Fuel-resistant polysulfide sealant and preparation method thereof

Abstract

The invention belongs to the technical field of adhesives, and particularly relates to a fuel-resistant polysulfide sealant and a preparation method thereof. The fuel-resistant polysulfide sealant is composed of a main agent and a vulcanizing paste, the main agent is prepared from the following components in parts by weight: 40 to 80 parts of liquid polysulfide rubber, 20 to 40 parts of reinforcing filler, 1 to 6 parts of fluorine modified fumed silica and 2 to 10 parts of fluorine-containing silane coupling agent; the vulcanizing paste comprises the following components in parts by weight: 10-50 parts of a vulcanizing agent, 1-6 parts of a vulcanization accelerator and 20-70 parts of a plasticizer. The fumed silica modified by the perfluorinated straight-chain fatty acid is adopted as the filler, the fluorine-containing silane coupling agent is added into the main agent, and the fumed silica has a relatively large specific surface area, so that the modified filler has a good oleophobic effect, and the fuel oil resistance of the polysulfide sealant can be improved.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, specifically relating to a fuel-resistant polysulfide sealant and its preparation method. Background Technology

[0002] Polysulfide sealants are widely used in the aerospace field due to their excellent mechanical properties, water resistance, and weather resistance, with aircraft fuel tank sealants being particularly important.

[0003] When polysulfide sealants are applied to aircraft fuel tanks, the low degree of cross-linking of polysulfide rubber molecular chains makes them prone to swelling when immersed in fuel. This increases the internal molecular network space of the material, and some small-molecule plasticizers can also enter the fuel, creating voids within the material and reducing interfacial adhesion. Chinese patent CN108641666A uses fluorinated polyoxysilanes bonded to the surface of hollow glass microspheres to form a low-surface-energy micro / nano oleophobic structure, thereby reducing the wetting of the sealant by aviation kerosene and thus reducing its swelling. However, the hollow glass microspheres have a small specific surface area and few functional groups available for reaction with fluorosilanes. Even after acid washing, alkali washing, and surface modification, the surface grafting reaction is ineffective, and the modified filler has a low fluorine content, resulting in limited oleophobic effects.

[0004] Therefore, it is necessary to find a polysulfide sealant with better oleophobic properties. Summary of the Invention

[0005] The purpose of this invention is to provide a fuel-resistant polysulfide sealant and its preparation method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A fuel-resistant polysulfide sealant, composed of a base agent and a curing paste. The main agent comprises, by weight parts: 40-80 parts of liquid polysulfide rubber, 20-40 parts of reinforcing filler, 1-6 parts of fluorine-modified fumed silica, and 2-10 parts of fluorine-containing silane coupling agent. The vulcanizing paste comprises, by weight, 10-50 parts of vulcanizing agent, 1-6 parts of vulcanization accelerator, and 20-70 parts of plasticizer; The mass ratio of the main agent to the vulcanizing paste is 100:(8~12).

[0007] The polysulfide sealant is obtained by mixing the main agent and the vulcanizing paste at a mass ratio of 100:(8~12) and then curing.

[0008] The average molecular weight of the liquid polysulfide rubber in the main agent is 500~4000.

[0009] The main component contains 1.1% to 7.7% mercapto groups in liquid polysulfide rubber.

[0010] The fluorine-modified fumed silica is perfluorinated linear fatty acid-modified fumed silica, and its preparation method is as follows: 2-5 parts by weight of hydrophilic fumed silica are added to 100-150 parts by weight of anhydrous ethanol and ultrasonically dispersed for 1-2 hours. Then, 50-100 parts by weight of a 2wt% ethanol solution of perfluorinated linear fatty acids are added. The pH is adjusted to 3-5 using acetic acid, and the mixture is stirred at 50-60°C for 24-48 hours. After the reaction is complete, the bottom solid is collected by centrifugation, washed, and dried.

[0011] The perfluoro linear fatty acid is one or more of perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, and perfluorodecanoic acid.

[0012] The specific surface area of ​​the hydrophilic fumed silica is 150~380m². 2 / g.

[0013] Fluorine-modified fumed silica, by weight: 2-5 parts hydrophilic fumed silica, 100-150 parts anhydrous ethanol, and 50-100 parts a 2wt% ethanol solution of perfluorinated straight-chain fatty acids.

[0014] The reinforcing filler in the main agent is one or more of the following: heavy calcium carbonate, light calcium carbonate, nano calcium carbonate, fumed silica, carbon black, talc, and mica powder.

