Flame-proofed artefact and a method of manufacture thereof

Abstract

A method of fabricating an artifact (15) includes treating natural fibers (110) with a non-halogenated flame retardant agent (120), the fibers (110) also being treated with a smoke suppressant (120). At least one pre-preg is formed (170, 180) from the treated natural fibers and from a resin composition (160) including a smoke suppressant (150) admixed therein (160). An uncured artifact is formed from a core or substrate (12) and the pre-preg, which provides a skin, and is cured (210). A non-fibrous silicate fire resistant material (190, 230) is introduced by: (i) admixing the fire resistant material with the resin composition, and/or (ii) applying the fire resistant material to an outer surface of the pre-preg or an outer surface of the skin of the uncured artifact, and/or (iii) applying the fire resistant material to an outer surface of the skin of the cured artifact. The invention extends to a flame-proofed artifact (15).

Claims

1. A method of fabricating an artefact, the method including treating natural fibres by applying a non-halogenated flame retardant agent to the fibres; forming at least one pre-preg from the treated natural fibres and a resin composition, the formation of the pre-preg including impregnating the treated natural fibres with the resin composition; forming an uncured artefact from a core or substrate and said at least one pre-preg, the formation of the uncured artefact including using the at least one pre-preg to provide a skin on at least one side of the core or substrate; and forming a cured artefact by curing the uncured artefact and thereby also bonding the skin to the core or substrate, wherein curing the uncured artefact is effected by compression moulding of the uncured artefact in a pre-heated mould which is at an initial temperature of between 100° C. and 120° C., the temperature in the mould subsequently being increased to between 130° C. and 145° C., the method further including introducing a non-fibrous silicate fire resistant material using one or more of the following steps: (i) admixing the non-fibrous silicate fire resistant material with the resin composition prior to or during the forming of the at least one pre-preg, (ii) applying the non-fibrous silicate fire resistant material to an outer surface of the at least one skin of the uncured artefact, or to a surface of the pre-preg used to provide the skin, (iii) applying the non-fibrous silicate fire resistant material to an outer surface of the at least one skin of the cured artefact, the method further including treating the natural fibres with a smoke suppressant prior to the impregnation of the natural fibres with the resin composition and admixing a smoke suppressant in the resin composition that impregnates the fibres, wherein the non-halogenated flame retardant agent applied to the natural fibres includes a phosphate-based flame retardant and zinc borate.

2. A method as claimed in claim 1, in which the artefact is a panel, the formation of the uncured artefact including using the at least one pre-preg to provide a skin at least on opposed sides of the core.

3. A method as claimed in claim 1, in which the non-halogenated flame retardant agent is applied to the natural fibres in the form of an aqueous solution or aqueous dispersion of the flame retardant agent, and in which the treated natural fibres are dried prior to impregnating the treated natural fibres with the resin composition.

4. A method as claimed in claim 1, in which the non-halogenated flame retardant agent includes a non-halogenated flame retardant which acts in the condensed phase.

5. A method as claimed in claim 1, in which the smoke suppressant with which the fibres are treated is included in the non-halogenated flame retardant agent which is applied to the fibres.

6. A method as claimed in claim 1, in which the smoke suppressant with which the natural fibres are treated prior to their impregnation is a zinc borate.

7. A method as claimed in claim 1, in which the smoke suppressant admixed with the resin composition that impregnates the fibres is a zinc borate.

8. A method as claimed in claim 1, in which the non-fibrous silicate fire resistant material is admixed with the resin composition using step (i), the non-fibrous silicate fire resistant material being in the form of an aqueous dispersion of the non-fibrous silicate fire resistant material when it is admixed with the resin composition.

9. A method as claimed in claim 1, in which forming at least one pre-preg from the treated natural fibres and a resin composition includes heating the impregnated natural fibres in an oven at a temperature range of 120° C. to 140° C.

10. A method as claimed in claim 1, in which the core or substrate is of a honeycomb or foam material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in greater detail by way of non-limiting, illustrative examples with reference to the following diagrammatic drawings in which:

(2) FIG. 1 shows schematically in a three-dimensional view a flame-proofed artefact in accordance with the invention; and

(3) FIG. 2 shows schematically process steps forming part of a method in accordance with the invention for fabricating an artefact in accordance with the invention.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

(4) Referring to FIG. 1, an embodiment of a flame-proofed artefact in accordance with the invention is designated generally by reference numeral 15. The artefact 15 is in the form of a panel and is suitable for use in aircraft. The panel 15 includes a honeycomb core 12 and cured skins 14 and 16, between which the core 12 is sandwiched. It should be noted that, instead of a honeycomb core, foam can be used as a core for making artefacts, such as panels, suitable for use in other applications, such as in construction of buildings, for example.

