Modified soft polyurethane sponge and preparation method thereof

Abstract

The invention relates to the field of sponges, and particularly discloses a modified soft polyurethane sponge which is of an integrally-formed three-layer gradient structure and sequentially comprises a substrate bottom layer, a supporting core layer and a surface layer from bottom to top, and the substrate bottom layer is made of a biodegradable polyurethane material with a main chain containing ester bonds and glucosidic bonds; the supporting core layer is compounded on the substrate bottom layer and is made of a composite material of lignin-based polyurethane and natural plant fibers; the surface layer is compounded on the supporting core layer and is formed by a composite material of non-isocyanate polyurethane and biodegradable microcapsules encapsulated with an antibacterial agent; the preparation method of the modified soft polyurethane sponge comprises the following steps: preparing a surface layer foaming material, preparing a supporting core layer foaming material, preparing a substrate bottom layer foaming material, carrying out layered pouring and integrated foaming, and carrying out compression shaping, cutting and surface functionalization treatment on the cured sponge to obtain a final product. The spanning from single performance optimization to system problem solving is realized, and normal form transformation of a polyurethane sponge modification technology is represented.

Description

Technical Field

[0001] This invention relates to the field of sponges, specifically to modified soft polyurethane sponges and their preparation methods. Background Technology

[0002] Polyurethane foam is widely used in many fields such as home furnishings, mattresses, car seats, medical supplies, and packaging due to its lightweight, porous, elastic, and cost-effective properties. However, traditional polyurethane foam has many inherent drawbacks: First, the isocyanates used in its production are toxic, posing a threat to the production environment and the health of operators; second, the porous structure of polyurethane foam makes it highly absorbent of moisture, becoming a breeding ground for bacteria and mites; third, traditional polyurethane foam is flammable, with an oxygen index of only about 20%, and releases highly toxic hydrogen cyanide and carbon monoxide fumes when burned; in addition, polyurethane materials are difficult to degrade naturally, with a degradation cycle of 2-5 years, causing long-term "white pollution" after disposal, and the recycling rate is less than 15%.

[0003] Existing modification technologies mostly focus on single-point improvements, making it difficult to systematically address the multi-dimensional defects of polyurethane foam. For example, antibacterial modified foam still suffers from insufficient flame retardant properties; flame-retardant modified foam often sacrifices softness and comfort; while the application of bio-based raw materials reduces the carbon footprint, the production process may still involve toxic chemicals, and the degradation mechanism remains imperfect.

[0004] Existing technologies have not yet solved the triangular balance problem of "performance-environmental protection-cost" and have failed to achieve dynamic synergy of multiple functions such as antibacterial, degradation, flame retardancy, softness and support. Therefore, a modified soft polyurethane foam and its preparation method are proposed to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a modified soft polyurethane foam and its preparation method to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] Modified soft polyurethane foam, which has a one-piece molded three-layer gradient structure, comprising, from bottom to top:

[0008] The base layer is composed of a biodegradable polyurethane material containing ester bonds and glycosidic bonds in the main chain, with a micro-closed-pore structure and an open-pore ratio of 30-40%; the biodegradable polyurethane has a three-step synergistic degradation mechanism of enzymatic hydrolysis-oxidation.

[0009] The supporting core layer, composited on the bottom layer of the substrate, is composed of a composite material of lignin-based polyurethane and natural plant fibers. The main chain of the lignin-based polyurethane is embedded with ester bonds and / or glycosidic bonds, and contains a composite crosslinking agent composed of rigid aromatic ring groups and flexible ether bonds. It has a gradient pore structure with the pore size gradually decreasing from the center to both sides, and the pore size gradient coefficient is 1.2-2.0.

[0010] The surface layer, composited on the supporting core layer, is composed of a composite material of non-isocyanate polyurethane and biodegradable microcapsules encapsulated with antibacterial agents. It has a highly open-pore structure with an open-pore ratio of not less than 95%. The non-isocyanate polyurethane is obtained by stepwise polymerization of cyclic carbonate oligomers and bio-based polyamines, and the raw materials do not contain isocyanates.

[0011] The surface layer, the supporting core layer, and the substrate bottom layer are bonded together without an interface through interlayer chemical bonding; the interlayer chemical bonding includes at least one of urethane bonds, urea bonds, and ester bonds;

[0012] The degradation rate of the biodegradable microcapsules in the surface layer matches that of the overall sponge, with a degradation half-life difference of no more than 15%, in order to achieve dynamic synergistic release of antibacterial agents.

[0013] The sponge has a compression set of no more than 3.5% after being compressed for 22 hours at 70℃, a limiting oxygen index of no less than 32%, a bio-based carbon content of no less than 40%, and takes 1-2 years to lose 90% of its weight under natural conditions.

[0014] Another object of the present invention is to provide a method for preparing any of the modified soft polyurethane foams described above, comprising the following steps:

[0015] Step 1: Preparation of surface foaming material

[0016] Non-isocyanate polyurethane prepolymer, biodegradable microcapsules encapsulated with antibacterial agent, chitosan oligosaccharide, cell opener, foaming agent, foam stabilizer and catalyst are added to a mixing tank and stirred for 10-30 seconds at 20-30℃ and 1000-2000 r / min to obtain surface foam material.

[0017] Step 2: Preparation of the supporting core foam material

[0018] The lignin-based polyurethane prepolymer, surface-modified natural plant fibers, composite crosslinking agent, nano-reinforcing filler, foam stabilizer, cell opener, foaming agent and catalyst are added to a mixing tank and stirred for 15-40 seconds at 20-30℃ and 1500-2500 r / min to obtain the supporting core foam material.

[0019] Step 3: Prepare the base foaming material

[0020] A biodegradable polyurethane prepolymer containing ester bonds and glycosidic bonds, a foaming agent, a foam stabilizer, and a catalyst are added to a mixing vessel and stirred for 10-20 seconds at 20-30℃ and 1000-1500 r / min to obtain the base layer foaming material.

