FOAM FOR ABSORBING HYDROPHOBIC LIQUIDS

Abstract: The use of a polyurethane foam for absorbing/adsorbing hydrophobic liquid.

Description: Foam for absorbing hydrophobic liquids The present invention is related to the use of a polyurethane foam as a material for the adsorption / absorption of hydrophobic liquid. The use of polyurethane materials and foams . for use in adsorbing/absorbing hydropobic liquids like oil are known. In GB 1170959 and US3869385 it has been described to spray formulations suitable for making polyurethane foam on water or sand in order to remove oil. EP-370349 discloses the use of an isocyanate terminated prepolymer for removing hydrocarbons, in particular oil, by preparing a gel. Removal of the gel would be cumbersome since its strength is relatively weak. EP-370349 discloses the use of a prepolymer having an NCO value of 4.2% by weight which has been made from toluene diisocyanate and a polyether polyol which has been tipped with about 2% by weight of propylene oxide. DE3315596 discloses the use of polyurethane prepolymers, made from polyether polyols comprising 70-95% by weight of ethylene oxide units and polyisocyanates, as floculating agents in order to clean water comprising industrial waste. The floculated waste precipitates and would therefore be difficult to recover. Two prepolymers, having an NCO value of 7% by weight and which were made from a polyol comprising EO and PO units in a weight ratio of 75/25 and having a nominal functionality of 2 and a molecular weight of 4000, have been used; the one prepolymer having been made from toluene diisocyanate and the other from a 50/50 w/w mixture of 2,4'- and 4,4'-diphenylmethane diisocyanate. The amounts of prepolymer used are small. EP-415127 also disclosed the use of prepolymers as floculating agents. WO95/31402 discloses a process for removing polluting material like oil from water or wet solid material by spraying a prepolymer containing isocyanate groups onto the oil/water. The prepolymer forms a polyurethane foam by reaction with the water, which foam absorbs /adsorbs / includes the oil. WO97/01512 discloses an improved variant of WO95/31402, also using a prepolymer. Surprisingly a new class of polyurethane foams have been found which have excellent capabilities for absorbing /adsorbing hydrophobic liquids. These foams are known as such. They have been disclosed in WO96/35744. Improvement of such foams are the subject of pending applications EP 96203136.5, 96203135.7, 96203132.4, 96203134.0 and 96203133.2. Therefore the present invention is concerned with the use of a flexible polyurethane foam having no major glass-rubber transition between -100°C and + 25°C for the absorption and/or adsorption of hydrophobic liquids and with a process for absorbing and/or adsorbing a hydrophobic liquid by bringing the above foam into contact with the liquid or vice versa. Conventional flexible polyurethane foams are widely known. Such foams show a relatively high resilience (ball rebound), a relatively low modulus, a relatively high sag factor and a relatively low hysteresis loss. Such foams further show a major glass-rubber transition below ambient temperature, generally in the temperature range of -100°C to -10°C. The commonly applied relatively high molecular weight polyether and polyester polyols in such foams are responsible for the sub-ambient glass transition temperature (Tg s ). These polyether and polyester polyols are often referred to as soft segments. Above Tg s the foam displays its typical flexible properties until softening and/or melting of the isocyanate-derived urethane/urea clusters ("hard domains") takes place. This softening and/or melting temperature (Tg h and /or Tm h ) often coincides with the onset of thermal degradation of polymer segments. The Tg h and /or Tm h for flexible polyurethane foams is generally higher than 100°C, often even exceeding 200°C. At the Tg s a sharp decrease of the modulus of the flexible foam is 5 observed. Between Tg s and Tg h /Tm h the modulus remains fairly constant with increasing temperature and at Tg h /Tm h again a substantial decrease of the modulus may take place. A way of expressing the presence of Tg s is to determine the ratio of the Young's storage modulus E' at -100°C and +25°C as per Dynamic Mechanical Thermal Analysis (DMTA measured according to ISO/DIS 6721-5). o For conventional flexible polyurethane foams the E'-100°C ratio is at least 25. E' +25°C Another feature of Tg s by DMTA (ISO/DIS 6721-5) is that for conventional 5 flexible polyurethane foams the maximum value of the Young's loss modulus E" ratio of (tan δ max ) over the Young's storage modulus E' -100°C/+25°C temperature range varies from 0.20 - 0.80 in general. The Young's 0 loss modulus E" is measured by DMTA (ISO/DIS 6721-5) as well. The foams used in the present application are foams having no major glass-rubber transition between -100°C and +25°C. In more quantitative terms these foams show a ratio E _ 100°c / E' +25 =c of 1.3 to 15.0, preferably of 1.5 to 10 and most preferably of 1.5 to 7.5. The tan δ max over the -100°C to +25°C temperature range 5 is below 0.2. The apparent core density of such foams may range from 4-30 kg/m 3 and preferably ranges from 4-20 kg/m 3 (measured according to ISO/DIS845). Such foams are made by crushing a rigid foam. In the context of the present application a flexible polyurethane foam is a crushed foam having a ball rebound (measured according to ISO 8307) of at least 40%, preferably at least 50% and most preferably 55-85% in at least one of the three dimensional directions. Preferably such flexible foams have a Young's storage modulus at 25°C of at most 500 kPa, more preferably at most 350 kPa and most preferably between 10 and 200 kPa (Young's storage modulus measured by DMTA according to ISO/DIS 6721-5). Further, such flexible foams preferably have a sag factor (CLD 65/25) of at least 