Infrared spectrum quantitative method for trace chlorinated 1-butyl-3-methylimidazole in polylactic acid fiber

Abstract

The invention discloses an infrared spectrum quantification method for trace chlorinated 1-butyl-3-methylimidazole in polylactic acid fiber. The method comprises the following steps: preparing a standard substance of chlorinated 1-butyl-3-methylimidazole with known content in polylactic acid fiber; pressing the standard product into a sheet; performing an infrared spectrum test by using a transmission mode to obtain an infrared spectrum curve; processing the infrared spectrum curve of the standard substance; establishing a quantitative mathematical function of the characteristic infrared intensity and content of the chlorinated 1-butyl-3-methylimidazole; treating a polylactic acid fiber sample with unknown content to obtain a characteristic infrared intensity value of the polylactic acid fiber sample; and substituting the characteristic infrared intensity value of an unknown sample into the quantitative mathematical function, and calculating the content of chlorinated 1-butyl-3-methylimidazole. The infrared spectrum quantitative method solves the problems of trace component quantitative methods in preparation and application of the existing modified polylactic acid material.

Description

Technical Field

[0001] This invention relates to the fields of oily wastewater separation research and trace testing, and in particular to an infrared spectroscopic quantitative method for trace amounts of 1-butyl-3-methylimidazole chloride in polylactic acid fibers. Background Technology

[0002] Polylactic acid (PLA), a biodegradable material, can be electrospun and loaded with trace amounts of ionic liquids (such as chlorinated (1-butyl-3-methylimidazolium)) to form fibrous membranes for separating oily wastewater. The content of ionic liquids in the fibers directly affects their hydrophilicity and separation efficiency; therefore, reliable quantitative methods for trace components need to be established to ensure material performance and quality monitoring.

[0003] Currently, infrared spectroscopy has limitations in related research. It can only characterize the distribution of ionic liquids in fibers, and there is no precise quantitative analysis method. For polylactic acid-coated metal-organic frameworks (MOFs), although it can characterize MOF loading, it cannot sensitively and accurately test trace components below 5%. For PLA with 1010 antioxidant, infrared spectroscopy can only qualitatively prove the presence of antioxidant. Due to the different chemical structures and characteristic responses of different coating components, there is also no precise quantitative analysis method.

[0004] Existing infrared analysis methods lack systematic background subtraction and quantitative modeling steps, making it impossible to accurately eliminate matrix interference and hindering the reliable determination of trace components. Therefore, there is an urgent need to establish an infrared spectroscopic method capable of accurately quantifying trace ionic liquids in polylactic acid fibers. Summary of the Invention

[0005] In view of the problems existing in the above-mentioned quantitative infrared spectroscopy methods, the present invention is proposed.

[0006] Therefore, the purpose of this invention is to provide an infrared spectral quantitative method for trace amounts of 1-butyl-3-methylimidazole chloride in polylactic acid fibers, which aims to solve the problem of existing methods for quantitative analysis of trace components in the preparation and application of modified polylactic acid materials.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution, comprising the following steps: A series of standards for polylactic acid fibers with known concentrations of 1-butyl-3-methylimidazolium chloride were prepared.

[0008] The standard sample is pressed into a sheet with a thickness of one micrometer.

[0009] Infrared spectroscopy was performed using the transmission mode to obtain the infrared spectral curve of the standard.

[0010] The infrared spectrum of the standard was processed, and 1-butyl-3-methylimidazole chloride was selected at 1169 cm⁻¹.-1 The characteristic peaks of polylactic acid at 1753 cm⁻¹ are similar to those of polylactic acid at 1753 cm⁻¹. -1 The characteristic peak at 1169 cm⁻¹ was subtracted from the peak at 1169 cm⁻¹ for polylactic acid. -1 Background signal at the location.

[0011] A quantitative mathematical function was established to correlate the characteristic infrared intensity and content of 1-butyl-3-methylimidazole chloride.

[0012] The same tableting, testing, and spectral processing were performed on polylactic acid fiber samples with unknown content to obtain their characteristic infrared intensity values.

[0013] The content of 1-butyl-3-methylimidazole chloride was calculated by substituting the characteristic infrared intensity value of the unknown sample into the quantitative mathematical function.

