Field of the disclosure

[0001] The present disclosure relates to flexible fire retardant membranes composed of a flexible non-combustible substrate coated with a fire retardant coating containing crosslinked polysiloxane elastomer, polyphosphate salt, expandable graphite, and fire retardant additives. When applied to a structure the flexible membranes protect the structure against fire.

Background of the disclosure

[0002] Wooden utility poles are widely used to provide critical infrastructure (e.g. power lines). To increase their durability, these wooden poles are often pressure treated with copper chromated arsenate (CCA) before being placed in service. Treated poles can be damaged by passing bushfires, and this damage can be due to the direct effect of the fire and also due to continuing smouldering of the poles after a fire has passed. The latter is known to be more severe in poles treated with CCA, which enables smouldering combustion at lower temperatures. Once established, this smouldering process may cause complete destruction of a pole; with the effect that even minor thermal damage from relatively small bushfires can potentially cause loss of a wooden asset if it leads to smouldering.

[0003] The most relevant standard for the fire safety of building in bushfires is AS 3959. This standard fulfils a dual purpose: it defines the potential severity of a bushfire at a building site, based on the local weather, vegetation and topographical conditions. Additionally, this standard specifies construction requirements according to the expected bushfire severity on a building site. The bushfire severity is classified by Bushfire Attack Level (BAL), which contains, BAL-LOW (no requirements for building elements), BAL-12.5, BAL-19, BAL-29, BAL-40 and BAL-FZ (flame zone). Each BAL is associated with the maximum expected exposure heat flux that a structural element might experience during a bushfire (i.e. BAL-29 anticipates a maximum exposure heat flux of 29 kW/m ² ). In addition, higher BALs also anticipate the accumulation of embers or contact with flames.

[0004] Requirements for buildings and their individual elements depend on the local BAL and the type of building element. Due to its combustibility, the use of timber is generally limited to lower BALs. Some species of timber, including spotted gum (Corymbia maculata), are classified as bushfire resisting timbers and may be used for certain applications in BAL-29. For higher BALs the use of timber has to be assessed within the intended building element. Up to BAL-40 this testing is performed with a time varying heat flux representing the exposure from a passing bushfire. The exposure is also complemented by a burning wood crib which simulates the accumulation of embers or burning debris near a building structure. The requirements for this test are defined in AS 1530.8.1. AS 1530.8.2 specifies that BAL-FZ testing of building systems must be undertaken in a furnace following 30 minutes of a standard temperature time curve according to AS 1530.4.

[0005] Fire retardant coatings act in a fire to insulate a structure thereby extending the time before the structure is damaged by fire. These coatings are often in the form of composition that is applied to the structure, for example by brushing or spraying.

[0006] Such coatings may have intumescent properties such that they react to heat by swelling, producing a carbonaceous char that acts as an insulating layer to protect the structure.

[0007] Fire retardant coatings typically contain a number of components that work to address these property desires, however in view of the complexity of the compositions it is difficult, if not impossible, to predict performance in terms of resistance to weathering, and, ultimately, fire protection.

[0008] Fire retarding coatings often require multiple coatings to be effective and each coating must dry before subsequent coatings are applied. This substantially increases labour costs. Furthermore, if the structure requires maintenance, coatings are difficult to remove.

[0009] In view of the foregoing, there is a need for alternative fire retardant solutions to protect critical infrastructure, such as, for example, wooden utility poles.

[0010] Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and/or combined with other pieces of prior art by a skilled person in the art. Summary of the disclosure

[0011] In one aspect the present disclosure provides a flexible fire retardant membrane comprising a flexible, non-combustible substrate coated on at least one surface with a fire retardant coating, said fire retardant coating comprising: about 30 wt.% to about 70 wt.% of one or more crosslinked polysiloxane elastomers; about 10 wt.% to about 30 wt.% expandable graphite; about 5 wt.% to about 25 wt.% of one or more polyphosphate salts having a solubility in water of less than 2 wt.% at 20°C; and about 5 wt.% to about 25 wt.% of one or more fire retardant additives; based on the total weight of the fire retardant coating.

