WO2017076688A1

WO2017076688A1 - Polymer composition having improved impact strength

Info

Publication number: WO2017076688A1
Application number: PCT/EP2016/075624
Authority: WO
Inventors: Sathish NAGARAJACHAR; Chandrashekhar Lingannaiah; B Parthipan
Original assignee: Sabic Global Technologies B.V.
Priority date: 2015-11-06
Filing date: 2016-10-25
Publication date: 2017-05-11

Abstract

The present invention relates to a polymer composition comprising: (d) 40.0-90,0 % by weight of polypropylene; (e) 9,0-49,0 % by weight of a core-shell polymer composition comprising poly(C_1-12-alkyl-(meth)acrylate) core particles onto which a shell is formed by polymerisation of acrylonitrile, styrene and C_1-12-alkyl-(meth)acrylate; and (f) 1.0-40,0 % by weight of a block copolymer comprising polystyrene and poly(ethylene/alkylene); wherein the amount of each component is based on the combined weight of the components, and the combined percentage of the components totals 100%, Such polymer composition has an improved impact strength, and a good balance of resistance to environmental stress cracking and tensile properties.

Description

Polymer composition having improved impact strength

The present invention relates to a polymer composition comprising polypropylene having improved impact strength. The invention further relates to a process for the production of such polymer composition, and to shaped articles comprising such polymer composition.

Polypropylene is widely used in a variety of applications including for example automotive applications, building and construction applications, in thermoforming, in household appliances, and in fibre applications. For certain applications, however, there is a need for further improvement of the properties of polypropylene. An example of such property that is desired to be further improved is the impact strength. in order to arrive at such improved impact strength, attempts have been made by preparing polymer compositions comprising polypropylene together with other polymer materials. For example, in US4871805, polypropylene compositions comprising SEBS or SEPS block copolymers are presented. In

However, the above presented attempts do not provide an improvement of the impact strength of polypropylene to the extent as desired. For that reason, there is an ongoing need to develop polymer compositions having an increased impact strength.

This has now been achieved according to the present invention by a polymer composition comprising:

(a) 40.0-90.0 % by weight of polypropylene;

(b) 9.0-49.0 % by weight of a core-shell polymer composition comprising poly(C_{1 -12}- alkyl-(meth)acrylate) core particles onto which a shell is formed by polymerisation of acrylonitrile, styrene and C_{1 -12}-alkyl-(meth)acrylate; and (c) 1.0-40.0 % by weight of a block copolymer comprising polystyrene and

poly(ethylene/alkylene); wherein the amount of each component is based on the combined weight of the components, and the combined percentage of the components totals 100%.

Such polymer composition may result in an improved impact strength. Furthermore, such polymer composition may show a good color stability, as well as a good retention of environmental stress cracking resistance and tensile properties. Preferably, the polymer composition comprises 50.0-90.0, more preferably 60.0-80.0 % by weight of polypropylene; 9.0-33.0, more preferably 10,0-25.0 % by weight of the core- shell polymer composition (b); and 1.0-30.0, more preferably 5.0-25.0 % by weight of the block copolymer (c), with regard to the total weight of the polymer composition. The polypropylene component can be a propylene homopolymer or a copolymer of propylene with an a-olefin, for example an α-olefin chosen from the group of a-olefins having 2 or 4 to 10 carbon atoms. Such a-olefin may for example be one or more selected from ethylene, 1-butene, 1-hexene, 3-methyl-1 -pentene, or 1 -octene. Such copolymers of propylene may for example be random copolymers or block copolymers. Polypropylene and a copolymer of propylene with an α-olefin can be made by any polymerization technique and any polymerization catalyst system. Some polymerization techniques include slurry, solution or gas phase polymerizations. Some catalysts systems include Ziegler-Natta, metallocene or single-site catalyst systems. Preferably, the polypropylene used is a propylene

homopolymer. The polypropylene component may for example comprise a quantity of graft-modified polypropylene. Such graft-modified polypropylene may for example be a polypropylene to which a quantity of maleic anhydride moieties are grafted

The polypropylene may have a melt flow index from 0.1 to 12.0 g/10 min, preferably from 1.0 to 11.0 g/10 min, as determined according to ISO 1133-1 (2011 ), at 230°C using a load of 2.16 kg. Exemplary commercially available propylene homopolymers include Repol- PPH1 10MA (Reliance Industries, India) and Repol-PPH030SG (Reliance Industries, India). Exemplary commercially available propylene copolymers include PP 83EK10 (Sabic), a propylene block copolymer produced using ethylene as comonomer.

