FILM FORMING FLUOROPROTEIN FOAM CONCENTRATE

Abstract: A foam concentrate for use in diluted form for fire fighting comprises an aqueous mixture of hydrolysed protein, a fluorinated surfactant with a surface tension of from 19 to 35 mNm<-1> at 0.1 %, a second fluorinated surfactant with a surface tension of from 15 to 20 mNm<-1> at 0.1 % and a non-fluorinated hydrocarbon surfactant.

Description: FILM FORMING FLUOROPROTEIN FOAM CONCENTRATE Fires on burning hydrocarbon fuels are usually extinguished by superficial application of a low expansion foam produced from a solution of a foam concentrate. Three types of commercial foam concentrate are normally distinguished and indeed in the United Kingdom, there are three Defence Specifications to cover the three types, which are called protein, fluoroprotein and fluorochernical. The third is more commonly known as aqueous film-forming foam (abbreviated to AFFF). Fluroprotein foam concentrates are normally prepared from protein concentrates by addition of a fluorosurfactant. This makes the foam more fluid and less affected by fuel pick-up, while maintaining foam quality as measured by expansion and drainage. However, the fluorosurf ctants used do not reduce surface tension sufficiently to produce surface films on the more volatile hydrocarbons. Fluorochemical foam concentrates are prepared by combining a fluorosurfactant with a hydrocarbon surfactant, without the presence of protein. The surface tension and interfacial tension are both reduced sufficiently to give stable film production even on fuels of low surface tension. Fluorochemical foams are very fluid and fast-draining; they give more rapid extinction butless effective after- protection than protein or fluoroprotein foams. However this description of the three types is an over-simplification. All three usually contain water miscible solvents to boost expansion and to retain the surfactants in solution, while protein and fluoroprotein concentrates contain salts of divalent metals (e.g. iron, magnesium, zinc) to improve the heat resistance of the foam. It would be advantageous to combine the rapid extinction and film formation of a fluorochemical foam with the longer term protection of a fluoroprotein foam, to give a film-forming fluoroprotein foam (FFFP) , but previous attempts to achieve this have been only partly successful. One commercial concentrate of this type contains protein and one specific fluorosurfactant but no hydrocarbon surfactant, the addition of which is claimed to be harmful. Long-term stability of a foam concentrate at tropical temperatures is an important requirement. Some fluorosurfactants used in FFFP formulations produce sludging when stored at 50°C, others produce acidity under ' such conditions. The reduction in pH may eventually cause precipitation of the protein. Some water miscible solvents also produce acidity under tropical storage conditions. • According to the present invention a fire fighting foam concentrate comprises an aqueous mixture containing hydrolysed protein, a first fluorinated surfactant having a surface tension of 17 to 35 mNm at 0.1%, a second fluorinated surfactant having a surface tension of 15 to 20 preferably 15 to 17 mNm~ at 0.1% and a non-fluorinated hydrocarbon surfactant. The surface tensions and interfacial tensions referred to in this specification are determined at equilibrium in aqueous solution using conventional apparatus supplied by White Electrical Instruments Co.Limited. Concentrates in accordance with this invention exhibit long term stability on storage and form effective fire fighting foams which give good after-protection and burnback properties. A preferred concentrate has been found to meet the Defence Specifications for both fluoroprotein and fluorochemical foams and produces a long lasting foam blanket which adheres to hot vertical surfaces. Concentrates in accordance with this invention have the advantage that there is no need for addition of divalent metal salts to enhance foam stability and fire resistance. Absence of significant amounts of divalent metals is beneficial in reducing sludge formation on prolonged storage, particularly at high temperatures. Concentrates in accordance with this invention preferably include a solvent selected from: hexylene glycol, butyl cellosolve, butyl digol and others used in formulation of fluoroprotein foams. Use of hexylene glycol is especially preferred. An amount of 5 to 25% preferably 5 to 15% by weight may be employed, more preferably 7%. Preferred concentrates