Note: Descriptions are shown in the official language in which they were submitted.
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BARRIER PREVENTING WOOD PEST ACCESS
TO WOODEN STRUCTURES
FIELD OF THE INVENTION
The present invention relates to barriers for
preventing wood pest (e. g. termite and boring insect)
access to wooden structures for the long-term protection
of wooden structures. More particularly, it relates to a
composition and method which creates and maintains an
exclusion zone for insect pests such as termites, ants
and other boring insects. As used herein, the term
"bioactive" means stimulating an organism, usually in a
negative way up to and including death for purposes of a
deterrent.
BACKGROUND OF THE INVENTION
Wood which is in contact with concrete, such as in
wooden building construction and wood which is in contact
with soil for example fence posts, utility poles,
railroad cross-ties and wooden supports, can be
structurally degraded by the action of termites, ants and
other boring insects. Insecticides are available to
protect wood from the action of such pests.
In wooden building construction, wood in contact with
concrete may be structurally degraded by action of one or
more wood pests including but not limited to termites,
ants and other boring insects. Present methods of
preventing or retarding the advance of insects includes
fumigation wherein the entire structure may be sealed and
an insecticide released therein. Disadvantages of this
method include ecological and human health concerns as
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well as the limited time until the fumigant is
sufficiently reduced in concentration to permit insect
ingress.
Although insecticides are effective against the
action of the boring insects, the insecticides must be
repeatedly applied at intervals of from a few days to a
few months or a year to remain effective. If
insecticides are applied by themselves in sufficient
quantity to be effective over a period of time, they pose
ecological concerns, human health, and may present
unpleasant odors, soil leaching and volatility of the
insecticide. Furthermore, even the greatest amounts of
insecticides applied by themselves dissipate within a
relatively short time and need to be reapplied.
A further disadvantage of conventional application
methods is that the concentration of bioactive
ingredients resulting from a single application of
insecticide starts out well above the minimum level
necessary for effectiveness, but decreases rapidly and
within a relatively short period of time drops below the
minimal effective level necessary to maintain a barrier.
To this end, a number of techniques for the
controlled release of chemicals such as insecticides have
been developed in recent years. These methods employ
polymer matrices and microcapsules to release
insecticide.
Cardarelli U.S. Patent 4,400,374 discloses the use of
polymer matrices generally made of polyethylene,
polypropylene, ethylene vinyl acetate, polyamide,
polystyrene, polyvinyl acetate, or polyurethane to
control the release of insecticides such as the
insecticide commercially available under the tradename
Dursban. The polymer matrices disclosed in U.S. Patent
4,400,374, incorporate porosigen and a porosity reducing
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agent which upon contact with soil moisture or an aqueous
environment dissolves the matrix.
Similarly, Cardarelli U.S. Patent 4,405,360 relates
to a polymer release matrix which can be composed of
polyamide, polyurethane, polyethylene, polypropylene,
polystyrenes and other polymers. The control release
mechanism works in combination with a porosigen to
release a herbicide in a moist environment.
A disadvantage of the Cardarelli methods is the
necessity of sufficient moisture to dissolve the matrix.
Periods of dryness, while extending the life of the
matrix, would result in a decrease in the insecticide
concentration thereby permitting access to the insects.
In addition, the longevity of the matrix is variable and
dependent upon moisture content.
In addition, Wysong U.S. Patent 4,435,383 teaches the
use of a controlled release mechanism for insecticides
including carbamates, organothiophosphates,
organophosphates, perchlorinated organics and synthetic
pyrethroids. The release mechanism comprises a
hydrophobic barrier monomer namely styrene and/or methyl
styrene in combination with a monomer selected from one
or more unsaturated mono- or di-carboxylic acids.
Another reference, T c er U.S. Patent 4,282,209
discusses a process for the preparation of insecticide-
polymer particles. The insecticide, methomyl, is used to
control insects which attack a tobacco, cotton or
agricultural crops. Methomyl is dissolved with polymers
such as polyamides, urethanes and epoxies to provide
extended residual insecticidal activity.
A second Tocker patent, U.S. Patent 4,235,872,
discloses the use of slow-release insecticide
microcapsules having a core of methomyl surrounded by a
cover of allaromatic, uncrosslinked polyurea. In the
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arrangement disclosed in this patent, methomyl is used to
protect vegetables, field crops and fruit crops.
A sixth reference, Youna et al U.S. Patent
4,198,441, discloses the use of insecticides such as
Dursban in a controlled release matrix comprising an
organopolysiloxane, a hydrolyzable silane and a
hydrolyzable organic titanium.
Additionally, Youna et al. U.S. Patent 4,160,335
discloses a,mode of dispersing insect control substances
by applying stripes to sheets of cellophane. The insect
control substance which can include Dursban is placed in
a polymer as well.
Another method is described in an Australian patent
AU-B-82443/91. In this patent, there is described two
sheets of plastic drawn from supply rolls. The upper
face of the lower sheet and the lower face of the upper
sheet are drawn past respective coating rollers which
apply a coating of pesticide (e.g. permethrin) in a
volatile solvent to the faces of the sheets. The coated
faces of the sheets are brought together by passing them
between compressive rollers. The coated and pressed
sheets are laid under building foundations, or placed
around trees or plants to prevent termite attack.
Disadvantages of this product and method include (1)
severance of a layer permits rapid escape of the coating,
and (2) the coating is not integral to the sheets thereby
permitting faster diffusion through the sheets and
limiting the effective life.
Coated granules have a pesticide absorbed onto a
matrix such as clay and then coated with cross-linked
resins which helps slow the release rate. Clay loses or
releases pesticide over a short period of at most a few
weeks.
