Cross-linking of antioxidant-containing polymers
View Patent ↗The present invention relates to methods for making cross-linked, oxidatively stable, and highly crystalline polymeric materials. The invention also provides methods of treating irradiation-cross-linked antioxidant-containing polymers and materials used therewith.
1. A method of making highly cross-linked, oxidatively stable, and highly crystalline polymeric material comprising:
a) blending antioxidant with UHMWPE resin, powder, or flake in the absence of a supercritical fluid, thereby providing a polymeric blend, wherein the blend is mixed with virgin UHMWPE resin, powder, or flake, thereby forming a composition having antioxidant rich and poor regions;
b) consolidating the blend from step (a) to provide a consolidated polymeric material having antioxidant rich and poor regions;
c) irradiating the consolidated polymeric material from step (b) at a temperature that is above the room temperature and below the melting point of the polymeric material to provide an irradiated and consolidated polymeric material having antioxidant rich and poor regions; and
d) annealing the irradiated and consolidated polymeric material in air or under an inert environment at a temperature below the melting temperature of the polymeric material, thereby forming a highly cross-linked, oxidatively stable, and highly crystalline polymeric material.
2. The method according to claim 1 , wherein the crystallinity of the polymeric material is greater than about 51%.
3. The method according to claim 1 , wherein one or more types of resin, flakes, or powder are blended with different concentrations of an antioxidant.
4. The method according to claim 1 , wherein the polymeric material is further homogenized following the irradiation step by heating to below the melt to allow diffusion of the antioxidant from the antioxidant rich to antioxidant poor regions and oxidative stability throughout the polymeric material.
5. The method according to claim 1 , wherein the polymeric material is homogenized before and/or after irradiation, by thermally annealing at a temperature below the melting point of the polymeric material.
6. The method according to claim 1 , wherein the highly cross-linked, oxidatively stable, and highly crystalline polymeric material is further doped with an antioxidant by diffusion at a temperature below the melting point of the polymeric material.
7. The method according to claim 6 , wherein the doping is carried out by soaking the medical implant in the antioxidant for about 0.1 hours to about 72 hours.
8. The method according to claim 1 , wherein the antioxidant is vitamin E.
9. The method according to claim 1 , wherein a portion or all of the highly cross-linked, oxidatively stable, and highly crystalline polymeric material is further thermally annealed below the melting point of the polymeric material.
10. The method according to claim 1 , wherein the antioxidant blended polymeric material, the consolidated polymeric material, or the highly cross-linked, oxidatively stable, and highly crystalline polymeric material is compression molded to another piece or a medical implant, thereby forming an interface or an interlocked hybrid material.
11. The method according to claim 1 , wherein the polymeric material is a polyolefin, a polypropylene, a polyamide, a polyether ketone, a hydrogel or a mixture thereof.
12. The method according to claim 11 , wherein the polyolefin is selected from a group consisting of a low-density polyethylene, high-density polyethylene, linear low-density polyethylene, ultra-high molecular weight polyethylene (UHMWPE), or a mixture thereof.
13. The method according to claim 1 , wherein the irradiation is carried out in an atmosphere containing between about 1% and about 22% oxygen.
14. The method according to claim 1 , wherein the irradiation is carried out in an inert atmosphere, and wherein the atmosphere contains gases selected from the group consisting of nitrogen, argon, helium, neon, or the like, and a combination thereof.
15. The method according to claim 1 , wherein the radiation dose is about 65 kGy.
16. The method according to claim 1 , wherein the irradiated polymeric material is thermally annealed in contact with a non-oxidizing medium, thereby achieving reduction of free radicals in the cross-linked polymeric material, wherein the non-oxidizing medium is an inert gas, an inert fluid, or a polyunsaturated hydrocarbon selected from the group consisting of acetylenic hydrocarbons such as acetylene; conjugated or unconjugated olefinic hydrocarbons such as butadiene and (meth)acrylate monomers; and sulphur monochloride with chloro-tri-fluoroethylene (CTFE) or acetylene.
17. The method according to claim 1 , wherein the highly cross-linked, oxidatively stable, and highly crystalline polymeric material is further homogenized at a temperature below the melting point of the polymeric material for a period of about an hour to several days.
18. The method according to claim 1 , wherein the highly cross-linked, oxidatively stable, and highly crystalline polymeric material is further homogenized at a temperature below melting point.
19. The method according to claim 1 , wherein the consolidated polymeric material is irradiated at a temperature of about 40° C.
20. The method according to claim 1 , wherein the consolidated polymeric material is irradiated at a temperature that is above the room temperature and below 135° C.
21. The method according to claim 1 , wherein the radiation dose is between about 25 and about 1000 kGy.
22. The method according to claim 1 , wherein the radiation dose is about 75 kGy.
23. The method according to claim 1 , wherein the radiation dose is about 65 kGy.
24. The method according to claim 1 , wherein the consolidated polymeric material is irradiated at a temperature of about 135° C.
25. The method according to claim 1 , wherein the consolidated polymeric material is irradiated at a temperature of about 130° C.
26. The method according to claim 1 , wherein the consolidated polymeric material is irradiated at a temperature of about 120° C.
27. The method according to claim 1 , wherein the consolidated polymeric material is irradiated at a temperature of about 110° C.
28. The method according to claim 1 , wherein the consolidated polymeric material is irradiated at a temperature of about 100° C.
29. The method according to claim 1 , wherein the consolidated polymeric material is irradiated at a temperature of about 75° C.
30. A method of making highly cross-linked, oxidatively stable, and highly crystalline polymeric material comprising:
a) blending antioxidant with UHMWPE resin, powder, or flake in the absence of a supercritical fluid, thereby providing a polymeric blend, wherein the blend is mixed with virgin UHMWPE resin, powder, or flake, thereby forming a composition having antioxidant rich and poor regions;
b) consolidating the blend from step (a) to provide a consolidated polymeric material having antioxidant rich and poor regions;
c) irradiating the consolidated polymeric material from step (b) at a temperature that is above the room temperature and below the melting point of the polymeric material to provide an irradiated and consolidated polymeric material having antioxidant rich and poor regions; and
d) quenching residual free radicals by annealing the irradiated and consolidated polymeric material in air or under an inert environment at a temperature below the melting temperature of the polymeric material, thereby forming a highly cross-linked, oxidatively stable, and highly crystalline polymeric material.
31. The method according to claim 30 , wherein residual free radicals in the irradiated polymeric material are quenched by annealing in air or under an inert environment at a temperature below or above the melting temperature of the polymeric material.