A FLAME-PROOFED ARTEFACT AND A METHOD OF MANUFACTURE THEREOF
INTRODUCTION
This invention relates to a method of fabricating an artefact and to a flameproofed
artefact.
BACKGROUND TO THE INVENTION
The use of synthetic fibre-reinforced petroleum based plastics for
aerospace and automotive applications is creating problems with depleting oil reserves
and growing ecological damage. Currently, materials used in aircrafts for various
applications include glass fibre/carbon-fibre reinforced epoxy/phenolic composites.
An answer in solving these problems may be provided by natural fibrereinforced
composites or biopolymers based on renewable resources. The major
attractions of these composites are that they are lightweight (leading to energy savings),
environmentally-friendly, fully degradable and sustainable, that is, they are truly 'green'.
Other advantages of the use of such composites are that it contributes to the greening
of aircraft components, the implementation of REACH (Registration, Evaluation,
Authorization and Restriction of Chemicals) and is in line with the European Union's
Clean Sky Initiative. The use of natural fibres, however, poses problems because of
their flammability and smoke generation.
One of the challenges in the aviation sector is to address flame, smoke
and toxicity (FST) requirements. It is highly critical that panels for aviation applications
should comply with FST standards, e.g. as per the United States of America's Federal
Aviation Authority's (FAA) airworthiness criteria. Generally, the main flame retardant
agents are applied in the matrix polymer.
US 5,309,690 elaborates on the development of a composite panel
comprising of sheets of natural fibre, such as corrugated cardboard impregnated with a
thermosetting resin. The panel also contains a cellular core which is sandwiched
between the sheets of natural fibre and contains inorganic insulating material and a
material in granular form that releases water at elevated temperatures. A flame
retardant agent such as diammonium phosphate may be included in the liquid
composition used to impregnate the sheets with resin. It is to be noted that the panel
does not include a fire protective coating and that the natural fibres were not treated
with a flame retardant agent prior to impregnation with the resin. Glue was used to
bond the core to the sheets.
WO 2007/20657 is based on the manufacture of a natural fibre thermoset
composite of high tensile strength, compressive strength, high cross breaking point and
high water absorption properties. In this disclosure, the composite is manufactured by
impregnation of bamboo and jute fibre in a slurry of resin solution and additives,
followed by compression moulding. In this document, it is mentioned that additives
(possibly flame retardant agents) can be added in the resin.
IN 200300400 describes the manufacture of a moulded natural fibre
thermoset fire proof composite sheet. The method involves dissolving modified resin
with cross linking agents, forming a slurry by mixing filler and additives in a resin
solution and impregnating jute cloth of any form in the slurry followed by compression
moulding.
IN 200300729 describes the manufacture of a moulded natural fibre
thermoset fire proof composite sheet. The method involves dissolving resin in methanol
with cross linking agents, forming slurry by mixing filler and additives in a resin solution
and impregnating jute cloth of any form in the slurry followed by compression moulding.
EP 1842957 describes providing a flame retardant fibre sheet with flame
retardancy by coating a sheet with poly-ammonium phosphate having an average
degree of polymerization in the range of between 10 and 40. The sheet may include
synthetic and/or natural fibres. To mould the fibre sheet, the fibres in the sheet may be
bonded with a synthetic resin binder. The resin may be a thermosetting resin. In the
illustrative examples provided in the specification, a resin binder is applied and the
polyammonium phosphate is either added with a resin binder or is applied after the
application of a resin binder. The fibre sheet may be moulded into a panel shape or
other shape, generally by hot-press moulding. A plural number of sheets can be
laminated together upon moulding.
EP 1369464 describes a flame retardant agent which is a phosphatecontaining
compound which does not contain a halogen. The specification describes
the treatment of polyester fibre woven fabric by immersion thereof in a solution
containing the flame retardant agent followed by heat treatment at a prescribed
temperature. The specification also describes the manufacture of articles with polymer
materials that have been treated with the flame retardant material, the flame retardant
material having been added to the polymer when it is molten.
