PHENOLIC-BASED METAMATERIALS AND METHODS OF FORMING PHENOLIC-BASED METAMATERIALS

Abstract

The present invention relates tophenolic-based metamaterials and methods for preparing phenolic-based materials. The present invention also relates to composites formed from phenolic-based metamaterials. More specifically, the present invention is concerned with phenolic materials formed by heating phenolic resin mixtures.

Claims

1. A method for preparing a phenolic metamaterial, the method comprising providing: (i) 1 part by weight of a phenolic resin; (ii) 2 to 4 parts by weight of a transition metal hydroxide and/or aluminium hydroxide; mixing components (i) and (ii) to form a phenolic resin mixture; and heating the phenolic resin mixture at a temperature of greater than 200 C. to form the phenolic metamaterial.

2. A method according to claim 1, wherein 2.5 to 3.5 parts by weight of the metal hydroxide are provided in (ii).

3. A method according to claim 1 or claim 2, wherein the mixing is conducted in the presence of 0.2 to 1 parts by weight, relative to the phenolic resin, of a viscosity controlling agent.

4. A method according to claim 3, wherein the mixing is conducted in the presence of 0.4 to 0.9 parts by weight of the viscosity controlling agent.

5. A method according to any preceding claim, wherein the viscosity controlling agent is a liquid, preferably selected from one or more of butanol, chloroform, ethanol, water, acetonitrile, hexane and isopropyl alcohol.

6. A method according to claim 5, wherein the viscosity controlling agent is water.

7. A method according to any one of the preceding claims, wherein the phenolic resin is a phenolic resole resin, preferably a phenolic resole resin that includes less than 10% by weight of free formaldehyde, preferably less than 1% by weight, more preferably less than 0.5% by weight, for example less than 0.1% by weight.

8. A method according to any one of the preceding claims, wherein the metal hydroxide comprises particles having a particle size distribution with a D90 from 50 to 70 m, and/or a D50 from 15 to 35 m, and/or a D10 from 1 to 10 m.

9. A method according to claim 8, wherein the metal hydroxide comprises particles having a particle size distribution with a D90 from 55 to 65 m, and/or with a D50 from 20 to 30 m, and/or with a D10 from 2 to 5 m.

10. A method according to any one of the preceding claims, wherein the metal of the metal hydroxide is one or more of scandium, vanadium, chromium, manganese, iron, cobalt and aluminium.

11. A method according to any one of the preceding claims, wherein the metal hydroxide is of the formula M(OH).sub.3, wherein M is a metal.

12. A method according to any one of the preceding claims, wherein the metal hydroxide is aluminium hydroxide.

13. A method according to any one of the preceding claims, wherein the step of heating the phenolic resin mixture at a temperature of greater than 200 C. is conducted in the substantial absence of oxygen.

14. A method according to any one of the preceding claims, wherein the heating is at a temperature of around 300 C. or greater, preferably around 400 C. or greater, more preferably 500 C. or greater, for example 600 C. or greater.

15. A method according to any one of the preceding claims, wherein the phenolic resin mixture is heated for at least about one minute, preferably at least about 5 minutes, more preferably at least about 10 minutes, for example at least about 15 minutes.

16. A method according to any one of the preceding claims, further comprising applying the phenolic resin mixture to a substrate prior to heating the mixture at a temperature of greater than 200 C. to form a composite material.

17. A method according to claim 16, wherein the substrate is in the form of a sheet.

18. A method according to claim 17, wherein the phenolic resin mixture is distributed in a layer on a surface of the sheet.

19. A method according to any one of claims 16 to 18, wherein the substrate comprises a metal, polymer and/or an inorganic material.

20. A method according to claim 19, wherein the substrate comprises aluminium.

21. A method according to any one of claims 16 to 20, further comprising the step of applying a second substrate to the phenolic resin mixture.

22. A method according to claim 21, wherein the second substrate is as defined in any one of claim 17, 19 or 20.

23. A method according to claim 21 or claim 22, wherein the phenolic resin mixture is applied so as to form a layer between two aluminium sheets.

