A method for recycling silica gel

Abstract

This invention relates to the field of polymer material recycling, specifically to a method for recycling silicone. The method includes recycling, crushing, washing, surface modification, liquid nitrogen freezing, grinding, construction of a multi-level filler system, mixing, and processing. First, recycled and classified silicone waste is crushed into small pieces, then washed and dried. Next, surface modification is performed, followed by freezing to prevent embrittlement. Then, grinding and grading are carried out to construct a multi-level filler system. Finally, the mixture is mixed and processed into silicone products. The entire process achieves the recycling of silicone waste, which is environmentally friendly and efficient. Through surface modification technology and a multi-level filler synergistic reinforcement system, the interfacial bonding strength between recycled and new silicone is significantly improved, solving the problem of interfacial debonding. This allows for a significant increase in the proportion of recycled silicone added, reaching up to 90%, far exceeding the 60% of existing technologies.

Description

Technical Field

[0001] This invention relates to the field of polymer material recycling, specifically to a method for recycling silicone, and particularly to a method for efficiently recycling and reusing waste silicone using liquid nitrogen cold solidification technology and a multi-stage filler synergistic reinforcement system. Background Technology

[0002] Silicone is widely used in electronics, medical, automotive, and construction industries due to its excellent heat resistance, weather resistance, electrical insulation, and biocompatibility. However, with the large-scale use of silicone products, the disposal of waste silicone has become increasingly prominent. As a cross-linked polymer, silicone's cross-linked structure makes it difficult to degrade. Traditional disposal methods often involve landfilling or incineration, which not only wastes resources but also causes environmental pollution.

[0003] Currently, there are two main methods for recycling silicone: physical crushing and chemical pyrolysis. Physical crushing involves breaking waste silicone into powder and adding it to new silicone as a filler. For example, Chinese patent CN1421306A discloses a silicone recycling process and its application. Its main steps include crushing and mixing waste silicone material, then adding it as a filler to new silicone products for molding. While this method is simple to operate, the proportion of recycled material added is limited (generally not exceeding 60%), and poor interfacial bonding leads to a significant decrease in the mechanical properties of the product. Furthermore, this method does not take effective measures to improve the interfacial bonding between recycled and new silicone, nor does it solve the problem of high energy consumption during the grinding process.

[0004] Chemical pyrolysis involves breaking down silica gel into low-molecular-weight organosilicon monomers or oligomers using high temperatures and catalysts, which are then repolymerized for reuse. While this method can yield high-quality recycled silica gel, it is complex, energy-intensive, and may produce harmful byproducts, making it unsuitable for large-scale industrial applications.

[0005] Therefore, there is an urgent need for an efficient, economical, and environmentally friendly method for recycling silica gel that can both increase the proportion of recycled materials added and maintain the excellent performance of the product. Summary of the Invention

[0006] The purpose of this invention is to address the problems existing in the prior art by providing a method for recycling silica gel. This method employs liquid nitrogen cold solidification technology and a multi-stage filler synergistic reinforcement system, which can effectively solve problems such as poor interface bonding between recycled silica gel and new silica gel and limited recycling ratio, thereby achieving efficient reuse of high-ratio recycled silica gel.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for recycling silica gel includes the following steps: a) Recycling process: Collect silicone components from consumer electronics products and silicone waste from industrial production, classify them according to material, color and hardness, and remove metal, plastic impurities and severely aged silicone. b) Crushing process: The recycled silicone is put into a special silicone crusher to crush the silicone into small pieces of 2-5 cm; c) Cleaning process: Place the broken silicone fragments into a cleaning tank, soak them in a 1-3% NaOH aqueous solution, and then clean them with ultrasonic waves at a frequency of 20-40kHz and a power of 300-500W for 30-60 minutes at a temperature of 40-60℃. After that, rinse them with clean water 3-5 times and dry them until the moisture content does not exceed 0.5%. d) Surface modification step: Immerse the dried silica gel fragments in a solution prepared with 5-10 parts by weight of γ-aminopropyltriethoxysilane, 85-90 parts by weight of anhydrous ethanol and 5 parts by weight of deionized water. The solution pH is 4-5. Stir and sonicate at 40-60℃ for 30-60 minutes, and then heat cure at 110-130℃ for 2-3 hours. e) Liquid nitrogen freezing process: The modified silicone fragments are placed in a liquid nitrogen freezing device and frozen at -196℃ for 5-15 minutes to make the silicone reach a brittle state with a Shore D hardness of 70 or higher. f) Grinding process: The brittle silicone fragments are placed in a cryogenic grinder at 1500-3000 rpm and ground for 10-20 minutes. Then, the ground silicone powder is separated into three particle sizes: 50-150 mesh, 151-300 mesh, and 301-500 mesh, with proportions of 40%, 40%, and 20%, respectively, using air classification technology. g) Construction of multi-level filler system: The ground silica powder and surface-modified nano silica are mixed at a weight ratio of 80-95:5-15, and 2-5 parts by weight of organosilicon-modified polyether and 0.1-0.5 parts by weight of antioxidant are added. The mixture is homogenized in a high-speed mixer at 500-1000 rpm for 10-15 minutes. h) Mixing step: Liquid silicone rubber, the constructed multi-stage filler system and 0.8-1.2 parts by weight of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane crosslinking agent are added sequentially to a twin-screw mixer and mixed for 10-15 minutes at 100-120℃ and 40-60 rpm. i) Processing stage: According to product requirements, the mixed materials are processed into silicone products through molding processes such as injection molding, extrusion or compression molding.

