Compositions for use with polysulfide sealants and related methods

Abstract

To provide compositions for use with polysulfide sealants, and methods of using the compositions.SOLUTION: Compositions for modifying a degree of cure in a polysulfide sealant are provided. In embodiments, the composition comprises a water-miscible organic solvent, water, and a dithiol. Polysulfide sealant systems comprising the compositions are also provided. Methods for modifying a degree of cure in a polysulfide sealant using the compositions are also provided.SELECTED DRAWING: None

Description

[Background technology]

[0001] Polysulfide sealants are used throughout the aerospace industry, for example, to protect and seal fuel tank components. These sealants must be removed periodically. However, removing them is difficult because polysulfide sealants are extremely durable and designed to adhere strongly to the substrate they come into contact with. Existing polysulfide sealant removal techniques involve scraping or sanding the sealant, which is time-consuming and can damage the surrounding substrate. Compositions for removing polysulfide sealants are available, but they contain harsh chemicals. While these harsh chemicals can be effective, they also emit foul odors, pose environmental and health hazards, and can damage surrounding substrates. Summary of the Invention [Problem to be solved by the invention]

[0002] Compositions for use with polysulfide sealants are provided, as are methods for using the compositions. [Means for solving the problem]

[0003] In one aspect, a composition for varying the degree of cure of a polysulfide sealant is provided. In a first embodiment, the composition includes a water-miscible organic solvent, water, and a dithiol. In the first embodiment, the dithiol may be 1,4-dithiol. In any of the foregoing embodiments, the dithiol may be dithiothreitol (DTT), dithioerythritol (DTE), or both DTT and DTE. In any of the foregoing embodiments, the water-miscible organic solvent may be a ketone, an aldehyde, an alcohol, or a combination thereof. In any of the foregoing embodiments, the composition may contain more organic solvent than water. In any of the foregoing embodiments, the dithiol may be present in an amount ranging from 0.1% to 10% by weight. In any of the foregoing embodiments, the composition may have a pH ranging from 7 to 10, or a pH ranging from 8 to 9. In any of the foregoing embodiments, the composition may further include a gelling agent, a basic pH agent, or both. In any of the foregoing embodiments, the composition can consist essentially of a water-miscible organic solvent, water, a dithiol, and optionally a gelling agent, a basic pH agent, or both.

[0004] In another aspect, a polysulfide sealant system is provided. In a first embodiment, the system includes a composition for varying the degree of cure of a polysulfide sealant, the composition including a water-miscible organic solvent, water, and a dithiol, and a curable polysulfide composition for forming the polysulfide sealant. In the first embodiment, the polysulfide sealant has a T g may have

[0005] In another aspect, a method of using any of the embodiments of the polysulfide sealant system is provided. In a first embodiment, the method includes forming a polysulfide sealant from a curable polysulfide composition and applying a composition that alters the degree of cure of the polysulfide sealant to a surface of the polysulfide sealant for a period of time. In a first embodiment, the polysulfide sealant is cured at a Tg may have

