Polyethylene composition with improved processing properties

Abstract

The present invention relates to a polymer composition comprising an ethylene-based polymer and a polylactic acid. Such polymer composition exhibits desirably good melt fracture prevention properties, in particular in production of polymer films.

Description

24POLY0137-WO-ORD 1Polyethylene composition with improved processing properties.

[0001] The present invention relates to polyethylene compositions with improved processing properties, processes for extrusion moulding of such compositions, and articles produced using such compositions.

[0002] In manufacturing of articles from polyethylene materials, the achievement of high productivity and thereby advantageous process economics requires a high extrusion speed of the resin materials in melt extrusion and moulding equipment. However, it is essential that the product quality of the extrudate is not negatively impacted when operating at such high extrusion speeds.

[0003] A critical parameter is this regard is the shear rate. If, during melt extrusion and moulding, the material is exposed to an excessively high shear rate, detrimental effects on notably the surface of the objects formed, observable as for example roughness, may occur. In a great number of applications of extrudates, it is a prerequisite that the surface quality is high. Particular examples of such critical applications are films and sheets.

[0004] Accordingly, in polyethylene extrusion moulding, one strives for an optimum of the balance between extrusion speed and surface quality of the moulded objects. Moreover, it is desired to be able to shift this balance towards higher productivity without compromise to the surface quality.

[0005] A means to influence this balance is by addition of so-called processing aids. These processing aids act to modify the flow behaviour of the polymer molecules, and thereby postpone the occurrence of undesired surface properties, which are also referred to as melt fracture, to higher extrusion speeds. By so, the process efficiency of extrusion moulding can be desirably increase without compromising the quality.

[0006] In particular, melt fracture issues may occur when using resins of certain narrow molecular weight distribution. Such resins include for example polyethylene resins produced using single-site type catalysts, such as metallocene-type catalysts.24POLY0137-WO-ORD 2

[0007] Commonly, a means of mitigating the occurrence of such effects is by using fluorcontaining polymer processing aids, also referred to as PFAS-containing polymer processing aids. There now is a desire to seek for alternative solutions that provide the desired processing effects.

[0008] This has now been achieved in by a polymer composition comprising an ethylene-based polymer and a polylactic acid.

[0009] Upon extrusion processing, such as in film production, the surface property qualities of such films are desirably improved.

[0010] Preferably, the composition comprises > 500 and < 3000 ppm by weight, mofre preferably > 500 and < 2000 ppm by weight, even more preferably > 500 and < 1500 ppm by weight, of the polylactic acid, with regard to the total weight of the polymer composition.

[0011] It is preferred that the polylactic acid has a weight-average molecular weight (Mw) of > 50 kg / mol and < 300 kg / mol, more preferably of > 100 and < 300 kg / mol, even more preferably of > 100 and < 250 kg / mol, yet even more preferably of > 150 and < 250 kg / mol.

[0012] It is also preferred that the polylactic acid has a number-average molecular weight (Mn) of > 50 kg / mol and < 150 kg / mol, more preferably of > 75 and < 120 kg / mol.

[0013] The polylactic acid may for example have a molecular weight distribution Mw / Mnof > 1.5 and < 5.0, preferably of > 1.5 and < 4.0, more preferably of > 1.5 and < 3.0.

[0014] The weight-average molecular weight and the number-average molecular weight of the polylactic acid may for example be determined by gel-permeation chromatography (GPC), using PS standards.

[0015] It is further also preferred that the polylactic acid has a density of > 1.00 and < 1.50 g / cm3, preferably of > 1.10 and < 1.40 g / cm3, as determined in accordance with ASTM D792 (2013).

[0016] The polylactic acid may for example have a melt mass-flow rate at 210°C under a load of 2.16 kg of > 1.0 and < 20.0 g / 10 min, preferably of > 1.0 and < 15.0 g / 10 min, more preferably of > 2.0 and < 10.0 g / 10 min, even more preferably of > 3.0 and < 8.0 g / 10 min, as determined in accordance with ASTM D 1238- 13.24POLY0137-WO-ORD 3

[0017] The polylactic acid may for example be a poly-L-lactide. Such poly-L-lactide is the product resulting from polymerization of L, L-lactide, which is also known as L-lactide or poly-DL-lactide (PDLLA), which is amorphous. The polylactic acid may for example be produced using stereospecific catalysts, which may lead to heterotactic polylactic acid. Different ratios of D to L enantiomers of lactic acid may generate a large number of extended types of polylactic acid stereospecific biopolymers. Polylactic acids may be produced using a fraction of lactic acid O-carboxyanhydride.

