RU2850270C1 - Method of increasing strength characteristics of para-aramid yarns and fabric by treatment in non-equilibrium low-temperature plasma - Google Patents

Abstract

FIELD: performing operations.

SUBSTANCE: invention relates to the technology of industrial treatment of threads and fabric made from para-aramid fibres. Disclosed is a method of increasing strength characteristics of para-aramid threads and fabric by treatment in nonequilibrium low-temperature plasma, involving treatment in modified plasmatron, with constant injection of gas mixture and continuous movement of thread or fabric. Para-aramid threads or fabric are prepared by sampling threads or fabric and determining their technical characteristics in a labouratory way, after which parameters of the mode of processing materials in low-temperature plasma are determined based on the obtained labouratory data. Next, installed in the chamber of the modified plasmatron, the broaching device is loaded with threads or fabric and performing preliminary evacuation of the volume of the plasmatron chamber, and then, first, for 10 minutes, performing injection of oxygen and then constant injection of gas mixture of argon and methane, wherein continuously moving threads or fabric through drawing device with simultaneous action of nanometric high-frequency capacitive discharge on hydrocarbon molecules, with the following processing parameters: high-frequency capacitive discharge intensity range HF 750_min-3500_max W, wherein the drawing speed is set depending on the processing time of 1-25 minutes per unit area, and the pressure in the plasmatron chamber ranges from 20 to 40 PA, and the plasma temperature is from 40 °C to 70 °C.

EFFECT: proposed approach provides improved protective properties of para-aramid threads and fabrics, as well as their efficiency at impact action due to improved strength characteristics, such as tensile strength, elasticity and elongation, as well as in the expansion of the range of technical means.

4 cl, 5 dwg, 1 ex

Description

Field of technology

The technical solution proposed as an invention relates to the technology of industrial processing of threads and fabrics produced from para-aramid fibers, which allows for providing them with increased strength characteristics and protective properties for their subsequent use in various industries - space, aviation, transport, light industry, fuel, chemical, defense, construction, in the manufacture of ultra-strong materials and products of various types, for example, ultra-strong and lightweight composites, vehicle frames, tire cords, personal protective equipment, reinforcing elements of high-pressure pipelines, construction fittings, the manufacture of sports equipment, etc.

State of the art

Para-aramid fibers are significantly stronger than steel, but are 5 times lighter and are used in many industrial fields, for example, as cord for tires and for the production of lightweight ballistic materials, and are widely used in the aerospace industry and composite manufacturing.

A significant disadvantage of para-aramid and materials made from it is its susceptibility to photodegradation, high price, and increased hydrophilicity, along with a pronounced instability to cutting and a significant reduction in strength characteristics when wet.

Materials from the para-aramid family, manufactured in accordance with the requirements of GOST 33842-2016, have a number of improved properties, such as high tensile strength and increased carbonization temperature. However, their indicators required for the manufacture of final products remain at the same level: low resistance to cutting and insufficient strength indicators, including tensile strength, under full or partial wetting.

A method for obtaining modified fiber with subsequent production of fabric, composites and products from them is known from the existing level of technology, in which the fibers are washed and modified by plasma treatment or corona charge treatment at atmospheric pressure (patent RU 2614278 C2, publication date 03/24/2017), as a result of which the specific strength is increased.

In addition, from source RU 212137352 A, publication date 10.03.2014, a method for increasing the adhesive capacity of aramid fiber is known, which consists in the fact that the aramid fiber is exposed to nonequilibrium low-temperature plasma of a high-frequency capacitive discharge in a vacuum chamber in an argon environment for 90-210 s at an anode voltage of 3.5-4.5 kV, anode current of 0.3-0.5 A, an operating pressure of 26.6±0.1 Pa, a gas flow rate of 0.04±0.005 g/s; which leads to the creation of a composite material with increased adhesive strength of aramid fiber to epoxy binders.

The main objectives of the proposed invention are to create para-aramid threads and fabrics that will have increased (improved) strength characteristics, namely, improved resistance to tearing, an increased modulus of elasticity, and have increased elongation at break, as well as to develop a method for industrial processing of para-aramid threads and fabrics that will ensure an increase in the said characteristics.

