WO2019070193A1

WO2019070193A1 - Method of manufacturing silica aerogel composite

Info

Publication number: WO2019070193A1
Application number: PCT/SG2017/050497
Authority: WO
Inventors: Mahesh Sachithanadam; Whye Tho NG
Original assignee: Bronx Creative & Design Centre Pte Ltd
Priority date: 2017-10-03
Filing date: 2017-10-03
Publication date: 2019-04-11

Abstract

Disclosed is a method of manufacturing a silica aerogel composite. The method comprises providing an aqueous solution comprising a water soluble polymeric binder and a surfactant, adding a silyl-modified silica aerogel to the aqueous solution, adding a water soluble crosslinking agent, and freeze-drying the mixture at a pre-determined pressure and temperature. The material is subsequently cured to form the composite. Also disclosed is a silica aerogel composite manufactured by the method described herein.

Description

METHOD OF MANUFACTURING SILICA AEROGEL COMPOSITE

Field of the Invention The present disclosure relates to a method of manufacturing silica aerogel composite. The present disclosure also relates to a silica aerogel composite manufactured by the presently disclosed method.

Background of the Invention

Aerogel is a special class of nano-porous solids with complex interconnectivity and branched structure in the nanometer to micrometer range, and can have large internal surface area. It can come with variety of forms, colors and shapes from monolithic to powders. Aerogels have very little solid component and almost made up of 99.8% of air which gives the product a "foam like" and ghostly appearance. Aerogels are synthesized via a sol-gel technique where the liquid in a gel is removed above its critical temperature and pressure and replaced with air, thus forming a skeletal solid (i.e. networked structure). At the critical parameters, there is no liquid-vapor phase, and thus no surface tension present on the gel. This allows the aerogel matrix to remain intact without large shrinkage. As such, the resultant aerogels are very light solid materials, have high porosity and are known to have good thermal insulation properties.

Silica aerogels are a type of aerogel which uses silica as a base material. However, exploitation of silica aerogels as a viable commercial product is inhibited by two factors: brittleness and volumetric shrinkage. The brittleness of silica aerogels makes their processing and handling extremely difficult. Volumetric shrinkage occurs during production of the aerogels and it becomes more apparent at elevated temperatures. These limitations hinder any form of post synthesis treatment of the aerogels, and as a result increase difficulty to mix with other materials of interest to provide adequate mechanical properties for structural, thermal and acoustics applications. Furthermore, the potential problem of having to compromise its ultra-low density due to possible infiltration of these additional elements into the nano-pores of the silica surface structure that can affect the physical and mechanical properties. Silica aerogel composites with organic and inorganic materials have been researched extensively over the last decade. These composites were prepared in the same way as monolithic aerogels except that the second constituent was added to the wet gel prior to the drying process. Thus, composites of aerogels with various polymers, metals and other inorganic compounds are synthesized to achieve the desired properties. These composites may exhibit high strength, flexibility and high modulus to weight ratio. However, the production of such composites is costly due to expensive equipment used and as well as long and tedious processes involved in the preparation of the aerogels. The incorporation of organic and inorganic materials may also not occur homogenously or occur only on the surface of the aerogel as this modification step is based on diffusion into a solid. Additionally, achieving homogeneity on a large scale production is difficult due to the agglomerative behavior of the polymers used. Further, one of the major hindrances in deploying binder treatment is the impact of this material on the ultra-low density and low thermal conductivity of the aerogels.

Commercial and business uses of aerogels have been limited. Firstly, commercial scale production of aerogels is limited by the high cost and lengthy time of production. Secondly, proper control of the reaction conditions is difficult when scaling up from a lab-scale synthesis to a factory scale synthesis. Thirdly, due to the larger size and thickness of the aerogel composite, application of uniform and proportional parametric conditions throughout the aerogel composite is difficult. This may result in an aerogel which is even more inconsistent, for example unevenness from volumetric shrinkage. Fourthly, there can be inhomogeneity in the distribution of the materials in the aerogel due to gravitational, phase separation and/or aggregation of materials. Fifthly, the incorporation of additional components make the potential issues faced as mentioned above even more pronounced. In spite of the above, there exists a need for commercially feasible methods of preparing non-combustible aerogel based insulation composites that can be applied as an integral system of an embedded wall insulation or fire rated acoustic doors in the building and construction company. There is also a need for production methods to be simple and easy to adopt, as well as being economically and commercially viable. There is also a need for commercial scale non-combustible aerogel based insulation products for wall insulation and acoustic door insulation.

As such, it is generally desirable to overcome or ameliorate one or more of the above described difficulties.

Summary of the Invention

In accordance with the present disclosure, there is provided a method of manufacturing a silica aerogel composite. The method comprises firstly providing an aqueous solution which comprises a water soluble polymeric binder and a surfactant. A silyl-modified silica aerogel is added to the aqueous solution to form a first mixture, after which a water soluble crosslinking agent is added to the first mixture to form a second mixture. The second mixture is freeze dried at a first pre-determined pressure and at a first pre-determined temperature sufficient for sublimation of ice to form a composite and then cured to form the composite.

In accordance with the present disclosure, there is also provided a silica aerogel composite manufactured by a method of manufacturing a silica aerogel composite as disclosed. The method comprises firstly providing an aqueous solution which comprises a water soluble polymeric binder and a surfactant. A silyl-modified silica aerogel is added to the aqueous solution to form a first mixture, after which a water soluble crosslinking agent is added to the first mixture to form a second mixture. The second mixture is freeze dried at a first pre-determined pressure and at a first pre- determined temperature sufficient for sublimation of ice to form a composite and then cured to form the composite.

In accordance with the present disclosure, there is also provided a silica aerogel composite comprising a silica aerogel, a surfactant, a polymer binder and a crosslinking agent. The silica aerogel composite has a homogenous distribution of all components throughout its cross-section. Further, the silica aerogel composite may be manufactured in a large size. The silica aerogel composite has at least a compressive strength of at least 2.5 MPa. Brief Description of the Drawings

Preferred embodiments of the invention are hereafter described, by way of non- limiting example only, with reference to the accompanying drawings, in which :

Figure 1 is a flowchart diagram of an example of the disclosed method.

Figure 2 is a flowchart diagram of an example of the manufacturing of silica aerogel composite.

Figure 3 illustrates a list of the machines used in the method of manufacturing as described herein.

Figure 4 illustrates a general protocol for manufacturing silica aerogel composite up to the step of molding the silica aerogel composite.

Figure 5 illustrates an example of freeze drying the silica aerogel composite.

Figure 6 illustrates an example of a composition usable in the method of manufacture as described herein.

Figure 7 illustrates aerogel composite properties obtainable following the method of manufacture as described herein. Figure 8 illustrates another example of a composition usable in the method of manufacture as described herein.

Figure 9 illustrates aerogel composite properties obtainable following the method of manufacture as described herein.

Figure 10 illustrates other examples of compositions usable in the method of manufacture as described herein.

Figure 11 illustrates aerogel composite density and thermal insulation properties obtainable following the method of manufacture as described herein. Figure 12 illustrates aerogel composite water sorption properties obtainable following the method of manufacture as described herein. Figure 13 illustrates the water sorption properties of silica aerogel composites with and without crosslinking agent.

Figure 14 illustrates aerogel composite acoustic absorption properties obtainable following the method of manufacture as described herein.

Detailed Description of Embodiments of the Invention

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, preferred methods and materials are described. For the purposes of the present invention, the following terms are defined below. As used herein, the term "aerogel" has the common meaning as would be understood by the person skilled in the art. Aerogel refers to a synthetic, porous ultralight material which is derived from a gel, in which the liquid component in the gel has been replaced with a gas or air. Aerogels are usually produced by extracting the liquid component of the gel through supercritical drying. This allows the liquid to be removed without causing the solid matrix to collapse from capillary action. As a result, aerogels have a porous solid matrix network that contains gas or air pockets, with the gas or air pockets taking up majority of space within the aerogel. More than 90% of the volume of aerogel is gas or air. Preferably, more than 95% of the volume of the aerogel is gas or air. Even more preferably, more than 98% of the volume of the aerogel is gas or air.

As used herein, "silica aerogel" refers to an aerogel which has silica as a base component. In the simplest form, silica is an oxide of silicon, and silica aerogel is an aerogel which comprises of silicon-oxygen bond (siloxane bridges) as the basis of its framework. Each silicon atom can form 4 bonds, of which all 4 bonds are siloxane bridges, 3 bonds are siloxane bridges, 2 bonds are siloxane bridges, 1 bond is siloxane bridge, or none of the bonds are siloxane bridges.

The term "silica aerogel composite" refers to a silica aerogel which in addition to the silica framework, comprises at least another part, element, substance, salt, molecule or compound. Such elements can be either of an organic or inorganic nature, can interact in a physical or chemical manner, or not interact with the silica framework. Silica aerogel composites can have physical or chemical characteristics that are substantially similar or different from its individual elements. For example, if thermal insulation is the desired characteristic of the aerogel, an aerogel composite may improve the brittleness of the aerogel and at the same time retain substantially similar or improve the thermal insulation properties as the aerogel.