[0006] In another aspect, a method for varying the degree of cure of a polysulfide sealant is provided. In a first embodiment, the method includes applying a composition comprising a water-miscible organic solvent, water, and a dithiol to a surface of the polysulfide sealant for a period of time, thereby forming a treated polysulfide sealant. In any of the foregoing embodiments, the treated polysulfide sealant may comprise at least partially uncured polysulfide sealant. The method may also include applying a force sufficient to remove at least a portion of the at least partially uncured polysulfide sealant. In any of the foregoing embodiments, the polysulfide sealant may be in contact with an aerospace structure. In any of the foregoing embodiments, applying the composition may vary the T of the treated polysulfide sealant. g The method may further include the step of exposing the treated polysulfide sealant to an oxidizing atmosphere for an additional period of time. In any of the foregoing embodiments involving such exposure, the exposure may result in a decrease in the T of the polysulfide sealant by at least 5°C compared to the polysulfide sealant, a decrease in the Shore A hardness of the treated polysulfide sealant by at least 5 units compared to the polysulfide sealant, or both. g T of treated polysulfide sealant compared to g In any of the foregoing embodiments involving such exposure, the exposure may increase the T of the treated polysulfide sealant relative to the Shore A hardness of the polysulfide sealant, or both. g Polysulfide sealant T gThe polysulfide sealant may be heated to a temperature within ±2°C of the oxidizing atmosphere for an additional period of time, or the Shore A hardness of the treated polysulfide sealant may be increased to ±2 units of the Shore A hardness of the polysulfide sealant, or both. In any of the foregoing embodiments involving such exposure, the polysulfide sealant may contain defects. The method may also further include repairing the defects prior to exposing the treated polysulfide sealant to an oxidizing atmosphere for an additional period of time. In any of the foregoing embodiments, the polysulfide sealant may be heated to a temperature within ±2°C of the oxidizing atmosphere for an additional period of time, or the Shore A hardness of the treated polysulfide sealant may be increased to ±2 units of the Shore A hardness of the polysulfide sealant. g may have

[0007] Other principal features and advantages of the present disclosure will become apparent to those skilled in the art upon review of the detailed description of the invention and the appended claims. DETAILED DESCRIPTION OF THE INVENTION

[0008] Compositions for use with polysulfide sealants are provided, as are methods for using the compositions.

[0009] definition The terms "cured / crosslinked" can be used interchangeably depending on the context. Terms such as "uncured / uncrosslinked" and "re-cured / re-crosslinked" are similarly interchangeable. Expressions such as "crosslink cleavage" refer to breaking the covalent bonds associated with the crosslinks, thus resulting in uncrosslinked / uncured.

[0010] Expressions such as "degree of cure" and "degree of crosslinking" refer to the T g It refers to the amount of cross-linking in the relevant material as determined by its hardness or Shore A hardness or both.

[0011] As used herein, the term "water-soluble" means having a solubility in water of at least 1 mg / ml at room temperature (20 to 25°C).

[0012] As used herein, the term "water-miscible" refers to the ability of two substances to be mixed together in any proportion.

[0013] The term "polysulfide sealant" refers to a material comprising organic polysulfide polymer chains cross-linked via disulfide bonds. This term does not include biological materials that may contain disulfide bridges, such as DNA, RNA, proteins, enzymes, etc. The term "polysulfide sealant" is intended to refer to a polysulfide sealant in a cured / cross-linked state, although this term does not necessarily imply 100% cure, nor is it intended to limit the polysulfide sealant to a particular degree of cure.

[0014] The expression "aerospace structure" may refer to any device, vessel, machine, part or component used in the aerospace industry, for example aircraft such as airplanes, rotorcraft, etc., space vehicles such as spacecraft, drones, satellites, aircraft fuselages, wings, composites, etc.

[0015] The present composition includes an aqueous solvent system and active ingredients that are more environmentally friendly, safer, and less irritating than those of existing polysulfide sealant removal compositions. The composition can vary the degree of cure, or crosslinking, in various polysulfide sealants. Varying the degree of cure involves breaking crosslinks within the polysulfide sealant, a feature that makes the sealant easier to remove. However, under certain conditions, polysulfide sealants treated with the composition can also re-cure, i.e., breakage of crosslinks can be regenerated. This feature allows the polysulfide sealant to be repaired. This reversibility is believed to be unique to the present composition compared to existing polysulfide sealant removal compositions.

[0016] In one aspect, a composition for use with a polysulfide sealant, such as to vary the degree of cure of the polysulfide sealant, is provided. The composition includes a water-miscible organic solvent, water, and a dithiol. In an embodiment, the dithiol is water-soluble and has a water solubility of at least 1 mg / ml at room temperature (20-25°C). In the unoxidized state, each thiol group of the dithiol exists as -HS. In the oxidized state, the dithiol forms a disulfide bond. One disulfide bond, i.e., an internal disulfide bond, can be formed such that the dithiol is in the form of a cyclic structure in the oxidized state. In an embodiment, the dithiol is 1,4-dithiol. In an embodiment, the dithiol is dithiothreitol (DTT), dithioerythritol (DTE), a similar material, or a mixture thereof. Combinations of different types of dithiols, such as a combination of both DTT and DTE, may also be used.

