Low creep fiber

Abstract

The invention relates to a process for the preparation of a gel spun UHMWPE fiber comprising the steps of providing an ultra high molecular weight polyethylene composition having an intrinsic viscosity (IV) of at least 8 dl/g, a co-monomer content (CBR) of a least 0.05 SCB/1000TC, a mass averaged distribution of the co-monomer (CMAD) of at least 0.05, wherein the co-monomer has at least 4 carbon atoms, dissolving the composition in a solvent to form a polymer solution having a UHMWPE concentration of between 2 and 40 wt %, spinning the polymer solution through a multi orifice die plate to form a solution fibers, cooling the solution fiber to below 80 C. to form a gel fiber, drawing the fiber in at least one step to form a drawn fiber, removing at least a portion of the solvent before, during or after the drawing, wherein the ratio CMAD to CBR is greater than 1.0. The invention further relates to a gel-spun UHMWPE fiber obtainable by the process and products comprising said gel-spun UHMWPE fiber.

Claims

1. A process for the preparation of a gel spun ultrahigh molecular weight polyethylene (UHMWPE) fiber comprising the steps of: (a) providing an ultra high molecular weight polyethylene (UHMWPE) composition having an intrinsic viscosity (IV) of at least 8 dl/g, a co-monomer content (C.sub.BR) of a least 0.05 SCB/1000TC, and a mass averaged distribution of the co-monomer (C.sub.MAD) of at least 0.05, wherein the co-monomer has at least 4 carbon atoms and a ratio of C.sub.MAD to C.sub.BR is greater than 1.0, (b) dissolving the composition in a solvent to form a polymer solution having a UHMWPE concentration of between 2 and 40 wt %, (c) spinning the polymer solution through a multi orifice die plate to form a solution fiber, (d) cooling the solution fiber to below 80 C. to form a gel fiber, (e) drawing the gel fiber in at least one step to form a drawn fiber, and (f) removing at least a portion of the solvent before, during or after the drawing.

2. The process of claim 1, wherein the ratio of C.sub.MAD to C.sub.BR is greater than 1.05.

3. The process according to claim 1, wherein the UHMWPE composition comprises at least 2 different UHMWPE polymers A and B.

4. The process according to claim 3, wherein the UHMWPE polymer A has an IV of 8-40 dl/g, and a C.sub.BR of less than 0.1 SCB/1000TC, and/or the UHMWPE polymer B has an IV of 8-40 dl/g, and a C.sub.BR from 0.1 to 5.0 SCB/1000TC.

5. The process according to claim 3, wherein a ratio of the IV of the polymer A to the IV of the polymer B is less than 1.

6. The process according to claim 3, wherein the polymer A and the polymer B are present in a weight ratio of the polymer A to the polymer B which is between 0.02 and 50.

7. The process according to claim 3, wherein the polymer A is a Ziegler catalyzed polymer and the polymer B is a molecular catalyst polymer.

8. The process according to claim 1, wherein the co-monomer is one or more monomers selected from the group consisting of alpha-olefins with at least 4 carbon atoms, cyclic olefins having 5 to 20 carbon atoms and linear, branched or cyclic dienes having 4 to 20 carbon atoms.

9. The process according to claim 1, wherein the co-monomer is one or more monomers selected from the group consisting of 1-butene, 1-pentene, 1-hexene and 1-octene.

10. The process of claim 1, wherein the ratio of C.sub.MAD to C.sub.BR is greater than 1.1.

11. The process according to claim 5, wherein the ratio of the IV of the polymer A to the IV of the polymer B is at most 0.9.

12. The process according to claim 5, wherein the ratio of the IV of the polymer A to the IV of the polymer B is at most 0.8.

13. The process according to claim 6, wherein the weight ratio of polymer A to polymer B is between 0.1 and 10.

14. The process according to claim 6, whereby the weight ratio of polymer A to polymer B is between 0.25 and 4.

15. The process according to claim 9, wherein the comonomer is selected form the group consisting of 1-butene and 1-hexene to provide ethyl or butyl branches to the UHMWPE polymer B.

16. A gel spun UHMWPE fiber obtained by the process of claim 1.

17. The gel spun UHMWPE fiber of claim 16, wherein C.sub.MAD to C.sub.BR is greater than 1.2.

18. The gel spun UHMWPE fiber of claim 16, wherein the fiber has a tenacity of at least 25 cN/dtex.

19. The gel spun fiber of claim 16, wherein the fiber has a tenacity of at least 32 cN/dtex.

20. The gel spun fiber of claim 16, wherein the fiber has a tenacity of at least 38 cN/dtex.

21. A product comprising the gel spun fiber according to claim 18, wherein the product is selected from the group consisting of chains, medical devices, laminates and composite articles.

