THERMALLY INSULATING AEROGEL COMPOSITE FIBER

Abstract

The present application provides a preparation method of an all-polymer aerogel composite fiber by compounding fiber material(s) with polymer-based micro-aerogel powder using a melting process, comprising of the following steps: (a) Weighing the materials to form the aerogel composite fibers, which should compose of 0.1-20% (w/w) polymer micro-aerogel powder and 80-99.9% (w/w) fiber material(s); (a) Mixing the polymer micro-aerogel powder and fiber material(s) to form a homogenized composite mixture; and (b) Heating the composite mixture up to the melting point of the fiber material(s) to disperse the polymer micro-aerogels throughout the molten fiber material(s), then extruded to form aerogel composite fibers.

Description

TECHNICAL FIELD

Embodiments of the present disclosure relate to the technical field of thermally insulating material, and in particular, relate to thermally insulating aerogel composite fiber.

BACKGROUND

In regions with cold weather, thermal insulation is important for survival and comfort, allowing humans to conserve their body temperature despite the surroundings. Thermal insulation is present in many products such as building walls, cooling systems, engines, however the most common use of thermal insulation is in our clothing apparels. Having the proper insulating clothes during cold weather can help us maintain our health and reduce the amount of heating needed.

Aerogels are synthetic porous ultralight materials that has one of the lowest thermal conductivities and densities of any known material. Its excellent thermally insulating properties has been used extensively in cooling, building, and aerospace applications, however the use of aerogels in the textile industry is still limited. Aerogels are most often prepared in a bulk sheet form and derived from inorganic materials which has poor adhesion with conventional textile materials that are typically organic based. Furthermore, commercially available aerogels are usually prepared using an expensive supercritical drying process because requires large quantities of pressurized gases. Because of these reasons, use of aerogels in textiles has been limited to thick garments such as jackets, vests, or gloves that are big enough to fit sheets of bulk aerogel inside them. The prices of these products are also very expensive.

The present application aims to solve these problems by introducing a novel low-cost method of producing aerogel-enhanced thermally insulating textile fibers that can be weaved into garments of any form, thus promoting the commercialization and availability of aerogel insulated garments to consumers.

SUMMARY

The present application provides a low-cost method to enhance the thermal insulation of textiles by incorporating micro-sized aerogels inside textile fibers to produce thermally insulating aerogel composite fibers. Low-cost aerogel-enhanced garments of any shape can be prodeced since the aerogels are integrated inside the fibers.

The micro-aerogels are prepared using a low-cost method to produce aerogels derived from a background patent (U.S. Pat. No. 10,807,059). The micro-aerogels were made using organic polymers and dried using an improved low-cost freeze-drying process. The resulting micro-aerogels have very low thermal conductivity, good adhesion to textiles fibers, can withstand high temperatures during melt extrusion, small enough to be incorporated into fibers, and cheap to produce. Furthermore, these polymeric micro-aerogels can be added to any polymer material as a thermally insulating additive.

The aerogel composite fibers are prepared by mixing the micro-aerogels and PET pellets together in a melt extruder where the micro-aerogels are dispersed in the molten PET and extruded into aerogel composite fibers. The resulting aerogel composite fibers has improved thermal insulation compared to pristine fibers, without significant changes to its mechanical properties.

The porous micro-aerogels are dispersed inside the fiber material, inducing a porous structure inside the fiber. These pores reduce the mean free path of heat conduction inside the fibers, reducing the thermal conductivity of the fiber and increasing its thermal insulating properties. Additionally, because the micro-aerogels are prepared from organic polymers, they have good adhesion with the organic fiber materials and does not significantly affect its mechanical properties.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments are illustrated by way of example, and not by limitation, in the figures of the accompanying drawings, wherein elements/modules and steps having the same reference numeral designations represent like elements/modules and steps throughout. The drawings are not to scale, unless otherwise disclosed.

FIG. 1 is an illustration of the aerogel composite fiber cross-section, showing how the aerogels reduces the mean free path of heat conduction.

FIG. 2 is a flowchart of polyimide (PI)-based micro aerogel synthesis, depicting a PI/DMAc/Ethanol mixture as the precursor.

FIG. 3 is a SEM image of a PI micro aerogel at 10,000× magnification, showing the intact pore structure of the micro aerogel.

FIG. 4 is an illustration of PI micro aerogel mixed with PET pellets and PI/PET aerogel composite fibers.