[0018] The composition may for example comprise > 60.0 wt% of the ethylene-based polymer, preferably > 80.0 wt%, more preferably > 90.0 wt%, even more preferably > 95.0 wt%, with regard to the total weight of the polymer composition.

[0019] The ethylene-based polymer may for example be a low-density polyethylene (LDPE), a polyethylene elastomer, a linear low-density polyethylene, a medium-density polyethylene, or a high-density polyethylene, preferably a linear low-density polyethylene.

[0020] The ethylene-based polymer may for example have a molecular weight distribution Mn / Mwof < 4.5, preferably of < 3.5, wherein wherein Mwis the weight average molecular weight and Mnis the number average molecular weight, as determined in accordance with ASTM D6474 (2012).

[0021] In certain embodiments of the invention, the ethylene-based polymer may for example be a copolymer of ethylene and a comonomer selected from 1 -butene, 1 -hexene and 1 -octene, preferably wherein the ethylene-based polymer comprises < 30.0 wt% of polymeric units derived from the comonomer, preferably > 0.5 and < 30.0 wt%, more preferably > 1.0 and < 20.0 wt%, even more preferably > 2.0 and < 15.0 wt%. The comonomer content may for example be determined via13C-NMR.

[0022] The ethylene-based polymer may for example have a melt mass-flow rate at 2.16 kg load, determined at 190°C, in accordance with ASTM D1238-13, of > 0.1 and < 100 g / 10 min, preferably of > 0.2 and < 20.0 g / 10 min, more preferably of > 0.5 and < 10.0 g / 10 min, even more preferably of > 0.5 and < 5.0 g / 10 min.24POLY0137-WO-ORD 4

[0023] The ethylene-based polymer may for example have a density of > 850 and < 970 kg / m2, preferably of > 905 and < 930 kg / m2, more preferably of > 910 and < 925 kg / m2, even more preferably of > 912 and < 920 kg / m2, as determined in accordance with ASTM D792 (2013).

[0024] It is preferred that the composition does not contain intentionally added PFAS.

[0025] The polymer composition may further comprise > 500 and < 3000 ppm, preferably > 1500 and < 2500 ppm, by weight, of 1,2-ethylenebis(stearamide), with regard to the total weight of the polymer composition.

[0026] The polymer composition may further comprise > 500 and < 2000 ppm, preferably > 500 and < 1500 ppm, by weight, of boron nitride, with regard to the total weight of the polymer composition.

[0027] The invention also relates to a film comprising or consisting of the polymer composition. Such film may be a blown film or a cast film.

[0028] In the production of such film, the ethylene-based polymer and the polyethylene glycol may be provided as separate ingredients, or as a melt-compounded formulation.

[0029] A cast film extrusion process involves the production of thin, flat films from molten polymer resins using a casting technique. The process begins with the heating of the polymer resin to a temperature above its melt flow point, typically in a heated barrel or a zone melter. The molten resin is then forced through a die, which has a die gap much smaller than the width of the molten resin, causing it to spread out and form a thin film. This film is then cooled and solidified in a chill roll system or a water bath, which can be either flat or calendared to achieve desired thicknesses and surface finishes. The cooled film may then be unwound from the chill roll and wound onto a take-up roll or a spool for further processing or packaging. The process typically involves precise temperature and pressure control for optimal film quality and uniformity.

[0030] In cast polymer film extrusion, the shape of the dies used may be selected depending on the specific type of film being produced. Generally, a flat die or slit die is used to ensure uniform thickness and width of the film. However, for specialized films like biaxially oriented films, more complex dies with multiple zones and cooling sections may be used. These dies may help to orient the molten polymer in multiple directions, which increases the film's strength and clarity.24POLY0137-WO-ORD 5

[0031] A blown film extrusion process is an industrial technique used for producing polymer films with excellent mechanical properties, optical clarity, and thermal stability. This process involves the heating, melting, and extrusion of the polymer resins through a circular or annular die, followed by the inflation of the molten polymer into a bubble by a blowing agent. The bubble is then cooled and solidified as it is carried along by a pair of nip rolls, which also ensure uniform thickness of the film. The cooled film is then transported to winders for reeling and further processing. This process allows for the production of films with varying thicknesses and widths, making it a versatile and widely used manufacturing method.

[0032] It is preferred that the extrusion moulding process is operated at a shear rate of > 200 s preferably > 500 s-1. For example, the shear rate may be > 500 and < 7000 s-1. A shear rate range in extrusion moulding may for example be > 500 and < 1000 s-1, or >1000 and < 2500 s-1, or > 2500 and < 7000 s-1

[0033] During extrusion moulding, the materials that is undergoing extrusion is, along the walls of the extrusion die, subject to a shear stress, which may be referred to as the wall shear stress. It is preferred that the wall shear stress is < 0.40 MPa, further preferred < 0.35 MPa.

