Stabilization treatment method for nitrocotton with extra-high viscosity

Abstract

The invention relates to the technical field of nitrocellulose, in particular to a stabilizing treatment method for ultrahigh-viscosity nitrocotton. The technical problem is that a conventional stabilizing treatment method cannot perfectly protect cellulose molecular chains from being damaged while instable substances are thoroughly removed. According to the technical scheme, the stabilizing treatment method for the ultra-high-viscosity nitrocotton comprises an esterification step, a mixed acid supply step, a boiling and washing step and a rinsing step, the boiling and washing step is used for boiling and washing the esterified nitrocotton, the boiling and washing step comprises a plurality of sub-steps, and the boiling and washing temperature is gradually reduced to a lower temperature from a higher temperature; the viscosity of the nitrocotton product is stabilized at 15000 seconds or above by combining low-temperature esterification viscosity keeping, large-flow mixed acid homogenization, temperature decline stage difference boiling washing impurity removal and mechanical stirring quality stabilization, the stability (Abeler value) of the nitrocotton product is broken through to 15 minutes or above, unstable substances are removed, and meanwhile cellulose molecular chains are protected against damage.

Description

Technical Field

[0001] This invention relates to the field of nitrocellulose technology, and more particularly to a method for stabilizing ultra-high viscosity nitrocellulose. Background Technology

[0002] Nitrocellulose is an important chemical raw material with an irreplaceable role in fields such as fireworks fuse coatings and protective coatings for disposable combustible materials. These applications place extremely high demands on the viscosity of nitrocellulose (e.g., above 10,000 seconds), because high viscosity means longer molecular chains and superior film-forming and mechanical properties.

[0003] However, in the manufacturing process of nitrocellulose, in order to obtain a high-viscosity product, it is necessary to minimize the damage to the cellulose molecular chains during the esterification reaction stage. Unstable substances such as residual sulfate esters and mixed nitrate-sulfur esters after the esterification reaction must be thoroughly removed through subsequent boiling and washing processes to ensure the chemical stability of the product during storage and use (usually measured by the Abel test value). Existing boiling and washing processes often use high temperatures (such as above 100°C) or strong acid and alkali environments to effectively remove unstable substances, which inevitably leads to the breakage and hydrolysis of cellulose molecular chains, resulting in a significant decrease in product viscosity.

[0004] Currently, existing technology can produce nitrocellulose with a viscosity of about 10,000 seconds, but its stability (Abel value) can usually only reach about 10 points, which poses a huge safety risk. For ultra-high viscosity nitrocellulose products with higher viscosity requirements (such as above 15,000 seconds) and higher stability requirements (Abel value above 15 points), existing technology has not yet made a breakthrough. The fundamental reason is that conventional stabilization treatment methods cannot completely remove unstable substances while perfectly protecting the cellulose molecular chains from damage.

[0005] Therefore, to address the issue of unfamiliarity, a method for stabilizing ultra-high viscosity nitrocellulose is proposed. By combining low-temperature esterification for viscosity preservation, high-flow-rate mixed acid homogenization, temperature-decreasing graded washing and impurity removal, and mechanical stirring for stabilization, the viscosity of the nitrocellulose product is stabilized at over 15,000 seconds, and its stability (Abel value) is improved to over 15 points. This method removes unstable substances while protecting the cellulose molecular chains from damage. Summary of the Invention

[0006] To overcome the problem that conventional stabilization methods cannot completely remove unstable substances while perfectly protecting the cellulose molecular chains from damage.