The core-shell polymer composition comprises poly(C_{1 -12}-alkyl-(meth)acrylate) core particles onto which a shell is formed by polymerisation of acrylonitrile, styrene and C_{1 -12}- alkyl-(meth)acrylate. The core particles may be formed by emulsion polymerisation of one or more C_{1 -12}-alkyl-(meth)acrylate. The core particles may be formed by polymerisation of one or more C_{1 -12}-alkyl-(meth)acrylate monomer or mixtures of such monomers. Suitable C_{1 -12} alkyl-(meth)acrylate monomers include, but are not limited to, C_{1 -12} alkyl-acrylate monomers, such as for example ethyl acrylate, butyl acrylate, isopentyl acrylate, n-hexyl acrylate, and 2- ethyl hexyl acrylate; and C1-12 alkyl-methacrylate monomers, such as for example methyl methacrylate, ethyl methacrylate, propyl methacrylate, iso-propyl methacrylate, butyl methacrylate, and hexyl methacrylate. The poly(C_{1 -12}-alkyl-(meth)acrylate) core particles may for example be formed by emulsion polymerisation of a reaction mixture comprising butyl acrylate. the poly(C_{1 -12}-alkyl-(meth)acrylate) core particles are poly(butylacrylate) core particles.

The core-shell polymer composition may be formed by subjecting the poly(C_{1 -12}-alkyl- (meth)acrylate) core particles to an polymerisation process, for example an emulsion polymerisation process, in the presence of acrylonitrile, styrene and one or more C_{1 -12}-alkyl- (meth)acrylate to form a shell, For example, the C_{1 -12}-alkyl-(meth)acrylate used in the formation of the shell may be selected from C_{1 -12} alkyl-acrylate monomers, such as for example ethyl acrylate, butyl acrylate, isopentyl acrylate, n-hexyl acrylate, and 2-ethyl hexyl acrylate; and C1-12 alkyl-methacrylate monomers, such as for example methyl methacrylate, ethyl methacrylate, propyl methacrylate, iso-propyl methacrylate, butyl methacrylate, and hexyl methacrylate.

The invention preferably relates to a polymer composition wherein the core-shell polymer composition (b) comprises poly(C_{1 -12}-alkylacrylate) core particles onto which a shell is formed by polymerisation of acrylonitrile, styrene and methyl methacrylate. The C_{1 -12}-alkyl-(meth)acrylate used in the shell emulsion polymerisation process may for example be methyl methacrylate. The shell may be formed by subjecting the poly(C_{1 -12}- alkyl-(meth)acrylate) core particles to an emulsion polymerisation process in the presence of acrylonitrile, styrene and methyl methacrylate. More preferably, the core-shell polymer composition may be formed by subjecting polybutylacrylate core particles to an emulsion polymerisation process in the presence of acrylonitrile, styrene and methyl methacrylate.

Such core-shell polymer composition may be referred to as a methyl-methacrylate- acrylonitrile-styrene polybutylacrylate, also referred to as MA-ASA.