[0034] The die may contain capillary zones, wherein such capillary zones have a length I diameter ratio of < 20, preferably < 15, more preferably < 10.

[0035] Alternatively, the die may be an annular die.

[0036] Further alternatively, the die is a slit die, preferably having a die gap of < 200 pm, more preferably of > 5 and < 200 pm; and preferably having a width of < 10.0 m, more preferably of > 0.5 and < 10.0 m.

[0037] The invention also relates to the use of a polylactic acid in a polymer composition comprising an ethylene-based polymer, for reduction of melt fracture in polymer films.

[0038] The invention also relates to the use of > 500 and < 3000 ppm by weight, preferably > 500 and < 2000 ppm by weight, of a polylactic acid, with regard to the total weight of the polymer composition, in a polymer composition comprising an ethylene-based polymer, for reduction of melt fracture in polymer films.24POLY0137-WO-ORD 6

[0039] The invention also relates to the use of > 500 and < 3000 ppm by weight, preferably > 500 and < 2000 ppm by weight, of a polylactic acid, with regard to the total weight of the polymer composition, in a polymer composition comprising an ethylene-based polymer, for reduction of melt fracture in polymer films, wherein the polylactic acid has:• a weight-average molecular weight (Mw) of > 50 kg / mol and < 300 kg / mol; and / or • a number-average molecular weight (Mn) of > 50 kg / mol and < 150 kg / mol; and / or • a molecular weight distribution Mw / Mnof > 1.5 and < 5.0.

[0040] The invention also relates to the use of > 500 and < 3000 ppm by weight, preferably > 500 and < 2000 ppm by weight, of a polylactic acid, with regard to the total weight of the polymer composition, in a polymer composition comprising an ethylene-based polymer, for reduction of melt fracture in polymer films, wherein the polylactic acid has:• a density of > 1.00 and < 1.50 g / cm3, as determined in accordance with ASTM D792 (2013); and / or• a melt mass-flow rate at 210°C under a load of 2.16 kg of > 1.0 and < 20.0 g / 10 min, as determined in accordance with ASTM D1238-13.

[0041] The invention also relates to the use of > 500 and < 3000 ppm by weight, preferably > 500 and < 2000 ppm by weight, of a polylactic acid, with regard to the total weight of the polymer composition, in a polymer composition comprising an ethylene-based polymer, for reduction of melt fracture in polymer films, wherein the ethylene-based polymer is an LLDPE having a density of > 905 and < 930 kg / m2, and a melt mass-flow rate at 190°C at 2.16 kg load of > 0.5 and < 5.0 g / 10 min, wherein the polylactic acid has:• a weight-average molecular weight (Mw) of > 50 kg / mol and < 300 kg / mol; and / or • a number-average molecular weight (Mn) of > 50 kg / mol and < 150 kg / mol; and / or • a molecular weight distribution Mw / Mnof > 1.5 and < 5.0.

[0042] In a particular embodiment, the invention relates to a polymer composition comprising an ethylene-based polymer and a polylactic acid, wherein:• the composition comprises > 95.0 wt%, preferably > 98.0 wt%, with regard to the total weight of the polymer composition, of the ethylene-based polymer; and• the ethylene-based polymer haso a density of > 910 and < 925 kg / m2; and24POLY0137-WO-ORD 7o a melt mass-flow rate at 190°C at 2.16 kg load of > 0.5 and < 5.0 g / 10 min; and the composition comprises of > 500 and < 3000 ppm by weight, of the polylactic acid.

[0043] In a particular embodiment, the invention relates to a polymer composition comprising an ethylene-based polymer and a polylactic acid, wherein:• the composition comprises > 95.0 wt%, preferably > 98.0 wt%, with regard to the total weight of the polymer composition, of the ethylene-based polymer; and• the ethylene-based polymer haso a density of > 910 and < 925 kg / m2; ando a melt mass-flow rate at 190°C at 2.16 kg load of > 0.5 and < 5.0 g / 10 min; and • the composition comprises of > 500 and < 3000 ppm by weight, of the polylactic acid; and• the polylactic acid has:o a weight-average molecular weight (Mw) of > 50 kg / mol and < 300 kg / mol; and / or o a number-average molecular weight (Mn) of > 50 kg / mol and < 150 kg / mol; and / oro a molecular weight distribution Mw / Mnof > 1.5 and < 5.0.

