Chemically Stiffened Fibers In Sheet Form

Abstract

A method for making stiffened cellulosic fiber in sheet form, and the resultant stiffened cellulosic fiber. The method of making the stiffened fibers involves impregnating a cellulosic base fiber in sheet form with a treatment composition solution, drying and curing the impregnated sheet, and thereafter adding water or an aqueous solution of odor removing agent to the cured sheet to produce a sheet of stiffened cellulosic fiber having a moisture content of at least about 6.0 weight %. When defiberized, the stiffened fiber has a low content of fines and knots and nits. The stiffened fiber also exhibits a low degree of yellowing and is substantially free of a burnt-like odor. The stiffened fiber may be used in an absorbent article, such as in a liquid acquisition layer or absorbent core of a baby diaper.

1 . A method of making stiffened cellulosic fiber in sheet form having a low degree of yellowing and low odor, said method comprising:
 providing a treatment composition comprising an aqueous solution of a cross-linking agent and a catalyst;   providing cellulosic base fiber in sheet form;   applying the treatment composition to the cellulosic base fiber to impregnate the cellulosic base fiber;   drying and curing the impregnated fiber; and   applying water to the cured sheet of fiber to increase its moisture content to more than about 6.0 weight %.   
     
     
         2 . The method of  claim 1 , wherein the cross-linking agent is selected from the group consisting of: a polycarboxylic acid, an aldehyde, a urea-based derivative, and combinations and mixtures thereof. 
     
     
         3 . The method of  claim 1 , wherein the cross-linking agent is a polycarboxylic acid comprising an alkanepolycarboxylic acid selected from the group consisting of: 1,2,3,4-butanetetracarboxylic acid, 1,2,3-propanetricarboxylic acid, oxydisuccinic acid, citric acid, itaconic acid, maleic acid, tartaric acid, glutaric acid, iminodiacetic acid, citraconic acid, tartarate monsuccininc acid, benzene hexacarboxylic acid, cyclohexanehexacarboxylic acid, and mixtures and combinations thereof. 
     
     
         4 . The method of  claim 1 , wherein the cross-linking agent is a polymeric polycarboxylic acid prepared from one or more monomers selected from the group consisting of: acrylic acid, vinyl acetate, maleic acid, maleic anhydride, carboxy ethyl acrylate, itanoic acid, fumaric acid, methacrylic acid, crotonic acid, aconitic acid, acrylic acid ester, methacrylic acid ester, acrylic amide, methacrylic amid, butadiene, styrene, and combinations and mixtures thereof. 
     
     
         5 . The method of  claim 1 , wherein the cross-linking agent is a polycarboxylic acid comprising a combination of polymeric polycarboxylic acid and alkanepolycarboxylic acid. 
     
     
         6 . The method of  claim 1 , wherein the cross-linking agent is an aldehyde selected from the group consisting of: formaldehyde, glyoxal, glyoxylic acid, glutaraldehyde, glyceraldehydes, and combinations and mixtures thereof. 
     
     
         7 . The method of  claim 1 , wherein the cross-linking agent is a urea-based derivative selected from the group consisting of: urea based-formaldehyde addition products, methylolated ureas, methylolated cyclic ureas, methylolated lower alkyl cyclic ureas, methylolated dihydroxy cyclic ureas, dihydroxy cyclic ureas, lower alkyl substituted cyclic ureas, dimethyldihydroxy urea (1,3-dimethyl-4,5-dihydroxy-2-imidazolidinone), dimethylol urea (bis[N-hydroxymethyl]urea), dihydroxyethylene urea (4,5-dihydroxy-2-imidazolidinone), dimethylolethylene urea (1,3-dihydroxymethyl-2-imidazolidinone), glyoxal adducts of urea, polyhydroxyalkyl urea, hydroxyalkyl urea, β-hydroxyalkyl amide, and combinations and mixtures thereof. 
     
     
         8 . The method of  claim 1 , wherein the treatment composition has a pH of about 1.5 to about 4.5. 
     
