Preparation method of modified ardealite filler and liquid silicone rubber

Abstract

The invention discloses a modified ardealite filler for liquid silicone rubber and a preparation method thereof.According to the method, impurity removal and dehydration treatment of ardealite are achieved through high-temperature roasting, and a three-step synergistic process of surface hydroxylation modification, silane coupling agent grafting and stearic acid surface treatment is combined; the modified ardealite filler with good hydrophobicity and interfacial compatibility is obtained. The filler and a liquid silicone rubber material form good interface bonding, the tensile strength and the elongation at break of the silicone rubber can be improved, and meanwhile the excellent heat-resistant stability of the silicone rubber is kept. The method has the characteristics of simple process, low cost and strong industrial adaptability, and opens up a new way for resource utilization of the phosphogypsum solid waste.

Description

Technical Field

[0001] The present invention relates to the field of liquid silicone rubber fillers, and particularly to a preparation method of modified phosphogypsum for use as a reinforcing filler in liquid silicone rubber. Background Art

[0002] Phosphogypsum is an industrial solid waste generated in the wet-process phosphoric acid process. Its main component is CaSO4·2H2O, and it also contains impurities such as phosphorus, fluorine, free acid, and organic matter. The large-scale stacking of phosphogypsum will pose potential hazards to the soil and the surrounding environment. Therefore, the resource utilization of phosphogypsum is an important task. As an inorganic material, phosphogypsum can be used as a reinforcing filler for polymer materials to improve the performance of the materials. The technical difficulties are as follows: (1) The interfacial compatibility between phosphogypsum and polymer materials is poor; (2) The impurities in phosphogypsum may have an adverse effect on the material properties. Patent CN105330965B discloses a polypropylene plastic using phosphogypsum as a filler and its preparation method. This method uses phosphogypsum as a filler and forms an optimized polypropylene plastic formula through the combination with components such as nano-silica, titanium dioxide, and paraffin, forming particulate fillers with a void structure, reducing the density, and improving the plasticity and rheology. Patent CN103435937B modifies phosphogypsum by screening, calcining, grinding, and adding aluminate coupling agent to form anhydrous fine powder, and uses a high-speed mixer for self-friction heating to form aluminate-modified phosphogypsum suitable as a filler for polyvinyl chloride resin. It improves the whiteness and processing performance of phosphogypsum, improves the compatibility with polyvinyl chloride resin, meets the standards for unplasticized polyvinyl chloride profiles for doors and windows, and reduces the cost. CN105462108A provides a process for producing PVC profiles using phosphogypsum treated with acid and alkali as a filler, improving the purity and particle uniformity of phosphogypsum, and enhancing the structural stability, tensile strength, and hardness of PVC profiles.

[0003] The above technologies mainly focus on the application field of phosphogypsum as a plastic filler, and there is no report in the field of liquid silicone rubber. The main mechanical properties of silicone rubber come from the reinforcing filler, which is commonly fumed silica. However, the production process of fumed silica is complex and the price is high. As an industrial solid waste, phosphogypsum can be used as a reinforcing filler for liquid silicone rubber through certain technical modifications, improving the comprehensive utilization rate of phosphogypsum and saving costs. Summary of the Invention

[0004] The present invention aims to provide a modified phosphogypsum filler for liquid silicone rubber and its preparation method to realize the resource utilization of phosphogypsum. The modified phosphogypsum prepared by this method has good interfacial compatibility with the silicone rubber compound and can be used as a reinforcing filler for liquid silicone rubber, having an obvious effect of improving the mechanical properties of liquid silicone rubber.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions: A modified phosphogypsum filler for liquid silicone rubber and its preparation method, characterized in that it comprises the following steps: S1: Grind phosphogypsum using a high-speed grinder, place it in a muffle furnace, and calcine the phosphogypsum by two-stage heating to remove organic impurities and crystal water. Screen the calcined phosphogypsum using a 200-mesh sieve to remove large particle impurities; S2: Add the phosphogypsum obtained in S1 to a NaOH solution, stir at room temperature for 30 min, wash with ultrapure water, and dry to obtain hydroxylated phosphogypsum; S3: Perform surface hydrophobic modification on the hydroxylated phosphogypsum in a mixed solution containing a modifier, wash and dry, and then grind to obtain the modified phosphogypsum filler.