FIG. 5 is a SEM image of PI/PET fiber cross-section at 20,000× magnification showing the micro aerogel pores inside of the fiber.

FIG. 6 is a bar graph of thermal conductivity measurements of PET, 1 w % PI/PET, and 2 w % PI/PET fibers.

FIG. 7 is a bar graph of Fiber tenacity strength measurements of PET, 1 w % PI/PET, and 2 w % PI/PET fibers.

DETAILED DESCRIPTION

The present disclosure is further described with reference to some exemplary embodiments. The embodiments hereinafter facilitate further understanding of the present disclosure for a person skilled in the art, rather than causing any limitation to the present disclosure. It should be noted that persons of ordinary skill in the art may derive various variations and modifications without departing from the inventive concept of the present disclosure. Such variations and modifications shall pertain to the protection scope of the present disclosure.

For better understanding of the present disclosure, the present disclosure is described in detail with reference to attached drawings and specific embodiments. Unless the context clearly requires otherwise, throughout the specification and the claims, technical and scientific terms used herein denote the meaning as commonly understood by a person skilled in the art. Additionally, the terms used in the specification of the present disclosure are merely for describing the objectives of the specific embodiments, and are not intended to limit the present disclosure. As used herein, the term “and/or” in reference to a list of one or more items covers all of the following interpretations of the term: any of the items in the list, all of the items in the list and any combination of the items in the list.

It should be noted that, in the absence of conflict, embodiments of the present disclosure and features in the embodiments may be incorporated, which all fall within the protection scope of the present disclosure.

The present application introduces a new way of enhancing thermally insulating garments with aerogel technology. Currently, the application of aerogels in the textile industry is hindered by the bulky shape of aerogels and its expensive cost, limiting the types of apparel that can be made. With the present application, it will be possible to produce low-cost aerogel-enhanced thermally insulating apparel that can be of any size and more accessible to a wider range of customers. The introduction of products made using our invention will drive other textile companies to develop their own aerogel technologies and spur the next generation of aerogel applications in the industry.

According to Business Wire, the global market for winter wear was estimated at 422.9 billion USD in 2020 and projected to reach 582.4 billion USD in 2027. Being the most advanced aerogel-enhanced textiles in the market, our invention will be able to capture a significant portion of the market. Textiles made with our invention will require less thickness/material to achieve the same level of insulation as conventional textiles, resulting in garments that are thinner, lighter, and more comfortable for the consumers.

The term “aerogel” is also a lucrative marketing term because of its ties to NASA and space technology. Many companies have tried to use the term on their products despite having little to no aerogels and no apparent increase in insulation. Our invention will produce apparels that properly utilizes the thermal insulation of aerogels and will be more affordable than other aerogel apparels in the market.

As shown in FIG. 2, a suitable organic polymer material, which could be a polyimide or aramid, is mixed in a polar aprotic organic solvent such as dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), dimethylformamide (DMF), or n-methyl-2-pyrrolidone (NMP) and stirred at 60° C. until it forms a homogeneous polymer solution. The solvent serves to disrupt the intermolecular bonds of the polymer and separate them into individual polymer chains. A suitable non-solvent, which could be water, ethanol, or another organic solvent, is added into the polymer solution until near the precipitation point of the solution, then mixed together until homogeneous. The non-solvent serves to reduce the solubility of the polymer in the solvent, which will aid the gelation process, and act as a porogen for the gel.

The polymer mixture is then transferred into a mould and frozen at a suitable freezer until it forms a fully frozen wet gel. The suitable temperature of the freezer will depend on the solvent and non-solvent used for the polymer mixture; the non-solvent should remain as a liquid phase at the freezing temperature. As the solvent in the mixture freezes, the concentration of solvent will decrease, causing the polymer to phase separate and restore its intermolecular bonds, forming physically cross-linked porous structures known as a gel. The pores of the wet gel are typically in the nanometer or micrometer scale, depending on the polymer and non-solvent concentration.

Afterwards, the frozen wet gel is extracted from its mould and immersed in a non-solvent bath, the same one added into the mixture, and left at its freezing temperature until the solvent exchange process is complete. The frozen solvent crystals inside the wet gel will be washed out by the non-solvent bath through a diffusion process, this is done to stabilize the wet gel for further processing to prevent the melted solvent from dissolving the polymer and disrupting the gel structure. The resulting wet gel is brought to room temperature to be cracked into micro wet gels.

