Process for preparing emulsions that are polymerizable to absorbent foam materials

What is claimed is:

1. A continuous process for the preparation of a high internal phase emulsion which is suitable for subsequent polymerization and dewatering to thereby form an absorbent foam material, which process comprises:

A) providing a liquid feed stream of an oil phase comprising

i) from about 3% to 41% by weight of a substantially water-insoluble, monofunctional glassy monomer component;

ii) from about 27% to 73% by weight of a substantially water-insoluble, monofunctional rubbery comonomer component;

iii) from about 8% to 30% by weight of a substantially water-insoluble, polyfunctional cross-linking agent component, and

iv) from about 2% to 33% by weight of an emulsifier component which is soluble in the oil phase and which is suitable for forming a stable water-in-oil emulsion;

B) providing a liquid feed stream of a water phase comprising an aqueous solution containing from about 0.2% to 40% by weight of water-soluble electrolyte;

C) simultaneously introducing said liquid feed streams into a dynamic mixing zone at flow rates such the the initial weight ratio of water phase to oil phase being introduced ranges from about 2:1 to 10:1;

D) subjecting the combined feed streams in said dynamic mixing zone to sufficient shear agitation to at least partially form an emulsified mixture in said zone while maintaining steady, non-pulsating flow rates for the oil and water phase stream;

E) steadily increasing the ratio of water to oil feed streams being introduced into said dynamic mixing zone to within the range of from about 12:1 to 100:1 at a rate of increase which does not destroy the emulsified nature of the contents of said dynamic mixing zone, while maintaining the emulsified contents of said dynamic mixing zone at a temperature of from about 25.degree. C. to 70.degree. C., and while subjecting the emulsified contents of said zone to continued shear agitation which is sufficient to eventually form a high internal phase emulsion that, upon subsequent polymerization, provides a foam having an average cell size of from about 5 to 100 microns;

F) continuously withdrawing the emulsified contents of said dynamic mixing zone and continuously introducing said emulsified contents into a static mixing zone wherein said emulsified contents are further subjected to sufficient shear mixing to thereby completely form a stable high internal phase emulsion having a water to oil phase weight ratio of from about 12:1 to 100:1; and

G) continuously withdrawing said stable high internal phase emulsion from said static mixing zone such that said stable high internal phase emulsion can be thereafter polymerized and dewatered to form a solid absorbent foam.

2. A process according to claim 1 wherein:

A) the glassy monomer component comprises from about 7% to 40% by weight of the oil phase;

B) the rubbery comonomer component comprises from about 27% to 66% by weight of the oil phase;

C) the cross-linking agent component comprises from about 10% to 25% by weight of the oil phase;

D) the emulsifier component comprises from about 4% to 25% by weight of the oil phase; and

E) the water phase comprises an aqueous solution containing from about 0.05% to 20% by weight of the electrolyte.

3. A process according to claim 2 wherein:

A) the initial weight ratio of the water phase to oil phase introduced into the dynamic mixing zone ranges from about 2.5:1 to 5:1;

B) the weight ratio of the water phase to oil phase introduced into the dynamic mixing zone is increased to within the rage of from about 20:1 to 70:1; and

C) the water to oil phase weight ratio of the stable high internal phase emulsion formed in the static mixing zone ranges from about 20:1 to 70:1.

4. A process according to claim 3 wherein:

A) the temperature of the emulsified contents of the dynamic mixing zone is maintained within the range of from about 35.degree. to 65.degree. C.; and

B) shear agitation is imparted to the emulsified contents of the dynamic mixing zone to the extent which is sufficient to eventually form a high internal phase emulsion that, upon subsequent polymerization, provides a foam having an average cell size of from about 10 to 90 microns.

5. A process according to claim 4 wherein:

A) the substantially water-insoluble, monofunctional glassy monomer component of the oil phase comprises one or more styrene-based monomer types;

B) the substantially water-insoluble, monofunctional rubbery comonomer component of the oil phase comprises comonomer types selected from butylacrylate, 2-ethylhexylacrylate, butadiene, isoprene and combinations of these comonomer types;

C) the substantially water-insoluble cross-linking agent component of the oil phase comprises a difunctional monomer type selected from divinylbenzene, divinyltolulene, diallylphthalate, one or more diacrylic acid esters of a polyol or combinations of such difunctional monomer types; and

D) the emulsifier component of the oil phase comprises an emulsifier selected from sorbitan fatty acid esters, polyglycerol fatty acid esters, polyoxyethylene fatty acids and esters and combinations of such emulsifiers.

