Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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INSECT REPELLENT POLYMER
Background of the Invention
Field of the Invention
The present invention relates to an insecticide treated polymeric product that
is
used to manufacture treated polymer articles. More particularly, the invention
pertains to
treated polymeric articles for use in construction and building applications
such as
insulating foams.
2. Description of the Prior Art
For many years polymeric foams have been used as insulating materials in the
construction industry with a high degree of success. Recent legislation in
certain building
code jurisdictions, however, has banned the use of these polymeric foams in
certain
applications because of infestation problems. These bans have limited the use
of these
highly effective building materials and seen less effective materials used in
their place.
The problem is twofold in nature. First, the insects attack (tunnel or bore)
the polymeric
foam reducing the functional and physical properties of the foam. Second, the
insects are
hidden from view when they are tunneling in the foam making their detection
more
difficult.
The treated polymeric materials can be transformed into any number of treated
f coshed polymeric articles that includes insulating foams. These insulating
foams are
resistant to insect attack therefore they do not suffer from functional or
physical property
damage and they do not provide hidden avenues for the insects to enter the
building. The
insect resistant polymeric articles can then be used in combination with
standard pest
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control practices to provide a significant barrier to infestation for a new
building or
construction project.
Although many insecticides are effective against the action of boring insects,
these insecticides usually must be applied repeatedly at intervals that can
range from
every few days to every few months to annually to remain effective. This need
to re-
apply the insecticides is a result of the insecticide being volatile,
degrading in some way,
or leaching from the system it is protecting. To this end, the typical
application
concentration initially applied is of a higher concentration than that which
is needed to be
effective. The concentration can drop rapidly, however, and within a
relatively short
period of time this concentration could have fallen below the minimum required
concentration for efficacy. Further, if the insecticides are applied in
concentrations
sufficiently high to last for longer periods of time, they can pose ecological
concerns,
2 0 h~~ health concerns, health concerns for pets or livestock, and may
present unpleasant
odors or other undesirable attributes.
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. Pat. No. 4,400,374 discloses the use of polymer matrices
generally
30 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. Pat. No. 4,400;374, incorporate porosigen and a porosity
reducing agent
which upon contact with soil moisture or an aqueous environment dissolves the
matrix.
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Similarly, Caraderelli U.S. Pat. No. 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 Caraderelli 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.
Wysong U.S. Pat. No. 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, Tocker U.S. Pat. No. 4,282,209 discusses a process for the
preparation of insecticide-polymer particles. The insecticide, methomyl, is
used to control
insects which attack 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. Pat. No. 4,235,872, discloses the use of slow-
release
insecticide microcapsules having a core of methomyl surrounded by a cover of
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allaromatic, uncrosslinked polyurea. In the arrangement disclosed in this
patent,
methomyl is used to protect vegetables, field crops and fruit crops.
A sixth reference, Young et al. U.S. Pat. No. 4,198,441, discloses the use of
insecticides such as Du_rsban in a controlled release matrix comprising an
organopolysiloxane, a hydrolyzable silane and a hydrolyzable organic titanium.
Additionally, Young et al. U.S. Pat. No. 4,190,680 teaches the use of a
controlled
release device for insecticides such as Dursban utilizing a hydrolyzable
organic titanium
compound.
Von Kohorn et al. U.S. Pat. No. 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 well.
Voris et al. U.S. Patent No. 5,801,194 discloses a method and device which
prevent the intrusion of insects onto wood structures by using a controlled
release device
capable of releasing insecticide. In the disclosed method, the device
maintains a minimal
effective level of insecticide for a predetermined period of time.
The Voris reference teaches the creation and maintenance of an effective
exclusion zone lasting several years or more. One disadvantage of the Voris
controlled
release system is that it requires the use of a dual insecticide system to
compensate for the
differences in release rates of various insecticides. Further, it is necessary
for the Voris
apparatus and method to start with an elevated level of insecticide which can
be slowly
released into the environment over time.
An alternative approach is to apply insecticides that are relatively benign to
the
environment. Such an approach has been taken by Savoy, U.S. Patent No.
5,194,323
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where a boron based insecticide (di-sodium octoborate tetrahydrate or
commercially
know as TIM-BOR~) is used to treat expandable polystyrene (EPS) foam
insulation that
is sandwiched between two exterior skins of oriented strand board by a
urethane
laminating cement. The problem with this approach is that the necessary
concentration of
the TIM-BOR needs to be very high when this approach is reduced to practice.
Commercially, the concentrations can be 2500 ppm and more.