Although the prior art does disclose the use of an
insecticide incorporated into a polymer matrix as
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controlled release agents, none of the references teach
the creation and maintenance of a completely effective
exclusion zone lasting several years or more. It is
desirable to create a zone so as to prevent any contact
$ between the wood structure and insects capable of
damaging such structures. A reliable exclusion zone is
necessary to protect wood structures for periods of time
substantially greater than one year.
Therefore, in view of the above, it is an object of
this invention to provide a zone of insecticide to
protect wooden structures. Such zone consisting of a
long term low volatility barrier and a high volatility
short term barrier to protect soil.
It is a further object of this invention to maintain
1$ an exclusion zone for relatively great lengths of time of
about 10 to 20 years.
SUMMARY OF THE INVENTION
The present invention is a wood pest barrier having a
lifetime that is effective over the life of the
structure. The lifetime is achieved by binding the
pesticide within the polymer matrix thereby substantially
preventing release of the pesticide from the polymer.
2S Binding may be achieved by mixing the pesticide with a
carrier as a bound friable mix prior to placing the bound
friable mix within the polymer matrix.
The barrier may be supplemented with additional
layers) including but not limited to scrim, mesh, sheet,
and combinations thereof. The additional layers) may
contain a second pesticide that is the same or different
compared to the pesticide in the barrier. In addition,
the second pesticide may be permitted to release from the
additional layers) for enhanced short term protection.
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The barrier and/or additional layers) are made with
a polymer selected from the group consisting of
thermoplastic polymers, thermoset polymers, elastomeric
polymers and copolymers thereof. By incorporating the
insecticides into the polymers, the insecticides can be
held or released at such a rate that they will continue
to be effective as toxicants or repellents for insects
capable of damaging wood structures for a prolonged
period of time while at the same time maintaining
sufficient concentrations within the barrier to prevent
insect penetration through the barrier.
According to one aspect of this invention, there is
provided a polymeric-carrier system wherein the pesticide
is bound to the carrier as a bound friable mix. The
sheeting with the bound friable mix is then placed near a
wooden structure to provide a barrier that wood pests do
not penetrate. An additional layer may provide means for
a slow and relatively constant release of the volatile
insecticide in order to create a barrier zone beyond the
barrier itself in the soil around a wood structure. The
polymers include thermoplastic polymers, thermoset
polymers, elastomeric polymers as well as copolymers
thereof and the insecticide comprises the family of
insecticides known as pyrethrins.
According to another aspect of this invention, an
exclusion zone is created by placing an extrusion near
the wooden structure to be protected. The extrusion has
a polymeric delivery system capable of controlled release
of the insecticide. The carrier system maintains a
steady and effective concentration of insecticide in the
exclusion zone for great lengths of time.
According to another aspect of this invention, a
pellet comprising a polymer and insecticide is provided
to create and maintain an equilibrium concentration of
insecticide for ants, termites and other wood boring
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insects in an exclusion zone for the wooden structure.
The pellet is placed near a wooden structure to treat the
soil in order to shield the wooden structure from
termites, ants and other boring insects. The pellet can
be placed near the structure by a variety of means.
Additionally, the pellet can be embedded in a board or
even included in a foam. In preferred embodiments the
polymers include thermoplastic polymers, thermoset
polymers, elastomeric polymers as well as copolymers
thereof and the insecticide are pyrethrins.
According to another aspect of this invention, an
exclusion zone is created by injecting a hot melt
polymeric mixture. The controlled release device
comprises one or more pyrethrins and the polymer is
selected from the group consisting of thermoplastic
polymer, elastomeric polymers and copolymers thereof.
According to further aspects of the invention,
temperature driven controlled release devices are used to
provide the exclusion zones.
According to another aspect of this invention, the
controlled release device is used to fumigate structures.
It is desirable to place a barrier or create a zone so
as to prevent any contact between the wood structure and
insects capable of damaging such- structures. An
exclusion zone is necessary to protect wood structures
for extended periods of time.
In a further aspect of the present invention a high
density polymer having a low volatility insecticide
providing a low release rate of insecticide is combined
with a low density (soft) polymer having a more volatile
insecticide to provide a reliable exclusion zone.
Therefore, in view of the above, it is an object of
this invention to provide a barrier of insecticide to
protect wooden structures.
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It is a further object of the present invention to
provide a barrier and an exclusion zone having of a long
term low volatility barrier and a high volatility short
term barrier to protect adjacent soil.
It is a further object of this invention to maintain
a barrier for relatively great lengths of time or about
to 20 years.
The present invention, together with attendant
objects and advantages, will be best understood with
10 reference to the detailed description below read in
conjunction with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a first embodiment of the
invention, comprising spun-bonded polymeric sheeting, and
a physical melt-bonded mixture of polymer and
insecticide, wherein the mixture of polymer and
insecticide is bonded in spots to the polymeric sheeting.
FIG. 2 illustrates a second embodiment of the
invention, comprising spun-bonded polymeric sheeting, and
a physical melt-bonded mixture of polymer and
insecticide, wherein the mixture of polymer and
insecticide is bonded in stripes to the polymeric
sheeting.
FIG. 3 illustrates a first manner of using the
embodiments of the invention shown in FIGS. 1 and 2 and
the exclusion zone created by the release of insecticide.
FIG: 4 illustrates a second manner of using the first
and second embodiments of the invention to create an
exclusion zone.
FIG. 5 illustrates a third manner of using the
embodiments of the invention shown in FIGS. 1 and 2
creating an exclusion zone.
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FIG. 6 illustrates a third embodiment of the
invention, in the form of a cylindrical extrusion.
FIG. 7 illustrates a fourth embodiment of the
invention, in the form of a flat strip extrusion.
