Note: Descriptions are shown in the official language in which they were submitted.
21 07+9 6
1 60557-4535
The invention relates to barriers for containment of
liquids, for example liquids from spills or leaks, particularly
for containment of spills of noxious or hazardous substances. The
invention also relates to compositions and methods for forming
such barriers.
BACKGROUND OF THE INVENTION
Petroleum-Oil.-Lubricant (POL) facilities require, by
law, a secondary containment dike capable of containing
hydrocarbons for a short; time in the event of a leakage or rupture
of a primary storage vessel. Several materials have been used for
secondary containment d3.kes. These include polyethylene,
polypropylene, polyvinyl chloride, concrete, asphalt, geosynthetic
clay liners, and geotextiles. Each of these materials has
disadvantages. Concrete is too brittle in the severe Arctic
environment. Asphalt is attacked by hydrocarbon fuels.
Geosynthetic clay liners and geotextiles are only suitable for
containment of water or solids. Polyethylene, polypropylene and
polyvinyl chloride are available as sheets and require heat
sealing between sheets, which leaves them susceptible to failure
at the joined seams. These liners are also susceptible to
cracking, puncture and tearing. Further, they are difficult to
repair.
It will be appreciated that the demands upon the
material forming a secondary containment dike are substantial. It
must have high integrity; the function of the dike is to contain
liquids when primary containers fail. It must be impermeable to
the liquid to be contained. It must be weather resistant. In
_.._~___ ..,..._..~......_._....~w.....,..........r.._.._...~,.._.....
~.._...._.A.~...._ __.__.~~ _.
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2 60557-4535
some applications there: will be foot traffic or even vehicular
traffic over the dike arid the material must have the mechanical
strength to withstand that, so it must be tough and wear-and-
abrasion-resistant. Ideally, it should also be easily formed, of
inexpensive materials.
Lagoon liners; and artificial ponds for the containment
of tailings from mining operations, for instance, are subject to
similar demands.
DISCUSSIQN OF THE PRIOR ART
United States Patent number 3,719,050 discloses a
technique for stabilizing soils, by injecting a polyurethane
prepolymer having terminal isocyanate groups, alone or in
admixture with water, into the soil to stabilize the soil. Soil
stabilizing effects and containment of water are mentioned but
there is no suggestion that this technique can be used for
containment of naxious or hazardous liquids. The technique
involves injection of isocyanate into the soil, and soil may, in
effect, be regarded as a filler in the composition formed thereby.
There is mention, in passing, of mixing the polyurethane
prepolymer with inorganic materials such as clay, cement, and the
like, but there is no discussion of quantities of inorganic
filler, and no exemplification of this suggestion.
United States Patent number 4,315,703, and Patent number
4,476,276, which is divided out of 4,315,703, disclose a
composition and method for sealing structures such as sewer lines,
to minimize or prevent water leakage through voids, joints,
.~ _ _.~ ~,~.r..~-.,..._.__..~~__..~_.~ ... ......w_.~...._..-...._.-.._._....
..~..~.~._~.....~.....__ ____.._.__~_.~. _~_.~._.
2107~E96
3 . 60557-4535
cracks, fissures or otruer openings therein. The composition is a
curable latex-reinforced polyurethane composition, which may
contain up to 60s by weight of fillers, organic or inorganic,
having a specific gravity in the range of 0.1 to 4.0, preferably
1.0 to 3Ø The fillers are required to have a particular size of
500 microns or less, which requires use of refined or
synthetically prepared fillers. Preferably the composition
contains 5 to 20 parts by weight of filler per 100 parts by weight
of composition. In examples there are used diatomaceous silica
filler and clay fillers.
United States Patent number 4,749,592 is also concerned
with a two part grouting composition and uses a composition
composed of a hydrophilic prepolymer having olefinic terminal
groups, a tertiary amine catalyst and a water soluble peroxy
initiator.
SUMMARY OF THE INVENTION
In one aspect the present invention provides a
continuous barrier fox containing a liquid, which barrier is
composed of the gelled product of reaction between water, a
gelling agent that comprises a hydrophilic isocyanate-terminated
prepolymer and optionally up to 40 parts by weight, based on 100
parts by weight of the hydrophilic isocyanate-terminated
prepolymer, of a hydrophobic isocyanate-terminated prepolymer, and
a water insoluble high density filler, wherein the weight of the
water insoluble high density filler exceeds twice the weight of
the gelling agent.
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The continuous barrier, which is sometimes referred to
hereafter as a Geosynthetic Barrier, may be formed, for example on
the ground surrounding a POL facility, i.e., on bare earth. The
gelled product, although having some flexibility, can be shaped,
or can be laid on earth, that is shaped to form the required
containment dike. In other applications the barrier serves as a
lagoon liner or to form an artificial pond for containment of
liquids such as, for example, tailings from mining operations.
Typical flow rates of most fluids through the gelled composition
are very low, being in the range of 10~~ to 10-8 cm/sec, and toluene
shows a flow rate of 10-~ cm/sec.