US 201 0/03241 92 (corresponding published applications including CA
2667407 and EP 2089456) describes a process for the improvement of flameproofing
fibre composite materials containing fibre materials embedded in a polymer, e.g. phenol
resin. Pre-pregs are manufactured, preferably by known pre-preg or SMC-tooling
methods, with the surface of the fibre-composite material being covered with a layer
which includes a flame-proofing material, and in this regard the specification describes
the use of aluminium hydroxide as a flame-proofing material . Instead or in addition, the
fibre material may be treated with a flame-proofing material by soaking, spraying,
coating or other methods before embedding the fibres in the polymer, and in this regard
the specification describes the use of a flame-proofing material which is supplied under
the trade name Flavacon GP {sic). It is believed that "Flavacon" should read "Flacavon",
and it is believed to be a phosphorus-based flame retardant agent. More particularly, it
is believed that the active ingredient is an organic phosphorus and nitrogen containing
compound. An artefact manufactured with natural fibres in accordance with this method
was found to exhibit the following heat release values: Heat release (peak, 5 min): 47
kW/m2 and Heat release (2 min): 60 kW/m2.
US 2006/01 89236 describes a panel having a three-dimensional artistic
design on its surface and the manufacture thereof. The panel includes a first and a
second outer layer which each comprise of fire retardant material or material which has
been treated such that the material is fire retardant. The layers of fire retardant
materials can comprise paper, fabric, foam, honeycomb or paper-backed adhesive. For
example, one of the layers may comprise of paper or fabric and the other layer may
comprise of foam, honeycomb or paper. The layers can be bonded by means of a
welding machine such as an ultrasonic sound machine or attached by a thermoplastic,
thermoset, thermobond or other fire resistant adhesive. The production of the fireretardant
layers is not described, the illustrative examples provided in the specification
describing the use of various commercially available materials.
US 7,232,605 describes composite structural members (e.g. panels or
beams) which include polymers arranged in a two- or three- dimensional cellular
skeletal structure and reinforced with fibres, which may be natural, and with nano-scale
clay particles. The invention seeks to overcome the lower material stiffness of
biocomposites by the use of cellular and sandwich structures. The polymers can be
thermoset. It is stated that clay particles can double the tensile modulus and strength of
numerous thermoset resins and, in addition, make the resin less permeable to liquids
and gases, more flame retardant and tougher. The specification describes the
manufacture of cellular beams and plates in which green hemp fibres or chopped flax
fibres were impregnated with unsaturated polyester resin, with cells being formed with
the use of removable rods. After the impregnation, curing was effected in an oven.
Hybrid cellular sandwich panels are also described, which include skins cured integrally
with a cellular core, the skins comprising a thermoset polymer, which may be nano-clay
reinforced, and a natural or synthetic fibre mat.
US 2007/0238379 describes ballistic resistant composites and articles
formed therefrom for use in airplanes and other vehicles. A central layer, preferably
comprising of an aerospace-specification grade honeycomb material, is positioned
between panels comprising of a plurality of non-woven fibrous layers, and then moulded
into a structural member. Various high strength fibres are mentioned as being suitable
for the panels including polyethylene fibres, aramid fibres, polybenzazole fibres,
polyolefin fibres, polyvinyl alcohol fibres, polyamide fibres, polyethylene terephthalate
fibres, polyethylene naphthalate fibres, polyacrylonitrile fibres, liquid crystal copolyester
fibres, glass fibres, carbon fibres and rigid rod fibres. The fibrous layers are coated or
impregnated with a polymeric composition and consolidated to form the panel. The
polymeric composition is preferably a thermosetting plastics material. The panels may
be attached to the honeycomb layer by means of an adhesive, with the panels
preferably being independently moulded or consolidated prior to attachment to the
honeycomb layer. Optionally, one or more layers of fire resistant material, such as fibre
glass, aramid paper or a fibrous material impregnated with a fire resistant composition,
may be attached to one or more surfaces of the panels to provide fire resistance.
Alternatively, a fire resistant additive may be blended with the polymeric composition
which is coated on the fibres. It is stated that the composites of the invention are
particularly useful for the formation of structural members of airplanes or other vehicles,
such as doors or bulkhead structures.
