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Claims  |
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I claim:
1. A multilayer degradable thermoplastic article having at least three
layers of thermoplastic material comprising a first outer layer, a second
outer layer, and a core layer, wherein the first outer layer and second
outer layer are characterized as containing an effective amount of a
prodegradant to promote photodegradation and/or thermal degradation and
said core layer is characterized as being more water soluble and/or more
biodegradable than said first outer layer and said second outer layer.
2. A multilayer degradable thermoplastic article according to claim 1
wherein said core layer is substantially more water soluble and/or more
biodegradable than said first outer layer and said second outer layer.
3. A multilayer degradable thermoplastic article according to claim 1 or
claim 2 wherein said first outer layer and said second outer layer are
selected from the group consisting of polyethylene, polypropylene,
polybutene, polymethylpentene, nylon, polyolefinic adhesive resins,
ethylene-vinyl acetate copolymers, ethylene acid copolymers,
ethylene-ethyl acrylate, ethylene-methyl acrylate, polyesters, ethylene
propylene rubbers, and mixtures thereof and said core layer is selected
from the group consisting of polyvinyl alcohol, ethylene-vinyl alcohol,
polycaprolactone, polyethylene oxide, and mixtures thereof.
4. A multilayer degradable thermoplastic article according to claim 1
wherein said first outer layer and said second outer layer comprise a
modified polyolefinic adhesive resin, said core layer comprises a water
soluble, biodegradable polyvinyl alcohol and said prodegradant is cerium
stearate.
5. A multilayer degradable thermoplastic article according to claim 3
wherein said first outer layer and said second outer layer comprise a
nylon and said core layer comprises a polyvinyl alcohol.
6. A multilayer degradable thermoplastic article according to claim 3
wherein said first outer layer and said second outer layer comprise a low
density polyethylene and said core layer comprises a blend of polyvinyl
alcohol and at least one biodegradable additive.
7. A multilayer degradable thermoplastic article according to claim 6
wherein said biodegradable additive is selected from the group consisting
of polycaprolactone, starch, starch derivatives, natural proteins,
cellulosic materials, sugars, natural rubbers, natural gums, and mixtures
thereof.
8. A multilayer degradable thermoplastic article according to claim 4
wherein said first outer layer and said second outer layer comprises
modified polyolefin resin and said core layer comprises a blend of water
soluble, biodegradable polyvinyl alcohol and a biodegradable
polycaprolactone.
9. A multilayer degradable thermoplastic article according to claim 6
wherein said first outer layer and said second outer layer comprise a
linear low density polyethylene and said core layer comprises a water
soluble, biodegradable polyvinyl alcohol.
10. A multilayer degradable thermoplastic article according to claim 1
wherein said first outer layer and said second outer layer contain an
effective amount of at least one organic salt of a polyvalent transition
metal as said prodegradant and said core layer comprises a water soluble,
biodegradable polyvinyl alcohol.
11. A multilayer degradable thermoplastic article according to claim 10
wherein said first outer layer and said second outer layer comprise a
polyolefin polymer or copolymer blended with a graft copolymer of
polyethylene and an unsaturated fused ring carboxylic acid anhydride
containing an effective amount of a prodegradant selected from the group
consisting of manganese stearate, iron stearate, cerium stearate and
mixtures thereof and said core layer comprises a water soluble,
biodegradable polyvinyl alcohol.
12. A multilayer degradable thermoplastic article according to claim 10
wherein said first outer layer and said second outer layer comprise a
linear low density polyethylene and said core layer comprises a water
soluble, biodegradable polyvinyl alcohol.
13. A multilayer degradable thermoplastic article according to claim 12
wherein said first outer layer and said second outer layer comprise a
linear low density polyethylene containing an effective amount of cerium
stearate and said core layer comprises polyvinyl alcohol and said
multilayer degradable thermoplastic article is further characterized as
having a ratio of said first outer layer to said core layer to said second
outer layer of between 2:1:2 to 1:10:1.
14. A multilayer degradable thermoplastic article according to claim 10
wherein said first outer layer and said second outer layer comprise a
linear low density polyethylene having a density of between about 0.915
g/cm.sup.3 and about 0.945 g/cm.sup.3 and a melt index of between about
0.6 and about 1.5 and said core layer comprises: (1) a polyvinyl alcohol
characterized as a homopolymer having a degree of hydrolysis from 84-95%
and having an external plasticizer to permit conventional thermoplastic
extrusion; or (2) a polyvinyl alcohol copolymer as characterized by a
degree of hydrolysis from 84%-88% and having as an internal plasticizer to
permit conventional thermoplastic extrusion grafted comonomer segments
comprising oligomeric polyethylene glycol having 1-30 repeating units in
addition to a few percent of an external plasticizer; or (3) mixtures
thereof.