2.0, more preferably at least 3.5 and most preferably 4.5-10 (measured according to ISO 3386/1). Still further such flexible foams preferably have a CLD hysteresis loss (ISO 3386/1) of below 55%, more preferably below 50% and most preferably below 45%. In the context of the present patent application a rigid polyurethane foam is an uncrushed foam having a ball rebound measured in the direction of foam rise of less than 40% (ISO 8307 with the proviso that no preflex conditioning is applied, that only one rebound value per sample is measured and that test pieces are conditioned at 23°C ± 2°C and 50 ± 5% relative humidity) and/or having a CLD 65/25 sag factor measured in the direction of foam rise of less than 2.0 (ISO 3386/1 with the proviso that the sag factor is determined after the first load - unload cycle); these properties both being measured at an apparent core density of the foam of 3-27 kg/m 3 (ISO 845). Preferably the ratio E , . 100 . c /E , +25 . c of such a rigid foam is 1.3-15. If in the present application ISO 8307 and ISO 3386/1 are mentioned in relation to rigid foams they refer to the tests as described above including the provisos. In the context of the present invention the following terms have the following meaning: 1) isocyanate index or NCO index or index: the ratio of NCO-groups over isocyanate-reactive hydrogen atoms present in a 5 formulation, given as a percentage: ΓNCQIXI OO (%). [active hydrogen] In other words the NCO-index expresses the percentage of isocyanate actually used in a formulation with respect to the amount of isocyanate theoretically o required for reacting with the amount of isocyanate-reactive hydrogen used in a formulation. It should be observed that the isocyanate index as used herein is considered from the point of view of the actual foaming process involving the isocyanate ingredient and the isocyanate-reactive ingredients. Any isocyanate groups 5 consumed in a preliminary step to produce modified polyisocyanates (including such isocyanate-derivatives referred to in the art as quasi or semi-prepolymers and prepolymers) or any active hydrogens consumed in a preliminary step (e.g. reacted with isocyanate to produce modified polyols orpolyamines) are not taken into account in the calculation of the isocyanate index. Only the free isocyanate 0 groups and the free isocyanate-reactive hydrogens (including those of the water) present at the actual foaming stage are taken into account. 2) The expression "isocyanate-reactive hydrogen atoms" as used herein for the purpose of calculating the isocyanate index refers to the total of active hydrogen atoms in hydroxyl and amine groups present in the reactive compositions; this 5 means that for the purpose of calculating the isocyanate index at the actual foaming process one hydroxyl group is considered to comprise one reactive hydrogen, one primary amine group is considered to comprise one reactive hydrogen and one water molecule is considered to comprise two active hydrogens. 3) Reaction system : a combination of components wherein the polyisocyanates are kept in one or more containers separate from the isocyanate-reactive 5 components. 4) The expression "polyurethane foam" as used herein refers to cellular products as obtained by reacting polyisocyanates with isocyanate-reactive hydrogen containing compounds, using foaming agents, and in particular includes cellular products obtained with water as reactive foaming agent (involving a reaction of o water with isocyanate groups yielding urea linkages and carbon dioxide and producing polyurea-urethane foams) and with polyols, aminoalcohols and/or polyamines as isocyanate-reactive compounds. 5) The term "average nominal hydroxyl functionality" is used herein to indicate the number average functionality (number of hydroxyl groups per molecule) of 5 the polyol or polyol composition on the assumption that this is the number average functionality (number of active hydrogen atoms per molecule) of the initiator(s) used in their preparation although in practice it will often be somewhat less because of some terminal unsaturation. 6) The word "average" refers to number average unless indicated otherwise. 0 7) pK a refers to the strength of a protolyte compared to that of water (pK a = -logK a wherein K a is the dissociation constant of the acid or the salt). 8) Liquid means liquid at 25°C and ambient pressure; preferably the viscosity of the hydrophobic liquid is not more than 8000 cP. 9) Hydrophobic liquid is an organic liquid which shows phase separation within 1 hour under ambient conditions (temperature 25 °C) after having been mixed with water in a 50/50% weight ratio using a hand mixer for 1 minute at 3000 rounds per minute at ambient conditions (25°C). The foam is in particular 5 usefull to absorb/adsorb hydrophobic liquids as hydrocarbons, mixtures of hydrocarbons, oils and fractions thereof. The hydrocarbons may be aliphatic, aromatic of araliphatic, they may be saturated or unsaturated, cyclic or not and they may contain other atoms than carbon and hydrogen, in particular oxygen, nitrogen and sulphur. The oils may be essential oils, liquid oils produced from oil o shale, vegetale oils and petroleum (crude oil) and fractions thereof, like gasoline, naphta, kerosene, fuel oil, diesel oil. The foams according to the present invention are prepared by reacting a polyisocyanate (1), an isocyanate-reactive compound (2), said compound (2) having an average equivalent weight of at most 374 and an average number of 5 isocyanate-reactive hydrogen atoms of from 2 to 8, an isocyanate-reactive compound (3), said compound (3) having an average equivalent weight of more than 374 and an average number of isocyanate-reactive hydrogen atoms of from 2 to 6 and water to prepare a rigid polyurethane foam and by crushing this rigid polyurethane foam to prepare a flexible polyurethane foam. 0 More in particular the foams