the present process can be used for treating all types of cellulose - containing fabrics , such as , those made from cotton fibers , regenerated cellulose , jute , manila , hemp , sisal , and ramie . the process is especially useful for the treatment of cotton fabrics for clothing materials , tents and awning materials . generally , the process of the present invention and the products obtained therefrom are advantageous in those cases where cellulose - containing materials are exposed to the danger of fire and wherein , in addition to high flame resistance , high mechanical strength after repeated washing is required . preferably , the fabrics used in the present process possess a cellulose content of at least about 65 % by weight of the total fabric . in accordance with the present invention , the fabric is first impregnated with a water soluble , hardenable aminoplast . such an impregnation can be carried out by methods well known to the art such as dipping or padding , with padding being preferred . preferably , the amount of aminoplast applied to the fabric is in the range from about 2 to 25 %, and most preferably from about 8 to 18 % based upon the weight of the fabric . water soluble , hardenable aminoplasts suitable for use in the present process primarily include hardenable aminotriazine resins that are soluble in water or possess limited solubility in water and which may be etherified . such aminoplasts are obtained by methods well known in the art , such as , the condensation of formaldehyde with melamine , acetoguanamine , benzoguanamine , or formoguanamine . mixtures of such condensation products are also suitable . particularly preferred condensation products are those of 2 - 3 moles of formaldehyde with one mole of melamine . those condensation products of limited water - solubility are colloidal intermediate products which are first produced on further condensation beyond the crystalline methylol stage . they are characterized in that they are precipitated from the concentrated aqueous solution by the addition of water ( see kolloid - zeitschrift , vol . lvii , october - december 1931 , page 233 ). the completely water - soluble condensation products may be applied in the form of aqueous solutions . the condensation products of limited solubility may be used either in the form of solutions of the solubilized condensation products , i . e ., those made soluble with acids , or in the form of emulsions . generally , the solution or emulsion contains hardening catalysts , such as , acids , including hydrochloric acid , sulfuric acid or formic acid . alternatively , salts of strong acids with weak bases , such as , ammonium salts of strong inorganic or organic acids , e . g ., ammonium chloride , ammonium sulfate , ammonium nitrate , ammonium oxalate , and ammonium lactate can be used . when solutions of aminoplasts containing acids are used , such solutions must be freshly prepared inasmuch as , on standing the solutions undergo changes which render them unsuitable for use in the present process . another suitable class of catalysts is water - dispersible oxidizing agents which when in aqueous phase do not possess either strong alkali - or acid binding properties and which exert an accelerating effect on the polymerization of the aminoplast due to the formation of oxidation products . as an oxidizing agent possessing sufficient oxidizing power to oxidize formaldehyde to formic acid at elevated temperatures or during long storage of the treated fabric , hydrogen peroxide is suitable as are addition products of hydrogen peroxide to certain inorganic or organic compounds , such as , for example , &# 34 ; perborate &# 34 ; nabo 2 h 2 o 2 , or the addition compound of hydrogen peroxide and urea . another suitable oxidizing agent is chlorine dioxide or its stable addition products especially the addition product of clo 2 to pyridine . the salts of peroxymonosulfuric acid , h 2 so 5 , and peroxydisulfuric acid , h 2 s 2 o8 , e . g ., its alkali salts , are also suitable for use as oxidizing agents . following the impregnation step , the aminoplast is polymerized while the fibers are maintained in a wet and swollen state . such a process is generally termed &# 34 ; wet fixing &# 34 ;. this polymerization may be carried out under steam and / or under pressure . the usual process used for the polymerization is to first remove any excess of the impregnation solution from the fabric as by squeezing or centrifugation . the fabric is then stored in a closed chamber such that the fabric remains wet for the entire period of storage . the storage time depends on the temperature of the storage . thus , for example , the storage may be carried out for one minute if steam is used to control temperature , i . e ., direct application of steam to the fabric : for 15 minutes if the storage temperature is 85 °: and for 20 - 24 hours if the temperature is room temperature . it is critical , however , that the fabric not be allowed to dry during the storage period . thus , it may also be necessary to control the humidity of the storage chamber . specific methods for such wet fixing are well known in the art ( see for example textile research journal , pages 44 - 64 , january , 1971 : bullock , j . b . and welch c . m . textile research journal 35 , pages 459 , 471 , 1965 ; and u . s . pat . no . 