6. A process according to claim 5 wherein:

A) the molar ratio of monofunctional glassy monomer component to monofunctional rubbery comonomer component in the oil phase ranges from about 1:25 to 1.5:1; and

B) the cross-linking agent component is present in a concentration ranging from about 5 to 60 mole percent, based on total monomers present in the oil phase.

7. A process according to claim 5 wherein:

A) the water-soluble electrolyte in the water phase comprises one or more water-soluble salts of an alkali metal or alkaline earth metal; and

B) the water phase additionally comprises from about 0.02% to 0.4% by weight of a water-soluble, free radical polymerization initiator.

8. A process according to claim 7 wherein shear agitation of from about 1000 to 7000 sec..sup.-1 is imparted to the combined water and oil phase feed streams in the dynamic mixing zone.

9. A process according to claim 8 wherein shear agitation is imparted to the emulsified contents of the dynamic mixing zone by means of a pin impeller.

10. A process according to claim 9 wherein the shear agitation imparted to the emulsified contents of the static mixing zone ranges from about 100 to 7000 sec..sup.-1.

11. A process according to claim 9 wherein the water phase liquid feed stream is initially fed to the dynamic mixing zone at the pilot plant scale flow rate of from about 0.04 to 2.0 liters/minute and the oil phase liquid feed stream is initially fed to the dynamic mixing zone at the pilot plant scale flow rate of from about 0.02 to 0.2 liter/minute.

12. A process according to claim 11 wherein, after the water to oil phase ration has been increased, the effluent from the dynamic mixing zone is withdrawn at the pilot plant scale flow rate of from about 0.8 to 2.2 liters/minute.

13. A process according to claim 9 wherein the water phase liquid feed stream is initially fed to the dynamic mixing zone at the commercial scale flow rate of from about 25 to 250 liters/minute and the oil phase liquid feed stream is initially fed to the dynamic mixing zone at the commercial scale flow rate of from about 10 to 25 liters/minute.

14. A process according to claim 13 wherein, after the water to oil phase ratio has been increased, the effluent from the dynamic mixing zone is withdrawn at the commercial scale flow rate of from about 35 to 800 liters/minute.

15. A continuous process for the preparation of a high internal phase emulsion which is suitable for subsequent polymerization and dewatering to form an absorbent foam material, which process comprises:

A) providing a liquid feed stream of an oil phase comprising

i) from about 7% to 40% by weight of a styrene monomer component;

ii) from about 27% to 66% by weight of a comonomer component selected from butylacrylate, 2-ethylhexylacrylate, isoprene, and combinations of these comonomers;

iii) from about 10% to 25% by weight of a divinylbenzene cross-linking agent component, and

iv) from about 4% to 25% by weight of an emulsifier component selected from sorbitan monooleate and a mixture of sorbitan monooleate and sorbitan trioleate in a monooleate to trioleate weight ratio of from about 2:1 to 5:1;

B) providing a liquid feed stream of a water phase comprising an aqueous solution containing from about 0.5% to 20% by weight of calcium chloride and from about 0.1% to 0.2% by weight of a water-soluble, free radical polymerization initiator;

C) simultaneously introducing said liquid feed streams into a dynamic mixing zone at flow rates such that the initial weight ratio of water phase to oil phase being introduced ranges from about 2.5:1 to 5:1;

D) subjecting the combined feed streams in said dynamic mixing zone to shear agitation of from about 1500 to 3000 sec..sup.-1 for a period of time sufficient to at least partially form an emulsified mixture in said zone while maintaining steady, non-pulsating flow rates for the oil and water phase streams;

E) steadily increasing the ratio of water to oil feed streams being introduced into said dynamic mixing zone to within the range of from about 20:1 to 70:1 at a rate of increase which does not destroy the emulsified nature of the contents of said dynamic mixing zone, while maintaining the emulsified contents of said dynamic mixing zone at a temperature of from 35.degree. C. to 65.degree. C., and while subjecting the emulsified contents of said zone to continued shear agitation of from about 1500 to 3000 sec..sup.-1 for a period of time which is sufficient to form a high internal phase emulsion that, upon subsequent polymerization, provides a foam having an average cell size of from about 10 to 90 microns;

