STRETCHED POLYOLEFIN FIBERS

Abstract

The present invention relates to stretched polyolefin fibers comprising a polymer comprising at least one polymeric modifier selected from olefinic polymers modified with an acid and/or an acid anhydride, the use of these fibers in the reinforcement of cementitious compositions, and cementitious composition containing these fibers.

Claims

1. A polyolefm fiber, stretched at a draw ratio of about 4:1 to 6:1, comprising a) 90 to 99.5 weight % of a polyolefin; and b) 0.5 to 10 weight % of at least one polymeric modifier selected from olefinic polymers comprising acid functional groups and/or acid anhydride functional groups.

2. The fiber of claim 1, wherein the polyolefin a) is a homopolymer; or a copolymer comprising at least two different types of polymerized olefm monomers selected from the group consisting of ethylene, propylene, 1-butylene, butadiene and styrene or a mixture of two or more thereof.

3. The fiber of claim 2, wherein the olefin monomer of polymer a) is propylene.

4. The fiber of claim 1, wherein the polymeric modifier b) has an acid number in the range of 3 to 400.

5. The fiber of claim 4, wherein the polymeric modifier b) is a polyolefin comprising units derived from a carboxylic acid, units derived from a carboxylic acid anhydride, and/or units derived from a sulfonic acid.

6. The fiber of claim 5, wherein the polymeric modifier b) is a polyolefin comprising units derived from maleic anhydride.

7. The fiber of claim 1, wherein the polymeric modifier b) is a polyolefin comprising 0.1 to 20.0 weight % of units derived from a carboxylic acid, units derived from a carboxylic acid anhydride, and/or units derived from a sulfonic acid.

8. The fiber of claim 7, wherein the polymeric modifier b) is a polyolefin comprising 0.1 to 20.0 weight % of units derived from maleic anhydride.

9. The fiber of claim 1, wherein the polymeric modifier b) comprises 80 to 99.9 weight % of unmodified units derived from at least one monomer selected from the group consisting of ethylene, propylene, 1-butylene, butadiene and styrene.

10. The fiber of claim 9, wherein the monomer is propylene or styrene.

11. The fiber of claim 1, having a tensile strength of at least about 4 gf/denier.

12. A method for utilizing the fiber according to claim 1, comprising reinforcing an inorganic binder composition.

13. An inorganic binder composition comprising fibers according to claim 1.

14. The inorganic binder composition according to claim 13, comprising from 0.5 to 20 vol. % of the fibers.

15. The inorganic binder composition according to claim 13, wherein the composition is a cementitious composition.

Description

DESCRIPTION OF THE FIGURES

[0046] In FIG. 1, graphs of the experimental comparisons of the tensile strengths of microfibers according to examples 3-1 (FIG. 1-2), 3-2 (FIG. 1-3), 3-3 (FIG. 1-4) and 3-4 (FIG. 1-5) and a control microfiber (polypropylene microfiber without polymeric modifier, FIG. 1-1) are displayed.

[0047] In FIG. 2, graphs of the experimental comparison (“dog bone test”) of the ductility of mortars with varying microfibers (1.85% microfiber dosage) after 7 days of curing are displayed.

[0048] In FIG. 3, graphs of the experimental comparison (“dog bone test”) of the ductility of mortars with varying microfibers (1.85% microfiber dosage) after 14 days of curing are displayed.

[0049] In FIG. 4, graphs of the experimental comparison (“dog bone test”) of the ductility of mortars with varying microfibers (1.85% or 2.82% microfiber dosage) after 14 days of curing are displayed.

[0050] In FIG. 5, the multiple cracking patterns resulting from “dog bone tests” of mortars with microfibers according to examples 3-1, 3-3 and 3-4 and a control microfiber (polypropylene microfiber without polymeric modifier) are compared.

EXAMPLES

Example 1

[0051] In this example, the production of a fiber according to the invention is described.

[0052] Poly(styrene-co-maleic anhydride), cumene terminated (Mn˜1900, determined by GPC) was obtained by copolymerization of styrene (75 wt.-%) and maleic anhydride. The acid number was in the range of 265 to 305. This polymeric modifier was incorporated into a polypropylene homopolymer flake resin (Profax 6301) with a melt flow in dex (MFI) of 12 g/10 min through a mixing step in a high speed Henschel-type adiabatic mixer according to the following table.