Such concentrations are supported by a second patent by Winter. The Winter
Patent, No. 5,224,315, cites very high concentrations (2-10 weight percent) in
order for
the TIM-BOR to be effective. These high concentrations can greatly effect the
quality of
the finished polymeric article, in the case of the last two cited patents,
EPS. The high
level of insecticide interferes with the ability of the EPS to fuse with
itself creating foam
materials that are weaker (lower flexural and compressive strengths as
compared to
2 0 untreated material) then their untreated counter-parts. In some instances,
this problem
can be overcome by extreme processing conditions during the molding of the EPS
foam.
The aggressive molding conditions require longer molding cycle times thereby
reducing
the effective capacity of the molding equipment. While these aggressive or
extreme
molding conditions can be used to alleviate the mechanical strength problem,
they are not
a desirable solution because of the limits on molding equipment capacity that
result.
30 ~ s~'Y~ the prior art discloses two possible means by which to protect
polymeric articles. The first discloses the use of an insecticide incorporated
into a
polymer matrix as controlled release agents. These agents are designed to
leach out of
the polymer matrix and will eventually drop below minimum effective levels.
The
second discloses the use of an insecticide that is relatively benign to the
environment, but
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one that requires high concentrations to be effective. These high
concentrations can
compromise the quality of the finished polymeric article. Alternatively, the
limitations
on the quality of the finished molded articles created by the high
concentrations can be
overcome with extreme processing conditions. These extreme processing
conditions
however, place limitations and or restrictions on the capacity of the
equipment used to
transform the polymeric material into the finished polymeric articles.
Desirably, a polymeric material could be treated with a non-volatile
insecticide
that was compatible with the polymeric material and any finished polymeric
article
produced from that material. The insecticide would be designed to reside in
the finished
article rather than to permeate or leach out into the environment as indicated
in the
previously cited works. In order for such a design to be effective, the
insecticide must
have a certain repellency characteristic to insure that the insects do not
attack the article
being protected since the insecticide will not be emitted into the surrounding
environment. Additionally, it is desirable that the insecticide will provide
such
characteristics at concentrations low enough to not interfere with the
production of the
finished polymeric articles from the treated polymeric material. Lastly, the
insecticide
would be highly effective for boring insects such as termites and carpenter
ants.
SUMMARY OF THE INVENTION
The invention comprises a polymer or polymeric material (the terms "polymeric
material" and "polymer" are used interchangeably throughout) that is treated
with an
insecticide. The insecticide treatment insures that any articles produced from
the
polymeric material will have insect resistance characteristics. The treated
polymeric
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material is transformed into an insect repellent polymeric article through any
number of
standard commercial processes. Insect repellent articles produced from the
polymeric
material of the invention are suitable for use in a variety of different
building or
construction applications.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Sect resistant characteristics are desirable because insect attack will lead
to
degradation of untreated finished polymeric articles. This degradation can be
observed as
loss of mechanical strength properties such as flexural or compressive
strength,
deterioration in appearance, or loss in insulating value in the case of a foam
insulation
product. Such degradations will pose serious concerns when these finished
polymeric
articles are used in building and construction projects. Additionally,
treatment with a
suitable insecticide is especially important for polymeric foams (used in
construction or
other applications like seedling trays for example) as these low density
lightweight
finished foam articles are even more susceptible to attack then most non-
foamed
polymeric articles.
The polymeric product that is treated with the insecticide can come from the
family of thermoplastic polymers, thermoset polymers, elastomeric polymers,
and blends
or copolymers thereof. The choice of polymeric product is highly dependent on
the final
applications of the finished polymer article. Examples of polymers that may be
used
include polyolefins, polyvinyl polymers, polyamides and polyurethanes. The
polyolefins
can be either straight or branched hydrocarbons and include such examples as
polyethylene and polypropylene. Examples of the polyvinyl polymers include
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polystyrenes (rubber or elastomer modified, unmodified, and co-polymers there
of such
as acrylonitrile-butadiene-styrene or ABS), polyvinyl chlorides, polyvinyl
alcohols and
esters and their derivatives, and acrylic polymers. The polyurethanes include
polyurethane foams, polyisocyanurate foams and polyurethane elastomers.
The insecticide used in the preferred embodiments is selected from the family
of
insecticides including pyrethroids and 1H-Pyrazole-3-carbonitrile, 5-amino-1-
[2,6-
dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl], commonly
known as
fipronil. Additionally, those schooled in the art will recognize that any
number of other
insecticides can be used effectively. These include bifenthrin., lamda-
cyhalthrin,
cyfluthrin, esfenvalerate, cypermethrin, permethrin and natural pyrethrin. The
choice of
the insecticide is based on a number of factors including:
~ compatibility with the processing conditions that will be employed to
convert
the monomer to a polymeric material if the insecticide is added during the
polymerization.
