Process for the preparation of a low temperature resistant chlorinated polyethylene

Abstract

This invention discloses a method for preparing low-temperature resistant chlorinated polyethylene, belonging to the technical field of chlorinated polyethylene preparation. The preparation method includes the following steps: raw material preparation, chlorination reaction, and post-treatment. In the chlorination reaction, deionized water, high-density polyethylene powder, a swelling agent, and a first dispersant are added to a reaction vessel for swelling. Alkaline earth metal oxides are added, and the mixture is stirred at room temperature. A second dispersant, emulsifier, and initiator are added, and the mixture is stirred again. An anti-adhesion agent is added, the reaction vessel is sealed, and the temperature is raised to 75-80°C. A vacuum is drawn to a pressure of -0.04 MPa to -0.03 MPa, and a first chlorine gas is introduced. The temperature is raised to 110-115°C, and a second chlorine gas is introduced. The temperature is raised to 134-136°C, and a third chlorine gas is introduced. The chlorine gas introduction is stopped, and the mixture is cooled to room temperature. The chlorinated polyethylene prepared by this invention exhibits good low-temperature resistance, low colored particle number and ash content, high tensile strength, and low Shore hardness.

Description

Technical Field

[0001] This invention relates to the field of chlorinated polyethylene preparation technology, and specifically to a method for preparing low-temperature resistant chlorinated polyethylene. Background Technology

[0002] Chlorinated polyethylene (CPE) is a high-molecular-weight polymer material produced by the free radical chlorination reaction of high-density polyethylene (HDPE) and chlorine. Based on its structure and applications, CPE can be classified into resin-type CPE, coating / adhesive-type CPE, and rubber-type CPE. Resin-type CPE has a high relative molecular mass, strong toughness, low melting temperature, and low plasticizing temperature. It is mainly used as a modifier to improve the weather resistance and impact resistance of general-purpose resins such as polyvinyl chloride (PVC), polypropylene (PP), and polyethylene (PE). Coating / adhesive-type CPE has good corrosion resistance and weather resistance, excellent solubility, strong adhesion, and rapid drying. It is mainly used to manufacture flame-retardant, wear-resistant anti-corrosion coatings, high-grade adhesives, and high-grade inks. Rubber-type CPE has moderate mechanical strength, low melt viscosity, and low plasticizing temperature, and is mainly used as a specialty rubber.

[0003] Existing methods for preparing chlorinated polyethylene mainly include solvent methods, aqueous suspension methods, and gas-solid phase methods. Among these, the aqueous suspension method involves suspending high-density polyethylene powder in water, then adding dispersants, initiators, defoamers, and antistatic agents. Under stirring, a certain amount of chlorine gas is pressurized and introduced to initiate the reaction. The reaction is stopped when the chlorine content reaches the desired level, followed by washing, neutralization, dehydration, and drying to obtain the chlorinated polyethylene product. The aqueous suspension method not only offers advantages such as stable operation, high chlorine utilization, and stable chlorine content in the product, but also, compared to the solvent method, lower production costs, better product quality, and suitability for large-scale production due to the use of water as the reaction solvent. Therefore, chlorinated polyethylene manufacturers in my country currently primarily use the aqueous suspension method.

[0004] During the preparation of chlorinated polyethylene, the introduction of chlorine alters the regularity of high-density polyethylene, transforming it from a highly crystalline rigid structure into an amorphous flexible structure. Therefore, the resulting rubber-type chlorinated polyethylene not only exhibits good heat resistance, chemical resistance, and processing performance, but also has a low brittle temperature. Consequently, the overall performance of oil-resistant hoses and cable sheaths made from rubber-type chlorinated polyethylene is superior to that of other synthetic rubbers. With the global energy structure shifting towards renewable energy, and the continuous expansion of deep-sea wind power and polar power transmission and distribution projects, the performance degradation of cable sheath materials under extreme low-temperature environments has become a bottleneck restricting the reliability of power systems. When the ambient temperature is too low, the chain segment movement of rubber-type chlorinated polyethylene is hindered, leading to embrittlement and cracking, thus affecting its application as a cable sheath material in extreme low-temperature environments.

[0005] Studies have shown that the low-temperature resistance of rubber-type chlorinated polyethylene is related to its chlorine content, chlorine atom distribution, and residual crystallinity. Generally speaking, when the chlorine content of rubber-type chlorinated polyethylene varies between 25% and 40%, the higher the chlorine content, the higher the glass transition temperature and the worse the low-temperature resistance. The more uniform the chlorine atom distribution, the more flexible the molecular chain of rubber-type chlorinated polyethylene, and the better the low-temperature resistance. The lower the residual crystallinity, the more flexible the molecular chain of rubber-type chlorinated polyethylene, and the better the low-temperature resistance. However, when preparing rubber-type chlorinated polyethylene using the aqueous suspension method, the traditional chlorination method employs a two-stage chlorination reaction. The temperature of the first-stage chlorination reaction is generally controlled at 75-90℃, and the temperature of the second-stage chlorination reaction is generally controlled at 100-125℃. Its advantages are that the reaction is easy to control, the operation is convenient, the production efficiency is high, and the energy-saving effect is obvious. However, since the first-stage chlorination reaction is carried out at a relatively low temperature, chlorine atoms are bound to the surface of high-density polyethylene and are densely distributed. As the second-stage chlorination reaction proceeds, although the chlorination reaction can take place inside the high-density polyethylene, the crystals of the high-density polyethylene are not completely broken because the chlorination reaction temperature is much lower than the crystallization melting point of high-density polyethylene. Therefore, the chlorine atom distribution of the obtained rubber-type chlorinated polyethylene product is uneven, and the residual crystallinity is high, which in turn affects the low-temperature resistance of the rubber-type chlorinated polyethylene product.

