Apparatus and method for measuring molecular crystallinity in polymer forming processes

Abstract

The application belongs to the technical field of polymer molecular crystallinity measurement, and discloses a device and a measurement method for measuring the molecular crystallinity in a polymer forming process. i : wherein, Δν i is the volume fraction of the crystal region, ε r is the relative dielectric constant of the measured polymer measured by the complex dielectric constant measurement module, ε ri is the relative dielectric constant of the completely crystallized polymer, ε rj is the relative dielectric constant of the completely non-crystallized polymer, ρ i is the density of the crystalline region, ρ j is the density of the non-crystalline region, and the application can realize the measurement of the crystallinity in multiple directions, has strong anti-interference capability, and is very suitable for industrial application.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of polymer molecular crystallization measurement, and more particularly relates to a device and a method for measuring molecular crystallinity in a polymer forming process. BACKGROUND

[0002] In the polymer forming process, due to the cooling of the melt, the polymer molecular chains form an ordered structure, i.e. a crystalline structure, tending to a thermodynamic stable state. The crystallization of the polymer molecules significantly affects the important properties of the polymer product, such as force, heat, light, electricity, etc. Therefore, the measurement of the molecular crystallinity in the polymer forming process is of great significance to the high performance of the polymer product. At present, common methods for measuring the polymer molecular crystallinity include density method, infrared spectroscopy, DSC method, nuclear magnetic resonance (NMR), X-ray diffraction (XRD), etc. Among them, it is difficult to determine whether the crystallinity calculated by NMR is related to the orientation state (an ordered structure) of the polymer or whether it only describes the orientation state of the molecules. The density method cannot completely penetrate the non-crystalline region with the liquid for density measurement, so the obtained crystallinity is not accurate. X-ray scattering is based on Bragg scattering and cannot distinguish between crystalline and non-crystalline regions, so there is an error in the measured crystallinity. Therefore, the prior art cannot measure the crystallinity in multiple directions, and there is an urgent need to design a device for measuring the crystallinity in the polymer forming process. SUMMARY

[0003] In view of the above defects or improvement needs of the prior art, the present application provides a device and a method for measuring the molecular crystallinity in a polymer forming process, which can measure the crystallinity in multiple directions, has strong anti-interference ability, is especially suitable for sudden cooling and sudden heating conditions, and is very suitable for industrial application.

[0004] To achieve the above-mentioned purpose, according to one aspect of the present application, a device for measuring the molecular crystallinity in a polymer forming process is provided, which comprises an interdigital electrode, a complex permittivity measurement module connected with the interdigital electrode, and a crystallinity calculation module connected with the complex permittivity measurement module, wherein the crystallinity calculation module obtains the crystallinity Δχ of the polymer corresponding to the detection position of the interdigital electrode according to the following formula i :

[0005]

[0006] wherein Δv i is the volume fraction of the crystalline region, ε r is the relative dielectric constant of the polymer to be measured measured by the complex permittivity measurement module, ε ri is the relative dielectric constant of the polymer when it is completely crystallized, and ε rjis the relative dielectric constant of the polymer when the polymer is completely non-crystalline; ρ i is the density of the crystalline region, ρ j is the density of the non-crystalline region, constant is an empirical constant.

[0007] Preferably, the interdigital electrode is a plurality of interdigital electrodes, and the plurality of interdigital electrodes are arranged uniformly or in an array on the substrate.

[0008] Preferably, the material of the interdigital electrode is a conductive material, and the material of the substrate is rigid glass, FR4 or flexible polyimide.

[0009] Preferably, the melting point of the interdigital electrode is greater than the melting point of the polymer to be measured.

[0010] Preferably, the number of interdigital electrodes is an even number, and two of the interdigital electrodes are arranged vertically.

[0011] Preferably, the relative dielectric constant of the polymer when the polymer is completely crystalline and the relative dielectric constant of the polymer when the polymer is completely non-crystalline are obtained by molecular dynamics calculation or extrapolation based on dielectric measurement experiments.

[0012] Another aspect of the present application provides a measurement method of the above-mentioned device for measuring the molecular crystallinity in the polymer forming process, the measurement method comprising installing the interdigital bottom electrode on the polymer forming mold cavity and protruding the interdigital electrode from the wall of the polymer mold cavity, and using a crystallinity calculation module to calculate the crystallinity in the corresponding position and direction of each interdigital electrode.

[0013] Overall, compared with the prior art, the device and measurement method for measuring the molecular crystallinity in the polymer forming process provided by the present application mainly have the following beneficial effects:

[0014] 1. The interdigital electrode structure of the present application is simple, single-sided contact measurement of the polymer is convenient to install, and the combination of the complex dielectric constant measurement module and the crystallinity calculation module can obtain the measurement of the molecular crystallinity of various polymers, especially suitable for sudden cooling and sudden heating working conditions.

