A thermally insulating porous material with oriented channels and its preparation method

Abstract

This invention provides a thermally insulating porous material with oriented channels and its preparation method. The material comprises a polyvinyl alcohol composite foam matrix with oriented through-channels, heat-storing microcapsules dispersed in the matrix and distributed along the channels, and a heat-reflective layer covering the outer surface of the matrix. Its preparation mainly includes: uniformly dispersing the heat-storing microcapsules in a slurry containing polyvinyl alcohol and nanofibers; forming a matrix with parallel columnar channels through directional freezing and freeze-drying; subsequently, performing glutaraldehyde vapor crosslinking and curing; and finally coating the matrix surface with a heat-reflective layer. This invention constructs an oriented channel structure that effectively extends the heat conduction path and utilizes still air for insulation. By encapsulating phase change materials, it achieves heat storage and temperature buffering. The surface heat-reflective layer reflects radiant heat, giving the porous material comprehensive properties of thermal insulation, temperature regulation, and heat radiation reflection.

Description

Technical Field

[0001] This invention relates to the field of thermal insulation porous materials technology, specifically to a thermal insulation porous material with oriented channels and its preparation method. Background Technology

[0002] Thermal insulation materials are core materials in the field of energy conservation, widely used in building envelopes, cold chain transportation, and industrial equipment insulation. Their core requirement is to achieve heat transfer barrier through low thermal conductivity. Traditional thermal insulation materials are mostly disordered porous structures, resulting in messy heat conduction paths, limited insulation efficiency, and a lack of heat storage capacity, making them difficult to cope with fluctuations in ambient temperature, leading to poor energy-saving performance.

[0003] With the continuous improvement of energy-saving standards, single thermal insulation functions can no longer meet the needs of practical applications. Composite insulation materials with both thermal insulation and heat storage properties have become a research and development focus. Phase change materials have latent heat storage characteristics and can absorb or release heat through the phase change process to stabilize the ambient temperature. However, when used directly, they are prone to leakage and agglomeration, affecting the overall performance of the material. Hexagonal boron nitride has high thermal conductivity and insulation, but its dispersion uniformity in the matrix is ​​poor, making it difficult to fully exert its thermal conductivity regulation function. The porous structure of existing composite insulation materials is mostly disordered, and heat can easily be transferred through the pores via convection and radiation, further reducing the insulation effect. At the same time, the material surface lacks an effective heat reflection mechanism, and ambient radiant heat can easily penetrate the material, affecting the insulation stability.

[0004] To address the aforementioned technical challenges, it is essential to develop composite insulation materials that combine oriented channel structures, heat storage capabilities, and heat reflection performance. Through rational structural design and component control, synergistic effects of insulation, heat storage, and heat reflection can be achieved, while simultaneously resolving technical pain points such as phase change material leakage and uneven dispersion of hexagonal boron nitride, thus meeting the application requirements of high-end energy-saving scenarios. Summary of the Invention

[0005] The technical problem to be solved: This invention addresses the problems of low thermal insulation efficiency, easy leakage of phase change materials, uneven dispersion of thermally conductive fillers, insufficient radiative heat barrier, and poor structural stability of traditional thermal insulation materials by constructing oriented channels through directional freezing and freeze drying, microencapsulating phase change materials with hexagonal boron nitride and glutaraldehyde vapor crosslinking and curing the matrix, and coating and curing a heat reflective layer.

[0006] Technical solution: A thermal insulation porous material with oriented channels, the thermal insulation porous material comprising: a polyvinyl alcohol composite foam matrix with oriented through channels, heat storage microcapsules dispersed in the matrix and distributed along the through channels, and a heat reflective layer covering the outer surface of the matrix.

[0007] Preferably, the through-channel is a columnar structure, and its arrangement direction is parallel to the thickness direction of the polyvinyl alcohol composite foam base.

[0008] The above-mentioned method for preparing heat-storing microcapsules includes the following steps: S11. Polyethylene glycol is melted in a water bath, hexagonal boron nitride nanosheets are added, the water bath temperature is maintained, and high-speed shear mixing is performed to obtain a uniformly dispersed hexagonal boron nitride composite melt. S12. Prepare an aqueous gelatin solution as aqueous phase A, heat it, add the hexagonal boron nitride composite melt to aqueous phase A, and disperse it under high-speed shear to obtain a coarse dispersion of composite melt O / W type; S13. Prepare an aqueous solution of gum arabic as aqueous phase B, slowly add the coarse dispersion to aqueous phase B under continuous stirring, adjust the pH value of the mixture, stir the reaction, and obtain a microcapsule slurry with a primary capsule wall. S14. The microcapsule slurry was slowly cooled under stirring, and glutaraldehyde aqueous solution was added. Stirring was continued to crosslink and solidify the mixture. Then the temperature was raised to strengthen the shell. After the reaction was completed, the solid was collected by centrifugation, washed and vacuum dried to obtain heat-storing microcapsules.

