Solvent-recoverable linear polyurethane flexible foam and aqueous phase process for making same

Abstract

This invention provides a solvent-recoverable linear polyurethane flexible foam and its aqueous phase preparation method. Addressing the difficulties in foaming traditional linear polyurethane and the challenges in solvent recovery of bulk polyurethane, this invention utilizes the reaction of polyether diol and diisocyanate to generate a linear prepolymer, which is then mixed with a liquid medium containing a long-chain quaternary ammonium salt chain extender. Through intermolecular physical entanglement of the long alkyl side chains, a reversible physical cross-linking network is formed, allowing for rapid foaming and molding in an aqueous phase. The resulting linear polyurethane flexible foam exhibits high resilience, intrinsic antibacterial properties, and complete solubility in organic solvents for recycling and reprocessing. This method requires no supercritical CO2 or organic solvents, making it environmentally friendly. Furthermore, it can be in-situ composited with two-dimensional materials such as MXene, black phosphorus, and graphene oxide to prepare multifunctional foams, showing broad application prospects in flexible sensing, biomedicine, and other fields.

Description

Technical Field

[0001] This application relates to the field of polymer materials technology, and more specifically, to a solvent-recoverable linear polyurethane flexible foam and its aqueous phase preparation method. Background Technology

[0002] Polyurethane foam, with its excellent comprehensive properties, has broad application prospects in packaging, cushioning, sound insulation, and biomedicine. Traditional polyurethane foam is mainly divided into two categories: linear polyurethane and three-dimensional polyurethane. Linear polyurethane has a linear molecular chain structure. Although it can be recycled and reprocessed through solvent dissolution, its foaming and molding are extremely difficult. Due to the insufficient strength of the cell walls during foaming, linear molecular chains are prone to collapse, making it difficult to form a stable foam structure. Complex technologies such as supercritical carbon dioxide are usually required to assist foaming, resulting in cumbersome processes and high costs. Therefore, linear polyurethane is mainly used to prepare elastomer materials, not foam materials. Three-dimensional (crosslinked) polyurethane forms a chemical crosslinking network through the condensation polymerization of polyols and diisocyanates. It has a stable cell structure and can efficiently foam to construct porous foams. However, the crosslinking bonds are irreversible, making the material impossible to recover through simple solvent dissolution. It can usually only be degraded through physical crushing or alcoholysis catalysis, resulting in high recycling and reprocessing costs.

[0003] In the prior art, several improved solutions have been disclosed. For example, CN115873228B uses triols to prepare polyurethane foam, but its three-dimensional cross-linked structure makes the material difficult to dissolve and recycle; CN116333251B uses volatile organic solvents such as toluene in the preparation process, resulting in poor biocompatibility and high post-processing costs; CN120842833A has a foaming time of 25-35 minutes, leading to low production efficiency; and the polyurethane foam prepared by CN119708820B does not have antibacterial properties, limiting its application areas.

[0004] It is evident that existing polyurethane foam technology struggles to simultaneously achieve both rapid and stable foaming and solvent recyclability. On one hand, recyclable linear polyurethane is difficult to foam; on the other hand, easily foamable three-dimensional polyurethane cannot be recycled. This technological contradiction severely restricts the application and development of polyurethane foam in high-end fields such as green environmental protection and biomedicine.

[0005] Therefore, there is an urgent need in this field to develop a linear polyurethane flexible foam that can be rapidly and stably foamed and molded, and can be recycled and reprocessed through solvents, as well as its green and efficient preparation method. At the same time, it is expected that the method will have additional advantages such as rapid molding, no VOC emissions, and the ability to impart antibacterial properties to the material. Summary of the Invention

[0006] To address the aforementioned issues, this invention provides a rapid foaming technology for preparing highly resilient, solvent-recyclable linear polyurethane flexible foam directly in an aqueous phase, resolving the technical contradiction between rapid foaming and solvent recyclability in existing polyurethane foams. A linear polyurethane prepolymer is prepared using polyether diol and diisocyanate as raw materials, and then mixed with a liquid medium containing a long-chain quaternary ammonium salt chain extender. A reversible physical cross-linking network is constructed using the intermolecular physical entanglement of the long alkyl side chains, allowing for rapid foaming and molding through an aqueous phase reaction without the need for supercritical carbon dioxide or organic solvents. This method not only achieves stable and rapid preparation of linear polyurethane flexible foam, but also allows the resulting foam to be dissolved in organic solvents for recycling and reprocessing. Furthermore, it exhibits high resilience, antibacterial properties, and the ability to be composited with two-dimensional materials such as MXene, effectively solving the industry pain points of traditional recyclable linear polyurethane being difficult to foam and easy-to-foam polyurethane being difficult to recycle.

