Polypropylene composition

Abstract

The invention relates to a process to produce irradiated polypropylene granulate wherein granulate comprising 1. a propylene polymer and 2. a vitamin E comprising stabilizer package is irradiated by electron beam radiation.

Claims

1. A process to produce irradiated polypropylene granulate characterised in that granulate comprising: 1. propylene polymer, and 2. vitamin E comprising stabilizer package, is irradiated by electron beam irradiation.

2. The process according to claim 1, wherein the irradiated polypropylene granulate has a strain hardening coefficient as determined via extensional viscosity measurement at a temperature of 170° C. at a strain elongation rate of 1.0 s.sup.−1 measured at 2.75 s of ≥8.0; a zero shear viscosity as determined using DMS with fit according to the Cross-model of ≥7000 Pa.Math.s; and degree of shear thinning defined as the ratio of complex viscosity η* at a frequency of 10 rad/s:complex viscosity at a frequency of 0.01 rad/s (η.sub.0.01) of ≤0.15, wherein the complex viscosity is determined via DMS wherein for determining the DMS spectrum, an ARES G2 rheometer was used at 200° C. measuring at frequencies of 0.01 rad/s to 100 rad/s, at a linear viscoelastic strain of 5%, using plates of 0.5 mm thickness produced according to ISO 1872-2 (2007).

3. The process according to claim 1, wherein the amount of vitamin E in the composition of polypropylene and Vitamin E is lower than 0.5 wt % relative to the amount of polypropylene.

4. The process according to claim 1, wherein Vitamin E is α-tocopherol.

5. The process according to claim 1, wherein the dose applied in electron beam irradiation ranges between 10 and 200 KGy.

6. A foamed object obtained with irradiated polypropylene granulate obtained with the process according to claim 1.

7. The process according to claim 2, wherein the amount of vitamin E in the composition of polypropylene and Vitamin E is lower than 0.5 wt % relative to the amount of polypropylene, and wherein Vitamin E is α-tocopherol.

8. The process according to claim 7, wherein the dose applied in electron beam irradiation ranges between 10 and 200 KGy.

9. The process according to claim 2, wherein the amount of vitamin E in the composition of polypropylene and Vitamin E is lower than 0.5 wt % relative to the amount of polypropylene, and wherein the dose applied in electron beam irradiation ranges between 10 and 200 KGy.

10. The process according to claim 2, wherein Vitamin E is α-tocopherol, and wherein the dose applied in electron beam irradiation ranges between 10 and 200 KGy.

11. The process according to claim 1, wherein the amount of vitamin E in the composition of polypropylene and Vitamin E is lower than 0.5 wt % relative to the amount of polypropylene, and wherein Vitamin E is α-tocopherol.

12. The process according to claim 11, wherein the dose applied in electron beam irradiation ranges between 10 and 200 KGy.

13. The process according to claim 1, wherein the amount of vitamin E in the composition of polypropylene and Vitamin E is lower than 0.5 wt % relative to the amount of polypropylene, and wherein the dose applied in electron beam irradiation ranges between 10 and 200 KGy.

14. The process according to claim 1, wherein Vitamin E is α-tocopherol, and wherein the dose applied in electron beam irradiation ranges between 10 and 200 KGy.

Description

EXAMPLE I

(1) Irradiated Polypropylene Granulate

(2) 99.925% by weight of polypropylene (PP) homopolymer with a MFI=0.3 dg/10 min (12; ISO 1133) was compounded on a Berstorf ZE25A-43D where the additives (0.05% by weight calcium stearate and 0.025% by weight Vitamin E) were dosed under nitrogen to the powder. The throughput was 16.1 kg/h. The additives were dosed via a pre-blend or direct dosing to the extruder. The temperature setting of the extruder was between 20° C. and 240° C. The obtained granulate was irradiated by an E Beam process. The E Beam radiation process was performed in three steps: Radiation of granulate with a dose of 100 kGy. Heating of the radiated granulate for 30 minutes at 60° C. De-activating the radicals by heating 30 minute at 140° C.