15. A multilayer degradable thermoplastic article according to claim 10
wherein said first outer layer adhesive resin and said second outer layer
comprises a modified polyolefin characterized as having a density of
between about 0.91 and about 0.96 gm/cm.sup.3 and a melt index of between
about 0.3 and about 13 gm/10 min and contain an effective amount of a
transition metal stearate and said core layer comprises: (1) a polyvinyl
alcohol characterized as a homopolymer having a degree of hydrolysis from
84-95% and having an external plasticizer to permit conventional
thermoplastic extrusion; or (2) polyvinyl alcohol copolymer as
characterized by a degree of hydrolysis from 84%-88% and having as an
internal plasticizer to permit conventional thermoplastic extrusion
grafted comonomer segments comprising oligomeric polyethylene glycol of
1-30 repeating units in addition to a few percent of an external
plasticizer; o (3) mixtures thereof.
16. A multilayer degradable thermoplastic article according to claim 1 or
claim 10 or claim 15 wherein said effective amount of prodegradant in each
of said first outer layer and said second outer layer is an effective
amount between about 0.01 weight percent and about 3.0 weight percent
based upon the weight of said layer in which said transition metal
stearate is present.
17. A multilayer degradable thermoplastic article according to claim 16
wherein said prodegradant is present in an effective amount between about
0.1 and about 1.5 weight percent.
18. A multilayer degradable thermoplastic article according to claim 17
wherein said prodegradant is present in an effective amount between about
0.3 and about 1.0 weight percent.
19. A multilayer degradable thermoplastic article according to claim 1
wherein an effective amount of an antioxidant is present.
20. A multilayer degradable thermoplastic article according to claim 16
wherein an effective amount of an antioxidant is present.
21. A multilayer degradable thermoplastic article according to claim 20
wherein said antioxidant is present in an effective amount between about
0.001 and about 1.0 weight percent.
22. A multilayer degradable thermoplastic article according to claim 21
wherein said antioxidant is present in an effective amount between about
0.0025 and about 0.1 weight percent.
23. A multilayer degradable thermoplastic article according to claim 16
wherein said core layer contains between about 0.01 weight percent and
about 3.0 weight percent transition metal stearate with the proviso that
the weight percent of said transition metal stearate in said core layer is
less than the weight percent transition metal stearate in said first outer
layer or said second outer layer.
24. A multilayer degradable thermoplastic article according to claim 23
wherein said prodegradant is present in an effective amount between about
0.1 and about 1.5 weight percent.
25. A multilayer degradable thermoplastic article according to claim 24
wherein said prodegradant is present in an effective amount between about
0.3 and about 1.0 weight percent.
26. A multilayer degradable thermoplastic article according to claim 24
wherein an effective amount of an antioxidant in said core layer is
correlated to the effective amount of said prodegradant in said first and
second outer layers.
27. A multilayer degradable thermoplastic article according to claim 24
wherein an effective amount of an antioxidant is also present in said core
layer and in first and second outer layers.
28. A multilayer degradable thermoplastic article according to claim 27
wherein said antioxidant is present in an effective amount between about
0.001 and about 1.0 weight percent.
29. A multilayer degradable thermoplastic article according to claim 28
wherein said antioxidant is present in an effective amount between about
0.0025 and about 0.1 weight percent.
30. A multilayer degradable thermoplastic article according to claim 16
wherein the weight ratio of said first outer layer to said core layer to
said second outer layer is between about 10:1:10 and about 1:50:1.
31. A multilayer degradable thermoplastic article according to claim 30
wherein said weight ratio is between about 2:1:2 and about 1:10:1.
32. A multilayer degradable thermoplastic article according to claim 30
wherein said multilayer degradable thermoplastic article is a film having
a thickness between about 0.1 mil and about 5.0 mils.
33. A multilayer degradable thermoplastic article according to claim 32
wherein said film has a thickness between about 0.5 mil and about 3.0
mils.
34. A multilayer degradable thermoplastic article according to claim 1 or
claim 10 or claim 15 comprising at least five layers comprising:
(i) a first outer layer of linear low density polyethylene;
(ii) a first tie layer of a modified polyolefin adhesive resin;
(iii) a core layer of a polyvinyl alcohol;
(iv) a second tie layer of a modified polyolefin adhesive resin;
(v) a second outer layer of a linear low density polyethylene;
wherein said core layer comprises at least 50 weight percent of the total
weight of the multilayer degradable film and said first outer layer and
second outer layer contain an effective amount of a prodegradant.
35. A degradable bag formed from a multilayer degradable thermoplastic
article as defined in claim 1.
36. A degradable bag formed from a multilayer degradable thermoplastic
article as defined in claim 2.