[0014] As a preferred embodiment of the infrared spectroscopy quantitative method of the present invention, the content of 1-butyl-3-methylimidazole chloride in the standard is in the range of 0% to 5%, and it is prepared by impregnation and volatilization method, which includes soaking polylactic acid fiber in a methanol solution containing 1-butyl-3-methylimidazole chloride, followed by ultrasonic evaporation and drying.

[0015] As a preferred embodiment of the infrared spectroscopy quantitative method of the present invention, in the tableting step, the standard or the polylactic acid fiber sample with unknown content is pressed into a sheet with a thickness of micrometers under constant pressure of 15 MPa for 3 minutes, and multiple sheets are pressed for each sample to ensure representativeness.

[0016] As a preferred embodiment of the infrared spectroscopy quantitative method of the present invention, the infrared spectroscopy test adopts the transmission mode, the pressed sheet is fixed on the sample holder, and the infrared light passes through the sheet into the detector. At least 3 points of each sample are tested in parallel to obtain multiple spectral curves.

[0017] As a preferred embodiment of the infrared spectroscopy quantitative method of the present invention, the infrared spectral curve processing includes baseline correction, with the baseline range selected at 2700 cm⁻¹. -1 Up to 2000 cm -1 The region between which there is no infrared absorption signal.

[0018] As a preferred embodiment of the infrared spectroscopy quantitative method of the present invention, wherein the characteristic peak of 1-butyl-3-methylimidazolium chloride is selected at 1169 cm⁻¹. -1 Centered on , the integral range is 1169 cm. -1 Up to 1154 cm -1 To include all regions of the absorption peak as much as possible and avoid matrix signal interference.

[0019] As a preferred embodiment of the infrared spectroscopy quantitative method of the present invention, the polylactic acid characteristic peak is selected at 1753 cm⁻¹. -1 Centered on , the integral range is 1783 cm. -1 Up to 1723 cm -1 Furthermore, this peak does not overlap with the spectrum of 1-butyl-3-methylimidazole chloride.

[0020] As a preferred embodiment of the infrared spectroscopy quantitative method of the present invention, wherein: the subtraction of polylactic acid at 1169 cm⁻¹ -1 The background signal at that location is expressed using the following formula:

[0021] in, The sample is at 1169 cm. -1 Peak area at that location It is pure polylactic acid at 1169 cm. -1 Peak area at that location It is pure polylactic acid at 1753 cm. -1 Peak area at that location The sample is at 1753 cm. -1 Peak area at that location.

[0022] As a preferred embodiment of the infrared spectroscopy quantitative method of the present invention, the quantitative mathematical function is established based on 1169 cm⁻¹ after background subtraction. -1 Peak area and 1753 cm -1 The ratio of peak area to characteristic infrared intensity was linearly regressed with the content of 1-butyl-3-methylimidazole chloride, with the function form Y = a + bX, where Y is infrared intensity and X is content.

[0023] As a preferred embodiment of the infrared spectroscopy quantitative method of the present invention, the application of the quantitative mathematical function includes substituting the characteristic infrared intensity value of the unknown sample as Y into the function, calculating the X value, and obtaining the content of 1-butyl-3-methylimidazole chloride, the result of which is expressed as a percentage.

