In-situ infrared test method for monitoring curing reaction process of pbt-tdi-al composite system

Abstract

This invention relates to an in-situ infrared testing method for monitoring the curing reaction process of a PBT-TDI-Al composite system, comprising the following steps: S1: Establishing the relative peak intensity I of NCO 2270 / I 2870 Linear regression model curve with NCO concentration; S2: Obtain infrared spectral data of the PBT-TDI-Al composite system during the curing reaction process, and calculate the real-time intensity I of the relative peak of NCO. 2270 / I 2870 S3: The real-time intensity I of the relative peak of NCO 2270 / I 2870 By mapping the linear regression model curve, real-time quantitative data of NCO are obtained, thereby achieving in-situ monitoring of the curing reaction process of the PBT-TDI-Al composite system. Compared with the prior art, this invention establishes an in-situ infrared testing method suitable for real-time monitoring of the curing reaction process of the PBT-TDI-Al composite system, and obtains the relative peak intensity I of NCO. 2270 / I 2870 The entire testing method, from the creation of a linear regression model curve of NCO concentration to real-time quantitative analysis of NCO concentration during the reaction process.

Description

Technical Field

[0001] This invention relates to an in-situ infrared testing method, and more particularly to an in-situ infrared testing method for monitoring the curing reaction process of a PBT-TDI-Al composite system. Background Technology

[0002] Azide polyether composite solid propellants possess characteristics such as high energy, high insensitivity, and low characteristic signals, making them a crucial direction for the development of solid propellant technology. Among them, 3,3-bis(azidomethyl)oxybutylcyclohexane co-polyether with tetrahydrofuran, abbreviated as PBT, is a commonly used azide polyether binder, while toluene diisocyanate, abbreviated as TDI, is a curing agent. The curing reaction occurs through the terminal hydroxyl groups on the PBT binder and the isocyanate NCO groups in the TDI curing agent, generating an energetic thermoplastic polyurethane elastomer that encapsulates high-energy solid fillers such as ammonium perchlorate and aluminum powder (Al), thus forming a composite solid propellant. However, the physicochemical properties of PBT change significantly before and after the curing reaction, and in-situ testing of the curing reaction and interfacial effects of the PBT-TDI-Al composite system has always been a challenge in reaction kinetics research.

[0003] The relationship between the signal intensity and the concentration of the analyte in Fourier transform infrared (FTIR) spectra follows Beer-Lambert's law, meaning the characteristic signal intensity is directly proportional to the concentration of characteristic functional groups. FTIR spectroscopy allows for real-time, dynamic tracking of the reaction process. For the PBT-TDI-Al composite system, only the hydroxyl groups in PBT and the NCO groups in TDI participate in the curing reaction. The NCO peak in the FTIR spectrum is located at 2270 cm⁻¹. -1 The carbon-carbon double bonds in PBT do not change before and after the reaction, and their peak is located at 2870 cm⁻¹. -1 The relative peak intensity of NCO is obtained by comparing the peak intensity of NCO with that of the carbon-carbon double bond, which is used to characterize the change in NCO concentration during the reaction. In existing technologies, there are no reports on in-situ monitoring of the PBT-TDI-Al curing reaction process using in-situ infrared spectroscopy. Existing techniques mainly involve coating a prepared reaction solution onto one side of a potassium bromide window and placing it in an in-situ reaction cell. Infrared laser light is then transmitted through the potassium bromide window coated with the reaction solution, and the changes in the intensity of the characteristic infrared peaks transmitted through the window are collected to calculate the changes in the concentration of characteristic reaction groups, thus achieving in-situ monitoring of the chemical reaction. This method is suitable for general reaction systems, but when applied to the PBT-TDI-Al composite system, it suffers from low signal intensity and large fluctuations. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology by providing an in-situ infrared testing method for monitoring the curing reaction process of PBT-TDI-Al composite systems. This invention establishes an in-situ infrared testing method suitable for real-time monitoring of the curing reaction process of PBT-TDI-Al composite systems, and to obtain the relative peak intensity I of NCO. 2270 / I 2870 The entire testing method, from the creation of a linear regression model curve of NCO concentration to real-time quantitative analysis of NCO concentration during the reaction process.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] The purpose of this invention is to provide an in-situ infrared testing method for monitoring the curing reaction process of a PBT-TDI-Al composite system, comprising the following steps:

