A qualitative identification method for meta-aramid fiber and para-aramid fiber and its application

Abstract

The present invention discloses a qualitative identification method and application of meta-aramid fiber and para-aramid fiber, comprising the following steps: cutting the fiber to be identified into fiber specimens; mixing the fiber specimens with a window material evenly and pressing them into a transparent thin sheet on a tablet press; placing the transparent thin sheet in a temperature-rising infrared spectroscopy window; heating the infrared spectrometer to 500 °C and recording the infrared spectrograms of the molecular thermal motion and thermal decomposition of the fiber specimens at preset interval temperature points; comparing and analyzing the infrared spectrograms of the molecular thermal motion and thermal decomposition of the fiber specimens at the preset interval temperature points with the infrared spectrograms of the molecular thermal motion and thermal decomposition of a reference sample, and determining whether the fiber to be identified is meta-aramid fiber or para-aramid fiber based on the comparison and analysis results of the absorption peak conditions at a temperature above 400 °C and a wavenumber of 1205 cm-1 and the absorption peak conditions at a wavenumber of about 818 cm-1 during the temperature rising process to 500 °C.

Description

Technical Field

[0001] The invention relates to the technical field of textile fibers, and in particular to a qualitative identification method for meta-aramid fibers and para-aramid fibers and applications thereof. Background Art

[0002] Aramid is the abbreviation of aromatic polyamide fiber. It is a representative of new special fibers with ultra-high strength, high modulus, light weight, long-lasting thermal stability, flame retardancy, super radiation resistance, acid and alkali chemical stability, and excellent electrical insulation and anti-aging properties. Aramid is not only used in the textile industry, but also an important material in national defense, military industry, medical treatment, environmental protection and cutting-edge science. It is one of the key materials developed in my country's strategic emerging industries.

[0003] According to the relative position of the amide bond on the benzene ring, aramid fiber is divided into meta-aramid fiber (aramid 1313, chemical name is poly(m-phenylene isophthalamide fiber)) and para-aramid fiber (aramid 1414, chemical name is poly(p-phenylene terephthalamide fiber). The molecular chain of meta-aramid fiber is arranged in a zigzag shape, while the molecular chain of para-aramid fiber is arranged in a straight line. Since the rotational potential energy inside the meta-aramid molecule is relatively low, its macromolecular chain presents a flexible structure; while the hydrogen bonds between the para-aramid molecules also have a conjugated effect and present rigid characteristics, with a high degree of symmetry and regularity, which determines that the fiber has a high degree of crystallinity and the crystallization is relatively complete.

[0004] Meta-aramid fiber and para-aramid fiber are widely used, but the lack of relevant standards for their inspection has brought difficulties to related work. Since the types and contents of chemical elements in the molecular composition of the two are the same, only the molecular arrangement and crystallinity are different. In the current standard system, it is necessary to refer to the combustion method (FZ / T 01057.2-2007), the microscopy method (FZ / T 01057.3-2007) and the dissolution method (FZ / T 01057.4-2007) to analyze and identify the physical and chemical properties of meta-aramid fiber and para-aramid fiber. The above analytical identification methods will bring different problems when qualitatively identifying meta-aramid fiber and para-aramid fiber. For example, the dissolution method requires the use of solvents to dissolve the aramid fiber, which will inevitably produce environmentally unfriendly test wastewater after the identification operation; the microscope method requires the use of a microscope to determine the changes in the morphology of the aramid fiber, which requires high professional quality and experience of the identification personnel; other methods also require a large number of repeated tests to obtain average results to determine the type of aramid fiber, and there are also problems such as inaccurate identification results. There is currently no good, efficient, stable and environmentally friendly qualitative identification method for meta-aramid fiber and para-aramid fiber. Summary of the invention

[0005] To this end, it is necessary to provide a qualitative identification method and application of meta-aramid fiber and para-aramid fiber, so as to provide a qualitative identification method of meta-aramid fiber and para-aramid fiber that does not use any solution and solvent, is efficient, environmentally friendly, accurate and stable, so as to fill the technical gap of the existing technology that there is no effective, environmentally friendly, efficient and stable identification of meta-aramid fiber and para-aramid fiber, and avoid the risks of the conventional dissolution method that may produce toxic and harmful liquids that are harmful to the environment and the melting point method that may cause inaccurate identification results due to subjective errors in visual inspection by the detector.

[0006] To achieve the above object, in one aspect of the present invention, the inventor provides a method for qualitatively identifying meta-aramid fiber and para-aramid fiber, comprising the following steps:

[0007] Sample preparation: Cut the fiber to be identified into fiber samples;

[0008] Preparation of transparent samples: Cut the fibers to be identified into fiber samples;

[0009] Preparation of transparent sheet: the fiber sample and the window sheet material are mixed evenly, and then placed on a sheet press to be pressed into a transparent sheet;

[0010] The transparent sheet is placed in a temperature-elevable device and in front of the infrared spectrometer window;

[0011] The infrared spectrometer is heated to 500° C. to record infrared spectra of thermal motion and thermal decomposition of the fiber sample molecules at preset interval temperature points;

[0012] The infrared spectra of the molecular thermal motion and thermal decomposition of the fiber sample at the preset interval temperature points are compared with the infrared spectra of the molecular thermal motion and thermal decomposition of the reference sample, with the temperature being above 400°C and the wave number being 1205cm -1 The absorption peak at the position and the wave number when the temperature rises to 500℃ is 818cm -1 The absorption peaks at the left and right positions are compared and analyzed to determine whether the fiber to be identified is meta-aramid fiber or para-aramid fiber.

