A method for rapidly identifying a sheath-core polyester / polyamide composite fiber

Abstract

This invention relates to the field of fiber identification technology, specifically a method for rapidly identifying core-sheath type polyester / polyamide composite fibers, comprising the following steps: 1. Determining the morphology and structure of the composite fiber: Observing the longitudinal morphology of the composite fiber sample under a microscope; 2. Measuring the melting range of the sheath and core fibers: Continuously heating to two stages, observing the melting state of the sheath and core fibers respectively, wherein the first stage is heated to 215℃-225℃, and the second stage is heated to 250℃-258℃; 3. Determining the composition of the sheath fiber: Adding a hydrochloric acid solution with a volume ratio of 5:9 to the composite fiber sample, and then observing the dissolution of the composite fiber sample under a microscope; 4. Determining the composition of the core fiber: Adding concentrated nitric acid to the core fiber sample, and then observing the dissolution of the core fiber sample under a microscope. This invention can rapidly and accurately identify core-sheath type polyester / polyamide composite fibers.

Description

Technical Field

[0001] This invention relates to the field of fiber identification technology, specifically a method for rapidly identifying core-sheath type polyester / polyamide composite fibers. Background Technology

[0002] With the development of technology, new types of fibers are constantly emerging, and composite fibers are one of the most widely used types of new fibers. Composite fibers are fibers made from two or more polymers with different chemical properties or physical structures. They are classified by structural type into core-sheath type, parallel type, island type, split type, and fibrillar matrix type, and by material composition into bicomponent composite fibers and multicomponent composite fibers. Among these, bicomponent composite fibers are the most common. Bicomponent composite fibers possess the advantages of each single-component fiber while effectively avoiding its disadvantages, presenting styles, functions, and textures that single-component fibers cannot achieve. Currently, the most widely used composite fiber in the textile and apparel market is the bicomponent core-sheath type polyester / polyamide composite fiber. This composite fiber is made with polyamide fiber as the sheath and polyester fiber as the core, combining the excellent stiffness of polyester fiber with the excellent dyeing and moisture absorption properties of polyamide fiber. It is widely used in automotive interiors, cleaning products, weaving of imitation silk, or blending with cotton to create high-end clothing fabrics.

[0003] The existing research on the identification of composite fiber components mainly includes the following methods: 1. Identification by combining combustion method, microscopy, dissolution method (including heating and boiling test), differential scanning calorimetry and infrared spectroscopy; 2. Identification of core-sheath type composite fibers by combining combustion method, microscopy, dissolution method, melting point method and thermogravimetric analysis; 3. Identification of core-sheath type and parallel type low melting point polyester composite fibers by combining microscopy, dissolution method, infrared spectroscopy and melting point method.

[0004] The above methods for identifying core-sheath polyester / polyamide composite fibers have the following drawbacks: 1. All methods require the combination of four or more methods, which is cumbersome and time-consuming; 2. Equipment such as differential scanning calorimeter, infrared spectrometer, and thermogravimetric analyzer are required, and operators need to be trained before they can operate them, which is cumbersome, time-consuming, and costly; 3. In the first method, the dissolution method uses a boiling test, which increases the risk of the experiment; 4. All methods use the method of preparing the composite fiber as a whole sample for testing, which cannot identify core-sheath polyester / polyamide composite fibers quickly and accurately. Summary of the Invention

[0005] The present invention aims to provide a method for rapid identification of core-sheath type polyester / polyamide composite fibers, in order to solve the problems of existing identification methods requiring large-scale equipment, resulting in high costs, cumbersome operation, and long time consumption.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for rapid identification of core-sheath type polyester / polyamide composite fibers includes the following steps:

[0008] Step 1: Determine the morphology and structure of the composite fiber: Place the composite fiber sample under a microscope to observe its longitudinal morphology;

[0009] Step 2: Determine the melting range of the cortex fiber and the core fiber: Continuously heat to two stages and observe the melting state of the cortex fiber and the core fiber respectively. The first stage is heated to 215℃-225℃, and the second stage is heated to 250℃-258℃.