[0007] The technical solution of this invention is: a method for stabilizing ultra-high viscosity nitrocellulose, comprising the following steps: Esterification step: The refined cotton and mixed acid are esterified in an esterification machine, and the esterification temperature is controlled at 26-28℃. The low temperature environment can effectively inhibit the oxidative degradation of cellulose molecular chains by the mixed acid, and retain the high viscosity characteristics of the refined cotton raw material to the maximum extent from the source. Mixed acid supply step: In the esterification step, the flow rate of the mixed acid is controlled at 15.8-16.3 m³ / h; Due to the long length and high viscosity of refined cotton fibers, it is difficult to impregnate them with acid, which can easily lead to uneven reaction. Increasing the flow rate of the mixed acid can create a stronger fluid flushing and penetration effect, ensuring that the mixed acid is in full and uniform contact with each fiber, so that the esterification reaction is more thorough and avoids insufficient or excessive local reaction. Boiling and washing step: The esterified nitrocellulose is boiled and washed. The boiling and washing step includes multiple sub-steps, wherein the boiling and washing temperature is gradually reduced from a higher temperature to a lower temperature. This step is used to remove unstable substances of different properties in stages and in a targeted manner. At the same time, a low temperature stage is introduced immediately after the high temperature stage. After opening the fiber cavity to discharge impurities, the system temperature and acidity are rapidly reduced to terminate the hydrolysis and destruction of cellulose molecular chains. Rinsing steps: The boiled nitrocellulose is rinsed in a rinsing machine with agitation. The mechanical agitation can break up the tangles and clumps that are easy to form between the high-viscosity nitrocellulose fibers, ensuring that the residual trace unstable substances can be fully washed out, and at the same time making the viscosity of the final product more uniform in a macroscopic way, ensuring the consistency of batch product quality.

[0008] Preferably, the refined cotton is grade 1000 refined cotton; this grade of refined cotton itself has extremely high initial viscosity and long fiber length.

[0009] Preferably, the boiling and washing step includes: The rinsing process involves adding clean water to the rinsing tank containing nitrocellulose and rinsing under running water for 30-60 minutes until the initial acidity is ≤1.0 ml / g. The purpose is to quickly dilute and remove a large amount of free acid adhering to the fiber surface, rapidly reducing the initial acidity to ≤1.0 ml / g, thus providing an initial low-acid environment for subsequent heating and rinsing, and reducing the catalytic degradation of cellulose by acid during heating. Acid cooking step: Acid cooking is carried out at 86-90℃ for 2.5-4 hours; this temperature range is significantly higher than the 80℃ benchmark of the Abel stability test, which is sufficient to provide enough energy to open the fiber cavity by thermal expansion and to hydrolyze unstable substances with low bond energy and migrate them from the inside of the fiber; and this temperature range is far lower than the harsh conditions of more than 100℃ commonly used in traditional processes, thereby reducing the damage of high temperature to the cellulose molecular chain and achieving effective viscosity maintenance; Low-temperature boiling and washing steps: After acid boiling, drain the water, then add hot water at 60-70℃ and boil for 30 minutes; the purpose of draining the water is to remove the hydrolysis products and acid in the reaction system in time, so as to prevent them from partially seeping back into the fiber due to concentration balance in the subsequent process; the subsequent low-temperature boiling and washing is to further rinse the opened fiber cavities in a gentler environment and continue to remove residual unstable substances. Cold washing process: Perform two room temperature cold washes, each of which involves adding clean water to submerge the nitrocellulose and draining for 30 minutes; this step uses room temperature clean water for the final rinse, which aims to thoroughly cool the product and use the principle of concentration difference diffusion to replace the last trace amount of soluble impurities remaining inside the fiber, in order to consolidate the stability treatment effect.

[0010] Preferably, in the acid boiling step, the temperature difference between the upper, middle and lower parts of the boiling tank does not exceed 3°C, in order to ensure that the entire batch of nitrocellulose is heated evenly during the boiling process, and to avoid uneven quality problems caused by local overheating leading to viscosity loss or local undercooling leading to incomplete stabilization treatment.

[0011] Preferably, the acid boiling temperature range in the acid boiling step is 86-90℃.

[0012] Preferably, tap water is used for the cold washing step, which is economical and convenient, and the final purification is completed through physical diffusion.

[0013] Preferably, the rinsing step involves stirring and rinsing for 50 minutes. This duration ensures sufficient mixing and washing effects without causing unnecessary damage to the high-viscosity fibers due to excessive mechanical shearing.

