POLYMER COMPOSITIONS COMPRISING MIXTURES OF POLYOLEFINS

Abstract

The invention provides a polyolefin composition comprising (i) a polyolefin (A) comprising epoxy groups; and (ii) a polyolefin (B) comprising carboxylic acid groups and/or precursors thereof, with the proviso that at least one of (A) and (B) is polyethylene. Preferably one of (A) and (B) is a low density polyethylene (LDPE) and the other is a polypropylene.

Claims

1. A polyolefin composition comprising (i) a polyolefin (A) comprising epoxy groups; and (ii) a polyolefin (B) comprising carboxylic acid groups and/or precursors thereof, with the proviso that one of polyolefin (A) and polyolefin (B) is a low density polyethylene (LDPE) and the other of polyolefin (A) and polyolefin (B) is a polypropylene.

2. A polyolefin composition as claimed in claim 1, wherein the carboxylic acid groups and/or precursors thereof are grafted to said polyolefin (B).

3. A polyolefin composition as claimed in claim 1 or claim 2, wherein the carboxylic acid groups and/or precursor thereof is at least one of acrylic acid, maleic anhydride (MAH), or an alkyl (meth)acrylate such as tert-butyl methacrylate or tert-butyl acrylate, preferably maleic anhydride.

4. A polyolefin composition as claimed in any of claims 1 to 3, wherein polyolefin (A) is an LDPE and polyolefin (B) is a polypropylene.

5. A polyolefin composition as claimed in any of claims 1 to 3, wherein polyolefin (A) is a polypropylene and polyolefin (B) is an LDPE.

6. A polyolefin composition as claimed in any of claims 1 to 5, wherein component (i) is present in an amount of 2 to 98 wt %, preferably 50 to 98 wt %, relative to the total weight of the composition as a whole.

7. A polyolefin composition as claimed in any of claims 1 to 6, wherein component (ii) is present in an amount of 2 to 98 wt %, preferably 2 to 50 wt %, relative to the total weight of the composition as a whole.

8. A polyolefin composition as claimed in any of claims 1 to 7, wherein component (i) is present in an amount of 90 to 98 wt % and component (ii) is present in an amount of 2 to 10 wt %, relative to the total weight of the composition as a whole.

9. A polyolefin composition as claimed in any of claims 1 to 8, wherein the epoxy groups are present in the form of an epoxy-group-containing comonomer.

10. A polyolefin composition as claimed in claim 9, wherein said epoxy-group-containing comonomer is selected from the group consisting of 1,2-epoxy decene, 1,2-epoxy-5-hexene, 3,4-epoxy-1-butene, glycidyl methacrylate, glycidyl acrylate, and allyl glycidyl ether, preferably glycidyl methacrylate.

11. A polyolefin composition as claimed in any of claims 1 to 10, wherein said LDPE has an MFR.sub.2 (2.16 kg, 190° C.) of 0.1 to 10 g/10 min, such as 0.5 to 5.0 g/10 min.

12. A polyolefin composition as claimed in any of claims 1 to 11, wherein said LDPE has a density of 917 to 935 kg/m.sup.3.

13. A polyolefin composition as claimed in any of claims 1 to 12, wherein said polypropylene has a melting temperature (Tm) of greater than 140° C., preferably greater than 150° C.

14. A polyolefin composition as claimed in any of claims 1 to 13, wherein said composition is substantially free of peroxide, e.g. comprises less than 0.5 wt % peroxide, relative to the total weight of the composition as a whole.

15. A process for crosslinking a polyolefin composition as defined in any of claims 1 to 14, wherein said process comprises heating said polyolefin composition to a temperature greater than the melting point of at least the major polymer component(s) of the composition.

16. A process as claimed in claim 15, wherein said process does not use peroxide.

17. A cable, such as a power cable, comprising one or more conductors surrounded by at least one layer, wherein said layer comprises a polyolefin composition as defined in any of claims 1 to 14.

18. A cable as claimed in claim 17 where said one or more conductors are surrounded by at least an inner semiconductive layer, an insulation layer and an outer semiconductive layer, in that order.

19. A cable as claimed in claim 17 or 18, wherein said layer comprising said polyolefin composition is an insulation layer.

20. A cable as claimed in any of claims 17 to 19, wherein said cable is crosslinked.

21. A process for producing a cable comprising the steps of: applying on one or more conductors, a layer comprising a polyolefin composition as defined in any of claims 1 to 14.

22. The use of a polyolefin composition as defined in any of claims 1 to 14 in the manufacture of an insulation layer or semi-conductive layer in a cable, preferably a power cable.

Description

DESCRIPTION OF FIGURES

[0155] FIG. 1: Reaction scheme between PP-g-MAH and poly(E-stat-GMA). R.sub.1 is typically hydrogen or any alkyl group.

