Technical field of the invention

The present invention relates to polymer fibres. More specifically, the invention relates to hollow polymer fibres comprising aerogel particles in the fibre lumen.

Background of the invention

Aerogels are a special type of solid material with nanometre-scale pores. Porosity is often in excess of 90%, in some cases as high as 99.9%, and densities can be as low as 3 kg/m ³ . The unusual properties of the aerogels afford their suitability for many applications in commercial and high-tech fields, such as waste management (gas absorption, radioactive waste confinement), thermal insulation (cryogenic to high temperatures), super- insulating jackets, laser experiments, sensors (ultrasonic and gas), nuclear particle detection (Cherenkov), optics and light-guides, electronic devices, capacitors, high explosive research and catalysts. As an example, their thermal conductivity (0.014 W/m K at room temperature) is the lowest of any solids, and they have good transparency. Furthermore, the acoustic properties of aerogels make them effective insulators against noise, and aerogels have the lowest refractive index, and dielectric constant of all solid materials.

However, aerogel is vulnerable to moisture and tensile stress, and is rapidly spoiled, when the material is exposed to water or water vapour.

A research group at the University of Akron has reinforced an aerogel by incorporating a fibre in the block of the aerogel, and thereby improving the elastic properties. The American company Aspen markets various products with aerogel in a polymer matrix under the name Space Loft, but these suffer from the weakness that binding of aerogel is weak, and the material thus loses its properties over time when aerogel, through physical impact, is released.

EP0846802 discloses a process for filling a hollow portion of a hollow porous fibre with a gel. A hollow fibre with pores distributed throughout the surface, and communicating with the hollow portion, is placed in a liquid capable of turning into a gel and is left at room temperature. The liquid is absorbed through the communicating pores into the hollow portion until it fills that portion. Finally, the absorbed liquid is gelled. The pores are made by various techniques subsequently to the spinning of the hollow fibre.

The liquid may contain an agent, which can impart a functional property to the fibre. The liquid may include substances, such as titanium oxide, silica, alumina, zeolite, etc., which will give an electrical function for an electric conductor or a magnetic product. Zeolite may be in the form of an aerogel. None of the examples includes zeolite. Even if included, the use of such a fibre for insulating properties would be unsuccessful, since the pores in the fibre would result in water from the air entering the hollow portion. The aerogel present in the hollow portion is vulnerable to moisture, and is rapidly spoiled, when the material is exposed to water or water vapour.

Furthermore, the pore size in the fibre must be of a substantial diameter in order to provide an access port to the aerogel particles. The issue with the pore sizes is also disclosed therein, where the communicating pore preferably has a width of 0.2-10 microns, and a length of 5-20 microns. If the communicating pore has a width and length out of above range, the introduction into the pore of a gelable liquid, will be insufficient, or conversely, the gel having filled the hollow portion will be lost easily. CN102041562 discloses a method for preparing an antimicrobial hollow fibre. The hollow fibre is prepared by melt spinning process, and extruded in sheath-core form. The lumen in the fibre is prepared in the core component by injecting air, at a controllable airflow, into the core layer. The lumen in the core component of the hollow fibre accounts for 5-60% of the total volume. The lumen is empty. The core component may comprise silver zeolite as an antibacterial agent. Silver zeolite may be in the form of an aerogel. The lumen of the core component is empty. The core component contains 0.1 to 10% w/w inorganic particles (such as silver zeolite), with a particle diameter of 100 nm to 10 micron. The weight ratio between the core component and the sheath component is within the range of 1-20: 99-80.

Summary of the invention

Hence, one object of the present invention is to stabilise aerogel to make it suitable for many applications in commercial and high-tech fields.

A specific object of the present invention is to produce a material comprising aerogel, which can withstand mechanical stress, and at the same time protect the aerogel from climatic conditions.

