Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to fully biodegradable and
photodegradable polymer blends and to methods of making the
same.
More specifically, the present invention relates to
blends of polyisoprene and polycaprolactone which have
thermoplastic properties, and which are biodegradable in soil
and sea water environments, and photodegradable.
As a result of concerns about the environment and
disposal of waste materials, a great deal of effort has been
directed towards the development of biodegradable plastic
materials. The main emphasis of such effort has been placed
on the mechanisms of photodegradation and biodegradation.
Photodegradation is the decomposition of photosensitive
materials initiated by the ultraviolet component of natural
light, and biodegradation results from the action of
microorganisms such as bacteria, fungi or algae.
Photodegradablity is an inherent property of some
polymers and in certain cases it can be enhanced by the use of
photosensitizing additives. Photodegradable plastics have
found use in applications such as agricultural mulch film,
trash bags, and retail shopping bags.
Several different types of plastics have been
produced which are fully or partially biodegradable. Some
effort has been made to modify non-biodegradable polymers with
starch in concentrations of 2-15%. However some controversy
remains as to whether such materials are completely
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biodegradable. Some newer materials which use starch as part
of the polymer matrix at levels of 60-100~ are reported to be
completely biodegradable. Certain polyester polymers have
been shown to be biodegradable. These include aliphatic
esters such as polyhydroxybutyrate-valerate (PHBV) and
polycaprolactone.
Polycaprolactone blends are known which contain a
variety of thermoplastic resins including polyethylene,
polystyrene and nylon and are degradable in soil or sea water.
However, because of the presence of non-biodegradable resin
components, such blends are not completely biodegradable. In
addition, the blends do not possess accelerated photo-
degradation abilities as measured against the properties of
widely used commercial plastics.
The polyisoprene-polycaprolactone blend disclosed by
Canadian Patent No. 1,111,179 which issued to Eric G. Kent on
on October 20, 1981 is described as having thermoplastic
properties. The patented invention is used for molding
components of orthopedic devices specifically because of the
mechanical and thermal properties of the material. Canadian
Patent No. 1,080,875, which issued to Eric G. Kent on July 1,
1980 also describes a blend containing polyisoprene and
polycaprolactone. Because of its mechanical properties, the
blend is used in the manufacture of sporting goods,
specifically golf ball covers. Japanese Patent No. JP
89293048 describes a multi-component biodegradable coating
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consisting of polycaprolactone, olefinic polymers, wax,
petroleum resin and fats and their derivatives including metal
salts. The possibility of introducing a natural resin
(polyisoprene) into such a coating is mentioned. Moreover,
one of the resins mentioned is natural rubber. Fertilizer
grains are coated by such a coating, which is degraded by
microorganisms in the soil.
None of the above-mentioned patents suggests a
composition which is photodegradable or biodegradable in sea
water. Only the Japanese patent mentions a composition with
the ability to biodegrade in soil. None of the patents
suggests using a composition for manufacturing a product using
known plastic working methods such as injection molding,
extrusion, blow molding or similar techniques which have
significant importance in applications for biodegradable and
photodegradable plastics.
Known biodegradable polymers have suffered slow
acceptance due to limitations in processing and high costs
relative to conventional, non-degradable polymers.
An object of the present invention is to provide a
plastic material which is completely biodegradable and
photodegradable, and which has thermoplastic properties
comprising a blend of polyisoprene and polycaprolactone.
Another object of the invention is to provide a
biodegradable and photodegradable plastic material comprising
a blend of polyisoprene and polycaprolactone which can be used
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to manufacture articles using conventional plastic processing
techniques.
Another object of the invention is to provide a
biodegradable and photodegradable article formed from a blend
of polyisoprene and polycaprolactone which has improved
mechanical properties and performance at high temperatures
because of a post-forming radiation treatment.
Yet another object of the invention is to provide a
method of making a fully biodegradable and photodegradable
plastic article by mixing polyisoprene and polycaprolactone to
form a blend, and processing the thus produced blend using
conventional plastic working techniques to form the article.
The invention provides a polyisoprene/polycapro-
lactone polymer blend having thermoplastic properties which is
fully biodegradable in soil and sea water and is photo-
degradable.
The polyisoprene/polycaprolactone blend of the
invention includes 10 to 500 parts by weight (pbw) of
polycaprolactone per 100 pbw polyisoprene resin, preferably 50
to 200 pbw of polycaprolactone per 100 pbw polyisoprene.
Some additivies such as, inter alia, casein, antioxidants,
dyes, fillers, vulcanized vegetable oils, fatty acids and
pigments commonly used in the plastic and rubber industry may
be incorporated into the blends in small amounts.
