Bio-based memory 4d printed foam with pressure monitoring and methods of making the same

Abstract

The present application relates to a kind of biological base memory 4D printing foam with pressure monitoring, including polyurethane foam matrix and the optical fiber grating sensing network embedded in the polyurethane foam matrix inside;The polyurethane foam matrix includes bottom support layer, intermediate optical fiber sensing layer and upper layer temperature sensing layer;The optical fiber grating sensing network is jointly composed of several optical fiber grating sensing components arranged in intermediate optical fiber sensing layer;The bottom support layer, intermediate optical fiber sensing layer and upper layer temperature sensing layer are sequentially formed by 3D printing technology, and the optical fiber grating sensing network is arranged on the bottom support layer after printing the bottom support layer, and is integrally buried by the way of low-foaming wire low-temperature printing intermediate optical fiber sensing layer.The biological base memory 4D printing foam with pressure monitoring in the present application overcomes the deficiency of traditional petroleum-based shape memory foam, realizes the integrated collaborative promotion of environmental protection, mechanical property, intelligent responsiveness and sensing function.

Description

Technical Field

[0001] This invention relates to the field of polyurethane foam, and particularly to a bio-based memory 4D printed foam with pressure monitoring, as well as a method for preparing the above-mentioned foam. Background Technology

[0002] Polyurethane foam is one of the most widely used polymer foam materials. With its advantages such as low density, ease of processing, good cushioning and energy absorption, and adjustable firmness, it occupies a core market share in bedding products such as mattresses and pillows. Among them, shape memory polyurethane foam (commonly known as memory foam), as a type of smart foam material, softens under the stimulation of body temperature, adaptively conforming to the curves of the head, neck, and body, dispersing localized pressure, and reducing the number of times one tosses and turns during sleep, making it a core material for high-end bedding.

[0003] With the popularization of the concept of healthy sleep, the smart bedding industry has put forward core requirements for materials, namely intelligence, green environmental protection, health and safety. However, existing technologies have obvious bottlenecks. Specifically, most shape memory foams used in existing bedding are petroleum-based raw materials, which are non-renewable and easily release harmful substances, posing safety risks and not in line with the trend of green development. A few bio-based polyurethane foams have low bio-based content, poor shape memory and fatigue resistance, and cannot achieve personalized customization. External pressure sensors in smart bedding need to be fixed by slotting, which damages the matrix structure, increases the release of harmful substances, and has insufficient monitoring accuracy and stability. Existing 4D printing foam technology has poor controllability of cell structure, only has a single shape memory function, and does not take into account the needs of bio-based environmental protection and in-situ pressure monitoring.

[0004] Therefore, developing a foam material for bedding that is high in bio-based content, environmentally friendly with no harmful releases, excellent shape memory properties, built-in pressure monitoring function, and customizable for 4D printing has become a key technical problem that the smart bedding industry urgently needs to solve. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a bio-based memory 4D printed foam with high bio-based content, environmental protection with no harmful release, excellent shape memory performance, built-in pressure monitoring function, customizable 4D printed with pressure monitoring, and a method for preparing the above foam.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is: a bio-based memory 4D printed foam with pressure monitoring, the innovation of which is: including a polyurethane foam matrix and a fiber optic grating sensing network embedded in the polyurethane foam matrix. The polyurethane foam matrix includes a bottom support layer, a middle optical fiber sensing layer, and an upper temperature-sensitive bonding layer. The fiber grating sensing network is composed of several fiber grating sensing components arranged in the middle fiber sensing layer. The fiber grating sensing components include Bragg grating sensing fibers and temperature-compensated reference gratings. The bottom support layer, the middle optical fiber sensing layer, and the upper temperature-sensing bonding layer are formed sequentially using 3D printing technology. The fiber optic grating sensing network is laid on the bottom support layer after printing and is integrated into the middle optical fiber sensing layer by low-temperature printing of low-foaming filament.

[0007] Furthermore, the polyurethane foam matrix has a closed-cell microbubble structure, a foaming ratio of 1.10 to 2.00 times, a pore size of 10 to 30 μm, a closed-cell rate of ≥90%, a thermal programming shape fixation rate of ≥95%, a shape recovery rate of ≥95%, and a shape memory triggering temperature of 30 to 50 ℃.

[0008] Furthermore, the fiber Bragg grating sensing component can be arranged in at least one of parallel, orthogonal, or array arrangements. During arrangement, the Bragg grating sensing fiber and the temperature compensation reference grating are fixed without stress and embedded in the intermediate fiber sensing layer with low residual stress. The Bragg grating sensing fiber includes a fiber core layer and a PU protective layer covering the fiber core layer. The fiber core layer is a polymer-coated high-temperature resistant fiber with a short-term temperature resistance of ≥200 ℃. The pressure monitoring range of the fiber Bragg grating sensing component is 0~2 MPa, the detection accuracy is ±0.01 MPa, and the response time is <200 ms.

