GB2037304A - Polyurethane foam - Google Patents

Abstract

A reinforced hydrophilic polyurethane foam comprises a foam matrix of a poly(urea-urethane) having an oxyalkylene backbone containing at least 40 mole % oxyethylene, said matrix having uniformly distributed therein 1 to 15% wt of substantially hydrophilic reinforcing fibres of a homo- or copolymer of vinyl alcohol. The foams have improved tensile and tear properties when wet and a reduced resistance to swelling upon wetting and shrinking upon drying out. The foams are useful as sponges.

Description

SPECIFICATION Polyurethane foam This invention relates to reinforced hydrophilic polyurethane foams.

Foams swell considerably when saturated with liquid, e.g. in use as household sponges. Additionally, upon drying out, the foam often becomes distorted and shrinks. Furthermore, the foams, when wetted, are in a weakened condition and therefore tear easily, even in ordinary use.

One object of the present invention is to produce a reinforced hydrophilic polyurethane foam having improved resistance to swelling when wet. Another object is to produce a reinforced hydrophilic polyurethane foam having improved wet tensile and tear strength.

The present invention is a hydrophilic polyurethane foam comprising a foam matrix of a poly(ureaurethane) having an oxyalkylene backbone containing at least 40 mole percent oxyethylene. The foam matrix is reinforced by having substantially hydrophilic fibres formed from a homopolymer or copolymer of vinyl alcohol (hereinafter calied "PVA fibres", for brevity), distributed generally uniformly therein. The amount of such fibres employed is generally from about 1.0% to about 15% based on the weight of the foam matrix. If the amount of fibres employed exceeds about 15%, it is difficult to prepare the foams because of the high viscosities imparted to the various media by the fibres. If less than about 1% is employed, adequate reinforcing action is not obtained.

Use of the PVAfibres gives several advantages. Significantly, it has been found, as will be exemplified hereinafter, that the resulting foams are maintained in a hydrophilic state but are resistant to gross dimensional change on wetting and subsequent drying in comparison to non-reinforced foam. That is, the amount of swelling is reduced by 40-60% without loss of water-absorption characteristics. This is especially important for various applications such as a household or industrial cleaning sponge. Of even greater importance is the strength reinforcing action resulting from the use of the fibres of this invention. Most applications of hydrophilic urethane foams require the foam to be used while wet, a practice that leaves the water-swollen foam in a weakened condition.Surprisingly, the hydrophilic fibers interact with the hydrophilic polyurethane foam in such a way as to give the final sponge product a much higher wet tensile and wet tear strength than a fibre-free control sponge. In striking contrast, hydrophilic polyurethane foam sponges containing fibres of various other kinds commonly used in industry, e.g. a chopped glass, rayon, nylon and cellulose have a lower wet tensile and wet tear strength than the control sponge. Further, the foams of the invention have better fire retardancy, i.e. flame spread resistance.

U.S. Patent 3,214,375 relates to lubricated oil-releasing wicking materials for injecting into the bearing cavities of machinery and thereby keeping the bearings lubricated. The wicking materials consist of a mixture of oil and fibres. To prepare the fibres, paper stock can be coated with a vinyl alcohol-vinyl acetate copolymer.

U.S. Patent 3,357,939 relates to improving the properties of polyvinyl chloride by mixing it with from 1 to 200% of a polyurethane prepolymer. The examples show a higher notch impact strength but lower tensile strength and elongation compared with PVC without the prepolymer additive.

U.S. Patent 3,046,172 describes sponges of good tensile strength and good elongation properties, said sponges being prepared by incorporation of hollow spheres of fused clay into a plastisol of a copolymer of vinyl chloride and vinyl acetate and thereafter compressing the foam to crush the spheres.

Regarding the effect of water-wetting, polyurethane foam sponges generally show characteristics which fall short of those exhibited by the natural cellulose sponges. In an effort to improve hydrophilicity, U.S.

2,900,278 described a method of rendering polyurethane foam hydrophilic by impregnation with polyvinyl alcohol which may be insolubilized by treatment with formaldehyde and acid, e.g. sulfuric acid.

None of the above prior art suggests the incorporation in an already hydrophilic polyurethane foam of a polyvinyl alcohol copolymer, and in particular the improvement in wet strength thereby obtained.

Referring now to the present invention, the term "foam matrix" as used herein designates the organic polyurethane foam matrix excluding the weight of any water or fibres included therein. It is referred to, for convenience, as a polyurethane foam even though in practice the polymer will normally contain some -NH-CO-NH- linkages, and therefore more strictly be termed a poly(urea-urethane).

The fibres are hydrophilic in the sense that they are water-wettable. The term "hydrophilic" as used in relation to the foam matrix is intended to mean that the foam is water-wettable.

The PVA fibres used preferably have a denier of from about 0.1 to about 20 and a length of from about 1 to about 25, preferably 1 to 15 mm.

As used herein, the term "vinyl alcohol copolymer" includes bi- and terpolymers containing at least 20, preferably at least 50 mole % of polymeric vinyl alcohol units. The homopolymers and copolymers of vinyl alcohol used herein can be crosslinked, i.e. have a three-dimensional network structure. The term "copolymer" includes a graft copolymer.