TABLE-US-00001 Blend A Blend B [weight-%] [weight-%] Poly(styrene-co-maleic anhydride), 1.00 2.00 cumene terminated polypropylene homopolymer flake resin 98.65 97.65 (Profax 6301, LyondellBasell) Phosphite antioxidant 0.075 0.075 (Irgafos 168, BASF, CAS 31570-04-4) Phenolic antioxidant 0.075 0.075 (Irganox 3114, BASF, CAS 27676-62-6) Hindered amine light stabilizer 0.2 0.2 (Chimassorb 2020, BASF, CAS 192268-64-7)

[0053] The above homogeneous mixture was extruded on a fully intermeshing co-rotating twin screw extruder, 27 mm diameter, configured for high shear and with three separate kneading zones. An ascending temperature profile from 180° C. to 200° C. in eight heated barrel zones and 230° C. for a final melt temperature was employed. The feed rate was 150 grams per minute.

[0054] The extrudate was spun through a multifilament fiber spin head (e.g. 375 holes) in case of microfiber, or a single-filament head in case of macrofiber. The spun extrudate was quenched via rapid cooling to about 25 to about 30° C. using a water bath to obtain an undrawn fiber.

[0055] Conditions on the fiber extrusion line were zone temperatures from the feed zone to the melt pump of 232° C., 245° C., 258° C., and 273° C. for the melt pump (15.4 rpm) and the spinneret. The three Godet rolls were run at speeds as follows: feed 132 m/min (12° C.), draw at 728 to 806 m/min, and final at 747 to 808 m/min. The latter two rolls were not heated.

[0056] These combinations result in a high drawing ratio of 4:1 to 5:1 and a fiber diameter of 13 to 40 μm in case of microfibers and 300 to 1000 μm in case of macrofibers. The fibers are then finished—in case of the microfiber, oiled so that the fiber bundles do not stick together, and in case of the macrofiber, embossed. Embossing was performed in an embossment machine, in which the fiber is embossed at room temperature between two texturized rolls. Finally, the fibers are cut and packaged.

Example 2

[0057] Mortar and concrete mixes were obtained according to the following procedures.

Example 2-1

[0058] 320 g Portland cement (Mergelstetten), 880 g fly ash, 150 g quartz sand (0 to 0.3 mm) 150 g quartz flour, 4.3 g superplasticiser (Melflux 2641, BASF), 0.5 g stabilizer (Melvis F 40, BASF), and 300 g water are homogenized and 7.0 g microfiber are mixed in at about 600 r μm for 3 min to obtain a mortar mix.

Example 2-2

[0059] 484 kg limestone, 1190 kg river bed sand, 446 kg type I/II cement, 36 kg densified silica fume, and 193 kg water are homogenized and 5.3 kg of macrofiber are mixed in to obtain a concrete mix. The specimen is moist cured.

Example 3

[0060] Microfibers were obtained according to the following procedures.

Example 3-1

[0061] Microfiber was prepared from a mixture of polypropylene with 1 weight-% polyethylene-graft-maleic anhydride (0.5 weight-% maleic anhydride, acid number 6, viscosity 500 cP (140° C.), from Sigma-Aldrich) by a procedure analogous to that of example 1.

Example 3-2

[0062] Microfiber was prepared from a mixture of polypropylene with 1 weight-% polypropylene-graft-maleic anhydride (8 to 10 weight-% maleic anhydride, MW average 9100 g/mol (GPC), acid number 47, viscosity 4.0 P (190° C.), from Sigma-Aldrich) by a procedure analogous to that of example 1.

Example 3-3

[0063] Microfiber was prepared from a mixture of polypropylene with 2 weight-% polypropylene-graft-maleic anhydride (8 to 10 weight-% maleic anhydride, MW average 9100 g/mol (GPC), acid number 47, viscosity 4.0 P (190° C.), from Sigma-Aldrich) by a procedure analogous to that of example 1.

Example 3-4

[0064] Microfiber was prepared from a mixture of polypropylene with 1 weight-% “KRATON® FG1901 G Polymer” which is a linear triblock copolymer based on styrene and ethylene/butylene with a polystyrene content of 30% (1.4 to 2.0 weight-% maleic anhydride bound, melt flow index (MFI, 230° C., 5 kg) 14 to 28 g/10 min, from Kraton Polymers U.S. LLC) by a procedure analogous to that of example 1.

Example 4

[0065] Macrofibers were obtained according to the following procedures.

Example 4-1

[0066] Macrofiber was prepared from a mixture polypropylene with 3 weight-% polyethylene-graft-maleic anhydride (0.5 weight-% maleic anhydride; acid number 6, viscosity 500 cP (140° C.), from Sigma-Aldrich) by a procedure analogous to that of example 1.

Example 4-2

[0067] Macrofiber was prepared from a mixture of polypropylene with 3 weight-% polypropylene-graft-maleic anhydride (8 to 10 weight-% maleic anhydride, MW average 9100 g/mol (GPC), acid number 47, viscosity 4.0 P (190° C.), from Sigma-Aldrich) by a procedure analogous to that of example 1.