[0006] For the two-stage heating calcination, the temperature in the first stage is maintained at 200 - 300 °C for 1 - 2 h to remove organic impurities; the second stage is maintained at 500 - 600 °C for 1 - 2 h to remove crystal water.

[0007] For the phosphogypsum hydroxylation method S2, the mass ratio of phosphogypsum to sodium hydroxide solution is 1:3 - 1:5; the concentration of the sodium hydroxide solution is 0.5 - 2 M.

[0008] The mixed solution containing a modifier is characterized in that the modifier is a mixed solution containing a silane coupling agent and stearic acid, and the solvent is ethanol and water; the addition amount of the silane coupling agent is 0.5 - 5 wt% of the solvent; the addition amount of stearic acid is 1 - 3 wt% of the solvent.

[0009] The silane coupling agent is one or more of vinyltrimethoxysilane, vinyltriethoxysilane, methylvinyldimethoxysilane, phenylethyltrimethoxysilane, vinyltriisopropoxysilane, trivinylmethoxysilane, dimethoxydivinylsilane, allyltrimethoxysilane.

[0010] For the liquid silicone rubber, the components and parts by weight of each raw material in the liquid silicone rubber compound are as follows: 80 - 120 parts of vinyl silicone oil 0.1 - 1 part of hydrogen-containing silicone oil 10 - 25 parts of modified phosphogypsum 0.05 - 0.1 part of ethynylcyclohexanol 0.01 - 0.1 part of Karstedt catalyst. The present invention also provides a method for preparing liquid silicone rubber. After mixing the modified phosphogypsum filler, vinyl silicone oil, and hydrogen-containing silicone oil into a slurry, ethynylcyclohexanol and Karstedt catalyst are added and mixed evenly to obtain a liquid silicone rubber compound. The liquid silicone rubber compound is poured into a mold and cured to obtain a liquid silicone rubber film.

[0011] The curing process is carried out in a vacuum curing instrument. After exhausting the air, it is maintained at 110 - 150 °C for 15 - 20 min to obtain the liquid silicone rubber film.

[0012] The silane coupling agent contains a carbon-carbon double bond and can undergo a hydrosilylation reaction with the Si-H bond in the silicone rubber compound to enhance the interfacial force. Stearic acid contains a long carbon chain, and binding to the surface of phosphogypsum can improve the interfacial compatibility between the modified phosphogypsum and silicone rubber.

[0013] The molecular structure of the silane coupling agent usually has a hydrolyzable group at one end. After hydrolysis, it forms Si-OH and can bind to the hydroxylated phosphogypsum surface. The other end is an organic functional group, such as vinyl, epoxy, isocyanate, amino, mercapto, etc. In the present invention, a silane coupling agent containing vinyl is selected. Vinyl can react with the Si-H bond of the hydrogen-containing silicone oil in the liquid silicone rubber compound, enhance the interfacial force between the modified phosphogypsum and the liquid silicone rubber compound, and thus improve the mechanical properties of the liquid silicone rubber. Detailed implementation method

[0014] Example 1 (1) Grind phosphogypsum using a high-speed grinder, place it in a muffle furnace, calcine at 200 °C for 2 h, then raise the temperature to 600 °C and calcine for 2 h, and cool to room temperature. Screen it with a 200-mesh sieve, and the sieved phosphogypsum is denoted as PG-600. Add 120 g of PG-600 to 300 ml of 0.5 M NaOH solution, stir at room temperature for 30 min. Wash it three times with ultrapure water and dry it at 60 °C, denoted as PG-OH. Add 2.7 g of vinyltrimethoxysilane, 100 g of absolute ethanol, and 4 g of ultrapure water to a round-bottom flask, stir and hydrolyze at room temperature for 1 h. Then raise the temperature to 60 °C, add 25 g of PG-600 and 2 g of stearic acid, disperse evenly by ultrasound, and stir for 4 h. After the reaction is completed, wash it three times with absolute ethanol and dry it in an oven at 60 °C to obtain modified phosphogypsum A.

