Environment-friendly stiffening agent and preparation method thereof

Abstract

The present application belongs to the technical field of fabric finishing agent, and particularly relates to a green and environment-friendly stiffening agent and a preparation method thereof. The preparation method comprises the following steps: (1) preparing a prepolymer solution by taking diisocyanate and dihydric alcohol as raw materials; (2) adding first dihydroxy POSS, then adding a hydrophilic chain extender after reaction, and then adding dihydroxy POSS to continue the reaction, so as to obtain a POSS modified prepolymer solution; (3) end-capping, cross-linking and neutralizing by using a fluorine-containing end-capping agent; and (4) emulsifying, so as to obtain the green and environment-friendly stiffening agent. In the fluorine-containing waterborne polyurethane, dihydroxy POSS and a hydrophilic chain extender are added by using a dispersion feeding and step-by-step polymerization mode. The chemically bonded POSS unit can be uniformly dispersed in the polyurethane matrix to form a nanocomposite. The dispersion in the nanometer scale can produce a very strong interface effect, which can not only effectively transfer and disperse stress, but also improve the fabric stiffness and hydrophobic property.

Description

Technical Field

[0001] This invention belongs to the field of fabric finishing agent technology, specifically relating to a green and environmentally friendly stiffening agent and its preparation method. Background Technology

[0002] The modern textile industry mainly comprises two important parts: the textile manufacturing process, including spinning and weaving; and the finishing and beautification of textiles, namely pretreatment, dyeing, printing, and finishing processes. Textile finishing refers to improving the appearance and intrinsic quality of fabrics through physical, chemical, or physicochemical processing, thereby enhancing their performance or special functions.

[0003] Different finishing purposes require different finishing methods. Mechanical finishing achieves its purpose through the application of heat, moisture, tension, and pressure. Chemical finishing, on the other hand, uses chemicals with specific functions to react with fibers under certain conditions, thereby imparting special properties to the textiles. These chemicals can be categorized into different functional finishing agents based on the functions they provide to the textiles. Textile finishing agents mainly include softeners, wrinkle-resistant and shrink-resistant agents, water- and oil-repellent agents, stiffening agents, antistatic agents, easy-to-clean agents, optical brighteners, flame-retardant agents, coating agents, antibacterial and deodorizing agents, and UV-resistant agents, among others.

[0004] Stiffening agents are polymeric substances that form a thin film or cross-linking effect within, between, or on the surface of fibers, thereby giving the fabric a stiffer, thicker, and fuller hand feel. Stiffening finishing utilizes a film-forming polymer, commonly known as a sizing agent, to create a thin film or cross-linking effect within, between, or on the surface of fibers. After drying, this process gives the fabric a stiff, smooth, and thick hand feel. It is widely used in collars, tents, advertising banners, bed sheets, duvet covers, etc., and is particularly important for curtain fabrics, bag fabrics, and warp-knitted fabrics.

[0005] Currently, emulsions of certain thermoplastic resins are widely used as finishing agents. For example, fabrics are impregnated with emulsions of polyacrylates or polyethylene, and after heat treatment, water-insoluble resin particles or continuous films are formed and fixed onto the fabric. Depending on the type of resin, different stiffness, fullness, or softness can be imparted to the fabric. Thermoplastic acrylates can be made into polymers of varying softness and hardness using different monomers. Generally, increasing the length of the long aliphatic groups in the monomers increases the softness of the polymer product. For example, polymers made from polyacrylates with long aliphatic ethers are soft; while polymers made from tert-butyl acrylate have short and branched aliphatic chains and are relatively stiff. Polymers of different softness and hardness can be formulated into emulsions for impregnating fabrics according to different needs. During heat treatment, the polymer particles form a continuous film that adheres to the fibers, thereby producing a stiffening effect on the fabric. CN106008893A discloses a method for preparing a polyurethane waterproof stiffening agent emulsion and its product. This polyurethane stiffening agent uses polyester glycol, which has a relatively large molecular weight and a high phase transition temperature, as the soft segment phase region structure of the polyurethane. It also incorporates appropriate amounts of side-chain long-chain alkyl groups and terminal perfluoroalkyl groups. While significantly improving the stiffness and feel of various flexible textile products, it also imparts significant water and stain repellency. It can be widely used in stiffening finishing of various textile products and has a promising market prospect. The product is safe, environmentally friendly, and easy to use. CN121045498A introduces dynamic functional bonds with thermal response characteristics into polyurethane. Under elevated temperature conditions, these dynamic bonds promote reversible exchange rearrangement through enhanced molecular chain mobility, thereby endowing the material with excellent self-healing properties and recyclability. This introduces hydrophobic functionalized Mxene and self-healing polyurethane into ordinary fabrics, giving them photothermal conversion, self-cleaning, self-healing, and sensing functions. However, the above-mentioned stiffening agents have poor hydrophobicity and cannot meet actual production needs. With the continuous improvement of people's requirements for fabric quality, new environmentally friendly stiffening agents with excellent stiffening effects and effectively increasing the thickness and fullness of fabrics need to be developed. Summary of the Invention

[0006] The purpose of this invention is to provide a green and environmentally friendly stiffening agent and its preparation method, which solves the problems of high preparation cost and poor hydrophobicity of existing polyurethane resins, and improves the stiffness of waterborne polyurethane finishing agents to a certain extent, and can be used as a fabric stiffening agent.

[0007] To solve the above problems, the technical solution of the present invention is as follows:

[0008] A method for preparing a green and environmentally friendly stiffening agent includes the following steps:

[0009] (1) The diisocyanate and diol are heated and stirred until homogeneous, and then the catalyst is added. After the reaction, a prepolymer solution is obtained.

