A method for detecting recycled polyester fibers

Abstract

The application discloses a kind of detection methods of regenerated polyester fiber, comprising the following detection steps: step S1, detection cloth is laid on detection bearing seat, detection bearing seat includes arc surface in upper portion, cloth is laid with arc surface and is attached;Step S2, open detection light path, the light of detection light path is focused on the P point of cloth outer surface, the light of detection light path is shot and the included angle α is formed with the normal direction of cloth at P point;Step S3, adjust the height difference of detection light path and cloth, so that the included angle α changes, to adapt to the included angle α value required by different cloth;Step S4, using laser raman spectrometer as the light source of detection light path, to detect the regenerated polyester fiber of cloth.The application provides a kind of detection methods of regenerated polyester fiber, changes incident included angle α to meet the detection needs of different cloth.

Description

Technical Field

[0001] This invention relates to the field of recycled polyester fiber testing technology, and more specifically, to a method for testing recycled polyester fibers. Background Technology

[0002] In the process of distinguishing between recycled and virgin polyester using Raman spectroscopy, a laser is incident perpendicularly. When incident perpendicularly, the laser shines directly onto the surface along the normal direction, easily producing strong specular reflection. A large amount of reflected light returns to the Raman probe along the same path, submerging the weak characteristic Raman signals of the fibers. This results in characteristic peaks being masked, baseline elevation, and a sharp decrease in the signal-to-noise ratio. Dark and black polyester fabrics are prone to fluorescence interference and signal attenuation when incident perpendicularly, leading to weak effective Raman signals and increased impurity peaks, making it difficult to accurately distinguish the compositional differences between recycled and virgin polyester. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for detecting recycled polyester fibers, by changing the incident angle α to meet the detection requirements of different fabrics.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a method for detecting recycled polyester fibers, comprising the following detection steps: Step S1, laying the detection fabric on the detection support, the detection support including an upper arc surface, the fabric being laid in close contact with the arc surface; Step S2, turning on the detection optical path, focusing the light of the detection optical path on point P on the outer surface of the fabric, the direction of the light of the detection optical path forming an angle α with the normal direction of the fabric at point P; Step S3, adjusting the vertical height difference between the detection optical path and the fabric to change the angle α, thereby adapting to the required angle α value for different fabrics; Step S4, using a laser Raman spectrometer as the light source of the detection optical path to detect the recycled polyester fibers in the fabric.

[0005] Furthermore, the light rays in the detection optical path are directed horizontally.

[0006] Furthermore, the main body of the testing support is cylindrical, and the curved surface is the upper semicircular surface of the testing support.

[0007] Furthermore, the included angle α ranges from 0° to 15°.

[0008] Furthermore, the fabric includes ends located on the left and right sides, with the ends suspended downwards.

[0009] Furthermore, the probe of the laser Raman spectrometer, which serves as the light source for the detection optical path, is fixed in the vertical direction, and a lifting device is connected to the bottom of the detection support to adjust the vertical height of the detection support.

[0010] Furthermore, after each adjustment of the vertical height difference between the detection optical path and the fabric, the light from the detection optical path is refocused on the outer surface of the fabric.

[0011] Furthermore, the method for initializing the included angle α is as follows: ① Move the detection carrier downwards; ② Focus the light rays of the detection optical path to the upper vertex of the detection carrier, and record the height position of the upper vertex of the detection carrier as d1; ③ Add the thickness value of the fabric to the height position d1 of the upper vertex of the detection carrier in step ② as the new height position, and record the new height position as d2, with the included angle α corresponding to d2 being 90°; ④ Move the detection carrier upwards so that the initial value of the included angle α is set to 7°.

[0012] Furthermore, the relationship between the height difference Δd caused by the movement of the bearing seat and the included angle α is: Δd=R×sinα1-R×sinα2, where α1 and α2 are the two included angle α values ​​before and after adjustment, α1 is the larger of the two values, and R is the sum of the radius of the arc surface and the thickness of the fabric.

