Modified PVC valve suitable for strong acid environment and preparation method thereof

Abstract

The invention discloses a modified PVC valve suitable for a strong acid environment and a preparation method of the modified PVC valve. The preparation method comprises the following steps: firstly, carrying out free radical copolymerization on butyl methacrylate, glycidyl methacrylate, 2, 2, 2-trifluoroethyl methacrylate and gamma-methacryloxypropyltrimethoxysilane to synthesize a polymeric auxiliary agent; then melting and mixing the auxiliary agent with chlorinated polyvinyl chloride resin, montmorillonite filler, a stabilizer, a flexibilizer and a processing auxiliary agent to prepare functional master batch; and finally, blending the master batch and resin, and carrying out injection molding. Through the synergistic effect of hydrophobicity of the fluorine-containing monomer and interface bonding of the silane coupling agent, a stable in-situ protection layer is constructed in the material, and the acid permeability resistance, the environmental stress cracking resistance and the long-term dynamic sealing performance of the valve are remarkably improved. The obtained valve has excellent corrosion-resistant durability and structural integrity in a strong acid environment, and is suitable for harsh working conditions such as chemical engineering and electroplating.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing technology, and in particular to a modified PVC valve suitable for strong acid environments and its preparation method. Background Technology

[0002] In industrial fields such as chemical engineering, metallurgy, electroplating, hydrometallurgy, and pickling, valves, as key components in fluid transport and control systems, are exposed to strong acidic media environments for extended periods, placing high demands on their corrosion resistance, structural stability, and service life. Polyvinyl chloride (PVC) and its modified materials are widely used in acidic media transport pipelines and valve systems due to their light weight, good processability, and certain corrosion resistance.

[0003] However, with increasingly harsh operating conditions, especially in environments with high concentrations of hydrochloric acid and other strong acids, and under mechanical loads or assembly stresses, traditional PVC valves are gradually revealing their insufficient durability. In existing technologies, modified PVC valves often improve their mechanical and processing properties by introducing fillers, toughening agents, or stabilizers. However, under long-term exposure to strong acids, the acidic medium can still easily penetrate along the micropores inside the material, the filler interface, or processing defects, leading to material performance degradation. Simultaneously, under the coupled effect of stress and chemical media, PVC valve bodies are prone to environmental stress cracking, resulting in valve sealing failure or even structural damage, seriously affecting system operational safety. Furthermore, some additives used in modified systems exhibit migration or failure issues in strong acid environments, making long-term stable protection difficult to achieve.

[0004] Therefore, how to effectively inhibit the penetration of strong acid media, improve interfacial stability, and significantly enhance environmental stress cracking resistance while maintaining the good processing performance of PVC materials remains a technical problem that urgently needs to be solved in the field of modified PVC valves. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a modified PVC valve suitable for strong acid environments and its preparation method, solving the technical problem that modified PVC valves are prone to environmental stress cracking and insufficient durability in high-concentration hydrochloric acid environments due to acid medium penetration and stress coupling.

[0006] This invention can be achieved through the following technical solutions: A method for preparing a modified PVC valve suitable for strong acid environments includes the following steps: Step 1: Dissolve butyl methacrylate, glycidyl methacrylate, 2,2,2-trifluoroethyl methacrylate and γ-methacryloyloxypropyltrimethoxysilane in toluene, and add an initiator under nitrogen atmosphere to carry out free radical copolymerization reaction to obtain a polymerization auxiliary. Step 2: Add the polymerization auxiliaries, chlorinated polyvinyl chloride resin, montmorillonite filler, stabilizer, toughening agent and processing aid to a twin-screw extruder for melt mixing to prepare functional masterbatch; Step 3: Mix the functional masterbatch with chlorinated polyvinyl chloride resin, dry it at 80-120℃ for 2-6 hours, and then use an injection molding machine to injection mold it to obtain the modified PVC valve.

[0007] Preferably, in step 1, the mass ratio of butyl methacrylate, glycidyl methacrylate, 2,2,2-trifluoroethyl methacrylate and γ-methacryloyloxypropyltrimethoxysilane is (40-60):(5-15):(5-20):(3-10).

[0008] Preferably, the initiator in step 1 is azobisisobutyronitrile or benzoyl peroxide.