[0010] (2) Add dihydroxyPOSS to the prepolymer solution and add solvent to reduce viscosity. After reacting for 0.5-1.5 h, add a hydrophilic chain extender for chain extension reaction for 0.5-1.5 h, and then add more dihydroxyPOSS to continue the reaction to obtain a POSS-modified prepolymer solution. The molar ratio of dihydroxyPOSS to diisocyanate added in the two additions is 0.5-2.5:50-56. Among them, the dihydroxyPOSS added in the first addition accounts for 10-30 mol% of the dihydroxyPOSS added in the two additions.

[0011] (3) Add a fluorine-containing end-capping agent, a crosslinking agent, and a neutralizing agent to the POSS modified prepolymer solution for end-capping, crosslinking, and neutralization, respectively;

[0012] (4) Add deionized water for emulsification, and remove the organic solvent by rotary evaporation to obtain a green and environmentally friendly stiffening agent.

[0013] Waterborne polyurethane, used as a textile coating, offers advantages such as good adhesion, applicability to various substrates, and abrasion resistance. Furthermore, its extremely low VOC emissions address current environmental concerns. However, some properties, such as hydrophilicity, result in poor water resistance. This invention introduces fluorine into polyurethane using a fluorinated end-capping agent to improve its water resistance. Fluorine is the most electronegative element in nature, with an electronegativity as high as 4.0. The helical distribution of fluorine atoms provides excellent shielding for the molecular chains, resulting in low intermolecular forces and chemical stability in fluorinated compounds. Fluorinated compounds also have extremely low surface free energy, leading to significant migration to the surface during drying and film formation, thus imparting excellent hydrophobic and oleophobic properties to the film. Moreover, using a fluorinated end-capping agent as the fluorine source is simpler and less costly than using fluorinated diisocyanates or diols. However, the fluorine content can be limited with fluorinated end-capping agents, and their introduction can reduce stiffness to some extent.

[0014] To address the aforementioned issues, this invention incorporates a specific amount of dihydroxy POSS during the polymerization process. The two hydroxyl groups of dihydroxy POSS allow it to react with isocyanates, similar to conventional polyols, and firmly integrate into the main chain of the waterborne polyurethane via chemical bonds. The inorganic siloxane cages of POSS possess extremely high rigidity and dimensional stability. These rigid POSS cages significantly restrict the movement of the surrounding polyurethane soft segments (flexible chains), raising the glass transition temperature of the entire polymer network. Macroscopically, this manifests as a significant increase in the rigidity and hardness of the coating film, thus imparting excellent stiffness to the fabric. The performance of waterborne polyurethane largely depends on the "microphase separation" structure of its soft and hard segments. As a polar, rigid unit, POSS alters the degree and morphology of this microphase separation, promoting the orderly arrangement of the hard segment regions, forming a more complete and stronger physical cross-linked network, and enhancing the stiffness and stability.

[0015] Furthermore, because POSS is chemically bonded, it is not easily dissolved during washing. The siloxane structure of POSS imparts a certain degree of hydrophobicity to the coating surface, resisting the intrusion of water molecules and protecting the polyurethane matrix from hydrolysis. The POSS migrating to the coating surface provides a certain low surface energy, resulting in auxiliary hydrophobic and stain-resistant effects, without causing a stiff feel like fluorinated compounds. Unlike simply increasing the thickness of the waterborne polyurethane coating to achieve stiffness, the nano-reinforcing effect of POSS allows for higher stiffness to be achieved with a thinner coating. This means that while achieving the desired stiffness, the fabric can better maintain its original softness, drape, and breathability. These two factors work together to give the finishing effect (stiffness, shape retention) excellent water resistance.

[0016] In one embodiment, the diisocyanate in step (1) is one or more of toluene diisocyanate, 1,6-hexane diisocyanate, 4,4-diphenylmethane diisocyanate, isophorone diisocyanate, 1,5-naphthalene diisocyanate, methylcyclohexyl diisocyanate, and dicyclohexylmethane diisocyanate.

[0017] In one embodiment, the diol in step (1) is one or more of polyether diols or polyester diols. Specifically, the diol is any one or more of polycaprolactone diol (PCL), polyethylene glycol (PEG), polypropylene glycol (PPG), polycarbonate diol (PCDL), and polytetrahydrofuran diol (PTMEG). In particular, the diol selected in this invention is PCL1000 or PEG1000.

[0018] In one embodiment, the molar ratio of diol to diisocyanate in step (1) is 15-20:50-56.

[0019] In one embodiment, the heating temperature in step (1) is 75-80°C. In particular, the heating is carried out in a device equipped with a stirrer and a reflux condenser.

[0020] In one embodiment, the catalyst in step (1) is an organotin catalyst, specifically at least one of dibutyltin dilaurate, stannous octanoate, and dibutyltin diesterate. In particular, the mass ratio of the catalyst to the diisocyanate is 0.5-1 wt%. Organotin catalysts can significantly reduce the activation energy of the reaction between isocyanate and hydroxyl groups, enabling the reaction to achieve high conversion rates at lower temperatures and in shorter times, thereby improving production efficiency and aligning with the direction of green chemistry.

[0021] In one embodiment, the reaction time in step (1) is 0.8-1.2 h.

[0022] In one embodiment, the dihydroxyPOSS in step (2) is one or more of 3,13-dihydroxypropyl octaphenyl bilayer silsesquioxane (i.e., 3,13-dihydroxypropyl DDSQ), trans-cyclohexanediol isobutyl silsesquioxane, dihydroxy-heptaphenyl cage silsesquioxane, and dihydroxy-heptaisooctyl cage silsesquioxane. Further, the molar ratio of dihydroxyPOSS to diisocyanate added twice is 1-2:50-56. An appropriate amount of dihydroxyPOSS can effectively improve the hydrophobicity and antifouling ability of waterborne polyurethane, while avoiding excessive POSS affecting the end-capping process of the fluorinated end-capping agent. If there is too much dihydroxyPOSS, its greater rigidity and hydrophobic effect will hinder the reaction of the fluorinated end-capping agent, which is detrimental to the improvement of product performance.

