Method for evaluating the plasticity of propellant based on microwave detection

Abstract

This application provides a method for evaluating the plasticity of propellant materials based on microwave detection, belonging to the field of microwave detection. The method includes: placing a standard sample known to be in a fully plasticized state into a microwave detection system, and measuring its microwave attenuation value S at multiple different temperature points. 21 The |S| of the standard sample was calculated. 21 The change in temperature with increasing temperature is used as a baseline value; the |S| value of the sample under test is measured under the same conditions. 21 | Variation range; The variation range of the sample under test is compared with the benchmark value, and the degree of plasticization is determined according to the three-level threshold. This application uses the variation range of microwave attenuation value with temperature increase as the evaluation index. By comparing the same sample at different temperatures, the interference of non-plasticizing factors such as packing density is effectively offset, realizing non-contact, rapid, and quantitative evaluation of the degree of plasticization, which is suitable for online monitoring and quality control at the propellant production site.

Description

Technical Field

[0001] This application relates to the field of microwave detection technology, and in particular to a method for evaluating the plasticity of propellant materials based on microwave detection. Background Technology

[0002] Propellants primarily use nitrocellulose (NC) as an energetic binder. NC molecular chains are semi-rigid and thermally decompose before reaching their melting point, thus preventing processing by heating and melting. Organic solvents or plasticizers are needed to dissolve and plasticize NC to impart plasticity. The propellant plasticization process is a crucial step in solvent-based manufacturing, as the degree of plasticization directly affects the quality of subsequent compression molding and the performance of the final product. Therefore, accurate evaluation of the material's plasticity during plasticization is of great importance.

[0003] Currently, the evaluation methods for the plasticity of propellant materials mainly include the following categories: First, the capillary rheometer shear viscosity method, which evaluates the degree of plasticization by pressing the plasticized material into strips and testing the shear viscosity. However, sample pretreatment is complex, the testing cycle is long, and it is a destructive test. Second, the torque rheometer method, which determines the plasticization endpoint by monitoring the torque-time curve during the kneading process until it tends to be horizontal and stable. However, it can only reflect macroscopic rheological behavior and has limited quantitative characterization capabilities. Third, the low-field nuclear magnetic resonance method, which evaluates the degree of melt plasticization by detecting the transverse relaxation time T2 of NC. It has high accuracy but the equipment is expensive, and the samples need to be processed into blocks of specified sizes (not larger than 15mm×10mm×10mm), making it difficult to achieve rapid online detection. In addition, the application of existing microwave detection technology in the field of energetic materials is mainly focused on defect detection and dielectric constant measurement. There are no reports of its use for quantitative evaluation of the degree of plasticization of propellant materials. In summary, existing methods generally suffer from drawbacks such as complex sample pretreatment, long operation time, mostly contact or destructive detection, difficulty in achieving rapid online evaluation, and lack of effective compensation mechanisms due to the influence of various factors such as sample temperature and density on the detection results. Summary of the Invention

[0004] This application provides a method for evaluating the plasticity of propellant materials based on microwave detection, so as to provide a method for rapidly and quantitatively evaluating the plasticity of propellant materials in a non-contact manner.

[0005] This application provides a method for evaluating the plasticity of propellant materials based on microwave detection, the method comprising the following steps:

[0006] S1. Place a standard propellant sample known to be in a fully plasticized state into a microwave detection system. At multiple different temperature points, emit microwave signals to the standard sample and receive the microwave signals after they penetrate the standard sample. Obtain the microwave attenuation value S of the standard sample at each temperature point. 21 Based on the microwave attenuation value S at each temperature point21 The |S| of the standard sample was calculated. 21 The magnitude of the change with increasing temperature is used as the benchmark value for evaluating the degree of plasticization.

[0007] S2. Place the propellant sample to be tested in the same microwave detection system. At multiple different temperature points (similar to step one), transmit microwave signals to the sample and receive the microwave signals after they penetrate the sample. Obtain the microwave attenuation value S of the sample at each temperature point. 21 Based on the microwave attenuation value S at each temperature point 21 The |S| of the sample to be tested was calculated. 21 The magnitude of change with increasing temperature;

[0008] S3, the |S| of the sample to be tested 21 |Variation range and standard sample|S 21 Compare the magnitude of change:

[0009] When the |S of the sample to be tested 21 |The change range reaches the standard sample|S 21 When the change range exceeds 90%, the sample is considered to be sufficiently plasticized.

[0010] When the |S of the sample to be tested 21 |The variation range is within the standard sample|S 21 When the change range is between 60% and 90%, the sample is considered partially plasticized.

[0011] When the |S of the sample to be tested 21 |The change was less than that of the standard sample|S 21 When the change range is 60%, the sample is deemed to be under-plasticized.

[0012] Optionally, in step S1, the standard propellant sample known to be in a fully plasticized state is obtained by: confirming the plasticization process endpoint of the propellant using a torque rheometer method, and using the material that reaches the process endpoint as the standard sample.

[0013] Optionally, the plurality of different temperature points include 25°C, 30°C, 35°C, 40°C, 45°C and 50°C.

[0014] Optionally, starting from 25°C, the temperature is slowly increased to each temperature point at a rate of 0.5°C per minute. After reaching each temperature point, the temperature is maintained for at least 5 minutes to ensure uniform internal temperature of the sample before microwave detection.

[0015] Optionally, prior to steps S1 and S2, the method further includes a sample preparation step:

[0016] The propellant material is loaded into a square material box. During loading, the material is allowed to fall naturally into the box and the surface is scraped flat to ensure consistent loading tightness.

[0017] Optionally, the material box has dimensions of 300mm × 120mm × 120mm, and the propellant packing density is 1.3–1.4 g / cm³. 3 .