[0009] An innovative method for preparing bio-based memory 4D printed foam with pressure monitoring includes the following steps: S1 Preparation of bio-based shape memory thermoplastic polyurethane: The dried bio-based polyester polyol is placed in a reaction vessel, and under the protection of an inert atmosphere, diisocyanate monomer is added and stirred at a constant temperature to prepare isocyanate-terminated polyurethane prepolymer. After cooling, bio-based 1,3-propanediol chain extender and polyurethane synthesis catalyst are added, mixed, and then poured into a mold for curing and solidification to obtain bio-based shape memory thermoplastic polyurethane material. S2 Foaming Modified Blending Granulation: The bio-based shape memory thermoplastic polyurethane material obtained in step S1 is crushed and then melt-blended. Chemical foaming agent, nucleating agent, and lubricant are added, and after mixing, the material is discharged and granulated to obtain foamed modified polyurethane granules. Simultaneously, low-foaming modified polyurethane granules for the intermediate optical fiber sensing layer are prepared. The amount of foaming agent added to the low-foaming modified polyurethane granules is lower than that of conventional foamed modified polyurethane granules. S3 3D printing filament preparation: The foamed modified polyurethane granules and the low-foamed modified polyurethane granules obtained in step S2 are extruded and molded respectively to prepare 3D printing filaments suitable for fused deposition modeling process. S4 Sensor Embedded Integrated 3D Printing: Using fused deposition modeling 3D printing equipment, a layered printing path and sensor embedding layer structure are designed. First, the bottom support layer is printed, and fiber optic grating sensor components are placed and fixed on the bottom support layer. The middle fiber optic sensing layer is printed using low-foaming modified polyurethane filament until the fiber optic grating sensor components are completely wrapped, ensuring that the ends of the fiber optic grating sensor components are not wrapped. Then, the upper temperature-sensing bonding layer is printed on the middle fiber optic sensing layer using foamed modified polyurethane filament. After cooling, a 4D printed foam preform is obtained. S5 Post-processing and performance calibration: The end of the fiber grating sensing component of the 4D printed foam preform obtained in step S4 is sealed, and temperature compensation calibration and pressure-response performance calibration are completed in sequence to finally obtain the required bio-based memory 4D printed foam with pressure monitoring.

[0010] Further, in step S1, the bio-based polyester polyol is poly(1,3-propylene succinate) prepared from corn oil derivatives, with a number-average molecular weight Mn of 3000~5000 g / mol; the bio-based polyester polyol is dried under vacuum, with a water content controlled to ≤0.05%; the diisocyanate monomer is diphenylmethane diisocyanate; the polyurethane synthesis catalyst is stannous octoate, and its amount is 0.01%~0.02% of the total mass of the bio-based shape memory thermoplastic polyurethane material; the [NCO] / [OH] molar ratio of the reaction system is (0.95~1.05):1, and the hard segment mass content of the prepared bio-based shape memory thermoplastic polyurethane material is 29%~35%.

[0011] Furthermore, in step S2, the chemical foaming agent is azodicarbonamide, whose decomposition temperature matches the extrusion or printing temperature. The foaming process occurs during the extrusion stage or the printing deposition stage to achieve controlled formation of the cell structure, with a gas emission rate ≥200 mL / g. The amount of the chemical foaming agent added to the foamed modified polyurethane granules is 0.8%~1.2% of the total mass of the bio-based shape memory thermoplastic polyurethane material, and the amount of the chemical foaming agent added to the low-foaming modified polyurethane granules is 0.4%-0.6% of the total mass of the bio-based shape memory thermoplastic polyurethane material. The nucleating agent is fumed nano silica, and the amount added is 0.2%~0.8% of the total mass of the bio-based shape memory thermoplastic polyurethane material. The lubricant is zinc stearate, and the amount added is 0.1%~0.3% of the total mass of the bio-based shape memory thermoplastic polyurethane material.

[0012] Furthermore, in step S3, the extrusion molding is performed using a single-screw extruder, and extrusion is carried out through a gradient temperature control process. After extrusion, cooling and shaping are performed to prepare 3D printing filaments with a diameter of 1.70~1.80 mm.

[0013] Furthermore, the single-screw extruder includes a first zone, a second zone, a third zone, and a die, arranged sequentially. The temperature of the first zone is 170~180 ℃, the temperature of the second zone is 180~190 ℃, the temperature of the third zone is 190~200 ℃, and the temperature of the die is 200~210 ℃.

[0014] Furthermore, in step S4, the basic process parameters of the fused deposition modeling (FDM) 3D printing equipment are adjusted according to the characteristics of the filament and structural requirements, including a nozzle diameter of 0.3~0.5 mm, a layer height of 0.10~0.25 mm, and a fill density of 80%~100%; the printing temperature of the main body area of ​​the FDM 3D printing equipment is 220~235 ℃, the printing temperature of the sensing area is 200~210 ℃, and the heated bed temperature is 35~45 ℃; the foam structure is a partitioned foaming structure, including a sensing area and a main body area. The sensing area is a middle fiber optic sensing layer, and the main body area is a bottom support layer and an upper temperature-sensitive bonding layer, wherein the foaming ratio of the sensing area is 20%~60% lower than that of the main body area.

[0015] Furthermore, in step S5, the specific steps of the temperature compensation calibration are as follows: The 4D-printed foam preform is placed in a constant temperature environment; within the target operating temperature range, the temperature is adjusted according to a set gradient; the center wavelength changes of the sensing fiber and the reference fiber are recorded; a temperature-wavelength drift fitting model is established to complete temperature compensation and eliminate the interference of temperature changes on the pressure monitoring accuracy. The specific steps of the pressure-response performance calibration are as follows: The 4D-printed foam preform is fixed in a mechanical testing device; within the target monitoring pressure range, static pressure is applied according to a set gradient; the center wavelength changes of the sensing fiber are recorded; a pressure-wavelength linear fitting curve is established; and the fitting degree R... 2 ≥0.98, enabling precise quantitative monitoring of pressure.

[0016] The beneficial effects of this invention are as follows: the bio-based memory 4D printing foam with pressure monitoring in this invention overcomes the shortcomings of traditional petroleum-based shape memory foam, and achieves an integrated and synergistic improvement in environmental protection, mechanical properties, intelligent responsiveness and sensing function. The foam preparation process is solvent-free and free of harmful by-products, and the finished product is formaldehyde-free and VOC-free, fully complying with the safety standards for skin contact products.