[0013] In summary, the present invention has the following beneficial effects:

[0014] 1. This invention employs a horizontal optical path with an adjustable incident angle α, reducing the defects of strong specular reflection easily caused by vertical incidence. This prevents reflected light from returning along the original path and interfering with probe detection, thus suppressing specular reflection interference and allowing the weak Raman characteristic signals of recycled polyester fibers to be clearly highlighted. Furthermore, this invention uses a cylindrical arc-shaped support base combined with a gravity-based self-adhesive method where the fabric ends are suspended, eliminating the need for manual stretching and flattening of the fabric. This avoids excessive fiber stretching and excessive compression of internal gaps, ensuring the consistency of the flattened state of each piece of fabric being tested, thereby stabilizing the testing conditions.

[0015] 2. This invention changes the incident angle α by simply raising and lowering the support base, replacing the traditional angle adjustment method of rotating optical path or rotating sample stage. It does not require a precision rotating stage, indexing plate and angle calibration components. The overall structure is simple, the assembly is easy, the equipment manufacturing cost is low and the later maintenance is convenient.

[0016] 3. The laser focusing spot always maintains a constant size and will not be distorted or enlarged with changes in the incident angle. This effectively avoids the spot covering the fabric texture, gaps, and warp and weft junction areas, reduces the mixing of irrelevant structural noise signals, prevents the spectrum from being averaged and the characteristic peaks from being blurred, accurately locks the detection area, and is conducive to the true restoration of the spectral characteristics of recycled polyester materials. Attached Figure Description

[0017] Figure 1 This is a first schematic diagram of this embodiment;

[0018] Figure 2 This is a second schematic diagram of this embodiment.

[0019] Reference numerals: 1. Detection support, 11. Arc surface, 2. Detection fabric, 21. End, 3. Detection optical path. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] like Figure 1 , Figure 2 As shown in the figure, this embodiment discloses a method for detecting recycled polyester fibers, including the following detection steps:

[0022] Step S1: Lay the testing fabric 2 on the testing support 1. The bottom of the testing support 1 is connected to a lifting device to adjust the vertical height of the testing support 1. The lifting device specifically adopts a combination of a stepper motor, a ball screw, and a linear slide.

[0023] The testing support 1 includes an upper arc surface 11, with fabric 2 laid in close contact with the arc surface 11. Specifically, the main body of the testing support 1 is cylindrical, the arc surface 11 is the upper semicircular surface of the testing support 1, and the fabric 2 includes end pieces 21 at both ends. The maximum length of the left and right ends of the fabric 2 is greater than the diameter of the testing support 1. The fabric 2 is the test sample. The fabric 2 is hung on the arc surface 11, with the end pieces 21 facing downwards and suspended in the air. That is, the end pieces 21 exert a downward force of gravity on the fabric 2 attached to the arc surface 11, and the fabric 2 maintains approximately left-right symmetry each time it is placed, which ensures that the flatness of each piece of fabric 2 tested is basically consistent.

[0024] If the traditional flat-laying setup is used for the testing of fabric 2, it needs to be forcibly flattened, which will stretch the fibers and compress the gaps. Therefore, the operator should try to keep fabric 2 flat and reduce the stretching of it, while ensuring the flattening consistency of each piece of fabric 2 being tested. This greatly increases the difficulty of operation. In order to reduce stretching, the operator may flatten fabric 2 differently each time, which will affect the consistency of testing.

[0025] By suspending the fabric 2 through the curved surface 11, and with the end 21 exerting natural gravity pull on the fabric 2 attached to the curved surface 11, the flattening formed by the fabric 2 attached to the curved surface 11 is more uniform for fabric 2 of the same size and specification, which can improve the consistency of inspection and reduce the requirements for the operator's skill level.

[0026] The roughness of the arc surface 11 is low. In order to achieve stable placement of the smooth fabric 2 on the arc surface 11, after the fabric 2 is placed, it is pressed and positioned on top by a pressure block. The pressure block and the detection support 1 rise and fall synchronously. Since the detection position is far away from the pressing point, the deformation of the fabric 2 caused by the pressing does not affect the detection.

[0027] Step S2: Activate detection optical path 3. The light from detection optical path 3 is directed horizontally. Focus the light from detection optical path 3 onto point P on the outer surface of fabric 2. The direction of the light from detection optical path 3 forms an angle α with the normal direction of fabric 2 at point P, thus distinguishing it from perpendicular incidence.