[0018] Optionally, the microwave detection system includes a vector network analyzer and a pair of metasurface lens antennas serving as transmitting and receiving antennas, respectively. The frequency range of the microwave signal is 23.5 GHz to 24.5 GHz, and the sample is placed between the transmitting and receiving antennas at equal distances from the antennas.

[0019] Optionally, in steps S1 and S2, before performing microwave detection at multiple different temperature points, the material box containing the sample is placed in a constant temperature chamber at 25°C for 2 hours to ensure that the sample temperature is uniform.

[0020] Optionally, the |S 21 The magnitude of change with increasing temperature satisfies the following relationship: Magnitude of change = |S| 21 (50℃)|−|S 21 (25℃)|, where |S 21 (T)| represents the temperature T at which S 21 The absolute value of the decibel value.

[0021] Optionally, the propellant material is a single-base propellant kneaded and plasticized material.

[0022] The technical solutions provided in this application have the following advantages compared with the prior art:

[0023] (1) By using microwaves to penetrate samples for non-contact testing, the damage and interference to the material caused by contact operations such as pressing pharmaceutical strips and cutting samples in traditional methods are fundamentally avoided. The transmitting antenna transmits microwave signals to the sample, and the receiving antenna captures the microwave signals after penetrating the sample. The antenna and the sample do not come into direct contact during the entire testing process, and the sample can be directly tested without any molding or processing, thus achieving non-destructive testing. At the same time, the highest temperature during the entire testing process does not exceed 50°C, which is far lower than the explosion temperature of nitrocellulose of 185°C, ensuring the safety of the testing process.

[0024] (2) By adopting microwave attenuation value |S 21Using the change in temperature as an evaluation index effectively eliminates the interference of non-plasticizing factors such as packing density on the test results. In traditional single-point microwave attenuation measurements, differences in packing density directly affect the degree of microwave signal absorption when penetrating the sample, resulting in different measurement values ​​for samples with the same degree of plasticization but different packing densities. This application uses the change in temperature at multiple points for the same sample as an evaluation index. 21 Using the variation range as the criterion, the self-comparison characteristics of samples in the same material box at different temperatures are utilized to effectively cancel out common factors such as packing density in the process of calculating the difference. The test results have higher specificity for the degree of plasticization and good measurement repeatability.

[0025] (3) A quantitative evaluation of the degree of plasticization was achieved by first confirming the fully plasticized standard sample and establishing a benchmark value using the torque rheometer method, and then comparing and judging the sample to be tested. First, the process endpoint of the fully plasticized state was determined using traditional mature methods. The material at the endpoint was then used as a standard sample and its |S was measured in a microwave detection system. 21 The range of change was used as a baseline value for complete plasticization; then, the sample was tested under identical conditions to determine its |S|. 21 | The variation range; Finally, the variation range of the sample to be tested is compared with the benchmark value, and the relative plasticization degree is quantitatively characterized in percentage form. Based on the three-level judgment threshold, the conclusion of sufficient plasticization, partial plasticization or insufficient plasticization is clearly given, eliminating the subjectivity of the traditional visual method.

[0026] (4) Rapid testing is achieved through simplified sample preparation and standardized testing procedures. The sample to be tested only needs to be naturally placed into the material box and the surface smoothed before it can be tested. No pressing, cutting or pre-forming treatment is required. The complete testing process for a single batch is about 2.5 hours, and the constant temperature chamber can accommodate multiple material boxes at the same time to achieve parallel testing. Compared with the several hours of testing time for a single sample by the capillary rheometer method, the testing efficiency is significantly improved, which is suitable for timed sampling and rapid feedback of the kneading process on the production site. Attached Figure Description

[0027] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1This is a flowchart illustrating a method for evaluating the plasticity of propellant materials based on microwave detection, as provided in an embodiment of this application. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the antecedent and consequent of a proportional expression, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0032] Figure 1 This is a flowchart illustrating a method for evaluating the plasticity of propellant materials based on microwave detection, as provided in an embodiment of this application.

[0033] like Figure 1 As shown in the figure, this application provides a method for evaluating the plasticity of propellant materials based on microwave detection, the method comprising the following steps:

[0034] S1. Place a standard propellant sample known to be in a fully plasticized state into a microwave detection system. At multiple different temperature points, emit microwave signals to the standard sample and receive the microwave signals after they penetrate the standard sample. Obtain the microwave attenuation value S of the standard sample at each temperature point. 21 Based on the microwave attenuation value S at each temperature point 21 The |S| of the standard sample was calculated. 21 The magnitude of the change with increasing temperature is used as the benchmark value for evaluating the degree of plasticization.

[0035] S2. Place the propellant sample to be tested in the same microwave detection system. At multiple different temperature points (similar to step one), transmit microwave signals to the sample and receive the microwave signals after they penetrate the sample. Obtain the microwave attenuation value S of the sample at each temperature point. 21 Based on the microwave attenuation value S at each temperature point 21 The |S| of the sample to be tested was calculated. 21 The magnitude of change with increasing temperature;

[0036] S3, the |S| of the sample to be tested 21 |Variation range and standard sample|S 21 Compare the magnitude of change:

[0037] When the |S of the sample to be tested 21 |The change range reaches the standard sample|S 21 When the change range exceeds 90%, the sample is considered to be sufficiently plasticized.

[0038] When the |S of the sample to be tested 21 |The variation range is within the standard sample|S 21 When the change range is between 60% and 90%, the sample is considered partially plasticized.

[0039] When the |S of the sample to be tested 21 |The change was less than that of the standard sample|S 21 When the change range is 60%, the sample is deemed to be under-plasticized.

