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This invention relates to a sealing material useful in sealing structures,
such as sewer lines and manholes, to minimize or prevent water leakage
through voids, joints, cracks, leached cement or other openings therein.
In another aspect, it relates to a method for sealing such structures with
said sealing material. In yet another aspect it relates to the structure
so sealed.
There are a host of man-made water-bearing or holding structures disposed
above or beneath ground level, such as sewer lines, manholes, aqueducts,
tunnels, wells, settling ponds, and basements of buildings, made of
materials such as siliceous materials, e.g., concrete, brick and mortar,
plastics, e.g., polyvinylchloride, cast iron, or wood, e.g., cypress or
cedar. Because of the nature of such construction material or the manner
of constructing such structures or their locations, such structures
inherently have, or develop with time, various discontinuities such as
openings, cracks, fissures, joints, or the like which provide an entry or
pathway for the undesirable ingress or egress of water into or from such
structures. Even hairline cracks or pin-hole size openings in an otherwise
sound or water-impervious structure can result in a damaging and costly
leakage from a temporary or permanent water source. For example, sewer
manholes made of concrete (a brittle and unyielding construction material)
normally experience the incursion or leakage of ground water via the
interfaces defined by the abutting components or members of the structure,
or via joints, holes, cracks, or fissures in the structure. Such leakage
is generally tolerable in sewers up to a certain point without affecting
the usefulness and servicability of the structure. However, when a heavy
rainfall occurs, a large amount of surface or run-off water penetrates the
soil and accumulates in excavations surrounding the sewer line, raising
the exterior hydrostatic head of the water, until the water leakage or
incursion into the structure increases to an undesirable and even
intolerable level. Since water has a propensity to find the path or
drainage area of least resistance, the incursion of water into the sewer
system may reach such high levels that the capacity of the downstream
sewage treatment reservoir or pond is exceeded and untreated or
insufficiently treated sewage is discharged to rivers or lakes causing
pollution thereof. The water resulting from such incursion may also cause
the flooding of basements of buildings.
Water-holding structures, such as concrete irrigation water courses or
aqueducts or dikes, bearing a static head or flowing stream of water, also
experience leakage due to holes, cracks, fissures, and the like, such
leakage being an uneconomical loss of water as well as hazardous in many
circumstances.
A host of sealing compositions and sealing techniques have been used to
prevent the ingress or egress of water into or from such structures. Some
sealing materials, such as mortar, shrink upon setting and curing to
create cracks or fissures. Some sealants which are pumped into soil
surrounding the structure to be sealed are limited to fine grain sand or
soil. Other sealing materials must be placed in a dry environment or used
in a dry, powdered form and they, consequently, lack mobility and cannot
be extensively dispersed or placed in large leakage or drainage areas.
Some sealing compositions require heat, or contain water-immiscible
hydrocarbon solvents, and thus, their application is costly and generally
limited to dry, clean environments. Other multi-component systems require
careful metering and mixing or have a limited pot life. The application
equipment for many of the prior art sealing techniques is cumbersome and
costly and many of these techniques are limited only to areas which are
readily accessible, easily dried, and suitable for cleaning.
Solvent-thinned compositions comprising isocyanate-terminated prepolymers
based on polyols, e.g., castor oil, polyester-polyols, and polyalkylene
glycols and catalysts such as N-methyl morpholine, have been disclosed as
coating and sealing agents for hydraulic cement (see U.S. Pat. No.
2,902,388). Also known are moisture curing urethane sealants resulting
from the reaction of isocyanate prepolymers with moisture in the air. A
group of isocyanate-terminated prepolymer sealants commercially available
is listed in "Sealant" by Damusis, Reinhold (1967), page 156. The prior
art isocyanate-terminated prepolymer sealants have generally been
water-immiscible due to the exclusion of large amounts of polyoxyethylene
from the prepolymer sealants which was previously thought necessary to
insure a good water-resistant sealant (see Damusis, supra, page 132).