The core-shell polymer composition (b) may for example comprise≥ 25.0 % by weight, alternatively≥ 30.0 % by weight, alternatively≥ 35.0 % by weight of such shell formed by polymerisation of acrylonitrile, styrene and methyl methacrylate, with regard to the total weight of the core-shell polymer composition. The core-shell polymer composition (b) may for example comprise≤ 70.0 % by weight, alternatively≤ 65.0 % by weight, alternatively≤ 60.0 % by weight of such shell formed by polymerisation of acrylonitrile, styrene and methyl methacrylate, with regard to the total weight of the core-shell polymer composition. The core-shell polymer composition (b) may for example comprise≥ 25.0 and≤ 70.0

% by weight, alternatively≥ 30.0 and≤ 65.0 % by weight of such shell formed by

polymerisation of acrylonitrile, styrene and methyl methacrylate, with regard to the total weight of the core-shell polymer composition. Preferably, the core-shell polymer composition (b) comprises 30,0-85,0 % by weight of a shell formed by polymerisation of acrylonitrile, styrene and methyl methacrylate and 35.0- 70.0 % by weight of polybutylacrylate core particles with regard to the total weight of the core-shell polymer composition (b). The shell of the core-shell polymer composition may for example comprise≥ 30.0 and

≤ 50.0 % by weight, alternatively≥ 35.0 and≤ 45.0 % by weight, of acrylonitrile-derived units, with regard to the total weight of the shell of the core-shell polymer composition (b). The shell of the core-shell polymer composition may comprise≥ 15.0 and≤ 35.0 % by weight, alternatively≥ 20.0 and≤ 30.0 % by weight, of styrene-derived units, with regard to the total weight of the shell of the core-shell polymer composition (b). The shell of the core- shell polymer composition may comprise≥ 25 0 and≤ 45.0 % by weight, alternatively≥ 30.0 and≤ 40.0 % by weight, of methyl methacrylate-derived units, with regard to the total weight of the shell of the core-shell polymer composition (b).

Prefereably, the invention relates to a polymer composition wherein the shell of the core-shell polymer composition (b) comprises: x) 35.0-45.0 % by weight of acrylonitrile-derived units; y) 20.0-30.0 % by weight of styrene-derived units; and z) 30.0-40.0 % by weight of methyl-methacrylate derived units; with regard to the total weight of the shell of the core-shell polymer composition (b). The core-shell polymer composition may for example comprise≥ 30.0 % by weight, alternatively≥ 35.0 % by weight of poly(Ci-i 2-alkyl-(meth)acrylate) core particles, with regard to the total weight of the core-shell polymer composition. For example, the core-shell polymer composition may comprise≤ 75.0 % by weight, alternatively≤ 70.0 % by weight of poly(Ci-i2-alkyl-(meth)acrylate) core particles, with regard to the total weight of the core-shell polymer composition. For example, the core-shell polymer composition may comprise≥ 30.0 and≤ 75.0 % by weight, alternatively≥ 35.0 and≤ 70.0 % by weight of poly{C_M2-aIkyl- (meth)acrylate) core particles, with regard to the total weight of the core-shell polymer composition.

For example, the core-shell polymer composition may comprise≥ 30.0 and≤ 65.0 % by weight of such shell formed by polymerisation of acrylonitrile, styrene and methyl methacrylate and≥ 35.0 and≤ 70.0 % by weight of the poly(C;.i2-alkyl-(meth)acrylate) core particles, with regard to the total weight of the core-shell polymer composition. For example, the shell of the core-shell polymer composition may comprise may comprise≥ 35.0 and≤ 45.0 % by weight of acrylonitrile-derived units, > 20.0 and≤ 30.0 % by weight of styrene- derived units, and≥ 30.0 and ≤ 40.0 % by weight of methyl methacrylate-derived units, with regard to the total weight of the shell of the core-shell polymer composition.

Preferably, the core-shell polymer composition (b) comprises polybutylacrylate core particles produced in a first emulsion polymerisation process producing polybutylacrylate seed latex particles which in a subsequent second emulsion polymerisation process are further polymerised with butyl acrylate. The mean particle size of the polybutylacrylate core particles may for example be > 400 rim, alternatively > 450 nm. Preferably, the mean particle size of the polybutylacrylate core particles is > 400 nm and < 1500 nm.

