Polypropylene for foam and polypropylene foam

1. A polypropylene composition comprising a polypropylene base resin, the polypropylene composition having

a XHU content of 0.10 to 0.30 wt. %;

a MFR (2.16 kg, 230° C., ISO 1133) of 1.0 to 5.0 g/10 min;

a F30 melt strength of at least 30 cN, determined in the Rheotens test at 200° C.; and

a melt extensibility v30 of at least 200 m/s, determined in the Rheotens test at 200° C.; wherein the polypropylene composition does not contain low density polyethylene (LDPE).

2. The polypropylene composition according to claim 1 having an MFR (2.16 kg, 230° C., ISO 1133) of at least 1.0 g/10 min and a LAOS−NLF(500%) of at least 7.0 defined as

LAOS

-

NLF

⁡

(

500

⁢

%

)

=



G

1

′

G

3

′



where G 1 40 —first order Fourier Coefficient

G 3 40 —third order Fourier Coefficient

with both coefficients being calculated from a measurement performed at 500% strain.

3. The polypropylene composition according to claim 1 wherein polypropylene base resin is present in an amount of at least 96 wt. % with respect to the total polypropylene composition.

4. The polypropylene composition according to claim 1 having a strain hardening factor (SHF) of 6.0 to 12.0 when measured at a strain rate of 3.0 s −1 and a Hencky strain of 2.5 and/or a strain hardening factor (SHF) of 3.6 to 8.0 when measured at a strain rate of 1.0 s −1 and a Hencky strain of 2.0.

5. The polypropylene composition according to claim 1 having a F30 melt strength of 31 to 60 cN determined at 200° C. in the Rheotens melt strength test.

6. The polypropylene composition according to claim 1 having a F200 melt strength of 8 to 30 cN determined at 200° C. in the Rheotens melt strength test.

7. A polypropylene composition having an MFR (2.16 kg, 230° C., ISO 1133) of 1.0 to 5.0 g/10 min and a xylene hot unsoluble (XHU) content of 0.10 to 0.30 wt. % with respect to the total weight of the polypropylene composition, comprising a polypropylene base resin, the polypropylene base resin being obtained by a process comprising:

producing an intermediate polypropylene having an MFR (2.16 kg, 230° C., ISO 1133) of 0.5 to 2.5 g/10 min in the presence of an asymmetric catalyst;

mixing the intermediate polypropylene with 0.3 wt% to 1.0 wt % peroxide and 0.3 wt % to 2.0 wt % butadiene at a temperature of 20 to 90° C. for at least 2 minutes to form a pre-mixed material;

melt mixing the pre-mixed material in a melt mixing device at a barrel temperature in the range of 180 to 300° C., whereby the melt mixing device is a melt mixing device includes a feed zone, a kneading zone and a die zone, whereby an initial barrel temperature T1 is maintained in the feed zone, a barrel temperature T2 is maintained in the kneading zone and a die barrel temperature T3 is maintained in the die zone, whereby the barrel temperatures T1, T2, and T3 satisfy the following relation: T1<T3<T2.

8. The polypropylene composition according to claim 7 having

a F30 melt strength of at least 30 cN, determined in the Rheotens test at 200° C.; and

a melt extensibility v30 of at least 200 m/s, determined in the Rheotens test at 200° C.

9. The polypropylene composition according to claim 7 wherein the polypropylene composition does not contain LDPE.

10. A process for the production of a polypropylene composition having

a XHU content of 0.10 wt % to 0.30 wt. %;

a F30 melt strength of at least 30 cN, determined in the Rheotens test at 200° C.; and

a melt extensibility v30 of at least 200 m/s, determined in the Rheotens test at 200° C.

whereby an asymmetric catalyst derived intermediate polypropylene having an MFR (2.16 kg, 230° C., ISO 1133) of 0.5 to 2.5 g/10 min is mixed with 0.3 wt % to 1.0 wt % peroxide and 0.3 wt % to 2.0 wt % butadiene at a temperature of 20 to 90° C. for at least 2 minutes to form a pre-mixed material; and

the pre-mixed material is melt mixed in a melt mixing device at a barrel temperature in the range of 180 to 300° C.

11. The process according to claim 10 wherein the melt mixing device includes a feed zone, a kneading zone and a die zone and a specific temperature profile is maintained along the screw of the melt-mixing device, having an initial temperature T1 in the feed zone, a maximum temperature T2 in the kneading zone and a final temperature T3 in the die zone, all temperatures being defined as barrel temperatures and fulfilling the following relation: T1<T3<T2.

12. The process according to claim 10 wherein the whole process does not involve visbreaking.

13. Foam comprising the polypropylene composition according to claim 1 .

14. The polypropylene composition according to claim 1 , having a F200 melt strength of 15 to 23 cN determined at 200° C. in the Rheotens melt strength test.