Briefly, the subject invention in one aspect provides a sealing composition
comprising a mixture of controlled molecular weight isocyanate-terminated
prepolymers of polyoxyethylene polyol in a compatible water-miscible
solvent. The sealing composition is intimately mixed with water at the
locus to be sealed, such as the interface between abutting or contiguous
members of a water-bearing structure, where it is desired to prevent or
minimize the ingress or egress of water. Said prepolymers react with the
water to form a crosslinked, foamed poly(urethane-urea) polymer. A
catalyst, e.g., tertiary amine, can be added to the water which reacts
with the prepolymer mixture to increase the reaction rate, and a foam
stabilizer may also be added to provide a more uniform foam. The foamed
polymer acts as a sealant to obstruct the flow of water into or from the
structure. The injection or placement of the sealing composition is
normally accomplished in a wet structure or during the leakage of water
into or from the structure.
An embodiment of the method useful for sealing a joint in a concrete sewer
line using the composition of this invention and to the joint so sealed is
illustrated in the accompanying drawing in which:
FIG. 1 is a view in elevation of a three element packer disposed in a sewer
line (shown in cross-section) in the vicinity of a joint in the line;
FIG. 2 is a view of the packer of FIG. 1 expanded at its ends to isolate
the joint and form a circular cavity at the locus of the joint which is
filled with polymeric foam; and
FIG. 3 is a view of the packer of FIG. 1 fully expanded to force the
polymeric foam from the cavity into the joint.
Referring to the accompanying drawing and initially to FIG. 1, reference
number 10 denotes generally a sewer line having a joint 11 through which
the incursion of water into the sewer line is occurring or may occur.
Disposed within the line 10 is a packer 12 with three inflatable diaphragm
sections 13, 14, 16, shown in FIG. 1 in their collapsed conditions, which
can be inflated by means of air. The air used to inflate the packer 12 is
delivered to the packer by means of the hoses 17, 18, 19, each hose
serving to inflate one of the packer sections. The prepolymer mixture of
this invention is delivered to the packer via hose 20 and the water
required for reaction via hose 21, all of said hoses being held together
by band 15. The packer 12 can be positioned by means of cables 22a,22b
attached to the packer and to an external means for moving the packer,
e.g., winches.
In FIG. 2, the outer sections 13, 14 of the packer 12 have been inflated,
isolating the joint 11 and forming a circular or annular cavity 23 at the
locus of the joint. The sealing composition of this invention is injected
in a controlled amount into the cavity 23 together with water, for example
by spraying separate streams of these materials into the cavity in such a
manner as to cause the two sprays to impinge, thus ensuring rapid
admixture and reaction.
In a short time, e.g., 30 seconds after the injection, a thick foamed cream
24 forms in the cavity 23 and the center section 16 is inflated as shown
in FIG. 3, forcing the still reacting cream into the joint 11. After about
5-7 minutes, the cream 24 will have formed a non-tacky, self-supporting
poly(urethane-urea) foam 25 which seals the joint 11. The packer 12 can be
deflated and moved by cables 22 to the next joint where the operation is
repeated.