37. A degradable bag formed from a multilayer degradable thermoplastic
article as defined in claim 4.
38. A degradable bag formed from a multilayer degradable thermoplastic
article as defined in claim 10.
39. A degradable bag formed from a multilayer degradable thermoplastic
article as defined in claim 11.
40. A degradable bag formed from a multilayer degradable thermoplastic
article as defined in claim 32.
41. A method for composting an organic material stored in a
thermoplastic/container comprising providing said organic material to a
shredding means wherein said thermoplastic container is shredded into
pieces smaller than the initial thermoplastic container, introducing the
organic material and shredded thermoplastic container to a composting
pile, composting said composting pile under effective composting
conditions for an effective period of time wherein said thermoplastic
container comprises a three layer structure characterized by a first outer
layer and a second outer layer which are characterized as containing an
effective amount of a prodegradant to promote photodegradation and/or
thermal degradation and a core layer wherein the core layer is
characterized as being more water soluble and/or more biodegradable than
said first outer layer and said second outer layer.
42. A composting method according to claim 41 having at least three layers
of thermoplastic material comprising a first outer layer, a second outer
layer, and a core layer, wherein the first outer layer and second outer
layer are characterized as containing an effective amount of a
prodegradant and said core layer is characterized as being more water
soluble and/or more biodegradable than said first outer layer and said
second outer layer.
43. A composting method according to claim 42 wherein said core layer is
substantially more water soluble and/or more biodegradable than said first
outer layer and said second outer layer.
44. A composting method according to claim 42 or claim 43 wherein said
first outer layer and said second outer layer are selected from the group
consisting of polyethylene, polypropylene, polybutene, polymethylpentene,
nylon, polyolefinic adhesive resins, ethylene-vinyl acetate copolymers,
ethylene acid copolymers, ethylene-ethyl acrylate, ethylene-methyl
acrylate, polyesters, ethylene propylene rubbers, and mixtures thereof and
said core layer is selected from the group consisting of polyvinyl
alcohol, ethylene-vinyl alcohol, polycaprolactone, polyethylene oxide, and
mixtures thereof.
45. A composting method according to claim 42 or claim 43 wherein said
first outer layer and said second outer layer comprise a modified
polyolefinic adhesive resin, said core layer comprises a water soluble,
biodegradable polyvinyl alcohol and said prodegradant is cerium stearate.
46. A composting method according to claim 44 wherein said first outer
layer and said second outer layer comprise a nylon and said core layer
comprises a polyvinyl alcohol.
47. A composting method according to claim 44 wherein said first outer
layer and said second outer layer comprise a low density polyethylene and
said core layer comprises a blend of polyvinyl alcohol and at least one
biodegradable additive.
48. A composting method according to claim 47 wherein said biodegradable
additive is selected from the group consisting of polycaprolactone,
starch, starch derivatives, natural proteins, cellulosic materials,
sugars, natural rubbers, natural gums, and mixtures thereof.
49. A composting method according to claim 45 wherein said first outer
layer and said second outer layer comprises modified polyolefin resin and
said core layer comprises a blend of water soluble, biodegradable
polyvinyl alcohol and a biodegradable polycaprolactone.
50. A composting method according to claim 47 wherein said first outer
layer and said second outer layer comprise a linear low density
polyethylene and said core layer comprises a water soluble, biodegradable
polyvinyl alcohol.
51. A composting method according to claim 41 wherein said first outer
layer and said second outer layer contain an effective amount of at least
one organic salt of a polyvalent transition metal as said prodegradant and
said core layer comprises a water soluble, biodegradable polyvinyl
alcohol.
52. A composting method according to claim 51 wherein said first outer
layer and said second outer layer comprise a polyolefin polymer or
copolymer blended with a graft copolymer of polyethylene and an
unsaturated fused ring carboxylic acid anhydride containing an effective
amount of a prodegradant selected from the group consisting of manganese
stearate, iron stearate, cerium stearate and mixtures thereof and said
core layer comprises a water soluble, biodegradable polyvinyl alcohol.
53. A composting method according to claim 51 wherein said first outer
layer and said second outer layer comprise a linear low density
polyethylene and said core layer comprises a water soluble, biodegradable
polyvinyl alcohol.
54. A composting method according to claim 53 wherein said first outer
layer and said second outer layer comprise a linear low density
polyethylene containing an effective amount of cerium stearate and said
core layer comprises polyvinyl alcohol and said multilayer degradable
thermoplastic article is further characterized as having a ratio of said
first outer layer to said core layer to said second outer layer of between
2:1:2 to 1:10:1.
