WO2023128928A1

WO2023128928A1 - Ultra-small nano-porous aerogel and method for synthesizing the same

Info

Publication number: WO2023128928A1
Application number: PCT/TR2022/050330
Authority: WO
Inventors: Cem ÜNSAL; Cengiz KARABULUT; Yaşar Dilek KUT; Zeynep ÖMEROĞULLARI BAŞYİĞİT
Original assignee: Formfleks Otomoti̇v Yan Sanayi̇ Ve Ti̇caret Anoni̇m Şi̇rketi̇
Priority date: 2021-12-28
Filing date: 2022-04-14
Publication date: 2023-07-06

Abstract

The present invention relates to an ultra-small, nano-porous aerogel for use in all fields that require thermal and acoustic insulation, particularly automotive, aircraft, aerospace, defense and construction industries and a method for synthesizing the same. The object of the invention is to provide an aerogel structure with a large pore size and use this aerogel structure as the reaction medium (reactor) and forming within the first aerogel structure a second aerogel structure with smaller sized pores.

Description

ULTRA-SMALL NANO-POROUS AEROGEL AND METHOD FOR SYNTHESIZING

THE SAME

Field of the Invention

The present invention relates to an ultra-small, nano-porous aerogel for use in all fields that require thermal and acoustic insulation, particularly automotive, aircraft, aerospace, defense and construction industries and a method for synthesizing the same.

Prior Art

Various studies have been conducted to synthetize a material in microreactors made of another material. These studies make use of a method known as microencapsulation or microcapsules. Microencapsulation is the process of converting solid, liquid or gaseous substances into small particles of solid or droplets of liquids and dispersions and applying relatively thin coating with an inert polymeric substance. This process involves the coating of particles ranging dimensionally from several tenths of micron to 5000 microns in size. This technique is an effective way of converting liquids to solids by changing their colloidal and surface properties. It also protects the core from the environment and controls the release properties of the coated material.

Microencapsulated components do not interact with other components. Maintenance of sensory properties and extendable shelf life can be listed among other significant properties. Said microencapsulated components can be added at any stage of the process and remain unchanged. In addition to these benefits, the environmental impact of polymer matrix, polymer additives and their decay products significantly varies in response to thermal, hydrolytic and biological agents. Therefore, further knowledge and skills are required to use this advanced and sophisticated technology. In prior art applications, it is difficult to obtain regular films in a consistent manner.

Layer by Layer (LbL) assembly has emerged as a versatile, gentle and simple method for immobilization of functional molecules in an easily controllable thin film morphology. Various substances including polyions, metals, ceramics, nanoparticles and biological molecules can be accumulated by employing the LbL method. The main drawback of layered structures is that physical and chemical properties of the structure within are limited.

All of the methods summarized above are used for obtaining microcapsules or surface coating with a specific or multiple functions (deodorization, perfume, cosmetic care, repair, etc.). Essentially, these methods aim to extend the life of the targeted function with controlled release. While these methods are suited to the textile, pharmaceutical and biotechnology industries, they have limited scope of application in improving the properties of composite materials. In automotive, aircraft, aerospace, defense and similar industries, composite structures are required to be formable and have high strength, high thermal resistance, wear resistance, high insulation properties (thermal, acoustic and electrical). Methods which produce the abovementioned embedded or overlapping multi-layered material structures cannot be used for integrating these properties into composite structures.

In conclusion, the drawbacks explained above and the shortcomings in existing solutions the problems have necessitated improvement in the related technical field.

Summary of the Invention

The present invention relates to an ultra-small nano-porous aerogel which satisfies the requirements listed above and eliminates all disadvantages while bringing additional benefits to the technical field and the method for synthesizing the same.

The main aim of the invention is to provide an aerogel structure and use this aerogel structure with nanometer-scale pores as the reaction medium (reactor) and forming within the first aerogel structure a second aerogel structure with smaller sized pores. Literature review has yielded certain studies where aerogel structures can be dropped to a minimum thermal conductivity coefficient of 0.015 W/m. K. Due to the nano-porous (pores/cells small enough to be measured at nanometric scale) nature of the aerogel structure and the atmospheric air content of these pores (theoretically up to 99.8%), thermal and acoustic insulation properties of aerogels are superior compared to all other known materials. In existing studies, aerogel pore size is typically between 20 nm and 40 nm. However, pore size distribution is not even in general. The present invention aims to provide different embedded aerogel structures inside the pores of an aerogel structure with a specific pore size and thereby reduce pore size by further downscaling the minimum pore size of the resulting integrated aerogel structure.