The PVA fibres will usually be of a copolymer (which can be a bipolymer of terpolymer) containing at least 20 mole % of polymeric vinyl alcohol. The vinyl alcohol copolymer can contain one or more hydrophobic monomers, e.g. ethylene, vinyl chloride, vinylidene chloride acrylonitrile, styrene, alkyl acrylates and the like. Hydrophilic monomers that can be used to form the PVA copolymer include vinylpyridine, vinylpyrrolidone acrylamide, acrylic acid, methacrylic acid and the like. Terpolymer combinations may be formed from mixtures of the above monomers.

The reinforcing fibres can be crosslinked or not as desired. Standard crosslinking procedures can be used in forming these fibres and include coupling of the hydroxy groups on adjacent molecules by reactions such as esterification or the use of tetrafunctional monomers in the preparation of the copolymer, e.g. ethylene glycol dimethacrylate.

An example of PVA fibres usable in the present invention is those described in U.S. Patent 3,111,370. This patent describes preparation fibres by emulsion of vinyl chloride in an aqueous solution of polyvinyl alcohol.

The vinyl chloride becomes at least partially grafted to the polyvinyl alcohol. Additionally polyvinyl alcohol is added in the emulsion, so that the proportion of polymerised vinyl chloride in the total polymerized material present is from 50 to 80% by weight. Subsequently, the emulsion is spun through a spinning head, dried and oriented (e.g. by heat stretching). Some of the hydroxyl groups present may also be acetylated. The resulting fibres are then cut into suitable lengths for use in the present invention. Preferably the polymerized vinyl chloride/polymerised vinyl alcohol weight ratio is about 50%/50%, i.e. about 1:1.

The hydrophilic polyurethane foam matrix and prepolymers from which it can be made are described in our U.S. Patent No.4,137,209.

The foams of the invention can be prepared by mixing a hydrophilic, isocyanate-capped polyurethane prepolymer having an oxyalkylene backbone containing at least 40 mole percent oxyethylene, with an aqueous reactant, incorporating in this reaction mixture, to provide a uniform distribution therein, 1.0 to 15% by weight of the prepolymer of substantially hydrophilic, reinforcing fibres as defined in any one of claims 1 to 5, and foaming the mixture. In a preferred procedure, the fibres are added to the aqueous reactant, e.g.

water, and uniformly dispersed therein before the aqueous reactant is mixed with the prepolymer.

Admixture of the fibre-containing aqueous reactant with the prepolymer results in generally uniform distribution of the fibres throughout the water/prepolymer admixture. An alternative procedure is to mix the fibres with the prepolymer. This procedure is less advantageous in that the resultant mixture of fibres and prepolymer has a high viscosity making processing difficult. Additionally, the hydrophilic fibres will often contain a small amount of water which can cause premature reaction with the NCO groups of the polymer, again contributing to an undesirably high viscosity.In a third procedure, the fibres can be added to an already prepared aqueous reactantlprepoiymer admixture, e.g. by spraying the fibres under pressure or pouring the fibres (without pressure other than that needed to release the fibres from their container) over the surface of the mixture.

The amount of water employed is at least 6.5 moles for each mole of NCO groups present in the prepolymer. Preferably, at least 25 moles of water are employed for each mole of NCO groups. A suitable range is from about 6.5 to about 390.

In adding the fibres directly to the water, it is preferred that a thickening agent be employed to increase the viscosity of the water/fibre dispersion. The increased viscosity tends to minimise settling out of the fibres.

Preferably, a sufficient amount of the thickening agent is employed so that the viscosity of the waterifibre dispersion is at least 80% of that of the urethane prepolymer. It has been found that this "matching" of the viscosities of the aqueous and prepolymer phases is especially advantageous when the foams are prepared in automatic machinery. For example, customary practice is to place the fibre/water dispersion in one container with the prepolymer in a second container and meter measured amounts of these components through a mixing head followed by extrusion into a container or over a surface where foaming takes place.

To promote mixing and reduce settling out, it is preferable that the viscosity of the two phases approach one another as described above. The thickening agent is usually added in the proportion of about 0.5-5% by weight of the water.

Any of the commonly employed thickening agents for aqueous media can be employed in the present invention. Thus, the type of thickening agent is not believed to be critical so long as it does not react to a great extent with any of the components of the system, especially the prepolymer. Fumed silicas (e.g.

"Cab-o-Sil" silicas of Godfrey L. Cabot, Inc.) or other particulate, insoluble, thickeners are useful although use of these materials with automatic foam machines should be closely scrutinized to avoid pumping difficulties. Other suitable thickening agents include water-soluble polymers having a molecular weight of from about 50,00 to about 10,000,000. Such materials are exemplified by the carboxy-methylcellulose gums, hydroxvethylcellulose, high molecular weight polyoxyethylene or copolymers of polyoxyethylene with polyoxypropylene. Another suitable class of materials is the polyacrylamides having the above characteristics.