F) continuously withdrawing the emulsified contents of said dynamic mixing zone and continuously introducing said emulsified contents into a static mixing zone wherein said emulsified contents are further subjected to sufficient shear mixing to thereby completely form a stable high internal phase emulsion having a water to oil phase weight ratio of from about 20:1 to 70:1; and

G) continuously withdrawing said stable high internal phase emulsion from said static mixing zone such that said stable high internal phase emulsion can be thereafter polymerized and dewatered to form a solid absorbent foam.

Description Submit all comments and votes

FIELD OF THE INVENTION

This invention relates to a continuous process for preparing certain high internal phase water-in-oil emulsions. Such emulsions contain particular types of monomeric materials dissolved in the oil phase of the emulsion such that, when the emulsions are subjected to polymerization conditions, especially useful polymeric foam structures are realized. The specific emulsions which are prepared by the process herein are those which, when polymerized, provide foam structures that find particular utility for absorbing aqueous body fluids. These foams are thus suitable for use in absorbent products such as diapers and other incontinence management products.

BACKGROUND OF THE INVENTION

Water-in-oil emulsions having a relatively high ratio of water phase to oil phase are known in the art as high internal phase emulsions ("HIPEs" or "HIPE" emulsions). Continuous processes for preparing HIPE emulsions are disclosed, for example, in Lissant; U.S. Pat. No. 3,565,817; Issued Feb. 23, 1971 and Bradley et al; British Patent Application 2194166A; Published Mar. 2, 1988.

HIPE emulsions which contain polymerizable comonomers in their external oil phase have been made and polymerized in order to study the geometric configuration of the oil and water phases of such emulsions. For example, Lissant and Mahan, "A Study of Medium and High Internal Phase Ratio Waver/Polymer Emulsions," Journal of Colloid and Interface Science, Vol. 42, No. 1, January, 1973, pp. 201-208 discloses the preparation of water-in-oil emulsions which contain 90% internal water phase and which utilize styrene monomer in the oil phase. Such emulsions are prepared by subjecting the combined oil and water phases to agitation using an emulsifier and are subsequently polymerized to form a rigid porous structures having a cellular configuration determined by the phase relationship of its emulsion precursor.

Preparation of HIPE emulsions suitable for polymerization to porous structures, e.g., foams, useful for carrying and/or absorbing liquids are also known. For example, Barby et al, U.S. Pat. No. 4,797,310, Issued Jan. 10, 1989; Jones et al, U.S. Pat. No. 4,612,334; Iissued Sep. 16, 1986; Haq et al, U.S. Pat. No. 4,606,958, Issued Apr. 19, 1986; and Barby et al, U.S. Pat. No. 4,533,953, Issued Jun. 11, 1989 all disclose porous polymeric materials which can be prepared from HIPE emulsions and which are useful for delivering liquids such as cleaning solutions to hard surfaces via products such as wipers and cleaning cloths.

The prior art has also recognized that the nature and characteristics of the porous polymeric foam materials formed by polymerizing HIPE emulsions is very much dependent on both the type of components which makeup the polymerizable HIPE emulsion and the process conditions used to form the emulsion. For example, Unilever, European Patent Application No. 60138, Published Sep. 15, 1982 discloses a process for preparing absorbent porous polymers (i.e., foams) from high internal phase emulsions comprising at least 90% by weight of water with the oil phase containing polymerizable monomers, surfactant and a polymerization catalyst. Edwards et al, U.S. Pat. No. 4,788,225, Issued Nov. 29, 1988 discloses the preparation of porous polymer materials which are rendered elastic by selecting certain monomer types (styrene, alkyl(meth)acrylates, crosslinker) and by using certain processing conditions to control the cell size of the eventually resulting porous polymer. Unilever, European Patent Application EP-A-299,762, Published Jan. 18, 1989 discloses that the use of an electrolyte in the water phase of polymerizable HIPE emulsions can affect the size of the openings between cells of the eventually resulting porous polymeric foam material.