[0021] Step 4: Layered casting and integrated foaming

[0022] Preheat the mold to 30-50℃, and pour the base layer foam, the supporting core layer foam, and the surface layer foam into the mold in sequence. Control the time interval between pouring two adjacent layers to be 30-120 seconds to ensure that a chemical bonding reaction occurs at the interlayer interface. After pouring, let it stand at 25-40℃ for 10-30 minutes to foam, and then transfer it to 50-80℃ for 2-6 hours to cure. After demolding, the modified soft polyurethane sponge is obtained.

[0023] Step 5: Compress, shape, cut, and surface functionalize the cured sponge to obtain the final product.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1. The surface layer focuses on ultimate softness, rapid moisture wicking, long-lasting antibacterial properties, and intrinsic safety. The surface layer uses non-isocyanate polyurethane as the matrix material. This non-isocyanate polyurethane is produced through a stepwise polymerization reaction of cyclic carbonate oligomers and polyamines, completely eliminating the use of isocyanates in the synthesis process. This eliminates the toxicity risks and residual monomer problems inherent in traditional polyurethane production, achieving green production. Furthermore, the surface layer utilizes cyclic carbonate oligomers obtained from the reaction of bio-based epoxy resin with CO2, and bio-based polyamines such as lysine and chitosan degradation products, resulting in a bio-based carbon content of over 60%. The surface layer has an open porosity of no less than 95%, ensuring excellent breathability and moisture conduction. Combined with the hydrophilic groups (amine groups, hydroxyl groups) in the non-isocyanate polyurethane matrix, it achieves rapid moisture wicking, keeping the surface dry and fundamentally improving the thermal comfort of the sponge.

[0026] 2. The surface layer also contains chitosan oligosaccharide as an auxiliary antibacterial component; chitosan oligosaccharide is a natural antibacterial substance with broad-spectrum antibacterial properties, good biocompatibility and biodegradability, and its antibacterial rate against Staphylococcus aureus and Escherichia coli can reach more than 99.9%; chitosan oligosaccharide and microcapsule antibacterial agents form a dual protection mechanism of "immediate surface antibacterial + deep long-lasting antibacterial".

[0027] 3. This invention integrates non-isocyanate synthesis technology, natural fiber reinforcement technology, bio-based flame retardant technology, molecular-level degradable reconstruction technology, dynamic antibacterial and flame retardant synergy, and composite crosslinking agent technology through a synergistic design of "gradient structure functional layering + molecular-level degradable reconstruction + dynamic antibacterial-flame retardant synergy + composite crosslinking agent for both softness and hardness". It systematically solves the seven core problems of traditional polyurethane foam: bacterial growth, toxic smoke from combustion, production toxicity, waste pollution, stuffiness and lack of breathability, collapse and aging, and the contradiction between softness and support. It has achieved a leap from "single performance optimization" to "system problem solving" and represents a paradigm shift in polyurethane foam modification technology.

[0028] 4. The surface layer uses non-isocyanate polyurethane technology, and the synthesis process does not use isocyanate at all, which completely eliminates the toxicity risks and residual monomer problems in traditional polyurethane production; at the same time, it uses a large amount of bio-based raw materials, reduces dependence on petroleum resources, reduces carbon footprint, and achieves greening of the entire life cycle from raw materials to products.

[0029] 5. The original rigid-flexible composite crosslinking agent of this invention forms a microphase separation structure through molecular-level block copolymerization of rigid aromatic ring groups and flexible ether bonds. This ensures both overall flexibility and local rigid support, resulting in a compression set of ≤3.5%, which is far superior to the 5-15% of the prior art. It truly achieves a long-term balance between flexibility and support.

[0030] 6. Both the base layer and the supporting core layer have ester bonds and glycosidic bonds embedded in the polyurethane main chain, making degradation an essential property of the material, rather than adding biodegradable fillers; the unique three-step synergistic degradation mechanism of enzymatic hydrolysis-oxidation ensures the thoroughness of degradation, with more than 90% weight loss in 1-2 years under natural environment, no microplastic residue, which can solve the environmental pollution problem after polyurethane foam is discarded from the source.

[0031] 7. By precisely controlling the time interval of layered casting and online viscosity monitoring, chemical bonding reactions occur at the interlayer interfaces, forming covalent bonds such as urethane bonds, urea bonds, and ester bonds, achieving an interface-free integrated structure; this completely solves the problems of easy delamination and insufficient interfacial bonding strength in traditional multilayer composite materials, ensuring the long-term stability of the gradient structure.

[0032] 8. The preparation method of this invention is based on the existing continuous production process of polyurethane foam, requiring no additional special equipment. Process parameters are easy to control, and production costs are controllable. The time window for layered casting is wide (30-120 seconds), adapting to the needs of industrial production of different scales; surface functionalization treatments (hydrophobic coatings, plasma treatment, etc.) can be flexibly adjusted to meet the customized needs of different application scenarios. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] Modified soft polyurethane foam, which has a one-piece molded three-layer gradient structure, comprising, from bottom to top:

[0036] The base layer is composed of a biodegradable polyurethane material containing ester bonds and glycosidic bonds in the main chain, with a micro-closed-pore structure and an open-pore ratio of 30-40%; the biodegradable polyurethane has a three-step synergistic degradation mechanism of enzymatic hydrolysis-oxidation.

[0037] The base layer uses a biodegradable polyurethane material with ester and glycosidic bonds in the main chain. By introducing breakable biodegradable bonds into the polyurethane main chain, degradation becomes an essential property of the material, rather than adding biodegradable fillers.

[0038] The supporting core layer, composited on the bottom layer of the substrate, is composed of a composite material of lignin-based polyurethane and natural plant fibers. The main chain of the lignin-based polyurethane is embedded with ester bonds and / or glycosidic bonds, and contains a composite crosslinking agent composed of rigid aromatic ring groups and flexible ether bonds. It has a gradient pore structure with the pore size gradually decreasing from the center to both sides, and the pore size gradient coefficient is 1.2-2.0.