[0015] The fluorosilane coupling agent in the main agent is one or more of the following: 1H,1H,2H,2H-perfluorooctyltrimethoxysilane, 1H,1H,2H,2H-perfluorooctyltriethoxysilane, 1H,1H,2H,2H-perfluorodecyltriethoxysilane, and 1H,1H,2H,2H-perfluorododecyltriethoxysilane.

[0016] The vulcanizing agent in the vulcanizing paste is either manganese dioxide or lead dioxide.

[0017] The vulcanization accelerator in the vulcanizing paste is one or both of diphenylguanidine and tetrasulfide bispentamethylene thiuram.

[0018] The plasticizer in the vulcanizing paste is one of butyl benzyl phthalate, dibutyl phthalate, or chlorinated paraffin.

[0019] A method for preparing the polysulfide sealant includes the following steps: 1) Preparation of main agent: Weigh liquid polysulfide rubber, reinforcing filler, fluorine-modified fumed silica and fluorosilane coupling agent according to the weight ratio, mix them in a homogenizer for 5-10 minutes, and then grind them to a fineness of ≤20μm on a three-roll mill to obtain the main agent; 2) Preparation of vulcanizing paste: Weigh the vulcanizing agent, vulcanization accelerator and plasticizer according to the weight ratio, mix and grind them on a three-roll mill to a fineness of ≤20μm to obtain vulcanizing paste; 3) Mix the main agent and the vulcanizing paste at a mass ratio of 100:(8~12) and cure to obtain polysulfide sealant; the curing conditions are: 25℃ for 14~28 days, or 25℃ for 24 hours and then 70℃ for 24~28 hours.

[0020] Compared with the prior art, the present invention has the following advantages: 1. This invention uses perfluorinated straight-chain fatty acid-modified fumed silica as a filler and adds a fluorinated silane coupling agent to the main agent. Fumed silica has a large specific surface area, which enables the modified filler to have good oleophobic effect and improve the fuel resistance of polysulfide sealant.

[0021] 2. Compared with conventional polysulfide sealants, the polysulfide sealant of the present invention has significant oleophobicity. When applied to aircraft fuel tanks, it can significantly reduce the swelling and wetting of the sealant by aviation kerosene. The modified filler, due to the fluorinated groups on its surface, can also stably disperse the fluorinated silane coupling agent in the main agent, thereby improving the oleophobic performance while maintaining good adhesion. Detailed Implementation

[0022] Preparation Example 1 The liquid polysulfide rubber LP-HEX-1 used in this experiment was prepared in the laboratory. The number average molecular weight of LP-HEX-1 was 1968.75 and the mercapto content was 3.67%. For details of its preparation method, please refer to Preparation Example 3 of Patent CN117683233A.

[0023] Preparation Example 2 Based on parts by weight, 2 parts with a specific surface area of ​​380m² 2 / g of hydrophilic fumed silica HL380 was added to 100 parts of anhydrous ethanol and ultrasonically dispersed for 2 h. Then, 100 parts of a 2wt% ethanol solution of perfluorooctanoic acid were added, and the pH was adjusted to 3.5 using acetic acid. The mixture was stirred at 50 °C for 24 h. After the reaction was complete, the bottom solid was collected by centrifugation, washed, and dried to obtain fluorine-modified fumed silica Al.

[0024] Example 1 1) Preparation of the main agent: 50 parts of liquid polysulfide rubber LP-HEX-1, 30 parts of nano calcium carbonate, 2 parts of fluorine-modified fumed silica Al, and 2 parts of 1H,1H,2H,2H-perfluorooctyltriethoxysilane were mixed in a homogenizer for 5 min, and then ground from 80µm to 5µm using a three-roll mill to obtain the main agent.

[0025] 2) Preparation of vulcanizing paste: Mix 25 parts of manganese dioxide, 55 parts of dibutyl phthalate, 3 parts of diphenylguanidine, and 3 parts of bis(pentamethylene)thiuram tetrasulfide (DPTT) evenly, and grind them from 80µm to 5µm using a three-roll mill to obtain vulcanizing paste.

[0026] When using, mix the main agent and the vulcanizing paste at a ratio of 100:8, and cure at 25°C for 14 days to obtain sealant 1.

[0027] Example 2 1) Preparation of the main agent: 50 parts of liquid polysulfide rubber LP-HEX-1, 30 parts of nano calcium carbonate, 4 parts of fluorine-modified fumed silica Al, and 2 parts of 1H,1H,2H,2H-perfluorooctyltriethoxysilane were mixed in a homogenizer for 5 min, and then ground from 80µm to 5µm using a three-roll mill to obtain the main agent.

