Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Ion-exchange polymer or process of preparing
Patent
1997-05-12
1998-09-08
Michl, Paul R.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Ion-exchange polymer or process of preparing
C08J 520
Patent
active
058046054
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an absorbent material, more particularly a material 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, 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 are usually 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.
Attempts have been made to counteract the salt poisoning effect and improve the performance of superabsorbents in absorbing electrolyte containing liquids such as menses and urine. Thus Japanese Patent Application OPI No. 57-45,057 discloses an absorbent which comprises a mixture of a superabsorbent such as a cross-linked polyacrylate with an ion exchange resin in powder or granular form. EP-A-0210756 relates to an absorbent structure comprising a superabsorbent and an anion exchanger, optionally together with a cation exchanger, wherein both ion exchangers are in fibrous form. Combining a superabsorbent with an ion exchanger attempts to alleviate the salt poisoning effect by using the ion exchanger, generally as a combination of both an anion exchanger and a cation exchanger, to reduce the salt content of the liquid. The ion exchanger has no direct effect on the performance of the superabsorbent and it may not be possible to reduce the salt content sufficiently to have the desired effect on the overall absorption capacity of the combination. In addition, besides being expensive, the ion exchanger has no absorbing effect itself and thus acts as a diluent to the superabsorbent.
An object of the present invention is to provide a superabsorbent with improved performance in the presence of electrolyte, for example in the case of menses or urine.
The present invention provides a superabsorbent material which comprises a combination of groups are in free acid form; and are in basic form.
The anionic superabsorbent preferably has from 50 to 100% and more preferably h
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Linman E. Kelly
Michl Paul R.
Rasser Jacobus C.
Roof Carl J.
The Procter & Gamble & Company
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