[0017] In this invention, the hard segment content and phase separation degree of the soft and hard segments of the material are precisely controlled through the directional design of the polyurethane molecular structure. The soft segment of the polyurethane is a flexible chain segment of bio-based polyester polyol, and the hard segment is a rigid chain segment generated by the reaction of diisocyanate and chain extender. This directional design is based on the number average molecular weight of bio-based polyester polyol as the basis for soft segment control. By precisely controlling the [NCO] / [OH] molar ratio of the reaction system and the feeding ratio of diisocyanate and chain extender, the directional optimization of hard segment content and phase separation degree is achieved. The prepared foam material has a shape fixation rate of ≥95% and a shape recovery rate of ≥95%. It still maintains excellent shape recovery performance after 1000 compression cycles and has an extremely low permanent deformation rate of indentation. This completely solves the problem of easy collapse and decreased support performance of traditional memory foam after long-term use. Moreover, the shape memory trigger temperature can be precisely controlled by the hard segment content to adapt to the human body temperature triggering requirements and achieve adaptive fit and support.

[0018] The preparation method in this invention adopts melt blending foaming modification combined with extrusion in-situ foaming process to achieve precise control of closed-cell microbubble structure, with uniform pores and high closed-cell rate, taking into account both lightweight and cushioning support performance. Relying on fused deposition modeling 3D printing technology, it can realize customized molding of any complex structure and differentiated partition support without secondary processing, perfectly adapting to personalized customization needs. By employing a low-temperature printing process with low-foaming filaments to embed the encapsulation layer, the in-situ integrated embedding of the fiber optic sensing component is achieved. This process avoids damage to the fiber optic cable caused by high-temperature printing, ensures excellent compatibility between the fiber optic cable and the substrate, and enables lossless deformation transmission. The built-in fiber optic grating sensing component features high monitoring accuracy, fast response speed, and strong anti-interference capability, enabling real-time and accurate monitoring of pressure distribution. Furthermore, it eliminates the need for grooving and gluing, does not damage the integrity of the substrate structure, and does not introduce additional harmful substances, thus balancing structural performance, environmental friendliness, and intelligent functionality.

[0019] The bio-based 4D printed foam prepared by this invention integrates green environmental protection, temperature-induced adaptive deformation, lightweight cushioning, and in-situ pressure monitoring. It has great application value in the field of high-quality mattresses, smart pillows, and other healthy sleep bedding. At the same time, it can be widely adapted to multiple scenarios such as medical care, smart wearables, and industrial cushioning, providing core material solutions for the intelligent and green upgrading of related industries. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the bio-based memory 4D printed foam with pressure monitoring according to the present invention.

[0021] Figure 2 This is a schematic diagram of the fiber Bragg grating sensing component in this invention.

[0022] Figure 3 This is a comparison diagram of the shape memory performance of the 4D printed foam in this invention and a comparative sample.

[0023] Figure 4 This is a pressure-wavelength linear fitting curve of the 4D printed foam in this invention. Detailed Implementation

[0024] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0025] like Figure 1 , Figure 2 The invention shown is a bio-based memory 4D printed foam with pressure monitoring, comprising a polyurethane foam matrix and a fiber optic grating sensing network embedded within the polyurethane foam matrix.

[0026] The polyurethane foam matrix comprises, from bottom to top, a bottom support layer 1, a middle optical fiber sensing layer 2, and an upper temperature-sensing bonding layer 3. The polyurethane foam matrix has a closed-cell microbubble structure with a foaming ratio of 1.10 to 2.00 times, a pore size of 10 to 30 μm, and a closed-cell rate of ≥90%. The polyurethane foam matrix has a thermal programming shape fixation rate of ≥95%, a shape recovery rate of ≥95%, and a shape memory triggering temperature of 30 to 50 ℃.

[0027] The fiber Bragg grating sensing network consists of several fiber Bragg grating sensing components 4 arranged in the middle fiber sensing layer 2. The fiber Bragg grating sensing component 4 adopts a fiber Bragg grating sensor and includes a Bragg grating sensing fiber and a temperature compensation reference grating.

[0028] The fiber Bragg grating sensing component 4 can be arranged in at least one of the following ways: parallel, orthogonal, or array arrangement. During the arrangement, the Bragg grating sensing fiber and the temperature compensation reference grating are fixed without stress and embedded in the intermediate fiber sensing layer in a low residual stress manner. The fiber includes a fiber core layer 41 and a PU protective layer 42 covering the fiber core layer 41. The fiber core layer 41 is a polymer-coated high-temperature resistant fiber with a short-term temperature resistance of ≥200 ℃. The pressure monitoring range of the fiber Bragg grating sensing component is 0~2MPa, the detection accuracy is ±0.01 MPa, and the response time is <200 ms.

[0029] The bottom support layer 1, the middle optical fiber sensing layer 2, and the upper temperature sensing bonding layer 3 are formed sequentially using 3D printing technology. The fiber optic grating sensing component 4 is printed on the bottom support layer 1 and then placed on the bottom support layer 1. It is also integrated into the middle optical fiber sensing layer 2 by low-temperature printing of the middle optical fiber sensing layer 2 using low-foaming filament.

[0030] The above-mentioned method for preparing bio-based memory 4D printed foam with pressure monitoring is achieved through the following steps: S1 Preparation of Bio-based Shape Memory Thermoplastic Polyurethane: Bio-based shape memory thermoplastic polyurethane was prepared using a prepolymer method. Vacuum-dried poly(1,3-propylene succinate) with a number-average molecular weight (Mn) of 3000–5000 g / mol was added to a reaction vessel. The drying conditions were 75–85 °C under vacuum for 1.5–2.5 h, with the moisture content controlled to ≤0.05%. Nitrogen gas was used for protection. Molten diphenylmethane diisocyanate was added at 80 °C and stirred for 60 min to obtain an isocyanate-terminated polyurethane prepolymer. The temperature was lowered to 65 °C, and bio-based 1,3-propanediol was added and stirred for 3–5 min. Stannous octoate catalyst was added and stirred for 1 min. The amount of stannous octoate was 0.01%–0.02% of the total mass of the bio-based shape memory thermoplastic polyurethane material. The mixture was poured into a preheated mold and cured at room temperature for 20–28 minutes. The reaction mixture was cured in a vacuum environment at 75-85℃ for 18-22 h to obtain a dense bio-based shape memory thermoplastic polyurethane block. The molar ratio of [NCO] / [OH] in the reaction system was (0.95-1.05):1. The hard segment content of the prepared bio-based shape memory thermoplastic polyurethane material was 29%-35%.

