Polyethylene articles
A polyethylene article comprises crystalline polyethylene in an orthorhombic unit cell. The b-axes of the crystalline polyethylene are substantially aligned with the machine direction of the article. In particular, the Herman's index of the b-axes in the machine direction is greater than zero and greater than the Herman's indices of the b-axes in both the transverse and normal directions. The unique physical attributes exhibited by a polyethylene article having this new morphology are also described.
1. A polyethylene article produced from a molten polyethylene polymer, the article having a thickness, the article having at least one local machine direction (MD local ) corresponding to a direction in which the molten polyethylene polymer flowed within a region in the article when the article was produced, the article having a corresponding local transverse direction (TD local ) perpendicular to each local machine direction within the article, the article having a local normal direction (ND local ) perpendicular to each local machine direction and corresponding local transverse direction and parallel to a line passing through the thickness of the article, the polyethylene polymer comprising a plurality of lamellae, each lamella comprising crystalline polyethylene, the crystalline polyethylene having a b-axis, the b-axes of the crystalline polyethylene in the lamellae having a Herman's orientation index at each local machine direction (F(MD local ,020)), a Herman's orientation index at each corresponding local transverse direction (F(TD local ,020)), and a Herman's orientation index at each corresponding local normal direction (F(ND local ,020)), the b-axes of the crystalline polyethylene in the lamella being oriented within the article such that F(MD local ,020)>0, F(MD local ,020)>F(TD local ,020), and F(MD local ,020)>F(ND local ,020).
2. The polyethylene article of claim 1 , wherein F(MD local ,020)>0.01, F(MD local ,020)−F(TD local ,020)>0.01, F(MD local ,020)−F(ND local ,020)>0.01.
3. The polyethylene article of claim 1 , wherein F(MD local ,020)>0.05, F(MD local ,020)−F(TD local ,020)>0.05, F(MD local ,020)−F(ND local ,020)>0.05.
4. The polyethylene article of claim 1 , wherein the article further comprises a nucleating agent for the polyethylene polymer.
5. The polyethylene article of claim 4 , wherein the nucleating agent comprises a compound conforming to the structure of Formula (I)
wherein R 1 is selected from the group consisting of hydroxy, halogens, alkyl groups, substituted alkyl groups, alkoxy groups, substituted alkoxy groups, aryl groups, and substituted aryl groups; n is zero or a positive integer from 1 to 4; L is a linking group comprising two or more atoms and at least one double bond between two atoms in the linking group; v is a positive integer from 1 to 3; R 2 is: (i) selected from the group consisting of alkyl groups, substituted alkyl groups, cycloalkyl groups, substituted cycloalkyl groups, aryl groups, substituted aryl groups, heteroaryl groups, and substituted heteroaryl groups when L is a divalent linking group and v is 1, (ii) selected from the group consisting of alkanediyl groups, substituted alkanediyl groups, cycloalkanediyl groups, substituted cycloalkanediyl groups, arenediyl groups, substituted arenediyl groups, heteroarenediyl groups, and substituted heteroarenediyl groups when L is a trivalent linking group and v is 1, (iii) selected from the group consisting of alkanediyl groups, substituted alkanediyl groups, cycloalkanediyl groups, substituted cycloalkanediyl groups, arenediyl groups, substituted arenediyl groups, heteroarenediyl groups, and substituted heteroarenediyl groups when L is a divalent linking group and v is 2, and (iv) selected from the group consisting of alkanetriyl groups, substituted alkanetriyl groups, cycloalkanetriyl groups, substituted cycloalkanetriyl groups, arenetriyl groups, substituted arenetriyl groups, heteroarenetriyl groups, and substituted heteroarenetriyl groups when L is a divalent linking group and v is 3; x is a positive integer; each M 1 is a metal cation; y is the valence of the cation; z is a positive integer; b is zero or a positive integer; when b is a positive integer, each Q 1 is a negatively-charged counterion and a is the valence of the negatively-charged counterion; and the values of v, x, y, z, a, and b satisfy the equation (vx)+(ab)=yz; wherein, when L is a divalent linking group, v is 1, and R 2 is a cycloalkyl group or a substituted cycloalkyl group, the cyclic portion of the cycloalkyl group or substituted cycloalkyl group comprises no more than two ring structures fused together.