[0010] Step 3: Determine the composition of the cortical fibers: Add a hydrochloric acid solution of hydrochloric acid and water in a volume ratio of 5:9 to the composite fiber sample, and then observe the dissolution of the composite fiber sample under a microscope;

[0011] Step 4: Determine the composition of the core fiber: Add concentrated nitric acid to the core fiber sample and then observe the dissolution of the core fiber sample under a microscope.

[0012] The principle of this scheme is as follows:

[0013] In step 1, under a microscope, the composite fiber sample is observed to have relatively straight strands and a smooth surface, indicating it is a synthetic fiber. Simultaneously, the composite fiber sample exhibits a clear boundary between the sheath and core layers, confirming it has a sheath-core structure. In step 2, the sheath fibers melt during the first heating stage, and the core fibers melt during the second heating stage. Ultimately, the sheath fibers are identified as possibly one of the following: polyamide fiber, vinyl ester, polybutylene terephthalate fiber, or polypropylene terephthalate fiber. The core fibers are identified as possibly one of the following: polyester fiber, acetate fiber, or nylon 66. In steps 3 and 4, the composition of the sheath and core fibers is determined using a dissolution method. Combining these methods, the composite fiber can be quickly and accurately identified as a sheath-core type polyester / polyamide composite fiber.

[0014] Beneficial effects:

[0015] Because the materials used in the dissolution method are simple and readily available, applicable to a wide variety of fibers, and have a broad range of applications, requiring no additional equipment besides a microscope and melting point apparatus, and being simple and quick to operate, the conventional approach in this field for identifying composite fibers is to first use the dissolution method. If the dissolution method cannot be used directly, other methods are then combined for verification. Therefore, the inventors attempted to use the dissolution method directly after step 1 for identification. However, in actual operation, all reagents need to be used sequentially for identification, requiring the preparation of a large number of test samples and repeated dissolution operations countless times. The dissolution of some fibers also requires additional heating and boiling conditions, which not only seriously affects the efficiency of identification but also poses safety hazards.

[0016] In light of this, the inventors attempted various methods to improve the efficiency of the dissolution method, but none yielded ideal results. After extensive research and experimentation, the inventors broke with the conventional approach of dissolving first and instead tried using the melting point method directly after step 1. Unexpectedly, they discovered that when the temperature reached the first stage, only four fibers—polyamide, vinylon, polybutylene terephthalate, and polypropylene terephthalate—melted. When the temperature reached the second stage, only three fibers—polyester, acetate, and nylon 66—melted. This effectively narrowed down the target range, eliminating many other fibers. Subsequent dissolution using the appropriate solvent for each of the possible fibers was then sufficient, without the need for additional methods. Compared to the conventional approach in this field, which prioritizes the dissolution method, this significantly reduced the need for testing with incorrect solvents, greatly improving identification efficiency and achieving rapid identification.

[0017] By adopting the method of first melting point method and then dissolution method, the inventors unexpectedly discovered that the target fibers identified in the melting point method can all be dissolved at room temperature, thus eliminating the heating and boiling process in the dissolution method. This not only makes the operation simpler and more convenient, further improving efficiency, but also avoids the safety hazards caused by heating and boiling solvents, making the operation safer.

[0018] In summary, this method combines microscopy, melting point method, and dissolution method to quickly and accurately identify core-sheath type polyester / polyamide composite fibers. Compared with existing technologies, it only uses three methods in combination and does not require any other equipment besides a microscope and melting point apparatus. It is simple, quick, and low in cost. In addition, using the melting point method first and then the dissolution method solves the safety hazard problem caused by the need for heating and boiling in the dissolution method in existing technologies.

[0019] Furthermore, in step 2, the heating rate for continuous heating is controlled to be 2℃ / min-3℃ / min.

[0020] The heating rate of this scheme can further improve efficiency while also making it easier to observe the melting state of the fiber; when the heating rate is lower than 2℃ / min, the efficiency is too low, and when it is higher than 3℃ / min, it is not easy to observe.