[0156] FIG. 2: Tensile creep strain vs. time for comparative and inventive examples [0157] a: Comparative example 1: Extruded at 220° C. for 5 minutes, pressed for 1 minute at 180° C. (gel content: 0%) [0158] b: Inventive example 1: Extruded at 200° C. for 5 minutes, pressed for 1 minute at 180° C. (gel content: 20%) [0159] c: Inventive example 2: Extruded at 220° C. for 5 minutes, pressed for 15 minutes at 180° C. (gel content: 40%)

EXAMPLES

Determination Methods

[0160] Unless otherwise stated in the description or claims, the following methods were used to measure the properties defined generally above and in the claims and in the examples below. The samples were prepared according to given standards, unless otherwise stated.
Wt %: % by weight

Melt Flow Rate

[0161] The melt flow rate (MFR) is determined according to ISO 1133 and is indicated in g/10 min. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR is determined at 190° C. for polyethylene and at 230° C. for polypropylene. MFR may be determined at different loadings such as 2.16 kg (MFR.sub.2) or 21.6 kg (MFR.sub.21).

Molecular Weight

[0162] Mz, Mw, Mn, and MWD are measured by Gel Permeation Chromatography (GPC) according to the following method:
The weight average molecular weight Mw and the molecular weight distribution (MWD=Mw/Mn wherein Mn is the number average molecular weight and Mw is the weight average molecular weight; Mz is the z-average molecular weight) is measured according to ISO 16014-4:2003 and ASTM D 6474-99. A Waters GPCV2000 instrument, equipped with refractive index detector and online viscosimeter was used with 2×GMHXL-HT and 1× G7000HXL-HT TSK-gel columns from Tosoh Bioscience and 1,2,4-trichlorobenzene (TCB, stabilized with 250 mg/L 2,6-Di tert-butyl-4-methyl-phenol) as solvent at 140° C. and at a constant flow rate of 1 mL/min 209.5 μL of sample solution were injected per analysis. The column set was calibrated using universal calibration (according to ISO 16014-2:2003) with at least 15 narrow MWD polystyrene (PS) standards in the range of 1 kg/mol to 12 000 kg/mol. Mark Houwink constants were used as given in ASTM D 6474-99. All samples were prepared by dissolving 0.5-4.0 mg of polymer in 4 mL (at 140° C.) of stabilized TCB (same as mobile phase) and keeping for max. 3 hours at a maximum temperature of 160° C. with continuous gentle shaking prior sampling in into the GPC instrument.

Comonomer Contents

[0163] a) Comonomer content in random copolymer of polypropylene:
Quantitative Fourier transform infrared (FTIR) spectroscopy was used to quantify the amount of comonomer. Calibration was achieved by correlation to comonomer contents determined by quantitative nuclear magnetic resonance (NMR) spectroscopy.
The calibration procedure based on results obtained from quantitative .sup.13C-NMR spectroscopy was undertaken in the conventional manner well documented in the literature.
The amount of comonomer (N) was determined as weight percent (wt %) via:

N=k1(A/R)+k2

wherein A is the maximum absorbance defined of the comonomer band, R the maximum absorbance defined as peak height of the reference peak and with k1 and k2 the linear constants obtained by calibration. The band used for ethylene content quantification is selected depending if the ethylene content is random (730 cm.sup.−1) or block-like (as in heterophasic PP copolymer) (720 cm.sup.−1). The absorbance at 4324 cm.sup.−1 was used as a reference band.
b) Quantification of alpha-olefin content in linear low density polyethylenes and low density polyethylenes by NMR spectroscopy:
The comonomer content was determined by quantitative 13C nuclear magnetic resonance (NMR) spectroscopy after basic assignment (J. Randall JMS—Rev. Macromol. Chem. Phys., C.sub.29(2&3), 201-317 (1989). Experimental parameters were adjusted to ensure measurement of quantitative spectra for this specific task.
Specifically solution-state NMR spectroscopy was employed using a Bruker AvanceIII 400 spectrometer. Homogeneous samples were prepared by dissolving approximately 0.200 g of polymer in 2.5 ml of deuterated-tetrachloroethene in 10 mm sample tubes utilising a heat block and rotating tube oven at 140 C. Proton decoupled 13C single pulse NMR spectra with NOE (powergated) were recorded using the following acquisition parameters: a flip-angle of 90 degrees, 4 dummy scans, 4096 transients an acquisition time of 1.6 s, a spectral width of 20 kHz, a temperature of 125 C, a bilevel WALTZ proton decoupling scheme and a relaxation delay of 3.0 s. The resulting FID was processed using the following processing parameters: zero-filling to 32k data points and apodisation using a gaussian window function; automatic zeroth and first order phase correction and automatic baseline correction using a fifth order polynomial restricted to the region of interest.
Quantities were calculated using simple corrected ratios of the signal integrals of representative sites based upon methods well known in the art.
c) Comonomer content of polar comonomers in low density polyethylene
(1) Polymers containing>6 wt % polar comonomer units
Comonomer content (wt %) was determined in a known manner based on Fourier transform infrared spectroscopy (FTIR) determination calibrated with quantitative nuclear magnetic resonance (NMR) spectroscopy. Below is exemplified the determination of the polar comonomer content of ethylene ethyl acrylate, ethylene butyl acrylate and ethylene methyl acrylate. Film samples of the polymers were prepared for the FTIR measurement: 0.5-0.7 mm thickness was used for ethylene butyl acrylate and ethylene ethyl acrylate and 0.10 mm film thickness for ethylene methyl acrylate in amount of >6 wt % Films were pressed using a Specac film press at 150° C., approximately at 5 tons, 1-2 minutes, and then cooled with cold water in a not controlled manner. The accurate thickness of the obtained film samples was measured. After the analysis with FTIR, base lines in absorbance mode were drawn for the peaks to be analysed. The absorbance peak for the comonomer was normalised with the absorbance peak of polyethylene (e.g. the peak height for butyl acrylate or ethyl acrylate at 3450 cm.sup.−1 was divided with the peak height of polyethylene at 2020 cm.sup.−1). The NMR spectroscopy calibration procedure was undertaken in the conventional manner which is well documented in the literature, explained below.

