Film of monomer-grafted polyolefin and poly(ethylene oxide)

The invention provides a water degradable polyolefin-containing film having greater than about 55 weight percent of a modified polyolefin and less than about 45 weight percent of unmodified poly(ethylene oxide). The polyolefin is modified by grafting thereto a monomer selected from 2-hydroxyethyl methacrylate and polyethylene glycol ethyl ether methacrylate in an amount ranging between about 0.1 weight percent and about 30 weight percent, based on the total weight of the polymer blend. The polyolefin-containing film, when immersed in water for about 30 seconds, loses at least 10% in two or more of the tensile properties: percent strain-to-break, peak stress, energy-to-break and modulus when compared to the dry or pre-immersion values. Also provided are flushable personal care articles such as infant diapers, feminine hygiene napkins, and adult incontinence garments having a backing or barrier layer comprising a water degradable polyolefin-containing film of the invention.

FIELD OF THE INVENTION 
The present invention relates to a water-degradable or flushable 
polyolefin-containing film. More particularly, the present invention 
relates to a water-degradable or flushable polyolefin-containing film 
having greater than about 55 weight percent of a modified polyolefin and 
less than about 45 weight percent of poly(ethylene oxide). 
BACKGROUND OF THE INVENTION 
Such articles typically have some portion, usually the backing layer, 
liner, or baffle constructed of a liquid repellent film material. This 
repellent material is appropriately constructed to minimize or prevent the 
exudation 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 soiled product is not without its problems. With 
greater interest being placed in protecting the environment today, there 
is a need to develop materials that are more compatible with the existing 
and developing waste disposal technologies while still delivering 
performance consumers have come to expect. An ideal disposal alternative 
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 addition to the article itself, typically the packaging in which the 
disposable article is distributed is also made from a water resistant 
material. Water resistivity is necessary to prevent the degradation of the 
packaging from environmental conditions and to protect the disposable 
articles therein. Although this packaging may be safely stored with other 
refuse for commercial disposal, and especially in the case of individual 
packaging of the products, it is often more convenient to dispose of the 
packaging in the toilet with the discarded disposable article. However, in 
the cases where such packaging is composed of a water resistant material, 
plugging of the drains to the toilet typically results. 
Desirably, a commercial, flushable product should be relatively responsive 
to water and be transportable in a sewer system. Commercially available 
water-soluble polymers, such as polyethylene oxide (PEO), polyvinyl 
alcohol (PVOH), acrylamide polymers, acrylic acid-based polymers, and 
cellulose derivatives, possess the desired characteristics for 
flushability, such as water solubility and/or water dispersibility. 
However, due to their in-use degradability and storage degradation, these 
materials function poorly as components in personal care products. Other 
disadvantages are that these polymers are difficult to process and are 
substantially more expensive than polyolefins. 
The requirements for a functional and flushable product provide a 
substantial challenge in finding suitable materials with the desired 
properties. 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. 
Polymer blends of polyolefins and poly(ethylene oxide) have been shown to 
be water modifiable at expectedly low weight % polyolefin levels. Such 
blends would be anticipated to be flushable when exposed to water in a 
toilet but do not possess the dry mechanical properties required for 
functionality in use. Moreover, the high content of poly(ethylene oxide) 
makes such materials prohibitively expensive for use in a disposable 
personal hygiene article such as a sanitary napkin, diaper and the like. 
Polymer blends of polyolefins and poly(ethylene oxide) containing greater 
than about weight percent of polyolefin are generally water resistant and 
are not water modifiable. 
In view of the problems of the prior art, it remains highly desirable to 
provide a water modifiable film having a substantial portion of thereof 
composed of a polyolefin. More desirably, the water modifiable film should 
have greater than about 55 weight percent of a polyolefin. When dry, the 
film should have the mechanical properties necessary for functionality. 
When wet, the films should lose at least a portion of its mechanical 
properties which would render the film flushable and transportable in a 
sewer system. Such films could be used for making flushable barrier films 
for personal care products. 
It is therefore an object of the invention to provide a 
polyolefin-containing film that is water modifiable or water-degradable 
which contains higher levels of polyolefin content. More specifically, it 
is an object of the invention to provide a polyolefin-containing film 
having greater than about 55 weight percent of a polyolefin and less than 
about 45 weight percent of poly(ethylene oxide) that is water-modifiable 
or water degradable. 
