Patent Application
20170044359
The present invention is related to blends of polypropylene and polyethylene, which contain a specific kind of compatibilizer. Due to the addition of the specific compatibilizer a simultaneous increase in stiffness as well as impact strength and heat deflection resistance is achieved. Furthermore the present invention is related to recycled blends of polypropylene and polyethylene, containing the specific kind of compatibilizer.
Polyolefins, like polypropylene and polyethylene are typical commodity polymers with many application areas and a remarkable growth rate. The reason is not only a favourable price/performance ratio, but also the versatility of these materials and a very broad range of possible modifications, which allows tailoring of end-use properties in a wide range.
Chemical modifications, copolymerisation, blending, drawing, thermal treatment and combination of these techniques can convert common-grade polyolefins to valuable products with special properties.
Blends of polypropylene and polyethylene have attracted much interest. It is well known that the impact strength of polypropylene (PP) increases at low temperatures through the addition of polyethylene (PE). Unfortunately, PP and PE are highly immiscible resulting in a blend with poor adhesion among its phases, coarse morphology and consequently poor mechanical properties. The compatibility between the phases of a blend can be improved by the addition of compatibilizers, which results in a finer and more stable morphology, better adhesion between the phases of the blends and consequently better properties of the final product.
From literature several kinds of compatibilizers are known, like block copolymers, e.g. ethylene-propylene block copolymer and styrene-ethylene/butylene-styrene or triblock copolymers, or ethylene propylene rubber (EPR), ethylene/propylene diene copolymer (EPDM) or ethylene/vinyl acetate copolymer (EVA).
According to Wei Zhu et al.; Journal of Applied Polymer Science, Vol. 58, p. 515-521 (1995) the addition of ethylene-propylene copolymer as compatibilizer to blends of polypropylene and polyethylene can remedy the situation of high incompatibility to some extent and that ethylene-propylene rubber (EPR) or ethylene-propylene-diene rubber (EPDM) can substantially improve the toughness of the blends, but at the expense of deteriorated moduli and tensile strength. As improvement the authors of this paper suggest to use a PP-block-PE-copolymer prepared by sequential polymerization, whereby first propylene is polymerized and then ethylene is polymerized in the second step. The use of this compatibilizer leads to a small increase of elongation at break and tensile strength. Since the compatibilizer described has a very high molecular weight as expressed by its intrinsic viscosity its addition further leads to a significant reduction of processability as expressed by the melt flow rate (MFR).
Also according to Teh et al., Adv. Polym. Technol. Vol. 13, p. 1-23 (1994) the addition of ethylene-propylene rubber (EPR) can be used to compatibilize blends of polypropylene and polyethylene, resulting in improved toughness but lower moduli and heat resistance.
While the compatibilizers described by Zhu et al. are not commercially available, it is commonly known that both EPR and EPDM are more expensive than the respective blend components PP and PE due to a more complex production process.
For several applications, like pipes, profiles, containers, automotive components or household articles it is of high importance that the PP/PE-blends show high stiffness as well as high impact strength and heat deflection temperature.
It was therefore an objective of the present invention that these three properties of PP/PE-blends should be increased simultaneously. This objective has not yet been addressed so far in literature.
Furthermore the demand of using recycled polyolefins, originating from recovered waste plastic material derived from post-consumer and/or post-industrial waste, in a compound with virgin polymer has increased within the last years, not the least because legal requirements exist in some segments like automotive applications.
One of the key problems in polyolefin recycling, especially when dealing with material streams from post-consumer waste (PCW) is the difficulty to quantitatively separate polypropylene (PP) and polyethylene (PE). Commercial recyclates from PCW sources have been found generally to contain mixtures of PP and PE, the minor component reaching up to <50 wt %.
Such recycled PP/PE-blends normally suffer from deteriorated mechanical and optical properties, have poor performance in odour and taste and they generally suffer from poor compatibility between the main polymer phases, resulting in both limited impact strength and heat deflection resistance. Such inferior performance is partly caused by PE with its lower stiffness and melting point forming the continuous phase even at PP concentrations up to 65% because of the normally higher viscosity of the PE components in PCW.