At least 40 mole % of the oxyalkylene units in the prepolymer backbone are oxyethylene units with the balance being oxypropylene, oxybutylene or other oxyalkylene units. In the resulting polyurethane foams, the branchpoints of the polymer chains are connected by essentially linear polyoxyalkyiene chains containing at least 40 mole % of oxyethylene units (excluding initiators at brarich-points) as described above.

Preferably at least 75 mole % of oxyethylene units are employed.

The prepolymers can be prepared by capping a polyoxyalkylene polyol with an excess of polyisocyanate, e.g. toluene diisocyanate. Prior to capping, the polyol should have a molecular weight of from about 200 to about 20,000 and preferably from about 600 to about 6,000. The hydroxy functionality of the polyol and the corresponding isocyanate functionality following capping is from 2 to about 8. If foams are formed from prepolymers with an isocyanate functionality of about 2, the resulting foam is essentially linear and does not have as much tensile strength as crosslinked foams. Accordingly, if the isocyanate functionality is about 2, a crosslinking agent should be employed.Suitable crosslinking agents are well-known in the polyurethane art and include by way of example tolylene-2,4,6-triamine, ethylene diamine, diethanolamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, and ethanolamine.

Examples of suitable polyols (to be capped with polyisocyanates) include: (A) essentially linear polyols formed for example by rection of ethylene oxide with ethylene glycol as an initiator. As discussed above, mixtures of ethylene oxide with other alkylene oxides can be employed so long as the mole percent of ethylene oxide is at least 40 percent. Also as stated, it may be desirable to use crosslinking agents with these systems in which case the crosslinking agent can be included in the water along with the PVA fibres into which the prepolymer is dispersed. Where the linear polyethers are mixtures of ethylene oxide with, e.g.

propylene oxide, the polymer can be either random or a block copolymer and the terminal units can be either oxyethylene or oxypropylene. A second class of polyol (B) includes those with a hydroxy functionality of 3 or more. Such polyols are commonly formed by reacting alkylene oxides with a polyfunctional initiator such as trimethylolpropane, pentaerythritol, etc. In forming the polyol B, the alkylene oxide used can be ethylene oxide or mixtures of ethylene oxide with other alkylene oxides as described above. Useful polyols can be further exemplified by (C), a mixture of linear and branched polyfunctional polyols as exemplified in A and B above together with an initiator or crosslinker. This crosslinker may itself be an isocyanate, e.g. the reaction product of TDI or a similar polyisocyanate with a monomeric polyol (e.g. TMOP, glycerol, pentaerythritol) containing 3 or 4 -OH groups.A specific example of type (C) is a mixture of polyethylene glycol (m. w. about 1,000) with trimethylol-propane, trimethylolethane or glycerine. This mixture can be subsequently reacted with excess polyisocyanate to provide a prepolymer useful in the invention. Alternatively, the linear (e.g.

polyethylene glycol) or branched polyols can be reacted separately with excess polyisocyanate. The initiator, e.g. trimethylolpropane (TMOP), can also be separately reacted with polyisocyanate. Subsequently, the two capped materials can be combined to form the prepolymer.

In general, reaction conditions, reactants and properties thereof as defined in U.S. Patent 4,137,200 are usable in the present invention. It should be noted, however, that the polyisocyanate preferably has an isocyanate functionality of from 2.0 to 3.0 (rather than 2.0 to 2.8) and the prepolymer component will usually contain from 0.5 to 10% (not necessarily merely 3.2 to 7.9%) by weight of excess poiyisocyanate, beyond that required for capping the polyol.Thus the foam preferably comprises the reaction product of A. an isocyanate-capped prepolymer consisting of a mixture of (1) an isocyanate-capped hydrophilic polyoxyethylene diol, said diol having an ethylene oxide content of at least 40 mole percent; and (2) an isocyanate-capped polyol having a hydroxyl functionality of 3 to 8 before capping; said isocyanate capped polyol being present in a proportion of 2.9 to 50% by weight of (1) and (2); B. 0.5 to 10.0% by weight of A and B of a polyisocyanate having an isocyanate functionality of 2.0 to 3.0; and C. 6.5 to 390 moles of water for each mole of unreacted isocyanate.

The process of forming said crosslinked hydrophilic urethane foam comprises admixing a hydrophilic polyoxyethylene diol having an ethylene oxide content of at least 40 mole percent with a polyol having a hydroxyl functionality in the range 3 to 8, said polyol being present in the admixture in an amount in the range 1.0 to 20% by weight, reacting with the admixture at a temperature in the range 0 to 120"C an amount of a polyisocyanate having an isocyanate functionality in the range 2.0 to 3.0 equal to 1.8 to 1.9 equivalents of NCO per equivalent of OH equivalents for a time sufficient to cap substantially all the hydroxyl groups of the admixture, adding additional poiyisocyanate having an isocyanate functionality in the range 2.0 to 3.0 to provide 0.1 to 0.3 equivalents of NCO per initial equivalent of OH in excess of the theoretical amount necessary to react with the hydroxyl groups of the starting diol and polyol and thereafter adding 6.5 to 390, usually 6.9 to 390 moles of water for each mole of unreacted isocyanate in the admixture.