[0015] 2. The crystallinity calculation module of the present application realizes the calculation of the crystallinity based on the measurement of the dielectric constant of the polymer. On the one hand, the dielectric constant of the polymer is easy to obtain, and on the other hand, the dielectric constant value of the polymer is accurate and not easily affected by the external environment, and the structural stability is high, and the calculated crystallinity is high in precision.

[0016] 3. The device of the present application can be installed on the inner wall of the polymer forming cavity with complex surface structure, and is not affected by the surface structure of the mold cavity, has high flexibility and wide adaptability, can realize non-destructive online detection of polymer molecular crystallization, and has high precision, that is, can accurately distinguish the crystalline region and the non-crystalline region.

[0017] 4. The melting point of the interdigital electrode material and the substrate material of the present application is obviously higher than that of the polymer, and the structure is stable, which can maintain uniform stability for a long time. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a structural schematic diagram of a device for measuring the molecular crystallinity in the polymer forming process;

[0019] Figure 2 is a structural schematic diagram of an interdigital electrode unit;

[0020] Figure 3 is a structural schematic diagram of interdigital electrode units perpendicular to each other;

[0021] Figure 4 is a schematic diagram of the application scene of the interdigital electrode units perpendicular to each other.

[0022] In all the drawings, the same reference signs are used to represent the same elements or structures, wherein:

[0023] 100-interdigital electrode array; 110-interdigital electrode; 120-substrate; 200-complex dielectric constant measurement module; 300-crystallinity calculation module; 500-laser; 600-automatic fiber laying platform. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0025] The present application provides a device for measuring the molecular crystallinity in the polymer forming process, as shown in Figure 1 and Figure 2 , the device comprises an interdigital electrode 110, a complex dielectric constant measurement module 200 and a crystallinity calculation module 300. The complex dielectric constant measurement module is connected with the interdigital electrode, and is used for measuring the relative dielectric constant of the polymer molecules in the corresponding direction to be measured. The crystallinity calculation module is connected with the complex dielectric constant measurement module, and the crystallinity calculation module obtains the crystallinity Δχ of the polymer corresponding to the detection position of the interdigital electrode according to the following formula i :

[0026]

[0027] wherein, Δv i is the volume fraction of the crystalline region, ε r is the relative dielectric constant of the measured polymer obtained by the complex dielectric constant measuring module, ε ri is the relative dielectric constant of the polymer when it is completely crystallized, ε rj is the relative dielectric constant of the polymer when it is completely non-crystallized; ρ i is the density of the crystalline region, ρ j is the density of the non-crystalline region, constant is an empirical constant.

[0028] After the material is crystallized, the dielectric constant of the material will change:

[0029] ε * = ε - jε' = ε r - jε r 'ε0

[0030] C * = ε r - jε r ' C0 = C mmut - j1 / R mut ω

[0031] wherein, ε * is the complex dielectric constant of the measured material, ε is the real part of the complex dielectric constant, ε' is the imaginary part of the complex dielectric constant, j is the imaginary unit in the complex number, ε r is the relative dielectric constant, ε r ' is the relative dielectric loss, ε0 is the dielectric constant in vacuum, C * is the complex number expression of the capacitance of the material when it is crystallized, C0 is the capacitance of the interdigital electrode in vacuum, C mut is the real-time capacitance obtained by the complex dielectric constant measuring module, R mut is the real-time resistance obtained by the complex dielectric constant measuring module, and ω is the frequency of the electric field during measurement.

[0032] The complex dielectric constant measuring module obtains the relative dielectric constant of the measured polymer according to the real-time capacitance, and the specific calculation formula is:

[0033] The plurality of interdigital electrodes are uniformly spaced or arranged in an array on the substrate 120 to form an interdigital electrode array 100. Of course, the interdigital electrodes are not limited thereto and can be arranged in large quantities according to actual conditions to measure the crystallization conditions at different positions and in different directions. In actual applications, due to the existence of continuous carbon fibers, the crystallinity of the polymer to be measured differs along the fiber direction and the direction perpendicular to the fiber direction. Therefore, a plurality of interdigital electrodes can be arranged to measure the crystallinity in different directions. When the number n of interdigital electrodes is greater than 1, information at multiple positions or directions can be obtained, for example, 0°, 45°, 90°, 135°, and the like.

[0034] In a further preferred scheme, the material of the interdigital electrode is a conductive material, and the material of the substrate is rigid glass, FR4, or flexible polyimide.

[0035] In a further preferred scheme, the melting point of the interdigital electrode is greater than the melting point of the polymer to be measured, and the material of the interdigital electrode is preferably brass.

[0036] In a further preferred scheme, the number of interdigital electrodes 110 is an even number, and two are arranged perpendicularly, as shown in FIGS. 1B and 1C. Figure 3 and Figure 4

[0037] The relative dielectric constant ε of the polymer when completely crystallized ri and the relative dielectric constant ε of the polymer when completely non-crystallized rj The above values can be obtained by molecular dynamics calculation or extrapolation based on dielectric measurement experiments.