[0039] The supporting core layer uses lignin-based polyurethane as the matrix material. Lignin is a renewable aromatic polymer that is abundant in nature. By grafting it onto the polyurethane main chain through chemical bonds, it can not only reduce dependence on petroleum resources (the bio-based carbon content can reach more than 30%), but also endow the material with inherent flame-retardant properties.

[0040] Natural plant fibers, selected from at least one of loofah fiber, hemp fiber, bamboo fiber, and coconut shell fiber, are introduced into a lignin-based polyurethane matrix, with a mass fraction of 2-6%. The fiber surface is treated with hydroxyl activation or silane coupling agent modification to form a strong interfacial bond with the polyurethane matrix.

[0041] The surface layer, composited on the supporting core layer, is composed of a composite material of non-isocyanate polyurethane and biodegradable microcapsules encapsulated with antibacterial agents. It has a highly open-pore structure with an open-pore ratio of not less than 95%. The non-isocyanate polyurethane is obtained by stepwise polymerization of cyclic carbonate oligomers and bio-based polyamines, and the raw materials do not contain isocyanates.

[0042] The surface layer, the supporting core layer, and the substrate bottom layer are bonded together without an interface through interlayer chemical bonding; the interlayer chemical bonding includes at least one of urethane bonds, urea bonds, and ester bonds;

[0043] The three layers are firmly bonded together by chemical bonding, which is the key technology to ensure the long-term stability of the gradient structure. During the layered casting process, the time interval between each layer is controlled (30-120 seconds) to allow the active groups at the interlayer interfaces (such as the amino groups on the NIPU surface, the hydroxyl groups on the LPUF surface, and the carboxyl groups on the biodegradable polyurethane surface) to react chemically and form covalent bonds such as urethane bonds, urea bonds, and ester bonds, achieving an interface-free integrated structure. The casting timing is adjusted in real time by an online viscosity monitoring system. When the viscosity of the previous layer reaches 5000-10000 mPa·s, the next layer is cast to ensure the optimal chemical bonding effect between the layers.

[0044] The degradation rate of the biodegradable microcapsules in the surface layer matches that of the overall sponge, with a degradation half-life difference of no more than 15%, in order to achieve dynamic synergistic release of antibacterial agents.

[0045] The sponge has a compression set of no more than 3.5% after being compressed for 22 hours at 70℃, a limiting oxygen index of no less than 32%, a bio-based carbon content of no less than 40%, and takes 1-2 years to lose 90% of its weight under natural conditions.

[0046] The surface layer focuses on extreme softness, rapid moisture wicking, long-lasting antibacterial properties, and intrinsic safety. It uses non-isocyanate polyurethane as the matrix material, which is produced through a stepwise polymerization reaction of cyclic carbonate oligomers and polyamines. The synthesis process completely eliminates the use of isocyanates, thus removing the toxicity risks and residual monomer problems inherent in traditional polyurethane production and achieving green production. Furthermore, it optimizes the use of cyclic carbonate oligomers obtained from the reaction of bio-based epoxy resin with CO2, and bio-based polyamines such as lysine and chitosan degradation products, resulting in a bio-based carbon content of over 60% in the surface layer.

[0047] Biodegradable microcapsules encapsulating antibacterial agents are introduced into a non-isocyanate polyurethane matrix. The microcapsules are chitosan-polylactic acid copolymer microcapsules or sodium alginate-chitosan composite microcapsules, with a diameter of 0.2-0.8 μm and a wall thickness of 50-150 nm. The degradation rate of the microcapsules matches the degradation rate of the sponge as a whole. The antibacterial agent is slowly released as the sponge degrades, achieving simultaneous "antibacterial-degradation" and avoiding the problems of early depletion or late failure of traditional antibacterial agents.

[0048] By using a special opening agent and process control, the surface porosity is increased to ≥95%, and the openings are three-dimensional through-structure; this ensures excellent air permeability and moisture conduction of the surface layer. Combined with the hydrophilic groups (amine groups, hydroxyl groups) in the non-isocyanate polyurethane matrix, it can achieve rapid moisture removal, keep the surface dry, and fundamentally improve the thermal comfort of the sponge.

[0049] This invention integrates non-isocyanate synthesis technology, natural fiber reinforcement technology, bio-based flame retardant technology, molecular-level degradable reconstruction technology, dynamic antibacterial technology, and composite crosslinking agent technology through a synergistic design of "gradient structure functional layering + molecular-level degradable reconstruction + dynamic antibacterial-flame retardant synergy + composite crosslinking agent that balances softness and hardness." It systematically solves the seven core problems of traditional polyurethane foam: bacterial growth, toxic fumes from combustion, toxicity during production, waste pollution, stuffiness and lack of breathability, collapse and aging, and the contradiction between softness and support. It achieves a leap from "single performance optimization" to "system problem solving" and represents a paradigm shift in polyurethane foam modification technology.

[0050] Example 2

[0051] This embodiment adds the following to embodiment 1:

[0052] The surface layer contains biodegradable microcapsules, which are chitosan-polylactic acid copolymer microcapsules or sodium alginate-chitosan composite microcapsules, with a diameter of 0.2-0.8 μm and a wall thickness of 50-150 nm. The encapsulated antibacterial agent is selected from at least one of silver ions, copper ions, chitosan oligosaccharides, ε-polylysine, and plant extracts. The surface layer also contains chitosan oligosaccharides, with a mass fraction of 1-3%, a molecular weight of 3000-8000 Da, and a degree of deacetylation of not less than 90%.

[0053] The surface layer also contains chitosan oligosaccharide as an auxiliary antibacterial component. Chitosan oligosaccharide is a natural antibacterial substance with broad-spectrum antibacterial properties, good biocompatibility and biodegradability. Its antibacterial rate against Staphylococcus aureus and Escherichia coli can reach more than 99.9%. Chitosan oligosaccharide and microcapsule antibacterial agents form a dual protection mechanism of "immediate surface antibacterial + deep long-lasting antibacterial".

