Inverse phase blends and films of poly(ethylene oxide) and polyolefin

A composition comprises a polyolefin, such as polyethylene, as a major constituent and poly(ethylene oxide) as a minor constituent. The composition exhibits an inverse phase morphology so that the poly(ethylene oxide) forms a continuous phase and the polyolefin forms a dispersed or discontinuous phase in the film. Desirably, the polyolefin and the poly(ethylene oxide) are grafted with a polar, vinyl monomer. The composition can be used in disposable personal hygiene articles.

FIELD OF THE INVENTION
 The present invention relates to compositions comprising a blend of
 polyolefin and poly(ethylene oxide) having inverse phase morphology and
 methods of making such inverse phase compositions.
 BACKGROUND OF THE INVENTION
 There are a wide variety of disposable plastic articles of manufacture in
 use today. Because of their low cost and convenience, they are very
 popular and have a high consumer demand. However, many of these articles
 are not degradable or easily disposed of. Consequently, they have caused
 and continue to cause a waste disposal problem.
 Personal care products, such as diapers, sanitary napkins, adult
 incontinence garments, and the like are generally constructed from a
 number of different components and materials. Such articles typically have
 some portion, usually the backing layer, liner, or baffle that is composed
 of a film constructed from a liquid repellent material. This repellent
 material is appropriately constructed to minimize or prevent the exuding
 of the absorbed liquid from the article and to obtain greater utilization
 of the absorbent capacity of the product. The liquid repellent film
 commonly used includes plastic materials such as polyethylene films and
 the like.
 Although such products are relatively inexpensive, sanitary and easy to
 use, disposal of a product once soiled is not without its problems. An
 ideal disposal method for such products would be to use municipal sewage
 treatment and private residential septic systems. Products suited for
 disposal in sewage systems can be flushed down a convenient toilet and are
 termed "flushable." While flushing such articles would be convenient, the
 liquid repellent material which normally does not disintegrate in water
 tends to plug toilets and sewer pipes. It therefore becomes necessary,
 although undesirable, to separate the barrier film material from the
 absorbent article prior to flushing.
 In an attempt to overcome the flushability problem of a water-resistant
 film the prior art has modified the water-resistant polymer. One of the
 more useful ways of modifying polymers involves blending them with other
 polymers of different structures and properties. In a few cases, polymer
 blend combinations are thermodynamically miscible and exhibit mechanical
 compatibility. However, by far a greater number of blends are phase
 separated and generally exhibit poor mechanical compatibility. Phase
 separated blends can in some cases exhibit mechanical compatibility where
 the polymer compositions are similar, for example, polyolefin blended with
 other similar polyolefins, or where interfacial agents are added to
 improve the compatibility at the interface between the constituents of the
 polymer blend.
 Polymer blends of polyolefins and poly(ethylene oxide) are melt processible
 but exhibit very poor mechanical compatibility. This poor mechanical
 compatibility is particularly manifested in blends having greater than 50
 weight percent of polyolefin. Generally the film is not affected by water
 since typically the majority phase, i.e. polyolefin, will surround and
 encapsulate the minority phase, i.e. the poly(ethylene oxide). The
 encapsulation of the poly(ethylene oxide) effectively prevents any
 degradability and/or flushability advantage that would be acquired by
 using poly(ethylene oxide).
 In view of the problems of the prior art, it remains highly desirable to
 provide water-degradable compositions comprising poly(ethylene oxide)
 incorporating greater amounts of lower cost polyolefin(s) while
 maintaining or at least not significantly decreasing the water
 responsiveness of the composition. Advantageously, such compositions can
 be used to manufacture flushable films and flushable fibers at lower cost.
 These films and fibers can be used as components in personal care products
 that are designed to be flushed down conventional toilets. Additionally,
 the unique water related properties of the compositions described herein
 compositions make the compositions desirable for the manufacture of filter
 membranes.
 SUMMARY OF THE INVENTION
 Briefly, the present invention provides for compositions comprising a
 volume of poly(ethylene oxide) and a greater volume of polyolefin relative
 to the volume of poly(ethylene oxide) wherein the compositions exhibit an
 inverse phase morphology. As used herein "inverse phase morphology" means
 that the volumetric majority constituent, which normally would be expected
 to form the continuous phase in the composition, is the dispersed phase
 and the volumetric minority constituent forms the continuous phase in
 which the volumetric majority constituent is dispersed. Inverse phase
 polyolefin and poly(ethylene oxide) compositions are desirable because
 they have improved water responsiveness and water dispersibility compared
 to compositions comprising the same relative amounts of the aforementioned
 polymers that do not have inverse phase morphology described above.
 The compositions of the present invention lose a substantial amount of mass
 when exposed to water. Consequently, films, fibers and articles
 manufactured from the compositions of the present invention exhibit a
 significant decrease in the their mechanical properties when exposed to
 water compared to the dry mechanical properties prior to exposure to
 water. The compositions of the present invention are substantially water
 degradable and may be used to produce flushable films, fibers and
 articles. Significantly, films, fibers and articles can be produced which
 incorporate greater amounts of essentially water-insoluble polyolefins
 relative to amount of water-soluble poly(ethylene oxide) while remaining
 water-degradable and flushable. Thus, flushable articles such as diapers
 and feminine pads can be manufactured with smaller amounts water-soluble
 and water-responsive resins, at lower cost.

