JPH037690B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to sponges that can be made from polyurethane repolymers that have the general appearance and wiping properties of cellulose sponges with minimal swelling when wet and non-curling properties during drying. It has been a goal of the sponge industry to replace cellulose foam with polyurethane foam in sponge-based composites such as wiping sponges or cleaning pads or bath mats. In general, prior art polyurethane foams that are sufficiently hydrophilic to be useful tend to swell significantly when they are wetted by more than, for example, 75-100% by volume. They dry slowly and unevenly and curl or wrinkle as they dry. This characteristic is not desirable for household sponge applications. The use of polyurethane foam as an alternative to flocked wall coverings has been proposed. However, in view of the curling and wrinkling nature of these foams and the resulting buckling, these foams are not suitable for use as replacements for flocked wall coverings. In US Pat. No. 3,806,474 a hydrophilic polyester urethane foam is disclosed. However, this foam does not wet out quickly and does not wipe to obtain a clean surface. In US Pat. No. 4,160,076 a pseudo-natural sponge based on hydrophilic polyurethane is disclosed. However, even though this simulates a natural sponge, it still has the problem of polyurethane sponges that they swell a lot when wet. A commonly used polyurethane foam is made from MDI, which is methylene-bis(phenylisocyanate). These forms MDI are hard or semi-soft due to their crystallinity. They are generally hydrophobic since MDI itself is hydrophobic. In British Patent No. 874430, a flexible polyurethane foam is made of a polyisocyanate mixture consisting of a polyether polyol having at least two hydroxyl groups and a diarylmethane diisocyanate and 5 to 10% by weight of a polyisocyanate with a functionality greater than 2. Produced by reaction in the presence of small amounts of water. Catalysts can be used in any embodiment. These foams are not hydrophilic and are not manufactured using sufficient amounts of water to transport large amounts of fibers, fillers, preservatives, or other water-soluble or water-dispersible ingredients into the foam; The disadvantage with any catalyst is that undesirable catalyst residues may remain. In U.S. Pat. No. 4,237,240, a flexible MDI with high load bearing and high energy absorption capacity
A foam based on is made by reacting diphenylmethane diisocyanate with a polyester polyol or a mixture of polyester polyols and polyether polyols in which the polyester polyol content is at least 60% by weight of the polyol mixture and a small amount of water. A catalyst is used as described in the claims. These foams have the same drawbacks as that of GB 874,430, including undesirable catalyst residues in the foam, and furthermore they require the use of more expensive polyester polyols. In British Patent No. 12090558, a flexible hydrophilic polyurethane foam is made of at least 10% by weight of a block copolymer of ethylene oxide capped with propylene oxide to provide hydrolytic stability.
It can be produced by reacting a polyether polyol containing polyisocyanate. This method requires that the fatty acid be catalyzed by at least two divalent tin salts and/or at least one tertiary amine. The foam products produced by this method are hydrophilic, but have the disadvantage that they can only be made using small amounts of water. Furthermore, there is no teaching of using MDI, which is hydrophobic, to produce hydrophilic foam products, and the resulting foam would contain undesirable catalyst residues. The object of the present invention is to have a shrinkage of less than 15% by volume with good water retention and wiping stability, dry quickly without curling. An object of the present invention is to provide an improved polyurethane foam having a density of 32.5 to 65.0 kg/m ³ (2 to 4 lb/ft ³ ). Another object of the present invention is to provide an improved polyurethane foam having good dimensional stability that can be used as a substrate for flocked wall coverings or various other foam applications as well as for sponge applications. These and other objects will become apparent as the description of the invention proceeds. The novel polyurethane polymer has at least 50
Poly(oxyethylene) with oxyethylene groups in weight%
C _2-4 alkylene) diol, consisting of a mixture of isocyanates containing MDI and derivatives of MDI
Diphenylmethane diisocyanate-containing isocyanates with a functionality greater than 2.0 and monomeric polyol crosslinkers with a hydroxyl functionality of 3 or 4 were derived. This prepolymer can be reacted with water in the absence of a catalyst to produce a durable polyurethane sponge that has many of the properties of cellulose sponge. These foams are white in color and are therefore aesthetically pleasing and suitable for medical and health supervision applications.
desirable for health care applications). Preferred ingredient is Carbo Wax 1000
(Carbowax 1000), trimethylolpropane (TMOP) as a crosslinking agent and upjohn polymer chemical (Upjohn Polymer) with a functionality of about 2.1 as an isocyanate.