[0023] Due to the significant steric hindrance of POSS, this invention employs a dispersed feeding and stepwise polymerization method to add dihydroxy POSS and a hydrophilic chain extender. Using this process, these chemically bonded POSS units can be uniformly dispersed in a polyurethane matrix, forming an organic-inorganic nanocomposite material. This nanoscale dispersion generates extremely strong interfacial interactions; under external forces, POSS can effectively transfer and disperse stress, thereby significantly improving the coating's performance. First, a small amount of dihydroxy POSS is added to the prepolymer solution, and after a period of reaction, a POSS-containing oligomer is formed. Then, the hydrophilic chain extender and the remaining dihydroxy POSS are added separately, which effectively promotes the dispersion of the POSS structure in the polymer chain. The initial small amount of dihydroxy POSS is directly embedded into the polyurethane backbone, tending to aggregate in the hard segment regions composed of isocyanate, providing strong skeletal support for the hard segments. After the addition of the hydrophilic chain extender, hydrophilic groups are introduced into the prepolymer molecular chain, and the chain begins to grow and become polar. At this point, a second batch of dihydroxy POSS is added. This portion of dihydroxy POSS reacts at the interface between the hard and soft segments. It acts as a nanoscale "rivet," enhancing the interfacial bonding between the soft and hard segments and alleviating stress concentration caused by excessive differences in the properties of the two phases. This improves both rigidity and toughness of the material. Furthermore, the dihydroxy POSS added after the hydrophilic chain extender reaction enhances the structural strength of the latex particles, making them more stable during shearing, storage, or film formation, and less prone to breakage or aggregation. In addition, the stepwise addition avoids the brittleness that might result from placing all POSS in the hard segments, achieving a balance of rigidity and toughness. This is crucial for fabric finishing agents that require both stiffness and a certain degree of durability and hand feel.

[0024] In one embodiment, the solvent in step (2) is at least one of acetone, butanone, tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0025] In one embodiment, the hydrophilic chain extender in step (2) is one or more of 2,2-dimethylolpropionic acid and 2,2-dimethylolbutyric acid. The molar ratio of the hydrophilic chain extender to the diisocyanate is 18-22:50-56. The hydrophilic chain extender imparts "hydrophilicity" to the polyurethane, enabling water dispersibility and making it more environmentally friendly. Furthermore, the chain extension reaction time is 0.8-1.2 h. If the time is too short, the reaction is insufficient, the prepolymer molecular weight is low and the distribution is wide, which easily leads to insufficient cohesive strength of the final film, poor stiffness, and poor wear resistance. If the time is too long, it not only easily leads to the occurrence of side reactions, resulting in increased branching or even gelation, but also hinders the reaction between the hydrophobic dihydroxy POSS and the fluorinated end-capping agent.

[0026] In one embodiment, the reaction time in step (2) is 2-3 hours.

[0027] In one embodiment, the fluorinated end-capping agent in step (3) is one or more of perfluorohexylethanol, perfluorohexyloctanol, and 3-(perfluoro-5-methylhexyl)-2-hydroxypropylacrylic acid. The end-capping reaction is carried out for 1.5-2 hours.

[0028] In one embodiment, the crosslinking agent in step (3) is one or more of trimethylolpropane, glycerol, pentaerythritol or butanetetraethanolamine; the crosslinking reaction time is 1-2 h.

[0029] In one embodiment, the molar ratio of fluorinated end-capping agent, crosslinking agent, and diisocyanate in step (3) is 8-10:1.5-4:50-56. Further, the molar ratio of fluorinated end-capping agent, crosslinking agent, and diisocyanate is 8-10:2-3:50-56. An appropriate amount of crosslinking agent can restrict molecular chain slippage, significantly improving modulus and rigidity. This makes the coating more wear-resistant, scratch-resistant, and wash-resistant, and the stiffening effect lasts longer. Excessive crosslinking agent not only prevents the POSS structure from exerting its hydrophobic and reinforcing effects but may also lead to a decrease in emulsion stability, causing the fabric to become stiff, rigid, and lose elasticity.

[0030] In one embodiment, the neutralizing agent in step (3) is triethylamine, with a molar ratio of 1:1 to the hydrophilic chain extender. The neutralization reaction is carried out by lowering the system temperature to 40-45°C and reacting for 0.4-0.8 hours. Triethylamine can form carboxylate ions in the form of quaternary ammonium salts, which become strong hydrophilic centers on the polyurethane molecular chain, endowing the polymer with self-emulsifying ability, enabling the polymer to be stably dispersed in water, effectively preventing particles from agglomerating and settling during storage and use, thereby obtaining a long-term stable aqueous emulsion.

[0031] On the other hand, the present invention also provides a green and environmentally friendly stiffening agent prepared by the above method, which improves the hydrophobic properties of the stiffening agent and gives it high stiffness, thus having broad application prospects.

[0032] Beneficial effects:

[0033] (1) In this invention, a certain amount of dihydroxy POSS is added during the polymerization process. The two hydroxyl groups of dihydroxy POSS enable it to react with isocyanate like conventional polyols, and firmly attach to the main chain of waterborne polyurethane in the form of chemical bonds. The inorganic siloxane cages of POSS have extremely high rigidity and dimensional stability. These rigid POSS cages greatly restrict the movement of the surrounding polyurethane soft segments (flexible chains), which increases the glass transition temperature of the entire polymer network. Macroscopically, this manifests as a significant increase in the rigidity and hardness of the coating film, thus giving the fabric an excellent stiffness. The performance of waterborne polyurethane largely depends on the "microphase separation" structure of its soft and hard segments. As a polar rigid unit, POSS changes the degree and morphology of this microphase separation, promotes the orderly arrangement of the hard segment region, forms a more complete and stronger physical cross-linking network, and enhances the stiffness and stability.