[0009] The preparation method of the above-mentioned thermal insulation porous material with oriented channels includes the following steps: S1. The heat storage microcapsules are uniformly dispersed in a mixed slurry composed of polyvinyl alcohol, cellulose nanofibers and water, injected into a mold, one side of the mold is contacted with a cold source for directional freezing and solidification, and then freeze-dried to obtain a polyvinyl alcohol composite foam matrix with columnar porous channels parallel to the thickness direction of the material. S2. The polyvinyl alcohol composite foam matrix is ​​subjected to glutaraldehyde vapor treatment to obtain a cross-linked and cured matrix; S3. A reflective layer is coated on the outer surface of the cross-linked and cured matrix to obtain a thermally insulating porous material with oriented channels.

[0010] Preferably, in step S11, the water bath temperature is 70~80℃, the amount of hexagonal boron nitride nanosheets added is 5~20% of the mass of polyethylene glycol, the high-speed shearing speed is 10000~20000 rpm, and the time is 20~40 min.

[0011] Preferably, in step S12, the concentration of the gelatin aqueous solution is 2-5 wt%, the heating temperature is 50-60°C, the high-speed shear dispersion speed is 8000-15000 rpm, and the time is 5-15 min.

[0012] Preferably, in step S13, the concentration of the gum arabic aqueous solution is 2-5 wt%, the pH of the mixed system is adjusted to 3.5-4.5, and the stirring reaction time is 30-60 min.

[0013] Preferably, in step S14, the cooling process involves cooling the microcapsule slurry to below 10°C, the concentration of the glutaraldehyde aqueous solution is 25 wt%, and its addition amount is 0.5~4% of the total mass of the microcapsule slurry. The stirring, cross-linking, and curing time is 2~4 h, and the temperature for heating to strengthen the shell layer is 40°C for 30~60 min.

[0014] Preferably, in step S1, the mixed slurry contains 5-15 parts by mass of polyvinyl alcohol, 0.8-2 parts by mass of cellulose nanofibers, 75-90 parts by mass of water, and 0.5-3 parts by mass of heat-storing microcapsules. The directional freezing involves placing the side of the mold on a liquid nitrogen cold source for 1-5 hours.

[0015] Preferably, the conditions for the glutaraldehyde vapor crosslinking treatment in step S2 are as follows: the polyvinyl alcohol composite foam matrix is ​​placed in a sealed container and exposed to glutaraldehyde saturated vapor at 50°C for 4 to 12 hours.

[0016] Preferably, the process of coating the heat-reflective layer in step S3 is as follows: the heat-reflective coating is uniformly applied to the outer surface of the cross-linked and cured substrate, and dried and cured at 15~50°C for 4~24h to form a heat-reflective layer with a thickness of 100~200μm.

[0017] Preferably, the heat-reflective coating comprises, by weight 100 parts: 10-25 parts of rutile nano-titanium dioxide, 20-40 parts of self-crosslinking acrylic emulsion, and the balance being water.

[0018] Beneficial effects: The thermal insulation porous material with oriented channels of the present invention has the following advantages: This invention utilizes directional freezing and freeze-drying technologies to construct columnar oriented channels parallel to the material's thickness within a polyvinyl alcohol composite foam matrix. These oriented, interconnected channels effectively block the randomness of heat transfer, increasing thermal resistance. The stagnant air within the channels further reduces the overall thermal conductivity. Glutaraldehyde undergoes an acetalization reaction with the hydroxyl groups on the polyvinyl alcohol molecular chains, forming a stable three-dimensional network covalent bond structure within the matrix. This not only improves the matrix's mechanical strength and structural stability but also endows it with excellent water and heat resistance, preventing softening or even structural collapse of the foam in humid or damp environments. This ensures the long-term integrity of the oriented channel structure and the durability of its insulation effect.

[0019] The heat storage microcapsules prepared in this invention achieve synergistic optimization of thermal energy storage and management through a unique composite structure. Polyethylene glycol (PEG) serves as the phase change core material within the microcapsules, absorbing or releasing a large amount of latent heat of phase change through its solid-liquid phase change process. This effectively stores and compensates for heat intrusion or loss during ambient temperature fluctuations, actively adjusting the internal temperature changes of the material. Hexagonal boron nitride (h-BN), as a highly thermally conductive filler, accelerates heat transfer within the PEG, improving the response rate of the phase change process and the efficiency of thermal energy storage / release. Furthermore, h-BN is uniformly dispersed within the core material, synergistically working with the glutaraldehyde-crosslinked and reinforced gelatin-arabic shell to enhance the overall mechanical strength and thermal stability of the microcapsules, ensuring no leakage of the core material during subsequent use and guaranteeing the long-term reliability of the material.