[0006] To address the above problems, common solutions include: employing a three-stage chlorination reaction method. The first stage chlorination reaction temperature is controlled at 75-110℃, the second stage at 110-125℃, and the third stage at 125℃, which is the melting point of high-density polyethylene. The uniformity of the chlorination reaction is ensured by controlling the amount of chlorine introduced in each stage. Furthermore, selecting high-density polyethylene raw materials with small particle size, low density, and loose surface further guarantees the uniformity of the chlorination reaction, thereby reducing the residual crystallinity of the resulting rubber-type chlorinated polyethylene product. However, the following problems still exist: First, in the aqueous suspension method, the chlorination reaction proceeds gradually from the surface of the high-density polyethylene powder inwards. Therefore, the chlorination reaction process is uneven across the entire high-density polyethylene powder. The lower the chlorine content, the lower the uniformity of the chlorination reaction process. In order to obtain low-temperature resistant chlorinated polyethylene, and considering the good low-temperature resistance of rubber-type chlorinated polyethylene with low chlorine content, the chlorine content of rubber-type chlorinated polyethylene is generally controlled to about 30%. This results in a generally uneven chlorination reaction, which in turn affects the low-temperature resistance and strength of rubber-type chlorinated polyethylene products. Secondly, in the three-stage chlorination reaction method, in the initial stage of the chlorination reaction, in order to prevent the chlorination reaction rate from being too fast and causing excessive chlorination on the surface of high-density polyethylene, the chlorine flow rate needs to be reduced. As the chlorination reaction intensifies, the chlorine flow rate is appropriately increased. The material layer is stirred and tumbled, resulting in a fast reaction rate and high chlorine utilization. When the reaction temperature approaches the melting point of high-density polyethylene (HDPE), the reaction takes place within the crystalline region of HDPE. The chlorine supply is then appropriately increased, and the reaction time is extended to ensure the complete chlorination reaction. This allows sufficient time to break down the HDPE crystals, making the chlorination reaction more uniform and reducing the residual crystallinity and Shore hardness of the chlorinated polyethylene. However, since the chlorination reaction is exothermic, the temperature may become too high in the third stage of the chlorination reaction, leading to discoloration of the prepared rubber-type chlorinated polyethylene. This, in turn, increases the number of colored particles and the ash content of the prepared rubber-type chlorinated polyethylene. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for preparing low-temperature resistant chlorinated polyethylene. The prepared chlorinated polyethylene exhibits good low-temperature resistance, low colored particle count and ash content, high tensile strength, and low Shore hardness.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for preparing low-temperature resistant chlorinated polyethylene, comprising the steps of: raw material preparation, chlorination reaction, and post-treatment; The raw material preparation involves weighing deionized water, high-density polyethylene powder, alkaline earth metal oxides, swelling agent, anti-adhesion agent, dispersant, emulsifier, and initiator. In the preparation of the raw materials, the mass ratio of deionized water, high-density polyethylene powder, alkaline earth metal oxide, swelling agent, anti-adhesion agent, dispersant, emulsifier, and initiator is 5000-6000:600:140-150:25-30:8-9:12-13:6-7:2.5-3. The alkaline earth metal oxide is treated magnesium oxide. The treatment method is as follows: magnesium oxide and deionized water are mixed and stirred at room temperature for 30-60 minutes. Sodium stearate and polyethylene glycol are added, the temperature is raised to 78-82℃, and the mixture is stirred at 78-82℃ for 1-1.5 hours. The mixture is then cooled to room temperature, centrifuged, and the precipitate is washed with deionized water and dried. In the treatment method for the treated magnesium oxide, the particle size of the magnesium oxide is 1 μm; The number average molecular weight of polyethylene glycol is 2000; The mass ratio of magnesium oxide, deionized water, sodium stearate, and polyethylene glycol is 200:2000-2200:12-13:4-4.5; The swelling agent is dibutyl phthalate; The anti-adhesion agent is treated quartz sand. The treatment method is as follows: mix quartz sand, nonionic surfactant and deionized water, stir at room temperature for 30-60 minutes, filter, take the precipitate and dry it. In the method for treating the quartz sand, the particle size of the quartz sand is between 20 and 40 mesh. The nonionic surfactant is nonionic surfactant NP-10; The mass ratio of quartz sand, nonionic surfactant, and deionized water is 10:0.6-0.65:1000-1200; The dispersant is a mixture of hydroxypropyl methylcellulose and polyvinyl alcohol; the mass ratio of hydroxypropyl methylcellulose to polyvinyl alcohol is 8-9:4; the hydroxypropyl methylcellulose is of type E15M and the polyvinyl alcohol is of type 17-88. The emulsifier is hexadecyltrimethylammonium chloride; The initiator is benzoyl peroxide; The chlorination reaction involves adding deionized water, high-density polyethylene powder, swelling agent, and a first dispersant to a reaction vessel for swelling. Alkaline earth metal oxide is then added, and the mixture is stirred at room temperature for 10-20 minutes. A second dispersant, emulsifier, and initiator are added, and the mixture is stirred for another 10-20 minutes. An anti-adhesion agent is then added, and the reaction vessel is sealed. The temperature is raised to 75-80°C, and a vacuum is drawn to a pressure of -0.04 MPa to -0.03 MPa. A first chlorine gas is introduced, and the temperature is raised to 110-115°C. A second chlorine gas is introduced, and the temperature is raised to 134-136°C. A third chlorine gas is introduced, and the chlorine gas introduction is stopped. The mixture is then cooled to room temperature to obtain a chlorinated polyethylene suspension. In the chlorination reaction, the mass ratio of deionized water, high-density polyethylene powder, swelling agent, first dispersant, alkaline earth metal oxide, second dispersant, emulsifier, initiator, and anti-adhesion agent is 5000-6000:600:25-30:4-4.2:140-150:8-8.8:6-7:2.5-3:8-9; The swelling method is as follows: stir at room temperature for 10-15 minutes, seal the reaction vessel, heat to 60-65℃, evacuate to a pressure of -0.04MPa to -0.03MPa inside the reaction vessel, introduce nitrogen gas to a pressure of 1.5-2MPa inside the reaction vessel, introduce chlorine gas at a rate of 10-15g / min, stir for 5-10 minutes, stop stirring and let stand for 30-60 minutes, replace the gas inside the reaction vessel with nitrogen gas, and then open the reaction vessel. The mass ratio of chlorine gas introduced during the swelling to the mass ratio of high-density polyethylene powder added during the chlorination reaction is 90-95:600. The rate of introducing the first chlorine gas is 10-15 g / min, and the mass ratio of the first chlorine gas to the high-density polyethylene powder is 240-250:600. The stirring speed should be controlled at 30-50 rpm when the first batch of chlorine gas is introduced. The rate of introducing the second chlorine gas is 10-15 g / min, and the mass ratio of the second chlorine gas to the high-density polyethylene powder is 150-160:600. The stirring speed should be controlled at 100-200 rpm when the second chlorine gas is introduced; The rate of introducing the third chlorine gas is 20-30 g / min, and the mass ratio of the third chlorine gas to the high-density polyethylene powder is 200-210:600. The stirring speed should be controlled at 200-300 rpm when the third chlorine gas is introduced; The post-processing involves separating the chlorinated polyethylene from the chlorinated polyethylene suspension by filtration, washing with deionized water until the pH of the washing water reaches 5-6, and then vacuum drying to obtain chlorinated polyethylene.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows: The chlorinated polyethylene prepared by this invention has a chlorine content of 30.2-30.5%, a residual crystallinity of 1.1-1.5%, a glass transition temperature of -25.5℃ to -25.4℃, a colored particle number of 26-30 / 200g, an ash content of 1.9-2.5%, a tensile strength of 13.9-14.5MPa, a Shore A hardness of 56-60, and low-temperature flexibility (-55℃, 4h) without cracks. Detailed Implementation