55. A composting method according to claim 51 wherein said first outer
layer and said second outer layer comprise a linear low density
polyethylene having a density of between about 0.915 g/cm.sup.3 and about
0.945 g/cm.sup.3 and a melt index of between about 0.6 and about 1.5 and
said core layer comprises: (1) a polyvinyl alcohol characterized as a
homopolymer having a degree of hydrolysis from 84-95% and having an
external plasticizer to permit conventional thermoplastic extrusion; or
(2) a polyvinyl alcohol copolymer as characterized by a degree of
hydrolysis from 84%-88% and having as an internal plasticizer to permit
conventional thermoplastic extrusion grafted comonomer segments comprising
oligomeric polyethylene glycol having 1-30 repeating units in addition to
a few percent of an external plasticizer; or (3) mixtures thereof.
56. A composting method according to claim 51 wherein said first outer
layer and said second outer layer comprises a modified polyolefin
characterized as having a density of between about 0.91 and about 0.96
gm/cm.sup.3 and a melt index of between about 0.3 and about 13 gm/10 min
and contain an effective amount of a transition metal stearate and said
core layer comprises: (1) a polyvinyl alcohol characterized as a
homopolymer having a degree of hydrolysis from 84-95% and having an
external plasticizer to permit conventional thermoplastic extrusion; or
(2) polyvinyl alcohol copolymer as characterized by a degree of hydrolysis
from 84%-88% and having as an internal plasticizer to permit conventional
thermoplastic extrusion grafted comonomer segments comprising oligomeric
polyethylene glycol of 1-30 repeating units in addition to a few percent
of an external plasticizer; or (3) mixtures thereof.
57. A composting method according to claim 56 wherein said effective amount
of transition metal stearate in each of said first outer layer and said
second outer layer is an effective amount between about 0.01 weight
percent and about 3.0 weight percent based upon the weight of said layer
in which said transition metal stearate is present.
58. A composting method according to claim 57 wherein said core layer
contains between about 0.3 weight percent and about 1.0 weight percent
transition metal stearate with the proviso that the weight percent of said
transition metal stearate in said core layer is less than the weight
percent transition metal stearate in said first outer layer or said second
outer layer.
59. A composting method according to claim 41 wherein the weight ratio of
said first outer layer to said core layer to said second outer layer is
between about 10:1:10 and about 1:50:1.
60. A composting method according to claim 59 wherein said weight ratio is
between about 2:1:2 and about 1:10:1.
61. A composting method according to claim 59 or claim 60 wherein said
multilayer degradable thermoplastic article is a film having a thickness
between about 0.I mil and about 5.0 mils.
62. A composting method according to claim 46 wherein said film has a
thickness between about 0.5 mil and about 3.0 mils.
63. A composting method according to claim 41 comprising at least five
layers comprising:
(i) a first outer layer of linear low density polyethylene;
(ii) a first tie layer of a modified polyolefin adhesive resin;
(iii) a core layer of a polyvinyl alcohol;
(iv) a second tie layer of a modified polyolefin adhesive resin;
(v) a second outer layer of a linear low density polyethylene;
wherein said core layer comprises at least 50 weight percent of the total
weight of the multilayer degradable film and said first outer layer and
second outer layer contain an effective amount of a prodegradant.
64. A method for composting an organic material according to claim 41
wherein said effective period of time for said composting of said organic
material and said shredded thermoplastic container does not substantially
exceed the effective composting period of time for said organic material
sans said shredded thermoplastic container.
65. A method for composting an organic material according to claim 41
wherein after composting under effective composting conditions the tensile
load of said thermoplastic container has decreased to less than 50 percent
of the original thermoplastic container prior to having undergone
composting.
66. A composting bag formed from a multilayer thermoplastic film having a
first outer layer, a core layer and a second outer layer wherein the first
outer layer and second outer layer are characterized as containing an
effective amount of prodegradant and said core layer is characterized as
being more water soluble and/or more biodegradable than said first outer
layer and said second outer layer and wherein the core layer comprises
greater than 50 percent by weight of the total film weight.
67. A composting bag according to claim 52 wherein said first outer layer
and said second outer layer contain an effective amount of cerium
stearate.
68. A composting bag according to claim 66 wherein said first outer layer
and said second outer layer are selected from the group consisting of: (a
linear low density polyethylene having a density of between about 0.915
g/cm.sup.3 and about 0.945 g/cm.sup.3 and a melt index of between about
0.6 and about 1.5; polyolefin polymer or copolymer blended with a graft
copolymer of polyethylene and an unsaturated fused ring carboxylic acid
anhydride, and mixtures thereof; and said core layer comprises a major
amount of at least one of: (1) a polyvinyl alcohol characterized as a
homopolymer having a degree of hydrolysis from 84-95% and having an
external plasticizer to permit conventional thermoplastic extrusion; and
(2) a polyvinyl alcohol copolymer as characterized by a degree of
hydrolysis from 84%-88% and having as an internal plasticizer to permit
conventional thermoplastic extrusion grafted comonomer segments comprising
oligomeric polyethylene glycol having 1-30 repeating units in addition to
a few percent of an external plasticizer. |
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Claims |
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Description |
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FIELD OF THE INVENTION
The instant invention relates to novel multilayer degradable thermoplastic
articles, preferably a multilayer degradable thermoplastic film structure.