Polyisoprene can be obtained form natural rubber, or
can be produced as a synthetic polymer. Natural rubber
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contains polyisoprene and is produced by many different plant
species. In its natural state, the rubber is biodegradable;
however, the use of stabilization techniques results in
reduced biodegradability. Natural rubber, in its pure form,
is not acceptable for producing useful products using
conventional techniques such as injection and blow molding,
and extrusion which are used for thermoplastic polymeric
materials. The main reasons for this are the poor flow
characteristics of natural rubber, unsuitable mechanical
properties, and tackiness prior to vulcanization.
Polycaprolactone is a synthetic polymer resin known
to be decomposed by microorganisms. However the applications
for polycaprolactone in commercial manufacturing are limited
because of its very low melting point of about 71 - 73C and
its relatively high price.
The properties of the polyisoprene/polycaprolactone
blends of this invention are very different from the
properties described above for the individual polymers. The
blends have thermoplastic properties which allow processing
using conventional plastic working techniques such as
injection molding, blow molding and extrusion. The blend has
no tackiness and does not stick to a cold metal mold. The
flow properties above the softening point of the blend permit
processing using known plastic working techniques. A blend in
accordance with the invention containing even low levels of
polycaprolactone (30%) is capable of being oriented when force
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is applied, and will significantly increase the tensile
modulus and reduce or eliminate the elastic property
characteristic of some grades of polyisoprene to levels
typical of some commonly used plastics.
The polyisoprene/polycaprolactone blends can be
produced using techniques known to be suitable for blending
rubber or plastic such as extrusion, two roll milling and
Banbury milling. The blending temperature should be above
60C and preferably in the range 65-75C. The thermoplastic
resin obtained from the mixing of the two polymers should be
ground or pelletized for future use if the resin is intended
for injection molding, blow molding or extrusion manufacturing
processes. When compression or transfer or transfer molding
processes are to be used for manufacturing goods, the resin
can be stored in the form of sheets.
Such polyisoprene/polycaprolactone blends have a
relatively stable chemical structure when exposed to heat
during processing. They can be processed with standard
equipment used for injection molding, blow molding,
thermoforming, extrusion, compression or transfer molding to
manufacture bottles, containers, films, etc.
The manufactured goods produced using the
polyisoprene/polycaprolactone blend can be improved by
exposing them to electron beam or gamma radiation. Under
irradiation, the polyisoprene present in the blend becomes
cross-linked, and mechanical properties such as tensile
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r
strength, elongation at break and impact strength are
significantly improved, especially when service at elevated
temperature is required.
Articles made from polyisoprene/polycaprolactone
blends which are placed in soil or sea water will biodegrade
at variable rates. The biodegradation rate depends on
conditions such as moisture level (soil), air (oxygen)
concentration, temperature, presence of microorganisms, etc.
It is expected that there should be no products of degradation
other than carbon dioxide and water. An article made from the
blends will degrade quickly when exposed to sunlight. The
presence of ultraviolet radiation in the sunlight, light
intensity and temperature will individually influence the
degradation rate.
The following examples describe preferred
embodiments of the invention.
EXAMPLE 1
30 lb of polyisoprene in the form of natural rubber
grade SMR-L was premasticated using a two roll mill at a
temperature of 50-75C. After fifteen minutes of mastication,
when the temperature rose to 75C, 15 lb of polycaprolactone,
in the form of Tone* P-787 Polymer (Union Carbide) was added
slowly over an 8 minute period. The blend was mixed at 75C
for the next 5 minutes, as per standard milling procedure, and
was then cooled and ground to achieve a particle size of 6-30
*Trademark
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mesh blend. The resulting blend is described in the following
examples as Blend A.
EXAMPLE 2
30 lb of polyisoprene in the form of natural rubber
grade SMR-L was mixed with 30 lb of polycaprolactone in the
form of Tone 2101 (NL Chemicals). Mixing and grinding were
done as described in Example 1 with the exception that the
time for addition of the polycaprolactone to the polyisoprene
was extended to 12 minutes. The resulting blend is described
in the following examples as Blend B.
EXAMPLE 3
20 lab of polyisoprene in the form of natural
rubber grade SMR-L was mixed with 40 lb of polycaprolactone in
the form of Tone P-787 Polymer and 10 oz of Orange* PV-RL 01
(Hoechst). Mixing and grinding were done according to the
method of Example 1 with the exception that the time for
addition of the polycaprolactone to the polyisoprene was
extended to 18 minutes. The blend is described in the
following examples as blend C.