Isonate 143L, a methylene-bis(phenyl isocyanate), hereinafter referred to as MDI, based on the isocyanate products of
(isocyamate Isonate143L). In a preferred process, Union Carbide's poly(oxyethylene) diol product, Carbowax, is used to impart water absorption properties to the final product. The preferred TMOP is added to impart strength to the foam product through its action as a crosslinking agent. It is important that the molar ratio of diol (such as Carbowax) to monomeric polyol crosslinker (such as TMOP) is in the range of approximately 4:1 to 8:1, preferably about 6:1. Similarly, the ratio of isocyanate equivalents to hydroxy equivalents in the prepolymer should be in the range of about 3 to 4:1, preferably 3.3 to 3.7:1. The isocyanate-containing product should be more than 50% by weight of the total prepolymer;
Should have a sensuality greater than 2.0. This would exclude pure MDI with a functionality of only 2.0 as only a single isocyanate. The use of Isonate 143L as the preferred isocyanate source is desirable. This is because it contains dimers, trimers, and a carbodiimide component that increases functionality to levels greater than 2.0 and is believed to contribute to the storage stability of the prepolymer and the strength and dimensional stability of the foam. The actual content of free MDI can be adjusted up or down in this isocyanate-containing product as long as the functionality is greater than 2.0. For example, you can add additional pure MDI. To further improve the durability of the sponge, approx.
% or less relatively short approximately 1.27 cm (1/
2 inches) or less of fiber is added to the aqueous suspension. The preferred fiber is polyester fiber. Thickening or suspending agents can be added to the aqueous phase to allow the mixture to be pumped through a foaming machine. For example, Carbopol 941, a high molecular weight acrylic acid polymer, can be added, which can be neutralized to a pH level of 7 with a base such as ammonium hydroxide. Sponge foam is made by reacting water and a prepolymer, preferably while heating both. Surfactants can be added to the water to control foam cells. Preferred isocyanate-containing products with functionality greater than 2.0 are mixtures of diphenylmethane diisocyanate (MDI) and isocyanate-containing derivatives of MDI. One commercial product that meets this requirement is isonate 143L, which is produced by reacting MDI to form a carbodiimide, which material is then reacted to form a trifunctional cyclic adduct.
The mixture of MDI, carbosiimide and cyclic adduct is in equilibrium. The mixture contains a predominant amount of pure diphenylmethane diisocyanate and a minor amount of the carbosiimide and trifunctional cyclic adduct of diphenylmethane diisocyanate. The mixture of components A and B below constitutes the 143L system. As used herein, the term derivatives of diphenylmethane diisocyanate refers to
Refers to products made from MDI. It will include adducts, dimers and trimers. It will not contain materials such as polymethylene polyphenyl isocyanate that are not made from MDI. The diol used to prepare the prepolymer is a poly( _oxyC2-4 alkylene) diol having at least 50% by weight oxyethylene groups, preferably at least 80% by weight oxyethylene groups. Thus, if the diol comprises oxypropylene or oxybutylene or mixtures thereof:
This minimum amount of oxyethylene must also be present. Preferred diols are hydrophilic poly(oxyethylene) diols having at least 80% by weight oxyethylene groups and made by Union Carbide under the product name Carbowax. Isonates as a single isocyanate source
When using 143L, it is preferable to use a carbo wax with a molecular weight of about 1000. 600~
Although other carbo wax formulations with a molecular weight of 1100 can be used, the most preferred form is 950.