The above objects are solved by using a composite fibre, in which the aerogel particle is encapsulated by a polymer matrix in the form of a hollow fibre. Hence, the aerogel is positioned within the lumen of the hollow fibre. Since the aerogel particle retains its structure within the lumen of the hollow fibre, the good insulation properties are transferred to the composite fibre. The hollow fibre of polymer component contributes with the mechanical properties. The material is designed in such a way that the aerogel particle is completely encapsulated by the hollow fibre. This encapsulation contributes to the protection against climatic conditions. One aspect of the invention relates to a composite fibre comprising a hollow fibre and aerogel particles, wherein the lumen of the hollow fibre is at least partially filled with said aerogel particles. A second aspect of the invention relates to a fibre comprising a wall and a lumen; wherein the lumen is at least partially filled with aerogel particles.

A third aspect of the invention relates to a composite fibre comprising a hollow fibre and aerogel particles;

wherein when the hollow fibre is porous, the lumen of the hollow fibre only contain aerogel particles and a gas;

wherein when the hollow fibre is substantially non-porous, the lumen of the hollow fibre contain aerogel particles and a gas. A fourth aspect of the invention relates to a composite fibre comprising a hollow fibre and aerogel particles;

wherein the lumen of the hollow fibre only contain aerogel particles and a gas. A fifth aspect of the invention relates to a method of production of a composite fibre, comprising the step of:

- Forming a hollow fibre, while simultaneously introducing aerogel particles into the lumen of the formed hollow fibre. A composite fibre according to the present invention can then be processed into a material, e.g. as a nonwoven material, a thermally insulating material, and/or a sound insulating material.

Brief description of the figures

Figure 1 shows non-limited examples of spinnerets for use according to the present invention, Figure 2 shows a hollow fibre produced with electrospinning through a coaxial spinneret, and

Figure 3 shows SEM pictures of different aerogel particles within a hollow fibre, and

Figure 4 shows results of an EDX analysis of a hollow fibre comprising aerogel within its lumen.

Detailed description of the invention

One object of the present invention is to stabilise aerogel to make it suitable for many applications in commercial and high-tech fields.

A specific object of the present invention is to produce an insulation material comprising aerogel particles, which can withstand mechanical stress, and at the same time protect the aerogel particles from climatic conditions.

The above objects are solved by using a composite fibre, in which the aerogel particles are encapsulated by a hollow fibre, as a material for producing products suitable for commercial and high-tech fields. Such a product could e.g. be an insulation material.

In the present context, the term "composite fibre" refers to a fibre of at least two components; a first component being the hollow fibre and a second component being the aerogel particles.

In the present context, an encapsulation of the aerogel particle is to be understood as the polymer matrix wall of the hollow fibre being disposed about the aerogel particle, thereby preventing the aerogel particle from being in contact with the surroundings. Hence, the aerogel is positioned within the lumen of the hollow fibre.

In the present invention, the term "fibre" refers to a unit of matter characterized by a high ratio of length-to-width. Preferably, the fibre can be spun into yarn, made into fabric by interlacing (weaving), interloping (knitting), or non-woven or membrane by interlocking (bonding).

In the present context, the term "hollow fibre" is to be understood as fibre with a wall defining one or more lumens within the fibre. Such fibres may be extruded. The walls may be porous, i.e. extending from the lumen and through the wall, substantially non-porous, i.e. only with minor pores due to manufacturing errors, or non-porous.

In the present invention, the term "aerogel" refers to an open-celled, mesoporous, solid foam that is composed of a network of interconnected nanostructures and that exhibit a porosity (non-solid volume) of no less than 50%. The term "mesoporous" refers to a material that contains pores ranging from 2 to 50 nm in diameter.

The term aerogel does not refer to a particular substance, but rather to a geometry which a substance can take on. Aerogels can be made of a wide variety of substances, including: Silica, transition metal oxides (for example, iron oxide), lanthanide and actinide metal oxides (for example, praseodymium oxide), main group metal oxides (for example, tin oxide), organic polymers (such as resorcinol-formaldehyde, phenol-formaldehyde, polyacrylates, polystyrenes, polyurethanes, and epoxies), biological polymers (such as gelatin, pectin, and agar agar), semiconductor nanostructures (such as cadmium selenide quantum dots), carbon, carbon nanotubes, and metals (such as copper and gold). Typically, an aerogel is made using sol-gel chemistry to form a solvent filled high-porosity gel. The gel is then dried by removing the solvent without collapsing the tenuous solid phase through a process called supercritical drying. Other processes for the production of aerogels have been developed to lower the production costs. The aerogel is provided as particles of variable size, and the inventors have used an aerogel (silica based, and in powder form) supplied by Insulgel High-Tech (Beijing) Co., Ltd. In the present context the term "powder" is to be understood as a dry, bulk solid composed of a large number of very fine particles that may flow freely when shaken or tilted.

