Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Patent
1997-07-10
1998-07-14
Kight, John
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
536 47, 536 56, 536 84, 536 88, 536106, 536124, C08B 1114, C08B 1510
Patent
active
057806160
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a cationic polymer more particularly a water absorbent polymer of the type commonly referred to as a "superabsorbent".
The substances currently termed "superabsorbents" are typically slightly cross-linked hydrophillic polymers. The polymers may differ in their chemical nature but they share the property of being capable of absorbing and retaining even under moderate pressure amounts of aqueous fluids equivalent to many times their own weight. For example superabsorbents can typically absorb up to 100 times their own weight or even more of distilled water.
Superabsorbents have been suggested for use in many different industrial applications where advantage can be taken of their water absorbing and/or retaining properties and examples include agriculture, the building industry, the production of alkaline batteries and filters. However the primary field of application for superabsorbents is in the production of hygienic and/or sanitary products such as disposable sanitary napkins and disposable diapers either for children or for incontinent adults. In such hygienic and/or sanitary products, superabsorbents are used, generally in combination with cellulose fibres, e.g. cellulose fluff, to absorb body fluids such as menses or urine. However, the absorbent capacity of superabsorbents for body fluids is dramatically lower than for deionised water. It is generally believed that this effect results from the electrolyte content of body fluids and the effect is often referred to as "salt poisoning".
The water absorption and water retention characteristics of superabsorbents are due to the presence in the polymer structure of ionisable functional groups. These groups may be carboxyl groups, a high proportion of which are in the salt form when the polymer is dry but which undergo dissociation and salvation upon contact with water. In the dissociated state, the polymer chain will have a series of functional groups attached to it which groups have the same electric charge and thus repel one another. This leads to expansion of the polymer structure which, in turn, permits further absorption of water molecules although this expansion is subject to the constraints provided by the cross-links in the polymer structure which must be sufficient to prevent dissolution of the polymer. It is assumed that the presence of a significant concentration of electrolytes in the water interferes with dissociation of the functional groups and leads to the "salt poisoning" effect. Although most commercial superabsorbents are anionic, it is equally possible to make cationic superabsorbents with the functional groups being, for example, quaternary ammonium groups. Such materials also need to be in salt form to act as superabsorbents and their performance is also affected by the salt-poisoning effect.
A cationic superabsorbent based on a polysaccharide such as cellulose will have polysaccharide hydroxyl groups reacted with a reagent (a derivatising reagent) which converts these hydroxyl groups into a cationic group, e.g. a quaternary ammonium group. For use as a superabsorbent, particularly in hygienic and/or sanitary products, it is advantageous that the product should be based on fibrous cellulose since this can be combined and processed more easily with cellulose fluff which also has a fibrous character.
WO 92/19652 relates to a fibrous cationic polysaccharide which can be obtained by reacting fibrous polysaccharides such as cellulose with an excess of quaternary ammonium compounds containing at least one group capable of reacting with the polysaccharide hydroxyl groups. Whilst the product of WO 92/19652 shows useful properties as a superabsorbent there is a limit to the absorption properties which can be achieved.
As explained above, the absorption of water by a superabsorbent involves the functional groups attached to the polymer chain and, in principle, the absorption capacity depends on the ratio of functional groups to the remainder of the polymer, i.e. the more functional groups that are introduced the
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Carlucci Giovanni
Fornasari Giancarlo
Torri Giangiacomo
Kight John
Lee Howard C.
Linman E. Kelly
Rasser Jacobus C.
Roof Carl J.
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