It has a molecular weight of 1050 to 1050. carbo wax 1000
It is this range of products that is produced when producing commercial grades of. If a molecular weight type lower than about 600 is used, the resulting sponge made from the prepolymer will lose its hydrophilicity.
This is because any sponge treatment would require large amounts of relatively hydrophobic isonates. Similarly, if a molecular weight form higher than 1100 is used, the resulting sponge will significantly lose its crosslink density and its dimensional stability and stiffness. Relatively short, low molecular weight monomeric polyols having 3 or 4 hydroxyl equivalents per mole are added to provide crosslinking strength to the final foam product to be produced from the prepolymer. Examples are trimethylolethane, trimethylolpropane, glycerol, triethanolamine, pentaerythritol or mixtures thereof. Preferred polyols have the formula is trimethylolpropane, TMOP. It is also desirable to control the ratio of diols such as carbowaxes to short crosslinked polyols in making the prepolymers. Generally, the moles should be in the range of about 4:1 to 8:1, with a preferred ratio of about 6:1. If the proportion is too low such that too much polyol is present, the resulting sponge made from the prepolymer will not lose its hydrophilicity and the foam will also have poor foam structure. On the other hand, if the proportion is increased such that less polyol such as TMOP is present, then a weak, brittle foam is obtained, which is characterized by fine and partially closed cells. There is.
The molar ratio expressed for these two materials defines the relative number of hydroxy equivalents present from each material. Thus, in the ratio of 1 mole of the preferred diol carbowax to 1 mole of the preferred polyol TMOP, the carbowax is
contributes 12 equivalents of hydroxyl to the equivalent weight. Carbo Wax 1000 is based on hydroxyl group.
has an equivalent weight of 500 but has a molecular weight of 134
TMOP has an equivalent weight of 45 per hydroxyl group.
Since isonate 143LL is used in combination with hydroxyl groups, the amount of isocyanate required is very sensitive to the amount of TMOP,
The amount of TMOP is therefore carefully controlled in pairs. The ratio of isocyanate to hydroxyl groups in the reactants should be in the range of 3 to 4, more preferably about 3.3 to 3.7. When the prepolymer is prepared, one isocyanate group of the polyisocyanate component reacts with the hydroxyl groups leaving unreacted residual isocyanate groups. These free isocyanate groups of the prepolymer react with water to form polyurea bonds, with a concomitant increase in molecular weight and the release of _CO2 , which facilitates the formation of a foamed sponge. The isocyanate-containing product should consist of more than 50% by weight of prepolymer to give the sponge the necessary stiffness. When reacting the components to form a prepolymer, it is advantageous to measure the isocyanate level by titration after the reaction has been carried out for about one hour.
From this follow-up and subsequent titration, it is possible to determine the additional reaction time required to reduce the isocyanate level below or near the theoretical point at which all of the hydroxyl groups would react with the isocyanate. can. If the reaction continues too much, the isocyanate water is further reduced, in which case the prepolymer viscosity increases, making it more difficult to subsequently mix the prepolymer with water. Overreacting the prepolymer components increases the foam density and reduces the water absorption of the resulting foam. The fibers are preferably added to the aqueous phase for insertion into the foam composition to provide sufficient structural rigidity. Polyester fibers are particularly advantageous, and they can be cut to lengths of about 1/2 inch or less. For aqueous suspensions, the fibers can be added in varying amounts, although preferably they constitute no more than about 10% by weight. This is because above that level the suspension is too difficult to pump. High molecular weight suspending or thickening agents are added to serve two functions. First, it keeps the ingredients in suspension so that water does not drain out of the fibers and the fibers do not float. Second, the thickener acts as a lubricant to the fibers so they do not tangle, dehydrate and jam up as they pass through the mixing pump.