[0020] This invention constructs a room-temperature curing heat-reflective layer on the outer surface of a substrate. The coating uses a self-crosslinking acrylic emulsion with a low glass transition temperature as a binder, and can be cured into a film under mild conditions, avoiding thermal damage to the heat-sensitive substrate and the internal phase-change microcapsules. The rutile nano-titanium dioxide in the coating, as a high-refractive-index filler, can efficiently reflect incident solar radiation back, reducing the temperature rise of the material due to radiative heat absorption. Detailed Implementation

[0021] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments: The polyethylene glycol used in the embodiments and comparative examples of this invention was purchased from Nanjing Xinhuayuan Chemical Co., Ltd., with a molecular weight of 4000; the cellulose nanofibers were purchased from Hubei Maidehao Biotechnology Co., Ltd., with a length range of 20-50 nm.

[0022] Example 1

[0023] S11. Melt 100g of polyethylene glycol in a 70℃ water bath, add 5g of hexagonal boron nitride nanosheets, maintain the water bath temperature, and mix at high speed of 10000rpm for 20min to obtain a uniformly dispersed hexagonal boron nitride composite melt. S12. Prepare 200g of a 2wt% gelatin aqueous solution as aqueous phase A, and heat it to 50℃. Add the hexagonal boron nitride composite melt from S11 to aqueous phase A, and disperse it at 8000rpm for 5min to obtain a coarse dispersion of composite melt O / W type. S13. Prepare 300g of 2wt% gum arabic aqueous solution as aqueous phase B. Slowly add the coarse dispersion to aqueous phase B under continuous stirring. Adjust the pH of the mixture to 3.5 and stir for 60min to obtain microcapsule slurry with primary capsule walls. S14. The microcapsule slurry was slowly cooled to 8°C under stirring, and 3.8g of 25wt% glutaraldehyde aqueous solution was added. Stirring was continued for cross-linking and curing for 2h. Then the temperature was raised to 40°C and held for 30min to strengthen the shell. After the reaction was completed, the solid was collected by centrifugation, washed and vacuum dried to obtain heat-storing microcapsules.

[0024] A method for preparing a thermally insulating porous material with oriented channels includes the following steps: S1. Weigh 5 parts polyvinyl alcohol, 0.8 parts cellulose nanofibers and 90 parts water, mix them evenly, and then evenly disperse 0.5 parts heat storage microcapsules in them to obtain a mixed slurry. Inject the slurry into a mold, contact one side of the mold with a liquid nitrogen cold source, and perform directional freezing for 1 hour to solidify and shape it. Then place the sample in a freeze dryer and dry it for 36 hours under the conditions of cold trap temperature below -50℃ and vacuum degree below 10 Pa to obtain a polyvinyl alcohol composite foam matrix with columnar porous channels parallel to the thickness direction of the material. S2. Place the polyvinyl alcohol composite foam matrix in a sealed container filled with glutaraldehyde solution, place the container in an environment of 50°C, and expose the matrix to saturated glutaraldehyde vapor for 12 hours to obtain a cross-linked and cured matrix. S3. Mix 10 parts of rutile nano-titanium dioxide, 30 parts of self-crosslinking acrylic emulsion and 60 parts of water, disperse at high speed to prepare a heat-reflective coating, uniformly coat it on the outer surface of the crosslinked and cured substrate, dry and cure at 40°C for 24 hours to form a heat-reflective layer with a thickness of 150 μm, and obtain the heat-insulating porous material with oriented channels.

[0025] Example 2

[0026] S11. Melt 100g of polyethylene glycol in an 80℃ water bath, add 20g of hexagonal boron nitride nanosheets, maintain the water bath temperature, and mix at high speed of 20000 rpm for 40min to obtain a uniformly dispersed hexagonal boron nitride composite melt. S12. Prepare 200g of a 5wt% gelatin aqueous solution as aqueous phase A, and heat it to 60℃. Add the hexagonal boron nitride composite melt from S11 to aqueous phase A, and disperse it at 15000 rpm for 15 min to obtain a coarse dispersion of composite melt O / W type. S13. Prepare 300g of a 5wt% gum arabic aqueous solution as aqueous phase B. Slowly add the coarse dispersion to aqueous phase B under continuous stirring. Adjust the pH of the mixture to 4.5 and stir for 30min to obtain a microcapsule slurry with a primary capsule wall. S14. The microcapsule slurry was slowly cooled to 2°C under stirring, and 12.5g of 25wt% glutaraldehyde aqueous solution was added. Stirring was continued for cross-linking and curing for 4h. Then the temperature was raised to 40°C and held for 60min to strengthen the shell. After the reaction was completed, the solid was collected by centrifugation, washed and vacuum dried to obtain heat-storing microcapsules.

