Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1997-05-12
2000-07-04
Lipman, Bernard
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
526277, 526287, 526295, 526310, C08L13006
Patent
active
060840455
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, 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 solvation 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.
EP-A-0161762 relates to partially cross-linked copolymers of at least one diallylic quaternary ammonium salt, preferably a diallyldialkylammonium halide. The polymers are prepared by inverse suspension polymerisation with an oil phase as the continuous phase and an aqueous phase as the discontinuous phase. The polymers which are produced directly in salt form are said to be water-swellable polymers whose water absorbtion properties are not significantly diminished when used to absorb saline solutions. However, the specific example in EP-A-0161762 relates to a material which has, on the basis of the results reported in the specification, a water absorption capacity in 0.9% by weight NaCl solution only about 20% of its absorption capacity in deionised water.
It is an object of the present invention to provide a cationic water absorbent polymer with improved water absorption properties and in particular water absorption properties in respect of saline solution.
According to one aspect, the present invention provides a water-swellable, water-insoluble polymer comprising units derived from a diallylic quaternary ammonium salt monomer, cross-linked by a suitable polyfunctional vinyl compound, characterised in that the polymer has been produce
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Fornasari Giancarlo
Gagliardini Alessandro
Hentz Mary Catherine
Lipman Bernard
Milbrada Edward J.
Roof Carl J.
The Procter & Gamble & Company
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