EXAMPLE 4
30 lb of polyisoprene in the form of natural rubber
grade SMR-L was premasticated using a two roll mill at a
temperature of 50-95 for 15 minutes. After mastication, when
the temperature had risen to 95C, 5 lb of edible technical
grade casein (90 Mesh) was added and mixed for another 15
minutes 95C. At this time, the temperature of the blend was
*Trademark
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reduced to 75C and 15 lb of polycaprolactone in the form of
Tone P-787 Polymer was added slowly over an 8 minute period.
The blend was mixed at 75C for the next 5 minutes, as per
standard milling procedure, and was then cooled and ground to
achieve a particle size of 6-30 mesh blend. The resulting
blend is described in the following examples as Blend D.
EXAMPLE 5
An injection molding machine, with a reciprocating
screw, was fed with polyisoprene/polycaprolactone Blend A.
The temperature of the heating zones were as follows: Zone 1
- 180C, Zone 2 - 190C, Zone 3 - 200C. The nozzle heater
was at 70% capacity. A mold designed to produce test
specimens with variable thicknesses, including tensile bars
according to ASTM D-638M, was used. The mold was cooled with
tap water at 15C. Total shoot size was 23.5 g. The machine
was operated using standard procedures for molding plastics.
The moldings obtained showed adequate replication of cavities
and good surface finish.
EXAMPLE 6
A Keotex KEB-l extruder, with a 50 mm extruding
screw, was used for molding 100 ml bottles using polyisoprene/
polycaprolactone Blend C. The temperature of the heating zones
were as follows: Zone 1 - 150C, Zone 2 - 170C, Zone 3 -
170C. The extrusion head temperature was 190C. The 100 ml
bottle mold was cooled was tap water at 15C. The bottles
thus obtained had adequate finish and surface quality.
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EXAMPLE 7
A hot press with cooling system was equipped with a
mold heated to 120C. 6.5 g of polyisoprene/polycaprolactone
Blend B or D was placed in the mold cavity measuring 0.3 mm x
140 mm x 140 mm. The mold was closed under 300 psi pressure,
heat was shut down and the cooling system was actuated. A
molding was obtained in the sheet form with no defects and a
good surface flnish.
EXAMPLE 8
Injection molded specimens in the form of tensile
bars (produced according to ASTM D-638M) were obtained using
polyisoprene/polycaprolactone Blend A. Specimens were exposed
to electron beam (EB) radiation with 120 KGray. Specimens
were later tested according to ASTM D-638M for tensile
strength and elongation at break at a temperature of 23+2C,
together with control specimens not exposed to radiation. The
results of testing, which indicate improvement in the
mechanical properties of polyisoprene/polycaprolactone Blend A
after exposure to EB radiation, are shown in Table 1.
EXAMPLE 9
Blow molded bottles made from polyisoprene/poly-
caprolactone Blend C, produced as described in Example 6, and
bottles produced from high density polyethylene (HDPE) were
placed in exterior conditions in garden soil, approximately 5
cm deep, from late March to late May in Vancouver, B.C. The
bottles were inspected at the end of the experiment and tested
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for weight loss, as well as for surface damage visible with
the naked eye and under a microscope. The results listed in
Table 2 indicate biodegradation of bottles made from
polyisoprene/polycaprolactone Blend C. The bottles made from
polyethylene were unchanged.
EXAMPLE 10
Plastic sheets compression molded from polyisoprene/
polycaprolactone Blend B or D in a similar manner to that
described in Example 7, and identical sheets made from HDPE
were immersed in sea water for a period of 30 or 90 days (at
water temperature of 10+2C) from the beginning of February
to the end of May. The specimen exposure area was screened
from direct sunlight. The sheets were inspected at the end of
the period and tested for weight loss, change in dimensions,
surface damage, and growth of microorganisms visible with the
naked eye and under a microscope. The results listed in Table
3 indicate biodegradation of the sheets made from the
polyisoprene/polycaprolactone blends.
EXAMPLE 11
Hot-pressed film specimens approximately 0.25 mm (10
mil) made from polyisoprene/polycaprolactone Blend C were
placed in a Q W accelerated weathering machine along with
linear low density polyethylene (LLDPE - Dupont Sclair 2114)
film specimens prepared in similar manner and were tested
according to ASTM D4329. UVB-313 lamps were employed to
irradiate the specimens with ultraviolet rays. The test
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condition consisted of alternating cycles of 8 hours of UV
light followed by 4 hours of condensation. The temperature
for the light cycle was 40C and 50C for the condensation
cycle. Sample specimens were tested for tensile strength (TS)
and elongation at break (EB) after 200 hours and 400 hours
accelerated aging according to ASTM D882. The results are
shown in Table 4 and Table 5. The polyisoprene/polycapro-
lactone Blend C showed greater loss of tensile strength and
elongation at break in comparison with polyethylene.