22. A product comprising the gel spun fiber according to claim 16, wherein the product is selected from the group consisting of yarns, ropes, cables, nets, fabrics, and protective appliances.

23. The product according to claim 22, wherein the product is a ballistic resistant article.

24. A product comprising the gel spun fiber according to claim 16, wherein the product is selected from the group consisting of chains, medical devices, laminates and composite articles.

25. A gel spun ultrahigh molecular weight polyethylene (UHMWPE) fiber comprising: an intrinsic viscosity (IV) of at least 4 dl/g, a co-monomer content (C.sub.BR) of a least 0.05 SCB/1000TC, and a mass averaged distribution of the co-monomer (C.sub.MAD) of at least 0.05, wherein a ratio of C.sub.MAD to C.sub.BR is greater than 1.

26. The gel spun UHMWPE fiber of claim 25, wherein the C.sub.MAD to C.sub.BR is greater than 1.05.

27. The gel spun UHMWPE fiber of claim 25, wherein the C.sub.MAD to C.sub.BR is greater than 1.1.

28. A product comprising the gel spun fiber according to claim 25, wherein the product is selected from the group consisting of yarns, ropes, cables, nets, fabrics, and protective appliances.

29. The product according to claim 28, wherein the product is a ballistic resistant article.

30. A product comprising the gel spun fiber according to claim 25, wherein the product is selected from the group consisting of chains, medical devices, laminates and composite articles.

Description

(1) The invention will be further explained by the following examples and comparative experiment, however first the methods used in determining the various parameters used hereinabove are presented.

(2) Methods of Measurement:

(3) IV: the Intrinsic Viscosity for UHMWPE is determined according to ASTM D1601/2004 at 135 C. in decalin, while shaking the mixture for 16 hours, with BHT (Butylated Hydroxy Toluene) as anti-oxidant in an amount of 2 g/l solution. IV is obtained by extrapolating the viscosity as measured at different concentrations to zero concentration. dtex: fibers' titer (dtex) was measured by weighing 100 meters of fiber. The dtex of the fiber was calculated by dividing the weight in milligrams by 10; Tensile properties of fibers and yarns: tensile strength (or strength) and tensile modulus (or modulus) and elongation at break are defined and determined on multifilament yarns as specified in ASTM D885M, using a nominal gauge length of the fiber of 500 mm, a crosshead speed of 50%/min and Instron 2714 clamps, of type Fiber Grip D5618C. On the basis of the measured stress-strain curve the modulus is determined as the gradient between 0.3 and 1% strain. For calculation of the modulus and strength, the tensile forces measured are divided by the titer; values in GPa are calculated assuming a density of the UHMWPE of 0.97 g/cm.sup.3. Branching (C.sub.BR), i.e. the number of short chain branches, e.g. ethyl or butyl side chains, per thousand total carbon atoms (SCB/1000TC): was determined by FTIR on a 2 mm thick compression molded film by quantifying the absorption at 1375 cm.sup.1 using a calibration curve based on NMR measurements as in e.g. EP 0 269 151 (in particular pg. 4 thereof). Creep properties were determined in accordance with the methodology described in the paper Predicting the Creep Lifetime of HMPE Mooring Rope Applications by M. P. Vlasblom and R. L. M. BosmanProceedings of the MTS/IEEE OCEANS 2006 Boston Conference and Exhibition, held in Boston, Mass. on Sep. 15-21, 2006, Session Ropes and tension Members (Wed 1:15 PM-3:00 PM) and as further detailed in WO2009/043597, pages 18 to 20. SEC-MALS: The molecular mass distributions (Mn, Mw, Mz, Mw/Mn) were measured using a PL-210 Size Exclusion Chromatograph coupled to a multi-band infrared detector (IR5 PolymerChar) and a multi-angle light scattering (MALS) detector (laser wavelength 690 nm) from Wyatt (type DAWN EOS). Two PL-Mixed A columns were used. 1,2,4-trichlorobenzene was used as the solvent, the flow rate was 0.5 ml/min, and the measuring temperature was 160 C. Data acquisition and calculations were carried out via Wyatt (Astra) software. The UHMWPE should be completely dissolved under such conditions that polymer degradation is prevented by methods known to a person skilled in the art. Co-monomer distribution or the co-monomer incorporation over the molar mass, br(M), was obtained from infrared data collected with infrared detector IR5. The detector and analytical techniques are described by Ortin et al. (Journal of Chromatography A, 1257, 2012, 66-73). The detector contains band filters which allow separating CH.sub.3 and CH.sub.2 signals during chromatographic run and determine the number of methyl groups per one thousand total carbons over the molar mass distribution. The detector is calibrated with polyethylene short chain branching calibration standards characterized by NMR. The standards are samples with different co-monomer type (ethyl and butyl branches). For practical purposes, if the co-monomer distribution br(M) of a polyethylene sample was below the accuracy of the IR measurement, the following procedure was used. First, a reference polyethylene sample was synthesized, with a higher co-monomer dosage during reaction and otherwise polymerization conditions identical to the sample under the scope. The co-monomer level during the polymer synthesis of the reference sample was chosen such, that it led to a co-monomer distribution br.sub.ref(M) well-detectable by the IR method, as can be judged by a person skilled in the art. Secondly, the branching in the reference sample C.sub.BRref and in the sample under the scope C.sub.BR were measured by the corresponding method, as described above. Finally, the co-monomer distribution br(M) of the sample under the scope was calculated by Formula 2