[0021] Furthermore, in step 3, concentrated nitric acid is dropped onto another composite fiber sample, and then the dissolution of the composite fiber sample is observed under a microscope.

[0022] Using this method can further confirm that the dermis fiber is a polyamide fiber, ensuring the accuracy of the identification results.

[0023] Furthermore, in step 4, concentrated sulfuric acid is dropped onto another core fiber sample, and then the dissolution of the core fiber sample is observed under a microscope.

[0024] Using this method can further confirm that the core fiber is polyester fiber, increasing the accuracy of the identification results.

[0025] Furthermore, in step 4, 75% sulfuric acid is dropped onto another core fiber sample, and then the dissolution of the core fiber sample is observed under a microscope.

[0026] Using this method can further confirm that the core fiber is polyester fiber, increasing the accuracy of the identification results.

[0027] Furthermore, in step 4, dimethylformamide is dropped onto another core fiber sample, and then the dissolution of the core fiber sample is observed under a microscope.

[0028] Using this method can further confirm that the core fiber is polyester fiber, ensuring the accuracy of the identification results.

[0029] Furthermore, the method for preparing the core fiber sample is as follows: the melting point apparatus is heated to the first stage, the cortex fiber is melted, and the obtained core fiber is used to prepare the core fiber sample according to the fiber longitudinal morphology sheet preparation method.

[0030] In this method, the cortex fibers are melted to form core fiber samples for dissolution treatment. This avoids interference from the cortex fibers and allows for more direct and effective dissolution treatment of the core fibers. Attached Figure Description

[0031] Figure 1 This is a longitudinal morphological diagram of the polyester / polyamide composite fiber in Example 1 of the present invention;

[0032] Figure 2 This is a cross-sectional view of the polyester / polyamide composite fiber in Example 1 of the present invention;

[0033] Figure 3 This is a morphological diagram of the sheath fibers beginning to melt in Embodiment 1 of the present invention;

[0034] Figure 4 This is a morphological diagram of the core fibers after the sheath fibers have melted in Embodiment 1 of the present invention;

[0035] Figure 5 This is a morphological diagram of the sheath fiber and core fiber after melting in Embodiment 1 of the present invention;

[0036] Figure 6 This is a morphological diagram of the core fiber beginning to dissolve in Embodiment 1 of the present invention. Detailed Implementation

[0037] The following detailed description illustrates the specific implementation method:

[0038] Example 1:

[0039] A method for rapid identification of core-sheath type polyester / polyamide composite fibers includes the following steps:

[0040] Step 1: Determine the morphology and structure of the composite fibers:

[0041] Select yarn A, use an awl to disperse the fibers to be tested, and cut fibers with a length of 0.3cm-0.5cm. Place the cut fibers parallel to the glass slide, cover with a coverslip, and you will obtain a composite fiber sample. Prepare three composite fiber samples on each slide simultaneously. Place one drop of paraffin wax on the prepared composite fiber sample to moisten the sample, being careful not to introduce air bubbles. Observe the longitudinal morphology of the composite fiber sample under a microscope. If the longitudinal morphology of the composite fiber sample is as shown... Figure 1 As shown, if the fiber strands are relatively straight, the surface is smooth, and there is a clear boundary between the sheath and core layers, it can be determined that the fiber under test has a sheath-core structure. If the sheath-core structure is not obvious, the cross-sectional morphology of the composite fiber sample can be further observed. The specific operation is as follows: Prepare a sample of an appropriate amount of the fiber under test according to the method in Section 7.2.1 of FZ / T 01057.3-2007 to obtain a cross-sectional sample of the fiber under test. Observe the cross-sectional sample of the fiber under test under a microscope. If the cross-sectional sample of the fiber under test appears as shown... Figure 2 The two concentric circles shown indicate that the fiber being tested has a core-sheath structure.