[0009] Preferably, the temperature of the free radical copolymerization reaction in step 1 is 60-80℃, and the reaction time is 6-12h.

[0010] Preferably, in step 2, the amounts of polymerizing additives, montmorillonite, stabilizers, toughening agents, and processing aids added are (0.5%-5.0%), (1%-10%), (0.8%-3.0%), (5.0%-15.0%), and (0.5%-2.5%) of the mass of chlorinated polyvinyl chloride resin, respectively.

[0011] Preferably, the melting and mixing temperature in step 2 is 160-200℃.

[0012] Preferably, the barrel temperature for injection molding in step 3 is 180-220℃.

[0013] Preferably, the mass ratio of functional masterbatch to chlorinated polyvinyl chloride resin in step 3 is (5-30):(70-95).

[0014] The beneficial effects of this invention are: This invention designs and prepares a polymerization aid by free radical copolymerization of butyl methacrylate, glycidyl methacrylate, 2,2,2-trifluoroethyl methacrylate, and γ-methacryloyloxypropyltrimethoxysilane. The fluorinated monomers in this aid impart excellent acid-repellent and low surface energy properties to the system, while the silane coupling monomers, through their hydrolyzable groups, form strong chemical bonds with chlorinated polyvinyl chloride resin and montmorillonite filler during subsequent processing. During melt mixing and injection molding, this aid can be uniformly dispersed and constructed in situ at the matrix-filler interface, forming a dense and stable "molecular protective layer." This unique structural design fundamentally solves the performance degradation problem of traditional modified PVC valves in strong acid environments caused by media penetration along micro-defects and weak interfacial bonding. The prepared valve, after being immersed in 20wt% hydrochloric acid for 90 days, showed a mass change rate of less than 0.6%, a tensile strength retention rate of over 96%, and an intact appearance. In a 1500-hour pressure-acid cycle test simulating harsh working conditions, the valve maintained zero leakage and stable operating torque, demonstrating excellent resistance to environmental stress cracking and long-term dynamic sealing reliability. Attached Figure Description

[0015] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 The tensile strength retention rate of the modified PVC valve in the strong acid immersion corrosion resistance test. Detailed Implementation

[0016] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0017] Example 1: A method for preparing a modified PVC valve suitable for strong acid environments, comprising the following steps: Step 1: Dissolve 4g butyl methacrylate, 0.5g glycidyl methacrylate, 0.5g 2,2,2-trifluoroethyl methacrylate and 0.3g γ-methacryloyloxypropyltrimethoxysilane in 40mL toluene, add 2g azobisisobutyronitrile under nitrogen atmosphere, and react at 60℃ for 12h to obtain the polymerization auxiliary agent; Step 2: Add 0.5g of polymerization auxiliaries, 100g of chlorinated polyvinyl chloride resin, 1g of montmorillonite filler, 0.8g of methyl tin mercapto compound heat stabilizer, 5g of chlorinated polyethylene and 0.5g of acrylate processing aids to a twin-screw extruder for melt mixing to prepare functional masterbatch. The temperature of the twin-screw extruder is 160℃, 175℃, 190℃, 200℃ and 190℃. Step 3: Mix 50g of functional masterbatch with 950g of chlorinated polyvinyl chloride resin, dry at 80℃ for 6 hours, and then use an injection molding machine to injection mold at 180℃ to obtain modified PVC valve.

[0018] Example 2: A method for preparing a modified PVC valve suitable for strong acid environments, comprising the following steps: Step 1: Dissolve 5g butyl methacrylate, 1.0g glycidyl methacrylate, 1.25g 2,2,2-trifluoroethyl methacrylate and 0.65g γ-methacryloyloxypropyltrimethoxysilane in 40mL toluene, add 2g benzoyl peroxide under nitrogen atmosphere, and react at 70℃ for 9h to obtain the polymerization auxiliary. Step 2: Add 2.75g of polymerization auxiliaries, 100g of chlorinated polyvinyl chloride resin, 5.5g of montmorillonite filler, 1.9g of methyl tin mercapto compound heat stabilizer, 10g of chlorinated polyethylene and 1.5g of acrylate processing aids to a twin-screw extruder for melt mixing to prepare functional masterbatch. The temperature of the twin-screw extruder is 160℃, 175℃, 190℃, 200℃ and 190℃. Step 3: Mix 175g of functional masterbatch with 825g of chlorinated polyvinyl chloride resin, dry at 100℃ for 4 hours, and then use an injection molding machine to injection mold at 200℃ to obtain modified PVC valve.

