HTPB cleaning solvent and application thereof in HTPB cleaning

Abstract

The invention belongs to the field of cleaning solvents, and particularly relates to an HTPB cleaning solvent and application thereof in HTPB cleaning. 1-fluoro-1, 1-dichloroethane and decane are mixed according to the mass ratio of (1: 6)-(6: 1) to obtain the mixed cleaning solvent. The cleaning solvent provided by the invention not only has the capability of efficiently removing HTPB and a propellant containing HTPB, but also has environmental friendliness, causes little harm to the health of operators and the production environment, and more importantly meets higher safety requirements (such as high flash point and high stability). The cleaning solvent and the to-be-cleaned target substance are infinitely and mutually soluble, the cleaning solvent needs to be replaced when the to-be-cleaned target substance is at a relatively high concentration, the cleaning solvent is easy to recover, and the safety of the cleaning process and the control of enterprise cost are facilitated.

Description

Technical Field

[0001] The present invention belongs to the field of cleaning solvents, and particularly relates to an HTPB cleaning solvent and its use in HTPB cleaning. Background Art

[0002] Hydroxyl-terminated polybutadiene (HTPB) is a liquid polymer widely used since its development in the 1960s. Its main synthesis routes include anionic polymerization, free radical polymerization, and chemical modification methods, etc. The molecular structure of HTPB consists of a polybutadiene main chain and hydroxyl-terminated functional groups. Among them, the proportion of the microscopic structure of the main chain (such as the proportion of cis-1,4, trans-1,4, and 1,2-vinyl structures) directly affects its physical and chemical properties. The hydroxyl-terminated functional groups endow HTPB with good chemical reactivity, making it have broad application potential in many fields, such as industrial rubber materials for adhesives, coatings, tires, paving materials, HTPB-type polyurethane elastomers, propellants, etc.

[0003] HTPB is usually mixed with other chemical agents to be used in the manufacture of slurry, and the slurry is poured into a mold for curing and forming. However, during the production process, a large amount of uncured slurry often remains in pipelines and equipment, and the removal of this part of the slurry has become an important issue in the production process. The traditional cleaning method is for workers to manually rinse the residual slurry in the pipeline directly with a low-boiling solvent (such as ethyl acetate), and this method has many deficiencies.

[0004] Using manual processing, the work efficiency is low;

[0005] Workers will be in direct contact with the slurry, and the operation safety risk is high;

[0006] The selected solvent is often a highly flammable solvent with a low flash point, and there is a fire risk;

[0007] The solvent is extremely volatile, and long-term contact causes great harm to human health;

[0008] The solvent is disposable and the cost is relatively high.

[0009] Current production enterprises adopt ultrasonic cleaning to replace the original manual cleaning method, which can not only improve production efficiency, reduce costs, but also reduce the risks of workers directly facing the slurry and the solvent. However, adding the external factor of ultrasound during the dissolution process, it is a technical problem to ensure safety and stability while achieving a good cleaning effect during the ultrasonic dissolution process. Summary of the Invention

[0010] The purpose of the present invention is to provide an HTPB cleaning solvent and its use in HTPB cleaning.

[0011] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0012] An HTPB cleaning solvent is obtained by mixing 1-fluoro-1,1-dichloroethane and decane in a mass ratio of 1:6 - 6:1 to obtain a mixed cleaning solvent.

[0013] Preferably, the HTPB cleaning solvent is obtained by mixing 1-fluoro-1,1-dichloroethane and decane in a mass ratio of 2 - 4:1 to obtain a mixed cleaning solvent.

[0014] The decane mentioned above is n-decane.

[0015] Another object of the present invention is to disclose the use of an HTPB cleaning solvent in the cleaning of HTPB or propellant:

[0016] When used for HTPB cleaning, the mixed cleaning solvent and HTPB are ultrasonically treated at 0°C - 30°C after mixing, wherein the mass fraction of HTPB when the mixed cleaning solvent and HTPB are mixed is not higher than 8%;

[0017] When used for the cleaning of propellant containing HTPB, the mixed cleaning solvent and the propellant are ultrasonically treated at 0°C - 30°C after mixing, wherein the mass fraction of the propellant when the mixed cleaning solvent and the propellant are mixed is not higher than 50%.

[0018] Preferably, the time of ultrasonic treatment is 5 - 30 min.

[0019] Furthermore, the mass fraction of the propellant when the mixed cleaning solvent and the propellant are mixed is not higher than 40%.

[0020] During the cleaning of HTPB, when the viscosity of the cleaning solution reaches 2.3 cP or more (including 2.3 cP), the mixed cleaning solvent needs to be replaced; the cleaning solution refers to the solution obtained by mixing the mixed cleaning solvent and HTPB.

[0021] Or, during the cleaning of propellant containing HTPB, when the viscosity of the cleaning solution reaches 2.3 cP or more (including 2.3 cP), the mixed cleaning solvent needs to be replaced; the cleaning solution refers to the solution obtained by mixing the mixed cleaning solvent and the propellant containing HTPB.

[0022] More preferably, during the cleaning of propellant containing HTPB, when the viscosity of the cleaning solution reaches 1.4 cP or more (including 1.4 cP), the mixed cleaning solvent needs to be replaced.

[0023] Another object of the present invention is to provide a recovery method for the HTPB cleaning solvent. After the mixed cleaning solvent is used to clean HTPB or propellant containing HTPB, the mixed cleaning solvent is recovered through a nanofiltration membrane or multi-stage filtration, or 1-fluoro-1,1-dichloroethane is recovered through rotary suction filtration.

[0024] The advantages of the present invention are as follows:

[0025] The cleaning solvent of the present invention not only has the ability to efficiently remove HTPB and propellants containing HTPB, but also has environmental friendliness, causing little harm to the health of operators and the production environment. More importantly, it meets higher safety requirements (such as high flash point and high stability). The cleaning solvent of the present invention is infinitely miscible with the target substance to be cleaned, and the cleaning solvent needs to be replaced only when the target substance to be cleaned is at a relatively high concentration. The cleaning solvent is easy to recycle, which helps to improve the safety of the cleaning process and control the enterprise cost.