[0054] The biodegradable polyurethane of the substrate is formed by covalently linking a bio-based monomer containing ester bonds and glycosidic bonds with a biodegradable polymer; the bio-based monomer is selected from at least one of algae oil-based polyether polyol, castor oil-based polyether polyol, and soybean oil-based polyether polyol; the biodegradable polymer is selected from at least one of polylactic acid, polycaprolactone, polyhydroxyalkanoate, and polybutylene succinate; the molar ratio of the ester bonds to the glycosidic bonds is 1:0.2-5.

[0055] The sponge has a Shore hardness of 5-20D, an open porosity of not less than 92% with a three-dimensional through-cell structure, an air permeability of not less than 200 mm / s, a VOC content of not more than 8 g / L, an antibacterial rate of not less than 99.5% against Staphylococcus aureus and Escherichia coli, a high temperature resistance of not less than 120℃, a tear strength of not less than 16 N / cm, a tensile strength of not less than 180 kPa, an elongation at break of not less than 200%, and a surface resistivity of not more than 10 Ω·cm. 10 Ω·cm.

[0056] The supporting core layer adopts lignin chemical grafting technology, making flame retardant elements an integral part of the material's main chain. Combined with a polydopamine / phytic acid multilayer coating, it achieves a synergistic effect of inherent flame retardancy and efficient smoke suppression. The limiting oxygen index reaches over 32%, achieving the UL-94 V-0 flame retardant rating. The peak heat release rate is reduced by over 70%, and the smoke generation is reduced by nearly 60%, fundamentally solving the safety hazards of polyurethane foam being "flammable and releasing highly toxic gases when burning".

[0057] The original rigid-flexible composite crosslinking agent of this invention forms a microphase separation structure through molecular-level block copolymerization of rigid aromatic ring groups and flexible ether bonds. This ensures both overall flexibility and local rigid support, resulting in a compression set of ≤3.5%, which is far superior to the 5-15% of the prior art. It truly achieves a long-term balance between flexibility and support.

[0058] The surface layer uses biodegradable microcapsules encapsulating antibacterial agents. The degradation rate of the microcapsules is precisely matched with the overall degradation rate of the sponge. The antibacterial agent is slowly released as the material degrades, achieving simultaneous antibacterial and degradation. The antibacterial rate is ≥99.5%, and the antibacterial efficacy is synchronized with the material's lifespan, avoiding the problems of early depletion or late failure of traditional antibacterial agents. Combined with the immediate antibacterial effect of chitosan oligosaccharides, it forms a dual protection of immediate surface protection and long-lasting deep protection.

[0059] Both the base layer and the supporting core layer have ester and glycosidic bonds embedded in the polyurethane main chain, making degradation an inherent property of the material, rather than adding biodegradable fillers. The unique three-step synergistic degradation mechanism of enzymatic hydrolysis-oxidation ensures the thoroughness of degradation. Under natural conditions, it loses more than 90% of its weight in 1-2 years with no microplastic residue, which can solve the environmental pollution problem after polyurethane foam is discarded from the source.

[0060] Example 3

[0061] This embodiment adds the following to embodiment 2:

[0062] In the supporting core layer, the natural plant fiber is selected from at least one of loofah fiber, hemp fiber, bamboo fiber, and coconut shell fiber, with a mass fraction of 2-6%. Its surface is treated with hydroxyl activation or silane coupling agent modification. The hydroxyl activation treatment includes crushing the fiber to 100-300 mesh, soaking it in a 1-10% alkaline solution at 50-80℃ for 1-3 hours, washing and drying it for later use.

[0063] The lignin-based polyurethane is a product of polyphenol lignin grafted onto the polyurethane backbone via chemical bonds, with a lignin grafting rate of 5-15%. The lignin is selected from at least one of alkali lignin, lignin sulfonate, and enzymatically hydrolyzed lignin, and is modified by hydroxypropylation or epoxidation.

[0064] Furthermore, in the supporting core layer, the composite crosslinking agent is a composite crosslinking agent containing rigid aromatic ring groups and flexible ether bonds. The rigid aromatic ring groups account for 30-45% of the total mass of the composite crosslinking agent, and the flexible ether bonds account for 55-70%. The rigid aromatic ring groups are selected from at least one of biphenyl, bisphenol A, and naphthyl. The flexible ether bonds are selected from at least one of polyethylene glycol ether chains and polypropylene glycol ether chains. The crosslinking agent has a functionality of 2-4 and a number average molecular weight of 500-2000.

[0065] Furthermore, the supporting core layer also contains nano-reinforcing fillers, which are composed of at least two of nano-SiO2, nano-cellulose whiskers, and carbon fiber microfilaments, with a mass ratio of 1:0.5-2, a particle size of 30-100nm, and an aspect ratio of 5-20.

[0066] The surface of the supporting core layer is also coated with a flame-retardant coating through a layer-by-layer self-assembly technology. The flame-retardant coating is a two- or multi-layer structure formed by polydopamine and phytic acid, with 2-10 layers and a single layer thickness of 10-50 nm.

[0067] The supporting core layer also contains nano-reinforcing fillers (a blend of at least two of nano-SiO2, nano-cellulose whiskers, and carbon fiber microfilaments) to further enhance mechanical properties. The surface of the supporting core layer is also coated with a double- or multi-layer fire barrier coating (2-10 layers, each layer 10-50 nm thick) formed from polydopamine (PDA) and phytic acid (PA) using a layer-by-layer self-assembly technology. This coating forms a dense protective layer on the material surface, expands into char when exposed to fire, and increases the limiting oxygen index to over 32%, achieving a UL-94V-0 flame retardant rating. Simultaneously, it reduces peak heat release rate by over 70% and smoke generation by nearly 60%.

[0068] Example 4

[0069] This embodiment provides a method for preparing any of the modified soft polyurethane foams described above, comprising the following steps:

[0070] Step 1: Preparation of surface foaming material

[0071] Non-isocyanate polyurethane prepolymer, biodegradable microcapsules encapsulated with antibacterial agent, chitosan oligosaccharide, cell opener, foaming agent, foam stabilizer and catalyst are added to a mixing tank and stirred for 10-30 seconds at 20-30℃ and 1000-2000 r / min to obtain surface foam material.