In the present context, the term "particle" is to be understood as a small localized object to which can be ascribed several physical or chemical properties such as volume or mass. The present invention is not limited to any specific particle size, which may range from 0.1 micrometers (pm) to several millimeters (mm).

Hence, one aspect of the invention relates to a composite fibre comprising a hollow fibre and aerogel particles, wherein the lumen of the hollow fibre is at least partially filled with said aerogel particles.

A second aspect of the invention relates to a fibre comprising a wall and a lumen; wherein the lumen is at least partially filled with aerogel particles.

A third aspect of the invention relates to a composite fibre comprising a hollow fibre and aerogel particles;

wherein when the hollow fibre is porous, the lumen of the hollow fibre only contain aerogel particles and a gas;

wherein when the hollow fibre is substantially non-porous, the lumen of the hollow fibre contain aerogel particles and a gas. A fourth aspect of the invention relates to a composite fibre comprising a hollow fibre and aerogel particles;

wherein the lumen of the hollow fibre only contain aerogel particles and a gas. In one or more embodiments, the hollow fibre is a sheath-core multi- component, e.g. bi-component, hollow fibre, and wherein the lumen is present in the sheath component and/or in the core component. This structure is employed when it is desirable for the surface/sheath to have the property of one of the polymers, such as luster, dyeability or stability; while the core may contribute to strength, reduced cost and the like. A highly contoured interface between sheath and core can lead to mechanical interlocking that may be desirable in the absence of good adhesion.

The most common way of production of sheath-core fibres is a technique where two polymer liquids are separately led to a position very close to the spinneret orifices, and then extruded in sheath-core form. In the case of concentric fibres, the orifice supplying the core polymer material is in the centre of the spinning orifice outlet; and flow conditions of core polymer fluid are strictly controlled to maintain the concentricity of both components when spinning. Eccentric fibre production could be performed by eccentric positioning of the inner channel and controlling of the supply rates of the two component polymers. The lumen within the sheath component and/or the core component can be formed by extrusion through an annulus in the spinneret; and a gas stream of e.g. air, or an inert gas, is introduced into the central bore of the spinneret to maintain a tubular shape until the fibre solidifies or coagulates. The aerogel is introduced into the lumen by use of the gas stream.

In one or more embodiments, the hollow fibre comprises one or more polymer(s). The hollow fibre of the present invention is not limited to a specific type of polymer, and may be made by inorganic or organic polymers, or mixtures thereof.

In one or more embodiments, the polymer(s) are homopolymers. In the present invention, the term "homopolymer" refers to a polymer which is formed from only one type of monomer. This is in contrast to a copolymer/heteropolymer where the polymer contains at least two different monomers.

In yet another embodiment of the present invention, the polymer(s) are block co-polymer(s).

In one or more embodiments, the aerogel particles are silica aerogel particles.

In one or more embodiments, the aerogel particles occupy 1-100% of the hollow fibres lumen, such as within the range of 2-99%, e.g. within the range of 5-95%, such as within the range of 10-90%, e.g. within the range of 15-85%, such as within the range of 20-80%, e.g. within the range of 25- 75%, such as within the range of 30-70%, e.g. within the range of 35-65%, such as within the range of 40-60%, e.g. within the range of 45-55% of the hollow fibres lumen. In one or more embodiments, the aerogel particles occupy at least 5% of the hollow fibres lumen, such as at least 10%, e.g. at least 15%, such as at least 20%, e.g. at least 25%, such as at least 30%, e.g. at least 35%, such as at least 40%, e.g. at least 45%, such as at least 50%, e.g. at least 55%, such as at least 60%, e.g. at least 65%, such as at least 70%, e.g. at least 75%, such as at least 80%, e.g. at least 85%, such as at least 90%, e.g. at least 95%, e.g. 97%, e.g. 99% of the hollow fibres lumen.