[0042] Step 2: Determine the melting range of the sheath fiber and core fiber:

[0043] The fibers to be tested were dispersed using an awl, and 0.3cm-0.8cm lengths were cut to prepare composite fiber samples. The heating rate of the melting point apparatus was adjusted to 2℃ / min, and the temperature was continuously increased. The first stage of heating was to 215℃-225℃. When the temperature reached 215℃, the cortex fibers began to melt, and the fibers began to adhere to each other. Figure 3When the temperature reaches 223℃, the melting morphology of the cortex fibers is more obvious; when the temperature reaches 225℃, all the cortex fibers melt, while the morphology of the core fibers remains unchanged. Figure 4 The second stage involves heating to 250℃-258℃. When the temperature reaches 250℃, the core fibers begin to melt; when the temperature reaches 258℃, all the core fibers have melted. Figure 5 The tests in both the first and second phases should be performed at least three times each.

[0044] Test results:

[0045] 1. The melting range of the dermis fiber is determined to be 215℃-225℃. Among them, the melting range of polyamide fiber is 215℃-225℃, the melting range of vinyl ester is 200℃-231℃, the melting range of polybutylene terephthalate (PBT) fiber is 205℃-220℃, and the melting range of polypropylene terephthalate (PTT) fiber is 220℃-228℃. The melting ranges of the latter three fibers overlap with those of the dermis fiber, so the dermis fiber is likely one of polyamide fiber, vinyl ester, polybutylene terephthalate fiber, or polypropylene terephthalate fiber.

[0046] 2. The melting range of the core fiber is determined to be 250℃-258℃. Among them, the melting range of polyester fiber is 250℃-258℃, the melting range of acetate fiber is 253℃-260℃, and the melting range of nylon 66 is 250℃-258℃. The melting range of the latter two fibers overlaps with that of the core fiber, so the core fiber is determined to be one of polyester fiber, acetate fiber, or nylon 66.

[0047] Step 3: Determine the composition of the dermal fibers:

[0048] Following the longitudinal morphology sample preparation method, two fiber samples were made from the composite fiber with a melting range of 215℃-225℃ in step 2. One drop of concentrated nitric acid was dropped onto one sample, and one drop of hydrochloric acid and water in a volume ratio of 5:9 was dropped onto the other sample. The experimental conditions were both at room temperature. The fiber dissolution performance was observed under a microscope. If the dermal fiber of the fiber sample dissolved in these two reagents and the dermal-core boundary disappeared, the core fiber may partially dissolve or not dissolve, thus identifying the dermal fiber as polyamide fiber.

[0049] Step 4: Determine the composition of the core fiber:

[0050] Following the method in step 2, after melting the outer layer fiber of the composite fiber with a melting range of 250℃-258℃, the remaining core fiber is taken out and made into 4 core fiber samples according to the longitudinal morphology sample making method.

[0051] One drop of concentrated nitric acid, concentrated sulfuric acid, 75% sulfuric acid, and dimethylformamide were dropped onto each of the four core fiber samples in turn. The experimental conditions were all at room temperature. The samples were then quickly placed under a microscope to observe the solubility of the fibers. If the core fiber was soluble in concentrated sulfuric acid but insoluble in the other three reagents, the core fiber could be identified as polyester fiber.

[0052] Example 2:

[0053] The difference between this embodiment and embodiment 1 is that the heating rate of the melting point apparatus is adjusted to 3℃ / min in step 2.

[0054] Comparative Example 1:

[0055] Includes the following steps:

[0056] Step 1: Observe the morphology and structure of the composite fibers using a microscope:

[0057] Select yarn A, use an awl to separate the fibers to be tested, and cut fibers with a length of 0.3cm-0.5cm with scissors. Place the cut fibers parallel to the glass slide, cover with a coverslip, and you will get a composite fiber sample. Prepare 3 composite fiber samples on each glass slide at the same time. Place one drop of paraffin wax on the prepared composite fiber sample to moisten the sample, being careful not to introduce air bubbles. Observe the longitudinal morphology of the composite fiber sample under a microscope. If the fiber strands are relatively straight, the surface is smooth, and there is a clear boundary between the cortex and the core, it can be determined that the fiber to be tested has a cortex-core structure. If the cortex-core structure is not obvious, the cross-sectional morphology of the composite fiber sample can be observed using the method in Example 1. If the cross-sectional sample of the fiber to be tested shows two concentric circles, it can be determined that the fiber to be tested has a cortex-core structure.

