Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF MAKING PLASTIC ASPHALT PAVING MATERIAL
AND PAVING MATERIAL AND PA ff&E MADE TREREBY
S
Field of Invention:
This invention relates to pavements and paving materials and the use of
recycled plastics in pavements and
paving materials. More particularly, this invention relates to pavements, to
paving materials for use therein, and to
methods for making paving materials and pavements having unsorted, residual or
other recycled or waste plastic as
a component of the paving material or pavement.
Backeround of the Invention:
Paving materials such as asphaltic concretes that are used for roadways,
parking areas, walkways and other
traffic surfaces have been the subject of various efforts to improve their
properties. Some of these efforts have
involved the addition of polymers, including plastics, in attempts to improve
the flexibility, strength and life of the
paving material. Such efforts have proved either ineffective or too costly.
The increasing need to dispose of, or find new uses for, previously used or
recycled plastics and waste plastics
has given incentives to efforts to introduce plastics from waste sources into
building or paving materials, either to
facilitate their disposal where it is hoped that their introduction does not
degrade building or paving material and does
not increase its cost, or where it is hoped that their introduction will
provide a cost effective improvement in the
properties of the building or paving materials. Work has been done to utilize
low density plastic and films of selected
and graded recycled plastic materials as an additive to the asphaltic binder
component of asphaltic concrete paving
material in an effort to improve the flexibility and reduce the propensity of
the paving material to crack. This effort
requires that the recycling task to collect suitable plastic material be
selective, or that the material be specifically
sorted from a general mixture of recycled plastic material. Such recycled
plastic material has a cost that is
significantly greater than that of the general ungraded or unsorted recycled
plastic material mixture or of the residual
recycled plastic material from which more useful grades have been removed.
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For example, it has been proposed to melt polystyrene foam with asphalt, to
add sand, and to mold the material
as a concrete substitute, thereby utilizing the waste plastic. Further, it has
been proposed to add waste polyethylene
to asphalt for road construction to increase pavement durability. Decreased
deformation resistance and increased
hardness and ductility have been reported by adding other plastic waste in
amounts of, for example, eight percent,
to paving compounds containing aggregate, where the plastic waste includes
specific plastics made of specific
combinations of low density polyethylene, cyclophane, cellophane,
polypropylene, and polyvinyl dichloride. Fiber
reinforced plastics and chopped glass have been proposed for addition to
asphalt to improve wear resistance and
water permeability.
Proposals to use specific waste plastics as additives to asphalt mixes have
had the disadvantage of requiring
specific collection of the individual material or the sorting of the desired
material from the generally collected plastic
waste. Therefore, such efforts calling for specific plastics are costly.
Furthermore, such efforts do little to solve the
problem of utilization of vast unsorted, unsortable or unclassified bulk
mixtures of plastic waste.
Waste plastics are found in several forms. In one form, bulk masses of
particular identified plastic materials are
produced as waste in the plastics industry. In other forms, plastics are found
in the form of discarded articles and
containers. Some such plastics, particularly plastic bags and plastic bottles,
are collected in recycling activities.
Recycled plastic bottles are classified according to a nationally recognized
identification system known as the Plastic
Container Code System (PCCS) into seven classes that are being identified by
markings on the bottles. These classes
are: class 1, polyethylene terephthalate (PETE); class 2, high density
polyethylene (HOPE); class 3, vinyl and
polyvinyl chloride or PVC (V); class 4, low density polyethylene (LDPE); class
5, polypropylene (PP);
class 6, polystyrene (PS); and class 7, all other resins and layered multi-
material. For convenience, these classes are
used below to identify waste plastics that are also in a form other than that
of bottles for which the classes were
specifically established.
Recycled plastics of types corresponding to PCCS classes 1 and 2, and
sometimes classes 4, 5 and 6, whether
in the form of used containers or other forms made of the materials, have been
sorted from the general mass of
recycled material or separately collected, all at increased cost. Bulk
mixtures of recycled plastics from more than one
of the PCCS classes, particularly materials from class 7 and from class 3 when
mixed with material from other
classes, generally have been regarded as lacking utility and are accordingly
routed to landfills. Such materials have
lacked an alternative use or manner of disposition.
The employment of plastics in asphalt mixes has presented various problems.
Many of the plastic additives have
lacked an ability to bond to or combine with the asphalt binders of the mix.
Chemical treatments have been proposed,
but such treatments have been ineffective, add to the cost, and introduce
additional noxious and toxic substances into
the process, aggravating the waste disposal problems.
Accordingly, there remains a need for a low cost manner of enhancing the
properties of paving material and there
remains a need for a use of residual plastic waste, particularly unclassified
or unseparated materials or materials of
mixed classes.
Summary of the Invention:
An objective of the present invention is to improve the properties of
pavements and of paving materials,
particularly asphaltic concrete materials, and most particularly, to improve
the strength and useful life of the
pavements made of the paving materials.
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A particular objective of the present invention is to improve the properties
of paving materials at a minimum
increase in cost or at a savings in cost from that of the standard asphaltic
paving material.
A further objective of the present invention is to provide a use for recycled
or waste plastic materials, particularly
thermosetting and other PCCS class 7 materials, and other combinations of
materials of more than one class,
particularly classes 3 through 7 and of those waste and recycled materials in
these groups that have few uses in
relation to their abundance.
A further objective of the present invention is to provide a method of making
a paving material, particularly an
asphaltic paving material, and of utilizing waste plastic in paving material
manufacture.
