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Patent Abstract
A transparent polyurethane-hydrogel composition includes a reaction
product in aqueous solvent of a prepolymer and a water-soluble crosslinker
in the substantial absence of organic solvent, and such a composition
can be prepared by admixing a prepolymer and a water-soluble crosslinker
in aqueous solvent and in the substantial absence of organic solvent.
A prepolymer is present in an amount of no greater than about 5
weight percent based on total weight of all hydrogel components.
The prepolymer is generally prepared from at least one water-soluble
polyol and an isocyanate. A water-soluble crosslinker generally
has a crosslinker functionality of at least 2 and is selected to
provide a site ratio of initial isocyanate to crosslinker (i.e.,
moles NCO.times.functionality/moles crosslinker.times.functionality)
of at least about 1.5 and no greater than about 2.6. In one embodiment,
a crosslinker is effective to react with and solubilize residual
isocyanate concurrently with the reaction between prepolymer and
crosslinker. A transparent polyurethane-hydrogel composition has
desirable gel physical properties and is useful for an air-freshener
application.
Patent Claims
What is claimed is:
1. A polyurethane-hydrogel composition, said composition being
prepared by a method comprising: (a) admixing at least one prepolymer
and at least one water-soluble crosslinker in aqueous solvent and
in the substantial absence of organic solvent to form a polyurethane-hydrogel
mixture, said prepolymer being prepared from at least one water-soluble
polyol and at least one isocyanate and being present in an amount
of no greater than about 5 weight percent, said weight percent being
based on total weight of all components; and (b) polymerizing said
mixture to form a composition, wherein said composition is substantially
polymerized, is transparent, and has an effective number-average
molecular weight between crosslinks.
2. A composition according to claim 1, wherein said crosslinker
comprises polyethylenimine.
3. A composition according to claim 1, wherein said crosslinker
comprises an amine end-capped poly(ethylene oxide) crosslinker.
4. A composition according to claim 1, wherein said crosslinker
comprises at least one of a 3-arm amine end-capped polyethyleneglycol
and polyoxyethylene bis(amine).
5. A composition according to claim 1, wherein said water-soluble
crosslinker comprises a polyamine, said polyamine having a charge
density of at least 0.8 meq charge per gram of crosslinker.
6. A composition according to claim 1, wherein said crosslinker
has a functionality effective to provide a reaction rate with said
prepolymer that is at least 10 times faster than the reaction rate
of water with said prepolymer.
7. A composition according to claim 1, wherein said prepolymer
is prepared from an aliphatic or cycloaliphatic isocyanate.
8. A composition according to claim 7, wherein said isocyanate
comprises isophorone diisocyanate.
9. A composition according to claim 1, wherein said prepolymer
is prepared from a polyoxyalkylene polyol.
10. A composition according to claim 9, wherein said polyol comprises
a 7,000 molecular-weight triol copolymer of 75% ethylene oxide and
25% propylene oxide.
11. A composition according to claim 1, wherein said prepolymer
is prepared from an isocyanate comprising isophorone diisocyanate
and a polyol comprising a 7,000 molecular-weight triol copolymer
of 75% ethylene oxide and 25% propylene oxide.
12. A composition according to claim 1, wherein said mixture is
formed by further admixing a fragrance composition with said at
least one prepolymer and said at least one water-soluble crosslinker.
13. A composition according to claim 12, wherein said fragrance
composition comprises a fragrance oil and a surfactant.
14. A composition according to claim 13, wherein said surfactant
comprises at least one of ethoxylated alkyl phenol, nonylphenol,
and ethoxylated alcohol.
15. A composition according to claim 1, wherein said mixture is
formed by admixing at least one additive with said at least one
prepolymer and said at least one water-soluble crosslinker.
16. An air-freshener composition, said composition being prepared
by a method comprising: (a) admixing at least one prepolymer, at
least one water-soluble crosslinker, and at least one fragrance
composition in aqueous solvent and in the substantial absence of
organic solvent to form a polyurethane-hydrogel mixture, said prepolymer
being prepared from at least one water-soluble polyol and at least
one isocyanate and being present in an amount of no greater than
about 5 weight percent, said weight percent being based on total
weight of all components; (b) polymerizing said mixture to form
a composition, wherein said composition is substantially polymerized,
is transparent, and has an effective number-average molecular weight
between crosslinks.
17. A composition according to claim 16, wherein said crosslinker
comprises polyethylenimine.
18. A composition according to claim 16, wherein said crosslinker
comprises an amine end-capped poly(ethylene oxide) crosslinker.
19. A composition according to claim 16, wherein said crosslinker
comprise at least one of a 3-arm amine end-capped polyethyleneglycol
and polyoxyethylene bis(amine).
20. A composition according to claim 16, wherein said water-soluble
crosslinker comprises a polyamine, said polyamine having a charge
density of at least 0.8 meq charge per gram of crosslinker.
21. A composition according to claim 16, wherein said prepolymer
is prepared from an aliphatic or cycloaliphatic isocyanate.
22. A composition according to claim 21, wherein said isocyanate
comprises isophorone diisocyanate.
23. A composition according to claim 16, wherein said prepolymer
is prepared from a polyoxyalkylene polyol.
24. A composition according to claim 23, wherein said polyol comprises
a 7,000 molecular-weight triol copolymer of 75% ethylene oxide and
25% propylene oxide.
25. A composition according to claim 16, wherein said prepolymer
is prepared from an isocyanate comprising isophorone diisocyanate
and a polyol comprising a 7,000 molecular-weight triol copolymer
of 75% ethylene oxide and 25% propylene oxide.
26. A composition according to claim 16, wherein said fragrance
composition comprises a fragrance oil.
27. A composition according to claim 25, wherein said fragrance
composition further comprises at least one of a surfactant and an
antifreeze.
28. A composition according to claim 27, wherein said surfactant
comprises at least one of ethoxylated alkyl phenol, nonylphenol,
and ethoxylated alcohol.
29. A composition according to claim 16, wherein said mixture is
formed by admixing at least one additive with said at least one
prepolymer and said at least one water-soluble crosslinker.
30. An air freshener, said air freshener comprising: (a) a container;
and (b) a polyurethane-hydrogel composition dispensed into said
container, said composition being prepared by a method comprising:
(i) admixing at least one prepolymer, at least one water-soluble
crosslinker, and at least one fragrance composition in aqueous solvent
and in the substantial absence of organic solvent to form a polyurethane-hydrogel
mixture, said prepolymer being prepared from at least one water-soluble
polyol and at least one isocyanate and being present in an amount
of no greater than about 5 weight percent, said weight percent being
based on total weight of all components; and (ii) polymerizing said
mixture in said container to form an air freshener, wherein said
air freshener is substantially polymerized, is transparent, and
has an effective number-average molecular weight between crosslinks.
31. An air freshener according to claim 30, wherein said crosslinker
comprises polyethylenimine.
32. An air freshener according to claim 30, wherein said crosslinker
comprises an amine end-capped poly(ethylene oxide) crosslinker.
33. An air freshener according to claim 30, wherein said crosslinker
comprises at least one of a 3-arm amine end-capped polyethyleneglycol
and polyoxyethylene bis(amine).
34. An air freshener according to claim 30, wherein said water-soluble
crosslinker comprises a polyamine, said polyamine having a charge
density of at least 0.8 meq charge per gram of crosslinker.
35. An air freshener according to claim 30, wherein said prepolymer
is prepared from an aliphatic or cycloaliphatic isocyanate.
36. An air freshener according to claim 35, wherein said isocyanate
comprises isophorone diisocyanate.
37. An air freshener according to claim 30, wherein said prepolymer
is prepared from a polyoxyalkylene polyol.
38. An air freshener according to claim 37, wherein said polyol
comprises a 7,000 molecular-weight triol copolymer of 75% ethylene
oxide and 25% propylene oxide.
39. An air freshener according to claim 30, wherein said prepolymer
is prepared from an isocyanate comprising isophorone diisocyanate
and a polyol comprising a 7,000 molecular-weight triol copolymer
of 75% ethylene oxide and 25% propylene oxide.
40. An air freshener according to claim 30, wherein said fragrance
composition comprises a fragrance oil.
41. An air freshener according to claim 40, wherein said fragrance
composition further comprises at least one of a surfactant and an
antifreeze.
42. An air freshener according to claim 30, wherein said composition
further comprises a gel object suspended within said composition.
43. An air freshener according to claim 30, wherein said mixture
is formed by further admixing a colorant with said prepolymer and
said water-soluble crosslinker.
44. A method for preparing a transparent polyurethane-hydrogel
composition, said method comprising: (a) admixing at least one prepolymer
and at least one water-soluble crosslinker in aqueous solvent and
in the substantial absence of organic solvent to form a polyurethane-hydrogel
mixture, said prepolymer comprising at least one water-soluble polyol
and at least one isocyanate and being present in an amount of no
greater than about 5 weight percent, said weight percent being based
on total weight of all components; and (b) polymerizing said mixture
to form a composition, wherein said composition is substantially
polymerized, is transparent, and has an effective number-average
molecular weight between crosslinks.
45. A method according to claim 44, wherein said crosslinker comprises
polyethylenimine.
46. A method according to claim 44, wherein said crosslinker comprises
an amine end-capped poly(ethylene oxide) crosslinker.
47. A method according to claim 44, wherein said crosslinker comprises
at least one of a 3-arm amine end-capped polyethyleneglycol and
polyoxyethylene bis(amine).
48. A method according to claim 44, wherein said water-soluble
crosslinker comprises a polyamine, said polyamine having a charge
density of at least 0.8 meq charge per gram of crosslinker.
49. A method according to claim 44, wherein said prepolymer is
prepared from an aliphatic or cycloaliphatic isocyanate.
50. A method according to claim 49, wherein said isocyanate comprises
isophorone diisocyanate.
51. A method according to claim 44, wherein said prepolymer is
prepared from a polyoxyalkylene polyol.
52. A method according to claim 51, wherein said polyol comprises
a 7,000 molecular-weight triol copolymer of 75% ethylene oxide and
25% propylene oxide.
53. A method according to claim 44, wherein said prepolymer is
prepared from an isocyanate comprising isophorone diisocyanate and
a polyol comprising a 7,000 molecular-weight triol copolymer of
75% ethylene oxide and 25% propylene oxide.
Patent Description
[0001] This application claims the benefit of U.S. Provisional Application
No. 60/292,545, filed May 21, 2001, which is hereby incorporated
by reference.