[0031] S2 Foaming Modified Blending and Granulation: The bio-based shape memory thermoplastic polyurethane material prepared in step S1 is crushed and added to a mixer. It is melt-blended for 2 minutes at a blending temperature of 160-170℃ and a speed of 40-60 rpm. Azodicarbonamide foaming agent, fumed silica nucleating agent, and zinc stearate lubricant are added, and the mixture is continued to be blended at the same temperature and speed for 5 minutes. The decomposition temperature of azodicarbonamide is matched to the extrusion or printing temperature, and the foaming process occurs during the extrusion or printing deposition stage to achieve controlled formation of the cell structure. The gas generation rate is ≥200 kJ / L. The amount of azodicarbonamide added to the foamed modified polyurethane granules is 0.8%~1.2% of the total mass of the bio-based shape memory thermoplastic polyurethane material, the amount of fumed nano silica nucleating agent added is 0.2%~0.8% of the total mass of the bio-based shape memory thermoplastic polyurethane material, and the amount of zinc stearate lubricant added is 0.1%~0.3% of the total mass of the bio-based shape memory thermoplastic polyurethane material. After discharge, the foamed modified polyurethane granules are obtained by hot pressing and crushing.

[0032] Simultaneously prepare low-foaming modified polyurethane granules for the sensing area, wherein the amount of azodicarbonamide added to the low-foaming modified polyurethane granules is 0.4%-0.6% of the total mass of the bio-based shape memory thermoplastic polyurethane material.

[0033] S3 3D printing filament preparation: The granules from step S2 are added to a single-screw extruder and an in-situ foamed 3D printing filament with a diameter of 1.70~1.80 mm is prepared through a temperature gradient extrusion process. The tolerance of the in-situ foamed 3D printing filament is ≤±0.05 mm. Simultaneously, a low-foaming special filament is prepared. The size requirements of the low-foaming special filament are consistent with those of the in-situ foamed 3D printing filament.

[0034] The single-screw extruder includes three zones and a die, arranged sequentially. The temperature of zone one is 170~180 ℃, the temperature of zone two is 180~190 ℃, the temperature of zone three is 190~200 ℃, and the temperature of the die is 200~210 ℃. The screw speed is 10~15 rpm, the diameter of the 3D printing filament is 1.70~1.80 mm, and the cooling and shaping method is air cooling.

[0035] S4 Sensor Embedded Integrated 3D Printing: It adopts a fused deposition modeling 3D printer with an optical fiber feed device. The layered printing path is designed in the slicing software. The middle optical fiber sensing layer 2 is set at 1 / 2 of the structure thickness. The basic parameters of the fused deposition modeling 3D printer are: nozzle diameter 0.4 mm, layer height 0.2 mm, infill density 100%, and heated bed temperature 40 ℃. The printing temperature and speed of the bottom support layer 1, the middle optical fiber sensing layer 2 and the upper temperature-sensing bonding layer 3 can be adjusted independently. Differentiated partitioned support structures can be customized according to the physiological curvature of the human body.

[0036] During printing, the bottom support layer 1 is first printed using in-situ foamed 3D printing filament. Then, fiber optic grating sensing components 4 are arranged on the bottom support layer 1 along orthogonal paths. Figure 1 As shown, the Bragg grating sensing fiber and the temperature compensation reference grating are positioned and fixed using high-temperature resistant tape. In this invention, in addition to arranging the fiber grating sensing component 4 in an orthogonal path manner, it can also be arranged in a parallel or array manner to control the bending radius of the Bragg grating sensing fiber and the temperature compensation reference grating to be ≥35 mm.

[0037] Then, a low-foaming special filament is used to print the middle optical fiber sensing layer 2 at low speed and low temperature until the Bragg grating sensing fiber and the temperature compensation reference grating are completely wrapped, and the end of the Bragg grating sensing fiber is not wrapped. Then, the original foaming 3D printing filament and printing parameters are restored to complete the printing of the upper temperature-sensing bonding layer 3. After cooling with the bed, a 4D printed foam preform is obtained.

[0038] S5 Post-processing and performance calibration: The ends of the Bragg grating sensing optical fibers of the 4D printed foam preform from step S4 are sealed with PU flexible potting compound, temperature compensation calibration is completed in a constant temperature oven, and pressure-wavelength linear fitting calibration is completed in an electronic universal testing machine, finally obtaining bio-based memory 4D printed foam with pressure monitoring.

[0039] The specific steps for temperature compensation calibration are as follows: place the 4D printed foam preform in a constant temperature environment, adjust the temperature according to the set gradient within the target operating temperature range, record the center wavelength changes of the sensing fiber and the reference fiber, establish a temperature-wavelength drift fitting model, complete temperature compensation, and eliminate the interference of temperature changes on the accuracy of pressure monitoring.

[0040] The specific steps for pressure-response performance calibration are as follows: Fix the 4D-printed foam preform in the mechanical testing equipment; apply static pressure according to a set gradient within the target monitoring pressure range; record the change in the center wavelength of the sensing fiber; establish a pressure-wavelength linear fitting curve; and determine the fitting degree R. 2 ≥0.98, enabling precise quantitative monitoring of pressure.

[0041] Temperature compensation calibration was completed with a gradient temperature increase in the range of 25–50 °C, and pressure-wavelength response calibration was completed with a gradient pressure increase in the range of 0–2 MPa. The goodness of fit R0 was [not specified]. 2 ≥0.98, ensuring the accuracy of pressure monitoring.