This normally excludes the application for high quality parts, and it only allows the use in low-cost and non-demanding applications.
It was therefore a further objective of the present invention to increase stiffness as well as impact strength and heat deflection resistance of recycled PP/PE-blends simultaneously, in order to make them suitable to be used in a compound with a virgin polymer for e.g. automotive applications.
The finding of the present invention is that with a special kind of compatibilizer being a heterophasic polyolefin composition comprising a combination of a polypropylene and a copolymer of ethylene and propylene or C4 to C10 alpha olefin, with specific properties a simultaneous increase of stiffness as well as impact strength and heat deflection resistance of virgin as well as recycled PP/PE-blends can be achieved.
Thus the present invention is directed to polypropylene-polyethylene blends comprising
In a preferred embodiment the Component A) is a recycled material, which is recovered from waste plastic material derived from post-consumer and/or post-industrial waste.
A further embodiment of the present invention is the use of a heterophasic polyolefin composition comprising
Yet a further embodiment is the use of a blend, wherein Component A) is a recycled material, which is recovered from waste plastic material derived from post-consumer and/or post-industrial waste, in a compound with one or more virgin polymers and optionally mineral fillers or reinforcing fibres. These compounds can for example be advantageously used for automotive applications.
Component A) of the blend of the invention comprises
The polypropylene of A-1) can comprise one or more polymer materials selected from the following:
For example, a polypropylene suitable for use as component A-1) may have a density of from 0.895 to 0.920 g/cm3, preferably from 0.900 to 0.915 g/cm3, and more preferably from 0.905 to 0.915 g/cm3 as determined in accordance with ISO 1183 and a melt flow rate (MFR) of from 0.5 to 300 g/10min, preferably from 1.0 to 150 g/10 min, and alternatively from 1.5 to 50 g/10 min as determined in accordance with ISO 1133 (at 230° C.; 2.16 kg load). Usually the melting temperature of component A-1) is within the range of 135 to 170° C., preferably in the range of 140 to 168° C., more preferably in the range from 142 to 166° C. In case it is a propylene homopolymer like item (I) above it will generally have a melting temperature of from 150 to 170° C., preferably from 155 to 168° C., and more preferably from 160 to 165° C. as determined by differential scanning calorimetry (DSC) according to ISO 11357-3. In case it is a random copolymer of propylene like item (II) above it will generally have a melting temperature of from 130 to 162° C., preferably from 135 to 160° C., and more preferably from 140 to 158° C. as determined by DSC according to ISO 11357-3.
Preferably, the polypropylene of A-1) does not comprise a heterophasic copolymer like item (III) above.
The polyethylene of A-2) is preferably a high density polyethylene (HDPE) or a linear low density polyethylene (LLDPE) or a long-chain branched low density polyethylene (LDPE).
The comonomer content of A-2 is usually below 50 wt. % preferably below 25 wt. %, and most preferably below 15 wt. %.
Herein an HDPE suitable for use as A-2) in this disclosure has a density as determined according to ISO 1183 of equal to or greater than 0.941 g/cm3, preferably from 0.941 to 0.965 g/cm3, more preferably from 0.945 to 0.960 g/cm3. In one embodiment, the HDPE is an ethylene homopolymer. An HDPE suitable for use as A-2) in this disclosure may generally have an MFR determined by ISO 1133 (at 190° C.; 2.16 kg load), of from 0.01 g/10 min to 50 g/10min, preferably from 0.1 to 30 g/10min, like from 0.5 to 20 g/10 min.
The HDPE may also be a copolymer, for example a copolymer of ethylene with one or more alpha-olefin monomers such as propylene, butene, hexene, etc.
An LLDPE suitable for use as A-2) in this disclosure may generally have a density as determined with ISO 1183, of from 0.900 to 0.920 g/cm3, or from 0.905 to 0.918 g/cm3, or from 0.910 to 0.918 g/cm3 and an MFR determined by ISO 1133 (at 190° C.; 2.16 kg load), of from 0.01 to 50 g/min, or from 0.1 to 30 g/10 min, like from 0.5 to 20 g/10 min. The LLDPE is a copolymer, for example a copolymer of ethylene with one or more alpha-olefin monomers such as propylene, butene, hexene, etc.
