Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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~ WO92/11298 PCr/US91/09731
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PHOTODEGRADABL~. PLASTIC COMPOSITION
FI~LD O~ THE INVENTION
This invention relates generally to plastic
compositions, and more particularly, to a thermo-
plastic composition which comprises a thermoplasticpolymer such as polyetheylene or ethylene
copolymers, polypropylene, polystyrene or
polyurethane which is photodegradable when exposed
to sunlight and~or ultraviolet light.
BACKGROUND OF' THE INVENTION
'
Plastic waste is normally disposed of by
recycling, incineration or burying in a landfill.
Unfortunately, some materials are improperly dis-
posed of and become litter. This litter is both
esthetically ob]ectionable and poses a threat to
wildlife through possible entrapment and/or inges-
tion. Therefore, there is a need for a material
which will degrade harmlessly when exposed to sun-
light, ultraviolet light or heat.
There are known additive compositions which may ~
be incorporated into thermoplastic materials to -
enhance degradation of the plastic. Por example,
U.S. patent 4,931,488 discloses a ther~oplastic
polymer composition to which has been added a bio-
2~ logi.cally degradable substance such as starch, an
iron compound, an oxidizable substance selected from
fatty acids and/or fatty acid esters and a transi-
tion metal. This composition demonstrates
; kiodegradation and photodegradation capability when
exposed to heat, ultraviolet light, sunlight, or
under compositing conditions. But, many states
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WO92/11298 2 ~ ~ ~ 9 ; - 2 - PCT/US91/09731 ~
today require only that a plastic compositlon only
be photodegradable. In this connectlon, the use of
a composition such as that disclosed in patent
- 4,931,488 may not be advantageous. The starch com-
ponent in the composition becomes unnecessary when
; biodegradation is not required, and the starch may
; cause the product to become sensitive to moisture
pickup during the produc~lon process and does little
to enhance photodegradation.
Therefore, a plastic composition which
possesses the desired properties of thermoplastic
materials, yet readily degrades when exposed to sun- ~ -
- light and/or ultraviolet light, is highly desirable.
~UMMARY AND OBJECT~ OF THE INVENTION
Accordingly, it is the primary object of the
present invention to provide a plastic composition
' which readily ~egrades when exposed to sunlight
and/or ultraviolet light and to provide such a plas-
tic composition for films, sheets or other moldings,
which possesses the desired propexties of known
thermoplastic materials.
In accordance with the present invention, there
is provided a thermoplastic composition which is
degradable under the action of sunlight and/or
ultraviolet light and heat. The thermoplastic com-
position comprises a thermoplastic polymer, a first
transition metal compound which may be a complex, a
second transition metal compound and an aromatic
ketone.
More ~articularly, the thermoplastic polymer
preferably comprises an olefin such as polyethylene,
ethylene copolymers, polypropylene, polystyrene or
~polyurethane. The first transition metal comprises
an iron compound such as ferric hydroxy stearate,
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"',~ WO92/11298 PCT/US91/09731
which is soluble in the composition and acts as an
initiator whlch promotes further degradation. The
second transition metal comprises a copper compound
which acts as a catalyst with the iron compound to
enhance degradation. The aromatic ketone includes
benzophenone. It has been found that: by using the
composition of the present invention in a thermo-
plastic material that a sisnificant synergisti,c deg-
radation effect occurs on the plastic when exposed
to sunlight and/or ultraviolet light.
BRIF.F DESCRIPTION OF THE DRAWING
Fig. l is a graph illustrating loss of elonga-
tion at break as a function of time in a plastic
film product including the composition of the pres-
lS ent invention. ,~
~ETAI~ED DESCRIPTION OF TMF, INVE~TI~
The thermoplastic composition in accordancewith the present invention facilitates
biodegradation of thermoplastic materials under the
action of sunlight and/or ultraviolet light and
heat. That is, the chemicals in the composition in ,
the presence of the sunlight or ultraviolet light
an~ heat react to form free radicals which break the
bonds cf the thermoplastic polymer resulting in a
reduction of molecular weight and loss of physical
properties. Thereafter, the thermoplastic material
becomes weak and brittle which results in a material ,,
that is easily disintegrated by exposure to the ele~
ments.
The thermoplastic composition of the present ''
invention comprises as one component thereof a ther-
moplastic base of any known thermoplastic polymer '~
and preferably polymers of olefins such as
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WO92/1129~ PCT/US91/09731 .i~
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polyethylene, ethylene copolymers, polypoypylene,
polystyrene or polyurethane. "Polyethylene" as used
herein, comprises any type of polyethylene, such as
LDPE, LLDPE, LMDPE, MDPE, ~DPE, ULDPE, etc. Exam-
ples of suitable ethylene copolymers include EVA,EBA, EAS, EMAA and ionomers. It is understood that
the composition of the present invention may be
formed in any of the following manners. The compo-
; sition may be added directly at the final production
stage by the manufacturer, formed in a concentrateand supplied to the manufacturer to be added to the
base resin or formed ~ith the base resin and
supplied to the manufacturer ready for use.