(5) The cured skins 14 and 16 each include natural fibres impregnated with a resin composition, the natural fibres having been treated with a non-halogenated flame retardant agent prior to being impregnated with the resin composition. Outer surfaces 18, 20 of the panel 15 (i.e. the outer surfaces of the cured skins 14, 16) are coated with vermiculite.

(6) The cured skins 14, 16 are formed from pre-pregs, which are then cured. In this example, the natural fibres used for the pre-pregs from which the cured skins 14 and 16 are formed are in the form of a woven flax fabric. The resin composition is a thermoset resin, more specifically a phenolic resin.

(7) FIG. 2 is a schematic diagram showing the method of fabricating the panel 15. Fabric 110 is subjected to treatment with an aqueous non-halogenated flame retardant agent 120. More specifically, in step 130, the non-halogenated flame retardant agent 120 is padded onto the fabric, which is then dried in a drying step 140, which takes place in an oven at a temperature of about 120° C. for a duration of about 1 minute. The non-halogenated flame retardant agent includes a non-halogenated flame retardant which is a proprietary product, Flammentin TL833, supplied by ACTI, Westville, 3630, South Africa. Flammentin TL833 is a liquid, marketed as a flame retardant based on ammonium salts of inorganic acids. It is believed that it contains di-ammonium phosphate as the major flame retardant in the composition, and may possibly also include an acrylic resin or polymer. The proportion of the flame retardant in the non-halogenated flame retardant agent is between about 15% and about 30% solids by mass, i.e. typically between about 20% and 25% solids by mass.

(8) The non-halogenated flame retardant agent 120 includes a smoke suppressant, in particular a zinc borate. The proportion of zinc borate in the non-halogenated flame retardant agent 120 is about 5% by mass. Zinc borate (5-hydrate) can be produced on-site by known methods.

(9) In an alternative embodiment of the invention, in place of the zinc borate, a nanoclay, in the form of a proprietary halloysite product, obtainable from e.g. Sigma-Aldrich, which has offices in many countries, e.g. Sigma-Aldrich (Pty) Ltd of PO Box 10434, Aston Manor 1630, South Africa, is admixed with the non-halogenated flame retardant agent (Flammentin TL833 in this example) and water to form an admixture, and the admixture is padded onto the fabric.

(10) Further, a zinc borate as a smoke suppressant, represented by block 150, is also admixed thoroughly with a phenolic resin composition 160, the proportion of zinc borate in the skins 14, 16 after the formation of the panel 15 amounting to approximately 11% of the solid resin. The phenolic resin composition is proprietary Eponol (trade name) Resin 2485 obtainable from Momentive Specialty Chemicals Inc. of 180 East Broad Street, Columbus, Ohio, USA. EPONOL™ Resin 2485 is a phenolic resin which is designed for pre-preg applications. The pre-pregs have a good draping quality, and are suitable for the production of composite components with, e.g., a Nomex (trade name) honeycomb core as used, for example, in the internal lining of aircraft (e.g. AIRBUS (trade name) side panels and luggage racks). After the drying step 140, the fabric 110 is impregnated with the resin composition with the zinc borate to form pre-pregs or skins in an impregnating step 170, and a heating step 180, in which the resin composition is partially cured to a B-stage. In the heating step 180, the heating is taking place in an oven at a temperature range of 120° C. to 140° C. for 10 minutes.

(11) In a step 200, a fire resistant material in the form of vermiculite (VMT) (obtained from Palabora Mining Company Limited, 1 Copper Road, 1389 Phalaborwa, South Africa; micron grade), represented by block 190, is applied onto surfaces of the pre-pregs or skins produced in step 180. The mass per unit area of vermiculite applied to the surfaces is approximately 45 g/m.sup.2.