[0007] In a first aspect, the present invention provides a method for preparing a solvent-recoverable linear polyurethane flexible foam in aqueous phase, comprising the following steps: Polymerizing polyether diol with diisocyanate yields a polyurethane prepolymer; The polyurethane prepolymer is mixed with a solution containing a long-chain quaternary ammonium salt chain extender and a liquid medium, so that the long-chain quaternary ammonium salt chain extender is attached to the polyurethane main chain, while the liquid medium reacts with the isocyanate groups to foam, thus obtaining the linear polyurethane flexible foam.

[0008] This invention utilizes long-alkyl chain quaternary ammonium salt chain extenders to introduce long-alkyl side chains onto the linear polyurethane backbone. These side chains dynamically form a reversible physical cross-linking network during in-situ foaming through intermolecular van der Waals forces and chain segment entanglement. This network imparts sufficient mechanical strength to the cell walls in the early stages of foaming, effectively inhibiting bubble coalescence and collapse. Therefore, stable pore formation can be achieved without supercritical CO2 or chemical cross-linking, enabling rapid foaming in the aqueous phase. Simultaneously, this physical cross-linking exhibits solvent-responsive reversibility; in organic solvents, chain entanglement is disrupted, and the linear molecular chains redisperse, allowing the foam to be completely dissolved and recovered, maintaining good performance even after reprocessing.

[0009] Preferably, the weight ratio of the polyether diol to the diisocyanate is 1:(1~15); the weight ratio of the polyether diol to the long alkyl chain quaternary ammonium salt chain extender is 1:(0.2~0.8); and the weight ratio of the polyether diol to water is 1:(1~20).

[0010] Preferably, the long alkyl chain quaternary ammonium salt chain extender has a structure as shown in Formula I: I: ; In Equation I, n is an integer from 0 to 20.

[0011] Preferably, the polyether diol is selected from one or more of polypropylene glycol, polytetrahydrofuran glycol, polycaprolactone diol, polycarbonate diol, and polyethylene adipate diol, and is mixed in any proportion.

[0012] Preferably, the diisocyanate is selected from one or more of dicyclohexyl diisocyanate, isophorone diisocyanate, toluene diisocyanate, and diphenylmethane diisocyanate, and is mixed in any proportion.

[0013] Preferably, when mixing the polyether diol and the diisocyanate, a catalyst is also added; the weight ratio of the polyether diol to the catalyst is 1:(0.01~0.05).

[0014] Preferably, when mixing and reacting polyether diol and diisocyanate, the reaction temperature is 70~110℃, the stirring speed is 300~800 rpm, and the reaction time is 30~60 minutes.

[0015] Preferably, when mixing the polyurethane prepolymer with the quaternary ammonium salt solution, the stirring speed is 400~700 rpm and the stirring time is 1~3 minutes; after mixing, the mixture is allowed to foam and mature freely at 50~80℃ for 10~30 minutes.

[0016] Preferably, the liquid medium is selected from one or more of water, MXene aqueous dispersion, black phosphorus aqueous dispersion, graphene oxide aqueous dispersion or regenerated cellulose aqueous dispersion, and is mixed in any proportion.

[0017] Secondly, the present invention provides a solvent-recoverable linear polyurethane flexible foam.

[0018] In summary, the present invention has at least one of the following beneficial technical effects: 1. This invention introduces long-alkyl-chain quaternary ammonium salt chain extenders into linear polyurethane, utilizing the intermolecular physical entanglement structure of the long-alkyl side chains to build a reversible physical cross-linking network. On the one hand, this imparts sufficient strength to the cell walls, enabling rapid foaming in the aqueous phase (forming within 2 minutes) without the need for supercritical CO2 or chemical cross-linking. On the other hand, the resulting foam can be completely dissolved in organic solvents such as DMF and hexafluoroisopropanol, achieving efficient recycling and reprocessing. This solves the technical contradiction of traditional recyclable linear polyurethane being difficult to foam and easy-to-foam polyurethane being difficult to recover from solvents.