also include up to 20%, preferably 15% by weight of sodium chloride. This has a beneficial effect on the properties and extinguishing effectiveness of the foam. Surfactants and solvents which develop acidity on storage at high temperatures e.g. 50°C, are preferably absent. The first fluorinated surfactant has a preferred surface tension of 17 to 25 mNm " at 0.1%. A non-ionic first surfactant is preferred. There are a wide variety of suitable surfactants although resistance to decomposition or reaction upon prolonged storage is important. The oligomers disclosed in U.S. patent specification No. 4460480 and having suitable surface tensions may be employed. Use of Lodyne K 78/22OB (Ciba Geigy Corporation) is preferred. Alternatively SURFLON S831 (Asahi Glass Co. Limited) or FOROFAC 1199 (Atochemie) may be employed. An amount of 0.05-2.0% by volume based on 100% active material has been found to be suitable. Ionic medium tension surfactants which may be used include sodium perfl oroalkylphenoxysulphonates e.g. MD 313 (I.C.I. ). The second fluorinated surfactant has a preferred surface tension of 15 to 18 more preferably 15 to 17 mNm at 0.1%. Non-ionic surfactants are preferred, for example the oliogomers disclosed in U.S.patent specification No. 4460480 and having suitable surface tensions. Use of LODYNE K 81'86 (Ciba Geigy Corporation) is preferred. An amount of at least 0.15% by volume based on 100% active material may be used. The non-fluorinated hydrocarbon surfactant preferably has an interfacial tension of 2-4 mNm after dilution and a surface tension of more than 25 mNm at 0.1%. Use of sodium or ammonium salts of alkyl ether sulphates is preferred, for example having a C„ to C-,^ alkyl chain and 1 to 3 ethylene oxide units. Preferred materials are C Q to C,, derivatives having 2 ethylene oxide units. The preferred hydrocarbon surfactants are used in a smaller amount than are normally employed with AFFFs. This improves both the expansion and drainage properties. Very surprisingly the heat resistance and burn-back properties are improved. An amount of not greater than 0.6%, by volume based on 100% active material is preferred. Concentrates in accordance with this invention may incorporate an inorganic salt, preferably sodium chloride, in an amount of up to 20% by weight. This enhances the properties of the foam and the extinguishing effectiveness thereof. The concentrate may be diluted in use to form an aqueous working solution for example having a surface tension of 15.0 to 17.0 preferably 15 to 16.5 mNm " . A generally accepted dilution is 6.0% v/v but other dilutions, for example 3.0%, v/v, can be prepared. Concentrates for use at higher dilutions may be prepared using increased proportions of the ingredients. The protein may comprise any protein used in formation of fire fighting foams, preferably hydrolysed keratin containing 15-25% protein, for example using calcium hydroxide. An amount of 60-95% by volume, preferably 85% for 6.0% v/v dilution, may be employed. The invention is further described by means of example and not in any limitative sense. EXAMPLE 1 The following formulation was prepared: Lodyne K81'86 (20% actives) 4.4 % v v /v Lodyne K78'220B( " " ) 0.8 % v /v Hydrocarbon surfactant CH 3 CCH 2 ) 8 _ 10 (OCH 2 CH 2 )-,S0 4 Na 0.5 % v v /v Butyl cellosolve 7.0 % v v /v Hydrolysed protein 87.3 % w w /w Sodium chloride 15 % w /w Film formation properties of this concentrate as a 6% premix solution were tested by placing droplets onto the surface of carious hydrocarbon fuels at room temperature. Some of the fuels used are listed below, all of which resulted in film formation: Cyclohexane = 25.9 mNm -1 Argas = 21.2 mNm -1 Avtur = 26.8 mNm -1 4-star petrol = 18.9 mNm -1 SBP 5 = 20.8 mNm -1 EXAMPLE 2 The following formulation was prepared: Lodyne K81'86 (20% actives) 4.4 & v v Forafac 1199 (40% actives) 0.6 % V /v Hydrocarbon surfactant CH 3 (CH 2 ) 8 _ 10 (OCH 2 CH 2 ) 2 S0 4 a 0.5 % V /v Hexylene glycol 7.0 % /v Hydrolysed protein 87.5 % w /w Sodium chloride 15 % /w This sample was stored at 60°C for 40 days after which it was tested (as described in DEF 42-24) with the following results Initial Final Expansion 9.3 9.5. 