[0058] Step 2: Determine the composition of dermal fibers using the dissolution method:

[0059] Nine samples were prepared using the longitudinal morphology sample preparation method. At room temperature, one drop each of concentrated nitric acid, 20% hydrochloric acid, 15% hydrochloric acid, concentrated sulfuric acid, 75% sulfuric acid, 60% sulfuric acid, 40% sulfuric acid, 2.5% sodium hydroxide, and dimethylformamide was added to each sample, and the samples were immediately placed under a microscope to observe the fiber's solubility. The cortex fiber dissolved in concentrated nitric acid, 20% hydrochloric acid, 15% hydrochloric acid, concentrated sulfuric acid, 75% sulfuric acid, 60% sulfuric acid, and 40% sulfuric acid, and the cortex-core boundary disappeared; it was insoluble in 2.5% sodium hydroxide and dimethylformamide, confirming that the cortex fiber is a polyamide fiber. The core fiber dissolved in concentrated sulfuric acid and may be partially soluble or completely insoluble in the other eight reagents. Fibers with similar chemical solubility properties include polyester fiber, polyamide ester fiber, and polysulfonamide fiber, so the specific type of fiber used for the core fiber cannot be determined.

[0060] Step 3: Melting point method to test the melting range of the sheath fiber and core fiber:

[0061] The fibers to be tested were dispersed using an awl to prepare fiber samples with a length of 0.3cm-0.8cm for testing. Three consecutive tests were performed using a melting point apparatus. The heating rate was adjusted to 3℃ / min-4℃ / min, and the temperature was continuously increased while observing the melting characteristics of the fibers during the heating process. Based on the experimental results, the melting range of the sheath fiber was determined to be 215℃-225℃, and the melting range of the core fiber was determined to be 250℃-258℃. This verifies that the sheath fiber is polyamide fiber, but it cannot be determined whether the core fiber is acetate fiber, nylon 66, or polyester fiber.

[0062] Step 4: Determine the composition of the core fiber using the dissolution method:

[0063] The melting point apparatus was heated to 225℃ and held for 10 seconds. After the outer layer fibers melted, the remaining core fibers adhered to the coverslip. After cooling, the fibers were removed with tweezers, and seven samples were prepared according to the longitudinal morphology sample preparation method. One drop each of paraffin, concentrated nitric acid, 20% hydrochloric acid, concentrated sulfuric acid, 75% sulfuric acid, 60% sulfuric acid, and dimethylformamide was added to each of the seven samples, and the samples were quickly placed under a microscope to observe the fiber's solubility. The composition of the core fibers was confirmed using a combination of microscopy and dissolution methods. Microscopic observation revealed that the core fibers had a smooth longitudinal morphology. Based on the dissolution test results, the core fibers were soluble in concentrated sulfuric acid but insoluble in concentrated nitric acid, 20% hydrochloric acid, 75% sulfuric acid, 60% sulfuric acid, and dimethylformamide, confirming that the core fibers were polyester fibers.

[0064] Combining these three methods can help identify polyester / polyamide composite fibers.

[0065] Comparative Example 2:

[0066] Includes the following steps:

[0067] Step 1: Combustion test to determine the combustion characteristics of the composite fiber:

[0068] Take a small sample from the sample container, hold it with tweezers, and slowly bring it close to the flame. Observe and record the fiber's reaction to heat (such as melting and shrinkage). Transfer the sample into the flame and allow it to burn completely. Observe and record the burning of the fiber in the flame. Remove the sample from the flame and observe and record the burning state of the fiber after removal from the flame. When the flame of the sample is extinguished, smell its odor and record it. After the sample cools, observe the state of the residue, gently rub the residue with your hand, and record it. Combine the state of the fiber when it is near the flame, in contact with the flame, and away from the flame, the odor produced during combustion, and the characteristics of the residue to identify the type of fiber. It can be determined that the composite fiber contains polyamide fiber.