It will be appreciated that the demands placed on a
composition for the purpose of the present invention differ from
the demands placed in United States Patent number 4,315,703 and
4,476,276. In those patents, the composition is present in
relatively small quantity and is contiguous with some other
material, for instance concrete if being used to seal fissures in
a concrete sewer. Goad adhesion to the concrete will be required
and also strength, to enable the composition to withstand high
pressures that can build. up in a sewer. The composition is not
exposed to the weather, so weather resistance is of no
significance, and it is not subjected to foot traffic or vehicular
traffic, so abrasion-resistance and wear-resistance are not major
concerns. The composition is taught to be of value only in
environments where the liquid to be contained is water. As it is
used in small quantities, it is not so critical that the materials
used to form the composition shall be inexpensive. Concrete
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sewers are not norma115~ used to contain hydrocarbons, so
resistance to hydrocark>ans is not a requirement. It is not clear,
therefore, that compositions in accordance with United States
Patent numbers 4,315,703 and 4,476,276 can be modified to yield
compositions that can be used to form secondary containment dikes
for containing, e.g., Liquid hydrocarbons.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As is well kn.awn, isocyanates react with water to form
urethanes, or there may occur elimination of carbon dioxide from
the urethane, resulting in the formation an amine which reacts
with an isocyanate to farm a urea. There is formed a crosslinked
structure that is foamed to some extent by carbon dioxide that is
released from the urethane but trapped in the crosslinked matrix
that is formed. The reactions proceed rapidly, so it is normally
necessary to supply the components in two or more streams, one
containing the isocyanate or isocyanates and one containing the
water. Usually the other components of the composition are
included in the water stream. Thus the water stream can be a
pumpable slurry in which water carries the water insoluble high
density filler.
As indicated above, the barrier requires strength and
wear-and abrasion-resistance. It is found that if only
hydrophilic isocyanate-terminated prepolymer is used the gelled
product is itself hydrophilic and will absorb water, which is
retained in the crosslinked matrix. As water is absorbed the gel
loses strength; the dry strength of the gel is considerably
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6 60557-4535
greater than the wet strength. If hydrophobic isocyanate
terminated prepolymer ~.s also incorporated, the hydrophobic
properties result in repulsion of water, so that less water, or
ideally no water, is ax>sorbed into the gel and hence the gel is
less susceptible to this weakening effect. Hydrophobic
isocyanate-terminated polymer gels only very slowly and
consequently is not suitable for use as the sole gelling agent.
The amount of hydrophobic prepolymer used is not greater than 40
parts per 100 parts by weight of hydrophilic prepolymer, and is
preferably not greater than about 35 parts. A particulary
preferred gelling agent. has from 15 to 30 parts by weight more
particulary 25 parts by weight, of hydrophobic prepolymer,
combined with 85 to 70 parts by weight, more particularly 75 parts
by weight of the,hydrophilic prepolymer, based on 100 parts by
weight of gelling agent. By varying the amount of hydrophobic
prepolymer it is possible to tailor to some extent the properties
of the gelled product.
When applied to the ground, little preparation of the
soil is required. Thus, the soil may be levelled or shaped
somewhat, but it is not necessary to remove small sharp objects,
as it is in the case when using sheet materials as a liner that
might be punctured by sharp objects.
One form of hydrophilic isocyanate-terminated prepolymer
useful in this invention may be expressed in terms of the formula:
RC(R'O}a-C(0)NH-R"(NCO)b~c
wherein R is an active hydrogen-free residue of a polyol, e.g.,
ethylene glycol, glycerol, or 1,1,1-trimethylolpropane, (R'0)a is a
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hydrophilic poly(oxyalH:ylene) chain having a plurality of randomly
distributed oxyethylene: and higher oxyalkylene units. The
subscript "a" is the number of oxyalkylene units in the
poly(oxyalkylene) chain, this number being sufficient to impart
water-solubility and preferably noncrystallinity to the prepolymer
and suitably has a value between about 50 and about 500. The
moiety -C(0)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 polyether
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. toluene,
and "b" is an integer, generally 1-5, where (b+1) is the number of
isocyanate moieties present in the polyisocyanate precursor. The
subscript "c" is a number equal to the functionality or number of
the active-hydrogen atoms in the polyether polyol, and generally
"c" will be 2-6. The terminating isocyanate groups can react with
water, resulting in the formation of a gelled mass.
Preferred hydrophilic prepolymers are those of the
formula:
CH3 n
R [ ( CHZCH20 ) a ( CHCHZO ) a ( CHZCHZO ) f-CNH-R"-NCo 1 c
where R, R", and "c" are as defined above, "d", "e" and "f" are
integers such that the ratio of (d+f):e is 2:1 to 4:1. For
adequate hydrophilicity, it is preferred that, of the alkylenoxy
moieties present in the isocyanate-terminated prepolymers, at
least about 70% shall be ethylenoxy moieties.