DETAILED DESCRIPTION OF THE INVENTION
 Although the present invention is described with reference to a film, one
 skilled in the art would understand the utility of the invention toward
 polymer compositions and to articles that can manufactured using the
 polymer compositions. The compositions of the present invention comprise a
 larger volume of a polyolefin and a lesser volume of a poly(ethylene
 oxide) where the poly(ethylene oxide) comprises the continuous phase and
 the polyolefin comprises the discontinuous phrase. In one embodiment, the
 inverse phase compositions of the present invention comprise a volume
 majority of a polyolefin. As used herein, "volume majority" means greater
 amount by volume. The compositions of the Examples are described by
 reference to weight percentages of the polyolefin component, low density
 polyethylene, and poly(ethylene oxide) component. Due to the greater
 density of the poly(ethylene oxide), about 1.2 g/cm.sup.3, relative to the
 low density polyethylene, about 0.9 to 0.94 g/cm.sup.3, the volume
 percentage of polyolefin incorporated in the compositions of the Examples
 is greater than the weight percentage, e.g. 55 weight percent of low
 density polyethylene is equal to about 60 volume percent of low density
 polyethylene.
 The compositions of the present invention may comprise as little as 51
 percent by volume to as much as 99 percent by volume of a polyolefin and
 any amount of poly(ethylene oxide) as long as there is sufficient amount
 of poly(ethylene oxide) to form a continuous phase around the polyolefin.
 In one embodiment, the compositions of the present invention comprise from
 about 51 volume percent to about 95 weight percent of a polyolefin and
 from about 49 volume percent to about 5 weight percent of poly(ethylene
 oxide) which may be grafted with a vinyl monomer. In another desirable
 embodiment, the compositions of the present invention comprise from about
 60 volume percent to about 85 volume percent of a polyolefin and from
 about 40 volume percent to about 15 volume percent of poly(ethylene oxide)
 grafted with a polar vinyl monomer. Desirably, the polyolefin and the
 poly(ethylene oxide) are grafted with at least one polar vinyl monomer. It
 has unexpectedly been discovered that an inverse phase morphology, where
 the hydrophilic moiety constitutes the continuous phase, can be achieved
 by a minority component in the film to greatly expand the water
 sensitivity and degradability of a film. Desirably, the composition of the
 present invention comprises a blend of from about 60 volume percent to
 about 85 volume percent of a polyolefin, such as polyethylene, and from
 about 40 volume percent to about 15 volume percent of poly(ethylene oxide)
 with an effective amount of monomer grafted onto the polyolefin and
 poly(ethylene oxide) to render the phase inversion.
 Suggested polyolefins useful for the practice of the invention include, but
 are not limited to, various thermoplastic polyethylenes, polypropylenes,
 polypropylenes and saturated ethylene polymers. Suggested saturated
 ethylene polymers useful in the practice of this invention are
 homopolymers or copolymers of ethylene and are essentially linear in
 structure. As used herein, the term "saturated" refers to polymers that
 are fully saturated, but also includes polymers containing up to about
 percent unsaturation. Homopolymers of ethylene include, but are not
 limited to, those prepared under either low pressure, i.e., linear low
 density or high density polyethylene, or high pressure, i.e., branched or
 low density polyethylene. High-density polyethylenes are generally
 characterized by a density that is about equal to or greater than 0.94
 grams per cubic centimeter (g/cc). Generally, high-density polyethylenes
 useful as the base resin in the present invention have a density ranging
 from about 0.94 g/cc to about 0.97 g/cc. The polyolefin can have a melt
 index, as measured at 2.16 kg and 190.degree. C., ranging from about 0.005
 decigrams per minute (dg/min) to 100 dg/min. Desirably, the polyolefin has
 a melt index of 0.01 dg/min to about 50 dg/min and more desirably of 0.05
 dg/min to about 25 dg/min. Alternatively, mixtures of polyolefins,
 particularly polyethylenes can be used as the base polyolefin resin in
 producing the graft copolymer compositions of the present invention, and
 such mixtures should have a melt index greater than 0.005 dg/min to less
 than about 100 dg/min.
 The low density polyethylene used as the polyolefin component in the
 following examples has a density of less than 0.94 g/cc and are usually in
 the range of 0.91 g/cc to about 0.93 g/cc. The low-density polyethylene
 has a melt index ranging from about 0.05 dg/min to about 100 dg/min and
 desirably from 0.05 dg/min to about 20 dg/min. Ultra low-density
 polyethylene can be used in accordance with the present invention.
 Generally, ultra low-density polyethylene has a density of less than 0.90
 g/cc.
 The above polyolefins can also be manufactured by using the well known
 multiple-site Ziegler-Natta catalysts or the more recent single-site
 metallocene catalysts. The metallocene catalyzed polyolefins have better
 controlled polymer microstructures than polyolefins manufactured using
 Ziegler-Natta catalysts, including narrower molecular weight distribution,
 well controlled chemical composition distribution, co-monomer sequence
 length distribution, and stereoregularity. Metallocene catalysts are known
 to polymerize propylene into atactic, isotactic, syndiotactic,
 isotactic-atactic stereoblock copolymer. Desirably, the polyolefin
 component of the compositions of the present invention is thermoplastic in
 order to facilitate the production of the compositions of the invention
 and to facilitate the processing of the compositions into articles,
 particularly, films.