~ compatibility with the processing conditions that will be used to convert
the
polymeric material into a finished polymeric article.
~ compatibility with the polymeric material itself
efficacy (required concentration) of the insecticide against the desired pest
Environmental issues also play an important role in the selection of the
insecticide. These factors include:
~ volatility of the material
~ solubility of the material in water or other solvents
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~ thermal, ultraviolet (if exposed to sunlight), and biodegradable stability
~ leachability of the material from the finished polymeric article into soil
or
groundwater
Additionally the efficacy, and as a result, the necessary concentration of the
insecticide can play an important role in determining the quality of the
finished polymeric
article as previously discussed. Insecticides that require high
concentrations, i.e. 2500
ppm and more, can have negative effects on the quality of the finished
articles. A
significant advantage to the system embodied here is that the insecticide can
be applied at
very low levels, 1000 ppm or less, which greatly reduces the impact of the
insecticide on
the quality of the finished article.
The insecticide can be "incorporated" into the polymeric product in numerous
ways and at various stages in the process of producing either the polymeric
material or
the finished polymeric article. For purposes of this invention, the term
"incorporate"
refers to coating, dipping and spraying, as well as more intimate chemical
bonding.
The first opportunity to add the insecticide to the polymeric material is
through
incorporation of the insecticide into the polymer during the reaction or
polymerization
process. The insecticide can be incorporated into the polymer in a manner
similar to the
incorporation of other additives while the monomer is converted to polymer.
Either the
insecticide can be chemically bonded to the polymer chains or it can be
occluded in the
free volume between the polymer chains.
Examples of other polymer additives that are currently introduced in this
fashion
would include internal mold release agents which provide processing advantages
to the
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polymeric material, any number of flame retarding chemicals which add flame
resistance
to the finished polymeric articles, and any number of internal plasticizers
which serve to
soften the finished polymeric article for either processing advantages or end
use
properties.
The second opportunity to add an insecticide to the polymeric material is as
an
external coating after the polymerization has been completed but still during
the normal
process of manufacturing the polymeric material (i.e. in subsequent processing
steps after
the monomer has been converted to polymer). The insecticide can either be a
solid, a
solid dissolved in a suitable solvent (solution), or a solid dispersed in a
suitable carrier
fluid (suspension). It can be added with other external coatings such as
lubricants during
the manufacturing process of the polymeric material or in a separate
processing step.
Additionally, the mixing can occur either as a dry blend or as a melt blend.
Dry blending
includes the addition of the insecticide to the polymeric material in any
number of
conventional mixers such as a V-blender, or ribbon blender just to name a few.
The
insecticide can be added as a second dry ingredient, or sprayed into the mixer
as a
solution or suspension as cited above. Melt blending includes applying the
insecticide as
above prior to melting the polymeric material, adding the insecticide as a
second dry feed
to the melt mixer, or injecting the dissolved or suspended insecticide into
the melt mixer.
Such melt mixers could be, but are not limited to, extruders and Farrel
Continuous Mixer.
In any case, the mixing of the polymeric material and the insecticide can be
done batch or
continuous.
It is also possible to spray (prepared as a solution or suspension) the
insecticide
onto the polymeric material after the normal process of converting the monomer
to
to
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polymer just prior to the conversion of the polymeric material to a finished
polymeric
article. The insecticide may be sprayed into a pneumatic conveying tube, into
a screw
conveyor, onto a weigh belt or any other device that is being used to convey
or process
the polymeric material through the processing steps where it is being
converted to a
finished article. It may be sprayed onto the outside of the finished polymeric
article or
the finished article could even be dipped into a solution containing the
insecticide. These
two processes, however, are not as ideal as the methods shown in the previous
examples
because the insecticide is no longer physically incorporated into the finished
polymeric
article, which greatly reduces the mechanism which "fixes" the insecticide to
that article.
The preferred polymeric material is polystyrene and the preferred insecticide
is
alpha-cyano-pyrethroid. Ranges of from about 1 part per million (ppm) to 1000
ppm, i.e.,
less than O.lpercent by weight of the polymer, of the alpha-cyano-pyrethroid
by weight of
~e polymer are preferred. More preferably, the concentration of insecticide
ranges from
10 to 500 ppm. Concentration may vary, however, depending on the point and
method of
application. The alpha-cyano-pyrethroid is available commercially under the
trade name
Delta-Tech~ and is manufactured by AgrEvo as an insecticide in the crop
industry.