[0012] In embodiments, the fire retardant coating comprises: about 35 wt.% to about 65 wt.% of one or more crosslinked polysiloxane elastomers; about 12 wt.% to about 23 wt.% expandable graphite; about 7.5 wt.% to about 22.5 wt.% of one or more polyphosphate salts having a solubility in water of less than 2 wt.% at 20°C; and about 7.5 wt.% to about 22.5 wt.% of one or more fire retardant additives; based on the total weight of the fire retardant coating.

[0013] In embodiments, the fire retardant coating comprises: about 40 wt.% to about 60 wt.% of one or more crosslinked polysiloxane elastomers; about 14 wt.% to about 20 wt.% expandable graphite; about 10 wt.% to about 20 wt.% of one or more polyphosphate salts having a solubility in water of less than 2 wt.% at 20°C; and about 10 wt.% to about 20 wt.% of one or more fire retardant additives; based on the total weight of the fire retardant coating. [0014] In embodiments, the flexible, non-combustible substrate comprises one or more of glass fibre, carbon fibre and basalt fibre.

[0015] In embodiments, the one or more crosslinked polysiloxane elastomers comprise one or more of crosslinked polydimethylsiloxane, crosslinked polymethylhydrogensiloxane, crosslinked polydiethylsiloxane, crosslinked polyphenylmethylsiloxane, and crosslinked polydiphenylsiloxane.

[0016] In embodiments, the one or more crosslinked polysiloxane elastomers comprise crosslinked polydimethylsiloxane.

[0017] In embodiments, the polyphosphate salt having a solubility in water of less than 2 wt.% at 20°C is one or both of ammonium polyphosphate and melamine polyphosphate.

[0018] In embodiments, the one or more polyphosphate salts has a solubility in water of less than 1 wt.% at 20°C, or less than 0.5 wt.% at 20°C.

[0019] In embodiments, the one or more polyphosphate salts comprise a particulate polyphosphate having an average particle size (D50) of 5 to 50 micron, preferably 10 to 30 micron.

[0020] In embodiments, the one or more fire retardant additives comprise one or more of aluminium trihydrate, basic magnesium carbonate, and magnesium dihydroxide.

[0021] In embodiments, the fire retardant additive is aluminium trihydrate.

[0022] In embodiments, the fire retardant coating further comprises one or more inorganic fillers.

[0023] In embodiments, the inorganic filler is present in an amount from about 0.5 wt.% to about 5 wt.%, based on the total weight of the fire retardant coating.

[0024] In embodiments, the inorganic filler is titanium dioxide.

[0025] In embodiments, the fire retardant coating comprises crosslinked polysiloxane elastomer, expandable graphite, ammonium or melamine polyphosphate, aluminium trihydrate, and titanium dioxide. [0026] In embodiments, the fire retardant coating has a thickness from about 0.5 mm to about 5 mm.

[0027] In embodiments, the flexible, non-combustible substrate is polymer coated.

[0028] In embodiments, the polymer comprises, for example, polyethylene terephthalate.

[0029] In embodiments, the polymer coating is present on the opposite surface of the non-combustible substrate to the fire retardant coating.

[0030] In embodiments, the flexible, non-combustible substrate has an areal weight from about of 200 g/m ² to about 600 g/m ² .

[0031] In embodiments, the presently disclosed flexible fire-retardant membrane has sufficient flexibility to be circumferentially wrapped around an approximately cylindrical structure of diameter 150 mm without cracking.

[0032] In another aspect the present disclosure provides a method of preparing the flexible fire retardant membrane according to any one of the herein disclosed embodiments, comprising: a) combining one or more curable polysiloxanes, expandable graphite, one or more polyphosphate salts, one or more fire retardant additives and, optionally, one or more inorganic fillers; b) casting the combination formed in a) onto at least one surface of a flexible non- combustible substrate or a polymer coated flexible, non-combustible substrate; and c) curing the curable polysiloxane to form crosslinked polysiloxane.

[0033] In embodiments, the combination formed in a) is cast onto the surface of the flexible, non-combustible substrate that is opposite to the polymer coating, if present.

[0034] In embodiments, the combination in step a) is mixed under high shear conditions.

