U.S. patent application number 13/847232 was filed with the patent office on 2013-08-29 for articles formed from polypropylene prepared with a single-site catalyst and poly(hydroxyl carboxylic acid) blends.
This patent application is currently assigned to TOTAL PETROCHEMICALS RESEARCH FELUY. The applicant listed for this patent is Fabienne Radermacher, Geert Snellings, Alain Standaert. Invention is credited to Fabienne Radermacher, Geert Snellings, Alain Standaert.
Application Number | 20130225707 13/847232 |
Document ID | / |
Family ID | 39847063 |
Filed Date | 2013-08-29 |
United States Patent
Application |
20130225707 |
Kind Code |
A1 |
Radermacher; Fabienne ; et
al. |
August 29, 2013 |
Articles Formed From Polypropylene Prepared with a Single-Site
Catalyst and Poly(hydroxyl carboxylic acid) Blends
Abstract
A resin composition comprising at least 0.1% by weight of
poly(hydroxy carboxylic acid) and at least 50% by weight of
polypropylene prepared with a single-site catalyst, preferably with
a metallocene catalyst.
Inventors: |
Radermacher; Fabienne;
(Obaix, BE) ; Standaert; Alain; (Bruxelles,
BE) ; Snellings; Geert; (Sint-lievens-houtem,
BE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Radermacher; Fabienne
Standaert; Alain
Snellings; Geert |
Obaix
Bruxelles
Sint-lievens-houtem |
|
BE
BE
BE |
|
|
Assignee: |
TOTAL PETROCHEMICALS RESEARCH
FELUY
SENEFFE (FELUY)
BE
|
Family ID: |
39847063 |
Appl. No.: |
13/847232 |
Filed: |
March 19, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12674516 |
May 19, 2011 |
8445595 |
|
|
13847232 |
|
|
|
|
Current U.S.
Class: |
521/134 ;
525/190 |
Current CPC
Class: |
C08L 67/04 20130101;
C08L 23/10 20130101; C08L 23/12 20130101; C08L 67/04 20130101; C08L
23/10 20130101; C08L 2666/18 20130101; C08L 2314/06 20130101; C08L
2666/06 20130101 |
Class at
Publication: |
521/134 ;
525/190 |
International
Class: |
C08L 23/12 20060101
C08L023/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 24, 2007 |
EP |
07114921.5 |
Aug 24, 2007 |
EP |
07114924.9 |
Aug 25, 2008 |
EP |
PCT/EP08/061098 |
Claims
1-13. (canceled)
14. An article formed from a resin composition comprising at least
0.1% by weight of poly(hydroxy carboxylic acid) and at least 50% by
weight of polypropylene prepared with a single-site metallocene
catalyst.
15. The article of claim 14, wherein the article is a thermoformed
article, a blow molded article, an injection stretch blow molded
article, an injection blow molded article, an extrusion blow
molded, a rotational molded article, a foamed article, an extruded
sheet, or a fiber.
16. The article of claim 14, wherein the article is a monolayer
article.
17. The article of claim 14, wherein the article is a multilayer
article, and wherein at least one of the layers comprises the resin
composition.
18. The article of claim 14, wherein the article is an injection
stretch blow molded article, and wherein the resin composition
exhibits a melt flow index ranging from 1.5 dg/min to 30
dg/min.
19. The article of claim 14, wherein the article is a blow molded
article, and wherein the resin composition exhibits a melt flow
index ranging from 0.3 dg/min to 3.0 dg/min.
20. The article of claim 14, wherein the article is an extruded
sheet, and wherein the resin composition exhibits a melt flow index
ranging from 2.0 dg/min to 10 dg/min.
21. The article of claim 14, wherein the article is an injection
molded article, and wherein the resin composition exhibits a melt
flow index ranging from 10 dg/min to 100 dg/min.
22. The article of claim 14, wherein the resin composition is free
of compatibiliser for compatibilising polypropylene and
poly(hydroxy carboxylic acid).
23. The article of claim 14, wherein the polypropylene is
isotactic.
24. The article of claim 14, wherein a molecular weight
distribution of the polypropylene resin is at most 5.
25. The article of claim 14, wherein the poly(hydroxy carboxylic
acid) is poly(lactic acid).
26. The article of claim 14, wherein the poly(lactic acid) is a
copolymer and the comonomers are chosen from one or more of:
aliphatic hydroxy carboxylic acids selected from glycolic acid,
3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric
acid, 5-hydroxyvaleric acid, 6-hydroxycaproic acid and combinations
thereof; and aliphatic polyesters of dihydric alcohols and dibasic
carboxylic acids.
27. The article of claim 14, wherein the single-site metallocene
catalyst comprises:
dimethylsilyl-bis(2-methyl-4-phenylindenyl)zirconium dichloride,
dimethylsilyl-bis(2-methylindenyl)zirconium dichloride,
dimethylsilyl-bis(2-methyl-4,5-benzoindenyl)zirconium dichloride,
isopropylidene(cyclopentadienyl)(fluorenyl)zirconium dichloride,
isopropylidene(2-methyl-4-tert-butyl-cyclopentadienyl)(fluorenyl)zirconiu-
-m dichloride,
isopropylidene(2-methyl-4-tert-butyl-cyclopentadienyl)(3,6-di-tert-butyl--
fluorenyl)zirconium dichloride, or combinations thereof.
28. The article of claim 14, wherein the resin composition
comprises: from 0.1 to 49.9 wt % of the poly(hydroxy carboxylic
acid) and from 50 to 99.9 wt % of the polypropylene.