Phosphoric acid and its salts have been used for a long time as flame
retardants for cellulosic fibres. Diammonium phosphate and ammonium phosphate, in
particular, being the most widely used non-durable flame retardants for cellulosics (see
for example Lyons J.W. Cellulose: Textiles in The Chemistry & Uses of Fire Retardants,
pp 169 - 170, Wiley Interscience, New York, 1970 and Lewin M. and Sello S.B.
Flameproofing of Cellulosics in Lewin M., Atlas S.M. and Pearce E.M. (Eds.), Flame-
Retardant Polymeric Materials, pp 23 - 24, Plenum Press, New York, 1975).
Matko et al. applied diammonium phosphate to lignocellulosic fillers in an
aqueous solution, followed by drying under an infrared lamp (see Matko Sz., Toldy A.,
Keszei S., Anna P., Bertalan, Gy. and Marosi Gy, Flame Retardancy of Biodegradable
Polymers and Biocomposites, Polymer Degradation and Stability, 88, pp 138 - 145,
2005). The lignocellulosic materials (fillers) were wood flake, of 1.2 mm size, and corn
shell, of 3-1 2 mm size. The polymer matrix was polyurethane.
It is to be appreciated that most current work on flame retardancy of
natural fibre reinforced composites is concerned mainly with thermoplastic resins such
as polypropylene.
Jang et al. produced paper-sludge / phenolic composites which contained
flame retardants selected from phosphate/halogen, halogenated and inorganic flame
retardants (see Jang J., Chung H., Kim M. and Sung H., The Effect of Flame Retardants
on the Flammability and Mechanical Properties of Papersludge/Phenolic Composites,
Polymer Testing, 19, pp 267 - 279, 2000). The inorganic flame retardants were mixed
with the resin whereas the phosphate/halogen combinations were dissolved in a solvent
before addition to the paper-sludge.
What is ideally required is a method of fabricating an artefact such as a
panel which is environmentally-friendly and which has suitable characteristics for use in
aircrafts i.e. lightness of weight, adequate strength and compliance with fire, smoke and
toxicity requirements.
In artefacts comprising of resin-fibre compounds, the use of natural fibres,
although advantageous from the view of being environmentally friendly, presents
particular challenges when the artefacts require suitable FST characteristics for use in
aircraft. In particular, the FAA Airworthiness maximum allowable values for OSU heat
release (peak, 5 min), OSU heat release (2 min) and smoke density for decorated
panels are 65 kW/m2, 65 kW.min/m2 and 200 Ds respectively, and the AIRBUS
maximum allowable 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/m2, 35 kW.min/m2
and 20 Ds, respectively.
Natural fibres are problematic in that they are particularly flammable and
thus tend to require more flame retardant treatment than synthetic fibres. However,
flame retardant agents tend to negatively affect the physical properties of the material.
For good fibre-matrix adhesion when natural fibres are used, a resin of low viscosity is
required to enable adequate penetration of the fibres. However, the addition of flameretardant
agents to the resin tends to increase the viscosity of the resin and can thus
lead to poor fibre-matrix adhesion. This limits the amount of flame retardant agent that
can be added to the resin in order to obtain adequate flame retardant properties. It is,
moreover, difficult to treat natural fibres in an environmentally-friendly manner. Nonhalogenated
flame retardants, although advantageous for environmental considerations,
tend to be less effective than halogenated flame retardants. The use of nonhalogenated
flame retardants on cellulosic materials generally increases smoke
production.
Thus, the fabrication of an artefact with natural fibres which has suitable
FST characteristics for use in aircraft is problematic, and there is a need for
improvement on existing fabrication methods and their products.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided 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 prepreg,
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,
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 prepreg
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.
In this specification, the term "non-halogenated flame retardant agent" is
intended to refer to a flame retardant agent which includes a non-halogenated flame
retardant as the only or as the major (highest concentration) flame retardant.
Conveniently, certain smoke suppressants may also act as flame retardants and may
be included in the non-halogenated flame retardant agent. Thus, the smoke
suppressant with which the natural fibres are treated may be included in the flame
retardant agent which is applied to the natural fibres.