[0024] The beneficial effects of this invention are as follows: By compressing the fibers into micron-thick sheets and combining this with infrared testing in a transmission mode, the intensity of the infrared signal is significantly enhanced. This makes it possible to reliably detect and quantify trace amounts of chlorinated (1-butyl-3-methylimidazolium) at a content of less than 5% in polylactic acid fibers, filling the gap in existing technologies that can only qualitatively identify but not precisely quantify. The infrared spectroscopy quantitative method of this invention selects independent and representative characteristic peaks (1169 cm⁻¹). -1 and 1753cm -1This invention establishes a scientific background signal subtraction model to effectively eliminate the interference of the polylactic acid matrix on the characteristic peaks of the target component. Quantification is performed using the peak area ratio method, further reducing measurement errors caused by minor differences in sample thickness and uniformity, ensuring the accuracy and reproducibility of the analytical results. This invention provides a complete and clear standardized operating procedure, with specific specifications given for everything from standard preparation, tableting parameters, testing modes to data processing (including baseline correction, integration range selection, background subtraction, and mathematical model establishment). This makes the method easy to repeat and promote, providing a practical and efficient testing tool for the quality control and application research of modified polylactic acid fiber products. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A schematic diagram of a transmission mode infrared spectroscopy test according to an embodiment of the present invention is shown; Figure 2 The infrared absorption spectrum of a sample distributed in standard fiber containing 0-2% 1-butyl-3-methylimidazolium chloride, according to an embodiment of the present invention, is shown. Figure 3 The infrared spectra of 1-butyl-3-methylimidazolium chloride ionic liquid and pure polylactic acid are shown in the embodiments of the present invention. Figure 4 The 1169 cm⁻¹ 1-butyl-3-methylimidazolium chloride ionic liquid of an embodiment of the present invention is shown. -1 Schematic diagram of baseline and integration range selection for characteristic peak integration; Figure 5 The polylactic acid 1753 cm⁻¹ of an embodiment of the present invention is shown. -1 Schematic diagram of baseline and integration range selection for characteristic peak integration; Figure 6 A schematic diagram of the concentration-infrared characteristic intensity curve of 1-butyl-3-methylimidazole chloride according to an embodiment of the present invention is shown. Detailed Implementation

[0027] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0028] The terminology used in this invention is that which is currently widely used in the art in consideration of the function of the invention; however, these terms may vary according to the intent of those skilled in the art, precedent, or new technology in the art. Furthermore, specific terms may be chosen by the applicant, and in such cases, their detailed meanings will be described in the detailed description of the invention. Therefore, the terms used in this specification should not be construed as simple names, but rather based on their meanings and the overall description of the invention.

[0029] Example 1, referring to Figures 1-6 This embodiment provides an infrared spectroscopy method for quantitative determination of trace amounts of 1-butyl-3-methylimidazole chloride in polylactic acid fibers, including the following steps: Step 100-Step 700.

[0030] Step 100: Prepare a series of standards for polylactic acid fibers with known concentrations of 1-butyl-3-methylimidazolium chloride.

[0031] Step 200: Press the standard sample into a sheet with a thickness of micrometers. A certain mass of the standard sample is placed in a tablet pressing mold and pressed into a sheet with a thickness of micrometers.

[0032] Step 300: Perform infrared spectroscopy testing using transmission mode to obtain the infrared spectrum curve of the standard. In transmission mode, test at least three test points in parallel for each sample to obtain infrared spectrum curves for multiple test points.

[0033] Step 400: Process the infrared spectrum of the standard, selecting 1-butyl-3-methylimidazole chloride at 1169 cm⁻¹. -1 The characteristic peaks of polylactic acid at 1753 cm⁻¹ are similar to those of polylactic acid at 1753 cm⁻¹. -1 The characteristic peak at 1169 cm⁻¹ was subtracted from the peak at 1169 cm⁻¹ for polylactic acid. -1 Background signal at 1169 cm⁻¹. The process includes the following steps: spectral preprocessing; automatic baseline correction; and identification of the quantitative characteristic peak of 1-butyl-3-methylimidazole chloride. -1 The strongest peak is characteristic of the 1-butyl-3-methylimidazolium cation and does not overlap with the strong peak of polylactic acid (PLA), so it can be used as a quantitative characteristic peak. The small characteristic peak of PLA at this location can be subtracted by calculation. 1169 cm⁻¹ -1 Quantitative peak background subtraction method. This method was used to subtract the background of polylactic acid at 1753 cm⁻¹ in the sample. -1 Peak intensity, converted to polylactic acid at 1169 cm⁻¹ -1 Background information. Determination of characteristic peaks for polylactic acid. 1753 cm⁻¹ -1 The strong peak is a characteristic of the carbonyl group in polylactic acid, and it does not intersect with the curve of 1-butyl-3-methylimidazole chloride, so it is regarded as the characteristic peak of polylactic acid.