[0017] As described further below, polysulfide sealants comprise a pair of polysulfide polymer chains crosslinked via disulfide bonds (i.e., S-S). Dithiols can cleave the disulfide bridges in polysulfide sealants via a thiol-disulfide exchange reaction, as shown in Scheme 1. R'SH + RSSR → RSSR' + RSH (Scheme 1)

[0018] In Scheme 1, R'SH represents a dithiol and RSSR represents a crosslinked polysulfide polymer chain. Another thiol-disulfide exchange reaction can occur to provide 2RSH (an individual, now uncrosslinked polysulfide polymer chain) and the oxidized form of the dithiol.

[0019] A variety of water-miscible organic solvents can be used, provided they can be mixed with water in any ratio. However, the water-miscible organic solvent can be selected based on its ability to dissolve the polysulfide polymer chains of the polysulfide sealant. Therefore, the specific selection of the organic solvent can vary depending on the polysulfide sealant. Water-miscible alcohols, water-miscible aldehydes, and water-miscible ketones can be used. Exemplary water-miscible alcohols include methanol, ethanol, and isopropanol. Exemplary water-miscible aldehydes include methanal / formaldehyde, ethanal, and propanal. Water-miscible ketones include acetone, methyl ethyl ketone, and methyl propyl ketone. Combinations of different types of water-miscible organic solvents can also be used.

[0020] Various relative amounts of water-miscible organic solvent and water can be used. The relative amounts can be selected based on considerations such as the solubility of the dithiol and the solubility of the polysulfide polymer chains of the polysulfide sealant. The ratio of water-miscible organic solvent to water can range from 99:1 to 1:99. Ratios include 50:1 to 1:50, 25:1 to 1:25, 10:1 to 1:10, and 5:1 to 1:5. In embodiments, the composition can contain more water-miscible organic solvent than water. When two or more water-miscible organic solvents are used, the amounts and ratios refer to the total amount of water-miscible organic solvent in the composition.

[0021] Various amounts of dithiol may be used. The amount of dithiol may be selected to achieve the desired degree of uncrosslinking. For example, a larger amount of dithiol may be used to increase the rate of the thiol-disulfide exchange reaction described above, so as to cleave more crosslinks in a given time. However, the amount of dithiol is typically not so large as to prevent dissolution in the selected aqueous solvent system. In embodiments, the dithiol may be present in an amount ranging from at least 0.1% by weight (relative to the total weight of the composition), including at least 0.5%, at least 1%, at least 3%, at least 5%, or in the range of 0.1% to 10% by weight.

[0022] The present composition can be characterized by its pH. Unlike existing polysulfide sealant removal compositions, the present composition can function (cleave crosslinks) under neutral and slightly alkaline conditions. In embodiments, the composition has a pH in the range of 7 to 10. This includes ranges of 7 to 10, 8 to 9, and a pH of about 7. The pH may be adjusted by including a basic pH agent, such as a basic amine, in the composition. Monoamines such as methylamine, dimethylamine, trimethylamine, allylamine, butylamine, and cyclohexylamine can be used. Diamines such as hexamethylenediamine, hexanediamine (e.g., 2,2,4(2,4,4)trimethyl-1,6-hexanediamine), propanediamine, piperidine, and pyrrolidine can be used. In embodiments, the basic pH agent does not contain hydroxide (OH).

[0023] The composition may contain other additives depending on the desired application. For example, viscosity modifiers, including gelling agents, such as cellulose derivatives, may be used. Exemplary cellulose derivatives include methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, and the like, and combinations thereof. When present in the composition, the viscosity modifier may be present in the range of 0.5% to 10% by weight, 1% to 6% by weight, or 1% to 4% by weight (relative to the total weight of the composition).