[0010] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0011] The high-density polyethylene powder used in Examples 1-6 was from the same production batch.

[0012] The high-density polyethylene powder used in Examples 1-6 is metallocene high-density polyethylene powder with a melt index of 1 g / 10 min at 190°C and 5 kg load, a melt flow ratio of 9.5, a water content of 0.15 wt%, and a particle size of 90 μm.

[0013] When detecting the chlorine content of the chlorinated polyethylene prepared in Examples 1-6, the oxygen flask combustion method was used. Specifically, the chlorinated polyethylene sample was burned in an oxygen flask containing potassium hydroxide and hydrogen peroxide with a platinum wire as a catalyst. The carbon and hydrogen in the chlorinated polyethylene sample were oxidized, and the chlorine was converted to potassium salt. Then, using diphenylazohydrazine as an indicator, titration was performed with a mercuric nitrate standard solution. The chlorine content in the chlorinated polyethylene sample was calculated according to the following formula: Chlorine content = [(V1-V2)×c×35.45×2] / m×100%; Wherein, V1 and V2 are the volumes (mL) of mercuric nitrate standard solution consumed by the chlorinated polyethylene test sample and blank control sample during titration, respectively. c represents the concentration (mol / L) of the mercuric nitrate standard solution. m represents the mass (mg) of the chlorinated polyethylene sample being tested.

[0014] When testing the residual crystallinity of the chlorinated polyethylene prepared in Examples 1-6, the method specified in the chemical industry standard was adopted. The specific testing method was as follows: After dissolving the chlorinated polyethylene test sample in a mixed solvent, the randomly chlorinated polyethylene dissolved in the solvent, while the unchlorinated crystalline polyethylene was separated by filtration and then dried to obtain the crystalline residue. The residual crystallinity of the chlorinated polyethylene test sample was calculated according to the following formula: Residual crystallinity = m1 / m × 100%; m1 is the mass (g) of the crystallized residue; m represents the mass (g) of the chlorinated polyethylene sample being tested.

[0015] When testing the tensile strength of the chlorinated polyethylene prepared in Examples 1-6, GB / T 528-2009 standard was used as a reference.

[0016] When testing the Shore hardness of the chlorinated polyethylene prepared in Examples 1-6, the standard GB / T 531-2008 was referenced.

[0017] When testing the glass transition temperature of the chlorinated polyethylene prepared in Examples 1-6, the standard GB / T19466-2004 was followed.