according to the present invention are prepared by reacting a polyisocyanate (1), a polyol (2) having a hydroxyl number of at least 150 mg KOH g and an average nominal hydroxyl functionality of from 2 to 8, a polyol (3) having a hydroxyl number of from 10 to less than 150mg KOH/g and an average nominal hydroxyl functionality of from 2 to 6 and water to prepare a 5 rigid polyurethane foam and by crushing this rigid polyxirethane foam to prepare a flexible polyurethane foam. Suitable organic polyisocyanates for use in the process of the present invention include any of those known in the art for the preparation of rigid polyurethane foams, like aliphatic, cycloaliphatic, araliphatic and, preferably, aromaticpolyisocyanates, such as toluene diisocyanate in the form of its 2,4 and 2,6-isomers and mixtures thereof and diphenylmethane diisocyanate in the form of its 2,4'-, 2,2'- and 4,4'-isomers and mixtures thereof, the mixtures of diphenylmethane diisocyanates (MDI) and oligomers thereof having an isocyanate functionality greater than 2 known in the art as "crude" or polymeric MDI (polymethylene polyphenylene polyisocyanates), the known variants of MDI comprising urethane, allophanate, urea, biuret, carbodumide, uretonimine and/or isocyanurate groups. Mixtures of toluene diisocyanate and diphenylmethane diisocyanate and/or polymethylene polyphenylene polyisocyanates may be used. Preferably MDI, crude or polymeric MDI and/or liquid variants thereof are used said variants being obtained by introducing uretonimine and/or carbodumide groups into said polyisocyanates, such a carbodumide and/or uretonimine modified polyisocyanate having an NCO value of at least 20% by weight, and/or by reacting such a polyisocyanate with one or more polyols having a hydroxyl functionality of 2-6 and a molecular weight of 62-500 so as to obtain a modified polyisocyanate having an NCO value of at least 20% by weight. Isocyanate-reactive compounds (2) include any of those known in the art for that purpose like polyamines, aminoalcohols and polyols. Of particular importance for the preparation of the rigid foams are polyols and polyol mixtures having hydroxyl numbers of at least 150 mg KOH/g and an average nominal hydroxyl functionality of from 2 to 6. Suitable polyols have been fully described in the prior art and include reaction products of alkylene oxides, for example ethylene oxide and/or propylene oxide, with initiators containing from 2 to 8 active hydrogen atoms per molecule. Suitable initiators include : polyols, for example ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butane diol, glycerol, trimethylolpropane, triethanolamine, pentaerythritol, sorbitol and 5 sucrose; polyamines, for example ethylene diamine, tolylene diamine,diaminodiphenylmethane and polymethylene polyphenylene polyamines; and aminoalcohols, for example ethanolamine and diethanolamine; and mixtures of such initiators. Other suitable polyols include polyesters obtained by the condensation of appropriate proportions of glycols and higher functionality o polyols with polycarboxylic acids. Still further suitable polyols include hydroxyl terminated polythioethers, polyamides, polyesteramides, polycarbonates, polyacetals, polyolefins and polysiloxanes. Still further suitable isocyanate-reactive compounds include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butane diol, glycerol, trimethylolpropane, 5 ethylene diamine, ethanolamine, diethanolamine. triethanolamine and the other initiators mentioned before. Mixtures of such isocyanate-reactive compounds may be used as well. Most preferably polyols are used which do not comprise primary, secondary or tertiary nitrogen atoms. Isocyanate-reactive compounds (3) include any of those known in the art for that 0 purpose, like polyamines, aminoalcohols and polyols. Of particular importance for the preparation of the rigid foams are polyols and polyol mixtures having a hydroxyl value of 10 to less than 150 and preferably of 15-60 mg KOH g and an average nominal hydroxyl functionality of from 2 to 6 and preferably of from 2 to 4. These high molecular weight polyols are generally 5 known in the art and include reaction products of alkylene oxides, for example ethylene oxide and/or propylene oxide, with initiators containing from 2 to 6 active hydrogen atoms per molecule. Suitable initiators include : polyols, for example ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butane diol. glycerol, trimethylolpropane, triethanolamine, pentaerythritol and sorbitol; polyamines, for example ethylene diamine, tolylene diamine, diaminodiphenylmethane and polymethylene polyphenylene polyamines; and aminoalcohols, for example ethanolamine and diethanolamine; and mixtures of 5 such initiators. Other suitable polyols include polyesters obtained by the condensation of appropriate proportions of glycols and higher functionality polyols with polycarboxylic acids. Still further suitable polyols include hydroxyl terminatedpolythioethers, polyamides, polyesteramides, polycarbonates, polyacetals. polyolefins and polysiloxanes. Preferred polyols are the polyether o polyols comprising ethylene oxide and/or propylene oxide units and most preferably polyoxyethylene polyoxypropylene polyols having an oxyethylene content of at least 20% by weight. Other polyols which may be used comprise dispersions or solutions of addition or condensation polymers in polyols of the types described above. Such modified polyols, often referred to as "polymer" 5 polyols have been fully described in the prior art and include products obtained by the in situ polymerisation of one or more vinyl monomers, for example styrene and acrylonitrile, in polymeric polyols, for example polyether polyols, or by the in situ reaction between a polyisocyanate and an amino- or hydroxy-functional compound, such as triethanolamine, in a polymeric polyol. 