[0024] In embodiments, the composition comprises a gelling agent, a basic pH agent, or both.

[0025] The composition can be made by combining and mixing the various components under ambient conditions. The water-miscible organic solvent and water can be mixed first, followed by the addition of the dithiol and any optional additives.

[0026] In embodiments, the composition consists essentially of, or consists of, a water-miscible organic solvent, water, a dithiol, and optionally one or more additives. In embodiments, the composition consists essentially of, or consists of, a water-miscible organic solvent, water, a dithiol, and optionally a gelling agent, a basic pH agent, or both.

[0027] It should be understood that the present disclosure extends to various combinations of the individual characteristics described above.As an example, the present disclosure includes compositions having any combination of the disclosed water-miscible organic solvent, water, and dithiol, wherein the ratio of the water-miscible organic solvent to water is any of the disclosed ratios, the dithiol is present in any of the disclosed amounts, the pH is any of the disclosed pH values, and the composition does not contain or contains any combination of the disclosed additives.As mentioned above, in embodiments, the additives include one or more gelling agents, such as methylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, and carboxymethylcellulose.

[0028] Polysulfide sealants to be used with the present compositions comprise organic polysulfide polymer chains crosslinked via disulfide bonds. Throughout this disclosure, when the term "polysulfide sealant" is used alone (e.g., without a modifying adjective), it is intended to refer to the polysulfide sealant in its cured / crosslinked state. However, this term does not necessarily imply 100% cure, nor is it intended to limit the polysulfide sealant to a particular degree of cure. The degree of cure is determined by the glass transition temperature (T g ) value (and that T g (The Shore A hardness may also be used to determine the degree of cure, as discussed above.) Again, the unmodified term "polysulfide sealant" refers, at least in embodiments, to a polysulfide sealant having a particular T gAlthough not intended to be limiting, polysulfide sealants may be used in a range of T g The polysulfide sealant may be formed from a curable polysulfide sealant composition that includes reactive moieties that, when mixed under appropriate conditions, cause curing / crosslinking to provide the polysulfide sealant. The present disclosure is not particularly limited to the type of polysulfide sealant. Indeed, various polysulfide sealants are formed from commercially available curable polysulfide sealant compositions according to manufacturer's instructions. When formed according to such instructions, the resulting polysulfide sealant, when in the cured state, has a relatively high or maximum degree of cure and exhibits a T value as specified by the manufacturer. g In embodiments, the polysulfide sealant may have a T in the range of -70°C to -40°C, -65°C to -45°C, or -60°C to -50°C. g It has.

[0029] The unmodified term "polysulfide sealant" is also not intended to limit the polysulfide sealant to a particular form / morphology. Illustratively, the polysulfide sealant may be in the form of a strip, layer, film, or coating. The polysulfide sealant may be in contact (e.g., direct contact) with an underlying or adjacent substrate. However, the polysulfide sealant may also be a separate physical structure integrated into other structures, such as aerospace structures.

[0030] In another aspect, the present disclosure provides a method for varying the degree of cure of a polysulfide sealant. The method includes applying any of the compositions described herein to the surface of any of the polysulfide sealants described herein. The technique for applying the composition is not particularly limited. Exemplary application techniques include dipping or immersing the polysulfide sealant in the composition, or spraying, painting, brushing, rolling, pouring, or pouring the composition onto the surface of the polysulfide sealant. The application technique can be carried out under ambient conditions, i.e., in air and at room temperature. However, other conditions may be used depending on the application environment. While the composition is in contact with the polysulfide sealant, the dithiol undergoes the thiol-disulfide exchange reaction described above, cleaving disulfide bridges in the polysulfide sealant and forming a treated polysulfide sealant comprising at least partially uncured polysulfide sealant.