[0027] A method for preparing a thermally insulating porous material with oriented channels includes the following steps: S1. Weigh 15 parts polyvinyl alcohol, 2 parts cellulose nanofibers and 75 parts water, mix them evenly, and then evenly disperse 3 parts heat storage microcapsules in them to obtain a mixed slurry. Inject the slurry into a mold, contact one side of the mold with a liquid nitrogen cold source, and perform directional freezing for 5 hours to solidify and shape it. Then place the sample in a freeze dryer and dry it for 36 hours under the conditions of cold trap temperature below -50℃ and vacuum degree below 10 Pa to obtain a polyvinyl alcohol composite foam matrix with columnar porous channels parallel to the thickness direction of the material. S2. Place the polyvinyl alcohol composite foam matrix in a sealed container filled with glutaraldehyde solution, place the container in an environment of 50°C, and expose the matrix to saturated glutaraldehyde vapor for 4 hours to obtain a cross-linked and cured matrix. S3. Mix 10 parts of rutile nano-titanium dioxide, 30 parts of self-crosslinking acrylic emulsion and 60 parts of water, disperse at high speed to prepare a heat-reflective coating, uniformly coat it on the outer surface of the crosslinked and cured substrate, dry and cure at 50°C for 6 hours to form a heat-reflective layer with a thickness of 100 μm, and obtain the heat-insulating porous material with oriented channels.

[0028] Example 3

[0029] S11. Melt 100g of polyethylene glycol in a 75℃ water bath, add 12g of hexagonal boron nitride nanosheets, maintain the water bath temperature, and shear mix at 15000 rpm for 30min to obtain a uniformly dispersed hexagonal boron nitride composite melt. S12. Prepare 200g of a 3.5wt% gelatin aqueous solution as aqueous phase A, and heat it to 55℃. Add the hexagonal boron nitride composite melt from S11 to aqueous phase A, and disperse it at 12000 rpm for 10 min to obtain a coarse dispersion of composite melt O / W type. S13. Prepare 300g of a 3.5wt% gum arabic aqueous solution as aqueous phase B. Slowly add the coarse dispersion to aqueous phase B under continuous stirring. Adjust the pH of the mixture to 4.0 and stir for 45min to obtain a microcapsule slurry with a primary capsule wall. S14. The microcapsule slurry was slowly cooled to 5°C under stirring, and 6.25g of 25wt% glutaraldehyde aqueous solution was added. Stirring was continued for 3h to crosslink and solidify. Then the temperature was raised to 40°C and held for 45min to strengthen the shell. After the reaction was completed, the solid was collected by centrifugation, washed and vacuum dried to obtain heat-storing microcapsules.

[0030] A method for preparing a thermally insulating porous material with oriented channels includes the following steps: S1. Weigh 10 parts polyvinyl alcohol, 1.5 parts cellulose nanofibers and 82 parts water, mix them evenly, and then evenly disperse 1.5 parts heat storage microcapsules in the mixture to obtain a mixed slurry. Inject the slurry into a mold, contact one side of the mold with a liquid nitrogen cold source, and perform directional freezing for 3 hours to solidify and shape the sample. Then place the sample in a freeze dryer and dry it for 36 hours under the conditions of cold trap temperature below -50℃ and vacuum degree below 10 Pa to obtain a polyvinyl alcohol composite foam matrix with columnar porous channels parallel to the thickness direction of the material. S2. Place the polyvinyl alcohol composite foam matrix in a sealed container filled with glutaraldehyde solution, place the container in an environment of 50°C, and expose the matrix to saturated glutaraldehyde vapor for 8 hours to obtain a cross-linked and cured matrix. S3. Mix 25 parts of rutile nano-titanium dioxide, 30 parts of self-crosslinking acrylic emulsion and 45 parts of water, disperse at high speed to prepare a heat-reflective coating, uniformly coat it on the outer surface of the crosslinked and cured substrate, dry and cure at 40°C for 18 hours to form a heat-reflective layer with a thickness of 150 μm, and obtain the heat-insulating porous material with oriented channels.