FIG. 8 illustrates a manner of creating an exclusion
zone using the embodiment of the invention shown in FIG.
6.
FIG. 9 illustrates a manner of using the embodiment
of the invention shown in FIG. 7 to create an exclusion
z one .
FIG. 10 illustrates another embodiment of the
invention in the form of pellets wherein the pellets are
being inserted into the ground near a wooden structure.
FIG. 11 illustrates a cross-sectional view of pellets
placed on a surface.
FIG. 12 illustrates the application of pellets to a
concrete structure utilizing foam.
FIG. 13 illustrates a cross-sectional view of a
concrete foundation after foam has been applied.
FIG. 14 illustrates pellets set on a board.
FIG. 15 illustrates a board containing pellets being
applied to a concrete foundation.
FIG. 16 illustrates a hot-melt injection.
FIG. 17 illustrates the spacing of the hot-melt
injunction.
FIG. 18 illustrates a plug fumigating cement blocks.
FIG. 19 illustrates a mode of applying plugs to
fumigate cement blocks.
FIG. 20 shows a layered apparatus of the present
invention.
FIG. 21 shows repellency of Eastern subterranean
termites.
FIG. 22 shows repellency of Formosan subterranean
termites.
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DETAILED DESCRIPTION
It has been found that there is a significant
reduction of insects capable of damaging wood structures
when a barrier alone or in combination with an exclusion
zone of insecticide is maintained for great lengths of
time in the soil surrounding such structures. An
exclusion zone is a zone having a sufficient amount of
chemical agent to deter fauna. In the present invention,
the chemical agent is an insecticide and the fauna are
insects especially boring insects, for example termites
and ants. According to the present invention, the
insecticide is held in a barrier and/or is released from
a controlled release device comprising a polymer matrix
system will last for at least 6 years.
A controlled release device refers to an apparatus
that results in controlled and sustained release of an
bioactive chemical to its surface and from its surface
into a surrounding medium, for example soil. The
apparatus provides a method for controlled release of the
chemical into the surrounding environment. The device
releases insecticide at a high rate initially and a
lower, steady rate thereafter. This release profile
assures that the wooden object becomes protected in a
relatively short period of time and that, subsequent to
reaching the minimum effective level only the amount of
insecticide necessary to replace the degraded insecticide
is released. This release profile diminishes potential
environmental and health problems of the treatment and
reduces the cost of the treatment. The apparatus release
rate is dependent only upon the apparatus construction
and is independent of external elements such as water.
The controlled release device provides a near to mid-
term solution by releasing the insecticide into the soil
at a desired rate to create a zone having the "minimal
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effective level« of insecticide necessary to prevent
insect intrusion. As used in this specification and the
appended claims, the term "minimal effective level~~ is
defined to mean the level of insecticide needed in the
zone to prevent insects from entering the zone, the
specific level depends on the specific insect and the
specific insecticide. When placed adjacent to a
foundation or below-grade structural portion, the
exclusion zone is created in the soil near the apparatus.
When placed between a non-wood structural portion and an
attached wood structural portion, the exclusion zone is
created at the interface between the non-wood structural
portion and the attached wood structural portion.
The insecticides used in preferred embodiments should
be U.S. Environmental Protection Agency approved
insecticides to kill or repel termites, ants and other
boring insects. The insecticide which is presently
preferred for use in the present invention are
pyrethrins, including tefluthrin, lambdacyhalothrin,
cyfluthrin and deltamethrin. It will, however, be
recognized by those skilled in the art that other
effective insecticides such as isofenphos, fenvalerate,
cypermethrin, permethrin and natural pyrethrin can also
be used. These are available from a number of commercial
sources such as Dow, Mobay, ICI, Velsicol and FMC
respectively. A combination of insecticides, or one or
more insecticides in combination with other bioactive
ingredients such as fungicides is also in accord with
this invention.
A first controlled release embodiment of the
invention, is illustrated in FIG. 1, utilizes a
polymeric-carrier apparatus for the controlled release of
insecticide to generate an exclusion zone. The
embodiment comprises spun-bonded polymeric sheeting 20,
and a physical melt-bonded mixture of polymer and
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insecticide (shown as spots 21 in Figs. 1 and 3-5). The
spun-bonded polymeric sheeting 20 can be either a woven
or non-woven textile or it can be a polymeric sheet.
Such textiles can be obtained from a number of
manufacturers such as Reemay, Exxon Fibers and Phillips
Fibers. Preferably, the textile is woven or non-woven
polypropylene.
The polymer in the melt-bonded mixture can comprise
any number of thermoplastic polymers, thermoset polymers,
elastomeric polymers or copolymers thereof. The
selection of the polymers depends upon the desired
release rate, the compatibility of the polymer with
insecticide and upon environmental conditions. By way of
example and not intending to limit the scope of this
IS invention, the following polymers can be used: high
density polyethylene, low density polyethylene, vinyl
acetate, urethane, polyester, santoprene, silicone, or
neoprene. However, the preferred polymers are high
density and low density polyethylene. Although the
above-mentioned insecticides can be used for best
results, the insecticide should ideally comprise
chlorpyrifos.
The mixture of polymer and insecticide may be placed
on the spun-bonded polymeric sheeting in spots. These
spots should be spaced so as to adequately maintain the
amount of insecticide above the minimal effective level
in an exclusion zone. The minimal effective level is the
least amount of insecticide needed in a zone so as to
prevent intrusion by insects. Spots 21 in FIGS. 1 and 3-
5 are preferably about 0.5 to 1.5 centimeters in
diameter, and about 0.5 to 1.5 centimeters in height.