3 , 434 , 875 ). we have also found that certain fire retardant materials may be added to the aminoplast impregnation solution . thus , for example , when treating blends of cotton with polyester , we have found it particularly desirable to include an organic halogenated phosphorus containing ester in the solution . suitable esters of this type include compounds selected from the group consisting of organic phosphorous containing esters having the general formula ## equ1 ## wherein r , r &# 39 ;, and r &# 34 ; can be the same or different and may be a halogenated lower alkyl group having from 2 to 8 carbon atoms , and from 1 to 7 halogen atoms , a nucleus selected from the phenyl series which is substituted with 1 to 5 halogen atoms , a nucleus selected from the napthyl series which is substituted with 1 to 7 halogen atoms , a lower alkyl phenyl group wherein the alkyl group contains from 1 to 5 carbon atoms , and the phenyl group is substituted with from 1 to 4 halogen atoms , and n is zero to 1 . preferably , the halogen is cl or br . illustrative of such compounds are tris ( 2 , 3 - dibromopropyl ) phosphate , tris 2 -( 1 , 3 - dibromopropyl ) phosphate , tris ( chloroethyl ) phosphate , tris ( 2 - bromo - 3 - chloropropyl ) phosphate , tris 2 -( 1 , 3 - dichloropropyl ) phosphate , bis ( 2 , 3 - dibromopropyl )- 2 , 3 - dibromopropyl phosphonate , tris -( 2 , 6 - dichlorophenyl ) phosphate , tris -( p - bromophenyl ) phosphate , tris -( 2 , 3 , 4 - tribromobutyl ) phosphate , tris - 2 -( 1 , 6 - dibromonaphthyl ) phosphate , bis ( chloroethyl ) phenyl phosphonate , tris -( 2 - bromo - 4 - methylphenyl ) phosphate , and the like . we have found it preferable to include the organic halogenated phosphorus containing ester in a concentration in the range from about 5 to 25 weight percent and , most preferably , from about 10 to 18 weight percent of the solution . such solutions are particularly useful for treating fabric composed of a blend of from about 20 to 80 weight percent polyester content , the remainder of the fabric being cellulosic derived fibers . after the polymerization is complete , the ph of the fabric is adjusted to a value of greater than about 7 . 0 and preferably , from about 8 . 5 to 9 . 6 . this ph adjustment may be carried out by treating the fabric with a solution of alkaline material . particularly preferred is a solution of sodium bicarbonate although other materials , such as , sodium carbonate , sodium hydroxide , potassium hydroxide , and sodium silicate may be used . we have found that the ph adjustment step is particularly critical to provide a fabric having a soft hand and desirable levels of tensile strength . thus , if the ph of the fabric is allowed to remain below the value of 7 . 0 , and the fabric is then subjected to the subsequent treatments described herein , the optimum physical properties will not be obtained in the end product . after the ph adjustment step , the fabric may be dried if desired . however , this drying step is optional . the fabric is then impregnated with a solution of tetrakis ( hydroxymethyl ) phosphonium hydroxide in water or alcohol , e . g ., methanol , isopropanol , etc ., and mixture thereof . this material may be applied to the fabric from a solution by known methods such as dipping , padding , spraying , etc . generally , the solution of the tetrakis ( hydroxymethyl ) phosphonium hydroxide has a concentration in the range from about 10 to 35 weight percent and preferably in the range from about 16 to 26 weight percent . in any event , sufficient solution is applied to the fabric to produce a final phosphorus content in the resulting fabric of from about 1 to 3 percent and preferably from about 1 . 4 to 2 . 