[0019] Example 3: A method for preparing a modified PVC valve suitable for strong acid environments, comprising the following steps: Step 1: Dissolve 6g butyl methacrylate, 1.5g glycidyl methacrylate, 2g 2,2,2-trifluoroethyl methacrylate and 1g γ-methacryloyloxypropyltrimethoxysilane in 40mL toluene, add 2g azobisisobutyronitrile under nitrogen atmosphere, and react at 80℃ for 6h to obtain a polymerization auxiliary agent; Step 2: Add 5g of polymerization auxiliaries, 100g of chlorinated polyvinyl chloride resin, 10g of montmorillonite filler, 3g of methyl tin mercapto compound heat stabilizer, 15g of chlorinated polyethylene and 2.5g of acrylate processing aids to a twin-screw extruder for melt mixing to prepare functional masterbatch. The temperature of the twin-screw extruder is 160℃, 175℃, 190℃, 200℃ and 190℃. Step 3: Mix 300g of functional masterbatch with 700g of chlorinated polyvinyl chloride resin, dry at 120℃ for 2 hours, and then use an injection molding machine to injection mold at 220℃ to obtain modified PVC valve.

[0020] Example 4: A method for preparing a modified PVC valve suitable for strong acid environments, comprising the following steps: Step 1: Dissolve 4g butyl methacrylate, 1.5g glycidyl methacrylate, 0.5g 2,2,2-trifluoroethyl methacrylate and 0.3g γ-methacryloyloxypropyltrimethoxysilane in 40mL toluene, add 2g benzoyl peroxide under nitrogen atmosphere, and react at 80℃ for 12h to obtain the polymerization auxiliary. Step 2: Add 5g of polymerization auxiliaries, 100g of chlorinated polyvinyl chloride resin, 5g of montmorillonite filler, 3g of methyl tin mercapto compound heat stabilizer, 5g of chlorinated polyethylene and 2.5g of acrylate processing aids to a twin-screw extruder for melt mixing to prepare functional masterbatch. The temperature of the twin-screw extruder is 160℃, 175℃, 190℃, 200℃ and 190℃. Step 3: Mix 300g of functional masterbatch with 700g of chlorinated polyvinyl chloride resin, dry at 100℃ for 4 hours, and then use an injection molding machine to injection mold at 220℃ to obtain modified PVC valve.

[0021] Comparative Example 1: The difference between this comparative example and Example 1 is that no polymerization auxiliaries are added.

[0022] Comparative Example 2: The difference between this comparative example and Example 1 is that only butyl methacrylate and glycidyl methacrylate are copolymerized.

[0023] Comparative Example 3: The difference between this comparative example and Example 1 is that no copolymerization reaction is performed, and each monomer and silane are added directly as physical mixing aids.

[0024] A method for preparing a modified PVC valve suitable for strong acid environments includes the following steps: Step 1: 4g butyl methacrylate, 0.5g glycidyl methacrylate, 0.5g 2,2,2-trifluoroethyl methacrylate, and 0.3g γ-methacryloyloxypropyltrimethoxysilane are used as physical mixing aids. They are then melt-mixed with 100g chlorinated polyvinyl chloride resin, 1g montmorillonite filler, 0.8g methyl tin mercapto compound heat stabilizer, 5g chlorinated polyethylene, and 0.5g acrylate processing aids in a twin-screw extruder to prepare functional masterbatch. The temperatures of the twin-screw extruder are 160℃, 175℃, 190℃, 200℃, and 190℃. Step 2: Mix 50g of functional masterbatch with 950g of chlorinated polyvinyl chloride resin, dry at 80℃ for 6 hours, and then use an injection molding machine to injection mold at 180℃ to obtain modified PVC valve.