FIELD OF THE INVENTION
[0002] The invention is directed to a transparent polyurethane-hydrogel
composition and to a method for making a transparent polyurethane-hydrogel
composition. More particularly, the invention is directed to a transparent
polyurethane-hydrogel composition prepared from a prepolymer in
an amount of no more than about 5 weight percent and a water-soluble
crosslinker. A transparent polyurethane-hydrogel composition of
the invention is particularly useful for applications containing
fragrance compositions, particularly air-freshener applications.
BACKGROUND OF THE INVENTION
[0003] A polyurethane gel is created from a polyurethane network
and a solvent. The polyurethane network envelops the solvent and
can prevent the solvent from flowing out of the network. The properties
of a polyurethane gel depend largely on the structure of the polyurethane
network that makes up the gel and the interaction of the network
and the solvent. The polyurethane network depends on the crosslink
structure of the network, which depends on, for example, the amount
and type of the reactants used to make the network and their ability
to react to near completion. The polyurethane network can be important
for determining the strength of the gel and can also be important
for the diffusion of molecules through the tortuous path in the
gel.
[0004] For some applications, one desirable characteristic of a
polyurethane gel is transparency. Transparency is determined by
the polyurethane network in combination with the solvent as well
as the residual reactants. Thus, some reactants that may provide
a desirable polyurethane network may be unable to provide transparency,
and some reactants that can provide transparency may be unable to
provide a desirable network.
[0005] A variety of polyurethane gels are known, and some of these
gels are transparent. The known transparent polyurethane gels are
less than desirable because they generally require large amounts
of polymer--e.g., more than 5 weight percent and even more than
20 weight percent in some applications. Using such large amounts
of polymer can be expensive and can negate or reduce transparency.
These gels are also typically prepared in an organic solvent, which
can be at least partly removed in a washing step after the gel is
formed. This washing step can be slow and expensive in high-volume
manufacturing applications.
[0006] Attempts to reduce the amount of polymer in known formulations
to no more than 5 weight percent can adversely affect gel formation.
And attempts to modify known formulations by altering the reactants
such that less than 5 weight percent of polymer can form a desirable
gel can adversely affect gel transparency.
[0007] Thus, it would be desirable to prepare a polyurethane gel
by using a reduced amount of polymer as compared to known formulations
while still obtaining a transparent gel and desirable physical properties.
It would also be desirable to prepare a polyurethane gel in the
substantial absence of volatile organic solvent, while still maintaining
gel transparency.
SUMMARY OF THE INVENTION
[0008] According to the invention, a transparent polyurethane-hydrogel
composition includes a reaction product of a prepolymer and a water-soluble
crosslinker in water and in the substantial absence of organic solvent.
Generally a composition of the invention is prepared by admixing
at least one prepolymer and at least one crosslinker in aqueous
solvent and in the substantial absence of organic solvent.
[0009] A prepolymer includes at least one water-soluble polyol
and at least one isocyanate.
[0010] A water-soluble crosslinker generally has a functionality
of at least 2 and is selected in a site ratio of isocyanate to crosslinker
(i.e., moles NCO.times.functionality/moles crosslinker.times.functionalit-
y) of at least about 1.4 and no greater than about 2.7.
[0011] In one embodiment, a water-soluble crosslinker includes
a polyamine having a charge density of at least 0.8 meq charge per
gram of crosslinker.
[0012] In another embodiment, a water-soluble crosslinker includes
polyethylenimine, which has a charge density of between about 20
and about 25 meq charge per gram of crosslinker.
[0013] In another embodiment, a water-soluble crosslinker includes
at least one of a 3-arm end-capped polyethyleneglycol and polyoxyethylene
bis(amine).
[0014] In yet another embodiment, a water-soluble crosslinker has
a functionality effective to provide a reaction rate with said prepolymer
that is at least 10 times faster than the reaction rate of water
with said prepolymer.
[0015] In still another embodiment, a water-soluble crosslinker
is selected to be effective to react with and solubilize residual
isocyanate at least concurrently with the reaction between prepolymer
and crosslinker.
[0016] In still another embodiment a crosslinker is chosen to be
an amine end-capped polyethylene oxide or polyalkylene oxide.
[0017] A composition of the invention can be prepared by admixing
a prepolymer in an amount of 5 weight percent and a water-soluble
crosslinker in water and in the substantial absence of organic solvent.
[0018] A composition of the invention has a desirable physical
gel property, particularly an effective number-average molecular
weight between crosslinks. In one embodiment, the composition has
a number-average molecular weight between crosslinks of at least
about 2,000 and no greater than about 10,000.
[0019] In another embodiment, a composition has a tensile modulus
of at least about 800 kPa and no greater than about 4000 kPa at
25.degree. C.
[0020] A composition of the invention can be included in a fragrance-containing
composition. One suitable fragrance-containing composition is an
air-freshener composition. An air-freshener composition includes
a prepolymer, a fragrance composition, and a water-soluble crosslinker.
[0021] A method of making a composition of the invention includes
admixing at least one prepolymer and at least one water-soluble
crosslinker in aqueous solvent and in the substantial absence of
organic solvent to form a polyurethane-hydrogel mixture and polymerizing
the mixture. The composition is substantially polymerized, is transparent,
and has an effective number-average molecular weight.
BRIEF DESCRIPTION OF THE FIGURES
[0022] FIGS. 1 and 2 show the percent transmittance of a composition
of the invention and a comparative composition over the visible
range of 400 nm to 800 nm. FIG. 1 represents compositions that have
2.7 weight-percent prepolymer, and FIG. 2 represents compositions
that have 5 weight-percent prepolymer.
[0023] FIG. 3 shows the percent transmittance of a composition
of the invention and a comparative composition over the visible
range of 400 nm to 800 nm. The composition of the invention was
prepared with 3 weight-percent prepolymer, and the comparative composition
was prepared with 7 weight-percent prepolymer.
DETAILED DESCRIPTION OF THE INVENTION
[0024] The invention is directed to a transparent polyurethane-hydrogel
composition and to a method for making a transparent polyurethane-hydrogel
composition. A transparent polyurethane-hydrogel composition according
to the invention is prepared from a prepolymer and a water-soluble
crosslinker in an aqueous solvent and in the substantial absence
of organic solvent.
[0025] The prepolymer is present in an amount effective to provide
a polyurethane hydrogel with desirable gel physical properties and
with transparency. Generally the prepolymer is present in an amount
of no more than about 5 weight percent, preferably no more than
about 4.5 weight percent, and preferably no more than about 4 weight
percent. But the prepolymer is generally present in an amount of
at least about 1 weight percent, preferably at least about 1.5 weight
percent, more preferably at least about 1.7 weight percent, and
still more preferably at least about 2 weight percent. In one embodiment,
the prepolymer is present in an amount of between about 2.5 weight
percent and about 3.5 weight percent.
[0026] A transparent polyurethane-hydrogel composition of the invention
is useful for applications that contain fragrance compositions,
particularly air-freshener applications.
[0027] The term "polymerized" or "polymerizing"
means the composition is in the form of gel and does not flow under
its own weight. This transformation from liquid components to polymer
generally produces molar mass increase, network formation, phase
separation, or a combination of these. When the composition does
not substantially flow when the substrate is tipped, the composition
is considered to be substantially polymerized. Generally the gel
is effectively polymerized if a 100-ml container that includes a
polyurethane-hydrogel composition can be inverted 180.degree. and
the composition does not flow out of the container (i.e., exhibits
finite yield stress).
[0028] One advantage of the composition of the invention is that
it is transparent. According to the invention, the term "transparent"
means that a polyurethane-hydrogel composition of the invention
is optically transparent. This means that a transparent polyurethane-hydrogel
composition generally transmits light similar to how water transmits
light at the same wavelength. Light transmittance can be determined
by the Beer-Lambert Law 1 [ ln ( I 0 I ) = - Cl ] ,
[0029] where .epsilon. is the specific molar absorptivity, I is
the intensity of transmitted light, I.sub.0 is the intensity of
incident light, and l is the cell length, and C is the concentration
of a light absorbing component.
[0030] Generally the term "transparent" means that a
polyurethane-hydrogel composition of the invention transmits at
least about 40 percent, preferably at least about 45 percent, and
more preferably at least about 50 percent of light at 600 nanometers
(nm) through a quartz cuvette having a cell pathlength of about
4 cm. One of skill in the art knows that transmittance varies with
wavelength and pathlength and that 600 nm represents the middle
of the visible spectrum, which ranges between 400 nm and 800 nm.
One of skill in the art will also recognize that percent transmittance
can be affected by adding a colorant to a composition of the invention.
Transparency should be determined before adding a colorant or by
choosing a wavelength of light that would transmit light without
substantial interference of the colorant.
[0031] In one embodiment, a transparent polyurethane-hydrogel composition
of the invention transmits at least about 1.5 times, preferably
at least about 2 times, more preferably at least about 3 times,
and still more preferably at least about 4 times more light at 600
nm through a quartz cuvette having a cell pathlength of about 4
cm than a gel composition prepared from a crosslinker (e.g., water,
ethylene diamine, diethylene diamine, and triethylene triamine)
other than a water-soluble crosslinker according to the invention.
Such a comparison uses the same testing conditions--e.g., time,
wavelength, cell thickness, and temperature--for each sample.
[0032] The percent transmission can be determined within at least
about 36 hours of preparing a composition, preferably within at
least about 24 hours of preparing a composition, and more preferably
within at least about 12 hours of preparing a composition. Deionized
water at about pH 7 can be used as the control.
[0033] A polyurethane hydrogel of the invention has physical gel
properties suitable for its intended end-use application. These
physical properties can be modified by selection of the amount and
type of hydrogel components, particularly isocyanate, polyol, and
water-soluble crosslinker.
