Fibers of UHMWPE and a process for producing thereof
The invention relates to a process for producing gel-spun ultra high molecular weight polyethylene (UHMWPE) fibres having high tensile strengths and improved creep rates wherein the UHMWPE used in said process is characterized by a difference in the phase angle according to Formula 1 Δδ=δ 0.001 −δ 100 (1) of at most 42°, wherein δ 0.001 is the phase angle at an angular frequency of 0.001 rad/sec; and δ 100 is the phase angle at an angular frequency of 100 rad/sec as measured with a frequency sweep dynamic rheological technique at 150° C. on a 10% solution of UHMWPE in paraffin oil, provided that δ 100 is at most 18°. The invention further relates to gel-spun UHMWPE fibres produced thereof. The gel-spun UHMWPE fibres of the invention have a tensile strength of at least 4 GPa, and a creep rate of at most 5×10 −7 sec −1 as measured at 70° C. under a load of 600 MPa. The gel-spun UHMWPE fibres produced thereof are useful in a variety of applications, the invention relating in particular to ropes, medical devices, composite articles and ballistic-resistant articles containing said UHMWPE fibres.
1. A process for producing gel-spun UHMWPE fibres having high tenacities and improved creep resistance, the process comprising the steps of:
(a) preparing a solution of an UHMWPE in a solvent, said UHMWPE having an intrinsic viscosity in decalin at 135° C. of at least 5 dl/g;
(b) spinning the solution of step a) through a spinneret containing multiple spinholes into an air gap to form fluid filaments;
(c) cooling the fluid filaments to form solvent-containing gel filaments; and
(d) removing at least partly the remaining solvent from the gel filaments to form solid filaments before or during drawing the solid filaments; wherein
the UHMWPE possesses a difference in the phase angle of at most 42° according to Formula 1
Δδ=δ 0.001 −δ 100 (1)
where,
δ 0.001 is the phase angle at an angular frequency of 0.001 rad/sec; and
δ 100 is the phase angle at an angular frequency of 100 rad/sec
as measured with a frequency sweep dynamic rheological technique at 150° C. on a 10% solution of UHMWPE in paraffin oil, provided that δ 100 is at most 18°.
2. The process of claim 1 , wherein the UHMWPE possesses a difference Δδ of at most 40° provided that δ 100 is at most 18°.
3. The process of claim 1 , wherein the process comprises drawing the gel-spun fibres such that an overall draw ratio (DR overall ) is at least 5000 as determined by the formula:
DR overall =DR fluid ×DR gel ×DR solid , where
DR fluid is a draw ratio of the fluid filaments;
DR gel is a draw ratio of the solvent-containing gel filaments; and
DR solid is a draw ratio of the solid filaments.
4. The process of claim 3 , wherein DR fluid is at least 100, wherein DR fluid =DR sp ×DR ag , where DR sp is a draw ratio of the fluid filaments in the spinholes of the spinneret and DR ag is a draw ratio of the fluid filaments in the air gap.
5. The process of claim 1 , wherein the solid filaments are drawn in at least one step with a draw ratio of the solid filaments (DR solid ) being at least 4.
6. The process of claim 1 , wherein the fluid filaments are drawn at a draw ratio DR fluid of at least 100, wherein DR fluid =DR sp ×DR ag , where DR sp is a draw ratio of the fluid filaments in the spinholes of the spinneret and DR ag is a draw ratio of the fluid filaments in the air gap.