The inherent advantage that the claimed invention has over other potential
treatments is that it contains a repellent that keeps the insects from
damaging the final
~icle for which the polymer is ultimately used. In expandable polystyrene
foam, for
example, the insecticide is part of the foam immediately, rather than
remedially. This
helps maintain the physical and functional properties of the foam such as
mechanical
strength and thermal insulating properties.
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Preferably, the combined polymer/insecticide is produced in the form of a bead
or
pellet. The beads or 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 can easily be adjusted.
Insulative foam made from the polymer/insecticide pellets can be utilized as
one
insect repellent polymeric article of the invention. By producing a foam with
the
insecticide already incorporated into the polymer, the integrity and
insulating ability of
the foamed article is maintained against boring insects and the sand, water,
dirt and other
foam-weakening materials associated with the insects. The foam may be molded
or
extruded, depending on the final application, into a variety of finished
polymeric
products. Examples of possible applications include exterior foundation wall
insulation
peels, insulation cores in structural panels, concrete forms, extended sheet
products,
molded block and articles cut therefrom, as well as adhesive systems used to
attach
insulation to foundation walls.
Preferably, the foam is made from extruded polystyrene, expandable polystyrene
or polyurethane. Most preferably, the foam is made from expanded polystyrene.
The
making of expandable particles of styrene-type polymers is well known. It
comprises two
basic aspects, polymerization of styrene-type monomer and the impregnation of
the
polymer with a blowing agent. The polymerization reaction is usually conducted
either in
bulk or in suspension. Where the bulk polymerization method is used to prepare
the
polymer the impregnation step is usually conducted in a separate reactor. In
the case of
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the suspension polymerization method the impregnation may be carned out either
as a
step contiguous to the polymerization by introducing the blowing agent to the
reactor at a certain point during the reaction or at the completion of the
polymerization, or
as a step completely separate and independent of the polymerization. In the
latter case,
the bead product of the suspension polymerization is taken from the reactor,
washed, and
the impregnation step is conducted by re-suspending the polymer in water. The
latter
method has the advantage that out of the total polymer beads obtained from the
suspension polymerization, one can select only those beads having a particle
size suitable
for expandable styrene-type polymer usage and use the rest for other purposes.
The impregnated particles are usually pre-expanded and aged before molding to
stabilize
the bead structure and control the final density of the molded article. The
pre-expansion is
carried out in either a batch or continuous expander using steam to heat the
unexpanded
p~icles above the softening point. The blowing agent in the resin causes the
beads to
expand to the density required for the final application. The expanded beads,
after a brief
period of stabilization, are steam chest molded into the finished foam which
may be
either a specific shape ready for end use or a block of foam requiring further
hot wire
fabrication.
In applications requiring the use of an extruded product, solid polymeric,
preferably polystyrene, pellets are processed in an extruder where a blowing
agent is
introduced to create the foam. The insecticide is either added to the
polymeric material
before the extrusion processing a separate mixing process or during the
extrusion process
as an additional additive.
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The following examples help to illustrate the preferred embodiments. Example 1
refers to the method of incorporating the insecticide into the polymeric
material during
the reaction or polymerization process. For the purposes of the example,
expandable
polystyrene (EPS) has been chosen as the polymeric material. The insecticide
that has
been chosen is a-cyano-pyrethroid. The polymerization process chosen is a
suspension
process where the blowing agent is incorporated into the polymer beads during
the
polymerization. Example 2 refers to the method of incorporating the
insecticide into the
polymeric material during the addition of external coatings and lubricants.
For the
purposes of the example, expandable polystyrene (EPS) has again been chosen as
the
polymeric material with the insecticide being a-cyano-pyrethroid. Examples 3-5
illustrates how the insecticide can be added to the polymeric material during
the
conversion of said material into a finished polymeric article.
2 0 E~pLE 1
A mixture of 87 parts water, 0.16 parts of sodium pyrophosphate, and 0.27
parts
of magnesium sulfate heptahydrate was reacted while stirring at ambient
temperature in a
stainless steel pressure resistant vessel. To this mixture a mixture of 100
parts styrene,
0.14 parts benzoyl peroxide, 0.5 parts dicumyl peroxide, 0.62 parts
hexobromocyclododecane , and 0.05 parts a-cyano-pyrethroid or deltamethrin was
added.