[0015] (2) Weigh 120 parts of vinyl silicone oil, 0.75 part of hydrogen-containing silicone oil, and 25 parts of modified phosphogypsum A, stir evenly at high speed to make it in a slurry state. Then add 0.05 part of ethynylcyclohexanol and 0.03 part of Karstedt catalyst to the slurry, mix evenly to obtain a liquid silicone rubber compound. Pour the compound into a mold, place it in a flat vacuum curing instrument, exhaust 10 times, and maintain at 110 °C for 20 min to obtain the liquid silicone rubber film.

[0016] Example 2 (1)Use a high-speed grinder to grind phosphogypsum finely, place it in a muffle furnace, calcine it at 200 °C for 2 h, raise the temperature to 600 °C and calcine for 2 h, and then cool it to room temperature. Screen it with a 200-mesh sieve, and the sieved phosphogypsum is denoted as PG-600. Add 120 g of PG-600 to 300 ml of 0.5 M NaOH solution, stir at room temperature for 30 min. Wash it three times with ultrapure water and dry it at 60 °C, denoted as PG-OH. Add 2.4 g of methylvinyl dimethoxysilane, 100 g of absolute ethanol and 4 g of ultrapure water to a round-bottom flask, stir and hydrolyze at room temperature for 1 h. Then raise the temperature to 60 °C, add 25 g of PG-600 and 2 g of stearic acid, disperse it evenly by ultrasonic wave and stir for 4 h. After the reaction is completed, wash it three times with absolute ethanol and dry it in an oven at 60 °C to obtain modified phosphogypsum B.

[0017] (2)Weigh 120 parts of vinyl silicone oil, 0.75 part of hydrogen-containing silicone oil and 25 parts of modified phosphogypsum B, stir evenly at high speed to make it into a slurry state. Then add 0.05 part of ethynylcyclohexanol and 0.03 part of Karstedt catalyst to the slurry, mix well to obtain a liquid silicone rubber compound. Pour the compound into a mold, place it in a flat-plate vacuum vulcanizer, exhaust 10 times, and keep it at 110 °C for 20 min to obtain a liquid silicone rubber film.

[0018] Example 3 (1)Use a high-speed grinder to grind phosphogypsum finely, place it in a muffle furnace, calcine it at 200 °C for 2 h, raise the temperature to 600 °C and calcine for 2 h, and then cool it to room temperature. Screen it with a 200-mesh sieve, and the sieved phosphogypsum is denoted as PG-600. Add 120 g of PG-600 to 300 ml of 0.5 M NaOH solution, stir at room temperature for 30 min. Wash it three times with ultrapure water and dry it at 60 °C, denoted as PG-OH. Add 4.5 g of styreneethyl trimethoxysilane, 100 g of absolute ethanol and 4 g of ultrapure water to a round-bottom flask, stir and hydrolyze at room temperature for 1 h. Then raise the temperature to 60 °C, add 25 g of PG-600 and 2 g of stearic acid, disperse it evenly by ultrasonic wave and stir for 4 h. After the reaction is completed, wash it three times with absolute ethanol and dry it in an oven at 60 °C to obtain modified phosphogypsum C.

[0019] (2)Weigh 120 parts of vinyl silicone oil, 0.75 part of hydrogen-containing silicone oil and 25 parts of modified phosphogypsum C, stir evenly at high speed to make it into a slurry state. Then add 0.05 part of ethynylcyclohexanol and 0.03 part of Karstedt catalyst to the slurry, mix well to obtain a liquid silicone rubber compound. Pour the compound into a mold, place it in a flat-plate vacuum vulcanizer, exhaust 10 times, and keep it at 110 °C for 20 min to obtain a liquid silicone rubber film.