 Copolymers of ethylene which can be useful in the present invention may
 include, but are not limited to, copolymers of ethylene with one or more
 additional polymerizable, unsaturated monomers. Examples of such
 copolymers include, but are not limited to, copolymers of ethylene and
 alpha olefins (such as propylene, butene, hexene or octene) including
 linear low density polyethylene, copolymers of ethylene and vinyl esters
 of linear or branched carboxylic acids having 1-24 carbon atoms such as
 ethylene-vinyl acetate copolymers, and copolymers of ethylene and acrylic
 or methacrylic esters of linear, branched or cyclic alkanols having 1-28
 carbon atoms. Examples of these latter copolymers include ethylene-alkyl
 (meth)acrylate copolymers, such as ethylene-methyl acrylate copolymers.
 Poly(ethylene oxide) polymers suitable for the present invention include
 homopolymers and copolymers of ethylene oxide that are water soluble. The
 poly(ethylene oxide) component of the present invention can have molecular
 weights ranging from about 50,000 to about 8,000,000 grams per mol and,
 desirably, can range from about 100,000 to about 8,000,000 g/mol. More
 desirably, the average molecular weight of the poly(ethylene oxide)
 component of the present invention ranges from about 200,000 to about
 6,000,000 g/mol. When the poly(ethylene oxide) component of the
 compositions of the present invention has a average molecular weight of
 less than 200,000 g/mol, the addition of the monomer and subsequent
 grafting of the monomer is not needed to get the desired phase inversion.
 In Example 4 below, the an inverse phase composition of poly(ethylene
 oxide) and polyolefin was achieved by melt blending 60 weight percent of a
 low density polyethylene and a 100,000 g/mol poly(ethylene oxide).
 Suggested commercial examples of water-soluble poly(ethylene oxide) are
 available from Union Carbide Corporation under the trade name POLYOX.RTM..
 Typically, poly(ethylene oxide) is a dry free flowing white powder having
 a crystalline melting point in the order of about 65.degree. C., above
 which poly(ethylene oxide) resin becomes thermoplastic and can be formed
 by molding, extrusion and other methods known in the art.
 The polyolefin and poly(ethylene oxide) components of compositions of the
 present invention have grafted thereto an effective amount of polar vinyl
 monomer. Grafting unexpectedly produces compositions and films having an
 inverse phase morphology. A variety of polar vinyl monomers may be useful
 in the practice of this invention. The term "monomer(s)" as used herein
 includes the traditional definition of a monomers as well as macromonomers
 which are oligomers and polymers capable of polymerization. As used herein
 monomers also include mixtures of monomers, oligomers and/or polymers as
 described above and any other reactive chemical species, which is capable
 of covalent bonding with the parent polymer(s). Ethylenically unsaturated
 monomers containing a polar functional group, such as hydroxyl, carboxyl,
 amino, carbonyl, halo, glycidyl, cyano, thiol, sulfonic, sulfonate, etc.
 are appropriate for this invention and are suggested. Desired
 ethylenically unsaturated monomers include acrylates and methacrylates.
 Suggested polar vinyl monomers include, but are not limited to,
 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, poly(ethylene
 glycol) acrylates, poly(ethylene glycol) methacrylates, poly(ethylene
 glycol) diacrylates, acrylic acid, methacrylic acid, maleic anhydride,
 itaconic acid, acrylamide, glycidyl methacrylate, 2-bromoethyl acrylate,
 2-bromoethyl methacrylate, carboxyethyl acrylate, sodium acrylate,
 3-hydroxypropyl methacrylalte, 3-hydroxypropyl acrylate,
 2-chloroacrylonitrile, 4-chlorophenyl acrylate, 2-cyanoethyl acrylate,
 glycidyl acrylate, 4-nitrophenyl acrylate, pentabromophenyl acrylate,
 poly(propylene glycol) acrylates, poly(propylene glycol) methacrylates,
 2-propene-1-sulfonic acid and its sodium salt, 2-sulfoethyl acrylate,
 2-sulfoethyl methacrylate, 3-sulfopropyl acrylate, 3-sulfopropyl
 methacrylate, and derivatives and analogs of the above. Suggested
 derivatives, include, but are not limited to, poly(ethylene glycol) ethyl
 ether acrylates, poly(ethylene glycol) alkyl ether acrylates,
 poly(ethylene glycol) alkyl ether methacrylates, and poly(ethylene glycol)
 ethyl ether methacrylates of various molecular weights.
 Any polar vinyl monomer or a mixture of monomers including a polar vinyl
 monomer or monomers may be added to the reactive mixture of the component
 polymers with or separately from, the polymers during the blending
 process. The addition of a polar vinyl monomer and an initiator to the
 process is desirable when a poly(ethylene oxide) of molecular weight
 greater than about 100,000 grams per mol is used as the volume minority
 component of the inverse phase blend. The polymers and the monomer(s) may
 be added simultaneously. For example, the polymer, the initiator and the
 monomer(s) and may be added together into the hopper of the extruder,
 barrel #1. It is more desirable to add the polymers to the reactive vessel
 first and to melt the polymers before adding either the initiator or
 monomer. Examples of such methods include melting the polymers and then
 injecting a solution comprising initiator and monomer into the molten
 polymers; and adding the initiator and then adding the monomer or mixture
 of monomers to the molten polymers. It is even more desirable to add and
 disperse the monomer(s) in the molten polymers before adding the
 initiator. Thus, it is desired to add the polymers to the extruder first
 and then inject and disperse the monomer(s) in the polymers before adding
 initiator.
