A POLYMER COMPOSITION SUITABLE FOR GAMMA-RAY STERILIZATION

Abstract

The present invention is directed to a polymer composition (C) comprising a first propylene homopolymer (H-PP), at least one hydrocarbon oil, at least one nucleating agent and at least one antioxidant, a moulded article formed from said polymer composition, a process for gamma-ray sterilization of said moulded article and uses of hydrocarbon oil in said polymer composition for improving resistance to gamma-ray radiation and reducing discoloration after gamma-ray sterilization in said polymer composition.

Claims

1. A polymer composition (C), comprising, based on the total weight of the polymer composition (C): (a) 91.0 to 98.0 wt.-% of a propylene homopolymer (H-PP), (b) 1.98 to 9.0 wt.-% of at least one hydrocarbon oil (WO), (c) 0.01 to 0.7 wt.-% of at least one nucleating agent (NA), and (d) 0.01 to 2.0 wt.-% of at least one antioxidant (AO); wherein the sum of components (a), (b), (c) and (d) adds up to at least 95 wt.-% of the total weight of the polymer composition (C) and the propylene homopolymer (H-PP) is an isotactic propylene homopolymer defined by (i) a melt flow rate MFR2 determined according to ISO1133 at 230° C. and 2.16 kg in the range from 4.0 to 22.0 g/10 min; (ii) a melting temperature in the range of 145 to 162° C. as determined by differential scanning calorimetry (DSC); and (iii) a content of 2,1 erythro regio-defects in the range from 0.1 to 1.3 mol % as determined by 13C-NMR spectroscopy.

2. The polymer composition (C) according to claim 1, having a melt flow rate MFR2 determined according to ISO1133 at 230° C. and 2.16 kg in the range from 5.0 to 25.0 g/10 min.

3. The polymer composition (C) according to claim 1, wherein the propylene homopolymer (H-PP) has a polydispersity (Mw/Mn) in the range from 2.0 to 4.5 as determined by GPC according to ISO 16014.

4. The polymer composition (C) according to claim 1, wherein the propylene homopolymer (H-PP) is prepared in the presence of a metallocene catalyst.

5. The polymer composition (C) according to claim 1, wherein the propylene homopolymer (H-PP) is characterized by a high isotacticity, defined as pentad regularity <mmmm> of more than 96.0 mol % as determined by 13C-NMR spectroscopy.

6. A moulded article comprising at least 90 wt. % of the polymer composition (C) as defined in claim 1, based on the total weight of the moulded article.

7. The moulded article according to claim 6 being a medical, pharmaceutical or diagnostic article.

8. The moulded article according to claim 6, which has been gamma-ray sterilized at a dose of at least 15 kGy.

9. The moulded article according to claim 6, having an overall migration in the polymer composition (C) as determined according to EN ISO 1186-14:2002 on injection moulded plaques, 60×60×1 mm.sup.3 of less than 60.0 mg/dm.sup.2.

10. The moulded article according to claim 6, having a discoloration of the polymer composition (C) after gamma-ray sterilization at 50 kGy and 60 days of aging as defined by yellowness index of not higher than 23 as determined on injection moulded plaques 60×60×1 mm.sup.3 according to standard method ASTM E313.

11. The moulded article according to claim 6, having a Charpy notched impact strength in the range of 2.5 to 15.0 kJ/m.sup.2, as determined according to ISO 179 1 eA, and a retention of said impact strength after gamma-ray sterilization at 50 kGy and 60 days of aging of more than 75%.

12. A process for gamma-ray sterilization of articles comprising the steps of: providing the moulded article as defined by claim 6, and subjecting said moulded article to gamma-ray sterilization.

13. The process according to claim 12, wherein the gamma-ray sterilization is carried out at a dose in the range of 15 to 150 kGy.

14-15. (canceled)

Description

EXAMPLES

A. Measuring Methods

[0112] The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples unless otherwise defined.