[0019] 2. This invention uses water as the foaming medium throughout the entire process, without using any organic solvents (such as toluene) or volatile organic compounds, resulting in no VOC emissions, low post-treatment costs, and excellent biocompatibility. Simultaneously, the quaternary ammonium salt structure endows the foam with intrinsic antibacterial properties, exhibiting significant killing effects against Staphylococcus aureus and other bacteria. It can be directly applied in biomedical fields such as antibacterial insoles and medical dressings without the need for additional antibacterial agents.

[0020] 3. The linear polyurethane flexible foam prepared by this invention exhibits high resilience (high single compression recovery rate), good fatigue resistance (small change in stress-strain curve after 25 cycles of compression), and a uniform and stable cell structure. Furthermore, this method can be used for in-situ composite with aqueous dispersions of two-dimensional materials such as MXene, black phosphorus, and graphene oxide to produce multifunctional composite foams with conductive, sensing, and flame-retardant properties in one step. These foams retain their sensing properties even after recycling and reprocessing, making them promising for applications in flexible sensors, wearable electronic devices, and other fields. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The diagram shows the solvent dissolution and recovery effect of the linear polyurethane flexible foam provided in the embodiments of this application; Figure 2 The stress-strain curve of a single compression cycle of a linear polyurethane flexible foam provided in an embodiment of this application is shown. Figure 3 The diagram shows the 25-cycle compressive stress-strain curve of the linear polyurethane flexible foam provided in the embodiments of this application; Figure 4 The diagram shows a comparison of the antibacterial properties of the linear polyurethane flexible foam provided in the embodiments of this application; wherein... Figure 4 A is a graph showing the quantitative antibacterial effect of linear polyurethane flexible foam on Staphylococcus aureus. Figure 4 B is a diagram showing the inhibition zone effect of linear polyurethane flexible foam on Staphylococcus aureus using the plate diffusion method. Figure 5 The real-time sensing response curves of the MXene composite linear polyurethane soft foam-based flexible sensor provided in the embodiments of this application for different joint movements of the human body are shown. Figure 6 The following is a sensor response curve of the recycled and reprocessed mesh material provided in an embodiment of this application; Figure 7 The following are scanning electron microscope (SEM) images of different composite linear polyurethane flexible foams provided in embodiments of this application; wherein... Figure 7 A is a scanning electron microscope image of the linear polyurethane flexible foam with MXene composite. Figure 7 B is a scanning electron microscope image of the linear polyurethane flexible foam composite with black phosphorus. Figure 7 C is a scanning electron microscope (SEM) image of the linear polyurethane flexible foam composited with graphene oxide. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention. Furthermore, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of the present invention.

[0024] Specific experimental steps or conditions are not specified in the embodiments; they can be performed according to the conventional experimental steps or conditions described in the prior art. Reagents and other instruments used, unless otherwise specified, are all commercially available conventional reagent products. Furthermore, the accompanying drawings are merely illustrative diagrams of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore, repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0025] Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of this specification.

[0026] In the description of this invention, it should be understood that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0027] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] To enable those skilled in the art to better understand this application, the following embodiments are provided to illustrate in detail a recyclable linear polyurethane flexible foam and its aqueous preparation method.

[0029] Example Example 1 Place 6 g of polypropylene glycol-2000 (PPG-2000) in a three-necked flask, add 4.72 g of dicyclohexyl diisocyanate (HMDI), and heat in a 75°C oil bath. After the oil bath temperature stabilizes, add 2 μL of dibutyltin dilaurate (DBTDL), start mechanical stirring at 300 rpm, and continue heating for about 1 hour until the viscosity of the system increases significantly, thus obtaining the polyurethane prepolymer.