A particular objective of the present invention is to improve the efficiency
of the method and of the apparatus
for making plastic asphalt material and to improve the properties of the
plastic asphalt product, especially of the
method, apparatus and product described in the related U.S. patents 6,000,877
and 5,702,199.
According to principles of the present invention, there is provided a method
of making a paving material that
includes the step of providing bulk residual plastic waste materials, the step
of processing the plastic to a form
suitable for combining with asphalt, and the step of combining the processed
plastic with asphaltic binder. The
processed plastic may serve as an aggregate in the paving material, and may
replace at least some of, or combines
with, the rock aggregate to form an asphaltic concrete paving material.
Further, the process of the invention may
include the step of forming a pavement with the paving material. In addition,
a paving material and pavement are
provided that are made according to such process.
According to one described embodiment of the embodiment of the invention,
recycled plastic material that is
either unclassified, or is in the form of bulk material containing plastics
corresponding to more than one of the PCCS
classes 3 through 7, or contains thermosetting plastics and other plastics of
PCCS class 7, or otherwise has few uses
for all that is available, are provided. By one method of the invention, the
plastic material is either pelletized,
shredded or otherwise mechanically granulated, or is otherwise formed into
particles. The particles are then processes
to activate their surfaces so that asphaltic binder adheres to them.
Conventional asphaltic binder material and graded
aggregate that includes rock particles ranging in size are mixed with the
treated plastic particles. The binder and
plastic material are, in the most common application of the invention,
premixed as an aggregate component with
binder and rock aggregate and applied as a pavement. In alternative
applications, the processed plastic is mixed with
the binder, then applied as a slurry, for example, over an existing pavement
or over a base or a pre-laid layer that may
contain a rock aggregate, with which it combines to form a pavement.
In one suitable mixture, the aggregate includes from five to seven sieve sizes
ranging from no. 40 to three-fourths
inch in size, and may be from no. 200 to one inch in size. The particles of
plastic are of a size that corresponds to
one of the intermediate sizes of the rock aggregate. Further, the paving
material is formed by mixing from five to
twenty-five percent or more of the plastic particles, measured by volume, with
the rock aggregate and the asphaltic
binder. In one form, an amount of rock aggregate is used which may be varied
from the standard ratio mixture of
rock aggregate and binder, and may reduce the amount of mid-range or
correspondingly sized rock aggregate by an
amount not more than the amount of added plastic, and by an amount that is
somewhat less than the amount of added
plastic. The particles of plastic are in the one-eighth to one-quarter inch
sieve range, and may be three-eighths inch
or larger. The particles of plastic will be generally flatter and more
elongated in shape than the shapes of the particles
of the rock aggregate component of the mixture.
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The formation of the granules of the plastic may be carried out in a number of
ways. One method that can be
employed at high efficiency is to first shred the plastic so that all
particles are roughly two inches or less in diameter
or smaller, then to feed this shredded plastic to a granulator that further
reduces the size of the particles to, for
example, one-quarter inch in diameter or less. Cooling the granules as they
are transported to and processed in the
granulator, for example by injecting cold gas, for example, carbon dioxide
gas, into the particle mass, produces more
fractured surfaces on the granules for better adhesion in the asphalt mixture,
reduces the energy needed by the
granulator by making the particles more brittle, and reduces the frequency of
necessary cleaning of the granulator
by generally maintaining the plastic at lower temperatures at which adhesion
of the plastic to the granulator surfaces
is less likely.
Further in accordance with the described embodiment of the present invention,
the plastic particles are processed
to activate the surfaces of the plastic particles to increase the surface
tension and to cause free or active carbon atoms
to be present in the molecules of the plastic material at the particle
surface. The activation of the particle surfaces
may perform with minimal heating, burning or melting of the plastic, and may
be achieved by exposing the surface
to high energy treatment-gas atoms, ions or molecules for a limited duration.
Such a gas may be in the form of a high
thermal energy gas, and may include a plasma or corona, or other electrically
or otherwise enhanced gas or vapor,
that will cause the activation or increased energization at the surfaces of
the plastic particles.
Treatment of the plastic is achieved, in one embodiment described below, by
exposing the surfaces of granulated
plastic particles to a reducing flame, for example, by exposing the particles
to the outer envelope of such flame. The
exposure may be carried out by passing the particles on a conveyor through the
flame, dropping the particles through
a flame treatment tower or otherwise contacting the particles briefly with a
flame.
Other processes of chemically or mechanically activating the surfaces of the
particles will improve adhesion of
the particles to the asphalt. Processes that can be used for increasing
surface adhesion include those which combine
chemical and wave energy as described in U.S. Patent Nos. 5,922,161 and
5,879,757, for example..