[0018] Example 1 This embodiment provides a method for preparing low-temperature resistant chlorinated polyethylene, the steps of which are as follows: 1. Raw material preparation: Weigh 5000g deionized water, 600g high-density polyethylene powder, 140g alkaline earth metal oxide, 25g swelling agent, 8g anti-adhesion agent, 12g dispersant, 6g emulsifier, and 2.5g initiator; The alkaline earth metal oxide is treated magnesium oxide. The treatment method is as follows: 200g of magnesium oxide with a particle size of 1μm and 2000g of deionized water are added to a reaction vessel. The stirring speed of the reaction vessel is controlled at 100rpm. Stir for 30min at room temperature. Add 12g of sodium stearate and 4g of polyethylene glycol with a number average molecular weight of 2000. Heat to 80℃ and stir at 100rpm for 1h at 80℃. Cool to room temperature, centrifuge, take the precipitate, wash it 3 times with deionized water, and dry it at 110℃. The swelling agent is dibutyl phthalate; The anti-adhesion agent is treated quartz sand. The treatment method is as follows: 10g of quartz sand with a particle size between 20-40 mesh, 0.6g of nonionic surfactant NP-10, and 1000g of deionized water are added to a reaction vessel. The stirring speed of the reaction vessel is controlled at 100rpm. The mixture is stirred at room temperature for 30min, filtered, and the precipitate is dried at 110℃. The dispersant is a mixture of hydroxypropyl methylcellulose and polyvinyl alcohol; the mass ratio of hydroxypropyl methylcellulose to polyvinyl alcohol is 8:4; the hydroxypropyl methylcellulose is of type E15M and the polyvinyl alcohol is of type 17-88. The emulsifier is hexadecyltrimethylammonium chloride; The initiator is benzoyl peroxide; 2. Chlorination Reaction: Add 5000g deionized water, 600g high-density polyethylene powder, 25g swelling agent, and 4g dispersant to the reactor. Control the stirring speed in the reactor at 200rpm and stir for 10min at room temperature. Seal the reactor, heat to 60℃, and evacuate to a pressure of -0.04MPa inside the reactor. Introduce nitrogen until the pressure inside the reactor reaches 1.5MPa. Introduce 90g chlorine gas at a rate of 10g / min and stir for 5min. Stop stirring and let stand for 30min. After purging the reactor with nitrogen, open the reactor, add 140g alkaline earth metal oxide, and control the stirring speed in the reactor at 30rpm. Stir at room temperature for 10 minutes, add 8g dispersant, 6g emulsifier, and 2.5g initiator, stir for 10 minutes, add 8g anti-adhesion agent, seal the reactor, heat to 75℃, evacuate to -0.04MPa inside the reactor, introduce 240g chlorine gas at a rate of 10g / min, control the stirring speed of the reactor at 100rpm, heat to 110℃, introduce 150g chlorine gas at a rate of 10g / min, control the stirring speed of the reactor at 200rpm, heat to 134℃, introduce 200g chlorine gas at a rate of 20g / min, stop introducing chlorine gas, cool to room temperature, and obtain chlorinated polyethylene suspension; 3. Post-processing: Taking advantage of the particle size difference between alkaline earth metal oxides, anti-adhesion agents, and chlorinated polyethylene, the chlorinated polyethylene in the suspension is separated by filtration. The suspension is washed with deionized water until the pH of the washing water is 5, and then vacuum dried at 80°C to obtain chlorinated polyethylene.

[0019] Example 2 This embodiment provides a method for preparing low-temperature resistant chlorinated polyethylene, the steps of which are as follows: 1. Raw material preparation: Weigh 6000g deionized water, 600g high-density polyethylene powder, 150g alkaline earth metal oxide, 30g swelling agent, 9g anti-adhesion agent, 13g dispersant, 7g emulsifier, and 3g initiator; The alkaline earth metal oxide is treated magnesium oxide. The treatment method is as follows: 200g of magnesium oxide with a particle size of 1μm and 2000g of deionized water are added to a reaction vessel. The stirring speed of the reaction vessel is controlled at 100rpm. Stir for 30min at room temperature. Add 12g of sodium stearate and 4g of polyethylene glycol with a number average molecular weight of 2000. Heat to 80℃ and stir at 100rpm for 1h at 80℃. Cool to room temperature, centrifuge, take the precipitate, wash it 3 times with deionized water, and dry it at 110℃. The swelling agent is dibutyl phthalate; The anti-adhesion agent is treated quartz sand. The treatment method is as follows: 10g of quartz sand with a particle size between 20-40 mesh, 0.6g of nonionic surfactant NP-10, and 1000g of deionized water are added to a reaction vessel. The stirring speed of the reaction vessel is controlled at 100rpm. The mixture is stirred at room temperature for 30min, filtered, and the precipitate is dried at 110℃. The dispersant is a mixture of hydroxypropyl methylcellulose and polyvinyl alcohol; the mass ratio of hydroxypropyl methylcellulose to polyvinyl alcohol is 9:4; the hydroxypropyl methylcellulose is of type E15M and the polyvinyl alcohol is of type 17-88. The emulsifier is hexadecyltrimethylammonium chloride; The initiator is benzoyl peroxide; 2. Chlorination Reaction: Add 6000g deionized water, 600g high-density polyethylene powder, 30g swelling agent, and 4.2g dispersant to the reactor. Control the stirring speed of the reactor at 300rpm and stir for 15min at room temperature. Seal the reactor, heat to 65℃, and evacuate to a pressure of -0.03MPa inside the reactor. Introduce nitrogen until the pressure inside the reactor is 2MPa. Introduce 95g chlorine gas at a rate of 15g / min and stir for 10min. Stop stirring and let stand for 60min. After replacing the gas inside the reactor with nitrogen, open the reactor, add 150g alkaline earth metal oxide, and control the stirring speed of the reactor at 50rpm. Stir at room temperature for 20 minutes, add 8.8g dispersant, 7g emulsifier, and 3g initiator, stir for 20 minutes, add 9g anti-adhesion agent, seal the reactor, heat to 80℃, evacuate to -0.03MPa inside the reactor, introduce 250g chlorine gas at a rate of 15g / min, control the stirring speed of the reactor at 200rpm, heat to 115℃, introduce 160g chlorine gas at a rate of 15g / min, control the stirring speed of the reactor at 300rpm, heat to 135℃, introduce 210g chlorine gas at a rate of 30g / min, stop introducing chlorine gas, cool to room temperature, and obtain chlorinated polyethylene suspension; 3. Post-processing: Taking advantage of the particle size difference between alkaline earth metal oxides, anti-adhesion agents, and chlorinated polyethylene, the chlorinated polyethylene in the suspension is separated by filtration. The suspension is washed with deionized water until the pH of the washing water is 6, and then vacuum dried at 85°C to obtain chlorinated polyethylene.