[0034] One such property is crosslink density. Crosslink density
affects the stiffness, tensile modulus, and compressive strength
of a material. One of skill in the art is familiar with these relationships,
but they will be briefly described here. 2 Crosslinkdensity = numberofcrosslinks
polymermass ( 1 )
[0035] The molecular weight between crosslinks of a system, M.sub.c,
will also be related to the crosslink density of a system. M.sub.c
is related to the density of the material by the approximation shown
in Equation (2). This parameter is related to the Shear Modulus
of the system via Equation (3) and to the Young's Tensile Modulus
by Equation (4). 3 N M c N A ( 2 )
[0036] where:
[0037] N is the number of chains per unit volume
[0038] N.sub.A is Avogadro's number 4 G = R T M c ( 3 )
[0039] where:
[0040] G is the shear modulus
[0041] .rho. is the density of the dry network (.apprxeq.1 gm/cc)
[0042] R is the gas constant
[0043] T is the temperature and
[0044] M.sub.c is the average molecular weight between elastically
effective crosslinks
[0045] The Young's Tensile Modulus, E, is given by: 5 E = 3 R T
M c = 3 G ( 4 )
[0046] One physical property is based on the number-average molecular
weight between crosslinks (M.sub.c). An effective M.sub.c provides
support to a three-dimensional gel configuration and a substantially
stable gel, and the M.sub.c generally is not so great or so low
that a composition of the invention becomes unsuitable for its intended
end-use application. A composition of the invention is unsuitable
for its intended end-use application if, for example, a fragrance
oil cannot diffuse out of the network of a polyurethane hydrogel
to release fragrance.
[0047] The number-average molecular weight between crosslinks can
be measured experimentally by swelling the gel and measuring the
gel's change in volume-mass ratio. The value of number-average molecular
weight between crosslinks can be controlled by varying the amount
and molecular weight of prepolymer and the amount and molecular
weight of water-soluble crosslinker. The nature of the gel and its
internal topology can be varied, and even optimized, by simulation
of gelation through the use of Monte Carlo gelation-simulation techniques.
These techniques allow for an estimate of gel characteristics including
such measures as the crosslink density of the network as well as
the number-average molecular weight between crosslinks.
[0048] According to simulation techniques, a composition according
to the claimed invention generally has an M.sub.c of at least about
2,000, preferably at least about 3,000, more preferably at least
about 4,000, and still more preferably at least about 5,000. But
the M.sub.c is generally no greater than about 8,000, preferably
no greater than about 7,000, and more preferably no greater than
about 6,000.
[0049] These M.sub.c values may be related to experimental observables--the
tensile modulus. An effective tensile modulus for a composition
of the invention is great enough to provide a shape suitable for
an end-use application. For a composition of the invention, the
tensile modulus can be difficult to measure due to its low value,
but the tensile modulus can be reliably estimated from the number-average
molecular weight between crosslinks.
[0050] Generally a transparent polyurethane hydrogel of the invention
has a tensile modulus of at least about 800 kiloPascal (kPa), preferably
at least about 1200 kPa, and more preferably at least about 1500
kPa at a temperature of about 25.degree. C. Generally the modulus
is no greater than about 4000 kPa, preferably no greater than about
3000 kPa, and more. preferably no greater than about 2000 kPa at
a temperature of about 25.degree. C.
[0051] Another physical property for a polyurethane hydrogel is
gel strength. An effective gel strength is great enough to support
a three-dimensional gel configuration and a substantially stable
gel but not so great that a composition of the invention becomes
unsuitable for its intended end-use application.
[0052] Gel strength can be determined by using a Stevens Texture
Analyzer (available from Stevens Company) and a 0.5-inch Bloom Gelometer
plunger (available from Stevens Company) as described in British
Standard BS 757 (1975). Generally a polyurethane hydrogel has a
gel strength of at least about 5 grams, preferably at least about
10 grams, and more preferably at least about 25 grams. But generally
the gel strength is no greater than about 500 grams, preferably
no greater than about 150 grams, and more preferably no greater
than about 300 grams.
[0053] The term "desirable physical properties" means
desirable values for number-average molecular weight between crosslinks,
tensile modulus, or gel strength as described above.
[0054] Also according to the invention, the term "polyurethane"
can refer to polyurethane, polyurea, or a mixture of polyurea and
polyurethane. A polyurethane material can be obtained by a reaction
of a polyol with an isocyanate. A polyurea material can be obtained
by reaction of an amine with an isocyanate. A polyurethane material
or a polyurea material can contain both urea functionality and urethane
functionality, depending on the components included in a composition.
Preferably a composition of the invention is a mixture of polyurethane
material and polyurea material, which is generally known as a polyureaurethane.
For purposes of this specification, no further distinction will
be made between polyurethane and polyurea.
[0055] A composition of the invention is prepared in an aqueous
solvent and in the substantial absence of an organic solvent. The
terms "substantially free of organic solvent" and "substantial
absence of organic solvent" mean an amount of organic solvent
insufficient for dispersing hydrogel components to induce transparency
in a polyurethane-hydrogel composition of the invention.
[0056] Generally the amount of organic solvent is no more than
about 3 weight percent, preferably no more than about 2 weight percent,
more preferably no more than about 1 weight percent, and even more
preferably no more than about 0.5 weight percent. Still more preferably,
the amount of organic solvent is no more than about 0.1 weight percent.
Examples of organic solvents include acetonitrile, dimethyl formamide,
dimethyl sulfoxide, tetrahydrofuran, dioxane, dichloromethane, acetone,
and methyl ethyl ketone. The term "weight percent" is
based on the total weight of the hydrogel components that are used
to prepare a transparent polyurethane-hydrogel composition of the
invention. The balance of all formulations is aqueous solvent.
[0057] The term "aqueous solvent" means any water-based
solution suitable for dispersing hydrogel components such as sterile
water, saline, and buffer.
[0058] The term "hydrogel component(s)" includes any
component used to prepare a polyurethane-hydrogel composition of
the invention such as isocyanate, polyol, water, water-soluble crosslinker,
and additives, for example, a fragrance oil, a surfactant, an antioxidant,
an antifreeze, a bittering agent, and other additives that can,
for example, control fragrance release.
[0059] The term "composition" or "polyurethane-hydrogel
composition" will be understood to one of skill in the art
having read this specification. To form a gel-based formulation,
hydrogel components are mixed together. Initially much of the components
will be dispersed in solution, but as the components begin to react
to completion (i.e., polymerize), a gel network having solvent molecules
dispersed throughout the network will form. Thus, a "composition"
of the invention includes a polymerized composition (i.e., the reaction
product of hydrogel components when the gel network is formed),
but the "composition" also includes a reaction mixture
when the hydrogel components are initially introduced and before
a network is substantially formed. The term "polyurethane hydrogel"
can be used to specifically refer to a composition that is polymerized.
[0060] A composition of the invention is particularly useful for
air-freshener applications.
[0061] Polyurethane-Hydrogel Composition
[0062] A polyurethane-hydrogel composition of the invention is
prepared by admixing a prepolymer with a water-soluble crosslinker
in an aqueous solvent and in the substantial absence of organic
solvent. A composition of the invention generally includes a reaction
product of at least one isocyanate, at least one polyol, and at
least one water-soluble crosslinker in aqueous solvent.
[0063] These components are chosen such that upon preparing a polyurethane
hydrogel of the invention, the polyurethane hydrogel is transparent
and has desirable physical properties for the intended end-use application.
[0064] A composition of the invention can also include additives
that are known to be useful in polyurethane-hydrogel compositions
for intended end-use applications.
[0065] Prepolymer
[0066] A polyurethane-hydrogel composition of the invention includes
a prepolymer. Any prepolymer suitable for preparing a transparent
polyurethane-hydrogel composition can be used.
[0067] An effective amount of the prepolymer is generally great
enough to result in a three-dimensional gel configuration but not
so great that the resulting polyurethane hydrogel is not transparent
according to the invention.
[0068] The prepolymer is generally present in an amount of no more
than about 5 weight percent, preferably no more than about 4.5 weight
percent, and preferably no more than about 4 weight percent. But
the prepolymer is generally present in an amount of at least about
1 weight percent, preferably at least about 1.5 weight percent,
and more preferably at least about 2 weight percent.
[0069] In one embodiment, the prepolymer is present in an amount
of between about 2.5 weight percent and about 3.5 weight percent.
In another embodiment, the prepolymer is present in an amount of
about 3 weight percent.
[0070] A prepolymer suitable for use with the invention generally
includes a reaction product of at least one water-soluble polyol
and at least one isocyanate. One of skill in the art having read
this specification would understand that isocyanates and polyols
that promote water solubility of the prepolymer and that do not
substantially adversely affect transparency of the composition would
be desirable.
[0071] The term "polyol" refers to a compound that has
two or more isocyanate-reactive functional groups per molecule.
These functional groups include hydroxyl --OH), sulfhydryl (--SH);
carboxyl (--COOH), and amino (--NHR, with R being hydrogen, an alkyl
moiety of C.sub.1 to C.sub.10, or epoxy) groups. The functional
group is preferably --OH. The term "polyol" includes diol.
[0072] A water-soluble polyol suitable for use in the invention
includes polyoxyalkylene polyols or polyols made up of ethylene-oxide
monomer units. For polyols made up of ethylene-oxide monomer units,
at least 50 weight percent, preferably at least 60 weight percent,
more preferably at least 70 weight percent, and still more preferably
at least 90 weight percent of the units should be ethylene oxide.
Even 100 weight-percent ethylene oxide-containing polyols can be
used. These polyols can include up to about 25 weight-percent propylene-oxide
monomer units.
[0073] The water-soluble polyol generally has an average molecular
weight of at least about 2,000, preferably at least about 5,000,
and more preferably at least about 7,000 gram/mole. But the molecular
weight generally is no greater than about 30,000, preferably no
greater than about 20,000, more preferably no greater than about
15,000, and still more preferably no greater than about 10,000 gram/mole.
In one embodiment, the water-soluble polyol has a molecular weight
of about 7,500 gram/mole.
[0074] Suitable polyols include diols such as a high molecular-weight
polyethyleneglycol of the formula H(OCH.sub.2CH.sub.2).sub.xOH where
x is an average number such that the glycol has an average molecular
weight of at least about 500, preferably at least about 1,000, and
more preferably at least about 2,000 gram/mole. But the average
molecular weight of the glycol generally is no greater than about
30,000, preferably no greater than about 20,000, more preferably
no greater than about 15,000, and still more preferably no greater
than about 10,000 gram/mole.
[0075] Preferably the polyol includes at least one triol (i.e.,
trihydroxy compound) and is synthesized using initiators such as
glycerol, trimethylolpropane, and triethanolamine.
[0076] Other polyols having more than 3 functional groups are also
suitable and can be synthesized using initiators such as sorbitol,
erythritol, sucrose, and pentaerythritol. These initiators can be
used to make polyoxyalkylene polyols as well as polyols made up
of ethylene-oxide monomer units.