[0026] The mixed cleaning solvent of 1-fluoro-1,1-dichloroethane and decane maintains a strong dissolving ability, and at the same time, its non-flash point property is not changed due to the addition of decane; the initial boiling point is increased from 32 °C to 38 °C, improving the safety.

[0027] Introducing a small amount of decane into the 1-fluoro-1,1-dichloroethane solution can maintain a relatively high HTPB dissolving ability while significantly reducing the solution viscosity at the same mass fraction and improving the fluidity. Brief Description of the Drawings

[0028] Figure 1 . Dissolution conditions of HTPB with different mass fractions in various solvents, a, dissolution condition in acetone; b, dissolution condition in ethyl acetate; d, dissolution condition in 1-fluoro-1,1-dichloroethane; e, dissolution condition in decane;

[0029] Figure 2 . Model of HTPB and 1-fluoro-1,1-dichloroethane (white atoms are hydrogen atoms, red atoms are oxygen atoms, blue atoms are fluorine atoms, and green atoms are chlorine atoms);

[0030] Figure 3 . Solubility parameter fitting curve graph;

[0031] Figure 4 . Particle size distribution graph of HTPB in different solvents, A, B, C, D are the particle size distributions of 5% HTPB solution respectively; a, b, c, d are the particle sizes of 10% HTPB solution respectively; A, a correspond to decane; B, b correspond to 1-fluoro-1,1-dichloroethane; C, c correspond to dichloromethane; D, d correspond to ethyl acetate;

[0032] Figure 5 . Solubility parameter of the cleaning solution;

[0033] Figure 6 . Viscosity comparison of 1-fluoro-1,1-dichloroethane and the mixed cleaning solvent after dissolving different mass fractions of HTPB;

[0034] Figure 7. Laser particle size distribution diagram of the mixed cleaning solvent (tests corresponding to 5% and 10% mass fractions are shown in a and b respectively);

[0035] Figure 8 . Solvent dissolution heat map;

[0036] Figure 9 . Supernatant state after ultrasonic dissolution of propellant solutions with different concentrations;

[0037] Figure 10 . Dissolution conditions of HTPB in 1-fluoro-1,1-dichloroethane (a) and the mixed cleaning solvent (b);

[0038] Figure 11 . Viscosity diagram of HTPB solution;

[0039] Figure 12 . Viscosity change diagram of the propellant;

[0040] Figure 13 . Wall sticking situation diagram (a shows the wall sticking situation of the binder solution when η = 4.5 cP; b shows the wall sticking situation of the propellant solution when η = 5.6 cP). Detailed implementation manners

[0041] The present invention will be specifically introduced below in conjunction with the accompanying drawings and specific embodiments.

[0042] The HTPB used herein has a theoretical hydroxyl value of 0.47 - 0.53 mmol / g, a theoretical number average molecular weight of 4000 - 4600, and a theoretical viscosity of 0 - 9 Pa·s; through actual measurement, the measured hydroxyl value of HTPB is 0.51 mmol / g, the measured number average molecular weight is 4250, and the measured viscosity is 8.6 Pa·s.

[0043] I. Selection of cleaning solvent

[0044] Starting from two aspects of solution polarity and solubility parameter, cleaning solvents with better dissolution performance are screened.

[0045] a. Influence of solution polarity on the dissolution of HTPB

[0046] Solvents with different polarities such as acetone, ethyl acetate, 1-fluoro-1,1-dichloromethane, and decane are selected to study the influence of solvent polarity on the dissolution performance of HTPB. The polarity of the solvents is in the order of: acetone > ethyl acetate > 1-fluoro-1,1-dichloromethane > decane.

[0047] First, prepare a solution of HTPB (with a mass fraction of 5%) (this solution is specifically composed of HTPB and a single cleaning solvent, and the single cleaning solvent is acetone, ethyl acetate, 1-fluoro-1,1-dichloromethane, or decane). Treat it by ultrasonic waves at 20 °C (power 400 W) for 20 minutes, and observe its dissolution situation. The experimental results show that the acetone solution presents a turbid state and undergoes a layering phenomenon during standing, indicating poor compatibility between acetone and HTPB; visible filamentous HTPB polymers exist in the ethyl acetate solution and gradually dissolve after a period of time, indicating that the diffusion rate of ethyl acetate molecules into the space between HTPB macromolecules is slow and the dissolution rate is also slow; the 1-fluoro-1,1-dichloromethane solution presents a clear state, showing good solubility and a fast dissolution rate, indicating its high compatibility with HTPB; colloidal HTPB can still be observed in the decane solution and gradually dissolves after standing for a period of time, indicating that decane is compatible with HTPB, but the dissolution rate is slow.

[0048] Subsequently, prepare HTPB solutions with different concentrations (mass fractions are 5%, 10%, 20%, 30%, 40%, and 50% respectively). This solution is specifically composed of HTPB and a single cleaning solvent, and the single cleaning solvent is acetone, ethyl acetate, 1-fluoro-1,1-dichloromethane, or decane. Treat it by ultrasonic waves at 20 °C (power 400 W) for 20 minutes, and observe the dissolution phenomenon (see Figure 1 ). The results show that in the acetone solution, as the HTPB concentration increases, the layering phenomenon occurs more rapidly; in the ethyl acetate solution, as the HTPB concentration increases, the remaining gel-like substances gradually increase and present a clear state after standing overnight, indicating that ethyl acetate can be miscible with HTPB, but has a low dissolution rate; the 1-fluoro-1,1-dichloromethane solution remains clear and uniform as the HTPB concentration increases, indicating its high compatibility with HTPB and a fast dissolution rate; in the decane solution, as the HTPB concentration increases, the remaining amount of gel-like substances gradually increases and still remains clear after standing overnight, indicating that decane can be miscible with HTPB, but the dissolution rate is slow.