29. The article of claim 14, wherein the resin composition
comprises: from 0.1 to 30 wt % of the poly(hydroxy carboxylic acid)
and from 70 to 99.9 wt % of the polypropylene.
30. The article of claim 14, wherein the resin composition
comprises: from 0.1 to 20 wt % of the poly(hydroxy carboxylic acid)
and from 80 to 99.9 wt % of the polypropylene.
31. The article of claim 14, wherein the resin composition
comprises: from 0.1 to 15 wt % of the poly(hydroxy carboxylic acid)
and from 85 to 99.9 wt % of the polypropylene.
32. The article of claim 14, wherein the resin composition
comprises: from 0.1 to 10 wt % of the poly(hydroxy carboxylic acid)
and from 90 to 99.9 wt % of the polypropylene.
Description
FIELD OF THE INVENTION
[0001] This invention is related to blends of poly(hydroxy
carboxylic acid)s with polypropylene. In particular the invention
is directed to blends of poly(lactic acid) with polypropylene
prepared with single-site catalysts, preferably metallocene
catalysts.
BACKGROUND OF THE INVENTION
[0002] In the past few years, the general public has become
increasingly apprehensive of the impact man-made waste has on the
environment. Hence there is a growing interest in developing novel
biodegradable (and preferably compostable) plastics from renewable
resources.
[0003] One particularly interesting candidate for this task is
poly(hydroxy carboxylic acid), in particular poly(lactic acid)
(PLA), now commercially available on a relatively large scale. The
lactic acid is obtained from plants such as corn and sugar-cane or
other sugar- or starch-producing plants. Not only is PLA obtainable
from renewable materials, it is also industrially compostable. For
these reasons, there is significant interest in using PLA as a
substitute in applications, where petroleum-based thermoplastics
have conventionally been used.
[0004] Unfortunately, PLA used on its own does not have the same
advantageous properties as conventional plastics do. In particular
PLA has performance problems related to heat resistance,
brittleness and limited flexibility, resulting in poor mechanical
strength. On the other hand, polyolefins, such as polypropylene,
have much better mechanical properties. It has been attempted to
combine these properties by blending PLA with polypropylene to
obtain a resin that is at least partially obtainable from renewable
resources, but still has acceptable mechanical properties. However,
it is known that blending PLA with conventional polypropylenes such
as Ziegler-Natta-catalysed polypropylenes provides heterogeneous
resin blends, due to the differences in polarity and molecular
weight distribution of the two components. In the past,
compatibilising agents were used to increase the homogeneity of the
blends. However, this requires an additional industrial step, as
well as specific conditions during extrusion. Furthermore, the
addition of compatibilising agents is expensive and changes the
properties of the desired product. Thus both the compatibilising
agent and the by-products change the properties of the desired end
product, be it a film, fibre or moulded object.
[0005] JP 2005307128 A discloses a blend of PLA and polypropylene
using a compatibilising agent, in this case a polypropylene grafted
with a vinyl carboxylic acid, vinyl anhydride or another vinyl
derivative.
[0006] JP 2006348060 A also describes a thermoplastic resin
comprising from 20-90wt % PLA and 10-80wt % polypropylene with 1-20
pts.wt of compatibiliser.
[0007] EP 1 777 263 A also teaches mixing polyolefins with PLA by
using a compatibiliser, wherein the compatibiliser is a
hydrogenated, diene-based polymer containing at least one
functional group selected from carboxyl group, acid anhydride
group, epoxy group, (meth)acryl group, amino group, alkoxysilyl
group, hydroxyl group, isocyan ate group and oxazoline group.
[0008] US 2005/0192405 A discloses a polymer blend of PLA and
polyolefins. The two components are mixed by including a
polyalkylacrylic ester and/or a polyvinyl ester, as well as a block
copolymer of a polyalkylacrylic ester and a polyolefin and/or a
block copolymer of a polyvinyl ester and a polyolefin, which act as
compatibilising agents.
[0009] It is hence an object of the invention to develop a
polypropylene-based resin, that is at least partially obtainable
from renewable resources and has better or at least similar
mechanical properties than hitherto known blends of polypropylene
with resins obtainable from renewable resources.
[0010] It is also an object of the invention to develop a resin
that is at least partially obtainable from renewable resources and
has improved mechanical properties in comparison with poly(hydroxy
carboxylic acid)s.
[0011] Additionally, it is an object of the invention to develop a
resin that is at least partially obtainable from renewable
resources and has similar mechanical properties to
polypropylene.
[0012] It is hence an object of the invention to develop a resin
that has better gas barrier properties than polypropylene.
[0013] It is also an object of the invention to develop a resin
with better surface tension properties than polypropylene.
[0014] Furthermore, it is an object of the invention to blend
polypropylene with poly(hydroxy carboxylic acid)s without having to
use compatibilising agents to obtain homogeneous blends.
[0015] It is also an object of the invention to find a resin at
least partially obtainable from renewable resources that can be
used in film, fibre, thermoforming, blow moulding, injection
stretch blow moulding, extrusion blow moulding or rotational
moulding applications.
[0016] At least one of the above objects is achieved with the
implementation of the current invention.
SUMMARY OF THE INVENTION
[0017] The present invention solves at least one of the problems
mentioned above by providing a resin composition comprising at
least 0.1% and less than 50% by weight of poly(hydroxy carboxylic
acid) and at least 50% by weight of polypropylene prepared with a
single-site catalyst, in particular metallocene catalysts.
[0018] According to another embodiment, the resin composition
comprises more than 50% by weight of polypropylene prepared with a
single-site catalyst, in particular metallocene catalysts.