[0020] Example 3 This embodiment provides a method for preparing low-temperature resistant chlorinated polyethylene, the steps of which are as follows: 1. Raw material preparation: Weigh 5000g deionized water, 600g high-density polyethylene powder, 140g alkaline earth metal oxide, 25g swelling agent, 8g anti-adhesion agent, 12g dispersant, 6g emulsifier, and 2.5g initiator; The alkaline earth metal oxide is treated magnesium oxide. The treatment method is as follows: 200g of magnesium oxide with a particle size of 1μm and 2200g of deionized water are added to a reaction vessel. The stirring speed of the reaction vessel is controlled at 300rpm. The mixture is stirred at room temperature for 60min. 13g of sodium stearate and 4.5g of polyethylene glycol with a number average molecular weight of 2000 are added. The temperature is raised to 82℃ and stirred at 300rpm for 1.5h at 82℃. The mixture is cooled to room temperature, centrifuged, and the precipitate is taken. It is washed 5 times with deionized water and dried at 120℃. The swelling agent is dibutyl phthalate; The anti-adhesion agent is treated quartz sand. The treatment method is as follows: 10g of quartz sand with a particle size between 20-40 mesh, 0.6g of nonionic surfactant NP-10, and 1000g of deionized water are added to a reaction vessel. The stirring speed of the reaction vessel is controlled at 100rpm. The mixture is stirred at room temperature for 30min, filtered, and the precipitate is dried at 110℃. The dispersant is a mixture of hydroxypropyl methylcellulose and polyvinyl alcohol; the mass ratio of hydroxypropyl methylcellulose to polyvinyl alcohol is 8:4; the hydroxypropyl methylcellulose is of type E15M and the polyvinyl alcohol is of type 17-88. The emulsifier is hexadecyltrimethylammonium chloride; The initiator is benzoyl peroxide; 2. Chlorination Reaction: Add 5000g deionized water, 600g high-density polyethylene powder, 25g swelling agent, and 4g dispersant to the reactor. Control the stirring speed in the reactor at 200rpm and stir for 10min at room temperature. Seal the reactor, heat to 60℃, and evacuate to a pressure of -0.04MPa inside the reactor. Introduce nitrogen until the pressure inside the reactor reaches 1.5MPa. Introduce 90g chlorine gas at a rate of 10g / min and stir for 5min. Stop stirring and let stand for 30min. After purging the reactor with nitrogen, open the reactor, add 140g alkaline earth metal oxide, and control the stirring speed in the reactor at 30rpm. Stir at room temperature for 10 minutes, add 8g dispersant, 6g emulsifier, and 2.5g initiator, stir for 10 minutes, add 8g anti-adhesion agent, seal the reactor, heat to 75℃, evacuate to -0.04MPa inside the reactor, introduce 240g chlorine gas at a rate of 10g / min, control the stirring speed of the reactor at 100rpm, heat to 110℃, introduce 150g chlorine gas at a rate of 10g / min, control the stirring speed of the reactor at 200rpm, heat to 134℃, introduce 200g chlorine gas at a rate of 20g / min, stop introducing chlorine gas, cool to room temperature, and obtain chlorinated polyethylene suspension; 3. Post-processing: Taking advantage of the particle size difference between alkaline earth metal oxides, anti-adhesion agents, and chlorinated polyethylene, the chlorinated polyethylene in the suspension is separated by filtration. The suspension is washed with deionized water until the pH of the washing water is 5, and then vacuum dried at 80°C to obtain chlorinated polyethylene.

