Creep-optimized UHMWPE fiber
The invention relates to a creep-optimized ultrahigh molecular weight polyethylene (UHMWPE) fiber obtained by spinning an UHMWPE comprising olefinic branches (OB) and having an elongational stress (ES), and a ratio (OB/1000 C/ES) between the number of olefinic branches per thousand carbon atoms (OB/1000 C) and the elongational stress (ES) of at least 0.2, wherein said UHMWPE fiber when subjected to a load of 600 MPa at a temperature of 70° C., has a creep lifetime of at least 90 hours.
1. A creep-optimized ultrahigh molecular weight polyethylene (UHMWPE) fiber obtained by spinning an UHMWPE having an intrinsic viscosity (IV) of at least 19 dl/g comprising ethyl branches or butyl branches and having an elongational stress (ES), wherein if
the fiber is obtained by spinning an UHMWPE comprising ethyl branches, the ratio
(
C
2
H
5
/
1000
C
ES
)
between the number of ethyl branches per thousand carbon atoms (C2H5/1000 C) and the elongational stress (ES) is between 1.0 and 3.00 mm 2 /N, wherein said UHMWPE fiber when subjected to a load of 600 MPa at a temperature of 70° C., has a creep lifetime of at least 125 hours, or wherein if
the fiber is obtained by spinning an UHMWPE comprising butyl branches the ratio
(
C
4
H
9
/
1000
C
ES
)
between the number of butyl branches per thousand carbon atoms (C4H9/1000 C) and the elongational stress (ES) is between 0.2 and 3.0 mm 2 /N, wherein said UHMWPE fiber when subjected to a load of 600 MPa at a temperature of 70° C., has a creep lifetime of at least 90 hours.
2. The fiber according to claim 1 , wherein the creep lifetime is at least 290 hours.
3. The fiber according to claim 1 , wherein the creep lifetime is at least 350 hours.
4. The fiber according to claim 1 , wherein the UHMWPE has an ES of at most 0.50 N/mm 2 .
5. The fiber according to claim 1 wherein the UHMWPE has a ratio
(
C
2
H
5
/
1000
C
ES
)
between the amount of ethyl branches per thousand carbon atoms (C2H5/1000 C) and the elongation stress (ES) of between 1.20 and 2.80 mm 2 /N.
6. The fiber according to claim 1 , wherein the UHMWPE is obtained by a slurry polymerisation process in the presence of an olefin polymerisation catalyst.
7. A rope, a crane rope, a mooring rope or a cordage comprising the fiber according to claim 1 .
8. A reinforced product containing reinforcing elements, wherein the reinforcing elements contain the fiber according to claim 1 .
9. A product comprising the fiber according to claim 1 , wherein the product is selected from the group consisting of fishing lines, fishing nets, ground nets, cargo nets, cargo curtains, kite lines, dental floss, tennis racquet strings, canvas, woven cloths, nonwoven cloths, webbings, battery separators, capacitors, pressure vessels, hoses, umbilical cables, automotive equipment, power transmission belts, building construction materials, cut and stab resistant articles, incision resistant articles, protective gloves, composite sports equipment, skis, helmets, kayaks, canoes, bicycles and boat hulls and spars, speaker cones, high performance electrical insulation, radomes, sails, and geotextiles.
10. The fiber according to claim 1 , obtained by a gel-spinning process.
11. The fiber according to claim 10 , wherein the polymerization process comprises the following sequence of steps:
(a) charging a stainless steel reactor with
(i) a non-polar aliphatic solvent with a boiling point at standard conditions of above that of the polymerization temperature, wherein said polymerisation temperature is preferably between 50° C. and 90° C.; wherein said boiling point of said solvent is between 60° C. and 100° C.;
(ii) an aluminium alkyl as co-catalyst;
(iii) ethylene gas to a pressure between 0.1 and 5 barg;
(iv) 1-butene gas, in a ratio of gas:total ethylene (NL:NL) of at most 325:1, preferably at most 150:1, most preferably at most 80:1;
wherein by total ethylene is understood the ethylene added in steps a)-iii) and b) or 1-hexene; and
(v) a Ziegler-Natta catalyst suitable of producing UHMWPE under the conditions a)-i) to a)-iv);
(b) gradually increasing the ethylene gas pressure inside the reactor, to reach an ethylene gas pressure of at most 10 barg during the course of the polymerization process; and
(c) allowing for the polymerisation of UHMWPE molecules to produce
UHMWPE particles having an average particle size (D50) as measured by ISO 13320-1 of between 80 μm and 300 μm.
12. A multi-layered composite article for ballistic applications, wherein the composite article comprises the fiber according to claim 1 .
13. The multi-layered composite article according to claim 12 , wherein the ballistic applications include at least one selected from the group consisting of body armor, helmets, hard shield panels, flexible shield panels and vehicle armouring panels.