[0031] Application is carried out by maintaining the composition in contact with the polysulfide sealant for a period of time. The contact time can vary depending on the amount of disulfide bridge cleavage desired, i.e., the degree of undercure to be achieved. As shown in the examples below, the degree of undercure after a particular contact time can be measured by the Shore A hardness and / or T hardness of the treated polysulfide sealant. g The Shore A hardness can be determined by measuring the T of the treated polysulfide sealant using a Type A durometer according to the manufacturer's instructions. g can be measured using a standard differential scanning calorimeter (DSC) instrument according to the manufacturer's instructions. The contact time can be selected to achieve the desired degree of undercure, e.g., maximum degree of undercure. The contact time determines the T of the treated polysulfide sealant. g The temperature may be selected to achieve a reduction in the Shore A hardness of the treated polysulfide sealant by at least 5°C, or a reduction in the Shore A hardness of the treated polysulfide sealant by at least 5 units, or both. This may include a reduction in the T gThis includes a reduction in Shore A hardness of at least 6 units, at least 8 units, at least 10 units, at least 12 units, or in the range of 5 to 12 units. These reductions are compared to the polysulfide sealant prior to treatment with the composition (which may be referred to as the polysulfide sealant or the pre-treated polysulfide sealant). The contact time at which these results can be achieved may depend on the composition selected, the polysulfide sealant selected, and the degree of cure of the polysulfide sealant prior to treatment, but in embodiments, the contact time is at least 1 hour, at least 2 hours, at least 4 hours, at least 6 hours, up to 8 hours, or in the range of 1 to 8 hours.

[0032] After the selected contact time, the method may further include removing at least a portion of the at least partially uncured polysulfide sealant. As much or as little of the at least partially uncured polysulfide sealant as possible may be removed. The technique for removing the at least partially uncured polysulfide sealant is not particularly limited. The technique may include applying a force to the treated polysulfide sealant, for example, by wiping, sanding, blowing, brushing, or scraping, which may be performed manually or mechanically. The method may further include repeating the applying and removing steps multiple times to form and remove additional amounts of at least partially uncured polysulfide sealant, for example, until most or all of the polysulfide sealant is uncured and removed. This repeated process is particularly beneficial for preventing damage to the substrate with which the polysulfide sealant has come into contact.

[0033] The following examples illustrate another beneficial feature of the present disclosure, namely, the reversible cleavage of disulfide bridges achieved by the present compositions. That is, cleaved disulfide bridges in the treated polysulfide sealant can reform, thereby re-hardening the treated polysulfide sealant. As noted above, re-hardening can be achieved by exposing the treated polysulfide sealant formed after the step of applying the composition to an oxidizing atmosphere for an additional time. The oxidizing atmosphere can be air, and exposure can be carried out at room temperature. However, other oxidizing atmospheres and temperatures can also be used. The additional contact time can be selected to achieve the desired degree of re-hardening, e.g., the maximum degree of re-hardening. The additional contact time can be used to increase the T of the treated polysulfide sealant. g The composition may be selected to increase the Shore A hardness of the treated polysulfide sealant, or to increase the Shore A hardness of the treated polysulfide sealant, or both. These increases are compared to the polysulfide sealant before treatment with the composition (i.e., pre-treated polysulfide sealant / polysulfide sealant). These increases are compared to the T g and Shore A hardness values ​​were restored to the values ​​of the polysulfide sealant before treatment, for example, the T g The hardness may be within ±2°C of 0.05°F, within ±2 units of Shore A hardness, or both. The additional contact time that can achieve these results may depend on the degree of uncuring of the treated polysulfide sealant, the composition selected, and the polysulfide sealant selected, but in embodiments the additional contact time is at least 2 hours, at least 4 hours, at least 6 hours, at least 12 hours, at least 16 hours, at least 18 hours, at least 20 hours, or in the range of 2 to 24 hours, or 4 to 24 hours. Prior to exposure to an oxidizing atmosphere, the treated polysulfide sealant may be separated from the composition used in the treatment.