The block copolymer (c) comprising polystyrene and poly(ethylene/alkylene) may for example be a block copolymer comprising polystyrene block segments and block segments comprising repeating units derived from conjugated dienes. The block copolymer (c) may be obtained by subjecting a block copolymer comprising polystyrene block segments and block segments derived from conjugated dienes to a hydrogenation treatment in which at least a fraction of the unsaturations in the block segments derived from conjugated dienes are hydrogenated. For example, the block copolymer (c) may be obtained by subjecting a polystyrene-polybutadiene-polystyrene (SBS) triblock copolymer or a polystyrene- polyisoprene-polystyrene (SIS) triblock copolymer to a hydrogenation treatment. The block copolymer may be subjected to such hydrogenation treatment in such way that all aliphatic unsaturations are hydrogenated; alternatively,

The poly(ethylene/alkylene) in block copolymer (c) may be derived from one or more conjugated dienes, and the block copolymer (c) may be hydrogenated to such degree that less than 20% of the aliphatic unsaturations in the aliphatic chain moieties derived from the conjugated dienes are not hydrogenated. Preferably, less than 15% of the aliphatic unsaturations in the aliphatic chain moieties derived from the conjugated dienes are not hydrogenated.

The presence of a higher quantity of aliphatic unsaturations in the aliphatic chain moieties derived from the conjugated dienes in the block copolymer (c) may result in undesirable levels of degradation of the polymer composition when exposed to

environmental conditions such as UV radiation.

The poly(ethylene/alkylene) blocks in the block copolymer (c) may for example be poly(ethylene/propylene) blocks or poly(ethylene/butylene) blocks. Such

poly(ethylene/alkylene) blocks may be derived from for example 1 ,3-butadiene or isoprene. Such poly(ethylene/a1kylene) blocks may for example have a number average molecular weight of 25000 to 150000, alternatively 50000 to 125000.

The block copolymer (c) may comprise 15.0-50.0 % by weight of moieties derived from styrene, alternatively 15.0-40,0 % by weight, alternatively 20,0-35,0 % by weight, with regard to the total weight of the block copolymer (c). Preferably, the block copolymer (c) comprises a fraction of moieties derived from styrene of 15.0 to 40,0 % by weight, with regard to the total weight of the block copolymer (c).

Preferably, the invention relates to a polymer composition wherein the block copolymer (c) is selected from a polys tyrene-poly(ethylene/propylene)-polystyrene triblock copolymer or a polystyrene-poly(ethylene/butylene)-polystyrene triblock copolymer.

The blocks of the block copolymer (c) may each independently have a number average molecular weight of 3000 to 300000 g/mol, alternatively 3000 to 20000 g/mol, preferably 5000 to 15000 g/mol. The number average molecular weight is determined in accordance with ISO 16014-2 (2012). It is preferred that the weight fraction of the core-shell polymer composition (b) is less than the weight fraction of the block copolymer (c).

The polymer composition according to the invention preferably is produced by melt blending of polypropylene (a), core-shell polymer composition (b) and block copolymer (c) in a melt extruder wherein melt blending occurs at a temperature of 180-250°C.

Preferably, the polymer composition according to the present invention comprises:

• 50.0-90.0, preferably 60.0-80.0 % by weight of polypropylene, with regard to the total weight of the polymer composition;

• 9.0-39.0, preferably 10.0-25.0 % by weight with regard to the total weight of the polymer composition of a core-shell polymer composition comprising 30.0-65.0

% by weight with regard to the total weight of the core-shell polymer composition of polybutylacrylate core particles onto which a shell is formed by polymerisation of acrylonitrile, styrene and 30.0 -40.0 % by weight with regard to the total weight of the shell of methyl methacrylate; and