0 The polymer modified polyols which are particularly interesting in accordance with the invention are products obtained by in situ polymerisation of styrene and/or acrylonitrile in poly(oxyethylene. oxypropylene) polyols and products obtained by in situ reaction between a polyisocyanate and an amino or hydroxy-functional compound (such as triethanolamine) in a 5 poly(oxyethylene. oxypropylene) polyol. Polyoxyalkylene polyols containing from 5 to 50% of dispersed polymer are particularly useful. Particle sizes of the dispersed polymer of less than 50 microns are preferred. Mixtures of such isocyanate-reactive compounds may be used as well. Most preferably polyols are used which do not comprise primary, secondary or tertiary nitrogen atoms. The relative amount of isocyanate-reactive compound (2) and (3) or polyol (2) and (3) may vary widely and preferably ranges from 0.1 :1 to 4:1 (w:w). The relative quantities of the polyisocyanate and the isocyanate-reactive 5 compounds to be reacted may vary within a wide range. In general an isocyanate index will be applied of from 25 to 300, preferably of from 30 to 200 and most preferably of from 102 to 150. In order to prepare a foam water is used as a blowing agent. However if the amount of water is not sufficient to obtain the desired density of the foam any o other known way to prepare polyurethane foams may be employed additionally, like the use of reduced or variable pressure, the use of a gas like air, N 2 and CO 2 , the use of more conventional blowing agents like chlorofluorocarbons, hydrofluorocarbons, hydrocarbons and fluorocarbons, the use of other reactive blowing agents, i.e. agents which react with any of the ingredients in the reacting 5 mixture and due to this reaction liberate a gas which causes the mixture to foam and the use of catalysts which enhance a reaction which leads to gas formation like the use of carbodiimide-formation-enhancing catalysts such as phospholene oxides. Combinations of these ways to make foams may be used as well. The amount of blowing agent may vary widely and primarily depends on the desired 0 density. Water may be used as liquid at below-ambient, ambient or elevated temperature and as steam. A preferred combination of blowing agent is water and CO 2 wherein the CO 2 is added to the ingredients for making the foam in the mixing head of a device for making the foam, to one of the isocyanate-reactive ingredients and preferably to 5 the polyisocyanate before the polyisocyanate is brought into contact with the isocyanate-reactive ingredients. Per 100 parts by weight of polyisocyanate (1), isocyanate-reactive compound (2) and compound (3) or polyol (2) and polyol (3) and water, preferably the amount of compound (2) or polyol (2) ranges from 2-20 parts by weight, the amount of 5 compound (3) or polyol (3) ranges from 5-35 parts by weight and the amount of water ranges from 1 to 17 parts by weight, the remainder being polyisocyanate. Most preferably these amounts are 55-80, 3-20, 10-30 and 2-6 parts by weight for the polyisocyanate, polyol (2), polyol (3) and water respectively. If a cyclic polyisocyanate and more in particular an aromatic polyisocyanate and most in o particular an MDI or polymethylenepolyphenylene polyisocyanate is used the content of cyclic and more in particular of aromatic residues in the flexible foam is relatively high as compared to conventional flexible polyurethane foams. The foams according to the invention preferably have a content of benzene rings, derived from aromatic polyisocyanates, which is 30 to 56 and most preferably 35 5 to 50% by weight based on the weight of the foam. Since polyols, polymer polyols, fire retardants, chain extenders and/or fillers which contain benzene rings may be used, the overall benzene ring content of the flexible foam may be higher and preferably ranges from 30 to 70 and most preferably from 35 to 65% weight as measured by calibrated Fourier Transform Infra Red Analysis. 0 The rigid polyurethane foams are prepared by reacting a polyisocyanate (1), a polyether polyol (2) having a hydroxyl number of at least 150 mg KOH g and an average nominal hydroxyl functionality of from 2 to 8, a polyether polyol (3) having a hydroxyl number of from 10 to less than 150 mg KOH/g and an average nominal hydroxyl functionality of from 2 to 6 and water, wherein the amount of 5 polyisocyante (1), polyol (2), polyol (3) and water is 55-80, 3-20, 10-30 and 2-6 parts by weight respectively per 100 parts by weight of polyisocyanate (1), polyol (2), polyol (3) and water, wherein the reaction is conducted at an isocyanate index of 102-150 and wherein the polyisocyanate is reacted with one or more isocyanate-reactive compositions comprising one or more of the aforementioned polyol (2), polyol (3) and water and not comprising compounds which have a primary, secondary or tertiary nitrogen atom. 5 Preferably the rigid foam is prepared by reacting a polyisocyanate ( 1 ), a polyether polyol (2) having an average equivalent weight of 70-300 and preferably of 70-150, having an average nominal hydroxyl functionality of from 2 to 6 and preferably from 2 to 3 and an oxyethylene content of at least 75% by weight, a polyether polyol (3) having an average equivalent weight of 1000-3000, having an o average nominal hydroxyl functionality of 2 to 3 and preferably of 2 and having the structure HO-(EO) x -(PO) z -(EO) γ -X[-0-(EO) γ -(PO) z -(EO) x H] n Formula 1 wherein EO is an ethylene oxide radical, PO is a propylene oxide radical, x=l-15 and preferably 3-10, y=0-6 and preferably 1-4, z is such so as to arrive at the 5 above equivalent weight, n = 1-2 and X is a hydrocarbon radical having 2-10 and preferably 2-6 carbon atoms or a radical having the formula -CH 2 -CH 2 -(OCH 2 -CH 2 ) ! . 