[0007] S1: Establish the relative peak intensity of NCO I 2270 / I 2870 Linear regression model curve with NCO concentration;

[0008] S2: Obtain infrared spectral data during the curing reaction of the PBT-TDI-Al composite system, and calculate the real-time intensity I of the NCO relative peak. 2270 / I 2870 ;

[0009] S3: Real-time intensity I of the NCO relative peak 2270 / I 2870 By mapping the linear regression model curve, real-time quantitative data of NCO can be obtained, thereby enabling in-situ monitoring of the curing reaction process of the PBT-TDI-Al composite system.

[0010] Furthermore, in S1, infrared spectral datasets of PBT-TDI-Al composite systems with different mixing ratios are obtained, thereby establishing the NCO relative peak intensity I. 2270 / I 2870 Linear regression model curve with NCO concentration.

[0011] Furthermore, in S1, the infrared spectral dataset of the PBT-TDI-Al composite system includes PBT-TDI-Al composite systems with different mixing ratios, where the wavenumber is at 2270 cm⁻¹. -1 The data includes the NCO signal peak of the TDI characteristic group at the location, as well as the carbon-carbon double bond signal peak data that do not participate in the curing reaction in the composite system.

[0012] Furthermore, in S1, the method for obtaining the linear regression model curve includes:

[0013] S1-1: Mix PBT, TDI, and Al evenly according to a preset ratio, and calculate the NCO concentration in the mixing system with different ratios;

[0014] S1-2: The relative peak intensity of NCO was calculated by using an infrared spectrometer to detect different proportions of the mixed system;

[0015] S1-3: The NCO concentration of the different mixing systems in S1-1 is compared with the relative peak intensity of NCO measured in the corresponding system in S1-2. 2270 / I 2870 Correlation, to produce NCO relative peak intensity I 2270 / I 2870 Linear regression model curve with NCO concentration.

[0016] Furthermore, the infrared spectral data in S1 and S2 are obtained by an in-situ infrared testing device, which includes an infrared spectrometer, an in-situ reaction cell matched with the infrared spectrometer, and a computer terminal.

[0017] Furthermore, the in-situ infrared testing device also includes an external component, which includes a water bath machine used for heating the in-situ reaction tank.

[0018] Furthermore, the external component also includes a protective gas path that matches the in-situ reaction tank.

[0019] Furthermore, the inlet of the protective gas path is filled with 99.999% high-purity nitrogen. The airflow is controlled by a flow meter. After being dried by a dryer composed of multiple anhydrous silica gels, the gas bypasses the water bath heater for preheating to prevent the air temperature from being too different from the experimental temperature in the in-situ reaction tank and thus lowering the reaction temperature. Then it enters the in-situ reaction tank to carry away the harmful gases generated in the in-situ reaction tank. Finally, it flows out from the outlet of the in-situ reaction tank and enters the external waste gas treatment device.

[0020] Furthermore, the in-situ reaction tank includes an in-situ reaction tank body and a closed window disposed on the in-situ reaction tank body;

[0021] The closed window consists of two calcium fluoride windows and two semi-circular clamps. Window A has a protruding frustum, and window B has a recess on one side that matches the frustum, used to hold the reaction liquid.

[0022] Furthermore, during the reaction, a measured amount of reaction liquid is dripped into the recess of window B, and then the frustum side of window A is pushed into window B to seal the reaction liquid between the two windows. Then, two semi-circular clamps are fitted onto the outer periphery of the assembled windows to limit the opening and closing of the assembled windows and prevent the reaction liquid from expanding and overflowing from the gap between window A and window B during the heating process.