The size and shape of the spots will depend upon the
user's preference and can be tailored to the job
contemplated by the buyer. The spots 21 can be
configured in rows with the spacing of the spots
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preferably being from about 1.5 to 4 centimeters from
adjacent spots. It will be recognized by those skilled
in the art that other configurations of spots can also be
used depending on the particular application. The
S insecticide releasing polymeric sheet is placed near or
around the wooden structure to create an exclusion zone
by the controlled release of insecticide.
A second controlled release embodiment of the
invention also utilizes a polymeric-carrier delivery
system for the controlled release of insecticide
comprising spun-bonded polymeric sheeting 20 and a
physical melt-bonded mixture of polymer and insecticide.
The polymeric sheeting 20 as in the first embodiment can
be either woven or non-woven polypropylene upon which is
bonded the physical melt-bonded mixture (shown as stripes
22 in FIG. 2). Similarly, the polymers and insecticide
described above with respect to the first embodiment may
also be used in the embodiment described in this section.
The mixture of polymer and insecticide of the second
embodiment may alternatively be placed on spun-bonded
polymeric sheeting using extruder systems which provide
stripes, e.g., as shown in FIG. 2. The stripes 22 can be
about 1 centimeter in height, and about 5 to 15
centimeters apart. Optimally the stripes should be
placed about 10 centimeters apart. It is desirable that
the stripes should be configured in such an arrangement
so as to permit a steady state concentration of
insecticide in the exclusion zone after an initial burst
of insecticide. After the stripes are applied to the
polymeric sheet, the sheet is placed on or near the
wooden structure to be protected from insects.
Binding filler and/or carriers may also be included
in all of the embodiments of the invention. The
inclusion of the binding filler and/or carrier permits
greater amounts of insecticide for a given release rate
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or permits a lower release rate for a given amount of
pesticide. The binding carrier binds the pesticide.
Binding carriers found to bind the pesticide include
carbon based carriers for example carbon black, activated
carbon and combinations thereof. It is believed that
alumina, silicoaluminate, hydroxyapatite and combinations
thereof may be comparable to carbon for binding bioactive
chemicals.
When a carbon based carrier is utilized, the first
step is to insure dryness of the carbon followed by
mixing the insecticide in a liquid form with the carbon.
Only sufficient carbon black (filler) is used to produce
a friable mixture. The term "friable" means
substantially dry or non-sticky flowable particles.
Certain pesticides may have to be heated to achieve a
liquid form. The liquid insecticide adheres or binds to
the extremely large surface area of the finely divided
carbon black and the mixture is cooled for incorporation
in the polymer. Polymers which may be used in a carbon
application are a polyethylene, polypropylene, copolymers
or blends of polyethylene and polypropylene,
polybutylene, epoxy polymers, polyamides, acrylate-
styrene-acrylonitrile, aromatic or unsaturated
polyesters, polyurethanes, silicones, or any other
suitable polymers or copolymers thereof.
The carbon-insecticide mixture in the first and
second embodiments (or just insecticide, if carbon is not
used) is then mixed with the polymer, preferably
polyurethane, in either the molten, powder or liquid
stage. Next this mixture is bonded to the polymeric
sheeting. In the first and second embodiments of the
invention, the polymer and insecticide are melt-bonded to
the polymeric sheeting.
Another mode of bonding the mixture of polymer and
insecticide to the polymeric sheeting is by "through-
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injection molding", a technique which is known in the
art. In 'through-injection molding", molten material is
injected from a heated nozzle through a porous web and
into a mold. The molten material flows through the web
under pressure and is solidified in the mold. While the
molten material is being injected, the porous web allows
air to escape, but it also retains the molten mass under
pressure until it has cooled.
A different method of bonding the mixture of polymer
and insecticide to the polymeric sheeting is by placing a
melted mixture of polymer and insecticide on the spun-
bonded polymeric sheeting. If the mixture is melted, it
must be allowed to cool, cure and solidify. As used
hereinafter, "a melted mixture of polymer and
insecticide" is intended to indicate that the polymer is
either melted or already in the liquid stage. The
insecticide may also be melted or contained in a slurry
solution, depending on its melting point. A "melted
mixture of polymer and insecticide" can also contain
carbon or other additives which do not melt but flow with
the melted polymer/insecticide mass.
The first and second embodiments of the invention
should provide release rates sufficient to maintain an
effective insecticide concentration iri the exclusion zone
to kill or repel insects but at sufficiently slow rates
to maintain an effective concentration for an extended
period of time.
Overall, a preferred composition for the first and
second embodiments of the invention comprises from about
70 to 95 parts by weight of carrier polymer, from about 0
to 15 parts by weight of carbon, and from about 5 to 30
parts by weight of insecticide. The design
considerations of the controlled release devices vary
according to such factors as user preference and
geographic conditions. The steady state release rate of
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the polymeric delivery system of these two embodiments
after the initial burst of insecticide can be maintained
for at least 6 years as a barrier to insects such as ants
and termites. However, the equilibrium concentration of
S this embodiment can easily be adjusted to meet the
specific needs of each user.
Optionally, the embodiments shown in Figs. 1-5 may
comprise a pesticide-impervious sheet (not shown? such as
a metallized foil. The metallized foil or an extruded
sheet of a polymer is laminated to one side of the spun-
bonded polymeric sheeting in order to direct the flow of
insecticide.
A further embodiment of the present invention is a
barrier of a pest-impervious sheet wherein a bound
friable mix of the bioactive chemical or pesticide with a
carbon carrier is placed within a polymer and exhibits
substantially no release of the bioactive chemical.