 The compositions of the present invention may be by any of several methods.
 For example, the components, the polyolefin, poly(ethylene oxide), monomer
 and initiator can be premixed before heating blending to produce an
 inverse phase composition. Alternatively, the components may be added
 simultaneously or separately to a reaction vessel for melting and
 blending. Desirably, the polyolefin and poly(ethylene oxide) should be
 melt blended before adding monomer or initiator. The monomer and initiator
 may be added to the molten polymers separately or combined in a solution
 comprising the monomer and initiator. In a reactive extrusion process, it
 is desirable to feed the polyolefin and poly(ethylene oxide) into an
 extruder before adding monomer further down the extruder and adding
 initiator even further down the extruder. This sequence facilitates mixing
 of the monomer or mixture of monomers into the polymers before the
 initiator is added and radicals are created.
 One skilled in the art would expect compositions comprising two or more
 dissimilar polymers such as a polyolefin and a water-soluble polymer such
 a poly(ethylene oxide) to form heterogeneous blends of the dissimilar
 polymers where the polymer component comprising the volume majority of the
 blend, greater than 50 volume percent, forms a continuous phase and the
 polymer component comprising the minority of the blend, less than 50
 volume percent, forms the discontinuous or disperse phase of the blend.
 The discontinuous phase is also referred to as the disperse phase because
 it is dispersed in the continuous phase formed by the majority component.
 This is illustrated in FIG. 1. FIG. 1 is a scanning electron microscopic
 (SEM) photomicrograph of a back-scattered electron image of a
 cross-sectional view of a 4 mil (0.004 inch) film of Comparative Example
 A, a blend of 60 weight percent of ungrafted polyethylene, the darker
 phase shown in the photomicrograph, and 40 weight percent of an ungrafted
 poly(ethylene oxide), the lighter phase shown in the photomicrographs. Due
 to the density difference between polyethylene and poly(ethylene oxide),
 the volume percentage of polyethylene in the blend of Comparative Example
 1 is about 67 percent and the volume percentage of poly(ethylene oxide) is
 only about 33 percent. In FIG. 1, it is observed that the volume majority
 component of the blend, the darker polyethylene, forms the continuous
 phase and the volume minority component of the blend, the lighter
 poly(ethylene oxide), forms the discontinuous/disperse phase.
 In contrast, the volume minority component of the compositions of the
 present invention forms a continuous phase and the volume majority
 component forms a discontinuous phase. This is illustrated in FIGS. 2-8.
 FIGS. 2-8 include scanning electron microscopic photomicrographs of
 back-scattered electron images of cross-sectional and topographical views
 by secondary electron images of 4 mil films of Examples 1, 2, 3, 11 and
 13. As can be observed from the photomicrographs, the compositions of the
 present invention comprise a volume majority of a polyolefin and a volume
 minority of polytethylene oxide) yet exhibit inverse phase morphology.
 Specifically, poly(ethylene oxide) which is the minority component of the
 compositions of the Examples appears as the lighter phase in the
 photomicrographs is the continuous phase even though the poly(ethylene
 oxide) is the volume minority component of the compositions and comprises
 less than half of the volume of the compositions of the present invention.
 The majority component, the darker polyolefin phase, is discontinuous and
 forms the disperse phase in the compositions of the present invention.
 Thus, compositions and films of the present invention have a poly(ethylene
 oxide) as the continuous phase and a polyolefin as the discontinuous phase
 notwithstanding that there is a significantly greater amount of
 polyolefin. For example, many of the inverse phase compositions
 demonstrated herein have a volume ratio of polyolefin to poly(ethylene
 oxide) of about 2 to 1.
 The amount of polar vinyl monomer grafted onto the polyolefin and
 poly(ethylene oxide) can vary and may range from a total of from about 0.1
 weight percent to about 30 weight percent, based on the sum of the weight
 of the polyolefin and the poly(ethylene oxide). Desirably, the polyolefin
 and poly(ethylene oxide) have a total of from about 1 weight percent to
 about 20 weight percent of monomer grafted there to. More desirably, the
 polyolefin and poly(ethylene oxide) have a total of from about 1 weight
 percent to about 10 weight percent of monomer grafted thereto. It is
 believed that the polar groups of the grafted polar vinyl monomer reduce
 the interfacial tension between the poly(ethylene oxide) phase and the
 polyolefin phase. The reduction in interfacial tension is believed to
 stabilize the polyolefin phase and allow the polyolefin to exist as the
 dispersed phase in the blend with poly(ethylene oxide).