[0049] Ethyl acetate, 1-fluoro-1,1-dichloromethane, and decane can all form miscible systems with HTPB, but the dissolution rate and dissolution behavior are affected by the polarity of the solvent. 1-fluoro-1,1-dichloromethane has the best solubility for HTPB because HTPB belongs to weakly polar polymer molecules and is closer in polarity to 1-fluoro-1,1-dichloromethane. The polarities of acetone, ethyl acetate, and decane are too large or too small relative to HTPB and are not the better choices as HTPB solvents.

[0050] b. Calculation of HTPB solubility parameter

[0051] The solubility parameter is an important physical parameter that characterizes the interaction strength between polymers and solvents.

[0052] 1) Calculating the solubility parameter by computer simulation

[0053] In this invention, the Forcite module and the Amorphous Cell (AC) module of Materials Studio are used to calculate the solubility parameter.

[0054] First, the HTPB, ethyl acetate, 1-fluoro-1,1-dichloroethane, and n-decane ( Figure 2 ) are constructed using the Amorphous Cell module, and a simulation system with a periodic structure is generated. The side length of the periodic box is about 2.5 nm to ensure sufficient interaction range in the system. Subsequently, molecular dynamics simulations are carried out using the Forcite module under the conditions of 298 K and 1 atm to obtain the equilibrium state configuration of the system. The calculation of the solubility parameter is based on the analysis of intermolecular interaction energy and is automatically calculated by the software.

[0055] After calculation, we obtained the solubility parameters of HTPB and 1-fluoro-1,1-dichloroethane (Table 1). The solubility parameters of other common solvents can be obtained by literature search.

[0056] Table 1. Solubility parameters of HTPB and different solvents

[0057]

[0058] The solubility parameters of ethyl acetate and 1-fluoro-1,1-dichloroethane are relatively close to that of HTPB; while the solubility parameter of n-decane has a large gap with that of HTPB, showing a low dissolution potential. However, the solubility parameter is not the only factor determining the dissolution performance, and the specific dissolution behavior is also comprehensively affected by the molecular structure of the solvent and intermolecular interactions.

[0059] 2) Determining the solubility parameter by viscosity method

[0060] Establish a one-dimensional solubility parameter curve graph to characterize the dissolution performance of different solvents.

[0061] Calculate the solubility parameter of the mixed solution obtained by mixing solutions with different solubility parameters (where δ m is the solubility parameter of the mixed solution, δ i is the solubility parameter of each component solution, x i is the volume fraction of each component solution, i = 1, 2...):

[0062] δ m = δ1x1 + δ2x2 + ……

[0063] By referring to the solubility parameters of different solvents and combining with experimental data, a one-dimensional curve of the solubility parameter of HTPB was plotted. During the experiment, to exclude the interference of polar solvents, non-linear fitting was performed on the data of non-polar solvents. The fitting results showed that the coefficient of determination R 2 = 0.9629, indicating a high degree of coincidence between the fitting curve and the actual measurement data, and the fitting degree was good. This shows that by predicting solubility through the one-dimensional solubility parameter model, the dissolution behavior of HTPB in different solvents can be described more accurately.

[0064] Through fitting calculation of experimental data, the solubility parameter of hydroxyl-terminated polybutadiene (HTPB) was determined to be 18.01, which was highly consistent with the result (17.99) obtained by computer simulation. This indicates that experimental measurement and theoretical prediction have good agreement. According to the principle of mutual solubility between polymer materials and solvents, when the difference between the solubility parameters of the two satisfies , the solvent and the polymer can be considered compatible; where δ h , δ r represent the solubility parameter of HTPB and the solubility parameter of the solvent, respectively. Therefore, solvents within the range can be considered as candidate components for the cleaner. Although the solubility parameter of 1-fluoro-1,1-dichloroethane is lower than that of HTPB, due to the similar polarity, it still shows good dissolution performance. In contrast, although the solubility parameter of ethyl acetate is relatively close to that of HTPB, its high polarity results in weak dissolution ability.

[0065] Different solvent solutions with 5% and 10% mass fractions of HTPB were prepared, treated by ultrasonic (power 400W) at 20°C for 25 minutes, and the particle size distribution of HTPB in different solvents was studied by laser particle size analysis to characterize the dispersion and aggregation behavior of the polymer in the solvent. When the particle size is small and the proportion of small particle sizes is high, it indicates excellent dissolution performance and dispersion. The experimental results are as Figure 4As shown in the figure, in the same solvent, with the increase of the solution concentration, the particle size of HTPB gradually increases; in the 10% solutions of different solvents, the particle size of HTPB in 1-fluoro-1,1-dichloroethane is smaller, showing better dispersion performance. The particle size of HTPB in ethyl acetate is larger and the dispersion is not good. The particle size of HTPB in decane is also relatively small, and the proportion of smaller particle sizes is better than that of other solvents. Among them, the proportion of particles with a particle size of 4 nm in 1-fluoro-1,1-dichloroethane reaches 62%, while the proportion of particles with a particle size of 4 nm in dichloromethane is 50%. Although the polarity of dichloromethane and 1-fluoro-1,1-dichloroethane is similar, the proportion of smaller particle sizes in the 10% solution during actual dissolution is less than that of 1-fluoro-1,1-dichloroethane, and the proportion of smaller particle sizes in the 5% solution of dichloromethane is significantly less than that of 1-fluoro-1,1-dichloroethane, indicating that the dissolution and dispersion properties of dichloromethane and 1-fluoro-1,1-dichloroethane with similar polarity are still significantly different. In addition, dichloromethane is volatile, toxic and carcinogenic; while 1-fluoro-1,1-dichloroethane is non-toxic and has strong safety.