2 -, and water wherein the amount of polyisocyanate (1), polyol (2), polyol (3) and water is 55-80, 3-20, 10-30 and 2-6 parts by weight respectively per 100 parts by weight of polyisocyanate (1), polyol (2), polyol (3) 0 and water and wherein the reaction is conducted at an isocyanate index of 102-200 and preferably of 102-150 and wherein the polyisocyanate is reacted with one or more isocyanate-reactive compositions comprising one or more of the aforementioned polyol (2), polyol (3) and water and not comprising compounds which have a primary, secondary or tertiary nitrogen atom. Preferably the amount 5 of water is 3-5 parts by weight calculated on the same basis as above. Preferably the weight ratio of water and polyol (3) is 0.1 to 0.4:1 and the weight ratio of polyol (3) and of polyol (2) + water is 0.9-2.5:1 Most preferred polyether polyols (3) are those according to formula 1. described hereinbefore. Those having a nominal hydroxyl functionality of 3 may be prepared by ethoxylation of an initiator, followed by propoxylation and again ethoxylation, wherein the initiator is a triol like glycerol and/or trimethylol propane. Those having a nominal hydroxyl functionality of 2 may be prepared by ethoxylation of ethylene glycol, diethylene glycol and/ortriethylene glycol, followed by propoxylation and again ethoxylation; or by propoxylation of ethylene glycol, diethylene glycol and/or triethylene glycol followed by ethoxylation; or by propoxylation of a polyoxyethylene polyol having 4-15 oxyethylene groups followed by ethoxylation. Mixtures of such most preferred polyols may be used as well. Although not necessary other polyols may be used together with these most preferred polyols according to formula 1, provided the amount does not exceed 30% by weight based on the weight of these polyols according to formula 1. Such polyols according to formula 1 are commercially available (e.g. Daltocel F 430 from Imperial Chemical Industries PLC). In addition to the polyisocyanate, the isocyanate-reactive compounds and the blowing agent, one or more auxiliaries or additives known per se for the production of polyurethane foams may be used. Such optional auxiliaries or additives include catalysts, foam-stabilizing agents or surfactants, for example siloxane-oxyalkylene copolymers and polyoxyethylene polyoxypropylene block copolymers and fire retardants, for example halogenated alkyl phosphates such as tris chloropropyl phosphate, melamine and guanidine carbonate, anti-oxidants, anti-static agents, UV stabilisers, anti-microbial and anti-fungal compounds and fillers like latex, TPU, silicates, barium and calcium sulphates, chalk, glass fibers or beads and polyurethane waste material. Preferbably additives and auxiliaries are used which do not comprise primary, secondary or tertiary nitrogen atoms. Catalysts which may be used are urethane/urea catalysts, for example tin compounds such as stannous octoate or dibutyltin dilaurate and/or tertiary amines such as dimethylcyclohexylamine or triethylene diamine and/or phosphates like NaH 2 P0 4 and Na 2 HPO 4 . A preferred catalyst combination is a tin salt of a carboxylic acid having 2-18 carbon atoms (hereinafter called "catalyst 1"), and a protic acid having at least 2 acidic hydrogen atoms and having a pK a in water of 2-10 and/or a lithium, sodium, potassium, cesium, magnesium, calcium, strontium and/or barium salt thereof (hereinafter called "catalyst 2"). For simplicity reasons the above protic acids and their salts are called "catalyst 2"; it is to be noted however that these compounds in fact have a deactivating effect upon catalyst 1. Without wishing to be bound by any theory it is believed that catalyst 2 supresses the formation of certain intermediate tin compounds during the preparation of the foam, which intermediate tin compounds would enhance certain undesirable hydrolytic processes which lead to said degradation. The weight ratio of catalysts 1 and 2 as used in this process may range from 30:70 to 95:5 and preferably from 50:50 to 90:10. The carboxylic acid in catalyst 1 may be selected from saturated or unsatured aliphatic, cycloaliphatic and araliphatic hydrocarbons and from aromatic hydrocarbons having one carboxylic acid groups. Preferably they have 2-18 carbon atoms. Most preferred monocarboxylic acids are the saturated aliphatic carboxylic acids having 2-12 carbon atoms, like acetic acid, propionic acid, n-butyric acid, isobutyric acid, n-valeric acid, caproic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid and dodecanoic acid. Examples of tin catalysts of this type are dibutyltin dilaurate and stannous octoate. Catalyst 2 may be selected from a wide range of compounds. Preferably such compounds are selected from those containing at least 2 groups selected from -COOH and aromatic thiol and their above salts. Preferably the number of acidic hydrogen atoms is at least 3. When metal salts of 5 these catalysts are used different metal salts may be used in combination. Further metal salts may be used wherein all or only a part of the acidic hydrogens has been replaced by themetal ion. Most preferred salts are the K- and Na-salts. Preferably catalyst 2 has a solubility in water of at least 5 gram of catalyst 2 per liter water at 25°C. Examples of useful catalysts are the following ones together 1 o with Li, Na, K, Cs, Mg, Ca, Sr and or Ba salts thereof : citric acid, 1 ,2,4,5 benzenetetracarboxylic acid (BCTA), ethylenediaminetetraacetic acid (EDTA), ethylenebis(oxyethylenenitrilo)tetraacetic acid (EGTA). N-(2-hydroxyethyl)- ethylenediaminetriacetic acid (HEDTA), l,3-diamino-2- hydroxypropane- N,N,N',N'-tetraacetic acid (DHPTA), 2-merca-ptobenzoic acid (MBA), 15 2,2'-thiodiglycolic acid (TDGA), poly(acrylic acid) (PAcA), poly (2-acrylamido-2-methyl-l-propanesulfonic acid) (PAcAmMPSA), copolymers of acrylamide and acrylic acid (PAcAm-co-PAcA), of acrylic acid and maleic acid (PAcA-co-PMA), of vinylpyrrolidone and acrylic acid (PVP-co-PAcA), said polymers and copolymers having average molecular weights between 500 and 20 1000000, preferably between 1000 and 