Notwithstanding the fact that the existence and synthesis of polymerizable HIPE emulsions is known in the art, preparation of HIPE emulsions suitable for polymerization to useful absorbent foam material is not without its difficulties. Such HIPE emulsions, and especially HIPE emulsions having a very high ratio of water phase to oil phase, tend to be unstable. Very slight variations in monomer/crosslinker content in the emulsion, emulsifier selection, emulsion component concentrations, and temperature and/or agitation conditions can cause such emulsions to "break" or to separate to at least some degree into their distinct water and oil phases. Even if stable emulsions can be realized, alterations in emulsion composition and processing conditions can significantly affect the properties and characteristics of the eventually realized polymeric foam materials, thereby rendering such foam materials either more or less useful for their intended purpose. Such HIPE emulsion preparation difficulties can become even more troublesome when there is a need to produce polymerizable emulsions via a continuous process on an industrial or pilot plant scale in order to provide commercially useful or developmental quantities of polymeric absorbent foam materials.

Given the foregoing considerations, it is an object of the present invention to provide a process for preparing certain types of high internal phase emulsions that can be polymerized to form foam materials especially useful as an absorbent for aqueous body fluids, i.e., foams which are useful in absorbent product such as diapers.

It is a further object of the present invention to provide such a HIPE emulsion preparation process which can be carried out on a continuous basis.

It is a further object of the present invention to provide such a continuous HIPE emulsion preparation process which can be operated on a commercially meaningful scale.

SUMMARY OF THE INVENTION

The present invention provides a continuous process for the preparation of certain types of high internal phase emulsions that are themselves suitable for subsequent polymerization into absorbent foam materials. This process comprises the steps of:

Providing separate water phase and oil phase liquid feed streams as hereinafter defined;

Simultaneously introducing these liquid feed streams into a dynamic mixing zone at flow rate such that the water to oil weight ratio of liquid introduced ranges from about 2:1 to 10:1;

Subjecting the combined water and oil phase feed streams to sufficient shear agitation in the dynamic mixing zone to at least partially form an emulsified mixture therein while maintaining steady, non-pulsating flow rates for the oil and water phase streams;

Steadily increasing the water to oil weight ratio of the feed streams fed to the dynamic mixing zone to a value of from about 12:1 to 100:1 at a rate of increase that does not break the emulsion in the dynamic mixing zone, while maintaining certain conditions in the dynamic mixing zone as hereinafter described;

Continuously withdrawing emulsified contents of the dynamic mixing zone and continuously feeding these contents into a static mixing zone wherein they are subjected to additional shear agitation suitable for forming a stable high internal phase emulsion having a water-to-oil ratio of from about 12:1 to 100:1; and

Continuous withdrawing the stable high internal phase emulsion from the static mixing zone so that it can be polymerized into a solid absorbent foam material.

In such a process, the liquid feed stream of the oil phase comprises from about 3 to 41 weight percent of a substantially water-insoluble, monofunctional glassy monomer component; from about 27 to 73 weight percent of a substantially water-insoluble, monofunctional rubbery comonomer component; from about 8 to 30 weight percent of a substantially water-insoluble, polyfunctional cross-linking agent component and from about 2 to 33 weight percent of an emulsifier component which is soluble in the oil phase and which is suitable for forming a stable water-in-oil emulsion. The liquid feed stream of the water phase comprises an aqueous solution containing from about 0.2% to 40% by weight of a water-soluble electrolyte.

As and after the water to oil weight ratio is increased by altering the rates at which the feed streams are introduced into the dynamic mixing zone, the emulsified contents of the dynamic mixing zone are maintained at a temperature of from about 25.degree. C. to 70.degree. C. Furthermore, the emulsified contents of the dynamic mixing zone are also subjected to continued shear agitation which is sufficient to eventually form a high internal phase emulsion that, upon subsequent polymerization, provides a foam material having an average cell size of from about 5 to 100 microns. The absorbent foams formed by polymerizing the emulsion prepared by the process herein will have these average cell size characteristics and will be especially suitable for use in absorbing aqueous body fluids.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 of the drawings is a photomicrograph of the interstices of a polymerized HIPE emulsion of the type produced by the process of the present invention.