 To prepare the compositions of the present invention, a polyolefin and a
 poly(ethylene oxide) are reacted with a monomer in the presence of a free
 radical initiator. The initiator serves to initiate free radical grafting
 of the monomer onto the polyolefin and poly(ethylene oxide). One method of
 grafting the polymer blends includes melt blending the desired volume or
 weight ratio of a mixture of the polyolefin and a poly(ethylene oxide) and
 adding a monomer and a free radical initiator in an extruder and at a
 reaction temperature where the polyolefin and poly(ethylene oxide) are
 converted to a molten state. Accordingly, a preferred method includes
 adding the polyolefin, poly(ethylene oxide), monomer and free radical
 initiator simultaneously to the extruder before the polymer constituents,
 i.e., the polyolefin and poly(ethylene oxide) have been melted. Desirably,
 the melt extruder used for melt blending can introduce various
 constituents into the blend at different locations along the screw length.
 For example, a polar vinyl monomer and initiator can be injected into the
 blend before or after one or more of the polymer constituents is melted or
 thoroughly mixed. More preferably, a polyolefin and poly(ethylene oxide)
 are added at the beginning of the extruder and polar vinyl monomer is
 added to melted polymers further down the extruder barrel, a free radical
 initiator is also fed to the melt blend. Methods of making blends are
 described in U.S. patent application Ser. No. 08/777,226 filed on Dec. 31,
 1996 and entitled "BLENDS OF POLYOLEFIN AND POLY(ETHYLENE OXIDE) AND
 PROCESS FOR MAKING THE BLENDS", now U.S. Pat. No. 5,700,872, the entire
 disclosure of which is incorporated herein by reference.
 In one embodiment of the invention, the method of making the compositions
 is achieved by reactive blending, desirably by a reactive extrusion
 process. The compositions of the present invention may be made by a batch
 blending process or a continuous process. For example, desired amounts of
 polyolefin, poly(ethylene oxide), monomer and initiator may be combined in
 a vessel and heated and mixed to graft monomer onto the polyolefin and
 poly(ethylene oxide) and form an inverse phase composition. Another method
 of making the compositions of the present invention includes melt blending
 desired amounts of polyolefin and poly(ethylene oxide) in an extruder. In
 an extruder, monomer and initiator may be added to the polyolefin and
 poly(ethylene oxide) contemporaneously with the polymers as they are fed
 into the extruder, after the polymers are fed into the extruder and even
 between the separate feeding of the polymers into the extruder. Desirably,
 the inverse phase compositions are pelletized. The extruded pellets have
 the desired inverse phase morphology and can be processed into various
 articles, including but not limited to films having inverse phase
 morphology.
 The extruded compositions can be used to manufacture various articles
 including pellets for later use and further processing. Desirably, the
 compositions of the present invention can be used to manufacture films and
 other articles that may be flushable, water sensitive, water responsive,
 water dispersible or water soluble, depending of the needs of the
 manufacturer. Generally, flushability, water sensitivity, water
 responsiveness, water dispersablity and water solubility of compositions,
 films and articles can be increased by increasing the ratio of
 water-soluble component, poly(ethylene oxide). The compositions of the
 present invention are amenable to melt processing and conventional
 thermoplastic processing techniques. Films can be made from compositions
 using casting, blowing, and compression molding processes.
 Processes used to make non-woven fabrics from extruded films of
 compositions of the present invention are described in greater detail in
 U.S. patent application Ser. Nos. 09/001,781 and 09/001,791 the entire
 disclosures of which is incorporated herein by reference. In one
 embodiment of the process of making non-woven fabrics, a film of an
 inverse phase blend is extruded and exposed to water. The water washes
 away and removes most of the water-soluble poly(ethylene oxide) leaving a
 non-woven web of polyolefin. The non-woven web of polyolefin may be a
 HEMA-grafted-polyolefin or PEGMA-grafted-polyolefin web. The non-woven web
 has been observed to be soft, very drapeable and "silk" like in texture.
 The non-woven fabric is also wettable and has desirable wicking and water
 spreading properties that are desirable for many personal care
 applications. For example, the non-woven fabric may be used as a liner
 material in diapers, feminine pads and pantiliners.
 A variety of vessels may be used in the practice of this invention. The
 inverse phase modification of the polymers can be performed in any vessel
 as long as the necessary mixing of the polymers, monomer and initiator is
 achieved and enough thermal energy is provided to effect grafting.
 Desirably, such vessels include any suitable mixing device, such as
 Bradender Plasticorders, Haake extruders, single or multiple screw
 extruders, or any other mechanical mixing devices which can be used to
 mix, compound, process or fabricate polymers. In a desired embodiment, the
 reaction device is a counter-rotating twin-screw extruder, such as a Haake
 extruder available from Haake, 53 West Century Road, Paramus, N.J. 07652
 or a co-rotating, twin-screw extruders, such as a ZSK-30 twin-screw,
 compounding extruder manufactured by Werner & Pfleiderer Corporation of
 Ramsey, N.J. It should be noted that a variety of extruders can be used to
 combine the component polymers in accordance with the invention provided
 that mixing and heating occur.