Suitable polyisocyanates useful in preparing prepolymers include toluene-2,4-diisocyanate, toluene-2,6diisocyanate, commercial mixtures of toluene-2,4- and 2,6-diisocyanates, ethylene diisocyanate, ethylidene diisocyanate, propylene-1 ,2-diisocyanate, cyclohexylene-1 ,2-diisocyanate, cyclohexylene-1 ,4-diisocyanate, m-phenylene diisocyanate, 3,3'-diphenyl-4,4'-biphenylene diisocyanate, 4,4'-biphenylene diisocyanate, 3,3'-dichloro-4,4' biphenylene diisocyanate, 1 ,6-hexamethylene diisocyanate, 1,4-tetramethylene diisocyan ate, 1,1 0-decamethylene diisocyanate, 1 ,5-napthalenediisocyanate, cu mene-2,4-diisocyanate, 4-methoxy- 1,3-phenylenediisocyanate, 4-chloro-1,3-phenylenediisocyanate, 4-bromo-1,3-phenylene-diisocyanate, 4,- ethoxy-1,3-phenylenediisocyanate, 2,4'-diisocyanatodiphenylether, 5,6-dimethyl-1,3-phenylene- diisocyanate, 2,4-dimethyl-1 ,3-phenylenediisocyanate, 4,4'-diisocyanatodiphenylether, benzidinediisocyan ate, 4,6-dimethyl-1 ,3-phenylenediisocyanate, 9, 1 0-anthracenediisocyanate, 4,4'-diisocyanatodibenzyl, 3,3'- dimethyl-4,4'-diisocyanatodiphenylmethane, 2,6-dimethyl-4,4'-diisocyanatodiphenyl, 2.4- diisocyanatostilbene, 3,3'-dimethyl-4,4'-diisocyanatodiphenyl, 3,3'-dimethoxy-4,4'-diisocyanatodiphenyl, 1,4-anthracenediisocyanate, 2,5-fluorenediioscyanate, 1,8-napthalenediisocyanate, 2,6- diisocyanatobenzfuran, 2,4,6-toluene-triisocyanate, and 4,4',4"-triphenyl methane triisocyanate.

Suitable initiators useful in preparing prepolymers include propylene glycol, trimethylene glycol, 1,2-butylene glycol, 1 ,3-butenediol, 1,4-butanediol, 1 ,5-pentanediol, 1 ,2-hexylene glycol, 1,1 0-decanediol, 1 ,2-cyclohexanediol, 2-butane-1 ,4-diol, 3-cyclohexene-1 ,1 -dimethanol, 4-methyl-3-cyclohexene-1 ,1- dimethanol, 3-methylene-1,5-pentanediol, diethylene glycol, 1,2,6-hexanetriol, 1,1,1-trimethylolpropane, 3-(2-hydroxyethoxy)-1 ,2-propanediol, 3-(2-hydroxypropoxy)-1 ,2-propanediol, 2,4-dimethy-2-(2 hydroxyethoxy)-methylpenta nedi ol-1,5, ,5,1 ,1 1 -tris[(2-hydroxyethoxy)-methlylethane, 1,1,1 ,-tris[(2- hydroxypropoxy)methyl]propane, triethanolamine, triisopropanolamine, resorcinol, pyrogallol, phloroglucinol, hydroquinone, 4,6-di-t-buty catechol, catechol, ethylene diamine and propylene diamine.

The following Examples illustrate the invention. Unless otherwise noted, all parts and percentages are by weight. "Pluronic" is a U.K. Registered Trade Mark.

EXAMPLE 1 Preparation of PrepolymerA A hydrophilic isocyanate-capped, urethane-containing prepolymer was prepared starting from a mixture of 2 molar equivalents of polyethylene glycol having an average molecular weight of 1,000 (PEG - 1,000) and one molar equivalent to trimethylopropane (TMOP). The mixture was dried at 100-11 0 C under a pressure of 5-15 Torr to remove water. The resulting dried mixture was slowly added over a period of about one hour to a vessel containing 6.65 molar equivalents oftoluene diisocyanate (TDI) while stirring the TDI and polyol mixture and maintaining the temperature at 60"C. The reaction was continued at 60"C with stirring for three additional hours.Then an additional 1.05 molar equivalent to TDI was added with stirring over a period of about 1 hour while maintaining the temperature at 60"C. The final reaction mixture contained a 10% molar excess of TDI. All hydroxyl groups were capped with isocyanate and some chain extension occurred between the polyols and TDI. The resultant prepolymer mixture will hereinafter be referred to as Prepolymer A.

Preparation of Prepolymer B.

A prepolymer was prepared as described above for Prepolymer A except that 0.66 molar equivalent of TMOP was employed for every 2 molar equivalents of PEG - 1,000. In the initial capping reaction with TDI, the amount of TDI employed was about 92% of that theoretically required to cap all hydroxyl groups in the polyol mixture. Subsequently, an additional 13% TDI was added to provide a theoretical molar excess of about 5%. All hydroxyl groups were capped with isocyanate and some chain extensions occurred between the polyols and TDI. The resultant prepolymer mixture is referred to hereinafter as Prepolymer B.