[0035] In embodiments, the curing is performed at a temperature above 100°C. [0036] In another aspect the present disclosure provides a method of protecting a structure against fire comprising the step of covering the structure with the flexible fire retardant membrane according to any one of the herein disclosed embodiments. The covering may include wrapping.

[0037] In embodiments, the flexible fire retardant membrane is applied to the structure such that the fire retardant coating faces away from the structure.

[0038] In another aspect the present disclosure provides the use of the flexible fire retardant membrane according to any one of the herein disclosed embodiments in protecting a structure against fire.

[0039] In embodiments, the structure comprises timber, brick, concrete, or metal.

[0040] In embodiments, the structure comprises timber. In some embodiments, the structure is a timber pole.

[0041] Advantages of the presently disclosed flexible fire retardant membranes include one or more of the following:

• they provide excellent protection to a structure against fire;

• on combustion, low amounts of toxic gas are formed;

• they are flexible, enabling them to follow the contours of a structure;

• they provide excellent weather resistance;

• they are easy to install and retrofit to existing structures; and

• installation is simple, as is removal if structure maintenance is required.

[0042] Any embodiment herein shall be taken to apply mutatis mutandis to any other embodiment unless specifically stated otherwise.

[0043] The present disclosure is not to be limited in scope by the specific embodiments described herein, which are intended for the purpose of exemplification only. Functionally-equivalent products, compositions and processes are clearly within the scope of the disclosure, as described herein. [0044] Further aspects of the present disclosure and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings.

Brief description of the drawings

[0045] Figure 1 shows photographs of timber substrates covered by flexible fire retardant membranes according to embodiments of the present disclosure after being subjected to a cone calorimeter test.

[0046] Figure 2 is a schematic illustration of timber pole radiant heat testing.

[0047] Figure 3 illustrates the thermal profiles of unprotected (upper trace) and flexible fire retardant membrane protected (two lower traces) timber pole sections after 10 minutes of exposure to 60 kW/m ² radiant heat.

[0048] Figure 4 illustrates 300°C isotherm (assumed char depth) after 10 minutes of testing for two heat exposures with and without flexible fire retardant membrane.

[0049] Figure 5 illustrates 300°C isotherm (assumed char depth) after 360 minutes of testing for two heat exposures with and without flexible fire retardant membrane.

[0050] Figure 6 shows photographs of the damage to flexible fire retardant membrane protected timber poles (a), and unprotected timber poles (b), after 10 minutes of exposure to 50 kW/m ² radiant heat.

Detailed description of the embodiments

[0051] It will be understood that the disclosure described and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the disclosure.

Definitions

[0052] For purposes of interpreting this specification, terms used in the singular will also include the plural and vice versa. [0053] As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives, components, integers or steps.

[0054] "About" as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of ±20% or ±10%, in some instances ±5%, in some instances ±1%, and in some instances ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods.

[0055] Ranges: throughout this disclosure, various aspects of the disclosure can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosure. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1 , 2, 2.7, 3, 4, 5, 5.3, and 6. This applies regardless of the breadth of the range.

[0056] As used herein, the term “flexible” in relation to a substrate or a membrane means the ability of the substrate or membrane to flex and allows a length of the substrate or membrane to bend at an angle that allows it to circumferentially wrap around an approximately cylindrical structure of diameter 150 mm, without cracking.

[0057] The present disclosure relates to flexible fire retardant membranes comprising a flexible non-combustible substrate coated with a fire retardant coating comprising crosslinked polysiloxane elastomer, polyphosphate salt, expandable graphite, and fire retardant additives. When applied to a structure the flexible membranes protect the structure against fire.

[0058] The present disclosure provides a flexible fire retardant membrane comprising a flexible, non-combustible substrate coated on at least one surface with a fire retardant coating comprising: a) about 30 wt.% to about 70 wt.% of one or more crosslinked polysiloxane elastomers; b) about 10 wt.% to about 30 wt.% expandable graphite; c) about 5 wt.% to about 25 wt.% of one or more polyphosphate salts having a solubility in water of less than 2 wt.% at 20°C; and d) about 5 wt.% to about 25 wt.% of one or more fire retardant additives; based on the total weight of the fire retardant coating.