An example of a thickener is Polyox WSR (Polyox
WSR), Natrosol, Xanthan gums, and Dow's
Polyacrylamide such as Separan AP30). A preferred suspending or thickening agent is Carbopol 934
(Carbopol934), Carbopol 940 (Carbopol940)
and especially Carbopol941
Carbopol resins manufactured by BFGoodrich Chemical Co.
Since Carbopol resins are acrylic acid polymers with acid moieties, neutralizing agents such as sodium or ammonium hydroxide can be added. There is an advantageous increase in the viscosity of the aqueous phase when adding ammonium hydroxide as a neutralizing agent for carbopol. Ammonium hydroxide is cheaper than carbopol and can create a more economical formulation with the same amount of thickening, which uses less carbopol. Some of the suspending agents or thickeners may have surface-active properties, so they may also be part of a surfactant system that controls the cell size of the resulting sponge. The surfactant has the correct cell size, shape,
It is chosen to give a form with good appearance without collapse or splits. Surfactants known to be useful with polyurethane foams can be used in this case. An example of a preferred surfactant is Wyandotte, Michigan.
BASF Wyandot Co., Ltd. (BASF
Pluronic Polyol surfactants manufactured by Wyandotte Corp. are block copolymers of oxyethylene and oxypropylene. A preferred surfactant is Pluronic L-62. In producing polyurethane foams, the preferred process is to add approximately equal amounts of the aqueous suspension with the prepolymer mixture and then mix the two together. The composition of the aqueous suspension is a prepolymer resin
It can also be expressed based on 100 copies. Thus, 100 parts water per 100 parts resin is written as 100 phr water.
The ratio of amounts of prepolymer mixture to aqueous suspension can vary over a wide range. However, if the amount of aqueous suspension is too large, the strength of the resulting foam will be reduced. On the other hand, if the amount of aqueous suspension is reduced too much, it will not be possible to fully add the fibers and fillers supplied via the aqueous suspension. A preferred method of foaming the prepolymer is to heat an aqueous suspension, such as a 2% solution of Pluronic L-62 surfactant, and the prepolymer to a temperature of about 35°C. These are poured or pumped together in a ratio of about 100 parts by weight of aqueous suspension to about 80 parts by weight of prepolymer and are mixed with a mechanical agitator, such as a blade attached to a drill motor, for 15 to 10 minutes.
Stir immediately for up to 30 seconds. This length of time allows complete mixing but does not allow any appreciable chemical reaction to occur. This mixture is immediately poured into a mold, where rising and curing of the foam product occurs. Depending on the fibers added, application materials, and thickening, the best surfactant is L-520 (Union
from highly hydrophobic silicone type or other silicone surfactants such as Brij-58 (ICI-
America) or even highly hydrophilic types such as ICI's other Brij, Span or Tween products. Pluronics for general use, especially L
-62, L-72, L-92, P-75 or P-85
Nonionic surfactants such as (BASF-Wyandotte) are preferred. The use of these surfactants will be familiar to those skilled in the art of formulating polyurethane foam products. Depending on the foaming conditions, these foams can ^be
can have a similar advantageous structure. The sponge has the appearance and wiping properties of a cellulosic sponge. It has large cells (pores) several millimeters in diameter, but the walls of these cells are perforated with numerous pinholes. This gives the sponge a high degree of strength and stiffness due to the thick cell walls but excellent ability of the openings to wick and absorb water by capillary action. It differs from other flexible urethane foams that are graded as fine-celled (smooth) or reticulated. The reticulated foams have most of the cell membrane removed so that they have a fibrous appearance. They are used as filters in furnaces and air conditioners. SEA
The SPONGE foam and the foam of the present invention are
In contrast, it has an intact but perforated cell membrane. This is different from the familiar polyurethane sponges on the market. This is because they absorb water into the polymer itself and wipe dry. Having described the basic aspects of the invention, the following examples illustrate specific aspects thereof. Tests Used to Evaluate Sponges The following test methods are used. All foam samples to be tested are dry and uniform 2.54 cm x 7.62 cm.