[0040] It should be noted that S 21 For microwave scattering parameters; S 21 (dB) represents the transmission coefficient in decibels; the |S| mentioned in this method 21 | Refers to S 21 The absolute value of the decibel value. The single-base propellant kneading material is mainly nitrocellulose, relying on alcohol-ether solvents for solution plasticization. When plasticization is sufficient, the solvent fully penetrates between the nitrocellulose molecular chains, weakening intermolecular hydrogen bonds, resulting in high freedom of movement of molecular chain segments. During heating, the orientation polarization behavior of polar groups and solvent molecules is temperature-sensitive, and the material's equivalent dielectric loss changes significantly with temperature. When plasticization is insufficient, nitrocellulose agglomerates severely, chain segment movement is restricted, and the dielectric properties change less with temperature. Under short-time gradient heating conditions of 25–50℃, the solvent evaporation is extremely low, and the change in microwave attenuation with temperature is mainly determined by the degree of plasticization.

[0041] The role of S1 is to establish an evaluation benchmark. Characterizing the degree of propellant plasticization requires a unified reference system. S1 involves placing a standard sample known to be in a fully plasticized state (this state needs to be confirmed beforehand by independent methods such as torque rheometer) in a microwave detection system and measuring its microwave attenuation value S at multiple temperature points. 21 Then, the |S| of the standard sample can be calculated. 21 The variation in temperature reflects the sensitivity of the material's dielectric properties to temperature under fully plasticized conditions. Using this variation as a benchmark for evaluating the degree of plasticization provides a unified standard for subsequent quantitative determination of the sample. The core value of this step lies in transforming the process concept of "fully plasticized" into quantifiable microwave physical parameters, making the evaluation objective and repeatable.

[0042] The purpose of S2 is to obtain the plasticity characteristic parameters of the sample under test. The sample is tested under the same detection conditions (same microwave detection system, same temperature sequence) to obtain its |S2|. 21 The change in dielectric loss with increasing temperature. This change is a key indicator of the degree of plasticization of the material: the higher the degree of plasticization, the more tightly the plasticizer molecules are bound to the nitrocellulose molecular chains, the greater the degree of freedom of molecular chain segment movement, and the more significant the change in dielectric loss with increasing temperature, as expressed by S. 21 The absolute value increases more significantly with increasing temperature. The essence of S2 is to convert the "plasticized state" of the sample into a quantifiable microwave characteristic parameter, which is directly related to the molecular mobility within the material.

[0043] The function of S3 is to quantitatively determine the degree of plasticization. By comparing the variation range of the test sample with the baseline value of the standard sample, the relative degree of plasticization of the test sample is quantitatively characterized as a percentage, and a clear process judgment conclusion is given based on three threshold levels (≥90%, 60%~90%, <60%). This judgment standard is based on the understanding of the plasticization process: when the variation range reaches more than 90% of the baseline value, it indicates that the material has been fully plasticized, and the molecular chain segment mobility is close to the fully plasticized state, and it can proceed to the next process; when it is between 60% and 90%, it indicates that the material is in the process of plasticization and kneading needs to continue; when it is below 60%, it indicates that the degree of plasticization of the material is seriously insufficient, and the process parameters need to be adjusted. It should be noted that the above-mentioned 60% and 90% judgment thresholds were obtained through experimental calibration for the single-base propellant system of the formulation described in this embodiment; for different formulation propellant materials, the same detection process can be used to re-establish the baseline value of the standard sample, and the plasticization degree judgment threshold can be adjusted adaptively.

[0044] Therefore, this application abandons the traditional evaluation model that relies on single-point absolute values ​​(such as viscosity or torque values ​​at a single temperature), and instead uses the change in microwave attenuation value with increasing temperature as an evaluation index of the degree of plasticization. This change essentially reflects the sensitivity of the material's dielectric properties to temperature, and this sensitivity is determined by the binding state of the plasticizer and nitrocellulose molecular chains, which is directly related to the degree of plasticization of the material. By comparing this change with the benchmark value of a known fully plasticized state, the degree of plasticization is transformed from "qualitative empirical judgment" to "quantitative objective evaluation." Furthermore, this method does not require pretreatment such as pressing or cutting of samples, making it a non-contact, non-destructive testing method suitable for rapid sampling and online monitoring in production sites.

[0045] In some embodiments, in step S1, the standard propellant sample known to be in a fully plasticized state is obtained by: confirming the plasticization process endpoint of the propellant using a torque rheometer, and using the material that has reached the process endpoint as the standard sample.

[0046] The endpoint of the plasticizing process was confirmed by torque rheometer method. This method is based on the rheological principle that the material reaches the optimal plasticizing state when the torque-time curve tends to be horizontal and stable during the material kneading process, and provides a calibration benchmark of "known fully plasticized state" for microwave detection.

[0047] In some embodiments, the plurality of different temperature points include 25°C, 30°C, 35°C, 40°C, 45°C, and 50°C.

[0048] In some implementations, the temperature is slowly increased from 25°C to each temperature point at a rate of 0.5°C per minute, and after reaching each temperature point, it is held for at least 5 minutes to ensure that the internal temperature of the sample is uniform before microwave detection is performed.

[0049] The selection of the temperature points reflects a multifaceted trade-off. Setting the upper limit at 50℃, rather than higher, is based on propellant safety considerations. Nitrocellulose has an explosive temperature of 185℃, and 50℃ provides sufficient safety margin. Furthermore, this temperature range is sufficient to fully reveal the difference in dielectric properties between fully plasticized and insufficiently plasticized samples. At each temperature point, S... 21 The changing trends are highly distinctive. The six temperature points allow for the depiction of a complete decay value curve without excessively increasing the detection time, supporting accurate calculation of the change amplitude. The slow heating rate of 0.5℃ / min and the 5-minute hold-attenuation period after reaching each temperature point ensure a uniform temperature field within the sample, eliminating the influence of temperature gradients on S. 21 Interference in the measured values ​​ensures that the changes in the measured attenuation values ​​truly reflect the temperature sensitivity of the material's dielectric properties, rather than measurement deviations caused by uneven sample temperature.