[0023] Compared with the prior art, the present invention has the following technical advantages:

[0024] 1) This invention proposes an in-situ infrared testing method suitable for real-time monitoring of the curing reaction process of PBT-TDI-Al composite systems, and establishes a method for measuring the relative peak intensity of NCO. 2270 / I 2870 The entire testing method from the creation of a linear regression model curve of NCO concentration to real-time quantitative analysis of NCO concentration during the reaction process;

[0025] 2) This invention establishes an in-situ infrared testing device suitable for the curing reaction process of PBT-TDI-Al composite system. An external gas path protection component is added to address the characteristics of TDI being toxic, volatile, and easily reacting with water.

[0026] 3) Based on the characteristics of the PBT-TDI-Al composite system, this invention improves the window used in existing infrared testing technology and proposes a novel closed window design, which can solve most of the problems currently faced in testing and minimize the impact of various adverse factors on experimental results. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the in-situ infrared spectrum of the curing reaction process in this technical solution;

[0028] Figure 2 This is the linear regression model curve in this technical solution;

[0029] Figure 3 This is a block diagram of the in-situ infrared testing device in this technical solution;

[0030] Figure 4 This is an exploded view of the closed window structure in this technical solution. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Component models, material names, connection structures, control methods, algorithms, and other features not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0032] The applicant analyzed existing technologies during the conceptualization process: The existing method of coating the reaction solution onto a potassium bromide window, when applied to the PBT-TDI-Al system, affects the test results due to the surface tension of the reaction solution. Specifically, the reaction solution, which was originally evenly coated on the window, rapidly agglomerates into multiple small droplets under heating conditions. This reduces the area of ​​the reaction solution that transmits the infrared laser while increasing its thickness. Consequently, the intensity of the internal standard peak, which does not participate in the reaction and whose concentration remains constant, and which originally normalized the reaction peak signal and whose signal intensity should remain unchanged, changes, such as at 2870 cm⁻¹.-1 The carbon-carbon double bond signal intensity decreases at 2100 cm⁻¹, while at 2100 cm⁻¹... -1 The signal intensity of the azide group at the point increases, and two significantly different experimental results appear when normalizing these two different internal standard peaks. Furthermore, because TDI is volatile and prone to side reactions with water in the air, some TDI in the reaction solution will evaporate from the window or react with water molecules under heating conditions, thus affecting the test results. Some methods involve covering the single-window coating with a layer of reaction solution to improve the problem of reaction solution aggregation and reduce the impact of TDI evaporation and water reaction. However, this method is still not perfect and introduces new problems. Adding a layer of window reduces the infrared signal, thus requiring an increase in the amount of reaction solution coated on the window. Excessive reaction solution will expand due to heat, covering or even squeezing out the window, causing the opposite problem as with the single-window method: the reaction solution area increases while the thickness decreases, affecting the signal intensity of the internal standard peak, and may even flow out of the window, contaminating the in-situ experimental platform. Moreover, the outward flow of the reaction solution due to expansion and downward flow due to gravity can cause Al particles to move, even leaving the infrared laser beam scanning range, thus affecting the test results.

[0033] This technical solution addresses the factors that easily affect test results when existing in-situ infrared testing methods are applied to PBT-TDI-Al systems, such as the surface area, thickness, and fluidity of the reaction liquid. It proposes an in-situ testing method and window design suitable for PBT-TDI-Al composite systems, which can eliminate the influence of the above factors on experimental results to the greatest extent.

[0034] Example 1

[0035] The technical solution of this invention mainly includes three steps. The first step is to obtain the infrared spectrum of the PBT-TDI-Al composite system based on different mixing ratios. This spectrum contains wavenumbers at 2270 cm⁻¹. -1 The NCO signal peak of the TDI characteristic group at the location, and the carbon-carbon double bond signal peak in the composite system that does not participate in the curing reaction, are used to establish the relative peak intensity I of NCO. 2270 / I 2870 The second step involves obtaining the linear regression model curve of NCO concentration; and obtaining the infrared spectrum of the PBT-TDI-Al composite system during the curing reaction process, such as... Figure 1 As shown, the real-time intensity I of the relative peak of NCO was calculated. 2270 / I 2870 The third step involves applying the real-time relative peak intensity of NCO to the linear regression model curve to complete the real-time quantitative analysis of NCO, thereby achieving in-situ monitoring of the curing reaction process of the PBT-TDI-Al composite system.