Cut to x12.7cm (1″ x 3″ x 5″) dimensions, and
Dry at 105±5°C to a constant weight without moisture.
The weight of the sample is approximately 0.1 grams. A group of 10 representative samples were used for testing. A Wet-Out time from dry state
time) In a pan filled with water, float the thoroughly dry foam to the surface. The time required for the entire sample to become wet, ie, for water to appear and wet the entire top surface of the sample, is recorded in seconds. B. Complete wetting time from wet condition The foam is fully wetted and passed through a washing machine wringer to obtain uniform wetness. The wet foam rises to the surface of the water-filled pan. The time required for complete wetting of the entire sample is recorded as 0.1 seconds. C. Determination of Washer Durability After drying a 2.54cm x 7.62cm x 12.7cm (1″ x 3″ x 5″) sample at 105°C ± 5°C for 1 hour, weigh it to the nearest ±0.02 grams. Maytag For the Maytag type, place 48 samples in a vertical washer filled with water and stir for 72 hours. Dry the samples and weigh again. Weight % loss = (initial dry weight - final dry weight) x 10
0/Initial Dry Weight This test is very demanding and should not be considered satisfactory for use as a sponge or for other foam applications, even though the foam will not last in one piece for a period of 72 hours. could be. If the sponge does not persist for a period of 72 hours, the results record the observation period in hours during which visible deterioration is observed. D. Determination of Tear Strength 2.54cm x 7.62cm x 12.7cm (1″ x 3″ x 5″) sample at a distance of 6.35cm (2-1/2″)
Tear at the (1″ x 3″) plane. Scotto tester,
Model J-1 (Scott Tester, Model J-1)
(or equivalent) with a 1 inch opening between the upper and lower jaws. Clamp one of the tear areas to each of the jaws of the Scott tester. Activate the Destar and record the tear resistance in pounds. E. Determination of breaking stress An Instron tester equipped with an instrument for testing sponges or similar materials.
Determine tenacity using a tester. Set the Instron tester's jaws to a 2.54 cm (1 inch) opening between the upper and lower jaws. Clamp the 7.62 cm (3 inch) dimension in each tube and activate the tester. Record toughness in pounds. Convert this value to kg/m ³ (pounds per square inch) by dividing the toughness by the width of the tube in contact with the sample. F. Determination of air permeability The test apparatus used consists of a fan connected to the tube by a part of the sample located on the end of the tube. Measure the air pressure upstream of the sponge.
Air gauge pressure is calibrated to continue to be 0.60 if the material is impermeable. If the continuation is zero, it indicates a very high porosity and a very open cell structure with very little pressure drop across the sponge. G Modulus of Elasticity This is measured from the stress-strain curve at 1% elongation. Example 1 (Reference Example) This example describes the preparation of a prepolymer used according to the invention. A mixture of Carbo Wax 1000 (412 g, 0.4 mol) and trimethylolpropane (9.05 g, 0.0675 mol) was heated at 70°C under a vacuum of ~0.003 atm (2 Torr).
It was dried by heating for 2 hours. Isonate into dry and degassed polyol mixture
507.5 g of 143 L (3.55 equivalents of isocyanate) was added. The temperature was held at 70°C for 2-1/2 hours and after this time the isocyanate content of the product per gram
It was found to be 2.67 meq. That's 25
It had an initial viscosity of 19000 cp at °C. 80
After a two week storage test at 0.degree. C. the viscosity increased only to 30,000 cp. Example 2 This example describes the preparation of a foam according to the invention using the prepolymer of Example 1. 700g of prepolymer heated to 35℃ in a beaker and 3
686 g of an aqueous solution containing 14 g of Pluronik L-62, a nonionic surfactant from Wyandot Co., was added. They were stirred together with a drill motor for 15 seconds and then poured into molds. Dry foam product per cubic meter
It had a density of 34.05 kg (2.1 pounds per cubic foot). Approximately 2.54cm x 7.62cm x 13.97cm (1″ x 3″ x 5-1/
A sponge with dimensions of 2") was cut from the foam block. When saturated with water, the
Holds 9x more water without dripping, capacity ranges from ^275.35cm3 to ^308.13cm3 (16.8 cubic inches)
18.8 cubic inches) (12% increase). When squeezed by hand, it released all but about 90% of its dry weight. It had a similar appearance and wiping properties to a cellulose sponge of the same dimensions. Example 3 (Reference Example) This prepolymer was prepared using the same reactants and conditions as Example 1, except that the reaction was stopped after the product had an isocyanate content of 2.61 milliequivalents per gram. Example 4 (Reference Example) This prepolymer has a product of 2.70 g/g.