FIG. 2 of the drawings is a schematic flow diagram showing an arrangement of apparatus and equipment which can be used for carrying out the process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The emulsions which are prepared via the process of the present invention are water-in-oil emulsions having therein a relatively high ratio of water phase to oil phase. As indicated hereinbefore, emulsions of this type which have these relatively high water to oil phase ratios are known in the art as high internal phase emulsions (i.e., "HIPEs" or "HIPE" emulsions). HIPE emulsions having the oil and water phase characteristics of the present invention are suitable for polymerization (and dewatering) into foam materials which are especially useful as absorbents for aqueous body fluids.

Each of the essential steps used to prepare HIPE emulsions of this type via a continuous process is described in detail as follows:

A) Provision of the Oil Phase Feed Stream

The particular oil phase incorporated into the HIPE emulsions prepared by the process of this invention comprises monomers which polymerize to form a solid foam structure when the emulsions made from such an oil phase are eventually subjected to polymerization conditions. The monomers essentially utilized in this oil phase include a principal monomer component, a comonomer component and a cross-linking agent component. Selection of particular types and amounts of monofunctional principal monomer(s) and comonomer(s) and polyfunctional cross-linking agent(s) can be important to the realization of absorbent HIPE-based foam materials having the desired combination of properties which render such foam materials suitable for use as absorbents for body fluids.

The principal monofunctional monomer component utilized in the oil phase used to prepare the HIPE emulsions herein comprises one or more monomers that tend to impart glass-like properties to the eventually resulting foam structure. Such monomers are hereinafter referred to as "glassy" monomers, and are, for purposes of this invention, defined as monomeric materials which would produce high molecular weight (greater than 6000) homopolymers having a glass transition temperature, T.sub.g, above about 40.degree. C. The preferred monofunctional glassy monomer type is a styrene-based monomer with styrene itself being the most preferred monomer of this kind. Substituted, e.g., monosubstituted, styrene such as p-methylstyrene may also be employed. The monofunctional glassy monomer component will normally comprise from about 3% to 41%, more preferably from about 7% to 40% by weight of the oil phase used to form the HIPE emulsions herein.

Along with the principal glassy monomer material, a monofunctional comonomer component will also be present in the oil phase used in the instant HIPE emulsion preparation process. Such a monofunctional comonomer component comprises one or more comonomers which tend to impart rubber-like properties to the foams which eventually result from the polymerization of the emulsions prepared herein. Such comonomers are hereinafter referred to as "rubery" comonomers and are, for purposes of this invention, defined as monomeric materials which would produce high molecular weight (greater than 10,000) homopolymers having a glass transition temperature, T.sub.g, of about 40.degree. C. or lower. Monofunctional rubbery comonomers of this type include, for example, alkylacrylates, alkylmethacrylates, allylacrylate, butadiene, substituted butadienes, vinylidine halides and combinations of such comonomers and comonomer types. Preferred rubbery comonomers include butylacrylate, 2-ethylhexylacrylate, butadiene, isoprene and combinations of these comonomers. Of all of these species, butylacrylate and 2-ethylhexylacrylate are the most preferred. The monofunctional rubbery comonomer component will generally comprise from about 27% to 73%, more preferably from about 27% to 66%, by weight of the oil phase used to form the HIPE emulsions herein.

Within the oil phase used to prepare the HIPE emulsions herein, both the monofunctional glassy principal monomer(s) and the monofunctional rubbery comonomer(s) must be present within the hereinbefore recited concentration ranges. In addition, the molar ratio of monofunctional glassy monomer component to the monofunctional rubbery component in the oil phase will generally range from about 1:25 to 1.5:1, more preferably from about 1:9 to 1.5:1.

Since the polymer chains formed from the glassy monomer(s) and the rubbery comonomer(s) are to be cross-linked when the emulsions prepared herein are subsequently polymerized, the oil phase must also contain a polyfunctional cross-linking agent. As with the monofunctional monomers and comonomers, selection of a particular type and amount of cross-linking agent can be very important to the eventual realization of HIPE emulsions which are polymerizable to foams having the desired combination of structural, mechanical, and fluid-absorbing properties.