Water-miscible isocyanate-terminated prepolymers useful in this invention
can be expressed in terms of the formula:
Y.sub.1 [(RO).sub.o --C(O)NH--R' (NCO).sub.p ].sub.z I
in formula I, Y.sub.1 is an active hydrogen-free residue of a compound
having a plurality of active hydrogen atoms such as a polyhydroxyalkane,
e.g., ethylene glycol, glycerol, or 1,1,1-trimethylolpropane. (RO).sub.o
is a hydrophilic poly(oxyalkylene)chain having a plurality of oxyethylene
units, such as (1) a poly(oxyethylene) chain (the preferred type of
chain), (2) a chain having alternating blocks or backbone segments of
oxyethylene units, or (3) a chain of randomly distributed (i.e., a heteric
mixture) of oxyethylene and oxypropylene units. The subscript o is the
number of oxyalkylene units in said poly(oxyalkylene) chain, this number
being sufficient to impart water-miscibility to the prepolymer. The moiety
--C(O)NH-- together with the adjacent oxygen atom of the poly(oxyalkylene)
chain is a carbamate (or urethane) group resulting from the reaction of a
hydroxy group from a poly(oxyalkylene) polyol precursor with an isocyanate
moiety from a polyisocyanate precursor. R' is a residue or nucleus of the
polyisocyanate precursor, and is preferably an aromatic nucleus, e.g.,
tolylene, and p is an integer generally 1-5 equal to q-l where q is the
number of isocyanate moieties of said polyisocyanate precursor. The
subscript z is a number equal to the functionality or number of said
active-hydrogen atoms in said compound (e.g., said polyhydroxyalkane or
polyaminoalkane) and generally z will be 2-6. The terminating isocyanate
groups can react with water, resulting in the formation of a
poly(urethane-urea) foam with limited water permeability.
The term "active hydrogen atom" as used herein refers to a hydrogen atom
which reacts with the isocyanate moiety under urethane or urea
bond-forming conditions, (determined by the Zerewitinoff procedure,
Journal of American Chemical Society, 49, p. 3181 (1927) such as that
disclosed in U.S. Pat. No. 3,330,782). The term "water miscible" in this
context means that the prepolymer is readily dispersible or soluble in
water.
Preferred water-miscible prepolymers within the scope of this invention are
those of the formula:
##STR1##
where Y.sub.1 is the active hydrogen-free residue of a low molecular
weight polyhydroxyalkane, such as ethylene glycol, and R' is an aromatic
nucleus, such as tolylene. The subscript o is the number of oxyethylene
units necessary to make the prepolymer water-miscible. The integers p and
z are as defined above for formula I.
Another subclass of water-miscible prepolymers useful in this invention can
be expressed by the formula:
##STR2##
where Y.sub.1, R' and z are as defined in the formula II and a, b, c are
integers such that the ratio of (a+c)/b is greater than one and thus the
prepolymers are water-miscible.
When the prepolymers of formulas I, II, and III are used in the application
of this invention, the polyurethane prepolymer mixtures react with the
water injected with the prepolymer, forming in situ a crosslinked, cured
poly(urethane-urea) polymer foam which will be slightly water-swellable
when in contact with water due to the hydrophilicity of the
polyoxyalkylene backbone of the foam seal.
Sealing compositions of this invention when reacted with water form a
stable self-supporting foam in a very short time, e.g., about 2-7 minutes,
although the time necessary to form a self-supporting foam will vary
depending on the ambient temperature, with a longer cure time usually
being necessary in colder conditions. This means, for example, a large
number of joints in a sewer line can be sealed in a working day. Sealant
compositions of this invention also form foams which exhibit good
compressive recovery and maintain a seal in a joint through cycles of
expansion and contraction as well as cyclical changes from wet to dry
conditions. The seal also has a substantial resistance to the chemical,
physical, and biological activity of sewage.
The isocyanate-terminated prepolymers used in this invention can be
tailored in structure to obtain controlled water-miscibility in order to
attain practical reaction times and achieve desired physical properties in
the reacted foam. Prepolymers, having a structure like formula II, with a
high molecular weight of about 1250-1550, have a high rate of reaction and
also a high degree of hydrophilicity. The high degree of hydrophilicity
results in a foam which undergoes marked swelling when wet. However,
contraction of the foam when dry can be great enough to break the seal
between a substrate such as concrete and the foam, resulting in water
incursion. Prepolymers having a structure like formula II, and a molecular
weight of about 850-1000, produce foam with improved resistance to cycles
of drying without separating from the structure sealed. However, these low
molecular weight prepolymers have a lowered degree of hydrophilicity,
e.g., about 40 percent of that of the high molecular weight prepolymers,
and the low molecular weight prepolymers will not usually cure quickly to
a self-supporting foam.
