FIELD OF INVENTION

The present disclosure relates to a method of manufacturing nonwoven aerogel blankets and in particular to the use of nonwoven aerogel blanket as insulative materials.

BACKGROUND

Aerogels are some of the lightest solid materials known and are characterised by their low thermal conductivity, high porosity, low density. Since their discovery in the 1930s, the potential applications of these nanostructured solids are numerous and include heat insulations, sound absorptions, sorbents for gases such as carbon dioxide, volatile organic compounds and hazardous gases, drug delivery and as construction materials.

The traditional aerogel fabrication process is typically manufactured in 3 distinct steps namely gelation, ageing and drying. As its name suggests, during the gelation step, precursor materials are allowed to disperse in a suitable solvent and are encouraged to gel thus transitioning to a colloidal network. This prevents shrinkage and the pores from collapsing, particularly during the drying stage.

Lastly, the gel is dried to remove the remaining liquid in a manner that minimises the surface tension of the pores of the solid network. This is typically achieved by supercritical drying or freeze-drying. In supercritical drying, the liquid within the aerogel is gasified and removed from the aerogel without crossing the liquid-gas boundary, thus eliminating the increase in surface tension that would otherwise result during evaporation which can lead to pore collapse.

While effective, supercritical drying is not only time consuming, typically requires several days to complete but also requires specialised equipment and presents a safety hazard due to the need to operate at high pressure and temperature and accordingly is a major reason that increases manufacturing costs and poses a significant challenge when it comes to scaling up production of aerogels. While more cost-effective than supercritical drying, freeze-drying can only be done in batches, each produces at best square metres of aerogels.

Consequently, this has prevented the widespread adoption of aerogels over traditional materials in all but the most demanding applications where it would be impossible or inefficient to use a material other than an aerogel. Hence there exists a need for a cost-effective method of manufacturing aerogels that is easiiy scalable and allows for continuous production of aerogels as opposed manufacturing in batches.

SUMMARY OF THE INVENTION

A primary embodiment of the present invention is a method of manufacturing nonwoven aerogel blanket comprising the steps of forming a fibre web comprising polymeric fibres and low melting-point polymer fibres using nonwoven web formation techniques, calendering the polymeric fibres, curing the polymeric fibres and applying a mixture comprising aerogel particles and an adhesive to the fibre web.

Optionally, the polymeric fibres are selected from a group consisting of acetate fibres, acrylic fibres, aramid fibres, azlon fibres, carbon fibres, melamine fibres, modacrylic fibres, olefin fibres, nylon fibres, poiybenzimidazoie fibres, polyacrylate fibres, polyester fibres, polyvinyl alcohol fibres, polyvinylidene fibres, polyurethane fibres, fibreglass, silica fibreglass, cellulose- based fibres or a combination thereof.

Optionally, the adhesive is selected from a group consisting of vinyl acetate, ethylene-vinyl acetate, acrylic ester, vinyl acetate-acrylic ester, styrene-acrylic ester, ethylene-vinyl acetate- vinyl ester, ethylene-vinyl acetate-acrylic ester, alkali silicates or a combination thereof

Optionally, the mixture further comprises an additive. Optionally, the additive is thermal stable up to a temperature of about 650°C. Optionally, the additive is selected from a group consisting of graphene oxide, carbon nitride, magnesium oxide, titanium dioxide, silicon carbide, sodium silicate, potassium silicate, magnesium oxide and titanium dioxide or a combination thereof. Optionally, the additive is sodium silicate, potassium silicate, magnesium oxide, titanium dioxide, silicon carbide or a combination thereof.

Optionally, the mixture is applied to the fibre web by dip-coating or spraying at a pressure of 1-100 kg/cm ² .

Optionally, the fibre web is formed is formed using needle-punching. Optionally, the needle punching comprises a pre-needling step with a stroke frequency of 5-50 Hz, a stroke of 10-100 mm, and a needle density of 1000-10000 s/m and a needle punching step with double-sided needling with a stroke frequency of 5 - 50 Hz, a stroke of 10-100 mm, and a needle density of 1000-10000 s/m.