The term "silyl modified" refers to any entity which is modified with one or more silyl group (-SiR, where R represents H, halogen, oxo/hydroxy, optionally substituted alkyl, optionally substituted cyano, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted alkoxy, optionally substituted alkenyloxy, optionally substituted alkynyloxy, optionally substituted amino, optionally substituted acyl, optionally substituted acylamino, optionally substituted acyloxy, optionally substituted oxyacyl, optionally substituted cycloalkyl, optionally substituted heterocyclyl, optionally substituted heterocyclylalkyl, optionally substituted aryl, optionally substituted arylalkyl, optionally substituted heteroaryl, optionally substituted heteroaryloxy, optionally substituted aryloxy, optionally substituted arylalkyloxy, optionally substituted cycloalkenyl, optionally substituted aminoacyloxy, optionally substituted oxyacylamino, optionally substituted oxyacyloxy, optionally substituted oxyacylimino, optionally substituted acylimino, optionally substituted acyliminoxy, optionally substituted oxyacylimino, optionally substituted thio, optionally substituted thioacyl, optionally substituted oxythioacyl, optionally substituted thioacyloxy, optionally substituted oxythioacyloxy, optionally substituted phosphorylamino, optionally substituted sulfinyl, optionally substituted sulfonyl, optionally substituted sulfinylamino, optionally substituted sulfonylamino, optionally substituted oxysulfinylamino, optionally substituted oxysulfonylamino, optionally substituted aminothioacyl, optionally substituted thioacylamino, optionally substituted aminosulfinyl, optionally substituted aminosulfonyl, or any protecting groups. In this specification "optionally substituted" is taken to mean that a group may or may not be further substituted or fused (so as to form a condensed polycyclic group) with one or more groups selected from hydroxyl, acyl, alkyl, alkoxy, alkenyl, alkenyloxy, alkynyl, alkynyloxy, amino, aminoacyl, thio, arylalkyl, arylalkoxy, aryl, aryloxy, carboxyl, acylamino, cyano, halogen, nitro, phosphono, sulfo, phosphorylamino, phosphinyl, heteroaryl, heteroarylalkyl, heteroaryloxy, heterocyclyl, heterocyclylalkyl, heterocyclyloxy, oxyacyl, oxime, oxime ether, hydrazone, oxyacylamino, oxysulfonylamino, aminoacyloxy, trihalomethyl, trialkylsilyl, pentafluoroethyl, trifluoromethoxy, difluoromethoxy, trifluoromethanethio, trifluoroethenyl, mono- and di-alkylamino, mono-and di-(substituted alkyl)amino, mono- and di-arylamino, mono- and di-heteroarylamino, mono- and di-heterocyclyl amino, and unsymmetric di- substituted amines having different substituents selected from alkyl, aryl, heteroaryl and heterocyclyl, and the like, and may also include a bond to a solid support material, (for example, substituted onto a polymer resin). For instance, an "optionally substituted amino" group may include amino acid and peptide residues.

The term "binder" refers to a substance that holds or draws other materials together to form a single entity. Binders can be organic or inorganic substances, and can be a liquid or a solid. Without wanting to be bound by theory, it is believed that binders draw materials together by either physical or chemical interactions or both. As used herein, "polymer binder" is hence a polymeric material which can act as a binder, i.e. capable of holding or drawing materials together. "Water soluble polymeric binder" thus refers to a polymer binder which is at least substantially soluble in an aqueous medium.

The term "surfactant" refers to a substance which tends to lower the surface tension of a liquid. Surfactants are usually, but not limited to, organic compounds that are amphiphilic. As such, the term "surfactants" include within its definition ionic surfactant, anionic surfactant, cationic surfactant, amphoteric surfactant or a mixture thereof. Examples of an anionic surfactant may include, but are not limited to, sodium dodecyl sulfate (SDS), sodium pentane sulfonate, dehydrocholic acid, glycolithocholic acid ethyl ester, ammonium lauryl sulfate and other alkyl sulfate salts, sodium laureth sulfate, alkyl benzene sulfonate, soaps, fatty acid salts or mixtures thereof. Examples of a cationic surfactant may include, but are not limited to, cetyl trimethylammonium bromide (CTAB), dodecylethyldimethylammonium bromide (D12EDMAB), didodecyl ammonium bromide (DMAB), cetylpyridinium chloride (CPC), polyethoxylated tallow amine (POEA), hexadecyltrimethylammonium p-toluenesulfonate, benzalkonium chloride (BAC), benzethonium chloride (BZT) and mixtures thereof. Examples of an amphoteric surfactant may include, but are not limited to, dodecyl betaine, sodium 2,3-dimercaptopropanesulfonate monohydrate, dodecyl dimethylamine oxide, cocamidopropyl betaine, 3-[N,N-dimethyl(3-palmitoylaminopropyl)ammonio]- propanesulfonate, coco ampho glycinate and mixtures thereof.

The term "crosslinking agent" refers to a substance that contains two or more ends capable of interacting with specific groups on other substance. This interaction can be by means of physical or chemical interaction. The crosslinking agent may form one or more interactions between itself and the other substance. In this sense, the crosslinking agent may assist in forming a three-dimensional network of interconnected substance(s).

The invention is based on the discovery that a method of manufacture is useful to obtain a silica aerogel composite on a large manufacturing scale, and which can overcome or ameliorate one or more of the above mentioned difficulties. Advantageously, the method of manufacture is useful for producing silica aerogel composite on a large scale with good homogeneity and consistency. Advantageously, the method of manufacture as disclosed herein has the benefit of a shorter processing time due to the addition of a crosslinking agent.

In a first aspect, various embodiments of the present invention refer to a method of manufacturing a silica aerogel composite. The term "manufacture", "manufacturing" refers to the make (or making) of something on a large scale. This can be either by manual labour or by machinery or by both. This is in contrast to a lab scale (or bench scale) production. Thus, in a manufacturing sense and in the context of the present invention, a silica aerogel composite of at least about 150 mm by about 150 mm is desired. Preferably, a silica aerogel composite of about 250 mm by 250 mm is desired. Preferably, a silica aerogel composite of about 300 mm by 300 mm is desired. Preferably, a silica aerogel composite of about 500 mm by 500 mm, or about 500 mm by about 1000 mm is desired. Even more preferably, a silica aerogel composite of about 700 mm by about 1400 mm is desired. The thickness of the mentioned silica aerogel composite may be in the range of about 5 mm to about 30 mm. The flowchart diagram shown in Figure 1 discloses an example of a method to manufacture silica aerogel composite. As mentioned, the manufacturing scale of the present invention should be distinguished from a lab scale production. The method of manufacturing a silica aerogel composite comprises firstly providing an aqueous solution. The aqueous solution can comprise a water soluble polymeric binder and a surfactant. Secondly, a silyl-modified silica aerogel is added to the aqueous solution to form a first mixture of polymer binder, surfactant and silica aerogel. A water soluble crosslinking agent is then added to the first mixture to form a second mixture of polymer binder, surfactant, silica aerogel and crosslinking agent. The second mixture is freeze dried at a first pre-determined pressure and at a first pre-determined temperature, sufficient for sublimation of ice to occur. Subsequently, the freeze dried silica aerogel composite is cured. The term "aqueous solution" used herein refers to a water based solvent or solvent system, and which comprises of mainly water. Such solvents can be either polar or non-polar, and/or either protic or aprotic. Solvent systems refer to combinations of solvents which resulting in a final single phase. Both 'solvents' and 'solvent systems' can include, and is not limited to, pentane, cyclopentane, hexane, cyclohexane, benzene, toluene, dioxane, chloroform, diethylether, dichloromethane, tetrahydrofuran, ethyl acetate, acetone, dimethylformamide, acetonitrile, dimethyl sulfoxide, nitromethane, propylene carbonate, formic acid, butanol, isopropanol, propanol, ethanol, methanol, acetic acid, ethylene glycol, diethylene glycol or water. Water based solvent or solvent systems can also include dissolved ions, salts and molecules such as amino acids, proteins, sugars and phospholipids. Such salts may be, but not limited to, sodium chloride, potassium chloride, ammonium acetate, magnesium acetate, magnesium chloride, magnesium sulfate, potassium acetate, potassium chloride, sodium acetate, sodium citrate, zinc chloride, HEPES sodium, calcium chloride, ferric nitrate, sodium bicarbonate, potassium phosphate and sodium phosphate. As such, biological fluids, physiological solutions and culture medium also fall within this definition. In most embodiments, the aqueous solution is water. In some embodiments, the aqueous solution is deionised water. In some embodiments, the aqueous solution is Millipore water. An aqueous solution is advantageously used in the present disclosure. In particular, water is used. Water can be evaporated or sublimed from an aqueous solution via heating through controlled pressure and temperature making it the most green, desirably non-hazardous and non-toxic solvent to be used. Since water does not penetrate affect the networked structure of the aerogels, the hydrophobic properties of the aerogels are not compromised.

The water soluble polymeric binder and surfactant may be added at the same time or in a sequential manner to the aqueous solution. For example, the water soluble polymeric binder may be added first, followed by the surfactant. Alternatively, the surfactant may be added first, followed by the polymeric binder. The polymeric binder may be partially, substantially or completely dissolved in the aqueous solution before the surfactant is added. Alternatively, the surfactant may be partially, substantially or completely dissolved in the aqueous solution before the polymeric binder is added.

Typically, manufacturing of silica aerogel composite without any crosslinking agent is difficult to control, and leads to product inconsistencies. In particular, it was found that silica aerogel composites without crosslinking agent have a tendency to be inhomogeneous throughout its thickness. For example, a cross-section analysis of the aerogel composite would show that the distribution of components in the aerogel composite to be unequal. Contrary to belief that allowing a crosslinking agent to react early in the synthesis would result in an unworkable mixture, it is noted that addition of a crosslinking agent early in the manufacturing, for example after forming the first mixture and before freeze drying, is crucial in the method of manufacturing silica aerogel composite. It is believed that this is caused by gravitational forces acting on the denser elements of the mixture and/or phase separation of the non-soluble elements from the aqueous mixture. The addition of crosslinking agent helped to increase the viscosity of the mixture which allows for a more homogenous silica aerogel composite final product. Furthermore, the volumetric shrinkage is also reduced, and in an embodiment, eliminated. The crosslinking agent also decreases the production time of the silica aerogel composite, which leads to cost savings and faster production.

Since freeze drying is a change in state from the solid phase to the gaseous phase, the material to be freeze dried must firstly be adequately frozen. The method of freezing and the final temperature of the frozen product can affect the ability to successfully freeze dry the material. For example, rapid cooling may result in small ice crystals, useful in preserving structures to be examined microscopically, but may result in a product that may be difficult to be freeze dried. However, slower cooling results in large ice crystals which produces less restrictive channels in the matrix during the drying process. Thus the conditions for freezing the second mixture contribute to the properties of the resultant silica aerogel composite.

