Note: Descriptions are shown in the official language in which they were submitted.
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USE OF RECYCLED PLASTICS FOR STRUCTURAL BUILDING FORMS
15
FIELD OF THE INVENTION
This invention pertains to new building forms made of degradation-resistant
composites; structures produced from such novel forms; and related methods of
producing and using such forms and structures.
BACKGROUND OF THE INVENTION
There presently are over 500,000 wooden vehicular bridges in the United
States assembled from chemically treated lumber. An estimated forty percent of
them
are in need of repair or replacement.
There are several types of chemically treated lumber such as creosoted lumber
and pressure treated lumber. These materials are relatively inexpensive to
make and
use, and they are just as versatile as any other form of wood. They also have
enhanced
resistance to microbial and fungal degradation and to water.
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However, the increasing popularity of chemically treated lumber has some
negative repercussions that are just now being realized. Chemically treating
lumber
takes a perfectly useable, recyclable, renewable resource and renders it
toxic. For
example "pressure treated" or "CCA" lumber is treated with very poisonous
chromated copper arsenic and cannot be burned. While CCA lumber can be buried,
the leaching of toxic chemicals makes such disposal strategies undesirable.
The
disposal of creosoted lumber requires the use of special incinerators. These
materials
are becoming far more difficult and expensive to dispose of than to use.
However,
because of the long useful life of these materials, the economic and
environmental
impact of chemically treated lumber is just beginning to be felt.
Structural recycled plastic lumber represents a possible alternative to
chemically treated lumber. U.S. Patent Nos. 6,191,228, 5,951,940, 5,916,932,
5,789,477, and 5,298,214 disclose structural recycled plastic lumber
composites made
from post-consumer and post-industrial plastics, in which polyolefins are
blended
with polystyrene or a thermoplastic coated fiber material such as fiberglass.
These
structural composites presently enjoy commercial success as replacements for
creosoted railroad ties and other rectangular cross-sectioned materials. The
market
has otherwise been limited for structural recycled plastic lumber, because it
is
significantly more expensive than treated wooden beams on an installed cost
basis,
despite the use of recycled waste plastics.
This significant cost difference became more evident in the construction of
bridge structures in which pressure-treated wooden beams were replaced with
structural recycled plastic lumber composite beams. While as strong as CCA
treated
wood, the recycled plastic composite beams were not as stiff, and tended to
sag, or
"creep." It was possible to compensate for this by increasing beam dimensions
and
using more beams of rectangular cross-section. However, this just added to the
already increased cost for materials and construction in comparison to treated
lumber.
Structural beams that do not "creep" can also be prepared from engineering
resins such as .polycarbonates or ABS. However, these are even more costly
than the
structural composites made from recycled plastics. There remains a need for
structural materials based on recycled plastics that are more cost-competitive
with
treated lumber on an installed cost basis.
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BRIEF SUMMARY OF THE INVENTION
It has now been discovered that the immiscible polymer blends of U.S. Patent
Nos. 6,191,228, 5,951,940, 5,916,932, 5,789,477, and 5,298,214 can be formed
into
structural shapes that are more cost-efficient than traditional recycled
plastic structural
beams with rectangular cross-sections. The structural shapes according to the
present
invention are molded as a single integrally-formed article and include modular
forms
such as I-Beams, T-Beams, C-Beams, and the like, in which one or more
horizontal
flanges engage an axially disposed body known in the art of I-Beams as a web.
The
reduced cross-sectional area of such forms represents a significant cost
savings in
terms of material usage without sacrificing mechanical properties. Additional
cost
savings are obtained through modular construction techniques permitted by the
use of
such forms.
Therefore, according to one aspect of the present invention, a modular plastic
structural composite is provided having web section disposed along a
horizontal axis
and at least one flange section disposed along a horizontal axis parallel
thereto and
integrally molded to engage the top or bottom surface of the web section,
wherein the
composite is formed from a mixture of (A) high density polyolefin and (B) a
thermoplastic-coated fiber material, polystyrene, or a combination thereof.
The high-
density polyolefin is preferably high-density polyethylene (HDPE). The
thermoplastic-coated fiber material is preferably a thermoplastic-coated
carbon, or
glass fibers such as fiberglass.