[0066] Safety performance analysis:

[0067] Volatile solvents such as acetone, ethyl acetate, benzene, and tetrahydrofuran have relatively low flash points and belong to Class 2 flammable substances. The mixtures formed by the vapors volatilized from their solutions and air can easily flash when encountering an ignition source, posing a fire risk. 1-F-1,1-dichloroethane is volatile and has no flash point, suitable as a cleaning solvent and will not flash or explode under normal conditions.

[0068] Benzene solvent has the greatest toxicity, dichloromethane and tetrahydrofuran have potential carcinogenicity, acetone and ethyl acetate also have certain toxicity, while 1-F-1,1-dichloroethane is non-toxic.

[0069] II. Determination of the mixed cleaning solvent

[0070] 1) Determination of components and proportions, verification of dissolution ability and viscosity

[0071] 1-fluoro-1,1-dichloroethane is an ideal main cleaning solvent. In terms of dissolution performance, 1-fluoro-1,1-dichloroethane shows strong dissolution ability and good volatility, suitable as an efficient cleaning solvent. From the analysis of chemical structure, this compound does not contain oxidizing or reducing active groups, and its chemical properties are extremely stable, and it will not react chemically with components such as adhesives, curing agents, and oxidants, with relatively high safety. In terms of the safety of the solvent itself, 1-fluoro-1,1-dichloroethane is not listed in the list of hazardous chemicals for control. It is a non-flammable liquid under normal temperature and pressure, no flash point is detected, and there is no risk of fire ignition; from the perspective of health hazards, it is not listed in the international or domestic carcinogen list and has relatively low health risks.

[0072] 1-Fluoro-1,1-dichloroethane also has deficiencies. Its boiling point is only 32 °C, and its volatility is too high, which may lead to an increase in the inhalation amount of operators, thus causing health hazards. At the same time, it is easy to cause a large loss of the cleaning agent. The high-temperature weather standard line in China is 35 °C. At the same time, in the "Identification of Major Hazard Sources of Hazardous Chemicals" (GB 18218-2018), 35 °C is also the dividing line for classifying liquid hazardous chemicals into health hazard categories J4 and J5. Therefore, to improve its use safety, an appropriate stabilizer is added to increase the boiling point of the solution to be greater than 35 °C.

[0073] Decane, as a liquid with stable chemical properties under normal temperature and pressure, is an ideal choice of stabilizer. Its molecular structure is composed only of carbon-carbon single bonds and carbon-hydrogen single bonds, with relatively high bond energy and is not prone to chemical decomposition or reaction under conventional conditions. At the same time, decane has a relatively high chemical inertness, low toxicity, and moderate volatility. To ensure that the dissolution performance of the cleaning solution is not significantly affected, 1-fluoro-1,1-dichloroethane and decane are mixed at a mass ratio of 3:1, and the performance of the mixed cleaning solvent is studied (in the specific implementation, unless otherwise specified, the mixed cleaning solvent is composed of 1-fluoro-1,1-dichloroethane and decane mixed at a mass ratio of 3:1).

[0074] Prepare a 5% mass fraction solution of HTPB pure solvent (1-fluoro-1,1-dichloroethane) and a mixed cleaning solvent solution. Ultrasonic (power 400 W) for 30 minutes at 20 °C, and use an Ubbelohde viscometer to measure the flow time of the solution and calculate the intrinsic viscosity of different solvent systems. The experimental results show that the mixed cleaning solvent of 1-fluoro-1,1-dichloroethane and decane with a mass ratio of 3:1 still theoretically maintains a strong dissolution ability (such as Figure 5 , the red dots represent the solution of 5% mass fraction of HTPB and the mixed cleaning solvent, and the blue dots represent the 5% mass fraction solution of HTPB pure solvent), and compared with the addition amount of decane in the mixed cleaning solvent, the influence of decane on the decrease in dissolution ability is slight. At the same time, its non-flash point characteristic is not changed due to the addition of decane. In addition, the initial boiling point of the mixed solution is increased from 32 °C to 38 °C (see Table 2), exceeding the high-temperature weather standard of 35 °C, further enhancing its feasibility and applicability in practical applications. And the addition of decane reduces the overall viscosity of the cleaning solution and increases its fluidity; the viscosity of decane itself is higher than that of 1-fluoro-1,1-dichloroethane; but the solution obtained by dissolving HTPB in the mixed solvent composed of 1-fluoro-1,1-dichloroethane and decane has a lower viscosity than the solution obtained by dissolving HTPB in 1-fluoro-1,1-dichloroethane.

[0075] Introducing a small amount of decane into the 1-fluoro-1,1-dichloroethane solution can significantly reduce the solution viscosity at the same mass fraction while maintaining a relatively high HTPB dissolution ability (such asFigure 6 As shown, the abscissa is the mass fraction of HTPB in the cleaning solution), thereby improving the fluidity of the solution and optimizing its industrial application performance. If a small amount of dichloromethane is introduced into the 1-fluoro-1,1-dichloroethane solution (the mass ratio of 1-fluoro-1,1-dichloroethane to dichloromethane is also 3:1), the solution viscosity at the same mass fraction is basically the same as that of the 1-fluoro-1,1-dichloroethane solution, and phenomena such as wall hanging are likely to occur during cleaning.