Substantially no release is defined as a release rate
Less than 0.4 ~g/cmz/day, preferably less than 0.1
~g/cm2/day, and most preferably less than 0.05
,ug/cm2/day. This embodiment encompasses a release rate of
0.0 or below detectable limits. In this embodiment,
pests are deterred upon "sniffing" or "scratching" a
polymer surface and detecting the presence of the pest
harmful bioactive chemical. Life time of the barrier is
much longer than a barrier with a higher release rate.
Moreover, a flaw or tear in the polymer will be less
prone to "leak" bioactive chemical. Hence, two or more
layers of this embodiment may be preferred to maintain a
complete barrier. Multiple layers would permit a tear or
hole in one layer but a pest would not pass a second or
subsequent untorn layer. It may further be desirable to
place a protective layer , for example scrim, on one or
both sides of a barrier layer to avoid tearing.
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Once made, the polymeric-carrier delivery systems of
the first and second embodiments are placed near the
structure desired to be protected from insects. Figs. 3-
illustrate various applications of either the spotted
5 or striped sheet embodiments of the invention. The Fig.
1 configuration is shown in Figs. 3-5, but it is
understood that the Fig. 2 configuration, or other
configurations can work as well.
In Fig. 3, the polymeric-carrier delivery system 1 is
placed under and alongside a concrete foundation 23 of a
wooden structure 100 creating an exclusion zone 10 to
protect the structure from termites, ants and other
boring insects.
In Fig. 4, the polymeric-carrier delivery system 2 is
placed under a structural member 24, such as a porch,
patio, sidewalk, or under a basement foundation beside
the wooden structure 101 to provide an exclusion zone 10.
In Fig. 5, the polymeric-carrier delivery system 3 is
placed over and on the sides of the concrete foundation
23 of a wooden structure 102, but under the wooden
portion 25 of the structure to create an exclusion zone.
Another embodiment of the invention is illustrated in
Figs. 6 and 7. This embodiment pertains to extrusions,
such as extruded flexible cylinders 26 and extruded
flexible flat, strips 27 shown respectively in Figs. 6 and
7. A wide variety of polymers which can be classified
into four broad subgroups can be utilized. The groups
include thermoplastic polymers, thermoset polymers,
elastomeric polymers and copolymers of the three groups
named above. By way of example, some polymers which can
be used from the four groups are: high density
polyethylene, low density polyethylene, EVA, vinyl
acetate, urethane, polyester, santoprene, silicone,
neoprene and polyisoprene. The preferred insecticide is
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chlorpyrifos although the insecticides described above
can be used. A filler may also be added.
Cylinders preferably have a size ranging from about 5
to 15 millimeters in diameter, but most preferably about
10 millimeters in diameter for the optimal steady state
delivery of insecticide into the exclusion zone. Flat
strips should preferably have a thickness of from about 1
to 6 millimeters and a width of from about 5 to 15
millimeters. It, however, should be noted that both
cylinders and flat strips can be designed to meet the
varying conditions encountered by user.
Overall, in order to maintain an equilibrium
concentration of pesticide in the exclusion zone for an
extended period of time, the composition of this
embodiment of the invention, should comprise from about
70 to about 95 parts by weight of polymer, from about 0
to about 30 parts weight of carbon, and from about 5 to
about 30 parts by weight of pesticide. The composition
of the extrusion can, however, be tailored to the
specific needs of the user. It is estimated that the
exclusion zone can be maintained for at least 6 years for
a cylinder and likewise for flat strips.
The extrusions can be positioned in a variety of
positions to create exclusion zones. Fig. 8 illustrates
a manner of using the extrusion shown in Fig. 6. One or
more flexible cylinders 26 are placed between the
concrete foundation 23' and the wooden portion 25~ of the
structure. The flexible cylinders 26 release insecticide
at a controlled rate to create an exclusion zone. An
advantage of this configuration is that flexible
cylinders 26 can be placed under a structure that has
already been built. Similarly, in a manner not shown,
the flexible cylinders can be placed vertically into the
ground as opposed to horizontally. As will be recognized
by those skilled in the art, the extrusions may have
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other suitable shapes and be placed in any suitable
position depending upon the particular use contemplated.
Fig. 9 illustrates a manner of using the flexible
flat strip extrusion shown in Fig. 7. One or more
flexible flat strips 27 create an exclusion zone by being
placed between or alongside the concrete foundation 23"
and the wooden portion 25" of the structure. The
flexible flat strips 27 can also be placed vertically
alongside a wall in an embodiment not illustrated in the
drawings. Again, any suitable placement of the flat
strips is considered as being within the scope of the
invention.
The controlled release of insecticide can also be
conveniently achieved by using pellets as illustrated in
the embodiments shown in Figs. 10-13. The pellet 13
comprises polymer, insecticide and preferably also
includes a filler. Various polymers can be used in this
embodiment. They can comprise polymers of four subgroups
consisting of thermoplastic polymers, thermoset polymers,
elastomeric polymers and copolymers thereof. Polymer
selection from these four subgroups depends upon design
considerations with the preferable polymer being either
high density polyethylene or low density polyethylene.
In turn, the insecticide preferable comprises tefluthrin,
but the following insecticides can also be used:
isofenphos, fenvalerate, cypermethrin, permethrin and
other pyrethrins. For optimal results, a carrier such as
carbon, can also be incorporated into the mixture.
The pellet 31 releases insecticide at a controlled
rate for an extended period of time in order to establish
an exclusion zone. The composition for such a pellet
needed for the maintenance of a zone in the soil is from
about 70 to about 95 parts by weight of polymer, from
about 0 to about 30 parts by weight of carbon black, and
from about 5 to about 30 parts by weight of insecticide.
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Ultimately, the compositions of the pellet depend upon
user preference.