[0036] Specifically, the steps for obtaining the linear regression model curve in step one are as follows: First, mix PBT / TDI / Al evenly according to a preset ratio and calculate the NCO concentration in the mixing system with different ratios; Second, use an infrared spectrometer to detect the mixing system with different ratios and calculate the relative peak intensity of NCO; Third, compare the NCO concentration of the mixing system with the relative peak intensity of NCO measured in the corresponding system in step two. 2270 / I 2870 Correlation, to produce NCO relative peak intensity I 2270 / I 2870 The linear regression model curve between NCO concentration and NCO concentration is shown below. Figure 2 .

[0037] This invention establishes an in-situ infrared testing device suitable for monitoring the reaction of this system. The structural diagram of this testing device is shown below. Figure 3 The system comprises an in-situ infrared testing system consisting of an infrared spectrometer, an in-situ reaction cell, and a computer processing unit (including software and hardware), as well as external accessory components consisting of a water bath heater and a protective gas path. The core functional area of ​​the in-situ infrared testing system consists of the infrared spectrometer, the in-situ reaction cell, and the computer. During testing, the laser emitter of the infrared spectrometer emits laser light, which passes through a calcium fluoride window located in the in-situ reaction cell. After being absorbed by the reaction liquid, the laser light is received by the receiver in the spectrometer, and then processed by the computer software (conventionally) into an infrared spectrum. The external components include a water bath heater and a protective gas path. The water bath heater is used to heat the in-situ reaction cell to achieve the required experimental temperature.

[0038] Because TDI volatilization generates toxic gases and readily reacts with water in the air, a protective gas path is added to the external part to eliminate the harm of TDI volatilization to experimental personnel and avoid TDI reacting with water and affecting the experiment. 99.999% high-purity nitrogen is introduced into the gas path inlet, and the airflow is controlled by a flow meter. After being dried by a dryer composed of multiple anhydrous silica gel filters, the gas bypasses the water bath heating device for preheating to prevent the air temperature from differing too much from the experimental temperature in the in-situ reaction tank, thus lowering the reaction temperature. The gas then enters the in-situ reaction tank and passes through a specially designed closed calcium fluoride window to remove any potentially harmful gases. Finally, the gas flows out from the outlet and into the waste gas treatment device.

[0039] Existing in-situ infrared testing devices rarely feature external gas paths. Because TDI is volatile, toxic, and readily reacts with water, the lack of a protective gas path could lead to the leakage of toxic gases and trigger side reactions. Therefore, this invention incorporates a high-purity dry nitrogen path to ensure the reactor remains dry while removing any potentially harmful gases.

[0040] This invention also proposes a closed window design, consisting of two calcium fluoride window panels and two semi-circular clamps, as shown in the structural diagram below. Figure 4 As shown, window A has a protruding frustum, and window B has a recess on one side to hold the reaction liquid. During the experiment, simply drop a measured amount of reaction liquid into window B, then push the frustum side of window A into window B to seal the reaction liquid between the two windows. Then, put on the two semi-circular clamps to prevent the reaction liquid from expanding and overflowing from the gap between A and B during heating.

