Drawn articles of low MTI metallocene polypropylene and process to produce such drawn articles

1. A drawn article comprising a polypropylene wherein:

the polypropylene has a melt flow index in the range from 1.5 to 4.5 g/10 min as determined according to ISO 1133, condition L, at 230° C. with a load of 2.16 kg;

a xylene soluble fraction of at most 0.8 wt %, relative to the total weight of the polypropylene as determined in accordance with ASTM D542-98;

a molecular weight distribution Mw/Mn ranging from 2.0 to 2.9; and

a melting temperature Tm of at most 155° C. as determined according to ISO 3146;

wherein the drawn article is selected from a fibre, a yarn, a tape, a staple fibre, or a continuous filament; and

wherein the drawn article has a tenacity of at least 45 cN/tex as determined on a Lenzing Vibrodyn according to norm ISO 5079:1995 with a testing speed of 10 mm/min at 23° C. and gauge length of 10 mm.

2. The drawn article according to claim 1 , wherein the polypropylene is a homopolymer of propylene.

3. The drawn article according to claim 1 , wherein the polypropylene has a xylene soluble fraction of from 0.5 to 0.8 wt %, relative to the total weight of the polypropylene as determined in accordance with ASTM D542-98.

4. The drawn article according to claim 1 , wherein the polypropylene has a molecular weight distribution Mw/Mn of at most 2.7.

5. The drawn article according to claim 1 , wherein the polypropylene has a melting temperature of at most 153° C. as determined according to ISO 3146.

6. The drawn article according to claim 1 , wherein the article is drawn at a draw ratio ranging from 2 to 12.

7. The drawn article according to claim 1 , wherein the article exhibits a tensile factor K of at least 40 g/denier, wherein the tensile factor is determined by formula (2):

K =Ten×Elong 1/2   (2)

wherein the Ten is the tenacity at max expressed in g/den, and Elong is elongation at max expressed in %, and wherein Ten and Elong are both determined on a Lenzing Vibrodyn according to norm ISO 5079:1995 with a testing speed of 10 mm/min at 23° C. and gauge length of 10 mm.

8. The drawn article according to claim 1 , wherein the polypropylene is produced by polymerization of propylene monomer and one or more optional comonomers in presence of a metallocene catalyst of the formula:

(Ind) 2 R 1 MQ 2   (1)

wherein: each Ind is the same and is a substituted or unsubstituted indenyl group;

R 1 is a structural bridge imparting stereorigidity to the component and is selected from —(CR 2 R 3 ) p — or —(SiR 2 R 3 ) p — with p=1 or 2;

R 2 is selected from the group consisting of hydrogen, C 1 -C 10 alkyl, C 5 -C 7 cycloalkyl, C 6 -C 15 aryl, alkylaryl with C 1 -C 10 alkyl and C 6 -C 15 aryl, or any two neighbouring R that may form a cyclic saturated or non-saturated C 4 -C 10 ring;

R 3 is selected from the group consisting of hydrogen, C 1 -C 10 alkyl, C 5 -C 7 cycloalkyl, C 5 -C 7 cyclocarbyl, C 6 -C 15 aryl, alkylaryl with C 1 -C 10 alkyl and C 6 -C 15 aryl, or any two neighbouring R that may form a cyclic saturated or non-saturated C 4 -C 10 ring;

M is selected from Ti, Zr, or Hf; and

Q is an hydrocarbyl radical such as an alkyl, aryl, alkenyl, alkylaryl, or arylalkyl radical having 1-20 carbon atoms or is a halogen.

9. A nonwoven or woven comprising the drawn article according to claim 1 .

10. A process for the production of a drawn article according to claim 1 , wherein the process comprises:

(a) producing a polypropylene by polymerization of propylene and one or more optional comonomers in presence of a single-site catalyst of the following formula:

(Ind) 2 R 1 MQ 2    (1)

wherein: each Ind is the same and is a substituted or unsubstituted indenyl group;

R 1 is a structural bridge imparting stereorigidity to the component and is selected from —(CR 2 R 3 ) p — or —(SiR 2 R 3 ) p — with p=1 or 2;

R 2 is selected from the group consisting of hydrogen, C 1 -C 10 alkyl, C 5 -C 7 cycloalkyl, C 6 -C 15 aryl, alkylaryl with C 1 -C 10 alkyl and C 6 -C 15 aryl, or any two neighbouring R that may form a cyclic saturated or non-saturated C 4 -C 10 ring;

R 3 is selected from the group consisting of hydrogen, C 1 -C 10 alkyl, C 5 -C 7 cycloalkyl, C 5 -C 7 cyclocarbyl, C 6 -C 15 aryl, alkylaryl with C 1 -C 10 alkyl and C 6 -C 15 aryl, or any two neighbouring R that may form a cyclic saturated or non-saturated C 4 -C 10 ring;

M is selected from Ti, Zr, or Hf; and Q is an hydrocarbyl radical such as an alkyl, aryl, alkenyl, alkylaryl, or arylalkyl radical having 1-20 carbon atoms or is a halogen;

(b) extruding the polypropylene produced in step (a) to form an extruded article and cooling the extruded article, wherein the extruded article is selected from a fibre, a yarn, a tape, a staple fibre, or a continuous filament; and

(c) drawing the extruded article of step (b) to form the drawn article.

11. The process of claim 10 , wherein the catalyst is (C 6 H 11 )(CH 3 )Si(2-Me-4-(4′BuPh)Ind) 2 ZrCl 2 .

12. The process of claim 10 , wherein the drawing is conducted at a draw ratio ranging from 2 to 12, wherein the draw ratio comprises:

a draw ratio ranging from 2 to 7 for a drawn article selected from fibre, yarn, continuous filament and tape.

13. The process of claim 10 , wherein the polymerization reaction of step (a) is performed in presence of one or more co-activators being a trialkyl aluminium selected from Tri-Ethyl Aluminum (TEAL), Tri-iso-Butyl Aluminum (TIBAL), Tri-Methyl Aluminum (TMA), and Methyl Methyl-Ethyl Aluminum (MMEAL).

14. The process of claim 10 , further comprising the step of (d) annealing the drawn article obtained instep (c).

15. The drawn article according to claim 1 , wherein the polypropylene has a xylene soluble fraction of at most 0.6 wt %, relative to the total weight of the polypropylene as determined in accordance with ASTM D542-98.

16. The drawn article according to claim 1 , wherein the drawn article is a tape.

17. The drawn article according to claim 1 , wherein the polypropylene has a xylene soluble fraction of from 0.5 to 0.6 wt %, relative to the total weight of the polypropylene as determined in accordance with ASTM D542-98.

18. The process of claim 10 , wherein the drawing is conducted at a draw ratio ranging from 2 to 12, wherein the draw ratio comprises:

a draw ratio ranging from 2 to 4 for a drawn article being a staple fibre produced according to a short spin process.

19. The drawn article according to claim 1 , wherein the polypropylene has a xylene soluble fraction of at most 0.5 wt %, relative to the total weight of the polypropylene as determined in accordance with ASTM D542-98.