It has been found that by mixing one prepolymer having a low molecular
weight with a second prepolymer having a high molecular weight, a
prepolymer mixture, with an average molecular weight of about 1000-1300,
is provided which rapidly reacts with water to produce a foam which will
not shrink excessively and pull away from the sealed structure upon
dehydration of the foam. Though the mechanism for this phenomenon is
unknown, it is believed that the more miscible high molecular weight
prepolymer component upon reacting with water provides a fast-setting
network of expanded surface which acts as a water carrier to increase the
reactivity of the low molecular weight prepolymer component with water.
The low molecular weight component provides the foamed product with the
higher strength levels and improved resistance to shrinkage under
dehydrated conditions. Other fomulations of polyoxyethylene prepolymer
mixtures having average molecular weights of about 1000-1300 can be
formulated which exhibit the desired properties of reactivity, strength,
and shrinkage resistance. Prepolymers containing polyoxypropylene can be
used as part of the prepolymer mixture because the polyoxypropylene units
in the prepolymer will confer additional control of the hydrophilicity and
shrinkage of the cured foam.
The preparation of isocyanate-terminated prepolymers, such as those used in
the sealing composition of this invention, and the reaction thereof with
water to form a polyurea, is disclosed in the art, e.g., U.S. Pat. Nos.
2,726,219 and 2,948,691, particularly Example 8, and
"Polyurethanes:Chemistry and Technology" by Saunders and Frisch, Part I,
Interscience Pub., N.Y. (1962).
The urethane prepolymers used in this invention can be prepared by reacting
an aliphatic or aromatic polyisocyanate with a polyoxyethylene polyol
using an NCO/OH equivalent ratio of at least 2/1 and preferably slightly
higher than this, e.g., 2.1/1 to 2.5/1.
To insure water-miscibility, the poly(oxyethylene) glycol will generally
having molecular weight range of about 500-1200. Commercially available
polyol precursors or bases useful in making the above-described
water-miscible isocyanate-terminated prepolymers are the hydrophilic
polyoxyethylene polyols, e.g., "Carbowax." The degree of overall
hydrophilicity of the prepolymeric mixtures can be modified by using small
amounts of poly(oxyethylene-oxypropylene) polyols sold under the trademark
"Pluronic," such as Pluronic-L35, F38, and P46, or hydrophilic polyols
with heteric oxyethylene-oxypropylene chain sold as Polyol Functional
Fluids, such as WL-580, WL-600, and WL-1400. Generally, the hydrophilic,
water-soluble oxyethylene-containing polyols to be used will have
molecular weights of at least 400 and as high as 2000; preferably they
will have molecular weights of 600-1000.
Polyisocyanates which can be used to prepare the isocyanate-terminated
prepolymer used in this invention and described above include conventional
aliphatic and aromatic polyisocyanates. The preferred polyisocyanates are
aromatic polyisocyanates because the prepolymers made therefrom will
generally react faster with water. One of the most useful polyisocyanate
compounds which can be used for this purpose is tolylene diisocyanate,
particularly as a blend of 80 weight percent of tolylene-2,4-isocyanate,
and 20 weight percent of tolylene-2,6-isocyanate; a 65:35 blend of the
2,4- and 2,6-isomers is also usable. These polyisocyanates are
commercially available under the trademark "Highlene TM, NACCONATE 80, and
MONDUR RD-80". Other usable polyisocyanate compounds which can be used are
other isomers of tolylene diisocyanate, hexamethylene-1,6-diisocyanate,
diphenylmethane-4,4'-diisocyanate, m- or p-phenylene diisocyanate and
1,5-naphthalene diisocyanate. Polymeric polyisocyanates can also be used,
such as polymethylene polyphenyl polyisocyanates, such as those sold under
trademarks, "Mondur MRS," and "PAPI." A list of useful commercially
available polyisocyanates is found in Encyclopedia of Chemical Technology
by Kirk and Othmer, 2nd Ed., Vol. 12, pages 46, 47, Interscience Pub.
(1967).