In one or more embodiments, the aerogel particles are less than 1000 μητι in their largest dimension, such as within the range of 0.1-950 μητι, e.g. within the range of 0.5-900 pm, such as within the range of 1-850 μηη, e.g. within the range of 5-800 μιη, such as within the range of 10-750 μιτι, e.g. within the range of 15-700 μιτι, such as within the range of 20-650 μιτι, e.g. within the range of 25-600 μητι, such as within the range of 30-550 μιτι, e.g. within the range of 35-500 μιτι, such as within the range of 40-450 μιη, e.g. within the range of 45-400 μητι, such as within the range of 50-350 μ ^ηη , e.g. within the range of 55-300 μητι, such as within the range of 60-250 μιτι, e.g. within the range of 65-200 μητι, such as within the range of 70-150 μητι, e.g. within the range of 75-100 μιτι in their largest dimension.

In one or more embodiments, the aerogel particles are less than 2000 μηι in their largest dimension, such as within the range of 0.1-1950 μιτι, e.g. within the range of 0.5-1900 μιτι, such as within the range of 1 -1850 μητι, e.g. within the range of 5-1800 μιη, such as within the range of 10-1750 μιτι, e.g. within the range of 15-1700 μηι, such as within the range of 20- 1650 μιη, e.g. within the range of 25-1600 μιτι, such as within the range of 30-1550 μηι, e.g. within the range of 35-1500 μητι, such as within the range of 40-1450 μητι, e.g. within the range of 45-1400 μιτι, such as within the range of 50-1350 μηη, e.g. within the range of 55-1300 μηι, such as within the range of 60-1250 μιτι, e.g. within the range of 65-1200 μητι, such as within the range of 70-1 150 μίτι, e.g. within the range of 75-1100 μηι in their largest dimension. In one or more embodiments, the aerogel particles are less than 3000 μηι in their largest dimension, such as within the range of 0.1 -2950 μιη, e.g. within the range of 0.5-2900 μητι, such as within the range of 1-2850 μιτι, e.g. within the range of 5-2800 μητι, such as within the range of 10-2750 μιτι, e.g. within the range of 15-2700 μηη, such as within the range of 20- 2650 μητι, e.g. within the range of 25-2600 μιτι, such as within the range of 30-2550 μιτι, e.g. within the range of 35-2500 μητι, such as within the range of 40-2450 μητι, e.g. within the range of 45-2400 μιτι, such as within the range of 50-2350 μηι, e.g. within the range of 55-2300 μητι, such as within the range of 60-2250 μιτι, e.g. within the range of 65-2200 μιτι, such as within the range of 70-2150 μιτι, e.g. within the range of 75-2100 μιη in their largest dimension.

The present invention is not limited to any specific particle size, which may range from 0.1 micrometers (μηι) to several millimeters (mm). However, when the aerogel particles and the material for forming the hollow fibre are passed through a multi-orifice or multi-channel spinneret, the aerogel particles cannot be larger than the orifice or channel through which the particles are passed.

In one or more embodiments, the aerogel particles are smaller in their largest dimension than the orifice or channel through which they are passed.

It is an advantage to use aerogel particles having a narrow particle size distribution, in order to produce a composite fibre that is homogeneous along its length. Through a narrow particle size, it is possible to produce fibres having a specific fibre count (dtex). Dtex is defined as mass in grams per 10.000 m fibre. By controlling the fibre count it is possible to influence the properties of the fibre and the properties of the material into which the fibre is processed. In one or more embodiments, the aerogel particles are within the range of 0.1-100 μιτι, or within the range of 50-150 μιτι, or within the range of 100- 200 μιτι, or within the range of 150-250 μητι, or within the range of 200-300 μηη, or within the range of 250-350 μηι, or within the range of 300-400 μιτι, or within the range of 350-450 μιη, or within the range of 400-500 μητι, or within the range of 450-550 μιη, or within the range of 500-600 μηι, or within the range of 550-650 μι-η, or within the range of 600-700 μιη, or within the range of 650-750 μητι, or within the range of 700-800 μιη, or within the range of 750-850 μηι, or within the range of 800-900 μητι, or within the range of 850-950 μητι, or within the range of 900-1000 μιτι in their largest dimension.