SUMMARY OF THE INVENTION 
In its principal embodiment, the present invention provides a 
water-modifiable or water-degradable film comprising greater than about 55 
weight percent of a modified polyolefin and less than about 45 weight 
percent of poly(ethylene oxide). The polyolefin is modified by having from 
about 0.1 weight percent to about 30 weight percent, based on the total 
weight of the polyolefin and poly(ethylene oxide), of a monomer grafted 
onto the polyolefin backbone. Preferably the monomer is 2-hydroxyethyl 
methacrylate or polyethylene glycol ethyl ether methacrylate. The film of 
the invention has a loss of at least 10% in two or more tensile properties 
selected from percent strain-to-break, peak stress, energy-to-break and 
modulus after being immersed in water for 30 seconds. 
In an alternative embodiment, the present invention provides a flushable 
personal care article having a backing or barrier layer comprising a 
water-modifiable or water-degradable film comprising greater than about 55 
weight percent of a modified polyolefin and less than about 45 weight 
percent of poly(ethylene oxide). The polyolefin is modified by having from 
about 0.1 weight percent to about 30 weight percent, based on the total 
weight of the polyolefin and poly(ethylene oxide), of a monomer grafted 
onto the polyolefin backbone. Preferably the monomer is 2-hydroxyethyl 
methacrylate or polyethylene glycol ethyl ether methacrylate. The film 
comprising the backing or barrier layer of the invention has a loss of at 
least 10% in two or more tensile properties selected from percent 
strain-to-break, peak stress, energy-to-break and modulus after being 
immersed in water for 30 seconds. 
DETAILED DESCRIPTION OF THE INVENTION 
As used herein "water modifiable" means that a four mil thick film (one mil 
equals 0.001 of an inch or 0.025 mm), when immersed in water for 30 
seconds, will have modified by greater than 10% two or more of the 
following tensile properties: percent strain-to-break, peak stress, 
energy-to-break and modulus. To determine the degree of modification, the 
"wet" values are compared to the pre-immersed or "dry" film values. 
The term "personal care product" or "personal care article" means articles 
such as infant diapers, sanitary napkins, adult incontinence garments, and 
the like. 
By the term "backing layer" or "barrier layer" is meant that component of 
an infant diaper, sanitary napkin, adult incontinence garment or the like 
which is worn during normal use furthest from the user's body and which 
serves to minimize or prevent the exudation of the absorbed liquid. 
Although the present invention is described with reference to a water 
modifiable film and, in particular, to personal care articles having a 
backing layer, liner, or barrier layer comprising such films, one skilled 
in the art will understand that the composition of the invention can be 
used to make other thermoplastic articles that can be extruded or 
injection molded in which the desired property of water degradability is 
needed such as packaging articles and the like. 
The saturated ethylene polymers useful in the practice of this invention 
are homopolymers or copolymers of ethylene and polypropylene and are 
essentially linear in structure. As used herein, the term "saturated" 
refers to polymers which are fully saturated, but also includes polymers 
containing up to about 5% unsaturation. The homopolymers of ethylene 
include 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. The 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, the 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 polyethylenes 
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 polyethylene 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 various grades of polyethylene can be used as 
the base resin in producing the graft copolymer compositions, and such 
mixtures can have a melt index greater than 0.005 dg/min to less than 
about 100 dg/min. 
The low density polyethylene 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. 
Generally, polypropylene has a semi-crystalline structure having a weight 
average molecular weight of about 40,000 or more, a density of about 0.90 
g/cc, a melting point of 168 to 171.degree. C. for isotactic polypropylene 
and a tensile strength of 5000 psi. Polypropylene can also have other 
tacticities including syndiotactic and atactic. 
The above polyolefins can also be manufactured by using the well known 
multiple-site Ziegler-Natta catalyst 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, 
co-momomer sequence length distribution, and stereoregularity. Metallocene 
catalysts are known to polymerize propylene into atactic, isotactic, 
syndiotactic, isotactic-atactic stereoblock copolymer. 
Copolymers of ethylene which can be useful in the present invention may 
include 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 use in the films of the 
invention are available from Union Carbide Corporation, Danbury, Conn. 
under the trade name of 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. 
In the principal embodiment of the invention, the water-modifiable film 
comprises greater than about 55 weight percent of a modified polyolefin 
and less than about 45 weight percent of unmodified poly(ethylene oxide). 
Desirably, the water modifiable film comprises from about 55 weight 
percent to about 85 weight percent of a modified polyolefin and from about 
45 weight percent to about 15 weight percent of unmodified poly(ethylene 
oxide). More desirably, the water-modifiable film comprises from about 65 
weight percent to about 85 weight percent of a modified polyolefin and 
from about 35 weight percent to about 15 weight percent of unmodified 
poly(ethylene oxide). 
The polyolefin is modified by having grafted thereto from about 0.1 weight 
percent to about 30 weight percent, based on the weight of the polyolefin 
and poly(ethylene oxide), of a monomer. Desirably, the polyolefin is 
modified by having grafted thereto from about 1 weight percent to about 20 
weight percent, and more desirably, from about 1 weight percent to about 
10 weight percent, based on the weight of the polyolefin and poly(ethylene 
oxide), of a monomer. Preferred and thus exemplary monomers for 
graft-polymerization modification of the polyolefins include 
2-hydroxyethyl methacrylate or polyethylene glycol ethyl ether 
methacrylate. 