; The first transition metal component preferably
comprises an iron compound generally having the for-
mula X-Fe, where X represents one or more ligands.
The compound may additionally be coupled to a fur-
ther ligand Y. Fe may designate iron in any known
valancy. The ligand X may be an inorganic or
! 20 organic acid radical or likewise another ligand
honded in a complex. For purposes of illustration,
' examples or suitable ligands X include OH-, Cl-,
j Br-, I-, oxalate-, H-citrate-, NO2, N3- EDTA or a
carbonyl, nitrosyl or porphyrin radical. Examples
of suitable ligands Y include carboxylic acid ions
; of aromatic or aliphatic monocarboxylic acid or of
dicarboxylic acids, the aliphatic carboxylic acid
preferably having l0 to 20 carbon atoms. Ligand Y
serves in general to increase the solubility of the
compound X-Fe in the polymer. The iron compound
~ore preferably is comprised of iron stearate pres-
ent in the final concentration of the present inve~-
~ion in an amount from about 0.0l weight percent to
about 0.5 weight percent, and more preferably in an
amount fron~ about 0.l weight percent t~ about 0.3
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WO92/11298 PCT/US91/09731
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weight percent. It is understood that the ranges
listed herein are for purposes of illustration. ~he
amount listed for the upper limits is based on eco-
nomics, and therefore, the components may be present
in the concentration in amounts greater than those
listed. Although, a saturation limit is reached at
which further addition does not provide greater
effectiveness. The minimum value listed provides
minimum ~easurable improvements in photodegradation.
The second transition metal compound of the
thermoplastic composition of the present invention
acts as a catalyst with the first transition com-
pound to enhance degradation of the thermoplastic
material. The compound may comprise a complex
having the general formula Z'-Me, wherein Me desig-
nates a transition metal other than iron if iron is
the first transition metal and Z' designates one or
more ligandc. For purposes of illustration onl~
and, not limitation, examples of ligands include
OH , Cl-, Br-, I-, oxalate-, H-citrate-, NO-~, N3-,
EDTA, as well as carboxylic acid i.ons of aromatic or
aliphatic monocarboxylic or cicarboxylic acids, the
aliphatic carboxylic acid preferably having l0 to 20 ~ -
carbon atoms. The preferred transition metals
comprising Me~are the transition metals of the first
transition metal row in the periodic table, and more
preferably copper and vanadium. The mos~ preferred
second transition metal compound is copper stearate
present in the final concentrate of the present
invention in an amount from about 0.005 weight per-
cent to about 0.l weight percent, and more pre-
ferabl~ cupric stearate in an amount from about 0.0l
weight percent to about 0.06 weight percent.
The aromatic ketone component o the composi-
3~ tion of the present invention has been found to have
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WO92/11~98 PCT/US91/09731
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a synergist1c effect that speeds up the
photodegradation of the thermoplastic. This is an
unobvious finding since aromatic ketones generally ~'
are ultraviolet stabilizers. For purposes of illus-
tration only and, not limitation, examples of aro-
matic ketones include benzophenone, anthraquinone,
anthrone or derivatives such as acetylbenzophenone
or 4-octyl benzophenone.
The more preferred aromatic ketone is
benzophenone which is present in the concentration
in an amount of from about 0.01 weight percen~ to
about 0.7 weight percent and more preferably in an
amount from about about 0.02 weight percent to about
0.15 weight percent.
Utilizing the composition of the present inven-
tion is further advantageous in that the degradation
can be controlled depending on the field of applica-
tion by varying the concentration of the individual
components, without the plastic material suf~ering a
deterioration in its properties under normal use
conditions. Particular fields of application of the
composition of the present invention include
packaging materials, films for garbage bags for com-
postable wastes, agricultural films, and in particu-
lar those materials which may become litter such asdisposable packaging. Furthermore, the present
invention makes it possible to manufacture products
which do not pollute the environment and which can
be degraded without additional energy consumption
and without releasing harmful substances.
The production of the thermoplastic composition
in a concentrate for~ in accordance with the present
invention and its processing to give sheets, films,
plates or other shapes is carried out by any conven-
3~ tiQnal method. For example, the polyethylene may be
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WO92/11298 PCT/US91/0973]
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combined with the appropriate amounts of iron
stearate, copper stearate and benxophenone in a twin
scre~ compounding extruder or equivalent and
extruded and pelletized into a concentrate or mas-
ter~atch. Extruded film, blow molded parts or
injection moulded parts are made by combining this
concentrate with polyethylene or other base resins
in a film extruder or injection molding extruder,
which is normally of the single screw type.
As an alternative the chemicals could be adde~
directly at the final production stage in the single
screw extruder, this however is not very practical.
