GLASS FIBER REINFORCED COMPOSITE WITH NARROW MWD POLYPROPYLENE

Abstract

Fiber reinforced composite comprising a polypropylene with high melting temperature and very narrow molecular weight distribution.

Claims

1. A fiber reinforced composite having a melt flow rate MFR.sub.2 (230° C., 2.16 kg) measured according to ISO 1133 in the range of 10 to 100 g/10 min and comprising: (a) 59 to 90 wt.-%, of a polypropylene, based on the fiber reinforced composite, (b) 9.0 to 40 wt.-%, of glass fibers, based on the fiber reinforced composite, and (c) 0.05 to 5.0 wt.-%, of a compatibilizer, based on the fiber reinforced composite, wherein the total amount of the polypropylene, the glass fibers and the compatibilizer in the fiber reinforced composite is at least 95 wt.-%, wherein the polypropylene has: (i) a melting temperature Tm determined by DSC according to ISO 11357-3 (heating and cooling rate 10° C./min) in the range of 152 to 160° C., (ii) a comonomer content determined by .sup.13C-NMR spectroscopy of not more than 0.5 wt.-%, the comonomer being ethylene, (iii) a melt flow rate MFR.sub.2 (230° C., 2.16 kg) measured according to ISO 1133 in the range of 20 to 500 g/10 min, and (iv) a molecular weight distribution (MWD) determined by gel permeation chromatography (GPC) in the range of 1.0 to below 3.0.

2. The fiber reinforced composite according to claim 1, wherein the polypropylene has 2,1 regio-defects determined by .sup.13C-NMR spectroscopy in the range of 0.10 to 0.90%.

3. The fiber reinforced composite according to according to claim 1, wherein the polypropylene complies with the inequation (II):
51<Tm/MWD<80  (II) wherein Tm is the melting temperature of the polypropylene [in ° C.] determined by DSC according to ISO 11357-3 (heating and cooling rate 10° C./min) MWD is the molecular weight distribution (MWD) of the polypropylene determined by gel permeation chromatography (GPC).

4. The fiber reinforced composite according to claim 1, wherein the polypropylene has a xylene cold soluble (XCS) fraction measured according to ISO 16152 (25° C.) in the range of 0.05 to 1.00 wt.-%.

5. The fiber reinforced composite according to claim 1, wherein the polypropylene is a visbroken polypropylene.

6. The fiber reinforced composite to claim 1, wherein the polypropylene forms the continuous phase in which the fibers are embedded.

7. The fiber reinforced composite according to claim 1, having a melt flow rate MFR.sub.2 (230° C., 2.16 kg) measured according to ISO 1133 in the range of 15 to 50 g/10 min.

8. The fiber reinforced composite according to claim 1, wherein the polypropylene is a monophasic polypropylene.

9. The fiber reinforced composite according to claim 8, wherein the monophasic polypropylene is a propylene homopolymer.

10. The fiber reinforced composite according to claim 9, wherein the propylene homopolymer has: (i) a melting temperature Tm determined by DSC according to ISO 11357-3 (heating and cooling rate 10° C./min) in the range of 152 to 160° C., (ii) a molecular weight distribution (MWD) determined by gel permeation chromatography (GPC) in the range of 1.5 to below 3.0, (iii) a xylene cold soluble (XCS) fraction measured according to ISO 16152 (25° C.) in the range of 0.10 to 0.90 wt.-%, (iv) a melt flow rate MFR.sub.2 (230° C., 2.16 kg) measured according to ISO 1133 in the range of 20 to 500 g/10 min, and (v) 2,1 regio-defects determined by .sup.13C-NMR spectroscopy in the range of 0.15 to 0.80%.

11. The fiber reinforced composite according to claim 1, wherein the fiber reinforced composite consists of (a) 59 to 90 wt.-%, of a polypropylene, based on the fiber reinforced composite, (b) 9.0 to 40 wt.-%, of glass fibers, based on the fiber reinforced composite, (c) 0.05 to 5.0 wt.-%, of a compatibilizer, based on the fiber reinforced composite, and (d) 0.1 to 5.0 wt.-%, of additives based on the fiber reinforced composite.