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8
When these prepol.ymers are used,.the prepolymer reacts
with water mixed with the prepolymer, forming in situ a cross-
linked, gelled polyurethane-urea) polymer. The mixture of water
and prepolymer i.:nitially and rapidly forms_a viscous mass,
typically having a viscosi.t:y of about 5 to 10 cpa When measured
with a BrookfieldTMViscomex.e~r at 25oC using a standard No. 3
spindle rotated at 20 rpm. In a very short perlod of Lime this
mass gels to form a cross-:linked mass having an infinite
viscosity. The composition may also contain other additives, as
discussed further below. t)epending upon the amount of fillers and
other additives, the initial viscosity of the viscous mass
typically varies between 5 and 1000 cps, the viscosity being
higher at higher loadings of additives.
The hydrophilic prepolymers, when reacted with water,
form a gelled mass in a very short time, e.g., about 5-200
seconds, although the time,necessary to gel will vary depending on
the ambient temperature, with a longer cure time usually being
observed in colder conditions. The curing time may be extended or
shortened by the addition of an appropriate agent. For example,
the curing time may be extended by the addition of minor amounts
of the aqueous solution ~:7f organic acids, e.g., from about 5% to
about 50°~ by weight of O,.1N oxalic acid. The curing time may be
shortened by the addition of from about 1% to 10% by weight of
dicyanoethylatecf polypropylene diamine.
Although a gelled mass with some green strength may be
formed very qui<:kly, curing and increasing of strength do continue
and days, or even weeks, may elapse before the full strength of
CA 02107496 2003-06-02
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9
the cured composition is realized.
The hydrophilic prepolymers form gels which exhibit good
compressive strength and shrink-resistance through cycles of
expansion and contraction <~s well as cyclical changes from wet to
dry conditions. It has been .found that the gels formed have high
compressive strength and substantial resistance to chemical,
physical, and biological a<:tivity.
The isocyanate-terminated prepolymers can be tailored in
structure to obtain controlled water-solubility in order to attain
practical reaction times and achieve desired physical properties
in the gelled mass.
The preparation of isocyanate-terminated prepolymers is
disclosed in, far instance,, t7nited States Patent numbers 4,315,703
and 4,476,276 arid in references mentioned in those patents.
The isocyanate 1>y-epolymers can be prepared by reacting
an aliphatic or aromatic poly-isocyanate with a polyoxyethylene
polyol using an NCOIOH equ:lva:lent ratio in the range of about 5=1
to about 1.0511.
The polyether palyo:l will generally have a molecular
weight range of about 3,000-20,000, preferably 5,000 to 10,000.
Commercially available polyol precursors useful in making the
above described hydrophilic: isocyanate-terminated prepolymers are
1M
the hydrophilic polyols, e.g., '"Carbowax", and ethylenoxy capped
polyether triols. The degree of overall hydrophilicity of the
prepolymeric mixtures can hemodified by using small amounts of
poly(oxyethylene-oxypropylene)polyols sold under the trade-mark
2107~9fi
60557-4535
"Pluronic", such as Plu,ronic-L35, F38, and P46.
Isocyanates which can be used to prepare the hydrophilic
isocyanate-terminated p~repolymer, i.e., the polyisocyanate
precursors mentioned above, include conventional aliphatic and
aromatic polyisocyanates. The preferred isocyanates are aromatic
isocyanates because the prepolymers made therefrom will generally
react faster with water. One of the most useful isocyanate
compounds which can be used for this purpose is tolylene
diisocyanate, particularly as a blend of 80 weight percent of
10 tolylene-2,4-diisocyana.te, and 20 weight percent of tolylene-2,6-
diisocyanate; a 65:35 blend of the 2,4- and 2,6-isomers is also
useable. These isocyan.ates are commercially available under the
trade-marks Hylene TM, Nacconate 80, and Mondur RD-80. Other
useable isocyanate comp~aunds which can be used are other isomers
of tolylene diisocyanat.e, hexamethylene-1,6-diisocyanate,
diphenyl-methane-4,4'diisocyanate, m- or p-phenylene diisocyanate,
isophorone diisocyanate, 1,5-naphthalene diisocyanate and the
triisocyanate that is available under the trade-mark Desmodur-N100
(Bayer). Polymeric isocyanates can also be used, such as
polymethylene polyphenyl. isocyanates, such as those sold under the
trade-mark, Mondur, MRS, and PAPI. A list of useful commercially
available polyisocyanat.es is found in Encyclopedia of Chemical
Technology by Kirk - Ot.hmer, 3rd Ed., Vol. 13, page 802,
Interscience Pub. (1981). The isocyanate moieties present in
excess over the hydroxy groups of the polyol, so that the product
will
2107496
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contain the free isocyanate groups necessary to enable it to serve
as the isocyanate-terminated prepolymer.
It is not normally necessary to include a catalyst in
the composition, but in some circumstances it may be desirable to
include one, and the presence of a catalyst is not outside the
scope of the invention. Compounds suitable for use as catalysts
in isocyanate reactions are well known; an example is dibutyl tin
dilaurate.
The isocyanate-terminated prepolymers are liquids or
greasy or pasty solids at room temperature. They are reactive in
the presence of water to form a cross-linked, water-insoluble,
water-containing gelatinous mass having a high degree of
elasticity. Reaction times to convert the prepolymer to the gel
in the presence of water may be on the order of less than a minute
to several hours.