[0014] Preferably, the esterification step further includes: adding refined cotton to the esterification machine through a refined cotton inlet pipe, and adding mixed acid to the esterification machine through a mixed acid inlet pipe.

[0015] Preferably, the esterification step is followed by a centrifugation step and a washing step. The centrifugation step and the washing step are conventional processes in the production of nitrocellulose, used to initially remove the mother acid and perform a preliminary washing to prepare for the boiling step.

[0016] Preferably, in the boiling and washing step, the temperature decreases in stages by controlling heating and drainage, and the power of the heating system and the drainage operation between each step are controlled by program or manual control.

[0017] The beneficial effects of this invention are: This invention employs low-temperature esterification (26-28℃) to maximize the protection of cellulose molecular chains from the reaction source, laying the foundation for high viscosity. Increasing the mixed acid flow rate (15.8-16.3 m³ / h) ensures the uniformity and thoroughness of the reaction of ultra-high viscosity raw materials. A temperature-decreasing graded washing process utilizes the physicochemical effects of different temperature ranges. First, at a sufficiently high temperature (86-90℃), the fiber structure is opened, hydrolyzed, and the main unstable substances are discharged. Then, rapid cooling and rinsing in a medium-low temperature environment effectively removes unstable substances while inhibiting the hydrolytic degradation of cellulose in a high-temperature, strong acid environment. Stirring and rinsing ensure the uniformity of the internal and external quality of the ultra-high viscosity product. Thus, through these steps, the viscosity of nitrocellulose is stabilized above 15,000 seconds while its stability exceeds 15 minutes, protecting the cellulose molecular chains from damage while removing unstable substances. Attached Figure Description

[0018] Figure 1 The diagram shows the steps of the stabilization treatment method for ultra-high viscosity nitrocellulose according to the present invention. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Example 1 Please see Figure 1 This invention provides an embodiment: a method for stabilizing ultra-high viscosity nitrocellulose, comprising the following steps: Esterification step: The refined cotton and mixed acid are esterified in an esterification machine, and the esterification temperature is controlled at 26-28℃. The low temperature environment can effectively inhibit the oxidative degradation of cellulose molecular chains by the mixed acid, and retain the high viscosity characteristics of the refined cotton raw material to the maximum extent from the source. Mixed acid supply step: In the esterification step, the flow rate of mixed acid is controlled at 15.8-16.3 m³ / h; Due to the long length and high viscosity of refined cotton fibers, it is difficult to impregnate them with acid, which can easily lead to uneven reaction. Increasing the flow rate of mixed acid can create a stronger fluid flushing and penetration effect, ensuring that the mixed acid is in full and uniform contact with each fiber, so that the esterification reaction is more thorough and avoids insufficient or excessive local reaction. Boiling and washing step: The esterified nitrocellulose is boiled and washed. The boiling and washing step includes multiple sub-steps, in which the boiling and washing temperature is gradually reduced from a higher temperature to a lower temperature. This step is used to remove unstable substances of different properties in stages and in a targeted manner. At the same time, a low temperature stage is introduced immediately after the high temperature stage. After opening the fiber cavity to discharge impurities, the system temperature and acidity are rapidly reduced to terminate the hydrolysis and damage to the cellulose molecular chain. Rinsing steps: The boiled nitrocellulose is rinsed in a rinsing machine with agitation. The mechanical agitation can break up the tangles and clumps that are easy to form between the high-viscosity nitrocellulose fibers, ensuring that the residual trace unstable substances can be fully washed out, and at the same time making the viscosity of the final product more uniform in a macroscopic way, ensuring the consistency of batch product quality.

[0021] Furthermore, the refined cotton is grade 1000 refined cotton; this grade of refined cotton itself has extremely high initial viscosity and long fiber length.