Depending upon the type and amounts of monofunctional monomers and comonomers utilized, and depending further upon the desired characteristics of the eventually realized polymeric foams, the polyfunctional cross-linking agent component for use in the oil phase can be selected from a wide variety of polyfunctional, preferably difunctional, monomers. Thus, the cross-linking agent may be a divinyl aromatic material such as divinylbenzene, divinyltolulene or diallylphthalate. Alternatively, divinyl aliphatic cross-linkers such as any of the diacrylic acid esters of polyols can be utilized. The cross-linking agent found to be suitable for preparing the most acceptable foam-forming HIPE emulsions herein is divinylbenzene.

The cross-linking agent of whatever type will generally be employed in the oil phase used in the emulsion-forming process herein in an amount of from about 8% to 40%, more preferably from about 10% to 25%, by weight. Amounts of cross-linking agent(s) within such ranges will generally provides a cross-linker molar concentration of from about 5 mole percent to about 60 mole percent, based on total monomers present in the oil phase.

The major portion of the oil phase used to prepare the HIPE emulsions herein will comprise the aforementioned monomers, comonomers and cross-linking agents which eventually form the polymeric foam absorbents. It is therefore essential that these monomers, comonomers and cross-linking agents be substantially water-insoluble so that they are primarily soluble in the oil phase and not the water phase of the emulsions herein. Use of such substantially water-insoluble monomer materials ensures that HIPE emulsions of appropriate characteristics and stability will be realized.

It is, of course, preferred that the monomers, comonomers and cross-linking agents used to form the foam precursor emulsions herein be of the type such that the eventually formed foam polymer is suitably non-toxic and sufficiently chemically stable. Thus such monomers, comonomers and cross-linking agent should preferably have little or no toxicity in the very low residual concentrations wherein they may be encountered during post-polymerization foam processing and/or use.

Another essential component of the oil phase used to form the HIPE emulsions in accordance with the present invention comprises an emulsifier which permits formation of stable HIPE emulsions. Such emulsifiers are those which are soluble in the oil phase used to form the emulsion. Emulsifiers utilized may be nonionic, cationic, anionic or amphoteric provided the emulsifier or combination of emulsifiers will form a stable HIPE emulsion. Preferred types of emulsifiers which can be used to provide an emulsifier component having suitable characteristics include the sorbitan fatty acid esters, polyglycerol fatty acid esters, polyoxyethylene (POE) fatty acids and esters. Especially preferred are the sorbitan fatty acid esters such as sorbitan monolaurate (SPAN.RTM. 20), sorbitan monooleate (SPAN.RTM. 80) and combinations of sorbitan trioleate (SPAN.RTM. 85) and sorbitan monooleate (SPAN.RTM. 80). One such particularly preferred emulsifier combination comprises the combination of sorbitan monooleate and sorbitan trioleate in a weight ratio greater than or equal to about 3.1, more preferably about 4:1. Other operable emulsifiers include TRIODAN.RTM. 20 which is a commercially available polyglycerol ester marked by Grindsted and EMSORB 2502 which is a sorbitan sesquioleate marketed by Henkel.

The emulsifier component will generally comprise from about 2% to 33% by weight of the oil phase used to form the HIPE emulsions herein which in turn are used to prepare polymeric absorbent foams. More preferably, the emulsifier component will comprise from about 4% to 25% by weight of the oil phase.

In addition to the monomeric and emulsifier components hereinbefore described, the oil phase used to form polymerizable HIPE emulsions herein may also contain additional optional components. One such optional oil phase component may be an oil soluble polymerization initiator of the general type hereinafter described. Another possible optional component of the oil phase may be a substantially water insoluble solvent or carrier for the oil phase monomer, cross-linker and/or emulsifier components. A solvent or carrier of this type must, of course, not be capable of dissolving the eventually polymerized monomers. Use of such a solvent is not preferred, but if such a solvent or carrier is employed, it will generally comprise no more than about 10% by weight of the oil phase.

The oil phase, as hereinbefore described, may itself be prepared in any suitable manner by combining the essential and optional components using conventional techniques. Such a combination of components may be carried out in either continuous or batch-wise fashion using any appropriate order of component addition. The oil phase so prepared will generally be formed and stored in a feed tank, from which tank the oil phase can be provided in a liquid feed stream of any desired flow rate as hereinafter described.