Freeze drying involves the removal of water or other solvent from a frozen product by sublimation. Sublimation occurs when a frozen liquid goes directly to the gaseous state without passing through the liquid phase and it allows the preparation of a stable product that is easy to use and aesthetic in appearance. It also allows the gel framework to retain its structure and not collapse under tension. Several factors can affect the ability to freeze dry a frozen mixture. For sublimation of ice to occur, careful control of the two parameters, temperature and pressure, is required. Without wanting to be bound by theory, it is believed that the rate of sublimation of ice from a frozen product depends upon the difference in vapour pressure of the product compared to the vapour pressure of the ice collector. Molecules migrate from the higher pressure sample to a lower pressure area. Since vapour pressure is related to temperature, it is necessary that the product temperature is warmer than the cold trap (ice collector) temperature. It is important that the temperature at which a product is freeze dried is balanced between the temperature that maintains the frozen integrity of the product and the temperature that maximizes the vapour pressure of the product. This balance is key to optimum drying.

For example, in freeze drying of water, if the pressure is higher than 6.11 mbar, water passes through all three phases (solid, liquid, gas) when the temperature is lowered or raised. At 6.11 mbar the melting pressure curve, vapour pressure curve and sublimation pressure curve meet in one point called triple point. At this point, all three phases occur simultaneously. Below this point, i.e. when the pressure is lower than 6.11 mbar, the ice is converted directly from a solid to a gaseous phase on reaching the sublimation pressure curve. The simultaneous action of vacuum and temperature has two effects on the composites. Firstly, the vacuum facilitates a tight packing order of the aerogels thus minimizing void and pores of the foamed mixture. Secondly, the double action of temperature and vacuum sublimes the water content in the foamed mixture thus leaving only the binder to be networked around the silyl-modified aerogel. Thus physio-chemical binding is achieved. The significance of this will allow any water soluble polymer to be physically bounded aided by the chemical bonds of the surface groups. In some embodiments, the second mixture is frozen well below their eutectic or glass transition point, and the temperature is raised to just below this critical temperature and the second mixture is subjected to a reduced pressure. At this point the freeze drying process is started. A third component essential in a freeze drying system is energy. Energy is supplied in the form of heat. Almost ten times as much energy is required to sublime a gram of water from the frozen to the gaseous state as is required to freeze a gram of water. Therefore, with all other conditions being adequate, heat must be applied to the product to encourage the removal of water in the form of vapour from the frozen product. The heat must be very carefully controlled, as applying more heat than the evaporative cooling in the system can remove warms the product above its eutectic or collapse temperature. Heat can be applied by several means. One method is to apply heat directly through a thermal conductor shelf such as is used in tray drying. Another method is to use ambient heat as in manifold drying. It is noteworthy that process parameters, such as minimum pressure, dew point and critical collapse temperature are essential to control the quality of the finished product. While these factors were independently discussed, it would be obvious to the skilled person that these parameters interact in a dynamic system, and it is this delicate balance between these factors that results in a properly freeze dried product with the desired properties.

The first pre-determined pressure and temperature is thus carefully chosen, not only to allow for the sublimation of ice to gas, but also to ensure a good end product with good consistency.

In some embodiments, the first pre-determined temperature is lower than about -5 °C, about -10 °C, about -15 °C, about -20 °C, about -25 °C, about -30 °C, about -35 °C, about -40 °C, about -45 °C, or about -50 °C. In some embodiments, the first predetermined pressure is in a range of about 100 Pa to about 400 Pa.

It is also found that a curing step can advantageously ensure that the silica aerogel composite is substantially or completely dehydrated. This ensures that the final product's strength and stability is not compromised. Additionally, the curing step also acts to ensure that the crosslinking agent is substantially or completely reacted with the elements.

The temperature and duration of the cure depends on the type and amount of crosslinking agent used, as well as the size and thickness of the silica aerogel composite. In some embodiments, the temperature of the cure is about 40 °C, about 45 °C, about 50 °C, about 55 °C, about 60 °C, about 65 °C, about 70 °C, about 75 °C, about 80 °C, about 85 °C, about 90 °C, about 95 °C, or about 100 °C. In some embodiments, the duration of the cure is about 1 h, about 1.5 h, about 2 h, about 2.5 h, about 3 h, about 3.5 h, about 4 h, about 4.5 h, about 5 h, about 6 h, about 8 h, about 10 h, about 12 h, or about 24 h.

In some embodiments, the step of providing the aqueous solution comprises a mixing step and an agitation step. In the mixing step, the materials or elements are combined or put together in the aqueous solution. The mixing step can be, but not limited to, stirring, beating, blending, creaming, whipping, folding, homogenising or sonicating. The energy required to combine the elements into the aqueous solution depends on the solubility of the elements and their interaction. In cases where the elements are easily solubilized, less energy and time would be needed. However, not all the elements need to be completely dissolved to proceed to the next agitation step. The agitation step introduces air bubbles into the aqueous solution. In some embodiments, the agitation step froths the aqueous solution. In this step, the aqueous solution is mixed vigorously and/or at a higher speed or energy such that air bubbles may be introduced. It should be noted that air bubbles may also be added to the aqueous solution via other means, such as via a tubing that bubbles external air into the aqueous solution. The agitation of the aqueous solution comprising binder and surfactant may cause the aqueous solution to froth or foam. As used herein, "froth" refers to an intimate mixture of gas and liquid, where the gas is present as bubbles and dispersed throughout the liquid.

In some embodiments, the step of providing the aqueous solution comprises a mixing step, wherein sonication is used in the mixing step. Sonication is the act of applying sound energy to agitate particles in a sample, which results in dispersion of the particles. Without wanting to be bound by theory, it is believed that upon irradiation with high intensity sound or ultrasound, acoustic cavitation usually occurs. Cavitation (the formation, growth, and implosive collapse of bubbles irradiated with sound) is the impetus for sono-chemistry. Bubble collapse in liquids produces enormous amounts of energy from the conversion of kinetic energy of the liquid motion into heating the contents of the bubble. The compression of the bubbles during cavitation is more rapid than thermal transport, which generates a short-lived localized hot-spot. These bubbles can have temperatures around 5000 K, pressures of roughly 1000 atm, and heating and cooling rates above 1010 K/s. These cavitations can create extreme physical and chemical conditions in otherwise cold liquids. With liquids containing solids, similar phenomena may occur with exposure to ultrasound. Once cavitation occurs near an extended solid surface, cavity collapse is non-spherical and drives high-speed jets of liquid to the surface. These jets and associated shock waves can damage the now highly heated surface. Liquid-powder suspensions produce high velocity inter-particle collisions. These collisions can change the surface morphology, composition, and reactivity. These physical events can help in improving the solubilisation of the polymer binder and surfactant.

In some embodiments, after the mixing step, the aqueous solution undergoes high speed mixing in the agitation step. The shear forces exerted on the solution by the mixer blades and the induction of surrounding air into solution promotes aeration and froth the solution into a slurry foam. It is desirable that the speed at which the mixer blades be controlled so as produce a froth with consistent air bubbles sizes. It is also desirable that the air pockets generated in the foam is stabilized and that the pressure within the foam does not collapse rapidly. As such, it is desirable that the speed of agitation be maintain to be greater than about 1500 rpm but lesser than 5000 rpm. The speed of agitation may be about 1500 rpm, about 1700 rpm, about 1900 rpm, about 2100 rpm, about 2300 rpm, about 2500 rpm, about 2700 rpm, about 2900 rpm, about 3100 rpm, about 3300 rpm, about 3500 rpm, about 3700 rpm, about 3900 rpm, about 4100 rpm, about 4300 rpm, about 4500 rpm, about 4700 rpm, or about 5000 rpm.

In some embodiments, the step of providing the aqueous solution comprises a mixing step and an agitation step, wherein the agitation step comprises of homogenising the aqueous solution. The mixing step ensures that the polymeric binder and the surfactant are uniformly dispersed in the aqueous solution. In this sense, the surfactant may help in the dispersion of the water soluble polymeric binder. As such, the water soluble polymeric binder may be partially, substantially or completed dissolved in the aqueous solution. The agitation step introduces air bubbles into the aqueous solution, and froths the aqueous solution. Homogenization, due to its shearing action on the liquid, may advantageously increases the volume of slurry up to about 300% as a result of the air pockets formed . This allows for easier mixing of the silyl-modified aerogel in the subsequent process.

Accordingly, in some embodiments, the step of providing the aqueous solution comprises a mixing step and an agitation step, wherein the mixing step comprises sonication and the agitation step comprises of homogenisation.

The aqueous solution comprising the mixing and agitation step can be performed at any workable temperature. For example, while the aqueous solution is most often formed mixed and agitated at an ambient temperature, a skilled person would know that any temperature would work as long as the aqueous solution does not totally solidify into ice or completely evaporate as a gas. Additionally, to assist in the mixing and agitation, the temperature may be varied in any way.

In some embodiments, the method of manufacturing silica aerogel composite further comprises a secondary drying step under a second pre-determined pressure and at a second pre-determined temperature and a coating step wherein the silica aerogel composite is coated with a hydrophobic material.

The secondary drying step may occur some time after the first freeze drying step had occurred. For example, after the first freeze drying, the product may be removed from the freeze drying machine and stored for any amount of time before the secondary drying step is performed. Alternatively, the secondary drying step may be a secondary freeze drying step. In this sense, the secondary drying step may occur sequentially and immediately after the first freeze drying step. The secondary freeze drying step may occur without removing the product from the freeze dryer. After the first freeze drying is completed and all ice has sublimed, the inventors have found that bound moisture is still present in the silica aerogel composite. While the product appears dry, it was found that the residual moisture content may be as high as 7-8%. Continued drying may be necessary at higher temperatures than the first pre-determined temperature to reduce the residual moisture content to optimum values. Without wanting to be bound by theory, it is believed that the process of isothermal desorption allows the bound water to be desorbed from the product. Secondary drying may be performed at a temperature higher than ambient but compatible with the sensitivity of the product. The secondary pre-determined pressure may remain the same as the first pre-determined pressure or may be lower than the first pre-determined pressure. Secondary drying may be carried out for approximately 1/3 to 1/2 the time required for primary freeze drying. Advantageously, this step improves the properties of the final aerogel composite, especially in high humidity environments. The second pre-determined temperature may be higher than the first pre-determined temperature. In other words, the first pre-determined temperature is lower than the second pre-determined temperature. In some embodiments, the second predetermined temperature is more than about 0 °C, about 10 °C, about 20 °C, about 30 °C, about 40 °C, about 50 °C, about 60 °C, about 70 °C, about 80 °C, or about 90 °C. The second pre-determined pressure may be lower than the first pre-determined pressure. In other words, the first pre-determined pressure is higher than the second pre-determined pressure. In some embodiments, the second pre-determined pressure is less than about 100 Pa, about 90 Pa, about 80 Pa, about 70 Pa, about 60 Pa, about 50 Pa, about 40 Pa, about 30 Pa, about 20 Pa, or about 10 Pa.