[0113] MFR.sub.2 (230° C.) is measured according to ISO 1133 (230° C., 2.16 kg load).

Quantification of Microstructure by NMR Spectroscopy

[0114] Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content and comonomer sequence distribution of the polymers. Quantitative .sup.13C {.sup.1H} NMR spectra were recorded in the solution-state using a Bruker Advance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz for .sup.1H and .sup.13C respectively. All spectra were recorded using a .sup.13C optimised 10 mm extended temperature probehead at 125° C. using nitrogen gas for all pneumatics. Approximately 200 mg of material was dissolved in 3 ml of1,2-tetrachloroethane-d.sub.2 (TCE-d2) along with chromium-(III)-acetylacetonate (Cr(acac).sub.3) resulting in a 65 mM solution of relaxation agent in solvent (Singh, G., Kothari, A., Gupta, V., Polymer Testing 28 5 (2009), 475). To ensure a homogenous solution, after initial sample preparation in a heat block, the NMR tube was further heated in a rotatary oven for at least 1 hour. Upon insertion into the magnet the tube was spun at 10 Hz. This setup was chosen primarily for the high resolution and quantitatively needed for accurate ethylene content quantification. Standard single-pulse excitation was employed without NOE, using an optimised tip angle, 1 s recycle delay and a bi-level WALTZ16 decoupling scheme (Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187 (2007) 225; Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128). A total of 6144 (6k) transients were acquired per spectra. Quantitative .sup.13C {.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs. All chemical shifts were indirectly referenced to the central methylene group of the ethylene block (EEE) at 30.00 ppm using the chemical shift of the solvent. This approach allowed comparable referencing even when this structural unit was not present. Characteristic signals corresponding to the incorporation of ethylene were observed Cheng, H. N., Macromolecules 17 (1984), 1950).

[0115] For polypropylene homopolymers all chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at 21.85 ppm.

[0116] Characteristic signals corresponding to regio defects (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253; Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157; Cheng, H. N., Macromolecules 17 (1984), 1950) or comonomer were observed.

[0117] The tacticity distribution was quantified through integration of the methyl region between 23.6-19.7 ppm correcting for any sites not related to the stereo sequences of interest (Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443; Busico, V., Cipullo, R., Monaco, G., Vacatello, M., Segre, A. L., Macromoleucles 30 (1997) 6251).

[0118] Specifically the influence of regio defects and comonomer on the quantification of the tacticity distribution was corrected for by subtraction of representative regio defect and comonomer integrals from the specific integral regions of the stereo sequences.

[0119] The isotacticity was determined at the pentad level and reported as the percentage of isotactic pentad (mmmm) sequences with respect to all pentad sequences: [mmmm] %=100*(mmmm/sum of all pentads)

[0120] The presence of 2,1 erythro regio defects was indicated by the presence of the two methyl sites at 17.7 and 17.2 ppm and confirmed by other characteristic sites.

[0121] Characteristic signals corresponding to other types of regio defects were not observed (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253).

[0122] The amount of 2,1 erythro regio defects was quantified using the average integral of the two characteristic methyl sites at 17.7 and 17.2 ppm:

P.sub.21e=(I.sub.e6+I.sub.e8)/2

[0123] The amount of 1,2 primary inserted propene was quantified based on the methyl region with correction undertaken for sites included in this region not related to primary insertion and for primary insertion sites excluded from this region:

P.sub.12=I.sub.CH3+P.sub.12e

[0124] The total amount of propene was quantified as the sum of primary inserted propene and all other present regio defects:

P.sub.total=P.sub.12+P.sub.21e

[0125] The mole percent of 2,1 erythro regio defects was quantified with respect to all propene:

[21e] mol%=100*(P.sub.21e/P.sub.total)

[0126] For copolymers characteristic signals corresponding to the incorporation of ethylene were observed (Cheng, H. N., Macromolecules 17 (1984), 1950).