[0031] Example 4

[0032] The method for preparing heat-storing microcapsules includes the following steps: S11. Melt 100g of polyethylene glycol in a 78℃ water bath, add 15g of hexagonal boron nitride nanosheets, maintain the water bath temperature, and shear mix at 18000 rpm for 35min to obtain a uniformly dispersed hexagonal boron nitride composite melt. S12. Prepare 200g of a 4.5wt% gelatin aqueous solution as aqueous phase A, and heat it to 58℃. Add the hexagonal boron nitride composite melt from S11 to aqueous phase A, and disperse it at 14000 rpm for 12 min to obtain a coarse dispersion of composite melt O / W type. S13. Prepare 300g of a 4.5wt% gum arabic aqueous solution as aqueous phase B. Slowly add the coarse dispersion to aqueous phase B under continuous stirring. Adjust the pH of the mixture to 4.2 and stir for 50min to obtain a microcapsule slurry with a primary capsule wall. S14. The microcapsule slurry was slowly cooled to 6°C under stirring, and 9.5g of 25wt% glutaraldehyde aqueous solution was added. Stirring was continued for 3h to crosslink and solidify. Then the temperature was raised to 40°C and held for 50min to strengthen the shell. After the reaction was completed, the solid was collected by centrifugation, washed and vacuum dried to obtain heat-storing microcapsules.

[0033] A method for preparing a thermally insulating porous material with oriented channels includes the following steps: S1. Weigh 12 parts of polyvinyl alcohol, 1.8 parts of cellulose nanofibers and 83 parts of water, mix them evenly, and then evenly disperse 2.2 parts of heat storage microcapsules in the mixture to obtain a mixed slurry. Inject the slurry into a mold, contact one side of the mold with a liquid nitrogen cold source, and perform directional freezing for 4 hours to solidify and shape the sample. Then place the sample in a freeze dryer and dry it for 36 hours under the conditions of cold trap temperature below -50℃ and vacuum degree below 10 Pa to obtain a polyvinyl alcohol composite foam matrix with columnar porous channels parallel to the thickness direction of the material. S2. Place the polyvinyl alcohol composite foam matrix in a sealed container filled with glutaraldehyde solution, place the container in an environment of 50°C, and expose the matrix to saturated glutaraldehyde vapor for 7 hours to obtain a cross-linked and cured matrix. S3. Mix 25 parts of rutile nano-titanium dioxide, 30 parts of self-crosslinking acrylic emulsion and 45 parts of water, disperse at high speed to prepare a heat-reflective coating, uniformly coat it on the outer surface of the crosslinked and cured substrate, dry and cure at 40°C for 18 hours to form a heat-reflective layer with a thickness of 150 μm, and obtain the heat-insulating porous material with oriented channels.

[0034] Example 5

[0035] S11. Melt 100g of polyethylene glycol in a 72℃ water bath, add 8g of hexagonal boron nitride nanosheets, maintain the water bath temperature, and mix at high speed of 12000 rpm for 25min to obtain a uniformly dispersed hexagonal boron nitride composite melt. S12. Prepare 200g of a 2.5wt% gelatin aqueous solution as aqueous phase A, and heat it to 55℃. Add the hexagonal boron nitride composite melt from S11 to aqueous phase A, and disperse it at 10000 rpm for 8 min to obtain a coarse dispersion of the composite melt O / W type. S13. Prepare 300g of a 2.5wt% gum arabic aqueous solution as aqueous phase B. Slowly add the coarse dispersion to aqueous phase B under continuous stirring. Adjust the pH of the mixture to 3.8 and stir for 55 min to obtain a microcapsule slurry with a primary capsule wall. S14. The microcapsule slurry was slowly cooled to 7°C under stirring, and 5g of 25wt% glutaraldehyde aqueous solution was added. The mixture was stirred and crosslinked for 2.5h. Then the temperature was raised to 40°C and held for 40min to strengthen the shell. After the reaction was completed, the solid was collected by centrifugation, washed and vacuum dried to obtain heat-storing microcapsules.

[0036] A method for preparing a thermally insulating porous material with oriented channels includes the following steps: S1. Weigh 8 parts polyvinyl alcohol, 1.2 parts cellulose nanofibers and 86 parts water, mix them evenly, and then evenly disperse 1 part heat storage microcapsules in them to obtain a mixed slurry. Inject the slurry into a mold, contact one side of the mold with a liquid nitrogen cold source, and perform directional freezing for 2 hours to solidify and shape it. Then place the sample in a freeze dryer and dry it for 36 hours under the conditions of cold trap temperature below -50℃ and vacuum degree below 10 Pa to obtain a polyvinyl alcohol composite foam matrix with columnar porous channels parallel to the thickness direction of the material. S2. Place the polyvinyl alcohol composite foam matrix in a sealed container filled with glutaraldehyde solution, place the container in an environment of 50°C, and expose the matrix to saturated glutaraldehyde vapor for 8 hours to obtain a cross-linked and cured matrix. S3. Mix 25 parts of rutile nano-titanium dioxide, 30 parts of self-crosslinking acrylic emulsion and 45 parts of water, disperse at high speed to prepare a heat-reflective coating, uniformly coat it on the outer surface of the crosslinked and cured substrate, dry and cure at 50°C for 12 hours to form a heat-reflective layer with a thickness of 120 μm, and obtain the heat-insulating porous material with oriented channels.