[0034] Step 500: Establish a quantitative mathematical function for the characteristic infrared intensity and content of 1-butyl-3-methylimidazolium chloride. This includes the following steps: determination of quantitative parameters. (Using 1169 cm⁻¹) -1 Peak area (after deducting the polylactic acid background signal) and 1753 cm⁻¹ -1 The peak area ratio multiplied by 100 is used as the quantitative parameter. The average value of the processed data from each test point of the standard is taken, and a quantitative function is obtained using Y = infrared intensity and X = concentration. This function should be linear.

[0035] Step 600: Perform the same tableting, testing, and spectral processing on the polylactic acid fiber sample with unknown content to obtain its characteristic infrared intensity value. The polylactic acid fiber sample with unknown content is subjected to tableting, testing, and spectral data analysis according to the same procedure parameters as the standard to obtain the characteristic infrared intensity value of the sample with unknown content.

[0036] Step 700: Substitute the characteristic infrared intensity value of the unknown sample into the quantitative mathematical function to calculate the content of 1-butyl-3-methylimidazole chloride. Substitute the infrared intensity value of the sample with unknown content as the Y value into the mathematical model to obtain the content X.

[0037] In one specific embodiment, the standard contains 0% to 5% 1-butyl-3-methylimidazole chloride and is prepared by impregnation and evaporation, which includes immersing polylactic acid fibers in a methanol solution containing 1-butyl-3-methylimidazole chloride, followed by ultrasonic evaporation and drying.

[0038] In this process, a certain amount of polylactic acid fibers were soaked in a methanol solution containing a certain mass of 1-butyl-3-methylimidazole chloride. The soaking container was then placed in an ultrasonic cleaner at 50°C. As the methanol evaporated to dryness, 1-butyl-3-methylimidazole chloride was uniformly attached to the fibers. The fibers were then dried in an oven at 105°C for 0.5 hours, removed, and cooled in a desiccator to prepare a standard product with a content of 0-5%.

[0039] In one specific embodiment, during the tableting step, a standard or polylactic acid fiber sample of unknown content is pressed into a sheet with a thickness of micrometers under constant pressure of 15 MPa for 3 minutes, and multiple sheets are pressed for each sample to ensure representativeness.

[0040] The tableting process must ensure consistency and reproducibility. A fixed mass of sample is weighed and placed in a tableting mold of a specific diameter. Under a preset constant pressure, the sample is held for a fixed period of time to compress the loose fibrous sample into micron-sized sheets of uniform thickness and good light transmittance. Multiple parallel sheets should be pressed for each sample to reduce errors.

[0041] In one specific implementation, the infrared spectroscopy test adopts a transmission mode, in which the pressed sheet is fixed on the sample holder, and infrared light passes through the sheet into the detector. At least 3 points are tested in parallel for each sample to obtain multiple spectral curves.

[0042] Infrared spectroscopy measurements were performed using transmission mode. The pressed sheet was securely placed in a fixed position on the sample holder, allowing the infrared beam to pass perpendicularly through the sheet. To assess sample uniformity and obtain representative data, multiple parallel scans were performed at different locations on each pressed sheet.

[0043] In one specific embodiment, the infrared spectral curve processing includes baseline correction, with the baseline range selected at 2700 cm⁻¹. -1 Up to 2000 cm -1 The region between which there is no infrared absorption signal.

[0044] Before processing the spectral data, baseline correction must be performed on all acquired spectral curves. During correction, a flat region with no significant absorption signal in the spectrum should be selected as the baseline range, for example, 2700 cm⁻¹. -1 Up to 2000 cm -1 The range is defined to eliminate the effects of background drift and scattering.

[0045] In one specific embodiment, the characteristic peak of 1-butyl-3-methylimidazolium chloride is selected at 1169 cm⁻¹. -1 Centered on , the integral range is 1169 cm. -1 Up to 1154 cm -1 To include all regions of the absorption peak as much as possible and avoid matrix signal interference.

[0046] The quantitative characteristic peak of 1-butyl-3-methylimidazole chloride was selected from its unique region that does not overlap with the main absorption peak of polylactic acid, for example, at 1169 cm⁻¹. -1 The spectral band centered on this characteristic peak should be used to determine the integration range, which should be appropriately extended to both sides to completely cover the entire absorption peak shape, while avoiding the inclusion of neighboring polylactic acid absorption signals as much as possible.