Revealing the essence

The technical result of the technical solution claimed as an invention consists in increasing the protective properties of para-aramid threads and fabrics, as well as their effectiveness under impact by providing increased strength characteristics of para-aramid threads and fabrics, such as resistance to tearing, elasticity and elongation, as well as in expanding the arsenal of technical means.

The claimed technical result is achieved by implementing a method for increasing the strength characteristics of para-aramid threads and fabric by processing in a nonequilibrium low-temperature plasma, which consists in the fact that the processing is carried out in a modified plasmatron, with a constant injection of a gas mixture, and continuous movement of the thread or fabric, while preparing the para-aramid threads or fabric, taking samples of the threads or fabric and determining their technical characteristics in the laboratory, after which, according to the obtained laboratory data, the parameters of the mode of processing the materials in low-temperature plasma are determined, and then, threads or fabric are loaded onto a drawing device installed in the chamber of the modified plasmatron, and a preliminary vacuuming of the plasmatron chamber volume is performed, and then, first, oxygen is injected for 10 minutes, and then a constant injection of a gas mixture of argon and methane is carried out, while continuously moving the threads or fabric through the drawing device with the simultaneous implementation of the effect of a nanometric high-frequency capacitive discharge on hydrocarbon molecules, with the following processing parameters: the intensity range of the high-frequency capacitive discharge HF 750 _min - 3500 _max W, while the drawing speed is set depending on the processing time of 1-25 minutes per unit area, and the pressure in the plasma torch chamber is from 20 to 40 Pa, and the plasma temperature is from 40°C to 70°C.

In this case, the technical characteristics for threads are determined by the diameter, coating, twist, elastic modulus, tensile strength and elongation, for fabrics – surface density, coating, weave, elastic modulus, tensile strength and elongation.

In this case, the pulling device contains vertical shafts, rotating bobbins with threads or horizontal shafts, rotating rolls with fabric, tension shafts, feed and receiving bobbins.

In this case, during the process of continuous injection of the gas mixture, argon and methane are supplied in a ratio of 70/30.

Brief description of accompanying figures

Fig. 1, 2 – device and diagram for drawing para-aramid threads and fabric, respectively, in non-equilibrium low-temperature plasma;

Fig. 3 – graph of the change in strength indicators of control samples and samples of pararamid thread after exposure to nonequilibrium low-temperature plasma;

Fig. 4 – view of threads C – before modification, D – after modification;

Fig. 5 – graph of changes in the crystalline structure of tissues, where A is the control untreated sample.

Implementation of the invention

To implement the method proposed as an invention, which ensures an increase in the strength characteristics of para-aramid threads and fabrics by treating them in low-temperature plasma, thin para-aramid fibers are used - monofilaments twisted into a compacted single-core thread, or fabric made from such threads, and they are processed (Figs. 1 and 2) according to the following scheme:

1. Prepare para-aramid threads or fabrics for processing in low-temperature plasma, during which samples of threads or fabrics are taken, after which the input technical characteristics are assessed using laboratory methods: for para-aramid threads - diameter, coating, twist, elastic modulus, tensile strength and elongation, for fabrics - surface density, coating, weave, elastic modulus, tensile strength and elongation.

2. Based on the laboratory data obtained, the specific parameters of the applied material processing mode in a nonequilibrium low-temperature plasma are determined. In particular, the RF and processing time are selected, which determines the speed, where speed is the speed of the thread/fabric movement, RF is the discharge power, and time is the time the thread/fabric remains between the electrodes. Threads have different thicknesses, and fabrics, depending on the weaving method and the thread thickness, have different surface densities (e.g., from 145 grams/ ^m2 to 200 grams/ ^m2 ). With increased thickness and surface density, the intensity of the high-frequency capacitive discharge (RF) and the processing time per unit area of the material (thread or fabric) increase, and, consequently, the drawing speed decreases.

3. Load the thread or fabric onto the feeding device.

4. Preliminary vacuuming of the plasma torch chamber is carried out.

5. Oxygen is injected for 10 minutes, followed by continuous injection of a gas mixture, during which argon and methane are supplied in a ratio of 70/30.