[0034] The reversibility of the present compositions indicates that any uncured portions in the treated polysulfide sealant, including uncured portions due to unintended application of the composition, can be repaired by recuring the treated polysulfide sealant as described above. Reversibility also means that the softening associated with uncuring can be utilized to repair the polysulfide sealant. By way of example, defects in a polysulfide sealant or in an incorrectly applied polysulfide sealant, such as nicks, tears, divets, or cracks, can be repaired by forming a treated polysulfide sealant using the methods described above and then reshaping, repositioning, or otherwise manually adjusting the treated polysulfide sealant. The treated polysulfide sealant can then be exposed to an oxidizing atmosphere for recuring as described above.

[0035] The present compositions may be provided with a curable polysulfide composition as part of a polysulfide sealant system. Any of the curable polysulfide compositions described above or commercially available curable polysulfide compositions may be used. Any of the present compositions, appropriately configured, may be used to vary the degree of cure of a polysulfide sealant formed from a selected curable polysulfide composition. Methods of using such systems are also provided. These methods include forming a polysulfide sealant from a curable polysulfide composition, e.g., according to manufacturer's instructions, and applying the present composition to the surface of the polysulfide sealant for a period of time. Further removal of at least a portion of the treated polysulfide sealant, repair of defects, recuring, and combinations thereof may be performed as described above.

[0036] In an embodiment, a method of using the polysulfide sealant system includes the steps of forming a polysulfide sealant from a curable polysulfide composition, and applying a composition that alters the degree of cure of the polysulfide sealant, the composition comprising a water-miscible organic solvent, water, and a dithiol, to a surface of the polysulfide sealant for a period of time, thereby forming a treated polysulfide sealant, wherein said application alters the T cure of the treated polysulfide sealant. g the temperature of the treated polysulfide sealant by at least 5°C compared to the polysulfide sealant, the Shore A hardness of the treated polysulfide sealant by at least 5 units compared to the polysulfide sealant, or both.

[0037] In an embodiment, a method for varying the degree of cure of a polysulfide sealant includes applying a composition comprising a water-miscible organic solvent, water, and a dithiol to a surface of the polysulfide sealant containing a defect for a period of time, thereby forming a treated polysulfide sealant, repairing the defect, and exposing the treated polysulfide sealant to an oxidizing atmosphere for an additional period of time.

[0038] The compositions and associated methods can be used with various types of polysulfide sealants, such as those used in the aerospace, automotive, and submarine industries.

[0039] Example Polysulfide sealant removal compositions were formed by mixing isopropanol and water in a 3:1 volume ratio in a container, adding 1% by weight of either DTE or DTT, and mixing until the DTE / DTT was dissolved. Each container contained a polysulfide sealant test specimen (WS-8035 B-2 from Royal Adhesives and Sealants, cured under standard temperature and humidity conditions). Each polysulfide sealant test specimen was approximately 1 inch long, 1 inch wide, and 0.25 inch thick. After a specified time, the test specimens were removed from their respective containers (see Tables 1 and 2). The surfaces of the test specimens exposed to the polysulfide sealant removal compositions were tacky, and the color of the exposed specimens changed (from black) to light brown. The weight loss, Shore A hardness, and glass transition temperature (T) of the removed specimens were measured. g ) was tested.

[0040] For weight loss measurements, loose or sticky material was physically removed from the test specimens exposed to the polysulfide sealant removal composition by wiping prior to weighing. Weight loss was calculated as the difference between the original weight of the test specimen (before exposure to the polysulfide sealant removal composition) and the weight of the test specimen after exposure, and reported as a percentage of the original weight. Shore A hardness and T g For measurements, the exposed specimens were not wiped prior to testing. Shore A hardness was measured on the exposed specimens with a Type A durometer used in accordance with ASTM standard D2240. A DSC system from TA instruments was used to measure the Shore A hardness. g Measurements were carried out. g A small piece of loose or sticky material was taken from the exposed specimen to provide a sample for measurement. The results are shown below in Table 1 (DTE) and Table 2 (DTT). The control sample refers to a polysulfide sealant specimen that was not exposed to any of the polysulfide sealant removal compositions.