[0020] Example 4 (1) Grind phosphogypsum finely using a high-speed grinder, place it in a muffle furnace, calcine at 200 °C for 2 h, raise the temperature to 600 °C and calcine for 2 h, then cool to room temperature. Screen it with a 200-mesh sieve, and the screened phosphogypsum is denoted as PG-600. Add 120 g of PG-600 to 300 ml of 0.5 M NaOH solution, stir at room temperature for 30 min. Wash it three times with ultrapure water and dry at 60 °C, denoted as PG-OH. Add 2.4 g of allyltrimethoxysilane, 100 g of absolute ethanol and 4 g of ultrapure water to a round-bottom flask, stir and hydrolyze at room temperature for 1 h. Then raise the temperature to 60 °C, add 25 g of PG-600 and 2 g of stearic acid, disperse evenly by ultrasonic wave, and stir for 4 h. After the reaction is completed, wash it three times with absolute ethanol and dry it in an oven at 60 °C to obtain modified phosphogypsum D.

[0021] (2) Weigh 120 parts of vinyl silicone oil, 0.75 part of hydrogen-containing silicone oil and 25 parts of modified phosphogypsum D, stir evenly at high speed to make it into a slurry state. Then add 0.05 part of ethynylcyclohexanol and 0.03 part of Karstedt catalyst to the slurry, mix well to obtain a liquid silicone rubber compound. Pour the compound into a mold, place it in a flat plate vacuum vulcanizer, exhaust 10 times, and keep it at 110 °C for 20 min to obtain a liquid silicone rubber film.

[0022] Comparative Example 1 Weigh 120 parts of vinyl silicone oil, 0.75 part of hydrogen-containing silicone oil, stir evenly at high speed to make it into a slurry state. Then add 0.05 part of ethynylcyclohexanol and 0.03 part of Karstedt catalyst to the slurry, mix well to obtain a liquid silicone rubber compound. Pour the compound into a mold, place it in a flat plate vacuum vulcanizer, exhaust 10 times, and keep it at 110 °C for 20 min to obtain a liquid silicone rubber film.

[0023] Comparative Example 2 (1) Grind phosphogypsum finely using a high-speed grinder, place it in a muffle furnace, calcine at 200 °C for 2 h, raise the temperature to 600 °C and calcine for 2 h, then cool to room temperature. Screen it with a 200-mesh sieve, and the screened phosphogypsum is denoted as PG-600. Add 120 g of PG-600 to 300 ml of 0.5 M NaOH solution, stir at room temperature for 30 min. Wash it three times with ultrapure water and dry at 60 °C, denoted as PG-OH.

[0024] (2) Weigh 120 parts of vinyl silicone oil, 0.75 part of hydrogen-containing silicone oil, and 25 parts of hydroxylated phosphogypsum PG-OH, and stir them evenly at high speed to make a slurry. Subsequently, add 0.05 part of ethynylcyclohexanol and 0.03 part of Karstedt catalyst to the slurry, and mix them thoroughly to obtain a liquid silicone rubber compound. Pour the compound into a mold, place it in a flat-plate vacuum vulcanizer, exhaust 10 times, and maintain at 110 °C for 20 min to obtain a liquid silicone rubber film.

[0025] Comparative Example 3 (1) Grind phosphogypsum with a high-speed grinder, place it in a muffle furnace, calcine at 200 °C for 2 h, raise the temperature to 600 °C and calcine for 2 h, and cool to room temperature. Screen it with a 200-mesh sieve, and the sieved phosphogypsum is denoted as PG-600. Add 120 g of PG-600 to 300 ml of 0.5 M NaOH solution, and stir at room temperature for 30 min. Wash it three times with ultrapure water and dry it at 60 °C, denoted as PG-OH. Add 3.5 g of γ-glycidoxypropyltrimethoxysilane, 100 g of absolute ethanol, and 4 g of ultrapure water to a round-bottom flask, stir and hydrolyze at room temperature for 1 h. Subsequently, raise the temperature to 60 °C, add 25 g of PG-600 and 2 g of stearic acid, disperse them evenly by ultrasonic wave, and stir for 4 h. After the reaction is completed, wash it three times with absolute ethanol and dry it in an oven at 60 °C to obtain modified phosphogypsum E.