[0034] (2) This invention employs a dispersed feeding and stepwise polymerization method to add dihydroxy POSS and a hydrophilic chain extender. Using this process, these chemically bonded POSS units can be uniformly dispersed in the polyurethane matrix, forming an organic-inorganic nanocomposite material. This nanoscale dispersion generates extremely strong interfacial interactions; under external force, POSS can effectively transfer and disperse stress, thereby significantly improving the coating's performance. This enhances the hydrophobic properties of the stiffening agent while also giving it high stiffness. Detailed Implementation

[0035] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention are described in detail below with reference to examples. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Unless otherwise specified, the types of raw materials and processes used in the following embodiments are the same.

[0036] Performance Testing: Under the same conditions, fabrics prepared using the stiffening agents described in the following examples and comparative examples were treated with a two-dip, two-nip-pre-dry, and baking process. The water contact angle and stiffness were then tested using a contact angle meter and an electronic stiffness meter, respectively.

[0037] Example 1

[0038] A method for preparing a green and environmentally friendly stiffening agent includes the following steps:

[0039] (1) Isophorone diisocyanate and diol PCL1000 were heated to 75°C and stirred evenly. Then, the catalyst dibutyltin dilaurate was added and reacted for 0.8 h to obtain a prepolymer solution. The mass ratio of catalyst to diisocyanate was 0.6 wt%; the molar ratio of diol to diisocyanate was 16:50.

[0040] (2) Add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to the prepolymer solution, and add acetone as a solvent to reduce viscosity. After reacting for 0.5 h, add the hydrophilic chain extender 2,2-dimethylolpropionic acid for chain extension reaction for 0.7 h, and then add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to continue the reaction for 2 h to obtain a POSS modified prepolymer solution. The molar ratio of dihydroxyPOSS to diisocyanate added in the two additions is 0.5:50. Among them, the dihydroxyPOSS added in the first addition accounts for 10 mol% of the dihydroxyPOSS added in the two additions; the molar ratio of hydrophilic chain extender to diisocyanate is 21:50.

[0041] (3) Add the fluorinated end-capping agent perfluorohexylethanol to the POSS modified prepolymer solution and react for 1.5 h. Then add the crosslinking agent trimethylolpropane and crosslink for 1 h. Lower the system temperature to 40 °C and add the neutralizing agent triethylamine to neutralize for 0.4 h. The molar ratio of the neutralizing agent to the hydrophilic chain extender is 1:1. The molar ratio of the fluorinated end-capping agent, crosslinking agent and diisocyanate is 8:3.2:50.

[0042] (4) Add deionized water for emulsification, and remove the organic solvent by rotary evaporation to obtain a green and environmentally friendly stiffening agent. The contact angle is 145.8° and the stiffness is 40.5 mm.

[0043] Example 2

[0044] A method for preparing a green and environmentally friendly stiffening agent includes the following steps:

[0045] (1) Isophorone diisocyanate and diol PCL1000 were heated to 80°C and stirred evenly. Then, the catalyst dibutyltin dilaurate was added and reacted for 1.2 h to obtain a prepolymer solution. The mass ratio of catalyst to diisocyanate was 0.9 wt%; the molar ratio of diol to diisocyanate was 20:56.

[0046] (2) Add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to the prepolymer solution, and add acetone as a solvent to reduce viscosity. After reacting for 1.5 h, add the hydrophilic chain extender 2,2-dimethylolpropionic acid for chain extension reaction for 1.3 h, and then add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to continue the reaction for 3 h to obtain a POSS modified prepolymer solution. The molar ratio of dihydroxyPOSS to diisocyanate added in the two additions is 2.3:56. Among them, the dihydroxyPOSS added in the first addition accounts for 30 mol% of the dihydroxyPOSS added in the two additions; the molar ratio of hydrophilic chain extender to diisocyanate is 22:56.

[0047] (3) Add the fluorinated end-capping agent perfluorohexylethanol to the POSS modified prepolymer solution and react for 2 h, then add the crosslinking agent trimethylolpropane and crosslink for 2 h, lower the system temperature to 45℃, add the neutralizing agent triethylamine and neutralize for 0.8 h; the molar ratio of neutralizing agent to hydrophilic chain extender is 1:1; the molar ratio of fluorinated end-capping agent, crosslinking agent and diisocyanate is 10:2.5:56;

[0048] (4) Add deionized water for emulsification, and remove the organic solvent by rotary evaporation to obtain a green and environmentally friendly stiffening agent. The contact angle was tested to be 148.6° and the stiffness was 45.6 mm.

[0049] Example 3

[0050] A method for preparing a green and environmentally friendly stiffening agent includes the following steps:

[0051] (1) Isophorone diisocyanate and diol PCL1000 were heated to 77°C and stirred evenly. Then, the catalyst dibutyltin dilaurate was added and reacted for 1 hour to obtain a prepolymer solution. The mass ratio of catalyst to diisocyanate was 0.8wt%; the molar ratio of diol to diisocyanate was 18:52.

[0052] (2) Add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to the prepolymer solution, and add acetone as a solvent to reduce viscosity. After reacting for 1 hour, add 2,2-dimethylolpropionic acid as a hydrophilic chain extender for chain extension reaction for 1 hour. Then add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) and continue the reaction for 2.5 hours to obtain a POSS-modified prepolymer solution. The molar ratio of dihydroxyPOSS to diisocyanate added in the two additions is 2.5:52. Among them, the dihydroxyPOSS added in the first addition accounts for 20 mol% of the dihydroxyPOSS added in the two additions. The molar ratio of hydrophilic chain extender to diisocyanate is 20:52.