[0072] Step 2: Preparation of the supporting core foam material

[0073] The lignin-based polyurethane prepolymer, surface-modified natural plant fibers, composite crosslinking agent, nano-reinforcing filler, foam stabilizer, cell opener, foaming agent and catalyst are added to a mixing tank and stirred for 15-40 seconds at 20-30℃ and 1500-2500 r / min to obtain the supporting core foam material.

[0074] Step 3: Prepare the base foaming material

[0075] A biodegradable polyurethane prepolymer containing ester bonds and glycosidic bonds, a foaming agent, a foam stabilizer, and a catalyst are added to a mixing vessel and stirred for 10-20 seconds at 20-30℃ and 1000-1500 r / min to obtain the base layer foaming material.

[0076] Step 4: Layered casting and integrated foaming

[0077] Preheat the mold to 30-50℃, and pour the base layer foam, the supporting core layer foam, and the surface layer foam into the mold in sequence. Control the time interval between pouring two adjacent layers to be 30-120 seconds to ensure that a chemical bonding reaction occurs at the interlayer interface. After pouring, let it stand at 25-40℃ for 10-30 minutes to foam, and then transfer it to 50-80℃ for 2-6 hours to cure. After demolding, the modified soft polyurethane sponge is obtained.

[0078] Step 5: Compress, shape, cut, and surface functionalize the cured sponge to obtain the final product.

[0079] Example 5

[0080] This embodiment is based on embodiment 4 with the following additions:

[0081] After step 2, the process further includes: immersing the foamed support core preform in polydopamine solution and phytic acid solution in sequence, forming a double or multi-layer fire barrier coating on its surface through layer-by-layer self-assembly technology, with each immersion time being 10-60 minutes and the immersion temperature being 20-40℃, repeating the operation 2-10 times after interlayer washing and drying, and then drying, before proceeding to step 4.

[0082] In step 5, the surface functionalization treatment includes at least one of silicone hydrophobic coating spraying, plasma treatment, and antibacterial coating spraying; the silicone hydrophobic coating thickness is 5-15μm, and it is dried at 50-80℃ for 10-20 minutes after spraying.

[0083] In step 1, the preparation method of the non-isocyanate polyurethane prepolymer includes: reacting a bio-based cyclic carbonate oligomer with a bio-based polyamine at 60-100°C for 1-3 hours. The bio-based cyclic carbonate oligomer is prepared by reacting a bio-based epoxy resin with carbon dioxide in the presence of a catalyst. The bio-based polyamine is selected from at least one of lysine, chitosan degradation products, and soybean protein hydrolysis products.

[0084] In step 2, the preparation method of the lignin-based polyurethane prepolymer includes: reacting hydroxypropylated lignin with polyether polyol and diisocyanate at 70-90℃ for 2-4 hours, controlling the NCO / OH molar ratio to be 1.5-2.5:1, to obtain -NCO-terminated lignin-based polyurethane prepolymer.

[0085] In step 4, the pouring time interval is controlled in real time by an online viscosity monitoring system. When the viscosity of the previous layer of mixture reaches 5000-10000 mPa·s, the next layer is poured to ensure the optimal chemical bonding effect between layers.

[0086] By precisely controlling the time interval of layered casting and online viscosity monitoring, chemical bonding reactions occur at the interlayer interfaces, forming covalent bonds such as urethane bonds, urea bonds, and ester bonds, achieving an interface-free integrated structure; this completely solves the problems of easy delamination and insufficient interfacial bonding strength in traditional multilayer composite materials, ensuring the long-term stability of the gradient structure.

[0087] The preparation method of this invention is based on the existing continuous production process of polyurethane foam, requiring no additional special equipment, and the process parameters are easy to control, making production costs controllable. The time window for layered casting is wide (30-120 seconds), adapting to the needs of industrial production of different scales; surface functionalization treatments (hydrophobic coatings, plasma treatment, etc.) can be flexibly adjusted to meet the customized needs of different application scenarios.

[0088] Experimental Example 1

[0089] Step 1: Preparation of Skin-Friendly Surface Foaming Material

[0090] 100 parts of non-isocyanate polyurethane (NIPU) prepolymer (cyclic carbonate equivalent 350 g / eq), 3 parts of chitosan-polylactic acid microcapsules encapsulated with silver ions (diameter 0.5 μm, wall thickness 100 nm, silver ion content 5%), 2 parts of chitosan oligosaccharide (molecular weight 5000 Da, degree of deacetylation 95%), 2 parts of cell opener (Evonik ORTEGOL® 501), 4 parts of deionized water (as foaming agent), 1 part of foam stabilizer (DC-193) and 0.8 parts of catalyst (triethylenediamine, TEDA) were added to a mixing vessel and stirred for 20 seconds at 25°C and 1500 r / min to obtain layer A mixture for later use.

[0091] The preparation method of the non-isocyanate polyurethane prepolymer is as follows: 100 parts of castor oil-based epoxy resin (epoxy equivalent 240 g / eq) and 2 parts of tetrabutylammonium bromide are added to a high-pressure reactor, CO2 is introduced to a pressure of 2.0 MPa, and the temperature is raised to 120°C for 6 hours to obtain castor oil-based cyclic carbonate (cyclic carbonate equivalent 320 g / eq). 100 parts of this cyclic carbonate and 35 parts of lysine (polyamine) are added to a reactor and reacted at 80°C for 2 hours to obtain a -NH2-terminated NIPU prepolymer.

[0092] Step 2: Preparation of the supporting core foam material

[0093] 100 parts of lignin-based polyurethane (LPUF) prepolymer (hydroxyl value 56 mg KOH / g, NCO content 8.5%), 4 parts of hydroxyl-activated loofah fiber (LF, 200 mesh), 3 parts of composite crosslinking agent (40% rigid aromatic ring groups, 60% flexible ether bonds, number average molecular weight 1200), 2 parts of nano-reinforcing filler (nano SiO2 to nano cellulose whiskers mass ratio 2:1, particle size 50-80 nm), 1 part of foam stabilizer (DC-3042), 1 part of cell opener (polyether type cell opener), 4 parts of deionized water and 1 part of catalyst (TEDA) were added to a mixing vessel and stirred for 25 seconds at 25℃ and 2000 r / min to obtain layer B mixture for later use.