30 The vessel was heated for at least 2 hours at a constant rate to
85°C and then to 130°C
over a period of at least 4 hours. Fifty to seventy-five minutes after the
vessel has
reached 80°C, a solution of 3 parts of a 10% aqueous solution of poly-n-
vinylpyrrolidone
was added to the reaction mixture. After an additional 100-150 minutes 7.5
parts of n-
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pentane was added to the reaction vessel. Upon reaching 130 °C, the
vessel was held at
that temperature for 3 hours, whereupon it was cooled to ambient temperature
over three
hours. The EPS product, which is spherical in shape with sizes range from 0.4-
1.8 mm
then needs to be dried, screened, and coated with external lubricants. The
resulting EPS
was screened to 0.6-1.3 mm which is a size typical for most construction
applications.
The resulting polymeric material was easily foamed and molded into polystyrene
foam
insulation through known industrial processes. In this example, all of the
polymeric
material produced in the reactor is treated with the insecticide.
EXAMPLE 2
A polystyrene polymer was prepared substantially as described in Examplel,
however, the insect repellent material was not included. During the normal
commercial
production of such polymers, the polymeric beads are contained in a water
suspension.
2 0 The water is then removed and the beads are dried. The dried beads were
screened to 0.6-
1.3 mm and then coated with 0.15 weight percent of a mixture of powdered
lubricants
and insecticide. The powder blend included a mixture of lubricants commonly
used in
the industry as screening aids and anti-lumping agents as well as the
insecticide, alpha-
cyano-pyrethroid. The lubricants accounted for 80 weight percent of the total
coating
blend while the insecticide accounted for the other 20 weight percent. The
total amount
30 of insecticide added to the polymeric material based on weight percent of
the polymeric
material was 0.03 weight percent or 300 ppm. The resulting EPS product was
easily
foamed and molded into polystyrene foam insulation through known industrial
processes.
A further advantage of adding the insecticide to the EPS beads during the
external coating
CA 02293867 1999-12-30
stage of the process is that it allows the insecticide to be incorporated into
beads of a
select size rather then all of the beads that have been produced in the
polymerization.
EXAMPLE 3
A polystyrene polymer was prepared substantially as described in Examplel,
l0
however, the insect repellent material was not included. The EPS is fed via a
screw
conveyor to a batch pre-expander at a rate of 750 lbs per hour (15 lbs per
batch). The
insecticide, a-cyano-pyrethroid, is metered into the inlet of the screw
conveyor at a rate
of 0.225 lbs per hour. Alternatively, the a-cyano-pyrethroid can be added to
the weigh
hopper as the beads are filling it prior to addition to the batch pre-
expander. The later
approach is consistent with the methods employed to color EPS commercially by
those
skilled in the art of expanding and molding EPS. Once the treated EPS has been
expanded to the desired density, typically about 0.9 pounds per cubic foot
(pcf), it is
2 0 molded and then if necessary, hot wire cut material consistent with
standard commercial
practice.
EXAMPLE 4
A polystyrene polymer was prepared substantially as described in Examplel,
however, the insect repellent material was not included. The EPS is fed via a
screw
conveyor to a batch pre-expander at a rate of 750 lbs per hour (15 lbs/batch).
The
30 insecticide, oc-cyano-pyrethroid, is suspended in water or other suitable
liquid and
sprayed into the batch expander during the expansion process at a rate of
0.225 lbs of
insecticide per hour or 0.0045 lbs per batch. The method of metering such
small
quantities is consistent with the methods employed to add oil as a processing
aid to EPS
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commercially by those skilled in the art of expanding and molding EPS. Once
the treated
EPS has been expanded to a density of 0.9 pcf, it is molded and then hot wire
cut into
insulation material consistent with standard commercial practice.
EXAMPLE 5
A polystyrene polymer was prepared substantially as described in Examplel,
however, the insect repellent material was not included. The EPS is fed via a
screw
conveyor to a batch pre-expander at a rate of 750 lbs per hour (15 lbs/batch)
to a density
of 0.9 pcf. The pre-expanded beads are conveyed to a storage silo and aged for
a period
of 4-24 hours which is consistent with current industrial practice. The beads
are then
pneumatically conveyed to a block mold and molded into a foam block or billet.
The
insecticide, a,-cyano-pyrethroid, which is suspended in water or other
suitable liquid is
sprayed onto the pre-expanded beads at a rate of 0.03 weight percent as they
are
pneumatically conveyed to the block mold. The method of addition is consistent
with the
methods employed to add oil as a processing aid to EPS commercially by those
skilled in
the art of expanding and molding EPS. Once the treated billet has been molded,
it is hot
wire cut, if necessary into material consistent with standard commercial
practice. A
further refinement to this example would be to include the insecticide in the
oil that is
already being added during the process as a processing aid.
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