Preparation of Polyurethane Foam A.

100 parts of Prepolymer A were admixed with 100 parts of water containing 2.0 parts of Wyandotte "Pluronic L-62" as a surfactant. The mixture was stirred and allowed to foam. The resultant non-reinforced, hydrophilic foam was used as a control and is hereinafter referred to as Foam "A".

Fibre-reinforced Polyurethane Foam Polyurethane Foam samples were prepared from the reactants used for foam A. The first foam (designated "V") contained 6.3 parts of vinyl alcohol/vinyl chloride copolymer fibres ("Cordelan", a 50%/50% vinyl alcohol/vinyl chloride copolymer, commercially available from Amerimex Corp.) per 100 parts by weight of the prepolymer. A second foam designated as "W" contained 10 parts of the same copolymerfibres per 100 parts of the prepolymer. The copolymer fibres were about 2 denier with an average length of about 1.5 mm and were incorporated into the surfactant-containing aqueous phase. The aqueous phase was used to prepare a foam as for foam A above.

Samples A, V and W were dried under the same conditions, i.e. at60 C, 150-400 Torrfor about 16 hours and the physical characteristics observed in the dried foams were as listed in Table 1 below. "Wet-in" time is obtained by introducing droplets of water onto the foam surface and measuring the time taken for their absorption into the foam.

TABLE 1 Pts. of Water Fibres per Vol. "Wet-In Absorption 100 pts. Density Shrinkage Time", %viol.

Foam Prepolymer (Ib./ft.3) % Seconds Increase A 0.0 5.4 45 4.5 88 V 6.3 4.9 26 1.0 39 W 10.0 5.4 26 1.0 41 As evidenced by the data in TABLE 1, volume shrinkage in the fibre-containing foams was greatly reduced in comparison with Sample A which did not contain the fibres, i.e. the dried foam exhibited much better dimensional stability upon drying. Also swelling due to water absorption was also greatly reduced.

As shown in Tables 2a and 2b, improved dry and wet tensile and tear properties were also observed for the fibre-containing foams.

TABLE 2A Tensile and tear properties of dry foams - see Example 1 Foam Modulus, Tensile strength, Elongation Tear strength Sample p.s.i. p.s.i. (Kg/cm2) to failure, Ib/in, (Kg/cm) (Kg/cm2) A 28 19 160 2.4 (1.97) (1.34) (0.43) V 51 21 64 2.5 (3.59 (1.48 (0.45) W 58 25 59 3.4 (2.67) (1.76) (0.61) TABLE 2B Tensile andtearproperties of wet foams - see Example 1 Foam Modulus, Tensile strength, Elongation Tear strength Sample p.s.i. p.s.i. (Kg/cm2) to failure, Ib/in (Kg/cm) (Kg/cm2) A 11 10 142 0.7 (0.77) (0.70) (0.13) V 36 12 57 1.0 (2.53) (0.84) (0.18) W 40 18 56 1.1 (2.81) (1.27) (0.20) EXAMPLE 2 Preparation of Polyurethane Foam B 100 parts of Prepolymer B were mixed with 100 parts of water containing 4.0 parts Wyandotte "Pluronic L-62". as a surfactant. The mixture was stirred and allowed to foam.The resultant non-reinforced, hydrophilic foam is used as a control and will be referred to hereinafter as Foam "B".

Polyurethane foam samples were prepared from the reactants used for foam B. 10 parts of fibres of a crosslinked vinyl alcohol homopolymer ("Kuralon" fibres sold by Kuraray International) were added to the water phase and foaming was carried out as above for foam B. Three sets of experiments were carried out, each with fibre-containing foam (X, Y, Z), and its control foam (B, B', B"). The fibres used had the following lengths and deniers respectively: 3 mm, 1 denier; 6 mm, 2 denier; and 12 mm, 5 denier. In the second set of experiments the procedure for foam B was varied by heating the prepolymer at 65"C for 16 hours and cooling it to room temperature before mixing it with the water. The fibre-containing foams had higher densities than the control foams. The densities in Ib./ft.3 (g/cm.3) were: Set 1 (X and B) : 7.4 and 5.4 (0.119 and 0.087); Set 2 (Y and B'): 7.0 and 6.4 (0.112 and 0.103): and Set 3 (Z and B50): 8.1 and 6.6 (0.130 and 0.106). The tensile and tear properties of the dry and wet foams measured on 3 samples for each experiment.

As shown in Tables 3a and 3b, the foam containing the PVAfibres had greatly improved wet and dry tensile and tear properties.