[0008] Preferably, the above method further includes a cage-type polysiloxane modification step, which is located between step f) and step g), including synthesizing octaphenyl cage-type silsesquioxane, preparing vinyl-functionalized polysiloxane, preparing amino-functionalized polysiloxane, and surface modifying the ground silica gel powder with amino-functionalized polysiloxane.

[0009] In one embodiment of the present invention, the method for synthesizing the octaphenyl cage-type silsesquioxane includes: dissolving phenyltrichlorosilane in anhydrous tetrahydrofuran, adding an aqueous tetrahydrofuran solution dropwise under nitrogen protection, the reaction temperature being 0-5°C, the dropwise addition time being 2 hours, raising the temperature to room temperature after the dropwise addition is completed and continuing the reaction for 24 hours, then adding sodium hydroxide solution for neutralization, separating the organic phase and drying, removing the solvent by vacuum distillation, and obtaining the octaphenyl cage-type silsesquioxane by recrystallization from hot toluene.

[0010] Preferably, the preparation method of the vinyl-functionalized polysiloxane includes: dissolving octaphenyl cage-type silsesquioxane and potassium hydroxide in anhydrous tetrahydrofuran, stirring at room temperature for 30 minutes under nitrogen protection, then slowly adding vinyltrichlorosilane dropwise over 1 hour, continuing the reaction at room temperature for 24 hours, filtering after the reaction is complete, removing the solvent by vacuum distillation, and purifying by column chromatography to obtain the vinyl-functionalized polysiloxane.

[0011] Furthermore, the preparation method of the amino-functionalized polysiloxane includes: dissolving vinyl-functionalized polysiloxane in anhydrous tetrahydrofuran, adding 5% platinum carbon catalyst, introducing ammonia gas under nitrogen protection, reacting at 40°C for 6 hours, cooling to room temperature after the reaction is completed, filtering to remove the catalyst, and removing the solvent by vacuum distillation to obtain the amino-functionalized polysiloxane.

[0012] Meanwhile, the method for surface modification of the ground silicone powder with amino-functionalized polysiloxane includes: mixing the ground silicone powder with 0.5-2.0% of the mass of the silicone powder in a tetrahydrofuran solvent, reacting at 50-70°C for 4-6 hours, and then drying at 80-100°C for 4-6 hours.

[0013] In another embodiment of the present invention, the surface modification method of the nano-silica includes: dispersing nano-silica in ethanol and sonicating for 30 minutes, adding vinyltriethoxysilane, reacting at 60°C for 4 hours, centrifuging after the reaction is completed, washing with ethanol 3 times, and drying at 80°C for 12 hours to obtain surface-modified nano-silica.

[0014] Preferably, the parameters for injection molding in step i) are: injection temperature 170-190℃, injection pressure 15-25MPa; or the parameters for extrusion molding are: extrusion temperature 150-170℃; or the parameters for compression molding are: compression temperature 160-180℃, compression pressure 10-20MPa.

[0015] Furthermore, the material composition after mixing in step h) may be: a) 70-80 parts by weight of surface-modified recycled silica powder, 5-10 parts by weight of surface-modified nano silica and 20-30 parts by weight of liquid silicone rubber; or b) 60-70 parts by weight of surface-modified recycled silica powder, 5-15 parts by weight of surface-modified nano silica and 25-35 parts by weight of liquid silicone rubber; or c) 80-90 parts by weight of surface-modified recycled silica powder, 5-10 parts by weight of surface-modified nano silica and 10-20 parts by weight of liquid silicone rubber.

[0016] Finally, the method also includes a quality inspection step, which includes visual inspection, Shore hardness test, tensile strength test, tear strength test, compression set test, heat resistance test, and electrical insulation test.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. By using surface modification technology and a multi-level filler synergistic reinforcement system, the interfacial bonding strength between recycled silica gel and new silica gel is significantly improved, solving the problem of interfacial debonding. This allows the proportion of recycled silica gel to be added to be greatly increased, up to 90%, which is much higher than the 60% of the existing technology.

[0018] 2. Liquid nitrogen cryogenic solidification technology is used to rapidly embrittle silica gel at ultra-low temperatures (-196℃), significantly reducing grinding energy consumption and improving grinding efficiency and powder quality. Simultaneously, the liquid nitrogen cryogenic solidification treatment generates micro-stress within the silica gel, forming microcracks, which is beneficial for obtaining silica gel powder with regular shapes and rough surfaces during the grinding process.

[0019] 3. Introducing cage-like polysiloxanes (POSS) as interface modulators, utilizing their nanoscale size (1-3nm) and special cage-like molecular structure as "nano-crosslinking points" to connect recycled silica gel with new silica gel, thereby enhancing interfacial bonding at the molecular level.

[0020] 4. By designing a multi-stage filler system and particle size gradient distribution, the spatial arrangement of the filler was optimized, achieving the best filling efficiency and improving the mechanical properties and thermal stability of the composite material.

[0021] 5. The method and process of the present invention are highly versatile and can be applied to various molding processes such as injection molding, extrusion, and compression molding. It can also meet the performance requirements of different products and has broad application prospects. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0023] This invention provides a method for recycling silica gel. This method organically combines a variety of innovative techniques, such as surface modification technology, liquid nitrogen cold solidification technology, multi-level filler synergistic reinforcement system, and cage-type multi-component siloxane interface control technology, to solve technical problems such as weak interface bonding between recycled silica gel and new silica gel and limited recycling ratio, thereby achieving efficient reuse of high-ratio recycled silica gel.