[0042] The bio-based memory 4D printed foam with pressure monitoring prepared by the method of this invention has a shape fixation rate of ≥95% and a shape recovery rate of ≥95% in compression mode; its pressure monitoring range is 0~2 MPa and the detection accuracy is ±0.01MPa; its shape memory trigger temperature is 30~50 ℃ and the response time is <200 ms, which can realize real-time and accurate monitoring of pressure distribution.

[0043] The raw materials used in this invention are sourced as follows: poly(1,3-propylene succinate) was provided by Alfa Chemistry, Inc., USA; diphenylmethane diisocyanate was purchased from Wanhua Chemical Group Co., Ltd.; bio-based 1,3-propanediol was purchased from DuPont Tate & Lyle BioProducts; stannous octoate catalyst was purchased from Sinopharm Chemical Reagent Co., Ltd.; azodicarbonamide was purchased from Jiangsu Suopu Chemical Co., Ltd.; fumed silica nanoparticles were purchased from Degussa (China) Investment Co., Ltd.; zinc stearate was purchased from Sinopharm Chemical Reagent Co., Ltd.; Bragg grating sensing optical fiber was purchased from Wuhan University of Technology Optoelectronics Co., Ltd.; and PU flexible potting compound was purchased from Shanghai Huitian New Materials Co., Ltd. All the above raw materials, except for poly(1,3-propylene succinate), were vacuum dried at 40 °C for 24 h before use.

[0044] The instruments used in this invention are as follows: a field emission scanning electron microscope (Regulus 8100, Hitachi High Technology Co., Ltd., Japan) for observing foam morphology; a differential scanning calorimeter (DSC, Q200, TA Instruments, USA) for analyzing thermal transformation behavior; a thermogravimetric analyzer (TGA, Pyris 1, PerkinElmer, USA) for evaluating thermal stability; a universal testing machine (LE3504, Lishi (Shanghai) Scientific Instruments Co., Ltd.) for pressure calibration; a Shore hardness tester (TY-810A, Shandong Tianyan Instruments Co., Ltd.) for testing mechanical properties; a dynamic mechanical analyzer (DMA, Q800, TA Instruments, USA) for determining shape memory properties and fatigue resistance; a fiber optic demodulator (MOI, si155, MicronOptics, USA) for acquiring fiber optic wavelength signals and pressure monitoring; a single-screw extruder (TY-7008, Jiangsu Tianyuan Experimental Equipment Co., Ltd.) for preparing 3D printing filaments; and an FDM 3D printer (Ender-7, The Shenzhen Creality 3D Technology Co., Ltd. modified the fiber optic feed device for 4D printing; the gas chromatograph (Nexis GC-2030, Shimadzu, Japan) was used for VOC emission detection.

[0045] The preparation method of the bio-based memory 4D printed foam with pressure monitoring of the present invention will be further explained below with reference to examples and comparative examples: Example 1: Preparation of a universal 4D printed foam suitable for smart pillows This embodiment provides a method for preparing bio-based memory 4D printed foam with pressure monitoring suitable for smart pillows, including the following steps: (1) Synthesis of bio-based shape memory polyurethane: 730 g of poly(1,3-propene succinate) was vacuum dried at 80 °C for 2 h, with a water content controlled to be <0.05% and Mn in 1,3-propene succinate = 4000 g / mol. It was added to a 2 L three-necked flask under nitrogen protection. 276 g of diphenylmethane diisocyanate, which had been melted at 80 °C for 4 h in advance, was added at 80 °C. The mixture was stirred at 250 rpm for 60 min to obtain isocyanate-terminated polyurethane prepolymer. The temperature was lowered to 65 °C, and 67.5 g of bio-based 1,3-propanediol was added and stirred for 4 min. 0.2 g of stannous octoate catalyst was added and stirred for 1 min. The mixture was quickly poured into a polytetrafluoroethylene mold preheated at 80 °C, aged at room temperature for 24 h, and then vacuum cured at 80 °C for 20 h to obtain a dense polyurethane block with a hard segment content of 32 wt%, a bio-based content of 72%, and a shape memory trigger temperature of 38 °C. ℃, adapted to human body temperature triggering.

[0046] (2) Foaming modified blending and granulation: The polyurethane block is crushed into 10 mm particles, added to a mixer, melt-mixed at 165 ℃ and 50 rpm for 2 min, 10 g of azodicarbonamide foaming agent, 3 g of fumed nano silica, 1 g of zinc stearate, and 1% of the total mass of the azodicarbonamide matrix are added. The mixture is then mixed at the same temperature and speed for 5 min. After discharge, it is hot-pressed into 1 mm sheets at 165 ℃, cooled and crushed into 2~3 mm particles.

[0047] Simultaneously prepare special granules for the intermediate optical fiber sensing layer 2 with an azodicarbonamide foaming agent dosage of 0.5%.

[0048] (3) 3D printing filament extrusion: The crushed granules are added to a single screw extruder with a temperature gradient of 175 ℃ in zone 1, 185 ℃ in zone 2, 195 ℃ in zone 3, and 205 ℃ at the die. The screw speed is 13.1 rpm, the traction speed is 3.4 m / min, and the material is cooled by air to obtain 1.75±0.05 mm printing filament. Low foaming special filament is prepared simultaneously.

[0049] (4) Integrated printing molding: Using an FDM 3D printer, a standard pillow structure of 60×40×10 cm was printed. The partitioned support structure was designed according to the physiological curvature of the cervical spine. The basic parameters were: nozzle 0.4 mm, layer height 0.2 mm, filling 100%, and heated bed temperature 40 ℃. First, a 4 cm bottom support layer was printed at a nozzle temperature of 230 ℃ and a speed of 12 mm / s. On the bottom support layer 1, according to the head and neck pressure distribution characteristics, three sets of orthogonal double Bragg grating sensing fibers and temperature compensation reference gratings were arranged, corresponding to the supine, left lateral, and right lateral areas of the pillow, respectively. The grating area was aligned with the core pressure bearing area, with a bending radius of 35 mm. The two ends were fixed with high-temperature resistant tape. The low-foaming special filament was switched, and a 2 cm middle fiber sensing layer 2 was printed at a nozzle temperature of 205 ℃ and a speed of 22 mm / s, completely wrapping the Bragg grating sensing fiber. The conventional filament and parameters were restored, and the upper temperature-sensitive bonding layer 3 was printed. The layer was cooled to room temperature with the bed to obtain a 4D printed foam preform.