[0050] In some embodiments, the method further includes a sample preparation step prior to steps S1 and S2:

[0051] The propellant material is loaded into a square material box. During loading, the material is allowed to fall naturally into the box and the surface is scraped flat to ensure consistent loading tightness.

[0052] In some embodiments, the material box has dimensions of 300mm × 120mm × 120mm, and the propellant charge density is 1.3–1.4 g / cm³. 3 .

[0053] Packing density: 1.3–1.4 g / cm³ 3 Due to limitations, combined with the material box size and the operational procedures of natural material drop and surface leveling, the following measures are taken: First, ensure the repeatability of the microwave penetration path length and the sample's volumetric microwave absorption in each measurement. Excessive packing density will cause excessive microwave signal attenuation or even prevent penetration, while insufficient density will result in a short effective absorption path and insignificant signal changes. The packing density should be 1.3–1.4 g / cm³. 3 The range has been experimentally verified to achieve a moderate signal attenuation; secondly, it achieves the consistency of sample state without pressing or damaging the original state of the material, maintaining the advantages of non-destructive testing, while eliminating the influence of non-plasticizing factors such as the difference in packing tightness on the microwave attenuation value.

[0054] In some embodiments, the microwave detection system includes a vector network analyzer and a pair of metasurface lens antennas serving as transmitting and receiving antennas, respectively. The frequency range of the microwave signal is 23.5 GHz to 24.5 GHz, and the sample is placed between the transmitting and receiving antennas at equal distances from the antennas.

[0055] The vector network analyzer can simultaneously provide S 21 The amplitude (attenuation value) and phase information are measured, with the amplitude parameter serving as the core quantitative indicator in this scheme. The metasurface lens antenna exhibits high gain and beam-focusing characteristics in the 24GHz band, efficiently converging microwave energy through the sample and reducing the impact of edge effects and scattering losses on measurement accuracy. The selection of the 23.5GHz–24.5GHz band strikes a balance between spatial resolution (shorter wavelengths in the high-frequency band are more sensitive to changes in the sample's internal structure) and penetration depth (too high a frequency would cause microwaves to attenuate too quickly in energetic materials, preventing penetration of a 300mm thick material box). In this band, S... 21 It is most sensitive to changes in the degree of plasticization. The constraint of placing the sample in the exact center of the two antennas at equal distances ensures that the microwave propagation path and spatial irradiation conditions are consistent for each measurement, avoiding systematic errors introduced by fluctuations in the antenna-sample distance.

[0056] In some implementations, before performing microwave detection at multiple different temperature points in steps S1 and S2, the material box containing the sample is placed in a constant temperature chamber at 25°C for 2 hours to ensure that the sample temperature is uniform.

[0057] Before starting the gradient temperature rise test, the samples were equilibrated at 25°C for 2 hours to eliminate the influence of residual process heat history and ambient temperature differences on the initial test state, ensuring the starting point of the test for all samples (reference S at 25°C). 21 (Values) have the same temperature state.

[0058] In some implementations, the |S 21 The magnitude of change with increasing temperature satisfies the following relationship: Magnitude of change = |S| 21 (50℃)|−|S 21 (25℃)|, where |S 21 (T)| represents the temperature T at which S 21 The absolute value of the decibel value.

[0059] This application uses the range of change rather than a single temperature point (S). 21 The absolute value, used as an evaluation index, is the core innovation of this scheme; the S value at a single temperature point... 21 The absolute value is significantly affected by various non-plasticizing factors such as packing density, material moisture content, and ambient humidity. The range of change reflects the sensitivity of the material's dielectric properties to temperature. This sensitivity is determined by the binding state of the plasticizer and nitrocellulose molecular chains and is directly related to the degree of plasticization. Furthermore, the self-comparison of the same sample at different temperatures effectively offsets the influence of common factors such as packing density, making the evaluation results more specific and reliable.

[0060] In some embodiments, the propellant material is a single-base propellant kneaded and plasticized material.

[0061] Single-base propellants use nitrocellulose as the main energetic binder. Their plasticization process involves the solubilizing effect of plasticizers / solvents on NC molecular chains. The changes in the mobility of molecular chain segments during this process have significant temperature-sensitive differences in dielectric properties. Therefore, this method is particularly suitable for evaluating the degree of plasticization of single-base propellants.

[0062] Therefore, the method for evaluating the plasticity of propellant materials based on microwave detection provided in this application has the following advantages:

[0063] (1) Non-contact non-destructive testing. The microwave antenna does not directly contact the sample during the testing process, eliminating the need for pretreatment operations such as pressing the propellant into strips or cutting samples. This completely preserves the original state of the sample and avoids measurement errors and material losses introduced by sample processing in traditional methods. The highest temperature during the entire testing process does not exceed 50℃, which is far below the burst temperature of nitrocellulose (185℃). The testing process is safe and reliable, and there is no risk of thermal decomposition or combustion of energetic materials.

[0064] (2) High detection efficiency and simple operation. The traditional capillary rheometer method requires pressing the sample into standard strips and cutting them one by one to the specified size. A single test takes several hours and is cumbersome. This method only requires loading the material into the material box, equilibrating at a constant temperature, and then performing gradient temperature testing. The whole process takes about 2.5 hours. The sample only needs to be loaded and does not require complicated pretreatment, making it easy to promote and implement on the production site.

[0065] (3) Quantitative evaluation with strong objectivity. Traditional visual or empirical methods rely on the subjective judgment of operators to evaluate the degree of plasticization, resulting in poor consistency of evaluation results between different personnel and different batches. This method uses a vector network analyzer to accurately measure the microwave attenuation value S. 21 And based on the |S| of the sample to be tested and the standard sample 21 The results of the comparison of the change range are quantitatively judged, and the judgment thresholds are clearly defined (90%, 60%). The evaluation results are objective, quantifiable, and reproducible, eliminating the interference of human factors on the judgment conclusion.