[0024] In this invention, the main raw materials used include: recycled silicone (derived from silicone components in consumer electronics and silicone waste from industrial production), liquid silicone rubber (LSR), γ-aminopropyltriethoxysilane (KH550, CAS No.: 919-30-2, domestic industrial grade, purity ≥98%), vinyltriethoxysilane (VS-6011, CAS No.: 78-08-0, domestic industrial grade, purity ≥97%), and nano-silica (A200 type, produced by Degussa GmbH, Germany, average particle size 20-30nm, specific surface area 200m²). 2 / g), 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (CAS No.: 78-63-7, Arkema Luperox 101 brand), organosilicon modified polyether (compatibility agent) and antioxidant 2,6-di-tert-butyl-4-methylphenol (BHT, CAS No.: 128-37-0), etc.

[0025] Example 1: Preparation method of standard recycled silica gel composite material This embodiment provides a method for preparing a standard recycled silica gel composite material, which includes the following steps: (1) Recycling process: Collect discarded silicone buttons and sealing rings from an electronics factory, classify them according to material, color and hardness, and use magnets and manual screening to remove impurities such as metal and plastic, while discarding silicone parts that are severely aged, discolored and cracked.

[0026] (2) Crushing stage: The sorted recycled silicone is fed into a specially designed silicone crusher. The crusher's blades are made of carbide and designed with serrated edges to accommodate the high elasticity of silicone. The crusher speed is adjusted to 800 rpm to crush the silicone into small pieces with an average size of about 3 cm.

[0027] (3) Cleaning process: Prepare a 2% NaOH aqueous solution as the cleaning solution. Place the broken silica gel fragments into a stainless steel cleaning tank and clean them using an ultrasonic cleaning device with a frequency of 30kHz and a power of 400W. The temperature is controlled at 50℃ and the cleaning time is 45 minutes. After cleaning, rinse four times with tap water to ensure that the alkali solution is completely removed. Finally, use a centrifugal dehydrator to remove most of the water and then put it into a ventilated drying oven to dry at 90℃ for 3 hours to reduce the moisture content to below 0.3%.

[0028] (4) Surface Modification Step: Prepare a surface modification solution by mixing 7 parts by weight of γ-aminopropyltriethoxysilane (KH550), 88 parts by weight of anhydrous ethanol, and 5 parts by weight of deionized water, and adjusting the pH to 4.5 with glacial acetic acid. Immerse the dried silica gel fragments in this solution and sonicate at 50°C with stirring (150 rpm) for 45 minutes. After treatment, remove the silica gel fragments and place them in a ventilated oven for heat curing at 120°C for 2.5 hours to allow the silane coupling agent to fully react with and cure the silica gel surface.

[0029] (5) Liquid nitrogen freezing process: The surface-modified silica gel fragments are placed in a dedicated liquid nitrogen freezing chamber, and liquid nitrogen is slowly injected to ensure that the silica gel fragments are completely immersed in the liquid nitrogen. Freezing is then carried out at -196℃ for 10 minutes. During this process, the silica gel rapidly becomes brittle due to the ultra-low temperature, reaching a hardness of Shore D 75. At this point, the silica gel becomes brittle and easily broken, and numerous micro-cracks are generated internally, which is beneficial for subsequent grinding. Approximately 0.8 kg of liquid nitrogen is consumed per kilogram of silica gel fragments.

[0030] (6) Grinding process: The brittle silica fragments were immediately transferred to a cryogenic grinder and ground for 15 minutes at 2000 rpm. The ground silica powder was then separated into three particle sizes by an air classifier: 50-150 mesh (coarse), 151-300 mesh (medium), and 301-500 mesh (fine), and mixed in a ratio of 40%:40%:20%.

[0031] (7) Cage-type polysiloxane modification process: includes the following sub-steps: a. Synthesis of octaphenylcage-type silsesquioxane (OPS): In a 500 mL three-necked flask, 40 g of phenyltrichlorosilane and 200 mL of anhydrous tetrahydrofuran were added. Under nitrogen protection and mechanical stirring, 21 g of water dissolved in 100 mL of tetrahydrofuran was slowly added dropwise to the reaction system at 0-5 °C over 2 hours. After the addition was complete, the temperature was raised to room temperature and the reaction continued for 24 hours. A suitable amount of 10% sodium hydroxide solution was added to the reaction mixture for neutralization. The organic phase was separated, dried over anhydrous magnesium sulfate, filtered, and the solvent was removed by vacuum distillation to obtain the crude product. The crude product was dissolved in hot toluene for recrystallization to obtain white crystalline octaphenylcage-type silsesquioxane in a yield of 78%.

[0032] b. Preparation of vinyl-functionalized polysiloxanes (VI-POSS): In a 250 mL three-necked flask, 10 g of octaphenylcage-type silsesquioxane (OPS), 2 g of potassium hydroxide, and 100 mL of anhydrous tetrahydrofuran were added, and the mixture was stirred at room temperature for 30 minutes under nitrogen protection. Subsequently, 5 g of vinyltrichlorosilane was slowly added dropwise over 1 hour, and the reaction was continued at room temperature for 24 hours. After the reaction was complete, the solid was removed by filtration, and the solvent was removed by vacuum distillation of the filtrate to obtain the crude product. Purification was performed using silica gel column chromatography (eluent: hexane / ethyl acetate = 20:1) to obtain partially vinyl-substituted POSS (VI-POSS) in 68% yield.