The solvents 'which may be used if needed 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 is located. For example, where
the ambient temperature is about 50°F, a solution of about 60-90
weight percent of prepo:lymer solids in dry acetone is a very
effective composition. rather useful water-miscible solvents
include tetrahydrofuran,, dimethyl formamide, ethylene glycol
monoethyl ether acetate (sold under the trade designation
"Cellosolve" acetate) ethylene glycol mono-and di-lower alkyl
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12 60557-4535
ether such as ethylene glycol monomethyl, dimethyl, monoethyl and
diethyl ethers, and diethyl acetal.
The water-reaction product of the prepolymer is a
gelatinous mass, sometimes referred to herein as a gel or
hydrogel. While the reaction produces by-product carbon dioxide,
which normally produces a foamed structure in a cured
polyurethane, foaming of the gelatinous mass is normally not noted
since the amount of carbon dioxide by-product produced will
generally be readily dissolved in the water contained within the
gelatinous mass and/or readily liberated from the water or the gel
because of the low viscosity of the gel.
Suitable hydrophobic prepolymers include compounds that
are similar in structure to the hydrophilic polymers discussed
above, except that in the alkyleneoxy moieties the number of
ethyleneoxy moieties is reduced and the number of propyleneoxy or
higher alkyleneoxy moieties is increased. To ensure adequate
hydrophobicity it is desirable that, of the total alkylenoxy
moieties present, less than 70% are ethyleneoxy moieties.
It is preferred that the hydrophobic prepolymer contains
propylene oxide units as the alkylene oxide portion of the
polymer. Other hydrophobic moieties such as butadiene,
acrylonitrile and castor oil can be included in the prepolymer
backbone.
Examples of suitable hydrophobic prepolymers include:
Prepolymer A= prepared from a mixture of a polypropylene
oxide diol having a molecular weight of about 3000, a triol based
on glycerol and having a molecular weight of about 6000, (all Arco
chemicals), the ratio of diol to triol being 1:1, and tolylene
CA 02107496 2003-06-02
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13
diisocyanate (TDI, 80/20 isomer), the ratio of NCO: OH being 2:1;
Prepolymer B: ~~repared from a mixture of a diol having a
molecular weight: of about:: 2000, a triol having a molecular weight
of about 4000, the ratio of diol to triol being 1:2 and TDI, the
ratio of NCO:OH being 2::'a; and
Prepolymer C= prepared from a mixture of a triol based
polymer polyol t:hat has ~~ high content of acrylonitrile/styrene
and an OH equivalent weight of 1635 (Arco 34-28, from Arco
Chemicals), an ethylene c7xide capped polyether triol of OH
equivalent weight 1602 (Poly G 85-34, from Olin Chemicals) and
IPDI (isophorone diisocy~~nate), the ratio NCO: OH being 2:1.
Prepol.ymer D: based on Castor oil and aromatic
TM
isocyanate, such as Vorit:e 689 from Caschem Inc.
It is preferred that the gelling agent is reacted with
water at a water=gelling agent weight ratio of from about 4:1 to
about 10:1, preferably ataout 6:1. Generally it is preferred to
keep the water to the minimum that is required to obtain a
pumpable slurry with the filler and other components of the water
stream.
The water inso:kuble high density filler material may be
any of the fillers used in the coating industry including, for
example, siliceous mater~.als such as sand and silane treated
TM
fillers such as silane treated Wollastonite, rubber particles,
TM
mini fibers such as the laulk form of Kevlar (Du Pont), clay and
calcium carbonate. Hy high density is meant that the material has
a specific gravity of at least about 1.1, preferably at least
about 1.6. Hydrophobic fillers are preferred and hydrophobicity
can be enhanced by, for c}xample, coating a filler with a silane
2107496
14 60557-4535
material. Sand is part;icularly preferred. The particle size,
provided it does not interfere with the formation of a slurry, is
not important. Thus the particle size may be as high as about
6500 microns, although usually it will be less. The invention
does not impose stringent demands on the filler; for instance it
does not require the refined, finely divided fillers of United
States Patent numbers 9.,315,703 and 4,476,276, although finely
divided filler can be used. The smaller the particle size, the
closer the particles can pack in the gelled composition and
therefore the denser an,d stronger in compression the composition
will be. For reasons o~f economy it is anticipated that in many
instances the filler will be ordinary sand, of a particle size
between about 1000 and about 6500 microns, preferably between
about 2500 and 6500 microns.
The quantity of filler material is at least 200 parts by
weight based on 100 parts by weight of the total gelling agent.
However, larger quantities of filler are normally used, say in
excess of 80%. If this is expressed as a percentage of filler,
based on the weight of filler plus gelling agent, the quantity of
filler is 67%. Preferably the filler ranges from 90% to 99%, more
preferably at least 95% up to 98%, by weight of the combined total
of gelling agent and filler.
As is usual with isocyanate-terminated prepolymers, the
final product is formed by combining at least two separate streams
of ingredients. The isocyanate is in an "A" stream and the
isocyanate-reactive components are in a "B" stream. In the
present case, water is the major isocyanate reactive component.
