High porosity chlorinated polyethylene special resin and method for preparing the same

Abstract

The application belongs to the technical field of polymer materials, and particularly discloses a high-pore-volume special resin for chlorinated polyethylene and a preparation method thereof, which comprises the following steps: S1, powder polyethylene resin is put into a first stirring kettle, vacuum is drawn to a predetermined vacuum degree, constant pressure is kept, and oxygen in the first stirring kettle and the pores of the polyethylene resin is discharged; S2, inert gas is introduced into the first stirring kettle to a predetermined pressure, the inert gas is allowed to permeate into the pores of the polyethylene resin, and the temperature is raised to a predetermined temperature; as the temperature rises, the polyethylene resin gradually softens; S3, the softened polyethylene resin filled with inert gas is transported to a low-temperature and low-pressure second stirring kettle, under the action of pressure difference, the inert gas in the pores of the polyethylene resin instantaneously expands and releases, the pores of the softened resin are enlarged by the gas expansion effect, and as the polyethylene resin is in a low-temperature environment, the polyethylene resin solidifies, the resin pores no longer shrink, and thus the high-pore-volume special resin for chlorinated polyethylene is obtained.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a high-porosity chlorinated polyethylene resin and its preparation method. Background Technology

[0002] Chlorinated polyethylene (CPE) is an important polymer material produced by modifying polyethylene (PE) through chlorination. During the chlorination process, chlorine atoms partially replace hydrogen atoms in the polyethylene molecular chain, endowing the material with excellent weather resistance, oil resistance, flame retardancy, and good elasticity and plastic compatibility. It is widely used in fields such as wires and cables, hoses, tapes, waterproof membranes, plastic modification, and coatings.

[0003] Currently, the industrial production of chlorinated polyethylene mainly employs aqueous suspension or acid suspension methods. These methods involve suspending powdered polyethylene resin in water or hydrochloric acid, and then introducing chlorine gas under the action of an initiator to initiate a substitution reaction. However, the reaction rate and chlorination uniformity of this method are largely limited by the microstructure of the polyethylene resin used, particularly its porosity and pore volume. Commercially available ordinary powdered polyethylene resin typically has low pore volume, a dense structure, and a limited specific surface area. During the chlorination reaction, chlorine gas mainly diffuses and permeates slowly from the surface of the resin particles into the interior. For dense resin particles, chlorine gas cannot effectively and quickly penetrate into the interior, leading to uneven chlorination levels inside and outside the particles in the later stages of the reaction, a phenomenon known as "half-chlorination" (over-chlorination on the surface and insufficient chlorination inside). This not only prolongs the reaction time and increases energy consumption, but more importantly, it results in uneven distribution of chlorine atoms on the molecular chain of the final product, severely affecting the performance stability of the chlorinated polyethylene product, causing problems such as fluctuations in processing performance, decreased mechanical properties, poor thermal stability, and yellowing color.

[0004] To improve the efficiency and uniformity of chlorination reactions, existing technologies typically focus on either improving the initial pore structure of the resin or optimizing chlorination process conditions. For example, using polyethylene resin with high initial porosity produced by specific grades and special polymerization processes as raw materials. However, these specialized resins often involve complex and costly production processes, and the increase in porosity is limited. Other technologies attempt to swell the polyethylene resin before chlorination, using organic solvents or surfactants for pretreatment to temporarily increase pore size. However, this method introduces additional solvent separation and recovery steps, increasing process complexity and environmental costs, and may result in solvent residue affecting product purity. Furthermore, mechanical or chemical pretreatment of the resin can increase its specific surface area, but this may damage the integrity of the resin particles or introduce impurities.

[0005] Therefore, developing a pretreatment method that can effectively and controllably increase the pore volume of polyethylene powder resin without significantly increasing costs or introducing harmful substances, thereby significantly improving its permeability and reaction uniformity in the subsequent chlorination process, is of great industrial significance for producing high-performance chlorinated polyethylene products and improving production efficiency and economic benefits. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a high-pore-volume chlorinated polyethylene special resin and its preparation method. The method can significantly increase the pore volume of powdered polyethylene resin and solve the problems of slow chlorination reaction rate and poor uniformity caused by low pore volume of polyethylene resin in the prior art.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: The preparation method of high-porosity chlorinated polyethylene special resin includes the following steps: S1. Powdered polyethylene resin is added to the first mixing vessel, sealed, stirred and vacuumed to the predetermined vacuum level, and kept at constant pressure to remove oxygen from the first mixing vessel and the pores of the polyethylene resin. S2. Inert gas is introduced into the first stirring vessel to a predetermined pressure, allowing the inert gas to penetrate into the pores of the polyethylene resin. The temperature is then raised to a predetermined temperature, and as the temperature increases, the polyethylene resin gradually softens. S3. The softened polyethylene resin filled with inert gas is transported to the second low-temperature and low-pressure stirred tank. Under the action of pressure difference, the inert gas inside the pores of the polyethylene resin expands and is released instantaneously. The softened resin pores are enlarged by the gas expansion. Due to the low-temperature environment, the polyethylene resin solidifies and the resin pores no longer shrink, thus obtaining a high-pore-volume chlorinated polyethylene special resin.