[0028] Before starting the detection, an initial value adjustment of the included angle α is required. This adjustment is not needed during subsequent continuous detection. The initialization method for the included angle α is as follows:

[0029] ① Move the testing support 1 downwards;

[0030] ② The light rays from the detection optical path 3 are focused to the upper vertex of the detection carrier 1. The included angle α corresponding to this height position of the detection carrier 1 is 90°. This height position of the upper vertex of the detection carrier 1 is recorded as d1.

[0031] ③ Add the height position d1 of the upper vertex of the detection support 1 in step ② to the thickness value of the fabric 2 as the new height position. The new height position is recorded as d2. That is, the placement of the fabric 2 changes the radius of the cylinder of the detection support 1. Since the light path hits the fabric 2, not the detection support 1, the calculation is based on the sum of the radius of the arc surface 11 and the thickness value of the fabric 2 as the calculation radius.

[0032] ④ Using d2 as the height reference and corresponding to an included angle α of 90°, move the detection bearing seat 1 upward so that the initial value of the included angle α is set to 7°.

[0033] The relationship between the height difference Δd (i.e., the height difference between the location of d2 and the point P hit by the detection optical path 3) caused by the movement of the detection support 1 and the included angle α is expressed by the following formula (using trigonometric functions): Δd = R × sinα1 - R × sinα2, where α1 and α2 are the two included angle α values ​​before and after adjustment, α1 is the larger of the two values ​​(α1 and α2), and R is the sum of the radius of the arc surface 11 and the thickness of the fabric 2. The stroke of the detection support 1 is controlled according to the required included angle α value (7°).

[0034] Step S3: Adjust the vertical height difference between the detection optical path 3 and the fabric 2 to change the included angle α, thereby adapting to the included angle α value required for different fabrics 2.

[0035] The included angle α ranges from 0° to 15°, and the value of included angle α varies for different fabrics. For example, for lightweight plain-weave polyester fabrics with moderate surface reflectivity, a small angle can avoid specular reflection and achieve a high signal-to-noise ratio, with α ranging from 4° to 6°; for medium-weight polyester woven fabrics with coarser weave, a slightly larger included angle can reduce texture scattering interference, with α ranging from 7° to 9°; for polyester knitted fabrics with slightly undulating knitted surfaces, α ranges from 5° to 7°; for dark / black polyester fabrics, dark colors tend to have higher specular reflectivity, requiring a larger included angle to reduce reflection and improve the characteristic peak signal-to-noise ratio, with α ranging from 8° to 11°.

[0036] The optimal angle α for different fabrics 2 was determined by collecting Raman spectra of the fabrics at various angles within the range of 0° to 15°. The evaluation indicators were signal-to-noise ratio, characteristic peak intensity, baseline stability, and specular reflection interference. The weights of the indicators were: signal-to-noise ratio 40%, characteristic peak intensity 30%, baseline stability 20%, and specular reflection interference 10%. The comprehensive score was calculated according to the weights, and the angle with the highest score was the optimal angle α for that fabric.

[0037] The change in the included angle α can also be detected by rotating the optical path 3 angle, which is different from the lifting method in this embodiment. However, the rotation method requires a precision rotary table, indexing plate, rotary support, angle closed-loop coding, and angle calibration. The program is complicated, there are many parts, and the assembly is complicated. In contrast, the linear drive method has a relatively simple structure, greatly reduces the cost, and is also easy to maintain.

[0038] By rotating the detection optical path 3, the focal point of the detection optical path 3 on the fabric 2 will vary in size due to different tilt angles. As the tilt angle increases, the spot size increases; for example, an originally circular spot becomes an ellipse after tilting. Even after focusing, its shape cannot be changed, resulting in changes in spot size under different detection angles, which is detrimental to maintaining detection consistency. Furthermore, a large spot size will simultaneously illuminate the fabric texture, seams, and warp-weft junctions, mixing in irrelevant structural signals. The composition spectrum will be averaged, characteristic peaks will become blurred, and the true material information will be indistinguishable.

[0039] In this embodiment, the size of the spot of the detection light path 3 hitting the fabric 2 remains consistent, which is beneficial for locking the detection area for comparative analysis.