[0022] Further steps include boiling and washing: The rinsing process involves adding clean water to the rinsing tank containing nitrocellulose and rinsing under running water for 30-60 minutes until the initial acidity is ≤1.0 ml / g. The purpose is to quickly dilute and remove a large amount of free acid adhering to the fiber surface, rapidly reducing the initial acidity to ≤1.0 ml / g, thus providing an initial low-acid environment for subsequent heating and rinsing, and reducing the catalytic degradation of cellulose by acid during heating. Acid cooking step: Acid cooking is carried out at 86-90℃ for 2.5-4 hours; this temperature range is significantly higher than the 80℃ benchmark of the Abel stability test, which is sufficient to provide enough energy to open the fiber cavity by thermal expansion and to hydrolyze unstable substances with low bond energy and migrate them from the inside of the fiber; and this temperature range is far lower than the harsh conditions of more than 100℃ commonly used in traditional processes, thereby reducing the damage of high temperature to the cellulose molecular chain and achieving effective viscosity maintenance; Low-temperature boiling and washing steps: After acid boiling, drain the water, then add hot water at 60-70℃ and boil for 30 minutes; the purpose of draining the water is to remove the hydrolysis products and acid in the reaction system in time, so as to prevent them from partially seeping back into the fiber due to concentration balance in the subsequent process; the subsequent low-temperature boiling and washing is to further rinse the opened fiber cavities in a gentler environment and continue to remove residual unstable substances. Cold washing process: Perform two room temperature cold washes, each of which involves adding clean water to submerge the nitrocellulose and draining for 30 minutes; this step uses room temperature clean water for the final rinse, which aims to thoroughly cool the product and use the principle of concentration difference diffusion to replace the last trace amount of soluble impurities remaining inside the fiber, in order to consolidate the stability treatment effect.

[0023] Furthermore, in the acid boiling step, the temperature difference between the upper, middle, and lower parts of the boiling tank does not exceed 3°C. This is to ensure that the entire batch of nitrocellulose is heated evenly during the boiling process, and to avoid uneven quality issues caused by local overheating leading to viscosity loss or local undercooling leading to incomplete stabilization treatment.

[0024] Furthermore, in the acid boiling step, the acid boiling temperature range is 86-90℃.

[0025] Furthermore, in the cold washing step, tap water is used for cold washing, which is economical and convenient, and the final purification is completed through physical diffusion.

[0026] Furthermore, in the rinsing step, the stirring and rinsing time is 50 minutes. This duration ensures sufficient mixing and washing effects without causing unnecessary damage to the high-viscosity fibers due to excessive mechanical shearing.

[0027] Furthermore, before the esterification step, the process includes: adding refined cotton to the esterification machine through a refined cotton inlet pipe, and adding mixed acid to the esterification machine through a mixed acid inlet pipe.

[0028] Furthermore, the esterification step is followed by a centrifugation step and a washing step. The centrifugation step and the washing step are routine processes in the production of nitrocellulose, used to initially remove the mother acid and perform a preliminary washing to prepare for the boiling step.

[0029] Furthermore, in the boiling and washing process, the temperature decreases in stages by controlling heating and drainage, and the power of the heating system and the drainage operation between each step are controlled by program or manual control.

[0030] Through the above steps, low-temperature esterification (26-28℃) maximizes the protection of cellulose molecular chains from the reaction source, laying the foundation for high viscosity. Increasing the mixed acid flow rate (15.8-16.3 m³ / h) ensures the uniformity and thoroughness of the reaction of ultra-high viscosity raw materials. The temperature-decreasing graded washing process utilizes the physicochemical effects of different temperature ranges to first open the fiber structure, hydrolyze and remove the main unstable substances at a sufficiently high temperature (86-90℃), followed by rapid cooling and rinsing in a medium-low temperature environment. This effectively removes unstable substances while inhibiting the hydrolytic degradation of cellulose in a high-temperature, strong acid environment. Stirring and rinsing ensure the uniformity of the internal and external quality of the ultra-high viscosity product. Thus, through the above steps, the viscosity of nitrocellulose products is stabilized at over 15,000 seconds, while its stability exceeds 15 minutes, protecting the cellulose molecular chains from damage while removing unstable substances.