[0076] Particle size distribution analysis was carried out on the mixed cleaning solution (HTPB was mixed with the mixed cleaning solvent, and the mass fraction of HTPB after mixing was 5%, 10%, ultrasonicated (power 400W) at 20°C for 25 minutes, and then particle size distribution was measured), as Figure 7 shown, in the cleaning solution with 5% concentration of HTPB (the solute is HTPB, and the solvent is the mixed cleaning solvent obtained by mixing 1-fluoro-1,1-dichloroethane and decane in a mass ratio of 3:1), the main peak of particle size analysis appears at 4.238 nm, and the proportion of this particle size reaches 72.2%; while in the cleaning solution with 10% concentration of HTPB (the solute is HTPB, and the solvent is the mixed cleaning solvent obtained by mixing 1-fluoro-1,1-dichloroethane and decane in a mass ratio of 3:1), the main peak position is 4.658 nm, and the proportion is 65.8%. These results indicate that within the low concentration range, appropriately increasing the concentration of the binder has little effect on the dissolution ability of the cleaning solution, and the aggregation phenomenon of HTPB is not significant. This shows that the solution can still maintain good dispersibility at different concentrations and there is no obvious agglomeration phenomenon, indicating that the mixed cleaning solution has good stability and cleaning effect in practical applications. Comparing Figure 4 and Figure 7 , the dissolution performance, dispersibility, and stability of the mixed cleaning solution of the present invention are superior to Figure 4 any of the single solvent solutions in

[0077] 2) Safety assessment of the mixed cleaning solvent

[0078] (1) Change in flash point of the cleaning solvent

[0079] Through flash point and boiling point tests on 1-F-1,1-dichloroethane and the mixed cleaning solvent, the experimental results show that the addition of decane does not change its flash point, but increases the boiling point of the mixed cleaning solvent.

[0080] Table 2. Flash point and boiling point table of the cleaning solvent before and after mixing

[0081]

[0082] (2) Permeability and swelling property tests of the cleaning solvent

[0083] Permeability refers to the ability of a liquid to pass through a porous medium or a semi-permeable membrane, and can also be used to characterize the permeability of a cleaning solvent to gloves and skin; Swelling refers to the phenomenon that a porous material or polymer swells in volume after contacting with a solvent due to the penetration of solvent molecules into the interior of the material, and can be used to characterize the strength of the permeability of a cleaning solvent to gloves and human skin.

[0084] Cut equal-mass films and soak them in different cleaning solvents. After standing for 6 h, take them out, gently remove the residual liquid on the surface, and then weigh the mass of the film samples to calculate the swelling ratio:

[0085]

[0086] Among them, Q is the swelling ratio, M swollen and M dry are the masses of the sample after swelling and in the dry state respectively. The film is made of rubber material. The following table shows the swelling ratios of different cleaning solvents:

[0087] Table 3. Swelling ratios of different cleaning solutions

[0088]

[0089] The experimental results show that after sufficient soaking, the swelling ratio of 1-fluoro-1,1-dichloroethane is relatively high, while the permeability of the mixed cleaning solvent is weaker than that of 1-fluoro-1,1-dichloroethane, improving the permeability. And compared with the small addition amount of decane in the mixed cleaning solvent, the improvement of the permeability of decane to 1-fluoro-1,1-dichloroethane is significant.

[0090] (3) Solvent dissolution heat analysis

[0091] For the selected mixed solvent, a dissolution heat test was carried out. In the experiment, the binder HTPB and the cleaning solvent were mixed at a mass ratio of 1:1, and the dissolution heat of the mixed solution was measured to be 1.579 J / kg at 21.1 °C to 38.1 °C, as Figure 8 shown. The dissolution process is an exothermic reaction, indicating that this process is spontaneous under normal temperature and pressure, and at the same time indicating that there are no safety risk problems during the dissolution process.

[0092] (4) Solvation free energy calculation

[0093] To quantify the dissolution performance of HTPB in different solvents, the present invention uses the Forcite module of Materials Studio for molecular dynamics simulation and calculates the solvation free energy using the thermodynamic integration method. During the model construction process, the Amorphous Cell module of Materials Studio is used to generate models of HTPB and solvent molecules, and periodic boundary conditions are adopted to simulate the periodic behavior of the system. Specifically, the side length of the periodic box of the HTPB model is about 2.5 nm to ensure accurate simulation of the intermolecular interactions during the calculation process. By constructing models of HTPB molecules and solvent molecules, simulations are carried out under the conditions of 298 K and 1 atm using the COMPASSⅡ force field to obtain the stable configuration of the system. On this basis, the free energy change value of HTPB transferred from vacuum to the solvent is calculated. This method can effectively describe the interaction between solvent and solute molecules and provide a reliable basis for the quantitative evaluation of dissolution performance.

[0094] The calculation results show (Table 4) that the solvation free energy of HTPB in 1-fluoro-1,1-dichloroethane is the lowest, -98.179 kcal / mol, indicating that this solvent has the strongest dissolution ability. The solvation free energy of ethyl acetate is -86.816 kcal / mol, showing suboptimal dissolution performance. The solvation free energy of n-decane is -75.057 kcal / mol, with relatively weak dissolution ability. The solvation free energy of the mixture of 1-fluoro-1,1-dichloroethane and n-decane with a mass ratio of 3:1 is -93.751 kcal / mol, indicating that the mixed solvent system has both strong dissolution ability and potential safety optimization effect. By comparison, the differences in the polarity and molecular structure of different solvents significantly affect the dissolution behavior of HTPB.

[0095] Table 4. Solvation Free Energy of HTPB in Different Solvents

[0096]

[0097] It can be seen from the calculation results that the polarity of the solvent has a significant impact on the dissolution performance of HTPB. Weakly polar solvents (such as 1-fluoro-1,1-dichloroethane) form a stable solvation shell with HTPB molecules through stronger van der Waals forces and dipole-dipole interactions, so the solvation free energy value is more negative, showing stronger dissolution ability. In contrast, n-decane, as a non-polar solvent, has a weak interaction with HTPB molecules, resulting in a higher solvation free energy value. In addition, it can be seen from the solvation free energy and its contribution components that the dissolution performance of HTPB by different solvents is affected by the combined effects of van der Waals forces and electrostatic energy contributions:

[0098] The contribution of van der Waals forces dominates the dissolution performance:

[0099] The solvation free energy of all solvents is mainly determined by the contribution of van der Waals forces, and the absolute value of the van der Waals force contribution dominates in the solvation free energy. The van der Waals force contribution of 1-fluoro-1,1-dichloroethane is -99.643 kcal / mol, which is the largest among all solvents, resulting in the lowest solvation free energy (-98.179 kcal / mol) and showing the best dissolution performance. Similarly, ethyl acetate (-81.864 kcal / mol) also has a significant van der Waals force contribution, supporting its good dissolution ability. This result indicates that the interaction between HTPB and solvent molecules mainly depends on weak intermolecular forces (such as van der Waals forces), rather than electrostatic interactions.