TABLE 3A Tensile and tear properties of dry foams - see Example 2 Foam Modulus, Tensile strength, Elongation Tear strength Sample p.s.i. p.s.i. (Kg/cm2) to failure Ib/in (Kg/cm) (Kg/cm2) B 13#0.9 33#0.6 478#26 3.76#0.04 (0.91 + 0.06) (2.32 i 0.04) (0.671 + 0.007) X 151167 62 + 29 5817 4.85#0.35 (10.61 + 4.71) (4.36 + 2.04) (0.866#0.063) B' 14#0.06 37#1 436#22 4.4#0.1 (0.98 + 0.042) (2.60 + 0.07) (0.786 1 0.018) Y 88#20 41#9 64#4 4.9#0.1 (6.19#1.41) (2.88#0.63) (0.875#0.018) B" 13#0.9 39#3.2 476#19 4.1#0.2 (0.91 + 0.06) (2.74 + 0.22) (0.723 + 0.036) Z 46#11 34#3.4 98#20 6.1#0.6 (3.23 + 0.77) (2.39 + 0.24) (1.089 + 0.107) TABLE 3B Tensile and tear properties of wet foams - see Example 2 Foam Modulus Tensile strength, Elongation Tear strength p.s.i. p.s.i. (Kg/cm2) to failure, Ib/in (Kg/cm) (Kg/cm2) B 1110.9 1110.2 134112 0.69#0.03 (0.77 + 0.06) (0.77 + 0.01) (0.123 + 0.005) X 93130 23 + 3.8 41 + 10.8 1.92#0.04 (6.54#2.11) (1.62#0.27) (0.342#0.007) B' 10+1.2 14#0.1 200 + 26 1.29 + 0.31 (0.70 + 0.08) (0.98 + 0.01) (0.230 + 0.055) Y 59#26 24#9 52#14 2.87#0.08 (4.15 + 1.83) (1.69#0.63) (0.513 + 0.014) B" 10+1.1 13 + 0.3 176 + 12 0.74#0.07 (0.70 + 0.08) (0.91 1 0.02) (0.132 1 0.012) Z 25#9.2 14.4.0 82#6.6 1.62#0.32 (1.76 + 0.65) (0.98 t 0.28) (0.289 #0.057) EXAMPLE 3 (Comparative Example) Preparation ofPrepolymer C.

A hydrophilic polyurethane prepolymer "C" was prepared as in Example 1 for prepolymer "A" except that a polyethylene glycol having an average molecular weight of 600, was used instead of that of m.w. 1,000.

Fibre-rein forced polyurethane foam The following tests show that many other kinds of fibres do not improve the dry and wet tensile and tear properties of a hydrophilic polyurethane foam.

In all experiments the additives were added to the water reactant except that the Prepolymer C was added to Prepolymer A. The prepolymer and water reactants were mixed with stirring and allowed to foam. The resultant foams were microwave-dried, vacuum over-dried and then air-dried for 2 days. Table 4 shows the various amounts of additives added to the foams and Tables 5a and 5b shows the resultings tensile and tear properties. In tables 5a and 5b sample 3h, which did not contain fibres, had the highest values for wet and dry tensile and tear strengths of any of the foams.

The analysis of the results of the effect of the various additives by the standard Plackett-Burman procedure is given in Table 6. The analysis is performed by adding the single physical property values for the four samples containing the additive and determining the average value (by dividing by 4) and adding the single physical property values for the four samples not containing the additive and determining the average value (by dividing by 4). All of the four fibre-containing foams had poorer dry and wet tear and tensile strengths than without the fibres present, according to the Plackett-Burman analysis.

TABLE 4 Parts by weight Parts by weight Parts by weight of fibre additives of reactants of surfactants Example Prepolymers B-26 L-520 Chopped Rayon Nylon Beaten No. "A" "C" H20 (5) (6) Glass fibres fibres cellulose Fibres (2) (3) fibres (1) (4) 3a 100 20 200 0 0 20 10 10 0 3b 100 0 200 3.0 0 0 10 10 10 3c 100 20 100 0 1.0 0 0 10 10 3d 100 20 100 3.0 0 20 0 0 10 3e 100 20 100 3.0 1.0 0 10 0 0 3f 100 0 100 3.0 1.0 20 0 10 0 39 100 0 200 0 1.0 20 10 0 10 3h 100 0 100 0 0 0 0 0 0 (1) Chopped fibreglass 1/32" (0.8 mm) (2) Rayon 0.15 denier.

(3) Nylon 3.0 denier.

(4) Solka Floc - a beaten cellulose fibre commercially available from Brown Co.

(5) B-26 - a surfactant commercially available from BASF-Wyandotte.

(6) L-520 - a surfactant commercially available from Union Carbide.