6. The polyethylene article of claim 5 , wherein the nucleating agent comprises a compound conforming to the structure of Formula (CX)
wherein R 111 is selected from the group consisting of a cyclopentyl group and moieties conforming to the structure of Formula (CXI); R 112 is selected from the group consisting of hydrogen and hydroxy; Formula (CXI) is
R 115 is selected from the group consisting of hydrogen, a halogen, methoxy, and phenyl; x is a positive integer; each M 1 is a metal cation; y is the valence of the cation; z is a positive integer; b is zero or a positive integer; when b is a positive integer, each Q 1 is a negatively-charged counterion and a is the valence of the negatively-charged counterion; and the values of x, y, z, a, and b satisfy the equation x+(ab)=yz.
7. The polyethylene article of claim 6 , wherein R 111 is a moiety conforming to the structure of Formula (CXI).
8. The polyethylene article of claim 7 , wherein R 115 is a halogen.
9. The polyethylene article of claim 8 , wherein R 115 is chlorine.
10. The polyethylene article of claim 9 , wherein R 112 is hydrogen.
11. The polyethylene article of claim 10 , wherein x is 1, M 1 is a sodium cation, y is 1, z is 1, and b is zero.
12. The polyethylene article of claim 4 , wherein the nucleating agent is present in the article in an amount of about 100 to about 5,000 parts-per-million (ppm), based on the total weight of the polyethylene polymer.
13. The polyethylene article of claim 12 , wherein the nucleating agent is present in the article in an amount of about 250 to about 3,000 parts-per-million (ppm), based on the total weight of the polyethylene polymer.
14. The polyethylene article of claim 4 , wherein the nucleating agent is present in the form of a plurality of particles, the particles having a length and a width, and the ratio of the length to the width is about 2:1 or greater.
15. The polyethylene article of claim 1 , wherein the polyethylene polymer is a linear low density polyethylene.
16. The polyethylene article of claim 1 , wherein the polyethylene polymer is a high density polyethylene.
17. A polyethylene article produced by extruding a molten polyethylene polymer through an orifice in a direction, the article having a thickness, the article having a machine direction (MD) corresponding to the direction in which the molten polyethylene polymer exited the orifice, the article having a transverse direction (TD) perpendicular to the machine direction and perpendicular to a line passing through the thickness of the article, the article having a normal direction (ND) perpendicular to the machine direction and the transverse direction and parallel to a line passing through the thickness of the article, the polyethylene polymer comprising a plurality of lamellae, each lamella comprising crystalline polyethylene, the crystalline polyethylene having a b-axis, the b-axes of the crystalline polyethylene in the lamellae having a Herman's orientation index in the machine direction (F(MD,020)), a Herman's orientation index in the transverse direction (F(TD,020)), and a Herman's orientation index in the normal direction (F(ND,020)), the b-axes of the crystalline polyethylene in the lamella being oriented within the article such that F(MD,020)>0, F(MD,020)>F(TD,020), and F(MD,020)>F(ND,020).
18. The polyethylene article of claim 17 , wherein F(MD,020)>0.01, F(MD,020)−F(TD,020)>0.01, F(MD,020)−F(ND,020)>0.01.
19. The polyethylene article of claim 18 , wherein F(MD,020)>0.05, F(MD,020)−F(TD,020)>0.05, F(MD,020)−F(ND,020)>0.05.
20. The polyethylene article of claim 17 , wherein the article further comprises a nucleating agent for the polyethylene polymer.