Optionally, the method comprises a further step of applying a coating to the nonwoven aerogel blanket. Optionally, the coating is selected from a group consisting of hydrophobic coating fire retardant coating, flame retardant coating, weather, and UV resistant coating, heat resistant coating, chemical resistant coating, oxidation and corrosion-resistant coating or combination thereof.

DETAILED DESCRIPTION OF THE INVENTION

The illustrative embodiments described in the detailed description and claims are not meant to be inclusive. Other embodiments can be utilized, and other changes can be made, without departing from the spirit or scope of the invention.

A primary embodiment of the invention is a method of manufacturing nonwoven insulation blanket using techniques traditionally associated with the manufacture of nonwovens The method is preferably performed by non-woven machinery assembled in a conveyor system to allow the continuous production of aerogels.

Polymeric fibres are fed into a fibre opening machine used in the manufacture of nonwovens that employs a fibre web formation technique. Suitable web formation techniques include dry- laid carding, air-laid and spun-laid. A suitable polymeric fibre generally include natural fibres or synthetic fibres such as but not limited to acetate fibres, acrylic fibres, aramid fibres, azlon fibres, carbon fibres, melamine fibres, modacrylic fibres, olefin fibres, nylon fibres, Polybenzimidazo!e fibres, polyarylate fibres, polyester fibres, polyvinyl alcohol fibres, polyvinylidene fibres, polyurethane fibres, fibreglass, silica fibreglass, cellulose based fibres or a combination thereof. In a preferred embodiment, polyethene terephthalate fibres, polyethene fibres, polypropylene fibres, fibreglass, silica fibreglass, and cellulose fibres is used as the polymeric fibres. In a preferred embodiment, cellulose-based fibres can be derived from cotton, flax, hemp, jute, ramie, sisal and coir or any other fibre where cellulose is a major constituent.

In addition to the polymeric fibres, at least one low melting point polymer is used in combination with the polymeric fibres to strengthen the non-woven structure. Low melting point polymers are polymers that have a melting point of not more than 200°C and is lower than that of the melting point of the polymeric fibres. The low melting point polymer in the form of fibres is incorporated into the polymeric fibres, that is, low melting point polymeric fibres are mixed in along with the polymeric fibres and a bundle comprising low melting point polymeric fibres and polymeric fibres are present during fibre opening. These low melting point polymers will provide the bonding between the polymeric fibres after the calendering process. While typically performed after the cross-lapping step, the adhesive can be applied to the fibre web at any time after the formation of the fibre web and before the calendaring step. Non-limiting examples of suitable polymers include polyethene terephthalate, polyethene, and polypropylene. More than one low melting point polymer may be used simultaneously. The web formation process gives rise to a highly porous structure.

After the formation of the fibre web, the fibre web may in some embodiments be optionally thickened by being subjected to cross-lapping in order to be paved to a desired thickness. Next, the fibres are bonded to create mechanical resistance between the fibres that make up the fibre web using known bonding methods employed in the manufacture of non-woven. In one embodiment, the fibre web is formed by needle punching by a non-woven needle punching machine.

In the context of the present invention, needle punching involves a pre-needling step to initially tangle and create a pre-formed tension in the fibres, with a stroke frequency of 5-50 Hz, a stroke of 10-100 mm, and a needle density of 1000-10000 s/m, depending on the fibre sources or the production rate. This is followed by a needle punching step to form a coherent matrix and preferably involves double-sided needling with both stages having a stroke frequency of 5-50 Hz, a stroke of 10-100 mm, and a needle density of 1000-10000 s/m, depending on the fibre sources and/or the production rate. Alternatively, other known bonding methods used in the manufacture of non-woven that may be used are stitch bonding, chemical bonding, and thermal bonding.

The fibre web can then be subjected to a calendering process where the calendar rolls are heated to a temperature of 100°C-300°C to smoothen the surface of the aerogel before curing the fibre web at a temperature of less than 100°C-300°C to cure the crosslinks and if present, a surface coating It is understood by a person skilled in the art that the temperature used is dependent on the nature of the crosslinking/surface coating agent used.