[0019] According to another embodiment, the resin composition
essentially consists of poly(hydroxy carboxylic acid) and
polypropylene prepared with a single-site catalyst, in particular
metallocene catalysts.
[0020] The invention also covers the process for making the resin
composition of the present invention.
[0021] Furthermore, the invention covers the use of poly(hydroxy
carboxylic acids) to change the properties of polypropylene
prepared with single-site catalysts, for example metallocene
catalysts.
[0022] The invention also includes the use of polypropylene resin,
in particular, polypropylene prepared with a single-site catalyst,
as an impact resistance modifier for poly(hydroxy carboxylic
acid)s.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 shows scanning electron microscope (SEM) image of the
microstructure of a cast film according to the invention comprising
a metallocene-catalysed polypropylene (mPP) and PLA.
[0024] FIG. 2 shows an SEM image of the microstructure of a cast
film comprising Ziegler-Natta catalysed (znPP) and PLA.
[0025] FIG. 3 shows an SEM image of a film comprising mPP and
PLA.
[0026] FIG. 4 shows an SEM image of the surface of an injection
moulded sample comprising mPP and PLA.
[0027] FIG. 5 shows an SEM image of the surface of an injection
moulded sample comprising znPP and PLA.
DETAILED DESCRIPTION OF THE INVENTION
[0028] As described above the present invention relates to a
composition comprising a resin blend of poly(hydroxy carboxylic
acid) and polypropylene prepared with a single-site catalyst, in
particular metallocene catalysts.
[0029] Until now, it has been assumed that it would be impossible
to achieve homogeneous blends of poly(hydroxy carboxylic acid)s and
polypropylene without using a compatibilising agent, especially in
view of the difference in polarities. However, surprisingly this is
not the case. In fact, the blends are sufficiently homogeneous and
provide surprisingly acceptable properties, such that they can be
used in compositions for films, fibres, thermoforming, injection
blow moulding, extrusion blow moulding, injection stretch blow
moulding and rotational blow moulding and the like. It is thought
that the more similar the molecular structure of the two
components, the more miscible they become, despite differences in
polarity.
[0030] The Poly(Hydroxy Carboxylic Acid)
[0031] The poly(hydroxy carboxylic acid) can be any polymer wherein
the monomers are derived from renewable resources and comprise at
least one hydroxyl group and at least carboxyl group. The hydroxy
carboxylic acid monomer is preferably obtained from renewable
resources such as corn and sugar cane or other sugar- or
starch-producing plants. Preferably, the poly(hydroxy carboxylic
acid) used according to the invention is at least partially
obtainable from renewable resources. The term "poly(hydroxy
carboxylic acid)" includes homo- and co-polymers herein as well as
blends of one or more such polymers.
[0032] The poly(hydroxy carboxylic acid) can be represented as in
Formula I:
##STR00001##
wherein [0033] R9 is hydrogen or a branched or linear alkyl
comprising from 1 to 12 carbon atoms; [0034] R10 is optional and
can be a branched, cyclic or linear alkylene chains comprising from
1 to 12 carbon atoms; and [0035] "r" represents the number of
repeating units of R and is any integer from 30 to 15000.
[0036] The monomeric repeating unit is not particularly limited, as
long as it is aliphatic and has a hydroxyl residue and a carboxyl
residue. Examples of possible monomers include lactic acid,
glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid,
4-hydroxyvaleric acid, 5-hydroxyvaleric acid and 6-hydroxycaproic
acid to make for example poly(lactic acid), poly(glycolic acid),
poly(3-hydroxybutyric acid), poly(4-hydroxybutyric acid),
poly(4-hydroxyvaleric acid), poly(5-hydroxyvaleric acid) and
poly(6-hydroxycaproic acid), respectively.
[0037] The monomeric repeating unit may also be derived from a
cyclic monomer or cyclic dimer of the respective aliphatic
hydroxycarboxylic acid. Examples of these include lactide,
glycolide, .beta.-propiolactone, .beta.-butyrlactone,
.gamma.-butyrolactone, .gamma.-valerolactone,
.delta.-valerolactone, .epsilon.-caprolactone and the like.
[0038] In the case of asymmetric carbon atoms within the hydroxy
carboxylic acid unit, each of the D-form and the L-form as well as
mixtures of both may be used. This includes racemic mixtures can
also be used.
[0039] The poly(hydroxy carboxylic acid) may optionally comprise
one or more comonomer(s).
[0040] The comonomer can be a second different hydroxycarboxylic
acid as defined above in Formula I. The weight percentage of each
hydroxycarboxylic acid is not particularly limited.
[0041] The comonomer can also comprise dibasic carboxylic acids and
dihydric alcohols. These react together to form aliphatic esters,
oligoesters or polyesters as shown in Formula II having a free
hydroxyl end group and a free carboxylic acid end group, capable of
reacting with hydroxy carboxylic acids, such as lactic acid and
polymers thereof.
##STR00002##
wherein [0042] R11 and R12 are branched or linear alkylenes
comprising from 1 to 12 carbon atoms and can be the same or
different; [0043] "t" represents the number of repeating units T
and is any integer of at least 1
[0044] These copolymers are also within the scope of the invention.
The sum of the number of repeating units "r" (Formula I) and "t"
(Formula II) is any integer from 30 to 15000. The weight
percentages of each monomer i.e. the hydroxycarboxylic acid monomer
and the aliphatic ester, oligoester or polyester comonomer of
Formula II are not particularly limited. Preferably, the
poly(hydroxy carboxylic acid) comprises at least 50 wt % of
hydroxycarboxylic acid monomers and at most 50 wt % of aliphatic
ester, oligoester or polyester comonomers.