 Free radical initiators which can be used to graft the monomer onto the
 polyolefin include, but are not limited to, acyl peroxides such as benzoyl
 peroxide; dialkyl; diaryl; or aralkyl peroxides such as di-t-butyl
 peroxide; dicumyl peroxide; cumyl butyl peroxide; 1,1-di-t-butyl
 peroxy-3,5,5-trimethylcyclohexane; 2,5-dimethyl-2.5-di(t-butylperoxy)
 hexane; 2,5-dimethyl-2,5-bis(t-butylperoxy) hexyne-3 and bis(a-t-butyl
 peroxyisopropylbenzene); peroxyesters such as t-butyl peroxypivalate;
 t-butyl peroctoate; t-butyl perbenzoate; 2,5-dimethylhexyl-2,
 5-di(perbenzoate); t-butyl di(perphthalate); dialkyl peroxymonocarbonates
 and peroxydicarbonates; hydroperoxides such as t-butyl hydroperoxide,
 p-methane hydroperoxide, pinane hydroperoxide and cumene hydroperoxide and
 ketone peroxides such as cyclohexanone peroxide and methyl ethyl ketone
 peroxide. Azo compounds such as azobisisobutyronitrile may also be used as
 an initiator for grafting in the present invention.
 The amount of free radical initiator added to the polyolefin and
 poly(ethylene oxide) should be an amount sufficient to graft from about 1
 percent to 100 percent of the polar vinyl monomer onto the polyol(e,fin
 and poly(ethylene oxide). The amount of initiator can vary and should
 range from about 0.05 weight percent to about 1 weight percent, desirably,
 from about 0.1 weight percent to about 0.75 weight percent and, more
 desirably, from about 0.1 weight percent to about 0.5 weight percent. The
 above weight ranges are based on the weight of initiator added to the
 total combined weight of polyolefin and poly(ethylene oxide) used to
 produce the composition.
 Characteristic of the invention, a film when viewed using a scanning
 electron microscope and using back-scattered electron detector images
 shows that the poly(ethylene oxide) forms the continuous phase wherein the
 polyolefin is in a discontinuous phase, that is, dispersed throughout the
 poly(ethylene oxide) phase. Back-scattered electron detector imaging
 produces an image wherein the higher average atomic number constituent
 produces a higher intensity of back-scattered electrons that appear
 brighter in the photographic image. A constituent having a lower atomic
 number produces a lower intensity of back-scattered electrons that appear
 as darker images in the photograph. Back-scattered electron microscope
 imaging is described in greater detail in Linda C. Sawyer and David T.
 Grubb, Polymer Microscopy, Chapman & Hall, London, 1987, p. 25. Desirably,
 the polyolefin portions of the thermoplastic film have an average
 cross-sectional diameter ranging from about 0.1 microns to about 50
 microns, preferably from about 0.5 microns to about 30 microns and more
 preferably from about 0.5 microns to about 25 microns. Such "polyolefin
 portions" can be solidified pockets of polyolefin, fibers or combinations
 thereof.
 The present invention is illustrated in greater detail by the specific
 examples presented below. It is to be understood that these examples are
 illustrative embodiments and are not intended to be limiting of the
 invention, but rather are to be construed broadly within the scope and
 content of the appended claims.
 COMATIVE EXAMPLE A
 A 60/40 weight percent resin mixture of low-density polyethylene and
 poly(ethylene oxide) (hereinafter abbreviated as PEO) was melt blended
 using an extruder. The low-density polyethylene had a melt index of 1.9
 decigrams per minute (dg/min) and a density of 0.917 grams per cubic
 centimeter (g/cc) (Dow 503I; available from Dow Chemical Company, Midland,
 Mich.). The PEO had a molecular weight of 200,000 g/mol (POLYOX.RTM.)
 WSRN-80; available from Union Carbide Corp.). The extruder used for making
 the blend was a Werner & Pfleiderer ZSK-30 extruder (available from Werner
 & Pfleiderer Corporation, Ramsey, N.J.). The resin blend was fed to the
 extruder at a rate of 34 pounds per hour. The extruder had a pair of
 co-rotating screws arranged in parallel. The center distance between the
 two shafts was 26.2 mm. The nominal screw diameter was 30 mm. The actual
 outer screw diameter was 30 mm. The inner screw diameter was 21.3 mm. The
 thread depth was 4.7 mm. The extruder had 14 processing barrels, with 13
 heated barrels divided into 7 heating zones. The overall processing length
 was 1340 mm. The seven heating zones were all set at 180 degrees
 Centigrade (.degree.C). The screw speed was set at 300 rpm.
 All films of the melt blends in this Comparative Example and Examples 1-9
 were made using a Haake counter-rotating twin screw extruder (available
 from Haake, 53 West Century Road, Paramus, N.J., 07652) equipped with a
 four inch slit die. The extruder had a length of 300 millimeters. The
 conical screws had 30 millimeters diameter at the feed port and a diameter
 of millimeters at the die. The extruder had four heating zones set at 170,
 180, 180 and 190.degree. C. The screw speed was 30 rpm. A chilled wind-up
 roll was used to collect the film. The chilled roll was operated at a
 speed sufficient to form a film having a thickness of about 4 mils (about
 0.004 of an inch) and was maintained at a temperature of 15-20.degree. C.
 Referring to FIG. 1, the polyethylene formed the continuous phase and the
 poly(ethylene oxide) formed the discontinuous phase.