[0053] (3) Add the fluorinated end-capping agent perfluorohexylethanol to the POSS modified prepolymer solution and react for 1.8 h, then add the crosslinking agent trimethylolpropane and crosslink for 1.5 h, lower the system temperature to 43 °C, add the neutralizing agent triethylamine and neutralize for 0.5 h; the molar ratio of the neutralizing agent to the hydrophilic chain extender is 1:1; the molar ratio of the fluorinated end-capping agent, crosslinking agent and diisocyanate is 9:3:52;

[0054] (4) Add deionized water for emulsification, and remove the organic solvent by rotary evaporation to obtain the green and environmentally friendly stiffening agent. The test results show that its contact angle is 146.9° and its stiffness is 42.5 mm.

[0055] Example 4

[0056] A method for preparing a green and environmentally friendly stiffening agent includes the following steps:

[0057] (1) Isophorone diisocyanate and diol PEG1000 were heated to 75°C and stirred evenly. Then, the catalyst dibutyltin dilaurate was added and reacted for 1.2 h to obtain a prepolymer solution. The mass ratio of catalyst to diisocyanate was 0.5 wt%; the molar ratio of diol to diisocyanate was 20:52.

[0058] (2) Add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to the prepolymer solution and add acetone solvent to reduce viscosity. After reacting for 0.6 h, add hydrophilic chain extender 2,2-dimethylolpropionic acid for chain extension reaction for 1.2 h. Then add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) and continue the reaction for 2.2 h to obtain POSS modified prepolymer solution. The molar ratio of dihydroxyPOSS to diisocyanate added in the two additions is 1.3:52. Among them, the dihydroxyPOSS added in the first addition accounts for 14 mol% of the dihydroxyPOSS added in the two additions. The molar ratio of hydrophilic chain extender to diisocyanate is 18:52.

[0059] (3) Add the fluorinated end-capping agent perfluorohexylethanol to the POSS modified prepolymer solution and react for 1.6 h. Then add the crosslinking agent trimethylolpropane and crosslink for 2 h. Lower the system temperature to 45 °C and add the neutralizing agent triethylamine to neutralize for 0.6 h. The molar ratio of the neutralizing agent to the hydrophilic chain extender is 1:1. The molar ratio of the fluorinated end-capping agent, crosslinking agent and diisocyanate is 8.2:3.3:52.

[0060] (4) Add deionized water for emulsification, and remove the organic solvent by rotary evaporation to obtain the green and environmentally friendly stiffening agent. The test results show that its contact angle is 147.1° and its stiffness is 43.2 mm.

[0061] Example 5

[0062] A method for preparing a green and environmentally friendly stiffening agent includes the following steps:

[0063] (1) Isophorone diisocyanate and diol PCL1000 were heated to 77°C and stirred evenly. Then, the catalyst dibutyltin dilaurate was added and reacted for 1 hour to obtain a prepolymer solution. The mass ratio of catalyst to diisocyanate was 0.8wt%; the molar ratio of diol to diisocyanate was 18:52.

[0064] (2) Add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to the prepolymer solution, and add acetone solvent to reduce viscosity. After reacting for 1 h, add hydrophilic chain extender 2,2-dimethylolpropionic acid for chain extension reaction for 1.5 h, and then add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to continue the reaction for 2.5 h to obtain POSS modified prepolymer solution; the molar ratio of dihydroxyPOSS to diisocyanate added in the two additions is 1.8:52; of which, the dihydroxyPOSS added in the first addition accounts for 20 mol% of the dihydroxyPOSS added in the two additions; the molar ratio of hydrophilic chain extender to diisocyanate is 20:52;

[0065] (3) Add the fluorinated end-capping agent perfluorohexylethanol to the POSS modified prepolymer solution and react for 1.8 h, then add the crosslinking agent trimethylolpropane and crosslink for 1.5 h, lower the system temperature to 43 °C, add the neutralizing agent triethylamine and neutralize for 0.5 h; the molar ratio of the neutralizing agent to the hydrophilic chain extender is 1:1; the molar ratio of the fluorinated end-capping agent, crosslinking agent and diisocyanate is 9:3:52;

[0066] (4) Add deionized water for emulsification, and remove the organic solvent by rotary evaporation to obtain a green and environmentally friendly stiffening agent. The contact angle is 147.4° and the stiffness is 45.3 mm.

[0067] Example 6

[0068] A method for preparing a green and environmentally friendly stiffening agent includes the following steps:

[0069] (1) Isophorone diisocyanate and diol PCL1000 were heated to 76°C and stirred until homogeneous. Then, dibutyltin dilaurate catalyst was added and reacted for 0.9 h to obtain a prepolymer solution. The mass ratio of catalyst to diisocyanate was 0.7 wt%; the molar ratio of diol to diisocyanate was 17:52.

[0070] (2) Add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to the prepolymer solution, and add acetone as a solvent to reduce viscosity. After reacting for 0.7 h, add the hydrophilic chain extender 2,2-dimethylolpropionic acid for chain extension reaction for 0.9 h, and then add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to continue the reaction for 2.2 h to obtain POSS modified prepolymer solution; the molar ratio of dihydroxyPOSS to diisocyanate added in the two additions is 1:52; of which, the dihydroxyPOSS added in the first addition accounts for 18 mol% of the dihydroxyPOSS added in the two additions; the molar ratio of hydrophilic chain extender to diisocyanate is 21:52;

[0071] (3) Add the fluorinated end-capping agent perfluorohexylethanol to the POSS modified prepolymer solution and react for 1.6 h, then add the crosslinking agent trimethylolpropane and crosslink for 1.2 h. Lower the system temperature to 42 °C and add the neutralizing agent triethylamine to neutralize for 0.6 h. The molar ratio of the neutralizing agent to the hydrophilic chain extender is 1:1. The molar ratio of the fluorinated end-capping agent, crosslinking agent and diisocyanate is 8.5:3.8:52.

[0072] (4) Add deionized water for emulsification, and remove the organic solvent by rotary evaporation to obtain the green and environmentally friendly stiffening agent. The test results showed that its contact angle was 146.8° and its stiffness was 41.7 mm.