[0030] Dissolve 0.60 g of dihydroxydodecyl quaternary ammonium salt (DHDMAC) in 2 mL of deionized water and stir until a clear, homogeneous solution is formed. Then, add this solution to the polyurethane prepolymer and add 10 mL of deionized water. Adjust the system temperature to 55°C and continue stirring for about 2 minutes to obtain linear polyurethane flexible foam.

[0031] Example 2 Place 6g of PPG-2000 in a three-necked flask, add 4.72g of HMDI, and heat in a 75°C oil bath. After the oil bath temperature stabilizes, add 2μL of DBTDL, turn on the mechanical stirrer at 300 rpm, and continue heating for about 1 hour until the viscosity of the system increases significantly, thus obtaining the polyurethane prepolymer.

[0032] Dissolve 0.60 g of DHDMAC in 2 mL of deionized water and stir until a clear, homogeneous solution is formed. Add this solution to the polyurethane prepolymer and then add 10 mL of MXene aqueous dispersion. Adjust the system temperature to 55°C and continue stirring for about 2 minutes to obtain the MXene-composite linear polyurethane flexible foam.

[0033] Example 3 Place 6 g of PPG-2000 in a three-necked flask, add 4.72 g of HMDI, and heat in a 75°C oil bath. After the oil bath temperature stabilizes, add 2 μL of DBTDL, turn on the mechanical stirrer at 300 rpm, and continue heating for about 1 hour until the viscosity of the system increases significantly, thus obtaining the polyurethane prepolymer.

[0034] Dissolve 0.60 g of DHDMAC in 2 mL of deionized water and stir until a clear, homogeneous solution is formed. Add this solution to the polyurethane prepolymer and then add 10 mL of black phosphorus aqueous dispersion. Adjust the system temperature to 55°C and continue stirring for about 2 minutes to obtain the black phosphorus composite linear polyurethane flexible foam.

[0035] Example 4 Place 6 g of PPG-2000 in a three-necked flask, add 4.72 g of HMDI, and heat in a 75°C oil bath. After the oil bath temperature stabilizes, add 2 μL of DBTDL, turn on the mechanical stirrer at 300 rpm, and continue heating for about 1 hour until the viscosity of the system increases significantly, thus obtaining the polyurethane prepolymer.

[0036] Dissolve 0.60 g of DHDMAC in 2 mL of deionized water and stir until a clear, homogeneous solution is formed. Add this solution to the polyurethane prepolymer and then add 10 mL of graphene oxide aqueous dispersion. Adjust the system temperature to 55°C and continue stirring for about 2 minutes to obtain the graphene oxide composite linear polyurethane flexible foam.

[0037] The performance of the foam material prepared by the present invention will be tested below with reference to the accompanying drawings. Unless otherwise specified, the samples used for each test item are pure linear polyurethane soft foam prepared in Example 1; the MXene composite foam prepared in Example 2 will be used for the sensing performance test.

[0038] (1) Solvent recovery performance test The linear polyurethane flexible foam prepared in Example 1 was dried in a vacuum oven at 60°C for 30 minutes. 1.0 g of the dried foam sample was accurately weighed and immersed in 20 mL of hexafluoroisopropanol solvent. The foam was allowed to swell and dissolve at room temperature for 30 minutes. Upon contact with the solvent, the foam swelled rapidly and gradually disintegrated over time, eventually forming a uniform and transparent polyurethane homogeneous solution with no obvious insoluble matter or gel particles remaining.

[0039] The homogeneous solution was transferred to a custom mold, and the solvent was slowly evaporated in a 60°C vacuum oven. After complete solvent evaporation, the mold was removed to obtain injection-molded recycled polyurethane products. This process can produce reprocessed materials with different morphologies and specifications (such as films, dumbbell-shaped splines, and mesh structures). The related recycling molding effects are as follows: Figure 1 As shown.

[0040] Depend on Figure 1 It is evident that the linear polyurethane flexible foam prepared by this invention exhibits excellent solubility in hexafluoroisopropanol, producing a clear and transparent solution with no cross-linked gel residue. This demonstrates that an irreversible chemical cross-linking network did not form within the foam, and its physical cross-linking structure can be completely dissociated in organic solvents. After injection molding, the recycled material can be reprocessed into complete products, indicating that the foam of this invention possesses excellent solvent recovery and reprocessing performance.