[0041] [Table 1]

[0042] [Table 2]

[0043] Results show that exposure to DTE / DTT leads to weight loss, a decrease in Shore A hardness, and reduced cross-linking. g The results show that after prolonged exposure, e.g., more than about 18 hours, the crosslinking is restored (hardness / T g The figure also clearly shows a rise in the number of

[0044] An additional experiment similar to the one above was performed, except that hexamethyleneethylenediamine was added to the vessel to provide a pH of about 8. The results are shown in Table 3 below.

[0045] [Table 3]

[0046] Finally, experiments similar to those described above were performed, but with increasing amounts of DTT / DTE. For example, a polysulfide sealant removal composition containing 5 wt. % DTT and a neutral pH achieved approximately 45% weight loss in 18 hours.

[0047] Additionally, the present disclosure includes embodiments described in the following clauses.

[0048] 1. A composition for varying the degree of cure of a polysulfide sealant, comprising: a water-miscible organic solvent; Water and Dithiol and A composition comprising:

[0049] 2. The composition of claim 1, wherein the dithiol is 1,4-dithiol.

[0050] 3. The composition of clause 1, wherein the dithiol is dithiothreitol (DTT), dithioerythritol (DTE), or both DTT and DTE.

[0051] 4. The composition of any of clauses 1 to 3, wherein the water-miscible organic solvent is a ketone, an aldehyde, an alcohol, or a combination thereof.

[0052] 5. A composition according to any of clauses 1 to 4, comprising an amount of organic solvent greater than water.

[0053] 6. The composition of any of clauses 1 to 5, wherein the dithiol is present in an amount ranging from 0.1% to 10% by weight.

[0054] 7. The composition of any of clauses 1 to 6, having a pH in the range of 7.7 to 10.

[0055] 8. The composition according to clause 7, wherein the pH is in the range of 8 to 9.

[0056] 9. The composition of any of clauses 1 to 8, further comprising a gelling agent, a basic pH agent, or both.

[0057] 10. The composition of any of clauses 1 to 9, consisting essentially of a water-miscible organic solvent, water, a dithiol, and optionally a gelling agent, a basic pH agent, or both.

[0058] 11. A composition for varying the degree of cure of a polysulfide sealant, the composition comprising a water-miscible organic solvent, water, and a dithiol; a curable polysulfide composition for forming a polysulfide sealant; Polysulfide sealant systems, including:

[0059] 12. Polysulfide sealant has a T value in the range of -70℃ to -40℃. g 12. The polysulfide sealant system of claim 11, comprising:

[0060] 13. A method of using a system according to clause 11 or 12, the method comprising: forming a polysulfide sealant from the curable polysulfide composition; applying a composition that alters the degree of cure of the polysulfide sealant to the surface of the polysulfide sealant for a period of time; A method comprising:

[0061] 14. A method for varying the degree of cure of a polysulfide sealant, the method comprising applying a composition comprising a water-miscible organic solvent, water, and a dithiol to a surface of the polysulfide sealant for a period of time, thereby forming a treated polysulfide sealant.

[0062] 15. The method of clause 14, wherein the treated polysulfide sealant comprises at least partially uncured polysulfide sealant, the method further comprising applying a force sufficient to remove at least a portion of the at least partially uncured polysulfide sealant.

[0063] 16. The method of clause 14 or 15, wherein the polysulfide sealant is in contact with an aerospace structure.

[0064] 17. The application step determines the T of the treated polysulfide sealant. g 17. The method of any of clauses 14 to 16, wherein the temperature of the treated polysulfide sealant is reduced by at least 5°C compared to the polysulfide sealant, the Shore A hardness of the treated polysulfide sealant is reduced by at least 5 units compared to the polysulfide sealant, or both.

