Visbreaking process

Abstract

A process for increasing MFR.sub.2 of a polyethylene copolymer or an ethylene plastomer or elastomer comprising: (I) extruding a copolymer of polyethylene copolymer having a density of 910 to 970 kg/m.sup.3 and an MFR.sub.2 of 1 and 100 g/10 min or an ethylene plastomer or elastomer having a density of 855 to 910 kg/m.sup.3 and an MFR.sub.2 of 0.5 and 100 g/10 min in the presence of 0.1 to 2 wt % of a non-peroxide radical initiator so as to produce a polyethylene copolymer having an MFR.sub.2 of 200 g/10 min or more, or an ethylene plastomer or elastomer having a MFR.sub.2 of 200 g/10 min or more.

Claims

1. A process for increasing the MFR.sub.2 of a polyethylene copolymer or an ethylene plastomer or elastomer, the process comprising: extruding a copolymer of polyethylene having a density of from 910 to 970 kg/m.sup.3 and an MFR.sub.2 of from 1 to 100 g/10 min in the presence of from 0.1 to 2 wt % of a radical initiator so as to produce a polyethylene copolymer having an MFR.sub.2 of 200 g/10 min or more, or extruding an ethylene plastomer or elastomer having a density of from 855 to 910 kg/m.sup.3 and an MFR.sub.2 of from 0.5 to 100 g/10 min in the presence of 0.1 to 2 wt % of a radical initiator so as to produce an ethylene plastomer or elastomer having an MFR.sub.2 of 200 g/10 min or more, wherein the radical initiator comprises a non-peroxide radical initiator, a radical initiator which decomposes at a temperature greater than 200 C., or a combination thereof.

2. The process of claim 1, wherein the radical initiator decomposes at a temperature greater than 200 C.

3. The process of claim 1, wherein the extruding is performed by an extruder operated with a screw speed of from 300 to 1400 rpm.

4. The process of claim 1, wherein the produced polyethylene copolymer or ethylene plastomer or elastomer has an MFR.sub.2 which is 200 g/10 min or more higher than the MFR.sub.2 before extrusion.

5. The process of claim 1, wherein the MFR.sub.2 of the polyethylene copolymer or ethylene plastomer or elastomer after extrusion is at least 500 g/10 min.

6. The process of claim 1, wherein the MFR.sub.2 of the polyethylene copolymer or ethylene plastomer or elastomer before extrusion is from 1 to 10 g/10 min.

7. The process of claim 1, wherein the extruding is performed by an extruder comprising a barrel, wherein heat is applied to the barrel at a maximum temperature of at least 300 C.

8. The process of claim 3, wherein the screw speed in the extruder is from 300 to 1200 rpm.

9. The process of claim 3, wherein the extruder provides a specific energy input (SEI) of 0.15 kWh/kg or more.

10. The process of claim 1, wherein all of the radical initiator is added at the start of the extrusion.

11. A method comprising using extruder screw speed or radical initiator content to control the MFR.sub.2 of a visbroken polyethylene copolymer or ethylene plastomer or elastomer in a process in which: a polyethylene copolymer having a density of from 910 to 970 kg/m.sup.3 and an MFR.sub.2 of from 1 to 100 g/10 min, or an ethylene plastomer or elastomer having a density of from 855 to 910 kg/m.sup.3 and an MFR.sub.2 of from 0.5 to 100 g/10 min is extruded in the presence of from 0.1 to 2 wt % of a radical initiator so as to produce: a polyethylene copolymer having an MFR.sub.2 of 200 g/10 min or more, or an ethylene plastomer or elastomer having a MFR.sub.2 of 200 g/10 min or more.

Description

(1) The invention will now be described with reference to the following non limiting examples and figures.

(2) FIG. 1 shows molecular weight distribution (by GPC) of the Ex 1 material (d 882 and MFR2 85) before and after visbreaking; also in comparison with in-reactor Dow material Affinity GA1900 (MFR21000):

(3) TABLE-US-00001 Material Mw/Mn (GPC) IE6 (MFR ~635.6) 2.65 Ethylene Octene Plastomer (MFR ~85) 2.60 Dow Affinity GA1900 (MFR~1000) 2.04

(4) FIG. 2 shows the molecular weight distribution (by GPC) of the Ex 2 material (d 870 and MFR2 7) before and after visbreaking showing quite similar properties to that of Ex 1 (d 882 and MFR2 85).