[0077] Suitable polyoxyalkylene polyols include polyols that have
at least one oxyethylene, oxypropylene, or oxybutylene repeat unit.
Examples include polyoxypropylene glycols (e.g., VORANOL P-2000
polyol and VORANOL P-4000 polyol, both trademarks of, and available
from, The Dow Chemical Company); polyoxypropylene-oxyethylene glycols
(e.g., DOWFAX DM-30 surfactant and SYNALOX 25 D-700 polyglycol,
both trademarks of, and available from, The Dow Chemical Company);
polyoxyethylene triols (e.g., TERRALOX WG-98 lubricant and TERRALOX
WG-116 lubricant, both trademarks of, and available from, The Dow
Chemical Company); polyoxypropylene-oxyethylene triols (e.g, VORANOL
CP 1421, VORANOL CP 3001 polyol, and VORANOL CP 6001 polyol, all
trademarks of, and available from, The Dow Chemical Company); and
polyoxyethylene hexols (e.g., TERRALOX HP-400 lubricant, trademark
of, and available from, The Dow Chemical Company).
[0078] Suitable polyols made up of ethylene-oxide monomer units
include polyols made from initiators reacted with ethylene oxide.
[0079] Functionality of the polyol is effective to facilitate processability
of a prepolymer of the invention. The functionality should not be
so low that a composition of the invention can take an undesirable
amount of time to gel. But the functionality should not be so high
that it substantially adversely effects gel time, transparency,
or physical properties of the polyurethane hydrogel.
[0080] According to the invention, a polyol can have a functionality
of at least about 2, preferably at least about 3, more preferably
at least about 4, and even more preferably at least about 5. Generally
the functionality is no greater than about 10, preferably no greater
than about 9, and more preferably no greater than about 8.
[0081] In one embodiment, the functionality is at least 3. In another
embodiment, the functionality is between about 2 and about 5.
[0082] Preferably the polyol is a 7,000 molecular-weight triol
copolymer of ethylene oxide (75%) and propylene oxide (25%) (e.g.,
PLURACOL 1123 polyol and PLURACOL VY polyol, both a trademark of,
and available from, BASF, Mount Olive, N.J.).
[0083] A prepolymer according to the invention includes an isocyanate.
One of skill in the art having read the specification would understand
that the selection of the isocyanate will depend on such factors
as the selection of the polyol, the degree of handling or shaping
used to prepare the polyurethane-hydrogel composition, and the end-use
application of the composition.
[0084] The isocyanate can be advantageously selected from at least
one of an organic isocyanate or at least one of a multifunctional
polyisocyanate. These include aliphatic isocyanates and cycloaliphatic
isocyanates. Examples of aliphatic isocyanates and cycloaliphatic
isocyanates include hexamethylene diisocyanate; trans, trans-1,4-cyclohexyl
diisocyanate; 2,4-and 2,6-hexahydrotoluenediisocyana- te; 4,4'-,2,2'-,2,4'-dicyclohexylmethanediisocyanate;
1,3,5-tricyanato cyclohexane; isophorone diisocyanate trimers; and
isophorone diisocyanate. Preferably the isocyanate is isophorone
diisocyanate.
[0085] Although less preferred because they can discolor over time,
the isocyanate can also include aromatic isocyanates. Examples of
aromatic isocyanates include toluene-2,4-diisocyanate; toluene-2,6-diisocyanate;
commercial mixtures of toluene-2,4 and 2,6-diisocyanates; m-phenylene
diisocyanate; 3,3'-diphenyl-4,4'-biphenylene diisocyanate; 4,4'-biphenylene
diisocyanate; 4,4'-diphenylmethane diisocyanate; 3,3'-dichloro-4,4'-biphenylene
diisocyanate; cumene-2,4-diisocyanate; 1,5-napthalene diisocyanate;
p-phenylene diisocyanate; 4-methoxy-1,3-phenylene diisocyanate;
4-chloro-1,3-phenylene diisocyanate; 4-bromo-1,3-phenylene diisocyanate;
4-ethoxy-1,3-phenylene diisocyanate; 2,4-dimethyl-1,3-phenylene
diisocyanate; 5,6-dimethyl-1,3-phenylene diisocyanate; 2,4-diisocyanatodiphenylether;
4,4'-diisocyanatodiphenylether benzidine diisocyanate; 4,6-dimethyl-
1,3 -phenylene diisocyanate; 9,10-anthracene diisocyanate; 4,4'-diisocyanatodibenzyl;
3,3'-dimethyl-4,4'-diisocyanatodiphenylmethane- ; 2,6-dimethyl-4,4'-diisocyanatodiphenyl;
2,4-diisocyanatostilbene; 3,3'-dimethoxy-4,4'-diisocyanatodiphenyl;
1,4-anthracenediisocyanate; 2,5-fluorenediisocyanate; 1,8-naphthalene
diisocyanate; 2,6-diisocyanatobenzfuran; 2,4,6-toluene triisocyanate;
p,p',p"-triphenylmethane triisocyanate; and polymeric 4,4'-diphenylmethane
diisocyanate.
[0086] A composition of the invention generally includes isocyanate
in an amount effective for providing a desirable tensile modulus
or number-average molecular weight between crosslinks. This amount
should not be so high that a prepolymer becomes unprocessable or
so low that the tensile modulus or number-average molecular weight
between crosslinks of a polyurethane hydrogel is substantially adversely
affected.
[0087] A prepolymer according to the invention generally includes
an isocyanate-to-hydroxyl (NCO/OH) site or group (i.e., moles NCO.times.functionality/moles
crosslinker.times.functionality) ratio of at least about 2, preferably
at least about 2. 1, and more preferably at least about 2.2. But
this ratio is generally no greater than about 4, preferably no greater
than about 3, and more preferably no greater than about 2.5.
[0088] A prepolymer according to the invention is generally dispersed
in aqueous solvent to form an aqueous prepolymer solution. An aqueous
prepolymer solution desirably has a viscosity effective for processing
a composition according to the invention. This solution can also
contain additives that facilitate solubility of the prepolymer so
long as the additives are not substantially incompatible with the
components in a composition of the invention.
[0089] A prepolymer according to the invention can be prepared
by methods known in the art and can be obtained commercially. Known
methods for preparing a prepolymer according to the invention generally
involve admixing a polyol with an isocyanate and heating the mixture
to a temperature effective to facilitate the reaction between the
polyol and isocyanate. Examples of prepolymers suitable for use
according to the invention, as well as methods for making such prepolymers,
are included in U.S. Pat. No. 5,462,536. One such prepolymer is
Hypol G-50 hydrophilic polymer (a trademark of The Dow Chemical
Company, Midland, Mich.), which is described in Example 1 of this
specification. One of skill in the art will also appreciate that
the age of a prepolymer (i.e., the amount of time that passes between
initial formation of the prepolymer and when the prepolymer is incorporated
into a polyurethane-hydrogel composition) may affect the molecular
weight of the prepolymer, which in turn, may affect how a particular
prepolymer affects a polyurethane-hydrogel composition of the invention.
One of skill in the art will also readily recognize that it may
be less preferred to use a prepolymer immediately after it is prepared
(i.e., fresh prepolymer), and it may be preferred to allow the prepolymer
to build some additional molecular weight before incorporating it
into a composition of the invention. This phenomenon is known in
the polymer field, and one of skill in the art can readily determine
the optimal age of a prepolymer without undue experimentation.
[0090] Water-Soluble Crosslinker
[0091] A composition of the invention also includes a water-soluble
crosslinker. A crosslinker suitable for use in the invention is
selected to provide a desirable gel time for a polyurethane-hydrogel
composition of the invention and to provide a transparent composition.
[0092] The term "gel time" means the time that elapses
between the time when a prepolymer and a crosslinker are first mixed
together in aqueous solvent and the time at which that mixture polymerizes.
Gel time can vary depending on the amount and type of hydrogel components
selected as well as on the reaction conditions such as pH and temperature.
The gel time is not critical for the composition and method of the
invention. A suitable gel time will depend on the end-use application.
That is, the gel time should be sufficiently long to allow for dispensing
of the composition but not so long that the process for making the
composition becomes prohibitively expensive or unfeasible for commercial
purposes. For some applications, the gel time at 25.degree. C. is
generally less than about 5 minutes, preferably less than about
4 minutes, and more preferably less than about 2 minutes.
[0093] A crosslinker can be selected based on its functionality
and water solubility. Generally a crosslinker should have a functionality
(both number and type) that provides a reaction rate with the prepolymer
that is at least 10 times faster than the reaction rate of water
with the prepolymer. And the functionality preferably provides a
reaction rate that is at least 100 times faster, more preferably
at least 1,000 times faster, even more preferably at least 10,000
times faster, and still more preferably at least 100,000 times faster
than the reaction rate of water with the prepolymer.
[0094] A crosslinker generally has a functionality of at least
2, preferably at least 3, more preferably at least 4, still more
preferably at least 5, and even more preferably at least 6. But
a crosslinker generally has a functionality of no more than about
40, preferably no more than about 30, and more preferably no more
than about 20. In one embodiment, a crosslinker has a functionality
of at least about 8 and no more than about 16. The term "functionality"
is known to one of skill in the polyurethane art and generally refers
to the number of active hydrogens per molecule able to react with
the unreacted isocyanate groups of the prepolymer. The functionality
generally provides about 2 or more active hydrogen groups per molecule.
The active hydrogen groups can be hydroxyl, mercaptyl, or amino
groups.
[0095] The site or group (i.e., moles NCO.times.functionality/moles
crosslinker.times.functionality) ratio of initial isocyanate to
crosslinker is generally at least about 1.4, preferably at least
about 1.6, and more preferably at least about 1.8. But this ratio
is generally no greater than about 2.7, preferably no greater than
about 2.4, and more preferably no greater than about 2.1.
[0096] The combination of functionality and water solubility of
a crosslinker is selected to provide a polyurethane hydrogel of
the invention with a desirable tensile modulus or number-average
molecular weight between crosslinks and transparency.
[0097] It has surprisingly been found that the selection of the
crosslinker is important to obtaining a transparent polyurethane
hydrogel of the invention. Although this invention is not limited
to any particular theory, it is believed that the selection of crosslinker
according to the invention facilitates solubility of the polyurethane
network as well as serving to scavenge residual isocyanate. As a
result, selection of crosslinker facilitates maintaining an aqueous
phase and helps prevent formation of an insoluble phase that may
arise from a nonuniform distribution of crosslinks.