These patents describe methods of modifying or tailoring the surface
of polymers, polymer matrix composite material or polymer based materials by
oxidizing the surface of the polymer
or polymer matrix material and then treating the oxidized surface with an
organofunctional coupling agent or
chelating agent or both, simultaneously with a static and/or a high frequency
alternating physical field. The field may
be an ultrasonic field, a microwave field or a radio frequency field, for
example. The surface of the polymer or
polymer matrix material is oxidized by corona discharge, flame treatment,
plasma treatment, chemical oxidation or
ultraviolet radiation. The oxidized surface may be treated with a low
concentration of an aqueous or non-aqueous
solution of the organofunctional coupling agent and/or chelating agent. The
agent may be, for example, an
organofunctional silane, organo-zirconate, organo-titanate, organo-tin or
organo-alununate. Such agent may have the
general structure XS;Yb, where X is an organoreactive alkyl group, Y is an
hydrolyzable group, a is an integer from
I to 3, and b is 4-a. The agent may be an aminofunctional coupling agent. The
energy fields may be, for example,
an ultrasonic field having a frequency in the range of approximately I to 500
kHz, particluarly in the range of
approximately 10 to 50 kHz, a microwave field having a frequency in the range
of approximately 1 GHz to 300 GHz,
or a radio frequency field having a frequency in the range of approximately 10
kHz to I GHz. Other variations of
treating the oxidized surface may include treatment with a multifunctional
amine-containing organic compound to
bind said compound to the oxidized polymer surface wherein the multifunctional
amine-containing organic
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compound consists of the elements carbon, hydrogen and nitrogen and optionally
comprises one or more elements
selected from the group consisting of oxygen, sulphur, halogen and phosphorous
and comprises at least one amine
functional group which is not a nitrogen heterocyclic group and at least one
further functional group which may be
an amine or other functional group. The multifunctional amine-containing
organic compound may be applied to the
oxidized polymer surface in admixture with an acidic group containing compound
and at a ratio of amine to acidic
group of greater than 1. Such methods when used in the paving material of the
present invention and in the method
of making such material are expected to produce treated material with a
greater shelf-life and with improved strength,
durability and other physical properties.
The use of ionized gas atoms or a plasma enhanced gas to activate the particle
surfaces is particularly suitable,
and may be carried out by transporting the particles on an electrically
conductive conveyor. Other forms of gas
reactant treatment may be used to activate or etch the surface. In one
process, granulated plastic particles are fed into
the top of a vertical plasma treatment column with the gas that occupies the
space between the particles being ionized
by arrays of electrodes along the height of the column. The ionized gas in the
column plasma treats the surfaces of
the particles as the particles pass through the column from top to bottom, so
that the particles are discharged from
the bottom of the column with highly stable activated surfaces.
The activated surfaces of the plastic particles are thought to enhance the
bonding between the asphaltic binder
and the plastic particles and do so with minimal or insignificant heating of
the plastic. Such plastic particles are
blended with the asphaltic binder and with rock aggregate at normal low
temperatures, such as at temperatures below
300 F. The treated plastic may be used to form a paving material by combining
it with a binder before the activated
state of the surfaces of the particles decays. Typically, this time ranges
from days to months, depending on the
treatment process used, the extent of the treatment and other various
treatment parameters such as the energy level
of the treatment gas and the time duration of the particles in the gas during
treatment.
The present invention provides a paving material and pavement that is believed
to be up to fifty percent or more
stronger than the required strength of road paving materials or than standard
asphaltic concrete that is not modified
with the addition of the plastic particles as described above. The invention
provides a use for the low utility or
otherwise useless recycled and waste plastic compositions, and provides a use
for unclassified or residual class plastic
material. The cost of the added plastic material is very low, with some
untreated plastic material approaching no
added cost at all, considering the cost of its disposal as waste. The
invention allows the reduction in the total amount
of paving material used for making a pavement in proportion to the increased
strength of the material, thereby
providing a cost savings in the reduced amount of asphaltic concrete required,
which may more than offset the cost
of providing, treating and blending the plastic.
One embodiment of the present invention provides for the flowing of ionizable
gas through the granulated plastic
material during plasma treatment thereof. The gas is flowed, for example, from
a plurality of ports and sources,
counter to the flow of the material through an ionizing chamber. In the
described embodiment, granulated plastic
material is caused to move downward through a vertical column while ionizable
gas flows upward through the
column. The gas may be air, but according to one described embodiment of the
invention, the gas is a plasma
enhancing gas, that is, is a gas that sustains a plasma more easily or more
efficiently than does air. Such a gas should
be a gas of low humidity and low oxygen content to minimize arcing and
combustion of the plastic material. Such
a gas may be an inert gas, such as argon which enhances plasma and reduces the
likelihood of arcing and combustion.
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The gas may alternatively be helium, neon, krypton, or xenon. Argon gas is
particularly suitable due to its low cost.
Other gases that are effective in enhancing plasma, given the plastic material
and the process conditions, may be used.
Gas compounds, including, for example, carbon dioxide, as well as gas
mixtures, for example, of argon and carbon
dioxide, as well as other plasma enhancing gases or gas mixtures may be used.
Such other gases may be selected
from among those plasma enhancing gases used in certain types of arc welding
such as TIG (tungsten inert gas) and
IvlG (metal inert gas) welding, for example. In addition, prior to being fed
into the column, the granulated plastic
material may be pre-mixed with the plasma enhancing gas, or at least mixed
with dehumidified air or an inert gas or
other gas having a low humidity content or gases at low temperature so as to
pre-cool the plastic. Carbon dioxide,
for example, from a liquified or compressed gas source, may be used as a
plasma enhancing gas as well as a cooling
gas. Cooled air can also be supplied using cooling devices such as vortex
tubes, examples of which are those
manufactured under the mark EXAJR by Tech Sales Co. of Toronto, Canada. The
particles may also be subjected
to magnetic fields before plasma treatment to remove certain metals.