[0013] Aramid is a new type of special polymer material with outstanding properties such as flame retardancy, high temperature resistance, high strength, high modulus, and insulation. The molecular chains of meta-aramid fibers are arranged in a zigzag shape, while the molecular chains of para-aramid fibers are arranged in a straight line. Since the rotational potential energy inside the meta-aramid molecules is relatively low, its macromolecular chain presents a flexible structure; while the hydrogen bonds between the para-aramid molecules also have a conjugated effect and present rigid characteristics, with a high degree of symmetry and regularity, which determines that the fiber has a high degree of crystallinity and relatively complete crystallinity. At present, meta-aramid and para-aramid have achieved widespread commercial application and production. The application of meta-aramid in the field of safety protection in China has grown rapidly, such as various protective equipment used by military, police, and industrial workers; para-aramid is mainly used for individual soldier protection, weapons and equipment, etc. in the military. The current conventional fiber identification methods such as the dissolution method require the use of solvents to dissolve the aramid fiber, which will inevitably produce environmentally unfriendly test wastewater after the identification operation; the microscopy method requires the use of a microscope to determine the changes in the morphology of the aramid fiber, which requires high professional quality and experience of the identification personnel; other methods also require a large number of repeated tests to obtain average results to determine the type of aramid fiber, and there are also problems such as inaccurate identification results. Meta-aramid fiber and para-aramid fiber at room temperature are all high-temperature resistant fibers, the fiber molecules are below the glass transition temperature, and the molecular motion is subject to certain constraints. In addition, at room temperature, since the types and contents of the chemical elements that make up the molecules of meta-aramid fiber and para-aramid fiber are the same, only the molecular arrangement and crystallinity are different, the infrared spectra produced by the mid-infrared at room temperature are too subtle, and a strong professional basic knowledge and careful distinction are required to make preliminary identifications. Therefore, it is not feasible to distinguish the two fibers based on the molecular motion spectrum at room temperature. There are great differences between meta-aramid and para-aramid in terms of performance and price, but there is currently a lack of efficient, stable and environmentally friendly qualitative identification methods, which to some extent has caused difficulties in the application of meta-aramid and para-aramid in different industries.

[0014] It is in this context that the inventors, through unremitting research and exploration, have discovered through a large number of practices that there are differences in the molecular chain arrangement of meta-aramid fibers and para-aramid fibers, which in turn affects the molecular motion of the two aramid fibers, and the internal motion of the molecules in turn affects the properties of the molecular spectrum. Based on the principles of thermal motion and thermal stability of fiber molecules, the inventors collected infrared spectra of meta-aramid and para-aramid fiber samples to be tested at different temperatures without using any solutions or solvents to reflect the changes in molecular microscopic thermal motion and pyrolysis properties, so that they can be displayed in the form of absorption spectra to achieve the purpose of qualitative identification.

[0015] Infrared light is a type of electromagnetic wave. Electromagnetic waves are arranged in a certain order of wavelength or wave number, and are mainly divided into radio waves, microwaves, infrared light (rays), visible light, ultraviolet light (rays), X-rays and gamma rays. Infrared light (rays) belongs to molecular spectrum, and there are two types: infrared emission spectrum and infrared absorption spectrum. The commonly used one is infrared absorption spectrum. The absorption of infrared light by molecules is recorded by instruments to obtain infrared spectrum. Infrared absorption spectrum is produced by the constant vibration and rotation of molecules. Molecular vibration refers to the relative movement of atoms in molecules near the equilibrium position. Polyatomic molecules can form a variety of vibration patterns. When atoms in a molecule perform simple harmonic vibrations near the equilibrium position at the same frequency and the same phase, this vibration mode is called simple normal vibration (such as stretching vibration and angular vibration). The energy of molecular vibration corresponds exactly to the energy of infrared light quanta. Therefore, when the vibration state of the molecule changes, infrared spectrum can be emitted, and infrared absorption spectrum can also be produced due to the vibration of the molecule caused by infrared radiation. The energy of molecular vibration and rotation is not continuous but quantized. However, since the vibration transition of molecules is often accompanied by rotation transition, the vibration spectrum is band-shaped. Classification of infrared absorption spectrum: According to the infrared wave number test range, the infrared spectrum can be divided into three types: near infrared, mid infrared and far infrared. Near infrared light refers to the frequency between 12500-4000cm -1 The near-infrared spectrum is generated by electromagnetic waves in the range of (wavelength 0.8-2.5μm), mainly due to the non-resonance of molecular vibration, which makes the transition of molecular vibration from the ground state to the high energy level possible. In the near-infrared spectrum range, what is measured is mainly the double frequency and combined frequency absorption of the vibration of hydrogen-containing groups XH (X=C, N, O, S, etc.). The main technical features of near-infrared spectroscopy analysis are as follows: (1) fast analysis speed; (2) high analysis efficiency; (3) low analysis cost; (4) good test reproducibility; (5) easy to realize online analysis; (6) typical non-destructive analysis. Modern near-infrared spectroscopy also has its inherent weaknesses: first, the test sensitivity is relatively low, which is mainly because the near-infrared spectrum has a low probability of non-resonant absorption transition as a molecular vibration. Generally, the spectral band intensity of near-infrared harmonics and combined frequencies is 10 to 10,000 of its fundamental frequency absorption. As far as the analysis of components is concerned, its content should generally be greater than 0.1%; second, it is an indirect analysis technology. The model on which the method relies must first use standard reference methods or reference methods to determine the composition or property data of samples within a certain range. Therefore, the establishment of the model requires certain chemometric knowledge, costs and time.