25% drainage/mins 4.5 4.75 pH 7.2 7.2 Suspended solids <0.2 % <0.2 % There was no evidence of stratification and the long term storage properties were excellent. EXAMPLE 3 The following formulation was prepared: Lodyne K81'86 (20% active) 6.6 % v /v Forafac 1199 (40% active) 0.4 % v /v Hydrocarbon surfactant CH 3 (CH 2 ) 8 - 10 (OCH 2 CH 2 ) 2 S0 4 Na 0.5 % V /v Hexylene glycol 7.0 % v /v Hydrolysed protein 85.5 % /w Sodium chloride 15 % /w 2 This sample was tested according to DEF 42-24 on a 0.25m fire using Avtur as the fuel with the following results which are compared to a conventional AFFF. Ex 3 Conventional AFFFF Expansion 9.3 25% Drainage 4.6 mins 90% control 18 sees 18 Extinction 20 sees 26 100% Burnback 26.0 mins 17.1 The formulation was tested according to DEF 42-22 with results as follows: 90% control 20 sees Extinction 40 sees 100% Burnback 23.75 mins Formulation given above shows 30% and 52% improvement in extinction and burnback times respectively compared to the AFFF. It therefore exceeds specifications for DEF 42-22 and DEF 42-24. EXAMPLE 4 To investigate the foam compatibility properties, 2x9 litre cartridge extinguishers were used; one being charged with a 6% premix solution of the formulation given in Example 3 above (a) whilst the second was charged with a 6% premix solution of fluoroprotein foam concentrate (b) 150 litres of 2 petrol were added to a fire area of 5.75 M . The fuel was ignited and allowed to burn for one minute. It was then partially extinguished with extinguisher (a) and complete extinction attained by following up with extinguisher (b); there was no rapid breakdown of either foam indicating foam compatibility. EXAMPLE 5 The following formulation was prepared: Lodyne K81'86 4.4 % v /v SurfIon S831 0.26% v /v Butyl Diglycol 7.0 % v /v Hydrocarbon Surfactant 0.5 % v /v Hydrolysed protein CH-(CH 2 )-_ 10 (0CH 2 CH 2 ) 2 S0 4 a 87.8 % W /w Sodium chloride 15 % w/w A 6% premix solution (in fresh water) of this formulation was stored at 60°C for seven days. Visual examination showed no precipitation indicating excellent storage properties of the concentrate. EXAMPLE 6 The formulation described in Example 5 above was tested as a 6% solution on a larger fire of area 4.55 sq.m. using a 9 litre extinguisher, foam being applied continuously. 150 litres of petrol were used and a preburn of 1 minute allowed. Results were as follows: 90% control - 26 seconds 100% burnback - 3 min. 46 sees. Similar trials were carried out with an AFFF formulation with the following results: 90% control - 28 seconds 100% burnback - 2 in 1 sec. These results indicate the effectiveness of the formulation in fire fighting.

Claims: CLAIMS 1. A fire fighting foam concentrate comprising an aqueous mixture of hydrolysed protein, a fluorinated surfactant having a surface tension of 17 to 35 mNm at 0.1%, another fluorinated surfactant having a surface tension of 15 to 20 mNm and a non-fluorinated hydrocarbon surfactant. 2. A concentrate as claimed in Claim 1, wherein the second fluorinated surfactant has a surface tension of 15 to 17 mNm " at 0.1%. 3. A concentrate as claimed in Claim 1 or Claim 2, further comprising a solvent. 4. A concentrate as claimed in Claim 3, wherein the solvent is hexylene glycol, butyl cellosolve or butyl digol. 5. A concentrate as claimed in any preceding claim, and comprising up to 20% by weight of an inorganic salt. 6. A concentrate as claimed in any preceding claim, wherein the first fluorinated surfactant is present in an amount of 0.05 to 2.0% by volume based on the total volume of active material. 7. A concentrate as claimed in any preceding claim, wherein the first fluorinated surfactant is non-ionic. 8. A concentrate as claimed in any preceding claim, wherein the second fluorinated surfactant is present in an amount of at least 0.15% by volume based on the volume of active material. 9. A concentrate as claimed in any preceding claim, wherein the second fluorinated surfactant is non-ionic. 10. A concentrate as claimed in any preceding claim, wherein the non-fluorinated hydrocarbon surfactant has a surface tension of more than 25 mNm at 0.1%. 11. A concentrate as claimed in any preceding claim, wherein the non-fluorinated -hydrocarbon surfactant is present in an amount of not more than 0.6% by volume based on the volume of active material. 12. A concentrate as claimed in any preceding claim, wherein the aqueous hydrolysed protein is present in an amount of 60 to 95% by volume. 13. A concentrate substantially as described herein with reference to any of the Examples. 14. An aqueous solution comprising a concentrate as claimed in any preceding claim, said solution having a surface tension of 15.0 to 17.0 mNm .

Inventors: THOMPSON GERARD, THOMPSON, GERARD
Applicants: KERR & CO LTD JOHN, JOHN KERR & CO. (M/C) LIMITED
Application year: 1987
Main classification: A62D1
IPC codes: A62D1