· 1.0-30.0, preferably 5.0-25.0 % by weight with regard to the total weight of the polymer composition of a block copolymer selected from a polystyrene- poly(ethylene/propylene)-polystyrene triblock copolymer or a polystyrene- poly(ethylene/butylene)-polystyrene triblock copolymer, wherein the block copolymer comprises a fraction of moieties derived from styrene of 15,0 to 40,0 % by weight with regard to the total weight of the block copolymer, wherein the block copolymer is produced using a conjugated diene selected from butadiene or isoprene and wherein the block copolymer is hydrogenated to such degree that less than 20% of the unsaturations in the aliphatic chain moieties of the block copolymer that are derived from the conjugated diene are not hydrogenated; wherein the polymer composition has

• a notched Izod impact strength as measured according to ISO 180 (2000), using test specimens of type A of > 15 kJ/m²;

• a tensile modulus as determined according to ISO 527-1 (2012) of > 800 MPa;

• an elongation at break as determined according to ISO 527-1 (2012) of > 250 %; and

• a resistance to environmental stress cracking as determined according to ISO 22088-3 (2008), presented as the percentage of retention of elongation at break as determined according to !SO-527-1 (2012), of > 90% ,

Polymer compositions according to the present invention may further also comprise additives including, but not limited to, stabilizers, such as color stabilizers, heat stabilizers, light stabilizers, antioxidants, UV screeners, and UV absorbers; lubricants, flow promoters and other processing aids; plasticizers, antistatic agents, mold release agents, impact modifiers, fillers, and like additives. Illustrative additives include, but are not limited to, silica, silicates, zeolites, stone powder, glass fibers or spheres, carbon fibers, graphite, mica, calcium carbonate, talc, lithopone, zinc oxide, zirconium silicate, iron oxides, diatomaceous earth, calcium carbonate, magnesium oxide, chromic oxide, zirconium oxide, aluminum oxide, titanium dioxide, crushed quartz, clay, calcined clay, talc, kaolin, asbestos, cellulose, wood flour, cork, cotton and synthetic textile fibers, especially reinforcing fillers such as glass fibers, carbon fibers, metal fibers, and metal flakes, including, but not limited to aluminum flakes. Furthermore, polymer compositions according to the invention may comprise one or more additives selected from the group consisting of lubricants, stabilizers, heat stabilizers, light stabilizers, antioxidants, UV screeners, UV absorbers, and mixtures thereof.

The invention further relates to a shaped article comprising polymer compositions according to the invention. Such article may for example be prepared by thermoplastic processing techniques. Thermoplastic processing techniques which can be used include, but are not limited to, extrusion, calendering, kneading, profile extrusion, sheet extrusion, coextrusion, molding, extrusion blow molding, therm oforming, compression molding, injection molding, co-injection molding, rotomotding, fiber spinning, film blowing and film casting. The invention further contemplates additional fabrication operations on said articles, such as, but not limited to, welding, machining, in-mold decoration, baking in a paint oven, surface etching, lamination, and/or thermoforming.

Illustrative articles that may comprise a polymer composition according to the present invention include those which require resistance to weathering such as articles used in outdoor applications and/or in applications where the article is exposed to sunlight. Such articles include, but are not limited to, those which are prepared by an injection molding process, a profile extrusion process, a sheet extrusion process or a fiber spinning process. The articles may comprise multilayer articles comprising at least one layer comprising a disclosed composition and at least one layer comprising a different composition. Articles comprising disclosed compositions include, but are not limited to, sheet, pipe capstock, hollow tubes, solid round stock, square cross-section stock, fibers and the like. More complex shapes can also be made, such as those used for building and construction applications, especially a window frame, a sash door frame, corner guards, house siding, gutters, handrails, down-spouts, fence posts, and the like. Illustrative articles comprising a composition of the invention can also comprise electrical enclosures, parts and housing used in heating, ventilating, and air conditioning applications, cable tying fibers, air filter housings, parts used in telecommunication applications, parts used in lawn and garden applications, electrical components, appliance components and housings, washing machine components and housings, dishwasher components and housings, refrigerator components and housings, network enclosures, parts and housing used in personal protection and alarm systems, parts and housing used in ATM and ticket machine applications, parts and housing used in computer and consumer electronic applications, copier covers, printer covers, server bezels, gas detector parts and enclosures, and the like.