Also provided is a modular plastic structural composite comprising a web
section disposed along a horizontal axis and at least one flange section
disposed along
a horizontal axis parallel thereto and integrally molded to engage the top or
bottom
surface of said web section, wherein said composite is formed from a mixture
of (A)
high density polyolefin and (B) a thermoplastic-coated fiber material,
poly(methyl
methacrylate), or a combination thereof.
The flange dimensions relative to the dimensions of the web section cannot be
so great to result in buckling of the flange sections upon the application of
a load.
Preferably, the vertical dimension (thickness) of the flange section is about
one-tenth
to about one-half the size of the vertical dimension of the web section
without any
flange section(s) and the width dimension of the entire flange section
measured
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perpendicular to the horizontal axis of the flange section is about two to
about ten
times the size of the width dimension measured perpendicular to the horizontal
axis of
the web section.
Other efficient structural shapes according to the present invention include
tongue-in-groove shaped boards that form interlocking assemblies. It has been
discovered that interlocking assemblies reduce the required board thickness
because
of the manner in which the assembly distributes loads between the interlocked
boards.
This also represents a significant cost savings in terms of material usage
without
sacrificing mechanical properties, with additional cost savings also obtained
through
the modular construction techniques these forms permit.
Therefore, according to another aspect of the present invention, an
essentially
planar modular plastic structural composite is provided having a grooved side
and an
integrally molded tongue-forming side, each perpendicular to the plane of the
composite, in which the composite is formed from a mixture of (A) high-density
polyolefin and (B) a thermoplastic-coated fiber material, polystyrene, or a
combination thereof, wherein the grooved side defines a groove and the tongue-
forming side is dimensioned to interlockingly engage a groove having the
dimensions
of the groove defined by the grooved side, and the grooved side and tongue-
forming
side are dimensioned so that a plurality of the essentially planar modular
plastic
structural composites may be interlockingly assembled to distribute a load
received by
one assembly member among other assembly members.
According to another embodiment of this aspect of the present invention, a
modular structural composite is provided in which polystyrene is replaced with
poly(methyl methacrylate) (PMMA). Preferably, at least 90% and, more
preferably,
all of the polystyrene is replaced with poly(methyl methacrylate). In one
embodiment, the composite includes from about 20 to about 65 wt% of a
poly(methyl
methacrylate) component containing at least about 90 wt% poly(methyl
methacrylate)
and from about 40 to about 80 wt% of a high-density polyolefin component
containing at least about 75 wt% high-density polyethylene (HDPE).
Preferred planar modular plastic structural composites have at least one pair
of
parallel opposing grooved and tongue-forming sides, defining therebetween a
width
or length dimension of the composite. Preferred composites also have board-
like
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dimensions in which the length dimension is a matter of design choice and the
width
dimension is between about two and about ten times the size of the height, or
thickness, dimension of the composite.
The modular plastic structural composites have utility in the construction of
load-bearing assemblies such as bridges. Therefore, according to yet another
aspect
of the present invention, a bridge is provided, constructed from the I-Beams
of the
present invention, having at least two pier-supported parallel rows of larger
first 1-
beams, and a plurality of smaller second 1-beams disposed parallel to one
another and
fastened perpendicular to and between two rows of the larger first I-Beams,
wherein
The distance between the rows of first I-Beams and the rows of second I-
Beams will depend upon factors such as the flange and web dimensions, the
plastic
components of the composite and the load to be supported by the bridge.
Furthermore,
Because the second 1-Beams are nested within the opening defined by the top
and bottom flanges of the first I-Beams, the top surfaces of the second I-
Beams are
20 recessed below the top surfaces of the first I-Beams by a distance that
is at least the
thickness dimension of the top flange of the first I-Beam. Bridges constructed
according to this aspect of the present invention will therefore further
include a deck
surface fastened to the first or second I-Beams. Preferred deck surfaces are
dimensioned to fit between the top flanges of the parallel rows of the first I-
beams.
25 Even more preferred deck surfaces have a thickness dimension selected to
provide the
deck surface with a top surface that is essentially flush with the top
surfaces of the
parallel rows of first I-Beams. Other preferred deck surfaces are formed from
the
essentially planar modular plastic structural composites of the present
invention
having interlocking grooved and tongue-forming sides.
30 The modular components of the present invention permit the construction
of
load-bearing assemblies with fewer required fasteners, reducing the initial
bridge cost,
as well as the long-term cost of maintaining and replacing these corrosion-
prone
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components. The plastic composite material also outlasts treated wood and
requires
significantly less maintenance than wood over its lifetime, further
contributing to cost
savings.