[0016] Frequency is 4000-400cm -1The mid-infrared wavelength region (wavelength of 2.5-25μm) is the most commonly used region. The main technical features of mid-infrared spectroscopy analysis are as follows: Mid-infrared spectroscopy is mainly used for qualitative or quantitative analysis of organic compounds. However, conventional mid-infrared spectroscopy is not suitable for the determination of trace components because the sensitivity and signal intensity of testing trace components are relatively low. This is mainly due to the low probability of non-resonant absorption transitions of infrared spectroscopy as molecular vibrations; if there is no change in the dipole moment of the vibration of the group, it is infrared inactive and cannot provide information about the existence of the group; it is not suitable for analyzing aqueous samples because the hydroxyl peak in water interferes with the determination; the confirmation of the overall structure of the compound requires a standard spectrum or a known pure substance, otherwise the compound cannot be confirmed by a simple infrared spectrum.

[0017] The frequency of the far infrared spectrum is between 400-10cm -1 (wavelength is 25-100μm). The absorption bands in this region are mainly caused by pure rotational transitions in gas molecules, vibration-rotational transitions, stretching vibrations of heavy atoms in liquids and solids, certain angular vibrations, skeleton vibrations, and lattice vibrations in crystals. Since low-frequency skeleton vibrations can sensitively reflect changes in the structure of substances, it is particularly convenient for isomer research. In addition, far-infrared spectroscopy is also effective for quantitative analysis of organic metal compounds (including complexes), hydrogen bonds, and adsorption phenomena. In environmental analysis tests, the energy of the light source in the far-infrared spectral region is weak, unless it is used for phase identification; phase content analysis in samples; element content analysis in crystals; gem identification; polymorph variant research; isomorphic substitution research; crystal order research; gene existence form judgment; study of the molecular structure, molecular arrangement and functional group orientation of the material surface.

[0018] The conventional operation of infrared spectrometer is carried out at room temperature and includes the following steps:

[0019] 1. Turn on the power switch of the infrared spectrometer.

[0020] 2. Click on the computer screen to open the OMINIC workstation software.

[0021] 3. Click Settings to switch the screen to the settings interface and then initialize the instrument.

[0022] 4. Prepare potassium bromide blank tablets, sample tablets, or directly prepare potassium bromide tablets for samples.

[0023] 5. Place the pressed potassium bromide blank sheet (a blank potassium bromide sheet without sample) on the sample rack in the sample compartment of the spectrometer.

[0024] 6. Click the background button under the measurement button, enter the spectrum name, and confirm the collection of the reference background spectrum.

[0025] 7. After the background spectrum is collected, place the sample to be tested into the spectrometer and close the lid.

[0026] 8. The software can perform various processing on the spectrum as required, such as marking peaks, selecting Print from the File menu, and printing the spectrum as a report in different forms.

[0027] 9. Exit the system.

[0028] Different from the prior art, the technical solution of the present invention adopts mid-infrared heating technology, and uses the infrared absorption spectrum of the fiber sample to be identified to show the changes in molecular microscopic thermal motion and pyrolysis performance, and then compares it with the absorption peaks of the meta-aramid fiber reference sample and the para-aramid fiber reference sample at a specific wave number position and a specific temperature. The fiber sample to be identified is determined and distinguished based on the comparison results, and the discrimination result is simpler and more intuitive. The technical solution of the present invention is essentially different from the methods such as mid-infrared and far-infrared room temperature identification of meta-aramid fiber and para-aramid fiber that may be used in the prior art. The technical solution of the present invention does not use any additional solvents, nor does it require other pretreatment of the fiber to be identified. It only takes about 30 minutes from obtaining the fiber to be identified to obtaining the identification result. This method is very efficient, environmentally friendly and accurate, and is suitable for wide promotion in market entities and testing institutions that purchase and apply meta-aramid fiber and para-aramid fiber and their textiles.