[0047] In one specific embodiment, the characteristic peak of polylactic acid is selected at 1753 cm⁻¹. -1 Centered on , the integral range is 1783 cm. -1 Up to 1723 cm -1 Furthermore, this peak does not overlap with the spectrum of 1-butyl-3-methylimidazole chloride.

[0048] For polylactic acid, the internal standard characteristic peak should be an independent peak with high intensity that is not affected by 1-butyl-3-methylimidazole chloride, such as 1753 cm⁻¹. -1The carbonyl stretching vibration peak is located at this point. Its integration range is also set centered on this peak to ensure that the area of ​​this characteristic peak can be fully captured.

[0049] In one specific embodiment, polylactic acid is deducted at 1169 cm⁻¹. -1 The background signal at that location is expressed using the following formula:

[0050] in, The sample is at 1169 cm. -1 Peak area at that location It is pure polylactic acid at 1169 cm. -1 Peak area at that location It is pure polylactic acid at 1753 cm. -1 Peak area at that location The sample is at 1753 cm. -1 Peak area at that location.

[0051] The method for removing background interference from polylactic acid (PLA) is based on the "fingerprint" principle of infrared spectroscopy. This is achieved by measuring the intensity of pure PLA at 1169 cm⁻¹. -1 and 1753cm -1 Calculate the inherent ratio of the peak areas at the two locations. When analyzing the sample, use this ratio and the sample's peak area at 1753 cm⁻¹. -1 Based on the actual peak area, the concentration of polylactic acid in the sample at 1169 cm⁻¹ was calculated. -1 The background contribution value generated at 1169 cm⁻¹, and from the sample at 1169 cm⁻¹ -1 The area of ​​the peak is deducted from the total peak area.

[0052] In one specific implementation, the quantitative mathematical function is established based on 1169 cm after background subtraction. -1 Peak area and 1753 cm -1 The ratio of peak areas multiplied by 100 is used as the characteristic infrared intensity, and a linear regression is performed with the content of 1-butyl-3-methylimidazole chloride. The function is Y = a + bX, where Y is the infrared intensity and X is the content.

[0053] In establishing the quantitative mathematical model, the ratio of the characteristic peak intensity of 1-butyl-3-methylimidazolium chloride (after background subtraction) to the characteristic peak intensity of polylactic acid internal standard was used as the dependent variable (Y), and the known content of the standard was used as the independent variable (X). A linear regression algorithm was used to fit the data to obtain a linear quantitative function of the form Y = a + bX. This function needs to be verified for its linearity using indicators such as the correlation coefficient.

[0054] In one specific implementation, the application of the quantitative mathematical function includes substituting the characteristic infrared intensity value of the unknown sample as Y into the function, calculating the X value, and obtaining the content of 1-butyl-3-methylimidazole chloride, the result of which is expressed as a percentage.

[0055] When applying the established quantitative model, the ratio of characteristic intensities measured after the unknown sample has undergone the same treatment is used as the Y value. This value is directly substituted into the established mathematical function Y = a + bX to solve for the X value. The X value is the content of chlorinated (1-butyl-3-methylimidazole) in the unknown sample, and the result is finally reported in the form of mass percentage.

[0056] Example 2: Based on Example 1 above, this example provides a more detailed description of the technical solution of this application in conjunction with actual production.

[0057] The analysis of 1-butyl-3-methylimidazole chloride content in polylactic acid nanofibers according to embodiments of the present invention includes the following steps: Step 100: Preparation of standards with concentrations of 0-2%. The fibers were immersed in 100 mL of methanol solution, with dissolved 1-butyl-3-methylimidazole in each solution weighing to a precision of 0 g, 0.02 g, 0.05 g, 0.08 g, 0.10 g, and 0.20 g respectively. The fibers were gently pressed with a watch glass to ensure complete immersion. The containers were placed in an ultrasonic cleaner at 50°C. After complete evaporation of the methanol, the 1-butyl-3-methylimidazole chloride was evenly distributed in the fibers. The fibers were then dried in a 105°C oven for 0.5 hours, and then cooled in a desiccator for later use. This yielded standards with concentrations of 0%, 0.2%, 0.5%, 0.8%, 1.0%, and 2.0%.