As formed silica aerogel composite is hydrophilic as the polymer binders contain hydrophilic functional groups and can absorb water. If a hydrophobic aerogel is desired, a further coating step may be performed. The coating step is performed by coating the silica aerogel composite with a hydrophobic material, for example a silane coupling agent. The silane coupling agent will react with the hydrophilic functional groups and render then hydrophobic, and thus turn the aerogel hydrophobic. Specifically, the coating process involves heating the silane coupling agent to vaporize the silanes, allowing the silanes to diffuse into the air spaces in the silica aerogel composite and react with the hydrophilic functional groups of the polymer binders to form the hydrophobic coating. The duration and temperature of coating depends on the desired degree of hydrophobicity and the type of siloxane used. In some embodiments, the duration of the coating step is about 1 h, about 1.5 h, about 2 h, about 2.5 h, about 3 h, about 3.5 h, about 4 h, about 4.5 h, about 5 h, about 6 h, about 8 h, about 10 h, about 12 h, or about 24 h. In some embodiments, the temperature of the coating step is about 40 °C, about 45 °C, about 50 °C, about 55 °C, about 60 °C, about 65 °C, about 70 °C, about 75 °C, about 80 °C, about 85 °C, about 90 °C, about 95 °C, about 100 °C, about 105 °C, about 110 °C, about 115 °C, or about 120 °C. The hydrophobic coating imparts a hydrophobic nature to the aerogel composite, thus giving the aerogel composite a better shelf-life. This is especially so in a high humidity environment. The hydrophobic coating may also further enhance the water repellence or water resistance of the aerogel composite. Accordingly, the degree of coating can be controlled by varying the amount of hydrophobic material used. The degree of coating can be tested using a water sorption test or measuring the contact angles of a water/oil droplet.

The hydrophobic material can be any hydrophobic material that interacts with silica aerogel composite. Such interaction may be chemical or physical. For example, silane coupling agent may be used. Examples of silane coupling agents are, but not limited to, methyltrichlorosilane, methyltrimethoxysilane, methyltriethoxysilane, methyltri-n- propoxysilane, methyltris(methoxyethoxy)silane, methyltriacetoxysilane, tris(dimethylamino)methylsilane, tris(cyclohexylamino)methylsilane, methyltris(methylethylketoximino)silane, trimethylsiloxytrichlorosilane, dimethyltetramethoxydisiloxane, dimethyldichlorosilane, trimethylchlorosilane, dimethyldimethoxysilane, trimethylmethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane, trimethyl-n-propoxysilane, methoxypropoxytrimethylsilane, dimethyldiacetoxysilane, acetoxytrimethylsilane, bis(dimethylamino)dimethylsilane, dimethylaminotrimethylsilane, bis(diethylamino)dimethylsilane, diethylaminotrimethylsilane, hexamethylcyclotrisilazane, hexamethyldisilazane, dichlorotetramethyldisiloxane, tetramethyldiethoxydisiloxane, pentamethylacetoxydisiloxane, dichlorohexamethyltrisiloxane, bis(trimethylsiloxy)methylmethoxysilane, 1,5-diethoxyhexamethyltrisiloxane, bis(trimethylsiloxy)dichlorosilane, chlorine terminated polydimethylsiloxane, methoxy terminated polydimethylsiloxane, ethoxy terminated polydimethylsiloxane, dimethylamine terminated polydimethylsiloxane, silanol terminated polydimethylsiloxane, dimethylethoxysilane, [tris(trimethylsiloxy)silylethyl]dimethylchlorosilane, ethyltrichlorosilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriacetoxysilane, propyltrichlorosilane, propyltrimethoxysilane, propyltriethoxysilane, n-butyltrichlorosilane, n- butyltrimethoxysilane, pentyltrichlorosilane, pentyltriethoxysilane, hexyltrichlorosilane, hexyltrimethoxysilane, hexyltriethoxysilane, heptyltrichlorosilane, octyltrichlorosilane, octyltrimethoxysilane, octyltriethoxysilane, decyltrichlorosilane, decyltriethoxysilane, undecyltrichlorosilane, dodecyltrichlorosilane, dodecyltriethoxysilane, tetradecyltrichlorosilane, hexadecyltrichlorosilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, octadecyltrichlorosilane, octadecyltrimethoxysilane, octadecyltriethoxysilane, Siliclad®/Glassclad®18, eicosyltrichlorosilane, docosyltrichlorosilane, triacontyltrichlorosilane, ethylmethyldichlorosilane, ethyldimethylchlorosilane, propylmethyldichlorosilane, propyldimethylchlorosilane, propylmethyldimethoxysilane, propyldimethylmethoxysilane, dipropyltetramethyldisilazane, n-butyldimethylchlorosilane, n- butyldimethyl(dimethylamino)silane, hexylmethyldichlorosilane, heptylmethyldichlorosilane, octylmethyldichlorosilane, octyldimethylchlorosilane, octyldi methyl methoxysi lane, octylmethyldiethoxysilane, octyldimethyl(dimethylamino)silane, dioctyltetramethyldisilazane, decylmethyldichlorosilane, decyldimethylchlorosilane, dodecylmethyldichlorosilane, dodecyldimethylchlorosilane, dodecylmethyldiethoxysilane, octadecylmethyldichlorosilane, octadecyldimethylchlorosilane, octadecylmethyldimethoxysilane, octadecyldimethylmethoxysilane, octadecylmethyldiethoxysilane, octadecyldimethyl(dimethylamino)silane, docosylmethyldichlorosilane, triacontyldimethylchlorosilane, isobutyltrichlorosilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, t-butyltrichlorosilane, cyclopentyltrichlorosilane, cyclopentyltrimethoxysilane, (3,3- dimethylbutyl)trichlorosilane, thexyltrichlorosilane, cyclohexyltrichlorosilane, cyclohexyltrimethoxysilane, bicycloheptyltrichlorosilane, (cyclohexylmethyl)trichlorosilane, isooctyltrichlorosilane, isooctyltrimethoxysilane, cyclooctyltrichlorosilane, adamantylethyltrichlorosilane, 7- (trichlorosilylmethyl)pentadecane, (di-n-octylmethylsilyl)ethyltrichlorosilane, 13- (trichlorosilylmethyl)heptacosane, isopropylmethyldichlorosilane, isopropyldimethylchlorosilane, isobutyldimethylchlorosilane, isobutylmethyldimethoxysilane, t-butylmethyldichlorosilane, t- butyldimethylchlorosilane, (3,3-dimethylbutyl)dimethylchlorosilane, thexyldimethylchlorosilane, cyclohexylmethyldichlorosilane, cyclohexyldimethylchlorosilane, cyclohexylmethyldimethoxysilane, bicycloheptyldimethylchlorosilane, isooctyldimethylchlorosilane, (dimethylchlorosilyl)methylpinane, (di-n-octylmethylsilyl)ethyldimethylchlorosilane, l l-(chlorodimethylsilylmethyl)tricosane, 13-(chlorodimethylsilylmethyl)heptacosane, phenyltrichlorosilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltriacetoxysilane, phenyltris(methylethylketoximino)silane, benzyltrichlorosilane, benzyltriethoxysilane, 1-phenyl-l-trichlorosilylbutane, phenethyltrichlorosilane, phenethyltrimethoxysilane, 4-phenylbutyltrichlorosilane, phenoxypropyltrichlorosilane, phenoxyundecyltrichlorosilane, phenylhexyltrichlorosilane, p-tolyltrichlorosilane, p- tolyltrimethoxysilane, ethylphenethyltrimethoxysilane, p-(t- butyl)phenethyltrichlorosilane, 3-(p-methoxyphenyl)propyltrichlorosilane, 1- napthyltrimethoxysilane, (l-napthylmethyl)trichlorosilane, phenylmethyldichlorosilane, phenyldimethylchlorosilane, phenylmethyldimethoxysilane, phenylmethyldiethoxysilane, phenyldimethylethoxysilane, phenylmethylbis(dimethylamino)silane, benzyldimethylchlorosilane, 1-phenyl-l- methyldichlorosilylbutane, phenethylmethyldichlorosilane, phenethyldimethylchlorosilane, phenethyldimethyl(dimethylamino)silane, (3- phenylpropyl)methyldichlorosilane, (3-phenylpropyl)dimethylchlorosilane, 4- phenylbutylmethyldichlorosilane, 4-phenylbutyldimethylchlorosilane, phenoxypropylmethyldichlorosilane, phenoxypropyldimethylchlorosilane, p- tolylmethydichlorosilane, p-tolyldimethylchlorosilane, (p- methylphenethyl)methyldichlorosilane, p-(t-butyl)phenethyldimethylchlorosilane, 3- (p-methoxyphenyl)propylmethyldichlorosilane, m-phenoxyphenyldimethylchlorosilane, p-nonylphenoxypropyldimethylchlorosilane, (3,3,3-trifluoropropyl)trichlorosilane, (3,3,3-trifluoropropyl)trimethoxysilane, nonafluorohexyltrichlorosilane, nonafluorohexyltrimethoxysilane, nonafluorohexyltriethoxysilane, nonafluorohexyltris(dimethylamino)silane, (tridecafluoro- 1,1,2,2- tetrahydrooctyl)trichlorosilane, (tridecafluoro- 1,1,2,2- tetrahydrooctyl)trimethoxysilane, (tridecafluoro- 1,1,2,2- tetrahydrooctyl)triethoxysilane, (heptadecafluoro- 1,1,2,2- tetrahydrodecyl)trichlorosilane, (heptadecafluoro- 1,1,2,2- tetrahydrodecyl)trimethoxysilane, (heptadecafluoro-1, 1,2,2- tetrahydrodecyl)triethoxysilane diethyldichlorosilane, diethyldiethoxysilane, diisopropyldichlorosilane, diisopropyldimethoxysilane, di-n-butyldichlorosilane, di-n- butyldimethoxysilane, diisobutyldimethoxysilane, diisobutyldiethoxysilane, isobutylisopropyldimethoxysilane, dicyclopentyldichlorosilane, dicyclopentyldimethoxysilane, di-n-hexyldichlorosilane, dicyclohexyldichlorosilane, di- n-octyldichlorosilane, (3,3,3-trifluoropropyl)methyldichlorosilane, (3,3,3- trifluoropropyl)dimethylchlorosilane, (3,3,3-trifluoropropyl)methyldimethoxysilane, bis(trifluoropropyl)tetramethyldisilazane, nonafluorohexylmethyldichlorosilane, nonafluorohexyldimethylchlorosilane, (tridecafluoro- 1,1,2,2- tetrahydrooctyl)methyldichlorosilane, (tridecafluoro-1, 1,2,2- tetrahydrooctyl)dimethylchlorosilane, (heptadecafluoro- 1,1,2,2- tetrahydrodecyl)methyldichlorosilane, (heptadecafluoro- 1,1,2,2- tetrahydrodecyl)dimethylchlorosilane, diethoxydimethylsilane, diethoxydiphenylsilane, diethoxy(methyl)phenylsilane, dimethyldiphenylsilane, dimethoxy-methyl(3,3,3- trifluoropropyl)silane, ethoxytrimethylsilane, ethoxydimethylphenylsilane, isobutyl(trimethyl)silane, methoxy(dimethyl)octadecylsilane, methoxy(dimethyl)octylsilane, methoxytrimethylsilane, triethoxyphenylsilane, trimethoxyphenylsilane, trimethoxy(3,3,3-trifluoropropyl)silane, or the like. In some embodiments, the hydrophobic material is methyltrimethoxysilane. In some embodiments, the hydrophobic material is propyltrimethoxysilane. In an embodiment, the hydrophobic material is a mixture of silane coupling agents, for example methyltrimethoxysilane and propyltrimethoxysilane.

