HIGH PERFORMANCE FIBRES HYBRID SHEET

Abstract

The present invention relates to hybrid sheet comprising: i) high-performance polyethylene (HPPE) fibers; ii) a polymeric resin, wherein the polymeric resin is selected from a group consisting of a homopolymer of ethylene, a homopolymer of propylene, a copolymer of ethylene, and a copolymer of propylene and wherein said polymeric resin has a density as measured according to ISO1183-2004 in the range from 860 to 970 kg/m.sup.3, a peak melting temperature in the range from 40 to 140 C. and a heat of fusion of at least 5 J/g; iii) non-polymeric fibers; and iv) optionally, a matrix material. Furthermore, the present invention relates to a process to manufacture the hybrid sheet and to the use of the hybrid sheet in various fields, such as in automotive field, in aerospace field, in sports equipment, in marine field, in military field; and in wind and renewable energy field.

Claims

1. A hybrid sheet comprising: i) high-performance polyethylene (HPPE) fibers; ii) a polymeric resin, wherein the polymeric resin is selected from a group consisting of a homopolymer of ethylene, a homopolymer of propylene, a copolymer of ethylene, and a copolymer of propylene, wherein the polymeric resin has a density as measured according to ISO1183-2004 in the range from 860 to 970 kg/m.sup.3, a melting temperature in the range from 40 to 140 C. and a heat of fusion of at least 5 J/g; and iii) non-polymeric fibers.

2. The hybrid sheet according to claim 1, wherein the non-polymeric fibers are selected from a group consisting of carbon fibers, glass fibers, wollastonite fibers, basalt fibers and/or mixtures thereof.

3. The hybrid sheet according to claim 1, wherein the HPPE fibers are continuous filaments or staple fibers.

4. The hybrid sheet according to claim 1, wherein the HPPE fibers are prepared by a melt spinning process, a gel spinning process or solid state powder compaction process.

5. The hybrid sheet according to claim 1, wherein the polymeric resin is applied as a coating on the HPPE fibers, preferably the polymeric resin is applied as a coating obtained from aqueous suspension on the HPPE fibers.

6. The hybrid sheet according to claim 1, wherein the HPPE fibers have a tenacity of at least 1.0 N/tex, preferably at least 1.5 N/tex, more preferably at least 1.8 N/tex.

7. The hybrid sheet according to claim 1, wherein the HPPE fibers comprise ultra-high molecular weight polyethylene (UHMWPE), preferably the HPPE fibers substantially consist of UHMWPE.

8. The hybrid sheet according to claim 1, wherein the amount of polymeric resin in the hybrid sheet is from 1 to 10 vol %, relative to the total volume of the hybrid sheet.

9. The hybrid sheet according to claim 1, wherein the density of the polymeric resin is in the range from 870 to 930 kg/m.sup.3, preferably from 870 to 920 kg/m.sup.3, more preferably from 875 to 910 kg/m.sup.3.

10. The hybrid sheet according to claim 1, wherein the polymeric resin comprises an ethylene acrylic acid copolymer.

11. The hybrid sheet according to claim 1, further comprising a matrix material, preferably the matrix material is a thermoset resin, more preferably a resin selected from a group consisting of an epoxy resin, a polyurethane resin, a vinylester resin, a phenolic resin, a polyester resin and/or mixtures thereof.

12. A process for manufacturing the hybrid sheet according to claim 1, the process comprising the steps of: a) providing high performance polyethylene (HPPE) fibers, a polymeric resin and non-polymeric fibers, wherein the polymeric resin is selected from a group consisting of a homopolymer of ethylene, a homopolymer of propylene, a copolymer of ethylene, and a copolymer of propylene and wherein said polymeric resin has a density as measured according to ISO1183-2004 in the range from 860 to 970 kg/m.sup.3, a peak melting temperature in the range from 40 to 140 C. and a heat of fusion of at least 5 J/g; b) applying a solvent solution or a suspension, preferably an aqueous suspension of a polymeric resin to the HPPE fibers before, during or after assembling, with the solution or suspension preferably being applied to the HPPE fibers before assembling the HPPE fibers; c) assembling the HPPE fibers and the non-polymeric fibers to form a sheet; d) at least partially drying the solution or suspension of the polymeric resin, preferably during the assembling step c) being carried out before or after step d), preferably step d) being carried out before step c); to obtain a hybrid sheet upon completion of steps a), b), c) and d); e) optionally applying a temperature in the range from the melting temperature of the resin to 153 C. to the sheet of step c) before, during and/or after step d) to at least partially melt the polymeric resin; f) optionally applying a matrix material, preferably impregnating the hybrid sheet with a matrix material in order to obtain a hybrid composite sheet; and g) optionally applying a pressure to the sheet during and/or after step f) to at least partially compact the hybrid composite sheet.