[0066] (4) Applicable to online monitoring at the production site. The microwave detection system mainly consists of a vector network analyzer and a metasurface lens antenna. The equipment is small in size and compact in structure, and can be installed near the kneader or stretching process. During the kneading and plasticizing process, operators can take samples at regular intervals and quickly complete the detection, promptly detect abnormal states such as insufficient plasticization or over-plasticization, guide the accurate judgment of the kneading endpoint and the real-time adjustment of process parameters, avoid the scrapping of the entire batch of materials due to poor plasticization, and help to realize intelligent quality control of the propellant production process.

[0067] (5) Strong anti-interference ability and high measurement accuracy. Traditional single-point microwave attenuation value measurement is easily affected by non-plasticizing factors such as sample packing density, moisture content, and ambient temperature and humidity, leading to inaccurate measurement results. This method uses the change range of microwave attenuation value with temperature increase as the evaluation index. Since this change range is obtained by self-comparison of the same sample at different temperatures, common factors such as packing density and material uniformity are effectively offset in the calculation process, and the specificity of the measurement is significantly improved. The relative standard deviation of multiple independent repeated tests is less than 3.5%, which reflects good repeatability and measurement accuracy.

[0068] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards / industry standards / the disclosure herein; if there are no corresponding national standards / industry standards / the disclosure herein, they are performed according to generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer.

[0069] Example 1

[0070] (1) Experimental materials and sample preparation

[0071] On a single-base propellant kneading and plasticizing production line, the same batch of nitrocellulose (nitrogen content 12.6%, degree of polymerization approximately 1200) based propellant formulation was used. One sample of material, approximately 500 grams each, was taken from the kneader at plasticizing times of 0 minutes, 15 minutes, 30 minutes, 45 minutes, and 60 minutes. Each sample was placed into a dedicated square material box (made of polytetrafluoroethylene, dimensions 300mm × 120mm × 120mm). During filling, the material was allowed to fall naturally into the box, and a scraper was used to level the surface along the upper edge of the box, controlling the filling density to 1.35 g / cm³. 3 This ensures that the tightness of the filling is consistent each time.

[0072] (2) Confirmation of process endpoint

[0073] Before establishing microwave testing criteria, the endpoint of the plasticizing process on the production line was first confirmed using a torque rheometer method. The specific method was as follows: approximately 60 grams of material was sampled every 5 minutes from the kneader and added to a torque rheometer (rotor speed 50 r / min, temperature 70℃) for kneading testing, and the torque-time curve was recorded. The endpoint of plasticizing was determined when the curve reached a stable horizontal state (torque fluctuation less than 3% of the initial peak torque, and lasting for more than 10 minutes). Testing showed that the torque-time curve of this batch of material tended to be stable horizontally after 60 minutes of kneading, indicating that the material was fully plasticized, the plasticizer and nitrocellulose molecular chains were well bonded, the material components were uniformly mixed, and the performance was stable, meeting the process requirements for entering the next compression molding process. Therefore, the material plasticized for 60 minutes was identified as a standard sample with a known fully plasticized state, and this was used as the calibration benchmark for the microwave testing method.

[0074] (3) Instruments and equipment

[0075] The microwave detection system mainly consists of the following equipment:

[0076] The vector network analyzer has a frequency scanning range of 23.5 GHz to 24.5 GHz, 201 scan points, and an intermediate frequency bandwidth of 1 kHz.

[0077] A pair of metasurface lens antennas, operating at a frequency of 24 GHz and with a gain of 18 dBi, are used as a transmitting antenna and a receiving antenna, respectively. The antenna aperture is 100 mm × 100 mm, and they are fixed on both sides of the testing platform with a spacing of 400 mm between them.

[0078] Thermostatic chamber, temperature control accuracy ±0.5℃, temperature uniformity ±1℃;

[0079] The material box positioning fixture ensures that the sample material box is placed exactly in the middle of the transmitting antenna and the receiving antenna, and that the distance between the material box and the two antennas is equal (50mm for both).

[0080] (4) Detection steps

[0081] Five sample boxes were placed simultaneously in a 25°C constant temperature chamber for 2 hours to ensure uniform sample temperature and eliminate the influence of ambient temperature differences on the test results.

[0082] After temperature equilibration, the sample boxes are sequentially removed and placed into the positioning fixture of the microwave detection system. The vector network analyzer is started, and the transmitting antenna emits microwave signals of 23.5 GHz to 24.5 GHz towards the sample, while the receiving antenna captures the microwave signals that have penetrated the sample. The system records the S values ​​at each frequency point. 21 Parameters, extract S at the center frequency of 24.0 GHz 21 The value (unit: dB) is used as the baseline data at 25℃. Each sample is measured three times consecutively, and the average value is taken.

[0083] The sample container was returned to the incubator, and the temperature was set to 30℃. The temperature was slowly increased at a rate of 0.5℃ per minute, and maintained at 30℃ for 5 minutes to ensure uniform internal temperature. The sample was then removed for microwave detection, and the S values ​​at 30℃ were recorded. 21 Value. Following the above procedure, set the temperature of the constant temperature chamber to 35℃, 40℃, 45℃, and 50℃ in sequence. After maintaining the temperature at each point for 5 minutes, perform microwave detection and record the detection data at each temperature point.

[0084] S of five samples at various temperature points 21 The test results are shown in Table 1 (the average of three measurements is taken).