[0100] Minor effect of electrostatic energy:

[0101] Compared with van der Waals forces, the contribution of electrostatic energy to the solvation free energy of HTPB is smaller, and it is positive in some solvents. For example, the electrostatic energy contribution of n-decane is +0.886 kcal / mol, indicating that there is almost no electrostatic interaction between HTPB and this non-polar solvent. In addition, although the electrostatic energy contribution in ethyl acetate is relatively large (-4.051 kcal / mol), the ratio to the van der Waals force is still small (the electrostatic energy accounts for less than 5% of the total contribution), further verifying that HTPB is a non-polar or weakly polar molecule.

[0102] Synergistic effect of mixed cleaning solvents and balance of solvent properties:

[0103] 1-fluoro-1,1-dichloroethane is a solvent between non-polar and polar. In its interaction with HTPB molecules, the van der Waals force contribution dominates (-99.643 kcal / mol), while the electrostatic energy contribution is small (-0.274 kcal / mol). n-decane, as a non-polar solvent, shows more non-polar characteristics in its interaction with HTPB, with an electrostatic energy contribution of +0.886 kcal / mol. After mixing 1-fluoro-1,1-dichloroethane and n-decane in a ratio of 3:1, the comprehensive performance of the solvent is optimized, showing a lower electrostatic energy contribution (-0.125 kcal / mol) and a significant van der Waals force contribution (-90.972 kcal / mol). This balance shows that the mixed solvent system can moderately adjust the polarity attribute of the solvent on the basis of ensuring the dissolution ability. This synergistic effect indicates that the dissolution performance of HTPB mainly depends on non-polar or weakly polar interactions. 1-fluoro-1,1-dichloroethane provides the main van der Waals force in the mixed system, and the introduction of n-decane further optimizes the dissolution performance and stability of the system by adjusting the solvent polarity.

[0104] III. Establishment of solvent replacement standards

[0105] By analyzing the service life of the cleaning solution, clarify the critical point at which the dissolution efficiency decreases during repeated use, and avoid the decline of the cleaning effect caused by overuse, so as to meet the high-efficiency cleaning requirements of industrial production. By optimizing the time node of solvent replacement, reduce unnecessary early replacement, and reduce material waste and economic costs in the production process.

[0106] 1) Safety:

[0107] To ensure the safety during the cleaning process, flash point tests were carried out on propellant solutions with concentrations of 40%, 50%, and 60% respectively (this solution includes propellant containing HTPB and a mixed cleaning solvent, the mixed cleaning solvent is obtained by mixing 1-fluoro-1,1-dichloroethane and decane in a mass ratio of 3:1, the mass fractions of the propellant are 40%, 50%, and 60% respectively, and ultrasonic treatment (power 400W) was carried out at 20°C for 30 minutes) to evaluate whether potential safety hazards would be caused after dissolving other propellant components. The test results show that the propellant solutions with concentrations of 40%, 50%, and 60% have no flash points under the experimental conditions, indicating that the solution will not cause safety risks due to dissolving other drug components during use. Therefore, the selected cleaning solution has good safety in the production environment.

[0108] The propellant in this article is HTPB propellant, and its main components include ammonium perchlorate (60%-80%), HTPB (10%-20%), aluminum powder (5%-15%), curing agent, crosslinking agent, etc., and % is the mass fraction. During the dissolution of the propellant by the mixed cleaning solvent, not only HTPB is dissolved, but also the remaining organic components are dissolved.

[0109] By preparing propellant solutions with different concentrations (such as Figure 9 ), and ultrasonic treatment for different times to measure the safety of the propellant dissolution process (see Table 5), ultrasonic conditions: 20°C, power 400W, and no dangerous phenomena occurred, indicating that there is no violent chemical reaction during the dissolution of the propellant by the mixed cleaning solvent, and the dissolution process is mild and controllable.

[0110] Table 5. Safety evaluation of propellant solutions with different concentrations under ultrasonic conditions at 20°C

[0111]

[0112]

[0113] 2) Dissolution limit and fluidity:

[0114] HTPB was added into 1-fluoro-1,1-dichloroethane and the aforementioned mixed cleaning solvent respectively to prepare solution systems of HTPB with different mass fractions (5%, 10%, 20%, 30%, 40%, 50%), and the solubility limit, rheological properties and viscosity differences of HTPB were investigated. Figure 10 The dissolution of cleaning solutions with different mass fractions was shown. The experimental results indicated that HTPB could be infinitely miscible with 1-fluoro-1,1-dichloroethane and the mixed cleaning solution, the solutions were clear and transparent, and no solubility limit was observed. This result further illustrated the significant advantages of 1-fluoro-1,1-dichloroethane and its mixed solvent system in dissolution ability, providing strong support for its industrial application as an efficient cleaning solvent.

[0115] 3) Viscosity measurement:

[0116] The viscometer determines the viscosity of a liquid by measuring the internal friction force it experiences during flow. Common measurement methods include rotational viscometers and rheometers. In this experiment, we selected a rotational viscometer for testing. Viscosity, as a physical quantity characterizing the flow resistance of a liquid, is closely related to the intermolecular interaction forces in the solution and the tightness of its structure. Through viscosity measurement, the fluidity, viscosity of the solution and the dispersion state of the polymer in the solvent can be effectively reflected. When the viscosity of the solution is too high, the fluidity of the liquid on the pipe wall decreases, and it often adheres to the surface of the pipe wall, ultimately affecting the cleaning effect. Therefore, viscosity can not only provide quantitative information on the flow characteristics of the solution, but also be a key indicator for judging whether the cleaning solution needs to be replaced.