In one or more embodiments, the aerogel particles are within the range of 0.1-100 prn, or within the range of 0.1-200 μιτι, or within the range of 0.1- 300 μιτι, or within the range of 0.1-400 μιτι, or within the range of 0.1 -500 μιη in their largest dimension.

In one or more embodiments, the aerogel particle size distribution is monomodal.

In one or more embodiments, the average aerogel particle size is less than 1000 pm in its largest dimension, such as within the range of 0.1-950 μητι, e.g. within the range of 0.5-900 μητι, such as within the range of 1-850 μητι, e.g. within the range of 5-800 μιη, such as within the range of 10-750 μηη, e.g. within the range of 15-700 μιτι, such as within the range of 20-650 μητι, e.g. within the range of 25-600 μιτι, such as within the range of 30-550 μηι, e.g. within the range of 35-500 μιτι, such as within the range of 40-450 μιτι, e.g. within the range of 45-400 μιη, such as within the range of 50-350 μιτι, e.g. within the range of 55-300 μιτι, such as within the range of 60-250 μιτι, e.g. within the range of 65-200 μιτι, such as within the range of 70-150 μητι, e.g. within the range of 75-100 μιη in its largest dimension.

In one or more embodiments, the average aerogel particles are less than 2000 μιη in their largest dimension, such as within the range of 0.1-1950 μητι, e.g. within the range of 0.5-1900 μιτι, such as within the range of 1 - 1850 μιη, e.g. within the range of 5-1800 μιη, such as within the range of 10-1750 μηπ, e.g. within the range of 15-1700 μιη, such as within the range of 20-1650 μηι, e.g. within the range of 25-1600 μιη, such as within the range of 30-1550 μιτη, e.g. within the range of 35-1500 μιτι, such as within the range of 40-1450 μιη, e.g. within the range of 45-1400 μητι, such as within the range of 50-1350 μητι, e.g. within the range of 55-1300 μιτη, such as within the range of 60-1250 μιτι, e.g. within the range of 65-1200 μιτι, such as within the range of 70-1150 μητι, e.g. within the range of 75-1 100 μητι in their largest dimension.

In one or more embodiments, the average aerogel particles are less than 3000 μιτι in their largest dimension, such as within the range of 0.1-2950 μιτι, e.g. within the range of 0.5-2900 μηι, such as within the range of 1- 2850 μιτι, e.g. within the range of 5-2800 μιτι, such as within the range of 10-2750 μιη, e.g. within the range of 15-2700 μιη, such as within the range of 20-2650 μιτι, e.g. within the range of 25-2600 μιη, such as within the range of 30-2550 μιη, e.g. within the range of 35-2500 μητι, such as within the range of 40-2450 μητι, e.g. within the range of 45-2400 μιη, such as within the range of 50-2350 μιτι, e.g. within the range of 55-2300 μητι, such as within the range of 60-2250 μητι, e.g. within the range of 65-2200 μηη, such as within the range of 70-2150 μητι, e.g. within the range of 75-2100 μιτι in their largest dimension.