     
         9 . The method of  claim 1 , wherein applying the treatment composition to cellulosic base fiber comprises spraying, dipping, rolling, or applying with a puddle press, size press or a blade-coater. 
     
     
         10 . The method of  claim 1 , wherein the treatment composition is applied to the cellulosic based fiber to provide from about 10 weight % to about 150 weight % of treatment composition on fiber, based on the total weight of the fiber. 
     
     
         11 . The method of  claim 1 , wherein the treatment composition is applied to the cellulosic base fiber to provide from about 2 weight % to about 7 weight % of the cross-linking agent on fiber, and from about 0.3 weight % to about 2.0 weight % of catalyst on fiber, based on the total weight of the fiber. 
     
     
         12 . The method of  claim 1 , wherein the catalyst is an alkali metal salt of phosphorous containing an acid selected from the group consisting of: alkali metal hypophosphites, alkali metal phosphites, alkali metal polyphosphonates, alkali metal phosphates, alkali metal sulfonates, and combinations and mixtures thereof. 
     
     
         13 . The method of  claim 1 , wherein the treatment composition comprises from about 2 weight % to about 10 weight % cross-linking agent. 
     
     
         14 . The method of  claim 1 , wherein the weight of the catalyst in the treatment composition is about 10% to about 50% of the weight of the cross-linking agent in the treatment composition. 
     
     
         15 . The method of  claim 1 , wherein the cellulosic base fiber is a conventional cellulose fiber derived from hardwood cellulose pulp, softwood cellulose pulp, cotton linters, bagasse, kemp, flax, grass, or combinations or mixtures thereof. 
     
     
         16 . The method of  claim 15 , wherein the hardwood cellulose pulp is selected from the group consisting of: gum, maple, oak, eucalyptus, poplar, beech, aspen, and combinations and mixtures thereof. 
     
     
         17 . The method of  claim 15 , wherein the softwood cellulose pulp is selected from the group consisting of: Southern pine, White pine, Caribbean pine, Western hemlock, spruce, Douglas fir, and mixtures and combinations thereof. 
     
     
         18 . The method of  claim 1 , wherein the sheet of cellulosic base fiber is formed using a wet-laid process, and has a basis weight of about 200 grams per square meter (gsm) to about 800 gsm and a density of about 0.15 grams per cubic centimeter (g/cc) to about 0.6 g/cc. 
     
     
         19 . The method of  claim 1 , wherein the drying and curing occurs in a one-step process conducted for about 3 minutes to about 15 minutes at a temperature within the range of about 130° C. to about 225° C. 
     
     
         20 . The method of  claim 1 , wherein the drying and curing is a two-step process comprising:
 first drying the impregnated cellulosic fiber at a temperature below curing temperature; and   curing the dried cellulosic fiber for about 1 to 10 minutes at a temperature within the range of about 150° C. to about 225° C.   
     
     
         21 . The method of  claim 1 , wherein applying the water to the cured sheet of fiber comprises spraying, dipping, rolling, printing, or applying with a puddle press, size, press, or a blade-coater. 
     
     
         22 . The method of  claim 1 , wherein an odor removing agent is applied with the water to the cured sheet of fiber. 
     
     
         23 . The method of  claim 22 , wherein the odor removing agent is selected from the group consisting of hydrogen peroxide, chlorine dioxide, peracetic acid, perbenzoic acid, chlorine, chlorine dioxide, ozone, sodium hypochlorite, baking soda, talc powder, cyclodextrin, ethylenediamine tetra-acetic acid or other chelating agents, zeolites, activated silica, activated carbon granules, DOUBLE-O, UN-DUZ-IT, X-O, NOK-OUT, and combinations and mixtures thereof. 
     
     
         24 . The method of  claim 22 , wherein the odor removing agent is applied to the stiffened fiber to provide from about 0.001 weight % to about 1.0 weight % of odor removing agent on fiber, based on the total weight of the fiber. 
     
     
         25 . Stiffened cellulosic fiber having low degree of yellowing and low odor produced by the method of  claim 1 . 
     
     
         26 . The stiffened cellulosic fiber of  claim 25 , having an ISO Brightness of greater than 77%. 
     