Generally, the modified polyolefin is made by feeding to an extruder an 
amount of polyolefin, monomer and a free radical initiator. The modified 
polyolefin and poly(ethylene oxide) is then melt blended in an extruder to 
form the water modifiable film. The method of making the modified 
polyolefin is described in greater detail in copending U.S. patent 
application Ser. No. 08/733,410 filed Oct. 18, 1996, allowed, entitled 
"Method of Making Polyolefins Having Greater Than 5 Percent 2-Hydroxyethyl 
Methacrylate Grafted Thereto", the entire disclosure of which is 
incorporated herein by reference. In accordance with this embodiment of 
the invention, suitable poly(ethylene oxide) polymers can have an average 
molecular weight ranging from 100,000 to about 8,000,000 gm/mole. 
The free radical initiators which can be used to graft the monomer onto the 
polyolefin include 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-(p-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-(per phthalate); dialkyl 
peroxymonocarbonates and peroxydicarbonates; hydroperoxides such as 
t-butyl hydroperoxide, p-menthane hydroperoxide, pinane hydroperoxide and 
cumene hydroperoxide and ketone peroxides such as cyclohexanone peroxide 
and methyl ethyl ketone peroxide. Azo compounds such as 
azo-bis-isobutyronitrile may also be used. 
When modifying the polyolefin, the amount of free radical initiator added 
to the extruder should be an amount sufficient to graft from about 1 
percent to 100 percent of the monomer onto the polymer, i.e., the 
polyolefin. This can range from about 0.1 weight percent to about 2 weight 
percent of initiator. Preferably, the amount of initiator added to the 
extruder ranges from about 0.1 weight percent to about 1 weight percent 
wherein all such ranges are based on the amount of monomer added to the 
melt blend. 
The water-modifiable modified polyolefin-containing films of the present 
invention will, when immersed in water for about 30 seconds, have modified 
at least two of the tensile properties: percent stain-to-break, peak 
stress, energy-to-break and modulus by greater than 10%. Desirably, at 
least two of the tensile properties will be reduced greater than about 
25%. More desirably, at least two of the tensile properties will be 
reduced from about 25% to about 98%, and even more desirably at least two 
of the tensile properties: percent stain-to-break, peak stress, 
energy-to-break and modulus will be reduced from about 30% to about 80%. 
The values in determining the extent of the tensile property or properties 
modification are relative to the dry condition, i.e. pre-immersion value 
for that measured property.

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 blend of low density polyethylene (PE) having a melt 
index of 1.9 decigrams per minute (dg/min) and a density of 0.922 grams 
per cubic centimeter (g/cc) (Dow 503I; available from Dow Chemical 
Company, Midland, Mich.) and poly(ethylene oxide) (PEO) having a molecular 
weight of 200,000 g/mol (POLYOX.RTM. WSRN-80 available from Union Carbide 
Corp., Danbury, Conn.) was fed to a Haake counter-rotating twin screw 
extruder at a rate of 5 lb/hr (2.27 kg/hr). The extruder had a length of 
300 millimeters. Each conical screw had 30 millimeters diameter at the 
feed port and a diameter of 20 millimeters at the die. The extruder had 
four heating zones set at 170.degree. C., 180.degree. C., 180.degree. C. 
and 190.degree. C. The screw speed of the extruder was 150 rpm. 
Film processing of all the blends was performed using a Haake extruder 
counter-rotating twin screw extruder as described above with the following 
modifications. The extruder included a 4 inch (101.6 mm) slit die at a 
temperature of 195.degree. C. The screw speed was at 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 0.102 mm) and was maintained at a temperature of 15-20.degree. C. 
Dry tensile tests were performed on a Sintech 1/D tensile tester available 
from MTS Systems Corp., Machesny Park, Ill. The film was cut into a type V 
dogbone shape in accordance with ASTM D638. The test was performed with a 
grip separation of 30 millimeters and a crosshead speed of 4 
millimeters/second. 