[0033] c. Preparation of amino-functionalized polysiloxanes (NH2-POSS): In a 100 mL three-necked flask, 5 g of VI-POSS, 50 mL of anhydrous tetrahydrofuran, and 0.1 g of platinum-carbon catalyst (5%) were added. Under nitrogen protection, ammonia gas was introduced, and the reaction was carried out at 40 °C for 6 hours. After the reaction was completed, the mixture was cooled to room temperature, the catalyst was removed by filtration, and the solvent was removed by vacuum distillation of the filtrate to obtain NH2-POSS in 82% yield.

[0034] d. POSS modification of polished silica gel: The polished silica gel powder obtained in step (6) was mixed with 1% by weight (relative to silica gel) of NH2-POSS in 100 mL of tetrahydrofuran and reacted at 60 °C for 5 hours to allow NH2-POSS to fully bond with the silica gel surface. After the reaction was completed, the mixture was filtered, and the solid was dried at 90 °C for 5 hours to obtain POSS-modified silica gel powder.

[0035] (8) Surface modification of nano-silica: 20g of nano-silica (A200 type) was dispersed in 200mL of anhydrous ethanol and sonicated for 30 minutes to ensure thorough dispersion. Then, 5g of vinyltriethoxysilane (VS-6011) was added, and the reaction was carried out at 60℃ for 4 hours. After the reaction was completed, the solid was separated by centrifugation (5000rpm, 10 minutes), washed three times with ethanol, and dried at 80℃ for 12 hours to obtain surface-modified nano-silica (VS-SiO2).

[0036] (9) Construction of the multi-stage packing system: The components were mixed according to the following ratio: 75 parts by weight of POSS-modified silica powder, 5 parts by weight of surface-modified nano silica (VS-SiO2), 3 parts by weight of organosilicon-modified polyether (composite agent), and 0.2 parts by weight of antioxidant BHT. The mixture was placed in a high-speed mixer and homogenized at 700 rpm for 12 minutes to obtain the multi-stage packing system.

[0037] (10) Mixing step: 20 parts by weight of liquid silicone rubber (LSR), 83.2 parts by weight of the multi-stage filler system in step (9) and 0.8 parts by weight of crosslinking agent (2,5-dimethyl-2,5-di(tert-butylperoxy)hexane) are added to a twin-screw mixer in sequence and mixed at 110°C and 50 rpm for 12 minutes to obtain a uniform composite material.

[0038] (11) Molding and processing: The mixed material is processed into silicone button samples by injection molding. The injection temperature is 180℃, the injection pressure is 20MPa, the mold temperature is 160℃, and the vulcanization time is 60 seconds / mm thickness.

[0039] (12) Quality Inspection: A series of performance tests were conducted on the prepared silicone button samples, and the results are as follows: Hardness: Shore A 55; Tensile strength: 6.5 MPa; Elongation at break: 350%; Tear strength: 20 kN / m; Compression set (70℃ / 22h): 15%; Heat resistance: Tensile strength retention rate is 87% after 200℃ / 72h; Example 2: Preparation method of high-performance recycled silica gel composite material This embodiment provides a method for preparing a high-performance recycled silicone composite material, mainly applicable to silicone products with high strength requirements, such as automotive seals. The method includes the following steps: (1) Recycling process: Collect waste silicone sealing strips and gaskets from an auto parts factory, classify them according to material, color and hardness, and use a combination of magnetic separation equipment and manual screening to remove impurities such as metal and plastic, and discard severely aged and oil-contaminated silicone parts.

[0040] (2) Crushing process: The sorted recycled silicone is put into a special silicone crusher, and the speed is set to 1000 rpm to crush the silicone into small pieces with an average size of about 2.5 cm.

[0041] (3) Cleaning process: Prepare a 3% NaOH aqueous solution as the cleaning solution. Place the crushed silica gel fragments into a stainless steel cleaning tank and clean them using an ultrasonic cleaning device with a frequency of 40kHz and a power of 500W. The temperature is controlled at 60℃ and the cleaning time is 60 minutes. After cleaning, rinse five times with tap water to ensure that the alkali solution is completely removed. Finally, dry the silica gel using a hot air drying device at 100℃ for 4 hours to reduce the moisture content to below 0.2%.

[0042] (4) Surface modification step: Prepare a surface modification solution by mixing 10 parts by weight of γ-aminopropyltriethoxysilane (KH550), 85 parts by weight of anhydrous ethanol, and 5 parts by weight of deionized water, and adjusting the pH to 4.0 with glacial acetic acid. Immerse the dried silica gel fragments in this solution and sonicate at 60°C with stirring (200 rpm) for 60 minutes. After treatment, remove the silica gel fragments and place them in a ventilated oven for heat curing at 130°C for 3 hours.

[0043] (5) Liquid nitrogen freezing process: The surface-modified silica gel fragments are placed in a dedicated liquid nitrogen freezing chamber, and liquid nitrogen is slowly injected to ensure that the silica gel fragments are completely immersed in the liquid nitrogen. The chamber is then frozen at -196°C for 15 minutes. During this process, the silica gel hardness value reaches Shore D 80, and approximately 1.0 kg of liquid nitrogen is consumed per kilogram of silica gel fragments.

[0044] (6) Grinding process: The brittle silicone fragments were immediately transferred to a cryogenic grinder and ground for 20 minutes at 3000 rpm. The ground silicone powder was then separated into three particle sizes by an air classifier: 50-150 mesh (coarse), 151-300 mesh (medium), and 301-500 mesh (fine), and mixed in a ratio of 40%:40%:20%.

[0045] (7) Cage-type polysiloxane modification step: similar to step (7) in Example 1, but the amount of NH2-POSS used is adjusted to 2% of the mass of silica gel, the reaction temperature is increased to 70°C, and the reaction time is extended to 6 hours to obtain better surface modification effect.

