was no attempt made to record the dual break initially and the tensile test was set to be stop when the load reduced to 75% of the peak load. The objective at that point was to make a yarn that retained its high tenacity while there were loops on the surface that would increase the surface area and therefore the binding with a composite. In most of the tests the sheath filaments begin to take up load after only after there is a greater drop than 75%. In a few tests however the phenomenon was observed and recorded.

Experiment-1: To study the level of overfeed that will produce well-covered Sheath- Core yarn.

JET-TE 370 INPUT YARN PARAMETERS AIR-140 PSI CORE YARN-KEVLAR Linear Density: 850/1000 Dn STRETCH-3% SHEATH YARN-KEVLAR Linear Density: 600/670 Dn WINDING TENSION-2% SPEED 150 m/min SNO CORE EFFECT 1 2% 15% 2 2% 30% 3 2% 70% 4 2% 100% These preliminary trials demonstrated that Sheath-Core yarns could be produced. The overfeed determined the cover on the yarn. A overfeed of 15% produces yarn with very poor cover of the sheath filaments this leaves large

lengths of core filaments exposed. An overfeed of 100% produces yarn with a vary large loop size. However the process is unstable to the random generation of loops of very large size. These loops tend to get entangled with the traversing guide and these results in the frequent stoppage of the machine.

At 70% overfeed there is good cover and the loop size reduced. There was no stoppage during the trial. However the run was very short and a few large loops were noticed. At 30% overfeed the loop size is reduced. The appearance of the yarn is not adversely affected. Therefore an overfeed of 30- 40% seems to be appropriate.

Experiment-2: JET-T370 INPUT YARN PARAMETERS AIR-140 PSI CORE YARN-KEVLAR Linear Density 850/1000 Dn STRETCH-3% SHEATH YARN-KEVLAR Linear Density 600/670 Dn WINDING EFFECT OVERFEED 30% CORE OVERFEED SPEED 5% 10% 15% 100 X 200 300 X X= UNSTABLE There was no attempt made to record the dual break during the initial phase of the testing. The objective was to investigate the effect of core overfeed on the peak load. As per standard testing procedure the break was recorded at 75% of the peak load. However during the testing it was observed that most yarns were not fully broken. Therefore in the following samples shown in Figures 21-33 a few (Figures 27-33) were allowed to break fully. This brought to notice the characteristic"dual break".

EXPERIMENT-3 : JET-TE370 INPUT YARN PARAMETERS AIR-140 PSI CORE YARN-850 DN KEVLAR SHEATH YARN-600 DN KEVLAR EFFECT OVERFEED-40% STRETCH-3% SPEED-100 mts/min SNO CORE WATER 1 3% Yes 2% Yes 3 2% No 1% No At a very low overfeed there is periodic fluctuation in the tension. This is due to the stick slip in the stretch zone. It is possible that the low level of core overfeed causes the stick slip to occur. It is understood that the sum of the stretch and the winding tension should be less than the overfeed by at least 2- 3% to reduce stick slip.

Application of water results in more intense texturing of the sheath filaments that result in compact loops that do not protrude too farform the body of the yarn. Dry textured yarn shows large lengths of exposed core filament.

The loops are fuzzy and large. The possibility of entanglement with the traversing guide is very high.

Summarily, applicants believe that a delamination resistant high strength composite material can be made from one or more reinforcement layers formed from air-jet textured high modulus core/sheath yarns (preferably KEVLARe or Spectra). The core yarn should be between 400-1200 denier and 600-1300 filaments, and the sheath yarn between 300-900 denier and 400-700 filaments.

The core yarn should be overfed between 2.0%-10% (preferably 2.0%-7.0%) and the sheath yarn overfed 30%-70% (preferably 30%-40%). The core and sheath yarns should be air-jet textured at between 140-190 p. s. i.

Applicants further believe that the delamination resistant high strength

composite can be made from one or more reinforcement layers formed from air-jet textured high modulus yarn (preferably KEVLAR or Spectra) between 400-4000 denier and 300-3000 filaments. The yarn should be overfed between 20%-40% and air-jet textured at between 140-190 p. s. i.

It will be understood that various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation-the invention being defined by the claims.