In the context of the present invention, the notched Izod impact strength at 23°C as determined in accordance with ISO 180 (2000) is used as indicator for the impact strength. The discoloration as result of weathering of the polymer composition according to the present invention is indicated by the color difference ΔΕ measured in accordance with ASTM D2244-1 1 of samples before and after a weathering treatment according to SAE J 1960 (2008). The invention will now be illustrated by the following non-limiting examples.

In a 25mm twin screw melt extruder, operated at a temperature of 210°C at a speed of 250 RPM, granules of polymer compositions were prepared using the materials shown in table 1.

Table 1

The melt mass-flow rate was determined in accordance with ISO 1133-1 (2011 }, at 230X using a load of 2.16 kg. ISO 1133-1 (2011 ) relates to the determination of the melt mass-flow rate and the melt volume-flow rate of thermoplastics.

Preparation of MA-ASA

A poly(butyl acrylate) latex was prepared by charging in a stainless steel reactor equipped with a bladed turbine agitator 131 parts by weight (pbw) of demineralized water and 0.15 pbw of tetrasodium pyrophosphate. Agitation was started and the reactor contents were heated to 60°C while purging the reactor contents with nitrogen for one hour. After purging was completed, 0.8 pbw of sodium lauryl sulfate were added and agitated for 5 min. The nitrogen feed was changed from purging to blanketing.

The following feed streams were prepared for charging to the reactor:

(!) 89 pbw of butyl acrylate; (ii) a solution of 0.47 pbw of triallyl cyanurate in 10.53 pbw butyl acrylate;

(iii) an activator solution containing 0.132 pbw sodium formaldehyde solfoxylate, 0.025 pbw of the monosodium salt of ethylenediaminetetraacetic acid, 0.005 pbw ferrous sulfate heptahydrate, and 15 pbw demineralized water;

(iv) 0.120 pbw cumene hydroperoxide; and (v) a surfactant solution containing 0.10 pbw of sodium lauryl sulfate in 7.2 pbw demineralized water.

To begin the reaction, 6% of the total weight of (i) and (ii) were batch charged to the reactor followed by 20% by weight of (iii). Then 6% by weight of (iv) was added to initiate polymerization, wherein an exothermic reaction was typically observed within 5 min. from the addition of (iv).

Thirty minutes after observation of the first exotherm was taken as time zero (t=0). The solution (v) was then gradually fed to the reactor during a period starting at t=0 min. and completed at t=210 min. The remainder of feed streams (i), (ii), (iii) and (iv) were gradually fed to the reactor during a period starting at t=35 min, and completed at t=210 min. The reaction was maintained at 60°C. A poly(butyl acrylate) latex was obtained. Subsequently, a stainless steel reactor equipped with a bladed turbine agitator was charged with 127.4 pbw of demineralized water and 0.15 pbw of tetrasodium pyrophosphate. Agitation was started and the reactor contents were heated to 60°C while purging the reactor contents with nitrogen for one hour. After purging was completed, 2.5 pbw of the poly(butyl acrylate) latex that was previously prepared was added and agitated for 5 min. The nitrogen feed was changed from purging to blanketing.

The following feed streams were prepared for charging to the reactor:

(i) 87,75 pbw of butyl acrylate;

(ii) a solution of 0,47 pbw of trialIyl cyan urate in 11 ,28 pbw butyl acrylate; (iii) an activator solution containing 0.132 pbw sodium formaldehyde solfoxylate,

0.025 pbw of the monosodium salt of ethylenediaminetetraacetic acid, 0.005 pbw ferrous sulfate heptahydrate, and 15 pbw demineralized water;

(iv) 0.120 pbw cumene hydroperoxide; and

(v) a surfactant solution containing 0.40 pbw of sodium lauryl sulfate in 3.6 pbw demineralized water.