[0044] In another particular embodiment, the invention relates to a polymer composition comprising an ethylene-based polymer and a polylactic acid, wherein:• the composition comprises > 95.0 wt%, preferably > 98.0 wt%, with regard to the total weight of the polymer composition, of the ethylene-based polymer; and• the ethylene-based polymer haso a density of > 910 and < 925 kg / m2; ando a melt mass-flow rate at 190°C at 2.16 kg load of > 0.5 and < 5.0 g / 10 min; and o and Mn / Mw of < 4.5, preferably of < 3.5; and• the composition comprises of > 500 and < 3000 ppm by weight, of the polylactic acid; and• the polylactic acid has:o a weight-average molecular weight (Mw) of > 50 kg / mol and < 300 kg / mol; and / or o a number-average molecular weight (Mn) of > 50 kg / mol and < 150 kg / mol; and / oro a molecular weight distribution Mw / Mnof > 1.5 and < 5.0.24POLY0137-WO-ORD 8

[0045] In another particular embodiment, the invention relates to a polymer composition comprising an ethylene-based polymer and a polylactic acid, wherein:• the composition comprises > 95.0 wt%, preferably > 98.0 wt%, with regard to the total weight of the polymer composition, of the ethylene-based polymer; and• the ethylene-based polymer haso a density of > 910 and < 925 kg / m2; ando a melt mass-flow rate at 190°C at 2.16 kg load of > 0.5 and < 5.0 g / 10 min; and o and Mn / Mw of < 4.5, preferably of < 3.5; and• the ethylene-based polymer is a copolymer of ethylene and a comonomer selected from 1-butene, 1-hexene and 1-octene, preferably wherein the ethylene-based polymer comprises < 30.0 wt% of polymeric units derived from the comonomer, preferably > 0.5 and < 30.0 wt%, more preferably > 1.0 and < 20.0 wt%, even more preferably > 2.0 and < 15.0 wt%; and• the composition comprises of > 500 and < 3000 ppm by weight, of the polylactic acid.

[0046] In another particular embodiment, the invention relates to a polymer composition comprising an ethylene-based polymer and a polylactic acid, wherein:• the composition comprises > 95.0 wt%, preferably > 98.0 wt%, with regard to the total weight of the polymer composition, of the ethylene-based polymer; and• the ethylene-based polymer haso a density of > 910 and < 925 kg / m2; ando a melt mass-flow rate at 190°C at 2.16 kg load of > 0.5 and < 5.0 g / 10 min; and o and Mn / Mw of < 4.5, preferably of < 3.5; and• the ethylene-based polymer is a copolymer of ethylene and a comonomer selected from 1-butene, 1-hexene and 1-octene, preferably wherein the ethylene-based polymer comprises < 30.0 wt% of polymeric units derived from the comonomer, preferably > 0.5 and < 30.0 wt%, more preferably > 1.0 and < 20.0 wt%, even more preferably > 2.0 and < 15.0 wt%; and• the composition comprises of > 500 and < 3000 ppm by weight, of the polylactic acid;and• the polylactic acid has:o a weight-average molecular weight (Mw) of > 50 kg / mol and < 300 kg / mol; and / or o a number-average molecular weight (Mn) of > 50 kg / mol and < 150 kg / mol;and / or24POLY0137-WO-ORD 9o a molecular weight distribution Mw / Mnof > 1.5 and < 5.0.

[0047] The invention will now be illustrated by the following non-limiting examples.

[0048] In the context of the present invention, the below materials were used in the experiments.Table 1: Materials used.

[0049] The PE was an ethylene / 1 -hexene copolymer LLDPE, having a melt mass flow rate of 1.0 g / 10 min at 190°C, under a load of 2.16 kg, as determined in accordance with ASTM D1238-13. The PE had a density of 918 kg / m3, as determined in accordance with ASTM D792 (2013). The PE had a weight-average molecular weight (Mw) of 120 kg / mol, and an Mw / Mnof 3.3, wherein Mwand Mnare determined in accordance with ASTM D6474 (2012). The PE had a comonomer content of 8.5 wt%, as determined via13C-NMR. The PE was produced using a metallocene-type catalyst.

[0050] The PPA1 had a density of 1240 kg / m3, and a melt mass-flow rate at 210°C under load of 2.16 kg of 6.0 g / 10 min. The PPA1 has an Mwof 180 kg / mol, and Mnof 100 kg / mol, and an Mw / Mn of 1.8. The Mwand Mnof the polylactic acid may be determined by GPC using PS standards.