13. The process according to claim 12, wherein the concentration of polymeric resin in the aqueous suspension is at most 30 vol %, relative to the total volume of the aqueous suspension.

14. An article comprising the hybrid sheet according to claim 1, the article being selected from wheel rim for cars, bicycles and motorcycles, interiors for cars, impact panels, aircrafts, satellites, bicycles frames, cockpits, seats, hockey sticks, baseball bats, tennis and squash rackets, ski and snowboards, surfboards, paddle boards, helmets such as for cycling, football, climbing, motorsport, boat hulls, masts, sails, boats, wind turbines and tidal turbines.

15. Use of the article according to claim 14 in automotive field, preferably in wheel rims for cars and motorcycles, interiors for cars, impact panels; in aerospace field, preferably in aircrafts and satellites; in sports equipment, preferably in bicycles, bicycles frames, cockpits, seats, hockey sticks, baseball bats, tennis and squash rackets, ski and snowboards, surfboards, paddle boards, helmets such as for cycling, football, climbing, motorsport; in marine field, preferably in boat hulls, masts, sails, boats; in military field; and in wind and renewable energy field, preferably in wind turbines and tidal turbines.

Description

EXAMPLES

Methods

[0077] Dtex: yarn's or filament's titer was measured by weighing 100 meters of yarn or filament, respectively. The dtex of the yarn or filament was calculated by dividing the weight (expressed in milligrams) by 10. [0078] Heat of fusion and peak melting temperature have been measured according to standard DSC methods ASTM E 794 and ASTM E 793 respectively at a heating rate of 10K/min for the second heating curve and performed under nitrogen on a dehydrated sample. [0079] The density of the polymeric resin is measured according to ISO 1183-2004. [0080] IV: the Intrinsic Viscosity is determined according to method ASTM D1601(2004) at 135 C. in decalin, the dissolution time being 16 hours, with BHT (Butylated Hydroxy Toluene) as anti-oxidant in an amount of 2 g/I solution, by extrapolating the viscosity as measured at different concentrations to zero concentration. [0081] Tensile properties of HPPE fibers: tensile strength (or strength) and tensile modulus (or modulus) 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 titre, as determined above; values in GPa are calculated assuming a density of 0.97 g/cm.sup.3 for the HPPE. [0082] Tensile properties of fibers having a tape-like shape: tensile strength, tensile modulus and elongation at break are defined and determined at 25 C. on tapes of a width of 2 mm as specified in ASTM D882, using a nominal gauge length of the tape of 440 mm, a crosshead speed of 50 mm/min. [0083] Tensile strength and tensile modulus at break of the polyolefin resin were measured according ISO 527-2. [0084] Number of olefinic branches per thousand carbon atoms was determined by FTIR on a 2 mm thick compression moulded film by quantifying the absorption at 1375 cm-1 using a calibration curve relative to NMR measurements as in e.g. EP 0 269 151 (in particular pg. 4 thereof). [0085] Areal density (AD) of a sheet was determined by measuring the weight of a sample of preferably 0.4 m0.4 m with an error of 0.1 g. The areal density of a tape was determined by measuring the weight of a sample of preferably 1.0 m0.1 m with an error of 0.1 g. [0086] Flexural strength and modulus were measured by a 3-point flexural test according to ASTM D790-07, on specimens with a width of 12.7 mm and an L/D ratio of 16. The warp direction of the fibers was the length direction of the specimens in all cases. The modulus was determined between the points with 1% and 1.9% flexural strain. The flexural strength was determined at maximum load. [0087] Short beam flexural strength (also called interlaminar shear strength testing ILSS) was measured by a 3-point Flexural test similar to ASTM D790-07, on specimens with a length of 30 mm, a width of 7 mm and a reduced load span of about 22 mm such that a L/D of 5 was obtained. This low L/D value promotes interlaminar shear failure, between the fibers in the plane of the specimen, instead of failure of the fibers. The length direction was in the fiber load direction in all cases. Such short specimens typically fail by shearing along the warp fibers when subjected to 3-point bending. Thus, a measure for the resistance against that inter-laminar shear stress (ILSS) can be obtained. ILSS is calculated from the maximum load (Fmax), according to formula: ILSS value=0.75Fmax/(W*D), where W is the width, being 7 mm for the present specimens and D is the measured thickness of the hybrid composite sheet. [0088] Tensile tests on the composites were performed according to ASTM D3039, using tabs at the clamped ends of the specimens, in order to prevent clamping damage.