6. The treatment of para-aramid threads or fabric in the plasmatron chamber with non-equilibrium low-temperature plasma is carried out with continuous pulling of the thread or fabric through the pulling device and continuous injection of a gas mixture, by means of the nanometric effect of a high-frequency capacitive discharge on hydrocarbon molecules, according to the selected treatment mode.

The parameters of the low-temperature plasma processing mode are characterized by the following ranges of values: the intensity range of the high-frequency capacitive discharge HF 750 _min - 3500 _max W; the drawing speed is determined by the processing time of 1-25 minutes per unit area, the pressure in the plasma torch chamber from 20 to 40 Pa and the plasma temperature from 40°C to 70°C.

The proposed method for increasing the strength characteristics of para-aramid yarns and fabrics in non-equilibrium low-temperature plasma uses the following equipment:

- laboratory equipment for incoming inspection of the physical and mechanical properties of para-armid thread and fabric, in particular the Shumadzu AG-X plus tensile testing machine with a software package for determining the modulus of elasticity, elongation and strength of fabric/thread;

- equipment operating on electronic-physical and vacuum principles - a device for creating low-temperature plasma - a plasmatron, for example, the "VATT 4000 PT PLASMA", which has been modernized to allow for the continuous supply of para-aramid threads or fabric.

The plasma torch used to implement the method contains two main units:

- a unit for generating nonequilibrium low-temperature plasma, which carries out plasma action on the workpiece - para-armide threads or fabric, this is a device used in various fields of technology, in particular for processing fabric, metals, plastics, glass;

- a para-aramid thread or fabric feed unit - a device that allows for large-scale rewinding of thread or fabric from feed reels to receiving reels between rewinding units, while during the rewinding process the para-aramid thread or fabric is treated with non-equilibrium low-temperature plasma, and the treatment process is continuous.

To implement the proposed method on standard plasma torch equipment, such as the VATT 4000 PT PLASMA, a special mechanism—a drawing device—was installed in the torch. The use of such modified equipment—a drawing device tailored specifically for a specific task, using standard components—allows for adapting technological processes to the specific needs and requirements of industrial processing. The diagram of the drawing device and its placement in the plasma torch are shown in Figs. 1-2, where Fig. 1 depicts filament processing, and Fig. 2 — fabric processing, and the following main units are designated by positions: 1a, b — shafts rotating threads or fabric, 2a, b — electrodes, 3a, b — threads or fabric passing between the electrodes in a plasma environment, 4a, b — thread or fabric tension shafts, 5a, b — shafts rotating the feed spools with threads or fabric, 6a, b — a plasma environment between the electrodes and the passing threads or fabric, 7a, b — a take-up spool with threads or fabric. In this case, vertical shafts 5a and 7a are installed in the plasma torch for thread processing, and horizontal shafts 5b and 7b for fabric processing. If it is necessary to process threads or fabric for a longer period of time, for example, when it is necessary to process high-density threads and fabrics, additional shafts can also be installed in the drawing device, which thereby allow to increase the path of movement of threads or fabric, and, accordingly, the processing time.

The use of low-temperature plasma and the processing of para-aramid threads and fabrics under vacuum conditions allows for the following effects:

- Chemical Bonding, since plasma treatment allows functional groups to be brought to the surface of aramid fibers, improving their compatibility with various matrices (e.g. resins in composites) or improving the adhesion between fibers, and, over time, these newly formed bonds can continue to develop and strengthen, leading to improved mechanical properties;

- cross-linking, since plasma treatment causes cross-linking reactions on the surface of the fibers, increasing their molecular weight and intermolecular forces, which leads to improved mechanical properties such as tensile strength and elastic modulus;

- Annealing Effect, due to the fact that gentle heating during plasma treatment causes an annealing effect on aramid fibers, relieving internal stresses and increasing their overall structural integrity, while this effect continues to manifest itself and improve the strength characteristics of the fibers over time.