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TABLE 1
TENSILE PROPERTIES OF SPECIMENS
Specimen Dose Temperature Tensile Strength Elongation
No. (kGy) (C) (kg/cm2)At Break
(%)
1 120 23 122.2 1355.0
2 0 23 32.1 232.9
TABLE 2
DEGRADATION IN GARDEN SOIL OF BOTTLES
MADE FROM BLEND C IN COMPARISON WITH
POLYETHYLENE BOTTLES
BottleExposure WeightWeightWeight Appearance
Materials Period Initial After Loss
(days) (g)Exposure (g)
(g)
Blend C 70 13.66112.787 0.874 Extensive
surface
deterioration
and coloniza-
tion.
Polyethylene 7013.312 13.294 0.018 No change
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TABLE 3
DEGRADATION IN SEA WATER OF SHEETS
MADE FROM BLEND B AND D IN COMPARISON
WITH HDPE SHEETS
Sheet ExposureWeight Loss Appearance
Materials Periodper 100 cm2
(days) Sample (g)*
Blend B 30 0.07 Deposit of micro-
organisms beginning
100 0.26 surface
deterioration
Blend D 30 0.08 Deposit of micro-
organisms beginning
100 0.38 surface
deterioration
HDPE 30 0 No visible
change
100
* Based on one side of specimen.
TABLE 4
TENSILE STRENGTH (TS) OF BLEND C IN
COMPARISON WITH LLDPE AFTER
EXPOSURE TO ACCELERATED WEATHERING
Polymer Exposure 200 Hours Exposure 400 Hours
TS TS Changes TS TS Changes
Initial Final (%) Initial Final (%)
kg/cm2 kg/cm2 kg/cm2 kg/cm2
Blend C 192 134 -30 192 78 -59
Polyethylene 125 149 +19 125 99 -21
..
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TABLE 5
ELONGATION AT BREAK (EB) OF BLEND C
IN COMPARISON WITH POLYETHYLENE AFTER
EXPOSURE TO ACCELERATED WEATHERING
PolymerExposure 200 Hours Exposure 400 Hours
EB EB Changes EB EB Changes
Initial Final (%) Initial Final (%)
(%) (%) (~
Blend C1120 666 -41 1120 18 -98
Polyethylene 36 17 -53 36 7 -81
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SUMMARY
The material described hereinbefore, namely the
blend of polyisoprene and polycaprolactone resins, possesses a
unique combination of the following properties:
(1) thermoplastic properties that allow the material to
be processed using conventional thermoplastic-
working techniques; and
(2) degradability properties that allow the material to
completely degrade following the natural mechanisms
of biodegradation and photodegradation.
Blends of the material can be successfully processed
using techniques such as injection molding, blow molding,
thermoforming, extrusion, compression molding, and transfer
molding to produce articles commonly made with thermoplastic
resins.
The addition of polycaprolactone to polyisoprene
results in increased tensile modulus, and significantly
reduced or eliminated elasticity in comparison to the original
polyisoprene properties and imparts the ability for polymer
orientation. Moreover, polycaprolactone eliminates the
problem of polyisoprene sticking to cold metal molds during
thermoplastic processing.
Blends of the material will biodegrade in soil or
sea water and will photodegrade upon exposure to sunlight, and
are expected to generate only carbon dioxide and water as
products of degradation.
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The composition of the blends includes 10 to 500
parts hy weight (pbw) of polycaprolactone per 100 pbw
polyisoprene, with the preferred range being 50 to 200 pbw
polycaprolactone to 100 pbw polyisoprene. Additives commonly
used in the plastic and rubber industry may be added to the
blends in small amounts in order to enhance properties.
The prior art describes polyisoprene/polycapro-
lactone blends which possess thermoplastic properties (see
Canadian Patents Nos. 1,080,875 and 1,111,179) but, because of
the use of components such as sulphur vulcanized natural
rubber or ionomer copolymer, the feature of degradability is
not addressed. Manufacturing goods using conventional
thermoplastic processes is not mentioned. In the one case
where biodegradability is mentioned, (Japanese Patent
89293048), polyisoprene/polycaprolactone comprise a part of a
formulation, which does not possess thermoplastic properties,
and which is not photodegradable. Hence, the known prior art
does not teach combined thermoplasticity and degradability
properties.
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