[0041] (2) Single compression rebound performance test Compression tests were performed on the linear polyurethane flexible foam prepared in Example 1 using a universal testing machine. The foam samples were cut into cubic specimens with dimensions of 20 mm × 20 mm × 20 mm. Under a loading rate of 0.5 mm / min, the specimens were compressed to 99% of their original height (i.e., compressive strain of 99%), and then unloaded back to their initial state at the same rate. The stress-strain curves for the entire loading-unloading cycle were recorded. The results are shown below. Figure 2 As shown.

[0042] The linear polyurethane flexible foam of this invention maintains its intact foam structure even under ultra-high compressive strain of 99%, without rupture or irreversible collapse. The small area of ​​the hysteresis loop formed between the loading and unloading curves indicates low internal friction and minimal energy loss during compression. After unloading, the foam rapidly recovers to its original size, with a resilience rate exceeding 95%, demonstrating excellent resilience performance. This characteristic is attributed to the dynamic physical cross-linking network formed by long alkyl side chains, which enables rapid recovery to its original shape through chain segment rearrangement after compression deformation.

[0043] (3) Repeated compression fatigue performance test To further evaluate the long-term service durability of the foam, cyclic compression fatigue testing was conducted on the linear polyurethane flexible foam prepared in Example 1. The foam specimen (20 mm × 20 mm × 20 mm) was fixed on a universal testing machine, and 25 consecutive load-unload cyclic compressions were performed at a deformation rate of 2 mm / min, with each cycle compressing to 50% strain. The stress-strain curves for each cycle were recorded, with particular attention paid to the changes in maximum stress and resilience with the number of cycles. The results are shown below. Figure 3 As shown.

[0044] After 25 cycles of compression, the linear polyurethane flexible foam exhibits good overlap in its stress-strain curves, retaining approximately 92% of the initial stress, with a resilience rate still above 90%, and no significant distortion in the curve shape. This indicates that the foam of this invention possesses excellent fatigue resistance, and its physical cross-linked network remains stable during multiple cyclic deformation processes, meeting the requirements for repeated use in practical applications.

[0045] (4) Antibacterial performance test The antibacterial properties of the foam of this invention were evaluated using the agar plate diffusion method. The linear polyurethane flexible foam (containing DHDMAC quaternary ammonium salt, denoted as PU-1) prepared in Example 1 was used as the experimental group, and polyurethane foam prepared according to the same process but without the addition of DHDMAC was used as the negative control group (denoted as PU-2). Staphylococcus aureus (… Staphylococcus aureusThe bacterial suspension (ATCC6538) was evenly spread on the surface of nutrient agar medium. Then, PU-1 and PU-2 foam samples were respectively attached to the surface of the medium and incubated in a constant temperature incubator at 37℃ for 24 hours. The formation of transparent inhibition zones around the foam samples was observed. The results are as follows: Figure 4 As shown.

[0046] A distinct transparent inhibition zone, approximately 15-20 mm in diameter, appeared around the PU-1 foam sample, while no inhibition zone formed around the PU-2 control group. These results indicate that the long-chain quaternary ammonium salt structure in the linear polyurethane flexible foam of this invention endows the material with intrinsic antibacterial activity, effectively inhibiting the growth and reproduction of Staphylococcus aureus. This antibacterial property stems from the electrostatic interaction between the quaternary ammonium salt cations and the bacterial cell membrane, disrupting the bacterial membrane structure and causing leakage of contents, thereby achieving a bactericidal effect. This characteristic makes the foam of this invention promising for applications in antibacterial insoles, medical dressings, and hygiene protection.

[0047] (5) Sensing performance test The MXene composite linear polyurethane flexible foam prepared in Example 2 was cut into cubic samples with dimensions of 10 mm × 10 mm × 10 mm. Copper foil electrodes were attached to the top and bottom sides of each sample and connected to an electrochemical workstation. A fixed test current of 10 μA was used to record the resistance change of the foam during deformation in real time. The assembled sensor was worn on the knee, elbow, and other joints of the human body. Cyclic compressive strain was induced in the foam through regular flexion and extension movements of the joints. The relative change in resistance (ΔR / R0, where R0 is the initial resistance at rest and ΔR is the real-time resistance change) was recorded over time. The results are shown below. Figure 5 As shown.