[0040] Step S4: A laser Raman spectrometer is used as the light source for detection optical path 3 to detect recycled polyester fibers in fabric 2. Detection can be performed directly to obtain numerical values, or by comparing the results with a standard sample for data analysis. The laser wavelength is selected as 785nm (suitable for detecting characteristic peaks of recycled polyester and reducing fluorescence interference); the laser power is controlled between 50-100mW (avoiding damage to fibers from excessive power and weak signals from excessive power); the integration time is 1-3s, and the number of scans is 3-5 (to ensure stable spectral signals); the target wavenumber range for the characteristic peaks of recycled polyester is limited to 800-1800cm⁻¹. -1 (Covering the key range of characteristic peaks of recycled polyester and eliminating irrelevant wavenumber interference).

[0041] The probe of the laser Raman spectrometer, which serves as the light source for the detection optical path 3, is fixed in the vertical direction. Along the axial direction of the detection support 1, the probe of the laser Raman spectrometer can be mounted on a movable base to perform translational movements to complete measurements at multiple points.

[0042] After each adjustment of the vertical height difference between the detection optical path 3 and the fabric 2, the light from the detection optical path 3 is refocused on the outer surface of the fabric 2.

[0043] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for detecting recycled polyester fibers, characterized in that, The testing steps include the following: Step S1, the detection fabric (2) is laid on the detection support (1), the detection support (1) includes an arc surface (11) located at the top, and the fabric (2) is laid in close contact with the arc surface (11); Step S2, turn on the detection optical path (3), focus the light of the detection optical path (3) on point P on the outer surface of the fabric (2), and the direction of the light of the detection optical path (3) forms an angle α with the normal direction of the fabric (2) at point P; Step S3: Adjust the vertical height difference between the detection optical path (3) and the fabric (2) to change the included angle α, thereby adapting to the included angle α value required by different fabrics (2); Step S4: Use a laser Raman spectrometer as the light source for the detection optical path (3) to detect the recycled polyester fibers in the fabric (2).

2. The method for detecting recycled polyester fiber according to claim 1, characterized in that, The light rays of the detection optical path (3) are directed in a horizontal direction.

3. The method for detecting recycled polyester fiber according to claim 1, characterized in that, The main body of the detection support (1) is cylindrical, and the arc surface (11) is the upper semicircular surface of the detection support (1).

4. The method for detecting recycled polyester fiber according to claim 1, characterized in that, The included angle α ranges from 0° to 15°.

5. The method for detecting recycled polyester fiber according to claim 1, characterized in that, The fabric (2) includes end pieces (21) located on the left and right sides, with the end pieces (21) suspended downwards.

6. The method for detecting recycled polyester fiber according to claim 2, characterized in that, The probe of the laser Raman spectrometer, which serves as the light source for the detection optical path (3), is fixed in the vertical direction. The bottom of the detection support (1) is connected to a lifting device to adjust the vertical height of the detection support (1).

7. The method for detecting recycled polyester fiber according to claim 1, characterized in that, After each adjustment of the vertical height difference between the detection optical path (3) and the fabric (2), the light from the detection optical path (3) is refocused on the outer surface of the fabric (2).

8. The method for detecting recycled polyester fiber according to claim 1, characterized in that, It also includes the method for initializing the included angle α, specifically: ① Move the detection support (1) downwards; ② The light rays of the detection optical path (3) are focused to the upper vertex of the detection carrier (1), and the height position of the upper vertex of the detection carrier (1) is recorded as d1; ③The height position d1 of the upper vertex of the detection support (1) in step ② is added to the thickness value of the fabric (2) as the new height position, and the new height position is recorded as d2. The included angle α corresponding to d2 is 90°. ④ Move the detection support (1) upward so that the initial value of the included angle α is set to 7°.

9. The method for detecting recycled polyester fiber according to claim 8, characterized in that, The relationship between the height difference Δd generated by the movement of the detection support (1) and the included angle α is: Δd = R × sinα1 - R × sinα2, where α1 and α2 are the two included angle α values ​​before and after adjustment, α1 is the larger of the two values, and R is the sum of the radius of the arc surface (11) and the thickness of the fabric (2).

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