(12) The panel 15 is formed by sandwiching a honeycomb core 12 [e.g. a Nomex (trade name) honeycomb core] between the vermiculite coated pre-pregs or skins produced in step 200, and bonding of the skins to the core 12 is effected by compression moulding, in a compression moulding step 210, the step 210 taking place in a pre-heated mould at an initial temperature of 110° C. for 10 minutes which is later increased to between 130° C. and 145° C. for 70 minutes, to ensure full curing of the resin composition in the pre-pregs/skins. It is to be mentioned that no adhesives are necessary in this process for bonding the core 12 to the skins, during which the skins are also fully cured. The proportion of resin in the cured skins 14, 16 is approximately 50% by mass.

(13) In an alternative embodiment of the invention, an aqueous dispersion of vermiculite, represented in FIG. 2 by block 230, may be applied to the outer surfaces of the panel 15, once the panel 15 has been formed, and the panel 15 may then be dried at temperatures of between 70° C. and 90° C. in an oven. FIG. 2 illustrates both the application of a fire resistant material (such as vermiculite) to the skins and the application of a fire resistant material to the outer surfaces of the cured skins after compression moulding.

(14) In yet another alternative embodiment of the invention (not shown), an aqueous dispersion of vermiculite can, instead of or in addition to being applied to the outer surfaces of cured or uncured skins, be added into the resin, 160, for example prior to the impregnation of the natural fibres. In the fabrication of the panel 15 described above, however, the vermiculite is only applied to the uncured skins prior to the compression moulding and curing thereof.

(15) As indicated in Table 2 below, various panels, referred to as Panels 1, 3, 4, 5, 6 and 15 were fabricated and their characteristics were tested, including their flammability, smoke density and heat release values. Panel 15 was fabricated as described above. Panel 1 was produced using the same method as for Panel 15 save that no vermiculite was applied to the surfaces of the panel, there was no pre-heating of the mould prior to compression moulding, the panel has lower resin content and the non-halogenated flame retardant agent had a lower concentration of Flammentin TL833 and zinc borate. Panel 3 was produced using the same method as for Panel 1 save that a higher resin content was used for Panel 3. Panel 4 was produced using the same method as for Panel 3 save that the aqueous solution of Flammentin TL833 and zinc borate used for Panel 4 had a lower concentration of Flammentin TL833. Panel 5 was produced using the same method as for Panel 3 save that halloysite nano-clay, instead of zinc borate, was included in the formulation of the non-halogenated flame retardant agent which was applied to the natural fibres prior to impregnation with the resin. Panel 6 was produced using the same method as for Panel 3 save that the aqueous solution of Flammentin TL833 and zinc borate used for Panel 6 had a higher concentration of both Flammentin TL833 and zinc borate.

(16) TABLE-US-00002 TABLE 2 Tested characteristics of various panels Panel 15 Airbus Limit (with Test FAA Limit (undecorated panel) 1 3 4 5 6 15 décor) Flammability 60 s - burn length (mm) 152 80 88 70 102 85 79 89 80 Flammability 60 s - flame time (s) 15 0 0 0 0 0 0 0 0 Flammability 60 s - flame time - 3 0 0 0 0 0 0 0 0 drips (s) Flammability 12 s - burn length (mm) 203 60 32 27 37 28 17 39 57 Flammability 12 s - flame time (s) 15 0 0 0 0 0 0 0 0 Flammability 12 s - flame time - 5 0 0 0 0 0 0 0 0 drips (s) Smoke density - flaming (Ds) 200 20 27 35 23 37 29 13 76 Toxicity: HCN (ppm) N/A 150 2 2 2 2 2 2 2 Toxicity: CO (ppm) N/A 1000 248 244 240 225 293 206 283 Toxicity: NOx (ppm) N/A 100 8 11 12 10 12 12 11 Toxicity: SO.sub.2 (ppm) N/A 100 2 3 3 4 2 9 8 Toxicity: HF (ppm) N/A 0 0 0 0 0 0 0 113 Toxicity: HCl (ppm) N/A 0 0 0 0 0 0 0 50 Heat release (2 mins) OSU 65 35 52 50 57 54 50 27 52 (kW .Math. min/m.sup.2) Peak heat release OSU(kW/m.sup.2) 65 35 48 60 62 63 49 29 59 Heat release (2 mins) Cone Cal. N/A N/A 9.9 57.9 90.5 81.4 13.1 4.5 — (kW .Math. min/m.sup.2) Peak heat release Cone Cal. N/A N/A 13.2 135.8 241.3 180.7 10.7 8.2 — (kW/m.sup.2) Time to ignition Cone Cal.(s) N/A N/A N/A 67 49 56 96 N/A — FAA Limits: DOT/FAA/AR-00/12, Aircraft Materials fire test Handbook, April, 2000. Airbus Limits: based on experience of the state of the art for undecorated panels which fulfil, when decorated, ABD0031, Issue: F, Fire Worthiness Requirements Pressurized Section of Fuselage, June 2005. ABD0031 sets limits for parts inside an aircraft only and these parts would typically be decorated. Flammability testing according to Airbus methods AITM2.0002A, AITM2.0002B (FAR 25.853 and FAR 25.855) Smoke density testing according to Airbus AITM2.20007 (FAR 25.853) Toxicity testing according to Airbus AITM3.0005 Peak heat release and heat release (2 mins) testing according to Airbus method AITM2.0006 (FAR 25.853) Cone Calorimeter testing according to ISO 5660-1