[0048] When the joint flexes and compresses the foam, the resistance value decreases significantly; when the joint extends and the foam recovers its deformation, the resistance value synchronously rises back to its initial value. The relative change in resistance exhibits a regular periodic fluctuation with joint movement, with a response time of less than 0.5 seconds, and the waveform is stable with a high signal-to-noise ratio. In 50 consecutive flexion-extension cycles, the sensing signal showed no significant attenuation, indicating that the MXene composite linear polyurethane flexible foam prepared in this invention possesses good strain sensitivity and cyclic stability. This sensing mechanism is mainly attributed to the increased conductive pathways and decreased contact resistance of the MXene conductive network during compression, as well as the recoverable deformation capability imparted to the foam by the physically cross-linked network.

[0049] (6) Sensing performance testing of recycled and reprocessed materials The MXene composite linear polyurethane flexible foam prepared in Example 2 was dried in a vacuum oven at 60°C for 30 minutes. 0.5 g of the dried foam was weighed and completely dissolved in 10 mL of hexafluoroisopropanol. The solution was stirred at room temperature until a homogeneous polyurethane / MXene composite solution was formed. This solution was injected into a custom-made mesh mold and dried in a vacuum oven at 90°C for 12 hours. After the solvent had completely evaporated, the mold was removed to obtain the injection-molded and reprocessed mesh composite material.

[0050] Following the same method as test (5), electrodes were connected to both ends of the mesh material, a fixed current of 10 μA was applied, and cyclic compressive strain was applied. The curve of the relative change in resistance over time was recorded, and the results are as follows: Figure 6 As shown.

[0051] After recycling and reprocessing, the resistance of the network material still changes sensitively with applied strain, and its sensing sensitivity (ΔR / R0) is comparable to that of the initial foam. The response speed does not decrease significantly, and the waveform is regular and repeatable. This indicates that after the dissolution-reforming process, the MXene conductive network in the composite foam prepared in this invention remains well dispersed in the polymer matrix, and the physical cross-linking structure of the long-chain quaternary ammonium salt is reconstructed, thus preserving its strain-sensitive conductivity. This characteristic provides technical support for the circular economy utilization of polyurethane foam, enabling multi-lifecycle use of the material without sacrificing functionality.

[0052] (7) Microscopic morphological characterization The microstructure of foam samples prepared in Examples 2 (MXene composite), 3 (black phosphorus composite), and 4 (graphene oxide composite) was observed using field emission scanning electron microscopy. Sample preparation method: Foam samples were cut into approximately 2 mm thick slices using a blade, adhered to conductive tape, vacuum dried to remove moisture, and then sputter-coated with gold for 30 seconds to enhance conductivity. The accelerating voltage was set to 5 kV. Microscopic images of the samples were taken at different magnifications. The results are shown below. Figure 7 As shown.

[0053] The linear polyurethane flexible foam composited with MXene exhibits a uniform black appearance, while the linear polyurethane flexible foam composited with black phosphorus is brown, and the linear polyurethane flexible foam composited with graphene oxide is gray. This indicates that the three two-dimensional materials were successfully composited into the polyurethane foam matrix and are uniformly distributed without obvious agglomeration. Scanning electron microscopy images clearly show that all three foams possess a three-dimensionally interconnected open-cell structure. The cells are approximately spherical or ellipsoidal in shape, with diameters ranging from 100 to 300 μm. The cell walls are smooth and continuous, and distinct open-cell windows are visible between adjacent cells. The formation of this uniform porous structure is attributed to the physical entanglement of the long alkyl side chains, which provides sufficient cell wall strength during foaming, effectively suppressing bubble coalescence and collapse, thus resulting in a porous foam elastomer with stable cell dimensions.

[0054] In summary, this invention addresses the technical contradictions of traditional linear polyurethane being difficult to foam and three-dimensional polyurethane being difficult to recycle. It innovatively proposes a method for rapidly preparing high-resilience, solvent-recoverable linear polyurethane flexible foam using an aqueous phase. The core of this method lies in: preparing a linear prepolymer using polyether diol and diisocyanate, and introducing a quaternary ammonium salt chain extender containing long alkyl chains during the foaming process. This utilizes the intermolecular physical entanglement structure of the long alkyl side chains to build a reversible physical cross-linking network, thereby achieving stable foaming and molding within 2 minutes without the use of supercritical CO2 or organic solvents. The resulting foam possesses excellent mechanical properties, intrinsic antibacterial activity, and complete organic solvent dissolution and recovery capabilities.