In one or more embodiments, the aerogel particles are within the range of 0.1-100 μιτι and with an average particle size of 50-80 μηι, or within the range of 0.1-150 μιτι and with an average particle size of 100-130 μητι, or within the range of 0.1-200 μιη and with an average particle size of 150-180 μιτι, or within the range of 0.1-250 μιτι and with an average particle size of 200-230 μιτι, or within the range of 0.1-300 μιη and with an average particle size of 250-280 μηι, or within the range of 0.1-350 μηη and with an average particle size of 300-330 μητι, or within the range of 0.1-400 μηι and with an average particle size of 350-380 μηη, or within the range of 0.1-450 μητι and with an average particle size of 400-430 μιτι, or within the range of 0.1 -500 μητι and with an average particle size of 450-480 μητι, or within the range of 0.1-550 μητι and with an average particle size of 500-530 μιτι, or within the range of 0.1-600 μιτι and with an average particle size of 550-580 μιη, or within the range of 0.1-650 μιτι and with an average particle size of 600-630 μιτι, or within the range of 0.1-700 μιτι and with an average particle size of 650-680 μιτι, or within the range of 0.1-750 μιτι and with an average particle size of 700-730 μητι, or within the range of 0.1-800 μητι and with an average particle size of 750-780 μιτι, or within the range of 0.1-850 μηη and with an average particle size of 800-830 μητι, or within the range of 0.1-900 μηι and with an average particle size of 850-880 μιη, or within the range of 0.1 -950 μιτι and with an average particle size of 900-930 μητι, or within the range of 0.1-1000 μιη and with an average particle size of 950-980 μιη in their largest dimension. Another aspect of the invention relates to a method of production of a composite fibre, comprising the step of:

- Forming a hollow fibre, while simultaneously introducing aerogel particles into the lumen of the formed hollow fibre. In one or more embodiments, the hollow fibre is formed by wet spinning, dry spinning, melt spinning, gel spinning or electrospinning.

In order to introduce the aerogel particle simultaneously with the formation of the hollow fibre during spinning, the inventors have used a spinneret with multiple orifices/channels - one or more orifices/channels for spinning the hollow fibre, and one or more orifices/channels for introducing the aerogel particles. An orifice/channel for introducing the aerogel particles is encircled by one or more orifices/channels for spinning the hollow fibre. Non-limited examples of such spinnerets are shown in Figure 1.

In one or more embodiments, the composite fibre is formed by passing the material for forming the hollow fibre through a first orifice/channel in a spinneret; and simultaneously passing the aerogel particles through one or more orifices/channels positioned within said first orifice/channel. In one or more embodiments, a gas is passed through the one or more orifices/channels positioned within said first orifice/channel simultaneously with passing the material for forming the hollow fibre through the first orifice/channel in the spinneret. Thereby, the gas stream will have a dual function - a) to maintain a tubular shape until the fibre solidifies or coagulates; and b) to help the aerogel particles to enter the lumen as it is formed.

In one or more embodiments, a plurality of orifices/channels are positioned within said first orifice/channel in the spinneret.

In one or more embodiments, the aerogel particles and the material for forming the hollow fibre are passed through a multi-orifice/multi-channel spinneret.

In one or more embodiments, the material for forming the hollow fibre may be passed through the spinneret as a polymeric solution or a pure polymer or polymeric mixture being pre-heated or melted. In one or more embodiments, the aerogel particles are introduced into the lumen of the hollow fibre by use of supercritical fluid, gravity, pump means, an injection pump, or combinations thereof.

To avoid that the aerogel will collapse, or change property, during processing of such a composite fibre, the inventors have developed a process where the aerogel particles are introduced into the lumen by the aid of supercritical fluid.

In order to introduce the aerogel particle simultaneously with the formation of the hollow fibre during electrospinning, the inventors have used a method comprising: providing a spinneret having a needle defining a bore, the needle fluidly connected to a first liquid comprising a spinnable polymeric solution, and a capillary/tube having a proximal end connected to a second liquid (supercritical fluid comprising the aerogel particles) and a distal end disposed in the needle bore such that an annular aperture is defined between the needle and the capillary/tube;

providing a conducting collector disposed a distance from the needle;

applying a voltage between the needle and the conducting collector; and feeding the polymeric solution through the needle and feeding the second liquid through the capillary/tube;

wherein the applied voltage is sufficiently high to induce a jet made of the polymeric solution to travel from the spinneret to the collector to form a composite nanofiber; and wherein pump means is configured to pump the second liquid through the capillary/tube.

When performing an electro-spinning step, the solvents of the polymeric solution should be volatile. The temperature of the electro-spinning step is usually performed within the range from room temperature to the melting temperature of the polymer. Temperatures lower than room temperature may also be used. The utilized pressure is typically about 1 bar under these conditions, but can be lowered in the case of a less volatile solvent to aid the evaporation process.