[0058] Step 200: Accurately weigh 0.15 grams of each standard sample and place it into a tableting mold with a diameter of 10 mm. Press it into a thin sheet under a pressure of 15 MPa for 3 minutes. Press two parallel tablets for each standard sample.

[0059] Step 300: Refer to Figure 1 The infrared spectrum curves of the standard were obtained. The fiber was pressed into a sheet with a thickness of micrometers and fixed on the sample holder. Infrared light passed through the sheet and entered the detector. Using the transmission mode of the infrared spectrometer, three points were tested at different positions of each pressed sheet, and the infrared spectrum curves were recorded.

[0060] Step 400: Refer to Figure 2 , Figure 3 Preprocessing was performed on the spectrum curves using automatic baseline correction. The baseline was determined to be 1753 cm⁻¹. -1 The sensitive characteristic peak of polylactic acid is 1169 cm⁻¹. -1These are sensitive characteristic peaks for 1-butyl-3-methylimidazolium chloride ionic liquids. Both of these characteristic peaks are independent of the other component's spectrum, except for 1-butyl-3-methylimidazolium chloride at 1169 cm⁻¹. -1 There is a slight absorption of polylactic acid at the peak, which can be subtracted. Therefore, selecting these two characteristic peaks can improve the quantitative sensitivity.

[0061] In the infrared spectrum of 1-butyl-3-methylimidazolium chloride, 1169 cm⁻¹ -1 The strongest peak is characteristic of the imidazole group and does not overlap with the strong infrared peaks characteristic of polylactic acid. Therefore, it can be used as a quantitative characteristic peak, with a baseline range of (2700~2000) cm⁻¹. -1 Integration range (1169~1154) cm -1 The small characteristic peak of polylactic acid at this location can be subtracted through calculation. Finally, the background of polylactic acid at the quantitative peak is subtracted because the infrared spectral curve distribution has a "fingerprint-like" characteristic, namely, the 1169 cm⁻¹ peak of polylactic acid. -1 With 1753cm -1 The peak ratio remains unchanged; however, the peak value at 1169 cm⁻¹ should be subtracted if 1-butyl-3-methylimidazole chloride is present. -1 The background signal of polylactic acid can be detected through 1753 cm⁻¹ in the sample. -1 Peak intensity, converted to 1169 cm⁻¹ -1 Peak intensity can be subtracted. The subtraction formula is as follows:

[0062] in, The sample is at 1169 cm. -1 Peak area at that location It is pure polylactic acid at 1169 cm. -1 Peak area at that location It is pure polylactic acid at 1753 cm. -1 Peak area at that location The sample is at 1753 cm. -1 Peak area at [location]. (Refer to...) Figure 5 The characteristic peak of polylactic acid was determined to be 1753 cm⁻¹. -1 The strong peak is characteristic of the carbonyl group in polylactic acid (PLA) and does not intersect with the ionic liquid curve; therefore, it is considered a characteristic peak of PLA, with a baseline of (2700~2000) cm⁻¹. -1 The integration range is (1783~1723) cm. -1 .

[0063] Reference Figure 4 For example, the 1-butyl-3-methylimidazolium chloride ionic liquid 1169 cm⁻¹ -1 Baseline and integration range selection for characteristic peak integration: 2000 cm⁻¹ -1Using the region with no nearby infrared absorption signal as a baseline, the integration range can reach 1169 cm. -1 Centered on the target area, the target should encompass as much of the absorption peak region as possible while minimizing the inclusion of matrix signals to improve test sensitivity. (Refer to...) Figure 5 Polylactic acid 1753 cm -1 Baseline and integration range selection for characteristic peak integration: 2000 cm⁻¹ -1 Using the region with no nearby infrared absorption signal as a baseline, the integration range can reach 1753 cm. -1 The central area.