The novel degradable articles comprise a first outer layer, core layer and
a second outer layer, wherein the first outer layer and second outer layer
are formed from a degradable thermoplastic material containing a
prodegradant and the core layer is formed from a water soluble and/or
biodegradable thermoplastic material. The novel degradable thermoplastic
articles are characterized by their novel dual-degradation mechanism, as
hereinafter discussed. Bags made from the multilayer degradable
thermoplastic film are well suited for use in composting.
BACKGROUND OF THE INVENTION
The use of thermoplastic materials for the manufacture of numerous
products, including containers, e.g., bags of all varieties, is well known
in the art. The use of thermoplastic articles is so widespread that the
disposal of thermoplastic articles has become a significant world wide
problem. Although it is preferable to recycle as great a portion of these
thermoplastic articles as possible into new products, it is acknowledged
that at least some finite portion of these articles will ultimately be
discarded as unsuitable for recycle applications. The two most traditional
mechanisms by which such articles are disposed are by incineration or by
depositing the thermoplastic articles in a landfill. The growing use of
thermoplastic articles and, accordingly, their ever increasing disposal
has resulted in considerable activity relating to methods for controlling
the evergrowing volume of thermoplastic materials to be disposed.
Unfortunately, as above noted, recycle programs are not effective for all
thermoplastic articles such as the case where the article acts as the
container for refuse, such as is the case for household trash, and other
types of disposable bags made from thermoplastic films. The particular
problems associated with disposer bags is multifaceted owing to the wide
array of uses for such bags and, further, owing to the need to manufacture
such bags from a multifunctional thermoplastic material that meets both
the performance and varied use requirements of today's consumer. In
addition, such thermoplastic bags must be disposable in an environmentally
responsible way when disposed after the article's useful life.
Although many learned individuals have considered the above disposal
problems, it is painfully clear that very few ideas have seen the
"commercial light of day". Currently, the disposal problem associated with
thermoplastic bags, although only a minute segment of the total quantity
of thermoplastic articles disposed of on an annual basis, is being
addressed by two different approaches. The first approach is to add a
prodegradant, e.g., iron stearate, to the thermoplastic material whereby
the rate of photodegradation and/or thermal degradation is increased over
that of the original thermoplastic material. Although this approach is
extremely useful when the thermoplastic article is placed in sunlight or a
thermally activating environment, it is too often the case that the
thermoplastic article will be placed in a landfill prior to having
significant degradation occur. The second approach involves the use of
small amounts of biodegradable fillers for the thermoplastic material. The
use of a biodegradable filler typically incorporates a prodegradant also,
as above discussed. The biodegradable filler is generally a starch,
modified starch or cellulosic component which would be degradable by
microorganisms in an oxygen-rich landfill environment. Unfortunately, long
term management of landfills has made this approach only a partial
solution. It has been observed that many landfills are maintained as dry,
anerobic environments as a result of the desire to minimize the leaching
of landfill contaminants into ground water. Accordingly, the long term
degradation mechanism for the starch component may be halted before it can
progress to any meaningful degree. Further, the addition of starch
components in amounts up to about ten (10) weight percent have been
reported to significantly decrease the strength of thermoplastic film
products such as the various polyethylenes. In fact, the net result of
adding the starch component will in all likelihood be an overall increase
in the amount of thermoplastic employed in manufacturing the article,
since an overall increase in the amount of the thermoplastic will be
required to maintain the necessary performance characteristics of the
thermoplastic article. Further, the addition of a starch or other
component as a "filler" for a thermoplastic article does not render the
thermoplastic material biodegradable. The thermoplastic material remains
after the biodegradable filler is removed, although the form of
thermoplastic article may fragment to some extent as a result of the
degradation of the biodegradable component.
The aforementioned considerations have resulted in numerous patents and
voluminous prior art relating to degradable thermoplastic materials. A
review of the more interesting and relevant prior art is considered
hereinafter.
U.S. Pat. No. 4,016,117 is directed towards a biodegradable synthetic resin
composition which includes a polymer, a biodegradable filler (which may be
starch, as set forth in claim 2), and an auto-oxidizable substance, which
may be a fatty acid, which auto-oxidizes when in contact with a transition
metal salt. It is said that the composition degrades in the soil, although
clearly it is only the biodegradable filler that undergoes biodegradation.