[0098] The term "residual isocyanate" means that amount
of isocyanate that did not react in the formation of the prepolymer.
That is, "residual isocyanate" means that amount of isocyanate
that is still available for reaction after a prepolymer is formed.
It is believed that residual isocyanate can react with water and
contribute to formation of an insoluble phase, thereby adversely
affecting transparency.
[0099] According to the invention, the site or group (i.e., moles
NCO.times.functionality/moles crosslinker.times.functionality) ratio
of residual isocyanate to initial crosslinker functionality is no
greater than about 0.8, preferably no greater than about 0.7, and
more preferably no greater than about 0.6. In one embodiment, this
ratio is between about 0.4 and about 0.5. In another embodiment,
this ratio is about 0.47.
[0100] A crosslinker is present in an amount effective to form
a network with the prepolymer and to scavenge or solubilize enough
residual isocyanate to prevent formation of an insoluble phase,
which substantially adversely affects transparency. A crosslinker
should not be included in so large of an amount that it substantially
adversely affects gel formation. The amount of crosslinker suitable
for use with the invention will typically depend on the type of
crosslinker selected and the prepolymer. One of skill in the art
having read this specification would understand how to determine
the amount of crosslinker suitable for the invention such that gelation
occurs and the resulting polyurethane hydrogel has strength suitable
for its end-use application.
[0101] In one embodiment, a crosslinker is solubilized in aqueous
solvent, preferably water, to form a crosslinker solution. To control
reactivity between a crosslinker and a prepolymer, the pH of the
crosslinker solution can be controlled to promote reaction with
prepolymer. For example, the pH of a 1 weight-percent solution of
an amine-functionalized crosslinker (e.g., polyethylenimine) generally
is at least about 7, preferably at least about 7.4, and more preferably
at least about 7.8. But the pH generally is no greater than about
9.5, preferably no greater than about 8.6, and more preferably no
greater than about 8.2. The pH of, for example, polyethylenimine
can be controlled by addition of an acid, such as hydrochloric acid.
[0102] In one embodiment, the pH of a 1 weight-percent solution
of an amine-functionalized crosslinker is about 8. The effective
pH will depend on the type of crosslinker used. One of skill in
the art having read this specification will recognize that any desirable
pH control of the crosslinker solution will be unnecessary if a
composition of the invention is prepared in an aqueous solvent that
contains a pH buffer or some other pH control.
[0103] Examples of suitable crosslinkers include polyamines, amine
end-capped polyols, polyols, and amine end-capped ethylene-oxide
sugars.
[0104] Polyamines suitable for use with the invention have at least
about 0.8 milliequivalent (meq) charge per gram of crosslinker.
Suitable polyamines can have a charge density much higher than 0.8
meq charge per gram.
[0105] In one embodiment, a polyamine has 1.0 meq charge per gram,
and in another embodiment, a polyamine has between 20 and 25 meq
charge per gram. Suitable polyamines generally have a molecular
weight of at least about 140 gram/mole, preferably at least about
170 gram/mole, and more preferably at least about 200 gram/mole.
But suitable polyamines generally have a molecular weight no greater
than about 2,000 gram/mole, preferably no greater than about 1,800
gram/mole, and more preferably no greater than 1,500 gram/mole.
[0106] In one embodiment, the polyamine is polyethylenimine having
a molecular weight between about 600 gram/mole and about 800 gram/mole.
Other molecular weights of polyethylenimine are also useful with
the invention.
[0107] Polyols and amine end-capped polyols suitable for use with
the invention are water soluble. Preferably they are ethylene-oxide
based. Examples of polyamines include polyethylenimine (e.g., 600,
800, and 1200 molecular weight; e.g., CAS No. 25987-06-8), polyvinyl
amine, and chitosan.
[0108] Although less preferred, other amine end-capped polyols
include the water-soluble JEFFAMINE T-Series amines (e.g., JEFFAMINE
T-403 [CAS 39423-51-3], which is a polyoxypropylenetriamine having
an average molecular weight of approximately 440) and the JEFFAMINE
ED-2003 amine [CAS 65605-36-9], which is a water-soluble aliphatic
diamine derived from a propylene oxide-capped poly(ethylene oxide)
with an approximate molecular weight of 2000 (trademark of, and
available from, Huntsman, Austin, Tex.). The functionality of an
amine end-capped polyalkyleneoxide may be increased by initiating
polymerization with a sugar (e.g., polyacrylic acid, sorbitol, sucrose,
erythritol, and pentaerytheratol).
[0109] Examples of polyols include VORANOL RN-482 polyol (trademark
of, and available from, The Dow Chemical Company) and VORANOL CP-450
polyol (trademark of, and available from, The Dow Chemical Company).
[0110] Water-soluble crosslinkers such as 3-, 4-, 5-, and higher
functional amine end-capped polyethylene glycols should have sufficient
molecular weight such that upon incorporation into a polyurethane
hydrogel, the Mc is at least about 2,000, preferably at least about
3,000, more preferably at least about 4,000, and still more preferably
at least about 5,000. But the M.sub.c should be no greater than
about 8,000, preferably no greater than about 7,000, and more preferably
no greater than about 6,000.
[0111] Another exemplary crosslinker includes multifunctional amine
end-capped ethyleneoxides. One such crosslinker is shown here (I)
and is a 4-functional poly(oxy- 1,2-ethanediyl, .alpha.-hydroxy-.OMEGA.-(2-amino-
ethoxy)-, ether with 2,2-bis(hydroxymethyl)-1,3-propanediol (4:1)
(9C1)[CAS 169501-65-9], where n, which is the degree of polymerization
in the structure below, can vary per chain but, in the end, typically
corresponds to a final molecular weight of between about 484 and
1,189 grams/mole. Typically n can range from n=1 to n=5. 1
[0112] Other examples of amine end-capped poly(ethylene oxide)
crosslinkers having a functionality of 2 to 12 can be found in the
literature and include CAS Registry numbers 177986-99-1P; 179189-24-3;
52379-15-4; 244235-34-5; 244235-35-6; 244235-36-7; 244235-38-9;
172355-14-5; 180273-44-3; and 158948-29-9. Mono-, di-, and multifunctional
polyalkylene oxides including poly(ethylene oxide) or polyethylene
glycol are commercially available from Shearwater Polymers, Inc.
(Huntsville, Ala.; e.g., Shearwater Corporation catalog number 0J2V0L13).
One of skill in the art having read this specification can easily
imagine derivatives of these crosslinkers that would also be useful
for the invention and such derivatives are considered to be within
the scope of this invention. These types of compounds have been
described in, for example, Urrutigoity and Souppe, Biocatalysis,
2:145 (1989); Cordes and Kula, J. Chromat., 376:375 (1986); and
Okada and Urabe, Meth. Enzymol., 136:34 (1987) for uses other than
as described for this invention, but they have surprisingly been
found to be useful for this invention.
[0113] One of skill in the art having read this specification will
readily be able to select the type and amount of water-soluble crosslinker
useful according to the invention.
[0114] Additives
[0115] A composition of the invention can also include known additives
and other known components to prepare a polyurethane-hydrogel composition.
Generally any additive known to one of skill in the art to be useful
in preparing a transparent polyurethane-hydrogel composition can
be included in a composition of the invention so long as the additive
is not substantially incompatible with other components in the composition
and so long as the additive does not substantially adversely affect
the transparency of the composition.
[0116] Examples of additives include antioxidants, surfactants,
and antifreezes.
[0117] Suitable surfactants are effective to solubilize hydrogel
components or other additives and include TRITON X-100 surfactant,
TRITON X-102 surfactant (Union Carbide Corporation), and DOWFAX
63N40 surfactant (The Dow Chemical Company, Freeport, Tex.).
[0118] Suitable antifreezes are effective to facilitate freeze
stability of a composition of the invention and include methanol,
ethanol, ethylene glycol, and isopropyl alcohol. If any antifreeze
is added and such an antifreeze can be considered an organic solvent,
the amount should be small enough such that no more than a trace
amount of organic solvent is introduced into the composition and
certainly substantially less than an amount that would disperse
hydrogel components.
[0119] The balance of a composition of the invention is water.
The amount of water can vary depending on the intended end-use application.
[0120] Method
[0121] A method of the invention includes admixing a prepolymer,
and a water-soluble crosslinker in an aqueous solvent and in the
substantial absence of organic solvent. The hydrogel components
are admixed in a manner effective to disperse the hydrogel components
in water. According to the invention, the method is carried out
substantially free of organic solvent. One of skill in the art having
read this specification would understand that conventional mixing
methods can be used to disperse the prepolymer in water.
[0122] Additives can be included in a composition of the invention
at any time during the method. For example, an additive can be dispersed
with a prepolymer in aqueous solvent to form a prepolymer solution,
which can be subsequently admixed with a water-soluble crosslinker.
As another example, an additive can be dispersed with a water-soluble
crosslinker to form a crosslinker solution, which can be subsequently
admixed with a prepolymer to form a composition of the invention.
[0123] The conditions are generally selected such that they are
not substantially incompatible with hydrogel components. These conditions
can be selected without undue experimentation by one of skill in
the art having read this specification. These conditions, for example,
temperature, pH, and mixing, will vary depending on the hydrogel
components selected and the intended end-use application.
[0124] Also according to the invention, the reaction mixture can
be deposited onto a substrate during any step. For example, all
hydrogel components can be admixed and the mixture can be deposited
into a container. Alternatively, the prepolymer can be deposited
into a container and then polymerized with crosslinker.
[0125] The following description provides one example of a method
of the invention. To prepare a polyurethane-hydrogel composition
of the invention, a prepolymer can be dispersed in aqueous solvent.
One of skill in the art having read this specification would understand
that conventional mixing methods can be used to disperse the prepolymer
in aqueous solvent.
[0126] Next, a crosslinker solution can be added to the prepolymer,
and the mixture can be stirred for an amount of time effective to
disperse hydrogel components in aqueous solvent. Again, one of skill
in the art having read this specification would understand that
conventional mixing methods can be used.
[0127] The composition can then be deposited into a container suitable
for an intended end-use application.
[0128] In one embodiment, 100 ml of a mixture of the prepolymer
and crosslinker are mixed for about 15 seconds using a mechanical
stirrer.
[0129] The gel time for a composition of the invention desirably
allows effective processing and dispensing of the composition.