(5) FIG. 3 shows the relationship between MFR and SEI. It is clear that as SEI increases, MFR increases.

TEST METHODS

(6) MFR.sub.2 (190 C.) is measured according to ISO 1133 (190 C., 2.16 kg load).

(7) Density is measured according to ISO 1183.

(8) Melting Temperature Tm

(9) The melting temperature Tm, was measured with a TA Instruments Q2000 differential scanning calorimetry device (DSC) according to ISO 11357/3 on 5 to 10 mg samples. Melting temperatures were obtained in a heat/cool/heat cycle with a scan rate of 10 C./min between 30 C. and 180 C. Melting and crystallisation temperatures were taken as the peaks of the endotherms and exotherms in the cooling cycle and the second heating cycle respectively.

(10) Number average molecular weight (Mn), weight average molecular weight (Mw) and polydispersity (Mw/Mn) are determined by Gel Permeation Chromatography (GPC) according to the following method:

(11) The Weight Average Molecular Weight

(12) Mw and the polydispersity (Mw/Mn), wherein Mn is the number average molecular weight and Mw is the weight average molecular weight) is measured by a method based on ISO 16014-1:2003 and ISO 16014-4:2003. A Waters Alliance GPCV 2000 instrument, equipped with refractive index detector and online viscosimeter was used with 3TSK-gel columns (GMHXL-HT) from TosoHaas and 1,2,4-trichlorobenzene (TCB, stabilized with 200 mg/L 2,6-Di tert butyl-4-methyl-phenol) as solvent at 145 C. and at a constant flow rate of 1 mL/min. 216.5 L of sample solution were injected per analysis. The column set was calibrated using relative calibration with 19 narrow MWD polystyrene (PS) standards in the range of 0.5 kg/mol to 11 500 kg/mol and a set of well characterized broad polypropylene standards. All samples were prepared by dissolving 5-10 mg of polymer in 10 mL (at 160 C.) of stabilized TCB (same as mobile phase) and keeping for 3 hours with continuous shaking prior sampling in into the GPC instrument.

(13) Comonomer content in polyethylene was measured in a known manner based on Fourier transform infrared spectroscopy (FTIR) calibrated with 13C-NMR, using Nicolet Magna 550 IR spectrometer together with Nicolet Omnic FTIR software. Films having a thickness of about 250 m were compression molded from the samples. Similar films were made from calibration samples having a known content of the comonomer. The comonomer content was determined from the spectrum from the wave number range of from 1430 to 1100 cm-1. The absorbance is measured as the height of the peak by selecting the so-called short or long base line or both. The short base line is drawn in about 1410-1320 cm-1 through the minimum points and the long base line about between 1410 and 1220 cm-1. Calibrations need to be done specifically for each base line type. Also, the comonomer content of the unknown sample needs to be within the range of the comonomer contents of the calibration samples.

(14) Viscosity Eta0.05

(15) The characterization of polymer melts by dynamic shear measurements complies with ISO standards 6721-1 and 6721-10. The measurements were performed on an Anton Paar 10 MCR501 stress controlled rotational rheometer, using cone-plate geometry (diameter 25 mm, angular of 1 of the cone). Measurements were undertaken on compression molded plates, using nitrogen atmosphere and setting a strain within the linear viscoelastic regime. The oscillatory shear tests were done at a temperature of 190 C. applying a frequency of 0.05 rad/s and setting a gap of 1.3 mm. The values of viscosity (*) were obtained as a function of frequency ({acute over ()}). Thereby, e.g. *0.05 rad/s (eta0.05) is used as abbreviation for the viscosity at the frequency of 0.05 rad/s. The values are determined by means of a single point interpolation procedure, as defined by Rheoplus software, the option from Rheoplus -Interpolate y-values to x-values from parameter and the logarithmic interpolation type was applied.

(16) XHU

(17) About 0.5 g of the polymer (mp) are weighed and put in a mesh of metal (mm) which is weighed (mp+mm). The polymer in the mesh is extracted in a soxhlet apparatus with boiling xylene for 5 hours. The eluent is then replaced by fresh xylene and the boiling is continued for another hour. Subsequently, the mesh is dried and weighed again (mXHU+mm).

(18) The mass of the xylene hot insoluble (mXHU) obtained by the formula (mXHU+mm)mm=mXHU is put in relation to the weight of the polymer to obtain the fraction of xylene insolubles mXHU/mp.