However, the selection of the solvents may in some embodiments be limited to solvents that have a relatively high vapour pressure, in order to promote the stabilization of an electro-spinning jet to create a fibre as the solvent evaporates. In embodiments involving higher boiling point solvents, it is often desirable to facilitate solvent evaporation by warming the polymeric solution, and optionally the electro-spinning jet itself, or by electro-spinning in reduced atmospheric pressure. It is also believed that creation of a stable jet resulting in a fibre is facilitated by a low surface tension of the polymeric solution. Solvent choice can also be guided by this consideration.

In one embodiment of the invention, the solvent(s) has a boiling point below 120 degrees Celsius, such as within the range of 50-110 degrees Celsius, e.g. within the range of 55-105 degrees Celsius, such as within the range of 60-100 degrees Celsius, e.g. within the range of 65-95 degrees Celsius, such as within the range of 70-90 degrees Celsius. In another embodiment, the solvent(s) are selected from the group consisting of an alcohol having a boiling point below 120 degrees Celsius, such as within the range of 50-110 degrees Celsius, e.g. within the range of 55-105 degrees Celsius, such as within the range of 60-100 degrees Celsius, e.g. within the range of 65-95 degrees Celsius, such as within the range of 70-90 degrees Celsius.

In a specific embodiment, the alcohol is mixed with water.

Since the aerogel retains its structure within the composite fibre, the good insulation properties are transferred to the composite fibre. The polymer component/matrix contributes with the mechanical properties. The material is designed in such a way that the aerogel is encapsulated by the polymer matrix of the hollow fibre. This encapsulation contributes to the protection against climatic conditions. One aspect relates to the use of a composite fibre according to the present invention, for the production of a nonwoven textile.

Another aspect relates to a composite fibre prepared by a process comprising the step of:

- Forming a hollow fibre, while simultaneously introducing aerogel particles into the lumen of the formed hollow fibre. A composite fibre according to the present invention can then be processed into an insulation material, e.g. as a nonwoven material, a thermally insulating material, and/or a sound insulating material.

In the present invention, the term "nonwoven" refers to a manufactured sheet, web or batt of directionally or randomly oriented fibres, bonded by friction, and/or cohesion and/or adhesion, excluding paper and products which are woven, knitted, tufted, stitch-bonded incorporating binding yarns or filaments or felted by wet-milling, whether or not additionally needled. The fibres may be of natural or fabricated origin. They may be staple or continuous filaments or be formed in situ. In the present context, at least a part of the fibres, are fibres of the present invention.

It should be noted that embodiments and features described in the context of one of the aspects of the present invention also apply to the other aspects of the invention.

The invention will now be described in further details in the following non- limiting examples.

Examples

Proof of concept

The main object of this study was to provide a composite fibre with aerogel particles encapsulated by polymer(s) in the form of a hollow fibre. The proof of concept was achieved, using an aerogel (silica based, and in powder form) supplied by Insulgel High-Tech (Beijing) Co., Ltd, and a poly(ethylene-glycol) with a chain length of 900 kDa obtained from Sigma Aldrich. The hollow fibres were produced with electrospinning through a spinneret with two orifices/channels (coaxial); an inner and an outer orifice/channel. A PET solution was passed through the outer orifice/channel. The samples were spun with 6 cm collector distance. The needle voltage was 4.1 kV and the collector voltage was -4.6kV. The flow rate was 0.5 ml/hour for the shell solution. The needle was moved with a velocity of 400 mm/s, over the silicon wafer substrates in order to collect parallel-aligned fibres. The aerogel particles were simultaneously introduced (i.e. at the same time as the electrospinning process) into the lumen of the formed hollow fibre through the inner orifice/channel. In Figure 2, cross sections of aerogel containing hollow fibres are shown. As the aerogel particles used are not circular, the thickness of the wall varies between 0.1 pm and 3.2 pm. The thicknesses are measurable on the SEM images.

Energy-dispersive X-ray spectroscopy (EDX) was conducted to prove the presence of aerogel within the hollow fibre. The results are shown in Figure 3. The EDX analysis showed that the white are within the hollow fibre contained silicon, proving that the silicon-based aerogel is indeed positioned within the hollow polymer fibre.