[0031] Example 2 Optionally, the present invention provides another embodiment, which provides a method for stabilizing ultra-high viscosity nitrocellulose, the specific implementation steps of which are as follows: Raw material preparation and feeding: 1000 grade refined cotton is added to the esterification machine through the refined cotton inlet pipe. The refined cotton has an α-cellulose content of ≥95% and a degree of polymerization controlled within the range of 1800-2000. Mixed acid is continuously added to the esterification machine through the mixed acid inlet pipe. The mixed acid composition is: nitric acid 58-60%, sulfuric acid 28-30%, and water 10-14%.

[0032] Esterification reaction: The esterification reaction temperature is controlled within the range of 26-28℃, and the temperature is precisely controlled by the jacket cooling water system; the mixed acid flow rate is stably controlled at 15.8-16.3 m³ / h to ensure that the mixed acid and refined cotton fibers are in full contact; the esterification reaction time is controlled at 45-60 minutes; at this stage, the low temperature environment effectively protects the cellulose molecular chains from being damaged, laying the foundation for obtaining high viscosity products in the future.

[0033] Its reaction principle can be represented by the following equation:

[0034] Here, n represents the degree of polymerization of cellulose, and maintaining a high n value is key to obtaining high-viscosity products.

[0035] Preliminary separation and washing: After the esterification reaction is completed, the material is sent to a centrifuge for centrifugal separation to remove most of the mother acid; then it enters a water washing machine for preliminary water washing to remove the residual acid adhering to the surface.

[0036] The boiling and washing process involves progressively decreasing temperatures and is divided into four stages: Thorough washing stage: Transfer the material into the washing tank, add clean water to completely submerge the nitrocellulose, and turn on the continuous flow of water for thorough washing; control the washing time to 45 minutes, and continuously monitor the acidity of the discharged water during the process. When the acidity drops to ≤1.0 ml / g, proceed to the next stage; this stage mainly removes free acid and some water-soluble impurities from the fiber surface.

[0037] Pickling stage: Turn off the continuous water flow and start heating to 86-90℃; maintain this temperature for 3 hours; during the boiling process, the temperature is monitored in real time by temperature sensors distributed in the upper, middle and lower layers of the boiling tank to ensure that the temperature difference between each layer does not exceed 3℃; the purpose of this stage is to use the moderate temperature to heat and expand the fiber cavity, which promotes the hydrolysis and dissolution of unstable substances such as sulfate esters and nitrate-sulfur mixed esters inside. The main chemical reactions during the pickling process are:

[0038]

[0039] R represents a cellulose group.

[0040] Low-temperature boiling and washing stage: After the acid boiling is complete, quickly drain the hot acid water and immediately add hot water at 60-70℃ to continue boiling for 30 minutes. The temperature selection at this stage ensures the continued removal of unstable substances while avoiding excessive damage to the cellulose molecular chains.

[0041] Cold washing stage: Perform two cold washes at room temperature, each time adding tap water to submerge the nitrocellulose, letting it stand for 30 minutes, and then draining the water; this stage utilizes the principle of rapid temperature drop and concentration difference diffusion to further remove trace impurities remaining inside the fibers.

[0042] Stirring and rinsing steps: After boiling and washing, the product is transferred to a rinsing machine with agitation and stirred at 30-40 rpm for 50 minutes. The stirring action ensures the uniformity of the high molecular weight, high viscosity nitrocellulose product and promotes the removal of the final residual impurities.

[0043] Example 3 Optionally, the present invention provides another embodiment, the main difference between this embodiment and embodiment 2 being the optimization of the boiling and washing process parameters: During the acid cooking stage, a stepped heating method is adopted: first, maintain at 86℃ for 1 hour, then maintain at 88℃ for 1.5 hours, and finally maintain at 90℃ for 0.5 hours. This stepped heating method can better control the opening process of fiber cavities and avoid fiber damage caused by rapid temperature changes.

[0044] During the low-temperature washing stage, the temperature is controlled at 65°C and the time is extended to 45 minutes; this optimization is suitable for products with longer fibers and higher viscosity, and can more thoroughly remove unstable substances inside the fibers.