U.S. Pat. No. 4,256,851 is directed towards an environmentally degradable
plastic composition which comprises an admixture of a polyolefin and an
ethylenically unsaturated alcohol. Claim 6 recites a specific antioxidant.
U.S. Pat. No. 4,021,388 is a divisional of U.S. Pat. No. 4,016,117,
discussed above. The '388 patent has claims directed towards a
biodegradable composition which includes a polymer having carbon to carbon
linkages with starch granule dispersed therein. The claims further recite
that the surface of the granules are modified by reaction with a compound
which reacts with hydroxyl groups to form an ether or an ester.
U.S. Pat. No. 4,133,784 has claims directed towards a biodegradable film
composition which comprises a dry composite of a starchy material and a
water-dispersable ethylene acrylic acid copolymer.
U.S. Pat. No. 4,337,181 has claims which are directed towards a
biodegradable film and method of making such a film. The method involves
mixing a gelatinized starchy material with an ethylene acrylic acid
copolymer to produce a plasticized matrix which is then shaped into a
film. The method further includes the steps of adding an ammonia
neutralizing agent to the mixture, adjusting the moisture content to a
specified range and extrusion blowing the mixture into a film.
U.S. Pat. No. 4,454,268 is directed towards a semi-permeable film and
method of making such a film. The film includes an ethylene acrylic acid
copolymer and a starchy material.
U.S. Pat. No. 4,324,709 has claims directed towards a plastic-based
composition and method of making such a composition. The composition
includes a synthetic polymer and starch granules which have a modifying
substance absorbed therein.
U.S. Pat. No. 3,935,141 discloses an environmentally degradable ethylene
polymer composition comprising: about 0.01 to about 40 percent by weight
of at least one auto-oxidative susceptible additive; about 0.002 to about
2.0 percent by weight of the metal atom of at least one salt of at least
one polvalent metal selected from the group consisting of titanium,
vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc and
cerium; and about 0.0025 to about 1 percent by weight of an antioxidant
for the ethylene polymer. The patentee discloses the use of organic salts
of the polyvalent metals, including stearate, octoate, dodecyl
acetoacetate, oleate and distearate. In selecting the antioxidant the
patentee discloses that commonly employed antioxidants may be employed, as
described at column 8, line 19 to column 9, line 12. The patentee notes,
at column 2, lines 40 to 51, that one can proportion the amounts of
antioxidant and additives to give a structurally stable product during the
useful life period of the product but which will undergo embrittlement
within a relatively short time after exposure to the elements.
PCT/GB88/00386 (PCT application), to Griffin discloses a degradable polymer
composition wherein an antioxidant and pro-oxidant are combined whereby as
the antioxidant is stated to be depleted with time. After total depletion
of the antioxidant a residual concentration of prooxidant remains and is
stated to provide a sharp loss in the physical strength of the degradable
polymer composition. The application discloses use of a stable polymer
such as low-density polyethylene, linear low density polyethylene, high
density polyethylene, polypropylene, or polystyrene, together with a less
stable unsaturated elastomer type compound made from the polymerization of
1:4 dienes, or the copolymerization of such 1:4 dienes with ethenoid
comonomers, such as styrene-butadiene elastomer or natural rubber. The
invention embodies less stable substances capable of auto-oxidation
because such substances are more readily initiated by the oxidation
process by virtue of their unsaturation. Once the auto-oxidation process
is initiated, the process is said to involve more resistant saturated
substances such as polyolefins, although no data is disclosed to support
this claim.
Although not directly related to degradable thermoplastic compositions,
several patents are of interest owing to their disclosure of multilayer
films. U.S. Pat. Nos. 4,254,169 and 4,239,826 disclose multilayer barrier
films having a core layer of ethylene vinyl alcohol polymers or vinyl
alcohol polymers or copolymers thereof. The patentee in U.S. Pat. No.
4,254,169 discloses that a delamination resistant multilayer structure of
a barrier layer comprising a substantially pure polymer or copolymer of
vinyl alcohol may be formed with an adhered layer of a modified polyolefin
which consists essentially of a polyolefin polymer or copolymer blended
with a graft copolymer of polyethylene and an unsaturated fused ring
carboxylic acid anhydride. Modified polyolefin blends of this type are
discussed by the patentee in column 3, lines 1 to 21 wherein the patentee
discloses that such modified polyolefin blends are available under the
name PLEXAR.RTM.. The patentee discusses the nature of the multilayer
barrier film and the goals to be achieved in several ways. For example, as
noted at column 2, lines 42 to 53, because of the core layer's excellent
barrier properties, the core layer can be made quite thin, in the range of
0.1 mil or less. The patentee views this as an advantage which results
from using the modified polyolefin blends as an outer film layer. Further,
at column 2, lines 20 to 38, the patentee characterizes the multilayer
barrier film for its high resistance to the passage of gas and moisture.