The filler is normally in the "B" stream and, with the water forms
CA 02107496 2003-06-02
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a slurry, e.g., a sand and water slurry. Whilst it is preferred
to avoid the use of surfactant, some surfactant may be used to
assist in the formation ~~f a pumpable slurry. The presence of
suspending agent may increase the gelling time so it is preferred
to use as little as poss~.ble, desirably Sts by weight or less,
based on the weight of gelling agent. Ln some instances success
has been achieved with ass little as 0.5%.
The compression strength of the composition, both wet
strength and dry st.rengtlv, can be enhanced by incorporation of a
10 polyurethane dispersion. The pH of the polyurethane dispersion
preferably is below 9.5, more preferably below 9 and particularly
should be maintained aro~~nd 8. A preferred polyurethane
TM
dispersion is Neo Rez R-X679 (available from ICI) which is an
aliphatic aqueous colloi<~al dispersion of a urethane polymer with
excellent chemical and U~ light resistance.
The weight ratio of: polyurethane dispersion to gelling
agent is preferably between the limits of about 1~1 and 2~1"
Preferably the ~fispersion should contain not more than 10%
volatile organic; compone7ats and preferably much less.
The strength of they composition can be enhanced by
inclusion of a Aatex, for example an acrylonitrile-butadiene-
styrene latex or a natural rubber latex, or a polyethylene
dispersion. This is somet.ime~s accompanied by the disadvantage
that surfactant contained i.n the latex or dispersion may lead to
enhanced water uptake by t;he cured composition. The use of such
latexes and dispersions is still within the scope of the
invention, however.
CA 02107496 2003-06-02
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16
The sand/water slurry may contain the minimum amount of
suspending agent: necessary to produce a pumpable slurry. There
are known polys<~ccharides for this purpose and mention is made
particularly of a heteropoly~saccharide available from the Kelco
Division of Merck & Co. J_nc. To the extent possible, it is
preferred to avoid the ueae of: suspending agents, and surfactants,
since they block the iso::vyanate moieties and may increase the
gelling time, and also they encourage uptake of,water, which is
undesirable.
Other additives which may be used include UV
stabilizers, defoamers, titanates, silane coupling agents,
accelerators or retarders to control the gelling time,
antioxidants and pigments.
Particularly useful additives are defoaming agents such
TM
as Surfynol DF :L10L (a h:i.gh molecular weight acetylenic glycol
non-ionic defoamer available from Air Products and Chemicals,
Inc.), DB-31 additive and DB--65 additive (silicone additives
TM
available from Dow Corning) and UV stabilizers such as Tinuvin 292
TM
(a hindered amine photostabilizer) and Tinuvin 328 (an ultraviolet
absorber) which are availablE~ commercially from Ciba-Geigy Ltd.
A topcoat is preferably applied to the surface of the
cured consolidated hydroge:l-filler mass to protect it from UV
radiation. Since the wet compression strength of the hydrogel is
less than the d:ry strength, it is preferred to protect it also
from unnecessary exposure to water, for example, rain water. The
topcoat is suitably a moi~>ture-cured polyurethane layer. It
should be durable, flexib7.e, water-resistant and resistant to UV
radiation. It should also be easy to apply as a thin film.
21074qfi
17 ~ 60557-4535
Suitable moisture-curable polyurethanes include isocyanate-
terminated or thioisocyanate terminated polyurethane prepolymers
which cure by reaction with atmospheric moisture, such as
prepolymers obtained by reaction of an equivalent excess of at
least one organic polyisocyanate or polythioisocyanate with one or
more organic compounds having a plurality of hydroxy, thiol or
amine groups. As polyisocyanate, commercially available mixtures
of toluene diisocyanates, such as a mixture of 80% 2,4-toluene
diisocyanate and 20% 2,6-tolylene diisocyanate, are suitable.
Suitable hydroxy-group containing compounds are hydroxy terminated
polyesters such as polyethylene propylene adipate and polyethylene
adipate and hydroxy terminated polyethers such as glycols for
example poly (oxyethylene} glycols, poly (oxypropylene) glycols
and poly (oxybutylene) glycols. The reaction of the moisture-
curable isocyanate can be catalyzed, for example with oxazolidine,
which is supplied separately, giving a two part system. The top
coat prepolymer preferably also contains fillers such as titanium
dioxide or carbon black. Moisture-curable polyisocyanates that
are suitable for use in the top coat are described in United
States Patent number 3,'723,163.
Alternatively, a top coat can be provided by means of a
two part system, one part being an isocyanate-terminated
prepolymer and the other part being a golyol or a hydroxy-
terminated polyether po:lyol. Suitable isocyanate-terminated
prepolymers include those useful as moisture-curable prepolymers,
discussed above. Again" the top coat can contain filler, for
example titanium dioxide or carbon black.