[0164] For the determination of the content of methyl acrylate a 0.10 mm thick film sample was prepared. After the analysis the maximum absorbance for the peak for the methylacrylate at 3455 cm.sup.−1 was subtracted with the absorbance value for the base line at 2475 cm.sup.−1 (A.sub.methylacrylate−A.sub.2475) Then the maximum absorbance peak for the polyethylene peak at 2660 cm.sup.−1 was subtracted with the absorbance value for the base line at 2475 cm.sup.1 (A.sub.2660−A.sub.2475). The ratio between (A.sub.methylacrylate−A.sub.2475) and (A.sub.2660−A.sub.2475) was then calculated in the conventional manner which is well documented in the literature.

The weight-% can be converted to mol-% by calculation. It is well documented in the literature.
Quantification of copolymer content in polymers by NMR spectroscopy
The comonomer content was determined by quantitative nuclear magnetic resonance (NMR) spectroscopy after basic assignment (e.g. “NMR Spectra of Polymers and Polymer Additives”, A. J. Brandolini and D. D. Hills, 2000, Marcel Dekker, Inc. New York). Experimental parameters were adjusted to ensure measurement of quantitative spectra for this specific task (e.g “200 and More NMR Experiments: A Practical Course”, S. Berger and S. Braun, 2004, Wiley-VCH, Weinheim). Quantities were calculated using simple corrected ratios of the signal integrals of representative sites in a manner known in the art.
(2) Polymers containing 6 wt. % or less polar comonomer units
Comonomer content (wt. %) was determined in a known manner based on Fourier transform infrared spectroscopy (FTIR) determination calibrated with quantitative nuclear magnetic resonance (NMR) spectroscopy. Below is exemplified the determination of the polar comonomer content of ethylene butyl acrylate and ethylene methyl acrylate. For the FT-IR measurement a film samples of 0.05 to 0.12 mm thickness were prepared as described above under method 1). The accurate thickness of the obtained film samples was measured.
After the analysis with FT-IR base lines in absorbance mode were drawn for the peaks to be analysed. The maximum absorbance for the peak for the comonomer (e.g. for methylacrylate at 1164 cm.sup.−1 and butylacrylate at 1165 cm.sup.−1) was subtracted with the absorbance value for the base line at 1850 cm.sup.−1 (A.sub.polar comonomer−A.sub.1850). Then the maximum absorbance peak for polyethylene peak at 2660 cm.sup.−1 was subtracted with the absorbance value for the base line at 1850 cm.sup.−1 (A.sub.2660−A.sub.1850). The ratio between (A.sub.comonomer−A.sub.1850) and (A.sub.2660−A.sub.1850 was then calculated. The NMR spectroscopy calibration procedure was undertaken in the conventional manner which is well documented in the literature, as described above under method 1).

[0165] The weight-% can be converted to mol-% by calculation. It is well documented in the literature.

[0166] Below is exemplified how polar comonomer content obtained from the above method (1) or (2), depending on the amount thereof, can be converted to micromol or mmol per g polar comonomer as used in the definitions in the text and claims:

[0167] The millimoles (mmol) and the micro mole calculations have been done as described below.