[0045] The dihydric alcohols and the dibasic acids that can be used
in the aliphatic polyester unit as shown in Formula II are not
particularly limited. Examples of possible dihydric alcohols
include ethylene glycol, diethylene glycol, triethyleneglycol,
propylene glycol, dipropylene glycol, 1,3-butanediol,
1,4-butanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol,
1,7-octanediol, 1,9-nonanediol, neopentyl glycol,
1,4-cyclohexanediol, isosorbide and 1,4-cyclohexane dimethanol and
mixtures thereof.
[0046] Aliphatic dibasic acids include succinic acid, oxalic acid,
malonic acid, glutaric acid, adipic acid, pimelic acid, suberic
acid, azelaic acid, sebacic acid; undecanoic diacid, dodecanic
diacid and 3,3-dimethylpentanoic diacid, cyclic dicarboxylic acids
such as cyclohexanedicarboxylic acid and mixtures thereof. The
dibasic acid residue in the hydroxy carboxylic acid copolymer can
also be derived from the equivalent diacylchlorides or diesters of
the aliphatic dibasic acids.
[0047] In the case of asymmetric carbon atoms within the dihydric
alcohol or the dibasic acid, each of the D-form and the L-form as
well as mixtures of both may be used. This includes racemic
mixtures.
[0048] The copolymer can be an alternating, periodic, random,
statistical or block copolymer.
[0049] Polymerisation can be carried out according to any method
known in the art for polymerising hydroxy carboxylic acids.
Polymerisation of hydroxy carboxylic acids and their cyclic dimers
is carried out by polycondensation or ring-opening polymerisation,
respectively.
[0050] Copolymerisation of hydroxycarboxylic acids can be carried
out according to any method known in the art. The hydroxycarboxylic
acid can be polymerised separately prior to copolymerisation with
the comonomer or both can be polymerised simultaneously.
[0051] In general, the poly(hydroxy carboxylic acid), homo- or
copolymer (copolymerised with a second different hydroxy carboxylic
acid or with an aliphatic ester, oligoester or polyester as
described above), may also comprise branching agents. These
poly(hydroxy carboxylic acid)s can have a branched, star or
three-dimensional network structure. The branching agent is not
limited so long as it comprises at least three hydroxyl groups
and/or at least three carboxyl groups. The branching agent can be
added during polymerisation. Examples include polymers such as
polysaccharides, in particular cellulose, starch, amylopectin,
dextrin, dextran, glycogen, pectin, chitin, chitosan and derivates
thereof. Other examples include aliphatic polyhydric alcohols such
as glycerine, pentaerythritol, dipentaerythritol,
trimethylolethane, trimethylolpropane, xylitol, inositol and the
like. Yet another example of a branching agent is an aliphatic
polybasic acid. Such acids include cyclohexanehexacarboxylic acid,
butane-1,2,3,4-tetracarboxylic acid, 1,3,5-pentane-tricarboxylic
acid, 1,1,2-ethanetricarboxylic acid and the like.
[0052] The total molecular weight of the poly(hydroxy carboxylic
acid) depends on the desired mechanical and thermal properties and
mouldability of the final resin composition. It is preferably from
5,000 to 1,000,000 g/mol, more preferably from 10,000 to 500,000
g/mol and even more preferably from 35,000 to 200,000 g/mol. Most
preferably the total molecular weight of the polymer is from 50,000
to 150,000 g/mol.
[0053] The molecular weight distribution is generally monomodal.
However, in the case of mixtures of two or more fractions of
poly(hydroxy carboxylic acid)s of different weight average
molecular weight and/or of different type, the molecular weight
distribution can also be multimodal e.g. bi- or trimodal.
[0054] From a standpoint of availability, transparency, renewable
resources and compostability the poly(hydroxy carboxylic acid) is
preferably a poly(lactic acid) (PLA). Preferably, the PLA is a
homopolymer obtained either directly from lactic acid or from
lactide, preferably from lactide.
[0055] The Polypropylene
[0056] The polypropylenes used in this invention are prepared using
single-site catalysts, preferably metallocene catalysts.
[0057] The term "polypropylene" herein includes homopolymers and
copolymers having .alpha.-olefin comonomers. The term
"polypropylene" herein also includes blends of two or more
polypropylenes as defined below.
[0058] If the polypropylene is a copolymer, the comonomer can be
any a-olefin i.e. any 1-alkylene comprising from 2 to 12 carbon
atoms (except propylene itself), for example, ethylene, 1-butene,
1-pentene and 1-hexene. The copolymer can be an alternating,
periodic, random, statistical or block copolymer.
[0059] Preferably, the polypropylene used in the resin composition
of the invention is a homopolymer or a copolymer of propylene and
ethylene.
[0060] Propylene is polymerised at low-pressure in the presence of
a single-site catalyst. Preferably, the catalyst is a metallocene
catalyst. If required, more than one catalyst of the same or
different type can be used, either simultaneously in one reactor,
in two parallel reactors or in two reactors connected to each other
in series, to obtain multimodal or broader molecular weight
distributions.
[0061] The polypropylene can be syndiotactic, isotactic or atactic.
Isotactic polypropylenes can be obtained using Ziegler-Natta
catalysts or appropriate single-site catalysts (in particular
metallocene catalysts). Syndiotactic and atactic polypropylenes are
obtainable using appropriate single-site catalysts (in particular
metallocene catalysts). Isotactic polypropylene is generally
selected.