Reducing the average pore size leads to a decrease in the thermal conductivity coefficient of the aerogel structure. Approximately a decrease of 30% in thermal conductivity coefficient can be achieved by using this method. Lower thermal conductivity coefficient means higher thermal insulation. The present invention aims to further improve the thermal insulation performance of aerogel materials which already have the highest level of thermal insulation among all known materials. A similar trend is also observed in acoustic insulation.

The present invention provides for embedded aerogel structures which can be used in applications that require formability (flexibility, shear strength, etc.), high thermal resistance, chemical resistance and filtration.

Another aim of the invention is to synthesize a new type of embedded aerogel by using an aerogel as reactor medium thanks to its open porous structure, infiltrating of this reactor with a sol solution and performing gelation, aging and supercritical drying processes again. There is a wide array of aerogel compositions used in the technical field. However, the common point of all aerogel compositions is the main aspects in which they are synthesized and processed. Aerogels are typically prepared with a wet chemical synthesis approach. The first steps in the synthesis of aerogels are critically important. Because sol-gel process is generally used to form a solid phase. The solid phase forms the backbone of aerogel and during the process, all parameters including the concentration and type of reagents and solvents, temperature and pH significantly impact gel formation. For the production of aerogels at the design stage, it is necessary to understand the consequences and effects of each stage (1 ). Aerogels are produced in several consecutive process steps. The first step is the solution preparation step. In this step, a homogenous solution is prepared by reacting various starting materials with suitable solvents. These steps are generally followed by hydrolysis, polymerization, condensation, gelation, washing and aging (2). After these steps, aerogel formation is enabled by supercritical CO2 drying. Supercritical drying is a step in which the liquid in the substance is converted to gas without surface tension and capillary tension, and is the method used to convert gels into aerogels. The present invention makes use of the open porous structures of aerogels to further downscale the pore size of aerogels with different pore diameters and an aerogel with new properties is obtained by forming aerogel structures of this type with different components. Through repeated application of this production method, the final aerogel structure characteristics can be changed to have the desired performance properties including the average pore diameter, material type, etc. composition parameters. Literature review yields hybrid studies where aerogels are transferred to material through incorporation into various matrices (resins, plastic structures, fibrous structures, etc.) in powder form, coating, etc. methods, and combined after certain preliminary preparation stages. The present invention does not show similarity in terms of monolithic aerogel synthesis and transfer to a material through incorporation into various matrices such as resins, plastic structures, fibrous structures, etc. in powder form, spraying, coating, etc. processes. Moreover, it is not a type of hybrid aerogel that is derived by forming a pre-polymer-like structure in monolithic structure and then combining two different components in a single bath.

The below drawings and the detailed description set out with reference to the accompanying drawings provide for a clearer understanding of the structural and characteristic properties and all benefits of the present invention; therefore, the evaluation needs to take these drawings and the detailed description into account.

Brief Description of the Drawings

Figure 1 is a schematic view of the production process of the aerogel structure.

Figure 2 is a schematic view of the infiltration process and the subsequent derivation of the new aerogel structure.

List of Reference Numerals

101 Precursor preparation process step in solution for the aerogel structure to be used as reactor

102 Sol solution preparation process step 103 Gel formation process step

104 Aging process step

105 Drying process step

106 First aerogel (reactor) structure production process step

107 Sol solution preparation process step for the aerogel structured to be formed inside the reactor

108 Infiltration process step

109 Final aerogel production process step

Detailed Description of the Invention

In order to facilitate a better understanding of the present invention, this detailed description demonstrates the preferred embodiments of the ultra-small and nano-porous aerogel and the synthesis method for producing the same in a non-limiting manner.

The present invention relates to an ultra-small and nano-porous aerogel for use in all fields that require thermal and acoustic insulation, particularly automotive, aircraft, aerospace, defense and construction industries and a method for synthesizing same. Specifically, the invention involves the production method of multiple embedded aerogel structures. In different embodiments of the invention, dual, triple or more aerogel structures can be produced in embedded form.