500000. The amount of catalyst 1 and catalyst 2 may vary between wide ranges. In general an amount of 0.1-5% by weight and preferably 0.2-3% by weight may be used calculated on the weight of all ingredients used to prepare the polyurethane foam. Catalysts 1 and 2 are preferably mixed with the isocyanate-reactivecompounds 25 before the foaming reaction takes place. More preferably catalyst 1 is mixed with a part of the isocyanate-reactive compounds and catalyst 2 is mixed with another part of the isocyanate-reactive compounds; subsequently these mixtures are fed to a mixing head of a foaming device where they are mixed with the polyisocyanate. This preferred catalyst combination gives foams with reduced thermal degradation, especially when such foams are made as large buns e.g. on a moving 5 conveyor belt (slab-stock foam), the foams have improved stability and a low amount of extractables. In operating the process for making rigid foams according to the invention, the known one-shot, prepolymer or semi-prepolymer techniques may be used together with conventional mixing methods and the rigid foam may be produced in the o form of slabstock, mouldings including foam in fabric and pour-in-place applications, sprayed foam, frothed foam or laminates with other materials such as hardboard, plasterboard, plastics, paper or metal or with other foam layers. It is convenient in many applications to provide the components for polyurethane production in pre-blended formulations based on each of the primary 5 polyisocyanate and isocyanate-reactive components. In particular, an isocyanate-reactive composition may be used which contains the auxiliaries, additives and the blowing agent in addition to the isocyanate-reactive compounds (2) and (3) in the form of a solution, an emulsion or dispersion. The isocyanate-reactive components may also be supplied independently to the 0 polyisocyanate as two or more compositions containing the additives and auxiliaries; e.g. one composition comprising catalyst 2, water and polyol (2) and another composition comprising polyol (3), catalyst 1 and antioxidant may be fed from different storage tanks into the mixing head of a device for making foam, in which mixing head they are mixed with the polyisocyanate. The rigid foam is prepared by allowing the aforementioned ingredients to react and foam until the foam does not rise any more. After rise curing of the foam may be continued as long as desirable. In general a curing period of 1 minute to 24 hours and preferably of 5 minutes to 12 hours will be sufficient. If desired curing may be conducted at elevated temperature. Subsequently the foam may be crushed. It is however preferred to allow the rigid foam obtained to cool down to below 80°C, preferably below 50°C and most preferably to ambient temperature prior to crushing. The rigid foam (i.e. before crushing) preferably has an apparent core density of 3-27, more preferably of 3-18 kg/m 3 and most preferably of 3-15 kg/m 3 (ISO 845). The rigid foam (i.e. before crushing) prepared has a substantial amount of open cells. Preferably the cells of the rigid foam are predominantly open. The crushing may be conducted in any known manner and by any known means. The crushing may for instance be conducted by applying mechanical force onto the foam by means of a flat or pre-shaped surface or by applying variations of external pressure. In most cases a mechanical force sufficient to decrease the dimension of the foam in the direction of the crushing by 1-90%, preferably by 50-90% will be appropriate. If desired crushing may be repeated and or carried out in different directions of the foam. Due to the crushing the ball rebound increases considerably in the direction of the crushing. Due to the crushing the density of the foam may increase. In most cases this increase will not exceed 50% and preferably 30% of the density before crushing. The foam may be crushed in the direction of foam rise. A special foam is obtained when the crushing is conducted in a direction perpendicular to the direction of foam rise : then a foam is obtained with a highly anisotropic cell structure. Although it is difficult to give more precise directions for the crushing since it will inter alia depend on the density of the foam, the rigidity of the foam, the type of crushing device used, we believe those skilled in the art are sufficiently aware of the phenomenon of crushing of polyurethane foams that they will be able to determine the appropriate crushing manner and means with the above guidance, certainly in the light of the following examples. By crushing the ball rebound is increased at least in the direction of crushing. The increase is at least 10%. After the crushing the foam may be subjected to a heat treatment in order to reduce the density increase caused by the crushing. This heat treatment is conducted at 70-200°C and preferably at 90-180°C for 0.5 minute to 8 hours and preferably for 1 minute to 4 hours. After the crushing and optionally the heating a flexible foam is obtained which has exceptional properties. The flexible foam has an apparent core density of 4-30 kg/m 3 , preferably of 4-20 kg/m 3 and most preferably of 4-16 kg/m 3 (ISO 845) Despite the fact that the foam is flexible, it does not show a significant change of the Young's storage modulus E' over a temperature range from -100°C to +25°C, as described before. The oxygen index of the foam prepared from aromatic polyisocyanates preferably is above 20 (ASTM 2863). Further it shows a Young's storage modulus at 25°C of at most 500 kPa, preferably at most 350 kPa, most preferably between 10-200 kPa and a sag factor (CLD 65/25, ISO 3386/1) of at least 2.0, preferably at least 3.5 and most preferably of 4.5-10. CLD hysteresis loss values for the foams are below 55% and preferably below 50% (which is calculated by the formula ,A - B , x lOO%, A wherein A and B stand for the area