Also provided is a composite building material formed from a mixture of high
density polyolefin and poly(methyl methacrylate). This material can be formed
into
various articles such as railroad ties and structural sheets.
Further, despite the unpredictability of polymer blending, it has also been
discovered that polyolefin and poly(methyl methacrylate) can form immiscible
polymer blends by replacing polystyrene with PMMA. This observation is
surprising
because there is no way to predict which plastics will form acceptable
immiscible
polymer blends with polyolefin. For example, polyvinyl chloride does not form
such
a blend with polyolefin.
The polyolefin/PMMA blends of the present invention possess unexpected
properties. For example, they are stiffer than the polyolefin/polystyrene
blends even
though polystyrene and PMMA alone each have essentially the same stiffness, as
measured by tensile modulus. It is also surprising that the polyolefin/PMMA
blends
are nearly as strong as PMMA alone.
The foregoing and other objects, features and advantages of the present
invention
are more readily apparent from the detailed description of the preferred
embodiments set
forth 'below taken in conjunction with the accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG.1 depicts a cross-sectional view of an I-Beam according to the present
invention;
FIG. 2 is a side-view of the I-Beam of FIG. 1, perpendicular to the cross-
sectional view;
FIG. 3 depicts a cross-sectional view of a C-Beam according to the present
invention;
FIG. 4 is a side view of the C-Beam of FIG. 3, perpendicular to the cross-
sectional view;
FIG. 5 depicts a cross-sectional view of a T-Beam according to the present
invention;
FIG. 6 is a bottom view of the T-Beam of FIG. 5;
FIG. 7 depicts a cross-sectional view of tongue and groove decking panels
according to the present invention;
FIG .8 depicts a side view of a bridge according to the present invention
assembled from the I-Beams of the present invention;
FIG. 9 is a top cutaway view of the bridge of FIG. 8;
FIG. 10 is a top cutaway view depicting the perpendicular fastening of a
smaller I-Beam according to present invention to a larger I-Beam according to
the
present invention.
FIG. 11 is a plot of log viscosity versus log shear rate comparing extruded
composites having various percentages of PMMA;
FIG. 12 is a plot of log viscosity versus percent PMMA for extruded
composites;
FIG. 13a is a heat flow analysis to determine the melting point of extruded
composites upon initial heating;
FIG. 13b is a heat flow analysis to determine the melting point of extruded
composites following the initial heating shown in FIG. 13a;
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FIG. 13c is a plot of the melting temperatures of extruded composites as a
function of percent PMMA;
FIG. 13d is a plot of the heat of fusion of extruded composites as a function
of
percent PMMA;
FIG. 14 is a plot of stress versus strain for extruded composites;
FIG. 15 is a plot of modulus as a function of percent PMMA for extruded
composites;
FIG. 16 a plot of log modulus versus log time for extruded composites;
FIG. 17 is a series of SEM images of the surface structure of extruded
composites;
FIG. 18 is a series of SEM images of the surface structure of a 60/40
PMMA/HDPE extruded composite;
FIG. 19 is a plot of peak stress of composites formed via injection molding as
a function of percent PMMA;
FIG. 20 is a plot of strain at fracture of composites formed via injection
molding as a function of percent PMMA;
FIG. 21 is a plot of stress versus strain for composites formed via injection
molding;
FIG. 22 is a plot of modulus as a function of percent PMMA for composites
formed via injection molding; and
FIG. 23 is a plot of HDPE phase melting temperature as a function of percent
PMMA for composites formed via injection molding.
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DETAILED DESCRIPTION OF THE INVENTION
The modular plastic structural composites of the present invention are
prepared using the co-continuous polymer blend technology disclosed by U.S.
Patent
Nos. 5,298,214 and 6,191,228 for blends of a high-density polyolefin and
polystyrene
and by U.S. Patent No. 5,916,932 for blends of a high-density polyolefin and
thermoplastic-coated fiber materials.
As disclosed in U.S. Patent No. 6,191,228, composite materials may be
employed containing from about 20 to about 50 wt% of a polystyrene component
containing at least about 90wt% polystyrene and from about 50 to about 80 wt%
of a
high-density polyolefin component containing at least about 75 wt% high-
density
polyethylene (HDPE). Composite materials containing about 25 to about 40 wt%
of a
polystyrene component are preferred, and composite materials containing about
30 to
about 40 wt% of a polystyrene component are even more preferred. Polyolefin
components containing at least about 80 wt% HDPE are preferred, and an HDPE
content of at least about 90 wt% is even more preferred.