[0029] According to some embodiments of the present invention, if the absorption peak comparison result is: starting from 400°C, the wave number is 1205cm -1 There is an absorption peak around 500℃, with a wave number of 818cm -1 If the absorption peaks around 1205cm are significantly weakened, it is determined that the fiber to be identified is meta-aramid fiber; if the absorption peak comparison result is: from room temperature to temperature 500℃, the wave number is 1205cm -1 There is no absorption peak on the left and right sides; from room temperature to 500℃, the wave number is 818cm -1 If the absorption peak intensity around 818cm does not change, the fiber to be identified is para-aramid fiber. -1 The absorption peaks on the left and right reflect the relative position of the amide bond on the benzene ring. Since the hydrogen bonds between the para-aramid molecules also have a conjugated effect and show rigidity, the intensity of the absorption peak does not change when the temperature rises to 500°C. The rotational potential energy inside the meta-aramid molecule is relatively low. Starting from 400°C, the wave number is 1205cm -1 The absorption peaks appearing on the left and right correspond to the changes in the molecular structure caused by thermal decomposition. For the present invention, not only is the use of infrared absorption spectra with heating in the mid-infrared band a breakthrough in traditional identification methods, but how to analyze the identification results and draw identification conclusions is also a major contribution of the present invention.

[0030] According to some embodiments of the present invention, based on the qualitative identification method of meta-aramid fiber and para-aramid fiber, when the temperature of the heating device is raised to 500°C, the temperature can be raised at a heating rate of 10-30°C / min. This is related to the characteristics of meta-aramid fiber and para-aramid fiber that change with temperature. When the heating rate is less than 10°C / min, the identification time will be prolonged due to the slow heating rate, and heat accumulation will occur, making the actual temperature of the fiber sample to be tested higher than the temperature displayed on the temperature control device; when the heating rate is greater than 30°C / min, the temperature response of the fiber sample to be tested cannot keep up, making the actual temperature of the fiber sample to be tested lower than the temperature displayed on the infrared spectrometer temperature control device, affecting the identification result.

[0031] The qualitative identification method of meta-aramid fiber and para-aramid fiber provided by the present invention also has some specific embodiments, wherein the preset interval temperature points are configured to be 10°C-100°C. The preset interval temperature points are related to the density of the infrared spectra of the thermal motion and thermal decomposition of the obtained fiber sample molecules. The smaller the value of the preset interval temperature points, the denser the infrared spectra of the thermal motion and thermal decomposition of the obtained fiber sample molecules; otherwise, the more dispersed. Too frequent acquisition frequency will prolong the identification time; too dispersed acquisition frequency may miss key change information, affecting the identification results.

[0032] In some preferred embodiments of the qualitative identification method of meta-aramid fiber and para-aramid fiber, the window material is potassium bromide. Potassium bromide crystals are in the mid-infrared spectrum test band (4000-600cm -1 ) is one of the most transparent (almost no absorption peak) window materials, the cheapest and most readily available, not seriously deliquescing, easy to use in actual measurements for a long time, and has mechanical strength that is easy to apply and suitable for processing into practical windows. In addition, cesium iodide (CsI) is also one of the most ideal window materials, but cesium iodide is slightly more expensive and slightly more deliquescent than potassium bromide. The present application prefers potassium bromide as the window material for identifying meta-aramid fibers and para-aramid fibers based on the above considerations.

[0033] In some other preferred qualitative identification method embodiments of meta-aramid fiber and para-aramid fiber, during the transparent sheet preparation step, after the fiber to be identified is cut into fine fiber samples, 0.1-1 mg of the fiber sample is mixed with 20-40 mg of the window material. Too little sample amount will weaken the infrared spectrum signal, or even cause spectrum peak loss; too much sample amount will saturate the infrared signal and make analysis and identification impossible. Too little window material will cause incomplete sample preparation; and too much window material will cause the pressed sheet to be too thick, affecting the infrared spectrum signal.

[0034] In some other preferred qualitative identification method embodiments of meta-aramid fiber and para-aramid fiber, the pressure when the fiber is placed on a tablet press to be pressed into a transparent sheet is 6-10 MPa. If the pressure is too low during the tableting operation, the tablet will be thick and opaque, which will seriously affect the infrared signal; if the pressure is too high, the tablet will break and it will be impossible to carry out the identification experiment.

[0035] In some other preferred qualitative identification method embodiments of meta-aramid fiber and para-aramid fiber, the average length of the fiber sample is 0.01-0.1 mm. The fiber sample to be identified with an average length that is too short is difficult to handle when mixed with potassium bromide for tableting; the fiber sample to be identified with an overly long length will reduce the light transmittance of the sample and weaken the infrared signal.

[0036] In some other preferred qualitative identification method embodiments of meta-aramid fiber and para-aramid fiber, the fiber to be identified is meta-aramid fiber or para-aramid fiber. When the qualitative identification method provided by the present invention is used, the fiber to be identified can of course also be other unknown fibers except meta-aramid fiber and para-aramid fiber, but for more practical industrial applications, the more efficient application is to identify and distinguish the fiber to be identified as either meta-aramid fiber or para-aramid fiber.

[0037] To achieve the above-mentioned purpose of the present application, in another aspect of the present invention, the inventor provides the application of the qualitative identification method of meta-aramid fiber and para-aramid fiber described in the first aspect in identifying and distinguishing meta-aramid fiber and para-aramid fiber.