[0089] Comparative Experiment 1

[0090] 3 yarns of glass fiber of 136 tex with a 1383 sizing commercially available from PPG were assembled into one yarn with a titer of 408 tex glass fibers. A woven fabric was produced with a warp of these assembled 408 tex glass fibers and yarns of gel spun UHMWPE fibers, commercially available as Dyneema SK75 yarn of 176 tex and having a tenacity of 3.3 N/tex. 6.8 yarns per cm were applied in the warp yarn and a total of 136 of yarns were applied in the warp yarn. The first two yarns were glass fibers, then the third yarn was Dyneema fibers. This was repeated till the total number of yarns of 136 was reached. So, every third yarn was a Dyneema yarn, i.e. about 33 vol % Dyneema, relative to the total volume of the fabric. The fabric was made with a weft of 43 tex glass fibers, such that the volume of the weft fibers was 9 vol % of the total fabric volume. The aerial density of the fabric was 246 grams per square meter. The width of the fabric was 20 cm.

Example 1

[0091] Comparative Experiment 1 was repeated, but now the Dyneema SK75 yarn having a tenacity of 3.3 N/tex used was coated with a diluted suspension of an acrylate modified polyolefin, i.e. ethylene acrylic acid (EAA) copolymer with a melting peak at 78 C. and a heat of fusion of 29 J/g in water, purchased from Michelman under the trade name of Michem Prime 5931. The concentration of EAA in water was 2 vol %, related to the total volume of the hybrid sheet. The dilution was chosen such that that about 2 vol % aqueous dispersion was added to the Dyneema SK75 yarn. The coated yarn was dried in an oven at 130 C., such that all water evaporated and the EAA reached the melting point, providing a good connection to the Dyneema SK75 yarn after cooling to room temperature. The concentration of EAA on the yarn was about 1 vol %, relative to the total volume of the hybrid sheet. The final linear density of the yarn was about 180 tex. The resulting aerial density of the final woven fabric, i.e. the hybrid sheet was negligibly higher than the density of the woven fabric of Comparative Experiment 1.

[0092] Comparative Experiment 2

[0093] A hybrid composite sheet was made by stacking 10 woven fabrics obtained with Comparative Experiment 1 on top of each other from, such that the warp fibers in the yarn were all in the same direction. The stack was then impregnated with 55 vol %, relative to the total volume of the hybrid sheet of an epoxy resin commercially available as L 285 from Hexion with Hardener 285 and cured under near vacuum (about 150 mbar) at 50 C. during one hour. The total fiber volume content was 45 vol %, relative to the total volume of the hybrid sheet. The resulting average thickness of the hybrid composite sheet was 2.75 mm. The flexural modulus of the hybrid composite sheet of Comparative Example 2 was 17.8 GPa and the flexural strength was 405 MPa.

Example 2

[0094] A hybrid composite sheet was made by stacking on top of each other 10 fabrics obtained according to Example 1, such that the warp fibers were all in the same direction and then the stack was impregnated with 56 vol %, relative to the total volume of the hybrid sheet of an epoxy resin commercially available as L 285 from Hexion with Hardener 285 and then cured under near vacuum (about 150 mbar) at 50 C. during one hour. The resulting average thickness of the hybrid composite sheet was 2.9 mm. The total fiber volume was 43 vol %, relative to the total volume of the hybrid sheet. The flexural modulus of the hybrid composite sheet of Example 2 was 18.9 GPa and the flexural strength was 477 MPa (about 20% higher than of the flexural strength of the hybrid composite sheet obtained according to Comparative Experiment 2).

[0095] Comparative Experiment 3

[0096] A hybrid composite sheet was made by stacking 15 fabrics on top of each obtained according to Comparative Experiment 1, such that the warp fibers were all in the same direction and then impregnated with an epoxy resin commercially available as L 285 from Hexion with Hardener 285 and then cured under near vacuum (about 150 mbar) at 50 C. during one hour. The resulting average thickness of the hybrid composite sheet was 4.4 mm. The total fiber volume content was 43 vol %, relative to the total volume of the hybrid sheet. The apparent ILSS was 14.4 MPa.