[0008] Preferably, in step S1, the predetermined vacuum degree is between -0.06 and -0.1 MPa.

[0009] Preferably, in step S1, the stirring speed of the first stirring vessel is controlled at 10-50 rpm. The stirring speed must be determined according to the state of the material. If the speed is too slow, the material cannot be tumbled, and the oxygen inside the resin is difficult to be discharged. If the speed is too fast, the material tumbles violently, and the fine resin particles are easily sucked away by the vacuum pump.

[0010] Preferably, in step S1, the constant pressure is maintained for 20 to 40 minutes.

[0011] Preferably, in step S2, inert gas is introduced into the first stirring vessel to a predetermined pressure of 0.5 to 1.5 MPa, which can better allow the inert gas to enter the pores of the resin and prevent the resin from being flattened due to lack of gas in the pores when it softens due to heating.

[0012] Preferably, in step S2, the temperature is raised to a predetermined temperature of 110-135°C. If the temperature is too low, it will be difficult to expand the pore space when the gas expands. If the temperature is too high, the resin particles will easily burst or soften excessively and block the pores when the gas expands.

[0013] Preferably, in step S2, the inert gas is N2 or CO2 to avoid oxygen causing a chain oxidation reaction on the broken molecular chains of the resin under high temperature, which would affect product quality.

[0014] Preferably, in step S3, the set pressure of the second stirring vessel is a micro-vacuum state, preferably -0.03 to 0 MPa. This utilizes a large pressure difference to cause the inert gas in the resin pores to expand instantaneously, thereby expanding the resin pores using the gas expansion force.

[0015] Preferably, in step S3, the set temperature of the second stirring vessel is 0 to 30°C. The large temperature difference allows the expanded resin to solidify quickly, avoiding the resin shrinkage and the pore space not being fixed after the inert gas in the pores expands and is discharged.

[0016] Preferably, in step S3, the stirring speed of the second stirring vessel is controlled at 30-80 rpm so that the material can be cooled down quickly without being sucked away.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: Based on powdered polyethylene resin, the powdered polyethylene resin is added to a sealed device, vacuumed, filled with inert gas, pressurized and heated to a predetermined value, and the inert gas fills the pores of the resin. After the resin softens to a certain extent, it is transported to a low-temperature and low-pressure device. Due to the decrease in pressure, the inert gas in the powdered polyethylene resin expands instantaneously, enlarging the pores of the resin. The resin cools and solidifies rapidly, forming loose pores inside the resin. The pore volume increases several times over, which can significantly improve its permeability and reaction uniformity in the subsequent chlorination process. This allows chlorine gas to smoothly enter the resin for reaction during the chlorination process, greatly increasing the contact area of ​​chlorine gas. While increasing the reaction rate, it also greatly improves the uniformity of chlorination, thereby improving the product performance of chlorinated polyethylene. Attached Figure Description

[0018] The following figures are intended only to illustrate and explain the present invention and do not limit the scope of the invention. Wherein: Figure 1 This is an electron microscope image of the polyethylene resin before treatment in Example 1 of the present invention; Figure 2 This is an electron microscope image of the high-porosity chlorinated polyethylene special resin (i.e., the treated polyethylene resin) prepared in Example 1 of the present invention. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the following detailed description, only certain exemplary embodiments of the invention are described by way of illustration. Undoubtedly, those skilled in the art will recognize that various modifications can be made to the described embodiments without departing from the spirit and scope of the invention. Therefore, the drawings and description are illustrative in nature and not intended to limit the scope of the claims.

[0020] Example 1 The preparation method of high-porosity chlorinated polyethylene special resin includes the following steps: S1. Add 1000Kg of powdered polyethylene resin (HDPE) with batch number 25311051 to the first mixing vessel, seal it and start stirring. Control the stirring speed at 30rpm, evacuate to -0.06MPa, maintain constant pressure for 40min, and remove oxygen from the first mixing vessel and the pores of the polyethylene resin. S2. Introduce N2 into the first stirring vessel until the pressure reaches 1.5 MPa, allowing N2 to penetrate into the pores of the polyethylene resin. Heat the vessel to 110°C. As the temperature rises, the polyethylene resin gradually softens. S3. The softened polyethylene resin filled with inert gas is transported to a second stirring vessel with a preset pressure of -0.03MPa and a temperature of 5℃. The stirring speed is controlled at 50rpm. Under the action of pressure difference, the inert gas inside the pores of the polyethylene resin expands and is released instantaneously. The softened resin pores are enlarged by the gas expansion. Due to the low temperature environment, the polyethylene resin is cured and the resin pores no longer shrink, thus obtaining a high-pore-volume chlorinated polyethylene special resin.