[0046] (8) Surface modification of nano-silica: Same as in Example 1.

[0047] (9) Construction of the multi-stage packing system: The components were mixed according to the following ratio: 65 parts by weight of POSS-modified silica powder, 10 parts by weight of surface-modified nano silica (VS-SiO2), 4 parts by weight of organosilicon-modified polyether (composite agent), and 0.3 parts by weight of antioxidant BHT. The mixture was placed in a high-speed mixer and homogenized at 800 rpm for 15 minutes to obtain the multi-stage packing system.

[0048] (10) Mixing step: 25 parts by weight of liquid silicone rubber (LSR), 79 parts by weight of the multi-stage filler system in step (9) and 1.0 parts by weight of crosslinking agent (2,5-dimethyl-2,5-di(tert-butylperoxy)hexane) are added to a twin-screw mixer in sequence and mixed at 120°C and 60 rpm for 15 minutes to obtain a uniform composite material.

[0049] (11) Molding process: The mixed material is processed into silicone sealing ring samples by compression molding. The molding temperature is 180℃, the molding pressure is 15MPa, and the vulcanization time is 120 seconds.

[0050] (12) Quality Inspection: A series of performance tests were conducted on the prepared silicone sealing ring samples, and the results are as follows: Hardness: Shore A 60; Tensile strength: 8.0 MPa; Elongation at break: 320%; Tear strength: 25 kN / m; Compression set (70℃ / 22h): 12%; Heat resistance: Tensile strength retention rate is 92% after 72 hours at 200℃. Example 3: Preparation method of ultra-high recyclability recycled silica gel composite material This embodiment provides a method for preparing an ultra-high recyclability recycled silicone composite material, suitable for silicone products with high cost requirements and relatively low performance requirements, such as building sealing strips and general industrial rubber gaskets. The method is characterized by a recycled silicone addition ratio as high as 85%, maximizing the utilization of waste silicone. The specific steps are as follows: (1) Recycling process: Waste silicone sealing strips from a building materials factory and silicone scraps generated during industrial production are collected and roughly classified according to material, color, and hardness. Silicone parts containing metal inserts and severely aged silicone products are removed. During the sorting process, a combination of simple magnetic separation and manual selection is used to ensure the basic purity of the recycled materials.

[0051] (2) Crushing stage: The sorted recycled silicone is put into a regular rubber crusher, and the speed is adjusted to 600 rpm to crush the silicone into small pieces with an average size of about 4-5 cm. Since this embodiment focuses more on cost control, the crushing degree requirement is relatively low.

[0052] (3) Cleaning process: Prepare a 1% NaOH aqueous solution as the cleaning solution. Place the broken silica gel fragments into a regular cleaning tank and clean them using an ultrasonic cleaning device with a frequency of 20kHz and a power of 300W. The temperature is controlled at 40℃ and the cleaning time is 30 minutes. After cleaning, rinse three times with tap water, dehydrate by centrifugation, and dry at 80℃ for 2 hours to reduce the moisture content to about 0.5%.

[0053] (4) Surface modification step: Prepare a surface modification solution by mixing 5 parts by weight of γ-aminopropyltriethoxysilane (KH550), 90 parts by weight of anhydrous ethanol, and 5 parts by weight of deionized water, and adjusting the pH to 5.0 with glacial acetic acid. Immerse the dried silica gel fragments in this solution and sonicate at 40°C with stirring (100 rpm) for 30 minutes. After treatment, remove the silica gel fragments and place them in a ventilated oven for heat curing at 110°C for 2 hours.

[0054] (5) Liquid nitrogen curing step: The surface-modified silicone fragments are placed in a simple liquid nitrogen treatment container, and liquid nitrogen is added to completely immerse the silicone fragments. The mixture is then cured at -196°C for 5 minutes. Considering cost factors, the amount of liquid nitrogen used in this embodiment is relatively small, approximately 0.7 kg liquid nitrogen / kg silicone, and the curing time is correspondingly shortened. The silicone hardness value only needs to reach approximately Shore D 70.

[0055] (6) Grinding process: The brittle silica fragments were immediately transferred to a regular grinder and ground for 10 minutes at 1500 rpm. The ground silica powder was then separated into three particle sizes using a simple sieving system: 50-150 mesh (coarse), 151-300 mesh (medium), and 301-500 mesh (fine), and mixed in a ratio of 40%:40%:20%.

[0056] (7) Cage-type polysiloxane modification step: Similar to Example 1, but in order to reduce costs, the amount of NH2-POSS used in this example is reduced to 0.5% of the mass of silica gel, the reaction temperature is 50°C, and the reaction time is 4 hours.

[0057] (8) Nano silica surface modification: Same as in Example 1, but with reduced amount.

[0058] (9) Construction of the multi-stage packing system: The components were mixed according to the following ratio: 85 parts by weight of POSS-modified silica powder, 7 parts by weight of surface-modified nano silica (VS-SiO2), 5 parts by weight of organosilicon-modified polyether (composite agent), and 0.4 parts by weight of antioxidant BHT. The mixture was placed in a high-speed mixer and homogenized at 500 rpm for 10 minutes to obtain the multi-stage packing system.

[0059] (10) Mixing step: 8 parts by weight of liquid silicone rubber (LSR), 97.4 parts by weight of the multi-stage filler system in step (9) and 1.2 parts by weight of crosslinking agent (2,5-dimethyl-2,5-di(tert-butylperoxy)hexane) are added to a twin-screw mixer in sequence and mixed at 100°C and 40 rpm for 10 minutes to obtain a uniform composite material.