[0059] In embodiments, the fire retardant coating comprises: a) about 35 wt.% to about 65 wt.% of one or more crosslinked polysiloxane elastomers; b) about 12 wt.% to about 23 wt.% expandable graphite; c) about 7.5 wt.% to about 22.5 wt.% of one or more polyphosphate salts having a solubility in water of less than 2 wt.% at 20°C; and d) about 7.5 wt.% to about 22.5 wt.% of one or more fire retardant additives; based on the total weight of the fire retardant coating.

[0060] In embodiments, the fire retardant coating comprises: a) about 40 wt.% to about 60 wt.% of one or more crosslinked polysiloxane elastomers; b) about 14 wt.% to about 20 wt.% expandable graphite; c) about 10 wt.% to about 20 wt.% of one or more polyphosphate salts having a solubility in water of less than 2 wt.% at 20°C; and d) about 10 wt.% to about 20 wt.% of one or more fire retardant additives; based on the total weight of the fire retardant coating. Crosslinked polysiloxane elastomer

[0061] The crosslinked polysiloxane elastomer serves as a polymeric binder in the presently disclosed fire retardant coating.

[0062] In embodiments, the one or more crosslinked polysiloxane elastomers comprise one or more of crosslinked polydimethylsiloxane, crosslinked polymethylhydrogensiloxane, crosslinked polydiethylsiloxane, crosslinked polyphenylmethylsiloxane, and crosslinked polydiphenylsiloxane.

[0063] In embodiments, the one or more crosslinked polysiloxane elastomers comprise crosslinked polydimethylsiloxane.

[0064] The crosslinked polysiloxanes elastomers may be prepared using methods well known in the art.

[0065] In embodiments, the amount of one or more crosslinked polysiloxane elastomers in the fire retardant coating is about 20 wt.% to about 70 wt.%, or about 25 wt.% to about 65 wt.%, or about 30 wt.% to about 60 wt.%, or about 35 wt.% to about 55 wt.%, or about 40 wt.% to about 50 wt.%, based on the total weight of the fire retardant coating.

Expandable graphite

[0066] Expandable graphites are graphites in which the interstitial layers contain foreign groups (for example sulfuric acid) which lead to thermal expansion. They include nitrosated, oxidised and halogenated graphites. The expandable graphite expands when in a temperature range of from 80°C to 250°C or more, expanding the fire retardant coating so that it forms an insulating char layer on a substrate.

[0067] In embodiments, the amount of expandable graphite in the presently disclosed fire retardant coating is about 5 wt.% to about 30 wt.%, or about 10 wt.% to about 30 wt.%, or about 5 wt.% to about 20 wt.%, or about 10 wt.% to about 20 wt.%, based on the total weight of the fire retardant coating.

Polyphosphate salt

[0068] Polyphosphate salt fire retardants may include ammonium polyphosphate (Type II) or melamine polyphosphate. [0069] In embodiments, the one or more polyphosphate salts may have a solubility in water of less than 1 wt.% at 20°C, or less than 0.5 wt.% at 20°C.

[0070] In embodiments, the one or more polyphosphate salts comprise a particulate polyphosphate having an average particle size (D50) of 5 to 50 micron, preferably 10 to 30 micron. The average particle size may be determined by, for example, laser diffraction.

[0071] The amount of polyphosphate salt in the fire retardant coating is about 5 wt.% to about 30 wt.%, or about 10 wt.% to about 30 wt.%, or about 5 wt.% to about 20 wt.%, or about 10 wt.% to about 20 wt.%, based on the total weight of the fire retardant coating.

Fire retardant additives

[0072] In embodiments, the one or more fire retardant additives comprise one or more of aluminium trihydrate, basic magnesium carbonate, and magnesium dihydroxide.

[0073] In embodiments, the fire retardant additive is aluminium trihydrate.

[0074] The amount of fire retardant additives in the fire retardant coating is about 5 wt.% to about 30 wt.%, or about 10 wt.% to about 30 wt.%, or about 5 wt.% to about 20 wt.%, or about 10 wt.% to about 20 wt.%, based on the total weight of the fire retardant coating.