[0028] 2) Preparation of vulcanizing paste: Mix 25 parts of manganese dioxide, 55 parts of dibutyl phthalate, 3 parts of diphenylguanidine, and 3 parts of bis(pentamethylene)thiuram tetrasulfide (DPTT) evenly, and grind them from 80µm to 5µm using a three-roll mill to obtain vulcanizing paste.

[0029] When using, mix the main agent and the vulcanizing paste at a ratio of 100:8, and cure at 25°C for 14 days to obtain sealant 2.

[0030] Example 3 1) Preparation of the main agent: 50 parts of liquid polysulfide rubber LP-HEX-1, 30 parts of nano calcium carbonate, 6 parts of fluorine-modified fumed silica Al, and 2 parts of 1H,1H,2H,2H-perfluorooctyltriethoxysilane were mixed in a homogenizer for 5 min, and then ground from 80µm to 5µm using a three-roll mill to obtain the main agent.

[0031] 2) Preparation of vulcanizing paste: Mix 25 parts of manganese dioxide, 55 parts of dibutyl phthalate, 3 parts of diphenylguanidine, and 3 parts of bis(pentamethylene)thiuram tetrasulfide (DPTT) evenly, and grind them from 80µm to 5µm using a three-roll mill to obtain vulcanizing paste.

[0032] When using, mix the main agent and the vulcanizing paste at a ratio of 100:8, and cure at 25°C for 14 days to obtain sealant 3.

[0033] Comparative Example 1 1) Preparation of the main agent: 50 parts of liquid polysulfide rubber LP-HEX-1, 30 parts of nano calcium carbonate, 6 parts of fumed silica HB630, and 2 parts of 1H,1H,2H,2H-perfluorooctyltriethoxysilane were mixed in a homogenizer for 5 min, and then ground from 80µm to 5µm using a three-roll mill to obtain the main agent.

[0034] 2) Preparation of vulcanizing paste: Mix 25 parts of manganese dioxide, 55 parts of dibutyl phthalate, 3 parts of diphenylguanidine, and 3 parts of bis(pentamethylene)thiuram tetrasulfide (DPTT) evenly, and grind them from 80µm to 5µm using a three-roll mill to obtain vulcanizing paste.

[0035] When using, mix the main agent and the vulcanizing paste at a ratio of 100:8, and cure at 25°C for 14 days to obtain sealant 4.

[0036] Comparative Example 2 1) Preparation of main agent: 50 parts of liquid polysulfide rubber LP-HEX-1, 30 parts of nano calcium carbonate and 6 parts of fumed silica HB630 are mixed in a homogenizer for 5 min and then ground from 80µm to 5µm by a three-roll mill to obtain the main agent.

[0037] 2) Preparation of vulcanizing paste: Mix 25 parts of manganese dioxide, 55 parts of dibutyl phthalate, 3 parts of diphenylguanidine, and 3 parts of bis(pentamethylene)thiuram tetrasulfide (DPTT) evenly, and grind them from 80µm to 5µm using a three-roll mill to obtain vulcanizing paste.

[0038] When using, mix the main agent and the vulcanizing paste at a ratio of 100:8, and cure at 25°C for 14 days to obtain sealant 5.

[0039] Comparative Example 3 Comparative Example 3 is PPG's commercially available product P / S890.

[0040] Performance tests were conducted on the sealants of the above embodiments and comparative examples: Contact angle measurement: Surface wettability was measured using a TrackerHTHP optical contact angle meter manufactured by TECLIS, France. During measurement, a 5 μL drop of ASTM FUELF aviation standard fuel was placed on the sample surface, and the liquid contact angle was measured using a droplet profile analysis system. For each measurement, five locations were randomly selected on the surface, and the static contact angle of the liquid on the surface was obtained by averaging the liquid contact angle measurements at these five locations.

[0041] The contact angle between aviation standard fuel (ASTM FUEL F) and cured polysulfide sealant was measured, and the test results are shown in Table 1.

[0042] Table 1. Air-aviation kerosene-sealant contact angle test table

[0043] Mechanical property testing: Hardness was tested according to GB / T531.1-2008 "Test Method for Indentation Hardness of Vulcanized Rubber or Thermoplastic Rubber"; tensile strength and elongation at break were tested according to GB / T528-2009 "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber", with a tensile speed of 500 mm / min. The changes in tensile strength, elongation at break, hardness, and peel strength of the samples before and after immersion in ASTM FUEL F aviation standard fuel at 25℃ for 72 h are shown in Table 2.