[0060] (11) Molding and processing: The mixed material is processed into silicone sealing strip samples by extrusion molding. The extrusion temperature is 150℃ and the vulcanization time is 180 seconds.

[0061] (12) Quality Inspection: A series of performance tests were conducted on the prepared silicone sealing strip samples, and the results are as follows: Hardness: Shore A 65; Tensile strength: 5.0 MPa; Elongation at break: 280%; Tear strength: 18 kN / m; Compression set (70℃ / 22h): 18%; Heat resistance: Tensile strength retention rate is 80% after 72 hours at 200℃; Comparative Example 1: Preparation method for recovering silica gel using conventional physical pulverization method To verify the technical effects of this invention, the following comparative examples were designed, using a conventional physical pulverization method to prepare recycled silica gel composite materials, without surface modification, liquid nitrogen cold solidification, and a multi-stage filler synergistic reinforcement system. The specific steps are as follows: (1) Recycling and sorting: Same as in Example 1.

[0062] (2) Crushing: Same as in Example 1.

[0063] (3) Cleaning: Simply rinse the silica gel fragments with tap water to remove surface dust and impurities, and then dry them at 80°C for 2 hours.

[0064] (4) Grinding: The dried silica gel fragments were ground directly at room temperature using a regular rubber grinder at 1200 rpm for 40 minutes. Since the powder was not subjected to liquid nitrogen cooling treatment, the grinding process was very difficult and energy-intensive, and the resulting powder had an uneven particle size distribution, mostly concentrated between 100-300 mesh.

[0065] (5) Mixing: Mix 60 parts by weight of the ground silica gel powder with 40 parts by weight of liquid silicone rubber (LSR) and 1 part by weight of crosslinking agent, and mix at 110°C for 15 minutes. Because the surface of the recycled silica gel is untreated, its compatibility with new silica gel is poor, resulting in uneven dispersion during the mixing process.

[0066] (6) Molding process: The silicone button sample was processed using the same injection molding process as in Example 1.

[0067] (7) Quality Inspection: The performance of the produced product was tested, and the results are as follows: Hardness: Shore A 58; Tensile strength: 3.2 MPa; Elongation at break: 220%; Tear strength: 12kN / m; Compression set (70℃ / 22h): 25%; Heat resistance: Tensile strength retention rate is 60% after 200℃ / 72h; Comparative Example 2: Preparation method of high-proportion recycled silica gel (without synergistic reinforcement system) This comparative example uses conventional surface treatment methods and a high proportion (75%) of recycled silica gel, but does not employ liquid nitrogen cold-setting technology or a multi-stage filler synergistic reinforcement system. The specific steps are as follows: (1) Recycling, sorting and crushing: Same as in Example 1.

[0068] (2) Cleaning: Same as in Example 1.

[0069] (3) Surface treatment: Ordinary silane coupling agent was used for treatment, but POSS modification and multi-level filler construction were not carried out. The silica gel fragments were immersed in a 5% concentration of KH550 ethanol solution and treated at room temperature for 2 hours, and then dried at 100℃ for 1 hour.

[0070] (4) Grinding: Grinding is carried out at room temperature using a regular grinder, with the grinding time extended to 60 minutes to compensate for the lack of liquid nitrogen cooling. Grinding has high energy consumption, low efficiency, and results in uneven particle size distribution of the powder.

[0071] (5) Mixing: Mix 75 parts by weight of the ground silica gel powder with 25 parts by weight of liquid silicone rubber (LSR) and 1 part by weight of crosslinking agent, and mix at 110°C for 20 minutes.

[0072] (6) Molding process: The silicone button sample was processed using the same injection molding process as in Example 1.

[0073] (7) Quality Inspection: The performance of the produced product was tested, and the results are as follows: Hardness: Shore A 62; Tensile strength: 4.0 MPa; Elongation at break: 230%; Tear strength: 14 kN / m; Compression set (70℃ / 22h): 23%; Heat resistance: Tensile strength retention rate is 65% after 200℃ / 72h.

[0074] Analysis of Results from Examples and Comparative Examples To more intuitively compare the performance differences between the various embodiments of the present invention and the comparative examples, the main performance indicators are summarized in the table below: ; As can be seen from the table above, all three embodiments of the present invention exhibit significant performance advantages compared to the comparative examples: 1. Regarding the proportion of recycled silica gel added: Example 3 of the present invention achieves a high recycling rate of 85%, which is much higher than the 60% of Comparative Example 1 and the 75% of Comparative Example 2, demonstrating the advantages of the present invention in increasing the proportion of recycled materials used.

[0075] 2. Mechanical properties: Even with the same proportion of recycled material (75% in both Example 1 and Comparative Example 2), the tensile strength, elongation at break, and tear strength of the present invention were increased by 62.5%, 52.2%, and 42.9%, respectively. Even with an ultra-high recycling ratio (85% in Example 3), the performance was still better than that of Comparative Example 2 (75%), which fully demonstrates the effectiveness of the multi-level synergistic reinforcement system of the present invention.

[0076] 3. Heat resistance: The heat resistance of each embodiment of the present invention is significantly better than that of the comparative example, especially the heat resistance of Example 2, which is the most outstanding. After 200℃ / 72h, the strength retention rate reaches 92%, which is 27 percentage points higher than that of Comparative Example 2, indicating that the material prepared by the method of the present invention has excellent thermal stability.

[0077] 4. Regarding compression set: The compression set value of the present invention is significantly lower than that of the comparative example, indicating that it has better resilience and long-term performance.