[0127] With regio defects also observed (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem.

[0128] Rev. 2000, 100, 1253; Wang, W -J., Zhu, S., Macromolecules 33 (2000), 1157; Cheng, H. N., Macromolecules 17 (1984), 1950) correction for the influence of such defects on the comonomer content was required.

Number Average Molecular Weight (Me), Weight Average Molecular Weight (Mw) and Molecular Weight Distribution (MWD)

[0129] Molecular weight averages (Mw, Mn), and the molecular weight distribution (MWD), i.e. the Mw/Mn (wherein Mn is the number average molecular weight and Mw is the weight average molecular weight), were determined by Gel Permeation

[0130] Chromatography (GPC) according to ISO 16014-4:2003 and ASTM D 6474-99. A PolymerChar GPC instrument, equipped with infrared (IR) detector was used with 3× Olexis and lx Olexis Guard columns from Polymer Laboratories and 1,2,4-trichlorobenzene (TCB, stabilized with 250 mg/L 2,6-Di tert butyl-4-methyl-phenol) as solvent at 160° C. and at a constant flow rate of 1 mL/min 200 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 0.5 kg/mol to 11 500 kg/mol. Mark Houwink constants for PS, PE and PP used are as described per ASTM D 6474-99. All samples were prepared by dissolving 5.0-9.0 mg of polymer in 8 mL (at 160° C.) of stabilized TCB (same as mobile phase) for 2.5 hours for PP or 3 hours for PE at max. 160° C. under continuous gentle shaking in the autosampler of the GPC instrument. DSC analysis, melting temperature (T.sub.m) and melting enthalpy (H.), crystallization temperature (T.sub.e) and crystallization enthalpy (He): measured with a TA Instrument Q200 differential scanning calorimetry (DSC) on 5 to 7 mg samples. DSC is run according to ISO 3146/part 3/method C2 in a heat/cool/heat cycle with a scan rate of 10° C./min in the temperature range of −30 to +225° C. Crystallization temperature (T.sub.c) and crystallization enthalpy (H.sub.c) are determined from the cooling step, while melting temperature (T.sub.m) and melting enthalpy (H.sub.m) are determined from the second heating step.

[0131] Density of the polymer is measured according to ISO 1183-187. Sample preparation is done by compression moulding in accordance with ISO 1872-2:2007. Density of the hydrocarbon oil is determined according to ASTM D 4052 at 15° C.

[0132] The xylene solubles (XCS, wt.-%): Content of xylene cold solubles (XCS) is determined at 25° C. according ISO 16152; first edition; 2005-07-01. The part which remains insoluble is the xylene cold insoluble (XCI) fraction.

[0133] Flexural Modulus: The flexural modulus was determined in 3-point-bending according to ISO 178 on injection molded specimens of 80×10×4 mm prepared in accordance with ISO 294-1:1996.

[0134] Impact: Charpy notched impact strength is determined according to ISO 179/1 eA at 23° C. by using injection moulded test specimens as described in EN ISO 1873-2 (80×10×4 mm).

[0135] Haze was determined according to ASTM D1003-00 on 60×60×1 mm.sup.3 plaques injection molded in line with EN ISO 1873-2 using a melt temperature of 200° C. and on cast films of 50 μm thickness produced on a monolayer cast film line with a melt temperature of 220° C. and a chill roll temperature of 20° C.

[0136] B-Viscosity was determined according to ASTM D 3236 at 190° C.

Overall Migration

[0137] Overall Migration is determined according to EN ISO 1186-14:2002 on injection moulded plaques, 60×60×1 mm.sup.3.