An LDPE suitable for use as A-2) in this disclosure may generally have a density as determined with ISO 1183, of from 0.915 to 0.935 g/cm3, and an MFR determined by ISO 1133 (190° C.; 2.16 kg), of from 0.01 to 20 g/min. The LDPE is an ethylene homopolymer.
The melting temperature of component A-2) is preferably within the range of 100 to 135° C., more preferably in the range of 105 to 132° C.
In a preferred embodiment Component A) is a recycled material, which is recovered from waste plastic material derived from post-consumer and/or post-industrial waste.
Such post-consumer and/or post-industrial waste can be derived from inter alia waste electrical and electronic equipment (WEEE) or end-of-life vehicles (ELV) or from differentiated waste collection schemes like the German DSD system, the Austrian ARA system or the Italian “Raccolta Differenziata” system.
The blends can be either PP-rich or PE-rich materials or blends with approximately equivalent amounts of PP and PE.
The term “waste” is used to designate polymer materials deriving from at least one cycle of processing into manufactured articles, as opposed to virgin polymers. As mentioned above, all kinds of polyethylene, preferably HDPE, LLDPE or LDPE, or polypropylene can be present.
Such recyclates are commercially available, e.g. from Corpela (Italian Consortium for the collection, recovery, recycling of packaging plastic wastes), Resource Plastics Corp. (Brampton, ON), Kruschitz GmbH, Plastics and Recycling (AT), Vogt Plastik GmbH (DE) etc.
The amounts of component A-1 and component A-2 can be from 30 to 70 wt % of the PP component A-1 and from 70 to 30 wt % of the PE component A-2, preferably 40 to 60 wt % of the PP component A-1 and 60 to 40 wt % of the PE component A-2.
Component A) of the blend of the invention preferably has an MFR (230° C., 2.16 kg, ISO 1133) of 0.5 to 150 g/10 min, more preferably of 1 to 120 g/10 min.
Component (A) is usually free of a disperse phase. Thus, component (A) is usually not a heterophasic polymer.
Component B) of the blend according to the invention is a heterophasic polyolefin composition comprising
Heterophasic polyolefin compositions are generally featured by a xylene cold soluble (XCS) fraction and a xylene cold insoluble (XCI) fraction.
For the purpose of the present application the xylene cold soluble (XCS) fraction of the heterophasic polyolefin compositions is essentially identical with Component B-2) of said heterophasic polyolefin compositions.
Accordingly when talking about the intrinsic viscosity and the ethylene content of B-2) of the heterophasic polyolefin compositions the intrinsic viscosity and the ethylene content of the xylene cold soluble (XCS) fraction of said heterophasic polyolefin compositions is meant.
Polypropylenes suitable for use as Component B-1) may include any type of isotactic or predominantly isotactic polypropylene homopolymer or random copolymer known in the art. Thus the polypropylene may be a propylene homopolymer or an isotactic random copolymer of propylene with ethylene and/or C4 to C8 alpha-olefins, such as for example 1-butene, 1-hexene or 1-octene, wherein the total comonomer content ranges from 0.05 to 10 wt %.
A polypropylene suitable for use as component B-1) may have a density of from 0.895 to 0.920 g/cm3, preferably from 0.900 to 0.915 g/cm3, and more preferably from 0.905 to 0.915 g/cm3 as determined in accordance with ISO 1183.
Usually component B-1) has a melting temperature of 130 to 170° C., preferably from 135 to 168° C. and most preferably from 140 to 165° C.
In case it is a propylene homopolymer it will have a melting temperature of from 150 to 170° C., preferably from 155 to 168° C., like from 160 to 165° C. as determined by differential scanning calorimetry (DSC) according to ISO 11357-3. In case it is a random copolymer of propylene with ethylene and/or C4 to C8 alpha-olefins it will have a melting temperature of from 130 to 162° C., preferably from 135 to 160° C., like from 140 to 158° C. as determined by DSC according to ISO 11357-3.