The patentee further states that the invention is preferrably manufactured
by cast coextrusion, but can be manufactured by blown film coextrusion,
water quench coextrusion, or lamination and that the resultant film can be
satisfactorily heat sealed.
U.S. Pat. No. 4,640,852 is directed towards a multiple layer film (see:
Claim 2) which comprises a nylon layer, an ethylene vinyl alcohol
copolymer layer, and a layer of nylon.
Another area of interest relating to the use of degradable thermoplastic
bags is in the field of composting. Although the prior art has broadly
addressed the issue of degradable polymers, the issue of use of degradable
thermoplastic bags in composting has not received wide spread attention.
In the majority of current composting applications a Kraft paper leaf bag
has been employed. Typically, if a thermoplastic bag has been employed to
contain yard waste a preparatory step of debagging the yard waste from the
thermoplastic bag has been required. In an attempt to improve the utility
of thermoplastic bags in composting the use of biodegradable additives,
e.g., starch, in the thermoplastics has been suggested. Unfortunately, as
above discussed, the addition of small amounts, typically on the order of
1 to 10 weight percent, of a biodegradable additive does not make the
remaining thermoplastic material degradable, although it may result in
some loss in the tensile strength of the thermoplastic bag. A
thermoplastic bag specifically designed for use in composting is needed.
The instant invention is directed towards the problem of improving the
degradation of thermoplastic articles when such are subjected to
environmental conditions as encountered in landfills and composting.
SUMMARY OF THE INVENTION
The instant invention relates to novel multilayer degradable thermoplastic
articles. In one embodiment the novel multilayer degradable thermoplastic
article comprises a first outer layer, core layer and a second outer
layer, wherein the first outer layer and second outer layer are a
degradable thermoplastic material containing an effective amount of a
prodegradant and the core layer is a water soluble and/or biodegradable
thermoplastic material. The multilayer degradable thermoplastic articles
of the instant invention find use in the manufacture of thermoplastic
articles of various types and are particularly useful in the construction
of bags wherein the multilayer structure is provided in the form of a film
from which various types of bags may be manufactured.
DETAILED DESCRIPTION OF THE INVENTION
The instant invention relates to a multilayer degradable thermoplastic
article and also relates to a multilayer degradable thermoplastic film
structure useful in the manufacture of products formed from multilayer
thermoplastic laminates, including molded containers, bags and films for a
variety of uses, including bags useful in composting.
The multilayer degradable thermoplastic articles comprise a first outer
layer, core layer and a second outer layer, wherein the first outer layer
and second outer layer are generally characterized as being
photodegradable and/or thermally degradable thermoplastic materials and
preferably contain an effective amount of a prodegradant. The core layer
is characterized as being a water soluble and/or biodegradable
thermoplastic material, and, is characterized as being more biodegradable
and/or water soluble than the first outer layer and second outer layer.
The characterization of a thermoplastic material herein as being
photodegradable, thermally degradable, biodegradable and/or water soluble
are discussed hereinafter.
The terms "photodegradable", "thermally degradable", "biodegradable" and
"water soluble" are employed herein to refer to physical and chemical
properties of the thermoplastic materials.
The term "photodegradable" as used herein is meant to denote a
thermoplastic material characterized by susceptability to ultraviolet (UV)
light initiated oxidative chain scission reactions resulting in molecular
weight reduction, (preferably substantially complete loss) of tensile
strength, and embrittlement to the extent that mechanical stresses, such
as those arising from wind or rain break the thermoplastic material into
smaller fragments.
The term "thermally degradable" as used herein is meant to denote a
thermoplastic material characterized by a susceptibility to the
scissioning of main chain chemical bonds as a result of overcoming bond
dissociation energies under the influence of moderately elevated
temperature e.g., such as heating at temperatures above room temperature,
e.g., at a temperature between about 100.degree. F. and about 160.degree.
F., preferably between about 110.degree. F. and about 150.degree. F. The
results of thermal degradation include changes in the physical and
chemical properties of the thermoplastic material, such as molecular
weight reduction, loss of tensile strength, and embrittlement, to the
extent that mechanical stress (such as that encountered when an article
made from the thermoplastic material is treated in such a heated
environment, buried, and tilled in soil or compost) break the article into
minute fragments.
The term "biodegradable" is used herein to denote a material (thermoplastic
or non-thermoplastic in nature) characterized by susceptibility to attack
from living organisms which are capable of producing enzymes or pH changes
that hydrolyze chemical bonds present in the material to form specific
decomposition products that can be utilized by the attacking organisms or
by other organisms for energy production or synthesis of new compounds.
