Note: Descriptions are shown in the official language in which they were submitted.
' CA 022~7033 1998-12-24
METHOD AND APPARATUS FOR THE CONVERSION OF
POLYPROPYLENE TWINE INTO FIBRE
5 TECHNICAL FIELD
The present invention is directed to a method and apparatus for processing used
polypropylene twine into fibres suitable for use as secondary reinforcement additives.
10 BACKGROUND OF THE INVENTION
It is well known to use polypropylene fibres have been used as a secondary
reinforcement additive to concrete. As well7 work has been done with polypropylene fibres in
shotcrete, asphalt and other composite materials. However, the fibres used have been
15 manufactured from virgin resin which adds cost to the concrete and overlooks the potential
resource of used polypropylene material.
The agricultural community generates many thousands of metric tonnes of used
polypropylene baler twine during the normal course of its activities. Polypropylene twine is
20 used to bale hay and straw by farmers and ranchers. After its first instance of usage, the used
polypropylene twine is normally discarded and transported to landfills. This discarded
polypropylene twine is problematic for landfill operators as it tends to wrap around crawler
tractor undercarriages thereby causing premature wear and damage to exposed bearings and
lubrication seals. Incineration of polypropylene is not a optimal alternative because of the
25 production of noxious gases. Incineration of this material creates environmental air quality
concerns.
Used polypropylene twine is usually contaminated with hay, straw, twine and
fecal matter. It is dii:ficult to process because it is collected in tangled piles and is of varying
30 lengths. For these reasons, traditional methods of recycling polypropylene such as melt and
' CA 022~7033 1998-12-24
re-extrude, are not effective. As well, the different sources of the polypropylene results in a
wide variance in melt temperatures which further complicates prior art recycling methods.
In order to be recycled into fibres suitable for use as a reinforcing additive, the
S twine must be cleaned, skeined or bundled and cut to pre-determined and uniform lengths,
and broken down into individual component fibres.
It would therefore be advantageous to have a method and apparatus for
processing the used polypropylene twine into individual component fibres which are suitable
10 for use as a secondary reinforcing material for concrete and other structural materials.
BRIEF DESCRIPTION OF THE DRAWINGS
The preferred embodiments of the invention will now be described with
15 reference to the drawings in which:
Figure 1 is a schematic flowchart of the method of the present invention.
Figure 2 is a representation of the apparatus of the present invention
Figure 2A is a representation of the longitudinal bundler of an alternative
Figure 3 is a sectional view of the skeiner portion of the apparatus.
Figure 4 is a sectional view of the apparatus used to untwist the twine segmentsinto individual fibres.
Figure 4(A) is a view of an alternate apparatus used to untwist the twine
segments into individual fibres and simultaneously dry the fibres.
CA 022~7033 1998-12-24
Figures 5, 5A and 6 are depictions of the shear means of the present invention.
DETAILED DESCRIPTION OF INVENTION
The present invention provides a method and apparatus for recycling used
polypropylene twine into useful polypropylene fibres.
In general terms, the method first provides for the bundling of the twine into
longitudinal bundles which may be processed using suitable apparatus. The twine may be
bundled by skeining the twine into a coiled bundle which may then be severed to produce a
longitudinal bundle or by directly bundling the twine longitudinally. The method next .
provides for the separation of the polypropylene from the organic materials it may be
cont~min~ted with due to exposure to these materials during the normal course of its usage of
the first instance such as hay, straw, urine and fecal matter and any other matter it may
normally be exposed to. After cleaning, the twine is cut into appropriate lengths and the
resulting lengths of twine are broken down into individual component fibres. The resulting
fibres are then dried and may thereafter be packaged.
1. The Method
In one preferred embodiment, the first step is to skein the material into loose
coils in its cont~min~ted state after its first instance of usage. This skeining process takes
place after the bale twine is cut and the baled material is separated from the twine. It is
preferable that the skeining step take place at the collection site which may be distant from
the processing site although skeining may take place at the processing site. The twine is fed
into a skeining device and when a full skein has been accumulated it is tied off and removed
from the skeining device and stored in skeined form until sufficient skeined material has been
accumulated to transport to a processing plant.
CA 022~7033 1998-12-24
The next step is to sever the skein at one point transversely to render the skein
into a bundle of relatively equal length strands.