[0021] Example 4 This embodiment provides a method for preparing low-temperature resistant chlorinated polyethylene, the steps of which are as follows: 1. Raw material preparation: Weigh 5000g deionized water, 600g high-density polyethylene powder, 140g alkaline earth metal oxide, 25g swelling agent, 8g anti-adhesion agent, 12g dispersant, 6g emulsifier, and 2.5g initiator; The alkaline earth metal oxide is treated magnesium oxide. The treatment method is as follows: 200g of magnesium oxide with a particle size of 1μm and 2000g of deionized water are added to a reaction vessel. The stirring speed of the reaction vessel is controlled at 100rpm. Stir for 30min at room temperature. Add 12g of sodium stearate and 4g of polyethylene glycol with a number average molecular weight of 2000. Heat to 80℃ and stir at 100rpm for 1h at 80℃. Cool to room temperature, centrifuge, take the precipitate, wash it 3 times with deionized water, and dry it at 110℃. The swelling agent is dibutyl phthalate; The anti-adhesion agent is treated quartz sand. The treatment method is as follows: 10g of quartz sand with a particle size between 20-40 mesh, 0.65g of nonionic surfactant NP-10, and 1200g of deionized water are added to a reaction vessel. The stirring speed of the reaction vessel is controlled at 300rpm. The mixture is stirred at room temperature for 60min, filtered, and the precipitate is taken and dried at 120℃. The dispersant is a mixture of hydroxypropyl methylcellulose and polyvinyl alcohol; the mass ratio of hydroxypropyl methylcellulose to polyvinyl alcohol is 8:4; the hydroxypropyl methylcellulose is of type E15M and the polyvinyl alcohol is of type 17-88. The emulsifier is hexadecyltrimethylammonium chloride; The initiator is benzoyl peroxide; 2. Chlorination Reaction: Add 5000g deionized water, 600g high-density polyethylene powder, 25g swelling agent, and 4g dispersant to the reactor. Control the stirring speed in the reactor at 200rpm and stir for 10min at room temperature. Seal the reactor, heat to 60℃, and evacuate to a pressure of -0.04MPa inside the reactor. Introduce nitrogen until the pressure inside the reactor reaches 1.5MPa. Introduce 90g chlorine gas at a rate of 10g / min and stir for 5min. Stop stirring and let stand for 30min. After purging the reactor with nitrogen, open the reactor, add 140g alkaline earth metal oxide, and control the stirring speed in the reactor at 30rpm. Stir at room temperature for 10 minutes, add 8g dispersant, 6g emulsifier, and 2.5g initiator, stir for 10 minutes, add 8g anti-adhesion agent, seal the reactor, heat to 75℃, evacuate to -0.04MPa inside the reactor, introduce 240g chlorine gas at a rate of 10g / min, control the stirring speed of the reactor at 100rpm, heat to 110℃, introduce 150g chlorine gas at a rate of 10g / min, control the stirring speed of the reactor at 200rpm, heat to 134℃, introduce 200g chlorine gas at a rate of 20g / min, stop introducing chlorine gas, cool to room temperature, and obtain chlorinated polyethylene suspension; 3. Post-processing: Taking advantage of the particle size difference between alkaline earth metal oxides, anti-adhesion agents, and chlorinated polyethylene, the chlorinated polyethylene in the suspension is separated by filtration. The suspension is washed with deionized water until the pH of the washing water is 5, and then vacuum dried at 80°C to obtain chlorinated polyethylene.

[0022] Example 5 This embodiment provides a method for preparing low-temperature resistant chlorinated polyethylene, the steps of which are as follows: 1. Raw material preparation: Weigh 5000g deionized water, 600g high-density polyethylene powder, 140g alkaline earth metal oxide, 25g swelling agent, 8g anti-adhesion agent, 12g dispersant, 6g emulsifier, and 2.5g initiator; The alkaline earth metal oxide is magnesium oxide with a particle size of 1 μm; The swelling agent is dibutyl phthalate; The anti-adhesion agent is treated quartz sand. The treatment method is as follows: 10g of quartz sand with a particle size between 20-40 mesh, 0.6g of nonionic surfactant NP-10, and 1000g of deionized water are added to a reaction vessel. The stirring speed of the reaction vessel is controlled at 100rpm. The mixture is stirred at room temperature for 30min, filtered, and the precipitate is dried at 110℃. The dispersant is a mixture of hydroxypropyl methylcellulose and polyvinyl alcohol; the mass ratio of hydroxypropyl methylcellulose to polyvinyl alcohol is 8:4; the hydroxypropyl methylcellulose is of type E15M and the polyvinyl alcohol is of type 17-88. The emulsifier is hexadecyltrimethylammonium chloride; The initiator is benzoyl peroxide; 2. Chlorination Reaction: Add 5000g deionized water, 600g high-density polyethylene powder, 25g swelling agent, and 4g dispersant to the reactor. Control the stirring speed in the reactor at 200rpm and stir for 10min at room temperature. Seal the reactor, heat to 60℃, and evacuate to a pressure of -0.04MPa inside the reactor. Introduce nitrogen until the pressure inside the reactor reaches 1.5MPa. Introduce 90g chlorine gas at a rate of 10g / min and stir for 5min. Stop stirring and let stand for 30min. After purging the reactor with nitrogen, open the reactor, add 140g alkaline earth metal oxide, and control the stirring speed in the reactor at 30rpm. Stir at room temperature for 10 minutes, add 8g dispersant, 6g emulsifier, and 2.5g initiator, stir for 10 minutes, add 8g anti-adhesion agent, seal the reactor, heat to 75℃, evacuate to -0.04MPa inside the reactor, introduce 240g chlorine gas at a rate of 10g / min, control the stirring speed of the reactor at 100rpm, heat to 110℃, introduce 150g chlorine gas at a rate of 10g / min, control the stirring speed of the reactor at 200rpm, heat to 134℃, introduce 200g chlorine gas at a rate of 20g / min, stop introducing chlorine gas, cool to room temperature, and obtain chlorinated polyethylene suspension; 3. Post-processing: Taking advantage of the particle size difference between alkaline earth metal oxides, anti-adhesion agents, and chlorinated polyethylene, the chlorinated polyethylene in the suspension is separated by filtration. The suspension is washed with deionized water until the pH of the washing water is 5, and then vacuum dried at 80°C to obtain chlorinated polyethylene.

