Process for making high-strength polylactic acid filament

1. A process for making a polylactic acid (PLA) elongated object comprising the steps of:

a) making a solution of PLA having an intrinsic viscosity (IV) measured in chloroform at 25° C. of at least 4 dL/g, in a solvent, wherein the solution has a concentration cc P of 5 to 50 mass% expressed as the mass of the PLA per total mass of the solution;

b) spinning the solution through a spinplate comprising at least 1 spinhole to form a fluid elongated object;

c) optionally applying a draw ratio DR fluid to the fluid elongated object;

d) contacting the fluid elongated object with a cooling medium having a temperature T q of less than 0° C. to form a solvent-containing gel elongated object;

e) removing at least partly the solvent from the gel elongated object to form a solid elongated object; and

f) drawing the elongated object in at least one step before, during and/or after step e), while applying a draw ratio (DR solid ) of at least 2, to form a PLA elongated object.

2. The process according to claim 1 , wherein T q is less than −5° C.

3. The process according to claim 1 , wherein

T

q

=

T

0

⁡

(

c

P

50

⁢

⁢

mass

⁢

⁢

%

-

1

)

,

where

T 0 is at least 20° C.

4. The process according to claim 1 , wherein the polylactic acid has an intrinsic viscosity in a range of 5 to 15 dL/g.

5. The process according to claim 1 , wherein the polylactic acid comprises at least 90 mol% of monomeric units derived from L-lactic acid.

6. The process according to claim 1 , wherein the total draw ratio of the elongated object (DR total ) is at least 5.

7. The process according to claim 1 , wherein the PLA solution has a concentration c P of between 6 and 40 mass%.

8. The process according to claim 1 , wherein the cooling medium is a fluid.

9. The process according to claim 1 , wherein the cooling medium has limiting activity coefficient measured at a temperature of between 90-190° C. of between 1 and 2.

10. A gel-spun polylactic acid elongated object obtained by the process according to claim 1 .

11. A gel-spun polylactic acid elongated object which comprises a polylactic acid (PLA) with an IV in a the range of 5-15 dl/g, and having a tenacity (Ten) measured according to ISO 5079 in N/tex such that Ten≥f 1 * IV, wherein factor f 1 is 0.150.

12. The gel-spun polylactic acid elongated object according to claim 11 , wherein the object has an elongation at break of at least 10% = , measured according to ISO 5079.

13. The gel-spun polylactic acid elongated object according to claim 11 , wherein the elongated object is a filament, a fibre, a strap, a strip, a tape, a film or a tube.

14. The gel-spun polylactic acid elongated object according to claim 11 , wherein the factor f 1 is 0.155.

15. The gel-spun polylactic acid elongated object according to claim 11 , wherein the factor f 1 is 0.160.

16. An article containing the gel-spun polylactic acid elongated object of claim 11 , wherein the article is selected from the group consisting of yarn, rope, fishing line, fishing net, cargo nets and curtains, kite lines, tennis racket strings, canvas, non-woven fabrics, webbings, hoses, cut resistant articles, and stab resistant articles, protective gloves, sport equipment, helmets, sails, geotextiles, membranes and medical devices.

17. A gel-spun polylactic acid elongated object which comprises a polylactic acid (PLA) with an IV in a range of 5-15 dl/g, and having a tenacity in N/tex (Ten) measured according to ISO 5079 and a filament titer in tex (t) such that Ten≥f 2 * t −0.3 , wherein factor f 2 is 1.40 N.tex −0.7 .

18. The gel-spun polylactic acid elongated object according to claim 17 , wherein the factor f 2 is 1.50.

19. The gel-spun polylactic acid elongated object according to claim 17 , wherein the factor f 2 is 1.60.

20. The gel-spun polylactic acid elongated object according to claim 17 , wherein the factor f 2 is 1.70.