Polymeric materials falling within the term "biodegradable", as employed
herein, include polyvinyl alcohol resins, ethylene alcohol resins and
polycaprolactone-based resins. In addition, other biodegradable
thermoplastic polymers may be employed as the core layer, e.g., the
biodegradable graft copolymers of U.S. Pat. No. 4,891,404, incorporated
herein by reference.
The biodegradation of certain thermoplastic polymers is well known in the
prior art. The microbial degradation of synthetic polymers is discussed at
pages 164 to 174 of the text entitled, Polymer Degradation, Professor Dr.
Wolfram Schnabel, Macmillan Publishing Co., Inc., New York (1981).
Polyvinyl alcohol and polycaprolactone polymers are reported to have quite
high biodegradation rates. Further, the author discusses the various
thermophilic, aerobic microorganisms existing in soil and capable of
proliferating at temperatures above about 60.degree. C. (e.g., the
numerous bacillus [e.g., calidolactis, pepo therminalis, thermodiastaticus
and tostus], actinomyces [e.g., monodiastaticus, spinosporus,
thermodiastaticus, thermofuscus and thermophilus] and fungi [e.g.,
aurantiacus and sulfureum]).
The term "water-soluble" as used herein is meant to denote a material
(thermoplastic or non-thermoplastic) characterized by a susceptibility to
solvolysis by water which causes the breaking of hetero bonds containing
carbon and either O, N, P, S, Si, or halogens either in the main-chain or
in pendant chains and/or the breakup of secondary bonding forces such as
hydrogen-bonding to render a major amount (greater than fifty (50) weight
percent) of the material dissolved in water at temperatures no greater
than about 100.degree. F. and preferably no greater than about 120.degree.
F. and more preferably no greater than about 140.degree. F., at ambient
pressure.
In one embodiment the first outer layer and second outer layer are
characterized as thermoplastic materials that are less water soluble than
the core layer. These outer layers provide protection from water to the
more water soluble core layer and limit dissolution of the core layer in a
moist environment. This ultimately extends the physical usefulness in a
moist environment of the article for a period longer than the period of
use for an article formed from the core layer alone. Further, the first
and second outer layers possess photo and/or thermal degradation
characteristics. After a predictable time of usefulness in service in the
presence of UV light or after thermal influence on an outer layer(s) by
the sun or otherwise, the first and/or second outer layers become cracked,
comminuted and/or increasingly more porous whereby they effectively lose
their moisture protection characteristics for the core layer. As the first
outer layer and second outer layers become increasingly porous as a result
of photo and/or thermal degradation, the unprotected water soluble core
layer material can undergo solubilization (and if biodegradable also
undergo biodegradation) as a result of exposure to the surrounding
environment. The protodegradation and/or thermal degradation
characteristics of the first and second outer layers are preferably
brought about by incorporation of a prodegradant material that imparts
improved photodegradation and/or thermal degradation characteristics to
the first outer layer and second outer layer. Although chemically
activated prodegradants may be employed within the scope of this
invention, such are not typically employed or preferred owing to the
careful balancing of a multiplicity of chemical components required to
correctly time the initiation of such a chemically activated degradation.
Accordingly, it is preferred to add a prodegradant having its degradation
activity activated by UV light or by an elevated thermal environment (such
thermal environments are found in composting piles and in some landfills).
Finally, the first and second outer layers are preferably further
characterized as being substantially less water soluble than the core
layer at temperatures between about 100.degree. F. and about 212.degree.
F.
In one embodiment of the instant invention the first outer layer and second
outer layer may be formed of the same or different thermoplastic
materials. Further, the first outer layer or the second outer layer may
comprise a multilayered layer. The first and second outer layers may be
selected from a wide variety of thermoplastic materials. In one embodiment
the thermoplastic material is selected as at least one material selected
from the group consisting of very low density polyethylene; low density
polyethylene; linear low density polyethylene (including the 1-butene,
1-hexene and 1-octene copolymers); ethylene-ethyl acrylate,
ethylene-methyl acrylate, ethylene-acrylic acid, ethylene-methacrylic
acid, ethylene-vinyl acetate, ultra low density polyethylene (e.g., having
a density less than 0.915 g/cm.sup.3), medium and high density
polyethylene, polyolefinic extrudable adhesive resins having anhydride
moieties (such as PLEXAR.TM. available from the USI Division of Quantum,
Rolling Meadows, Ill., BYNEL.TM. available from E.I. DuPont DeNemoirs,
Wilmington, Del., or ADMER.TM. available from Mitsui Petrochemical,
Houston, Tex.), polypropylene, ethylene-propylene rubbers, poly-1-butene,
polyisobutylene, poly (4-methyl pentene), polyesters, polyamides
(including polyamides such as nylons, including nylon-6/6, nyl | | |