[0026] (2) Weigh 120 parts of vinyl silicone oil, 0.75 part of hydrogen-containing silicone oil, and 25 parts of modified phosphogypsum E, and stir them evenly at high speed to make a slurry. Subsequently, add 0.05 part of ethynylcyclohexanol and 0.03 part of Karstedt catalyst to the slurry, and mix them thoroughly to obtain a liquid silicone rubber compound. Pour the compound into a mold, place it in a flat-plate vacuum vulcanizer, exhaust 10 times, and maintain at 110 °C for 20 min to obtain a liquid silicone rubber film.

[0027] For the liquid silicone rubber films obtained in Examples 1-4 and Comparative Examples 1-3, cut them into pieces according to the test requirements for mechanical property testing. Shore A hardness: Test according to GB / T 531-200; Tear strength: Use a right-angle test piece and test according to GB / T 529-200; Tensile strength and elongation at break: Use a dumbbell-shaped test piece and test according to GB / T 528-2008.

[0028] Table 1 Mechanical Property Testing of Liquid Silicone Rubber

[0029] The test results are shown in Table 1. It can be seen that the modified phosphogypsum prepared by the technology provided by the present invention can effectively improve the mechanical properties of liquid silicone rubber.

Claims

1. A preparation method of a modified phosphogypsum filler, characterized in that, It includes the following steps: S1: After phosphorus gypsum is ground and calcined, it is added to a sodium hydroxide solution to obtain hydroxylated phosphorus gypsum; S2: The hydroxylated phosphorus gypsum is subjected to surface hydrophobic modification in a mixed solution containing a modifier, washed, dried, and then ground to obtain a modified phosphorus gypsum filler.

2. The preparation method of the modified phosphogypsum filler according to claim 1, characterized in that, The calcination process uses two-stage heating calcination. The temperature in the first stage is maintained at 200 - 300 °C for 1 - 2 h; the second stage is kept at 500 - 600 °C for 1 - 2 h.

3. The preparation method of the modified phosphogypsum filler according to claim 1, characterized in that, The mass ratio of the phosphorus gypsum to the sodium hydroxide solution is 1:3 - 5; the concentration of the sodium hydroxide solution is 0.5 - 2 M.

4. The preparation method of the modified phosphogypsum filler according to claim 1, characterized in that In the mixed solution containing the modifier, the modifier is a mixed solution containing a silane coupling agent and stearic acid, and the solvent is ethanol and water.

5. The preparation method of the modified phosphogypsum filler according to claim 4, characterized in that, The silane coupling agent is one or more of vinyltrimethoxysilane, vinyltriethoxysilane, methylvinyldimethoxysilane, styrylethyltrimethoxysilane, vinyltriisopropoxysilane, trivinylmethoxysilane, dimethoxydivinylsilane, allyltrimethoxysilane.

6. The preparation method of the modified phosphogypsum filler according to claim 5, characterized in that, The addition amount of the silane coupling agent is 0.5 - 5 wt% of the solvent.

7. The preparation method of the modified phosphogypsum filler according to claim 4, characterized in that The addition amount of stearic acid is 1 - 3 wt% of the solvent.

8. A liquid silicone rubber, characterized in that, The components and parts by weight of each raw material in the liquid silicone rubber compound are as follows: 80 - 120 parts of vinyl silicone oil 0.1 - 1 part of hydrogen-containing silicone oil 10 - 25 parts of modified phosphorus gypsum 0.05 - 0.1 part of ethynylcyclohexanol 0.01 - 0.1 part of Karstedt catalyst.

9. A preparation method of liquid silicone rubber, characterized in that, After mixing the modified phosphorus gypsum filler, vinyl silicone oil, and hydrogen-containing silicone oil described in any one of claims 1 - 7 into a slurry, add ethynylcyclohexanol and Karstedt catalyst, and mix evenly to obtain a liquid silicone rubber compound. Pour the liquid silicone rubber compound into a mold and cure it to obtain a liquid silicone rubber film.

10. The preparation method of the liquid silicone rubber according to claim 9, wherein, The curing process is carried out in a vacuum curing instrument. After exhausting, keep it at 110 - 150 °C for 15 - 20 min to obtain a liquid silicone rubber film.

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