In one embodiment, the particles are caused to move downwardly through a
column through which argon or
other ionizable gas flows upwardly. The particles are caused to circulate in
the column, and the gas may be injected
into the column in such a way as to facilitate the circulation and prevent the
particles from binding. Pulsed or jetted
air can be used to free the particles and prevent their jamming in the column.
The plasma is produced by high voltage
DC potential on electrodes embedded in opposite side walls of the column,
although RF energy may be used. The
column walls, or at least portions thereof, are not electrically conductive.
Energy is coupled from the electrodes
through the electrically non-conductive wall to produce a field inside of the
column that energizes a plasma in the
gas in the column. A removable plastic liner covers the inner wall of the
column. The liner protects the more
permanent walls from damage from the plasma or sticking of the plastic. The
liner can be replaced, thereby making
cleaning of the inside of the column easier and reducing the down-time of the
equipment.
These and other objectives and advantages of the present invention will be
more readily apparent from the
following detailed description of the of the described embodiments of the
invention.
Brief Description of the Drawings:
Fig. 1 is a flowchart of one embodiment of a method according to the present
invention;
Fig. 2 is a diagram of a granulating system suitable for use with the method
of Fig. 1.
Fig. 2A is a diagram of a two step version of the plastic granulating system
of Fig. 2.
Fig. 3 is a diagram of a flame treatment tower suitable for use with
embodiments of the method of Fig. 1.
Fig. 4 is a diagram of an alternative form of flame treatment apparatus
suitable for use with embodiments of the
method of Fig. 1.
Fig. 5 is a diagram of one form of a plasma treatment apparatus suitable for
use with embodiments of the method
of Fig. 1.
Fig. 6 is a cross-sectional diagram of a roadway according to certain
embodiments of the present invention.
Fig. 7 is an enlarged view of a portion of Fig. 6.
Fig. 8 is a diagram, similar to Fig. 5, of an alternative form of a plasma
treatment apparatus suitable for use with
embodiments of the method of Fig. 1.
Fig. 9 is a more detailed diagram of the apparatus of Fig. 8.
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Figs. 9A-9C are cross-sectional views along lines 9A-9A, 9B-9B and 9C-9C of
the column of the apparatus of
Fig. 9.
Fig. 9D is a cross-sectional view of an alternative configuration of the
column of the apparatus of Fig. 9 taken
along line 9B-9B.
Detailed Description of the Drawings
One embodiment of the invention is set forth herein in the form of a
description of a test or example of a process
(Fig. 1) of making a paving material. In accordance with this embodiment of a
method of the present invention, a
standard asphaltic mix is selected (70). One such suitable mix is, for
example, New Mexico State Highway and
Transportation Department (NMSHTD) type I A asphaltic mix. Further, a mixture
of local rock aggregate suitable
for asphaltic concrete for use in highway construction is selected (71). Such
a rock aggregate mixture used in this
example includes particles of the following sizes, as set forth in Table 1:
TABLE 1
Sieve Size Percent Passing
l inch 100
3/4 inch 86
1/z inch 67
3/8 inch 57
No.4 42
No. 10 34
No.40 21
No. 200 5.1
Where aggregate is used as a component of the paving material, as in the
illustrated example, this step (71) may
be performed at any time prior to the blending step (75) discussed below. In
other applications, the aggregate
providing step (71) is omitted from the paving material blended in step (75),
but may be in a previously applied layer
of pavement to which the blended plastic and binder are to be applied.
In the example, a volume of bulk recycled plastic material is selected (72).
The bulk plastic material may be
ungraded or unsorted and thereby predominantly contain plastics of types
corresponding to PCCS classes 1 through
7. A suitable plastic is a residual ungraded bulk of recycled plastic from
which most of the items of class 1
(polyethylene terephthalate) and class 2 (high density polyethylene) have been
removed. It is also contemplated that
some of the class 4 plastic (low density polyethylene) and low density foam
plastic from class 6 (polystyrene) may
have been removed, as well as other grades or classes for which other uses
have been found. The bulk material may
contain plastic bottles and other waste plastic articles, layered,
thermosetting or miscellaneous plastic articles from
class 7, PVCs from class 3, or masses of waste plastic from plastic production
and molding industries, for example.
In the example, a representative average sample including primarily an
assortment of plastic waste corresponding
to the plastics of classes 3 through 7 was selected. The plastic waste may
include used containers but may contain,
in addition or in the alternative, other plastic waste having compositions
corresponding to the PCCS classes.
Then, the plastic material is granulated (73). The granulation process
typically involves the shredding of the
plastic material 31 in a granulating system 30 that employs a shredder or
granulator having, for example, plurality
of knife blades 32 to reduce the mass of plastic to a uniform blend of
particles'33, as illustrated in Fig. 2. The
particles include a large percentage of generally flat flake or plate-like
pieces that are generally more elongated than
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the particles of the rock aggregate referred to above. In the example, the
sizes of the granulated plastic particles
included 18 percent that passed sieve no. 10, with all of the particles
passing sieve no. 4. It is contemplated, however,
that, for use with the rock aggregate described above, most of the plastic
particles will be in the 1/4 inch to 3/8 inch
range, and perhaps larger. They will nonetheless be smaller than, and may be
less than half the size of, the largest
rock aggregate particles for applications in which the plastic particles are
to be blended with the aggregate before
paving to form an asphalt mix.