Irradiation

[0138] Injection moulded test specimen of 80×10×4 mm.sup.3 for Charpy or 60×60×1 mm.sup.3 for

[0139] Yellowness Index, both prepared in accordance with EN ISO 1873-2, were exposed to gamma-ray irradiation at 50 kGy using a 60Co γ-ray source. Consecutively the samples were aged at 80° C. in a circulating air oven up to 60 days as indicated below. Once the desired time was reached, the samples were taken out from the oven and aged at 23° C. for 24 hours before the impact test according to Charpy ISO 179/1eA+23° C. was performed.

[0140] Parallel to the irradiated samples, according non-irradiated samples were aged at 80° C. in a circulating air oven up to 60 days.

B. Examples

1. The First Propylene Homopolymer (H-PP1):

[0141] The first propylene homopolymer (H-PP1) was prepared by polymerization using a metallocene catalyst as described in detail in WO 2015/011135 A1 (metallocene complex MC1 with methylaluminoxane (MAO) and borate resulting in Catalyst 3 described in WO 2015/011135 A1) with the proviso that the surfactant is 2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3-heptafluoropropoxy)-1-propanol. The metallocene complex (MC1 in WO 2015/011135 A1) is prepared as described in WO 2013/007650 A1 (metallocene E2 in WO 2013/007650 A1).

Off-Line Prepolymerization Procedure

[0142] The catalyst used in the polymerization process was prepared as follows:

[0143] The metallocene (MC1) (rac-anti-dimethylsilandiyl(2-methyl-4-phenyl-5-methoxy-6-tert-butyl-indenyl)(2-methyl-4-(4-tert-butylphenyl)indenyl)zirconium dichloride) has been synthesized as described in WO 2013/007650.

[0144] The catalyst was prepared using metallocene MC1 and a catalyst system of MAO and trityl tetrakis(pentafluorophenyl)borate according to Catalyst 3 of WO 2015/11135 with the proviso that the surfactant is 2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3-heptafluoropropoxy)-1-propanol.

[0145] The catalyst MC-1 was pre-polymerized according to the following procedure: Off-line pre-polymerization experiment was done in a 125 mL pressure reactor equipped with gas-feeding lines and an overhead stirrer. Dry and degassed perfluoro-1.3-dimethylcyclohexane (15 cm.sup.3) and the desired amount of the catalyst to be pre-polymerized were loaded into the reactor inside a glove box and the reactor was sealed. The reactor was then taken out from the glove box and placed inside a water cooled bath kept at 20° C. The overhead stirrer and the feeding lines were connected and stirring speed set to 450 rpm. The experiment was started by opening the propylene feed into the reactor. The total pressure in the reactor was raised to about 5 barg and held constant by propylene feed via mass flow controller until the target degree of polymerization was reached (10 min). The reaction was stopped by flashing the volatile components. Inside glove box, the reactor was opened and the content poured into a glass vessel. The perfluoro-1,3-dimethylcyclohexane was evaporated until a constant weight was obtained to yield the pre-polymerized catalyst.

TABLE-US-00001 TABLE 1 Off-line prepolymerization Catalyst amount Prepolymerization Degree Metallocene [mg] [wt %/wt %] MC-1 104 3.19

TABLE-US-00002 TABLE 2 Preparation of propylene homopolymer (H-PP1) and final properties H-PP1 Prepolymerization Temperature ° C. 20 Pressure kPa 5304 Residence Time h 0.41 Loop Temperature ° C. 75 Pressure kPa 5332 Residence Time h 0.4 H2/C3-feeding mol/kmol 0.25 Split wt % 46 MFR g/10 min 9.7 First Gas Phase Reactor Temperature ° C. 85 Pressure kPa 2000 H2/C3-Feeding mol/kmol 3.3 Split wt % 54 MFR g/10 min 8.5 Final (H-PP-1) MFR g/10 min 7.5 TM ° C. 153 2.1 + 3.1 erythro defects mol % 0.7 mmmm % mol % 98.3

2. Preparation of the Polymer Composition (C)

[0146] The polymer composition (C) was prepared from the propylene homopolymer (H-PP1) by additivation of the propylene homopolymer H-PP1 with the list of additives as described below. The melt flow rate has been subsequently adjusted with peroxide to the value as indicated below.