[0023] Example 6 This embodiment provides a method for preparing low-temperature resistant chlorinated polyethylene, the steps of which are as follows: 1. Raw material preparation: Weigh 5000g deionized water, 600g high-density polyethylene powder, 140g alkaline earth metal oxide, 25g swelling agent, 8g anti-adhesion agent, 12g dispersant, 6g emulsifier, and 2.5g initiator; The alkaline earth metal oxide is magnesium oxide with a particle size of 1 μm; The swelling agent is dibutyl phthalate; The anti-adhesion agent is commercially available hydrophobic silica with a particle size of 500 nm; The dispersant is a mixture of hydroxypropyl methylcellulose and polyvinyl alcohol; the mass ratio of hydroxypropyl methylcellulose to polyvinyl alcohol is 8:4; the hydroxypropyl methylcellulose is of type E15M and the polyvinyl alcohol is of type 17-88. The emulsifier is hexadecyltrimethylammonium chloride; The initiator is benzoyl peroxide; 2. Chlorination Reaction: Add 5000g deionized water, 600g high-density polyethylene powder, 25g swelling agent, and 4g dispersant to the reactor. Control the stirring speed in the reactor at 200rpm and stir for 10min at room temperature. Seal the reactor, heat to 60℃, and evacuate to a pressure of -0.04MPa inside the reactor. Introduce nitrogen until the pressure inside the reactor reaches 1.5MPa. Introduce 90g chlorine gas at a rate of 10g / min and stir for 5min. Stop stirring and let stand for 30min. After purging the reactor with nitrogen, open the reactor, add 140g alkaline earth metal oxide, and control the stirring speed in the reactor at 30rpm. Stir at room temperature for 10 minutes, add 8g dispersant, 6g emulsifier, and 2.5g initiator, stir for 10 minutes, add 8g anti-adhesion agent, seal the reactor, heat to 75℃, evacuate to -0.04MPa inside the reactor, introduce 240g chlorine gas at a rate of 10g / min, control the stirring speed of the reactor at 100rpm, heat to 110℃, introduce 150g chlorine gas at a rate of 10g / min, control the stirring speed of the reactor at 200rpm, heat to 134℃, introduce 200g chlorine gas at a rate of 20g / min, stop introducing chlorine gas, cool to room temperature, and obtain chlorinated polyethylene suspension; 3. Post-processing: Taking advantage of the particle size difference between alkaline earth metal oxides, anti-adhesion agents, and chlorinated polyethylene, the chlorinated polyethylene in the suspension is separated by filtration. The suspension is washed with deionized water until the pH of the washing water is 5, and then vacuum dried at 80°C to obtain chlorinated polyethylene.

[0024] Results and Analysis The chlorine content, residual crystallinity, glass transition temperature, number of colored particles, and ash content of the chlorinated polyethylene prepared in Examples 1-6 were detected and statistically analyzed. After vulcanization, the tensile strength, Shore hardness, and low-temperature flexibility (-55℃, 4h) were detected and statistically analyzed. The vulcanization method is as follows: By weight, 100 parts of chlorinated polyethylene, 40 parts of carbon black N774, 20 parts of dioctyl phthalate, 4 parts of calcium stearate, 3 parts of dicumyl peroxide, 3 parts of triallyl cyanurate, and 3 parts of magnesium methacrylate are mixed and then subjected to intensive mixing and vulcanization. The statistical results are as follows:

[0025] The results in the table above show that the overall performance of the chlorinated polyvinyl chloride prepared in Examples 5-6 is lower than that of the chlorinated polyethylene prepared in Examples 1-4. The difference between the preparation method of Example 5 and Example 1 is that the alkaline earth metal oxide is untreated magnesium oxide; the difference between the preparation method of Example 6 and Example 1 is that the alkaline earth metal oxide is untreated magnesium oxide, and the anti-adhesion agent is untreated hydrophobic silica. The preparation method of Example 6 is a commonly used method for preparing chlorinated polyethylene.

[0026] Compared with the preparation method of Example 6 (the commonly used preparation method for chlorinated polyethylene), the preparation methods of Examples 1-4 use a combination of hydrophobic magnesium oxide and hydrophilic anti-adhesion agent, while the preparation method of Example 6 uses a combination of hydrophilic magnesium oxide and hydrophobic silica. The preparation methods in Examples 1-4 involve a combination of hydrophobic magnesium oxide and hydrophilic quartz sand. In the chlorination reaction, hydrophobic magnesium oxide and chlorinated polyethylene are first mixed. Through the hydrophobic interaction between the hydrophobic magnesium oxide and high-density polyethylene, the hydrophobic magnesium oxide can bind to the surface of the high-density polyethylene, thereby promoting the dispersion and heat dissipation of chlorine gas, improving the uniformity of the chlorination reaction, and reducing the contact area between chlorine gas and high-density polyethylene to a certain extent, avoiding over-chlorination. The hydrophilic quartz sand can be quickly and uniformly dispersed. As the chlorination reaction proceeds, magnesium oxide reacts with hydrogen chloride generated in the reaction system, resulting in an exothermic reaction. The nonionic surfactant NP-10 bound to the surface of the hydrophilic quartz sand desorbs, increasing the interaction force between the quartz sand and high-density polyethylene, further promoting the dispersion and heat dissipation of chlorine gas. In Example 6, however, magnesium oxide has strong hydrophilicity and poor mixing with high-density polyethylene. During the chlorination reaction, heat dissipation is mainly achieved through hydrophobic silica. However, relying solely on hydrophobic silica makes it difficult to achieve rapid heat dissipation in the later stages of the chlorination reaction.