Once the reaction temperature was back to 60°C, 20% by weight of (iii) was batch charged to the reactor. Then all the remaining feed streams were fed to the reactor during a period of 180 min. After all feed streams had been charged, the reaction was held at 60°C with agitation for another 30 min. to obtain a second poly(butyl acrylate) latex.

Subsequently, the MA-ASA was prepared by charging in a stainless steel reactor equipped with a bladed turbine agitator 203 pbw of water and 45.0 pbw of the second poly(butyl acrylate) latex. The contents of the reactor were heated to 60°C.

The following feed streams were prepared for charging to the reactor:

(i) 22.00 pbd styrene;

(ii) 8.25 pbw acrylonitrile;

(iii) 24.75 pbw methyl methacrylate;

(iv) 0.25 pbw cumene hydroperoxide;

(v) an activator solution containing 0.033 pbw ferrous sulfate heptahydrate, 0.0165 pbw of the disodium salt of ethylenediaminetetraacetic acid, 0.30 pbw sodium formaldehyde sulfoxylate and 5 pbw of water; and (νϊ) a solution containing 1.088 pbw sodium lauryl sulfate in 9.792 pbw

demineralized water.

The feed streams (i), (ii), (iii) and (vi) were fed to the reactor during a period starting at t=0 min. and completed at t=90 min. The feed streams (iv) and (v) were fed to the reactor during a period starting at t=0 min. and completed at t=125 min. The temperature of the reactor contents was kept at 60°C up until t=90 min, after which the temperature was gradually increased to reach 71 °C at t=125 min. The temperature was kept at 7ΓΟ until t=170 min. Then, the reactor contents were cooled to 49°C and removed from the reactor. The reactor contents were then coagulated by addition of 3 pbw calcium chloride per 100 pbw of dry MA-ASA at a temperature from 85 to 91 °C. The coagulated polymer mass was then dried in a fluid bed dryer with an outlet air temperature of 74°C to obtain the polybutylacrylate / acrylonitrile-styrene-methyl methacrylate MA-ASA.

Physical property testing was conducted using the methods and conditions shown in Table 2 Unless otherwise indicated, all test methods were those in effect in 2010,

Notched Izod impact strength is measured according to ISO 180 (2000), using test specimens of type A. ISO 180 (2000) relates to the determination of Izod impact strength of plastics.

MVR is the melt volume-flow rate as determined according to ISO 1 133-1 (2011 ). ISO 1133-1 (2011 ) relates to determination of the melt mass-flow rate (MFR) and melt volume- flow rate (MVR) of thermoplastics.

Tensile modulus, stress at yield and elongation at break are determined according to ISO 527-1 (2012). ISO 527-1 (2012) relates to determination of tensile properties of plastics,

ΔΕ is the color difference between molded plaques before and after exposure of the sample to a weathering test protocol as per SAE J 1960 (2008) for 1000 hours. ΔΕ was determined in accordance with ASTM D2244-1 1. ASTM D2244-1 1 relates to a standard practice for calculation of color tolerances and color differences from instrumentally measured color coordinates. The color coordinates were determined using a Gretag

Macbeth Color Eye 7000A. SAE J 1960 (2008) relates to accelerated exposure of automotive exterior materials using a controlled irradiance water-cooled xenon arc apparatus

ESCR is the resistance to environmental stress cracking presented as the percentage of retention of elongation at break as determined according to ISO-527-1 (2012). ESCR was determined in accordance with ISO 22088-3 (2006) using isopropyl alcohol. ISO 22088-3 (2006) relates to the determination of resistance to environmental stress cracking of plastics via bent strip method.

The compositions of the examples and the properties that were determined are presented in table 3.

Table 3.

Examples IV through VI are included for comparative purposes.

Comparing examples I and V shows that the addition of a core-shell copolymer in accordance with the present invention to a composition of a polypropylene and an SEBS improves the notched Izod impact strength whilst maintaining the tensile properties such as the tensile modulus, the stress at yield, and the elongation at break. Furthermore, the polymer composition according to the invention better retain the melt volume-flow ratio which has a positive effect on the processability of the material via melt processing methods.