[0037] Comparative Example 1 The difference between Comparative Example 1 and Example 4 is that Comparative Example 1 does not undergo directional freezing, but rather random and disordered freezing; The method for preparing heat-storing microcapsules includes the following steps: S11. Melt 100g of polyethylene glycol in a 78℃ water bath, add 15g of hexagonal boron nitride nanosheets, maintain the water bath temperature, and shear mix at 18000 rpm for 35min to obtain a uniformly dispersed hexagonal boron nitride composite melt. S12. Prepare 200g of a 4.5wt% gelatin aqueous solution as aqueous phase A, and heat it to 58℃. Add the hexagonal boron nitride composite melt from S11 to aqueous phase A, and disperse it at 14000 rpm for 12 min to obtain a coarse dispersion of composite melt O / W type. S13. Prepare 300g of a 4.5wt% gum arabic aqueous solution as aqueous phase B. Slowly add the coarse dispersion to aqueous phase B under continuous stirring. Adjust the pH of the mixture to 4.2 and stir for 50min to obtain a microcapsule slurry with a primary capsule wall. S14. The microcapsule slurry was slowly cooled to 6°C under stirring, and 9.5g of 25wt% glutaraldehyde aqueous solution was added. Stirring was continued for 3h to crosslink and solidify. Then the temperature was raised to 40°C and held for 50min to strengthen the shell. After the reaction was completed, the solid was collected by centrifugation, washed and vacuum dried to obtain heat-storing microcapsules.

[0038] A method for preparing a thermally insulating porous material with oriented channels includes the following steps: S1. Weigh 12 parts of polyvinyl alcohol, 1.8 parts of cellulose nanofibers and 83 parts of water, mix them evenly, and then evenly disperse 2.2 parts of heat storage microcapsules in the mixture to obtain a mixed slurry. Pour the mixture into a mold, place the mold in an ultra-low temperature freezer at -80℃ to freeze and solidify it. Then place the sample in a freeze dryer and dry it for 36 hours under the conditions of cold trap temperature below -50℃ and vacuum degree below 10 Pa to obtain a polyvinyl alcohol composite foam matrix with columnar porous channels parallel to the thickness direction of the material. S2. Place the polyvinyl alcohol composite foam matrix in a sealed container filled with glutaraldehyde solution, place the container in an environment of 50°C, and expose the matrix to saturated glutaraldehyde vapor for 7 hours to obtain a cross-linked and cured matrix. S3. Mix 25 parts of rutile nano-titanium dioxide, 30 parts of self-crosslinking acrylic emulsion and 45 parts of water, disperse at high speed to prepare a heat-reflective coating, uniformly coat it on the outer surface of the crosslinked and cured substrate, dry and cure at 30°C for 18 hours to form a heat-reflective layer with a thickness of 150 μm, and obtain the heat-insulating porous material with oriented channels.

[0039] Comparative Example 2 The difference between Comparative Example 2 and Example 4 is that: after obtaining the polyvinyl alcohol composite foam matrix in step S1, Comparative Example 2 does not place it in glutaraldehyde saturated vapor for treatment, but directly proceeds to step S3 to coat the heat reflective layer, and the remaining steps are the same as in Example 4.

[0040] Comparative Example 3 The difference between Comparative Example 3 and Example 4 is that no heat-storing microcapsules are added to the polyvinyl alcohol composite foam matrix in Comparative Example 3, while the remaining steps are the same as in Example 4.

[0041] Comparative Example 4 The difference between Comparative Example 4 and Example 4 is that hexagonal boron nitride nanosheets are not added in the preparation of the heat storage microcapsules in Comparative Example 4, while the remaining steps are the same as in Example 4.

[0042] Comparative Example 5 The difference between Comparative Example 5 and Example 4 is that Comparative Example 5 does not prepare heat-storing microcapsules, but instead adds the same amount of polyethylene glycol and hexagonal boron nitride nanosheets as in Example 4 to the mixed slurry in step S1, while the remaining steps are the same as in Example 4.

[0043] Comparative Example 6 The difference between Comparative Example 6 and Example 4 is that the heat storage microcapsule preparation in Comparative Example 6 omits the glutaraldehyde aqueous solution crosslinking and curing step S14, and only uses gelatin-gum arabic as the shell layer, while the remaining steps are the same as in Example 4.

[0044] Comparative Example 7 The difference between Comparative Example 7 and Example 4 is that Comparative Example 7 does not perform step S3 to coat the heat-reflective layer after obtaining the cross-linked and cured matrix; the remaining steps are the same as in Example 4.

[0045] Comparative Example 8 The difference between Comparative Example 8 and Example 4 is that no cellulose nanofibers are added to the mixed slurry in step S1 of Comparative Example 8.