To crack them into micro wet gels, the wet gels are placed inside a planetary ball-milling jar with zirconia milling balls and submerged in ethanol. As shown in FIG. 2, the wet gels are then ball-milled at 400 rpm for 1-3 hours, or until the desired particle size distribution is achieved. The resulting micro wet gel suspension is then extracted from the jars and centrifuged at 10,000 rpm to separate the micro wet gels from the liquid phase. The micro wet gels are then subsequently washed and centrifuged at least 1 more time, the washing liquid is preferably a suitable freeze-drying agent, which in this case is a 25v % tert-butanol/water mixture.

The fully washed micro wet gels are then re-suspended in 25v % tert-butanol/water and frozen at −30° C. until fully frozen. It is then placed inside a freeze-dryer where it is kept under the triple point pressure of the freeze-drying agent, which in this case is 3.97 kPa for tert-butanol, until all of them have dried into micro aerogels. Freeze-drying allows for the gradual extraction of the liquid phase from the micro wet gels, which helps prevent shrinkage and keeps the pore structures intact. Wet gel drying is commonly done by supercritical drying, which requires expensive high-pressure equipment and pure gases. Freeze-drying allows us to product aerogels or micro aerogels with lower cost and lower risks. FIG. 3 is a SEM image of a PI micro aerogel at 10,000× magnification, showing the intact pore structure of the micro aerogel. As shown in FIG. 3, the micro aerogels are mostly below 60 μm in size, maintains their porous structure through the ball-milling and freeze-drying process, and has an ultra-low thermal conductivity of 0.030-0.040 W/mK.

FIG. 4 is an illustration of PI micro aerogel mixed with PET pellets and PI/PET aerogel composite fibers. As shown in FIG. 4, to prepare the aerogel composite fibers, 1-5 wt % micro aerogels are mixed with the fiber material, in this case PET or PLA, in their raw pellet forms. The mixture is processed through a melt extruder at the melting temperature of the fiber material, where the micro aerogels are dispersed throughout the molten fiber material, and then extruded into aerogel composite fibers. FIG. 5 is a SEM image of PI/PET fiber cross-section at 20,000× magnification showing the micro aerogel pores inside of the fiber. FIG. 1 is an illustration of the aerogel composite fiber cross-section, showing how the aerogels reduces the mean free path of heat conduction. As shown in FIG. 1, the fully formed fibers contain the pores of the micro aerogels inside of them, reducing the mean free path of heat conduction inside the fibers and increasing its thermal insulating properties. FIG. 6 is a bar graph of thermal conductivity measurements of PET, 1 w % PI/PET, and 2 w % PI/PET fibers, showing the decrease in thermal conductivity through the addition of micro aerogels. FIG. 7 is a bar graph of Fiber tenacity strength measurements of PET, 1 w % PI/PET, and 2 w % PI/PET fibers showing that the addition of micro aerogels does not significantly impact the fiber tenacity. The 20% decrease bar is added as an acceptable threshold condition for industrial garment processing. As shown in FIG. 6 and FIG. 7, the aerogel composite fibers showed a significantly reduced thermal conductivity compared to pristine fibers, only with a minor reduction in fiber tenacity strength.

In some embodiments, the preparation method of an aerogel composite fiber includes the following steps:

• • (a) Weighing the materials to form the aerogel composite fibers, which should compose of 0.1-20% (w/w) polymer micro-aerogel powder and 80-99.9% (w/w) fiber material(s);
  • (a) Mixing the polymer micro-aerogel powder and fiber material(s) to form a homogenized composite mixture; and
  • (b) Heating the composite mixture up to the melting point of the fiber material(s) to disperse the polymer micro-aerogels throughout the molten fiber material(s), then extruded to form aerogel composite fibers.

In some embodiments, the polymer micro-aerogel powder has an average particle size of 0.1-100 μm, a porous structure with an average pore size of 10-2000 nm, and a thermal conductivity of 20-100 mW/mK.

In some embodiments, the polymer micro-aerogel powder is prepared by dissolving 0.1-30% (w/w) of polymer in a suitable solvent at 40-80° C., then adding 0-30% (v/v) of a suitable non-solvent before the mixture is frozen, gelled in a non-solvent bath, ball-milled into microgels, washed, and lastly freeze-dried with tert-butanol.

In some embodiments, the polymer is a polyimide or an aramid.

In some embodiments, the solvent is a chemical that can dissolve 0-30% (w/w) of the polymer material and can accept up to 0-30% of non-solvent without the polymer material precipitating.