     
         27 . The stiffened cellulosic fiber of  claim 25 , having a pH of less than about 4.2. 
     
     
         28 . The stiffened cellulosic fiber of  claim 25 , having an average kink angle of less than 55°. 
     
     
         29 . The stiffened cellulosic fiber of  claim 25 , having less than about 1.0 kink per millimeter. 
     
     
         30 . The stiffened cellulosic fiber of  claim 25 , having less than about 30% knots and nits when defiberized. 
     
     
         31 . The stiffened cellulosic fiber of  claim 25 , having at least about 70% accepts and not more than about 25% knots and nits when defiberized. 
     
     
         32 . An airlaid structure comprising the stiffened cellulosic fiber of  claim 25  and synthetic fibers. 
     
     
         33 . The airlaid structure of  claim 32 , having a basis weight of about 60 gsm to about 640 gsm. 
     
     
         34 . The airlaid structure of  claim 32 , having a density of about 0.02 g/cc to about 0.12 g/cc. 
     
     
         35 . The airlaid structure of  claim 32 , wherein the synthetic fiber is selected from the group consisting of polypropylene, polyethylene, bi-constituent fibers, and any combination or mixture thereof. 
     
     
         36 . The airlaid structure of  claim 32 , wherein the bi-constituent fiber is a polyethylene/polyester fiber. 
     
     
         37 . The airlaid structure of  claim 32 , wherein the airlaid structure is a thermally-bonded stabilized roll good material. 
     
     
         38 . The airlaid structure of  claim 32 , wherein the airlaid material is a stabilized roll good material that contains about 1.0 weight % to about 25.0 weight % of a bi-constituent fiber, based on the total weight of the stabilized roll good material. 
     
     
         39 . An absorbent article comprising the stiffened cellulosic fiber of  claim 25 . 
     
     
         40 . The absorbent article of  claim 39 , wherein the absorbent article is a disposable baby diaper, an adult incontinent device, or a feminine hygiene product. 
     
     
         41 . The absorbent article of  claim 39 , wherein the absorbent article has a top sheet, a back sheet, and a storage layer disposed at least partially between the top sheet and the backsheet. 
     
     
         42 . The absorbent article of  claim 39 , wherein the absorbent article further comprises a liquid acquisition layer disposed at least partially between the top sheet and the storage layer. 
     
     
         43 . The absorbent article of  claim 42 , wherein the liquid acquisition layer comprises stiffened cellulosic fiber. 
     
     
         44 . The absorbent article of  claim 43 , wherein the liquid acquisition layer comprises a mixture of SAP and the stiffened cellulosic fiber. 
     
     
         45 . The absorbent article of  claim 44 , wherein the liquid acquisition layer contains about 8 weight % to about 30 weight % SAP, based on total weight of the acquisition layer. 
     
     
         46 . The absorbent article of  claim 43 , wherein the liquid acquisition layer is an thermally-bonded airlaid structure comprising the stiffened cellulosic fiber and synthetic fibers. 
     
     
         47 . A method of making stiffened cellulosic fiber in sheet form having a low degree of yellowing and low odor, said method comprising:
 providing cellulosic base fibers;   providing a treatment composition comprising an aqueous solution of a cross-linking agent and a catalyst;   forming a suspension of the cellulosic fibers in the treatment composition solution;   converting the suspension into a wet-laid sheet;   pressing the wet-laid sheet until the sheet has a wet pick-up of about 50 weight % to about 200 weight %;   drying and curing the pressed sheet to form a sheet of stiffened cellulosic fiber;   applying water to the cured stiffened cellulosic fiber sheet to increase its moisture content to more than about 6.0 weight %.   
     
     
         48 . The method of  47 , wherein the cellulosic base fibers are provided in sheet or fluff form. 
     
     
         49 . The method of  47 , wherein the cellulosic base fibers are provided in dry or wet state. 
     
     
         50 . The method of  47 , wherein the sheet of stiffened cellulosic fibers has a density of at least about 0.15 g/cc.