[0025] Performance testing 1. Strong acid immersion corrosion resistance test The corrosion resistance of modified PVC valves was tested according to GB / T 11547-2008 standard. A 50mm × 25mm × 2mm cube was cut from the valve sample, the surface was cleaned with alcohol, and the valve was conditioned for 48 hours at 23±2℃ and 50±5%RH. Measure and record the initial mass m0 and initial tensile strength TS0 of the sample. Completely immerse the sample in a sealed glass container containing 20±2wt% hydrochloric acid solution, ensuring the liquid level is at least 20mm above the sample. Place the container in a constant temperature oven at 60±1℃. On the 7th, 28th, and 90th days of immersion, remove a pre-set set of samples. Rinse the removed samples thoroughly with deionized water, blot the surface moisture with filter paper, weigh the sample mass mt, and calculate the mass change rate Δm% = [(mt-m0) / m0] × 100%. Dry the sample to constant weight under standard conditions (23±2℃, 50±5%RH) (usually 24h), and then conduct a tensile test according to GB / T1040.1-2025. Record the tensile strength retention rate (TSR%) = (TSt / TS0) × 100%. Visually inspect and record whether the sample surface shows discoloration, blistering, cracking, loss of luster, or stickiness.

[0026] Table 1 Results of strong acid immersion corrosion resistance test

[0027] As shown in Table 1, the modified PVC valves prepared in Examples 1-4 exhibit excellent corrosion resistance under long-term immersion in strong acid. Their mass change rate (Δm%) was below +0.6% for 90 days, indicating that acid penetration was effectively suppressed; the tensile strength retention rate (TSR%) remained above 96.0% after 90 days, with minimal loss of mechanical properties; and the appearance remained smooth after 90 days, showing no obvious signs of deterioration. This demonstrates that the specific polymerizable additives (containing fluorinated hydrophobic monomers and silane coupling monomers) prepared by free radical copolymerization in this invention can effectively bond to the interface between the chlorinated polyvinyl chloride (CPVC) matrix and the montmorillonite filler after melt processing, constructing a dense and stable "in-situ protective layer," significantly enhancing the material's resistance to acid penetration and chemical corrosion.

[0028] In comparison, Comparative Example 1 (without polymerization additive) exhibited the worst performance. Its mass change rate reached +5.10% after 90 days, indicating that the acidic medium had extensively penetrated the material. The tensile strength retention rate dropped significantly to 74.6%, indicating severe deterioration of mechanical properties. Furthermore, obvious whitening and blistering occurred on the surface. This directly proves that the polymerization additive designed in this invention is the core key to improving the durability of PVC valves in strong acid environments; without this additive, the long-term protective performance of the material is severely inadequate. Comparative Example 2 (without fluorinated monomers and silane coupling monomers) performed worse than all examples, with its Δm% and TSR% data significantly worse than the example group. After 90 days, it showed loss of gloss and discoloration. This demonstrates that the low surface energy and acid-repellent properties provided by the fluorinated monomer (2,2,2-trifluoroethyl methacrylate), and the interface reinforcement and anti-permeation function provided by the silane coupling monomer (γ-methacryloyloxypropyltrimethoxysilane), are both indispensable and together constitute the material basis for the synergistic effect of the polymerization additive in this invention. The performance of Comparative Example 3 (physical mixing additive) was far inferior to that of all the examples. It was added only through physical mixing, and the components could not form stable and controllable chemical bonds and interface structures during the processing. Its protective effect was short-lived and unstable, which eventually led to the material showing obvious loss of gloss, stickiness and microcracks under long-term acid exposure.

[0029] 2. Long-term pressure-acid cycle durability test Install the valve sample in a dedicated circulating test circuit. The circuit includes an acid-resistant pump, a constant temperature bath, a pressure sensor, and a test section. The valve in the test section is in a half-open state. Inject 10 wt% hydrochloric acid solution into the circuit as the circulating medium. Control the medium temperature to 50±2℃. Start the system and circulate the circuit pressure between 0.2 MPa and 0.8 MPa at a frequency of 6 times per hour. Keep the medium flowing continuously (flow rate about 1 m / s). Stop the machine once every 168 hours (1 week) and perform the following checks: (1) Close the valve completely and apply a static water pressure of 1.0 MPa (using water) to the pipeline after the valve. Hold the pressure for 30 minutes and check and record the valve leakage rate (number of drips / minute); (2) Check whether there is any visible deformation, bulge, crack or discoloration inside or outside the valve. Manually operate the valve handle, feel and record its torque change. If the leakage rate exceeds the standard allowable value, the valve shows visible structural damage, the operating torque increases sharply, or the valve becomes stuck and cannot be opened or closed normally, the test is deemed a failure and terminated; if the valve can still maintain a seal and operate normally after the predetermined total test duration of 1500 hours, it is recorded as passed.