[0085] Table 1. S values ​​of samples with different plasticizing times at various temperatures. 21 parameter

[0086] Plasticization time 25℃ (dB) 30℃ (dB) 35℃ (dB) 40℃ (dB) 45℃ (dB) 50℃ (dB) <![CDATA[|S 21 |Amplitude of change (dB)]]> 0min -2.02 -2.58 -3.12 -3.58 -4.02 -4.48 2.46 15min -2.05 -2.92 -3.62 -4.28 -4.88 -5.52 3.47 30min -2.08 -3.48 -4.78 -5.98 -7.08 -8.22 6.14 45min -2.12 -4.05 -5.85 -7.32 -8.65 -10.42 8.30 60min -2.15 -4.35 -6.62 -8.25 -9.92 -12.18 10.03

[0087] Note: The 60-minute sample is a fully plasticized standard sample confirmed by the torque rheometer method. The 10.03 dB reference value in this example is only applicable to this batch of materials. When changing the raw material batch or adjusting the formula, the plasticizing process endpoint must be reconfirmed and its |S| value measured using the above method. 21 |The range of change serves as the baseline value for the new batch;|S 21 |Amplitude of change = |S 21 (50℃)| −|S 21 (25℃)|, characterizing S 21 The degree to which it becomes more negative as the temperature rises.

[0088] (5) Results analysis and determination of plasticization degree

[0089] Based on a standard sample plasticized for 60 minutes as confirmed by torque rheometer method, its |S 21 The temperature variation from 25℃ to 50℃ was 10.03dB, defined as the baseline value (100%) for complete plasticization. The judgment results for each sample are as follows:

[0090] Samples plasticized for 0 minutes: S 21 From -2.02dB to -4.48dB, |S 21 The change was 2.46 dB, reaching 24.5% of the baseline value (<60%), which was judged as insufficient plasticization. At this time, the solvent / plasticizer distribution in the material was extremely uneven, the movement of nitrocellulose molecular chain segments was severely restricted, and the effect of temperature increase on dielectric loss was weak. 21 The temperature only slightly increases, so the process parameters need to be adjusted.

[0091] Samples plasticized for 15 minutes: S 21 From -2.05dB to -5.52dB, |S 21 The change was 3.47 dB, reaching 34.6% of the baseline value (<60%), which was judged as insufficient plasticization. Although the degree of plasticization of the material has improved, the binding between the plasticizer molecules and the nitrocellulose molecular chains is still insufficient, and further kneading is required.

[0092] Samples plasticized for 30 minutes: S 21 The change from -2.08 dB to -8.22 dB, |S 21 The change was 6.14 dB, reaching 61.2% of the baseline value (between 60% and 90%), indicating partial plasticization. The material has acquired a certain degree of plasticity, but has not yet met the process requirements and needs to be kneaded further.

[0093] Samples plasticized for 45 minutes: S 21 From -2.12dB to -10.42dB, |S 21The change was 8.30 dB, reaching 82.7% of the benchmark value (between 60% and 90%), indicating partial plasticization. The material is nearly fully plasticized, but not yet fully compliant; it is recommended to appropriately extend the kneading time.

[0094] Samples plasticized for 60 minutes (standard samples): S 21 From -2.15dB to -12.18dB, |S 21 The change range was 10.03 dB, reaching 100% of the baseline value (≥90%), which was considered sufficient plasticization. At this point, the plasticizer molecules and nitrocellulose molecular chains were well bonded, the molecular mobility was high, and the dielectric loss increased significantly with increasing temperature. 21 As the temperature rises, the color becomes significantly negative, indicating that the process can proceed to the next pressing and stretching process.

[0095] (6) Repeatability verification

[0096] To verify the repeatability and objectivity of this method, repeatability tests were performed on the five samples with different plasticizing times. Three different operators (A, B, and C) independently completed all tests over three days. For each sample, measurements were taken three times consecutively at each temperature point, and the average value was calculated. The |S| value for each sample was then calculated. 21 |Relative standard deviation (RSD) of the variation range. The test results are shown in Table 2.

[0097] Table 2 |S| for each sample by different operators 21 |Change Amplitude Detection Results

[0098] Sample (plasticization time) Operator A (dB) Operator B (dB) Operator C (dB) RSD 0 min 2.43 2.49 2.46 1.20% 15 min 3.42 3.52 3.47 1.40% 30 min 6.21 6.02 6.19 1.60% 45 min 8.48 8.15 8.27 2.00% 60 min 9.91 10.25 9.93 1.80%

[0099] Table 2 shows that the test results of the three operators on the same batch of five samples exhibited good consistency. (Each sample |S) 21 The relative standard deviations (RSDs) of the variation ranges were 1.2% for the 0-minute sample, 1.4% for the 15-minute sample, 1.6% for the 30-minute sample, 2.0% for the 45-minute sample, and 1.8% for the 60-minute sample, all not exceeding 3.5%. These results demonstrate that the proposed method exhibits good operational robustness in sample loading, temperature control, microwave detection, and data reading. The measurement results do not show significant deviations due to differences in operator skill, verifying the method's good repeatability and objectivity, and meeting the accuracy requirements for on-site quality testing in propellant production.

[0100] This embodiment demonstrates that by pre-determining the endpoint of the plasticizing process using a torque rheometer method, and using the material at that endpoint as a calibration benchmark, a microwave S-type calibration system can be established. 21The criterion for determining parameter changes with temperature enables rapid, quantitative, and non-destructive evaluation of the plasticization degree of propellant materials. This method features a rigorous calibration process, yields results consistent with traditional rheological methods, and requires only approximately 2.5 hours, making it suitable for rapid sampling and online monitoring in production environments.

[0101] Example 2

[0102] (1) Sample source

[0103] In the continuous production process of a single-base propellant kneading and plasticizing production line, the kneader operates according to predetermined process parameters (kneading temperature 70℃, rotor speed 50 r / min). When kneading reaches an unknown time point, the on-site operator randomly takes a sample from the kneader, with a sample weight of approximately 500 grams. The actual kneading time of this sample is unknown to the testing personnel.