[0130] In one embodiment, the crosslinker solution is added to
the prepolymer in a container suitable for holding a polyurethane-hydrogel
composition of the invention. In this embodiment, the gel time can
be as fast as {fraction (1/2)} second at room temperature (25.degree.
C.).
[0131] In another embodiment, the crosslinker solution is added
to the prepolymer in a first container and then subsequently poured
into a second container suitable for holding a polyurethane-hydrogel
composition of the invention. In this embodiment, the gel time can
be as long as, for example, 30 minutes but can also be longer.
[0132] Suitable containers for holding an air-freshener composition
of the invention include any container that does not substantially
adversely interact with the composition of the invention, e.g.,
glass jar, plastic container, and ceramic container. Preferably
the container takes advantage of the transparency of the composition.
[0133] Other suitable containers will depend on the end-use application.
[0134] Air-Freshner Application
[0135] One application for a transparent polyurethane-hydrogel
composition of the invention includes an application that contains
a fragrance composition. Fragrance compositions are known for their
use in air-freshener compositions.
[0136] Traditionally air-freshener compositions have been valued
for imparting a desirable scent to the air to mask stale or unpleasant
odors. The containers used for air-freshener compositions have tended
to be more functional rather than aesthetically pleasing. More recently,
though, air-freshener compositions have been used to enhance a room's
decor or ambiance. Thus, it is desirable for an air-freshener composition
to be aesthetically pleasing, to harmonize with, or even enhance,
room decor.
[0137] One way to meet this need is to provide a transparent air-freshener
composition. Transparent air-freshener compositions are known, but
these compositions are typically made from gums, for example, carrageenates,
alginates, pectins, or gelatin. But gum-based air-freshener compositions
have several disadvantages.
[0138] One disadvantage of gum-based compositions is that the gel
shrinks in a manner that is not proportional to the external dimensions.
This shrinkage can affect the liberation of fragrance or fragrance
release, can be visually unappealing, and is, therefore, undesirable.
Particularly unattractive shrinking occurs when fragrance compositions
based on gum-based gels are left uncovered and exposed to air.
[0139] Another disadvantage of gum-based compositions is that they
have less than desirable heat stability. These gels can begin to
flow at temperatures as low as 40.degree. C., depending on the nature
of the gel network and the nature and composition of the gel. This
can cause problems with transporting gels as well as using gels
in warm climates. Thus, air-freshener compositions prepared from
a polyurethane-hydrogel composition of the invention can be particularly
advantageous--it not only can provide improved shrinkage and heat
stability as compared to gum-based gels, but the composition of
the invention can provide the aesthetically appealing transparency
character and desirable gel strength.
[0140] An air-freshener composition can be prepared from a transparent
polyurethane-hydrogel of the invention by admixing a prepolymer,
a fragrance composition, and a water-soluble crosslinker in aqueous
solvent and in the substantial absence of organic solvent.
[0141] A prepolymer suitable for use in the invention includes
a prepolymer as described above, which is prepared as described
above. The prepolymer generally includes a reaction product of at
least one water-soluble polyol and at least one isocyanate.
[0142] A fragrance composition includes at least a fragrance oil
but generally includes a fragrance oil, a surfactant, and water.
Any fragrance oil suitable for preparing an air-freshener composition
can be used. Generally the fragrance oil is selected so that its
bright, effervescent top notes are balanced with its heart, which
is also known as its middle note. The vapor pressure of a fragrance
oil suitable for use in an air-freshener composition at 20.degree.
C. generally does not exceed 0.1 mm Hg. Examples of fragrance oil
suitable for use in the invention include Berry Medley (Wessel Fragrance
Inc., Anglewood Cliff, N.J.) and Grape Fragrance (Flavor and Fragrance
Specialities, Mahwah, N.J.).
[0143] The amount of fragrance oil should not be so low that the
scent is too mild, and the amount of the fragrance oil should not
be so high as to make the manufacture of the air freshener prohibitively
expensive. The amount of fragrance oil is generally at least about
2.5 weight percent, preferably at least about 3.0 weight percent,
and more preferably at least about 3.5 weight percent. But the amount
of fragrance oil is generally no more than about 5.0 weight percent,
preferably no more than about 4.5 weight percent, and more preferably
no more than about 4.0 weight percent.
[0144] Because fragrance oil is generally insoluble in aqueous
solvents, to incorporate a fragrance oil into an aqueous solvent,
the fragrance oil can be formulated with a surfactant. Any surfactant
suitable for solubilizing a fragrance oil in an aqueous solvent
is suitable for use in the invention. The surfactant is generally
chosen such that it does not substantially adversely affect the
transparency of a polyurethane-hydrogel composition of the invention.
[0145] Examples of suitable surfactants include a nonionic surfactant
such as ethoxylated alkyl phenol (e.g., TRITON X-100 and TRITON
X-102, both available from Union Carbide Corporation), nonyl phenols,
and ethoxylated alcohols (e.g., DOWFAX 63N40 available from The
Dow Chemical Company, Freeport, Tex.).
[0146] The surfactant is present in an amount effective for solubilizing
the fragrance oil in an aqueous solvent. The amount of surfactant
should not be so low that the transparency of the gel is substantially
adversely effected, and the amount of surfactant should not be so
high that the air-freshener composition becomes prohibitively expensive
to manufacture. Generally the amount of surfactant should be no
more than about 15 weight percent, preferably no more than about
12 weight percent, and more preferably no more than about 10 weight
percent. In one embodiment, the surfactant is present in an amount
between about 7 weight percent and about 8 weight percent.
[0147] The type and amount of surfactant generally depends on the
type and amount of fragrance oil used. Thus, the selection of surfactant
and fragrance oil is generally interdependent. One of skill in the
art having read this specification would understand how to mutually
choose effective surfactant and fragrance oil.
[0148] The fragrance composition can be prepared by essentially
titrating fragrance oil in an aqueous solvent with surfactant. That
is, surfactant can be added to an aqueous solvent of fragrance oil
until the solution becomes transparent.
[0149] A fragrance composition can also include one or more additives.
Generally any additive known to one of skill in the art to be useful
in preparing a fragrance composition can be included in a composition
of the invention so long as the additive is not substantially incompatible
with other components in the composition. Examples of additives
include antifreeze, antioxidant, bittering agent, and colorant.
[0150] One desirable additive includes an antifreeze. Examples
of suitable antifreeze include methanol, ethanol, ethylene glycol,
and isopropyl alcohol. An antifreeze can be selected to enhance
fragrance release and can also aid freeze stability during, for
example, transportation or storage of an air-freshener composition.
[0151] The amount of antifreeze should not be so high as to make
the fragrance composition prohibitively expensive to manufacture
or so high that the antifreeze disperses the prepolymer. The antifreeze
is generally present in an amount of at least about 0.5 weight percent,
preferably at least about 1.0 weight percent, and more preferably
at least about 1.5 weight percent. But the antifreeze is generally
present in an amount of no greater than about 5 weight percent,
preferably no greater than about 4.0 weight percent, and more preferably
no greater than about 3.0 weight percent.
[0152] Another desirable additive includes a colorant. Examples
of suitable colorant include any water-based colorant such as food
coloring and Reactint polymeric colorant (available from Milliken
Chemical, Spartanburg, S.C.).
[0153] A polyurethane-hydrogel composition of the invention is
transparent as already described above. When a colorant is added
to the composition of the invention, the intent is to not substantially
alter the composition's transparency, but all colorants necessarily
absorb some amount of light at a particular wavelength that corresponds
to that color. Thus, a composition of the invention has a transparency
as described above in the absence of a colorant, but a colorant
in the composition can substantially alter the transmission of light
especially allowing for the transmission of light in a narrow range
of wavelength.
[0154] To prepare an air freshener from a transparent polyurethane-hydrogel
composition of the invention, a fragrance composition including
water, fragrance, and surfactant is generally mixed using methods
known to one of skill in the art until all components are dissolved.
Next, a prepolymer is added to the mixed fragrance composition.
The prepolymer and fragrance oil composition can also be mixed using
methods known to one of skill in the art. In one embodiment, the
prepolymer and the fragrance composition are mixed using a jiffy
mixer (available from Aldrich, Milwaukee, Wis.) for an amount of
time to disperse reactants in water. In one embodiment, the reactants
are mixed for about 4 minutes.
[0155] A water-soluble crosslinker can then be added to the mixture
of prepolymer and fragrance composition. The water-soluble crosslinker
can be added alone or in aqueous solvent (e.g., in water). This
mixture is stirred using methods known to one of skill in the art
for an amount of time effective to disperse the components in water.
In one embodiment, this mixing is done for about 15 seconds.
[0156] The gel time for an air-freshener composition desirably
allows for effective processing and dispensing of the composition.
[0157] In one embodiment, the water-soluble crosslinker is added
to the mixture of prepolymer and fragrance component in a container
suitable for holding an air-freshener composition prepared from
a transparent polyurethane-hydrogel composition of the invention.
In this embodiment, the gel time can be as fast as 1/2 second at
room temperature (25.degree. C.).
[0158] In another embodiment, the water-soluble crosslinker is
added to the mixture of prepolymer and fragrance component in a
first container and then subsequently poured into a second container
suitable for holding an air-freshener composition prepared from
a transparent polyurethane-hydrogel composition of the invention
before the composition polymerizes. In this embodiment, the gel
time can be as long as 30 minutes but can also be longer at room
temperature and 1 atmosphere pressure.
[0159] Suitable containers for holding an air-freshener composition
of the invention include any container that does not substantially
adversely interact with the composition of the invention, e.g.,
glass jar, plastic container, and ceramic container. The performance
of an air-freshener composition will depend on the shape and design
of the container as well as on the amount of, and hydrogel components
used in, the polyurethane hydrogel. One of skill in the art having
read this specification will readily be able to select a desirable
container in combination with selection of hydrogel components.
[0160] An air-freshener composition according to the invention
can also have a gel object suspended within the air-freshener composition
while maintaining the transparency, texture, and structure of the
transparent polyurethane-hydrogel of the air freshener. The gel
object can be prepared from a variety of known gels such as gum-based
gels and thermally-cured gels. But a preferred embodiment includes
a gel object prepared from a transparent polyurethane-hydrogel composition
of the invention. The gel object can be prepared in a variety of
shapes such as fruit, animals, hearts, leaves, and stars by forming
gel objects in molds. Examples of molds include candy molds, soap
molds, and ice-cube trays.