 EXAMPLES 1-3
 In accordance with the invention, a 60/40 weight percent resin blend of
 low-density polyethylene (LDPE) and poly(ethylene oxide), as described
 above in the Comparative Example, was fed to the ZSK-30 extruder at a rate
 of 34 lb/hr. The seven heating zones were all set at 180.degree. C. The
 screw speed was 300 rpm. At barrel 4 of the extruder, a monomer,
 poly(ethylene glycol) ethyl ether methacrylate (PEG--MA; available from
 Aldrich Chemical Company, Milwaukee, Wis.), was added at the specified
 rate. At barrel 5 of the extruder, a free radical initiator
 (2,5-dimethyl-2,5-di(t-butylperoxy) hexane, supplied by Atochem, 2000
 Market St., Philadelphia, Pa. under the tradename Lupersol 101) was added
 at the specified rate.
 For Example 1, the PEG--MA feed rate was 1.0 lb/hr and the initiator rate
 was 0.068 lb/hr.
 For Example 2, the PEG--MA feed rate was 1.9 lb/hr and the initiator rate
 was 0.068 lb/hr.
 For Example 3, the PEG--MA feed rate was 3.1 lb/hr and the initiator rate
 was 0.17 lb/hr.
 Referring to FIGS. 2-4, the thermoplastic film of the invention exhibited
 inverse phase morphology. The inverse phase compositions and films of
 Examples 1-3 comprise a minor amount/volume of poly(ethylene oxide) as the
 continuous phase and a major/volume amount polyolefin as the disperse
 phase. Particularly, Examples 1-3 are believed to comprise a continuous
 phase of PEGMA-g-PEO and a discontinuous phase of PEGMA-g-LDPE.
 EXAMPLE 4
 A 60/40 weight percent resin blend of low density polyethylene (Dow 503I)
 and poly(ethylene oxide) having a molecular weight of 100,000 g/mol
 (POLYOX.RTM. WSRN-10) was fed to the ZSK-30 extruder at a rate of 35
 lb/hr. The seven heating zones were all set at 180.degree. C. The screw
 speed was 300 rpm. A film of the melt blended resin exhibited an inverse
 phase morphology having the poly(ethylene oxide) as the continuous phase
 and the polyethylene as the discontinuous phase.
 EXAMPLES 5-9
 A resin blend having a 60/40 weight ratio of low density polyethylene (Dow
 503I) and poly(ethylene oxide) (POLYOX.RTM. WSRN-80) was fed to a Haake
 extruder at 5.0 lb/hr. The Haake extruder was similar to that described
 above in the Comparative Example except the extruder included a two-hole
 strand die instead of the four inch slit die. Simultaneously with the
 polymer feed to the extruder, specified amounts of the monomer, PEG--MA,
 and free radical initiator (Lupersol 101) were added at the feed throat.
 The extruder had four heating zones set at 170, 180, 180, and 190.degree.
 C. The screw speed of the extruder was 150 rpm. The strands were cooled in
 air and pelletized.
 For Example 5 the blend was 60/40 PE/PEO, the PEG--MA feed rate was 0.50
 lb/hr and the initiator rate was 0.025 lb/hr.
 For Example 6 the blend was 65/35 PE/PEO, the PEG--MA feed rate was 0.50
 lb/hr and the initiator rate was 0.025 lb/hr.
 For Example 7 the blend was 70/30 PE/PEO, the PEG--MA feed rate was 0.50
 lb/hr and the initiator rate was 0.025 lb/hr.
 For Example 8 the blend was 75/25 PE/PEO, the PEG--MA feed rate was 0.50
 lb/hr and the initiator rate was 0.025 lb/hr.
 For Example 9 the blend was 80/20 PE/PEO, the PEG--MA feed rate was 0.50
 lb/hr and the initiator rate was 0.025 lb/hr.
 The films and compositions of Examples 5-9 exhibit inverse phase morphology
 having a polar vinyl monomer grafted poly(ethylene oxide) as the
 continuous phase and a polar vinyl monomer grafted polyolefin as the
 discontinuous phase.
 For Example 5, the amount of monomer grafted onto the poly(ethylene oxide)
 was determined, by proton NMR spectroscopy in deuterated water, to be 9.52
 weight percent based on the amount of poly(ethylene oxide) in the blend.
 The amount of unreacted monomer was determined, by proton nuclear magnetic
 resonance (NMR) spectroscopy in deuterated water, to be 2.02 weight
 percent based on the amount of polyethylene and poly(ethylene oxide) in
 the blend. The amount of monomer grafted onto the polyethylene was
 determined to be 0.51 weight percent by Fourier-Transform Infrared (FT-IR)
 and oxygen content analysis as described in copending U. S. patent
 application Ser. No. 08/733,410 filed October 18, 1996 the entire
 disclosure of which is incorporated herein by reference.
 EXAMPLES 10-13
 In accordance with the invention, a 60/40 weight percent resin blend of low
 density polyethylene and poly(ethylene oxide), as described above in
 Comparative Example A, was fed to the ZSK-30 extruder at a rate of 34
 lb/hr. The seven heating zones were all set at 180.degree. C. The screw
 speed was 300 rpm. At barrel 4 of the extruder, a monomer, 2-hydroxyethyl
 methacrylate (abbreviated as HEMA; commercially available from Aldrich
 Chemical Company of Milwaukee, Wis.), was added at the specified rate. At
 barrel of the extruder, a free radical initiator was added at the
 specified rate. The free radical initiator used in the following examples
 was 2,5-dimethyl-2,5-di(t-butylperoxy) hexane and is commercially
 available from Atochem of Philadelphia, Pa. under the tradename Lupersol
 101
 For Example 10, the HEMA feed rate was 0.75 lb/hr and the initiator rate
 was 0.068 lb/hr.