[0038] Another aspect of the present application provides a measurement method of a device for measuring the molecular crystallinity in a polymer forming process, the measurement method comprising mounting the interdigital bottom electrode on a polymer forming mold cavity and protruding the interdigital electrode from the wall of the polymer mold cavity, and using a crystallinity calculation module to calculate the crystallinity at the corresponding position and direction of each interdigital electrode.

[0039] The polymer to be measured in the present embodiment is polyether ether ketone (PEEK), which is melted by laser heating. This method has the characteristics of rapid cooling and rapid heating. At the same time, the carbon fiber conducts heat very quickly along the axial direction, which meets the condition of complex crystallization.

[0040] ​After the interdigital electrode 110 is connected to the complex dielectric constant measurement module 200 and the crystallinity calculation module 300, the interdigital electrode 110 is installed on the laying flat plate. Specifically, a groove can be formed on the laying flat plate, and the interdigital electrode 110 is buried in the laying flat plate so that the surface of the interdigital electrode 110 protrudes slightly from the plane of the laying flat plate. Specifically, at least one interdigital electrode is installed on the platform of the automatic fiber laying platform 600, so that when the laser 500 is heated, the sensor interdigital electrode can be ensured to be in contact with the high-temperature polymer PEEK melt.

[0041] Then, a polymer forming process is performed so that the interdigital electrode 110 is in contact with the polymer material to be measured, and the automatic fiber laying platform 600 starts heating and cooling. The opening and closing of the laser 500 generates a large amount of heat, and at this time, the interdigital electrode is in contact with the polymer melt, and the dielectric properties of PEEK change during the cooling process, and the measured dielectric constant value also changes.

[0042] According to the preset sampling period timing, the output dielectric value of the complex dielectric constant measurement module 200 is collected to obtain the dielectric value of the polymer melt in two directions at the measurement point.

[0043] The crystallinity calculation module 300 obtains the crystallinity Δχ composed of the crystallization values in the direction corresponding to the electrode according to the following formula i :

[0044]

[0045] The volume fraction Δv of the crystalline region of the polymer (PEEK) to be measured i , the density ratio k of the crystalline region and the non-crystalline region, are calculated from the relative dielectric constant (ε r ) of the polymer (PEEK) measured by the interdigital electrode, the extrapolated value of the relative dielectric constant (ε ri ) of the polymer when it is completely crystallized, and the relative dielectric constant (ε rj ) of the polymer when it is completely non-crystalline.

[0046] The present application provides a device and a measurement method for measuring the crystallinity of molecules in a polymer forming process. The present application can measure the crystallinity in multiple directions, has strong anti-interference ability, and is very suitable for industrial production and application.

[0047] Those skilled in the art will readily understand that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An apparatus for measuring the molecular crystallinity in a polymer forming process, characterized by, The device comprises an interdigital electrode, a complex permittivity measuring module connected with the interdigital electrode, and a crystallinity calculating module connected with the complex permittivity measuring module, wherein the crystallinity calculating module obtains the crystallinity Δχ of the polymer corresponding to the detection position of the interdigital electrode according to the following formula i : wherein Δv i is the volume fraction of the crystalline region, ε r is the relative dielectric constant of the measured polymer measured by the complex dielectric constant measuring module, ε ri is the relative dielectric constant of the polymer when it is completely crystallized, ε rj is the relative dielectric constant of the polymer when it is completely non-crystallized; ρ i is the density of the crystalline region, ρ j is the density of the non-crystalline region, conStant is an empirical constant.

2. The apparatus of claim 1, wherein, The plurality of interdigital electrodes are uniformly spaced or arrayed on the substrate.

3. The apparatus of claim 2, wherein, The material of the interdigital electrodes is conductive material, and the material of the substrate is rigid glass, FR4 or flexible polyimide.

4. The apparatus of claim 1 or 3, wherein, The melting point of the interdigital electrodes is greater than the melting point of the polymer to be measured.

5. The apparatus of claim 1, wherein, The number of the interdigital electrodes is even, and two of the interdigital electrodes are arranged perpendicularly.

6. The apparatus of claim 1, wherein, The relative dielectric constant of the polymer when completely crystallized and the relative dielectric constant of the polymer when completely non-crystallized are obtained by molecular dynamics calculation or extrapolation based on dielectric measurement experiments.

7. A measuring method of the apparatus for measuring the molecular crystallinity in a polymer molding process according to any one of claims 1 to 6, characterized by, The measurement method comprises mounting the interdigital electrodes on a polymer forming mold cavity and protruding the interdigital electrodes from the wall of the polymer mold cavity, and using a crystallinity calculation module to calculate the crystallinity at the corresponding position and direction of each interdigital electrode.

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