B) Provision of the Water Phase Feed Stream

As indicated, an oil phase as hereinbefore described is the continuous external phase in the HIPE emulsions to be polymerized to realize absorbent foams. The discontinuous internal phase of such polymerizable HIPE emulsions is a water phase which will generally be an aqueous solution containing one or more dissolved components. Like the oil phase, the water phase used to form the HIPE emulsions herein will be fed to the process as a separate stream.

One essential dissolved component of the water phase is a water-soluble electrolyte. The dissolved electrolyte in the water phase used to form the HIPE emulsions herein serves to minimize the tendency of monomers and crosslinkers which are primarily oil soluble to also dissolve in the water phase. This, in turn, can minimize the extent to which, during subsequent polymerization of the emulsion, polymeric material fills the cell windows at the oil/water intefaces formed by the water phase bubbles. Thus the presence of electrolyte and the resulting ionic strength of the water phase can determine whether and to what degree the eventually resulting polymeric foams may be open-celled.

Any electrolyte which provides ionic species to impart ionic strength to the water phase may be used. Preferred electrolytes are mono-, di-, or tri-valent inorganics salts such as the water-soluble halides (e.g., chlorides), nitrates and sulfates of alkali metals and alkaline earth metals. Examples include sodium chloride, calcium chloride, sodium sulfate and magnesium sulfate. Calcium chloride is the most preferred electrolyte for use in the water phase.

Generally electrolyte will be present in the water phase used herein to form the HIPE emulsions in a concentration which ranges from about 0.2% to about 40% by weight of the water phase. More preferably, the electrolyte will comprise from about 0.5% to 20% by weigh of the water phase.

The HIPE emulsions formed via the process herein will, in addition to the essential oil and water phase components hereinbefore described, also typically contain a polymerization initiator. Such an initiator component will generally be added to the water phase used to form the HIPE emulsions and can be any conventional water-soluble free radical initiator. Materials of this type include peroxygen compounds such as sodium, potassium and ammonium persulfates, caprylyl peroxide, benzoyl peroxide, hydrogen peroxide, cumene hydroperoxides, tertiary butyl diperphthalate, tertiary butyl perbenzoate, sodium peracetate, sodium percarbonate and the like. Conventional redox initiator systems can also be utilized. Such systems are formed by combining the foregoing peroxygen compounds with reducing agents such as sodium bisulfite, L-ascorbic acid or ferrous salts.

The initiator material can comprise up to about 5 mole percent based on the total moles of polymerizable monomers present in the oil phase. More preferably, the initiator comprises from about 0.001 to 0.5 mole percent based on the total moles of polymerizable monomers (i.e., monomers, comonomers, cross-linkers) in the oil phase. When used in the water-phase, such initiator concentrations can be realized by adding initiator to the water phase to the extent of from about 0.02% to 0.4%, more preferably from about 0.1% to 0.2% by weight of the water phase.

As with the oil phase, the water phase, containing the essential and optional components hereinbefore described, may itself be prepared by combining these components in conventional manner. Thus, the water phase may be prepared in either continuous or batch-wise fashion using any appropriate order of addition of water phase components. As with the oil phase, the water phase will generally be prepared and stored in a separate feed tank which is equipped with means for delivering a water phase liquid stream from this tank at any desired flow rate.

C) Initial Introduction of Oil and Water Phase Feed Streams Into the Dynamic Mixing Zone

The liquid streams of both oil and water phases as hereinbefore described are initially combined by simultaneously introducing liquid feed streams of both these phases together into a dynamic mixing zone. This dynamic mixing zone, and the emulsion-forming agitation imparted to the liquid contents thereof, are hereinafter described in greater detail.

During this stage of initial combination of liquid feed streams of the oil and water phases, flow rates of these feed streams are set so that the weight ratio of water phase to oil phase being introduced into the dynamic mixing zone is well below that of the HIPE emulsions which are to be eventually realized. In particular, flow rates of the oil and water phase liquid streams are set such that the water to oil weight ratio during this initial introduction stage ranges from about 2:1 to 10:1, more preferably from about 2.5:1 to 5:1. The purpose of combining the oil and water phase streams at these relatively low water to oil ratios is to permit formation in the dynamic mixing zone of at least some amount of a water-in-oil emulsion which is relatively stable and does not readily "break"