Flexible non-combustible substrate

[0075] Useful flexible, non-combustible substrates include glass fibre fabrics, carbon fibre fabrics and basalt fibre fabrics. The fabrics may have a fabric areal weight from about 200 g/m ² to about 600 g/m ² , or from about 300g/m ² to about 600 g/m ² .

[0076] The flexible, non-combustible substrates may be coated with a polymer, for example polyethylene terephthalate. The polymer coating may serve to reinforce the flexible, non-combustible substrate. The polymer coating may be present on the surface of the flexible, non-combustible substrate which is opposite the surface coated with the fire retardant coating. Method of preparing the fire retardant membrane

[0077] The presently disclosed flexible fire-retardant membranes may be prepared by combining one or more crosslinkable polysiloxanes; expandable graphite; one or more polyphosphate salts having a solubility in water of less than 2 wt.% at 20°C; and one or more fire retardant additives. The components may be mixed under high shear conditions, for example at about 400 rpm for about 15 minutes.

[0078] The resulting mixture may then be cast on a flexible, non-combustible substrate using, for example, a knife coating machine to a thickness of, for example, 1.5-2 mm and then cured in an oven at elevated temperature, for example,150-160 °C.

[0079] If the flexible, non-combustible substrate is coated with a polymer on one surface then the fire retardant coating is preferably applied to the opposite surface of the substrate.

Properties of the fire retardant membranes

[0080] A key feature of the presently disclosed fire retardant membranes is their flexibility. It will be appreciated that in order to protect structures that have curved surfaces the membranes must possess sufficient flexibility such that minimal or no cracking of the membrane occurs, otherwise its fire retardant capability may be compromised.

[0081] The presently disclosed membranes possess excellent flexibility enabling them to be wrapped around an approximately cylindrical structure, such as a wooden utility pole, without cracking. In embodiments, the presently disclosed fire retardant membranes may be wrapped around an approximately cylindrical structure having a diameter from about 150 mm to about 300 mm without cracking.

[0082] This is advantageous, as cracking of the membrane may prejudice the ability of the membrane to protect a structure against fire.

[0083] There is also provided a method of protecting a structure against fire comprising the step of covering the structure with the flexible fire retardant membrane according to any one of the herein disclosed embodiments. [0084] In embodiments, the structure is covered by means of attachment. Numerous forms of attachment may be envisaged, for example, by nailing or stapling the membrane to the structure.

[0085] In embodiments, the structure is timber, brick, concrete or metal. In some embodiments, the structure is a wooden utility pole.

[0086] There is also provided the use of the flexible fire retardant membrane according to any one of the herein disclosed embodiments in protecting a structure against fire.

Examples

Example 1 : Membrane preparation

[0087] Flexible fire retardant membranes according to the present disclosure were prepared by combining about 30 wt.% to about 60 wt.% of one or more crosslinked polysiloxane elastomers; about 10 wt.% to about 20 wt.% expandable graphite; about 5 wt.% to about 20 wt.% of one or more polyphosphate salts having a solubility in water of less than 2 wt.% at 20°C; and about 5 wt.% to about 20 wt.% of aluminium trihydrate as fire retardant additive. The components were mixed under high shear conditions, typically at 400 rpm for about 15 minutes. The resulting mixture was then cast on 400 g/m ² Mylar® coated glass fibre fabric using a knife coating machine to a thickness of 1 .5-2 mm and then cured in an oven at 150-160 °C.