[0064] Table 1 Standard Product Test Data Table

[0065] Table 2 Parameters of Quantitative Mathematical Functions

[0066] Step 500: Determining quantitative parameters. (Refer to...) Figure 6 The concentration-infrared characteristic intensity curve of 1-butyl-3-methylimidazole chloride shown conforms to the linear distribution of Beer-Lambert law, indicating that the test scheme is scientific and reasonable. Tables 1 and 2 show the test data of the standard and the parameters of the quantitative mathematical function. Based on the principle of invariant fingerprinting of spectral curves, the peak / peak ratio of the same substance remains unchanged regardless of changes in the spectral signal caused by the micromorphology of the test. Therefore, when quantifying ionic liquids in the mixed system of "polylactic acid + 1-butyl-3-methylimidazole chloride", the ratio of (independent 1-butyl-3-methylimidazole chloride peak / independent polylactic acid peak) can be used for quantification, and the average value of data from multiple test points can be taken to improve the quantitative accuracy. The quantitative parameter Y is defined as 1169 cm⁻¹ after background subtraction. -1 Peak area and 1753 cm -1 Multiplying the ratio of peak areas by 100, we get... The average value of the processed data from each test point of each standard is taken, and a quantitative function is obtained with Y = infrared intensity and X = concentration. This function should be a linear function.

[0067] Step 600: The polylactic acid fiber sample with unknown content is subjected to tableting, testing, and spectral data analysis according to the same procedures and parameters as the standard to obtain the characteristic infrared intensity value of the sample with unknown content. For example, the average characteristic infrared intensity of a batch of samples is (A... corr / A (1753)i ) * 100 = 0.37.

[0068] Step 700: Substitute the infrared intensity value of the sample with unknown content as the Y value into the mathematical model to obtain the content X. For example, the concentration of a batch of samples is calculated according to the mathematical function Y=0.00971+0.50039X as X=0.20%±0.010%.

[0069] This invention provides a quantitative analysis method for trace amounts of 1-butyl-3-methylimidazolium chloride in polylactic acid fibers based on transmission infrared spectroscopy. The core of the technical solution lies in: compressing the fiber sample into a micrometer-thick sheet to enhance signal intensity, employing transmission mode for infrared testing, and selecting a 1169 cm⁻¹ section. -1 With 1753 cm -1 These two independent characteristic absorption peaks were eliminated by establishing a specific background subtraction model for the polylactic acid matrix at 1169 cm⁻¹. -1 To mitigate interference, a linear quantitative mathematical model conforming to the Lambert-Beer law was constructed using the ratio of the two peak areas and the concentration. This scheme successfully achieved rapid and accurate quantitative analysis of trace components with a content below 5%, significantly improving the sensitivity and accuracy of detection, and providing a stable and reliable detection method for the quality monitoring and application research of modified polylactic acid fiber products.

[0070] It is important to note that the constructions and arrangements of this application shown in several different exemplary embodiments are merely illustrative. Although only a few embodiments are described in detail in this disclosure, those who consult this disclosure will readily understand that many modifications are possible (e.g., changes in the size, dimensions, structure, shape, and proportions of various elements, as well as parameter values ​​(e.g., temperature, pressure, etc.), mounting arrangements, use of materials, color, orientation, etc.) without substantially departing from the novel teachings and advantages of the subject matter described in this application). For example, an element shown as integrally formed may be composed of multiple parts or elements, the position of elements may be inverted or otherwise altered, and the nature or number or position of discrete elements may be changed or altered. Therefore, all such modifications are intended to be included within the scope of the invention. The order or sequence of any process or method steps may be changed or rearranged according to alternative embodiments. In the claims, any "device plus function" clause is intended to cover the structure described herein that performs the function, and not only structurally equivalent but also equivalent in structure. Other substitutions, modifications, alterations, and omissions may be made in the design, operation, and arrangement of the exemplary embodiments without departing from the scope of the invention. Therefore, the invention is not limited to the specific embodiments, but extends to various modifications that still fall within the scope of the appended claims. Furthermore, for the purpose of providing a concise description of exemplary embodiments, not all features of actual embodiments (i.e., those features not relevant to the currently considered best mode for carrying out the invention, or those features not relevant to implementing the invention) may be omitted.