The blend technology disclosed in U.S. Patent No. 6,191,228 can also be
employed in the present invention to formulate composite materials comprising
a
poly(methyl methacrylate) component in place of or in addition to the
polystyrene
component. Composite materials may be employed containing a poly(methyl
methacrylate) (PMMA) component containing at least 90 wt% PMMA with the
balance of the composite material being a high-density polyolefin component
containing at least 75 wt% high-density polyethylene (HDPE). Polyolefin
components containing at least about 80 wt% HDPE are preferred, and an HDPE
content of at least about 90 wt% is even more preferred. The minimum amount of
the
PMMA component in the blend is that quantity effective to produce a
perceptible
increase in melt viscosity. Composite materials containing from about 0.1 to
about 65
wt% of poly(methyl methacrylate) (PMMA) are preferred. Composite materials
containing from about 10 to about 40 wt% of PMMA are more preferred, and
composite materials containing from about 20 to about 35 wt% of PMMA are most
preferred.
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The polyolefin/PMMA blends of the present invention possess unexpected
properties. For example, they are stiffer than the polyolefin/polystyrene
blends even
though polystyrene and PMMA alone each have essentially the same stiffness, as
measured by tensile modulus. They are also tougher than the
polyolefin/polystyrene
blends. "Toughness" is defined as the ability to absorb energy while being
deformed
without fracturing. For example, a bridge made from the polyolefin/PMMA blend
It
is also surprising that the polyolefin/PMMA blends are nearly as strong as
PMMA
alone.
According to the process disclosed by U.S. Patent No. 5,916,932 this
composite may be further blended with thermoplastic-coated fibers having a
minimum length of 0.1 mm so that the finished product contains from about 10
to
about 80 wt% of the thermoplastic-coated fibers. U.S. Patent No. 5,916,932
discloses
composite materials containing from about 20 to about 90 wt% of a polymer
component that is at least 80 wt% HDPE and from about 10 to about 80 wt% of
thermoplastic-coated fibers.
The polyolefin-polystyrene composite materials suitable for use with the
present invention exhibit a compression modulus of at least 170,000 psi and a
compression strength of at least 2500 psi. Preferred polyolefin-polystyrene
composite
materials exhibit a compression modulus of at least 185,000 psi and a
compression
strength of at least 3000 psi. More preferred polyolefin-polystyrene composite
materials exhibit a compression modulus of at least 200,000 psi and a
compression
strength of at least 3500 psi.
Preferred polyolefin-PMMA composite materials suitable for use with the
present invention exhibit a compression modulus of at least 227,000 psi and a
compression strength of at least 3900 psi. The most preferred polyolefin-PMMA
composite materials exhibit a compression modulus of at least 249,000 psi and
a
compression strength of at least 4300 psi.
Composite materials containing thermoplastic-coated fibers according to the
present invention exhibit a compression modulus of at least 350,000 psi. The
compression modulus exhibited by preferred fiber-containing materials is at
least
400,000 psi. The composite materials containing thermoplastic-coated fibers
exhibit a
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compression strength of at least 4000 psi. The compression strength exhibited
by
preferred fiber-containing materials is at least 5000 psi.
The polyolefin/PMMA blends of the present invention are suitable for
composite building materials, such as, dimensional lumber. Lumber made from
these
blends can be used as joists, posts, and beams, for example. The toughness of
polyolefin/PMMA lumber offers an additional safety feature as the material
would
sag before fracture to provide a warning of possible failure. The
thermoplastic fiber-
containing polyolefin/PMMA blends are also suitable for the fabrication of
railroad
ties.
For certain applications such as, for example, railroad ties, it is important
that
the composite building material exhibit some very specific properties. For
example,
the material must be non-water or fuel absorbent, resistant to degradation and
wear,
resistant to the typical range of temperatures through which train tracks are
exposed
and non-conductive. In addition, the railroad ties must meet certain
mechanical
criteria. For example, the plastic composite railroad tie will have a
compressive
modulus of at least about 170,000 psi along the tie's axis. By the term "tie's
axis" it is
meant the longest axis of the railroad tie. More preferably, the composite
building
material useful as a railroad tie will have a compressive modulus along the
tie's axis
of at least 200,000 psi and even more preferably 225,000 psi. Most preferably,
when
used for railroad ties, the plastic composite material will have a compressive
modulus
of at least about 250,000 psi.