21a749s
60557-4535
A particular topcoat composition which is suitable
contains titanium dioxide, carbon black, defoamer, ODEBA (octyl
diethyl bis aniline crosslinker), A 189 Silane, DBTDL (dibutyltin
dilaurate), Tinuvin 144,. Byk P104, toluene and DMDEE, (d-
morpholine-4,4'-(oxydi-1,2 ethanediyl)bis) from Union Carbide.
The topcoat moisture-curable polyurethane compositions
are preferably applied directly to the surface of the cured
hydrogel by spreading with a suitable tool such as a sawtooth
notched rubber squeezer, a paint roller, a standard push broom or
brushes. The topcoat is preferably spread thinly to provide a
thickness of from about. 0.25 mm to about 1 mm, preferably about
0.25 mm.
The topcoat gives the product resistance to UV light,
protects the product from water such as rain water and is
flexible. It is best t.a apply the topcoat after curing of the
hydrogel preferably after six hours of applying the hydrogel
ingredients, more preferably 16 hours and particularly 24 hours
afterwards.
The sand/water slurry may suitably be prepared by mixing
in a cement mixer. Any other additives, such as the polyurethane
dispersion, should also be included in the mixing of the slurry.
It is important that the ingredients are well mixed or the
performance of the cured hydrogel may be adversely affected. If a
cement mixer is used or other equipment which has previously been
used for cement, in view of the high alkalinity of some cement
mixes, it may be necessary to use some acid additive, such as
acetic acid, to ensure that the pH is not too high. Above a pH of
about 10.2 the gelling rnay be affected, gelling time may be
210796
19 60557-4535
increased and an unfavourable product obtained. It is preferred
that the pH is less than 9.5 and more preferred that it is less
than 9 and particularly less than 8.
After mixing, the sand/water slurry is combined with the
gelling agent. Suitably a concrete pumping device can be used to
pump the slurry to a mixing nozzle where the gelling agent is
introduced, mixed and directed at the support surface. Curing
takes place shortly thereafter. These same steps can be used to
repair a barrier layer that has been damaged; the invention
permits easy repair.
In the preferred embodiment using a topcoat, the
hydrogel composition is preferably allowed to cure for 6 hours,
more preferably ~6 hours, still more preferably 24 hours, before
applying the topcoat.
In one embodiment of the invention a
sand/water/polyurethane dispersion slurry is dumped into a
concrete pumping device. The slurry is then pumped to a mixing
nozzle where a hydrogel prepolymer is introduced, mixed and
propelled to the work surface. Curing takes place shortly
thereafter to produce the consolidated sand liner. This
application method using a concrete pumper allows easy placement
of a controlled thickness of hydrogel/consolidated sand mass.
Typically 25 to 50 mm of hydrogel mass and a 0.25 mm topcoat are
recommended for areas which are not subject to vehicular traffic.
If a high level of traffic is anticipated, then 50 to 100 mm of
consolidated sand and the 0.25 mm topcoat are recommended.
In one embodiment of the method, sand to be used as
filler is taken and placed in a container. Water is added to the
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20 60557-4535
container until it reac;hes the level of the surface of the sand.
The amount of water present is observed. To the water/sand slurry
so formed are added any other required ingredients, for instance a
suspending agent to prevent the sand from settling out and
defoaming agents. The formed slurry is pumped to the desired
location where it is admixed with the gelling agent that is
supplied from a separate stream. Just before gelling occurs the
composition can be sprayed into position and then shaped, if
necessary for instance by paddles or dikes or moulds or formwork.
The amount of gelling agent supplied is determined with regard to
the amount of water present and the desirability of having a
water: gelling agent ratio in the range of about 4:1 to 10:1,
preferably about 6:1. In tests it was found that when 200g
samples of sand was taken, about 40g of water was required to
raise the level of water to the level of the sand, and a pumpable
slurry could be formed. To react with 40g of water in 1:6 ratio,
6.7g of gelling agent was required. It was found that this amount
was sufficient to form a barrier composition with the required
properties, in accordance with the invention.
The amount of gelling agent, as a percentage of the
total pre-gelled composition, is 6.7 x 100 = 2.7%. The amount of
246.7
filler in the pre-gelled composition is 80%. It is surprising
that a satisfactory barrier composition can be formed with so
little gelling agent, together with the inexpensive materials sand
and water.
Cured compositions according to the invention, coated
with the topcoat, when immersed in water for a week had a water
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21 60557-4535
uptake of less than 5%. The permeability rate of the geosynthetic
barrier for water may be as low as 10 8cm/s and for gasoline and
toluene may be as low as 10 7cm/s. The wet compression strength
of a 19 mm thickness of: hydrogel mass (at 50% compression) can be
as great as about 700 l~:Pa and dry compressions strength (at 50%
compression) can be as great as about 3500 kPa. Compression
strength values may vary with the particle size of the filler.
The compositi.an of the invention can be used with other
materials to make a mul.ti-layer barrier or liner. For example,
there can be applied a layer of the composition over a shaped
surface of soil to a suitable depth, for instance about 6 mm.