In this specification, the term "flame retardant" refers to a substance
applied or added to a material which is capable of delaying the ignition of the material or
of suppressing or reducing the flammability of the material.
In this specification, the term "fire resistant material" refers to a material
which does not burn, or a material that is able to burn only with difficulty.
The artefact may be a panel. The formation of the uncured artefact may
thus include using the at least one pre-preg to provide a skin at least on opposed sides
of the core.
The natural fibres may be in the form of a structure, which may be a
woven or non-woven or knitted fabric or a combination thereof. In particular, the natural
fibre structure may be a woven flax fabric. Other natural cellulosic fibres may be suitable
for use in the invention, including bast fibres like hemp and kenaf, and other fibres such
as bamboo.
The resin composition may be or may include predominantly a thermoset
resin, more specifically a phenolic based resin.
The non-halogenated flame retardant agent may be applied to the natural
fibres in the form of a solution or dispersion of the non-halogenated flame retardant
agent, preferably an aqueous solution or dispersion. The treatment with the solution or
dispersion of the non-halogenated flame retardant agent may be performed by known
methods of impregnating natural fibres. In particular, the treatment with the solution or
dispersion of the non-halogenated flame retardant agent may be performed by padding
it onto the natural fibres. The treated natural fibres may be dried prior to impregnating
the treated natural fibres with the resin composition. In particular, the treatment may be
followed by drying the treated natural fibres at a temperature of between about 110°C
and about 130°C, preferably at about 120°C for about 1 minute.
The non-halogenated flame retardant agent may include a nonhalogenated
flame retardant which acts in the condensed phase. The non-halogenated
flame retardant agent may be based on or may include an ammonium salt of an
inorganic acid as the non-halogenated flame retardant. The non-halogenated flame
retardant agent may be or may include a phosphate-based flame retardant. More
specifically, the non-halogenated flame retardant in the flame retardant agent may be a
phosphoric acid salt. The non-halogenated flame retardant agent may be based on or it
may include a di-ammonium phosphate flame retardant.
As will be appreciated, the pre-preg includes the resin composition in a
partially cured state (often referred to as partially cured to a B-stage). The uncured
artefact thus includes said skin with partially cured resin composition and in the cured
artefact the resin composition in the skin is fully cured, bonding the skin to the core or
substrate.
The non-halogenated flame retardant agent may include an acrylic resin
or polymer.
The proportion of the non-halogenated flame retardant in the nonhalogenated
flame retardant agent may be between about 1% and about 50% solids by
mass, preferably between about 15% and about 30% solids by mass.
The non-halogenated flame retardant agent may include an alkali.
As indicated above, the smoke suppressant with which the natural fibres
are treated may be included in the flame retardant agent which is applied to the natural
fibres. The proportion of the smoke suppressant in the non-halogenated flame
retardant agent may be between about 1% and about 15% by mass, preferably about
5% by mass. The smoke suppressant is preferably one that has a relatively low toxicity
and is preferably hydrated. The smoke suppressant is preferably a zinc borate. More
preferably, the smoke suppressant is a zinc borate having a formulation such that it
undergoes a weight loss of about 1% when heated to between about 180 °C and 230
°C, and a weight loss of about 10% when heated to about 270 °C.
Conveniently, zinc borate is a smoke suppressant which also has flame
retardant properties. Zinc borate is more commonly used as an additive in polymers. It
is only sparingly soluble in water. The zinc borate (5-hydrate) may be produced on-site
by known methods. Otherwise, a commercial smoke suppressant such as Chemtura
ZB223 available from Chemtura Corporation, 1801 U.S Highway 52 West, West
Lafayette, IN 47906, USA may be used.
The presence of the zinc borate smoke suppressant in the nonhalogenated
flame retardant agent is more effective in achieving reduced heat release
values and a reduced smoke production than a non-halogenated flame retardant
without the zinc borate smoke suppressant, as is demonstrated by the results of a test
done on double fabric at a heat flux of 35 kW/m2 shown in Table 1. It is believed that
the non-halogenated flame retardant agent and the zinc borate smoke suppressant
operate synergistically to achieve the improved heat release values.