[0062] The overall properties of the polypropylene are dependent on
the method and type of single-site catalyst used. A single-site
catalyst is for example a metallocene catalyst or a constrained
geometry catalyst. It has been found that poly(hydroxy carboxylic
acid)s are more miscible with single-site catalysed polypropylene,
in particular metallocene-catalysed polypropylene, than those
blended with Ziegler-Natta polypropylene. Blends of single-site
catalysed polypropylenes, in particular metallocene-catalysed
polypropylenes, with poly(hydroxy carboxylic acid)s are very
homogeneous and do not require any compatibilisation. Examples of
suitable polypropylenes prepared with single-site catalysts include
those catalysed by one or more of the following metallocenes:
dimethylsilyl-bis(2-methyl-4-phenylindenyl)zirconium dichloride,
dimethylsilyl-bis(2-methylindenyl)zirconium dichloride,
dimethylsilyl-bis(2-methyl-4,5-benzoindenyl)zirconium dichloride,
isopropylidene(cyclopentadienyl)(fluorenyl)zirconium dichloride,
isopropylidene(2-methyl-4-tert-butyl-cyclopentadienyl)(fluorenyl)zirconiu-
m dichloride and
isopropylidene(2-methyl-4-tert-butyl-cyclopentadienyl)(3,6-di-tert-butyl--
fluorenyl)zirconium dichloride.
[0063] Compared to other polypropylenes, single-site catalysed
polypropylenes, in particular metallocene-catalysed polypropylenes,
have a much narrower molecular weight distribution. Preferably, the
molecular weight distribution is at most 10, preferably at most 7,
more preferably at most 5, most preferably at most 4. The narrow
molecular weight distribution is compatible with the similarly
narrow molecular weight distribution of poly(hydroxy carboxylic
acid)s.
[0064] Without wishing to be bound by theory, it is thought,that
the molecular structure of single-site catalysed polypropylenes, in
particular metallocene-catalysed polypropylenes, induces a better
compatibility with poly(hydroxy carboxylic acid)s as well. These
polypropylenes show no or very little long chain branching. The
incorporation of comonomers, if present, occurs very regularly
along the polypropylene's backbone resulting in a highly uniform
distribution of comonomers i.e. regular short chain branching. This
effect (known as very narrow "short chain branching distributions"
(SCBD)) in polypropylene is specific to single-site catalysed
polypropylenes, in particular metallocene-catalysed polypropylenes.
As a result, during crystallization from the melt, very small
crystallites are formed throughout the material, thus providing
excellent optical clarity. Ziegler-Natta-catalysed polypropylenes
on the other hand, have a poor and very random comonomer
incorporation, therefore a broad distribution of different sizes of
crystallites occurs during crystallisation, resulting in high haze
values.
[0065] The Applicant believes, without wishing to be bound by
theory, that since the molecular architecture of poly(hydroxy
carboxylic acid)s is similar to that of single-site catalysts (in
particular metallocene catalysts), i.e. narrow molecular weight
distribution, poly(hydroxy carboxylic acid)s are more compatible
with single-site catalysed polypropylenes, in particular
metallocene-catalysed polypropylenes, than with other
polypropylenes.
[0066] Additionally, additives can be included in one or more
components of the blend, they can be added during blending, and/or
they can be included in a product formed from the blend, such as a
film, as desired. Such additives are well known in the art, and can
include, for example: antioxidants (e.g., hindered phenolics such
as IRGANOX.TM. 1010 or IRGANOX.TM. 1076 available from Ciba.TM.);
phosphites (e.g., IRGAFOS.TM. 168 available from Ciba.TM.);
anti-cling additives; tackifiers, such as polybutenes, terpene
resins, aliphatic and aromatic hydrocarbon resins, alkali metal and
glycerol stearates and hydrogenated rosins; UV stabilizers; heat
stabilizers; anti-blocking agents; release agents; anti-static
agents; pigments; colorants; carbon black; dyes; waxes; silica;
fillers; talc, anti-acid compounds; peroxides; grafting agents;
lubricants; clarifying agents; nucleating agents and the like.
[0067] Blending of Poly(Hydroxy Carboxylic Acid) with
Polypropylene
[0068] The blending of the poly(hydroxy carboxylic acid) with the
polypropylene, prepared with a single-site catalyst, can be carried
out according to any physical blending method and combinations
thereof known in the art, dry blending, wet blending or melt
blending. The blending conditions depend upon the blending
technique and polypropylene involved. Depending on the method, the
polypropylene and the poly(hydroxy carboxylic acid) can be in any
appropriate form, for example, fluff, powder, granulate, pellet,
solution, slurry, and/or emulsion.
[0069] If dry blending of the polymer is employed, the dry blending
conditions may include temperatures from room temperature up to
just under the melting temperature of the polymer. The components
can be dry blended prior to a melt blending stage, which can take
place for example in an extruder.
[0070] Melt processing is fast and simple and makes use of standard
equipment of the thermoplastics industry. The components can be
melt blended in a batch process such as with a Banbury, Haake or
Brabender Internal Mixer or in a continuous process, such as with
an extruder e.g. a single or a twin screw extruder. During melt
blending, the temperature at which the polymers are combined in the
blender will generally be in the range between the highest melting
point of the polymers employed and up to about 80.degree. C. above
such melting point, preferably between such melting point and up to
30.degree. C. above such melting point. The time required for the
melt blending can vary broadly and depends on the method of
blending employed. The time required is the time sufficient to
thoroughly mix the components. Generally, the individual polymers
are blended for a time of at least 10 seconds, preferably of about
10 seconds up to about 10 minutes, preferably up to about 5
minutes, more preferably up to about 2 minutes.
[0071] The components can also be wet blended whereby at least one
of the components is in solution or slurry form. If solution
blending methods are employed, the blending temperature will
generally be 25.degree. C. to 50.degree. C. above the cloud point
of the solution involved. The solvent or diluent is then removed by
evaporation to leave behind a homogeneous blend of poly(hydroxy
carboxylic acid) and polypropylene.