12. The fiber reinforced composite according to claim 1, wherein the polypropylene has been produced by polymerizing propylene and optionally ethylene in the presence of a metallocene catalyst having the formula (I): ##STR00008## wherein each R.sup.1 are independently the same or can be different and are hydrogen or a linear or branched C.sub.1-C.sub.6 alkyl group, whereby at least one R.sup.1 per phenyl group is not hydrogen, R′ is a C.sub.1-C.sub.10 hydrocarbyl group and X independently is a hydrogen atom, a halogen atom, C.sub.1-C.sub.6 alkoxy group, C.sub.1-C.sub.6 alkyl group, phenyl or benzyl group, and subsequent the polypropylene has been visbroken, wherein the visbreaking ratio (VR) is in the range of 2.5 to 20.0, wherein the visbreaking ratio (VR) is determined according to equation
VR=MFR.sub.2(FINAL)/MFR.sub.2(START) wherein “MFR.sub.2(FINAL)” is melt flow rate MFR.sub.2 (230° C.; 2.16 kg) measured according to ISO 1133 of the polypropylene after visbreaking “MFR.sub.2(START)” is melt flow rate MFR.sub.2 (230° C.; 2.16 kg) measured according to ISO 1133 of the polypropylene before visbreaking.

13. The fiber reinforced composite according to claim 1, wherein the glass fibers are short glass fibers.

14. The fiber reinforced composite according to claim 13, wherein the glass fibers have an average fiber length of 2.0 to 10.0 mm and optionally an average diameter of 5 to 20 μm.

15. The fiber reinforced composite according to claim 1, wherein the compatibilizer is a polar modified polypropylene.

16. The fiber reinforced composite according to claim 15, wherein polar modified polypropylene is a maleic anhydride grafted polypropylene, having a maleic anhydride content of 0.1 to 5 wt.-% and a melt flow rate MFR.sub.2 (190° C., 2.16 kg) measured according to ISO 1133 in the range of 80 to 250 g/10 min.

17. The process for the manufacture of the fiber reinforced composite according to claim 1, comprising: adding (a) the polypropylene, (b) the glass fibers, (c) the compatibilizer, and (d) optionally additives to an extruder and extruding the same to obtain the fiber reinforced composite, wherein the polypropylene has been produced by polymerizing propylene and optionally ethylene in the presence of the metallocene catalyst having the formula (I): ##STR00009## wherein each R.sup.1 are independently the same or can be different and are hydrogen or a linear or branched C.sub.1-C.sub.6 alkyl group, whereby at least one R.sup.1 per phenyl group is not hydrogen, R′ is a C.sub.1—C.sub.10 hydrocarbyl group and X independently is a hydrogen atom, a halogen atom, C.sub.1-C.sub.6 alkoxy group, C.sub.1-C.sub.6 alkyl group, phenyl or benzyl group, and subsequent the polypropylene has been visbroken, wherein the visbreaking ratio (VR) is in the range of 2.5 to 20.0, wherein the visbreaking ratio (VR) is determined according to equation
VR=MFR.sub.2(FINAL)/MFR.sub.2(START) wherein “MFR.sub.2(FINAL)” is melt flow rate MFR.sub.2 (230° C.; 2.16 kg) measured according to ISO 1133 of the polypropylene after visbreaking “MFR.sub.2(sTART)” is melt flow rate MFR.sub.2 (230° C.; 2.16 kg) measured according to ISO 1133 of the polypropylene before visbreaking.

18. An article comprising at least 90 wt.-% of the fiber reinforced composite according to claim 1.

19. The fiber reinforced composite to claim 12, wherein R′ is a C.sub.1-C.sub.4 hydrocarbyl group.

20. The process according to claim 17, wherein R′ is a C.sub.1-C.sub.4 hydrocarbyl group.

Description

EXAMPLES

1. Determination Methods

[0359] The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples unless otherwise defined.

a) Melt Flow Rate

[0360] The melt flow rate (MFR.sub.2) is determined according to ISO 1133 and is indicated in g/10 min.