Claims

1. A method for preparing low-temperature resistant chlorinated polyethylene, characterized in that, The preparation method includes the following steps: raw material preparation, chlorination reaction, and post-treatment; The raw material preparation involves weighing deionized water, high-density polyethylene powder, alkaline earth metal oxides, swelling agent, anti-adhesion agent, dispersant, emulsifier, and initiator. The alkaline earth metal oxide is treated magnesium oxide. The treatment method is as follows: magnesium oxide and deionized water are mixed and stirred at room temperature. Sodium stearate and polyethylene glycol are added and stirred at 78-82°C. After cooling to room temperature, the mixture is centrifuged, the precipitate is collected, washed with deionized water, and dried. The anti-adhesion agent is treated quartz sand. The treatment method is as follows: mix quartz sand, nonionic surfactant and deionized water, stir at room temperature, filter, take the precipitate and dry. The chlorination reaction involves adding deionized water, high-density polyethylene powder, a swelling agent, and a first portion of dispersant to a reaction vessel for swelling. Alkaline earth metal oxide is then added, and the mixture is stirred at room temperature. A second portion of dispersant, emulsifier, and initiator are added, and the mixture is stirred again. An anti-adhesion agent is added, and the reaction vessel is sealed. The temperature is raised to 75-80°C, and a vacuum is drawn to a pressure of -0.04 MPa to -0.03 MPa. A first portion of chlorine gas is introduced, and the temperature is raised to 110-115°C. A second portion of chlorine gas is introduced, and the temperature is raised to 134-136°C. A third portion of chlorine gas is introduced, and the chlorine gas introduction is stopped. The mixture is then cooled to room temperature to obtain a chlorinated polyethylene suspension.

2. The method for preparing low-temperature resistant chlorinated polyethylene according to claim 1, characterized in that, In the preparation of the raw materials, the mass ratio of deionized water, high-density polyethylene powder, alkaline earth metal oxide, swelling agent, anti-adhesion agent, dispersant, emulsifier and initiator is 5000-6000:600:140-150:25-30:8-9:12-13:6-7:2.5-3.

3. The method for preparing low-temperature resistant chlorinated polyethylene according to claim 1, characterized in that, In the treatment method for the treated magnesium oxide, the particle size of the magnesium oxide is 1 μm; The number average molecular weight of polyethylene glycol is 2000; The mass ratio of magnesium oxide, deionized water, sodium stearate, and polyethylene glycol is 200:2000-2200:12-13:4-4.5; The swelling agent is dibutyl phthalate.

4. The method for preparing low-temperature resistant chlorinated polyethylene according to claim 1, characterized in that, In the method for treating the quartz sand, the particle size of the quartz sand is between 20 and 40 mesh. The nonionic surfactant is nonionic surfactant NP-10; The mass ratio of quartz sand, nonionic surfactant, and deionized water is 10:0.6-0.65:1000-1200.

5. The method for preparing low-temperature resistant chlorinated polyethylene according to claim 1, characterized in that, The dispersant is a mixture of hydroxypropyl methylcellulose and polyvinyl alcohol; the mass ratio of hydroxypropyl methylcellulose to polyvinyl alcohol is 8-9:4; the hydroxypropyl methylcellulose is of type E15M and the polyvinyl alcohol is of type 17-88. The emulsifier is hexadecyltrimethylammonium chloride; The initiator is benzoyl peroxide.

6. The method for preparing low-temperature resistant chlorinated polyethylene according to claim 1, characterized in that, In the chlorination reaction, the mass ratio of deionized water, high-density polyethylene powder, swelling agent, first dispersant, alkaline earth metal oxide, second dispersant, emulsifier, initiator, and anti-adhesion agent is 5000-6000:600:25-30:4-4.2:140-150:8-8.8:6-7:2.5-3:8-9.

7. The method for preparing low-temperature resistant chlorinated polyethylene according to claim 1, characterized in that, The swelling method is as follows: stirring at room temperature, sealing the reaction vessel, heating to 60-65℃, evacuating to a pressure of -0.04MPa to -0.03MPa inside the reaction vessel, introducing nitrogen to a pressure of 1.5-2MPa inside the reaction vessel, introducing chlorine at a rate of 10-15g / min, stirring, stopping stirring and letting stand, replacing the gas inside the reaction vessel with nitrogen, and then opening the reaction vessel. The mass ratio of chlorine gas introduced during the swelling to the mass ratio of high-density polyethylene powder added during the chlorination reaction is 90-95:

600.

8. The method for preparing low-temperature resistant chlorinated polyethylene according to claim 1, characterized in that, The rate of introducing the first chlorine gas is 10-15 g / min, and the mass ratio of the first chlorine gas to the high-density polyethylene powder is 240-250:

600. The stirring speed should be controlled at 30-50 rpm when the first batch of chlorine gas is introduced. The rate of introducing the second chlorine gas is 10-15 g / min, and the mass ratio of the second chlorine gas to the high-density polyethylene powder is 150-160:

600. The stirring speed should be controlled at 100-200 rpm when the second chlorine gas is introduced; The rate of introducing the third chlorine gas is 20-30 g / min, and the mass ratio of the third chlorine gas to the high-density polyethylene powder is 200-210:

600. The stirring speed should be controlled at 200-300 rpm when the third chlorine gas is introduced.

9. The method for preparing low-temperature resistant chlorinated polyethylene according to claim 1, characterized in that, The post-processing involves separating the chlorinated polyethylene from the chlorinated polyethylene suspension by filtration, washing with deionized water until the pH of the washing water reaches 5-6, and then vacuum drying to obtain chlorinated polyethylene.

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