EPOXY RESIN-BASED FIBRE MATRIX COMPOSITIONS CONTAINING ALKYL-SUBSTITUTED ETHYLENE AMINES

Abstract

Epoxy resin-based fibre matrix compositions contain alkyl substituted ethylene amines such as dimethyldiethylenetriamine (DMDETA, also dimethyl-1,4,7-triazaheptane), as a curing agent. These curing agents are characterized by a short curing time for a comparatively long processing time, and make it possible to obtain cured epoxy resins that exhibit low brittleness and high tensile strength and have a high glass transition temperature; as a result of which the fibre matrix composition is suitable particularly for use in pultrusion and winding processes.

Claims

1: A fiber-matrix composition, comprising: a fiber component consisting of reinforcing fibers, and a matrix component comprising epoxy resin and curing agent, wherein the curing agent comprises at least one alkyl-substituted ethyleneamine of the formula (I)
H.sub.2N-A-(NH-A-).sub.nNH.sub.2  (I) wherein A is independently an ethylene group of the formula —CHR—CH.sub.2— or CH.sub.2—CHR—, with R=H, ethyl or methyl, but at least one A of the at least one alkyl-substituted ethyleneamine of the formula (I) is an alkylethylene group of the formula —CHR—CH.sub.2— or —CH.sub.2—CHR—, with R=ethyl or methyl, and wherein n=1 to 4.

2: The fiber-matrix composition according to claim 1, wherein A is independently a methylethylene group of the formula —CH(CH.sub.3)—CH.sub.2— or CH.sub.2—CH(CH.sub.3)—, and wherein n=1 to 4.

3: The fiber-matrix composition according to claim 1, wherein the at least one alkyl-substituted ethyleneamine is a dimethyldiethylenetriamine of the formula (II)
H.sub.2N-A-NH-A-NH.sub.2  (II) wherein A is independently a methylethylene group of the formula —CH(CH.sub.3)—CH.sub.2— or —CH.sub.2—CH(CH.sub.3)—.

4: The fiber-matrix composition according to claim 1, wherein the at least one alkyl-substituted ethyleneamine accounts for at least 50% by weight, based on a total amount of curing agents in the fiber-matrix composition.

5: The fiber-matrix composition according to claim 1, wherein the epoxy resin is selected from the group consisting of diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, diglycidyl ether of hydrogenated bisphenol A, diglycidyl ether of hydrogenated bisphenol F, and a mixture thereof.

6: The fiber-matrix composition according to claim 1, wherein the reinforcing fibers are glass fibers, carbon fibers, or mixtures thereof.

7: The fiber-matrix composition according to claim 1, wherein the reinforcing fibers have been impregnated with the matrix component.

8: A method of producing a cured composite material, the method comprising: providing and then curing the fiber-matrix composition according to claim 1.

9: The method according to claim 8, wherein the curing is effected at a temperature in the range from 70 to 180° C.

10: The method according to claim 8, wherein the fiber-matrix composition is provided by impregnating the reinforcing fibers with the matrix component.

11: The method according to claim 8, comprising: a. arranging a multitude of reinforcing fibers to form a bundle, b. pulling the bundle through an impregnating device to impregnate the reinforcing fibers in the bundle with the matrix component, to give a bundle of impregnated reinforcing fibers, and c. pulling the bundle of impregnated reinforcing fibers through a heating device in which the bundle of impregnated reinforcing fibers is cured at a temperature in the range from 70 to 180° C., to give a cured composite material.

12: The method according to claim 8, comprising: a. impregnating one or more reinforcing fibers with the matrix component to obtain one or more impregnated reinforcing fibers, and then winding the one or more impregnated reinforcing fibers onto a winding cores to give an uncured composite material, and b. curing the uncured composite material at a temperature in the range from 70 to 180° C., to give a cured composite material.

13: The method according to claim 8, wherein the reinforcing fibers are in the form of continuous fiber filaments, continuous fiber rovings, or continuous fiber mats.

14: A cured composite material obtainable by the method according to claim 8.