[0072] According to an embodiment, the resin composition comprises
at least 0.1% and less than 50% by weight of poly(hydroxy
carboxylic acid) and at least 50% by weight of polypropylene,
preferably more than 50% by weight of polypropylene.
[0073] More preferably, the resin composition comprises from 0.1 to
49.9 wt % of poly(hydroxy carboxylic acid), preferably from 0.1 to
30 wt %, more preferably from 0.1 to 20 wt %, even more preferably
from 0.1 to 15 wt % and most preferably from 0.1 to 10 wt %. The
resin composition comprises from 50 to 99.9 wt % of polypropylene,
preferably from 70 to 99.9 wt %, more preferably from 80 to 99.9 wt
%, even more preferably from 85 to 99.9 wt % and most preferably
from 90 to 99.9 wt %.
[0074] Preferably, the resin composition essentially consists of
polypropylene and poly(hydroxy carboxylic acid) i.e. at least 0.1
and less than 50 wt % of poly(hydroxy carboxylic acid) and 50 to
99.9 wt % of polypropylene.
[0075] In a preferred embodiment, according to the invention, the
composition does not require compatibiliser for compatibilising
polypropylene and poly(hydroxy carboxylic acid) i.e. it is free of
such compatibilisation agents.
[0076] The resin composition according to the invention can also be
used in blends with other resin compositions to be used in the same
applications as mentioned in the following section.
[0077] The content of poly(hydroxy carboxylic acid) within the
composition of the invention renders it partially compostable.
[0078] Compostability is herein defined as provided by the standard
EN 13432:2000. In order for packaging material to be biodegradable
it must have a lifecycle, which can be described as follows: [0079]
a period of storage and/or use starting from time t.sub.0, which is
the moment the material comes off the production line; [0080] a
period of disintegration starting at time t.sub.1, during which the
polymer begins to significantly chemically disintegrate e.g. via
the hydrolysis of ester bonds; [0081] a period of biodegradation,
during which the partly hydrolysed polymer biologically degrades as
a result of the action of bacteria and micro organisms;
[0082] It is important to make the distinction between degradable,
biodegradable and compostable as often these terms are used
interchangeably. In addition to the above, a compostable plastic is
"capable of undergoing biological decomposition in a compost site
as part of an available program, such that the plastic is not
visually distinguishable and breaks down to carbon dioxide, water,
inorganic compounds, and biomass, at a rate consistent with known
compostable materials (e.g. cellulose) and leaves no toxic residue"
(ASTM). On the other hand a degradable plastic is one which is
merely chemically changed i.e. there is no requirement for the
plastic to be biologically degraded by microorganisms. Therefore, a
degradable plastic is not necessarily biodegradable and a
biodegradable plastic is not necessarily compostable (that is, it
breaks down too slowly and/or leaves toxic residue).
[0083] In particular, the EN 13432:2000 standard for compostability
has the following main features: [0084] Disintegration is measured
by sieving the material to determine the biodegraded size. To be
considered compostable, less than 10% of the material should be
larger than 2 mm in size. [0085] Biodegradability is determined by
measuring the amount of carbon dioxide produced over a certain time
period by the biodegrading plastic. To be considered compostable,
it must be 90% biodegraded within 90 days. [0086] Eco-toxicity is
measured by determining whether the concentration of heavy metals
is below the limits set by the standard and by testing plant growth
by mixing the compost with soil in different concentrations and
comparing it with controlled compost.
[0087] Applications of the Resin Composition
[0088] Due to the improved mechanical properties of the resin
composition stemming from the presence of polypropylene, as well as
the presence of material from renewable resources and
compostability of the resin composition resulting from the presence
of poly(hydroxy carboxylic acid), it is suitable for a wide variety
of applications, including films and moulding applications, as
described below.
[0089] The resin composition is particularly suitable for
transformation into a film, for example cast, blown, uni-oriented
and bi-oriented film. It has been surprisingly found that films
formed from polymer blends of the invention exhibit improved
properties, particularly improved dart impact properties and
tensile strengths, relative to films of 100% poly(hydroxy
carboxylic acid). Films comprising the resin composition of the
invention have improved printability in comparison to films
consisting only of polypropylene due to the higher surface tension
of poly(hydroxy carboxylic acid)s, like PLA. The films according to
the invention also have increased thermal and high frequency
sealability in comparison to 100% polypropylene films. The films
provide higher hot-tack strengths in comparison to
polypropylene-based films. The presence of poly(hydroxy carboxylic
acid)s also increases the stiffness of the film and provides
enhanced water breathability in comparison to polypropylene alone.
The film also has improved barrier properties against atmospheric
gases, in particular oxygen, carbon dioxide and nitrogen in
comparison to films consisting solely of polypropylene.
[0090] The polymer blends of the invention can be used to form cast
or blown films having a single layer (monolayer films) or multiple
layers (multilayer films). When used in multilayer films, the
polymer blends according to the invention can be used in any layer
of the film, or in more than one layer of the film, as desired.
When more than one layer of the film is formed using a polymer
blend of the present invention, each such layer can be individually
formulated, i.e. the layers formed can be the same or different in
chemical composition, density, melt index, thickness and so on,
depending upon the desired properties of the film. The other
layer(s) can include resins comprising only poly(hydroxy carboxylic
acid), for example PLA, or only a polypropylene, or also resins
comprising, for example, high-pressure polymerised low-density
polyethylene (LDPE), LLDPE, MDPE or HDPE. Further, one skilled in
the art will understand that the layers of a multilayer film must
have the appropriate viscosity match.