Experiments conducted as part of the invention are exemplified below to facilitate a better understanding of the method for producing the ultra-small and nano-porous aerogel according to the invention. These examples are related to studies where dual and triple embedded aerogel structures in silica + polyimide, polyurethane + silica and silica + polyurethane + polyimide form. To this end, the below examples and chemicals used in these examples are illustrated in a non-limiting manner only for the purposes of facilitating a better understanding of the subject. The invention can also be achieved by using different chemicals with different process parameters.

Initially, the method according to the invention involves the process step of preparing the precursor to the aerogel structure to be used as reactor in solvent. If silica is selected as the main component, the precursor (preferably TEOS) is dissolved in alcohol solution in inert environment to prepare an alkoxide solution. Generally, the first process step is preparing the precursor to aerogel structure in solvent. According to the invention, the precursor component (tetraorthosilicate) is used as a starter material in preparing the sol solution.

After a solution is obtained by dissolving the precursor in the solvent, the preparation step of the sol solution is initiated. pH, temperature, mixing speed, amounts/rates of component used, solvent type and catalyst are important factors in this process step. These factors will affect the gelation rate and the quality of the finished aerogel product. Depending on the type of gel to be produced, different process steps in the gel formation process work differently at different time scales. In general, a slower sol-gel step gives better results. Accelerating the reactions may cause precipitates to form instead of a gel network, or the gel to become weak or even not to form.

If silica is selected as the main component, after the preparation of the alkoxide solution for silica, the first step of the sol solution is completed by performing a two-step acid (HCI)/base (NH4OH) catalyzed hydrolysis-condensation process.

After leaving the sol solution to a stand for gel formation, aging and drying (preferably supercritical drying) is performed to obtain the first aerogel structure (aerogel structured to be used as reactor).

In the next process step, a new sol solution is prepared by using organic chemicals dissolved in organic solvent (N-methyl-2 pyrrolidone) and other chemicals in liquid form (polyimide and/or polyurethane chemicals).

Said first aerogel structure (reactor aerogel) is plunged into the new sol solution for the sol solution to infiltrate the first aerogel structure (reactor aerogel). By this way, the adsorbed precursors of the secondary structure diffuse into the aerogel structure pores as a reactor. This enables the use of the obtained aerogel structure with nanometerscale pores as the reaction medium (reactor) and the formation within the first aerogel structure of a second aerogel structure with smaller sized pores.

Gelation and aging processes are performed inside the new structure that is left to a stand for a certain period of time. Gel formation is achieved through the gelation inside the nanopores of the aerogel selected as the reactor.

In the aging process, the gel is kept in alcohol (preferably methanol) for 3 days. During this process, said alcohol solution is preferably replaced every 24 hours. It has been determined that the aging time has an impact on the aerogel properties. Therefore, in a preferred embodiment of the invention, the aging process is carried out in the range of 1 to 14 days. Since the aging process is an important process step for the final product, it is important to observe the impact on the chemical and physical properties of the aerogel by experimenting with different time intervals. It has been determined that the aging period has an impact on the pore structure in particular at certain intervals.

After the aging process, the supercritical drying process is carried out and the aerogel synthesis is completed. The supercritical drying time can be determined between 2.5 and 12 hours (preferably 5 hours) depending on the deformation in the material. During this process, the gel to be placed in the supercritical dryer is placed in the separator so that it is completely covered with the aging alcohol. In the supercritical drying process, it is important not to keep the supercritical drying time too long to avoid cracks, ruptures, etc. in the aerogel. In an embodiment of the invention, the aerogel can be soaked in liquid CO2 for 24 hours before performing the supercritical drying operation. This makes it possible to avoid cracks in the aerogel structure. Moreover, when the supercritical process is completed, CO2 should not be released quickly and abruptly. Otherwise, cracks and ruptures occur in the aerogel structure. Instead of supercritical drying, it is possible to form an aerogel with different drying processes, for example at subcritical temperatures.

Figure 1 shows the production process of the aerogel structure to be used as reactor. The process shown in Figure 2 is the process for producing new aerogel structure(s) within the reactor aerogel structure. The process in Figure 2 can be repeated multiple times to further downscale the pore size. By this means, it is possible to obtain a multicomponent aerogel structure with different or identical embedded aerogel structures. If polyimide is selected as one of the main components in producing a multi-component aerogel, chemical imidization can be performed by using carboxylic acid anhydride (Acetic anhydride) as a water-absorbing reagent with tertiary amine (Pyridine) as the catalyst. By this means, gel formation is performed faster without the need for high heat.