The melt flow rate of component B-1) ranges from 1.0 to 300 g/10 min, preferably from 2.0 to 200 g/10 min, and more preferably from 4.0 to 150.0 g/10 min, e.g. 4.5 to 150.0 g/10 min as determined in accordance with ISO 1133 (230° C.; 2.16 kg). In one embodiment the melt flow rate of component B-1) ranges from 4.0 to 75 g/10 min as determined in accordance with ISO 1133 (230° C.; 2.16 kg).
As Component B-2) a copolymer of ethylene and propylene or an C4 to C10 alpha olefin is used. The alpha olefin is preferably butene, hexene or octene, more preferably butene or octene and most preferably octene.
The copolymers of B-2) have a glass transition temperature Tg (measured with DMTA according to ISO 6721-7) of below −25° C., preferably below −28° C., more preferably below −30° C., more preferably below −45° C. and an intrinsic viscosity (measured in decalin according to DIN ISO 1628/1 at 135 ° C.) of at least 3.0 dl/g, preferably at least 3.1 dl/g, more preferably of at least 3.2 dl/g, more preferably of at least 3.3 dl/g.
The glass transition temperature Tg (measured with DMTA according to ISO 6721-7) of the copolymers of B-2) is usually −65° C. or above, preferably −60° C. or above and most preferably −58° C. or above.
The intrinsic viscosity (measured in decalin according to DIN ISO 1628/1 at 135° C.) of the copolymers of B-2) is usually 10.0 or less, preferably 9.0 or less and most preferably 8.5 or less.
In case the copolymer of B-2) is a copolymer of ethylene and propylene it has an ethylene content from 10 to 55 wt %, preferably from 15 to 50 wt %, more preferably from 18 to 48 wt % and most preferably from 20 to 46 wt. %.
In case the copolymer of B-2) is a copolymer of ethylene and a C4 to C10 alpha olefin it has an ethylene content from 60 to 95 wt %, preferably from 65 to 90 wt % and more preferably from 70 to 85 wt %.
Component B-2 is different from component A-2). Usually component B-2) differs from A-2) as regards their comonomer contents determined as weight percent. Preferably the comonomer content of A-2) is lower compared with the comonomer content of B-2), more preferably the comonomer content of A-2) is at least 2 percentage points lower compared with the comonomer content of B-2) and most preferably the comonomer content of A-2) is at least 5 percentage points lower compared with the comonomer content of B-2).
In the heterophasic polyolefin composition suitable as component B), B-1) is present in an amount of 55 to 90 wt %, preferably in an amount of 60 to 88 wt % and more preferably in an amount of 65 to 85 wt % and most preferably in an amount of 65 to 80 wt % and B-2) is present in an amount of 10 to 45 wt %, preferably in an amount of 12 to 40 wt %, more preferably in an amount of 15 to 40 wt %, even more preferably in an amount of 15 to 35 wt % and most preferably in an amount of 20 to 35 wt %.
Component B) preferably has a content of ethylene homopolymers of not more than 10 wt. %, more preferably not more than 5 wt. % and most preferably component B) is free of ethylene homopolymers.
The heterophasic polyolefin composition suitable as component B) can be prepared by mechanical blending of component B-1) and component B-2).
Polypropylene homopolymers or copolymers suitable as component B-1) for mechanical blending are commercially available, i.a. from Borealis AG or can be prepared by known processes, like in a one stage or two stage polymerization process comprising a loop reactor or a loop reactor with subsequent gas phase reactor, in the presence of highly stereospecific Ziegler-Natta catalysts or single-site catalysts like metallocene catalysts, known to the art skilled persons.
Copolymers suitable as component B-2) for mechanical blending can be any copolymer of ethylene and propylene or ethylene and C4 to C10 alpha olefin having the above defined properties, which may be commercial available, i.a. from Borealis Plastomers (NL) under the tradename Queo®, from DOW Chemical Corp (USA) under the tradename Engage®, or from ENI SpA (IT).
Alternately these copolymers can be prepared by known processes, in a one stage or two stage polymerization process, comprising solution polymerization, slurry polymerisation, gas phase polymerization or combinations therefrom, in the presence of highly stereospecific Ziegler-Natta catalysts, suitable vanadium oxide catalysts or single-site catalysts like metallocene or constrained geometry catalysts, known to the art skilled persons.