The present invention is particularly well suited for railroad ties because of
the
different properties exhibited by the composite building materials along
different
axes. Because of the highly oriented fiber content in the direction of the
floor (the
long axis of a railroad tie), the tie exhibits incredible strength and
rigidity along that
axis. At the same time, in a perpendicular axis which cuts across the
orientation of
the fiber content, the tie is relatively softer and flexible. Thus, a railroad
tie made
from the composite building material in accordance with the present invention
will
not bend or stress rail laid perpendicularly thereon, as there is some give in
that
direction. However, because of the strength of the tie along the tie's longest
axis, rails
attached thereto will not be allowed to shift laterally or separate. For this
reason, the
railroad ties of the present invention are vastly superior to either wood or
concrete ties
currently employed.
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In addition, in terms of railroad ties, it is important that rails attached
thereto
not be separated by more than about 0.3175 cm when placed under a lateral load
of a
least about 24,000 lbs. Lateral load refers to the outward pressure exerted by
the
train's wheels on the rails. The composite building material should also bear
a vertical
static load of at least about 39,000 lbs. This measures a tie's ability to
stand up to
having a train parked on top of it without permanent deformation, or having
the rail
driven into the tie. Further, the toughness of the polyolefin/PMMA material
improves
the ability of the material to accept a spike without fracturing. A vertical
dynamic
load of at least 140,000 lbs. is also required. This measures the ability of a
tie to
handle train traffic.
Both polyolefin/polystyrene and polyolefin/PMMA blends can also be used to
form the flanged structural members of the present invention. A cross-
sectional view
of an I-B earn 10 according to the present invention is depicted in FIG. 1,
with a side
view of the same I-Beam shown in FIG. 2. The I-beam has a traditional
structure
consisting of middle "web" or "body" section 20, an upper flange 30, and a
lower
flange 40. The flange sections include a protruding section 50 that extends
beyond
the width of the web 20. The face of the web 60 forms a structure that can
engage
other structures (e.g., smaller beams), as described further below. The width
A of the
flange sections is significantly wider than the width B of the web section.
The height
C of the flange sections is smaller than the height of the web sections.
Despite the
thin height of the flange section and the narrow width of the web section, the
I-Beam
is capable of supporting heavy structures and can be used in load-bearing
structures,
such as bridges and the like.
A cross-sectional view of a C-Beam 12 according to the present invention is
depicted in FIG. 3, with a side view of the same C-Beam shown in FIG. 4. The C-
beam also has a middle web section 20, an upper flange 30, and a lower flange
40.
The flange sections also include a protruding section 50 that extends beyond
the width
of the web 20. The face of the web 60 also forms a structure that can engage
other
structures (e.g., smaller beams), as described further below.
A cross-sectional view of a T-Beam 15 according to the present invention is
depicted in FIG. 5, with a bottom view of the same T-Beam shown in FIG. 6. The
T-
beam has a structure consisting of middle web section 20 and an upper flange
30, but
no lower flange. The flange section also includes a protruding section 50 that
extends
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beyond the width of the web 20. The face of the web 60 also forms a structure
that
can engage other structures (e.g., smaller beams), as described further below.
FIG. 7 shows assembled tongue-and-groove decking panels 100 and 150.
Panel 100 includes an end 110 having a tongue-shaped member 120 and an
opposite
end 130 defining a groove 140. Panel 150 includes an end 160 having a tongue-
shaped member 170 and an opposite end 180 defining a groove 190. Tongue-shaped
member 120 of panel 100 is depicted interlockingly engaging the groove 190 of
panel
150. The groove 140 of panel 100 is also capable of interlockingly engaging a
tongue-shaped member of another panel. Likewise, the tongue-shaped member 170
of panel 150 is capable of engaging a groove of another panel. Flat top 125 of
panel
100 and fiat top 175 of panel 150 can serve as a load-bearing surface or
barrier when
such panels are assembled into a structure.
FIG. 8 illustrates a side view and Fig. 9 a top partial cutaway view of a
portion
of a vehicular bridge 200 assembled from the above-described building forms.