[0091] The thickness of each layer of the film and of the overall
film, are not particularly limited, but are determined according to
the desired properties of the film. Typical film layers have a
thickness of about 1 to 1000 .mu.m, more typically about 5 to 100
.mu.m, and typical films have an overall thickness of 5 to 200
.mu.m, more typically 5 to 100 .mu.m.
[0092] Preferably, the present invention provides a single-layer
(monolayer) film formed using any of the polymer blends of the
invention. According to another embodiment this film is 10 to 150
.mu.m thick.
[0093] The films of the present invention may be formed by any
number of well-known extrusion or co-extrusion techniques. Any of
the blown or chill roll techniques commonly used are suitable. For
example, the composition can be extruded in a molten state through
a flat die and then cooled to form a film. Alternatively, the
composition can be extruded in a molten state through an annular
die and then blown and cooled to form a tubular, blown film, which
can then be axially slit and unfolded to form a flat film.
[0094] As a specific example, cast films can be prepared using a
pilot scale commercial cast film line machine as follows. Pellets
of the polymeric blend are melted at temperatures ranging from
about 220.degree. C. to about 270.degree. C., with the specific
melt temperature being chosen to match melt viscosities of the
various resins. The flow is then extruded through a single manifold
film extrusion die to the desired width. The die gap opening is
typically about 600 .mu.m. The material is then drawn down to the
final gauge. A vacuum box or air knife can be used to pin the melt
exiting the die opening to a primary chill roll maintained at a
temperature less than 35.degree. C., preferably at about 32.degree.
C.
[0095] As another example, blown films can be prepared as follows.
The film can be for instance produced using a blown film line using
a die with a die gap of 1.0-2.0 mm, a die diameter of 1-100 mm,
preferably 50 mm and a length to diameter ratio (UD) of 25. The
blow-up ratio (BUR) can range from 1.0 to 10.0, preferably from 1.0
to 5.0, more preferably 1.3-3.5. The film can then be extruded
through the die into a film and cooled, for example by blowing air
onto the surface of the film. In industrial processes, the film is
then preferably drawn from the die to form a cylindrical film that
is cooled, collapsed and optionally subjected to a desired
auxiliary process, such as slitting, treating, sealing or printing.
The finished film can be wound into rolls for later processing and
converting.
[0096] Multiple-layer films may be formed by methods well known in
the art. The materials forming each layer may be coextruded through
a co-extrusion feedblock and die assembly to yield a film with two
or more layers adhered together but differing in composition.
Co-extrusion can be adapted to the cast film or the blown film
processes. Multiple-layer films may also be formed by extrusion
coating, whereby a substrate material is contacted with the hot
molten polymer as the polymer exits the die.
[0097] There are many potential applications for the films produced
from the polymer blends described herein. These films can be made
into other forms, such as tape, by any one of a number of
well-known cutting, slitting, and/or rewinding techniques. They may
be useful as stretch, sealing, or oriented films. Surface tension
is improved in relation to polypropylene films. However, the
surface tension can be improved even further by any known and
conventional post-forming techniques such as corona discharge,
chemical treatment, flame treatment, and the like.
[0098] Films according to the invention can be used as cling films,
stretch films, shrink films, bags, lamination films, liners, diaper
films, candy wrappers or for a variety of other suitable end-use
applications that will be apparent to those skilled in the art. The
films can also be applied in packaging material, such as for
bundling and unitizing a variety of products; flexible food
packaging, including frozen food packaging; bags, such as trash
bags and bin liners, industrial liners, shipping sacks and produce
bags; and surface protection applications, with or without
stretching, such as in the temporary protection of surfaces during
manufacturing or transportation.
[0099] The composition is also suitable for typical injection,
extrusion, stretch and injection stretch blow moulding
applications, but also thermoforming, foaming and rotational
moulding applications. In particular, the addition of poly(hydroxy
carboxylic acid)s improve the mechanical properties of injection
moulded articles of polypropylene. In particular, rigidity is
increased. The articles made according to these processes can be
mono- or multilayer, at least one of the layers comprising the
resin composition of the invention.
[0100] The person skilled in the art is aware that the suitable
melt flow range of the resin composition depends upon the
respective method of forming an article. Thus, for injection
stretch blow molding (ISBM) the preferred melt flow index range is
from 1.5 dg/min to 30 dg/min. For cast film extrusion the preferred
melt flow index range is from 3.0 dg/min to 15 dg/min. For blown
film extrusion the preferred melt flow index range is from 0.3
dg/min to 3.0 dg/min. For blow molding the preferred melt flow
index range is from 0.3 dg/min to 3.0 dg/min. For sheet extrusion
the preferred range is from 2.0 dg/min to 10 dg/min. For injection
molding the preferred range is from 10 dg/min to 100 dg/min.
[0101] The following are non-limiting examples illustrating the
invention.
EXAMPLES
[0102] The PLA used in the examples is PLA Terramac.RTM. 6201. The
properties of this PLA are provided in Table 1 below.
TABLE-US-00001 TABLE 1 PLA Density/g/cm.sup.3 1.26 at 23.degree. C.
Melt index/g/10 min 9-10 at 233 ppm H.sub.20 18-20 at 1000 ppm
H.sub.20 MW/Da 106940 MWD 1.75
[0103] Densities of the PLA were measured according to ASTM D
1505.
[0104] Melt indices for PLA were measured according to ASTM D 1238,
i.e. at 190.degree. C. using a load of 2.16 kg, carried out once in
the presence of 233 ppm water and once in the presence of 1000 ppm
water.