[0361] The MFR.sub.2 of polypropylene is determined at a temperature of 230° C. and under a load of 2.16 kg.

b) Heat Deflection Temperature B (HDT B)

[0362] The Heat deflection temperature B (HDT B) was determined according to ISO 75 B at 0.45 MPa using 80×10×4 mm.sup.3 test bars injection molded in line with EN ISO 1873-2.

c) Xylene Cold Soluble Fraction (XCS, Wt %)

[0363] The amount of the polymer soluble in xylene is determined at 25.0° C. according to ISO 16152; 1.sup.th edition; 2005-07-01.

d) Melting Temperature T.sub.m and Crystallization Temperature T.sub.c

[0364] The melting temperature T.sub.m is determined by differential scanning calorimetry (DSC) according to ISO 11357-3 with a TA-Instruments 2920 Dual-Cell with RSC refrigeration apparatus and data station. A heating and cooling rate of 10° C./min is applied in a heat/cool/heat cycle between +23 and +210° C. The crystallization temperature (T.sub.c) is determined from the cooling step while melting temperature (Tm) and melting enthalpy (Hm) are being determined in the second heating step.

e) Tensile Modulus

[0365] Tensile modulus and elongation at break are measured according to ISO 527-2 using injection molded specimens as described in EN ISO 1873-2 (1 B dog bone shape, 4 mm thickness).

f) Charpy Impact Strength

[0366] The Charpy impact strength was measured according to ISO 179 1eU at +23° C. using injection molded bar test specimens of 80×10×4 mm.sup.3 prepared in accordance with EN ISO 1873-2.

g) Quantification of Copolymer Microstructure by .SUP.13.C-NMR Spectroscopy

[0367] Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content of the polymers. Quantitative .sup.13C{.sup.1H} NMR spectra were recorded in the solution-state using a Bruker Advance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz for .sup.1H and .sup.13C respectively. All spectra were recorded using a .sup.13C optimized 10 mm extended temperature probehead at 125° C. using nitrogen gas for all pneumatics. Approximately 200 mg of material was dissolved in 3 ml of 1,2-tetrachloroethane-d.sub.2 (TCE-d.sub.2) along with chromium-(III)-acetylacetonate (Cr(acac).sub.3) resulting in a 65 mM solution of relaxation agent in solvent (Singh, G., Kothari, A., Gupta, V., Polymer Testing 28 5 (2009), 475). To ensure a homogenous solution, after initial sample preparation in a heat block, the NMR tube was further heated in a rotatary oven for at least 1 hour. Upon insertion into the magnet the tube was spun at 10 Hz. This setup was chosen primarily for the high resolution and quantitatively needed for accurate ethylene content quantification. Standard single-pulse excitation was employed without NOE, using an optimised tip angle, 1 s recycle delay and a bi-level WALTZ16 decoupling scheme (Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187 (2007) 225; Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128). A total of 6144 (6k) transients were acquired per spectra. Quantitative .sup.13C{.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs. All chemical shifts were indirectly referenced to the central methylene group of the ethylene block (EEE) at 30.00 ppm using the chemical shift of the solvent. This approach allowed comparable referencing even when this structural unit was not present. Characteristic signals corresponding to the incorporation of ethylene were observed Cheng, H. N., Macromolecules 17 (1984), 1950).

[0368] With characteristic signals corresponding to 2,1 erythro regio defects observed (as described in L. Resconi, L. Cavallo, A. Fait, F. Piemontesi, Chem. Rev. 2000, 100 (4), 1253, in Cheng, H. N., Macromolecules 1984, 17, 1950, and in W-J. Wang and S. Zhu, Macromolecules 2000, 33 1157) the correction for the influence of the regio defects on determined properties was required. Characteristic signals corresponding to other types of regio defects were not observed.