In the
bridge structure, ends 211 and 212 of respective larger I-beam rails 213 and
214 are
secured to respective pilings 216 and 217 by fasteners (not shown). The
opposite
respective I-Beam ends 220 and 221 are similarly secured to respective pilings
223
and 224. Ends 225, 226 and 227 of smaller joist I-beams 228, 229 and 230 are
fastened to the face 260 of I-Beam 213, with respective opposing ends 231, 232
and
233 of the three smaller I-Beams fastened to the face 261 of I-Beam 214.
Similarly,
ends 234, 235 and 236 of smaller joist I-beams 237, 238 and 239 are fastened
to the
face 262 of I-Beam 214.
FIG. 10 is a top cutaway view depicting the fastening of end 225 of smaller
joist I-Beam 228 to the face 260 of larger I-Beam 213 using L-shaped brackets
243
and 244 and fasteners 245, 246, 247 and 248. Bracket 243 and fasteners 245 and
246
fastening the end 225 of I-Beam 228 to face 260 of I-Beam 213 is also shown in
FIG.
8. FIG. 8 also shows bracket 247 and fasteners 248 and 249 fastening end 231
of I-
Beam 228 to face 261 of I-Beam 214.
FIGS. 8 and 9 also show bridge deck 270 formed from interlocking panels 271
and 272 in which tongue 274 of panel 271 interlockingly engages groove 275 of
panel
272. Tongue 276 of panel 272 interlockingly engages groove 277, and so forth.
The
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respective top surfaces 279 and 280 of panels 271 and 272 comprise the surface
290
of bridge deck 270.
Suitable fasteners are essentially conventional and include, without
limitation,
nails, screws, spikes, bolts, and the like.
The molding processes disclosed in U.S. Patent Nos. 5,298,214, 5,916,932 and
6,191,228 may be employed to form the modular plastic structural composite
shapes
of the present invention. However, because articles are being formed having an
irregular cross section in comparison to the beams having rectangular cross-
sections
that were previously molded, the composite blends are preferably extruded into
molds
from the extruder under force, for example from about 900 to about 1200 psi,
to
solidly pack the molds and prevent void formation. Likewise, it may be
necessary to
apply force along the horizontal beam axis, for example using a hydraulic
cylinder
extending the length of the horizontal axis, to remove cooled modular shapes
from
their molds.
Composite I-Beams of polyolefin and polystyrene according to the present
invention having a 61 square-inch cross-sectional area exhibit a Moment of
Inertia of
900 in4. Poly-olefin-polystyrene composite I-Beams according to the present
invention having a 119 square-inch cross-sectional area exhibit a Moment of
Inertia of
4628 in4. This represents the largest Moment of Inertia ever produced by any
thermoplastic material for any structure, and compares to Moments of Inertial
measured between 257 and 425 in4 for rectangular cross-section wooden beams
having a 63 square-inch cross-sectional area and Moments of Inertial measured
between 144 and 256 in4 for rectangular cross-section wooden beams having a 48
square-inch cross-sectional area. The end result is that a polyolefin-
polystyrene
composite bridge that would have weighed 120,000 pounds for the required load
rating if prepared from rectangular cross-section composite materials, weighs
just
30,000 pounds instead when prepared from the I-Beams of the present invention.
Both polyolefin/polystyrene and polyolefin/PMMA blends can also be used to
form structural sheets having a thickness preferably from about 1/8 inch to
about 1
inch. The length and width of the sheets preferably independently range from
about 8
inches to about 20 feet. The structural sheets also have a compression modulus
of at
least 200,000 psi and a strength of at least 3,000 psi. "Strength" is defined
as the
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highest stress level a material can be subjected to without fracturing into
multiple
pieces.
The modular plastic structural composites of the present invention thus
represent the most cost-effective non-degradable structural materials prepared
to date
having good mechanical properties. The present invention makes possible the
preparation of sub-structures with given load ratings from quantities of
materials
reduced to levels heretofore unknown.
The foregoing description of the preferred embodiment should be taken as
illustrating, rather than as limiting, the present invention as defined by the
claims. As
would be readily appreciated, numerous variations and combinations of the
features
set forth above can be utilized without departing from the present invention
as set
forth in the claims. Such variations are not regarded as a departure from the
spirit and
scope of the invention, and all such variations are intended to be included
within the
scope of the following claims.
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EXAMPLES
The following examples provide representative preparation methods for
polyolefin/PMMA blends according to the present invention.