[0168] For example, if 1 g of the poly(ethylene-co-butylacrylate) polymer, which contains 20 wt % butylacrylate, then this material contains 0.20/M.sub.butylacrylate (128 g/mol)=1.56×10.sup.−3 mol. (=1563 micromoles).

The content of polar comonomer units in the polar copolymer C.sub.polar comonomer is expressed in mmol/g (copolymer). For example, a polar poly(ethylene-co-butylacrylate) polymer which contains 20 wt. % butyl acrylate comonomer units has a C.sub.polar comonomer of 1.56 mmol/g.
The used molecular weights are: M.sub.butylacrylate=128 g/mole, M.sub.ethylacrylate=100 g/mole, M.sub.methylacrylate=86 g/mole).

Density

[0169] Low density polyethylene (LDPE): The density was measured according to ISO 1183-2. The sample preparation was executed according to ISO 1872-2 Table 3 Q (compression moulding).
Density of the PP polymer was measured according to ISO 1183/1872-2B.

Method for Determination of the Amount of Double Bonds in the Polymer Composition or in the Polymer

[0170] This can be carried out following the protocol in WO2011/057928

Melting Temperature

[0171] Melting temperature™, is measured with Mettler TA820 differential scanning calorimetry (DSC) on 5-10 mg samples. Melting curves are obtained during 10° C./min cooling and heating scans between 30° C. and 225° C. Melting temperatures were taken as the peaks of endotherms and exotherms.

Gel Content

[0172] The gel content of crosslinked samples was determined gravimetric ally using a solvent extraction technique. The samples (˜250 mg) were placed in pre-weighed 100 mesh stainless steel baskets and extracted in 0.5 dm.sup.3 decalin by refluxing the solvent for 6 h. After the extraction, the samples were dried first at ambient overnight and then under vacuum for about 8 hours at 50° C. After this period, the non-soluble fraction that remained in the basket reached a constant weight, which was used to calculate the gel content.

Creep Tests Using Dynamic Mechanical Analyser

[0173] 20×5 mm pieces were cut from 1.25 mm thick melt-pressed films. Creep measurements were carried out using a TA Q800 DMA in tensile mode. First, samples were heated from 25° C. to 135° C. at 10° C. min.sup.−1 with a constant preload force of 0.001 N, corresponding to a stress of 0.16 kPa applied. Upon reaching 135° C., a constant stress of 5 kPa was applied for 100 min to the sample and the resulting strain was recorded as a function of time.

Materials

[0174] LDPE: The ethylene-glycidyl methacrylate copolymer poly(E-stat-GMA) with a GMA content of 4.5 wt %, a melt flow index MFI˜2 g/10 min (190° C./2.16 kg, provided by supplier), and a density of 0.93 g cm.sup.−3 was obtained from Arkema (Lotader series AX8820).
PP: The polypropylene-maleic anhydride graft copolymer PP-g-MAH with a MA content of 8-10 wt %, viscosity is 4 poise and a density of 0.93 g cm.sup.−3 was obtained from Sigma Aldrich (product number 427845).

Sample Preparation:

[0175] A polyolefin composition was prepared comprising 95 wt % LDPE and 5 wt % PP materials as defined above, by compounding through extrusion for 5 minutes at 220° C. using an Xplore Micro Compounder MC5. In a hot press, the extruded material was heated to 180° C. and the pressure was increased up to 37000 kN/m.sup.2. when the material was left for a further minute before cooling to room temperature. This procedure resulted in 1.25 mm thick plates.

Results

[0176] The samples for creep experiments were prepared by cutting 20×5 mm samples from 1.25 mm thick melt-pressed films. Creep results are shown in Table 1 and FIG. 2. The results clearly illustrate that the inventive examples have considerably higher creep resistance. For example, after 30 seconds of loading (5 kPa), the strain in the comparative composition is 147%, whereas the inventive compositions exhibit a strain below 6%.

TABLE-US-00001 TABLE 1 Comparative Inventive Inventive example 1 example 1 example 2 “LDPE” [weight %] 95 0 0 “LDPE-epoxy” [weight %] 0 95 95 “PP-MAH” [weight %] 0 5 5 “iPP” [weight %] 5 0 0 Compounding temperature [° C.] 220 200 220 Plaque press temperature [° C.] 180 180 180 Creep temperature [° C.] 135 135 135 Creep stress [kPa] 5 5 5 Creep strain at 15 sec [%] 62 4.6 4.2 Creep strain at 30 sec [%] 147 5.4 4.8 Creep strain at 1 min [%] fail 6.5 5.6 Creep strain at 15 min [%] fail 12.5 9.9 Creep strain at 55 min [%] fail 14.3 11.3 Creep strain at 100 min [%] fail 15 11.9