TABLE 5A Tensile and tear properties of dry foam - see Example 3 Tensile Modulus, Strength, Elongation Tear Ex. p.s.i. p.s.i. to failure, Strength Ib./in No. (kg/cm2) (kg./cm2) % (kg/cm) 3a 37.4#4.0 12.6#1.5 63#6 1.88#0.09 (2.63#0.28 (0.89#0.11) (0.336#0.016) 3b 7.4#1.7 4.5#0.6 96#14 1.76#0.11 (0.52 1 0.12) (0.32 1 0.04) (0.314# 0.020) 3c 40.010.8 13.9#0.6 77 + 4 1.54 + 0.03 (2.81 + 0.06) (0.98 # 0.04) (0.275 + 0.005) 3d 13.8#2.4 6.6#0.6 79#16 2.51#0.36 (0.97 + 0.17) (0.47 1 0.04) (0.448 # 0.064) 3e 20.8#3.5 9.8#1.7 100#17 1.66#0.06 (1.46#025) (0.69#0.12) (0.296#0.011) 3f 35.1#4.9 14.1#0.8 116#15 2.90#0.15 (2.47 + 0.34) (0.99 # 0.06) (0.518 + 0.027) 3g 67.1#11.5 18.0#0.4 81#13 2.02#0.12 (4.72 + 0.81) (1.26 + 0.03) (0.361 + 0.021) 3h 65#8.0 38.5#2.5 158#15 6.29#0.09 (4.57#0.56) (2.71#0.18) (1.123#0.016) TABLE SB Tensile and tear properties of wet foam - see Example 3 Tear Modulus, Tensile Elongation Strength, Ex. p.s.i. strength, to failure, Ib./in.

No. (kg./cm2) p.s.i. (kg./cm.2) % (kg./cm) 3a 13.0#2.1 5.0#0.2 49#6 0.66#0.07 (0.91#0.15) (0.35#0.01) (0.118#0.012) 3b 3.5 + 0.6 2.2 + 0.3 79 + 8 0.38 # 0.03 (0.25#0.04) (0.16#0.02) (0.0679#0.005) 3c 14.8#0.3 6.2#0.5 68#6 0.64#0.03 (1.04 ~ 0.02) (0.44 # 0.04) (0.#114# 0.005) 3d 6.5 # 0.5 3.8 # 0.8 66 * 9 0.65 ~ 0.14 (0.46 # 0.04) (0.27 * 0.06) (0.116 #0.025) 3e 7.4 + 0.0 5.3 + 0.4 76 # 3 0.55 + 0.02 (0.52 + 0.0) (0.37 + 0.03) (0.098 # 0.004) 3f 11.2#0.4 6.1#0.5 75#11 0.66#0.04 (0.79 + 0.03) (0.43 * 0.04) (0.118#0.007) 3g 17.7#0.9 6.9#0.2 61#3 0.64#0.02 (1.24 # 0.06) (0.49 # 0.01) (0.114 1 0.004) 3h 24.3#1.7 14.5#0.6 83#2 1.8#0.4 (1.71#0.12) (1.02#0.04) (0.321#0.07) TABLE 6 Plackett-Burman Matrix analysis for Table 5 figures Chopped Glass Fibres Rayon Fibres Dry Foam 30 parts 0 15 parts 0 Modulus, p.s.i. 38.4 * 14.4 33.3 + 19.2 33.2 + 19.1 38.5 # 14.1 (kg)cm2) (2.70 + 1.01) (2.34# 1.35) (2.33 # 1.34) (2.71 ~ 0.99) Tensile strength, p.s.i. 12.8#3.2 16.7#10.4 11.2#4.1 18.1#10.5 (kg/cm2) (0.90 + 0.22) (1.17 + 0.73) (0.79 > 0.29) (1.27 ~ 0.74) Elongation to failure 85#16 108#25 85#13 108#30 Tear strength Ib/in. 2.34 # 0.38 2.81 + 1.72 1.83 * 0.12 3.31 # 1.49 (kg/cm) (0.418 + 0.068) (0.502 # 0.307) (0.327 # 0.02) (0.59 + 0.266) TABLE 6 (continued) Plackett-Burman Matrix analysis for Table 5 figures Chopped Glass Fibres Rayon Fibres Wet foam 30 parts 0 15 parts 0 Modulus, p.s.i. 12.1#3.2 12.5#7.0 10.4#4.4 14.2#5.4 (kg/cm2) (0.85 + 0.22) (0.88 # 0.49) (0.73 + 0.31) (1.00 + 0.38) Tensile strength, p.s.i. 5.5 * 1.0 7.0 + 3.7 4.8 + 1.3 7.6 + 3.4 (kg/cm2) (0.39 + 0.07) (0.49 + 0.26) (0.34 + 0.09) (0.53 # 0.24) Elongation to failure % 63#8 77#5 66#14 73#3 Tear strength Ib./in. 0.66 + 0.01 0.84 # 0.47 0.56 + 0.09 0.94 + 0.43 (kg/cm) (0.118 + 0.00) (0.150 # 0.083) (0.100 + 0.016) (0.168 + 0.077) TABLE 6 (continued) Plackett-Burman Matrix analysis for Table 5 figures Nylon Fibres Beaten Cellulose Fibres Dry Foam 15 parts 0 15 parts 0 Modulus, p.s.i. 30.0 + 19.5 41.7 #24.5 32.1 + 20.2 39.6 + 12.8 (kg/cm2) (2.11 + 1.37) (2.93 + 1.72) (2.26 + 1.42) (2.78 + 0.90) Tensile strength, p.s.i. 11.3#3.4 18.2#10.1 10.8#5.2 18.8#9.4 (kg/cm2) (0.79 # 0.24) (1.28 # 0.71) (0.76 + 0.37) (1.32 + 0.66) Elongation to failure % 88#18 105#27 83#16 109#28 Tear strength, Ib./in. 2.02 + 0.44 3.12# 1.59 1.96 + 0.31 3.18 * 1.55 (kg/cm) (0.361#0.079) (0.557#0.284) (0.350#0.055) (0.568#0.277) TABLE 6 (continued) Plackett-Burman Matrix analysis for Table 5 figures Nylon Fibres Beaten Cellulose Fibres Wetfoam 15 parts 0 15 parts 0 Modulus p.s.i. 10.6+3.6 14.0*7.0 10.6*6.6 14.0*5.2 (kg/cm2) (0.75 ~ 0.25) (0.98 * 0.49) (0.75 * 0.46) (0.98 # 0.37) Tensile strength, p.s.i. 4.9*1.3 7.6*3.4 4.8*1.8 7.7 ~4.4 (kg/cm2) (0.34+0.09) (0.53 * 0.24) (0.34 * 0.13) (0.54 * 0.31) Elongation to failure % 68*9 72#8 69*5 71 11 Tear strength, Ib./in. 0.59*0.10 0.91*0.45 0.58+ 0.10 0.92~ 0.59 (kg/cm) (0.105 * 0.018) (0.163 * 0.080) (0.104 + 0.018) (0.164 ~ 0.105)