[0094] The hydroxyl activation treatment of the loofah fiber includes: crushing the loofah fiber to 200 mesh, soaking it in a 5% NaOH solution at 60°C for 2 hours, washing it until neutral, and drying it at 80°C to constant weight.

[0095] The preparation method of the lignin-based polyurethane (LPUF) prepolymer is as follows: 100 parts of alkali lignin, 15 parts of propylene oxide, and 1 part of KOH are added to a reactor and reacted at 140℃ and 0.8MPa pressure for 3 hours to perform hydroxypropylation modification, obtaining hydroxypropylated lignin (hydroxyl value 280 mgKOH / g). 40 parts of hydroxypropylated lignin, 60 parts of polyether polyol (molecular weight 3000), and 45 parts of MDI are added to a reactor and reacted at 80℃ for 3 hours, controlling the NCO / OH molar ratio to be 2.0:1, to obtain the -NCO-terminated LPUF prepolymer.

[0096] The composite crosslinking agent is prepared by adding 50 parts of bisphenol A diglycidyl ether (epoxy equivalent 190 g / eq) and 60 parts of polyethylene glycol diamine (molecular weight 600) to a reaction vessel and reacting at 70°C for 3 hours to obtain the composite crosslinking agent. Analysis shows that rigid aromatic ring groups (bisphenol A structure) account for 38% of the total mass of the crosslinking agent, flexible ether bonds (polyethylene glycol chains) account for 62%, and the number average molecular weight is 1100.

[0097] Step 21: Prepare a double-layer fire barrier coating

[0098] The support core preform obtained in step 2 was sequentially immersed in a 3 mg / mL polydopamine solution (Tris-HCl buffer, pH 8.5) for 30 minutes, washed with deionized water, and dried under nitrogen. Then, it was immersed in a 5 mg / mL phytic acid solution for 30 minutes, washed with deionized water, and dried under nitrogen. The above operation was repeated 3 times, and finally, it was vacuum dried at 50°C for 3 hours to obtain a support core preform with a multi-layer fire barrier coating.

[0099] Step 3: Preparation of the base foaming material

[0100] Add 100 parts of biodegradable polyurethane prepolymer (NCO content 6.5%), 3 parts of deionized water, 1 part of foam stabilizer (DC-193) and 0.5 parts of catalyst (TEDA) to a mixing vessel, and stir for 15 seconds at 25°C and 1200 r / min to obtain the C layer mixture for later use.

[0101] The preparation method of the biodegradable polyurethane prepolymer is as follows: 60 parts of algae oil-based polyether polyol (hydroxyl value 50 mgKOH / g) and 40 parts of polylactic acid glycol (molecular weight 2000) are mixed, 35 parts of HDI and 0.3 parts of stannous octoate are added, and the mixture is reacted at 90°C for 4 hours. The NCO / OH molar ratio is controlled at 2.0:1 to obtain the -NCO-terminated biodegradable polyurethane prepolymer.

[0102] Step 4: Layered casting and integrated foaming

[0103] Preheat the mold to 40°C and coat the inner wall with a silicone release agent. Monitor the viscosity of each layer of the mixture in real time using an online viscosity monitoring system. When the viscosity of the previous layer reaches 8000 mPa·s, pour the next layer. The specific operation is as follows: first pour the C layer mixture, let it stand for 50 seconds (viscosity reaches 8200 mPa·s), then pour the B layer mixture, and then let it stand for another 55 seconds (viscosity reaches 8500 mPa·s), then pour the A layer mixture.

[0104] After casting, the foam was allowed to stand at 30°C for 15 minutes, then transferred to 70°C for 4 hours to mature. After demolding, a crude product of three-layer gradient structure modified soft polyurethane foam was obtained.

[0105] Step 5: Post-processing

[0106] The cured sponge is compressed and shaped (compression ratio 20%, held for 1.5 hours), and then precisely cut to the preset size. An organic silicone hydrophobic coating (10 μm thickness) is sprayed onto the surface, and the mixture is dried at 60℃ for 15 minutes to obtain the final product.

[0107] Experiment Example 2

[0108] It is basically the same as Experiment 1, except that:

[0109] In step 1, the biodegradable microcapsules were replaced with sodium alginate-chitosan composite microcapsules containing a mixture of Artemisia argyi extract and peppermint extract (mass ratio 2:1), with a microcapsule diameter of 0.6 μm.

[0110] In step 2, the natural plant fiber was replaced with bamboo fiber modified with silane coupling agent (KH-550). The modification conditions were: 3% KH-550 ethanol solution, treated at 60℃ for 1.5 hours.

[0111] In step 2, the composite crosslinking agent is replaced with a formulation containing 35% rigid aromatic ring groups and 65% flexible ether bonds (prepared by reacting biphenyl diglycidyl ether with polypropylene glycol diamine).

[0112] In step 21, the number of layers is adjusted to 5.

[0113] In step 3, the biodegradable polyurethane is replaced with a copolymer of castor oil-based polyether polyol and PCL diol.

[0114] Experimental Example 3

[0115] It is basically the same as Experiment 1, except that:

[0116] In step 1, the mass fraction of chitosan oligosaccharide was adjusted to 3%, and 1% ε-polylysine was added as an auxiliary antibacterial agent.

[0117] In step 2, the nano-reinforcing filler is replaced with a composite system of nano-SiO2 and carbon fiber microfilaments in a mass ratio of 1:1.

[0118] Step 2 does not include step 21 (without multi-layer fire barrier coating).

[0119] In step 4, the pouring time interval is controlled by timing (not viscosity monitoring): the interval between layer C and layer B is 60 seconds, and the interval between layer B and layer A is 60 seconds.

[0120] In step 5, plasma surface treatment (300W power, 2 minutes) is added, followed by spraying an antibacterial coating (chitosan solution, 1%).

