Polypropylene compositions
The invention relates to a polypropylene composition comprising: (A) a first polypropylene which is a metallocene-catalyzed homopolymer, or a metallocene-catalyzed random copolymer of propylene and of a co-monomer having at most 0.5% by weight of co-monomer content, relative to the total weight of the random copolymer, as determined by 13 C NMR analysis; and (B) a second polypropylene which is a metallocene-catalyzed random copolymer of propylene and of a co-monomer; wherein said polypropylene composition is as defined in claim 1. The present invention also relates to a process for the preparation of said polypropylene composition. The present invention also relates to an article comprising said polypropylene composition.
1. A polypropylene composition comprising:
(A) a first polypropylene which is a metallocene-catalyzed homopolymer; and
(B) a second polypropylene which is a metallocene-catalyzed random copolymer of propylene and of a co-monomer;
wherein the polypropylene composition has:
a total co-monomer content of at least 1.1% by weight relative to the total weight of the polypropylene composition, as determined by 13 C NMR analysis, the co-monomer being an alpha-olefin different from propylene;
a melting temperature T m of at least 140° C., measured by DSC;
a crystallization temperature T c of at least 95° C., measured by DSC;
a ratio of weight average molecular weight (M w ) to number average molecular weight (M n ) [M w /M n ] of at least 3.5;
a ratio of z-average molecular weight (M z ) to weight average molecular weight (M w ) [M z /M w ] of at least 2.2; and
a co-monomer distribution ratio R(M z )/R(M n ) of at most 0.995, wherein R(M z ) is the ratio at M z of the IR signal measured at 2959 cm −1 on the signal at 2928 cm −1 , and R(M n ) is the ratio at M n of the IR signal measured at 2959 cm −1 on the signal at 2928 cm −1 , as determined by IR-detected gel permeation chromatography.
2. The polypropylene composition according to claim 1 , wherein the difference between the melting temperature T m and the crystallization temperature T c of the polypropylene composition (T m -T c ) is greater than 33° C.
3. The polypropylene composition according to claim 1 , having a ratio of z-average molecular weight (M z ) to number average molecular weight (M n ) [M z /M n ] of at least 6.0.
4. The polypropylene composition according to claim 1 , wherein the melt flow index of the first polypropylene is greater than the melt flow index of the second polypropylene; the values of melt flow index being measured according to ISO 1133:2005 Method B, condition M, at a temperature 230° C. and a 2.16 kg load.
5. The polypropylene composition according to claim 1 , wherein the co-monomer is ethylene.
6. The polypropylene composition according to claim 1 , wherein the melt flow index of the first polypropylene is greater than 30.0 g/10 min; as measured according to ISO 1133:2005 Method B, condition M, at a temperature 230° C. and a 2.16 kg load.
7. The polypropylene composition according to claim 1 , wherein the melt flow index of the second polypropylene is of at most 30.0 g/10 min; as measured according to ISO 1133:2005 Method B, condition M, at a temperature 230° C. and a 2.16 kg load.
8. The polypropylene composition according to claim 1 , having a melt flow index ranging from 1.0 to 200 g/10 min; as measured according to ISO 1133:2005 Method B, condition M, at a temperature 230° C. and a 2.16 kg load.
9. The polypropylene composition according to claim 1 , having a flexural modulus greater than 1000 MPa, the flexural modulus being measured at 23° C. according to ISO 178:2011 method A.
10. The polypropylene composition according to claim 1 , wherein the polypropylene composition comprises a physical blend of the first polypropylene and second polypropylene.
11. A process for the preparation of the polypropylene composition comprising:
(i) providing a first polypropylene which is a metallocene-catalyzed homopolymer
(ii) providing a second polypropylene which is a metallocene-catalyzed random copolymer of propylene and of a co-monomer,
(iii) and obtaining a polypropylene composition comprising the first and second polypropylene, wherein steps (i) and (ii) are carried out by polymerizing propylene and, if any, the co-monomer in the presence of a metallocene catalyst; the polypropylene composition having:
a total co-monomer content of at least 1.1% by weight relative to the total weight of the polypropylene composition, as determined by 13 C NMR analysis, the co-monomer being an alpha-olefin different from propylene;
a melting temperature T m of at least 140° C., measured by DSC;
a crystallization temperature T c of at least 95° C., measured by DSC;
a ratio of weight average molecular weight (M w ) to number average molecular weight (M n ) [M w /M n ] of at least 3.5;
a ratio of z-average molecular weight (M z ) to weight average molecular weight (M w ) [M z /M w ] of at least 2.2; and
a co-monomer distribution ratio R(M z )/R(M n ) of at most 0.995, wherein R(M z ) is the ratio at M z of the IR signal measured at 2959 cm −1 on the signal at 2928 cm −1 , and R(M n ) is the ratio at M n of the IR signal measured at 2959 cm −1 on the signal at 2928 cm −1 , as determined by IR-detected gel permeation chromatography.
12. The process according to claim 11 , wherein the polypropylene composition of step (iii) is obtained by physical blending of the first and second polypropylene.
13. The process according to claim 11 , wherein the polypropylene composition of step (iii) is obtained by chemical blending of the first and second polypropylene.
14. An article comprising a polypropylene composition according to claim 1 .