[0021] refer to Figure 1 and Figure 2 The surface morphology of the high-porosity chlorinated polyethylene special resin (i.e., the treated polyethylene resin) obtained after treatment by this method is significantly different from that of the polyethylene resin before treatment. The surface of the treated polyethylene resin particles is more porous than that before treatment.

[0022] Example 2 The preparation method of high-porosity chlorinated polyethylene special resin includes the following steps: S1. Add 500 kg of powdered polyethylene resin (HDPE) with batch number 25311053 to the first mixing vessel, seal it and start stirring. Control the stirring speed at 10 rpm, evacuate to -0.1 MPa, maintain constant pressure for 20 min, and remove the oxygen from the first mixing vessel and the pores of the polyethylene resin. S2. Introduce N2 into the first stirring vessel until the pressure reaches 1 MPa, allowing N2 to penetrate into the pores of the polyethylene resin. Heat the vessel to 120°C. As the temperature rises, the polyethylene resin gradually softens. S3. The softened polyethylene resin filled with inert gas is transported to a second stirring vessel with a preset pressure of -0.01MPa and a temperature of 15℃. The stirring speed is controlled at 60rpm. Under the action of pressure difference, the inert gas inside the pores of the polyethylene resin expands and is released instantaneously. The softened resin pores are enlarged by the gas expansion. Due to the low temperature environment, the polyethylene resin is cured and the resin pores no longer shrink, thus obtaining a high-pore-volume chlorinated polyethylene special resin.

[0023] Example 3 The preparation method of high-porosity chlorinated polyethylene special resin includes the following steps: S1. Add 1000Kg of powdered polyethylene resin (HDPE) with batch number 25311054 to the first mixing vessel, seal it and start stirring. Control the stirring speed at 40rpm, evacuate to -0.08MPa, maintain constant pressure for 30min, and remove oxygen from the first mixing vessel and the pores of the polyethylene resin. S2. Introduce N2 into the first stirring vessel until the pressure reaches 0.6 MPa, allowing N2 to penetrate into the pores of the polyethylene resin. Heat the vessel to 135°C. As the temperature rises, the polyethylene resin gradually softens. S3. The softened polyethylene resin filled with inert gas is transported to a second stirring vessel with a preset pressure of 0 MPa and a temperature of 25°C. The stirring speed is controlled at 60 rpm. Under the action of pressure difference, the inert gas inside the pores of the polyethylene resin expands and is released instantaneously. The softened resin pores are enlarged by the gas expansion. Due to the low temperature environment, the polyethylene resin is cured and the resin pores no longer shrink, thus obtaining a high-pore-volume chlorinated polyethylene special resin.

[0024] Example 4 The preparation method of high-porosity chlorinated polyethylene special resin includes the following steps: S1. Add 1000Kg of powdered polyethylene resin (HDPE) with batch number 25311055 to the first mixing vessel, seal it and start stirring. Control the stirring speed at 30rpm, evacuate to -0.06MPa, maintain constant pressure for 40min, and remove oxygen from the first mixing vessel and the pores of the polyethylene resin. S2. Introduce N2 into the first stirring vessel until the pressure reaches 1.5 MPa, allowing N2 to penetrate into the pores of the polyethylene resin. Heat the vessel to 105°C. As the temperature increases, the polyethylene resin gradually softens. S3. The softened polyethylene resin filled with inert gas is transported to a second stirring vessel with a preset pressure of -0.03MPa and a temperature of 5℃. The stirring speed is controlled at 50rpm. Under the action of pressure difference, the inert gas inside the pores of the polyethylene resin expands and is released instantaneously. The softened resin pores are enlarged by the gas expansion. Due to the low temperature environment, the polyethylene resin is cured and the resin pores no longer shrink, thus obtaining a high-pore-volume chlorinated polyethylene special resin.