Components used in the production of silica + polyimide and their usable amounts by weight are shown below in percentage terms:

Components used in the production of polyurethane + silica and their usable amounts by weight are shown below in percentage terms:

Components used in the production of silica + polyurethane + polyimide and their usable amounts by weight are shown below in percentage terms:

The functions of the components mentioned in the invention (the technical effect they produce) and the components that can be used as alternatives are given in the table below:

According to the invention, chemical imidization is performed by using carboxylic acid anhydride (Acetic anhydride) as a water-absorbing reagent with tertiary amine (Pyridine) as the catalyst. By this means, gel formation is performed faster without the need for high heat. It is also possible to perform thermal imidization or solution imidization instead of chemical imidization.

In another embodiment of the invention, the same object can be achieved by using chemicals of different main components (cellulose, etc.) that provide thermal and acoustic insulation through certain properties. Also, components with different pore sizes can be used to perform the desired aerogel synthesis with two or more additives.

In yet another embodiment of the invention, triethoxymethylsilane (MTES) and/or trimethylchlorosilane (TMCS) is added to provide functional properties such as flexibility and water repellency to the multi-component aerogel structure.

In order to solve the existing problems in the technical field and achieve the objectives described above, a method for producing aerogel for use in all fields that require thermal and acoustic insulation, particularly automotive, aircraft, aerospace, defense and construction industries, comprising the process steps of:

• Preparing the precursor to the aerogel structure to be used as reactor in solvent;

• Preparing a sol solution;

• Leaving the prepared sol solution for gelation;

• Performing aging operation on said gel;

• Performing drying process after aging to obtain the aerogel structure to be used as reactor;

• Preparing the sol solution of the aerogel structure to be formed inside the reactor;

• Plunging the aerogel structure to be used as reactor into the newly prepared sol solution and infiltrating the reactor aerogel structure with the prepared sol solution;

• Ensuring gelation within the nanopores of the aerogel structure used as reactor;

• Performing aging operation on said gel;

• Performing drying process after aging to obtain the final aerogel structure. REFERENCE LIST

1. Montes, Susan, and Hajar Maleki. "Aerogels and their applications." Colloidal Metal Oxide Nanoparticles. Elsevier, 2020. 337-399.

2. Handbook of Sol-Gel Science and Technology, 2018, Print + eBook ISBN 978-3- 319-32100-4.

Claims

CLAIMS 1. A method for producing aerogel for use in all fields that require thermal and acoustic insulation, particularly automotive, aircraft, aerospace, defense and construction industries, characterized by comprising the following process steps:

• preparing a sol solution;

• leaving the prepared sol solution for gelation;

• performing aging operation on said gel;

• performing drying process after aging to obtain the final aerogel structure.

2. The method for producing aerogel according to Claim 1 , characterized in that; TEOS and/or TMOS and/or Na2SiOa and/or organosilicon is used as precursor if silica is selected as the main component in the process step of preparing the precursor to the aerogel structure to be used as reactor in solvent

3. The method for producing aerogel according to Claim 1 or Claim 2, characterized in that; triethoxymethylsilane and/or trimethylchlorosilane is added to provide functional properties such as flexibility and water repellency to the aerogel structure.

4. The method for producing aerogel according to Claim 1 , characterized in that; the alcohol solution used in the aging process step is replaced every 24 hours for 3 days.

5. The method for producing aerogel according to Claim 4, characterized in that; methanol is used as alcohol in the aging process step.

6. The method for producing aerogel according to Claim 1 , characterized in that; supercritical drying process is performed in the drying process step.

7. The method for producing aerogel according to Claim 6, characterized in that; supercritical drying is performed for 2.5 to 12 hours.

8. The method for producing aerogel according to Claim 6 or Claim 7, characterized in that; supercritical drying is performed for 5 hours.

9. The method for producing aerogel according to Claim 1 , characterized by comprising of the following process steps are repeated multiple times to further downscale the pore size and/or obtain a multi-component aerogel structure with different or identical embedded aerogel structures:

• performing aging operation on said gel;