Example 4-3

[0068] Macrofiber was prepared from a mixture of polypropylene with 1 weight-% “KRATON® FG1901 G Polymer”, which is a linear triblock copolymer based on styrene and ethylene/butylene with a polystyrene content of 30% (1.4 to 2.0 weight-% maleic anhydride bound, melt flow index (MFI, 230° C., 5 kg) 14 to 28 g/10 min, from Kraton Polymers U.S. LLC), by a procedure analogous to that of example 1.

Example 5

[0069] In this example, the tensile strengths of microfibers according to examples 3-1, 3-2, 3-3 and 3-4 and a control microfiber (analogous polypropylene microfiber without polymeric modifier) were tested according to ASTM C1557-03 (“Standard Test Method for Tensile Strength and Young's Modulus of Fibers”). The measurements were repeated three times each. The results are depicted in FIG. 1 and show that the tensile strengths of the microfibers comprising a polymeric modifier are not significantly reduced in comparison to the high tensile strength of polypropylene microfibers without a polymeric modifier.

Example 6

[0070] In this example, the ductility of mortars with 1.85% of microfiber 3-3 or 3-4 of the invention or 1.85% of a control microfiber (analogous polypropylene microfiber without polymeric modifier) were tested after 7 days of curing via dog bone tests (DIN EN ISO 6892-1). The results are depicted in FIG. 2 and show that the ductility of mortars containing the microfibers 3-3 or 3-4 of the invention is superior to the mortar containing the control microfiber after 7 days of curing, presumably due to the improved bonding characteristics of the fibers according to the invention to inorganic binder compositions.

Example 7

[0071] In this example, the ductility of a mortar with 1.85% of microfiber 3-2 of the invention and a mortar with 1.85% of a control microfiber (analogous polypropylene microfiber without polymeric modifier) was tested after 14 days of curing via dog bone tests (DIN EN ISO 6892-1). The results are depicted in FIG. 3 and show that the ductility of mortars containing the microfiber 3-2 of the invention is superior to the mortar containing the control microfiber after 14 days of curing, presumably due to the improved bonding characteristics of the fibers according to the invention to inorganic binder compositions.

Example 8

[0072] In this example, the ductility of mortars with microfiber 3-1 or 3-3 of the invention or a control microfiber (analogous polypropylene microfiber without polymeric modifier) were tested after 14 days of curing via dog bone tests (DIN EN ISO 6892-1). Microfibers 3-1 and 3-3 were contained in the mortar at a dosage of 2.82%, whereas the control microfiber dosage was 1.85%, since the control microfiber could not be dispersed at 2.82% dosage. It was thereby shown that the addition of polymeric modifier according to the invention leads to an improved dispersibility of the thus treated fibers. The results are depicted in FIG. 4 and show that the ductility of mortars containing the microfibers 3-1 or 3-3 of the invention is superior to the mortar containing the control microfiber, presumably due to the improved bonding characteristics of the fibers according to the invention to inorganic binder compositions. With regard to examples 7 and 8, it was shown that an increase of the microfiber dosage leads to a further improved ductility of the thus treated mortar.

Example 9

[0073] In this example, the multiple cracking patterns resulting from the dog bone tests of mortars with microfibers (see examples 6 to 8) according to examples 3-1, 3-3 and 3-4 and a control microfiber (analogous polypropylene microfiber without polymeric modifier) are compared. The formation of multiple cracks in the mortars is a sign of a transfer of the force applied to the contained fibers towards other parts of the mortar and indicates an increased ductility of the mortar compared to mortars showing only a single crack. It was shown that the mortars containing microfibers of the invention have a superior ductility compared to mortars containing analogous polypropylene fibers without a polymeric modifier, presumably due to the improved bonding characteristics of the fibers according to the invention to inorganic binder compositions.

Example 10

[0074] In this example, the energy absorption of concretes containing the macrofiber 4-1, 4-2 or 4-3 according to the invention was compared to the energy absorption of the compartitive macrofiber MasterFiber 246 (BASF) according to ASTM C1550-10a (“Standard Test Method for Flexural Toughness of Fiber Reinforced Concrete (Using Centrally Loaded Round Panel) 1). The results are displayed in the following table:

TABLE-US-00002 Energy Absorption* Performance relative to Macrofiber at 5.4 kg/m.sup.3 (Joules) MasterFiber 246 MasterFiber 246 279 1.00 Example 4-1 498 1.78 Example 4-2 485 1.74 Example 4-3 468 1.68

[0075] It was shown that the concretes containing macrofibers according to the invention have a higher energy absorption than the concrete containing MasterFiber 246. This signifies an increased stability of the thus treated concrete, presumably due to the improved bonding characteristics of the fibers according to the invention to inorganic binder compositions.