[0117] We conducted viscosity tests on cleaning solutions of HTPB with different mass fractions (2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%) (ultrasonic treatment (power 400W) for 30 minutes at 20°C, and the solvent was a mixed cleaning solvent obtained by mixing 1-fluoro-1,1-dichloroethane and decane at a mass ratio of 3:1). The experimental results are as Figure 11 shown. As the concentration of the solution increased, the viscosity of the solution showed an upward trend. Compared with the change in refractive index, the increase in viscosity was more significant, and it was less affected by environmental changes, having good stability and high sensitivity, and could effectively distinguish cleaning solutions with different concentrations. Therefore, viscosity, as an index for detecting the performance of cleaning solutions, is more suitable for real-time monitoring and quality control in industrial production.

[0118] Meanwhile, we prepared propellant solutions with different mass fractions (5%, 10%, 20%, 30%, 40%, 50%, 60%) (ultrasonic treatment at 400 W for 30 minutes at 20°C, and the solvent was a mixed cleaning solvent obtained by mixing 1-fluoro-1,1-dichloroethane and decane in a mass ratio of 3:1), and measured their viscosities. The results are shown in Table 6. When the content of the added propellant is relatively low, the viscosity of the solvent increases steadily. When the mass fraction of the added propellant reaches 40%, and more propellant is added, the viscosity of the solution increases rapidly, approximately exponentially (as Figure 12 ), which is attributed to the fact that as the proportion of the propellant increases, the amount of the binder increases, and the volume of the cleaning agent decreases relatively, and the concentration of the binder does not increase linearly.

[0119] Table 6. Viscosity of Propellant Solution at 20°C

[0120]

[0121] The viscosity was measured using a rotational viscometer, which is easy to operate, has strong environmental adaptability, small measurement errors, and high reliability and repeatability. In addition, the use of a rotational viscometer has good industrial adaptability. By introducing a viscosity monitoring method, the scientific and precise replacement of the cleaning solution can be realized, further promoting the automation and unmanned operation of the production process, and improving the efficiency and safety of industrial production.

[0122] 4) Determination of the End Point for Replacing the Propellant Solution

[0123] Through the determination of the viscosity of the HTPB solution and the propellant solution (referring to the solution obtained by dissolving HTPB or the propellant and the mixed cleaning solvent by ultrasonic treatment at 400 W for 30 minutes at 20°C) in the above text, we obtained the adhesion of binder solutions with different viscosities to the surface of the rotor of the rotational viscometer (defined as the wall adhesion phenomenon, that is, when the tube wall is held vertically downward and the attached residual cleaning solution flows freely under the action of gravity and then stands for 5 minutes, there is still residual liquid attached to the surface of the tube wall, as Figure 13 a) in). The experimental results show that when the viscosity of the binder solution reaches 4.5 cP (the mass fraction of the binder is 12%), the fluidity of the cleaning solution begins to decline, and a slight wall adhesion phenomenon appears; when the viscosity is 5.9 cP (the mass fraction of the binder is 16%), the wall adhesion phenomenon on the rotor surface is significant, and the solution is no longer suitable for industrial production tasks.

[0124] Prepare propellant solutions with different mass ratio concentrations, measure their viscosities using a rotational viscometer, and observe the wall adhesion phenomenon of the propellant solutions at different concentrations (see Figure 13In item b). The experimental results show that there is no wall - hanging phenomenon for the 50% propellant solution, and the viscosity of the propellant solution at this time is 2.3 cP; when the concentration of the propellant solution increases to 60%, obvious wall - hanging phenomenon begins to be observed, and the viscosity of the binder solution is 5.6 cP at this time. This result is basically consistent with the results of the aforementioned binder simulation experiment, verifying the influence of viscosity on the fluidity and wall - hanging phenomenon of the propellant solution.

[0125] Considering the significant influence of temperature on the viscosity of the solution, in this experiment, the viscosities of the propellant solutions (obtained by mixing the propellant with the mixed cleaning solvent and then dissolving it by ultrasonic wave (power 400W) at 0 °C, 10 °C, 20 °C, 25 °C or 30 °C for 30 minutes) were systematically tested at 0 °C, 10 °C, 20 °C, 25 °C and 30 °C (see Table 7). Generally, the viscosity of a liquid is inversely proportional to temperature, that is, the viscosity decreases when the temperature rises and increases when the temperature drops. The experimental results show that compared with the viscosity at 20 °C, the viscosities of the propellant solutions at 10 °C and 0 °C increase significantly, which conforms to the conventional law of the change of liquid viscosity with temperature. However, when the temperature continues to rise, the viscosity of the propellant solution shows a trend of first increasing and then decreasing. The occurrence of this phenomenon can be attributed to the following two factors: First, the increase in temperature will cause the liquid molecules to expand, the molecular spacing to increase, and thus reduce the internal friction force, usually resulting in a decrease in viscosity; second, as the temperature rises, the solubility of HTPB polymer molecules in the solution increases, and the extensibility of the molecular chain increases, which leads to an increase in the interaction force between polymer molecules, thus resulting in a preliminary increase in the solution viscosity. To sum up, as the temperature rises, the viscosity of the propellant solution shows a non - linear change trend of first increasing and then decreasing.

[0126] Table 7. Comparison of viscosities of propellant solutions at different temperatures

[0127]

[0128] According to the experimental results, theoretically, the upper limit for replacing the solution can be set at a viscosity of 2.3 cP (the corresponding concentration of the binder solution is about 8%). However, to ensure the safe progress of industrial production and avoid the situation where the cleaning effect does not meet the standard, the cleaning solution should be replaced before the viscosity reaches 2.3 cP. Therefore, the upper limit of the replacement end - point viscosity can be advanced to the viscosity (η = 1.4 cP) corresponding to a propellant mass fraction of 40%, which can not only ensure the cleaning effect but also reduce the risk hazards.

