Apparatus and methods for producing superabsorbent foams

Details Apparatus and methods for producing superabsorbent foams Apparatus and methods for producing superabsorbent foams

1998-09-10

2001-10-30

Cooney, Jr., John M. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C264S045100, C366S243000, C366S244000, C366S276000, C366S279000, C366S341000, C366S342000, C521S050000, C521S050500, C521S084100, C521S149000, C604S358000, C604S369000, C604S370000, C604S372000

Reexamination Certificate

active

06310113

ABSTRACT:

FIELD OF INVENTION
The present invention relates to apparatus and a method for forming porous superabsorbent materials generally and more particularly to apparatus and a method for producing superabsorbent foams.
BACKGROUND OF THE INVENTION
Superabsorbent polymeric materials capable of absorbing large quantities of liquids are known in the art and used in many applications, in particular in sick-care and hygienic products such as wound dressings, diapers, adult incontinence pads, feminine sanitary pads and the like. Prior art methods for producing superabsorbent materials capable of absorbing water are based on the use of highly hydrophilic polymers, such as polyacrylates, polyacrylamides, acrylates and their derivatives, grafted on starch or cellulose. Polymeric molecules are usually crosslinked and form a gel-like three-dimensional network. These methods are described in an article entitled Water-absorbent polymers: a patent survey, published in the Journal of Macromolecular Science, Reviews Macromolecular Chemistry, 1994, C34, 607-662.
The water absorbing capacity (WAC) of water-absorbing polymers can be substantially increased by forming pores (preferably open-cell pores) within the polymer matrix. Prior art methods of making porous polymer matrices are based on foaming the reaction mixture before or during the run of polymerization and/or crosslinking reactions using a blowing agent, such as gases or volatile liquids. A method of making superabsorbent polymer foam having improved absorptive properties is described, for example, in U.S. Pat. Nos. 5,328,935 and 5,338,766 to Vah Phan et at.
Other prior art approaches for forming porous absorbent materials include crosslinking of a multiplicity of precursor particles into an interparticle macroaggregate (U.S. Pat. No. 5,372,766 to Roe), freezing hydrophilic polymers solutions in the form of prenucleated ice sheets with subsequent freeze-drying (PCT publication No. WO 95/05204 to Schonfeldt et al), carrying out polymerization reactions in conditions of a specific type of high internal phase emulsion (U.S. Pat. No. 5,334,621 to Beshouri).
Prior art methods of preparing highly superabsorbent porous materials, also termed herein superabsorbent foams, having high WAC are deficient in some respects. For example, each of the prior art methods can be applied only to polymers of a definite chemical nature. Also, the possibility of fine controlling the parameters of the porous structure are limited, in particular on scaling up these methods for industrial applications.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide apparatus and a method for producing superabsorbent foams applicable to a variety of different polymers.
A further object of the present invention is to provide a superabsorbent foam made of any reaction mixture capable of forming a superabsorbent foam and having high absorption capabilities of fluids comprising of both low and high molecular weight components, such as urine and blood, respectively.
Another object of the present invention is to provide superabsorbent foams made from a wide range of synthetic and/or natural polymers, such as polyacrylates and collagen.
Yet another object of the present invention is to provide a method for forming superabsorbent foams which includes the application of physical forces to a precursor reaction mixture of the polymer foam.
A further object of the present invention is to provide apparatus for forming superabsorbent foams which includes a novel chemical reactor capable of producing the superabsorbent foams of the present invention on an industrial scale.
According to one aspect of the present invention, the suitable chemical reaction mixtures are exposed to steps of physical treatment in a reactor to produce a superabsorbent foam comprising a branched system of interconnecting pores which form a highly porous structure.
According to another aspect of the invention, the foam properties are controlled by applying mechanical waves of controllable frequency, amplitude and wave form. These waves may be periodic waves, such as sinusoidal waves having frequencies from hundreds of Hz to few dozens of KHz i.e., in the sound and near ultrasound range.
According to a further aspect of the present invention, mechanical waves application is used not only during foam formation and solidification but also at further stages of producing the porous superabsorbent foams. For example, by applying wave treatment during compression of dry super absorbent foams in order to get it in the form of thin pliable sheets convenient for practical applications, involves additional breakage of partitions between pores of the porous superabsorbent foam, thus favoring formation of a more extensively branched system of interconnecting pores.
It is yet another object of the present invention to provide apparatus for producing superabsorbent foams operating to expose the entire reaction mixture to the application of mechanical waves.
According to yet another aspect of the present invention, the method for producing porous superabsorbent foams may also include, apart of or instead of mechanical waves application, the alternation of pressure in the reaction volume of the formed reaction mixture by means of introducing into it a blowing agent under alternating pressure values.
According to the present invention, the application of mechanical waves is not limited to any class of compounds which form the polymeric foam through different mechanisms (e.g., polymerization, gelling, cross-linking, sintering).
There is thus provided, in accordance with a preferred embodiment of the present invention, a method for producing a superabsorbent foam including forming a reaction mixture comprising at least one compound capable of forming a superabsorbent foam, stirring the reaction mixture, applying mechanical waves to the reaction mixture and repeating the stirring and applying a selected number of times thereby forming the superabsorbent foam.
Furthermore, in accordance with a preferred embodiment of the present invention, the compound is collagen.
Furthermore, in accordance with another preferred embodiment of the present invention, the superabsorbent foam has a high absorption capacity to protein solutions.
Furthermore, in accordance with yet another preferred embodiment of the present invention, the reaction mixture includes a natural polymer.
Furthermore, in accordance with still another preferred embodiment of the present invention, the reaction mixture includes a synthetic polymer.
Furthermore, in accordance with an additional preferred embodiment of the present invention, the reaction mixture the compound is a monomer capable of being polymerized.
Yet further, in accordance with an additional preferred embodiment of the present invention, the compound is acrylic acid.
Furthermore, in accordance with a preferred embodiment of the present invention, applying mechanical waves includes sonicating and the waves are ultrasonic waves. Additionally, it includes sonicating the reaction mixture and the additional mechanical and ultrasonic wave treatments.
Furthermore, in accordance with another preferred embodiment of the present invention, the method further includes alternating the pressure of the reaction mixture during the step of repeating and applying additional mechanical waves to the formed superabsorbent foam thereby increasing its absorbing capacity.
Furthermore, in accordance with a preferred embodiment of the present invention, the method further includes compressing the superabsorbent foam, thereby increasing its absorbing capacity and reducing its volume.
Furthermore, in accordance with a preferred embodiment of the present invention, alternating includes employing a blowing agent under alternating pressure values.
Furthermore, in accordance with a preferred embodiment of the present invention, the method further includes drying the superabsorbent foam and sonicating the dry superabsorbent foam thereby increasing its absorbing capacity.
Furthermore, in accordance with yet another preferr

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