Example 3

[0097] A hybrid composite sheet was made by stacking 15 fabrics from Example 1 on top of each other, such that the warp fibers were all in the same direction and then impregnated with an epoxy resin commercially available as L 285 from Hexion with Hardener 285 and cured under near vacuum at 50 C. during one hour. The resulting average thickness of the hybrid composite sheet was 4.3 mm. The total fiber volume content was 44 vol %, relative to the total volume of the hybrid sheet. The apparent ILSS of the sample obtained according to Example 3 was 16.5 MPa.

[0098] Comparative Experiment 4

[0099] Comparative experiment 1 was repeated, but now all yarns in the warp direction were 408 tex glass fibers, the aerial density of the fabric was 300 grams per square meter. It should be noted that the volume of a 176 tex Dyneema fiber is about the same as that of a 408 tex glass fiber, because the density of Dyneema is 0.975 grams/cm.sup.3 and glass has a density of 2.55 grams/cm.sup.3. The about equal volume follows from the elementary calculation: 408*0.975/2.55=156 tex, so close to the tex number of 176 of the Dyneema yarn. So, composites made from fabrics according to Comparative Experiment 1 and Comparative Experiment 4, can be compared on the basis of equal fabric fiber volume.

[0100] Comparative Experiment 5

[0101] A composite sheet was made by stacking 2 woven fabrics obtained with Comparative Experiment 4 on top of each other from, such that the warp fibers in the yarn were all in the same direction. The stack was then impregnated with 62 vol %, relative to the total volume of the composite sheet of an epoxy resin commercially available as L 285 from Hexion with Hardener 285 and cured under near vacuum (about 150 mbar) at 50 C. during one hour. The fiber volume content was 38%, based on the total volume of the composite sheet. The specimens were subjected to tensile tests. The measured modulus was 15.1 GPa, and the measured fracture strength was 438 MPa.

[0102] Comparative Experiment 6

[0103] A hybrid composite sheet was made by stacking 2 woven fabrics obtained with Comparative Experiment 1 on top of each other from, such that the warp fibers in the yarn were all in the same direction. The stack was then impregnated with 59 vol %, relative to the total volume of the composite sheet of an epoxy resin commercially available as L 285 from Hexion with Hardener 285 and cured under near vacuum (about 150 mbar) at 50 C. during one hour. The fiber volume content was 41%, based on the total volume of the composite sheet. The specimens were subjected to tensile tests. The measured modulus was 16.1 GPa, and the measured fracture strength was 493 MPa.

Example 4

[0104] A hybrid composite sheet was made by stacking 2 woven fabrics obtained with Example 1 on top of each other from, such that the warp fibers in the yarn were all in the same direction. The stack was then impregnated with 71 vol %, relative to the total volume of the composite sheet of an epoxy resin commercially available as L 285 from Hexion with Hardener 285 and cured under near vacuum (about 150 mbar) at 50 C. during one hour. The fiber volume content was 28%, based on the total volume of the composite sheet. The specimens were subjected to tensile tests. The measured modulus was 13.5 GPa, and the measured fracture strength was 405 MPa.

[0105] It was argued before that high fiber volume (vf) content implies a higher strength, because the fibers are the load carrying composite backbone. This is well known in the art as fiber dominated behavior. The resin rather connects the fibers together, so the best comparison of the different strength properties (except ILLS which is a matrix dominated property) is done by normalizing strength against fiber volume content. The same applies to the modulus, because also the modulus in fiber direction is known as a fiber dominated property. Therefore, the fiber dominated properties are presented in the table below, also after normalizing against the fiber volume content, vf. E is the modulus in GPa and S is the strength in MPa

TABLE-US-00001 Flexural test Tensile test CE 2 Example 2 CE 5 CE 6 Example 4 E [GPa] 18.8 18.9 15.1 16.1 13.5 S [MPa] 405 477 438 493 405 E/vf 41.8 44.0 39.7 39.3 48.2 S/vf 900 1109 1153 1202 1446

[0106] The results obtained clearly demonstrate that a hybrid sheet showing improved structural properties, e.g. improved flexural strength and bending strength, thus a lower sensitivity to delamination, while maintaining high impact resistance properties, and thus enabling more and various application opportunities was obtained by the present invention. Moreover, the real difference in the flexural strength and modulus values obtained according to Examples and the Comparative Experiments may be even higher as typically the production of composite samples is subject to some scatter and, as a consequence, the Comparative Experiment 2 has a higher fiber volume content than Example 2, thus being more advantageous apparently than Example 2. This is also related to a slight difference in the thickness between the samples of the Examples and the Comparative Experiments but the effect that may result from this difference is typically ruled out by the beam theory equations in the standard applied for ILSS method. Furthermore, it is especially advantageously to have better structural properties at lower fiber volume content.