(19) Material Used:

(20) An ethylene-octene plastomer was used in the experiments. The plastomer is produced in a solution polymerisation process (Compact) using a metallocene catalyst and has the following properties as shown in Table 1.

(21) TABLE-US-00002 TABLE 1 Property Unit Value Density Kg/m.sup.3 882 MFR2 g/10 min 85 Melting point C. 76 C8 content Wt % 26.8 C2 content Wt % 73.2 MWD 2.6
Extrusion Conditions:

(22) The plastomer of table 1 was subjected to a one step extrusion process in the presence of a radical initiator, Perkadox 30 (Akzo Nobel) used in a solid state. The extruder used was a Coperion W&P ZSK 32 MC Plus. The temperature profile is set as the following: barrel 1 at 20 C., barrel 2 at 100 C., barrel 3 to 12 at 350 C. and die-plate at 150 C.

(23) The screw speed varies between 450 and 1200 revolutions per minute and throughput is kept in the range of 10-30 kg/hour.

(24) The main polymer is dosed in the main hopper of the extruder. The radical initiator is either dosed at once to the first barrel of the extruder or at both first and sixth barrels at the same time based on half-split of its amount.

(25) The visbroken material exiting the extruder die was taken for MFR measurement.

(26) As the barrel temperature was set at 350 C., the polymer melt temperature coming out of the die was at least 335 C.

(27) Further details of the extrusion process are explained in table 2.

(28) TABLE-US-00003 TABLE 2 Melt R.I R.I. temper- Eta content content ature (0.05 Cross- Screw Through- at 1.sup.st at 6.sup.st at die Resi- rad/s) linking Initial speed, put, barrel, barrel, exit, dence SEI, 190 C. Final (XHU), Run MFR2 rpm kg/h wt.-% wt.-% C. time, s kWh/kg Pa .Math. s MFR2 wt.-% C1 85 450 20 340 60 0.25 88 116.3 0.09 IE1 85 450 20 0.2 337 60 0.25 27 319.8 0.15 IE2 85 450 20 0.2 0.2 338 60 0.25 26 337.3 0.05 IE3 85 1200 30 0.2 349 40 0.37 25 433.3 0.28 IE4 85 1200 20 0.2 0.2 359 40 0.37 31 361.5 0.00 IE5 85 1200 20 0.4 0.4 340 40 0.40 17 507.0 0.01 R.I. means Radical Initiator XHU means Xylol Hot Unsoluble

(29) The examples demonstrate that a final MFR (190 C./2.16 kg) of 500 g/10 min can be achieved based on the starting MFR of 85 g/10 min. Also, final MFR values can be controlled. Higher initiator content leads to higher MFR. Faster screw speed leads to higher MFR. Higher SEI leads to higher MFR.

Examples 6 to 9

(30) The experiment was repeated using different starting plastomers/elastomers but the same general extrusion conditions. The plastomers/elastomers used in example 2 are: Ex 6 plastomer density 882 kg/m.sup.3 and MFR2 of 85 g/10 min. Ex 7+8 plastomer density of 882 kg/m.sup.3 and MFR2 of 6.6 g/10 min. Ex 9 elastomer density of 870 kg/m.sup.3 and MFR2 of 7.0 g/10 min.

(31) These ethylene octene plastomers/elastomers were produced in a solution polymerisation process (Compact) using a metallocene catalyst

(32) TABLE-US-00004 TABLE 3 Melt R.I R.I. temper- Eta cont cont ature (0.05 Cross- Screw Through- at 1.sup.st at 6.sup.st at die Resi- rad/s) linking Density/ speed, put, barrel barrel exit, dence SEI, 190 C. Final (XHU), Run MFR2 rpm kg/h wt.-% wt.-% C. time, s kWh/kg Pa .Math. s MFR2 wt.-% IE6 882/85 1200 20 0.8 347 45 0.40 14 635.6 IE7 882/6.6 1200 20 0.4 0.4 341 44 0.50 16 712.3 0.005 IE8 882/6.6 450 10 0.4 0.4 338 95 0.42 24 490.1 0.005 IE9 870/7.0 1200 20 0.8 342 46 0.46 18 560.5 0.12
Examples demonstrate that high MFR values can also be achieved when initial MFR is much lower than 85 g/10 min.

(33) Visual observation of the product was conducted and all visbroken examples had a white shade/colour with an absence of yellowness.