Table : Tested characteristics of a natural fibre structure treated with nonhalogenated
flame retardant agent and/or a zinc borate smoke suppressant
Tested according to ISO 5660- 1, 5660-2 (Test time 5 minutes)
Smoke factor = product of peak heat release and total smoke release
Instead, the smoke suppressant with which the fibres are treated prior to
the impregation may be a nanoclay, which can have a flame retardant effect and can
also act as a smoke suppressant, the nanoclay being applied to the natural fibres , for
example by admixing it into the flame retardant agent prior to padding. The nanoclay
may be a proprietary product, e.g. a halloysite product which is obtainable from Aldrich.
Halloysite is a 1:1 aluminosilicate clay mineral with the empirical formula AI2Si20 5(OH) .
As indicated above, a non-fibrous silicate fire resistant material may be
admixed with the resin composition prior to or during the forming of the pre-preg. The
fire resistant material may be added in the form of a dispersion. More particularly, the
non-fibrous silicate fire resistant material may be admixed with the resin composition
using step (i) referred to above, 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.
The fire resistant material may be a silicate material belonging to the
group of minerals known as phyllosilicates (sheet silicates), including clay minerals, the
mica group of minerals, for example muscovite, and other phyllosilicates such as
pyrophyllite. Fibrous materials such as asbestos can be hazardous. As indicated
above, the fire-resistant material is non-fibrous. Instead of or in addition to
phyllosilicates, the fire resistant material may consist of or include non-fibrous silicate
materials such as perlite. The fire resistant material may be a naturally occurring
material.
In particular, the fire resistant material may be vermiculite. Vermiculite, a
phyllosilicate material, undergoes expansion on application of heat which is referred to
as exfoliation. The structure of the phyllosilicate materials includes a hydrated layered
configuration of silicates which forms hinged plates that unfold in a linear manner when
heated. This results in trapped water escaping as steam, aiding in fire resistance.
Vermiculite, a naturally occurring material, is light-weight, non-toxic, and has good
thermal insulating and fire resistance properties. If vermiculite is admixed with the resin
composition, the vermiculite may be added as a dispersion, in particular an aqueous
dispersion, and the proportion of vermiculite in the dispersion may be between about
5% and about 20% by mass in the dispersion, preferably between about 15% and about
17.5% by mass in the dispersion. The vermiculite is obtainable from W.R. Grace & Co,
U.S.A, being supplied under the name MicroLite®. The percentage of vermiculite
dispersion in the resin may be between about 5% and about 10% by mass.
The smoke suppressant that may be admixed with the resin composition
may be a zinc borate, preferably a zinc borate having a formulation such that it
undergoes a weight loss of about 1% when heated to between about 250 °C and 330
°C, and a weight loss of about 10% when heated to about 400 °C. The proportion of
smoke suppressant in the resin composition may be between about 1% and about 15%
by mass of resin solids.
Forming at least one pre-preg from the treated natural fibres and a resin
composition may include heating the impregnated natural fibres, e.g. in an oven. In
particular, the impregnated natural fibres (pre-pregs) may be heated at a temperature
range of about 120°C to about 140°C.
The percentage of resin composition in the skin or skins of the artefact
may vary from about 40% to about 60% by mass, preferably approximately 50% by
mass.
The core or substrate is typically cellular, and may be of a honeycomb or
foam material. Typically, honeycomb structures are used. Suitable material for the core
include fire-resistant Nomex (trade name), flame retarded polymers, balsa wood and
aluminium.
The non-fibrous silicate fire resistant material that may be applied to an
outer surface of the at least one skin of the uncured or cured artefact may be a silicate
material belonging to the group of minerals known as phyllosilicates (sheet silicates), as
hereinbefore described, e.g. vermiculite (a naturally occurring material). As
hereinbefore described, the vermiculite is obtainable from W.R. Grace & Co, U.S.A,
being supplied under the name MicroLite®. Instead, the vermiculite may be micron
grade vermiculite (a hydrated phlogopite mica) obtainable from Palabora Mining
Company Limited, 1 Copper Road, 1389 Phalaborwa, South Africa.