[0038] Different from the prior art, the above technical scheme can efficiently and accurately determine whether the fiber to be identified is meta-aramid fiber or para-aramid fiber when it is known that the fiber to be identified is either meta-aramid fiber or para-aramid fiber. There is no need to add other organic solvents, photoelectric detection or rely on subjective visual inspection, and there is no need to operate the instrument for a long time to wait for the results. It is more environmentally friendly, efficient and accurate, and provides an innovative fiber identification technology scheme, filling the technical gap in non-solvent identification of meta-aramid fiber and para-aramid fiber. It is suitable for large-scale production practice in industry, is conducive to promotion and application in the textile industry, and can promote the development of inspection and testing technology.

[0039] The above-mentioned records related to the invention content are only an overview of the technical solution of the present application. In order to enable ordinary technicians in the field to more clearly understand the technical solution of the present application, and then implement it according to the text of the specification and the contents recorded in the drawings, and to make the above-mentioned purpose and other purposes, features and advantages of the present application easier to understand, the following is an explanation in combination with the specific implementation mode and drawings of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The drawings are only used to illustrate the principles, implementation methods, applications, characteristics and effects of the specific embodiments of the present application and other related contents, and shall not be considered as limitations of the present application.

[0041] Figure 1 They are schematic diagrams of the molecular structures of meta-aramid fiber and para-aramid fiber at room temperature;

[0042] Figure 2 This is the infrared spectrum of the thermal motion and thermal decomposition (25-500°C) of meta-aramid fiber molecules;

[0043] Figure 3 This is the infrared spectrum of the thermal motion and thermal decomposition (25-500°C) of para-aramid fiber molecules. DETAILED DESCRIPTION

[0044] In order to explain in detail the possible application scenarios, technical principles, specific schemes that can be implemented, and the purposes and effects that can be achieved, the following is a detailed description of the specific embodiments listed in conjunction with the accompanying drawings. The embodiments described herein are only used to more clearly illustrate the technical solutions of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0045] Reference to "embodiment" herein means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The term "embodiment" appearing in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or association with other embodiments. In principle, in the present application, as long as there is no technical contradiction or conflict, the various technical features mentioned in the embodiments can be combined in any way to form a corresponding implementable technical solution.

[0046] Unless otherwise defined, the technical terms used in this document have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms in this document is only for describing specific embodiments and is not intended to limit this application.

[0047] In the description of this application, the term "and / or" is an expression used to describe the logical relationship between objects, indicating that three relationships may exist, for example, A and / or B, which means: A exists, B exists, and A and B exist at the same time. In addition, the character " / " in this article generally indicates that the objects before and after are in an "or" logical relationship.

[0048] In the present application, terms such as “first” and “second” are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship of quantity, priority or sequence between these entities or operations.

[0049] Without further limitations, in this application, the words "include", "comprises", "has" or other similar expressions used in the sentences are intended to cover non-exclusive inclusion. These expressions do not exclude the presence of additional elements in the process, method or product including the elements, so that the process, method or product including a series of elements may include not only those limited elements, but also other elements not explicitly listed, or also include elements inherent to such process, method or product.

[0050] Similar to the understanding in the Examination Guidelines, in this application, expressions such as "greater than", "less than", "exceed" and the like are understood to exclude the number itself; expressions such as "above", "below", "within" and the like are understood to include the number itself. In addition, in the description of the embodiments of this application, "multiple" means more than two (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups", "multiple times", etc., unless otherwise clearly and specifically limited.

[0051] In the description of the embodiments of the present application, space-related expressions used, such as "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "vertical", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicate the orientation or position relationship based on the orientation or position relationship shown in the specific embodiments or drawings, and are only for the convenience of describing the specific embodiments of the present application or facilitating the reader's understanding, and do not indicate or imply that the referred device or component must have a specific position, a specific orientation, or be constructed or operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0052] Unless otherwise expressly specified or limited, in the description of the embodiments of the present application, the terms such as "install", "connect", "connect", "fix", "set", etc. used should be understood in a broad sense. For example, the "connection" can be a fixed connection, a detachable connection, or an integrated setting; it can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. For technicians in the technical field to which the present application belongs, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0053] The infrared spectrometer used in the examples of this application is a Nicolet 380 Fourier transform infrared spectrometer from Thermo Scientific; the spectral resolution is set to 4 cm -1 , the number of scans is set to 32 times.

[0054] The temperature control instrument used in the embodiments of the present application is the Beijing UPSCO YPS-AT700 intelligent PID temperature controller.

[0055] The tablet press used in the examples of the present application is a YP-2 tablet press produced by Shanghai Shanyue Scientific Instrument Co., Ltd.

[0056] The potassium bromide used in the examples of the present application is potassium bromide crystal commonly used in infrared spectroscopy in the technical field, spectrally pure, dried in a drying oven for 24 hours before use, and operated under an infrared lamp during use.

[0057] The infrared lamp used in the embodiments of the present application is the Shanghai Minghua Yaming HW-250W infrared lamp.