Comparing examples I and IV shows that polymer compositions according to the invention show an improved resistance to environmental stress cracking as compared to a polypropylene, in addition to the improvement of the impact strength.

Comparing examples I and VI shows that the use of a polymer composition comprising polypropylene, ABS and SEBS does not result in the desired improvement of the impact strength. Furthermore, such composition shows higher color difference upon weathering treatment.

Claims

1 . A polymer composition comprising;

(a) 40.0-90,0 % by weight of polypropylene;

(b) 9.0-49.0 % by weight of a core-shell polymer composition comprising poly(Ci.i2- alkyl-(meth)acrylate) core particles onto which a shell is formed by polymerisation of acrylonitrile, styrene and Ci-i2-alkyt-(meth)acrylate; and

(c) 1.0-40.0 % by weight of a block copolymer comprising polystyrene and

2. Polymer composition according to claim 1 wherein the polymer composition comprises 50.0-90.0, preferably 60.0-80.0 % by weight of polypropylene; 9.0-39.0, preferably 10.0-25.0 % by weight of the core-shell polymer composition (b); and 1.0-30.0, preferably 5.0-25.0 % by weight of the block copolymer (c), with regard to the total weight of the polymer composition.

3. Polymer composition according to any one of claims 1-2 wherein the core-shell

polymer composition (b) comprises poly(Ci-i2-alkylacrylate) core particles onto which a shell is formed by polymerisation of acrylonitrile, styrene and methyl methacrylate.

4. Polymer composition according to any one of claims 1-3 wherein the core-shell

polymer composition (b) comprises 30.0-65.0 % by weight of a shell formed by polymerisation of acrylonitrile, styrene and methyl methacrylate and 35.0-70.0 % by weight of polybutylacrylate core particles with regard to the total weight of the core- shell polymer composition (b).

5. Polymer composition according to any one of claims 1 -4 wherein the shell of the core- shell polymer composition (b) comprises: x) 35.0-45.0 % by weight of acrylonithle-derived units; y) 20.0-30.0 % by weight of styrene-derived units; and z) 30.0-40.0 % by weight of methyl-methacrylate derived units; with regard to the total weight of the shell of the core-shell polymer composition (b).

6. Polymer composition according to any one of claims 1-5 wherein the core-shell

polymer composition (b) comprises polybutylacrylate core particles produced in a first emulsion polymerisation process producing polybutylacrylate seed latex particles which in a subsequent second emulsion polymerisation process are further polymerised with butyl acrylate.

7. Polymer composition according to any one of claims 4-6 wherein the mean particle size of the polybutylacrylate core particles is > 400 nm and < 1500 nm.

8. Polymer composition according to any one of claims 1-7 wherein the

poly(ethylene/alkylene) in block copolymer (c) is derived from one or more conjugated dienes, and wherein the block copolymer (c) is hydrogenated to such degree that less than 20% of the aliphatic unsaturations in the aliphatic chain moieties derived from the conjugated dienes are not hydrogenated.

9. Polymer composition according to any one of claims 1-8 wherein the block copolymer (c) has a fraction of moieties derived from styrene of 15.0 to 40.0 % by weight, with regard to the total weight of the block copolymer (c).

10. Polymer composition according to any one of claims 1-9, wherein the block copolymer (c) is selected from a polystyrene-poly(ethylene/propylene)-polystyrene triblock copolymer or a polystyrene-poly(ethylene/butylene)-polystyrene triblock copolymer.

11. Polymer composition according to any one of claims 1-10 wherein the weight fraction of the core-shell polymer composition (b) is less than the weight fraction of the block copolymer (c).

12. Process for the production of the polymer composition according to any one of the claims 1-11 by melt blending of polypropylene (a), core-shell polymer composition (b) and block copolymer (c) in a melt extruder wherein melt blending occurs at a temperature of 180-250°C.

13. Shaped article comprising to polymer composition according to any one of claims 1-11.