The pellets can be any convenient size depending upon
the intended use, such as 1 to 25 millimeters in diameter
(or width and thickness, if rectangular) by 2 to 20
centimeters or more in length. Furthermore, in order to
fit specific user needs, the dimension of the pellets and
the concentrations of the insecticide can easily be
adjusted. However, an exclusion zone can be maintained
for at least 6 years.
Additionally, pellets 31 have the advantage that they
can be conveniently placed most anywhere. The pellets of
this embodiment of the invention are shown in Fig. 10. A
pellet 31 is inserted near a wooden structure 25. The
pellets as illustrated in Fig. 10 can be placed under a
cement foundation 23'p or they can be placed directly
under the wood structure (not illustrated) so as to
permit the creation of a zone 10 surrounding the wooden
structure 25'" to exclude insects capable of damaging
such structures. Fig. 11 shows a cross-sectional view of
pellets 31 inserted on a surface 40.
Pellets are easily applied to a wide variety of uses.
Fig. 12 illustrates pellets sprayed 50 onto a concrete
structure surface 40. Fig. 15 illustrates treating a
surface by placing pellets 33 on preformed boards 300.
Pellets 32 are applied onto a surface 40 such as soil
or concrete via a foam 41 as illustrated in Fig. 13. The
pellets are first incorporated into a foam in a manner
known in the art. The foam 41 containing the fine
pellets is then sprayed 50 as illustrated onto the
surface 41 via a motorized sprayer 70 in Fig. 12 so as to
provide a protective coating for the surface. The
pellets 32 then release the insecticide to create a
protective barrier in the soil to protect the wood from
harmful insects. For best results, the foam 50 is
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comprised of polyurethane. It is also possible to use
silicone, polyester, or polyvinyl acetate. The pellets
32 can vary in size depending upon the foam thickness and
the desired concentration of insecticide in the exclusion
zone. The thickness of the foam to be applied to a
surface can vary according to user's preference. The
exclusion zone can be maintained for at least 6 years.
In addition to being used as a carrier for insecticide,
the foam also cures cement and acts as an insulator.
A preformed board with embedded pellets 33 can also
be utilized as an embodiment of this invention as
illustrated in Fig. 14. This board 30o can be made of
any type of material which can suitably hold the pellets
33. Preferably, the board is comprised of Styrofoam
which is registered as a Dow trademark. The board can be
applied in any variety of fashions and can also work as
an insulating device. One manner of application is
illustrated in Fig. 15, where the board 300 with pellets
33 is placed above a concrete surface 42. The embedded
pellets are regularly spaced with the spacing being
specified by the devised amount of insecticide.
In another embodiment as shown in Figs. 16 and 17,
the controlled release device comprising the polymer
matrix and insecticide can be applied via a hot melt.
This embodiment is designed to meet the needs of
structures already in place. As stated above, the
polymer matrix can comprise any of the four above-named
polymer groups. Similarly, any of the above-named
insecticides can be utilized. However, it is preferable
to use high or low density polyethylene with either a
pyrethrin. Although tailored to the user, the
concentrations of the various substances in the hot-melt
application should range from about 70 to about 95 for
the polymer, from about 5 to about 30 for the insecticide
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and from about 0 to about 30 for filler/carrier for
optimal results.
Fig. 16 shows hot melt 50 being injected by a syringe
400 into the ground near a concrete foundation 43. The
concrete structure 43 supports a wooden structure 250.
Fig. 17 shows the spacing between the hot melt 50 which
has already been injected into the ground.
In another embodiment, Figs. 18 and 19 illustrate the
use of insecticide to fumigate a structure 500. By
injecting or placing the controlled release device in or
near a structure which can be fumigated, the insecticide
release from the controlled release device can vaporize
thereby fumigating the structure. Fig. 18 illustrates
the use of plugs 34 to fumigate a structure 500 made of
building blocks 502. Similarly, FIG. 19 illustrates a
mode of applying the controlled release device by using a
drill 800 to bore a hole 700 into a cement slab 900.
Once inserted, the plug is able to fumigate the
structure.
CURRE1~1TLY PREFERRED Z~ODIMENT
The currently preferred embodiment of the apparatus
of the present invention as shown in FIG. 20 combines a
first polymer 200 of medium or high density polymer
having a low vapor pressure insecticide with a second
polymer 202 of low density having a more volatile, vis
higher vapor pressure, insecticide. High, medium and low
density are terms well known in the polymer art referring
to the degree of cross linking within a polymer. High
vapor pressure is defined as vapor pressure in excess of
about 1 millipascal and preferably ranges from about 10
millipascals to about 100 millipascals. Low vapor
pressure is defined as less than 3 millipascal and
preferably ranges from about 0.05 millipascals to about
0.5 millipascals. The first polymer 200 preferably has a
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thickness in the range from about 1/32 to 1/8 inch. The
low vapor pressure insecticide, is preferably permethrin
or lambdacyhalothrin. The preferred material of the
first polymer 200 is selected from among polyurethane,
high density polyethylene and polypropylene. The second
polymer 202 is placed adjacent to and, preferably
attached to the first polymer 200_ It is preferred that
the first polymer 200 be water and radon impermeable.
Hence, the first polymer 200 is preferably a sheet that
may be a film or spun bonded. According to the present
invention, the first polymer 200 may be in two sub-parts
with one sub-part 204 a permeable medium or high density
polymer containing the low vapor pressure insecticide and
another sub-part 206 an impermeable layer having no
insecticide within. The impermeable layer has an
advantage for handling of preventing or reducing
exposure/contact of the installer with the bioactive
chemical. The impermeable layer may be, for example
Mylar, saran or saranax.
The second polymer 202 is a Iow density polymer,
preferably an ethylene vinyl acetate, a low density
polyethylene or blend thereof. The more volatile or
higher vapor pressure insecticide placed within the
second polymer is preferably a synthetic pyrethroid, for
example tefluthrin.