In an alternative embodiment, the first step is to bundle the twine into
5 longitudinal bundles in its cont~min~ted state. Because it is convenient to bundle the material
at the collection site, a bundler of the type described below is preferably used. The bundle
may then be bagged into a bag sleeve which prevents tangling of the bundle and maintains the
longitudinal orientation of the twine. The bagged bundles may then be stored or transported
for further processing immediately after bagging.
The bundle is then fed into a high pressure washing system via a sandwich feed
roller to a sandwich open mesh conveyor past and through a primary high pressure water and
detergent jet system. The jets preferably aid in the feed mechanism to assist in the movement
of the bundle through the jet washer.
It is desirable to reuse and recycle the effluent from the primary wash by
running it past a screening system, a gravel bath and an activated charcoal filtration system to
a holding tank for reheating and reuse. The effluent recovered from the primary wash may
also be used as a source of compostable material or for use as a field dressing or fertilizer
20 optionally in conjunction with enzymes which may be used to accelerate the breakdown of
this material.
The bundle may then be immersed in a soda rinsing bath to neutralize the
acidity resulting from residual urine cont~min~tion. The soda bath is monitored to maintain
25 an appropriate pH and is replenished or replaced as required.
The bundle may then be immersed in a disinfectant bath to neutralize any
bacterial or viral cont~min~nt. Suitable disinfecting agents are well known.
CA 022~7033 1998-12-24
After disinfection, the bundle is then rinsed with clean water to remove the
residual soda bath and disinfecting bath material. The final rinse water runs through an
activated charcoal filter to a storage tank for reuse.
The bundle of cleaned polypropylene twine is next cut into specified lengths
with a shear system consisting of one or preferably a series of guillotine knives. The interval
of cut on the polypropylene twine bundle will be determined by the end product specification
of the fibre being produced at the time. The interval of cut will be controlled by the spacing
between the guillotine knives which cut or sever the polypropylene twine into predetermined
1 0 lengths.
The cut twine will be removed from the cutting device and transported to a reel
or series of reels with alternating herring bone rub bars at clearances determined by the nature
of the material being processed. The reels will untwist the twine segments and break down
the segments into individual fibres. The reels may be equipped with a water jet or fountain to
dampen the surface at the rub bars and the material being processed to control temperature
and to facilitate the mechanical untwisting and breaking down of the polypropylene twine
segments into individual fibres. Alternatively, it may be necessary to dry the twine segments
before this step and to avoid adding water during this processing. Whether or not water is
present or added is dependent on the nature of the twine being processed.
The fibre is then collected on a conveyor and runs via a sandwich open mesh
conveyor through a hot air drying system at a rate sufficient to produce a thoroughly dry
product.
Alternatively, the cut twine segments may be untwisted with a air make-up unit
and a venturi leading to a pipe which contains flighting enclosed by the pipe. The flighting
contains a central shaft which serves to separate the enclosed flighting pipe into two spiralling
tubes. The twine segments are introduced into the pipe through the venturi and are blown
through the spiralling tubes. The physical agitation caused by the spiralling motion and the
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.
CA 022~7033 1998-12-24
friction against the flighting and air turbulence causes the segments to untwist. This method
of untwisting also dries the segments and the end products fibres at the same time. To
facilitate the drying process, the incoming air through the air make-up unit may be heated.
2. The Apparatus
The present invention in its apparatus form is, in general terms, a system
10 comprising a skeiner, a b-mdle maker, a primary jet wash, pH/disinfectant baths, rinse bath,
shearing means, untwisting means and a dryer. A skein in this specification shall mean a
circular or coiled bundle of twine.
When the bale twine is cut and removed from the baled material, it is inserted
15 into a skeiner. As may be seen in Figure 2, the skeiner comprises an external flat belt
conveyor and an internal flat belt conveyor. The external conveyor wraps around the internal
conveyor such that the two belts sandwich twine fed between the two belts and carries the
twine around in a circular fashion. The internal and external conveyors recirculates the twine
through the sandwich conveyor until sufficient strands of twine have been accumulated to
20 form a skein. Once a skein has formed, the internal belt may be loosened to allow removal
of the skein.
In the bundle maker, the skein is laid flat and open on a table and a single cutby a blade, severs the skein transversely to the direction of the skein stands rendering the
25 skein into a longitudinal bundle.