(4) $\begin{array}{cc}\mathrm{br}\left(M\right)={\mathrm{br}}_{\mathrm{ref}}\left(M\right).Math.\frac{C_{\mathrm{BR}}}{C_{\mathrm{BRref}}}& \mathrm{Formula}2\end{array}$ Co-Monomer Mass Average Distribution (C.sub.MAD): In order to characterize the degree to which the co-monomer is distribute across the molecular weight of the polymer, the SEC-MALS with online IR was used to calculate a parameter named co-monomer mass average distribution, C.sub.MAD. Its definition is given by the Formula 1

(5) $\begin{array}{cc}{C}_{\mathrm{MAD}}=\frac{{}_0^{}\mathrm{br}\left(M\right).Math.M.Math.\frac{\mathrm{dw}}{\mathrm{dM}}\mathrm{dM}}{{}_0^{}M.Math.\frac{\mathrm{dw}}{\mathrm{dM}}\mathrm{dM}}& \mathrm{Formula}1\end{array}$ wherein

(6) $\frac{\mathrm{dw}}{\mathrm{dM}}$ is the number weight distribution of the UHMWPE composition, as obtained by, e.g., SEC-IR; br(M) is the co-monomer distribution (co-monomer incorporation over the molar mass), expressed as the number of branches per 1000 total carbon in the molecules of UHMWPE composition, having molar mass M, as measured by SEC-IR. For practical purposes, the integration in Formula 1 can be substituted by a summation as shown in Formula 3

(7) $\begin{array}{cc}{C}_{\mathrm{MAD}}=\frac{\underset{i=1}{\overset{N}{.Math.}}\mathrm{br}\left(M_i\right).Math.M_i.Math.w_i}{\underset{i=1}{\overset{N}{.Math.}}{M}_i.Math.w_i}& \mathrm{Formula}3\end{array}$ where w.sub.i is the normalized weight fraction of the material fraction with molar mass M.sub.i in the UHMWPE composition. The weight fraction w.sub.i can be determined, e.g., by SEC-IR. Formulas 1 and 3 are also applicable if a blend of at least two polymers A and B is used

(8) $\mathrm{Formula}4$$C_{\mathrm{MAD}}=\frac{X_A.Math.{\left(\underset{i=1}{\overset{N}{.Math.}}\mathrm{br}\left(M_i\right).Math.M_i.Math.w_i\right)}_A+X_B.Math.{\left(\underset{i=1}{\overset{N}{.Math.}}\mathrm{br}\left(M_i\right).Math.M_i.Math.w_i\right)}_B}{X_A.Math.{\left(\underset{i=1}{\overset{N}{.Math.}}{M}_i.Math.w_i\right)}_A+X_B.Math.{\left(\underset{i=1}{\overset{N}{.Math.}}{M}_i.Math.w_i\right)}_B}$ where X.sub.A and X.sub.B are the mass fractions of the polymers A and B in the blend (X.sub.B=1X.sub.A) and the subscripts A and B indicate that the corresponding sums must be calculated for the polymer A or polymer B, respectively. If more than two polymers (A, B, C, etc.) are blended, the Formula 4 takes the form of Formula 5

(9) $\begin{array}{cc}{C}_{\mathrm{MAD}}=\frac{\underset{k}{.Math.}{X}_k.Math.{\left(\underset{i=1}{\overset{N}{.Math.}}\mathrm{br}\left(M_i\right).Math.M_i.Math.w_i\right)}_k}{\underset{k}{.Math.}{X}_k.Math.{\left(\underset{i=1}{\overset{N}{.Math.}}{M}_i.Math.w_i\right)}_k}& \mathrm{Formula}5\end{array}$ where k=A, B, C, etc., X.sub.k is the mass fractions of the polymer k in the UHMWPE composition and whereby .sub.kX.sub.k=1. Both the continuous definition, Formula 1, and its discrete version, Formula 3, emphasize the asymmetry of the co-monomer incorporation into the low and high molar mass part of the molecular weight distribution. Indeed: If the co-monomer is incorporated homogeneously, then br(M) is constant over the whole range of molar masses M and, therefore, C.sub.MAD=C.sub.BR. If the co-monomer is preferentially present in the higher molar mass molecules, then C.sub.MAD>C.sub.BR. If the co-monomer is preferentially present in the lower molar mass molecules, then C.sub.MAD<C.sub.BR.
Preparation of UHMWPE

(10) Molecular catalyst polymerized UHMWPE: 7 UHMWPE polymers have been synthesized as ethylene homopolymers or copolymers of ethylene with 1-butene or 1-hexene. The polymerization procedure as described in WO 2015/059280 with the molecular catalyst (MC) of Example 4 described therein. Details of the produced polymers I, III, IV, V, VII and VIII are reported in table 1.