This technique would require either a premixing step
or a number of additional additive feeders on the
extrusion machine. In addition, single screw
extruders are typically poor mixing devices. By
producing a concentrate first the active ingredients
are predispersed in the thermoplastic hase i.e.,
polyethylene, making the final dispersal in the sin-
gle screw machine much easier.
The degradation process appears to proceedaccording to the following mechanism, with reference
to A.C. Albertsson, B. Randy, J. Appln. Polym. Sci
Appl. Polym Sypm., 35 (l979) p. 423 and the publica-
tion of A.C. Albertsson mentioned therein, which ishereby incorporated hy reference.
Plastics with C-C bonds in the main chain
biodegrade extremely slow ~ith the formation of C02
and H20. ~he half life of biological degradation of
polyethylene was extra~olated to be at least l00
years. ~1nder the action of ultraviolet light, sun-
~; light or heat free radicals such as, for example OH*
are formed due to ~he presence of iron ions, and
these can react with the polymers forming other free
radicals. These free polymer radicals are extremely
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WO92/11298 , PCT/US91/09731
reactive and can, inter alia, react further withoxygen, other chains, iron ions, and the like.
Polymer chains are thus split and small chains with
or without oxygen-containing groups, such as alco-
hols, ketones, etc. are forme~. During this pro-
cess, iron ions act both as an initiator and as a
reaction promoter since iron-(III) hydroxide com-
plexes are highly reactive. This can be illustrated
the by the following equation:
3 - 2 2+
(l) Fe + OH [FeOH] + Fe OH*
The observed catalytic effect of the transition
metal compounds, copper or vanadium compounds, is
probably attributed to an acceleration of the Fe3+
Fe2+ Fe3 cycle. Without these compounds, the
Fe2 formed according to equation (l) may be
reoxidized by other free radicals or other interme-
diates at the expense of chain splitting as for
example, shown in the following equation:
Fe + ROO~ Fe + OH + RO* (2)
In the presence of copper compounds, the Fe2
formed is reoxidized faster accordin~ to the follow-
ing equation:
F~2+ + Cu Fe + Cu (3)
and Cu+ ions are reoxidized very fast to Cu2 ions
~y free radicals as follows:
CU + RO* Cu2 + RO (4)
- This prooess repeats itself as long as the
polymer is exposed to ultraviolet light, sunlight or
heat. In this phase, the plastic materials become
brittle and fragile and disintegrate into small
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particles of about a few mm2 up to about a few cm2.
Depending on the prevailing conditions, this phase
takes in general from about 10 to 60 days,
The following table sets forth a preferred for-
mulation for the thermoplastic composition of thepresent invention formed in a concentrate wherein
the compos~tional ranges of the various components
are by weight percent of the total concentrate.
TABLE A
a. From about 0.01 percent to about 0.5 per-
cent first transition metal compound;
b. From about 0.005 percent to about O.l per-
cent second transition metal compound;
c. From about O.Ol percent to about 0.2 per-
lS cent aromatic ketone;
d. Balance thermoplastic polymer.
The following table sets forth a more preferredformulation for the thermoplastic composition of the
present invention formed in a concentrate wherein
the compositional ranges of the various components
are by weight percent of the total concentrate.
,
TABLE B
a. From about O.l percent to about 0.3 per-
cent iron stearate;
b. From about O.Ol percent to about 0.06 per-
cent copper stearate;
c. From about .02 percent to about 0.15 per-
cent benxophenone;
d. Balance thermoplastic polymer.
The following tables set forth a still more
preferred formulation for the thermcplastic
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compositlon of the present invention formed in a
concentrate wherein the compositional ranges of the
various components are ~y weight percent of the
total concentrate.
TAsLE C
a. Abou~ 0.124 percent ferrlc 12 hydroxy
stearate;
b. About 0.024 percent cupric stearate;
c. About 0.052 percent benxophenone;
cl. Balance thermoplastic polymer.
TABLE D
a. About 0.31 percent ferric 12 hydroxy
stearate;
b. About 0.06 percent cupric stearate;
c. About 0.l3 percent benxophenone;
d. Balance thermoplastic polymer.
With reference to Figure l, there is shown loss
of elongation at break using a film product to which
,~ the composition of the present invention has been
i 20 added, an~ a control comprised of polyethylene with-
out the additive composition. The film product
indicated by Formulation l in Figure l has the com-
position of Table C added thereto. The film product
indicated by formulation 2 in Figure l has the com- -
position of Table D added thereto. The control
film, Formulations l and 2 were exposed in a "QVV"
weatherometer, a testing device which uses ultravio-
let light and moisture tv simulate outdoor exposure.
;It is;apparent from Figure l tha_ films comprised
;~ 30 with the composition of the present invention
photodegrade at a much faster rate than the control
film without the compositlon of the present
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WO92~11298 2 ~ PCT/~'S91/09731
It will be understood that the foregoing
description and illustration is by way of example
only and that such modifications and changes as may
suggest themselves to those skilled in the art are
intended to fall within the scope of the present
invention.
What is claimed is:
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