In some embodiments, the non-solvent is a chemical that causes the polymer material to precipitate when added in excess.

In some embodiments, the gelation occurs inside a refrigerator, freezer, or liquid nitrogen.

In some embodiments, the gels are ball-milled into microgels for 0.1-48 hours.

In some embodiments, the washing and freeze drying uses a suitable solvent that can be frozen and sublimated at a pressure below 600 Pa.

In some embodiments, the fiber material(s) are polyethylene terephthalate, polylactic acid, and/or nylon.

In some embodiments, the composite mixture is molten and formed into a fiber with melt spinning or melt extrusion.

In some embodiments, the fiber diameter is 10-200 μm.

In some embodiments, the fiber shows a 1-50% reduction in thermal conductivity and a change of ±30% in fiber tenacity strength when compared to fibers produced with only the fiber material.

Other embodiments of the present application provide an textile product, the textile product includes the aerogel composite fibers manufactured by the preparation method in above.

Finally, it should be noted that the above embodiments are merely used to illustrate the technical solutions of the present disclosure rather than limiting the technical solutions of the present disclosure. Under the concept of the present disclosure, the technical features of the above embodiments or other different embodiments may be combined, the steps therein may be performed in any sequence, and various variations may be derived in different aspects of the present disclosure, which are not detailed herein for brevity of description. Although the present disclosure is described in detail with reference to the above embodiments, persons of ordinary skill in the art should understand that they may still make modifications to the technical solutions described in the above embodiments, or derive equivalent replacements to some of the technical features; however, such modifications or replacements do not cause the essence of the corresponding technical solutions to depart from the spirit and scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. A preparation method of an aerogel composite fiber, comprising of the following steps: (a) Weighing the materials to form the aerogel composite fibers, which should compose of 0.1-20% (w/w) polymer micro-aerogel powder and 80-99.9% (w/w) fiber material(s);(a) Mixing the polymer micro-aerogel powder and fiber material(s) to form a homogenized composite mixture; and(b) Heating the composite mixture up to the melting point of the fiber material(s) to disperse the polymer micro-aerogels throughout the molten fiber material(s), then extruded to form aerogel composite fibers.

2. The preparation method of an aerogel composite fiber according to claim 1, wherein the polymer micro-aerogel powder has an average particle size of 0.1-100 μm, a porous structure with an average pore size of 10-2000 nm, and a thermal conductivity of 20-100 mW/mK.

3. The preparation method of an aerogel composite fiber according to claim 1, wherein the polymer micro-aerogel powder is prepared by dissolving 0.1-30% (w/w) of polymer in a suitable solvent at 40-80° C., then adding 0-30% (v/v) of a suitable non-solvent before the mixture is frozen, gelled in a non-solvent bath, ball-milled into microgels, washed, and lastly freeze-dried with tert-butanol.

4. The preparation method of an aerogel composite fiber according to claim 3, wherein the polymer is a polyimide or an aramid.

5. The preparation method of an aerogel composite fiber according to claim 3, wherein the solvent is a chemical that can dissolve 0-30% (w/w) of the polymer material and can accept up to 0-30% of non-solvent without the polymer material precipitating.

6. The preparation method of an aerogel composite fiber according to claim 3, wherein the non-solvent is a chemical that causes the polymer material to precipitate when added in excess.

7. The preparation method of an aerogel composite fiber according to claim 3, wherein the gelation occurs inside a refrigerator, freezer, or liquid nitrogen.

8. The preparation method of an aerogel composite fiber according to claim 3, wherein the gels are ball-milled into microgels for 0.1-48 hours.

9. The preparation method of an aerogel composite fiber according to claim 3, wherein the washing and freeze drying uses a suitable solvent that can be frozen and sublimated at a pressure below 600 Pa.

10. The preparation method of an aerogel composite fiber according to claim 1, wherein the fiber material(s) are polyethylene terephthalate, polylactic acid, and/or nylon.

11. The preparation method of an aerogel composite fiber according to claim 1, wherein the composite mixture is molten and formed into a fiber with melt spinning or melt extrusion.

12. The preparation method of an aerogel composite fiber according to claim 1, wherein the fiber diameter is 10-200 μm.

13. The preparation method of an aerogel composite fiber according to claim 1, wherein the fiber shows a 1-50% reduction in thermal conductivity and a change of ±30% in fiber tenacity strength when compared to fibers produced with only the fiber material.

14. An textile product, comprising the aerogel composite fibers manufactured by the preparation methodin claim 1.