15: A molding consisting of the cured composite material according to claim 14.

16: A rebar consisting of the cured composite material according to claim 14.

17. (canceled)

Description

EXAMPLES

Example 1a: Preparation of DMDETA from Aminopropanol (MIPOA) and Propanediamine (PDA)

[0059] A tubular reactor was charged with 600 ml of Cu catalyst. The catalyst was activated by heating it to a temperature in the range from 180 to 200° C. under a nitrogen stream at standard pressure. Hydrogen was metered into the nitrogen stream under careful control of the exothermicity of the activation. Finally, pure hydrogen was passed over the catalyst at standard pressure and a temperature of 200° C. for a period of 6 h. After the catalyst had been activated, the reactor was put under 200 bar of hydrogen pressure and, at a temperature in the range from 180 to 200° C., a stream of 100 g/h of 1-aminopropan-2-ol (mixed with about 10% 2-aminopropan-2-ol), 200 g/h of propane-1,2-diamine, 80 g/h of NH.sub.3 and 100 L (STP)/h of H.sub.2 was passed through the reactor. The product stream was expanded to standard pressure and collected. The crude product thus obtained, which comprised about 20% to 30% by weight of DMDETA, was purified by distillation under reduced pressure in order to obtain the DMDETA fraction. This DMDETA fraction had a purity of >99% (for the sum total of all DMDETA isomers) and an isomer ratio (in GC area %) of about 6:87:6 for the isomers of the formulae IIa:IIb:IIc.

Example 1b: Preparation of DMDETA from Aminopropanol (MIPOA)

[0060] A tubular reactor was charged with 800 ml of Co/Ni/Cu catalyst. The catalyst was activated by heating it to a temperature of 280° C. under a hydrogen stream at standard pressure. After the catalyst had been activated, the reactor was put under 200 bar of hydrogen pressure and, at a temperature in the range from 170 to 190° C., a stream of 320 g/h of 1-aminopropan-2-ol (mixed with about 10% 2-aminopropan-2-ol), 200 to 730 g/h of NH.sub.3 and 100 L (STP)/h of H.sub.2 was passed through the reactor. The product stream was expanded to standard pressure and collected. The crude product thus obtained, which comprised about 5% by weight of DMDETA as well as the main propanediamine (PDA) product, was purified by distillation under reduced pressure in order to obtain the DMDETA fraction. This DMDETA fraction had a purity of >99% (for the sum total of all DMDETA isomers) and an isomer ratio (in GC area %) of about 42:53:4 for the isomers of the formulae IIa:IIb:IIc.

Example 2: Curing of Epoxy Resin with DMDETA

[0061] DMDETA mixtures from example 1a or example 1b and epoxy resin (bisphenol A diglycidyl ether, Epilox A19-03, Leuna, EEW: 185 g/mol) according to the amounts stated in table 1 were mixed in a stirrer system (1 min at 2000 rpm). DSC measurements (differential scanning calorimetry) and rheological analyses were performed immediately after mixing. By way of comparison, corresponding compositions comprising IPDA (Baxxodur® EC 201, BASF), diethylenetriamine (DETA, BASF), 4-methyltetrahydrophthalic anhydride (MTHPA, Sigma-Aldrich) in combination with the accelerator 2,4,6-tris(dimethylaminomethyl)phenol (K54, Sigma-Aldrich) or MTHPA in combination with the accelerator 1-methylimidazole (1-MI, BASF) were also examined in the same way.

[0062] The DSC analyses of the curing reaction of DMDETA or IPDA, DETA, MTHPA/K54 or MTHPA/1-MI for determination of onset temperature (To), exothermic enthalpy (ΔH) and glass transition temperature (Tg) were conducted according to ASTM D 3418-15 (2015), using the following temperature profile: 0° C..fwdarw.20 K/min 200° C..fwdarw.10 min 200° C. The Tg was determined in the second run. The results are collated in table 1.

