DescriPtion of the Related Art Conventionally, the method of washing fabrics in water involves adding a laundry detergent which includes a blend of surfactants, generally anionic surfactants, and additives to the soiled fabrics to be cleaned, followed by agitating to remove soils and oil-containing micelles, and finally by multiple rinsing steps to remove the soils and detergent residues from the cleaned fabrics. However, the conventional method has the drawback that it is quite ineffective in removing oils from hydrophobic fabrics such as polyester and polypropylene.

SUMMARY OF THE INVENTION It is accordingly an object of the present invention to overcome the deficiencies in the prior art, such as noted above.

The present invention relates to a method of cleaning soiled fabric where an aqueous fabric cleaning composition comprising a non-ionic surfactant is applied to completely wet the soiled fabric at a temperature below the cloud point of the non-ionic surfactant. The soil is removed upon heating and cooling the soiled fabric wetted with the aqueous fabric cleaning composition followed by water rinse.

DETAILED DESCRIPTION OF THE INVENTION The method of cleaning soiled fabric according to the present invention takes advantage of the reverse solubility behavior of non-ionic surfactants. In contrast to ionic compounds, non-ionic surfactants become less water soluble and more hydrophobic at higher temperatures. Such a reverse solubility behavior is expressed by the cloud point, where the cloud point, which alludes to the observation that

the solution becomes turbid, is the temperature where insolubility of the non-ionic surfactant in water is reached.

In a standard test method, the cloud point of a surfactant is determined by heating a 1% aqueous solution to form a turbid solution where the non-ionic surfactant is above its solubility level in water, and then, as the solution is slowly cooled, monitoring the transition from a turbid solution to a clear solution.

It was discovered by the present inventor that this reverse solubility behavior of non-ionic surfactants in water can be used to effectively remove oily soils from hydrophobic fabrics where conventional detergent blends are ineffective in removing oils. The present method of cleaning fabric is thus particularly suited to removing oily and hydrophobic soils from fabrics that are hydrophobic and involves applying an aqueous fabric cleaning composition, which includes a non- ionic surfactant having a cloud point between 4 and 900C, to a soiled fabric. Preferably, the cloud point of the non- ionic surfactant used in the aqueous fabric cleaning composition is in the range of about 25 to 350C.

An important feature of the present method is that the aqueous fabric cleaning composition must be applied to the soiled fabric at a temperature below the cloud point of the non-ionic surfactant in the composition. The soiled fabric is agitated with the aqueous fabric cleaning composition to obtain complete wetting, followed by adding hot water to the wetted soiled fabric to raise the temperature for washing to above the cloud point of the non- ionic surfactant. By washing the soiled fabric at a temperature above the cloud point, the non-ionic surfactant becomes insoluble in the wash water and selectively dissolves into oils such as the soils of fabric to be cleaned. Cold water is later added to lower the wash temperature below the cloud point of the non-ionic surfactant and agitated to solubilize the non-ionic surfactant dissolved in the soil, and thereby remove the soil from the fabric into the wash water. Subsequent cold water rinse with agitation completely

removes residual and loose soils. An anionic and/or cationic surfactant can be optionally added in the wash cycle when the fabric to be cleaned has a high oily soil load or when the residual deposits on the fabric are to be reduced as low as possible.

A preferred embodiment of a fabric cleaning concentrate in percent by weight is as follows: linear alcohol ethoxylate propoxylate 97.5 polyvinyl pyrrolidone 2.0 N-octyl-2-pyrrolidone 0.5 where the concentrate is diluted with water to 3% by weight to arrive at the fabric cleaning composition. In this preferred embodiment, the polyvinyl pyrrolidone serves as an agent that prevents dye and soil transfer between different pieces of fabric and the N-octyl-2-pyrrolidone is a super wetting agent for facilitating the wetting or distribution of the non-ionic surfactant over the surface of the fabric.

Besides superwetting agents and agents that prevent dye/soil transfer, there may be other optional additives in the aqueous fabric cleaning composition, including, but not limited to: builders, such as sodium tripolyphosphate and zeolite; chelants, such as EDTA; agents for increasing the pH, such as sodium carbonate; washing machine protectants, such as silicates; fabric brighteners; processing aids, such as sodium sulfate; anti-redeposition agents, such as carboxymethyl cellulose; bleaching agents, such as sodium perborate and sodium hypochlorite; soil releasing polymers; enzymes, such as proteases and lipases; fabric softeners, such as quaternary amines; and solvents, such as glycol ethers and short chain alcohols. These additives as well as others which are well-known in the art of laundry detergents are well within the skill of those in the art.

Any commercially available laundry detergent having an anionic surfactant blend can be optionally added to the wash cycle according to manufacturer's instructions in order to provide addition cleaning. An example of a concentrate containing an anionic surfactant blend, which can be diluted with water to 3% by weight, is as follows: Percent sodium tripolyphosphate 5% tetrasodium EDTA 1% sodium carbonate 10% sodium metasilicate 2% sodium sulfate 10% carboxymethyl cellulose 2% sodium N-methyl-N-oleoyltaurate 70% The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.