Claims (16)

1. A reinforced, hydrophilic polyurethane foam comprising a foam matrix of a poly(urea-urethane) having an oxyalkylene backbone containing at least 40 mole percent oxyethylene, said foam matrix having uniformly distributed therein 1.0 to 15% by weight of the foam matrix of substantially hydrophilic, reinforcing fibres of a homopolymer or copolymer of vinyl alcohol.

2. A foam according to claim 1 wherein the fibres are of a crosslinked vinyl alcohol homopolymer.

3. A foam according to claim 1 wherein the fibres are of a vinyl chloride)vinyl alcohol copolymer.

4. A polyurethane foam according to claim 3 wherein the copolymer fibres contain at least 50 mole percent of polymerised vinyl alcohol.

5. A foam according to claim 1, 2,3 or 4 wherein the fibres are from about 0.1 to about 20 denier.

6. A polyurethane foam according to any preceding claim wherein the oxyalkylene backbone of the foam matrix contains at least 75 mole percent oxyethylene.

7. A foam according to any preceding claim, wherein the poly(urea-urethane) comprises the reaction product of A. an isocyanate-capped prepolymer consisting of a mixture of (1) an isocyanate-capped hydrophilic polyoxyethylene diol, said diol having an ethylene oxide content of at least 40 mole percent; and (2) an isocyanate-capped polyol having a hydroxyl functionality of 3 to 8 before capping; said isocyanate capped polyol being present in a proportion of 2.9 to 50% by weight of (1) and (2); B. 0.5 to 10.0% by weight of A and B of a polyisocyanate having an isocyanate functionality of 2.0 to 3.0; and C. 6.5 to 390 moles of water for each mole of unreacted isocyanate.

8. A foam according to claim 1 substantially as described in Example 1 or 2.

9. A method of preparing a fibre-reinforced polyurethane foam claimed in claim 1, which comprises mixing a hydrophilic polyurethane prepolymer having an oxyalkylene backbone containing at least 40 mole percent oxyethylene, with an aqueous reactant, incorporating in this reaction mixture, to provide a uniform distribution therein,1.0 to 15% by weight of the prepolymer of substantially hydrophilic, reinforcing fibres as defined in any one of claims 1 to 5, and foaming the mixture.

10. A method according to claim 9 wherein the fibres are added to the aqueous reactant and the mixture thereof is added to the prepolymer.

11. A method according to claim 10 wherein from 0.5 to 5.0% by weight of the water in the aqueous reactant of a thickening agent is added to the aqueous reactant, to promote uniform dispersion of the fibres in water.

12. A method according to claim 11 wherein the thickening agent is a high molecular weight water-soluble polymer.

13. A method according to claim 9, 10, 11 or 12 wherein the aqueous reactant consists of water.

14. A method according to any one of claims 9 to 13, wherein the reaction mixture is provided by mixing a hydrophilic polyoxyethylene diol having an oxyethylene content of at least 40 mole percent with a polyol having a hydroxyl functionality of from 3 to 8, so that the proportion of polyol in the mixture is from 1.0 to 20% by weight, reacting the mixture at a temperature of 0 to 120"C with sufficient of a polyisocyanate having an isocyanate functionality of from 2.0 to 3.0 to provide 1.8 to 1.9 equivalents of NCO per equivalent of OH in the diol or polyol, so as to cap substantially all the hydroxyl group of the diol and polyol, adding a further amount of a polyisocyanate having an isocyanate functionality of from 2.0 to 3.0 to provide 0.1 - 0.3 equivalents of NCO per equivalent of OH in the starting diol and polyol in excess of the theoretical amount necessary to react with the hydroxyl groups and, thereafter, adding 6.9 to 390 moles of water for each mole of unreacted isocyanate in the mixture to form a foam matrix.

15. A method according to claim 9, substantially as described in Example 1 or 2.

16. A reinforced polyurethane foam prepared by a method claimed in any one of claims 9 to 15.