[0129] IV. Recycling of the mixed cleaning solvent

[0130] In the initial experiments, commercial ultrafiltration membranes with various pore sizes and materials were tried for the recovery of the cleaning solution. However, most of the membranes failed to achieve effective filtration due to poor filtration performance or the formation of a polymer film of HTPB molecules on the membrane surface, which blocked the membrane pores and hindered the flow of the solution.

[0131] A 1kD nanofiltration membrane was used to filter the cleaning solution of the binder (HTPB, mass fraction 10%). Through the selective action of the membrane pore size in ultrafiltration technology, low-molecular solvents can pass through the membrane, while the relatively large-molecular-weight HTPB is effectively retained, thus achieving the separation of the solvent and the polymer. In this experiment, a pressure-driven osmosis process was adopted, and a transmembrane pressure of about 3 kg / cm 2 was applied to promote the passage of solvent molecules, while retaining HTPB molecules on one side of the membrane to achieve the separation purpose. The recovery of the cleaning solution was achieved through the 1kD nanofiltration membrane. By measuring the viscosity of the solution before and after filtration, the recovery rate of the 10% cleaning solution reached over 80%. The experimental results are shown in Table 8. For propellant solutions with more other components and particles, a multi-stage filtration method can be adopted for the recovery of the cleaning solution.

[0132] Table 8. Comparison of viscosities of the cleaning solution before and after filtration

[0133]

[0134] Meanwhile, we adopted a method of hierarchical filtration for the 50% propellant solution (after taking the ultrasonic supernatant, first passing through a 50kD ultrafiltration membrane and then through a 10kD ultrafiltration membrane). The final filtrate still achieved a recovery rate of over 80%. The following formula is the calculation formula for the recovery rate of the cleaning solution:

[0135]

[0136] With the continuous volatilization of 1-fluoro-1,1-dichloroethane in the cleaning solution, the cleaning effect of the recovered cleaning solvent gradually decreases. It is necessary to separately add a 1-fluoro-1,1-dichloroethane solution to the recovered cleaning solvent to restore its dissolving ability.

[0137] An additional solvent recovery method can also be adopted: suction filtration rotary evaporation experiments were carried out on the cleaning solvent to separate and recover each component in the solution. For example, 1-fluoro-1,1-dichloroethane was recovered by suction filtration at 30 °C for 30 minutes. During the experiment, the filtrate and the residual liquid were collected, and their component contents were analyzed respectively. The results showed that only a trace amount of 1-fluoro-1,1-dichloroethane remained in the rotary evaporation residue, indicating that after removing the explosive components in the cleaning solution through filtration pretreatment, distillation operation can be carried out to fractionate the cleaning solvent in the distillation column to separate solvents such as 1-fluoro-1,1-dichloroethane. After condensation recovery, the 1-fluoro-1,1-dichloroethane solvent with a large content and high price in the cleaning solvent can be effectively recovered.

[0138] The above embodiments are only used to illustrate the technical solutions of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form. Any technical solutions obtained by equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. An HTPB cleaning solvent, characterized in that: A mixed cleaning solvent is obtained by mixing 1-fluoro-1,1-dichloroethane and decane in a mass ratio of 1:6 - 6:

1.

2. The HTPB cleaning solvent according to claim 1, wherein: A mixed cleaning solvent is obtained by mixing 1-fluoro-1,1-dichloroethane and decane in a mass ratio of 2 - 4:

1.

3. An HTPB cleaning solvent according to claim 1, characterized in that: The decane described is n-decane.

4. Use of an HTPB cleaning solvent in the cleaning of HTPB or a propellant, characterized in that: When used for cleaning HTPB, the mixed cleaning solvent obtained in claim 1 or 2 is mixed with HTPB and then ultrasonically treated at 0°C - 30°C, where the mass fraction of HTPB when the mixed cleaning solvent obtained in claim 1 or 2 is mixed with HTPB is not higher than 8%. When used for cleaning a propellant containing HTPB, the mixed cleaning solvent obtained in claim 1 or 2 is mixed with the propellant and then ultrasonically treated at 0°C - 30°C, where the mass fraction of the propellant when the mixed cleaning solvent obtained in claim 1 or 2 is mixed with the propellant is not higher than 50%.

5. The use according to claim 4, characterized in that: The time of ultrasonic treatment is 5 - 30 min.

6. The use according to claim 4, wherein: The mass fraction of the propellant when the mixed cleaning solvent obtained in claim 1 or 2 is mixed with the propellant is not higher than 40%.

7. The use according to claim 4, characterized in that: During the cleaning of HTPB, when the viscosity of the cleaning solution reaches 2.3 cP or more, the mixed cleaning solvent needs to be replaced; the cleaning solution refers to the solution obtained by mixing the mixed cleaning solvent obtained in claim 1 or 2 with HTPB.

8. The use according to claim 4, wherein: During the cleaning of a propellant containing HTPB, when the viscosity of the cleaning solution reaches 2.3 cP or more, the mixed cleaning solvent needs to be replaced; the cleaning solution refers to the solution obtained by mixing the mixed cleaning solvent obtained in claim 1 or 2 with the propellant containing HTPB.

9. The use according to claim 4, characterized in that: During the cleaning of a propellant containing HTPB, when the viscosity of the cleaning solution reaches 1.4 cP or more, the mixed cleaning solvent needs to be replaced.

10. A method for recovering a cleaning solvent of HTPB, characterized in that: After the mixed cleaning solvent obtained in claim 1 or 2 is used to clean HTPB or a propellant containing HTPB, the mixed cleaning solvent is recovered through a nanofiltration membrane or multi-stage filtration, or 1-fluoro-1,1-dichloroethane is recovered through rotary suction filtration.

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