[0025] Example 5 The preparation method of high-porosity chlorinated polyethylene special resin includes the following steps: S1. Add 1000Kg of powdered polyethylene resin (HDPE) with batch number 25311157 into the first mixing vessel, seal it and start stirring. Control the stirring speed at 40rpm, evacuate to -0.08MPa, maintain constant pressure for 30min, and remove oxygen from the first mixing vessel and the pores of the polyethylene resin. S2. Introduce N2 into the first stirring vessel until the pressure reaches 0.6 MPa, allowing N2 to penetrate into the pores of the polyethylene resin. Heat the vessel to 140°C. As the temperature rises, the polyethylene resin gradually softens. S3. The softened polyethylene resin filled with inert gas is transported to a second stirring vessel with a preset pressure of 0 MPa and a temperature of 25°C. The stirring speed is controlled at 60 rpm. Under the action of pressure difference, the inert gas inside the pores of the polyethylene resin expands and is released instantaneously. The softened resin pores are enlarged by the gas expansion. Due to the low temperature environment, the polyethylene resin is cured and the resin pores no longer shrink, thus obtaining a high-pore-volume chlorinated polyethylene special resin.

[0026] The oil absorption rates of the high-pore-volume chlorinated polyethylene resin (i.e., the treated polyethylene resin) prepared in Examples 1 to 5 and the untreated polyethylene resin were tested respectively.

[0027] Experimental conditions: The resin was soaked in 2 ml of n-hexadecane in a sand core centrifuge tube for 10 minutes, the centrifugation speed was set to 1000 rpm, and the centrifugation time was set to 30 min.

[0028] Calculation formula: X: Oil absorption rate (%); m1: Core mass (g); m2: Dry mass of sample (g); m3: Total mass after centrifugation (g).

[0029] Test results: Table 1. Test data on oil absorption rate of polyethylene resin before treatment. Table 2. Oil absorption rate test data of polyethylene resins prepared in Examples 1 to 5 As can be seen from the comparison of Tables 1 and 2, the oil absorption rate of the chlorinated polyethylene special resin (i.e. the treated polyethylene resin) prepared by the method of the present invention in Examples 1 to 5 is significantly higher than that of the polyethylene resin before treatment.

[0030] As can be seen from Examples 1 to 5, when the softening temperature of polyethylene resin is 105°C or 140°C, the oil absorption rate of the chlorinated polyethylene resin prepared by the method of the present invention is lower than that of the chlorinated polyethylene resin obtained when the softening temperature is in the range of 110-135°C. This indicates that if the temperature is too low, the expansion of the pore space of the resin particles during gas expansion will be hindered, while if the temperature is too high, the pores of the resin particles are easily ruptured or over-softened during gas expansion, resulting in partial pore blockage.

[0031] Compared with the polyethylene resin before treatment, the chlorinated polyethylene resin prepared by the method of the present invention exhibits a significantly improved reaction rate and better chlorination uniformity during the chlorination reaction due to its higher pore volume.

[0032] The above description is merely an illustrative embodiment of the present invention and is not intended to limit the scope of the invention. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a special resin for high-porosity chlorinated polyethylene, characterized in that, Includes the following steps: S1. Powdered polyethylene resin HDPE is added to the first mixing vessel, sealed, stirred and vacuumed to the predetermined vacuum level, and kept at constant pressure to remove oxygen from the first mixing vessel and the pores of the polyethylene resin. S2. Inert gas is introduced into the first stirring vessel to a predetermined pressure, allowing the inert gas to penetrate into the pores of the polyethylene resin. The temperature is raised to a predetermined temperature of 110-135°C. As the temperature rises, the polyethylene resin gradually softens. S3. The softened polyethylene resin filled with inert gas is transported to the second low-temperature and low-pressure stirred tank. Under the action of pressure difference, the inert gas inside the pores of the polyethylene resin expands and is released instantaneously. The softened resin pores are enlarged by the gas expansion. Due to the low temperature environment, the polyethylene resin is cured and the resin pores no longer shrink, thus obtaining a high-pore-volume chlorinated polyethylene special resin. In step S1, the predetermined vacuum level is -0.06 to -0.1 MPa; the constant pressure is maintained for 20 to 40 minutes. In step S2, inert gas is introduced into the first stirred tank until the predetermined pressure is 0.5 to 1.5 MPa; In step S3, the set pressure of the second stirring vessel is -0.03 to 0 MPa.

2. The method for preparing the high-porosity chlorinated polyethylene special resin as described in claim 1, characterized in that: In step S1, the stirring speed of the first stirring vessel is controlled at 10-50 rpm.

3. The method for preparing the high-porosity chlorinated polyethylene special resin as described in claim 1, characterized in that: In step S2, the inert gas is N2 or CO2.

4. The method for preparing the high-porosity chlorinated polyethylene special resin as described in claim 1, characterized in that: In step S3, the set temperature of the second stirring vessel is 0 to 30°C.

5. The method for preparing the high-porosity chlorinated polyethylene special resin as described in claim 1, characterized in that: In step S3, the stirring speed of the second stirring vessel is controlled at 30-80 rpm.

6. A high-porosity chlorinated polyethylene resin prepared by the preparation method according to any one of claims 1 to 5.

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