[0050] (5) Post-processing and calibration: The junction of the Bragg grating sensing fiber and the pillow structure of the 4D printed foam prefabricated part was sealed with PU potting compound and cured at room temperature for 2 h; temperature compensation calibration was completed in the human body temperature range by gradient heating from 25 to 50 ℃; pressure-wavelength calibration was completed in the sleep pressure range from 0 to 2 MPa, and the fit R was determined. 2 =0.998, and finally the 4D printed foam for smart pillows is obtained, denoted as SMTPU-Foam-PILLOW-1.0.

[0051] Example 2: Preparation of 4D-printed foam suitable for infant head shaping pillows This embodiment optimizes the preparation parameters for the infant head shaping pillow scenario. The difference from Example 1 is as follows: In step (1), the hard segment content is adjusted to 29 wt%, poly(1,3-propylene succinate) 750 g, diphenylmethane diisocyanate 247.5 g, bio-based 1,3-propanediol 58.8 g, and the shape memory trigger temperature is 35 ℃ to match the infant's body temperature; In step (2), the amount of azodicarbonamide is adjusted to 0.8% to improve the softness of the foam; In step (4), the printed structure is an infant head shaping pillow, and the Bragg grating sensing fiber is arranged according to the head shape contact area matrix to monitor the pressure distribution of the infant's head and prevent flat head; The remaining steps are the same as in Example 1, and a special 4D printed foam for infant head shaping pillow is obtained, which is denoted as SMTPU-Foam-BABY.

[0052] Example 3: Preparation of 4D Printed Foam Suitable for Smart Mattresses This embodiment optimizes the preparation parameters for smart mattress scenarios. The difference from Example 1 is as follows: In step (1), the content of the hard segment is adjusted to 35 wt%, poly(1,3-propylene succinate) 700 g, diphenylmethane diisocyanate 301.5 g, and bio-based 1,3-propanediol 74.5 g to improve the support strength, and the shape memory trigger temperature is 40 ℃; In step (2), the amount of azodicarbonamide is adjusted to 1.2% to meet the lightweight requirements of the mattress; In step (4), the printed structure is a 60×40×10 cm mattress partition module, and the Bragg grating sensing fiber is arranged in a matrix according to the full area of ​​human sleep pressure distribution to realize real-time monitoring of the pressure distribution of the entire bed; The remaining steps are the same as in Example 1, and a special 4D printed foam for smart mattresses is prepared, denoted as SMTPU-Foam-MATTRESS.

[0053] Comparative Example 1: Commercially available ordinary petroleum-based memory foam pillow This comparative example uses a commercially available mainstream petroleum-based polyether memory foam pillow without pressure monitoring function, and is designated as CON-PILLOW as the control sample.

[0054] Comparative Example 2: Smart Pillow with External Sensor This comparative example uses a commercially available ordinary memory foam pillow with a built-in external thin-film pressure sensor array as a reference sample, denoted as CON-SMART-PILLOW.

[0055] Performance testing methods Foam structure characterization: Field emission scanning electron microscopy was used to observe the cell morphology and to statistically analyze the cell diameter and closed-cell ratio. The density of the sample was tested using a water displacement hydrometer, and the foaming ratio was calculated.

[0056] Shape memory performance test: The shape memory performance of the samples was evaluated by thermomechanical cycling tests using a dynamic mechanical analyzer. The samples were compressed by 50% at 38°C, and the deformation was maintained and cooled to room temperature for unloading. The shape retention rate (Rf) was measured. Subsequently, the samples were heated to 38°C without load, and the shape recovery rate (Rr) was recorded. After 1000 cycles, the remaining shape recovery rate was measured to evaluate the fatigue resistance.

[0057] Mechanical property testing: The Shore A hardness of the sample was tested using a Shore hardness tester.

[0058] Sensor performance test: A fiber optic grating demodulator was used in conjunction with a universal testing machine to test the pressure detection accuracy, response time, and long-term stability of the samples.

[0059] Environmental and safety testing: The formaldehyde content and volatile organic compound (VOC) release of the samples were tested using a gas chromatograph in accordance with GB 18401-2010 "National Basic Safety Technical Specifications for Textile Products".

[0060] The test results are shown in Table 1:

[0061] Table 1 Based on the data in Table 1 and the appendix Figure 3 Appendix Figure 4 It can be seen that the fully bio-based system constructed by using bio-based polyester polyols and bio-based diols has no formaldehyde or VOC release, is environmentally friendly and has no harmful burden, and fully complies with the safety standards for skin contact products.

[0062] With a foam closed-cell rate of ≥85% and uniform and controllable pore size, it combines lightweight and cushioning support performance. After 1000 compression cycles, the shape recovery rate still remains above 95%, and the permanent deformation rate of indentation is extremely low. It has excellent shape memory response and long-term support and fit, and can achieve a close and flexible fit to the curves of the human head, neck and body in smart bedding.

[0063] The in-situ sensor embedding and 4D printing integration technology enables the fiber optic grating sensor components to form a distributed monitoring network in the foam. The pressure monitoring range is 0~2 MPa, the detection accuracy is ±0.01 MPa, and the response time is <200 ms. It has excellent and stable pressure monitoring performance. The distributed fiber optic sensor network ensures the accuracy and real-time performance of pressure distribution monitoring. When used with a fiber optic grating demodulator, it can realize real-time acquisition and analysis of pressure data, avoiding the problem of external sensor slotting damaging the substrate structure.