under the stress/strain curve of the loading (A) and unloading (B) as measured according to ISO 3386/1). Still further these foams can be manufactured with a very low or even negative Poisson's ratio as determined by lateral extension studies under compression of the foams. Finally compression set values of the foams are generally low, preferably below 40% (ISO 1856 Method A, normal procedure). If the Tg h is not too high the foam might be used in thermoforming processes to prepare shaped articles. Preferably the Tg h of the foam is between 80 and 180°C, most preferably between 80°C and 160°C for such thermoforming applications. Further it was found that foams, which have been made by using a relatively low amountof the polyols having a low molecular weight, show a small or non-visible Tg h by DMTA (the modulus change at Tg h is small or the modulus changes gradually until the foam thermally decomposes); such foams may be used for thermoforming activities as well. Further the foams show good load-bearing properties like compression hardness values without the use of external fillers together with a good resilience, tear strength and durability (fatigue resistance) even at very low densities. In conventional flexible foams often high amounts of filler need to be used to obtain satisfactory load-bearing properties. Such high amounts of fillers hamper the processing due to a viscosity increase. Surprisingly the flexible foams excellently absorb and/or adsorb hydrophobic liquids. The hydrophobic liquids may be easily recovered by pressing the foam, which may be re-used. In order to absorb/adsorb the hydrophobic liquid the foam may be used as a mat, a pad, a filter, it may be used in layers, it may be used while it is held by, covered by or envelopped or encapsulated in other material, it may be used after having been shredded into smaller pieces or lumps. The absorption / adsorption process may be applied at ambient temperature and pressure. When the foam is used as a filter increased or decreased pressure may be applied to enhance the filtration process. If desired the absorption / adsorption process may be applied at a temperature lower or higher than the ambient one. The foam may be used in order to avoid the hydrophobic liquid is released into the environment or to clean a spill of hydrophobic liquid in the environment or to separte the liquid from water. Hydrophobic liquid may be absorbed / adsorbed by bringing the foam into contact with the liquid e.g. by immersing the foam into the liquid and/or by leading the hydrophobic liquid, while in contact with water or not, through the foam. The application is illustrated by the following examples. Example 1 A rigid and flexible foam were made as follows : a polyisocyanate mixture was prepared by mixing 49.1 parts by weight of polymeric MDI having an NCO value of 30.7% by weight and an isocyanate functionality of 2.7 and 42.5 parts by weight of a uretonimine modified MDI having an NCO value of 31% by weight, an isocyanate functionality of 2.09, a uretonimine content of 17% by weight and 2,4'-MDI content of 20% by weight. This polyisocyanate composition was reacted with the following ingredients at an index of 1 12; ingredients 1-4 were premixed as well as ingredients 5-7 : 1) 7.55parts by weight (pbw) of polyethylene glycol having a molecular weight of 200, 2) 2.35 pbw of triethylene glycol, 3) 5 pbw of water, 4) 0.1 1 pbw of NaH 2 PO 4 , 5) 20 pbw of an EO/PO polyol having a nominal functionality of 2. diethylene glycol as initiator, an EO content (except the initiator) of 20.2% by weight (all tipped) and a hydroxyl value of 30 mg KOH/g, 6) 0.64 pbw of Irganox ™ 5057 (anti-oxydant from Ciba-Geigy), 7) 0.3 pbw of 1 methyl- 1-oxo- phospholene and 8) 0.93 pbw of Dabco ™ T9 (catalyst from Air Products). The ingredients were fed to a low pressure mixing head, spread on a moving conveyor belt and allowed to react and expand freely. A rigid polyurethane foam was obtained. The apparent core density was 1 1 kg/m 3 (ISO 845). The foam was crushed in the rise direction giving a flexible foam having a resilience of more than 40% and no major glass rubber transition. These foams were tested together with other materials by the test described in Proceedings of the 17th Artie and Marine Oil Spill Program technical seminar by D. Cooper et al, 1994, pages 586-587 with the proviso that the sample size was 10 x 10 x 5 cm, the soaking time was 5 minutes, the dripping time was 10 seconds and a paper basket was used instead of a fine mesh basket. As hydrophobic liquid Flotta crude oil (viscosity 4-8 cP and weight per dm 3 of 837 grams) was used. The same tests were done with water. The absorption/adsorption in g/g foam is given in the following Table. * full absorption / adsorption reached in less than 1 minute. 1 ) commercially available granules from Petroleum Environmental Technologies Inc., used for cleaning oil spills. 2) commercially available powder from Sanol AB, used for cleaning oil spills. 5 3) conventional polyisocyanurate powder. 4) commercially available sorbent sheet from 3M used for general spill cleaning. 5) commercially available polypropylene sorbent sheet from 3M used for oil spill cleaning. 6) conventional flexible foam used in matresses and having a major glass o transition between - 100°C and + 25°C. 7) conventional rigid foam used for insulation purposes having a resilience below 40%. Example 2 Samples of equal size as in example 1 of Powersorb™ T 151 and the flexible foam from example 1 were allowed to float on the oil used in example 1. The time was recorded to obtain complete absoφtion/ adsoφtion of oil. The samples were allowed to drip for 10 seconds and then the weight difference before and after absoφtion/adsoφtion was obtained. Then the samples were squeezed by hand and the amount of oil recoverable was determined. The experiment was repeated twice with the same samples.