Alternatively, the coating may be a coating which adheres to the surface of the aerogel composite by physical interactions. For example, the coating may be spray painted or brush painted onto the surface of the aerogel composite with a lacquer, varnish, oil, wax, or the likes. Such methods of coatings are known in the art and accordingly is not limited to the disclosure herein. In some embodiments, the second mixture is shaped in a mold before freeze drying. The mold may be of any desired shape or size. Individual molds may be used to cast silica aerogel composites as panels. Alternatively, a mold may be used to cast the silica aerogel composite which is then subsequently cut into a desired shape and size. For example, the mold may be in one dimension about 150 mm, about 200 mm, about 250 mm, about 300 mm, about 350 mm, about 400 mm, about 450 mm, about 500 mm, about 600 mm, about 700 mm, about 800 mm, about 900 mm, about 1000 mm, about 1200 mm, about 1400 mm, about 1600 mm, about 1800 mm, about 2000 mm, about 2500 mm, about 3000 mm, about 4000 mm, about 5000 mm, about 7500 mm or about 10000 mm. In an embodiment, the size of the mold is about 600 mm by about 2500 mm. In some embodiments, the aqueous solution further comprises a plasticising agent, an inorganic filler, and a strengthening agent. Plasticising agent is an additive that may increase the plasticity or viscosity of a material, and may improve the particle density and tight packing of the silica aerogel composite to improve the thermal insulation and acoustic insulation. Plasticising agent may be added to improve the hydrophobicity of the matrix as well as the composite before the coating process. The plasticising agent may be selected from a group comprising of, but not limited to, glycerol, sorbitol, malic acid, or a combination thereof.

Strengthening agent is an additive which may improve the mechanical property of a material. The strengthening agent may be selected from a group comprising of, but not limited to, fumed silica, mineral fiber, calcium silicate, or a combination thereof. In some embodiments, the strengthening agent is fumed silica. In some embodiments, the strengthening agent is mineral fiber. In some embodiments, the strengthening agent is calcium silicate.

Inorganic filler is an additive to enhance the property of a material. The addition of inorganic filler may enhance the fire resistance, fire retardant properties and/or acoustic insulation properties of the silica aerogel composite. The inorganic filler may be selected from a group comprising of, but not limited to, amorphous silica, ceramics, quartz, zirconium dioxide, iron (III) oxide, titanium oxide, barium sulphate, or a combination thereof. Inorganic fillers may be used to improve or impart fire resistant property to the silica aerogel composite. Examples of fire resistant inorganic fillers are, but not limited to, ceramics, zirconium dioxide, iron (III) oxide, titanium oxide, fumed silica and borates of various types, for example zinc. Inorganic fillers may be used to improve or impart fire retardant property to the silica aerogel composite. Examples of fire retardant inorganic fillers are, but not limited to, zirconia fibers, ceramic fibers and mineral fibers. Inorganic fillers may be used to improve or impart acoustic insulation property to the silica aerogel composite. Examples of acoustic insulation inorganic fillers are, but not limited to, calcium silicate and barium silicate. In some embodiments, the inorganic filler is titanium oxide. In some embodiments, the inorganic filler is barium sulphate. As mentioned above, the polymeric binder may be used to hold or draw materials together. The water soluble polymeric binder may include at least one of -COOH or - NH₂ functional groups along the chain of the polymer. The water soluble polymeric binder may be selected from a group comprising of, but not limited to, gelatin, polyacrylamide, polyvinyl pyrrolidone, polymethacrylamide, polyvinylalcohol, or a combination thereof. In some embodiments, the polymeric binder is gelatin. Advantageously, gelatin is a bio-degradable polymer, and is non-toxic and non- hazardous. It is soluble in water and foams well. As gelatin has both polar and non- polar side chains and numerous amine and carboxyl sites, these attributes render it a good binding agent for silica aerogels, where the amine and carboxyl sites offer reactive sites for cross-linking, functionalization, and even grafting of hydrophobic materials onto its peptide chain. It is also versatile enough to be synthesized as polymer blends. The surfactant is added to induce and/or increase froth or foam in the aqueous solution. In various embodiments, the surfactant is an ionic surfactant selected from the group consisting of an anionic carboxylate, a cationic quaternary ammonium salt, an amphoteric sulfonate, an amphoteric carboxylate, an amphoteric phosphate, and combinations thereof. The surfactant may be selected from a group comprising of, but not limited to, sodium dodecyl sulfate, cetyl trimethylammonium bromide, perfluorononanoate, lecithin, or a combination thereof. In some embodiments, the surfactant is sodium dodecyl sulfate.

In order to prepare the silyl-modified silica aerogel, a skilled person may choose to start from a commercially available silica aerogel material. Such silica aerogel may be in any form suitable for use to make an aerogel composite. For example the silica aerogel may be in a granule, particle, needle, powder or micronized form. Such materials are, for example, obtainable from Cabot (e.g. ENOVA or LUMIRA aerogel) and Dow Corning (e.g. VM-2270). The silica aerogel may be of any suitable shape or size. Selection of the size and shape of the silica aerogel is important. If the size is too large, the silica aerogel may not disperse well in solution. The silica aerogel may also tend to sediment if the size is too large and thus heavier. The size of the aerogel may also affect the physical properties of the resultant silica aerogel composite. As used herein, silica aerogel may have a size in the range of about 0.05 cm to about 0.5 cm. In an embodiment, the silica aerogel have a size about 0.05 cm, about 0.1 cm, about 0.15 cm, about 0.2 cm, about 0.25 cm, about 0.3 cm, about 0.35 cm, about 0.4 cm, about 0.45 cm, about 0.5 cm, or a combination thereof. Accordingly, size of the silyl- modified silica aerogel may be in the range of about 0.05 cm to about 0.5 cm, such as about 0.1 cm to about 0.5 cm, about 0.2 cm to about 0.5 cm, about 0.3 cm to about 0.5 cm, about 0.05 cm to about 0.4 cm, about 0.05 cm to about 0.3 cm, about 0.1 cm to about 0.4 cm, about 0.1 cm to about 0.3 cm, or about 0.12 cm to about 0.26 cm. The person skilled in the art would understand that the silica aerogel sizes as mentioned indicates the average/mean size of the material and is as distributed over a Gaussian distribution.

The as bought silica aerogel may be hydrophobic due to the chemically inert trimethylsilyl or triethoxysilyl terminal groups present in the coating applied on the silica aerogel surface. To facilitate interaction with the rest of the composite materials, as bought silica aerogel may be modified by silyl groups. Such modification can increase the hydrophilicity or reduce the hydrophobicity of the silica aerogel and allows for the easier dispersion of these materials in solution. The modification can also provides a reactive site for chemical or physical interaction to occur. The silyl- modified silica aerogel may include one or more -SiR functional groups as defined herein. For example, the silyl-modified silica aerogel may include one or more of - Si(CH₃), -Si(C₂H₅), -Si(C₃H₇), to name only a few. In various embodiments, R is methyl, methoxy or ethoxy. For example, the silyl-modified silica aerogel may contain Si(CH₃) or Si(QC₂H₅) terminal groups. In other examples, the silyl-modified silica aerogel is modified to have one or more hydrophilic groups. For example, the silyl- modified aerogel may contain one or more -SiR groups, wherein R is selected from optionally substituted Ci-C₅ alkyl, optionally substituted cyano, optionally substituted oxyacyl, optionally substituted acyloxy, optionally substituted amino, optionally substituted aminoacyl, optionally substituted acylamino, or optionally substituted epoxy. Preferably, the silica aerogel is modified by using trimethylsilyl iodide. Such methods are known in the art and will not be herein described.