The second polymer 202 may be in the form of pellets
as previously described and the first and second polymers
deployed with the first polymer under a sill plate on a
foundation and the second polymer scattered in the soil
adjacent the foundation. More preferably, the second
polymer 202 is in the form of an open mesh, either woven
or non-woven as shown. Mesh openings may range from
touching but not sealed to about 1 to four inches square
and ribs 208 having a cross section width of from about 1
mil to about 1/8 inch. A scrim that can be made from
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polyethylene, polypropylene, or polyester may be used as
the mesh. With a first polymer 200 sheet and a second
polymer 202 open mesh, the apparatus of the combination
of the fist and second polymers 200, 202 is preferably
placed below grade. The first polymer sheet 200 is
placed adjacent the second polymer 202 open mesh with the
first polymer 200 sheet in contact or near a foundation
43 and between the foundation and the second polymer 202
open mesh. The mesh material may absorb bioactive
chemical and contribute to the reservoir of bioactive
material.
In operation, the first polymer 200 maintains a
physical/chemical barrier against insect intrusion.
However, because of the slow release of the first polymer
200, very little insecticide is released that would be
available to create an exclusion zone within about the
first year after installation. In addition, it is
impossible to install a defect free barrier because of
penetrations, for example electrical and plumbing, and
because of punctures or tears during construction.
Accordingly, the second polymer 202 is deployed to create
exclusion zones within a few days of installation thereby
preventing insect access through the imperfections of the
first polymer 200. The first polymer 200, therefore has
three functions: insect barrier, vapor/moisture barrier,
and radon barrier. The first polymer 200 is designed to
last at least 10 years and preferably up to and in excess
of 20 years. The second polymer 202 is designed to last
at least 5 years and preferably up to about 10 years. By
the time that the second polymer 202 is depleted and no
longer effective against insects, the first polymer 200
will have developed a concentration of released
insecticide sufficient to maintain the exclusion zone.
The following examples are provided by way of
explanation. As such, these examples are not viewed as
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limiting the scope of the invention as defined by the
appended claims.
EXAMPLE 1
Experiments were conducted to determine the release
rate of chlorpyrifos. Loading rates for the insecticide
were either 5 wt% or 10 wt% , depending on polymer.
Release rates were determined for all devices at 50°C.
Polymers evaluated included low melt polyethylene,
polyurethane, two epoxies, silicone rubber, and a low
melt polyethylene high in waxes to reduce thermal
decomposition of the chlorpyrifos. Studies indicated
that excessive thermal decomposition of the chlorpyrifos
occurred at temperatures in excess of approximately
240°C; thus, polymer selection was restricted to
formulations not requiring excessive heat processing.
Table 1 provides a summary of the results from these
studies. Overall, polymer compatibility with
chlorpyrifos did not appear to present a problem with the
loading rates employed. There was some loss of physical
integrity of the polyurethane polymer employed, however,
the other polymer systems exhibited no visible
degradation at 50°C. Release rates ranged from
10 ~.g/cm2/da for the silicone rubber, to 0.3 ~cg/cm2/da for
Epoxy B .
Using the data provided in Table 1, an estimated
product longevity can be approximated. Assuming a device
wt. of 0.5 g, with 10% load, then 50mg of chlorpyrifos is
available for release. Thus, for a polymer system having
an area of 4 cmz, and a release rate of 1 ~cg/cm2/da, there
is sufficient insecticide to last 30 years at elevated
temperature. These calculations indicate that a variety
of insecticidal products are possible.
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Table 1. Polymer Formulations and Release Rates for
Candidate Systems Employing Chlorpyrifos.
Polymer Class Chlorpyrifos Release Rate
Content (%) (~cg/cm2/da) a
Polyurethane 5 2.1t1.4b
Epoxy A 5 <0.1
Silicone 5 10.33.5
Urethane 10 l.Of0.3
Epoxy B 10 0.310.1
PE+Wax 10 1.9~0.3
Release rates performed at 50°C.
Material exhibited excessive cracking at elevated
temperature
~PLE 2
Studies were also conducted with similar polymer
systems as in Example 1 but with 80% pure pyrethrin.
Release rates at 40°C are provided in Table 2.
Table 2. Polymer Formulations and Release Rates for
Candidate Systems Employing Pyrethrin I.
Polymer Class Pyrethrin I Release Rate
Content (%) (~.g/cm2/da)a
Epoxy A 10 0.510.2
Silicone 10 21.25.4
Urethane 10 15.717.1
~~ B 10 0 210 1
Release rates performed at 40°C
The release rates were highest for urethane and
silicone and lowest for the epoxies. Substantial
variability in release rates Were encountered and
appropriate binders will need to be evaluated.
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From the data in Table 2, simple calculations can be
performed to determine the possible life of the
insecticide systems. As stated in Example 1, there are
many variables which can alter the lifetime of an
exclusion zone.
EXA~LE 3
Controlled release devices were made and tested to
obtain their release rates. All thermoplastic polymers
were formulated with 10 percent pesticide, 3 or 7 percent
carbon black to absorb liquid pesticide and 83 to 87
percent by weight of polymer and injection molded into
thin sheets about 1/8 inch thick. Specifically, devices
made from thermoplastic polymers and deltamethrin and
lambdacyhalothrin contained 3 percent of carbon black.
The devices made from the remaining pesticides and
thermoplastic polymers contained 7 percent of carbon
black.
The devices made from S-113 urethane (a thermoset
polymer) were made from a polymer mix containing 60% 5-
113, 40% castor oil and 5% of TIPA catalyst by weight.