[0161] Gel objects can be removed from the molds after a time period
effective for the gel object to have sufficient stability to withstand
demolding.
[0162] The gel object can be placed into containers suitable for
holding an air-freshener composition made from a polyurethane-hydrogel
composition, such as a glass jar, plastic container, and ceramic
container, and the mixture of the prepolymer and the crosslinker
can be added to the container that contains the gel object.
[0163] One advantage of using a transparent polyurethane-hydrogel
composition in this application is that the hydrogel is processed
at room temperature and is not thermally formed, which allows for
the integrity of the gel object to be maintained when the transparent
polyurethane-hydrogel composition is added to the container.
[0164] Another advantage of a transparent polyurethane-hydrogel
composition in this application is that a gel object made by a transparent
polyurethane-hydrogel does not have the shrinkage problems typically
found with gum-based gels. As a result, the gel object can maintain
its dimensional shape even when the air-freshener composition begins
to shrink when water and fragrance oil evaporate.
[0165] An air-freshener composition can include other suspended
objects that are advantaged by the composition's transparency such
as glitter or confetti.
[0166] A gel object can be transparent but need not be transparent.
In one embodiment, a gel object contains a pigment additive and
is opaque or less than transparent.
[0167] The invention will be further described by the following
Examples. These Examples are not meant to limit the invention but
to further illustrate embodiments of the invention. Any reference
to prepolymer in the Examples refers to the prepolymer in Example
1, unless the Example expressly states otherwise, and any reference
to polyethylenimine (PEI) in the Examples refers to polyethylenimine
having an average molecular weight of about 800 as first described
in Example 2, unless the Example expressly states otherwise.
EXAMPLES
Example 1
Preparation of a Prepolymer Suitable for Use in the Invention
[0168] To prepare one example of a prepolymer suitable for use
with the invention, a 7000 molecular-weight triol copolymer of ethylene
oxide (75%) and propylene oxide (25%) (PLURACOL 1123 available from
BASF, Mount Olive, N.J.) ("the polyol") was dried. Phosphoric
acid (20 ppm) was added to the polyol. Next, the polyol (1687.46
g) was mixed with 165.0 g isophorone diisocyanate (IPDI) (available
from Bayer, Pittsburgh, Pa.) and heated at 70.degree. C. under dry
nitrogen. Isocyanate levels were determined by addition of dibutylamine
and back titration with standard acid. Fourteen days were required
for the isocyanate concentration to reach 0.47 meq/g (0.39 meq/g=theoretical)
according to ASTM No. D5155-96. The resulting prepolymer was liquid
at room temperature (25.degree. C.). This prepolymer is available
from The Dow Chemical Company (HYPOL G-50 hydrophilic polymer).
Example 2
Determination of Transmittance of a Polyurethane-Hydrogel Composition
of the Invention
[0169] To determine the transmittance of a polyurethane-hydrogel
composition of the invention, a polyurethane-hydrogel composition
was prepared with the prepolymer of Example 1 according to the following
formulations. A formulation of the invention (Invention Formulation)
was compared to two comparative formulations. The first comparative
formulation (Formulation 1) did not contain a crosslinker--only
water--and the second comparative formulation (Formulation 2) did
contain a crosslinker but not a crosslinker as defined for the invention.
Table 1 shows the formulations used to make a composition that contains
about 5 weight-percent prepolymer, and Table 2 shows the formulations
used to make a composition that contains about 3 weight-percent
prepolymer.
1TABLE 1 Formulations for Composition With About 5 Weight-Percent
Prepolymer Formulation 1 Invention (weight Formulation 2 Formulation
Component percent) (weight percent) (weight percent) Water 95 94.96
94.8 Prepolymer 5.0 5.0 5.0 Polyethylenimine -- -- 0.2 Ethylene
Diamine -- 0.04 -- pH Neutral 10.0 7.7
[0170]
2TABLE 2 Formulations for Composition With About 2.7 Weight-Percent
Prepolymer Formulation 1 Invention (weight Formulation 2 Formulation
Component percent) (weight percent) (weight percent) Water 97.3
97.28 97.2 Prepolymer 2.7 2.7 2.7 Polyethylenimine -- -- 0.1 Ethylene
Diamine -- 0.02 -- pH Neutral 11.7 8.5
[0171] The prepolymer was prepared as described in Example 1. Polyethylenimine
has an average molecular weight of about 800 and was obtained from
Aldrich, Milwaukee, Wis. Ethylene diamine was obtained from The
Dow Chemical Company, Freeport, Tex.
[0172] For each formulation, the prepolymer was first dispersed
in water to form a prepolymer solution. For Formulation 1, all water
was added to the prepolymer. For Formulation 2 and Invention Formulation,
essentially all of the water was added to the prepolymer. The water
and prepolymer were mixed in a 100 ml beaker by a mechanical stirrer
for about 4 minutes.
[0173] For Formulation 2 the ethylene diamine crosslinker was added
at 0.04 and 0.02 weight percent as shown in Tables 1 and 2 respectively.
And for the Invention Formulation, a crosslinker solution of 1 weight
percent was prepared and aliquoted into the prepolymer to provide
the weight percent of crosslinker shown in Tables 1 and 2.
[0174] The pH of the crosslinker solution for Formulation 2 was
adjusted to about 11.7 (2.7 weight-percent prepolymer) and to about
10.0 (5.0 weight-percent prepolymer) by the addition of concentrated
hydrochloric acid. The pH of the crosslinker solution for Invention
Formulation was adjusted to about 8.5 (2.7 weight-percent prepolymer)
and to about 7.7 (5.0 weight-percent prepolymer) by the addition
of concentrated hydrochloric acid.
[0175] For Formulation 2 and Invention Formulation, the prepolymer
solution and crosslinker solution were admixed by use of a mechanical
stirrer for about 15 seconds at 200 rpm.
[0176] Formulation 1 was still not polymerized after 24 hours.
The approximate gel time for Formulation 2 was about 75 seconds
(2.7 weight-percent prepolymer) and about 180 seconds (5.0 weight-percent
prepolymer). And the approximate gel time for Invention Formulation
was about 55 seconds (2.7 weight-percent prepolymer) and about 120
seconds (5.0 weight-percent prepolymer).
[0177] Each formulation was evaluated for its percent transmittance
about 24 hours after the hydrogel components were mixed. Each formulation
was evaluated using a cuvette having a path length of about 4 cm.
[0178] Formulation 1 (2.7 weight-percent prepolymer) showed a transmittance
of about 0 percent at 600 nm relative to deionized water. Formulation
1 (5.0 weight-percent prepolymer) showed a transmittance of about
0 percent at 600 nm relative to deionized water.
[0179] The results for Formulation 2 and Invention Formulation
are shown in FIGS. 1 and 2. These Figures show percent transmittance
of a sample in the visible spectrum from 400 to 800 nanometers (nm).
[0180] FIG. 1 shows percent transmittance of formulations made
with 2.7 weight percent of prepolymer. Formulation 2 showed a percent
transmittance of 21 percent at 600 nm. And Invention Formulation
showed a percent transmittance of 81 percent at 600 nm.
[0181] FIG. 2 shows formulations made with 5 weight percent of
prepolymer. Formulation 2 showed a percent transmittance of 21 percent
at 600 nm. And Invention Formulation showed a percent transmittance
of 76 percent at 600 run.
Example 3
Preparation of an Air-Freshener Composition According to the Invention
[0182] To prepare an air-freshener composition according to the
invention, the prepolymer of Example 1 was first prepared.
[0183] Next, a fragrance composition was prepared by admixing 3
g fragrance oil (Berry Medley available from Wessel Fragrance Inc.,
Anglewood Cliff, N.J.), 2 g ethanol, 7 g TRITON X-100 (available
from Union Carbide Corporation), and 75 g water in a 250 ml beaker
using a mechanical stirrer until all components were dispersed.
This took about 30 minutes. The prepolymer (3 g) was then added
to this mixture, and the components were mixed for an additional
4 minutes.
[0184] A crosslinker solution was prepared by dissolving 1 weight
percent of polyethylenimine in 100 grams of water. The pH of the
crosslinker solution was adjusted to about 9 by adding concentrated
hydrochloric acid. The crosslinker solution was then added to the
mixture containing the prepolymer by adding 10 g of the 1% polyethylenimine
solution. All components were then mixed for about 15 seconds. After
60 seconds, a considerable increase in viscosity was observed. The
gel time was about 80 seconds.
[0185] The air-freshener composition in this Example included 2.5
weight-percent prepolymer, 85.4 weight-percent water, 7 weight-percent
Triton X-100, 3 weight-percent fragrance oil, 2 weight-percent ethanol,
and 0.1 weight percent polyethylenimine.
Example 4
Determination of the Effect of pH on an Air-Freshener Composition
of the Invention
[0186] Air-freshener compositions were prepared according to the
procedure described in Example 3, except that the pH of the crosslinker
solution was modified. Table 3 shows the pH of the crosslinker solution,
the time at which a substantial increase in viscosity was observed
(t.sub.1) and the gel time (t.sub.2). Time t.sub.1 can also be considered
as the time at which the onset of polymerization could be observed.
3TABLE 3 Effect of pH on an Air-Freshener Composition of the Invention
pH Gel Onset (t.sub.1) (seconds) Gel Time (t.sub.2) (seconds) 8.5
210 300 8.7 130 180 9.0 60 80 10.0 <3 <3
[0187] These data show that the pH of a crosslinker solution that
contains polyethylenimine (800 molecular weight) affects gel time
and that the selection of pH of the composition can be used to optimize
gel time.
Example 5
Effect of Amounts of Crosslinker on an Air-Freshener Composition
of the Invention
[0188] To determine the effect of crosslinker amount on an air-freshener
composition of the invention, four air-freshener compositions were
prepared using varying amounts of crosslinker for each composition.
[0189] The prepolymer of Example 1 was first prepared.
[0190] Next, a series of fragrance compositions was prepared by
admixing 3 g fragrance oil (Berry Medley available from Wessel Fragrance
Inc., Anglewood Cliff, N.J.), 2 g ethanol, 7 g Triton X-100 (available
from Union Carbide Corporation), and varying amounts of water (depending
on the amount of crosslinker solution added) in a 250 ml beaker
using a magnetic stirrer until a clear solution was obtained and
all components were dissolved. This took about 30 minutes. The prepolymer
(3 g) was then added to these mixtures, and the components were
mixed for an additional 4 minutes.