Further surface functionalization of the silica aerogel may be performed. This may be done with using amphiphilic polymers, for example pluronics, to increase the wettability or ammonium fluoride at elevated temperature. For example, a physisorption process using amphiphilic polymers can be used to functionalise silica aerogel or further functionalise silyl-modified silica aerogel. A water-soluble polymer binder may then subsequently be able to bind with the surface functionalised silica aerogels. Water-soluble polymer binders are hydrophilic and bonding with the silica aerogel is achieved through hydrogen bonds and weak Van Der Waals' interaction between the material and water. Inorganic fillers may further be added during homogenization to achieve non-combustibility. Strengthening agents may also be added. Thereafter hydrophobic plasticizers may be added to improve the hydrophobicity of the matrix as well as the composite before the coating process.

Chemical crosslinking may be used to promote the formation of a three-dimensional network of the aerogel composite. For example, carbonyls groups may be used to react with hydrazide, hydroxyl, amine groups or other functional groups. The rate of crosslinking is dependent on the reactivity of the groups and the temperature of the solution, among other parameters. Thus, careful control of these parameters is essential to allow for ease of handling and processing of the silica aerogel composite. For example, at a temperature of 25 °C, addition of about 1.8 wt% (final composite weight) of crosslinking agent would provide sufficient time for mixing and laying the mixture into a mold without the mixture solidifying too quickly. Accordingly, in some embodiments, the crosslinking process is initiated upon addition of the crosslinking agent. In another embodiment, the crosslinking process is initiated after all the crosslinking agent is added but before the freeze dry step. In another embodiment, the crosslinking process is initiated some time during the addition of the crosslinking agent. In another embodiment, the crosslinking process is initiated some time after the addition of the crosslinking agent. Preferably, the crosslinking process is initiated early in the manufacturing process, after formation of the first mixture but before freeze drying. The crosslinking agent may be selected from a group comprising of, but not limited to, glutaraldehyde, melamine, formaldehyde, mucochloric acid, mucobromic acid, polyphenols or a combination thereof. In some embodiments, the crosslinking agent is glutaraldehyde. The interplay between the combination of the water soluble polymeric binder, surfactant, crosslinking agent, plasticising agent, strengthening agent, inorganic filler, and aerogel serves to alter the property of a silica aerogel composite. In an embodiment, the brittleness of the silica aerogel composite is altered. In another embodiment, the thermal conductivity of the silica aerogel composite is altered . In another embodiment, the unequal volumetric shrinkage of the silica aerogel composite is altered. In another embodiment, the flexibility of the silica aerogel composite is altered. In another embodiment, the hydrophilicity of the silica aerogel composite is altered. In another embodiment, the hydrophobicity of the silica aerogel composite is altered. In another embodiment, the flexural strength of the silica aerogel composite is altered. In another embodiment, the compressive strength of the silica aerogel composite is altered. In another embodiment, the compressive modulus of the silica aerogel composite is altered. In another embodiment, the compressive strength of the silica aerogel composite is altered . In another embodiment, the fire resistance property of the silica aerogel composite is altered. In another embodiment, the fire- retardant property of the silica aerogel composite is altered. In another embodiment, the acoustic absorption of the silica aerogel composite is altered. In another embodiment, the thermal insulation property (lambda value) of the silica aerogel composite is altered. In another embodiment, the water affinity of the silica aerogel composite is altered. In another embodiment, the stability of the silica aerogel composite in water is altered.

The amount of water soluble polymeric binder may be added in a range of about 5 wt% to about 40 wt% of the final composite weight. For example, the amount of water soluble polymeric binder may be in a range of about 5 wt% to about 30 wt%, about 10 wt% to about 30 wt%, or about 10 wt% to about 20 wt%.

The amount of surfactant may be added in a range of about 0.1 wt% to about 1 wt% of the final composite weight. For example, the amount of surfactant may be in a range of about 0.1 wt% to about 0.9 wt%, about 0.1 wt% to about 0.8 wt%, about 0.1 wt% to about 0.7 wt%, about 0.1 wt% to about 0.6 wt%, about 0.1 wt% to about 0.5 wt%, about 0.1 wt% to about 0.4 wt%, about 0.1 wt% to about 0.3 wt%, or about 0.1 wt% to about 0.2 wt%.

The amount of silyl modified silica aerogel may be added in a range of about 20 wt% to about 90 wt% of the final composite weight. For example, the amount of silyl modified silica aerogel may be in a range of about 30 wt% to about 90 wt%, about 40 wt% to about 90 wt%, about 50 wt% to about 90 wt%, about 30 wt% to about 80 wt%, about 40 wt% to about 80 wt%, about 50 wt% to about 80 wt%, about 60 wt% to about 80 wt%, about 70 wt% to about 80 wt%, or about 70 wt% to about 90 wt%. The amount of crosslinking agent may be added in a range of about 0.5 wt% to about 10 wt% of the final composite weight. For example, the amount of crosslinking agent may be in a range of about 0.5 wt% to about 9 wt%, 0.5 wt% to about 8 wt%, 0.5 wt% to about 7 wt%, 0.5 wt% to about 6 wt%, 0.5 wt% to about 5 wt%, 1 wt% to about 5 wt%, 1.5 wt% to about 5 wt%, 2 wt% to about 5 wt%, 2.5 wt% to about 5 wt%, 3 wt% to about 5 wt%, or 3.5 wt% to about 5 wt%. The amount of crosslinking agent may be added at about 0.5 wt%, about 1.0 wt%, about 1.5 wt%, about 1.8 wt%, about 2.0 wt%, about 2.5 wt%, about 3.0 wt%, about 3.5 wt%, about 4.0 wt%, about 4.5 wt% or about 5.0 wt%.

The amount of inorganic filler may be added in a range of about 0.1 wt% to about 10 wt% of the final composite weight. For example, the inorganic filler may be in a range of about 0.1 wt% to about 10 wt%, 0.5 wt% to about 10 wt%, 1 wt% to about 10 wt%, 1.5 wt% to about 10 wt%, 2 wt% to about 10 wt%, 2.5 wt% to about 10 wt%, 3 wt% to about 10 wt%, 3.5 wt% to about 10 wt%, 4 wt% to about 10 wt%, 5 wt% to about 10 wt%, 6 wt% to about 10 wt%, 6 wt% to about 9.5 wt%, or 6 wt% to about 9 wt%.

The amount of strengthening agent may be added in a range of about 10 wt% to about 70 wt% of the final composite weight. For example, the strengthening agent may be in a range of about 10 wt% to about 60 wt%, about 10 wt% to about 50 wt%, about 10 wt% to about 40 wt%, about 10 wt% to about 30 wt%, about 20 wt% to about 60 wt%, about 20 wt% to about 50 wt%, or about 20 wt% to about 40 wt%. The amount of solvent component in the aqueous solution may be in a range of about 100 wt% to about 700 wt% of the final composite weight. For example, the solvent component may be in a range of about 100 wt% to about 650 wt%, about 100 wt% to about 600 wt%, about 100 wt% to about 550 wt%, about 150 wt% to about 550 wt%, about 200 wt% to about 550 wt%, about 200 wt% to about 500 wt%, about 200 wt% to about 450 wt%, about 200 wt% to about 400 wt%, about 200 wt% to about 350 wt%, or about 200 wt% to about 300 wt%.

Figure 2 illustrates a flowchart diagram of an example of the manufacturing of silica aerogel composite. The manufacturing stages may comprise a list from the start (stage 1) to finish (shipment, stage 14). As illustrated, after measurement of the raw materials (stage 2), the materials are sonicated to mix them (stage 3). In stage 4, the mixture is frothed and subsequently poured into molds (stage 5) . The molds are transferred to a rack for ease of movement (stage 6) and freezed (stage 7). Freeze drying occurs in stage 8 and the product is then cured (stage 9). The silica aerogel composite is removed from the molds (stage 10) and coated with a hydrophobic material (stage 11). Quality control checks are performed (stage 12) and if passed, the silica aerogel composites are packaged, documented (stage 13) and proceed for shipment (stage 14). In another aspect, the present invention discloses a silica aerogel composite manufactured by a method as herein described. The method comprises firstly providing an aqueous solution comprising a water soluble polymeric binder and a surfactant. To this aqueous solution, a silyl-modified silica aerogel is added to the aqueous solution to form a first mixture. A water soluble crosslinking agent is subsequently added to the first mixture to form a second mixture. The second mixture is freeze dried at a first pre-determined pressure and at a first pre-determined temperature sufficient for sublimation of ice to form a composite and then cured to form the silica aerogel composite. Advantageously, the silica aerogel composite can be produced at least on a large scale of about 250 mm by 250 mm with a thickness of about 5 mm to about 30 mm and with good homogeneity and consistency, i.e. homogenous distribution of all components throughout its cross-section. The silica aerogel composite may further comprise a plasticising agent, an inorganic filler and/or a strengthening agent. The plasticising agent, inorganic filler and/or strengthening agent may be added in the aqueous solution with the polymeric binder and surfactant. This aqueous solution is mixed and processed similarly as mentioned above to give the silica aerogel composite.

The silica aerogel composite may be subsequently coated with a hydrophobic material. The coating of a hydrophobic material renders the hydrophilic silica aerogel composite more hydrophobic. The degree of hydrophobicity may be varied by varying the amount and type of hydrophobic material (for example silane coupling material) as mentioned herein. The resultant silica aerogel composite may have a thermal conductivity in a range of about 0.010 W/mK to about 0.030 W/mK. For example, the silica aerogel composite may have a thermal conductivity of about 0.010 W/mK to about 0.030 W/mK, about 0.010 W/mK to about 0.028 W/mK, about 0.010 W/mK to about 0.026 W/mK, about 0.010 W/mK to about 0.024 W/mK, about 0.010 W/mK to about 0.022 W/mK, about 0.010 W/mK to about 0.020 W/mK, about 0.012 W/mK to about 0.026 W/mK, about 0.014 W/mK to about 0.026 W/mK, about 0.016 W/mK to about 0.026 W/mK, about 0.018 W/mK to about 0.026 W/mK, or about 0.018 W/mK to about 0.024 W/mK.