It was prepared using the same reactants and conditions as Example 1, except that the reaction was stopped after having milliequivalent isocyanate content. Examples 5 and 6 These examples illustrate the effect of using the prepolymers of Examples 3 and 4 and adding reinforcing fibers. In Example 5, the prepolymer of Example 3
700g of water and 686g of surfactant Pluronic L-
62 was mixed with an aqueous solution containing 14 g. In Example 6, the prepolymer of Example 4
700g, water 683.2g, surfactant Pluronic L-
62 14g, Weber, Virginia
Mini Fiber Co., Ltd. (City Virginia)
35 g of Polyester Fiber 2, a 1.27 cm (1/2 inch) fiber manufactured by Fibers, Inc., 2.8 g of the thickener Carbopol 941 neutralized with 7.0 g of a 33% solution of ammonium hydroxide. mixed with the containing aqueous solution. The results are listed in Table 1.

Table: The product of Example 5 contained only water and surfactant from the aqueous phase. These sponges had unusual properties. They had a bright white color and a well-developed uniform SEA SPONGE type structure. The density is 34.54Kg/ ^m3 (2.13lb/ft
³ ), which was a very low value. When this sponge is dry, it may be rigid depending on the surrounding conditions, but when wet it is soft. Although the initial drying time is relatively long, it is highly absorbent when wet. Sponges hold large amounts of water, clean well, wipe well, and have reasonable machine durability. Air permeability is moderate, but volume swelling is very low. This sponge has a good appearance and surface feel. The sample from Example 6 is a fiber reinforcement of the foam of Example 5 containing Carbopol 941 and 5 phr fibers in the aqueous suspension used to make the sponge. This sponge was able to pass a very aggressive 72 hour washer test with 0% weight loss. Tear strength for wet and dry conditions was high. It has very good air permeability and exhibits an open cell structure. Although the cellular structure may not be considered aesthetically pleasing as the foam in Example 5, the foam cleans well and wipes satisfactorily. This is very durable and has a large sponge. Example 7 This example describes the production of sponge foam without adding any surfactant to the water. The foam was prepared according to the method in Example 2, except that no surfactant was present in the water. The hydrophilic foam obtained was 48.64Kg/m ³ (3
lb/ft) and was similar to the foam in Example 2 except that it had a finer texture due to the small, partially closed cell structure.

