It is known that the fibres of cellulosic material, for instance paper pulp, lose their strength potential in the process of being dried, possibly resulting in so-called swelling collapse of the fibres. This can also be observed as an impaired ability to swell in water, and can be explained, for example, by the fact that strong hydrogen bonds are newly formed between hydrophilic groups in the fibre walls. This influences the absorption properties of the fibres, so as to reduce their absorption rate, absorption capacity and water retention properties.
It is also known to impregnate cellulosic fibres with a combined aluminium salt and silicon compound. This is described in BE 461 156 (U.S. Pat. No. 5,127,994), according to which an aluminium compound is introduced into stock which contains at least 50% fibres at pH 4-10, whereafter there is added a known mixture of polymeric silica, obtained by acidifying waterglass, and a polymeric cationic retention agent. It is stated that the polymeric silica used must present a high specific surface area, namely a specific area which exceeds 1050 m.sup.2 /g. The purpose of adding this combination of chemicals is to improve retention and dewatering when manufacturing paper by forming and dewatering a suspension of cellulosic fibres and filler on a forming wire.
The Swedish published specification SE-446 995 (corresponding to Swedish Patent Application No. 7900587-2) teaches a method of precipitating hydratised aluminium-silicate compounds onto fibres. This process is intended to modify the surfaces of inorganic fibres which are mixed with cellulose fibres or other organic fibres, with the intention of improving the bond between the organic and inorganic fibres so that the mechanical strength properties of the composite product will not be impaired. By treating the mixture of suspended inorganic and organic fibres first with aluminium sulphate and then with 0.05-10% by weight alkali silicate at a pH-value of 3-8, silicate is precipitated onto the inorganic fibres, thereby improving their ability to bond to the organic fibres, the resultant material being used to manufacture paper or board having good fire-retarding and dimension-stable properties.
A generally known problem within the field of the manufacture of absorbent materials for use primarily in the production of sanitary articles, such as diapers, incontinence guards etc., is one of achieving optimum absorption rates and liquid dispersion properties the fibre material of the fluff.