[0071] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An infrared spectroscopic quantitative method for trace amounts of 1-butyl-3-methylimidazolium chloride in polylactic acid fibers, characterized in that, Includes the following steps: A series of standards for polylactic acid fibers with known contents of 1-butyl-3-methylimidazolium chloride were prepared. The standard sample is pressed into a sheet with a thickness of one micrometer; Infrared spectroscopy was performed using the transmission mode to obtain the infrared spectral curve of the standard. The infrared spectrum of the standard was processed, and 1-butyl-3-methylimidazole chloride was selected at 1169 cm⁻¹. -1 The characteristic peaks of polylactic acid at 1753 cm⁻¹ are similar to those of polylactic acid at 1753 cm⁻¹. -1 The characteristic peak at 1169 cm⁻¹ was subtracted from the peak at 1169 cm⁻¹ for polylactic acid. -1 Background signal at the location; Establish a quantitative mathematical function for the relationship between the characteristic infrared intensity and content of 1-butyl-3-methylimidazole chloride; The same tableting, testing, and spectral processing were performed on polylactic acid fiber samples with unknown content to obtain their characteristic infrared intensity values; The content of 1-butyl-3-methylimidazole chloride was calculated by substituting the characteristic infrared intensity value of the unknown sample into the quantitative mathematical function.

2. The infrared spectroscopy quantitative method according to claim 1, characterized in that, The standard contains 0% to 5% 1-butyl-3-methylimidazole chloride and is prepared by impregnation and volatilization, which involves immersing polylactic acid fibers in a methanol solution containing 1-butyl-3-methylimidazole chloride, followed by ultrasonic evaporation and drying.

3. The infrared spectroscopy quantitative method according to claim 1, characterized in that, In the tableting step, the standard or the polylactic acid fiber sample with unknown content is pressed into a sheet with a thickness of micrometers under constant pressure of 15 MPa for 3 minutes, and multiple sheets are pressed for each sample to ensure representativeness.

4. The infrared spectroscopy quantitative method according to claim 3, characterized in that, The infrared spectroscopy test adopts the transmission mode, in which the pressed sheet is fixed on the sample holder, and infrared light passes through the sheet into the detector. At least 3 points are tested in parallel for each sample to obtain multiple spectral curves.

5. The infrared spectroscopy quantitative method according to any one of claims 4, characterized in that, The infrared spectral curve processing includes baseline correction, with the baseline range selected at 2700 cm⁻¹. -1 Up to 2000 cm -1 The region between which there is no infrared absorption signal.

6. The infrared spectroscopy quantitative method according to claim 1, characterized in that, The characteristic peak of 1-butyl-3-methylimidazolium chloride was selected at 1169 cm⁻¹. -1 Centered on , the integral range is 1169 cm. -1 Up to 1154 cm -1 To include all regions of the absorption peak as much as possible and avoid matrix signal interference.

7. The infrared spectroscopy quantitative method according to claim 1, characterized in that, The characteristic peak of polylactic acid was selected at 1753 cm⁻¹. -1 Centered on , the integral range is 1783 cm. -1 Up to 1723 cm -1 Furthermore, this peak does not overlap with the spectrum of 1-butyl-3-methylimidazole chloride.

8. The infrared spectroscopy quantitative method according to claim 1, characterized in that, The deduction of polylactic acid at 1169 cm -1 The background signal at that location is expressed using the following formula: in, The sample is at 1169 cm. -1 Peak area at that location It is pure polylactic acid at 1169 cm. -1 Peak area at that location It is pure polylactic acid at 1753 cm. -1 Peak area at that location The sample is at 1753 cm. -1 Peak area at that location.

9. The infrared spectroscopy quantitative method according to claim 1, characterized in that, The quantitative mathematical function was established based on 1169 cm after background subtraction. -1 Peak area and 1753 cm -1 The ratio of peak area to characteristic infrared intensity was linearly regressed with the content of 1-butyl-3-methylimidazole chloride, with the function form Y = a + bX, where Y is infrared intensity and X is content.

10. The infrared spectroscopy quantitative method according to claim 9, characterized in that, The application of the quantitative mathematical function includes substituting the characteristic infrared intensity value of the unknown sample as Y into the function to calculate the X value and obtain the content of 1-butyl-3-methylimidazole chloride, with the result expressed as a percentage.

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