REINFORCED COMPOSITE MATERIAL WITH IMPROVED MECHANICAL AND THERMAL PROPERTIES AND METHOD FOR OBTAINING THE SAME

Abstract

The present invention relates to a reinforced composite material, comprising an organic polymer, a silicon polymer, and an interphase between said organic polymer and said silicon polymer, wherein said interphase comprises chemical bonds between the organic polymer and the silicon polymer, and to a method to obtain said reinforced composite material. The present disclosure can be used to improve the mechanical properties of silica aerogels by functionalization of textile materials.

Claims

1. A reinforced composite material, comprising: an organic polymer; a silicon polymer; and an interphase between said organic polymer and said silicon polymer, wherein said interphase comprises chemical bonds between the organic polymer and the silicon polymer.

2. The reinforced composite material according to claim 1, wherein the organic polymer is a textile material.

3. The reinforced composite material according to claim 2, wherein the textile material is selected from the group consisting of cotton, polyamide fibers, polyester fibers and polyurethane fibers.

4. The reinforced composite material according to claim 3, wherein the polyamide fiber is an aramid fiber.

5. The reinforced composite material according to any one of claims 1-4, wherein the chemical bonds between the organic polymer and the silicon polymer comprise RH.sub.2N . . . HOSi hydrogen bonds between the surface NH.sub.2 groups of the polyamide fibers or polyurethane fibers and the SiOH groups of the silicon polymer or OH . . . HOSi hydrogen bonds between the surface OH groups of the polyester fibers and the SiOH groups of the silicon polymer, where R is the remainder of the fiber.

6. The reinforced composite material according to any one of claims 1-3, wherein the textile material is cotton and the chemical bonds between the organic polymer and the silicon polymer comprise COSi covalent bonds between the cellulose of the cotton fibers and the SiOH groups of the silicon polymer.

7. The reinforced composite material according to any one of the preceding claims, wherein the silicon polymer is a silica aerogel.

8. A method to obtain a reinforced composite material, the method comprising: providing an organic polymer; providing a silicon polymer precursor; and obtaining a silicon polymer from the silicon polymer precursor and an interphase between said organic polymer and a silicon polymer, wherein said interphase comprises chemical bonds between said organic polymer and said silicon polymer.

9. The method to obtain a reinforced composite material according to claim 8, wherein the organic polymer is a textile fabric and the step of obtaining an interphase between said organic polymer and said silicon polymer further comprises washing said textile fabric with a mixture comprising a basic compound and pretreating said fabric with a mixture comprising a silicon compound.

10. The method to obtain a reinforced composite material according to claim 8 or 9, wherein the organic polymer is a polyamide fiber or a polyurethane fiber.

11. The method to obtain a reinforced composite material according to claim 10, wherein the organic polymer is an aramid fiber.

12. The method to obtain a reinforced composite material according to claim 8, wherein the organic polymer is a cotton fiber.

13. The method according to any one of claims 8 to 12, wherein the basic compound is sodium hydroxide and the silicon compound is a silicon alkoxide.

14. The method according to claim 13, wherein the silicon alkoxide is tetraethyl orthosilicate.

15. The method to obtain a reinforced composite material according to claims 8 to 14, wherein the step of obtaining silicon polymer from the silicon polymer precursor comprises polymerizing the silicon polymer precursor.

16. The method to obtain a reinforced composite material according to claim 15, wherein the polymerizing the silicon polymer precursor comprises hydrolyzing the silicon polymer precursor, condensing the hydrolyzed silicon polymer precursor, and curing the condensed hydrolyzed silicon polymer precursor.

17. The method to obtain a reinforced composite material according to claim 15 or 16, wherein the method further includes drying.

18. The method to obtain a reinforced composite material according to claims 15 to 17, wherein the method is carried out at a temperature from about room temperature to about 200 C.

19. The method according to any one of claims 8 to 18, wherein the silicon polymer precursor comprises an alkyltrialkoxisilane.

20. The method according to claim 19, wherein the alkyltrialkoxisilane is methyltriethoxysilane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG. 1 shows the Fourier transform infrared spectroscopy (FTIR) spectrum of the untreated aramid fiber sample.

[0047] FIG. 2 shows the ratio of FTIR spectrum bands corresponding to the aliphatic chain (823 cm.sup.1) and the amides (1647 cm.sup.1) of aramid fiber samples.

[0048] FIG. 3 shows the results of transversal traction tests carried out on aramid fiber samples prepared with different surface preparation treatments as described herein.

[0049] FIG. 4 shows the results of longitudinal traction tests carried out on aramid fiber samples prepared with different surface preparation treatments.

[0050] FIG. 5 shows examples of polyamide hydrolysis, polyester hydrolysis, and polyurethane hydrolysis.

DETAILED DESCRIPTION OF THE INVENTION

[0051] The invention will be described in further detail with reference to the appended figures and examples.

[0052] As used herein, the term silica aerogel refers to a non-fluid ultralight silica polymer network dispersed in a gas such as air. When the polymerized precursor of silica is gelified in an alcoholic solvent, such as methanol or ethanol, the term silica alcogel is usually employed.

[0053] In general, the term silicon precursor or silicon polymer precursor refers to a compound from which a silicon polymer can be obtained.

[0054] As used herein, the term textile or textile material refers to a flexible material consisting of a network of woven or unwoven, natural or synthetic fibers.

[0055] As used herein, the term reinforced refers to material with one or more enhanced properties (e.g., increased physical properties, increased thermal resistance, enhanced adhesion between materials in a composite, etc.)