(11) Ziegler catalyst polymerized UHMWPE: 2 UHMWPE polymers have been synthesized according to the general preparation process described in WO 2012/139934 with a supported Ziegler catalyst (Z). Details of the produced polymers II and VI are reported in table 1.

(12) Preparation of UHMWPE Compositions

(13) Prior to gel-spinning the fibers, the prepared UHMWPE polymers have been blended by tumbling and later dispersion in the spinning solvent to form UHMWPE compositions. In case of blends of polymers, C.sub.BR and C.sub.MAD have been established by considering the C.sub.BR and C.sub.MAD of the individual polymers and their weight ratio in the composition.

(14) Gel Spinning Process

(15) A process such as the one disclosed in WO 2005/066401 was used to produce UHMWPE fibers from the described UHMWPE polymers or compositions. In particular, the UHMWPE solution was extruded with at a temperature setting of 180 C. through a spinneret having a 25 spinholes into an air atmosphere containing also decalin and water vapors with a rate of about 1.5 g/min per hole.

(16) The spinholes had a circular cross-section and consisted of a gradual decrease in the initial diameter from 2 mm to 0.8 mm with a cone angle of 15 followed by a section of constant diameter of 0.5 mm length, this specific geometry of the spinholes introducing a draw ratio in the spinneret of 6.25.

(17) From the spinneret the fluid fibers entered an air gap and then into a water bath, where the fluid fibers were taken up at a velocity 10 times higher than their velocity at the spinneret outlet, introducing a draw ratio in the air gap of 10.

(18) The fluid fibers were cooled in the water bath to form gel fibers, the water bath being kept at about 40 C. and wherein a water flow was being provided with a flow rate of about 50 liters/hour perpendicular to the fibers entering the bath. From the water bath, the gel fibers were taken-up into an oven at a temperature of 90 C. wherein partial solvent evaporation occurred to form solid fibers.

(19) The solid fibers were drawn in a first step at around 130 C. and in a second step at around 145 C. by applying a total solid draw ratio during which process most of the solvent evaporated. The total solid draw ratio is the product of the solid draw ratios used in the first and second drawing step.

(20) All reported samples were drawn to achieve a modulus of approximately 1200 cN/dtex and a strength of approximately 35 cN/dtex.

(21) The fibers' creep rates and the measurement conditions (temperature and load) for the Comparative Experiments A to D and of the Examples 1 to 3, are reported in Table 1. From said table it can be seen that for equal type of branching and comparable total short chain branching concentration the fibers of the invention have substantially increased creep rates. Alternatively it can be observed that similar creep rates can be attained by the inventive fibers at a substantially lower total amount of short chain branches C.sub.BR of the UHMWPE composition.

(22) TABLE-US-00001 TABLE 1 Creep creep Mn Mw PDI branching/ Fraction C.sub.BR/ rate cond. polymer kg/mol kg/mol Cat 1000C Co-mon. wt % 1000C C.sub.MAD C.sub.MAD/C.sub.BR 1/s MPa/ C. Examples 1 I 1500 3400 2.2 MC 0.51 1-butene 60 0.31 0.314 1.011 1.30E08 600/50 II 530 3300 6.2 Z 0 40 2 III 1610 3990 2.5 MC 0.6 1-butene 70 0.42 0.544 1.296 3.20E05 600/90 IV 190 960 4 MC 0 30 3 V 1310 3120 2.4 MC 0.4 1-hexene 70 0.28 0.354 1.263 9.00E07 300/90 IV 190 960 4 MC 0 30 Comp. Exp. A VI 595 3100 5.2 Z 0.7 1-butene 100 0.7 0.441 0.630 2.60E08 600/50 B VI 595 3100 5.2 Z 0.7 1-butene 100 0.7 0.441 0.630 4.70E05 600/90 C VII 38 110 2.9 MC 6.5 1-hexene 10 0.65 0.025 0.038 6.00E06 300/90 II 530 3300 6.2 Z 0 90 D VIII 380 1100 2.9 MC 0.66 1-butene 50 0.33 0.176 0.532 2.23E07 600/50 II 530 3300 6.2 Z 0 50