[0045] Example 4 Optionally, the present invention provides another embodiment, which optimizes the rinsing process, specifically as follows: During the mixing and rinsing stage, an intermittent mixing method is adopted: first, mix at 40 rpm for 10 minutes, then stop for 5 minutes, and then mix at 30 rpm for 15 minutes, and repeat this cycle twice; this intermittent mixing not only ensures the mixing effect, but also reduces the molecular chain breakage that may be caused by continuous shearing.

[0046] Comparative Example The traditional high-temperature boiling and washing process is adopted: esterification temperature 32-35℃, mixed acid flow rate 14-15 m³ / h, boiling and washing temperature 98-100℃, boiling and washing time 4 hours, without temperature reduction and graded boiling and washing steps.

[0047] Specifically, performance tests were conducted on the products obtained in Embodiments 2-4 and the comparative example of the present invention, and the results are shown in the table below:

[0048] Test results show that the nitrocellulose products prepared using the method of this invention all have a viscosity of over 15,000 seconds, and an Abel stability value of over 15 points, achieving a balance between high viscosity and high stability. In contrast, the traditional method used in the comparison sample, although achieving the basic stability requirements, resulted in significant viscosity loss, failing to meet the application requirements of ultra-high viscosity products.

[0049] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for stabilizing ultra-high viscosity nitrocellulose, characterized in that: Includes the following steps: Esterification step: The refined cotton and mixed acid are esterified in an esterification machine, and the esterification temperature is controlled at 26-28℃. Mixed acid supply step: In the esterification step, the flow rate of the mixed acid is controlled at 15.8-16.3 m³ / h; Boiling and washing step: The esterified nitrocellulose is boiled and washed. The boiling and washing step includes multiple sub-steps, wherein the boiling and washing temperature is gradually reduced from a higher temperature to a lower temperature. Rinsing steps: The boiled nitrocellulose is rinsed and stirred in a rinsing machine with agitation.

2. The stabilization treatment method for ultra-high viscosity nitrocellulose according to claim 1, characterized in that: The refined cotton is grade 1000 refined cotton.

3. The stabilization treatment method for ultra-high viscosity nitrocellulose according to claim 1, characterized in that: The boiling and washing steps include: Thorough rinsing procedure: Add clean water to the rinsing tank containing nitrocellulose and rinse with running water for 30-60 minutes until the acidity is ≤1.0 ml / g; Sour boiling process: Boil the seeds at 86-90℃ for 2.5-4 hours; Low-temperature boiling and washing steps: After acid boiling, drain the water, then add hot water at 60-70℃ and boil for 30 minutes; Cold wash procedure: Perform two room temperature cold washes. Each cold wash includes adding clean water to submerge the nitrocellulose and draining for 30 minutes.

4. The stabilization treatment method for ultra-high viscosity nitrocellulose according to claim 3, characterized in that: In the acid boiling step, the temperature difference between the upper, middle and lower parts of the boiling tank does not exceed 3°C.

5. The stabilization treatment method for ultra-high viscosity nitrocellulose according to claim 3, characterized in that: In the acid boiling step, the acid boiling temperature range is 86-90℃.

6. The stabilization treatment method for ultra-high viscosity nitrocellulose according to claim 3, characterized in that: In the cold washing step, tap water is used for cold washing.

7. The stabilization treatment method for ultra-high viscosity nitrocellulose according to claim 1, characterized in that: In the rinsing step, the stirring and rinsing time is 50 minutes.

8. The stabilization treatment method for ultra-high viscosity nitrocellulose according to claim 1, characterized in that: The process before the esterification step also includes: adding refined cotton to the esterification machine through a refined cotton inlet pipe, and adding mixed acid to the esterification machine through a mixed acid inlet pipe.

9. The stabilization treatment method for ultra-high viscosity nitrocellulose according to claim 1, characterized in that: The esterification step is followed by a centrifugation step and a water washing step.

10. The method for stabilizing ultra-high viscosity nitrocellulose according to claim 1, characterized in that: In the boiling and washing step, the temperature decreases in stages by controlling heating and drainage.

Images