[0069] Step 2: Observe the morphology and structure of the composite fibers using a microscope:

[0070] Spread an appropriate amount of fiber evenly on a glass slide, add a drop of transparent medium, cover with a coverslip, and place on the microscope stage. Observe its morphology at magnification of 100-500x. Prepare sections using a Hardy microtome by neatly arranging the fibers within the Hardy section, cutting it flat, and then adding a small drop of 5% collodion solution with a needle. After curing, cut the section with a blade, spread it evenly on a glass slide, add a drop of paraffin oil, cover with a coverslip, and observe the cross-sectional morphology under a microscope. This confirms that the fiber has a core-skin structure.

[0071] Step 3: Dissolution method (including heating and boiling test) to test the solubility of composite fibers:

[0072] Weigh approximately 0.5g of fiber sample and place it in a small beaker. Pour in approximately 50mL of reagent solution (using 6 acidic solvents and 2 organic solvents). Test the sample under two conditions: shaking for 5 minutes at room temperature (20℃-30℃) and heating to boiling and holding for 3 minutes. Observe the dissolution of the sample. During the dissolution process, a small amount of fine particles can be observed to dissolve, but it is not obvious and cannot be determined whether it is the dermis or core fiber that is dissolving, thus failing to identify the composition of the composite fiber.

[0073] Step 4: Differential scanning calorimetry (DSC) is used to determine the melting points of the cortex and core fibers.

[0074] Accurately weigh 5-10 mg of the dried sample and place it in an aluminum sample dish, sealing it with a sealer. Simultaneously, seal an empty sample dish as a reference. Place the prepared sample dish into a differential scanning calorimeter. Set the nitrogen atmosphere flow rate to 50 mL / min, and heat from room temperature to 300°C at a rate of 20°C / min, equilibrating at this temperature for 5 min to eliminate thermal history. Then, cool to 50°C at a rate of 20°C / min, equilibrating at this temperature for 5 min. Finally, heat from room temperature to 300°C at a rate of 10°C / min to obtain a two-stage heating curve. Based on the peak characteristics, the melting points of the cortex and core fibers can be obtained.

[0075] Step 5: Infrared spectroscopy test of the composite fiber's infrared spectrum:

[0076] A small bundle of the sample to be tested was taken, and a fiber segment of about 1 cm in length was cut off. This segment was placed between two glass slides and pressed firmly. The slide was then placed on a heating stage, and the temperature was raised to a certain level until the fiber segment was completely melted. A certain pressure was then applied to the glass slides to heat-press the molten fiber into a thin sheet, which was then scanned in an infrared spectrometer. The scanning wavenumbers were 550 cm⁻¹ to 4000 cm⁻¹, the number of scans was 16, and the resolution was 4 cm⁻¹. Based on the spectrum, it was determined that the composite fiber contained polyester and polyamide fibers.

[0077] Combining these five methods can help identify polyester / polyamide composite fibers.

[0078] Comparative Example 3:

[0079] Includes the following steps:

[0080] Step 1: Combustion test to determine the combustion characteristics of the composite fiber:

[0081] The composition of composite fibers is determined by combustion: Take a small amount of sample from the sample, hold it with tweezers, and slowly bring it close to the flame. Observe and record the fiber's reaction to heat (e.g., melting, shrinkage). Transfer the sample into the flame and allow it to burn completely. Observe and record the burning of the fiber in the flame. Remove the sample from the flame and observe and record the burning state of the fiber after removal from the flame. When the flame of the sample is extinguished, smell the odor and record it. After the sample cools, observe the state of the residue, gently rub the residue with your hand, and record it. Combining the state of the fiber when it is near, in contact with, and away from the flame, the odor produced during combustion, and the properties of the residue, it can be determined that the composite fiber contains polyamide fibers.