[0063] The rheological measurements for examination of the reactivity profile (pot life and gel time) of the various amino curing agents (IPDA, DETA and DMDETA) and the various anhydride curing agent systems (MTHPA/K54 and MTHPA/1-MI) with the epoxy resin were conducted at different temperatures on a shear stress-controlled plate-plate rheometer (MCR 301, Anton Paar) with a plate diameter of 15 mm and a gap of 0.25 mm. For the pot lives—as a measure of the period of time within which the reactive resin composition can be handled—the time taken for the freshly produced reactive resin composition to reach a viscosity of 6000 mPa*s was measured with rotation of the abovementioned rheometer at room temperature (23° C.). The gel times were determined with oscillation of the abovementioned rheometer at 90° C. or 110° C., with the point of intersection of the loss modulus (G″) and storage modulus (G′) giving the gel time according to standard ASTM D 4473-08 (2016). The mixed viscosities (η.sub.o) were measured at room temperature (23° C.) according to standard DIN ISO 3219 (1993) immediately after the components had been mixed, with the aid of a shear stress-controlled rheometer (e.g. MCR 301 from Anton Paar) with cone-plate arrangement (e.g. diameter of cone and plate: 50 mm; cone angle: 1°; gap width: 0.1 mm) For the determination of the B times that likewise serve as a measure of curing rate, samples (about 0.5 g) of the freshly produced reactive resin composition were applied to an unrecessed plate at 145° C. and, according to standard DIN EN ISO 8987 (2005), the time taken to form fibers (gel point) and until abrupt hardening (curing) were determined. The results of the rheological measurements are summarized in table 1. Immediately after the epoxy resin and amino curing agent or anhydride curing agent system had been mixed, the mixture was degassed at 1 mbar and then cured (8 h at 60° C., then 4 h at 100° C., then 2 h at 160° C.). After curing, the mechanical properties for the cured resin (tensile modulus of elasticity (E-t), tensile strength (σ-M), tensile elongation (ε-M), flexural modulus of elasticity (E-f), flexural strength (σ-fM) and flexural elongation (ε-fM)) were determined at room temperature according to standards ISO 527-2:1993 and ISO 178:2006. The results are likewise collated in table 1. Impact resistance was determined by means of the Charpy notched bar impact test according to standard DIN EN ISO 179-1 (2010) at room temperature. High impact resistance corresponds to low brittleness.

TABLE-US-00001 TABLE 1 Comparison of the curing of epoxy resin with various amino curing agents (inventive: DMDETA; comparative experiments: IPDA and DETA) or with the various anhydride curing agent systems (comparative experiments: MTHPA with K54 and MTHPA with 1-MI) DMDETA MTHPA IPDA DETA Ex. 1a Ex. 1b K54 1-MI AHEW.sub.emp 43 20.6 27 27 — — Amount of curing 23.2 11.1 14.6 14.7 81 81 agent (g) per 100 g of epoxy resin Amount of acceler- — — — — 2 2 ator (g) per 100 g of epoxy resin η.sub.o (mPas) at 23° C. 1930 1540 1435 1350 2580 1400 Pot life (min) at 47 31 54 60 854 600 23° C. Gel time (min) 18.0 6.0 11.0 11.5 24.0 30.0 at 90° C. Gel time (min) 7.5 2.6 4.6 5.0 7.0 9.4 at 110° C. B time of plate (sec) 130 25 80 80 110 110 at 145° C. (gel point) B time of plate (sec) 145 30 90 90 125 125 at 145° C. (curing) To (° C.) 68 62 66 68 105 103 ΔH (J/g) 467 540 487 488 326 370 Tg (° C.) 164.9 136.7 161.5 161.3 126.8 137.0 Flexural E-f (MPa) 2884 2865 3057 3024 3251 3089 Flexural σ-fM (MPa) 119.4 104 116.3 116.4 141.5 134 Flexural ε-fM (%) 6.08 5.9 6.09 6.10 6.1 6.1 Tensile E-t (MPa) 2734 2726 n.d. 2899 3112 2951 Tensile σ-M (MPa) 80.1 70.6 n.d. 83.2 80.4 84 Tensile ε-M (%) 7.8 6.2 n.d. 7.5 5.3 5.8 Charpy (kJ/m.sup.2) 38.9 22.6 26 23.8 19.2 18.7 .square-solid. (n.d.: not determined)