[0147] The properties of the comparative and inventive composition are found in Table 3.

TABLE-US-00003 TABLE 3 Properties of the comparative and inventive composition HD810MO H-PP1 Additives Calcium Steareate wt % 0.05 0.05 Arenox DL wt % 0.21 0.21 Irgafos 168 wt % 0.15 0.15 Primol 352 wt % 4.9 4.9 Millad 3988 wt % 0.15 0.15 Final properties MFR g/10 min 9.5 16.8 Tc ° C. 130 125 Tm ° C. 164 155 Hm J/g 102 97 XCS wt % 7.9 5.5 Flexural Modulus MPa 1201 1233 NIS 23° C. kJ/m.sup.2 5.5 4.5 Haze (1 mm) % 17.0 17.0 Overall Migration 81.9 48.0 (1 mm) Arenox DL dodecyl 3-{[3-(dodecyloxy)-3-oxopropyl]sulfanyl}propanoate (CAS-no. 123-28-4);, commercially available of BASF Irgafos 168 is Tris(2,4-tert-butylphenyl) Phosphite commercially available by BASF; Primol 352 While oil; a purified mixture of liquid saturated hydrocarbons; Kinematic viscosity (40° C.; ASTM D 445) = 65.0-75.0 mm.sup.2/s; Dynamic viscosity (20° C.; ASTM D 445) = 165 mPas, commercially available from ExxonMobil; Millad 3988 is 1.3: 2.4 bis(3,4-dimethylbenzylidene)sorbitol (CAS-no. 135861-56-2), commercially available of Milliken;

[0148] Comparative Example CE1 is the commercial polypropylene homopolymer HD810MO (Bormed™ of Borealis AG) is prepared from a Ziegler-Natta catalyst. It has a melt flow rate MFR.sub.2 of 10.0 g/10 min, a melting temperature Tm of 164° C., and a density of 907 kg/m.sup.3. The polymer chain has a pentad isotacticity (mmmm %) of 96.0 mol % and is free of regiodefects.

3. Overall Migration, Retention of Toughness and Discoloration after Gamma-Ray Sterilization

[0149] As derivable from the values shown in Table 3, the inventive composition has much lower overall migration than the comparative composition although the mechanical and optical properties of both compositions have been comparable. The mechanical profile have been analysed based on retention of Charpy notched impact strength (% NIS retention) of samples after gammy sterilization and thermal aging. Comparative and inventive samples were prepared from injection moulded specimen having size of 60×60×1 mm.sup.3. Samples were sterilized at 50 kGy and aged at 80° C. for 2 months (60 days) before analysis (Table 4). Analysis of discoloration after gamma-ray sterilization has been determined by yellowness index. Samples were sterilized at 50 kGy and aged at 80° C. for 2 months (60 days). Yellowness index of the aged samples was successively determined after ageing at 1, 7, 14, 30 and 60 days (Table 5).

TABLE-US-00004 TABLE 4 Retention of toughness after 60 days of aging CE1 H-PP1 Retention of Charpy notched impact strength (NIS %) 90 88

[0150] The NIS retention was essentially identical in the comparative and inventive materials.

TABLE-US-00005 TABLE 5 Successive discoloration over a period of 60 days of aging Yellowness index after n days CE1* CE1 H-PP1* H-PP1 1 0.2 8.0 0.0 4.9 7 0.2 16.3 0.1 8.1 14 0.2 17.3 0.0 9.2 30 0.2 20.2 0.2 11.7 60 0.3 25.1 0.2 14.6 *samples not gamma-ray sterilized;

[0151] It was further found that the degree of discoloration of the materials as indicated by yellowness index after gamma-ray sterilization and aging is substantially lower in the inventive material compared to the comparative material.