In another embodiment, the heterophasic polyolefin composition suitable as component B) can be prepared by sequential polymerization, comprising at least two reactors wherein first the polypropylene B-1) is produced and secondly the copolymer B-2) is produced in the presence of the polypropylene B-1).
A preferred sequential polymerization process comprises at least one loop reactor and at least one subsequent gas phase reactor. Such a process can have up to 3 gas phase reactors.
The polypropylene polymer B-1) is produced first, i.e. in the loop reactor, and subsequently transferred to the at least one gas phase reactor, where the polymerization of ethylene, propylene or a C4 to C10 alpha olefin or mixtures therefrom takes place in the presence of the polypropylene polymer B-1). It is possible that the so produced polymer is transferred to a second gas phase reactor.
A further possibility is that the polypropylene polymer B-1) is produced in the loop reactor and the first subsequent gas phase reactor. The polypropylene polymer B-1) is then transferred to the at least second gas phase reactor where the polymerization of ethylene and propylene or a C4 to C10 alpha olefin or mixtures therefrom takes place in the presence of the polypropylene polymer B-1). It is possible that the so produced polymer is transferred to a third gas phase reactor.
In a specific embodiment the heterophasic polyolefin composition suitable as component B) is prepared by sequential polymerization comprising at least four reactors wherein first the polypropylene polymer B-1) is produced in the loop reactor and the first subsequent gas phase reactor. The polypropylene polymer B-1) is then transferred to the second gas phase reactor where the polymerization of ethylene and propylene or a C4 to C10 alpha olefin or mixtures therefrom takes place in the presence of the polypropylene polymer B-1). The so produced polymer is then transferred to the third gas phase reactor where the polymerization of ethylene and propylene or a C4 to C10 alpha olefin or mixtures therefrom takes place in the presence of the product obtained in the second gas phase reactor.
The polymerization takes place in the presence of highly stereospecific Ziegler-Natta catalysts or single-site catalysts like metallocene catalysts, known to the art skilled persons.
A suitable sequential polymerization process is, i.a. the Borstar® process of Borealis AG.
Preferably the heterophasic polyolefin composition B) is produced by sequential polymerization if the copolymer B-2) is an ethylene-propylene copolymer.
If the copolymer B-2) is an ethylene-C4 to C10 alpha olefin, the heterophasic polyolefin composition B) is preferably produced by mechanical blending.
The polypropylene-polyethylene blends A) of the present invention comprising component B) as compatibilizer have improved mechanical properties compared to blends comprising only component A).
Component A) is present in an amount from 75 to 90 wt %, preferably 80 to 90 wt % and Component B) is present in an amount from 10 to 25 wt %, preferably 10 to 20 wt %.
Components A) and B) are, thus, usually different.
Blends comprising component A) as well as component B) have increased Charpy Notched Impact Strength (according to ISO 179-1eA, measured at 23° C.) as well as increased Flexural Modulus (according to ISO 178, measured at 23° C.) and higher heat deflection resistance as expressed by DMTA (according to ISO 6721-7) and by heat deflection temperature (HDT, according to ISO 75) compared to blends comprising only Component A).
The Charpy Notched Impact Strength (according to ISO 179-1eA, measured at 23° C.) of the blend according to the invention (comprising component A) and B)) is at least 2% higher, preferably at least 3% higher, than the Charpy Notched Impact Strength (according to ISO 179-1eA, measured at 23° C.) of the same blend A) without the compatibilizer B).
At the same time the Flexural Modulus (according to ISO 178, measured at 23° C.) of the blend according to the invention (comprising component A) and B)) is at least 3% higher, preferably at least 4% higher, than the same blend A) without the compatibilizer B).
Also, in the DMTA (according to ISO 6721-7) the temperature dependence of the storage modulus G′ of the blend according to the invention (comprising component A) and B)) shows a higher heat deflection resistance expressed by the temperature at which a G′ of 40 MPa is reached (T(G′=40 MPa) which is at least 4° C. higher, preferably at least 6° C. higher, than the same blend A) without the compatibilizer B).