[0056] With the method described herein, the inventors were able to generate an interphase between the textile and the aerogel. Said interphase comprises silanol groups which are chemically bonded to the textile, by means of covalent bonds in the case of cotton and hydrogen bonds in the case of polyamides (e.g., aramids), and that allows the growth of a silica aerogel on said interphase, where the aerogel comprises SiOSi covalent bonds.

[0057] In the case of polyamides (e.g., aramids), the textile fibers were treated by washing in a strong basic medium to generate a hydrolysis of the amide groups, resulting in surface NH.sub.2 groups, as it can be seen in FIGS. 1 and 2. Said amine functional groups can interact with the SiOH groups (for example, by hydrogen bonding). For reaction times of around 10 min (minutes), this surface hydrolysis treatment did not result in a decreased mechanical resistance of the obtained composite materials, as evidenced in the tests shown in FIGS. 3 and 4. In the case of cotton, surface treatment was not needed, since the OH groups in cellulose have sufficient reactivity to react with silicon precursors or silanols.

[0058] In the case of cotton, covalent COSi bonds are formed between cellulose units and silanols. In the case of polyamides (e.g., aramids) and polyurethanes, a hydrogen bond is formed between surface NH.sub.2 groups and SiOH groups, with RH.sub.2N.HOSi bonds.

[0059] The generated interphase, containing the aforementioned bonds, acts as an intermediary that allows the bonding of an organic polymer (e.g., natural or synthetic or a combination thereof) with a silicon polymer (e.g., an aerogel).

[0060] The obtained composite materials have a global structure, for example, given by (textile//surface groups in the textile from the hydrolysis process//surface silanol groups//aerogel), which confers the material the ability to withstand undesirable (e.g., severe) conditions and the possibility to be washed in order to remove pollutants, without a decrease in the thermal insulation properties.

[0061] The silicon polymer (e.g., aerogel) can be formed using various silicon compounds. Mixtures of silicon compounds can be used. For example, the silicon compound is a silicon alkoxide (e.g., a tetraalkoysilane). The silicon alkoxide may be a partially or completely alkylated silicon alkoxide. For example, the number of carbons in the alkyl portion of the alkoxide group being, for example, 1, 2, 3, 4, 5, or any the amount that can be partially hydrolyzed. In an example, the silicon alkoxide (e.g., partially hydrolyzed silicon alkoxide does not precipitate before the application on the textile and/or can form a covalent of hydrogen bond with the pre-hydrolyzed fibers. In another preferred embodiment of the method to obtain a reinforced composite material, the silicon alkoxide is tetraethyl orthosilicate and/or tetramethyl orthosilicate. In another preferred embodiment of the method to obtain a reinforced composite material, the silicon-containing compound is a silicate (e.g., sodium silicate).

[0062] The silicon polymer (e.g., aerogel) can have various thicknesses and fiber coverages. In an example, silicon polymer (e.g., aerogel) has a thickness (e.g., a dimension perpendicular to a surface of a fiber) of 1-100 nm, including all nm values and ranges therebetween. The silicon polymer (e.g., aerogel) may be a continuous or discontinuous layer disposed on a fiber surface.

[0063] The steps of the method described in the various embodiments and examples disclosed herein are sufficient to carry out the method of the present disclosure. Thus, in an embodiment, the method consists essentially of a combination of the steps of the method disclosed herein. In another embodiment, the method consists of such steps.

[0064] The following examples are presented to illustrate the present disclosure. They are not intended to limiting in any matter.

EXAMPLES

[0065] Washing of the Fiber Samples.

[0066] Preparation of Cotton Fibers

[0067] A washing solution was prepared by dissolving 5.0 g of NaOH in 20 mL of water. 1.5 g of Triton X-100 and 0.75 g of citric acid were added and the solution was completed with water to 500 mL.

[0068] The sample was covered with the washing solution and stirred at 100 C. for 1 h (h=hour(s)). The solution was removed, the sample was rinsed with water and air-dried.

[0069] Preparation of Aramid Fibers.

[0070] Aramid fiber samples were treated with NaOH at 10% (prepared with 10 g of NaOH in 100 mL of distilled water) for 10 min. The samples were washed with excess, neutralized with HCl at 0.1 mol/L, then re-washed with water.

[0071] Pretreatment of the Fibers with Silanols.

[0072] The washed samples were immersed in a 2% tetraethyl orthosilicate (TEOS) in an ethanol/water 80:20 mixture. The sample was recovered, thermally treated at 110 C. for 2 h and washed with ethanol.

[0073] Preparation of Silica Aerogels.

[0074] The silica alcogels were prepared via precursor hydrolysis and condensation, curing and subsequent drying at ambient pressure. Typically, the molar relation methyltriethoxysilane (MTES):methanol:oxalic acid (0.001 mol/L):NH.sub.3 (10 mol/L) is 1:27:4:4.

[0075] Precursor hydrolysis: 4 mL of MTES were mixed with 22.4 mL of methanol, 1.48 mL of oxalic acid solution (0.001 mol/L) were added. The resulting mixture was stirred for 24 h.

[0076] Condensation: After precursor hydrolysis, 0.36 g of silanol terminated polydimethylsiloxane (PDMS) and 1.48 mL NH.sub.3 (10 mol/L) were added dropwise and the resulting mixture was stirred for 2 h.

[0077] Subsequently, the fabrics treated with silanols were soaked with these alcoholic sols. The wet samples were cured in a furnace for 2 days at 50 C., and then washed with ethanol every 12 h, repeating twice.

[0078] Thereafter, the wet gels were dried at atmospheric pressure in a three-stage furnace, at 50 C. for 12 h, 80 C. for 2 h and finally at 200 C. for 2 h.