24. A method according to any one of the preceding claims, further comprising adding fibres to the phenolic resin mixture.

25. A method according to claim 24, wherein the fibres are woven or unwoven.

26. A method according to claim 24 or claim 25, wherein the fibres are in the form of a layer.

27. A method according to claim 26, wherein the fibres are in the form of a mat or fabric.

28. A method according to any one of claims 24 to 27, wherein the fibres are selected from one or more of mineral fibres (such as finely chopped glass fibre and finely divided asbestos), chopped fibres, finely chopped natural or synthetic fibres, and ground plastics and resins in the form of fibres.

29. A method according to claim 28, wherein the fibres are selected from one or more of carbon fibres, glass fibres and aramid fibres.

30. A method according to any one of the preceding claims, wherein the phenolic resin mixture has a viscosity of from 200 to 10,000 mPa.Math.s at 20 C.

31. A method according to any one of the preceding claims, wherein the phenolic resin mixture is caused or allowed to at least partially set prior to heating the mixture at a temperature of greater than 200 C.

32. A method according to claim 31, wherein the step of causing or allowing the phenolic resin mixture to at least partially set comprises heating the mixture to a suitable temperature.

33. A method according to claim 32, wherein the phenolic resin mixture is heated to a temperature of at least 50 C.

34. A method according to claim 32 or claim 33, wherein the phenolic resin mixture is heated to a temperature between 100 and 200 C.

35. A method according to any one of claims 32 to 34, wherein the phenolic resin mixture is heated to cause the mixture to at least partially set for at least one minute.

36. A method according to any one of the preceding claims, wherein the phenolic resin mixture is moulded or shaped prior to the step of heating the phenolic resin mixture to form the phenolic metamaterial.

37. A phenolic metamaterial or a composite prepared by a method according to of any one of claims 1 to 36.

38. A method for making a composite material comprising providing a phenolic

37. rial according to claim 37 and bonding the material to a substrate.

39. A composite material prepared according to the method of claim 38.

40. Use of a transition metal hydroxide and/or aluminium hydroxide to increase the hardness of a cured or uncured phenolic resin material, wherein the phenolic resin material comprising a transition metal hydroxide and/or aluminium hydroxide is heated to a temperature of greater than 200 C.

41. Use according to claim 40, wherein the step of heating the phenolic resin mixture at a temperature of greater than 200 C. is conducted in the substantial absence of oxygen.

42. Use according to claim 40 or claim 41, wherein the heating is at a temperature of around 300 C. or greater, preferably around 400 C. or greater, more preferably 500 C. or greater, for example 600 C. or greater.

43. Use according to any one of claims 40 to 42, wherein the heating is conducted for at least about one minute, preferably at least about 5 minutes, more preferably at least about 10 minutes, for example at least about 15 minutes.

44. Use according to any one of claims 40 to 43, wherein the metal hydroxide is as defined in any one of claims 8 to 12.

45. Use according to any one of claims 40 to 44, wherein the phenolic resin mixture comprises a mixture as defined in any one of claims 1 to 7 or 24 to 35.

46. Use according to any one of claims 40 to 45, wherein the phenolic resin mixture is applied to a substrate as defined in any one of claims 16 to 23.

Description

EXAMPLE 1

Preparation of the Phenolic Resin Mixture

[0129] A phenolic resin mixture was formed according to the composition shown in Table 1 by use of a mechanical mixer until such time that the components appeared to be homogeneously combined.

[0130] The phenolic resole resin used was an aqueous resole resin having a dry weight of 74-77% and less than 0.1% free formaldehyde obtained from Satef Huttenes-Albertus as LACFEN ES 81 LF.

[0131] The Al(OH).sub.3 is a ground aluminium hydroxide having 99.60% Al(OH).sub.3 content, d10 of 3.5 m, d50 of 23.0 m, and d90 of 57.0 m obtained from CellMark chemicals as ATH G200.