The isocyanate-terminated prepolymers and mixtures thereof used in this
invention have a freezing point range which is approximately
40.degree.-70.degree. F., thereby limiting the usefulness of the
prepolymer as a sealing agent in environments where the temperature is
often below the freezing points of the prepolymers or when the prepolymers
and associated equipment are above ground at the solidification
temperatures of the prepolymers. However, by dispersing the prepolymers in
a solvent, pumping and handling is enhanced and the range of temperatures
at which sealing operations can be conducted is extended. The solvents
used to dissolve the prepolymers are water-miscible, polar organic
solvents which are preferably volatile at the ambient conditions of the
environment where the sealing composition is to be used. The solvent
chosen should be such that the resulting solution of prepolymers and
solvent will not freeze at the ambient conditions present in the
environment where the structure to be sealed is located. For example,
where the ambient temperature is above 50.degree. F., a solution of about
60-90 weight percent of prepolymer solids in dry acetone is very effective
sealant composition.
The sealing composition of this invention will preferably include a foam
stabilizer which contributes to the formation of a uniform foam having
good mechanical properties and density. The cured foams will have
densities of about 5 to 35 pounds per cubic foot, preferably about 8-15
pounds per cubic foot. Foam stabilizers useful in this invention include
nonionic surfactants, e.g., the condensation products of ethylene oxide
with an alkyl phenol, ("Triton" X-100, "Tergitol" NP-27), silicone
surfactants, e.g., polyethylene oxide adducts of polyalkylsiloxane
("L-520", "L-540"), as well as other anionic, nonionic, or fluorochemical
surfactants.
Chlorinated solvents, e.g., dichloromethane, dichloroethylene,
trichloroethane, etc., or nitrogenated, e.g., nitromethane, nitroethane,
acetonitrile, etc., solvents also can be used. These solvents provide a
prepolymer solution which is less soluble in water and dispersing agents
or emulsifiers can be added to the solution to increase the miscibility of
the prepolymer solution and maintain a practical cure time.
The uncatalyzed curing rate of the polyurethane prepolymer mixture of this
invention at the ambient temperatures normally encountered in sewer lines
and other underground water-bearing structures is relatively slow. For
example, at 49.degree. F. the curing time of the polyurethane prepolymer
having a molecular weight of about 1350 with water is approximately 131/2
minutes and at 36.degree. F. the same prepolymer requires 18 minutes to
cure, with the gelled foam not reaching a tack-free state for at least 30
minutes. While this reaction time is considerably faster than many of the
prior art sealing compositions which require as much as 24 hours to cure,
it is insufficient where the prepolymer is to be used at the locus of
incursion of free-flowing water which will tend to carry the prepolymer
away from the site of water incursion. The addition of a base as a
catalyst, e.g., tertiary amine catalyst, 2,4,6-tridimethyl
aminomethylphenol, 1,4-diazabicyclo (2,2,2)-octane, triethylamine or other
amines and metal compound catalysts known in the urethane art, reduces the
cure time at ambient sewer temperatures (e.g., about 50.degree. F.) to
about 2-7 minutes under normal conditions. The tertiary amines are added
to the prepolymer in amounts of about 0.1 to 1.0 parts by weight of
prepolymer or the catalysts may be added to water used as a coreactant.
The basic catalyst used in small amounts results in improved cure rates
without detracting from the physical properties of cured foam.
The prepolymer can be mixed with various fillers, and pigments to change
the physical properties of the hydrogel. Fungicides may also be added to
prolong the life of the hydrogel and prevent attack by various fungi, or
phytotoxic agents, e.g., copper salts to prevent the encroachment of plant
roots. Also useful as fillers are latices, e.g., acrylic based latices,
which can be added to the water used as a coreactant with the prepolymer.
Care should be excerised in choosing fillers and other additives to avoid
fillers which will have a deleterious effect on the foams stability.
Objects and advantages of this invention are illustrated in the following
examples, however, various materials and amounts described in this
example, the various other conditions and details recited therein, should
not be construed to limit the scope of this invention. All parts of the
examples are given as parts by weight unless otherwise specified.