[0064] Successfully integrated environmental protection, shape memory, cushioning support and pressure monitoring functions into bio-based 4D printed foam.

[0065] The bio-based memory foam with pressure monitoring developed in this invention provides an innovative material solution for the fields of smart mattresses and smart pillows. Its core application advantages and scenarios are as follows: 1. Personalized smart pillow Leveraging 4D printing technology, the pillow's height, curvature, and zoned firmness can be customized based on parameters such as the user's height and cervical curvature, providing precise support for the cervical spine and preventing strain. Built-in distributed fiber optic sensing components monitor cervical spine pressure and sleep posture in real time, enabling sleep alerts and support structure optimization. Combined with bio-based materials, it ensures health and safety.

[0066] 2. Infant head shaping pillow The bio-based foam contains no harmful volatile substances and meets the safety standards for infant and toddler products. It adapts to body temperature at 35°C, evenly distributing head pressure and preventing flat head syndrome. The built-in pressure sensor monitors head pressure and sleeping position in real time, sending head shape development data and sleep safety warnings to parents to ensure the safety of infants' sleep and normal skull development.

[0067] 3. Smart Mattress for Healthy Sleep 4D printing enables customized support zones in the mattress, adapting to the pressure requirements of different parts of the body and relieving fatigue in the lower back; the whole-bed matrix fiber optic sensor can monitor sleep pressure, heart rate and other data in real time, generate health reports and issue risk warnings, and link with the smart home system to create a full-scene healthy sleep ecosystem.

[0068] 4. Medical pressure-reducing and anti-bedsore smart mattress The foam has excellent cushioning and pressure relief properties as well as shape memory fit, which can evenly distribute the body pressure of bedridden patients; the built-in sensor component monitors the pressure distribution 24 hours a day, warns of high pressure risks and reminds patients to turn over, and can automatically adjust the zoned support pressure to reduce the incidence of pressure ulcers and reduce the burden of nursing care.

[0069] The foam has excellent cushioning and pressure relief properties as well as shape memory conformation, which can evenly distribute the body pressure of bedridden patients and reduce the risk of local high pressure. The built-in sensor components can monitor the pressure distribution of the entire bed in real time 24 hours a day, provide intelligent early warning for high pressure risk areas and remind caregivers to turn over. It can also automatically adjust the zoned support pressure in combination with 4D printed structure, which can significantly reduce the incidence of pressure ulcers and reduce the burden of care.

[0070] The in-situ integrated fiber optic sensing components have excellent compatibility with the polyurethane matrix, eliminating any foreign body sensation and not affecting user comfort. They also possess advantages such as electromagnetic interference resistance, electrical insulation, and corrosion resistance, maintaining stable monitoring performance even in humid bedding environments with long-term pressure. Furthermore, the all-bio-based raw material system and solvent-free preparation process ensure the product's health and environmental protection attributes from the source.

[0071] The bio-based shape memory foam with pressure monitoring prepared by this invention overcomes the shortcomings of traditional petroleum-based shape memory foam, and achieves an integrated and synergistic improvement in environmental protection, mechanical properties, intelligent responsiveness and sensing functions. It not only redefines the functional dimensions of smart bedding, but also provides a new generation of material solutions for the bedding industry to move towards intelligence, greening and health.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A bio-based memory 4D printed foam with pressure monitoring, characterized in that: It includes a polyurethane foam matrix and a fiber optic grating sensing network embedded within the polyurethane foam matrix. The polyurethane foam matrix includes a bottom support layer, a middle optical fiber sensing layer, and an upper temperature-sensitive bonding layer. The fiber grating sensing network is composed of several fiber grating sensing components arranged in the middle fiber sensing layer. The fiber grating sensing components include Bragg grating sensing fibers and temperature-compensated reference gratings. The bottom support layer, the middle optical fiber sensing layer, and the upper temperature-sensing bonding layer are formed sequentially using 3D printing technology. The fiber optic grating sensing network is laid on the bottom support layer after printing, and is integrated into the middle optical fiber sensing layer by low-temperature printing of the middle optical fiber sensing layer using low-foaming filament.

2. The bio-based memory 4D printed foam with pressure monitoring according to claim 1, characterized in that: The polyurethane foam matrix has a closed-cell microbubble structure with a foaming ratio of 1.10 to 2.00 times, a pore size of 10 to 30 μm, a closed-cell rate of ≥90%, a thermal programming shape fixation rate of ≥95%, a shape recovery rate of ≥95%, and a shape memory triggering temperature of 30 to 50 ℃.

3. The bio-based memory 4D printed foam with pressure monitoring according to claim 1, characterized in that: The fiber Bragg grating sensing component is arranged in at least one of the following ways: parallel, orthogonal, or array. During arrangement, the Bragg grating sensing fiber and the temperature compensation reference grating are fixed without stress and embedded in the intermediate fiber sensing layer with low residual stress. The Bragg grating sensing fiber includes a fiber core and a PU protective layer covering the fiber core. The fiber core is a polymer-coated high-temperature resistant fiber with a short-term temperature resistance of ≥200 ℃. The pressure monitoring range of the fiber grating sensing component is 0~2 MPa, the detection accuracy is ±0.01 MPa, and the response time is <200 ms.