Fig. 2A illustrates an alternative or more detailed granulating sub-system 30a
that may be used for the
granulating system 30 of Fig. 2. As illustrated in Fig. 2A, the granulating
sub-system 30a may include a shredder
34 into which the raw plastic waste 31 is fed and which reduces the size of
the components of the plastic waste 31
to uniform medium size particles 33a of about two inches in diameter or less.
The rough sized particles 33a are then
conveyed in an auger conveyor 35 into a second-stage shredder or granulator 36
in which the particles 33a are further
reduced in size by a bank of knives 37, which are driven by a motor 37a, until
they pass through a screen 38 in the
bottom of the granulator 36 having openings of about 1/4 inch in size, thereby
producing the granulated particles 33.
A supply 39 of cold carbon dioxide gas is injected at various points into the
conveyor 35 and at various points into
the granulator 36 to cool the particles 33a as they are being transported and
ground to size. This cooling makes the
particles 33a more brittle, which causes them to fracture more readily in the
granulator 36 and prevents sticking of
the plastic to the knives 37 and the wall of the granulator 36, thereby
reducing the need to clean the drum and knives
of the granulator 36 and lowering the energy requirement of motor 37a. The
cooled granules 33a develop more
fractured surfaces in the granulator 36, which produces plastic particles 33
that bond better to the binderin the asphalt
mix.
The granulated plastic particles are then treated (74) to activate the
particle surfaces. The manner of activating
the surfaces of the plastic particles is, according to one embodiment of the
invention, by exposing the surfaces of the
particles to a flame treatment. With the flame treatment, It is helpful to
expose the plastic particles to the flame
intermittently, if increased exposure is desired, than to maintain the flame
constantly, which could unnecessarily heat
the plastic, or could burn or melt the plastic. The flame in this embodiment
may be a reducing flame.
A reducing flame may be produced by natural gas, propane, or other fuel. In
the example, an oxyacetylene
reducing flame is used and the plastic particles were spread on a screen and
brushed repeatedly with the flame from
above and below, using a torch maintained at a distance of about twelve inches
from the flame, with agitating and
turning of the plastic particles. The duration or dwell of the flame on any of
the particles may be kept sufficiently
short to avoid any significant melting or burning of the particles or causing
a visually perceivable change in the
appearance of the plastic particles. A small percentage of the plastic that
might be of the lower density, lower melting
point types or include exceptionally thin sheet shreds or narrow fibers may,
in such a process, melt or char without
adversely affecting the process or paving material to be produced.
In one embodiment of the invention, it is contemplated that the activating gas
treatment of the granulated plastic
particles 33 be carried out in a flame treatment tower 40, as illustrated in
Fig. 3. Such a tower may be a vertically
elongated cylindrical column 41 having a plurality of inwardly directed, and
possibly upwardly inclined, gas jets 42
spaced around the column and at vertical intervals. The fuel to oxygen mixture
of the flame is set to create a slightly
oxygen poor or reducing flame throughout the center of the column through
which the granulated particles are
dropped. Depending on the height of the column used, the particles 33 may be
repeatedly dropped through the flame.
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Use of a flame treatment tower 40 in which the particles are dropped through
the flame, rather than the use of a
conveyor or other structure to support the particles for treatment with the
flame, avoids possible sticking to the
support caused by a softening or melting of a small percentage of the plastic
material in the flame. Such a tower
should have a cool air region 43 at the bottom of the tower to facilitate a
rehardening of any softened plastic, and the
collection of treated particles 45 at the bottom of the tower should include a
fluidized air bed 44 or agitating
mechanism to avoid a sticking together of the treated particles.
In an alternative embodiment of the invention, flame treatment is performed in
an inclined drum tumbler 50, as
illustrated in Fig. 4. The tumbler 50 is in the form of an elongated
cylindrical barrel 51, inclined at less than 20 or
25 degrees to the horizontal, for example, at about 10 to 15 degrees to the
horizontal. The barrel has a plurality of
longitudinal vanes 52 running generally parallel or slightly spiraled relative
to the axis of the barrel. The reducing
flame 53 is made to flow upwardly through the center of the barrel around the
axis thereof as the barrel is rotated.
The granulated plastic particles 33 are fed into the top of the barrel and
proceed to be tumbled through the flame
several times as they proceed toward an outlet at the bottom end of the
inclined cylinder 51. The constant rotary
motion of the barrel, which is kept relatively cool, prevents the sticking to
the barrel of any particles 45 that might
have been softened.
It is further contemplated that the particles may, for some uses, be
pelletized following shredding or granulation
and prior to the activating treatment. To pelletize the particles of plastic,
the particles may be fed, for example, from
a hopper into a pelletizing extruder in which a mild heating element would
heat the particles to soften some of the
plastic components and promote sticking of the particles. An auger then
compresses the warmed particles and
extrude them through an extrusion die to be cut into pellets of more or less
uniform size. Such pellets may then be
treated as described above.
In other embodiments, a plasma, corona or ionized gas may replace or be
combined with the flame. For
example, as illustrated in Fig. 5, treatment is carried out by exposing the
particles to ionized gas, plasma, corona
discharge 60 or other electrically energized treatment medium. Such a
treatment may be carried out by presenting
the plastic particles 33 upon a conveyor 61, which may be effective to
maintain charge on the plastic particles, while
exposing the particles to the treatment medium 60.