There can be laid on the cured composition a sheet liner. High
density polyethylene, high density polypropylene and PVC are
suitable materials for such a liner and a suitable thickness of
liner is again about 6 mm. A further layer of the composition of
the invention can then be applied over the liner suitably of
thickness of about 38 mm, thereby providing a liner of about 50
mm. This can be covered with a UV-protective lining, as discussed
above.
The barrier campositions can be used in primary or
secondary containment. In secondary containment they may be
applied directly to the ground under or adjacent and around a
primary container. To ensure that no liquid escapes they can be
applied more thickly towards the perimeter and more thinly in the
centre to provide a gradient to keep liquid in the centre, or a
vertical lip or wall can be provided at the perimeter. They can
also be applied as a coating directly on the outer surfaces of a
primary container. Since the permeability rate of the barriers is
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low for gasoline and toluene they are suitable for use in
petroleum-oil-lubricant. secondary containment. The permeability
rate for water is also l.ow and they are suitable in a wide range
of uses such as, for example, as liners or barriers in primary or
secondary containers in settling ponds, at landfill sites and
transformer sites.
The invention has been described with particular
reference to containment. of toxic or noxious substances, but it
will be appreciated that. the invention can be used to contain non-
toxic or non-noxious substances.
The invention is further illustrated in the following
examples, in which parts are by weight unless otherwise indicated.
There are first described the experimental test methods.
EgPERIMENTAL TEST HETHODS
Density
Approximately a 1 inch square sample of Geosynthetic
Barrier was cut from the sample prepared. Exact measurements were
taken with a micrometer and the sample Weighed. From this
information the density of the sample could be obtained.
Note: Since Geosynthetic Barrier samples take up
water albeit slowly), in the name of accuracy
the water displacement method of determining
sample volumes was not used.
Water Absorption
After allowing the GB samples to cure for two weeks
water uptake was determined gravimetrically. The samples were
weighed, submerged in water for 1 week, removed and then re-
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weighed. Water uptake is reported as a percentage of weight
increase.
Permeability
Permeability was used to evaluate the water/solvent
resistance of Geosynthetic Barrier samples. The constant head
method of determining permittivity was used. A two week cure was
allowed before testing. At this time a head of water/solvent was
applied to the geosynthetic barrier and the rate of loss of
water/solvent monitored. The following equation was used to
determine the permittivi.ty of the Geosynthetic Barrier sample.
= 1 I n bo
t hl
where t is the time in seconds, hQ is the initial head in mm and hl
is the final head in mm.
The normal coefficient of permeability can be determined
by multiplying the permittivity by the sample thickness (ASTM
D4491).
Compression (Wet and Dry)
An instron 1123 was used to test the compression
resistance of the Geosynthetic Barrier samples. One inch square
samples were placed between instron compression plates. The
cross-head speed was 20 mm/min and the chart speed was maintained
at 50 mm/min. A maximum load of 25,000 N was placed on the
samples. The compression strength at 33% and 50~ compression was
determined and the integrity of the sample after full load was
recorded for comparison purposes.
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Ultraviolet (UV) Resistance
An atlas UVCON was used to expose the Geosynthetic
Barrier samples to UV radiation. Eight FS-40-T12 UV florescent
lamps were used as a source of radiation. The samples were
exposed for 2000 hours at a temperature of approximately 5loC.
The flexibility and degradation of the top coat was determined
after 2000 hours.
Additional samples were exposed to a 1000 hour xenon-arc
accelerated UV weathering cycle.
Weathering Cycles
The weathering cycle consists of placing samples at 40°C
for 20 hours, followed by room temperature for 4 hours followed by
-18°C for 20 hours. This cycle was repeated continually and
observations were recorded weekly. The flexibility, integrity and
peel strength of the geasynthetic barrier and top-coat were of
interest.
EBAMPLES
Example 1
A homogeneous. mixture of washed all-purpose anhydrous
sand (100 parts) and water (20 partsy was prepared and is referred
to as Part A (if the sand is wet the amount of water is adjusted
accordingly). Part B consists of 3.3 parts of a hydrophilic
isocyanate-terminated prepolymer E. Prepolymer E is an ethylene
oxide capped polyether triol derived from glycerol, of molecular
weight approximately 5000, that has been reacted with TDI with a
ratio of NCO:OH of 2:1, dissolved in acetone. Part B was added to
part A and the mixture stirred until just before gelation. The
composition was poured into a mold and allowed to cure for two
25 60557-4535
weeks before testing. A consolidated sand/polyurethane mixture of
density 1.3224 g/mL wa:c obtained. One week and four week water
absorptions were 13.03 and 23.3 weight per cent. The 50 per cent
wet and dry compression values were 380 and 2160 kPa respectively.
Permeability values of water, toluene and gasoline were 1.5 x 10~,
2.7 x 10-6 and 2.9 x 10-'' cm/s respectively.
In field trials the same hydrophilic isocyanate-
terminated prepo.lymer, but dissolved in diethylene glycol
monoethyl ether acetate, not acetone (Prepolymer F) was used and
similar results were obtained.
Example 2
A homogeneous mixture of sand (100 parts), water (16.7
parts) and polyurethane dispersion (6.7 parts, Neo Rez R-9679 from
ICI) was prepared and is referred to as part A. Part B consists of
3.3 parts of the hydrophilic isocyanate-terminated prepolymer E.