The polymer mix comprised 90% of the total weight of the
device. The pesticide, deltamethrin, comprised the
remaining l0% of the device. No carbon black was used in
this device. The polymer/pesticide mixture was cast into
a 1/8 inch thick sheet and heated at about 60°C for about
40 to 60 minutes to cure the cast sheet.
One inch squares were then cut from the thin sheets
that were injection molded or cast and the squares were
tested for release rates. The following release rates
were obtained:
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Pesticide Polymer Release Rate
Deltamethrin S-113 urethane
25.2 ~g/cm /day
Aromatic 80A 16.8
~.g/cm /day
Pellethane 2102-80A 8 , 8 ~,g/~=/~y
Pellethane 2102-55D 8.0
~.g/cmZ/day
Alipmtic PS-49-100 7.2 ~.g/cm'/day
Cyper<nethrin polyurethane 3100 p_4 z
~g/cm /day
polyurethane 2200 0.7 ~g/cm~/day
SVA 763 27.3 /Cg/cm~/day
1Q Polyethylene MA 778-000 4.6
hg/cm~/day
Lambdacyhalothrinpolyurethane 3100 0.4 ~.g/cm~/day
polyurethane 2200 0.7 ~g/cmz/day
EVA 763 27.3 ~.g/cm'/day
Polyethylene MA 778-000 4.6 ~Cg/cm~/day
15 Tefluthrin polyurethane 3100 6.4 ~.g/cmZ/day
Polyurethane 2200 25.0 ~g/cm=/day
EVA 763 40.4 ~,ig/~~/~y
Polyethylene MA 778-000 27.0 ~g/cmz/day
Permethrin of rethane 3100
p Y'u 1.4 ~cg/cm'/day
20
Polyurethane 2200 1.3 ug/cma/day
EVA 763 28.5 kg/cm2/day
Polyethylene MA 778-000 4.0 ~Cg/cm~/day
25 EXAMPLE 4
An experiment was conducted to determine the effect
of lambdacyhalothrin (pyrethroid) concentration and
insecticide/polymer combination on release rate of
insecticide from the polymer. The data are summarized in
30 Table 4.
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TABLE 4.Release Rate for Polymer/Pyrethroid Concentration
Combinations.
Polymer Pyrethroid Release Rate
Conc.(wt%) (mg/cm2/day)
Ethylvinyl Acetate (EVA) 1 0.3
5 2.2
10 2.5
Polyurethane 1 0.9
5 4.4
10 8.3
Polyurethane/EVA (50/50) 1 2.6
5 7.2
10 9.1
EXAMPLE 5
An experiment was conducted to determine the
effectiveness of the exclusion zone against termites.
Two species of termites were selected for the tests:
Eastern subterranean termite because it is the most
common, and Formosan subterranean termite because it is
the most aggressive.
Test cells were assembled with glass containers.
Wood shavings were placed in the bottom of the
containers. Insecticide impregnated polymer was placed
over the wood chips in a manner that no path or opening
existed from above the impregnated polymer to the wood
chips. A nutrient free auger was placed above the
impregnated polymer. The surface of the auger was the
zero datum and the impregnated polymer was mounted at a
distance of 5 cm below the surface of the auger.
Termites were placed on the surface of the auger and
their progress through the auger toward the impregnated
polymer noted each day.
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The impregnated polymer combinations are shown in
Table 5a.
TABLE 5a. Release Rate for 10 wt% Pyrethroid
Polymer Pyrethroid Release Rate
(mg/cm2/day)
Ethylvinyl acetate Permethrin 3,9
Ethylvinyl acetate Tefluthrin 4.3
Ethylvinyl acetate Tefluthrin (2 wt% 3.2
fatty acid)
Polyethylene Permethrin 1.4
Polyethylene Tefluthrin 2.2
Polyethylene Tefluthrin (2 wt% 2.0
fatty acid)
Controls having no pyrethroid in a polymer barrier
were also used. Results are shown in FIG. 21 and FIG 22.
In all controls, the termites ate through the polymer and
obtained access to the wood chips. The rate of access
through ethylvinyl acetate was slower than for
polyethylene. For all impregnated polymers, there was no
penetration. Because the Formosan subterranean termites
are so aggressive, they came closer to the impregnated
polymer than the less aggressive Eastern subterranean
termites. In fact, the polyethylene with permethrin
suffered mandible marks from the Formosan termites, but
no holes or penetration. After about 12-14 days, even
the Formosan termites were discouraged by the release of
insecticide and retreated from impregnated polymer.
EXAMPLE 6
An experiment was conducted to demonstrate the effect
of a binding carrier on release rate. The active
chemicals were tefluthrin and lambdacyhalothrin in an
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amount of 5 wt%, the binding carrier was carbon black in
amounts of 0 wt% and 10 wt%, with the balance high
density polyethylene (MA 778-000). Release rates were
measured at 6 weeks after fabrication wherein samples
were wiped weekly to remove surface accumulation of
released active chemical.
Results are shown in Table 6.
TABLE 6 - Release Rates for 0 wt% and 10 wt% Carbon Black
Active Chemical Carbon Black (wt%) Release Rate
(~.g/cm2/day)
tefluthrin 0 3.13
tefluthrin 10 0.71
lambdacyhalothrin 0 1.78
lambdacyhalothrin 10 O,gl
lambdacyhalothrin 20 0.61
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CLOSURE
From the foregoing description one skilled in the art
can easily ascertain the essential characteristics of
this invention and without department from the spirit and
scope of the invention thereof can make changes and
modifications of the invention in order to adapt it to
the various usages and conditions. It is intended that
the scope of the invention be defined by the following
claims including all equivalents which are intended to
define this invention.