[0065] 18. The method of any of clauses 14 to 17, further comprising exposing the treated polysulfide sealant to an oxidizing atmosphere for an additional period of time.

[0066] 19. The above exposure may cause the T of polysulfide sealant gT of treated polysulfide sealant compared to g 19. The method of claim 18, wherein the method is capable of increasing the Shore A hardness of the treated polysulfide sealant relative to the Shore A hardness of the polysulfide sealant, or both.

[0067] 20. The above exposure resulted in the T of the treated polysulfide sealant. g Polysulfide sealant T g 20. The method of claim 19, wherein the method is capable of increasing the Shore A hardness of the treated polysulfide sealant by ±2 units of the Shore A hardness of the polysulfide sealant, or both.

[0068] 21. The method of clause 18, wherein the polysulfide sealant contains a defect, further comprising the step of repairing the defect prior to the step of exposing the treated polysulfide sealant to an oxidizing atmosphere for an additional period of time.

[0069] 22. Polysulfide sealant has a T value in the range of -70℃ to -40℃. g 15. The method of claim 14, comprising:

[0070] The word "exemplary" is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects or designs. Further, for the purposes of this disclosure, unless otherwise indicated, "a" or "an" means "one or more."

[0071] The foregoing description of exemplary embodiments of the present disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form, as modifications and variations are possible in light of the above teachings or may be acquired from practice of the present disclosure. The embodiments were chosen and described to explain the principles of the disclosure and as practical applications thereof to enable those skilled in the art to implement the invention in various embodiments and to utilize the invention with various modifications as suited to the particular uses contemplated. It is intended that the scope of the present disclosure be defined by the claims appended hereto, and their equivalents.

Claims

1. A method of using a polysulfide sealant system, comprising: The polysulfide sealant system a composition for softening a polysulfide sealant, the composition comprising a water-miscible organic solvent, water, and a dithiol; a curable polysulfide composition for forming the polysulfide sealant; Including, the polysulfide sealant softening composition has a pH in the range of 7 to 10; the dithiol is dithioerythritol (DTE) or both dithiothreitol (DTT) and DTE; the dithiol is present in an amount ranging from 0.1 wt % to 10 wt % of the total weight of the polysulfide sealant softening composition; The method comprises: forming the polysulfide sealant from the curable polysulfide composition; applying a composition that softens the polysulfide sealant to the surface of the polysulfide sealant for a period of time; Including, applying the polysulfide sealant softening composition to the surface of the polysulfide sealant for a period of time comprises spraying, painting, brushing, rolling, injecting or pouring the polysulfide sealant softening composition onto the surface of the polysulfide sealant; method.

2. The polysulfide sealant has a T ｇ 2. The method of claim 1, comprising:

3. exposing the treated polysulfide sealant resulting from the step of applying the polysulfide sealant softening composition to an oxidizing atmosphere for an additional period of time. The method of claim 1 further comprising:

4. 1. A method for varying the degree of cure of a polysulfide sealant, said method comprising: applying a composition comprising a water-miscible organic solvent, water, and a dithiol to a surface of a polysulfide sealant for a period of time, thereby obtaining a treated polysulfide sealant; the composition has a pH in the range of 7 to 10; the dithiol is dithioerythritol (DTE) or both dithiothreitol (DTT) and DTE; the dithiol is present in an amount ranging from 0.1 wt. % to 10 wt. % of the total weight of the composition; The degree of cure refers to the degree of crosslinking, applying a composition comprising a water-miscible organic solvent, water, and a dithiol to the surface of the polysulfide sealant for a period of time, thereby obtaining a treated polysulfide sealant, comprises spraying, painting, brushing, rolling, injecting, or pouring the composition onto the surface of the polysulfide sealant; method.

5. The method of claim 4 , wherein the polysulfide sealant is in contact with an aerospace structure.

6. exposing the treated polysulfide sealant to an oxidizing atmosphere for an additional period of time. The method of claim 4 or 5, further comprising:

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