[0030] Table 2 Results of Long-Term Pressure-Acid Cycling Durability Tests

[0031] As shown in Table 2, the modified PVC valves of Examples 1-4 all successfully passed the 1500-hour rigorous pressure-acid cycle durability test. Throughout the entire test cycle, their leakage rate remained at 0, the operating torque showed no significant change, and the valve appearance and sealing surface remained intact. This is attributed to the excellent resistance to environmental stress cracking and the long-term effective barrier against acid media penetration of the modified material, thereby avoiding sealing failure caused by material swelling, corrosion, or cracking.

[0032] Compared to Example 1, Comparative Example 1 (without polymerizable additives) failed after 336 hours of testing, with a severely excessive leakage rate and operational sluggishness. Its failure mode was "corrosion damage to the sealing surface," directly attributed to the lack of protection from polymerizable additives. The valve sealing surface material was rapidly corroded and eroded under acid scouring and pressure, losing its sealing ability. Comparative Example 2 (without fluorine-containing, silicon functional monomers) failed at 672 hours, significantly shorter than the Example group. Its failure mode was "environmental stress cracking at the valve stem," indicating insufficient crack resistance under the coupled effects of stress and acid media. Comparative Example 3 (physically mixed additives) failed after 504 hours, with the failure mode being "deformation and leakage at the valve body connection due to media penetration and expansion." This indicates that physically mixed additive components cannot form a stable and durable protective network within the material, allowing the acid media to gradually penetrate and cause swelling and deformation, ultimately disrupting the structural integrity and leading to leakage.

[0033] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a modified PVC valve suitable for strong acid environments, characterized in that, Includes the following steps: Step 1: Dissolve butyl methacrylate, glycidyl methacrylate, 2,2,2-trifluoroethyl methacrylate and γ-methacryloyloxypropyltrimethoxysilane in toluene, and add an initiator under nitrogen atmosphere to carry out free radical copolymerization reaction to obtain a polymerization auxiliary. Step 2: Add the polymerization auxiliaries, chlorinated polyvinyl chloride resin, montmorillonite filler, stabilizer, toughening agent and processing aid to a twin-screw extruder for melt mixing to prepare functional masterbatch; Step 3: Mix the functional masterbatch with chlorinated polyvinyl chloride resin, dry it at 80-120℃ for 2-6 hours, and then use an injection molding machine to injection mold it to obtain the modified PVC valve.

2. The method for preparing a modified PVC valve suitable for strong acid environments according to claim 1, characterized in that, In step 1, the mass ratio of butyl methacrylate, glycidyl methacrylate, 2,2,2-trifluoroethyl methacrylate and γ-methacryloyloxypropyltrimethoxysilane is (40-60):(5-15):(5-20):(3-10).

3. The method for preparing a modified PVC valve suitable for strong acid environments according to claim 1, characterized in that, In step 1, the initiator is azobisisobutyronitrile or benzoyl peroxide.

4. The method for preparing a modified PVC valve suitable for strong acid environments according to claim 1, characterized in that, The temperature of the free radical copolymerization reaction in step 1 is 60-80℃, and the reaction time is 6-12h.

5. The method for preparing a modified PVC valve suitable for strong acid environments according to claim 1, characterized in that, In step 2, the amounts of polymerizing additives, montmorillonite, stabilizers, toughening agents, and processing aids added are (0.5%-5.0%), (1%-10%), (0.8%-3.0%), (5.0%-15.0%), and (0.5%-2.5%) of the mass of chlorinated polyvinyl chloride resin, respectively.

6. The method for preparing a modified PVC valve suitable for strong acid environments according to claim 1, characterized in that, The melting and mixing temperature in step 2 is 160-200℃.

7. The method for preparing a modified PVC valve suitable for strong acid environments according to claim 1, characterized in that, In step 3, the barrel temperature for injection molding is 180-220℃.

8. The method for preparing a modified PVC valve suitable for strong acid environments according to claim 1, characterized in that, In step 3, the mass ratio of functional masterbatch to chlorinated polyvinyl chloride resin is (5-30):(70-95).

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