[0044] Table 2. Test Table of Mechanical Properties of Sealants

[0045] As shown in Table 1, all samples (Examples 1-3) containing fluorinated modified fumed silica and fluorinated silane coupling agents had large contact angles. The contact angle of the sample with unmodified fumed silica in Comparative Example 1 decreased, while the contact angle of Comparative Example 2, which used unmodified fumed silica without fluorinated silane coupling agents, decreased even more significantly. This indicates that the synergistic effect of fluorinated modified fumed silica and fluorinated silane coupling agents can improve the oleophobicity of polysulfide sealants.

[0046] As shown in Table 2, with the increase of the amount of fluorinated modified fumed silica added (Examples 1-3), the impact of fuel immersion on the various mechanical properties of polysulfide sealants gradually decreased. However, the sample with unmodified fumed silica (Comparative Example 1) showed a significant decrease in mechanical properties after fuel immersion, particularly in tensile properties and peel strength. This indicates that fluorinated modified fumed silica effectively reduced swelling and plasticizer loss caused by fuel immersion, thus effectively preventing a decrease in tensile properties and peel strength. The rate of change in mechanical properties after fuel immersion in Examples 1-3 was significantly lower than that of commercially available products (Comparative Example 3), while the samples themselves also exhibited good mechanical properties. Because the fluorinated groups on the surface of the fluorinated modified fumed silica allow for the stable dispersion of fluorinated silanes in the main agent, the problem of a significant decrease in interfacial peel strength caused by fluoropolymers, common with the addition of fluorinated silane coupling agents, was not observed.

[0047] In summary, this invention employs a method of adding perfluorinated straight-chain fatty acid-modified fumed silica to the polysulfide sealant base and adding a fluorinated silane coupling agent to obtain a polysulfide sealant resistant to fuel immersion. The polysulfide sealant of this invention exhibits significant oleophobicity; the contact angle between aviation fuel and the cured polysulfide sealant can reach 151.3°, effectively resisting fuel immersion and reducing fuel tank leakage caused by fuel immersion.

Claims

1. A fuel-resistant polysulfide sealant, characterized in that, The fuel-resistant polysulfide sealant consists of a main agent and a vulcanizing paste. The main agent comprises, by weight parts: 40-80 parts of liquid polysulfide rubber, 20-40 parts of reinforcing filler, 1-6 parts of fluorine-modified fumed silica, and 2-10 parts of fluorine-containing silane coupling agent. The vulcanizing paste comprises, by weight, 10-50 parts of vulcanizing agent, 1-6 parts of vulcanization accelerator, and 20-70 parts of plasticizer.

2. The mass ratio of the main agent to the vulcanizing paste is 100:(8~12).

3. The polysulfide sealant according to claim 1, characterized in that: The fluorine-modified fumed silica is perfluorinated linear fatty acid-modified fumed silica. Its preparation method is as follows: hydrophilic fumed silica is added to anhydrous ethanol and ultrasonically dispersed, then added to a 2wt% ethanol solution of perfluorinated linear fatty acids, and the pH is adjusted to 3-5 to carry out the reaction. After the reaction is completed, the bottom solid is collected by centrifugation, washed, and dried.

4. The polysulfide sealant according to claim 2, characterized in that: The perfluoro linear fatty acid is one or more of perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid, and perfluorodecanoic acid. The specific surface area of ​​the hydrophilic fumed silica is 150~380m². 2 / g.

5. The polysulfide sealant according to claim 2, characterized in that: The fluorine-modified fumed silica, by weight, comprises: 2-5 parts hydrophilic fumed silica, 100-150 parts anhydrous ethanol, and 50-100 parts a 2wt% ethanol solution of perfluorinated straight-chain fatty acids.

6. The polysulfide sealant according to claim 1, characterized in that: The fluorosilane coupling agent in the main agent is one or more of the following: 1H,1H,2H,2H-perfluorooctyltrimethoxysilane, 1H,1H,2H,2H-perfluorooctyltriethoxysilane, 1H,1H,2H,2H-perfluorodecyltriethoxysilane, and 1H,1H,2H,2H-perfluorododecyltriethoxysilane.

7. A method for preparing the polysulfide sealant according to claim 1, characterized in that: Includes the following steps: 1) Preparation of main agent: Take liquid polysulfide rubber, reinforcing filler, fluorine-modified fumed silica and fluorosilane coupling agent, mix for 5~10 min, and grind to a fineness of ≤20μm to obtain the main agent; 2) Preparation of vulcanizing paste: Take vulcanizing agent, vulcanization accelerator and plasticizer, mix and grind to a fineness of ≤20μm to obtain vulcanizing paste; 3) Mix the main agent and the vulcanizing paste at a mass ratio of 100:(8~12) and cure to obtain polysulfide sealant; the curing conditions are: 25℃ for 14~28 days, or 25℃ for 24 hours followed by 70℃ for 24~48 hours.

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