[0058] Example 1

[0059] like Figure 1 As shown in the figure, there is only a slight difference between the molecular structure diagrams of meta-aramid fiber and para-aramid fiber at room temperature, that is, the molecular chain arrangement of meta-aramid fiber is zigzag, and the molecular chain arrangement of para-aramid fiber is straight. After heating them to 500℃ and observing them in the mid-infrared band, different spectral information can be obtained. Figure 2 The mid-infrared absorption spectrum of the meta-aramid fiber reference sample at 50° C. heating intervals is shown. This embodiment provides a method for obtaining a mid-infrared spectrum of molecular thermal motion and thermal decomposition of a meta-aramid fiber reference sample.

[0060] Specifically, 1 g of a known reference meta-aramid fiber was cut into fiber samples with an average length of 0.01 mm using a Hastelloy slicer; 0.1 mg of the meta-aramid fiber sample was mixed with 20 mg of potassium bromide powder and placed on a tablet press, and the tablet press pressed the meta-aramid fiber sample and the potassium bromide powder uniformly mixed product into a transparent sheet at a pressure of 8 MPa, placed in a ceramic heating ring and placed at the window of a Nicolet 380 Fourier transform infrared spectrometer, and the temperature control instrument was set to heat from room temperature 25°C to 500°C at a rate of 25°C / min, and the infrared spectra of the thermal motion and thermal decomposition of the meta-aramid fiber molecules at each temperature point of 50°C were recorded to obtain Figure 2 The meta-aramid fiber reference sample spectrum is shown.

[0061] from Figure 2 The analysis shows that the meta-aramid fiber reference sample starts at 400℃ and the wave number is 1205cm -1 At 500℃, the absorption peak is at 818cm -1 The absorption peaks on the left and right are significantly weakened.

[0062] Example 2

[0063] See also Figure 3 The mid-infrared absorption spectrum of the para-aramid fiber reference sample at 50° C. heating intervals is shown. This embodiment provides a method for obtaining a mid-infrared spectrum of molecular thermal motion and thermal decomposition of the para-aramid fiber reference sample.

[0064] Specifically, 1 g of a known reference para-aramid fiber was cut into a fiber sample with a length of 0.01 mm using a Hastelloy slicer; 0.1 mg of the para-aramid fiber sample was mixed with 20 mg of potassium bromide powder and placed on a tablet press, which was pressed into a transparent sheet at a pressure of 7 MPa and placed in a ceramic heating ring and placed at the window of a Nicolet 380 Fourier transform infrared spectrometer. The temperature control instrument was set to heat from room temperature 25°C to 500°C at a rate of 25°C / min, and the infrared spectra of thermal motion and thermal decomposition of the para-aramid fiber molecules at each temperature point of 50°C were recorded to obtain Figure 3 Shown is the reference sample spectrum of para-aramid fiber on which the technical solution of this application is based.

[0065] from Figure 3 From the analysis, we can see that as the temperature increases from room temperature to 500°C, the wave number at 1205cm -1 There is no absorption peak on the left and right sides; from room temperature to 500℃, the wave number is 818cm -1 There is no change in the intensity of the absorption peaks on the left and right.

[0066] The corresponding relationship between the infrared absorption peaks and the mid-infrared spectrum frequencies and temperatures of the meta-aramid fiber and para-aramid fiber reference samples obtained in Example 1 and Example 2 is shown in Table 1.

[0067] Table 1 Correspondence between infrared absorption peaks and mid-infrared spectrum frequencies and temperatures of meta-aramid fiber and para-aramid fiber reference samples

[0068]

[0069] Example 3

[0070] It is known that the fiber to be identified is one of meta-aramid fiber or para-aramid fiber, and the type of fiber to be identified is qualitatively identified. The specific method is as follows:

[0071] Sample preparation: Use a Hastelloy slicer to cut 1g of the fiber to be identified into fiber samples with an average length of 0.1mm;

[0072] Preparation of transparent thin sheets: 0.1 mg of the fiber sample was mixed evenly with 20 mg of dry spectrally pure potassium bromide crystals and placed on a tablet press and pressed into transparent thin sheets at a pressure of 6 MPa;

[0073] The transparent sheet was placed in the window of Nicolet 380 Fourier transform infrared spectrometer (heatable);

[0074] The heating rate of the Nicolet 380 Fourier transform infrared spectrometer was set to 25°C / min, and the temperature was raised from room temperature to 500°C, and the infrared spectra of the molecular thermal motion and thermal decomposition of the fiber sample were continuously recorded at every 25°C.

[0075] The infrared spectra of the molecular thermal motion and thermal decomposition of the fiber sample at every 25°C are compared with the infrared spectra of the molecular thermal motion and thermal decomposition of the meta-aramid reference sample obtained by the methods in Example 1 and Example 2. If the absorption peak comparison result is: starting from 400°C, the wave number is at 1205cm -1 There is an absorption peak around 500℃, with a wave number of 818cm -1 If the absorption peaks around 1205cm are significantly weakened, it is determined that the fiber to be identified is meta-aramid fiber; if the absorption peak comparison result is: from room temperature to temperature 500℃, the wave number is 1205cm -1 There is no absorption peak on the left and right sides; from room temperature to 500℃, the wave number is 818cm -1 If the absorption peak intensity on the left and right does not change, it is determined that the fiber to be identified is para-aramid fiber.