Example 2: Fire behaviour

[0088] A cone calorimeter is the most commonly used equipment to investigate the fire behaviour of various materials. It works on the principle that the amount of heat released by a burning sample (100 x 100 x 4 mm ³ ) subjected to a given heat flux (i.e. , 10-100 kW/m ² ) is proportional to the amount of oxygen consumption during combustion. The amount of heat produced by a material is directly related to the severity of a fire. Heat release rate (HRR), total heat release (THR), time to ignition (TTI), mass loss rate (MLR), total smoke release (TSR), and effective heat of combustion (EHC) are among the combustibility parameters provided by the test. The presently disclosed membranes were tested at different heat flux (35 kW/m ² and 50 kW/m ² ) using a cone calorimeter. [0089] The BAL ratings (BAL-40 and BAL-FZ) require a large scale-scale test according to the AS 1530.8.1 and AS 1530.8.2. The large-scale test according to AS 1530.8.1 is performed with a BAL-40 rating (Heat flux of 40 kW/m ² ) using a 3m x 3m radiant heat panel. Different systems are assessed according to this standard, including external walls and power poles. The performance criteria change with the system, for example, external walls are required to pass seven criteria, such as the mean and maximum temperatures of the internal face of construction including cavities, which should not exceed 250 °C and 300 °C respectively between 20 min and 60 min after the commencement of the test. The performance criteria for power poles are reduced to two main criteria. Flaming is not permitted on the fire exposed side at the end of the 60 minutes period and the heat release will not be greater than 3 kW/m ² between 20 and 60 min of the test.

Example 3: Sample preparation

[0090] Membranes according to Example 1 and having a fire retardant coating thickness of 1 .5 mm were applied on timber substrates of 100 mm x 100 mm x 20 mm. The membrane was applied to the timber using nails. Two different heat flux of 35 kW/m ² and 50 kW/m ² , equivalent to BAL-40 and FZ respectively, were used for testing.

Example 4: Cone calorimeter test

[0091] The samples were tested with the cone calorimeter at two different heat flux, 35 kW/m ² and 50 kW/m ² , being equivalent to BAL-40 and BAL-FZ respectively. These conditions were used to simulate the tests performed according to AS1530.8.1 (BAL-40) and AS1530.8.2 (BAL-FZ). From these tests, sample responses such as heat release rate (HRR), total smoke production (TSP) and mass loss rate (MLR) were considered for assessing the sample performance.

[0092] Figure 1 shows the sample conditions after the cone calorimeter test. The sample surfaces were not significantly affected by the cone test. Since the timber structure did not evidence significant changes and/or degradation, it corroborates the fact that the reported Peak-HRR is mostly contributed by the polymer ignition, rather than the degradation process of the timber. At 35 kW/m ² (equivalent to BAL-40), the peak heat release rate was found to be lower than 100 kW/m ² and mean heat release rate was significantly lower than 60 kW/m ² . Therefore, this passed the BAL-40 rating tests. At 50 kW/m ² (Equivalent to BAL-FZ), the peak heat release rate was 96 kW/m ² which was similar to at 35 kW/m ² . Table 1 is shows the key parameters of cone calorimeter tests of all samples at the two heat fluxes.

Exampe 5: Evaluation of toxic gas release

[0093] Cone calorimeter-FTIR was perfomed on a timber structure coated with 1 .5 mm thickness of a fire retardant membrane of the present disclosure. The purpose of the test was to determine the amount of toxic gases released during combustion. The results are collected in Table 2.

[0094] Carbon monoxide (CO) was the main gas generated from the material, however the concentration was low. All remaining gases were found in even lower concentrations.

Example 6: Alternative membranes

[0095] A series of alternative fire retardant membranes were tested to compare performance against the presently disclosed membranes, and the formulations and results are collected in Table 3.

[0096] The alternative membranes were prepared with different polymeric binders and other components as shown in Table 3, and compared to membranes prepared with crosslinked polysiloxane elastomer binder (Formulae 10 to 13) and in all formulations the amount of binder was 35-50 wt.%, the amount of APP was 5-20 wt.%, the amount of ATH (when used) was 5-15 wt.%, the amount of EG (when used) was 2- 20 wt.%, the amount of TiO2 (when used) was 1 -5 wt.%, and the amount of pentaerythritol (when used) was 5-10 wt.%, all based on the total weight of the fire retardant coatings. The coatings were applied to a glass fibre substrate as in Example 1 or to a glass fibre substrate absent the Mylar® layer.

[0097] Formulations were rated as poor, good or excellent based on an assessment of membrane flexibility, structure protection against fire, and weathering resistance.

[0098] Flexibility of the membranes was assessed by bending or rolling the membrane to simulate use in wrapping around a wooden utility pole. If the membrane cracked during the assessment then flexibility was considered as poor.