TABLE-US-00001 TABLE 1 Relative amount Aqueous phenolic resole 100 resin Grey sand 160 Al(OH).sub.3 220 Water 28 Black iron oxide 2 Glass fibres (chops) 200

EXAMPLE 2

[0132] The resin mixture of Example 1 was applied to an aluminium sheet having a thickness of greater than 0.5 mm and the resin was cured.

[0133] The composite was heated using a blowtorch flame (producing a temperature of around 1150 C.) applied to the surface of the aluminium sheet. After 10 to 15 minutes of heating, there was some melting of the aluminium in the local region where the flame was applied. However, the sheet as a whole substantially maintained its structural integrity and the phenolic material was structurally unaffected. The temperature at the centre of the area in which the flame is applied was measured to be 1150 C., dropping to around 600 C. at a radius of about 4 cm and then rapidly falling with increased radius. Even after more than 30 minutes heating, a layer of aluminium remained unmelted between the flame and the phenolic material.

[0134] When the aluminium sheet that was heated directly was removed from the phenolic material, the phenolic material underneath the aluminium was found to have formed a hard ceramic-like surface which was surprisingly found to have a hardness of from 300 to 600 HV on the Vickers scale. This surface was also found to conduct electricity, while the phenolic resin does not.

[0135] The phenolic material underneath the aluminium was found not to have burned and no ash was observed where temperatures of 600 C. or higher were measured. Where the temperature dropped to less than 400 C., some ash and burning of the resin was observed. Therefore, temperatures of greater than 400 C. appear to offer an advantage in forming the hard metamaterial.

[0136] At the rear surface of the cured resin from where the flame was applied, where the temperature was also lower, some ash was observed on the phenolic material.

EXAMPLE 3

[0137] Two aluminium sheets, each having a thickness of less than 0.5 mm, were bonded together by a layer of the resin mixture of Example 1. The resin was then cured.

[0138] The composite was heated as described in Example 2. The area of the first aluminium sheet directly in contact with the flame underwent some melting in the region in which the flame was applied. However, the composite as a whole substantially maintained its structural integrity and the second aluminium sheet did not distort or melt even after more than 30 minutes of heating.

[0139] As in Example 2, the same hard ceramic-like material was observed where the phenolic material was heated. Underneath the aluminium sheet opposite to where the heating was applied, the phenolic material was observed to char but not incinerate after 15 minutes of heating.

EXAMPLE 4

[0140] Two sheets of typical kitchen aluminium foil were attached together by a layer of the resin mixture of Example 1 and were also coated with the same resin, which was subsequently cured.

[0141] The composite was heated was heated as described in Example 2. The composite maintained structural integrity without breakage and the area of the phenolic material that was heated formed the hard ceramic-like material observed in Examples 2 and 3. The aluminium in the composite was found to be intact after the heating.

EXAMPLE 5

[0142] Aluminium shavings were immersed in the resin mixture of Example 1, which was then cured.

[0143] This composite was heated as described in Example 2 for more than 30 minutes and there was no structural failure or burning of the resin during this heating. The phenolic material was found to form the hard ceramic-like material where heated, without burning or formation of ash.

[0144] When aluminium shavings were applied only to the surface of a layer of the resin mixture, during the same heating for 30 minutes, the composite did not yield. Upon cooling of the composite, the area in which the flame was applied was less structurally strong than for the composite having shavings immersed in the resin mixture.

EXAMPLE 6

[0145] A layer of aluminium powder was deposited on front and rear surfaces of a layer of the resin mixture of Example 1, and the resin was cured.

[0146] When the composite was heated as described in Example 2, results similar to Example 5 were obtained, except that the area directly heated by the flame appeared to be harder in comparison.

EXAMPLE 7

[0147] Heating the resin mixture or composite at 450 C. with a hot air stream instead of a blowtorch was also found to form a hard ceramic-like material as observed in Examples 2 to 6.

[0148] The above examples demonstrate the formation of an unusually hard ceramic-like material that results from heating the resin mixture. Surprisingly, the material exposed to higher temperatures, for example higher than 400 C., was found to result in less ash formation and burning, or even substantially no ash formation or burning, compared to material heated at lower temperatures.