[0076] Example 4

[0077] The difference from Example 3 is that:

[0078] Sample preparation: Use a Hasse slicer to cut 0.1g of the fiber to be identified into fiber samples with an average length of 0.01mm;

[0079] Preparation of transparent sheets: 0.2 mg of the fiber sample was mixed evenly with 30 mg of dry spectrally pure potassium bromide crystals and placed on a tablet press to press into transparent sheets at a pressure of 9 MPa;

[0080] The heating rate of the Nicolet 380 Fourier transform infrared spectrometer was set to 10°C / min, and the temperature was raised from room temperature to 500°C, and the infrared spectra of the molecular thermal motion and thermal decomposition of the fiber sample were continuously recorded at every 50°C.

[0081] The infrared spectra of the molecular thermal motion and thermal decomposition of the fiber sample at every 50°C are compared with the infrared spectra of the molecular thermal motion and thermal decomposition of the meta-aramid reference sample and the para-aramid reference sample obtained by the method in Example 1 and Example 2, respectively. If the absorption peak comparison result is: starting from 400°C, the wave number is at 1205cm -1 There is an absorption peak around 500℃, with a wave number of 818cm -1If the absorption peaks around 1205cm are significantly weakened, it is determined that the fiber to be identified is meta-aramid fiber; if the absorption peak comparison result is from room temperature to temperature 500℃, the wave number is 1205cm -1 There is no absorption peak on the left and right sides; from room temperature to 500℃, the wave number is 818cm -1 If the absorption peak intensity on the left and right does not change, it is determined that the fiber to be identified is para-aramid fiber.

[0082] Example 5

[0083] The difference from Example 3 is that:

[0084] Sample preparation: Use a Hastelloy slicer to cut 0.2g of the fiber to be identified into a fiber sample with a length of 0.05mm;

[0085] Preparation of transparent thin sheets: 1 mg of the fiber sample was mixed evenly with 40 mg of dry spectrally pure potassium bromide crystals and placed on a tablet press to press into transparent thin sheets at a pressure of 10 MPa;

[0086] The heating rate of the Nicolet 380 Fourier transform infrared spectrometer was set to 30°C / min, and the temperature was raised from room temperature to 500°C, and the infrared spectra of the molecular thermal motion and thermal decomposition of the fiber sample were continuously recorded at every 50°C.

[0087] The infrared spectra of the molecular thermal motion and thermal decomposition of the fiber sample at every 50°C are compared with the infrared spectra of the molecular thermal motion and thermal decomposition of the meta-aramid reference sample and the para-aramid reference sample obtained by the method in Example 1 and Example 2, respectively. If the absorption peak comparison result is: starting from 400°C, the wave number is at 1205cm -1 There is an absorption peak around 500℃, with a wave number of 818cm -1 If the absorption peaks around 1205cm are significantly weakened, it is determined that the fiber to be identified is meta-aramid fiber; if the absorption peak comparison result is from room temperature to temperature 500℃, the wave number is 1205cm -1 There is no absorption peak on the left and right sides; from room temperature to 500℃, the wave number is 818cm -1 If the absorption peak intensity on the left and right does not change, it is determined that the fiber to be identified is para-aramid fiber.

[0088] Example 6

[0089] The difference from Example 3 is that:

[0090] Sample preparation: Use a Hasse slicer to cut 0.8g of the fiber to be identified into a fiber sample with a length of 0.03mm;

[0091] 0.5 mg of the fiber sample was mixed evenly with 40 mg of dry spectrally pure potassium bromide crystals and placed on a tablet press and pressed into a transparent sheet at a pressure of 7 MPa;

[0092] The heating rate of the Nicolet 380 Fourier transform infrared spectrometer was set to 20°C / min, and the temperature was raised from room temperature to 500°C, and the infrared spectra of the molecular thermal motion and thermal decomposition of the fiber sample were continuously recorded at every 50°C.

[0093] The infrared spectra of the molecular thermal motion and thermal decomposition of the fiber sample at every 50°C are compared with the infrared spectra of the molecular thermal motion and thermal decomposition of the meta-aramid fiber reference sample and the para-aramid fiber reference sample obtained by the methods in Example 1 and Example 2, respectively. If the absorption peak comparison result is: starting from 400°C, the wave number is at 1205cm -1 There is an absorption peak around 500℃, with a wave number of 818cm -1 If the absorption peaks around 1205cm are significantly weakened, it is determined that the fiber to be identified is meta-aramid fiber; if the absorption peak comparison result is from room temperature to temperature 500℃, the wave number is 1205cm -1 There is no absorption peak on the left and right sides; from room temperature to 500℃, the wave number is 818cm -1 If the absorption peak intensity on the left and right does not change, it is determined that the fiber to be identified is para-aramid fiber.