[0121] Comparative Example 1

[0122] Ordinary polyurethane foam was prepared using conventional methods: 100 parts of polyether polyol (hydroxyl value 56 mg KOH / g), 4 parts of deionized water, 1 part of foam stabilizer, 1 part of catalyst (TEDA) and 50 parts of TDI were mixed, stirred at high speed and then poured into the foam. The foam was then foamed at 30°C for 15 minutes and cured at 70°C for 4 hours to obtain ordinary polyurethane foam.

[0123] The sponges prepared in Examples 1-3 and Comparative Example 1 were tested for performance according to the following standards, and the results are shown in Table 1:

[0124] Table 1

[0125] Performance indicators Test Standards Experimental Example 1 Experiment Example 2 Experimental Example 3 Comparative Example 1 Shore hardness (D) ASTM D2240 8 12 10 25 Compression set (%, 70℃, 22h) ASTM D3574 2.5 3.2 2.8 15.3 Open area ratio (%) Mercury porosimetry 96 94 95 75 Air permeability (mm / s) GB / T 5453 245 218 232 85 Limiting Oxygen Index (LOI, %) ASTM D2863 33.5 32.8 29.5 19 UL-94 flame retardant rating UL 94 V-0 V-0 V-1 none Tensile strength (kPa) ASTM D3574 198 185 205 95 Tear strength (N / cm) ASTM D3574 17.2 16.5 18.5 8.5 Elongation at break (%) ASTM D3574 225 210 240 180 Antibacterial rate (%, Staphylococcus aureus) GB / T 20944.3 99.9 99.7 99.8 0 Antibacterial durability (after 6 months, %) 99.5 98.9 96.5 0 Bio-based carbon content (%) ASTM D6866 48 45 42 0 Biodegradability (90-day weight loss in compost, %) ISO 14855 42 38 35 Less than 1 Complete biodegradability (microplastic residue) Microscopic observation none none none large amount VOC content (g / L) ISO 16000-6 6 8 7 35 Formaldehyde emission (mg / m³) GB 18583 0.003 0.004 0.003 0.65 Upper limit of high temperature resistance (°C) Thermogravimetric analysis 125 120 118 80 Surface resistivity (Ω·cm) ASTM D257 <![CDATA[8×10 9 ]]> <![CDATA[9.2×10 9 ]]> <![CDATA[7.8×10 9 ]]> <![CDATA[Greater than 10 12 > Interfacial bond strength (interlayer peel force, N / cm) 12.5 11.8 10.2 Physical overlap

[0126] As shown in Table 1, the modified soft polyurethane foams prepared in Examples 1-3 of this invention are significantly superior to the comparative examples in many performance indicators:

[0127] Balancing softness and support: The example has a Shore hardness of 8-12D (soft), but a compression set of only 2.5-3.2% (high resilience), which is far superior to Comparative Example 1 (15.3%), proving that the composite crosslinking agent design effectively solves the problem of "softness inevitably leads to collapse".

[0128] Breathability and comfort: The example has an opening rate of 94-96% and an air permeability of 218-245 mm / s, which is far superior to Comparative Example 1 (85 mm / s), proving that the three-dimensional through-hole structure design is effective.

[0129] Flame retardant safety: The limiting oxygen index of Examples 1-2 was 32.8-33.5%, reaching the V-0 level, which is far superior to Comparative Example 1 (19%), proving that lignin is an effective flame retardant.

[0130] Degradability: The compost in Examples 1-3 lost 35-42% of its weight after 90 days and had no microplastic residue, while Comparative Example 1 showed almost no degradation, demonstrating the thoroughness of the molecular-level degradable design.

[0131] Interfacial bonding strength: The interlayer peeling force of the example was 10.2-12.5 N / cm, while the comparative example was a physical composite (easily delaminated), demonstrating the advantages of the chemically bonded integrated structure.

[0132] Overall performance: The embodiment demonstrates excellent performance in terms of mechanical properties, environmental friendliness (VOC, bio-based content), and antistatic properties, achieving a balance between performance, environmental protection, and cost.

[0133] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0134] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A modified soft polyurethane foam, characterized in that, The sponge has a one-piece molded three-layer gradient structure, which includes, from bottom to top: The base layer is composed of a biodegradable polyurethane material containing ester bonds and glycosidic bonds in the main chain, with a micro-closed-pore structure and an open-pore ratio of 30-40%; the biodegradable polyurethane has a three-step synergistic degradation mechanism of enzymatic hydrolysis-oxidation. The supporting core layer, composited on the bottom layer of the substrate, is composed of a composite material of lignin-based polyurethane and natural plant fibers. The main chain of the lignin-based polyurethane is embedded with ester bonds and / or glycosidic bonds, and contains a composite crosslinking agent composed of rigid aromatic ring groups and flexible ether bonds. It has a gradient pore structure with the pore size gradually decreasing from the center to both sides, and the pore size gradient coefficient is 1.2-2.

0. The surface layer, composited on the supporting core layer, is composed of a composite material of non-isocyanate polyurethane and biodegradable microcapsules encapsulated with antibacterial agents. It has a highly open-pore structure with an open-pore ratio of not less than 95%. The non-isocyanate polyurethane is obtained by stepwise polymerization of cyclic carbonate oligomers and bio-based polyamines, and the raw materials do not contain isocyanates. The surface layer, the supporting core layer, and the substrate bottom layer are bonded together without an interface through interlayer chemical bonding; the interlayer chemical bonding includes at least one of urethane bonds, urea bonds, and ester bonds; The degradation rate of the biodegradable microcapsules in the surface layer matches that of the overall sponge, with a degradation half-life difference of no more than 15%, in order to achieve dynamic synergistic release of antibacterial agents. The sponge has a compression set of no more than 3.5% after being compressed for 22 hours at 70℃, a limiting oxygen index of no less than 32%, a bio-based carbon content of no less than 40%, and takes 1-2 years to lose 90% of its weight under natural conditions.