An alternative apparatus 80 for plasma treatment of the particles is
illustrated in Fig. 8, in which a vertical
plasma treatment tower or column 81 is employed. The column 81 is equipped at
its top with a hopper-fed infeed
auger or other loading device 82 which is capable of loading a continuous
stream of granulated waste plastic particles
into the column 81 from its top. The particles may be allowed to fill the
column and form a loosely stacked bulk
mass of the particles 83 in the hollow interior of the column 81.
Opposite sidewalls of the column 81 are provided with electrodes 84 in the
form of arrays of pins, electrically
insulated from any metal such as a housing (not shown) spaced from and
surrounding the column 81, which may be
formed of a metal and grounded. The electrodes 84 connected to a high voltage
power supply which energizes the
electrodes 84 sufficiently to produce an electrical discharge in the gas that
occupies the spaces between the particles
in the column 81. The discharge results, for example, in a purplish-blue glow
resulting from the ionization of gas
within the column 81. The electrodes 84 may be located on opposite sides of
the column 81 in the upper half of the
column and on the front and back of the column 81 on the bottom half of the
column 81 (see Figs. 9A, 9B and 9C)
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to better insure uniform treatment of the particles as they descend vertically
down the column. Other electrode
arrangements may be used for this purpose.
At the bottom of the column 81 is provided an outfeed auger 85, which removes
treated particles of bulk plastic
material from the bottom of the column 81. After the column 81 is filled, the
plasma electrodes 84 are energized,
and after the plasma treatment has been applied to the particles in the filled
column 81 for a sufficient period of time
to activate the surfaces of the particles, the outfeed auger 85 and the infeed
auger 82 are operated at the same bulk
transfer rate so as to cause a constant volume flow of particles into the
column at the top, downwardly through the
column 81 and the plasma, and out of the outfeed 85 at the bottom of the
column 81. An initial quantity of about
one thousand pounds of treated plastic material should be run out of the
apparatus 80 when it is first started.
Thereafter, fully treated plastic is consistently produced. The initial
quantity may be collected and re-fed into a
hopper to the infeed auger 82 and retreated.
The column 81 may be provided with air jets to free the bulk plastic material
should it become compacted in
the column. In the event that the downwardly flowing particles become clogged
in the column 81 or are otherwise
unable to flow downwardly under the influence of gravity, air from compressor
90 or argon from tanks 93 may be
injected through nozzles 94,95 in bursts or pulses to free any clogged
particles.
In the plasma treatment of the plastic particles, the surfaces of the
particles are treated to a desired surface
tension, for example, which produces an ASTM wettability measurement of 50-55
dynes/cm or more, for example,
of about 68-70 dynes/cm or even higher. For a nominal treatment rate of
approximately 500-550 cubic feet per hour
of plastic, which, for example, may have a bulk density of about 27 pounds per
cubic foot. The column 81 that is
illustrated between 10 to 14 feet tall with an approximately 13 inch square
internal cross-section. Its electrodes 84
are energized to a high voltage determined by the geometry of the column 81
and electrodes. 84 to ionize the gas
within the chamber. The high voltage is supplied from a rectified output of
rectifier 88 connected to a center-tapped
secondary winding of a high voltage transformer 87. In one embodiment, the
transformer 87 is connected to an
input 86 of about 440-480 volts AC, 60 Hz, drawing about 30 input amps. The
output of the secondary winding of
the transformer for an apparatus of this configuration and capacity is about
5kVA. This power is adequate for
producing paving material in these quantities. For larger scale paving
projects, one skilled in the art can appreciate
that larger scale equipment is desired and providing such would be within such
person's skill.
Electrodes 84 may take many configurations and forms. For example, the arrays
of electrodes may be arranged
in a 1/4 inch grid pattern on polyethylene sheets 91. Connection of the
electrodes 84 to the output rectifier 88 can
be made with the use of a conductive oil layer 92 sealed in a thin volume that
communicates with the outer ends of
the electrodes 84. Plasma treatment equipment and the technology for designing
and producing such equipment is
known in the commercial industrial plasma treatment industry.
The plasma treatment can be satisfactorily performed where the gas in the
column 81 is air, which may be
supplied from the compressor 90. Much higher rates of productivity can be
achieved when an inert gas such as argon
is used, which may be supplied from the tanks 93 without the compressor 90
being activated. The argon tends to
support the plasma better and is less likely to result in a burning of the
plastic. Other inert or semi-inert gases and
gases such as nitrogen or carbon dioxide can be used with varying degrees of
plasma enhancing efficiency.
When the plastic has been treated, it is better that it be used as soon as
possible. Plastic treated by flame should
be mixed with asphalt within a day or days of treatment and treated plastic
should be kept out of contact with freely
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flowing air or sunlight until used. With plasma treatment, however, a longer
lasting activated particle surface results.
Where a plasma enhancing gas, such as argon for example, is used as the
processing gas of which the plasma is
formed, the activation of the plastic remains even longer. As such, plasma
treated particles can be stored in bulk for
from several weeks to several months without substantial degradation of the
activated state of the particle surfaces.
Nonetheless, use of the treated particles of plastic material should be used
as soon after treatment as practical to
realize the maximum benefit of their activated surfaces.
Plasma treatment of the particles is believed to roughen the surfaces of the
particles and increase the energy of
the atoms near the surface, increasing the frequency of chemical bonding
between the particle surfaces and the binder
and increasing the strength of the particle-binder bond.