EXAMPLE 1
This example illustrates the preparation of a high molecular weight
prepolymer useful in this invention.
One thousand parts polyoxyethylene diol ("Carbowax" 1000 having a molecular
weight of about 1000) was stirred and reacted with 351 parts of tolylene
diisocyanate (80/20 mixture of the 2,4- and 2,6-isomers) under
substantially anhydrous conditions for about 2 hours and the reaction
mixture allowed to stand for several days. The resulting
isocyanate-terminated hydrophilic prepolymer was a viscous liquid, at
25.degree. C., having a structure like said formula II where Y.sub.1 is a
residue of ethylene glycol, R' is tolylene, o is about 11, p is 1 and z is
2. The resulting material was then cooled and drained into 1 gallon cans
which had been purged with dry nitrogen.
EXAMPLE 2
An isocyanate-terminated prepolymer solution was prepared comprising 42.5
parts of 600 molecular weight polyoxyethylene glycol reacted with tolylene
diisocyanate, 42.5 parts of 1000 molecular weight polyoxyethylene glycol
reacted with tolylene diisocyanate, 14.9 parts urethane grade (dry)
acetone and 0.12 part nonionic surfactant ("Triton" X-100). The resulting
solution had an isocyanate equivalent weight of 762 (100% solids) and a
viscosity of 285 centipoise at 72.degree. F. (at least 85% solids
Brookfield). Water containing 0.4 parts
(2,4,6-tridimethylamino-methylphenol) tertiary amine catalyst was used as
a coreactant.
A 176 foot long sanitary sewer line 8 inches in diameter and with joints at
4 foot intervals was sealed with the above coreactants. Prior to sealing,
extensive ground water infiltration (of about 60 gallons per minute) was
observed visually. The equipment used for sealing was a three element
sewer packing device, such as that depicted in the drawing, with a
television monitor manufactured by Cherne Industrial Co. The sewer packing
device was moved by cables attached to two winches, the winches located at
manholes at each end of the sewer section to be sealed, these winches
allowing forward and backward movement of the sewer packer, with remote
television system, for proper positioning.
When the sewer packer was properly positioned astride the joint, two
pressurizable diaphragms were inflated with air to a pressure of up to 35
psi, sealing the sewer line and isolating a small section of the sewer
line. Water was pumped into the isolated section cavity between the
diaphragms and, if no detectable pressure rise was noted, excessive
leaking was indicated.
If the joint needed sealing, equal parts of the coreactants, about 8 fluid
ounces each, were pumped into the packer's cavity between the diaphragms,
the water and prepolymer being sprayed into the cavity as impinging
streams, thereby being thoroughly mixed during injection into the cavity.
The polymer solution and water were allowed to react for 25 seconds at
which time the reacting foam mass was displaced into the sewer joint and
held there for 2.5 minutes. This displacement was accomplished by
inflating with air a third inflatable diaphragm located between the two
diaphragms used to seal the sewer line, the foam mass being held in the
sewer joint by keeping the inflated diaphragms in place.
After the foam was cured to a non-tacky state, the center diaphragm was
deflated and water pumped into the cavity to determine if the joint was
sealed and the cavity would hold pressure. If the pressure rise was noted,
the joint was considered sealed and the packer moved to another defect. If
the seal did not hold pressure, additional prepolymer and water was pumped
into the cavity and the sealing process repeated until the defect or joint
tested water tight. The resulting foam seal was a partially cured,
self-supporting and substantially tack-free poly(urethane-urea) foam which
will continue to cure to a fully-cured foam in about 12-24 hours.
All of the joints in the 176 foot sewer section were sealed in this manner
and a substantial reduction in water infiltration was noted.
Various modifications and alterations of this invention will become
apparent to those skilled in the art without departing from the scope and
spirit of this invention, and it should be understood that this invention
is not to be limited to the illustrative embodiments set forth herein.
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