The amount of vermiculite applied per unit area of each surface treated
with the vermiculite may be between about 20 g/m2 and about 90 g/m2, e.g.
approximately 45 g/m2.
The non-fibrous silicate fire resistant material may be applied as a
dispersion, e.g. an aqueous dispersion, to an outer surface of the at least one skin of
the uncured or cured artefact. If the non-fibrous silicate fire resistant material is
vermiculite, the percentage of vermiculite in the dispersion may be between about 5%
and about 20% by mass, preferably between about 15% and about 17.5% by mass.
If necessary or desirable, the non-fibrous silicate fire resistant material
applied to an outer surface of the at least one skin of the cured artefact may be dried at
temperatures of between about 70 °C and about 90 °C.
Forming a cured artefact by curing the uncured artefact may be effected
by compression moulding of the uncured artefact, e.g. in a pre-heated mould which is at
an initial temperature of between about 100°C and about 120°C, the temperature in the
mould subsequently being increased to between about 130°C and about 145°C. Curing
also leads to bonding of the skin to the core or substrate.
More particularly, the compression moulding in the pre-heated mould may
be performed at an initial temperature of about 110°C for about 10 minutes. The
compression moulding in the pre-heated mould may be performed by later increasing
the temperature to between about 130°C to about 145°C for between about 50 minutes
and about 90 minutes, preferably about 70 minutes.
According to a second aspect of the invention there is provided a flameproofed
artefact suitable for use in an aircraft, the artefact including
a core or substrate with a cured skin on at least one side of the core or substrate,
the cured skin being formed from at least one pre-preg which includes natural fibres
impregnated with a resin composition, where the natural fibres have been treated with a
non-halogenated flame retardant agent prior to being impregnated with the resin
composition,
a non-fibrous silicate fire resistant material being included in or on one or more
components of the artefact in one or more of the following ways:
(i) the non-fibrous silicate fire resistant material being admixed with the
resin composition which impregnates the natural fibres, so that the cured skin
includes the non-fibrous silicate fire resistant material in a resin matrix of the skin
(ii) the non-fibrous silicate fire resistant material being applied to an outer
surface of the skin prior to curing of the skin, or to a surface of the pre-preg used
to provide the skin, so that the outer surface of the cured skin has a layer rich in
the non-fibrous silicate fire resistant material
(iii) the non-fibrous silicate fire resistant material being applied to an outer
surface of the cured skin, so that the outer surface of the cured skin has a layer
rich in the non-fibrous silicate fire resistant material,
the artefact including a smoke suppressant which has been admixed with the
resin composition which impregnates the natural fibres, so that the cured skin includes
the smoke suppressant in the resin matrix of the skin, a smoke suppressant also being
included in the natural fibres by the natural fibres having been treated with the smoke
suppressant prior to being impregnated with the resin composition.
The artefact may be a panel, in particular a panel with a cured skin at least
on opposed sides of the core.
The natural fibres may be as hereinbefore described and may thus be in
the form of a structure, which may be a woven or non-woven or knitted fabric or a
combination thereof. In particular, the natural fibre structure may be a woven flax fabric.
The resin composition may be as hereinbefore described and may thus be
or may thus include as a major component a thermoset resin, more specifically a
phenolic based resin.
The smoke suppressant with which the natural fibres have been treated
may have been included in the flame retardant agent with which the natural fibres are
treated, and may be a zinc borate or a nanoclay. As indicated above, a zinc borate or
a nanoclay also advantageously have flame retardant properties.
The proportion of smoke suppressant in the resin may be between about
1% and about 15% by mass of resin solids. The smoke suppressant in the resin may
advantageously also have flame retardant properties, for example the smoke
suppressant may be a zinc borate or nanoclay. Preferably, the smoke suppressant is a
zinc borate.
In an embodiment of the invention, the smoke suppressant admixed with
the resin composition that impregnates the fibres is a zinc borate and the smoke
suppressant which the natural fibres are treated prior to their impregnation is a zinc
borate.