EXAMPLE II

(3) Foaming Irradiated Polypropylene Granulate

(4) A foam composition using the irradiated polypropylene resin obtained in Example I was produced by a procedure wherein the polypropylenes were fed together with 1.0 wt % by weight with regard to the weight of the polypropylene of Schulman PHBFPE50T (a 50% by weight masterbatch of talc in LDPE and 1.0 wt % by weight of glycerol monostearate (CAS registry nr. 31566-31-1)) to a co-rotating ZSK 30 twin screw melt extruder having an LID ratio of 40, equipped with a Aixfotec melt cooler and an annular foam die. The extruder was operated at a throughput of 10 kg/h, and the die pressure was maintained at 30 bar. In the extruder, the polypropylene was heated to 260° C. at which the material was in a molten condition. A quantity of isobutane as blowing agent to produce the foam was introduced into the melt in the extruder via an inlet positioned at zone 7 of the extruder. The quantity of isobutane used was 2.3 wt % with regard to the weight of the polypropylene. By further melt mixing of the material composition comprising the molten polypropylene and the blowing agent, a molten foamed material was obtained having a uniform foam cell distribution. In the Aixfotec melt cooler, the melt was cooled to temperatures of 175° C. in the area before the die. The molten foamed material forced out of the extruder via the annular die and cooled to form a solidified foam structures. The temperature in the area of the die was reduced stepwise from 175° C. down to 160° C. in steps of 2-3° C. At each temperature, foamed material was collected from which the density and the closed cell content were measured in order to determine the foamability window.

(5) Determination of Properties

(6) The melt mass-flow rate, the strain hardening and the viscosity ratio were determined. The foamability window, the foam density of foam prepared at 162° C. and the quantity of closed cells of foam prepared at 162° C. were determined. The results are presented in Table I.

(7) TABLE-US-00001 TABLE I FW 20 CC >99% FD 125° C. MFR.sub.2.16 3 SH.sub.1.0 40 η.sub.0.1 5592 η.sub.1 2329 η.sub.10 877 η.sub.100 288 η.sub.0 19045
In which: FW is the foamability window (° C.) as determined via the method described above; CC is fraction of closed cells as determined by the above described water absorption method of the foam as produced at 162° C. (%); FD is the density of the foam as produced at 162° C., determined as the apparent overall density according to ISO 845 (2006) (kg/m.sup.3); MFR.sub.2.16 is the melt mass-flow rate as determined in accordance with ISO 1133-1 (2011), at a temperature of 230° C. and a load of 2.16 kg (g/10 min); SH.sub.1.0 is the strain hardening coefficient as determined according to the method described above (−). For determining the strain hardening coefficient, an ARES G2 rheometer equipped with an EVF (extensional viscosity fixture) was used at 170° C. η.sub.0 is the zero shear viscosity as determined using DMS (Pa.Math.s) where viscosity data are fit using the Cross-model. η.sub.0.1 is shear viscosity at an angular frequency of 0.1 rad/sec η.sub.1 is shear viscosity at an angular frequency of 1 rad/sec η.sub.10 is shear viscosity at an angular frequency of 10 rad/sec η.sub.100 is shear viscosity at an angular frequency of 100 rad/sec

(8) For determining the DMS spectrum, an ARES G2 rheometer was used at 200° C. measuring at frequencies of 0.01 rad/s to 100 rad/s, at a linear viscoelastic strain of 5%, using plates of 0.5 mm thickness produced according to ISO 1872-2 (2007). The melt mass-flow rate of the modified polypropylene obtained with radiation was determined according to ISO 1133-1 (2011). ISO 1133-1 (2011) relates to determination of the melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics. The melt mass-flow rate was determined at 230′C at a load of 2.16 kg.

(9) Granulate comprising PP and vitamin E can be irradiated and the irradiated product is suitable to be foamed, Vitamin E enhances the melt strength of the polypropylene based composition.

EXAMPLE III AND COMPARATIVE EXAMPLES A-C

(10) Example I is repeated with use of the components as summarized in Table Z

(11) TABLE-US-00002 TABLE II Example A B C III polypropylene % by 99.8 99.1 99.95 99.925 weight Irgafos 168 % by 0.05 — — — weight Irganox 1010 % by 0.1 0.05 — — weight Vitamin E % by — — — 0.025 weight Calcium Stearate % by 0.05 0.05 0.05 0.05 weight MFR.sub.2.16 before dg/min 0.6 1 1.6 0.6 irradiation MFR.sub.2.16 after dg/min 16.3 19 15.5 3 irradiation Melt strength cN 3 19 30 40 after irradiation

(12) The table shows that MFR.sub.2.16 of III is stable in contrast to A-C MER.sub.2.16 show that the product is degraded after irradiation.

(13) The melt strength of III is strongly improved when compared with A-C.

(14) The melt strength is determined with Rheatens® setup wherein the capillary radius was 1 mm and the entrance angle was 90° C. The pinching point of the rollers was at a vertical distance of 10 cm from the die exit. A weight of 10 kg was used to push the melt through the capillary.