[0055] Furthermore, this method can be in situ combined with aqueous dispersions of two-dimensional materials such as MXene, black phosphorus, and graphene oxide to prepare multifunctional composite foams with excellent conductive sensing properties and retaining their functions after recycling in one step. It has broad application prospects in fields such as flexible sensors, biomedical devices, antibacterial insoles, and green and environmentally friendly packaging.

[0056] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0057] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present application.

[0058] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

[0059] The above provides a detailed description of the aqueous phase preparation method for solvent-recoverable linear polyurethane flexible foam provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing a solvent-recoverable linear polyurethane flexible foam in aqueous phase, characterized in that, Includes the following steps: Polymerizing polyether diol with diisocyanate yields a polyurethane prepolymer; The polyurethane prepolymer is mixed with a solution containing a long-chain quaternary ammonium salt chain extender and a liquid medium, so that the long-chain quaternary ammonium salt chain extender is attached to the polyurethane main chain, while the liquid medium reacts with the isocyanate groups to foam, thus obtaining the linear polyurethane flexible foam.

2. The aqueous phase preparation method for a solvent-recoverable linear polyurethane flexible foam according to claim 1, characterized in that, The weight ratio of the polyether diol to the diisocyanate is 1:(1~15); the weight ratio of the polyether diol to the long alkyl chain quaternary ammonium salt chain extender is 1:(0.2~0.8); and the weight ratio of the polyether diol to water is 1:(1~20).

3. The aqueous phase preparation method for a solvent-recoverable linear polyurethane flexible foam according to claim 1, characterized in that, The long alkyl chain quaternary ammonium salt chain extender has a structure as shown in Formula I: I： ； In Equation I, n is an integer from 11 to 13.

4. The aqueous phase preparation method for a solvent-recoverable linear polyurethane flexible foam according to claim 1, characterized in that, The polyether diol is selected from one or more of polypropylene glycol, polytetrahydrofuran diol, polycaprolactone diol, polycarbonate diol, and polyethylene adipate diol, and is composed of any proportion of these components.

5. The aqueous phase preparation method for a solvent-recoverable linear polyurethane flexible foam according to claim 1, characterized in that, The diisocyanate is selected from one or more of dicyclohexyl diisocyanate, isophorone diisocyanate, toluene diisocyanate, and diphenylmethane diisocyanate, and is mixed in any proportion.

6. The aqueous phase preparation method for a solvent-recoverable linear polyurethane flexible foam according to claim 1, characterized in that, When polyether diol and diisocyanate are mixed, a catalyst is also added; the weight ratio of the polyether diol to the catalyst is 1:(0.01~0.05).

7. The aqueous phase preparation method for a solvent-recoverable linear polyurethane flexible foam according to claim 1, characterized in that, When polyether diol and diisocyanate are mixed and reacted, the reaction temperature is 70~110℃, the stirring speed is 300~800rpm, and the reaction time is 30~60 minutes.

8. The aqueous phase preparation method for a solvent-recoverable linear polyurethane flexible foam according to claim 1, characterized in that, When mixing the polyurethane prepolymer with the quaternary ammonium salt solution, the stirring speed is 400~700 rpm and the stirring time is 1~3 minutes; after mixing, it is allowed to freely foam and mature at 50~80℃ for 10~30 minutes.

9. The aqueous phase preparation method for a solvent-recoverable linear polyurethane flexible foam according to claim 1, characterized in that, The liquid medium is selected from one or more of water, MXene aqueous dispersion, black phosphorus aqueous dispersion, graphene oxide aqueous dispersion, or regenerated cellulose aqueous dispersion, and is composed of any proportion of these components.

10. A solvent-recoverable linear polyurethane flexible foam prepared by the aqueous phase preparation method of solvent-recoverable linear polyurethane flexible foam as described in any one of claims 1 to 9.

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