The non-halogenated flame retardant agent may include a flame retardant
which acts in the condensed phase, as hereinbefore described. The non-halogenated
flame retardant agent may thus be based on or may include an ammonium salt of an
inorganic acid as the flame retardant. The non-halogenated flame retardant agent may
be or may include a phosphate-based flame retardant. More specifically, the flame
retardant in the non-halogenated flame retardant agent may be a phosphoric acid salt.
The non-halogenated flame retardant agent may be based on or it may include a diammonium
phosphate flame retardant.
The non-halogenated flame retardant agent may include an acrylic resin
or polymer, as hereinbefore described.
The non-halogenated flame retardant agent may include an alkali, as
hereinbefore described.
As hereinbefore described, the percentage of resin composition in the skin
or skins of the artefact may vary from about 40% to about 60% by mass, preferably
approximately 50% by mass.
The core or substrate is typically cellular, and may be of a honeycomb or
foam material, as hereinbefore described.
The non-fibrous silicate fire resistant material that may be applied to an
outer surface of the skin prior to curing of the skin, so that the outer surface of the cured
skin has a layer rich in the non-fibrous silicate fire resistant material, may be a silicate
material belonging to the group of minerals known as phyllosilicates (sheet silicates), as
hereinbefore described, e.g. vermiculite (a naturally occurring material), as also
hereinbefore described. Similarly, the non-fibrous silicate fire resistant material that may
be applied to an outer surface of the cured skin, so that the outer surface of the cured
skin has a layer rich in the non-fibrous silicate fire resistant material, may be a silicate
material belonging to the group of minerals known as phyllosilicates (sheet silicates), as
hereinbefore described, e.g. vermiculite (a naturally occurring material), as also
hereinbefore described.
If vermiculite is used, the amount of vermiculite applied per unit area of
each surface treated with vermiculite may be between about 20 g/m2 and about 90 g/m2,
e.g. approximately 45 g/m2.
The artefact may have a heat release (peak) value, as measured from the
Ohio State University heat release apparatus (OSU), of less than 40 kW/m2, preferably
less than 35 kW/m2, more preferably less than 30 kW/m2, in an undecorated form.
The artefact may have a heat release (2 min) OSU value of less than 50
kW.min/m 2, preferably less than 40 kW.min/m 2, more preferably less than 35
kW.min/m 2, even more preferably less than 30 kW.min/m 2, in an undecorated form.
For avoidance of any doubt, it is to be noted that all of the core material,
the natural fibres, the resin composition, the non-halogenated flame retardant agent, the
smoke suppressant, the flame retardant and the non-fibrous silicate fire resistant
material may be as described hereinbefore with reference to the first aspect of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in greater detail by way of nonlimiting,
illustrative examples with reference to the following diagrammatic drawings in
which:
Figure 1 shows schematically in a three-dimensional view a flame-proofed
artefact in accordance with the invention; and
Figure 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
Referring to Figure 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.
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.
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.
Figure 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 diammonium
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.
The non-halogenated flame retardant agent 120 includes a smoke
suppressant, in particular a zinc borate. The proportion of zinc borate in the nonhalogenated
flame retardant agent 120 is about 5% by mass. Zinc borate (5-hydrate)
can be produced on-site by known methods.
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.
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.
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/m2.
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 2 10, the step 2 10 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.
In an alternative embodiment of the invention, an aqueous dispersion of
vermiculite, represented in Figure 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. Figure 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.
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.
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 lowFAA Letmr concentration of Flammentin TL833. Panel 5 was
produced using the same method as for Panel 3 save that halloysite nano-clay, instead
Ab
L trusm
of zinc borate, was included in the formula
(d)tuneco raepane
tion 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.