[0082] Step 2: Observe the morphology and structure of the composite fibers using a microscope:

[0083] Prepare longitudinal and cross-sectional samples of a suitable amount of fiber, add a drop of paraffin oil, cover with a coverslip, and observe the longitudinal and cross-sectional morphologies under a microscope. This confirms that the fiber has a core-sheath structure.

[0084] Step 3: Solvency test to test the solubility of the composite fiber:

[0085] Place the fiber sample in a small beaker and pour in approximately 50 mL of reagent solution (using a dissolution order from weak acid to strong acid, from weak base to strong base, and some organic reagents; employing 5 acidic solvents, 1 alkaline solvent, and 2 organic solvents). Let it stand at room temperature (20℃-30℃) for 3-5 minutes, stirring gently, and observe the sample's dissolution. Select partially dissolved samples and observe their morphology under a microscope. A total of 8 reagents were used, and each reagent was tested using this method. The results show that the outer layer fiber is polyamide fiber; the core fiber composition cannot be identified.

[0086] Step 4: Melting point method to test the melting range of the sheath fiber and core fiber:

[0087] The sample was placed in a melting point apparatus and heated to 215℃-225℃. The surface morphology of the fibers was observed under a microscope. The surface fibers (cortex structure) melted into a liquid state, and the melting range of the cortex fibers was determined. The temperature was further increased to 250℃-258℃, and the remaining fibers (core structure) melted into a liquid state. Finally, the entire cortex-core structure melted into a final pool of liquid, indicating that the core fibers had melted and the melting range was determined. However, the composition of the cortex and core fibers could not be determined. The melting point of vinyl ester is 200℃-231℃, that of polybutylene terephthalate (PBT) is 205℃-217℃, and that of polypropylene terephthalate (PTT) is 220℃-228℃. The melting point of the cortex fiber overlaps with the melting points of these three fibers. Furthermore, the melting point of chemical fibers is related to factors such as production process and molecular weight; the melting point of the same type of fiber can vary. Therefore, it cannot be accurately determined that the cortex fiber is a polyamide fiber. The melting point of the core fiber was measured to be 250℃-258℃ during the second stage of heating. The melting point of acetate fiber is 253℃-260℃, and the melting point of nylon 66 is 250℃-258℃, which overlaps with the melting point of polyester fiber. Therefore, it cannot be determined that the core fiber is polyester fiber.

[0088] Step 5: Thermogravimetric analysis to test the melting points of the cortex and core fibers:

[0089] The sample was placed in the crucible of a thermogravimetric analyzer, and the test was conducted under a nitrogen atmosphere at a temperature range of 80℃-300℃ with a heating rate of 20℃ / min. The weight loss curve of the sample was then scanned. Based on the peak characteristics, the melting points of the cortex and core fibers could be obtained, but the specific composition could not be determined.

[0090] Combining these five methods can help identify polyester / polyamide composite fibers.

[0091] Comparative Example 4:

[0092] Includes the following steps:

[0093] Step 1: Observe the morphology and structure of the composite fibers using a microscope:

[0094] A suitable amount of fiber is evenly spread on a glass slide, paraffin oil is dripped on it, and a coverslip is placed on top to obtain a longitudinal section. A small bundle of fiber is placed in the groove of a Hastelloy microtome, and a cross-sectional section is obtained according to the standard method of FZ / T 01057.3-2007. The two sections are placed on the stage of a fiber fineness tester, and the cross-sectional morphology of the fiber is observed at a certain magnification to determine that the fiber under test has a core-sheath structure.

[0095] Step 2: Dissolution test to test the solubility of composite fibers:

[0096] The composition of the cortex and core fibers could not be determined by using chemical reagents such as 75% sulfuric acid, concentrated sulfuric acid, 20% hydrochloric acid, concentrated hydrochloric acid, 88% formic acid, concentrated nitric acid, N,N-dimethylformamide, phenol, dichloromethane, and zinc chloride formate.

[0097] Step 3: Infrared spectroscopy test of the composite fiber's infrared spectrum:

[0098] Using a Fourier transform infrared spectrometer and the ATR method to test the composite fibers, it can be confirmed that the composite fibers contain polyester fibers and polyamide fibers.