Example 3: Pultrudates with a Matrix Composed of Epoxy Resin and DMDETA

[0064] Pultrusion profiles were produced by means of pultrusion methods. For this purpose, continuous glass fibers (E-CR glass: PulStrand® 4100 Type 30: from Owens Corning) were impregnated in a pultrusion apparatus (Px 750-08T; from Pultrex) with a matrix mixture composed of 100 parts epoxy resin (ER 5700, from Leuna Harze, EEW: 180.5), 15 parts DMDETA (from example 1a) and 3 parts separating agent (PAT C656/3-7, from Würtz), bundled, and cured at a pultrusion speed of 1.1 m/min and a temperature of 160° C. (length of the heating zone: 1 m). As well as these glass fiber-based pultrusion profiles (GF pultrudates), carbon fiber-based pultrusion profiles (CF pultrudates) were produced in a corresponding manner with continuous carbon fibers (Sigrafil C T50-4.0/240-E100, SGL), except using 5 parts of the separating agent and setting a pultrusion speed of 0.4 m/min.

[0065] The glass transition temperature (Tg) was measured according to ASTM D 3418-15 (2015) as described for example 2. For this purpose, some material was removed from the pultrudates and ground to powder, the fiber content thereof was removed by means of the density gradient, and the determination of Tg was conducted with the remaining pulverulent resin material. The GF pultrudates achieved a glass transition temperature of 88.7° C., and of 92.1° C. after further curing (6 h at 110° C.). The CF pultrudates achieved a glass transition temperature of 89.1° C.

[0066] The pultrudates had a fiber volume content of about 60%.

[0067] In a three-point bending test (instrument: Z050 Allround (fin: r=5 mm, support: r=5 mm), from Zwick/Roell) according to standard DIN EN ISO 14125 (2011), flexural modulus of elasticity (E-f), flexural strength (σ-fM) and flexural elongation (ε-fM) were determined, each longitudinally (0°) and transverse (90°) to the alignment of the fibers. In each case, 6 test specimens with dimensions of 3 mm×15 mm×200 mm (measurements in longitudinal orientation) or 5 test specimens with dimensions of 3 mm×15 mm×150 mm (measurements in transverse orientation) were analyzed at a temperature of 23° C., a relative humidity of 50%, a force sensor of 50 kN, a speed of 1%/min and a support width of 120 mm (measurements in longitudinal orientation) or 60 mm (measurements in transverse orientation). The measurements were corrected as required according to the standard for large deflections. The results are collated in table 2.

TABLE-US-00002 TABLE 2 Flexural mechanics for GF and CF pultrudates with epoxy resin/DMDETA matrix Orientation E-f (GPa) σ-fM (MPa) ε-fM (%) CF  0°  140 ± 4   1300 ± 200  1.0 ± 0.1 puitrudate 90°  7.7 ± 0.4  60 ± 30   0.8 ± 0.3 GF  0°   52 ± 1   1350 ± 60   2.6 ± 0.1 puitrudate 90° 14.8 ± 0.6  28 ± 2   0.20 ± 0.02

[0068] The interlaminar shear strength (ILSS) of the GF and CF pultrudates was determined by the three-point method according to standard DIN EN ISO 14130 (1998) (instrument: Z050 Allround; from Zwick/Roell; but with a support radius of 3 mm), in each case longitudinally (0°) to the alignment of the fibers. In each case, 6 test specimens having a thickness of 3 mm were analyzed at a temperature of 23° C., a relative humidity of 50% and a force sensor of 50 kN. The results are collated in table 3.

TABLE-US-00003 TABLE 3 Interlarninar shear strength (ILSS) for GF and CF pultrudates with epoxy resin/DMDETA matrix ILSS (MPa) CF pultrudate 72 ± 1 GF bultrudate 39 ± 3