[0099] Structure protection was assessed using a cone calorimeter following the procedure of Example 4 or by visual inspection after exposure to a blow torch. [0100] Samples that gave excellent fire testing results were exposed to accelerated weathering conditions for 1000 hours. The weathering conditions simulated that specified by ASTM D2898 Method B using a QUV accelerated weathering tester. After weathering the membranes were again assessed using a cone calorimeter following the procedure in Example 4. *ATH: Aluminium Trihydroxide EG: Expandable Graphite MMP: Melamine Polyphosphate APP: Ammonium Polyphosphate TiO2: Titanium Dioxide Penta: Pentaerythritol

[0101] Membranes coated with a fire retardant coating comprising epoxy or polyester binders had poor to good flexibility. Membranes coated with a fire retardant coating comprising crosslinked polysiloxane elastomer according to the present disclosure all showed excellent flexibility (Formulae 10 to 13).

[0102] The only membranes to provide excellent fire protection were those according to formulae 4, 6, 12 and 13.

[0103] Formulae 12 and 13 are according to the present disclosure and comprise crosslinked polysiloxane elastomer, ammonium polyphosphate or melamine polyphosphate, expandable graphite, and aluminium trihydrate as tested in Example 4 (Table 1 ). It is evident from the results that coatings comprising these components enabled excellent performance in terms of all of membrane flexibility, substrate protection against fire, and weathering resistance.

Example 7: Fire protection of timber power poles

[0104] This test was performed at the University of Queensland, Australia, fire testing facility. Spotted gum pole sections were wrapped with membranes according to the present disclosure (formula 13 of Example 6), thereby replicating a likely application in the field. The membranes were positioned such that the fire retardant surface of the membrane faced away from the timber poles. The tested timber specimens were cut from surplus pole sections to a height of around 500 mm and a diameter between 200 and 250 mm. All tested specimens were treated with copper chromated arsenate (CCA). The moisture content of the wood was measured with a moisture meter before each test. The mean moisture content was determined as 8.7 %, with a sample standard deviation of 0.4 %. [0105] All tested pole sections were instrumented with 1 .5 mm diameter stainless steel sheathed thermocouples (TC) into pre-drilled holes at varying distance from the exposed surface. Thermocouples were inserted from the bottom of the pole, in parallel to the progressing heat front. This allowed measurement of the progressing heat front from the surface to the centre of the pole and enabled determination as to whether smouldering was occurring or not. Before testing, the pole sections were wrapped in one layer of the fire retardant membrane, which was fixed in place using a staple gun.

[0106] The test procedure was derived from previous tests reported by Gardner and White (Assessing the ability of a large-scale fire test to predict the performance of wood poles exposed to severe bushfires and the ability of fire-retardant treatments to reduce the loss of wood poles exposed to severe bushfires"; in: Forest & Wood Products Australia Technical Report (2009)).

[0107] A constant thermal exposure, from propane fuelled radiative heating panels, was set at 50 kW/m ² or 60 kW/m ² at the surface of the poles. This was done to incrementally test the upper bound limits of the assessed membrane. This exposure was maintained constant for 10 minutes. The experimental set-up is shown schematically in Figure 2. After 5 minutes of heat exposure a propane burner flame was introduced to the surface to induce ignition if sufficient pyrolysis gases were present. After the 10-minute heating phase was completed, the heat was removed and the poles were subjected to a mild airflow (0.8 m/s at the pole surface) from a fan for 30 minutes to provide conditions favourable to inducing and maintaining smouldering and afterglow. Details of the tests are shown in Table 4. [0108] The membrane on the membrane protected poles ignited shortly after the heat flux was applied and the membrane formed an expanding char layer. For poles that were not protected with the membrane, the timber did not ignite initially. This is not unexpected as spotted gum is a bushfire resistant timber species with a high density. After five minutes of test time, a pilot flame was introduced to the timber surface in the form of a propane torch. This caused ignition and subsequent burning of the timber until the heat was removed.