An increase in the strength properties of para-aramid thread and fabric after exposure to nonequilibrium low-temperature plasma occurs immediately after their treatment, and, to evaluate the results of the exposure, laboratory tensile tests are again carried out, the modulus of elasticity and the elongation index are determined in a tensile testing machine, thus recording an increase in the strength properties of para-aramid thread and fabric after exposure to nonequilibrium low-temperature plasma.

The graph of changes in the technical characteristics of the control and modified yarn samples is presented in Fig. 3, where the breaking load increases by 65%, and an increase in the elastic modulus and elongation is also observed. The graph shows the results for 10 yarn samples. For the initial breaking load test, 5 yarn samples are taken from one untreated bobbin. All samples have different breaking load values, which are recorded on a tensile testing machine with software, and these untreated samples have a breaking load from 600 to 1000 N. After the yarn modification, tests are repeated on a tensile testing machine for 5 treated samples, and the tests record an increase in breaking load, since the treated samples have breaking load values from 1200 to 1800 N.

Also after processing, a pronounced chemical bonding of monofilaments, their cross-linking, is observed, which is shown in Fig. 4, where type C is before modification, type D is after modification, and remains unchanged even after long-term storage under natural conditions.

Low-temperature plasma treatment using nanometric high-frequency capacitive discharge on hydrocarbon molecules alters the crystal lattice structure, increasing crystallinity and forming additional bonds, as evidenced by the graphs shown in Fig. 5, where the difference in parameters between the control and treated samples is +15%. This change is calculated from the change, or decrease, in the peak half-width in the 8-32.5° 2Theta region, and the wave on the graph is an infrared "shot" that operates on the "echo sounder" principle, recording the response and demonstrating the density/crystallinity of the structure.

As an example of the method implementation, the processing of para-aramid technical fabric, manufactured by JSC Shchelkovskaya Silk Weaving Factory, TU: 8378-020-00320992-2004, is given, which is characterized by the following parameters:

Fabric type: para-aramid (technical)

Fabric art.: 84127 ready (with water-repellent impregnation)

Weave type: Twill

Width: 105 cm

P.P. (surface density): 145 g/ ^m2

Thread in the fabric composition: para-aramid (technical), manufacturer: JSC Kamenskvolokno, TU: 2272-036-51605609-2010

Art. threads: RUSLAN 29.4 (200)-A-A-1

Tex: 29.4.

The tests were carried out in accordance with GOST 29104.4-91 "TECHNICAL FABRICS. Method for determining the breaking load and elongation at break", using a Shumadzu AG-X plus tensile testing machine and CAS model CBL electronic laboratory scales - Fabric weight 145 g / m ^2. A preliminary modification of the VATT 4000 PT PLASMA plasma torch was carried out, and a drawing device was installed inside the chamber.

Sample preparation:

a) Cutting the fabric into strips 400 mm (along the base) in length and 40 mm in width.

b) 5 strips for each test.

c) Preparation of fabric samples – removing threads from the right and left along the length of the fabric, up to 25 mm in width.

d) Marking of samples.

Electron microscopy MIRA3 TESCAN SEM HV:7.0 kV of the obtained fabric sample and the thread included in it showed:

1. The surface of the fabric is uniform;

2. Twill weave;

3. The threads inside the fabric do not have mutual surface diffusion (“gluing”);

4. The thread in the fabric is uniform, homogeneous in cross-section, round, outer diameter – Dвн 418 μm;

5. The monofilaments in the thread are uniform for the most part over the surface, uniform in cross-section, round, outer diameter – Dвн 0.0131 μm;

6. Monofilaments in the thread composition with “artifactual” inclusions – figures of complex geometric shapes on their surface;

7. Monofilaments in the thread are fixed with a reduced diameter Dвн 0.07 μm – 0.08 μm.

Fabric samples by base before processing:

Average tensile strength: 950 N

Average value of elastic modulus: 3359.84 MPa.

Fabric samples by weft before processing:

Average tensile strength: 950 N

Average value of elastic modulus: 3359.84 MPa.

Next, in accordance with the above fabric characteristics, the processing mode parameters were selected:

- Vacuum, the pressure in the chamber was 19.3-20.4 Pa

- Oxygen 10 minutes

- Gas AR-CH4 70/30

- RF power 1700 Watts

- Processing time 9 minutes

- Feed speed 0.25 meters/1 minute

- Plasma working area is 12 meters.