4. A method for preparing bio-based memory 4D printed foam with pressure monitoring as described in claim 1, characterized in that: Includes the following steps: S1 Preparation of bio-based shape memory thermoplastic polyurethane: The dried bio-based polyester polyol is placed in a reaction vessel, and under the protection of an inert atmosphere, diisocyanate monomer is added and stirred at a constant temperature to prepare isocyanate-terminated polyurethane prepolymer. After cooling, bio-based 1,3-propanediol chain extender and polyurethane synthesis catalyst are added, mixed, and then poured into a mold for curing and solidification to obtain bio-based shape memory thermoplastic polyurethane material. S2 Foaming Modified Blending Granulation: The bio-based shape memory thermoplastic polyurethane material obtained in step S1 is crushed and then melt-blended. Chemical foaming agent, nucleating agent, and lubricant are added, and after mixing, the material is discharged and granulated to obtain foamed modified polyurethane granules. Simultaneously, low-foaming modified polyurethane granules for the intermediate optical fiber sensing layer are prepared. The amount of foaming agent added to the low-foaming modified polyurethane granules is lower than that of conventional foamed modified polyurethane granules. S3 3D printing filament preparation: The foamed modified polyurethane granules and the low-foamed modified polyurethane granules obtained in step S2 are extruded and molded respectively to prepare 3D printing filaments suitable for fused deposition modeling process. S4 Sensor Embedded Integrated 3D Printing: Using fused deposition modeling 3D printing equipment, a layered printing path and sensor embedding layer structure are designed. First, the bottom support layer is printed, and fiber optic grating sensor components are placed and fixed on the bottom support layer. The middle fiber optic sensing layer is printed using low-foaming modified polyurethane filament until the fiber optic grating sensor components are completely wrapped, ensuring that the ends of the fiber optic grating sensor components are not wrapped. Then, the upper temperature-sensing bonding layer is printed on the middle fiber optic sensing layer using foamed modified polyurethane filament. After cooling, a 4D printed foam preform is obtained. S5 Post-processing and performance calibration: The end of the fiber grating sensing component of the 4D printed foam preform obtained in step S4 is sealed, and temperature compensation calibration and pressure-response performance calibration are completed in sequence to finally obtain the required bio-based memory 4D printed foam with pressure monitoring.

5. The method for preparing bio-based memory 4D printed foam with pressure monitoring according to claim 4, characterized in that: In step S1, the bio-based polyester polyol is poly(1,3-propylene succinate) prepared from corn oil derivatives, with a number-average molecular weight Mn of 3000~5000 g / mol; the bio-based polyester polyol is dried under vacuum, with a water content controlled to ≤0.05%; the diisocyanate monomer is diphenylmethane diisocyanate; the polyurethane synthesis catalyst is stannous octoate, and its dosage is 0.01%~0.02% of the total mass of the bio-based shape memory thermoplastic polyurethane material; the [NCO] / [OH] molar ratio of the reaction system is (0.95~1.05):1, and the hard segment mass content of the prepared bio-based shape memory thermoplastic polyurethane material is 29%~35%.

6. The method for preparing bio-based memory 4D printing foam with pressure monitoring according to claim 4, characterized in that: In step S2, the chemical foaming agent is azodicarbonamide, whose decomposition temperature matches the extrusion or printing temperature. The foaming process occurs during the extrusion stage or the printing deposition stage to achieve controlled formation of the cell structure, with a gas emission rate ≥200 mL / g. The amount of the chemical foaming agent added to the foamed modified polyurethane granules is 0.8%~1.2% of the total mass of the bio-based shape memory thermoplastic polyurethane material, and the amount of the chemical foaming agent added to the low-foaming modified polyurethane granules is 0.4%-0.6% of the total mass of the bio-based shape memory thermoplastic polyurethane material. The nucleating agent is fumed nano silica, and the amount added is 0.2%~0.8% of the total mass of the bio-based shape memory thermoplastic polyurethane material. The lubricant is zinc stearate, and the amount added is 0.1%~0.3% of the total mass of the bio-based shape memory thermoplastic polyurethane material.

7. The method for preparing bio-based memory 4D printing foam with pressure monitoring according to claim 4, characterized in that: In step S3, the extrusion molding is carried out using a single screw extruder and a gradient temperature control process. After extrusion, cooling and shaping are performed to prepare 3D printing filaments with a diameter of 1.70~1.80 mm.

8. The method for preparing bio-based memory 4D printed foam with pressure monitoring according to claim 7, characterized in that: The single-screw extruder includes three zones and a die, arranged sequentially. The temperature of zone one is 170~180 ℃, the temperature of zone two is 180~190 ℃, the temperature of zone three is 190~200 ℃, and the temperature of the die is 200~210 ℃.

9. The method for preparing bio-based memory 4D printing foam with pressure monitoring according to claim 4, characterized in that: In step S4, the basic process parameters of the fused deposition modeling (FDM) 3D printing equipment are adjusted according to the characteristics of the filament and structural requirements, including a nozzle diameter of 0.3~0.5 mm, a layer height of 0.10~0.25 mm, and a fill density of 80%~100%. The printing temperature of the main body area of ​​the FDM 3D printing equipment is 220~235 ℃, the printing temperature of the sensing area is 200~210 ℃, and the heated bed temperature is 35~45 ℃. The foam structure is a partitioned foaming structure, including a sensing area and a main body area. The sensing area is a middle fiber optic sensing layer, and the main body area is a bottom support layer and an upper temperature-sensitive bonding layer. The foaming ratio of the sensing area is 20%~60% lower than that of the main body area.

10. The method for preparing bio-based memory 4D printing foam with pressure monitoring according to claim 4, characterized in that: In step S5, the specific steps of the temperature compensation calibration are as follows: The 4D-printed foam preform is placed in a constant temperature environment. Within the target operating temperature range, the temperature is adjusted according to a set gradient. The changes in the center wavelength of the sensing fiber and the reference fiber are recorded. A temperature-wavelength drift fitting model is established to complete temperature compensation and eliminate the interference of temperature changes on the pressure monitoring accuracy. The specific steps of the pressure-response performance calibration are as follows: The 4D-printed foam preform is fixed in a mechanical testing device. Within the target monitoring pressure range, static pressure is applied according to a set gradient. The changes in the center wavelength of the sensing fiber are recorded. A pressure-wavelength linear fitting curve is established, with a fitting degree R... 2 ≥0.98, enabling precise quantitative monitoring of pressure.

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