[0191] A 1 weight-percent crosslinker solution was prepared by
dissolving 1 gram of polyethylenimine in 99 grams of water. The
pH of the crosslinker solution was adjusted to about 9 by addition
of concentrated hydrochloric acid. The crosslinker solution was
then added to the mixture containing the prepolymer by adding varying
amounts of the 1% polyethylenimine solution. All components were
then mixed for about 15 seconds.
[0192] The compositions were evaluated by applying pressure to
the surface of the composition with a probe. This evaluation was
used to qualitatively determine the effect of crosslinker amount
on the firmness of the compositions. Each composition was rated
on a scale of 1 to 3, with 1 being very firm and 3 being less firm.
The results are shown in Table 5.
4TABLE 5 Effect of Crosslinker Amount on an Air-Freshener Composition
of the Invention PEI (1% Water solution) PEI (weight Sample No.
(grams) (grams) percent) Firmness 1 80 5 0.05 3 2 75 10 0.10 2 3
70 15 0.15 2 4 65 20 0.20 1
[0193] These data show that by altering the amount of polyethylenimine
(800 molecular weight), while maintaining the amount of prepolymer
constant, the gel firmness can be modified. The gel firmness increased
as the amount of polyethylenimine increased. Generally a composition
having a firmness of 3 has a higher number-average molecular weight
between crosslinks than a composition having a firmness of 1.
Example 6
Preparation of an Air-Freshener Composition of the Invention Having
a Gel Object Suspended Within the Composition
[0194] A gel object was first prepared by making an air-freshener
composition according to Example 3 except that 0.5 weight-percent
water was replaced with 0.5 weight-percent green food coloring and
the prepolymer was 5 weight percent instead of 3 weight percent.
After the final mixing step, the mixture was dispensed into an object
mold having a shape of a frog (1 inch by 3/4 inch by 1/2 inch) and
allowed to finish polymerizing for about 80 seconds. The object
mold was a candy mold. After 30 minutes, the gel object was placed
in a clear jar (200 ml).
[0195] An air-freshener composition for dispensing into the jar
was then prepared. To prepare an air-freshener composition according
to the invention, the prepolymer of Example 1 was first prepared.
[0196] Next, a fragrance composition was prepared by admixing 3
g fragrance oil (Berry Medley available from Wessel Fragrance Inc.,
Anglewood Cliff, N.J.), 2 g ethanol, 7 g TRITON X-100 (available
from Union Carbide Corporation), and 75 g water in a 250 ml beaker
using a mechanical stirrer until a clear solution was obtained and
all components were dissolved. This took about 30 minutes. The prepolymer
(2.5 g) was then added to this mixture, and the components were
mixed for an additional 4 minutes.
[0197] A crosslinker solution was prepared by dissolving 1 weight
percent of polyethylenimine in 100 grams of water. The pH of the
crosslinker solution was adjusted to about 9 by adding concentrated
hydrochloric acid. The crosslinker solution was then added to the
mixture containing the prepolymer by adding 10 g of the 1% polyethylenimine
solution. All components were then mixed for about 15 seconds and
subsequently dispensed into the glass jar that contained the gel
object. The gel time was about 80 seconds.
Example 7
Effect of Amounts of Crosslinker and Prepolymer on the Gel Strength
of an Air-Freshener Composition of the Invention
[0198] To determine the effect of crosslinker on the gel strength
of an air-freshener composition of the invention, air-freshener
compositions were prepared, and their gel strength was measured.
[0199] The prepolymer of Example 1 was first prepared.
[0200] Next, a fragrance composition was prepared by admixing 3
g fragrance oil (citrus Fresh, available from Flavor & Fragrance
Specialties, Mahwah, N.J.), 2 g Triton X-100 (Union Carbide Corporation,
Danbury, Conn.), and varying amounts of water (depending on the
amount of prepolymer and crosslinker added) in a 250 ml beaker using
a magnetic stirrer until a clear solution was obtained and all components
were dissolved. This took about 30 minutes. The prepolymer was then
added to this mixture, and the components were mixed for an additional
4 minutes.
[0201] Crosslinker solutions (1 weight percent) were prepared by
dissolving a water-soluble crosslinker (1 g) in water (99 g) and
then adjusting the pH by addition of concentrated hydrochloric acid.
[0202] Air-freshener compositions were prepared by admixing all
hydrogel components as described in Table 6. Generally all hydrogel
components were admixed for about 15 seconds and then poured into
a Bloom jar having an internal diameter of 59 mm, a height of 85
mm, and a capacity of 155 ml (available from Schott (Duran) and
described in DIN 53260 (Deutsche Industrie Norm). The compositions
were allowed to stand for 24 hours before any testing was done.
5TABLE 6 Formulations of Air-Freshener Composition Formulation
1 Formulation 2* Component (weight percent) (weight percent) Water
91.9 87.87 Prepolymer 3 7 Polyethylenimine 0.1 0.23 Citrus Fresh
3 3 Triton X-100 2 2 pH Polyethylenimine 9 8 *Formulation 2 is not
transparent according to the invention and is a comparative example.
[0203] The gel strength of each composition was determined using
a Stevens Texture Analyzer and a 0.5-inch Bloom Gelometer plunger
(both available from Stevens Company) as described in British Standard
BS 757 (1975).
[0204] Formulation 1 showed a gel onset (t.sub.1) of 35 seconds,
a gel time (t.sub.2) of 60 seconds (see Example 4 for description
of t.sub.1 and t.sub.2), and a gel strength of 70 grams. Formulation
2 showed a gel onset (t.sub.1) of 43 seconds, a gel time (t.sub.2)
of 72 seconds, and a gel strength of 370 grams.
[0205] Although the gel time was substantially the same for these
Formulations, the results indicate that the gel strength substantially
increased when the amounts of water-soluble crosslinker and prepolymer
were increased.
[0206] Each composition was also evaluated for its percent transmittance
about 24 hours after the hydrogel components were mixed. Each composition
was evaluated using a cuvette having a path length of about 4 cm.
[0207] FIG. 3 shows the percent transmittance for Formulation 1
and Formulation 2. Formulation 1 showed a percent transmittance
of about 80 percent at 600 nm, and Formulation 2 showed a percent
transmittance of about 25 percent at 600 nm.
[0208] Although the gel strength of Formulation 2 can be desirable
according to the invention, Formulation 2 is not transparent according
to the invention, and, therefore, is a comparative example. These
results suggest that the amounts of prepolymer and crosslinker used
in Formulation 2 are ineffective to provide a transparent polyurethane
hydrogel according to the invention.
Example 8
Effect of Amounts Crosslinker and Prepolymer on Evaporation of
Moisture from a Polyurethane Hydrogel
[0209] To determine the effect of crosslinker on the evaporation
of moisture from a polyurethane hydrogel, polyurethane hydrogels
were prepared, and the loss of moisture was measured.
[0210] The prepolymer of Example 1 was first prepared.
[0211] Next, crosslinker solutions (1 weight percent) were prepared
by dissolving a water-soluble crosslinker (1 g) in water (99 g)
and then adjusting the pH by addition of concentrated hydrochloric
acid.
[0212] Polyurethane hydrogels were prepared by admixing components
as described in Table 7. Generally all hydrogel components were
admixed for about 15 seconds and then poured into Bloom jars as
described in Example 7. The compositions were allowed to stand for
24 hours before any testing was done.
6TABLE 7 Formulations of Polyurethane Hydrogels Formulation 1 Formulation
2 Formulation 3 Component (weight percent) (weight percent) (weight
percent) Water 96.9 94.83 92.87 Prepolymer 3 5 7 Polyethyl- 0.1
0.17 .23 enimine pH Polyethyl- 9.5 7.7 7.3 enimine
[0213] Each polyurethane hydrogel was weighed (w.sub.1), and the
gel strength was measured as described in Example 7.
[0214] Formulation 1 showed a gel onset (t.sub.1) of 42 seconds,
a gel time (t.sub.2) of 82 seconds, and a gel strength of 53 grams.
Formulation 2 showed a gel onset (t.sub.1) of 58 seconds, a gel
time (t.sub.2) of 80 seconds, and a gel strength of 202 grams. Formulation
3 showed a gel onset (t.sub.1) of 58 seconds, a gel time (t.sub.2)
of 78 seconds, and a gel strength of 327 grams.
[0215] These results show that gel times were substantially the
same irrespective of amounts of water-soluble crosslinker and prepolymer
but that gel strength increased as the amounts of water-soluble
crosslinker and prepolymer increased.
[0216] The polyurethane hydrogels were allowed to stand at 20.degree.
C. and 50 relative humidity for 400 hours. The polyurethane hydrogels
were then weighed again (w.sub.2).
[0217] The percent loss of moisture (w.sub.2/w.sub.1).times.100%
was then determined for each Formulation. Formulation 1 lost about
63 weight percent, Formulation 2 lost about 54 weight percent, and
Formulation 3 lost about 54 weight percent. Although these Formulations
were not tested for percent transmissions, it is expected that Formulations
1 and 2 are transparent according to the invention and that Formulation
3 is not transparent according to the invention and, therefore,
is a comparative example.
[0218] These results indicate that a polyurethane hydrogel having
a higher gel strength loses moisture at a slower rate than does
a polyurethane hydrogel having a lower gel strength. This can be
useful to optimize fragrance release from an air-freshener composition.
Generally it is not commercially desirable to have too rapid of
fragrance release or too slow of fragrance release. One of skill
in the art having read this specification can readily optimize fragrance
release from an air-freshener composition.
Example 9
Preparation of a Polyurethane-Hydrogel Composition According to
the Invention
[0219] To investigate water-soluble crosslinkers useful according
to the invention, two polyurethane-hydrogel compositions are prepared
as follows.
[0220] The prepolymer solution is prepared by dissolving the prepolymer
of Example 1 in water to a concentration of 2.5% (w/v).
[0221] Formulations are prepared by adding to the prepolymer solution
20 mM potassium-phosphate buffer, pH 8.0 and either polyoxyethylene
bis(amine) (Sigma, catalog no. P-9906) (0.8% (w/v) (Formulation
1) (0.8% w/v) or a 3-arm amine end-capped polyethyleneglycol (Shearwater
Corporation, Huntsville, Ala., catalog no. 0J2V0L13) (0.8% (w/v))
(Formulation 2). The components are mixed by inversion.
[0222] Formulation 1 and Formulation 2 are transparent. |