Use of the plastic to produce an asphaltic pavement layer may involve the step
of blending (75) the plastic
particles with rock aggregate and with asphaltic mix binder in a manner that
is conventional for the formulation of
asphaltic paving material for road surfaces (Fig. 1), with the plastic
particles being added as an alternative or
supplement to the rock aggregate in the overall mix. The plastic particles
function more as the rock aggregate
component of the asphaltic concrete than as the asphaltic binder. Only a minor
or incidental portion of the plastic,
particularly that which has a lower density and a lower melting point, that
might remain in the plastic material bulk,
would soften and tend to blend with the asphaltic component. Instead, in the
described embodiments of the
invention, the plastic particles supplement the mid-size rock aggregate
components. The percentage of the mid-size
particles of the rock aggregate may be reduced in the mix, although that is
usually not necessary.
Rather than blending a mixture of the treated plastic, binder and, rock
aggregate, the present invention also
provides its advantages when used as a mixture of plastic with asphaltic or
oil based binder on road bases, or by
applying such a mix over a rock aggregate base layer, where the binder and
plastic mix flow down into the base
An example of the road surface produced is illustrated in Fig. 6 and includes
an asphaltic layer 10 overlying the
base gravel layer 11 to form a roadway 12. The asphaltic layer 10 may or may
not be the top layer of the roadway 12,
but the roadway 12 may also include a surface layer 13 overlying the asphaltic
layer 10. The asphaltic layer 10, as
illustrated in Fig. 7, is formed of an asphalt binder 20 and a rock aggregate
21 having mixed therewith at least five
percent by volume of plastic particles 22, most of which are no. 10 sieve size
or larger. The plastic particles 22 have
treated activated surfaces. A major portion, or substantially all, of the
plastic particles 22 are of a plastic material
composition corresponding to PCCS classes 3 through 7. Most of the particles
22 of plastic are typically of a size
at least 1/8 inch large, and may be of a size less than 3/8 inch large,
although smaller and larger size particles may
be used. The plastic material will typically include at least thirty percent
recycled plastic from the group consisting
of thermoset plastics, PVC, and high density polypropylene and polystyrene.
The particles of plastic are believed to strengthen the paving material by
adding a slightly flexible interlocking
aggregate component that bonds with the asphaltic binder with a partially
chemical molecular bond, developing an
increased shear resistance of the paving material. The paving material is also
more highly impermeable to water,
preventing such water from propagating into the gravel bed or subgrade.
Improved properties of the paving material made in accordance with the method
of the present invention are
illustrated by the example described above. In that example, the treated
plastic particles were tested by blending them
into the asphaltic mix (using asphaltic concrete 4.4% Navajo 60/70 asphalt
cement) that was first heated to a
temperature of 265 F then mixed with the plastic at room temperature. The
mixing temperature is usually that which
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produces an asphalt cement viscosity of 170 +/- 20 centistokes kinematic. The
plastic was added to the asphaltic
mix at a ratio of ten percent by volume, determined from the loose unit
weights of the plastic and asphaltic mix. The
material was tested by placing it in molds and compacting it to seventy-five
blows per side at approximately 250 F.
For comparison, other samples were similarly prepared, one sample using the
standard asphaltic concrete mix without
plastic, and two samples using untreated plastic of the same composition, one
added at five percent by volume to the
asphaltic mix and one added at ten percent by volume to the mix. The loose
unit densities of the components of the
mix for the tests were 1.45 grams per cubic centimeter (90.5 pounds per cubic
foot) for the asphaltic concrete mix
and 0.36 grams per cubic centimeter (22.2 pounds per cubic foot) for the
treated and untreated plastic. The five
percent by volume of plastic mixes included 1135.88 grams (2.5 pounds) of
asphaltic concrete mix and 14.67 grams
(0.032 pounds) of plastic, and the ten percent by volume of plastic mixes
included 1076.10 grams (2.370 pounds)
of asphaltic concrete mix and 39.69 grains (0.065 pounds) of plastic. The
tests performed as set forth below and the
component analysis as set forth above employed the standards set forth in
Table 2:
TABLE 2
Extraction ASTM D-2172
Sieve Analysis ASTM C-136
Bulk Unit Weight ASTM D-2726
Rice Unit Weight ASTM D-2041
Marshall Flow/Stability ASTM D-1559
The results of the test were as follows, as set forth in Table 3:
TABLE 3
Marshall Pro erties of Asphaltic Concrete
No plastic 5%-untreated 10%-untreated 20%-treated
Bulk Unit Wt.
gins/cm3 2.366 2.339 2.261 2.272
(pcf) (147.4) (145.7) (140.9) (141.5)
Rice gms/cm3 2.419 2.396 2.369 2.370
(pcf) (150.7) (149.3) (147.6) (147.7)
Air Voids (%) 2.2 2.4 4.6 4.1
Stability
pounds 2821 3078 2432 3404
Flow (1/100 in)
11 12 11 11
The above results can be compared with the NMSHTD stability requirements of
1640 pounds for non-interstate
highways and 1800 pounds for interstate highways. It is found from the tests
set forth above that, starting with 2821
pound asphaltic concrete (per the test), the strength increased with the
addition of untreated plastic to where it had
increased by almost ten percent with the addition of 5% untreated plastic
particles. However, the strength decreased
as the percentage of untreated plastic particles in the mix increased. With
the treated plastic, the strength increased
with the addition of the plastic, being about 21% higher than the original
asphaltic concrete with the addition of ten
percent plastic. It is believed that the strength will exceed that of the
original asphaltic concrete mix with treated
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plastic at up to about 25% with optimally treated and optimally sized plastic
particles. Other properties such as
flexibility, water impermeability, crack resistance and durability are also
expected to be improved over this range.