2. The modified soft polyurethane foam according to claim 1, characterized in that, The surface layer contains biodegradable microcapsules, which are chitosan-polylactic acid copolymer microcapsules or sodium alginate-chitosan composite microcapsules, with a diameter of 0.2-0.8 μm and a wall thickness of 50-150 nm. The encapsulated antibacterial agent is selected from at least one of silver ions, copper ions, chitosan oligosaccharides, ε-polylysine, and plant extracts. The surface layer also contains chitosan oligosaccharides, with a mass fraction of 1-3%, a molecular weight of 3000-8000 Da, and a degree of deacetylation of not less than 90%.

3. The modified soft polyurethane foam according to claim 1, characterized in that, In the supporting core layer, the natural plant fiber is selected from at least one of loofah fiber, hemp fiber, bamboo fiber, and coconut shell fiber, with a mass fraction of 2-6%. Its surface is treated with hydroxyl activation or silane coupling agent modification. The hydroxyl activation treatment includes crushing the fiber to 100-300 mesh, soaking it in a 1-10% alkaline solution at 50-80℃ for 1-3 hours, washing and drying it for later use. The lignin-based polyurethane is a product of polyphenol lignin grafted onto the polyurethane backbone via chemical bonds, with a lignin grafting rate of 5-15%. The lignin is selected from at least one of alkali lignin, lignin sulfonate, and enzymatically hydrolyzed lignin, and is modified by hydroxypropylation or epoxidation.

4. The modified soft polyurethane foam according to claim 3, characterized in that, In the supporting core layer, the composite crosslinking agent is a composite crosslinking agent containing rigid aromatic ring groups and flexible ether bonds. The rigid aromatic ring groups account for 30-45% of the total mass of the composite crosslinking agent, and the flexible ether bonds account for 55-70%. The rigid aromatic ring groups are selected from at least one of biphenyl, bisphenol A, and naphthyl. The flexible ether bonds are selected from at least one of polyethylene glycol ether chains and polypropylene glycol ether chains. The crosslinking agent has a functionality of 2-4 and a number average molecular weight of 500-2000.

5. The modified soft polyurethane foam according to claim 3, characterized in that, The supporting core layer also contains nano-reinforcing fillers, which are composed of at least two of nano-SiO2, nano-cellulose whiskers, and carbon fiber microfilaments, with a mass ratio of 1:0.5-2, a particle size of 30-100nm, and an aspect ratio of 5-20. The surface of the supporting core layer is also coated with a flame-retardant coating through a layer-by-layer self-assembly technology. The flame-retardant coating is a two- or multi-layer structure formed by polydopamine and phytic acid, with 2-10 layers and a single layer thickness of 10-50 nm.

6. The modified soft polyurethane foam according to claim 1, characterized in that, The biodegradable polyurethane of the substrate is formed by covalently linking a bio-based monomer containing ester bonds and glycosidic bonds with a biodegradable polymer; the bio-based monomer is selected from at least one of algae oil-based polyether polyol, castor oil-based polyether polyol, and soybean oil-based polyether polyol; the biodegradable polymer is selected from at least one of polylactic acid, polycaprolactone, polyhydroxyalkanoate, and polybutylene succinate; the molar ratio of the ester bonds to the glycosidic bonds is 1:0.2-5.

7. The modified soft polyurethane foam according to claim 1, characterized in that, The sponge has a Shore hardness of 5-20D, an open porosity of not less than 92% with a three-dimensional through-cell structure, an air permeability of not less than 200 mm / s, a VOC content of not more than 8 g / L, an antibacterial rate of not less than 99.5% against Staphylococcus aureus and Escherichia coli, a high temperature resistance of not less than 120℃, a tear strength of not less than 16 N / cm, a tensile strength of not less than 180 kPa, an elongation at break of not less than 200%, and a surface resistivity of not more than 10 Ω·cm. 10 Ω·cm.

8. A method for preparing a modified soft polyurethane foam according to any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Preparation of surface foaming material Non-isocyanate polyurethane prepolymer, biodegradable microcapsules encapsulated with antibacterial agent, chitosan oligosaccharide, cell opener, foaming agent, foam stabilizer and catalyst are added to a mixing tank and stirred for 10-30 seconds at 20-30℃ and 1000-2000 r / min to obtain surface foam material. Step 2: Preparation of the supporting core foam material The lignin-based polyurethane prepolymer, surface-modified natural plant fibers, composite crosslinking agent, nano-reinforcing filler, foam stabilizer, cell opener, foaming agent and catalyst are added to a mixing tank and stirred for 15-40 seconds at 20-30℃ and 1500-2500 r / min to obtain the supporting core foam material. Step 3: Prepare the base foaming material A biodegradable polyurethane prepolymer containing ester bonds and glycosidic bonds, a foaming agent, a foam stabilizer, and a catalyst are added to a mixing vessel and stirred for 10-20 seconds at 20-30℃ and 1000-1500 r / min to obtain the base layer foaming material. Step 4: Layered casting and integrated foaming Preheat the mold to 30-50℃, and pour the base layer foam, the supporting core layer foam, and the surface layer foam into the mold in sequence. Control the time interval between pouring two adjacent layers to be 30-120 seconds to ensure that a chemical bonding reaction occurs at the interlayer interface. After pouring, let it stand at 25-40℃ for 10-30 minutes to foam, and then transfer it to 50-80℃ for 2-6 hours to cure. After demolding, the modified soft polyurethane sponge is obtained. Step 5: Compress, shape, cut, and surface functionalize the cured sponge to obtain the final product.

9. The method for preparing the modified soft polyurethane foam according to claim 8, characterized in that, In step 5, the surface functionalization treatment includes at least one of silicone hydrophobic coating spraying, plasma treatment, and antibacterial coating spraying; the silicone hydrophobic coating thickness is 5-15μm, and it is dried at 50-80℃ for 10-20 minutes after spraying.

10. The method for preparing the modified soft polyurethane foam according to claim 8, characterized in that, In step 4, the pouring time interval is controlled in real time by an online viscosity monitoring system. When the viscosity of the previous layer of mixture reaches 5000-10000 mPa·s, the next layer is poured to ensure the optimal chemical bonding effect between layers.