Preferably, the heat deflection temperature (HDT, according to ISO 75 B) of the blend according to the invention (comprising component A) and B)) is at least 3° C. higher, preferably at least 4° C. higher, more preferably at least 10° C. higher than the same blend A) without the compatibilizer B).
The blends according to the present invention can be advantageously used in a compound with one or more virgin polymers for e.g. automotive applications, pipes or profiles for construction applications. Next to virgin polypropylene(s) and/or polyethylene(s) such a compound may further comprise inorganic or organic reinforcements like talc, glass fibres or wood fibres.
Optionally the Polypropylene-Polyethylene blends according to the present invention further comprise inorganic reinforcements agents, usually inorganic fillers. The total amount of inorganic reinforcements agents is preferably 1 to 20 wt. %, more preferably 2 to 15 wt.% based on the total amount of the Polypropylene-Polyethylene blend.
Suitable inorganic fillers are talc, chalk, clay, mica, clay, wood fibres or glass fibres and carbon fibres up to a length of 6 mm.
The mean particle size d50 of the filler may be chosen between 0.5 to 40 μm, preferably between 0.7 to 20 μm and more preferably between 1.0 to 15 μm.
The mean (or median) particle size is the particle diameter where 50% of the particles are larger and 50% are smaller. It is denoted as the d50 or D50.
In principle, this value may be determined by any particle measuring techniques, for example measuring techniques based on the principle of light diffraction.
Other techniques for determining particle sizes include, for example, granulometry in which a uniform suspension of a small quantity of the powder to be investigated is prepared in a suitable dispersion medium and is then exposed to sedimentation. The percentage distribution of the particle sizes can be estimated from the correlation between size and density of the spherical particles and their sedimentation rate as determined by Stokes law and the sedimentation time. Other methods for determining particle size include microscopy, electron microscopy, sieve analysis, sedimentation analysis, determination of the surface density and the like.
The particle size data appearing in the present specification were obtained in a well known manner with a standard test procedure employing Stokes' Law of Sedimentation by sedimentation of the particulate material in a fully dispersed condition in an aqueous medium using a Sedigraph 5100 machine as supplied by Micromeritics Instruments Corporation, Norcross, Ga., USA (telephone: +1 770 662 3620; web-site: www.micromeritics.com), referred to herein as a “Micromeritics Sedigraph 5100 unit”.
Preferably talc, glass fibres or wood fibres, more preferably talc is used as inorganic filler.
Before the talc is added it may be treated with various surface treatment agents, such as organic titanate coupling agents, silane coupling agents, fatty acids, metal salts of fatty acids, fatty acid esters, and the like, in a manner known in the state of the art. The talc may also be added without surface treatment. Preferably the talc is added without surface treatment.
For the recyclate the polyethylene content was calculated from the PE melting enthalpy in DSC (Hm(PE)) associated to the lower melting point for the composition (Tm(PE)) in the range of 110 to 130° C. For the determination of the present invention for fully crystalline PE a melting enthalpy of 298 J/g and an average degree of crystallinity of 50% was assumed.
For the virgin PP/PE blend, the following two components a) and b) were used as a 1:1 blend (weight ratio):
The catalyst was used in combination with dicyclopentyldimethoxysilane [Si(OCH3)2(cyclo-pentyl)2] as external donor (ED) and triethylaluminium (TEAL) as activator and scavenger in the ratios indicated in table 1. The catalyst was modified by polymerising a vinyl compound in the presence of the catalyst system. The respective process is described in EP 1 028 984 and EP 1 183 307.
The MFR (230° C., 2.16 kg, ISO 1133) of the product of GPR1 was 70 g/10 min.
For Comparative Example CE 1 BF970MO was used: heterophasic ethylene-propylene impact copolymer (PP-HECO) commercially available from Borealis AG, Austria, having an MFR2 (230° C.) of 20 g/10 min, a melting point (DSC) of 165° C. and a density of 0.905 g/cm3. The polymer has an XCS content of 17.5 wt % with 34 wt % C2 and an intrinsic viscosity of 2.6 dl/g.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14167409.3 | May 2014 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/059541 | 4/30/2015 | WO | 00 |