[0073] Example 7

[0074] A method for preparing a green and environmentally friendly stiffening agent includes the following steps:

[0075] (1) Isophorone diisocyanate and diol PCL1000 were heated to 77°C and stirred evenly. Then, the catalyst dibutyltin dilaurate was added and reacted for 1 hour to obtain a prepolymer solution. The mass ratio of catalyst to diisocyanate was 0.8wt%; the molar ratio of diol to diisocyanate was 18:52.

[0076] (2) Add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to the prepolymer solution, and add acetone as a solvent to reduce viscosity. After reacting for 1 hour, add the hydrophilic chain extender 2,2-dimethylolpropionic acid for chain extension reaction for 1 hour. Then add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) and continue the reaction for 2.5 hours to obtain a POSS modified prepolymer solution. The molar ratio of dihydroxyPOSS to diisocyanate added in the two additions is 1.8:52. Among them, the dihydroxyPOSS added in the first addition accounts for 20 mol% of the dihydroxyPOSS added in the two additions. The molar ratio of hydrophilic chain extender to diisocyanate is 20:52.

[0077] (3) Add the fluorinated end-capping agent perfluorohexylethanol to the POSS modified prepolymer solution and react for 1.8 h, then add the crosslinking agent trimethylolpropane and crosslink for 1.5 h. Lower the system temperature to 43 °C and add the neutralizing agent triethylamine to neutralize for 0.5 h. The molar ratio of the neutralizing agent to the hydrophilic chain extender is 1:1. The molar ratio of the fluorinated end-capping agent, crosslinking agent and diisocyanate is 9:3.5:52.

[0078] (4) Add deionized water for emulsification, and remove the organic solvent by rotary evaporation to obtain the green and environmentally friendly stiffening agent. The test results show that its contact angle is 148.2° and its stiffness is 44.7 mm.

[0079] Example 8

[0080] A method for preparing a green and environmentally friendly stiffening agent includes the following steps:

[0081] (1) Isophorone diisocyanate and diol PCL1000 were heated to 76°C and stirred evenly. Then, the catalyst dibutyltin dilaurate was added and reacted for 1 hour to obtain a prepolymer solution. The mass ratio of catalyst to diisocyanate was 0.8wt%; the molar ratio of diol to diisocyanate was 18:53.

[0082] (2) Add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to the prepolymer solution, and add acetone as a solvent to reduce viscosity. After reacting for 1.1 h, add the hydrophilic chain extender 2,2-dimethylolpropionic acid for chain extension reaction for 1.4 h, and then add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to continue the reaction for 2.3 h to obtain POSS modified prepolymer solution; the molar ratio of dihydroxyPOSS to diisocyanate added in the two additions is 2:53; of which, the dihydroxyPOSS added in the first addition accounts for 22 mol% of the dihydroxyPOSS added in the two additions; the molar ratio of hydrophilic chain extender to diisocyanate is 20:53;

[0083] (3) Add the fluorinated end-capping agent perfluorohexylethanol to the POSS modified prepolymer solution and react for 1.8 h, then add the crosslinking agent trimethylolpropane and crosslink for 1.7 h. Lower the system temperature to 43 °C and add the neutralizing agent triethylamine to neutralize for 0.8 h. The molar ratio of the neutralizing agent to the hydrophilic chain extender is 1:1. The molar ratio of the fluorinated end-capping agent, crosslinking agent and diisocyanate is 10:2.3:53.

[0084] (4) Add deionized water for emulsification, and remove the organic solvent by rotary evaporation to obtain the green and environmentally friendly stiffening agent. The test results showed that its contact angle was 149.4° and its stiffness was 46.2 mm.

[0085] Example 9

[0086] A method for preparing a green and environmentally friendly stiffening agent includes the following steps:

[0087] (1) Isophorone diisocyanate and diol PEG1000 were heated to 78°C and stirred evenly. Then, the catalyst dibutyltin dilaurate was added and reacted for 1.4 h to obtain the prepolymer solution. The mass ratio of catalyst to diisocyanate was 0.8 wt%; the molar ratio of diol to diisocyanate was 19:53.

[0088] (2) Add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to the prepolymer solution and add acetone solvent to reduce viscosity. After reacting for 1.2 h, add hydrophilic chain extender 2,2-dimethylolpropionic acid for chain extension reaction for 1.1 h. Then add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) and continue the reaction for 2.8 h to obtain POSS modified prepolymer solution. The molar ratio of dihydroxyPOSS to diisocyanate added in the two additions is 2.2:53. Among them, the dihydroxyPOSS added in the first addition accounts for 25 mol% of the dihydroxyPOSS added in the two additions. The molar ratio of hydrophilic chain extender to diisocyanate is 21:53.

[0089] (3) Add the fluorinated end-capping agent perfluorohexylethanol to the POSS modified prepolymer solution and react for 1.8 h. Then add the crosslinking agent trimethylolpropane and crosslink for 1.8 h. Lower the system temperature to 44 °C and add the neutralizing agent triethylamine to neutralize for 0.7 h. The molar ratio of the neutralizing agent to the hydrophilic chain extender is 1:1. The molar ratio of the fluorinated end-capping agent, crosslinking agent and diisocyanate is 9.5:1.7:53.

[0090] (4) Add deionized water for emulsification, and remove the organic solvent by rotary evaporation to obtain the green and environmentally friendly stiffening agent. The test results show that its contact angle is 150.9° and its stiffness is 44.3 mm.

[0091] Example 10

[0092] A method for preparing a green and environmentally friendly stiffening agent includes the following steps:

[0093] (1) Isophorone diisocyanate and diol PCL1000 were heated to 77°C and stirred evenly. Then, the catalyst dibutyltin dilaurate was added and reacted for 1 hour to obtain a prepolymer solution. The mass ratio of catalyst to diisocyanate was 0.8wt%; the molar ratio of diol to diisocyanate was 18:52.