Wet tensile tests were performed on a Vitrodyne V1000 mini-tensile tester 
available from Chatillon, Greensboro, N.C. The film samples were placed in 
the grips and the testing apparatus was submerged in ambient temperature, 
non-stirred water for 30 seconds. The test was then run under the same 
conditions as the dry tensile test. Peak stress, percent strain-to-break, 
energy-to-break (as area under stress versus strain curve) and modulus 
were calculated using the actual stress versus strain values recorded from 
the tensile tester for each dry or wet tensile test. The peak stress was 
recorded as the greatest stress value. The percent stain-to-break was 
recorded as the percent strain value at break. The energy-to-break (area 
under stress versus stain curve) was calculated by the summation of 
rectangular "slices" under the curve determined for each strain value 
recorded from the tensile test, using the following formula: 
EQU ((Strain value.sub.x -Strain value.sub.x-1).times.(Stress value.sub.x 
+Stress value.sub.x-1))/2 
where `X" is the sequential number of the slice. The modulus was calculated 
by linear regression of the initial region of the stress versus strain 
curve. The dry and wet properties of the film produced from the blend in 
Comparative Example A are indicated in Table 1 below. 
TABLE 1 
______________________________________ 
Loss in Tensile Properties Upon Wetting 
Comparative Example A 
Percent Loss from 
Property Dry Wet Dry to Wet 
______________________________________ 
Thickness (mil) 
4.1 4.2 
Percent Strain 550 500 9 
Peak Stress (MPa) 16.6 16.2 2 
Energy-to-Break 65.7 64.0 3 
( .times. 10.sup.6 J/m.sup.3) 
Modulus 77.0 62.3 19 
______________________________________ 
This example shows that a polymer blend of unmodified low density 
polyethylene with poly(ethylene oxide) having a weight average molecular 
weight of 200,000 is water resistant. The polymer blend was not water 
modifiable after 30 seconds of immersion in water. 
EXAMPLES 1-3 
For Examples 1-3, the low density polyethylene (Dow 5031) was modified by 
grafting thereto polyethylene glycol methacrylate (PEG-MA; available from 
Aldrich Chemical Company, Milwaukee, Wis.). A Haake extruder as described 
in Comparative Example A above was used. The extruder had four heating 
zones set at 170.degree. C., 180.degree. C., 180.degree. C. and 
190.degree. C. The screw speed of the extruder was 150 rpm. The feed to 
the extruder comprised contemporaneously adding, at the extruder feed 
throat, 5 lb/hr (2.27 kg/hr) of polyethylene and the specified amounts of 
PEG-MA and free radical initiator 
((2,5-dimethyl-2,5-di-(t-butylperoxy)hexane), supplied by Atochem, 2000 
Market St., Philadelphia, Pa. under the tradename Lupersol.RTM. 101). 
For Example 1 the PEG-MA feed rate was 0.125 lb/hr (0.057 kg/hr) and the 
initiator rate was 0.0125 lb/hr 0.057 kg/hr). 
For Example 2 the PEG-MA feed rate was 0.25 lb/hr (0.114 kg/hr) and the 
initiator rate was 0.025 lb/hr (0.011 kg/hr). 
For Example 3 the PEG-MA feed rate was 0.5 lb/hr (0.227 kg/hr) and the 
initiator rate was 0.025 lb/hr (0.011 kg/hr). 
A film comprising a 60/40 weight percent blend of polyethylene and 
poly(ethylene oxide) was prepared following the procedure of Comparative 
Example A, except the modified polyethylene of each example was 
substituted for the unmodified polyethylene of Comparative Example A. 
The dry and wet properties of the film produced from the blends in Examples 
1-3 are indicated in Table 2 below. 
In accordance with the invention, Examples 1-3 illustrate a 
water-modifiable or water-degradable film comprising a blend of a modified 
polyolefin comprising polyethylene with PEG-MA grafted thereto and 
unmodified poly(ethylene oxide). The films were water modifiable after 30 
seconds of submersion in water. 
TABLE 2 
__________________________________________________________________________ 
Loss in Tensile Properties Upon Wetting 
1 2 3 
Example % % % 
Property Dry Wet Change Dry Wet Change Dry Wet Change 
__________________________________________________________________________ 
Thickness 
4.5 4.5 
0 4.0 
4.0 0 5.0 5.0 
0 
(mil) 
Percent 550 183 67 553 117 78 283 50 82 
Strain-to- 
Break 
Peak Stress 13.8 7.0 49 11.4 4.9 57 12.2 3.1 75 
(MPa) 
Energy-to- 54.5 11.2 80 46.0 4.0 91 27.5 0.8 97 
Break 
(.times.10.sup.6 J/m.sup.3) 
Modulus 70.7 44.6 37 62.2 33.8 46 71.6 23.6 67 
(Mpa) 
__________________________________________________________________________ 
While the invention has been described with reference to the preferred 
embodiments and illustrated with regard to a range of optional features, 
those skilled in the art will appreciate that various substitutions, 
omissions, changes and modifications may be made without departing from 
the spirit of the invention as it is defined by the appended claims. 
Accordingly, it is intended that the foregoing description be deemed 
merely exemplary of the preferred scope of the present invention and not 
be deemed a limitation thereof.