In an alternative embodiment, the apparatus may comprise a longitudinal
bundler of the configuration illustrated in Figure 2A. The longitudinal bundler comprises an
elongated trough which has a hinged cover. Preferably, the bundler is raised to approximately
30 waist height and rests on supports or legs. At the snout end of the bundler, the bundler is
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CA 022~7033 1998-12-24
cylindrical with a circular opening at the end. As may be seen, a bag sleeve fits over the
snout to receive the longitudinal bundle after it is formed. In operation, the twine lengths are
placed in the bundler with one end aligned at the snout end of the bundler. The cover may be
used to collect and stretch the lengths and transferred into the trough from the cover simply
S by flipping the cover closed. Once sufficient twine is collected to form the bundle, with one
end of each length aligned at the snout, the sleeve bag may be slipped over the bundler and
the bundle removed, conveniently resulting in a longitudinal bagged bundle.
In the primary jet wash, one end of the longitudinal bundle is fed into a
10 sandwich roller and to a sandwich screen conveyor system that passes through a primary high
pressure jet system. The jet system may be used to feed and direct the bundle through the
washer. Detergent and/or enzymes may be used to aid in the primary wash process.
The bundle is then transported to the chemical treatment chambers. The first
15 chamber holds a soda rinsing bath. The second chamber holds a disinfectant bath. Finally,
the third chamber leads to a final clean water jet rinsing system.
Once cleaned, pH adjusted, disinfected and rinsed, the bundle is then delivered
to the shear means. As is illustrated in Figure 5, the shear means may consist of a conveyor
20 fed cutting table equipped with one or a series of blades to cut or sever the polypropylene
twine into predetermined lengths. The interval of cut on the polypropylene twine bundle will
be determined by the end product specification of the fibre being produced at the time. The
interval of cut will be controlled by the spacing between the blades
The cut twine will be removed from the cutting table by an air jet or a scrubberconveyor that will scrub the severed particles of polypropylene twine into a hopper from
which the severed polypropylene twine particles will be removed by auger, conveyor or
similar means.
CA 022~7033 1998-12-24
The apparatus to untwist the cut twine and break it down to individual fibres
comprises a series of reels having an alternating herring bone or any other such pattern with
rub bars at clearances determined by the nature of the material being processed. The
apparatus may be equipped with a water jet or fountain to dampen the surface at the rub bars
5 and the material being processed to control temperature and to facilitate the mechanical
untwisting of the cut polypropylene twine into a fibrous state.
The dryer preferably comprises a sandwich open mesh conveyor that runs
through a hot air drying system comprised of but not limited to a forced air furnace feeding
10 positive pressure hot air to the top of the sandwich conveyor by means of a ducting and hood
assemble and a negative pressure exhaust system that runs from a hood at the bottom of the
sandwich conveyor assembly past a venturi system with a flapper to control the negative air
pressure flow and through a hydrocyclone bag system to collect any particulate material and
to an external and or internal exhaust system. The positive hot air positive pressure hood is
15 joined to the negative pressure exhaust hood by a sealing strip and side labyrinth baffles
adjacent to the open mesh belts of the sandwich conveyor. This drying device may be
equipped with a multi stage exhaust manifold in which at various ports in the exhaust
manifold the humidity of the e~chaust air may be monitored by use of a hydrometer sensor
which may or may not be used to regulate the flow of material through the drying device by
20 controlling the speed of the conveyor.
In an alternative embodiment, the untwisting and drying the segments into a
end product fibre may be accomplished with an apparatus which comprises an air make-up
unit and a flighting enclosed within a pipe, as is illustrated in Figure 4A. The twine segments
25 from the cutter are introduced into one end of the pipe, just behind a venturi leading from a
forced air source, which may be heated. The remainder of the pipe contains helical flighting
with a central shaft. Preferably, the are two helical flights intertwined around the central
shaft. The twine segments are blown through the helical flighting by the forced air which
physically agitates the segments and untwists them into individual fibres. The air also dries
30 the segments and the fibres as they tumble through the pipe. Convenient collection means
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CA 022~7033 1998-12-24
may be provided at the collection end of the pipe. This alternative untwisting means is
preferably used for twine segments of a length less than one inch and more preferably less
than one-half inch. It is less effective with twine segments that are longer.
Although the embodiments of the invention have been described separately as a
method and an apparatus, it will be apparent that a description of the method may also be
found in the description of the apparatus. Also, the description of the apparatus may be
inferred from the description of the method.
