Method for manufacturing high molecular weight polyethylene fibers
A process for manufacturing high molecular weight polyethylene fibers, including subjecting a polyethylene tape with a weight average molecular weight of at least 500,000 grams/mole, a Mw/Mn ratio of at most 6, and a 200/110 uniplanar orientation parameter of at least 3 to a force in the direction of the thickness of the tape over the entire width of the tape. A polyethylene fiber having a Mw of at least 500 000 gram/mole, a Mw/Mn ratio of at most 6, and a 020 uniplanar orientation value of at most 55°.
1. A process for manufacturing high molecular weight polyethylene fibers, comprising:
forming a polyethylene tape with a weight average molecular weight of at least 500,000 grams/mole, a Mw/Mn ratio of at most 6, and a 200/110 uniplanar orientation parameter of at least 3 by subjecting a starting polyethylene to a stretching step in which a total stretching ratio applied is at least 80, and
subjecting the polyethylene tape to a force in a direction of a thickness of the tape over an entire width of the tape.
2. The process according to claim 1 comprising:
subjecting a starting UHMWPE with a weight average molecular weight of at least 500,000 grams/mole, an elastic shear modulus determined directly after melting at 160° C. of at most 1.4 MPa, and a Mw/Mn ratio of at most 6 to a compacting step and a stretching step under such conditions that at no point during the processing of the polymer is a temperature of the polymer raised to a value above a melting point of the polymer, wherein a total stretching ratio applied is at least 120, so as to form a polyethylene tape with a weight average molecular weight of at least 500,000 grams/mole, a Mw/Mn ratio of at most 6, and a 200/110 uniplanar orientation parameter of at least 3, and
subjecting the tape to a force in the direction of the thickness of the tape over the entire width of the tape.
3. The process of claim 2 wherein the starting UHMWPE has an elastic shear modulus determined directly after melting at 160° C. of at most 0.9 MPa.
4. The process of claim 2 wherein the total stretching ratio is at least 140.
5. The process of claim 1 wherein the tape is subjected to a force in the direction of the thickness of the tape over the whole width of the tape by contacting the tape with a stream of air or other ejected medium in the direction of the thickness of the tape, or by leading the tape over a roll applying a force in the direction of the thickness of the tape.
6. The process of claim 5 wherein the force applied on the tape is lower than 10 bar.
7. The process of claim 1 wherein the fibers obtained from the tape have an average linear density of at most 50 dtex.
8. The process of claim 1 wherein the fibers are obtained in the absence of a separate slitting step.
9. The process of claim 1 wherein the process yields fibers having a width of from 5 μm to 50 μm and a thickness of from 1 μm to 25 μm.
10. The process of claim 1 wherein the process yields fibers having an average linear density of at most 50 dtex.
11. The process of claim 1 wherein the process yields fibers having a tensile strength of at least 2.0 GPa and a tensile energy to break of at least 30 J/g.
12. The process of claim 1 wherein the total stretching ratio is at least 120.
13. The process of claim 1 wherein the total stretching ratio is at least 160.