Example 1 - Extrusion
HDPE (CP Chem Marlex HHM-5502BN) and PMMA (Atofina Plexiglass
V045100) were mechanically mixed and melt blended using a Randcastle special
compounding extruder operating at 180 RPM and 200 - 210 C. Composition ratios
of
HDPE/PMMA were: 100/0, 90/10, 80/20, 70/30, 65/35, 60/40, 50/50, 40/60, 30/70,
20/80, 10/90, and 0/100.
Rheological tests were conducted to investigate the viscosity of the
pelletized
extruded composites. As the PMMA content of the extruded composites increases
towards neat PMMA, the viscosity of the extruded composites increases (FIG.
11).
At both low and high shear rates, a non-linear dependence of viscosity on PMMA
concentration was observed (FIG. 12).
Thermal analysis of the extruded composites was conducted to examine the
melting temperature and heat of fusion (FIGS. 13a-d). The heat of fusion of
the
blends approximately correlates to the percentage of meltable polyolefin in
the blend.
Flexural experiments were conducted to investigate the mechanical properties
of the extruded composites. Sample diameter ranged from 1.18 ¨ 1.95 mm. The
support span was either 20 or 28 mm to maintain a 16:1 L:D ratio. FIG. 14 is a
plot of
stress versus strain for each extruded composite. Table I sets forth the
modulus (the
ratio of stress to strain in flexural deformation) of the extruded composites
according
to composition:
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Table I.
Modulus Standard Deviation Modulus
o/o PMMA o/o HDPE
(MPa) (MPa) (ksi)
0 100 1154 36 167
90 1508 94 219
80 1916 87 278
70 2017 104 292
65 1689 85 245
60 1805 113 262
50 2053 269 298
40 2495 250 362
30 2667 155 387
20 2761 147 400
100 0 3437 104 498
The modulus of the extruded composites increases with PMMA content (FIG. 15).
FIG. 16 is a plot of log modulus as a function of log time, which shows that
the
5 modulus of the blends and the resistance to deformation with time is
increased with
increasing PMMA content.
SEM images were obtained to examine the surface structure of the extruded
composites (FIG. 17). The composite of 60/40 PMMA/HDPE exhibits co-continuous
morphology (FIG. 18). Co-continuous morphologies have been known to exhibit
10 exceptionally high stress transfer between the phases.
Example 2 ¨ Injection molding
HDPE (CP Chem Marlex HHM-5502BN) and PMMA (Atofina Plexiglass
V045100) were mechanically blended and injection molded using a Negri Bossi
V55-
200 Injection Molding Machine. Composites were molded at 392 F. Composition
15 ratios of HDPE/PMMA: 100/0, 90/10, 80/20, 70/30, 65/35 60/40, 50/50, and
40/60.
The tensile strength of the blends remains fairly constant in all blends from
pure polyolefin up to and including the co-continuous region. (FIG. 19). The
tensile
strain drops as PMMA is blended at higher percentages to polyolefin in a non-
linear
manner, but remains much higher than pure PMMA itself. (FIG. 20).
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The modulus of the blends increases as PMMA is increased, but with lower
strain to failure and resulting toughness. (FIG. 21). Many of the blends
indicate
higher toughness than PMMA or polyolefin alone. Results from FIG. 21 are
summarized in Table II:
Table II.
% PMMA Width Thickness Modulus Peak Stress % Strain at
(inches) (inches) (ksi) (ksi) Fracture
0 0.494 0.138 180.682 3.7 73.447
0.495 0.138 227.439 3.9 50.713
0.495 0.137 248.911 4.3 19.046
0.496 0.138 267.694 4.5 6.716
0.496 0.137 284.208 4.5 5.326
0.496 0.137 294.963 4.4 3.639
0.497 0.132 328.982 4.6 2.873
0.496 0.135 346.735 4.3 2.013
The law of mixtures for modulus is generally followed in the blends,
indicating that remarkably good stress transfer between the phases is achieved
in this
blend system. (FIG. 22). DSC reheat results are provided in FIG. 23.
10 The foregoing examples and description of the preferred embodiments
should
be taken as illustrating, rather than as limiting the present invention as
defined by the
claims. As will be readily appreciated, numerous variations and combinations
of the
features set forth above can be utilized without departing from the present
invention
as set forth in the claims. Such variations are not regarded as a departure
from the
15 spirit and script of the invention, and all such variations are intended
to be included
within the scope of the following claims.
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