[0046] Testing: Thermal insulation performance testing was conducted according to standard GB / T 10295-2008 using a thermal conductivity meter. The test surface was perpendicular to the arrangement direction of the columnar oriented channels, ensuring that the heat flow direction was parallel to the thickness direction of the material and perpendicular to the channel axis. Under steady-state conditions, the thermal conductivity of the material at room temperature was measured. Cyclic stability testing involved placing the porous insulating material in a constant temperature and humidity chamber and subjecting it to multiple temperature cycles between 15℃ and 65℃. After 100 cycles, samples were taken, and the phase transition enthalpy change was measured using DSC. Mechanical property testing was conducted according to GB / T 8813-2008 using an electronic universal testing machine. The compression direction was perpendicular to the thickness direction of the material, the loading speed was 2 mm / min, and 500 compression cycles were performed.

[0047] Table 1 Thermal Insulation Performance Test

[0048] As shown in Table 1, the thermally insulating porous material with oriented channels prepared by this invention exhibits excellent comprehensive thermal insulation performance. The oriented channel structure constructed by directional freezing technology effectively regulates the heat conduction path and improves thermal insulation efficiency. At the same time, the glutaraldehyde crosslinking enhances the stability of the matrix structure. Microencapsulation integrates phase change material with hexagonal boron nitride, which not only endows the material with significant heat storage and temperature regulation capabilities, but also improves the encapsulation stability and cycle durability of the core material through shell crosslinking. The introduction of a surface heat reflective layer further blocks radiative heat transfer, thereby synergistically improving the overall thermal insulation performance of the material in terms of thermal insulation, heat storage, and reflection. Comparative Example 1 shows that the disordered channel structure leads to a significant decrease in thermal insulation performance due to the chaotic heat flow paths; Comparative Example 2 demonstrates that the uncrosslinked matrix, due to its loose structure and poor water resistance, affects thermal insulation and mechanical stability; Comparative Example 3 shows that the lack of microcapsules causes the material to completely lose its heat storage function, and the thermal insulation performance is also reduced; Comparative Example 4 shows that the absence of hexagonal boron nitride weakens the thermal conductivity uniformity of the core material, slightly affecting the heat storage efficiency and cycle stability; Comparative Example 5 shows that direct mixing of unencapsulated phase change materials leads to serious leakage, greatly impairing the material's heat storage durability and structural integrity; Comparative Example 6 reflects that the lack of crosslinking in the microcapsule shell reduces its mechanical strength and leak-proof capability, thus affecting cycle stability; Comparative Example 7 shows that the absence of a heat reflective layer weakens the overall thermal insulation effect under conditions where radiative heat transfer is dominant; Comparative Example 8 shows that the absence of cellulose nanofibers weakens the pore wall strength, slightly affecting thermal insulation and significantly reducing mechanical properties.

[0049] Table 2 Mechanical Performance Tests

[0050] As shown in Table 2, the material of the present invention exhibits excellent comprehensive mechanical properties. In Example 3, a stable three-dimensional network structure was formed in the polyvinyl alcohol matrix through glutaraldehyde crosslinking, which significantly enhanced the rigidity and compression resistance of the material. At the same time, the oriented channel structure formed by directional freezing has good load-bearing capacity and resilience in the thickness direction. The addition of microcapsules and nanofibers further strengthens the integrity of the matrix and the interfacial bonding, so that the material can still maintain a high strength retention rate after long-term cyclic compression, demonstrating good structural stability and fatigue resistance. Comparative Example 1, employing a disordered freezing structure, exhibited higher initial compressive strength due to its denser structure. However, its disordered structure led to uneven stress distribution, making it prone to localized damage accumulation during cyclic compression. Consequently, the strength retention rate after cycling was significantly reduced, reflecting the advantage of oriented structures in long-term mechanical stability. Comparative Example 2, without glutaraldehyde crosslinking treatment, relied solely on physical bonding, resulting in a loose structure, low strength, and poor water resistance. It was prone to plastic deformation and structural failure during compression and cycling, thus significantly deteriorating both compressive strength and cyclic stability. Comparative Example 8, lacking the addition of cellulose nanofibers, resulted in insufficient reinforcement and support for the foam pore walls. The material was generally soft and prone to collapse, leading to lower compressive strength and increased susceptibility to structural damage during cycling, resulting in a low strength retention rate. This demonstrates the crucial role of nanofibers in enhancing the mechanical strength of pore walls and maintaining the integrity of porous structures.

[0051] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A thermally insulating porous material with oriented channels, characterized in that, The thermal insulation porous material includes: a polyvinyl alcohol composite foam matrix with oriented through channels, heat-storing microcapsules dispersed in the matrix and distributed along the through channels, and a heat-reflective layer covering the outer surface of the matrix.