[0109] For membrane protected poles, the measured temperatures reduced once the heating was removed. For unprotected poles an initial decrease in temperatures was followed by a recurring increase in temperatures; this was caused by smouldering of the timber. The induced damage in both protected and unprotected poles can be inferred from the readings of the thermocouples, which measured the internal temperatures. The thermal profiles of the temperature measurement are shown for tests with exposure of 60 kW/m ² in Figure 3. From these temperatures profiles, the effect of the membrane is readily discernible. The expansion of the membrane significantly lowers the internal temperatures. The 300°C isotherm is of special interest, as this is often considered as a threshold between timber and char and therefore denotes complete loss of load bearing capacity. For the timber poles protected with the membranes, charring of the surface is limited to 2 mm. These measurements were confirmed by visual observations of the poles after the tests were completed, with only minor discolouration and surface charring visible for the protected poles. For the pole without a protective membrane the char progression after 10 minutes was about 12 mm.

[0110] The charring depth, inferred as 300°C isotherm from temperature profiles for tests with 50 and 60 kW/m ² , is shown in Figure 4. The protective effect of the membrane was observed to markedly reduce the char depth for protected specimens.

[0111] It can be concluded from Figure 3 and Figure 4 that the application of the membranes reduced char damage in the poles; however, while the char depths in unprotected poles constitute damage, they may not lead to complete failure of the poles. These tested poles have a diameter of up to 220 mm, so a 12 mm char depth translates into an approximate 5 % loss of diameter. CCA treated utility poles, like the ones tested herein, have the potential to smoulder after a fire has passed. Thus, it was necessary to consider a longer timespan after heating was completed in order to assess the real protection afforded by the tested membranes. The char depth after 6 hours of testing is shown in Figure 5. It was observed that at this time span the char depth in the protected poles did not progress further after the heating, i.e. the poles suffered only minor damage during the test regime. For unprotected poles however, the char depth significantly increased to around 80 mm; this constitutes significant damage and could reasonably be classified as a loss of the asset.

[0112] These measurements were also confirmed by visual assessment of the poles after the tests were completed, which is shown in Figure 6. These images show only minor damage of a pole that was protected by the membrane (Figure 6(a)) and severe burn damage of an unprotected pole (Figure 6(b)). In addition, the continuous smouldering of unprotected CCA treated poles can yield ash with relatively high levels of arsenic.

[0113] The protective fire retardant membranes were observed to effectively reduce the char depth in the pole sections by limiting heat transfer and the flow of pyrolysis gases to prevent burning. This has two advantages: (1 ) a reduced char depth effectively means reduced damage to the pole, and (2) reduced char and the shielding of the char from the fan flow reduces the probability of smouldering damaging to the pole after a fire.

[0114] The presently utilised testing regime is more demanding than those described in AS 1530.8.1 and more appropriate for the considerations of property protection of utility poles.

Example 8: Evaluation of further alternative membranes

[0115] Several further membranes were prepared according to Formula-13 of Example 6, but varying the other components. Crosslinked polysiloxane binder was utilised along with the other components as set out in Table 5. The membranes were tested applied to a timber substrate and with a cone calorimeter at heat flux of 50 kW/m ² for 10 minutes.

[0116] Formula 14 is similar to Formula 13 of Example 6, except that TiO2 was omitted. It is evident that omission of TiO2 increased the mean heat release rate (Mean HRR) and total smoke production (compare 50 kW/m ² results in Table 1 ). An increase in these parameters reflects poorer protection of the timber.

[0117] Formula 15 is similar to Formula 13 except that ATH was omitted. Again, the mean heat release rate and total smoke production both increased.

[0118] Formula 16 and Formula 17 replaced ATH with, respectively, MgCOa and Mg(OH)2 and omit TiC . Mean heat release rate and total smoke production both increased relative to Formula 13 (compare results in Table 1 ), indicating poorer protection of the timber.

[0119] Although all of formulations 14 to 17 produced flexible membranes and gave reasonable fire protection results, fire retardant membranes comprising crosslinked polysiloxane elastomer, expandable graphite, ammonium or melamine polyphosphate, aluminium trihydrate, and titanium dioxide gave the best fire protection performance (Formulae 12 and 13).