 For Example 11, the HEMA feed rate was 1.5 lb/hr and the initiator rate was
 0.068 lb/hr.
 For Example 12, the HEMA feed rate was 3 lb/hr and the initiator rate was
 0.068 lb/hr.
 For Example 13, the HEMA feed rate was 4.5 lb/hr and the initiator rate was
 0.17 lb/hr.
 Referring to FIGS. 5-8, films of 60/40 HEMA grafted LDPE/PEO exhibited
 inverse phase morphology having HEMA-g-PEO as the continuous phase and
 HEMA-g-LDPE as the discontinuous phase.
 The dry and wet mechanical properties of films from the four 60/40 PE/PEO
 of Examples 10-13 and Comparative Example A were determined and are
 presented in Table 1 below. The thickness of the tested films were measure
 and reported in thousandths of an inch. The elongation-at-break or
 strain-at-break of the tested films were measured and are reported as a
 percentage. The peak stress or tensile strength of the tested films was
 measured and is reported in units of MPa. The energy-to-break or toughness
 of the tested films was measure and is reported in units of MJ/m.sup.3.
 And, the modulus or rigidity of the tested films was measured and is
 reported in units of MPa.
 TABLE 1
 Dry and Wet Tensile Properties
 Example No. A 10 11 12 13
 Tested Condition DRY WET DRY WET DRY WET DRY WET
 DRY WET
 Thickness of film 4.5 4.4 4.5 4.6 4.2 4.7 4.5 4.5
 5.0 4.6
 Elongation-at-Break 650 650 580 80 650 70 700 70
 580 50
 Peak Stress 15.3 12.8 13.3 3.3 9.0 1.5 10.3 2.4
 8.7 1.9
 Energy-to-Break 70.3 69.2 55.5 1.5 44.5 0.6 54.5 0.9
 39.2 0.6
 Modulus 109 58 64 23 76 11 60 17 65
 14
 Percentage Loss in Measured Property from Dry to Set
 Elongation-at-Break 0% 86% 90% 90% 91%
 Peak Stress 16% 75% 83% 77% 78%
 Energy-to-break 2% 97% 99% 98% 98%
 Modulus 47% 64% 85% 71% 79%
 Films comprising compositions of the present invention are wettable and
 lose a significant portion of their water-soluble component, poly(ethylene
 oxide), with exposure to water or aqueous solutions. Consequently, such
 films lose most of their mechanical properties when exposed to water and
 possess only a small fraction of their dry mechanical properties. The
 decrease in mechanical properties of wet films of the present invention,
 Examples 10-13, versus dry films is illustrated in Table 1 above. Films of
 the present invention have dry properties comparable to non-inverse phase
 films of the same polyolefin and poly(ethylene oxide) content but have wet
 properties significantly less than films of non-inverse phase morphology.
 The dry and wet tensile curves for the non-inverse phase blend of
 Comparative Example A are shown in FIG. 9. As can be observed from FIG. 9,
 a film of non-inverse phase blend does not lose an appreciable amount of
 its mechanical properties when exposed to water. Specifically, the
 non-inverse phase film of Comparative Example A there showed no loss, 0
 percent, in elongation to break, and 16%, 2% and 47 percent losses in peak
 stress, energy-to-break and modulus, respectively. The non-inverse phase
 film of Comparative Example A was observed to be not wettable. In
 contrast, compositions and films of the present invention are wettable and
 lose a significant amount of the their mechanical properties, including
 tensile strength, upon exposure to water. A significant decrease in
 tensile strength is illustrated in FIG. 10. FIG. 10 shows the wet and dry
 tensile curves of a film of Example 10. It was determined that the film
 lost most of its tensile strength after 30 seconds of exposure to water.
 Other mechanical properties of the films were measured before exposure to
 water (dry) and after exposure to water (wet). From dry to wet, the
 percentages in loss of mechanical properties for the film of Example 10 in
 strain (elongation-at-break), strength (peak stress), toughness
 (energy-to-break), and rigidity (modulus) are 86%, 75%, 97% and 64%,
 respectively. The bar chart of FIG. 14 gives illustrates a comparison of
 the mechanical properties of dry and wet films of Example 10 versus
 Comparative Example A. Such decreases in mechanical properties after
 exposure to water are desirable in many flushable applications.
 Additionally, the film of Example 10 was observed to wettable by water and
 the surface of the film became slimy when submerged in water.
 The dry and wet tensile curves for the inverse phase blends of Examples 11,
 12 and 13 are shown in FIGS. 11, 12 and 13, respectively. Similarly,
 comparison bar charts comparing the mechanical properties of wet and dry
 films of Examples 15, 16 and 17 versus Comparative Example A are
 illustrated in FIGS. 15, 16 and 17.
 While the invention has been described with reference to a preferred
 embodiment, those skilled in the art will appreciate that various
 substitutions, omissions, changes and modifications may be made without
 departing from the spirit hereof. Accordingly, it is intended that the
 foregoing examples be deemed merely exemplary of the present invention an
 not be deemed a limitation thereof.