[0094] (2) Add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to the prepolymer solution, and add acetone as a solvent to reduce viscosity. After reacting for 1 hour, add the hydrophilic chain extender 2,2-dimethylolpropionic acid for chain extension reaction for 1 hour. Then add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) and continue the reaction for 2.5 hours to obtain a POSS modified prepolymer solution. The molar ratio of dihydroxyPOSS to diisocyanate added in the two additions is 1.8:52. Among them, the dihydroxyPOSS added in the first addition accounts for 20 mol% of the dihydroxyPOSS added in the two additions. The molar ratio of hydrophilic chain extender to diisocyanate is 20:52.

[0095] (3) Add the fluorinated end-capping agent perfluorohexylethanol to the POSS modified prepolymer solution and react for 1.8 h, then add the crosslinking agent trimethylolpropane and crosslink for 1.5 h, lower the system temperature to 43 °C, add the neutralizing agent triethylamine and neutralize for 0.5 h; the molar ratio of the neutralizing agent to the hydrophilic chain extender is 1:1; the molar ratio of the fluorinated end-capping agent, crosslinking agent and diisocyanate is 9:3:52;

[0096] (4) Add deionized water for emulsification, and remove the organic solvent by rotary evaporation to obtain a green and environmentally friendly stiffening agent. The test results showed that its contact angle was 151.3° and its stiffness was 46.6 mm.

[0097] Comparative Example 1

[0098] A method for preparing a green and environmentally friendly stiffening agent includes the following steps:

[0099] (1) Isophorone diisocyanate and diol PCL1000 were heated to 77°C and stirred evenly. Then, the catalyst dibutyltin dilaurate was added and reacted for 1 hour to obtain a prepolymer solution. The mass ratio of catalyst to diisocyanate was 0.8wt%; the molar ratio of diol to diisocyanate was 18:52.

[0100] (2) Add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to the prepolymer solution, and add acetone as a solvent to reduce viscosity. After reacting for 1 hour, add the hydrophilic chain extender 2,2-dimethylolpropionic acid for chain extension reaction for 1 hour. Then add dihydroxyPOSS (3,13-dihydroxypropylDDSQ) and continue the reaction for 2.5 hours to obtain a POSS modified prepolymer solution. The molar ratio of dihydroxyPOSS to diisocyanate added in the two additions is 1.8:52. Among them, the dihydroxyPOSS added in the first addition accounts for 50 mol% of the dihydroxyPOSS added in the two additions. The molar ratio of hydrophilic chain extender to diisocyanate is 20:52.

[0101] (3) Add the fluorinated end-capping agent perfluorohexylethanol to the POSS modified prepolymer solution and react for 1.8 h, then add the crosslinking agent trimethylolpropane and crosslink for 1.5 h, lower the system temperature to 43 °C, add the neutralizing agent triethylamine and neutralize for 0.5 h; the molar ratio of the neutralizing agent to the hydrophilic chain extender is 1:1; the molar ratio of the fluorinated end-capping agent, crosslinking agent and diisocyanate is 9:3:52;

[0102] (4) Add deionized water for emulsification, and remove the organic solvent by rotary evaporation to obtain a green and environmentally friendly stiffening agent. The test results showed that its contact angle was 133.3° and its stiffness was 36.4 mm.

[0103] Comparative Example 2

[0104] A method for preparing a green and environmentally friendly stiffening agent includes the following steps:

[0105] (1) Isophorone diisocyanate and diol PCL1000 were heated to 77°C and stirred evenly. Then, the catalyst dibutyltin dilaurate was added and reacted for 1 hour to obtain a prepolymer solution. The mass ratio of catalyst to diisocyanate was 0.8wt%; the molar ratio of diol to diisocyanate was 18:52.

[0106] (2) Add hydrophilic chain extender 2,2-dimethylolpropionic acid to the prepolymer solution, and add solvent acetone to reduce viscosity. Perform chain extension reaction for 1 h, then add dihydroxyPOSS (3,13-dihydroxypropylDDSQ), react for 1 h, and then add more dihydroxyPOSS (3,13-dihydroxypropylDDSQ) to continue the reaction for 2.5 h to obtain POSS modified prepolymer solution; the molar ratio of dihydroxyPOSS to diisocyanate added in the two additions is 1.8:52; of which, the dihydroxyPOSS added in the first addition accounts for 20 mol% of the dihydroxyPOSS added in the two additions; the molar ratio of hydrophilic chain extender to diisocyanate is 20:52;

[0107] (3) Add the fluorinated end-capping agent perfluorohexylethanol to the POSS modified prepolymer solution and react for 1.8 h, then add the crosslinking agent trimethylolpropane and crosslink for 1.5 h, lower the system temperature to 43 °C, add the neutralizing agent triethylamine and neutralize for 0.5 h; the molar ratio of the neutralizing agent to the hydrophilic chain extender is 1:1; the molar ratio of the fluorinated end-capping agent, crosslinking agent and diisocyanate is 9:3:52;

[0108] (4) Add deionized water for emulsification, and remove the organic solvent by rotary evaporation to obtain a green and environmentally friendly stiffening agent. The test results showed that its contact angle was 135.1° and its stiffness was 34.2 mm.