[0041] Most existing technologies use only a single window, meaning the reaction solution is coated on only one side of a single window. Since TDI is volatile, toxic, and readily reacts with water, this design can lead to the leakage of toxic gases and trigger side reactions. Even with the introduction of the aforementioned dry, high-purity nitrogen path, it's impossible to prevent the actual TDI concentration in the reaction solution from decreasing due to TDI volatilization. This will result in an overestimation of the NCO conversion rate measured by this method. Furthermore, due to surface tension, the reaction solution, which was originally evenly coated on the window, will rapidly agglomerate into multiple small droplets under heating conditions. This reduces the area of ​​the reaction solution that the infrared laser can pass through while increasing its thickness. Consequently, signal peaks that do not participate in the reaction and whose concentration remains constant, and whose peak intensity should also remain unchanged, such as those at 2870 cm⁻¹, will appear unchanged. -1 The intensity of the carbon-carbon double bond peak at 2100 cm⁻¹ decreases, while the intensity at 2100 cm⁻¹ decreases. -1 The increased intensity of the azide peak at the point of reaction leads to significantly different experimental results when these different signal peaks are used to process the relative peak intensity of NCO. The closed window design proposed in this invention can minimize the problems of TDI volatilization and reaction with water, and the double-layer window design avoids the problem of reaction liquid agglomeration due to surface tension. The area and thickness of the reaction liquid remain basically unchanged, and the carbon-carbon double bond signal intensity remains unchanged.

[0042] In existing technologies, a few cases have employed the method of covering a single-window coating with a reaction solution layer to improve the problem of reaction solution agglomeration and reduce the impact of TDI volatilization. However, this method is still not perfect and introduces new problems. Adding a window layer reduces the infrared signal, thus requiring an increase in the amount of reaction solution applied to the window. Excessive reaction solution can expand due to heat, covering or even squeezing out the window, causing the opposite problem as with the single-window design: increased reaction solution area and decreased thickness affect the intensity of characteristic peak signals, and may even overflow the window, contaminating the in-situ experimental platform. Furthermore, the outward flow of the reaction solution due to expansion and downward flow due to gravity can cause significant displacement of Al particles, even causing them to leave the infrared laser beam scanning range, thus affecting the test results. The closed-window design proposed in this invention allows the window to carry more reaction solution to obtain a better infrared signal. Simultaneously, the closed-window design restricts the expansion of the reaction solution, preventing it from overflowing and causing changes in the reaction solution area and thickness, or even contaminating the in-situ experimental platform. It also restricts the mobility of Al particles, ensuring that the variation in the number of Al particles within the infrared laser beam scanning range is controlled within a small range.

[0043] The core idea of ​​the closed-window design in this invention is to form a closed structure with minimal window thickness, thus keeping the reaction liquid within this closed structure and solving the aforementioned problems that may occur in such reaction systems. Other alternative solutions may utilize different window shapes to form a closed structure, or different clamps to achieve a similar sealing effect, such as designing holes at the edges of the window to release gas during the window closure process and then sealing the vents with clamps; or designing snap-on clamps, etc.

[0044] Comparative Example 1

[0045] CN112198147A discloses an in-situ testing method for the curing reaction of a PBT-TDI mixed system, comprising the following steps: First, based on PBT-TDI mixed systems with different mixing ratios, Raman spectra are acquired, and a linear regression model curve is established between the relative peak intensity of TDI (i.e., the ratio of isocyanate peak intensity in TDI to azide peak intensity in PBT) and the TDI concentration; Second, the Raman spectra of the PBT-TDI mixed system during the curing reaction are obtained, wherein the Raman spectra include the real-time characteristic peak intensity of isocyanate in TDI and the real-time characteristic peak intensity of azide functional groups in PBT, and the real-time relative peak intensity of TDI is calculated; Finally, the real-time relative peak intensity of TDI is applied to the linear regression model curve to monitor the TDI concentration in real time.

[0046] The testing principle of this invention is similar to that of the patent previously applied for by our unit, "In-situ Testing Method for Curing Reaction of PBT-TDI Mixed System", but the reaction system and testing method are very different. Compared with the simple PBT-TDI mixed system, the composite system formed after adding Al is more difficult to test and the testing method is more complicated. Compared with Raman detection, infrared spectroscopy detection technology is more difficult to prepare samples, so the closed window designed in this invention is required.