[0104] (2) Sample preparation

[0105] Place the collected sample into a polytetrafluoroethylene (PTFE) material box (300mm × 120mm × 120mm), allowing the material to fall naturally into the box. Use a scraper to smooth the surface along the upper edge of the material box, controlling the packing density to 1.35 g / cm³. 3 .

[0106] (3) Isothermal equilibrium

[0107] Place the sample-containing container in a 25°C constant temperature chamber and leave it for 2 hours to ensure uniform sample temperature.

[0108] (4) Microwave detection

[0109] After being kept at constant temperature and balanced, the sample material box is placed in the positioning fixture of the microwave detection system. The system is equipped with a vector network analyzer and a pair of metasurface lens antennas. The microwave frequency range is 23.5 GHz to 24.5 GHz. The sample is placed in the middle of the transmitting antenna and the receiving antenna and is equidistant from the two antennas.

[0110] First, the microwave attenuation value S of the sample was measured and recorded at 25℃. 21 Three consecutive measurements were taken, and the average value was recorded. The constant temperature chamber was then sequentially heated to 30℃, 35℃, 40℃, 45℃, and 50℃ at a rate of 0.5℃ per minute. After reaching each temperature point, the temperature was maintained for 5 minutes. Microwave detection was performed at each temperature point, and the S values ​​were recorded. 21 value.

[0111] (5) Test data

[0112] S of the unknown sample 21 The test results at each temperature point are shown in Table 1.

[0113] Table 3. S values ​​of unknown samples at various temperature points 21 Test data

[0114] Temperature point <![CDATA[S 21 (dB)]]> 25℃ -2.07 30℃ -3.52 35℃ -5.08 40℃ -6.55 45℃ -7.92 50℃ -9.48

[0115] The value of |S| for this sample was calculated from the data in Table 3. 21 The temperature change from 25℃ to 50℃ is: Change range = |S 21 (50℃)|−|S 21 (25℃)|=9.48−2.07=7.41dB.

[0116] (6) Determination of plasticization degree

[0117] Using the fully plasticized standard sample (plasticized for 60 minutes) confirmed by torque rheometer method in Example 1, |S 21 Using a variation range of 10.03 dB as a baseline, calculate the relative degree of plasticization of the unknown sample:

[0118] Relative plasticization degree = 7.41 / 10.03 × 100% = 73.9%.

[0119] According to the judgment criteria, the relative plasticization degree of this sample is 73.9%, which is within the range of 60% to 90%, and is judged to be partially plasticized.

[0120] (7) Judgment conclusions and process guidance

[0121] The sample was determined to be partially plasticized, indicating that although the material has a certain degree of plasticity and the plasticizer molecules have begun to combine with the nitrocellulose molecular chains, it has not yet reached a fully plasticized state, and the mobility of the molecular chain segments is still lower than the process requirements. Based on this, the following process guidance is given: The material in this batch needs to be kneaded further. It is recommended to extend the kneading time by 15-20 minutes and then take another sample for testing until the relative plasticization degree reaches 90% or more before proceeding to the next compression molding process.

[0122] To further verify the accuracy of the conclusion in this embodiment, after the kneading continued and the operator finally determined the discharge based on production experience, the production record of the material in the pot was reviewed. It was confirmed that the actual kneading time was 48 minutes, which is consistent with the test results of the 45-minute sample (partially plasticized, relative plasticization degree 82.7%) and the 60-minute sample (fully plasticized) in Example 1. This verifies the effectiveness of this method for testing samples with arbitrary unknown time.

[0123] This embodiment demonstrates that the method of this application can calculate |S| by performing gradient heating microwave detection on the sample when the plasticization time of the sample is completely unknown. 21The variation range is compared with a pre-established benchmark value, and a quantitative judgment on the degree of plasticization and clear process guidance suggestions are given within about 2.5 hours. This enables a rapid, objective, and non-contact evaluation of the plasticity of propellant materials, which can effectively serve the judgment of kneading endpoint and quality control on the production site.

[0124] Example 3

[0125] (1) Experimental background

[0126] A certain single-base propellant production line is producing normally according to a conventional batch (NC nitrogen content 12.60%, degree of polymerization 1200). This batch has been tested using a microwave detection standard established according to Example 1 (|S 21 The baseline value for the variation range is 10.03 dB, corresponding to the plasticizing endpoint at 60 minutes. The operator, following the production procedure, performs process monitoring sampling on the Xth batch of materials being kneaded.

[0127] (2) Process monitoring, sampling and testing

[0128] The planned total kneading time for the materials in this batch is 60 minutes. After 30 minutes of kneading, the operator removes approximately 500 grams of material from the kneader, places it in a material box, and immediately sends it to the microwave detection system to initiate a 25°C constant temperature equilibration (2 hours) and subsequent gradient temperature rise detection program. The entire detection cycle takes approximately 2.5 hours.

[0129] During this period, the kneader continued to operate. When the microwave detection results were output (approximately 2.5 hours after the sampling time), the actual cumulative kneading time of the material in the kneader was approximately 57 minutes, which was not yet the planned discharge time, leaving a window for process adjustment.

[0130] (3) Monitoring results and anomaly determination

[0131] The microwave detection results of the 30-minute sample are as follows: S 21 (25℃) = −2.35dB, S 21 (50℃) = −6.20dB, |S 21 The change range is 3.85 dB. Comparing this result with the baseline value (10.03 dB): 3.85 / 10.03 = 38.4% (<60%), it is determined to be insufficient plasticization.

[0132] As a reference, the normal material plasticized for 30 minutes in Example 1, its |S 21 The change was 6.14 dB (61.2% of the baseline value, indicating partial plasticization). The |S of the monitored sample... 21 The change (3.85dB) was far below the normal level, indicating that there was a serious abnormality in the plasticization process of the material in the pot.