Part B was added to part: A and the mixture stirred until just
before gelation. The composition was poured into a mold and
allowed to cure for two weeks before testing. A consolidated
sand/polyurethane mixture of density 1.8173 g/mL was obtained.
One week water absorption was 10.66 weight per cent. The 50 per
cent wet and dry compression values were 770 and 3415 kPa
respectively. Permeability values of water, toluene and gasoline
were 4.0 x 10-8, 2.8 x 10-6 and 4.6 x 106 cm/s respectively. The
marked increase in the wet compression value demonstrated the
effect of addition of the polyurethane dispersion.
Field trials with prepolymer F gave similar results.
210749fi
26 60557-4535
Example 3
A homogeneous mixture of sand (100 parts), water (20
parts) and polyurethane dispersion (3.33 parts, Neo Rez R-9679
from ICI) was prepared and is referred to as part A. Part B
consists of 3.33 parts of the hydrophilic isocyanate-terminated
prepolymer E. Part B was added to part A and the mixture stirred
until just before gelat.ion. The composition was poured into a
mold and allowed to cure for two weeks before testing. A
consolidated sand/polyu,rethane mixture of density 2.00 g/mL was
obtained. One week water absorption was 11.08 weight per cent.
The 50 per cent wet and. dry compression values were 700 and 2710
kPa respectively. Permeability values of water, toluene and
gasoline were <- 10-8, 1.6 x 10~? and <- 10-a cm/s respectively.
Field trials with prepolymer F gave similar results.
Example 4
A homogeneous mixture of sand (100 parts), water (20
parts ) and polyurethane dispersion (3.33 parts, Neo Rez R-9679
from ICI) was prepared and is referred to as part A. Part B
consists of 3.33 parts of a mixture of hydrophilic/hydrophobic
isocyanate-terminated prepolymers (prepolymer E/prepolymer A =
85/15). Part B was added to part A and the mixture stirred until
just before gelation. The composition was poured into a mold and
allowed to cure for two weeks before testing. A consolidated
sand/polyurethane mixture of density 2.302 g/mL was obtained. One
week water absorption was 9.76 weight per cent. The 50 per cent
wet and dry compression values were 770 and 1550 kPa respectively.
Permeability values of toluene and gasoline were 2.9 x 10~T and
s 108 cm/s respectively.
.. 2'~07~9~
27 60557-4535
Field trials with prepolymer F gave similar results.
Example 5
A homogeneou:c mixture of sand (100 parts), water (20
parts) and polyurethane: dispersion (3.33 parts, Neo Rez R-9679
from ICI) was prepared and is referred to as part A. Part B
consists of 3.33 parts of a mixture of hydrophilic/hydrophobic
isocyanate-terminated prepolymers (prepolymer E/prepolymer A
75/25). Part B was added to part A and the mixture stirred until
just before gelation to ensure a homogeneous mixture. The
composition was poured into a mold and allowed to cure for two
weeks before testing. A consolidated sand/polyurethane mixture of
density 1.971 g/mL was obtained. One week water absorption was
8.99 weight per cent. The 50 per cent wet and dry compression
values were 890 and 3875 kPa respectively. Permeability values of
toluene and gasoline were 1.63 x 10-~ and 1.4 x 10-6 cm/s
respectively.
Field trials with prepolymer F gave similar results.
Example 6
A homogeneous mixture of sand (100 parts) and water (20
parts) was prepared and is referred to as Part A. Part B consists
of 3.3 parts of the hydrophilic isocyanate-terminated prepolymer
E. Part B was added to part A and the mixture stirred until just
before gelation. The composition was poured into a mold and
allowed to cure for 16 hours after which time a top-coat
consisting of 5891E (3M: Company) was applied at a 10 mil.
thickness. The total Geosynthetic Barrier was allowed further
cure for 1 week and four weeks. One week water absorptions were
3.72 and 3.83 weight per cent respectively. UV resistance and
CA 02107496 2003-06-02
60557-4535
28
weathering of thE~ top-coat were excellent compared to the
Geosynthetic Barrier without: t:op-coat.
Field trials with prepolymer F gave similar results.
Example 7
A homogeneous mi~:t,ur.e of sand (100 parts) and water (20
parts) was prepared and is referred to as Part A. Part B consists
of 3.3 parts of the hydrophilic isocyanate-terminated prepolymer
E. Part B was added to part A and the mixture stirred until just
before gelation. The composition was poured into a mold and
allowed to cure for 16 hours <~fter which time a top-coat
consisting of 58'~lE (3M Company), 2 parts carbon black, 0.25 parts
TinuvinM328 and 0.1 parts Texacat DMDEE was applied at a 0.25 mm.
thickness. The total Geosynthetic Barrier was allowed further
cure for 1 week. Four week water absorption was 8.77 weight per
cent. UV resistance and V~e~athering resistance were excellent
compared to Geosynthetic Barrier materials in the absence of top-
coats.
Field trials with prepolymer F gave similar results.