Improved efficiency of the above method and apparatus can be attained with the
system illustrated in Fig. 9, in
which a counter flow of processing gas is produced in the upward direction in
the column 81 by injecting the
processing gas through inlets 101 in the opposite sides of the column 81. As
seen in the cross-sectional views of
Figs. 9A, 9B and 9C, electrodes 84 of opposite DC potential are supported on
opposite longitudinal sides of the
column 81, which is of a I to 1'/2 foot square cross-section. As seen in Fig.
9, inlets 94 are carried by the other
respective opposite transverse sides of the column 81 at four different levels
spaced throughout the height of the
column 8 1. These inlets 94 are off center and staggered so that a swirling
action is produced by gas entering the
column 81 through the inlets 94. At the bottom of the column, three inlets 95
are provided per side so that sufficient
gas is injected through the inlets 95 to fill the spaces between the particles
in the column 81 and to displace air from
these spaces. The inlets 95 are alternately connected to different sources of
gas, illustrated as pressurized tanks 93
of argon gas, each connected through a control valve 96 to opposing sets of
the inlets 94 and 95. The inlets 94 are
sized so that gas is supplied throughout the column 81 to fill the spaces
between the more loosely packed particles
toward the top of the column 81 and to insure that the air is displaced and
more uniform plasma is produced
throughout the colurrm 81.
Fig. 9D illustrates an alterative cross-section of a column 81a. The wall of
the column 8Ia is made of clear
plastic, which permits viewing of the progress of the particles 83 of the
granulated plastic as they flow through the
column 81a, as well as viewing of the glowing plasma in the gas, which is for
example argon. The cross-section
illustrated is taken at the section 9B-9B of Fig. 9 as an alternative thereto.
The column 81a is rectangular in shape,
approximately 24 inches by 13 inches, with the plastic panels 92 welded across
to the opposing sides of the column
8la, about 5 inches from the ends, to define a vertical space of about 13x13
inches containing the plastic 83. Fluid
tight chambers 97 are formed between the panels 92 and the short sides of the
column 81a to contain circulating
cooling oil. The electrodes 84 are embedded in the plastic panels 92 and are
in communication with the oil in
chambers 97 but not in communication with the argon gas or the plastic within
the column 81a. The electrodes 84
may be electrically connected to the leads from the rectifier 88 or through
conductive oil in the chambers 97 or by
wires or a metal plate 99 within the chamber 97, in which case the oil in the
chambers 97 may be non-conductive.
Because of the varied and unpredictable composition of the plastic waste
material, some components can melt,
reactor decompose in the treatment column 81,81a and stick to or form deposits
on the column walls. These deposits
eventually impede the smooth flow of plastic downward through the column or
interfere with the electrodes. Such
deposits must periodically be removed. When such deposits form on the
permanent walls of the column 81 or 81a,
the apparatus 80 must be shut down and cleaned. To minimize the equipment down-
time and to simplify the periodic
cleaning process, a removable liner 98 may provided to line the inside walls
of the column 81 or 81a, as illustrate
in Fig. 9D. The liner may be formed of a heat resistant low adhesion plastic
material, for example, HDPE, in the
form of a rectangular or square tube that covers the inside walls of the space
containing the plastic particles being
treated. The liner 98 may be in the form of a smooth solid tube of film, for
example, of 3/32 inch rigid plastic,
through which the static electric field from the electrodes propagates with
sufficient strength to sustain a plasma when
the gas in which the plastic particles 83 are mixed is argon. The liner 98
resists sticking of plastic material thereto,
but when such materials do stick to the liner, the liner 98 can be removed and
replaced, thereby avoiding buildup of
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material on the permanent walls of the column 81 and avoiding the need to shut
down the apparatus for an extended
time for cleaning.
A dehumidifier 79 supplies dehumidified air to the auger 82 to insure that the
particles of plastic arrive in the
column 81 in a controlled dry state more suitable for processing.
The ports 94 and 95 can also be alternatively connected to a compressor 90
through a valve 78 to supply bursts
of compressed air to the column 81, if and when necessary, to clear the column
81 or to unclog jams of plastic in the
event a bridge or dam of the plastic particles is formed, which can occur if
failures in operation occur, particularly
where the flow of plastic is stopped and restarted with particles in the
column 81 for any reason.
At the top of the column an exhaustplenum 77is provided, which has a plurality
of exhaust ports communicating
with the top of the interior of the column 8 1. The plenum 77 is connected to
an exhaust fan 76 which has an outlet
communicating through a roof vent to the exterior of the building housing the
unit 80. The fan 76 and the valves 96
are controlled by a controller 69 so that most or all of the processing gas
flows through the column 81 and out the
exhaust, with little or none of the air that arrives with the particles from
the auger 82 flowing downward with the
particles through the column, but rather is exhausted through the roof vent.
The controller 69 also controls the power
to the electrodes 84, the valve 78 from the anti-clog compressor 90, the
motors to the augers 82 and 85 and the
dehumidifier 79, which supplies dehumidified air supply to the auger 82.
Those skilled in the art will appreciate that the applications of the present
invention are many, and that the
invention is described in exemplary embodiments Accordingly, additions and
modifications can be made without
departing from the principles of the invention. Accordingly, the following is
claimed:
