RECYCLED POLYETHYLENE CONSTRUCTION PRODUCT AND METHOD OF MANUFACTURE

MATERIAU DE CONSTRUCTION FABRIQUE A PARTIR DE POLYETHYLENE RECYCLE ET METHODE DE PRODUCTION

English Abstract

A cast recycled polyethylene product, optionally
containing fibre reinforcement such as scrap polyester, contains
oil as a compatibilizer. Typically the oil is derived from
recycled containers. The product is made by comminuting
containers, adjusting the oil content to the desired range,
adding fibre reinforcement if desired, and heating the mix to a
temperature sufficient for the polyethylene to commingle with the
reinforcement if present, but insufficient to damage the fibers.
Typical cast products include guard rail posts, fence posts,
highway median dividers, parking curbs, and the like. These
products have the advantage of not being subject to weather
damage and loss of structural strength, as is the case with
timber and concrete.

Claims

8
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A heat cast recycled polyethylene product made by the process comprising:
comminuting polyethylene derived from recycled polyethylene containers;
blending oil compatibilizer, derived from residual oil in the recycled
polyethylene
containers, with the comminuted polyethylene until the oil in the mixture is
between 1%
and 10% by weight, adding oil if the oil level is too low and adding
comminuted
polyethylene substantially free of oil if the oil level is too high;
charging the mixture into a mould;
heating the filled mould to a temperature and for sufficient time for the
mixture to
become molten and substantially to fuse together;
applying sufficient pressure to the contents of the mould to expel any trapped
gas
and any excess mixture;
trimming any excess mixture forced out of the mould whilst still hot;
cooling the mould in a cooling pond to an initial temperature at which the
cast
mixture can be handled;
removing the cast product from the mould; and
cooling the casting further in the cooling pond until fully solidified and
cooled.
2. A product according to claim 1, further comprising an effective amount of
fibre
reinforcement material.
3. A product according to claim 1 wherein residual oil is present in at least
50% of
the recycled polyethylene containers.
4. A product according to claim 1 wherein the major proportion of the recycled

polyethylene is high density polyethylene, HDPE.
5. A product according to claim 4 wherein at least 90% of the recycled
polyethylene
is high density polyethylene, HDPE.
6. A product according to claim 2, wherein the fibre reinforcement material is
scrap
polyester in the form of fabric or yarn.
7. A product according to claim 6, wherein the polyester is polyethylene
terephthalate.
8. A product according to claim 6, wherein the scrap polyester contains a
major
proportion of polyester blended with a minor proportion of another fibre.
9. A product according to claim 1 containing in percentages by weight from 90-
98%
polyethylene; and from 2-10% oil compatibilizer.
10. A product according to claim 2 containing in percentages by weight from 90-
98%
polyethylene; from 1-10% oil compatibilizer; and from 1-8% fibre reinforcement
material.

10
11. A process for producing a cast recycled polyethylene product comprising
the steps
of:
- comminuting polyethylene derived from recycled polyethylene containers;
- blending oil compatibilizer, derived from residual oil in the recycled
polyethylene containers, with the comminuted polyethylene until the oil in the
mixture is
between 1% and 10% by weight, adding oil if the oil level is too low and
adding
comminuted polyethylene substantially free of oil if the oil level is too
high;
- charging the mixture into a mould;
- heating the filled mould to a temperature and for sufficient time for the
mixture to
become molten and substantially to fuse together;
- applying sufficient pressure to the contents of the mould to expel any
trapped gas
and any excess mixture;
- trimming any excess mixture forced out of the mould whilst still hot;
- cooling the mould in a cooling pond to a temperature at which the cast
mixture
can be handled;
- removing the casting from the mould; and
- cooling the casting further in the cooling pond until fully solidified and
cooled.
12. A process according to claim 11, wherein prior to the charging step an
effective
amount of fibre reinforcement material is incorporated with the blended
mixture.
13. A process according to claim 11, wherein the recycled polyethylene is
comminuted
to a particle size of 10-25mm × 1-2mm square.
14. A process according to claim 11, wherein the major proportion of the
recycled
polyethylene is high density polyethylene, HDPE.

11
15. A process according to claim 14, wherein at least 90% of the recycled
polyethylene is high density polyethylene, HDPE.
16. A process according to claim 12, wherein the fibre reinforcement material
comprises scrap polyester in the form of fabric or yarn.
17. A process according to claim 16, wherein the scrap polyester is
polyethylene
terephthalate.
18. A process according to claim 16, wherein the scrap polyester contains a
major
proportion of polyester blended with a minor proportion of another fibre.
19. A process according to claim 11 wherein the filled mould is heated to a
temperature of from about 130 - 180 degrees Celcius.
20. A process according to claim 19 wherein the temperature is from about 130 -
160
degrees Celcius.
21. A process according to claim 11 wherein the pressure applied to the mould
is 5 psi
or less.
22. A process according to claim 11 wherein the mixture in the mould comprises
in
percentages by weight from 90-98% polyethylene; and from 2-10% oil
compatibilizer.
23. A process according to claim 12 wherein the mixture in the mould comprises
in
percentages by weight from 90 - 98% polyethylene; from 1 - 10% oil
compatibilizer, and
from 1 - 8% fibre reinforcement material.

Description

CA 02101646 2005-09-O1
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TITLE OF THE INVENTION:
Recycled Polyethylene Construction Product and Method of Manufacture
FIELD OF THE INVENTION
The present invention relates to a recycled polyethylene construction
product and method for producing it. The method is particularly useful for
utilizing
disposable polyethylene containers, by employing a simple moulding technique.
1 o BACKGROUND OF THE INVENTION
The increasing costs of disposing of solid waste in landfill sites and recent
concern
over the longevity of material buried in such sites has prompted a search for
alternative
disposal methods, in particular the re-use of plastic materials. Additionally,
increasing costs
of oil-based plastic products have made the recycling of plastic products more
economically
i 5 attractive. A readily available source of high quality plastic is
disposable polyethylene
containers, such as lubricating oil containers, herbicide containers and many
others. Recycled
plastic can provide a useful construction material resisting weathering
effects and salt
degradation suffered by wood and concrete.
2 o In the past recycling of plastic products has been limited by
contamination of the
plastic material. Contaminants create difficulties in the recycling process,
and can impair
recycled product properties often in an unpredictable and random fashion.
Contaminants enter
the recycle plastic stream as residual materials in the containers (from both
the original
contents, and other materials put into the container for disposal purposes),
labels, tops,
25 undetected non-plastic material, and even debris from the processing
equipment itself. Much
effort is devoted to attempts to eliminate contaminants, by washing and by
sorting materials
for recycling. If an extruded or injection moulded product is to be made from
the recycled
plastic, then the feed material has to be substantially free of contaminants,
as otherwise the

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expensive dies are at risk. Removing contaminants is not only time consuming
and
expensive, but also can produce additional environmental pollution, especially
in the case of
lubricating oil containers. Recycled plastic derived from feed material which
has not been
cleaned and sorted has generally been regarded as having inferior quality and
only limited
s usefulness.
SUMMARY OF THE INVENTION
The present invention provides a superior construction product obtained by a
1 o simple process which in many cases eliminates the need to wash the
recycled polyethylene.
The process also does not require expensive plastic extrusion and injection
moulding
equipment. Residual lubricating oil often present as a residue in containers
for recycling has
been found to be an effective compatibilizer in recycling polyethylene
material. Polyethylene
is known to be a difficult plastic to recycle. Previous methods which have
been suggested in
1 s the prior art for reprocessing it have required absorbent additives to
counteract the effects of
the residual oil. It has now been found that provided the amount of residual
oil is kept to
within a specific effective range, the plastic can be recycled into useful
construction products
without further treatment. If the proportion of residual oil in the recycled
containers is too
high, then dry, oil-free containers, such as herbicide containers and the
like, or dry scrap
2 o polyethylene from other sources, must be blended in with the recycled
containers to bring the
oil level into the effective range. The inevitable other minor contaminants do
not compromise
the strength of the finished product.
As a further extension of the invention, it has been found that the addition
of fibre
2 5 reinforcement, especially polyester fibres, notably increases the strength
of the finished
product. Fibre reinforcement is especially useful in larger products. The
orientation of the
fibres can be controlled to provide enhanced structural strength.

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The invention seeks to provide a substantially solid casting of recycled
polyethylene suitable for numerous construction purposes. In a broad
embodiment, the
invention provides a heat cast recycled polyethylene product including
substantially fused
recycled polyethylene containing an effective amount of oil compatibilizer,
preferably
having embedded therein an effective amount of a compatible fibre
reinforcement
material.
There is considerable choice in the fibres which can be used as the
reinforcement
material. It is preferred to use polyester material, which is freely available
in the form of
1 o scrap fabric and yarn. These fabric materials are primarily of polyester,
often mixed with a
proportion of other fibres, such as cotton or wool. A preferred fibre
reinforcement is
polyethylene terephthalate, commonly referred to simply as "polyester". In the
preferred
embodiment, the scrap polyester contains a major proportion of polyester
blended with a
minor proportion of another fibre.
Preferably, the recycled polyethylene is high density polyethylene (HDPE), or
HDPE with not more than ten percent low density polyethylene (LDPE). In the
preferred
embodiment, at least 90% of the recycled polyethylene is high density
polyethylene, HDPE.
Separating containers made from these materials is not difficult, since they
are usually marked
2 o to show the polyethylene grade used. Minor amounts of other plastics may
also be present.
The lubricating oil compatibilizer may be present as residual material in the
recycled polyethylene containers. In the preferred embodiment, the oil
compatibilizer
comprises residual oil in at least some of the recycled containers, and more
preferably, the
residual oil is present in at least 50% of the recycled containers.
Polyethylene containers
including residual oil preferably make up 50% of the polyethylene material.
Most preferably the construction product includes comminuted polyethylene

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containers present in a range from 90-98%, oil compatibilizer present in a
range from 1-10%,
and fibre reinforcement material, if desired, in a range from 1-8%, in each
case by weight.
The product has proved particularly useful as a guard rail post, having an I-
beam
cross-section. The process according to the invention comprises the following
steps:
- comminuting recycled polyethylene;
- blending oil with the comminuted polyethylene to provide a mixture
containing an
effective amount of oil;
- charging the mixture into a mould;
to - heating the filled mould to a temperature and for sufficient time for the
mixture to
become molten and substantially to fuse together;
- applying sufficient pressure to the contents of the mould to expel any
trapped gas
and any excess mixture;
- trimming any excess mixture forced out of the mould whilst still hot;
- rapidly cooling the mould in a cooling pond to an initial temperature at
which the
cast mixture can be handled;
- removing the casting from the mould; and
- cooling the casting further in the cooling pond until fully solidified and
cooled.
2 o Preferably the mixture contains an amount of fibres sufficient to provide
reinforcement to the product, In that case, the mixture is heated to a
temperature sufficient to
cause the mixture to commingle with the fibre material, but insufficient to
damage the fibre
material. Thus if the reinforcement is polyester, the temperature is
sufficient for the
polyethylene to flow, but insufficient to melt the polyester. Typically, the
mould is heated
2 s to a temperature of from about 130 to 160 degrees Celcius, but not more
than 180 degrees
Celcius.
Preferably the comminuted polyethylene contains from about I to about 10% of

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lubricating oil residues, comprising residues left in the containers after
use. After the
polyethylene has been comminuted it is easy to determine the oil content, for
example by
removing it with a solvent from a known this is weight of material. the oil
level is too low,
corrected by adding oil. If the oil level is too high, this is corrected by
blending into the
s mixture sufficient comminuted dry polyethylene substantially free of oil. It
is often found
that equal parts of dry oil free containers, and containers with oil residues
left in them,
provide just about the right amount of oil in the comminuted mixture.
Preferably, the particle size of the comminuted polyethylene is approximately
10
10 - 25 mm. long and 1 - 2 mm. square, which is about the thickness of the
container wall. The
polyester reinforcement generally is only present in larger cast products, but
can be used in
any size of product.
The mould is charged with an appropriate amount of comminuted polyethylene,
oil, and, if necessary fibre reinforcement which is then compacted by hand, or
by using
vibration, to reduce cavities.
The mould containing the mixture of oil, comminuted plastic and, if desired,
polyester reinforcement is held at the required temperature for an extended
period of time,
2 o mainly because hot polyethylene is relatively viscous and flows quite
slowly. For a massive
product, such as a guard rail post, the time required can be as high as
approximately 16
hours. That is, the mould is left heated overnight. A low pressure,
approximately 5 psi or
less, is conveniently applied to the mould by means of a cover, which may be
contoured to
form a shape in the top of the article. The pressure applied by the cover is
sufficient to force
2s out at least the major proportion of any trapped air, and any excess
material in the mould.
This excess is most conveniently removed from the mould whilst still hot,
although
trimming can be left and carried out as part of any final finishing steps,
such as drilling
holes, painting, and the like. The mould and its contents are cooled slowly in
a cooling pond

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for thirty minutes to one hour, with the cover in place, to prevent warping.
Once removed
from the mould the casting continues to cool in the cooling pond or an
additional two hours.
Final trimming and finishing can be performed on the moulded article.
s The process precludes the need for expensive extruding equipment and
injection
moulds. Plastic articles produced by this method are ideally suited for use as
guard rail
posts, fence posts, highway median dividers, parking curbs, and the like where
resistance to
weathering and structural strength are required.
to As an example, a guard rail post is manufactured in a shaped steel mould,
which,
together with its cover, is contoured to provide a post with an 1-beam cross-
section, according
to the following procedure:
(i) equal parts of dry and oil containing high density polyethylene containers
are comminuted and blended to thoroughly mix in the oil;
1 s (ii) a steel mould is charged with alternate layers of the oil-containing
comminuted polyethylene and scrap polyester fabric, which is arranged
longitudinally in
the mould until 1/2 pound of fabric and 68 pounds of plastic have been added
and
compacted to fill the mould;
(iii) the charged mould is heated in an oven at 160 degrees Celcius for 16
hours;
20 (iv) the mould is removed from the oven, and the contoured cover is applied
under a low pressure of approximately S psi to form the top shape and remove
any excess
air and plastic;
(v) any excess plastic is trimmed off whilst still hot;
(vi) the mould containing the hot casting is placed in a cooling pond for 1 /2
- 1
2s hour to initiate cooling without warping; and
(vii) the formed post is removed from the mould and cooled in the cooling pond
for an additional two hours.

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The cooled cast post can then be drilled as final finishing to receive
mountings for
the guard rail.
s In this patent document, the word "comprising" is used in its non-limiting
sense to
mean that items following the word are included, but items not specifically
mentioned are not
excluded. A reference to an element by the indefinite article "a" does not
exclude the
possibility that more than one of the element is present, unless the context
clearly requires that
there be one and only one of the elements.
to
It will be apparent to one skilled in the art that modifications may be made
to the
illustrated embodiment without departing from the spirit and scope of the
invention as
hereinafter defined in the Claims.