(17) As indicated in Table 2, panel 15 in particular is suitable for aircraft applications. As can be noted from the table, panel 15, both with and without decor having been applied to a surface thereof, was shown to have suitable characteristics in terms of flammability, smoke density, toxicity and heat release values.

(18) Thus, the invention as illustrated and described above provides for the fabrication of bio-based panels suitable for use in the interior of an aircraft. It will be appreciated that the use of natural fibres is advantageous in that it can provide an artefact which is lightweight (as natural fibres have lower weight than glass fibres) and biodegradable. In particular, their use can lead to fuel and energy savings and can provide a CO.sub.2 credit in an aircraft life cycle analysis.

(19) The flame retardant treatment approach taken in this invention, i.e. the treatment of the fibres with the non-halogenated flame retardant agent prior to impregnation with a resin, advantageously avoids major polymer modification with additives which may otherwise have been required to impart suitable characteristics to permit use in aircraft applications, i.e. lightness of weight, adequate strength and compliance with fire, smoke and toxicity requirements.

(20) As indicated above, the AIRBUS limiting values for OSU heat release (peak, 5 min), OSU heat release (2 min) and smoke density for panels in an undecorated form are 35 kW/m.sup.2, 35 kW.Math.min/m.sup.2 and 20 Ds, respectively, and the FAA Airworthiness limiting values for OSU heat release (peak, 5 min), OSU heat release (2 min) and smoke density for decorated panels are 65 kW/m.sup.2, 65 kW.Math.min/m.sup.2 and 200 Ds, respectively. The Airbus values are not fixed but are based on the experience of Airbus and are mirrored in the state of the art.

(21) The surface coatings of vermiculite in conjunction with the non-halogenated flame retardant agent for panel 15 provide improved fire performance, and in particular provide OSU heat release (peak, 5 min) and OSU heat release (2 min) values below the abovementioned AIRBUS and FAA Airworthiness limiting values. As Table 2 indicates, the following superior heat release values were achieved: Undecorated panel: Heat release (peak, 5 min) 29 kW/m.sup.2 (OSU), Heat release (2 min) 27 kW.Math.min/m.sup.2 (OSU), Decorated panel: Heat release (peak, 5 min) 59 kW/m.sup.2 (OSU), Heat release (2 min) 52 kW.Math.min/m.sup.2 (OSU).

(22) The surface coatings of vermiculite in conjunction with the non-halogenated flame retardant agent for panel 15 provide improved smoke suppression and in particular provide smoke density values below the abovementioned AIRBUS and FAA Airworthiness limiting values. As Table 2 indicates, the following superior smoke density values were achieved: Undecorated panel: Smoke density 13 Ds, Decorated panel: Smoke density 76 Ds.

(23) It is believed that these favourable heat release values are achieved by a synergistic combination of the use of the non-halogenated flame retardant agent, comprising the non-halogenated flame retardant and the smoke suppressant, on the natural fibre structure and the use of non-fibrous silicate fire resistant material, which as indicated above was applied to the surfaces of the pre-pregs or skins. Further, the combination of the non-halogenated flame retardant agent with the non-fibrous silicate fire resistant material (vermiculite), which has thermal insulating and water release properties, results in the superior flammability, smoke and toxicity values for the artefact.

(24) Another advantage of the invention as illustrated and described is that a non-halogenated, environmentally benign flame retardant agent and environmentally benign fire resistant material is used. Furthermore, panel 15 can be easily and cost-effectively fabricated. In particular, no adhesive is needed to bond the core 12 to the skins 14, 16. On-site assembly of the panel 15 is possible.