[0109] As can be seen from the above examples and comparative examples, the present invention adds a certain amount of dihydroxy POSS to the waterborne polyurethane system using a fluorinated end-capping agent as the fluorine source. The two hydroxyl groups of dihydroxy POSS allow it to react with isocyanates like conventional polyols, firmly attaching to the main chain of the waterborne polyurethane in the form of chemical bonds. The inorganic siloxane cages of POSS possess extremely high rigidity and dimensional stability. These rigid POSS cages greatly restrict the movement of the surrounding polyurethane soft segments (flexible chains), significantly increasing the rigidity and hardness of the coating film, thereby giving the fabric an excellent stiffness. As a polar rigid unit, POSS alters the degree and morphology of this microphase separation, promoting the orderly arrangement of hard segment regions, forming a more complete and stronger physical cross-linking network, and enhancing the stiffness and stability. The siloxane structure of POSS imparts a certain degree of hydrophobicity to the coating surface, resisting water molecule intrusion and protecting the polyurethane matrix from hydrolysis; the POSS migrating to the coating surface provides a certain low surface energy, bringing auxiliary hydrophobic and antifouling effects, while not causing a stiff feel like fluorinated compounds. Unlike simply increasing the thickness of the waterborne polyurethane coating to achieve stiffness, POSS's nano-reinforcing effect allows for higher stiffness with a thinner coating. This means that while achieving the desired stiffness, the fabric can better maintain its original softness, drape, and breathability. These two factors work together to give the finishing effect (stiffness and shape retention) excellent hydrophobicity.

[0110] Specifically, compared to Example 10, Comparative Example 1 added too much dihydroxy POSS initially. Due to its extremely high rigidity, it excessively aggregated in the hard segment region composed of isocyanate, which is detrimental to enhancing the interfacial bonding between the soft and hard segments in the polyurethane, easily leading to stress concentration and hindering the film formation of waterborne polyurethane. Although Comparative Example 2 used a stepwise polymerization process, it first added a hydrophilic chain extender for chain extension. The excessively large molecular weight made molecular chain movement difficult, and due to the large steric hindrance of POSS, the subsequently added dihydroxy POSS could not be uniformly dispersed in the polyurethane matrix, failing to effectively form an organic-inorganic nanocomposite material. At the same time, the aggregated POSS structure affected the end-capping of the fluorinated end-capping agent, resulting in a decrease in hydrophobic properties.

[0111] This indicates that adding a small amount of dihydroxy POSS to the prepolymer solution, reacting for a period of time to form POSS-containing oligomers, and then adding a hydrophilic chain extender and the remaining dihydroxy POSS can effectively promote the dispersion of the POSS structure in the polymer chain. The initial small amount of POSS is directly embedded in the polyurethane backbone, tending to aggregate in the hard segment regions composed of isocyanates, providing strong skeletal support for the hard segments. After the addition of the hydrophilic chain extender, hydrophilic groups are introduced into the prepolymer molecular chain, and the chain begins to grow and become polar. At this point, a second batch of POSS is added. This portion of POSS reacts at the interface between the hard and soft segments, alleviating stress concentration caused by the large difference in properties between the two phases, thereby improving both rigidity and toughness, and enhancing the performance of the stiffening agent.

[0112] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described; these embodiments not explicitly stated should also be considered within the scope of this specification. Although the present invention has been described in detail above with general descriptions and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing an eco-friendly stiffening agent, characterized by, The method comprises the following steps: (1) uniformly heating and stirring diisocyanate and dihydric alcohol, then adding catalyst, and obtaining prepolymer solution after reaction; (2) adding dihydroxy POSS to the prepolymer solution, adding solvent to reduce viscosity, and after 0.5-1.5 hours of reaction, adding hydrophilic chain extender to perform chain extension reaction for 0.5-1.5 hours, then adding dihydroxy POSS to continue reaction, and obtaining POSS modified prepolymer solution; the molar ratio of dihydroxy POSS added twice to diisocyanate is 0.5-2.5:50-56; wherein, the dihydroxy POSS added first accounts for 10-30 mol% of the dihydroxy POSS added twice; (3) adding fluorine-containing end-capping agent to perform end-capping, adding crosslinking agent to perform crosslinking, and adding neutralizing agent to perform neutralization in the POSS modified prepolymer solution; (4) adding deionized water to perform emulsification, and removing organic solvent by rotary evaporation, and obtaining green and environmentally-friendly stiffening agent.

2. The preparation method of the green and environmentally friendly stiffening agent as described in claim 1, characterized in that, The diisocyanate in step (1) is one or more of toluene diisocyanate, 1,6-hexane diisocyanate, 4,4-diphenyl methane diisocyanate, isophorone diisocyanate, 1,5-naphthalene diisocyanate, methylcyclohexyl diisocyanate, and dicyclohexyl methane diisocyanate.

3. The preparation method of the green and environmentally friendly stiffening agent as described in claim 1, characterized in that, The dihydric alcohol in step (1) is one or more of polyether dihydric alcohol or polyester dihydric alcohol.

4. The preparation method of the green and environmentally friendly stiffening agent as described in claim 1, characterized in that, The catalyst in step (1) is organic tin catalyst.

5. The preparation method of the green and environmentally friendly stiffening agent as described in claim 1, characterized in that, The dihydroxy POSS in step (2) is one or more of 3,13-dihydroxypropyl octaphenyl bilayer silsesquioxane, trans-cyclohexanediol isobutyl silsesquioxane, dihydroxy-heptaphenyl cage silsesquioxane, and dihydroxy-heptaisooctyl cage silsesquioxane.

6. The preparation method of the green and environmentally friendly stiffening agent as described in claim 1, characterized in that, The solvent in step (2) is at least one of acetone, butanone, tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide.

7. The preparation method of the green and environmentally friendly stiffening agent as described in claim 1, characterized in that, The hydrophilic chain extender in step (2) is one or more of 2,2-dimethylol propionic acid and 2,2-dimethylol butyric acid.

8. The preparation method of the green and environmentally friendly stiffening agent as described in claim 1, characterized in that, The fluorine-containing end-capping agent in step (3) is one or more of perfluorohexyl ethanol, perfluorohexyl octanol, and 3-(perfluoro-5-methylhexyl)-2-hydroxypropyl acrylate.

9. The preparation method of the green and environmentally friendly stiffening agent as described in claim 1, characterized in that, The neutralizing agent in step (3) is triethylamine.

10. A green stiffening agent, characterized by, The green and environmentally-friendly stiffening agent is prepared by the method in any one of claims 1-9.