[0078] The fundamental reason for the above performance differences lies in the organic combination of several innovative methods employed in this invention, including surface modification technology, liquid nitrogen cold solidification technology, a multi-level filler synergistic reinforcement system, and cage-type multi-component siloxane interface control technology. These methods effectively address the problem of weak interfacial bonding between recycled and virgin silica gel. Specifically, liquid nitrogen cold solidification technology embrittles the silica gel, significantly improving grinding efficiency and powder quality; surface modification technology and POSS interface control technology enhance interfacial bonding at the molecular level; and the multi-level filler system and particle size gradient distribution optimize the filler spatial arrangement, achieving optimal filling efficiency.

[0079] To further verify the performance of the recycled silica composite material prepared by the method of the present invention in practical applications, simulated application tests were conducted on the material prepared in Example 1: 1. Keyboard key durability test: The silicone composite material prepared in Example 1 was processed into laptop keyboard keys and subjected to a pressing test on professional testing equipment. The pressing force was 5N, the frequency was 2 times / second, and the test was conducted continuously for 1 million times. The test results showed that the keys prepared with the material of this invention did not show obvious deformation, had good pressing resilience, and stable tactile feel, with a pass rate of 100%. In contrast, the keys prepared with the material of Comparative Example 1 began to show obvious deformation after about 600,000 presses, the tactile feel became hard, and the pass rate was only 65%.

[0080] 2. Oil-resistant sealing ring test: The silicone composite material prepared in Example 2 was processed into an automotive oil seal, immersed in engine oil at 90°C for 168 hours, and then removed to test its dimensional change, hardness change, and tensile strength. The test results show that the oil seal prepared by the material of this invention has a dimensional change of less than 2%, a hardness change of less than 5 degrees, and a tensile strength decrease of less than 10%, fully meeting the requirements for automotive oil seals. However, the oil seal prepared using the material of Comparative Example 2, under the same conditions, showed a dimensional change of more than 5%, a hardness change of 8 degrees, and a tensile strength decrease of more than 20%, failing to meet the requirements.

[0081] 3. Weather resistance test of building sealing strips: The silicone composite material prepared in Example 3 was processed into building sealing strips and placed in an artificial climate aging chamber for testing. The simulated conditions were: ultraviolet irradiation intensity of 0.68 W / m². 2 The temperature was cycled from -20℃ to 70℃, and the humidity from 30% to 90%, for a total testing time of 1000 hours (equivalent to approximately 5 years of actual use). Test results showed that the sealing strip prepared with the material of this invention exhibited no obvious surface cracking, an increase in hardness of less than 8 degrees, and a decrease in tensile strength of less than 15%, maintaining good elasticity and sealing performance. In contrast, the sealing strip prepared with the material of Comparative Example 2, under the same conditions, showed obvious surface cracking, an increase in hardness exceeding 15 degrees, a decrease in tensile strength exceeding 30%, and a significant decline in sealing performance.

[0082] The above simulation test results further demonstrate that the recycled silicone composite material prepared by the method of the present invention has excellent practical application performance, can meet the usage requirements of different fields, and has broad application prospects.

[0083] The silica gel recycling method provided by this invention has the following promising industrial applications: 1. Economic Benefits: According to cost accounting, the raw material cost can be reduced by 30-50% using the method of this invention, especially with ultra-high recovery rates (85%), where the cost advantage is even more significant. Meanwhile, although the liquid nitrogen cooling technology introduces liquid nitrogen costs, it greatly improves grinding efficiency and reduces grinding energy consumption, resulting in a significant overall cost advantage.

[0084] 2. Environmental Benefits: The method of this invention can effectively reduce the landfill and incineration of waste silicone, thereby reducing environmental pollution. Based on my country's current annual silicone production of approximately 1 million tons, if 10% of the waste silicone is recycled using this method, the annual amount of waste silicone to be processed can be reduced by 100,000 tons, resulting in a reduction of approximately 20,000 tons of carbon dioxide emissions.

[0085] 3. Expanding Application Areas: The recycled silicone composite material prepared by the method of this invention has excellent performance and can be widely used in various fields such as buttons and seals in electronic products, sealing strips and shock absorbers in the automotive industry, sealing strips in the construction industry, and non-implantable parts of medical devices.

[0086] 4. Technology Promotion Value: The innovative features of this invention, such as liquid nitrogen cold solidification technology, multi-level filler synergistic reinforcement system, and cage-type multi-component siloxane interface control technology, are not only applicable to the recycling of silicone, but can also be extended to the recycling and reuse of other elastomer materials, such as natural rubber and nitrile rubber, thus having broader technology promotion value.

[0087] In summary, the silicone recycling method provided by this invention has significant technological innovation and application value, and can provide an effective way to solve the problem of waste silicone disposal, while also providing new technical ideas for the recycling and reuse of rubber materials.