The silica aerogel composite may have a density in a range of about 0.06 g/cm³ to about 0.15 g/cm³. For example, the silica aerogel composite may have a density of about 0.065 g/cm³ to about 0.15 g/cm³, about 0.07 g/cm³ to about 0.15 g/cm³, about 0.07 g/cm³ to about 0.145 g/cm³, about 0.07 g/cm³ to about 0.14 g/cm³, about 0.07 g/cm³ to about 0.135 g/cm³, about 0.07 g/cm³ to about 0.13 g/cm³, about 0.07 g/cm³ to about 0.125 g/cm³, about 0.07 g/cm³ to about 0.12 g/cm³, about 0.07 g/cm³ to about 0.115 g/cm³, about 0.075 g/cm³ to about 0.12 g/cm³, or about 0.08 g/cm³ to about 0.12 g/cm³. The silica aerogel composite may have a compressive modulus in a range of about 10 MPa to about 40 MPa. For example, the silica aerogel composite may have a compressive modulus in a range of about 10 MPa to about 40 MPa, about 15 MPa to about 40 MPa, about 15 MPa to about 35 MPa, about 15 MPa to about 30 MPa, or about 15 MPa to about 25 MPa.

The silica aerogel composite may have a compressive strength in a range of about 1 MPa to about 4.5 MPa. For example, the silica aerogel composite may have a compressive strength at least about 1 MPa, about 1.5 MPa, about 2.0 MPa, about 2.5 MPa, about 2.8 MPa, about 3.0 MPa, about 3.5 MPa, about 3.8 MPa, about 4.0 MPa, or about 4.5 MPa.

The silica aerogel composite may have an acoustic absorption coefficient of more than about 0.2 when the octave band is more than about 1200 Hz. For example, the silica aerogel composite may have an acoustic absorption coefficient of more than about 0.25, about 0.3, about 0.35, about 0.4, about 0.45, about 0.5, about 0.55, about 0.6, about 0.65, about 0.7, about 0.75, about 0.8, about 0.85, about 0.9, about 0.95, or about 1.0.

The silica aerogel composite may have an acoustic absorption coefficient in a range of about 0.3 to about 1.0. For example, the silica aerogel composite may have an acoustic absorption coefficient in a range of about 0.35 to about 0.9, about 0.4 to about 0.9, about 0.45 to about 0.9, about 0.5 to about 0.9, about 0.55 to about 0.9, about 0.6 to about 0.9, about 0.65 to about 0.9, about 0.7 to about 0.9, about 0.35 to about 0.85, about 0.35 to about 0.8, about 0.35 to about 0.75, about 0.35 to about 0.7, about 0.35 to about 0.65, about 0.35 to about 0.6, about 0.35 to about 0.55, or about 0.35 to about 0.5.

The addition of crosslinking agent early in the manufacturing process improves the quality of silica aerogel composite manufactured as described above. For example, the matrix strength of the silica aerogel composite is improved as the addition of crosslinking agent prevented the disintegration of the matrix strength. In an embodiment, a silica aerogel composite comprising a silyl-modified silica aerogel about 30 wt% to about 80 wt% of the final composite weight; a surfactant about 0.1 wt% to about 0.5 wt% of the final composite weight; a polymer binder about 10 wt% to about 20 wt% of the final composite weight; and a crosslinking agent about 0.5 wt% to about 10 wt% of the final composite weight, the addition of crosslinking agent resulted in a silica aerogel composite which is less brittle. In another embodiment, a compressive strength of at least 2.5 MPa at 70% strain is obtainable. Accordingly, in another aspect, the present invention discloses a silica aerogel composite comprising a silica aerogel, a surfactant, a polymer binder and a crosslinking agent. The silica aerogel composite has a homogenously distribution of all components throughout its cross-section. Further, the silica aerogel composite may be manufactured in a large size, for example at least about 250 mm by about 250 mm. The silica aerogel composite has at least the following properties: a density in a range of about 0.07 g/cm³ to about 0.13 g/cm³, a thermal conductivity in a range of about 0.010 W/mK to about 0.030 W/mK and an acoustic absorption coefficient in a range of about 0.6 to about 0.9. Additionally, the silica aerogel composite has a compressive strength of at least 2.5 MPa. The surfactant used in the silica aerogel composite may be sodium dodecyl sulfate. The polymer binder may be gelatin and the crosslinking agent may be glutaraldehyde.

The silica aerogel composite may further comprise a plasticising agent, an inorganic filler and a strengthening agent. The plasticising agent may be selected from a group comprising of: glycerol, sorbitol, malic acid, or a combination thereof. The inorganic filler may be selected from a group comprising of: amorphous silica, zirconium dioxide, iron (III) oxide, titanium oxide, barium sulphate, fumed silica and borates of various types, for example zinc or a combination thereof. The strengthening agent may be selected from a group comprising of: fumed silica, mineral fiber, calcium silicate, or a combination thereof.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications which fall within the spirit and scope. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said steps or features.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that the prior art forms part of the common general knowledge.

Examples

Commercially procured hydrophobic silica aerogel granules are used to develop these composites. Silica aerogels although inherently hydrophilic, the procured aerogel granules are hydrophobic due to the chemically inert trimethylsilyl (TMS) or oxy- ethylene terminal groups present in the coating applied on the silica aerogels' surfaces. Before modification, hydrophobic silica aerogel granules used in the examples described herein are translucent, with bulk density of 0.08-0.10 g/cm³, porosity of >90%, pore diameter ~ 20nm, surface area of 600-800m2/g. Hydrophillic fumed silica is procured commercially as additive filler. The fumed silica has pore diameter of 2.5 nm, particle size of 12 μηη and a pore volume of 0.44 ml_/g. High strength gelatin from porcine skin (bloom strength 260; density ~1.043 g/cm3) is used in some of the embodiments. Gelatin contains polar functional amino acids, comprising of -NH₂ and - COOH functional groups. Other examples of materials with high concentration of polar type amino acids such as glycine, proline and hydroxyproline may also be suitable. Suitable materials with such amino acids may include gelatin from different sources such as porcine, bovine and the like.

Figure 3 illustrates a list of the machines used in the method of manufacturing as described herein. The machines used are co-related with the stages in Figure 2.

General Protocol for Manufacturing of Silica Aerogel Composite

As shown in Figure 4, cut out non porous ply (a), porous ply (b) and bleeder cloth (c) as required according to the size of a tray. Lay the non porous ply onto a flat surface (d) and tape the edges (e). Then lay the bleeder cloth over the non porous ply (f). Finally lay the porous ply over the bleeder cloth and tape the edges. The porous ply will allow excess residue from the composite to seep through and be absorbed by the bleeder cloth as shown in the Figure 4. Repeat the steps for laying the plies for the mold.

Aqueous solutions with 12-15 wt% quantities of gelatin in 320 wt% by wet composite of water were prepared at 55°C via homogenization for 1 hour to dissolve the gelatin granulates. Power settings can be from 30 to 50%. Various quantities of fumed silica, surfactants, sizing agents, inorganic materials and strengtheners are added into the aqueous solution for further homogenization for another 1.5 hours.

Froth the mixture into a foam in a high speed blender for 20 seconds at 5000rpm till a good consistency is attained. Transfer the foam mixture into a 1 litre plastic container. Add small amounts of the silica aerogel into the foam bit by bit. Use the mixing machine to mix the aerogel and foam together. Set the mixing speed at 1300 to 1400 rpm. Keep mixing till all the silica aerogels are mixed into the foam. If the mixture is too dry, add 10ml water per time. Mix till all the aerogels are mixed well and turn whitish. Wear a mask and then add the cross-linking agent glutaraldehyde and mix thoroughly throughout the foam. After adding, there will be slight pungent smell, and the foam may turn slightly green yellowish in colour. This shows that the cross linker has set and may become hardened quickly. Glutaraldehyde concentration should be diluted to 5% with water.

The composite is ready to be poured/laid onto the tray. Tilt the container at an angle. Scoop up the aerogel composite mixture bit by bit (Figure 4g) and spread out the mixture as evenly as possible (Figure 4h). After filling up the tray, use the (non- porous, bleeder and porous ply) in previous step and cover the tray (Figure 4i). Flip the trap upside down together with the plys as shown in Figure 4j . Put a 4 kg weight on the tray and let the composite set for 2 hours at room temperature.

Remove the weights on the tray and put the specimen into the freeze dryer. Pre freeze sample with the mold for 4 to 5 hours to harden the sample @ -20°C (Figure 5a). Before turning on the vacuum, remove the mold and the plys from the composite (Figure 5b). Freeze the composite for further 1 hour at -30 °C. The fully frozen sample is then sublimated at -30 °C under vacuum for 24 hours till it reaches 70 °C (Figure 5c). The pressure is maintained at 400 Pascals throughout the sublimation process. Full sublimation is achieved when the chamber pressure drops to 10 Pascals. Thereafter, the pressure is increased by slight opening of the vent valve on the chamber for 0.5 hours. Thermal probes may be placed on the sample to monitor the temperature variations to determine the dew point and critical collapse temperature.

After removing the sample, cure the sample for 3 hours at 55 °C. A fully cured sample will have approximately the same mass of all the raw materials in the composition. Take the sample, use a spray bottle to spray 5 to 6 squeezes on each side of the sample with MTMS. Put in an enclosed container. Place in the oven and set the temperature at 65 °C for 2 hours. After 2 hours, remove sample and spray another 5 to 6 squeezes of n-PTMS or other coupling agents.

In the examples which follow, in accordance with the above described procedures, the ingredients were used in the amount indicated for a 300 x 300 x 20 mm panel. Example 1

Figure 6 illustrates an example of a composition usable in the method of manufacture as described herein. As shown in Figure 7, the example was repeated twice (A and B) and the samples showed good reproducibility. The samples also showed good protection layer due to the inclusion of titanium oxide.