The fabric was loaded onto the feeder and processed in the chamber of the modified VATT 4000 PT PLASMA plasma torch. Subsequently, testing was conducted again, yielding the following results:

Fabric samples by base after processing:

Average break value: 1197 N (increase of +31%)

Average value of elastic modulus: 6537 MPa (increase in value +60%).

Fabric samples by weft after processing:

Average breaking strength: 1147 N (21%)

Average value of elastic modulus: 7002.23 MPa (108%).

Thus, according to the obtained data, it was concluded that as a result of processing the fabric in a nonequilibrium low-temperature plasma, according to the method proposed as an invention, an increase in the strength characteristics of the fabric was achieved, in particular, for the warp thread, the difference in the breaking strength index after processing increased by 31%, and the difference in the elastic modulus index after processing increased by 60%, for the weft thread, the difference in the breaking strength index after processing increased by 21%, and the difference in the elastic modulus index after processing increased by 108%.

As a result of implementing the proposed method, the para-aramid fibers included in the para-aramid thread and fabric, in addition to providing tear resistance, provide energy absorption from flying objects, reducing their impact. Treatment of the para-aramid thread and fabric with a nonequilibrium low-temperature plasma to impart enhanced strength properties improves the quality of the para-aramid thread and fabric.

Thus, the design of the claimed invention implements more advanced technical solutions for the industrial processing of para-aramid threads and fabrics in a nonequilibrium low-temperature plasma with continuous movement of the material, which allows for an increase in tensile strength, elastic modulus, and an increase in the elongation at break, which in turn increases the ability to absorb the energy of the moving element upon contact with the product, and improves the protective properties of para-aramid threads and fabrics, as well as their effectiveness.

The claimed invention consists of elements that are standard for this field of technology and can be used in industry, therefore the invention meets the patentability requirement of “industrial applicability”.

It should be understood that, after reviewing the description provided with the exemplary embodiment of the proposed invention, other changes, modifications, and embodiments of the invention will become apparent to a person skilled in the art. Therefore, all such changes, modifications, and embodiments, as well as other applications that do not deviate from the essence of the present invention, should be considered protected by the present invention within the scope of the appended claims.

Claims (4)

1. A method for increasing the strength characteristics of para-aramid threads and fabric by processing in a nonequilibrium low-temperature plasma, which consists in the fact that the processing is carried out in a modified plasmatron, with a constant injection of a gas mixture and continuous movement of the thread or fabric, while preparing the para-aramid threads or fabric, taking samples of the threads or fabric and determining their technical characteristics in the laboratory, after which, according to the obtained laboratory data, the parameters of the mode of processing the materials in low-temperature plasma are determined and then the threads or fabric are loaded onto a drawing device installed in the chamber of the modified plasmatron and a preliminary vacuum is performed in the volume of the plasmatron chamber, and then first oxygen is injected for 10 minutes and then a constant injection of a gas mixture of argon and methane is carried out, while continuously moving the threads or fabric through the drawing device with the simultaneous implementation of the effect of a nanometric high-frequency capacitive discharge on hydrocarbon molecules, with the following processing parameters: intensity range high-frequency capacitive discharge HF 750 _min -3500 _max W, while the drawing speed is set depending on the processing time of 1-25 minutes per unit area, and the pressure in the plasma torch chamber is from 20 to 40 Pa, and the plasma temperature is from 40°C to 70°C. 2. The method according to paragraph 1, characterized in that the technical characteristics for threads are determined by the diameter, coating, twist, modulus of elasticity, tensile strength and elongation, and for fabrics - surface density, coating, weave, modulus of elasticity, tensile strength and elongation. 3. The method according to paragraph 2, characterized in that the drawing device contains vertical shafts rotating bobbins with threads or horizontal shafts rotating rolls with fabric, tension shafts, feed and receive bobbins. 4. The method according to paragraph 3, characterized in that during the process of continuous injection of the gas mixture, argon and methane are supplied in a ratio of 70/30.