[0105] MW and MWD for PLA were determined using GPC, where the PLA
was dissolved in choloform and measurements were taken at
25.degree. C.
[0106] Cast Films
[0107] Cast films were prepared using a pilot scale commercial cast
film line machine as follows. Compounded and dry blends of 90 wt %
metallocene-catalysed polypropylene with 10 wt % of poly(lactic
acid) PLA Terramac.RTM. 6201 were prepared. The pellets of the
polymeric blend were melted. The flow was then extruded through a
single manifold film extrusion die at temperature of about
40.degree. C. to the desired width. The die gap opening was about
600 .mu.m. The material was then drawn down to the final gauge. The
melt exiting the die opening to a primary chill roll was maintained
at about 32.degree. C.
[0108] Films 1-7 had a film thickness of about 50 .mu.m.
[0109] The metallocene catalysed polypropylene mPP A is a
homopolymer polypropylene resin having a melt index of 15 g/10 min
as measured according to ISO 1133, condition L, at a temperature of
230.degree. C. under a load of 2.16 kg
[0110] The metallocene catalysed polypropylene mPP B is a
homopolymer polypropylene resin having a melt index of 25 g/10 min
as measured according to ISO 1133, condition L, at a temperature of
230.degree. C. under a load of 2.16 kg.
[0111] ZnPP is a Ziegler-Natta catalysed polypropylene.
[0112] The results are provided in Tables 2 and 3. Table 2 clearly
shows the improvements of the resin composition comprising mPP A in
comparison with the composition comprising znPP. Particularly the
tensile strengths are improved.
[0113] The SEM of films 3 and 4 are represented by FIGS. 1 and 2,
respectively.
TABLE-US-00002 TABLE 2 Film 1 Film 2 Film 3 Film 4 Compounded
Compounded Dry blend Dry blend 90 wt % mPP 90 wt % mPP of 90 wt %
of 90 wt % A + 10 A + 10 mPP A + 10 znPP + 10 Film 5 wt % PLA wt %
PLA wt % PLA wt % PLA mPP A Processing parameters Rolls .degree. C.
40 25 25 25 25 Temperature Rolls Speed m/min 6 4 4 4 4 Film
Properties Haze % 38 21 25 29 1.2 Gloss 45.degree. % 41 60 55 46.8
89 Average dart g <20 <20 <20 <20 244 impact Tensile
Strength at MPa 24 29 29 18 25 yield MD Strength at MPa 45 16 30 10
35 break MD Elongation % 695 233 321 188 522 at break MD Strength
at MPa 18 25 20 10 25 yield TD Strength at MPa 20 18 22 6 39 break
TD Elongation % 444 15 170 21 573 at break TD
[0114] The SEM of film 6 is shown in FIG. 3. It clearly
demonstrates the excellent dispersion of the PLA lamellas in the
polypropylene resin.
TABLE-US-00003 TABLE 3 Film 6 Compounded Film 7 90 wt % mPP B + 10
wt % PLA mPP B Processing parameters Rolls Temperature .degree. C.
25 25 Rolls Speed m/min 4 4 Film Properties Haze % 18.1 0.1 Gloss
45.degree. % 68.8 90.3 Average dart impact g <20 105 Elmendorf
tear resistance MD N/mm 13.9 17.0 Tensile Strength at yield MPa 28
24 MD
[0115] Elmendorf tear strength was measured in the machine
direction (MD) according to ASTM D 1922
[0116] Dart impact strength (Dart) was measured according to ASTM D
1709.
[0117] Measurements for tensile strength at yield in the machine
direction (MD) and in the transverse direction (TD) were carried
out according to ASTM D 882-02.
[0118] Gloss was measured according to ASTM D 2457 at an angle of
45.degree..
[0119] Haze was measured according to ISO 14782.
[0120] Injection Moulding
[0121] Table 4 shows the results obtained from injection moulding,
according to the processing parameters provided therein, a
compounded resin composition containing mPP A and PLA in comparison
with injection moulding of the mPP A resin alone. It clearly
demonstrates the improvements in mechanical properties obtained by
using PLA in mPP resins.
[0122] The metallocene catalysed polypropylene mPP A is a
homopolymer polypropylene resin having a melt index of 15 g/10 min
as measured according to ISO 1133, condition L, at a temperature of
230.degree. C. under a load of 2.16 kg.
TABLE-US-00004 TABLE 4 Sample 1 Compounded 90 wt % mPP A + Sample 2
10 wt % PLA mPP A Processing parameters Melt temperature .degree.
C. 230 200 Dynamic pressure bar 287 466 Holding pressure bar 320
520 Mechanical Properties Elastic modulus MPa 1576 1433 Modulus at
1% MPa 1423 1257 Flexural modulus MPa 1462 1311 Notched Izod at
23.degree. C. kJ/m.sup.2 2.8 3.4
[0123] Flexural modulus was measured according to ISO 178.
[0124] Notched Izod impact strength was measured according to ISO
180.
[0125] FIGS. 4 and 5 are SEM images of injected moulded samples of
90wt % mPP A and 10wt % PLA (Sample 3) and 90wt % znPP and 10 wt %
PLA (Sample 4). The nodes of PLA in Sample 3 have a diameter of on
average only 0.7 .mu.m in size, whereas the nodes of PLA in Sample
4 have a diameter of on average 1.4 .mu.m in size i.e. double the
size. Thus it can be said that PLA disperses more easily in
polypropylene prepared with a metallocene catalyst than in
polypropylene prepared with a Ziegler-Natta catalyst. The resin
composition of mPP and PLA is more homogeneous.
* * * * *