[0047] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. An in-situ infrared testing method for monitoring the curing reaction process of a PBT-TDI-Al composite system, characterized in that, Includes the following steps: S1: Establish the relative peak intensity of NCO I 2270 / I 2870 Linear regression model curve with NCO concentration; S2: Obtain infrared spectral data during the curing reaction of the PBT-TDI-Al composite system, and calculate the real-time intensity I of the NCO relative peak. 2270 / I 2870 ; S3: Real-time intensity I of the NCO relative peak 2270 / I 2870 By mapping the linear regression model curve, real-time quantitative data of NCO can be obtained, thereby enabling in-situ monitoring of the curing reaction process of the PBT-TDI-Al composite system. In S1, infrared spectral datasets of PBT-TDI-Al composite systems with different mixing ratios were obtained, and the relative peak intensity I of NCO was established accordingly. 2270 / I 2870 Linear regression model curve with NCO concentration; In S1, the methods for obtaining the linear regression model curve include: S1-1: Mix PBT, TDI, and Al evenly according to a preset ratio, and calculate the NCO concentration in the mixing system with different ratios; S1-2: The relative peak intensity of NCO was calculated by using an infrared spectrometer to detect different proportions of the mixed system; S1-3: The NCO concentration of the different mixing systems in S1-1 is compared with the relative peak intensity of NCO measured in the corresponding system in S1-2. 2270 / I 2870 Correlation, to produce NCO relative peak intensity I 2270 / I 2870 Linear regression model curve with NCO concentration; The infrared spectral data in S1 and S2 are obtained by an in-situ infrared testing device, which includes an infrared spectrometer, an in-situ reaction cell matched with the infrared spectrometer, and a computer terminal. In S1, the infrared spectral dataset of the PBT-TDI-Al composite system includes PBT-TDI-Al composite systems with different mixing ratios: the wavenumber signal is located at 2270 cm⁻¹. -1 TDI characteristic group NCO signal peak data at I 2270 The wavenumber signal of the carbon-carbon double bonds in the composite system that do not participate in the curing reaction is located at 2870 cm⁻¹. -1 Signal peak data I at the location 2870 .

2. The in-situ infrared testing method for monitoring the curing reaction process of the PBT-TDI-Al composite system according to claim 1, characterized in that, The in-situ infrared testing device also includes an external component, which includes a water bath machine used for heating the in-situ reaction tank.

3. The in-situ infrared testing method for monitoring the curing reaction process of the PBT-TDI-Al composite system according to claim 2, characterized in that, The external components also include a protective gas path that matches the in-situ reaction tank.

4. The in-situ infrared testing method for monitoring the curing reaction process of the PBT-TDI-Al composite system according to claim 3, characterized in that, The protective gas path is supplied with 99.999% high-purity nitrogen through its inlet. The airflow is controlled by a flow meter. After being dried by a dryer composed of multiple anhydrous silica gels, the gas bypasses the water bath heater for preheating to prevent the air temperature from being too different from the experimental temperature in the in-situ reaction tank and thus lowering the reaction temperature. Then it enters the in-situ reaction tank to carry away the harmful gases generated in the in-situ reaction tank. Finally, it flows out from the outlet of the in-situ reaction tank and enters the external waste gas treatment device.

5. The in-situ infrared testing method for monitoring the curing reaction process of the PBT-TDI-Al composite system according to claim 4, characterized in that, The in-situ reaction tank includes an in-situ reaction tank body and a closed window provided on the in-situ reaction tank body; The closed window consists of two calcium fluoride windows and two semi-circular clamps. Window A has a protruding frustum, and window B has a recess on one side that matches the frustum, used to hold the reaction liquid.

6. The in-situ infrared testing method for monitoring the curing reaction process of the PBT-TDI-Al composite system according to claim 5, characterized in that, During the reaction, a measured amount of reaction liquid is dripped into the recess of window B, and then the frustum side of window A is pushed into window B to seal the reaction liquid between the two windows. Then, two semi-circular clamps are placed on the outer periphery of the assembled windows to limit the opening and closing of the assembled windows and prevent the reaction liquid from expanding and overflowing from the gap between window A and window B during the heating process.

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