[0099] Step 4: Melting point test to determine the melting points of the sheath and core fibers:

[0100] Melting point testing was performed using a polarizing microscope equipped with a heating device. A small amount of fiber was placed between two glass slides and placed on the heating device at a heating rate of approximately 3°C / min. The focus was adjusted to ensure a clear image of the fiber. Changes in the fiber image were observed, and the temperature at which most of the fibers in the glass slide melted was recorded; this temperature is the melting point of the fiber. This method can determine the melting points of the cortex and core fibers.

[0101] Combining these four methods can help identify polyester / polyamide composite fibers.

[0102] The time taken to identify the composition of yarn A using Examples 1-2 and Comparative Examples 1-4 was recorded respectively. The results are shown in Table 1 below:

[0103] Table 1

[0104] Identification methods Duration / min Example 1 26 Example 2 24 Comparative Example 1 40 Comparative Example 2 160 Comparative Example 3 140 Comparative Example 4 100

[0105] As can be seen from Table 1:

[0106] 1. As can be seen from the comparison between Comparative Example 1 and Examples 1-2, the method of using the melting point method first and then the dissolution method can effectively shorten the total time. A single fiber sample can save at least 14 minutes in total, and the effect of rapid identification can be further highlighted in batch identification.

[0107] 2. As can be seen from the comparison between Comparative Examples 2-4 and Examples 1-2, Comparative Examples 2-4 take longer than Examples 1-2. A single fiber sample can save at least 74 minutes in total. Furthermore, Comparative Examples 1-4 require the use of more than 4 methods in combination for identification, which is cumbersome and time-consuming. They also require equipment such as differential scanning calorimeter, infrared spectrometer, and thermogravimetric analyzer, which increases costs.

[0108] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for rapid identification of core-sheath type polyester / polyamide composite fibers, characterized in that: Includes the following steps: Step 1: Determine the morphology and structure of the composite fiber: Place the composite fiber sample under a microscope to observe its longitudinal morphology; Step 2: Determine the melting range of the cortex fiber and the core fiber: Continuously heat to two stages and observe the melting state of the cortex fiber and the core fiber respectively. The first stage is heated to 215℃-225℃, and the second stage is heated to 250℃-258℃. Step 3: Determine the composition of the cortical fibers: Add a hydrochloric acid solution of hydrochloric acid and water in a volume ratio of 5:9 to the composite fiber sample, and then observe the dissolution of the composite fiber sample under a microscope; Step 4: Determine the composition of the core fiber: Add concentrated nitric acid to the core fiber sample and then observe the dissolution of the core fiber sample under a microscope; The method for preparing the core fiber sample is as follows: the melting point apparatus is heated to the first stage, the cortex fiber is melted, and the obtained core fiber is prepared into a core fiber sample according to the fiber longitudinal morphology sheet preparation method.

2. The method for rapid identification of core-sheath type polyester / polyamide composite fibers according to claim 1, characterized in that: In step 2, the heating rate is controlled to be 2℃ / min-3℃ / min for continuous heating.

3. The method for rapid identification of core-sheath type polyester / polyamide composite fibers according to claim 1, characterized in that: In step 3, concentrated nitric acid is dropped onto another composite fiber sample, and then the dissolution of the composite fiber sample is observed under a microscope.

4. The method for rapid identification of core-sheath type polyester / polyamide composite fibers according to claim 1, characterized in that: In step 4, concentrated sulfuric acid is dropped onto another core fiber sample, and then the dissolution of the core fiber sample is observed under a microscope.

5. The method for rapid identification of core-sheath type polyester / polyamide composite fibers according to claim 4, characterized in that: In step 4, 75% sulfuric acid is dropped onto another core fiber sample, and then the dissolution of the core fiber sample is observed under a microscope.

6. The method for rapid identification of core-sheath type polyester / polyamide composite fibers according to claim 5, characterized in that: In step 4, dimethylformamide is dropped onto another core fiber sample, and then the dissolution of the core fiber sample is observed under a microscope.

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