Example 2

Figure 8 illustrates another example of a composition usable in the method of manufacture as described herein. An insulative composition having a formulation previously described except that residual solution from the mixture were filtered and titanium oxide was replaced with barium sulphate. As shown in Figure 9, it was observed that the thermal conductivity and mechanical properties improved tremendously.

Example 3

Figure 10 illustrates other examples of compositions usable in the method of manufacture as described herein. The crosslinking agent was varied from about 1.1 wt% to about 2.35 wt% of the final composite weight. Before addition to the mixture, glutaraldehyde was diluted in water to make up a concentration ranging from about 0.5 wt% to about 7.5 wt%. Inorganic fillers such as zinc borate, titanium oxide and fumed silica can be used to modify the property of the silica aerogel composite. In these examples, the silica aerogel composites were able to resist a flame of above 1700 °C, with the surface temperature of the silica aerogel composite reaching about 700 °C to about 900 °C without catching fire. In comparison, a comparator silica aerogel composite deteriorates when the surface temperature reaches about 300 °C. Thermal conductivity tests show the temperature rise in the cold plate of about 1.7 °C to about 2.8 °C, and the temperature rise in the hot plate of about 36 °C to about 38.3 °C.

Experimental Studies

Density

The aerogel based composite panels were removed after curing at room temperature at the relatively humidity of 60% and weighed. The densities of the various types of composite blocks were determined from the known dimensions of those panels. As shown in Figure 11, the densities for all specimens are within the range of at least 0.08 to 0.10 g/cm³.

Compression Tests

Each sample block was then cut into a rectangular specimen of x-y dimensions of 75 x 45 mm with 17 to 20mm height (in z-direction. The specimens were compression tested in the z-direction at the rate of 2.0 mm/min, nominal strain up to 70%. Each specimen was loaded in compression using 50kN±4% load cell with the pre-load of 100N. Compressive strength at break and compressive modulus at break were recorded. The composite panels are tested under compression using INSTRON 5569 load frame. Results showed a compressive strength of at least 3.81 MPa, a Young Modulus of at least 56.6 MPa, and a maximum load of about 12000 N at 70% strain is obtainable. Thermal Conductivity

Thermal conductivity was measured using Lee's Disc Method. It consists of 3 copper plates (CP) with the dimensions of 75mm x 45mm x 3mm and a heater measuring 75mm x 45mm x 1mm. The heater is connected to the constant power source. Thermal probes are placed on top of the 1^st CP, at the side of 2^nd CP, at the side of the composite block and at the bottom of the 3^rd CP. The composite is sandwiched between the CPs and placed in an enclosed chamber at ambient pressure and temperature for 2 hours until the temperatures reached steady state with the various temperatures recorded at this juncture. Samples were tested at 34 +/- 1 °C. Figure 11 illustrates the thermal insulation properties of the silica aerogel composites. In particular, sample 4 shows the thermal properties of a silica aerogel composite without inorganic fillers and sample 5 shows the thermal properties of a silica aerogel composite with inorganic fillers.

Hydrophobic Quality

Sample size of 80 x80 mm and 100 x 100 mm were prepared and tested for water sorption as per ASTM C1511. Hydrophobic quality of the composition was evaluated based on water uptake into the specimen for at least 15 minutes. The ratio of difference between wet and dry mass to the dry mass were recorded and calculated. Figure 12 illustrates the water sorption property of silica aerogel composite before hydrophobic coating. In particular, sample 4 shows the water sorption properties of a silica aerogel composite without plasticising agents and sample 6 shows the water sorption properties of a silica aerogel composite with plasticising agents.

Figure 13 shows samples of silica aerogel composites with and without crosslinking agent. Sample 7 shows the silica aerogel composite made without crosslinking agent and sample 8 shows the silica aerogel composite made with crosslinking agent. As illustrated, silica aerogel composite is less stable when in contact with an aqueous solution when made without the crosslinking agent. Acoustics

The composite panels are tested for sound absorption with a calibrated impedance tube capable of measuring low frequency absorption of up to 1600 Hz. Figure 14 shows the results.

Claims

Claims Defining the Invention

1. A method of manufacturing a silica aerogel composite, including the steps of: a) providing an aqueous solution comprising a water soluble polymeric binder and a surfactant;

b) adding a silyl-modified silica aerogel to the aqueous solution to form a first mixture;

c) adding a water soluble crosslinking agent to the first mixture to form a second mixture;

d) freeze-drying the second mixture at a first pre-determined pressure and at a first pre-determined temperature suitable for sublimation of ice to form a composite; and e) curing the composite.

2. The method according to claim 1, wherein providing the aqueous solution comprises:

a) a mixing step; and

b) an agitation step;

wherein the agitation step introduces air bubbles into the aqueous solution, and froths the aqueous solution.

3. The method according to claim 1 or 2, wherein providing the aqueous solution comprises:

a) a mixing step comprising of sonication; and

b) an agitation step comprising of homogenisation;

4. The method according to any of claims 1 to 3, further including the steps of:

(a) secondary drying under a second pre-determined pressure and at a second pre- determined temperature; and

(b) coating the cured composite with a hydrophobic material.

5. The method according to any of claims 1 to 4, wherein the first pre-determined pressure is higher than the second pre-determined pressure, and the first pre- determined temperature is lower than the second pre-determined temperature.

6. The method according to any of claims 1 to 5, wherein the second mixture is shaped in a mold before freeze drying.

7. The method according to any of claims 1 to 6, wherein the aqueous solution further comprising a plasticising agent, an inorganic filler, and a strengthening agent.

8. The method according to claim 7, wherein the plasticising agent is selected from a group comprising of: glycerol, sorbitol, malic acid, or a combination thereof.

9. The method according to claim 7, wherein the strengthening agent is selected from a group comprising of: fumed silica, mineral fiber, calcium silicate, or a combination thereof.

10. The method according to claim 7, wherein the inorganic filler is selected from a group comprising of: amorphous silica, zirconium dioxide, iron (III) oxide, titanium oxide, barium sulphate, or a combination thereof.

11. The method according to any of claims 1 to 10, wherein the water soluble polymeric binder is selected from a group comprising of: gelatin, polyacrylamide, polyvinyl pyrrolidone, polymethacrylamide, polyvinylalcohol, or a combination thereof, and the surfactant is selected from a group comprising of: sodium dodecyl sulfate, cetyl trimethylammonium bromide, perfluorononanoate, lecithin, or a combination thereof.

12. The method according to any of claims 1 to 11, wherein the silyl-modified silica aerogel is provided as granules, the granules having a size in the range of about 0.05 cm to about 0.5 cm.

13. The method according to any of claims 1 to 12, wherein the crosslinking agent is selected from glutaraldehyde, melamine, formaldehyde, or a combination thereof.

14. The method according to any of claims 1 to 13, wherein the water soluble polymeric binder is added in a range of about 10 wt% to about 20 wt% of the final composite weight, wherein the surfactant is added in a range of about 0.1 wt% to about 0.5 wt% of the final composite weight,

wherein the silyl modified silica aerogel is added in a range of about 30 wt% to about 80 wt% of the final composite weight,

wherein the crosslinking agent is added in a range of about 0.5 wt% to about 10 wt% of the final composite weight,

wherein the inorganic filler is added in a range of about 0.1 wt% to about 10 wt% of the final composite weight,

wherein the strengthening agent is added in a range of about 20 wt% to about 50 wt% of the final composite weight.

15. The method according to any of claims 1 to 14, wherein the aqueous solution has a solvent component, the solvent component being in a range of about 200 wt% to about 300 wt% of the final composite weight.

16. The method according to claims 1 or 5, wherein the first pre-determined pressure is in a range of about 100 to about 400 Pascals, and the first pre-determined temperature is lower than about -15 °C.

17. A silica aerogel composite manufactured by a method comprising :

a) providing an aqueous solution comprising a water soluble polymeric binder and a surfactant;

d) freeze-drying the second mixture at a first pre-determined pressure and at a first pre-determined temperature sufficient for sublimation of ice to form a composite; and e) curing the composite.

18. A silica aerogel composite according to claim 17, the silica aerogel composite further comprising a plasticising agent, an inorganic filler, and a strengthening agent.

19. The silica aerogel composite according to either claim 17 or 18, wherein the silica aerogel composite has a thermal conductivity in a range of about 0.010 W/mK to about 0.030 W/mK.

20. The silica aerogel composite according to claim 19, wherein the silica aerogel composite has a density in a range of about 0.07 g/cm³ to about 0.13 g/cm³.

21. The silica aerogel composite according to any of claims 17 to 20, wherein the silica aerogel composite has a compressive modulus in a range of about 10 MPa to about 40 MPa .

22. The silica aerogel composite according to claims 17 to 21, wherein the silica aerogel composite has an acoustic absorption coefficient of more than about 0.4 when the octave band is more than about 1200 Hz.

23. The silica aerogel composite according to claims 17 to 22, wherein the silica aerogel composite has an acoustic absorption coefficient in a range of about 0.6 to about 0.9.

24. A silica aerogel composite comprising :

a) a silyl-modified silica aerogel about 30 wt% to about 80 wt% of the final composite weight;

b) a surfactant about 0.1 wt% to about 0.5 wt% of the final composite weight;

c) a polymer binder about 10 wt% to about 20 wt% of the final composite weight; and d) a crosslinking agent about 0.5 wt% to about 10 wt% of the final composite weight; wherein the silica aerogel composite is homogenously distributed throughout; and wherein the silica aerogel composite has a compressive strength of at least 2.5 MPa.

25. The silica aerogel composite according to claim 24, wherein the surfactant is sodium dodecyl sulfate, the polymer binder is gelatin and the crosslinking agent is glutaraldehyde.

26. The silica aerogel composite according to claims 24 or 25, further comprising a plasticising agent, an inorganic filler and a strengthening agent, wherein the plasticising agent is selected from a group comprising of: glycerol, sorbitol, malic acid, or a combination thereof, the inorganic filler is selected from a group comprising of: amorphous silica, zirconium dioxide, iron (III) oxide, titanium oxide, barium sulphate, or a combination thereof, and the strengthening agent is selected from a group comprising of: fumed silica, mineral fiber, calcium silicate, or a combination thereof.