[0094] The technical solutions represented by the above embodiments of the present invention do not use any solvents such as acid and alkali solutions, and no harmful substances such as wastewater and waste gas will be discharged during the identification process, so it has the characteristics of being environmentally friendly. Secondly, the main time of the identification operation, in addition to the cutting and sheeting of the fiber sample to be identified, is the heating time of the Nicolet 380 Fourier transform infrared spectrometer. Taking the heating rate of 20℃ / min as an example, it rises from room temperature 25℃ to 500℃, and then the infrared spectrometer automatically generates the infrared spectrum of the fiber sample to be identified and compares and analyzes it with the infrared spectrum of the existing meta-aramid fiber reference sample and the infrared spectrum of the para-aramid fiber reference sample. The total time required is less than 30min. In the fiber component analysis, 0.1-1g of sample is a large amount. The sample amount used in common fiber thermal analysis experiments or spectral experiments is 1-10mg; in addition, the large amount here also refers to the number of fibers, usually hundreds of fibers, which also reflects the integrity and representativeness of the sample, avoiding the defect that a single sample is not representative. Since a large number of fiber samples were used for the experiment, the experimental results are representative, so there is no need to repeat the infrared absorption spectrum test many times. In summary, the technical solution of the present application is aimed at the fiber to be identified is either meta-aramid fiber or para-aramid fiber, and has the advantages of high efficiency, accuracy and environmental protection. The inventors conducted repeated, large-scale and multiple tests (including blind selection tests) on samples of meta-aramid fiber and para-aramid fiber provided by fiber manufacturers or textile companies to verify that the identification results are consistent with the actual type of the product, and the repeatability of the identification accuracy is also consistent. The accuracy rate obtained by this identification method is as high as 100%.

[0095] Finally, it should be noted that although the above embodiments have been described in the specification and drawings of this application, this does not limit the scope of patent protection of this application. All technical solutions generated by replacing or modifying equivalent structures or equivalent processes based on the essential concept of this application using the contents recorded in the specification and drawings of this application, as well as directly or indirectly implementing the technical solutions of the above embodiments in other related technical fields, are included in the scope of patent protection of this application.

Claims

1. A qualitative identification method for meta-aramid fiber and para-aramid fiber, characterized in that: The following steps are involved: Sample preparation: Cut the fiber to be identified into fiber samples; Preparation of transparent sheet: the fiber sample and the window sheet material are mixed evenly, and then placed on a sheet press to be pressed into a transparent sheet; The transparent sheet is placed in a temperature-elevable device and in front of the infrared spectrometer window; The infrared spectrometer is heated to 500° C. to record infrared spectra of thermal motion and thermal decomposition of the fiber sample molecules at preset interval temperature points; The infrared spectra of the molecular thermal motion and thermal decomposition of the fiber sample at the preset interval temperature points are compared with the infrared spectra of the molecular thermal motion and thermal decomposition of the reference sample, with the temperature being above 400°C and the wave number being 1205cm -1 The absorption peak at the position and the wave number when the temperature rises to 500℃ is 818cm -1 The absorption peaks at the left and right positions are compared and analyzed to determine whether the fiber to be identified is meta-aramid fiber or para-aramid fiber. If the absorption peak comparison result is: starting from 400℃, the wave number is at 1205 cm -1 There is an absorption peak around 500℃, with a wave number of 818 cm -1 If the absorption peaks around 1205 cm-1 are significantly weakened, the fiber to be identified is meta-aramid fiber; if the absorption peak comparison result is: from room temperature to temperature 500℃, the wave number is around 1205 cm-1. -1 There is no absorption peak on the left and right sides; from room temperature to 500 °C, the wave number is 818 cm -1 If the absorption peak intensity on the left and right does not change, it is determined that the fiber to be identified is para-aramid fiber.

2. The method for qualitatively identifying meta-aramid fiber and para-aramid fiber according to claim 1, characterized in that: When the temperature of the infrared spectrometer is raised to 500°C, the heating rate is 10-30°C / min.

3. The method for qualitatively identifying meta-aramid fiber and para-aramid fiber according to claim 1, characterized in that: The preset interval temperature points are 10°C-100°C.

4. The method for qualitatively identifying meta-aramid fiber and para-aramid fiber according to claim 1, characterized in that: The window material is potassium bromide.

5. The method for qualitatively identifying meta-aramid fiber and para-aramid fiber according to claim 4, characterized in that: In the transparent sheet preparation step, 0.1-1 mg of the fiber sample is mixed with 20-40 mg of the window sheet material.

6. The method for qualitatively identifying meta-aramid fiber and para-aramid fiber according to claim 1, characterized in that: The pressure when the transparent sheet is pressed on a tablet press is 6-10 MPa.

7. The method for qualitatively identifying meta-aramid fiber and para-aramid fiber according to claim 1, characterized in that: The average length of the fiber sample is 0.01-0.1 mm.

8. The method for qualitatively identifying meta-aramid fiber and para-aramid fiber according to claim 1, characterized in that: The fiber to be identified is meta-aramid fiber or para-aramid fiber.

9. Use of the method for qualitatively identifying meta-aramid fibers and para-aramid fibers according to any one of claims 1 to 8 in identifying and distinguishing meta-aramid fibers and para-aramid fibers.

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