A mixture comprising aerogel particles and adhesives is then applied to the nonwoven insulation blanket. The particle size of the aerogel particles is typically in the range of 5pm - 5mm. Suitable adhesives include but are not limited to vinyl acetate, ethylene-vinyl acetate, acrylic ester, vinyl acetate-acrylic ester, styrene-acrylic ester, ethylene-vinyl acetate-vinyl ester, ethylene-vinyl acetate-acrylic ester, alkali silicates or a combination thereof. It would be understood by a person skilled in the art that most organic or inorganic adhesives may be suitable. In a non-limiting example, the mixture comprises approximately 10% aerogel particles, 10% ethylene vinyl acetate, 80% water, by weight percentage. The mixture may be applied to the non-woven insulation blanket by spraying or dip coating.

Adhesive used is typically available commercially as an emulsion or powder at room temperature. The mixture of adhesive and additives should be applied to the nonwoven insulation blanket by spraying the mixture at a pressure of 1-100 kg/cm ² or dip-coated, depending on the viscosity of the mixture of adhesives and additives. This will ensure that the adhesive is sprayed or dip-coated to the extent that sufficiently fine mist is generated which will in turn ensure sufficient penetration of the fibre, thus ensuring that the fibres are uniformly coated.

In another embodiment, the mixture further comprises at least one additive or a combination thereof. Suitable additives include but are not limited to graphene oxide, carbon nitride, magnesium oxide, titanium dioxide, silicon carbide, sodium silicate, potassium silicate, magnesium oxide and titanium dioxide. In a non-limiting example, the mixture composition as provided in Table 1 contains up to four additives, namely sodium silicate, potassium silicate, magnesium oxide, titanium dioxide and silicon carbide in quantities of up to 10 wt. %, depending on the target density and thermal conductivity of the nonwoven aerogel blankets.

Optionally, the mixture of adhesive and additives is applied by spraying or dip-coating onto one side, both sides, or through the nonwoven insulation blanket. This serves to strengthen the structure by forming bonds between the polymeric fibres. It would be understood that compounds with a high thermal stability, that is thermal stable at temperatures of up to approximately 650°C would be suitable for use as additives.

Table 1 depicts a mixture composition with up to four additives as described in example 1

It is understood that the specific fibre length or range of lengths of fibres suitable for use as understood by a person of ordinary skill in the art varies and may be dependent on both the web formation technique, bonding technique employed, along with machine manufacturer recommendations and application requirements.

Example 1

A typical working example for the mixture is prepared as follows: aerogel particles (20%), ethylene-vinyl acetate (10%), and water (70%) by weight are dispersed homogeneously at

5000 rpm for 20 minutes. The as-prepared mixture is then sprayed or dip-coated onto one side, both sides, or through the nonwoven insulation blanket at a pressure of 50 kg/cm ² to obtain the nonwoven aerogel blanket. Within this working example, the nowoven aerogel blanket has a pore size of 6 nm, a density of 90 kg/m ³ , a porosity of 90%, a surface area of 400 m ² /g, a thermal conductivity of 0 023 W/mK, a noise reduction coefficient of 050, and an oil absorption capacity of 35 g _oil /g _samples The mixture can be added with some additives such as sodium silicate, potassium silicate, magnesium oxide, titanium dioxide, and silicon carbide to increase the original product's thermal stability. The other characteristics of the nonwoven aerogel are also varied when adjusting the amount of aerogel particles, adhesives, and additives and will exhibit characteristics as depicted in Table 2.

In some embodiments, the method may include an optional step of applying a coating to the nonwoven aerogel blanket. Non-limiting examples of coatings include the application of hydrophobic coating fire retardant coating, flame retardant coating, weather and UV resistant coating, heat resistant coating, chemical resistant coating, oxidation and corrosion-resistant coating or combination thereof. More than one coating can be applied. It is envisaged that other coatings may be applied depending on application requirements of the aerogel The coating includes both the application of a thin polymer coat to the surface of the aerogel or the entire internal structure including the surface of pores and junction therebetween and includes surface modification by a coating For example, the application of MTMS leads to the modification of hydroxyl groups to methyl groups thus conferring hydrophobicity to the aerogel. The coating is applied preferably before calendaring/curing.