Claims (1)

Claims: 1. A foamed sponge that has minimal swelling when wet and does not curl when dry, comprising (a) at least 50% by weight of oxyethylene groups and at most 1100 (b) _a predominant amount of pure diphenylmethane diisocyanate and a minor amount of diphenylmethane diisocyanate; a diphenylmethane diisocyanate-containing isocyanate product having a functionality greater than 2.0 consisting of a mixture of a carbodiimide and a trifunctional cyclic adduct; and (c) a monomeric polyol crosslinker having 3 or 4 hydroxyl equivalents per mole. ,
the isocyanate product comprises greater than 50% by weight of the prepolymer, the diol and polyol crosslinkers are present in a molar ratio ranging from 4:1 to 8:1, and the ratio of isocyanate equivalents to total hydroxyl equivalents A foamed sponge made by mixing together and reacting a resin phase and an aqueous phase consisting of a prepolymer ranging from 3:1 to 4:1. 2. The foamed sponge of claim 1, wherein the poly( _oxyC2-4 alkylene) diol has a nominal number average molecular weight of 600 to 1100, and the diol has at least 80% by weight of oxyethylene groups. 3. The foamed sponge of claim 1, wherein the polyol crosslinker is selected from the group consisting of trimethylolpropane, trimethylolethane, glycerol, triethanolamine, pentaerythritol and mixtures thereof. 4. The foamed sponge of claim 3, wherein the polyol crosslinking agent is trimethylolpropane. 5. A foamed sponge which has minimal swelling when wet and which does not curl when dry, having (a) at least 50% by weight of oxyethylene groups and a nominal number average molecular weight of at most 1100; (b) a carbodiimide of pure diphenylmethane diisocyanate in a predominant amount and a minor amount of diphenylmethane diisocyanate _and a trifunctional cyclic (c) a monomeric polyol crosslinker having 3 or 4 hydroxyl equivalents per mole;
the isocyanate product comprises greater than 50% by weight of the prepolymer, the diol and polyol crosslinkers are present in a molar ratio ranging from 4:1 to 8:1, and the ratio of isocyanate equivalents to total hydroxyl equivalents A foamed sponge made by mixing and reacting with each other a resin phase consisting of a prepolymer and an aqueous phase containing a surfactant in a ratio ranging from 3:1 to 4:1. 6. A patent in which the surfactant is a diol prepared by capping a 1750 molecular weight poly(oxypropylene) with ethylene oxide such that the resulting liquid product contains 20% by weight ethylene oxide. A foamed sponge according to claim 5. 7 A foamed sponge which has minimal swelling when wet and does not curl when dry, having (a) at least 50% by weight of oxyethylene groups and a nominal number average molecular weight of at most 1100; (b) a carbodiimide of pure diphenylmethane diisocyanate in a predominant amount and a minor amount of diphenylmethane diisocyanate _and a trifunctional cyclic (c) a monomeric polyol crosslinker having 3 or 4 hydroxyl equivalents per mole;
the isocyanate product comprises greater than 50% by weight of the prepolymer, the diol and polyol crosslinkers are present in a molar ratio ranging from 4:1 to 8:1, and the ratio of isocyanate equivalents to total hydroxyl equivalents A foamed sponge made by mixing and reacting with each other a resin phase consisting of a prepolymer and an aqueous phase containing reinforcing fibers in the range of 3:1 to 4:1. 8. The foamed sponge of claim 7, wherein said reinforcing fibers are polyester fibers having a length of 1.27 cm or less. 9 A foamed sponge having minimal swelling when wet and no curling when dry, having (a) at least 50% by weight of oxyethylene groups and a nominal number average molecular weight of at most 1100; (b) a carbodiimide of pure diphenylmethane diisocyanate in a predominant amount and a minor amount of diphenylmethane diisocyanate _and a trifunctional cyclic (c) a monomeric polyol crosslinker having 3 or 4 hydroxyl equivalents per mole;
the isocyanate product comprises greater than 50% by weight of the prepolymer, the diol and polyol crosslinkers are present in a molar ratio ranging from 4:1 to 8:1, and the ratio of isocyanate equivalents to total hydroxyl equivalents A foamed sponge prepared by mixing and reacting with each other a resin phase consisting of a prepolymer and an aqueous phase containing a thickening or suspending agent in the range of 3:1 to 4:1. 10. The foamed sponge of claim 9, wherein said thickening or suspending agent is a high molecular weight polycarboxylic acid. 11. The foamed sponge of claim 10, wherein the polycarboxylic acid is a polyacrylic acid polymer having a molecular weight of 1,250,000. 12. The foamed sponge according to claim 10, wherein the polycarboxylic acid is neutralized. 13. The foamed sponge of claim 12, wherein the polycarboxylic acid is neutralized with ammonium hydroxide.