Claims

1. A method for recycling silica gel, characterized in that, The method includes the following steps: a) Recycling process: Collect silicone components from consumer electronics products and silicone waste from industrial production, classify them according to material, color and hardness, and remove metal, plastic impurities and severely aged silicone. b) Crushing process: The recycled silicone is put into a special silicone crusher to crush the silicone into small pieces of 2-5 cm; c) Cleaning process: Place the broken silicone fragments into a cleaning tank, soak them in a 1-3% NaOH aqueous solution, and then clean them with ultrasonic waves at a frequency of 20-40kHz and a power of 300-500W for 30-60 minutes at a temperature of 40-60℃. After that, rinse them with clean water 3-5 times and dry them until the moisture content does not exceed 0.5%. d) Surface modification step: Immerse the dried silica gel fragments in a solution prepared with 5-10 parts by weight of γ-aminopropyltriethoxysilane, 85-90 parts by weight of anhydrous ethanol and 5 parts by weight of deionized water. The solution pH is 4-5. Stir and sonicate at 40-60℃ for 30-60 minutes, and then heat cure at 110-130℃ for 2-3 hours. e) Liquid nitrogen freezing process: The modified silicone fragments are placed in a liquid nitrogen freezing device and frozen at -196℃ for 5-15 minutes to make the silicone reach a brittle state with a Shore D hardness of 70 or higher. f) Grinding process: The brittle silicone fragments are placed in a cryogenic grinder at 1500-3000 rpm and ground for 10-20 minutes. Then, the ground silicone powder is separated into three particle sizes: 50-150 mesh, 151-300 mesh, and 301-500 mesh, with proportions of 40%, 40%, and 20%, respectively, using air classification technology. g) Construction of multi-level filler system: The ground silica powder and surface-modified nano silica are mixed at a weight ratio of 80-95:5-15, and 2-5 parts by weight of organosilicon-modified polyether and 0.1-0.5 parts by weight of antioxidant are added. The mixture is homogenized in a high-speed mixer at 500-1000 rpm for 10-15 minutes. h) Mixing step: Liquid silicone rubber, the constructed multi-stage filler system and 0.8-1.2 parts by weight of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane crosslinking agent are added sequentially to a twin-screw mixer and mixed for 10-15 minutes at 100-120℃ and 40-60 rpm. i) Processing stage: According to product requirements, the mixed materials are processed into silicone products through molding processes such as injection molding, extrusion or compression molding.

2. The method for recycling silica gel according to claim 1, characterized in that, The method further includes a cage-type polysiloxane modification step, which is located between step f) and step g), including synthesizing octaphenyl cage-type silsesquioxane, preparing vinyl-functionalized polysiloxane, preparing amino-functionalized polysiloxane, and surface modifying the ground silica powder with amino-functionalized polysiloxane.

3. The method for recycling silica gel according to claim 2, characterized in that, The method for synthesizing the octaphenyl cage-type silsesquioxane includes: dissolving phenyltrichlorosilane in anhydrous tetrahydrofuran, adding an aqueous tetrahydrofuran solution dropwise under nitrogen protection, reacting at a temperature of 0-5°C for 2 hours, raising the temperature to room temperature after the addition is complete and continuing the reaction for 24 hours, then adding sodium hydroxide solution for neutralization, separating the organic phase and drying, removing the solvent by vacuum distillation, and recrystallizing from hot toluene to obtain the octaphenyl cage-type silsesquioxane.

4. The method for recycling silica gel according to claim 2, characterized in that, The method for preparing the vinyl-functionalized polysiloxane includes: dissolving octaphenyl cage-type silsesquioxane and potassium hydroxide in anhydrous tetrahydrofuran, stirring at room temperature for 30 minutes under nitrogen protection, then slowly adding vinyltrichlorosilane dropwise over 1 hour, and continuing the reaction at room temperature for 24 hours. After the reaction is completed, the mixture is filtered, the solvent is removed by vacuum distillation, and the vinyl-functionalized polysiloxane is obtained by column chromatography.

5. The method for recycling silica gel according to claim 2, characterized in that, The preparation method of the amino-functionalized polysiloxane includes: dissolving vinyl-functionalized polysiloxane in anhydrous tetrahydrofuran, adding 5% platinum carbon catalyst, passing ammonia gas under nitrogen protection, reacting at 40°C for 6 hours, cooling to room temperature after the reaction is completed, filtering to remove the catalyst, and removing the solvent by vacuum distillation to obtain amino-functionalized polysiloxane.

6. The method for recycling silica gel according to claim 2, characterized in that, The method for surface modification of ground silicone powder with amino-functionalized polysiloxanes includes: mixing the ground silicone powder with 0.5-2.0% (by weight of silicone) of amino-functionalized polysiloxane in tetrahydrofuran solvent, reacting at 50-70°C for 4-6 hours, and then drying at 80-100°C for 4-6 hours.

7. The method for recycling silica gel according to claim 1, characterized in that, The surface modification method of the nano-silica includes: dispersing nano-silica in ethanol and sonicating for 30 minutes, adding vinyltriethoxysilane, reacting at 60°C for 4 hours, centrifuging after the reaction is completed, washing with ethanol 3 times, and drying at 80°C for 12 hours to obtain surface-modified nano-silica.

8. The method for recycling silica gel according to claim 1, characterized in that, The parameters for injection molding in step i) are: injection temperature 170-190℃, injection pressure 15-25MPa; or the parameters for extrusion molding are: extrusion temperature 150-170℃; or the parameters for compression molding are: compression temperature 160-180℃, compression pressure 10-20MPa.

9. The method for recycling silica gel according to claim 1, characterized in that, The material composition after mixing in step h) includes: a) 70-80 parts by weight of surface-modified recycled silica powder, 5-10 parts by weight of surface-modified nano-silica, and 20-30 parts by weight of liquid silicone rubber; or b) 60-70 parts by weight of surface-modified recycled silica powder, 5-15 parts by weight of surface-modified nano-silica, and 25-35 parts by weight of liquid silicone rubber; or c) 80-90 parts by weight of surface-modified recycled silica powder, 5-10 parts by weight of surface-modified nano silica and 10-20 parts by weight of liquid silicone rubber.

10. The method for recycling silica gel according to claim 1, characterized in that, The method also includes a quality inspection process, which includes visual inspection, Shore hardness testing, tensile strength testing, tear strength testing, compression set testing, heat resistance testing, and electrical insulation testing.