21. The polyethylene article of claim 20 , wherein the nucleating agent comprises a compound conforming to the structure of Formula (I)
wherein R 1 is selected from the group consisting of hydroxy, halogens, alkyl groups, substituted alkyl groups, alkoxy groups, substituted alkoxy groups, aryl groups, and substituted aryl groups; n is zero or a positive integer from 1 to 4; L is a linking group comprising two or more atoms and at least one double bond between two atoms in the linking group; v is a positive integer from 1 to 3; R 2 is: (i) selected from the group consisting of alkyl groups, substituted alkyl groups, cycloalkyl groups, substituted cycloalkyl groups, aryl groups, substituted aryl groups, heteroaryl groups, and substituted heteroaryl groups when L is a divalent linking group and v is 1, (ii) selected from the group consisting of alkanediyl groups, substituted alkanediyl groups, cycloalkanediyl groups, substituted cycloalkanediyl groups, arenediyl groups, substituted arenediyl groups, heteroarenediyl groups, and substituted heteroarenediyl groups when L is a trivalent linking group and v is 1, (iii) selected from the group consisting of alkanediyl groups, substituted alkanediyl groups, cycloalkanediyl groups, substituted cycloalkanediyl groups, arenediyl groups, substituted arenediyl groups, heteroarenediyl groups, and substituted heteroarenediyl groups when L is a divalent linking group and v is 2, and (iv) selected from the group consisting of alkanetriyl groups, substituted alkanetriyl groups, cycloalkanetriyl groups, substituted cycloalkanetriyl groups, arenetriyl groups, substituted arenetriyl groups, heteroarenetriyl groups, and substituted heteroarenetriyl groups when L is a divalent linking group and v is 3; x is a positive integer; each M 1 is a metal cation; y is the valence of the cation; z is a positive integer; b is zero or a positive integer; when b is a positive integer, each Q 1 is a negatively-charged counterion and a is the valence of the negatively-charged counterion; and the values of v, x, y, z, a, and b satisfy the equation (vx)+(ab)=yz; wherein, when L is a divalent linking group, v is 1, and R 2 is a cycloalkyl group or a substituted cycloalkyl group, the cyclic portion of the cycloalkyl group or substituted cycloalkyl group comprises no more than two ring structures fused together.
22. The polyethylene article of claim 21 , wherein the nucleating agent comprises a compound conforming to the structure of Formula (CX)
wherein R 111 is selected from the group consisting of a cyclopentyl group and moieties conforming to the structure of Formula (CXI); R 112 is selected from the group consisting of hydrogen and hydroxy; Formula (CXI) is
R 115 is selected from the group consisting of hydrogen, a halogen, methoxy, and phenyl; x is a positive integer; each M 1 is a metal cation; y is the valence of the cation; z is a positive integer; b is zero or a positive integer; when b is a positive integer, each Q 1 is a negatively-charged counterion and a is the valence of the negatively-charged counterion; and the values of x, y, z, a, and b satisfy the equation x+(ab)=yz.
23. The polyethylene article of claim 22 , wherein R 111 is a moiety conforming to the structure of Formula (CXI).
24. The polyethylene article of claim 23 , wherein R 115 is a halogen.
25. The polyethylene article of claim 24 , wherein R 115 is chlorine.
26. The polyethylene article of claim 25 , wherein R 112 is hydrogen.
27. The polyethylene article of claim 26 , wherein x is 1, M 1 is a sodium cation, y is 1, z is 1, and b is zero.
28. The polyethylene article of claim 20 , wherein the nucleating agent is present in the article in an amount of about 100 to about 5,000 parts-per-million (ppm), based on the total weight of the polyethylene polymer.
29. The polyethylene article of claim 28 , wherein the nucleating agent is present in the article in an amount of about 250 to about 3,000 parts-per-million (ppm), based on the total weight of the polyethylene polymer.
30. The polyethylene article of claim 20 , wherein the nucleating agent is present in the form of a plurality of particles, the particles having a length and a width, and the ratio of the length to the width is about 2:1 or greater.
31. The polyethylene article of claim 17 , wherein the polyethylene polymer is a linear low density polyethylene.
32. The polyethylene article of claim 17 , wherein the polyethylene polymer is a high density polyethylene.
33. The polyethylene article of claim 17 , wherein the article is a film.
34. The polyethylene article of claim 17 , wherein the article is an extruded pipe.