Claims: CLAIMS 1. The use of a flexible polyurethane foam having no major glass-rubber transition between -100°C and + 25°C for the absoφtion and/or the adsoφtion of hydrophobic liquids. 5 2. The use of a flexible polyurethane foam having a E' _ m°c / E' + 25 » c ratio of 1.3-15 for the absoφtion and /or the adsoφtion of hydrophobic liquids. 3. The use according to claims 1-2, the foam having an apparent core density of 4-30 kg/m 3 . 4. The use according to claims 1-3, the foam having a content of benzene o rings of 30 to 70% by weight based on the weight of the foam. 5. The use according to claims 1-4, the foam having a sag factor of 4.5-10. 6. The use according to claims 1-5, the foam having aYoung's storage modulus at 25 °C of 10-200 kPa. 7. The use according to claims 1-6 wherein the foam is prepared by reacting a 5 polyisocyanate (1 ), a polyol (2) having a hydroxyl number of at least 150 mg KOH/g and an average nominal hydroxyl functionality of from 2 to 8, a polyol (3) having a hydroxyl number of from 10 to less than 150 and an average nominal hydroxyl functionality of from 2 to 6 and water to prepare a rigid polyurethane foam and by crushing this rigid polyurethane foam. 0 8. The use according to claim 7 wherein the amount of polol (2) , polyol (3) and water (per 100 parts by weight of polyisocyanate, polyol (2), polyol (3) and water) ranges from 2-20 parts by weight, 5-35 parts by weight and 1 -17 parts by weight respectively. 9. The use according to claims 7-8 wherein polyol (2) is a polyether polyol having an average equivalent weight of 70-300 , having an average 5 nominal hydroxyl functionality of from 2 to 3 and an oxyethylene content of at least 75% by weight, and polyether (3) is a polyether polyol having an average equivalent weight of 1000-3000, having an average nominal hydroxyl functionality of 2 to 3 and having the structure HO-(EO) x -(PO) z -(EO) γ -X[-0-(EO) γ -(PO) z -(EO) x H] n Formula 1 1 o wherein EO is an ethylene oxide radical, PO is a propylene oxide radical, x=l-15, y=0-6 , z is such so as to arrive at the above equivalent weight, n = 1-2 and X is a hydrocarbon radical having 2-10 carbon atoms or a radical having the formula -CH 2 -CH 2 -(OCH 2 -CH 2 ),. 2 -. 10. The use according to claims 7-9 wherein the foam is prepared in the 15 presence of a tin salt of a carboxylic acid having 2- 18 carbon atoms (catalyst 1 ) together with a protic acid having at least 2 acidic hydrogen atoms and having a pK a in water of 2-10 and/or a lithium, sodium, potassium, cesium, magnesium, calcium, strontium and/or barium salt thereof (catalyst 2). 20 11 • The use of claim 10 wherein the weight ratio of catalyst 1 and 2 ranges from 30:70 to 95:5. 12. The use according to claims 10-11 wherein catalyst 1 is a salt of a monocarboxylic saturated, aliphatic acid having 2-12 carbon atoms. 13. The use according to claims 10-12 wherein catalyst 2 is selected from those wherein the number of acidic hydrogen atoms is at least 3 and the salts thereof. 14. Process for absorbing and/or adsorbing hydrophobic liquid by bringing a foam described in claims 1-13 into contact with the liquid or vice versa.

Inventors: GERBER DIRK, STROOBANTS PETER FRANS EUGEEN, GERBER, DIRK, STROOBANTS, PETER, FRANS, EUGEEN, MARIA
Applicants: ICI PLC, IMPERIAL CHEMICAL INDUSTRIES PLC
Application year: 1998
Main classification: C02F1
IPC codes: B01D17, C02F1, C08G18