0 percent based on the total weight of the fabric . in addition to the tetrakis ( hydroxymethyl ) phosphonium hydroxide , the solution may also contain urea as well as other nitrogenous compounds capable of reacting with the hydroxy methyl ( methylol ) group . these may be in quantities from about 1 to 20 weight percent and preferably from about 1 to 10 weight percent . typical examples of materials are ethylene urea , propylene urea , guanidine , dicyandiamide , oxamide , thiourea , polyethylene imines , and the like . after application of the tetrakis ( hydroxymethyl ) phosphonium hydroxide solution , the fabric is subjected to a curing step . generally , the fabric is cured at a temperature ranging from about 300 ° to 400 ° f for a period of time from about 2 to 20 minutes . typically , in plant practice , a 4 to 8 minute cure at about 360 ° f would be used . a major advantage of the present invention is evident in the curing step . thus , with the present invention , a very &# 34 ; hard &# 34 ; cure can be used without suffering appreciable loss of softness , tensile strength , or fabric whiteness . additionally , as the temperature and time of the cure are increased , the efficiency of phosphorus fixation in the fabric is increased . after curing , the fabric is backwashed to remove any residual deposits including any soluble and / or unreacted material . thereafter , the fabric is dried in a manner well known in the art . the fabric is then subjected to a peroxidation step in order to eliminate any possible odor when the fabric is wet and to avoid losses in fire - retardancy when the fabric is exposed to sunlight . the peroxidation step involves treatment with an oxidant , such as , for example , hydrogen peroxide or sodium perborate . the peroxidation may be carried out at elevated temperatures in a continuous process , such as , in an &# 34 ; open soaper &# 34 ; or batchwise in a dye beck . alternately , the oxidant may be padded onto the fabric while cold , followed by holding the fabric in a wet state for from about 0 . 5 to 18 hours and then rinsing the fabric . such peroxidation methods are conventional in the art and the particular method used is not critical to the present invention . the resulting fabric possesses a soft hand , durable fire - retardancy and tensile properties similar to those of the fabric prior to treating . such fabric is characterized by a phosphorus content in the range from about 1 to 3 percent by weight and a nitrogen content in the range from about 3 to 6 percent by weight , all weights being based on the weight of the fabric . nitrogen was determined by the kjeldahl method as set forth in &# 34 ; analytical methods for a textile laboratory &# 34 ;, second edition , american association of textile colorists and chemists , page 155 . phosphorus was determined by the methods set forth in &# 34 ; organic functional group analysis by micro and semi - micro methods &# 34 ;, cheronis and m . a . wiley , 1964 , pages 551 - 554 . fabric hand was determined by subjective evaluation of two or more qualified fabric examiners . stiffness was determined by astm method d 1388 - 64 . tensile strength was measured by the grab tensile method ( astm d 1682 - 64 ). fire retardancy was measured by department of commerce doc , ff 3 - 71 or aatcc 34 - 1969 . a 100 % cotton flannel was impregnated by padding with 16 % by weight methylated trimethylomelamine , 1 % hydrochloric acid , and 83 % water . the fabric was then wrapped in a moisture - proof plastic bag and allowed to stand at room temperature for 20 hours . the ph of the fabric was then adjusted to 9 . 0 ± 0 . 5 by dipping in a 1 . 0 % soda ash solution and the fabric was then dried . a solution of tetrakis ( hydroxymethyl ) phosphonium hydroxide ( 26 % solids ) and urea ( 10 % solids ) was padded onto the dry fabric to 100 % pick up . the tetrakis ( hydroxymethyl ) phosphium hydroxide was prepared by neutralizing tetrakis ( hydroxymethyl ) phosphonium chloride with sodium hydroxide to a ph of 7 . 5 - 8 . 0 . thereafter the fabric was dried at a temperature from about 240 °- 270 ° f , and then cured for 4 minutes at 360 ° f . the cured fabric was padded with a solution of 1 . 0 % hydrogen peroxide , 0 . 2 % sodium carbonate , and 0 . 1 % of a wetting agent . the fabric was then held in the wet state for 4 hours , rinsed with hot water , rinsed with cold water , squeezed and dried . the fabric obtained was durably fire retardant , possessed a soft hand , and possessed a tensile strength only slightly less than that of the starting fabric . a plain weave fabric composed of 50 % polyester and 50 % cotton having a weight of 3 . 3 ounces per square yard was impregnated with a solution composed of 15 % ( solids ) of methylated trimethylol malamine resin , 12 . 5 % ( solids ) of emulsified tris ( dibrompropyl ) phosphate and 1 % hydrochloric acid . the fabric was maintained in the wet state at room temperature for 20 hours . thereafter it was dipped in a 1 % soda ash solution , rinsed and squeezed until the fabric ph was 7 . 5 - 8 . 0 and then dried . a solution of 16 % tetrakis ( hydroxymethyl ) phosphonium hydroxide and 7 . 5 % urea , prepared as described in example 1 , was padded onto the fabric . the wet fabric was dried at 260 °- 280 ° f and cured for 4 minutes at 360 ° f . the cured fabric was oxidized , rinsed , and dried in accordance with the procedure set forth in example 1 . the resulting fabric was fire retardant and possessed a soft hand . variations can , of course , be made without departing from the spirit and scope of the invention .