[0133] (4) Process correction and effect verification

[0134] Based on the abnormal warning from the microwave monitoring system, the operator immediately checked the process parameters for that batch and found that the plasticizer metering pump was leaking. The actual amount of plasticizer added was only 82% of the formula amount, resulting in a serious deficiency in the melt-plasticization. The operator took the following corrective measures: (1) added the missing plasticizer to the formula amount; (2) increased the kneading temperature from 70°C to 75°C to accelerate the penetration of the plasticizer; (3) extended the kneading time from the originally planned 60 minutes to 75 minutes.

[0135] Samples were taken again for microwave testing after 75 minutes of kneading, and the results are as follows:

[0136] S 21 (25℃) = −2.18dB, S 21 (50℃) = −11.74dB, |S 21 The change range is 9.56 dB. 9.56 / 10.03 = 95.3% (≥90%), which is considered sufficient plasticization. At this point, a discharge command is issued.

[0137] (5) Deduction of the consequences of not correcting the deviation

[0138] To verify the value of this monitoring, a simulation was performed on the material in the pot at the originally planned 60-minute mark (without corrective action). Based on the 30-minute timeframe |S 21 Based on a deterioration trend where the change is only 62.7% of the normal value (3.85 / 6.14), and assuming a discharge time of 60 minutes, its |S 21 The change is expected to be only around 6.3 dB (about 63% of the baseline value), indicating a partially plasticized state. If this material enters the compression molding process, its insufficient plasticity will lead to defects such as surface cracks and uneven internal density in the drug strips, and the entire batch of material is expected to be scrapped or downgraded.

[0139] This embodiment demonstrates that during normal production, operators take samples and perform microwave detection at regular intervals (e.g., every 30 minutes). Although the detection cycle for a single sample is approximately 2.5 hours, the detection results can still be fed back before material discharge thanks to the continuity of the production process. When microwave monitoring detects |S 21 When the variation range is abnormally low, it can promptly expose process abnormalities such as plasticizer feeding deviation, and guide operators to adjust the kneading temperature, add materials, or extend the kneading time, thereby effectively avoiding the scrapping of the entire batch of materials due to insufficient plasticization, and realizing quantitative monitoring and closed-loop quality control of the propellant plasticization process.

[0140] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for evaluating the plasticity of propellant materials based on microwave detection, characterized in that, The method includes the following steps: S1. Place a standard propellant sample known to be in a fully plasticized state into a microwave detection system. At multiple different temperature points, emit microwave signals to the standard sample and receive the microwave signals after they penetrate the standard sample. Obtain the microwave attenuation value S of the standard sample at each temperature point. 21 Based on the microwave attenuation value S at each temperature point 21 The |S| of the standard sample was calculated. 21 The magnitude of the change with increasing temperature is used as the benchmark value for evaluating the degree of plasticization. S2. Place the propellant sample to be tested in the same microwave detection system. At multiple different temperature points (similar to step one), transmit microwave signals to the sample and receive the microwave signals after they penetrate the sample. Obtain the microwave attenuation value S of the sample at each temperature point. 21 Based on the microwave attenuation value S at each temperature point 21 The |S| of the sample to be tested was calculated. 21 The magnitude of change with increasing temperature; S3, the |S| of the sample to be tested 21 |Variation range and standard sample|S 21 Compare the magnitude of change: When the |S of the sample to be tested 21 |The change range reaches the standard sample|S 21 When the change range exceeds 90%, the sample is considered to be sufficiently plasticized. When the |S of the sample to be tested 21 |The variation range is within the standard sample|S 21 When the change range is between 60% and 90%, the sample is considered partially plasticized. When the |S of the sample to be tested 21 |The change was less than that of the standard sample|S 21 When the change range is 60%, the sample is deemed to be under-plasticized.

2. The method according to claim 1, characterized in that, In step S1, the standard propellant sample known to be in a fully plasticized state is obtained by: confirming the plasticization process endpoint of the propellant using a torque rheometer, and using the material that reaches the process endpoint as the standard sample.

3. The method according to claim 1, characterized in that, The various temperature points include 25℃, 30℃, 35℃, 40℃, 45℃ and 50℃.

4. The method according to claim 3, characterized in that, Starting at 25°C, the temperature is slowly increased to each temperature point at a rate of 0.5°C per minute. After reaching each temperature point, the temperature is maintained for at least 5 minutes to ensure uniform internal temperature of the sample before microwave detection.

5. The method according to claim 1, characterized in that, Prior to steps S1 and S2, the method further includes a sample preparation step: The propellant material is loaded into a square material box. During loading, the material is allowed to fall naturally into the box and the surface is scraped flat to ensure consistent loading tightness.

6. The method according to claim 5, characterized in that, The material box measures 300mm × 120mm × 120mm, and the propellant charge density is 1.3–1.4 g / cm³. 3 .

7. The method according to claim 1, characterized in that, The microwave detection system includes a vector network analyzer and a pair of metasurface lens antennas serving as transmitting and receiving antennas, respectively. The frequency range of the microwave signal is 23.5 GHz to 24.5 GHz. The sample is placed between the transmitting and receiving antennas and is equidistant from the antennas.

8. The method according to claim 1, characterized in that, In steps S1 and S2, before performing microwave detection at multiple different temperature points, the material box containing the sample is placed in a constant temperature chamber at 25°C for 2 hours to ensure that the sample temperature is uniform.

9. The method according to claim 1, characterized in that, The |S 21 The magnitude of change with increasing temperature satisfies the following relationship: Magnitude of change = |S| 21 (50℃)|−|S 21 (25℃)|, where |S 21 (T)| represents the temperature T at which S 21 The absolute value of the decibel value.

10. The method according to claim 1, characterized in that, The propellant material is a single-base propellant kneaded and plasticized material.

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