[0051] Using the above materials, polyethylene formulations were produced as per below.

[0052] The above formulations were subject to melt extrusion processing. The melt extrusion processing was performed using a melt extruder setup comprising a capillary die to extrude24POLY0137-WO-ORD 10circular strands. The shear rate was 398 s-1, the polymer melt temperature 230°C, and the capillary die had an L / D ratio of 30.

[0053] Each of the formulations 2 and 3 were subjected to multi-run extrusion trials, wherein the material was extruded 5 runs. During run 5, the shear viscosity was determined, as an indicator for the flow stability improvement due to the PPA addition. It was observed that using the polylactic acid (formulation 2), one could achieve an 11% viscosity reduction vis-a-vis the formulation 1, thereby achieving a processing improvement effect, and thus melt fracture reduction effect, without addition of fluoropolymer compounds, such as in formulation 3.

Claims

24POLY0137-WO-ORD 11Claims1. Polymer composition comprising an ethylene-based polymer and a polylactic acid.

2. Polymer composition according to claim 1 , wherein the composition comprises > 500 and < 3000 ppm by weight, preferably > 500 and < 2000 ppm by weight, of the polylactic acid, with regard to the total weight of the polymer composition.

3. Polymer composition according to any one of claims 1-2, wherein the polylactic acid has:• a weight-average molecular weight (Mw) of > 50 kg / mol and < 300 kg / mol; and / or • a number-average molecular weight (Mn) of > 50 kg / mol and < 150 kg / mol; and / or • a molecular weight distribution Mw / Mnof > 1.5 and < 5.0.

4. Polymer composition according to any one of claims 1-3, wherein the polylactic acid has:• a density of > 1.00 and < 1.50 g / cm3, as determined in accordance with ASTM D792 (2013); and / or• a melt mass-flow rate at 210°C under a load of 2.16 kg of > 1.0 and < 20.0 g / 10 min, as determined in accordance with ASTM D1238-13.

5. Polymer composition according to any one of claims 1-4, wherein the composition comprises > 60.0 wt% of the ethylene-based polymer, preferably > 80.0 wt%, more preferably > 90.0 wt%, even more preferably > 95.0 wt%, with regard to the total weight of the polymer composition.

6. Polymer composition according to any one of claims 1-5, wherein the ethylene-based polymer is a low-density polyethylene (LDPE), a polyethylene elastomer, a linear low- density polyethylene, a medium-density polyethylene, or a high-density polyethylene, preferably a linear low-density polyethylene.

7. Polymer composition according to any one of the claims 1-6, wherein the ethylene-based polymer has a molecular weight distribution Mn / Mwof < 4.5, preferably of < 3.5, wherein wherein Mwis the weight average molecular weight and Mnis the number average molecular weight, as determined in accordance with ASTM D6474 (2012).24POLY0137-WO-ORD 128. Polymer composition according to any one of claims 1-7, wherein the ethylene-based polymer is a copolymer of ethylene and a comonomer selected from 1 -butene, 1 -hexene and 1 -octene, preferably wherein the ethylene-based polymer comprises < 30.0 wt% of polymeric units derived from the comonomer, preferably > 0.5 and < 30.0 wt%, more preferably > 1.0 and < 20.0 wt%, even more preferably > 2.0 and < 15.0 wt%.

9. Polymer composition according to any one of claims 1-8, wherein the ethylene-based polymer has a melt mass-flow rate at 2.16 kg load, determined at 190°C, in accordance with ASTM D1238-13, of > 0.1 and < 100 g / 10 min, preferably of > 0.2 and < 20.0 g / 10 min, more preferably of > 0.5 and < 10.0 g / 10 min, even more preferably of > 0.5 and < 5.0 g / 10 min.

10. Polymer composition according to any one of claims 1-9, wherein the ethylene-based polymer has a density of > 850 and < 970 kg / m2, preferably of > 905 and < 930 kg / m2, more preferably of > 910 and < 925 kg / m2, even more preferably of > 912 and < 920 kg / m2, as determined in accordance with ASTM D792 (2013).

11. Polymer composition according to any one of claims 1-10, wherein the composition does not contain intentionally added PFAS.

12. Film comprising or consisting of the polymer composition according to any one of claims 1-11.

13. Film according to claim 12, wherein the film is a blown film or a cast film.

14. Process for production of a film according to any one of claims 12-13, wherein the ethylene-based polymer and the polylactic acid are provided as separate ingredients or as a melt-compounded formulation.

15. Use of a polylactic acid in a polymer composition comprising an ethylene-based polymer, for reduction of melt fracture in polymer films.

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