Table 2 : Tested characteristics o f various panels
Panel
Test 1 3 4 5 6 1 5 1 5
(with
dec¬
or)
Flammability 60s - burn length (mm) 152 80 88 70 102 85 79 89 80
Flammability 60s - flame time (s) 15 0 0 0 0 0 0 0 0
Flammability 60s - flame time -
3 0 0 0 0 0 0 0 0
drips (s)
Flammability 1 s - burn length (mm) 203 60 32 27 37 28 17 39 57
Flammability 1 s - flame time (s) 15 0 0 0 0 0 0 0 0
Flammability 12s - 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: S0 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: HCI (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.min/m 2)
Peak heat release OSU(kW/ m2) 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 8 1.4 13.1 4.5 -
(kW.min/m 2)
Peak heat release Cone Cal.
N/A N/A 13.2 135.8 241 .3 180.7 10.7 8.2 -
(kW/ m2)
Time to ignition Cone Cal .(s) N/A N/A N/A 67 49 56 96 N/A -
FAA Limits: DOT/FAA/AFt-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
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.
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 C0 2 credit in an aircraft life cycle analysis.
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.
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/m2, 35 kW.min/m 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/m2, 65 kW.min/m 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.
The surface coatings of vermiculite in conjunction with the nonhalogenated
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/m2 (OSU), Heat release (2 min)
27 kW.min/m 2 (OSU), Decorated panel: Heat release (peak, 5 min) 59 kW/m2 (OSU),
Heat release (2 min) 52 kW.min/m 2 (OSU).
The surface coatings of vermiculite in conjunction with the nonhalogenated
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.
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.
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 costeffectively
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.
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 prepreg,
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,
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 prepreg
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.
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 or Claim 2, 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 any one of Claims 1 to 3 inclusive, 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 any one of Claims 1 to 4 inclusive, 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 any one of Claims 1 to 5 inclusive, 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 any one of Claims 1 to 6 inclusive, in which the
smoke suppressant admixed with the resin composition that impregnates the fibres is a
zinc borate.
8. A method as claimed in any one of Claims 1 to 7 inclusive, 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 any one of Claims 1 to 8 inclusive, 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 any one of Claims 1 to 9 inclusive, in which the
core or substrate is of a honeycomb or foam material.
11. A method as claimed in any one of Claims 1 to 10 inclusive, in which
forming a cured artefact by 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.
12. A flame-proofed artefact suitable for use in an aircraft, the artefact
including
a core or substrate with a cured skin on at least one side of the core or substrate,
the cured skin being formed from at least one pre-preg which includes natural fibres
impregnated with a resin composition, where the natural fibres have been treated with a
non-halogenated flame retardant agent prior to being impregnated with the resin
composition,
a non-fibrous silicate fire resistant material being included in or on one or more
components of the artefact in one or more of the following ways:
(i) the non-fibrous silicate fire resistant material being admixed with the
resin composition which impregnates the natural fibres, so that the cured skin
includes the non-fibrous silicate fire resistant material in a resin matrix of the skin
(ii) the non-fibrous silicate fire resistant material being applied to an outer
surface of the skin prior to curing of the skin, or to a surface of the pre-preg used
to provide the skin, so that the outer surface of the cured skin has a layer rich in
the non-fibrous silicate fire resistant material
(iii) the non-fibrous silicate fire resistant material being applied to an outer
surface of the cured skin, so that the outer surface of the cured skin has a layer
rich in the non-fibrous silicate fire resistant material, and
the artefact including a smoke suppressant which has been admixed with the resin
composition which impregnates the natural fibres, so that the cured skin includes the
smoke suppressant in the resin matrix of the skin, a smoke suppressant also being
included in the natural fibres by the natural fibres having been treated with the smoke
suppressant prior to being impregnated with the resin composition.
13. An artefact as claimed in Claim 12, in which the smoke suppressant
admixed with the resin composition that impregnates the fibres is a zinc borate and the
smoke suppressant with which the natural fibres are treated prior to their impregnation
is a zinc borate.
14 . An artefact as claimed in Claim 12 or Claim 13, in which the resin
composition is, or includes as a major component, a thermoset resin composition, and
the artefact is a panel with a cured skin at least on opposed sides of the core.
15. An artefact as claimed in any one of Claims 12 to 14 inclusive, which has
a heat release (peak) OSU value of less than 40 kW/m2 and a heat release (2 min) OSU
value of less than 50 kW.min/m2, in an undecorated form.