2. The thermal insulation porous material with oriented channels according to claim 1, characterized in that, The through-channels are columnar structures, and their arrangement is parallel to the thickness direction of the polyvinyl alcohol composite foam base.

3. The thermal insulation porous material with oriented channels according to claim 1, characterized in that, The method for preparing the heat-storing microcapsules includes the following steps: S11. Polyethylene glycol is melted in a water bath, hexagonal boron nitride nanosheets are added, the water bath temperature is maintained, and high-speed shear mixing is performed to obtain a uniformly dispersed hexagonal boron nitride composite melt. S12. Prepare an aqueous gelatin solution as aqueous phase A, heat it, add the hexagonal boron nitride composite melt to aqueous phase A, and disperse it under high-speed shear to obtain a coarse dispersion of composite melt O / W type; S13. Prepare an aqueous solution of gum arabic as aqueous phase B, slowly add the coarse dispersion to aqueous phase B under continuous stirring, adjust the pH value of the mixture, stir the reaction, and obtain a microcapsule slurry with a primary capsule wall. S14. The microcapsule slurry was slowly cooled under stirring, and glutaraldehyde aqueous solution was added. Stirring was continued to crosslink and solidify the mixture. Then the temperature was raised to strengthen the shell. After the reaction was completed, the solid was collected by centrifugation, washed and vacuum dried to obtain heat-storing microcapsules.

4. The method for preparing the thermal insulation porous material with oriented channels according to claim 1, characterized in that, Includes the following steps: S1. The heat storage microcapsules are uniformly dispersed in a mixed slurry composed of polyvinyl alcohol, cellulose nanofibers and water, injected into a mold, one side of the mold is contacted with a cold source for directional freezing and solidification, and then freeze-dried to obtain a polyvinyl alcohol composite foam matrix with columnar porous channels parallel to the thickness direction of the material. S2. The polyvinyl alcohol composite foam matrix is ​​subjected to glutaraldehyde vapor treatment to obtain a cross-linked and cured matrix; S3. A reflective layer is coated on the outer surface of the cross-linked and cured matrix to obtain a thermally insulating porous material with oriented channels.

5. The method for preparing the thermal insulation porous material with oriented channels according to claim 3, characterized in that: In step S11, the water bath temperature is 70~80℃, the amount of hexagonal boron nitride nanosheets added is 5~20% of the mass of polyethylene glycol, the high-speed shearing speed is 10000~20000 rpm, and the time is 20~40 min.

6. The thermal insulation porous material with oriented channels according to claim 3, characterized in that: In step S12, the concentration of the gelatin aqueous solution is 2-5 wt%, the heating temperature is 50-60°C, the high-speed shear dispersion speed is 8000-15000 rpm, and the time is 5-15 min.

7. The thermal insulation porous material with oriented channels according to claim 3, characterized in that: In step S13, the concentration of the gum arabic aqueous solution is 2-5 wt%, the pH of the mixed system is adjusted to 3.5-4.5, and the stirring reaction time is 30-60 min.

8. The thermal insulation porous material with oriented channels according to claim 3, characterized in that: In step S14, cooling involves cooling the microcapsule slurry to below 10°C. The concentration of the glutaraldehyde aqueous solution is 25 wt%, and its addition amount is 0.5-4% of the total mass of the microcapsule slurry. The stirring, cross-linking, and curing time is 2-4 hours. The temperature for heating and strengthening the shell layer is 40°C, and the time is 30-60 minutes.

9. The method for preparing the thermal insulation porous material with oriented channels according to claim 4, characterized in that: In step S1, the mixed slurry contains 5-15 parts by weight of polyvinyl alcohol, 0.8-2 parts by weight of cellulose nanofibers, 75-90 parts by weight of water, and 0.5-3 parts by weight of heat-storing microcapsules. The directional freezing involves placing the side of the mold on a liquid nitrogen cold source for 1-5 hours.

10. The method for preparing the thermal insulation porous material with oriented channels according to claim 4, characterized in that: The conditions for the glutaraldehyde vapor crosslinking treatment in step S2 are as follows: the polyvinyl alcohol composite foam matrix is ​​placed in a sealed container and exposed to saturated glutaraldehyde vapor at 50°C for 4-12 hours. The process for coating the heat-reflective layer in step S3 is as follows: the heat-reflective coating is uniformly applied to the outer surface of the crosslinked and cured matrix, and dried and cured at 15-50°C for 4-24 hours to form a heat-reflective layer with a thickness of 100-200 μm. The heat-reflective coating, by weight, comprises 10-25 parts rutile nano-titanium dioxide, 20-40 parts self-crosslinking acrylic emulsion, and the balance being water.

Images