[0369] The comonomer fraction was quantified using the method of Wang et. al. (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157) through integration of multiple signals across the whole spectral region in the .sup.13C{.sup.1H} spectra. This method was chosen for its robust nature and ability to account for the presence of regio-defects when needed. Integral regions were slightly adjusted to increase applicability across the whole range of encountered comonomer contents.

[0370] For systems where only isolated ethylene in PPEPP sequences was observed the method of Wang et. al, was modified to reduce the influence of non-zero integrals of sites that are known to not be present. This approach reduced the overestimation of ethylene content for such systems and was achieved by reduction of the number of sites used to determine the absolute ethylene content to:

E=0.5(Sββ+Sβγ+Sβδ+0.5(Sαβ+Sαγ))

Through the use of this set of sites the corresponding integral equation becomes:

E=0.5(I.sub.H+I.sub.G+0.5(I.sub.C+I.sub.D))

using the same notation used in the article of Wang et. al. (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157). Equations used for absolute propylene content were not modified.

[0371] The mole percent comonomer incorporation was calculated from the mole fraction:

E[mol %]=100*fE

[0372] The weight percent comonomer incorporation was calculated from the mole fraction:

E[wt %]=100*(fE*28.06)/((fE*28.06)+((1−fE)*42.08))

h) Number Average Molecular Weight (Mn), Weight Average Molecular Weight (Mw) and the Molecular Weight Distribution (Mw/Mn)

[0373] Number average molecular weight (M.sub.n), weight average molecular weight (M.sub.w) and the molecular weight distribution (M.sub.w/M.sub.n) were determined by Gel Permeation Chromatography (GPC) according to ISO 16014-4:2003 and ASTM D 6474-99. A PolymerChar GPC instrument, equipped with infrared (IR) detector was used with 3×Olexis and 1×Olexis Guard columns from Polymer Laboratories and 1,2,4-trichlorobenzene (TCB, stabilized with 250 mg/L 2,6-Di tert butyl-4-methyl-phenol) as solvent at 160° C. and at a constant flow rate of 1 mL/min. 200 μL of sample solution were injected per analysis. The column set was calibrated using universal calibration (according to ISO 16014-2:2003) with at least 15 narrow MWD polystyrene (PS) standards in the range of 0.5 kg/mol to 11 500 kg/mol. Mark Houwink constants for PS, PE and PP used are as described per ASTM D 6474-99. All samples were prepared by dissolving 5.0-9.0 mg of polymer in 8 mL (at 160° C.) of stabilized TCB (same as mobile phase) for 2.5 hours for PP or 3 hours for PE at max. 160° C. under continuous gentle shaking in the autosampler of the GPC instrument.

i) VOC and FOG

[0374] VOC values and FOG values were measured according to VDA 278 (October 2011; Thermal Desorption Analysis of Organic Emissions for the Characterization of Non-Metallic Materials for Automobiles, VDA Verband der Automobilindustrie) after sample preparation of injection moulding plaques according to EN ISO 19069-2:2016. These plaques were packed in aluminium-composite foils immediately after production and the foils were sealed.

[0375] According to the VDA 278 October 2011 the VOC value is defined as “the total of the readily volatile to medium volatile substances. It is calculated as toluene equivalent. The method described in this recommendation allows substances in the boiling/elution range up to n-pentacosane (C.sub.25) to be determined and analyzed.”

[0376] The FOG value is defined as “the total of substances with low volatility, which elute from the retention time of n-tetradecane (inclusive)”. It is calculated as hexadecane equivalent. Substances in the boiling range of n-alkanes “C.sub.14” to “C.sub.32” are determined and analysed.

j) Fogging:

[0377] Fogging was measured according to DIN 75201:2011-11, method B (gravimetric method) on compression-moulded specimens (diameter 80 mm+/−1 mm, thickness<1 cm) cut out from an injection-moulded plate. With this method, the mass of fogging condensate on aluminium foil in mg is determined by means of weighing of the foil before and after the fogging test. The term “fogging” refers to a fraction of volatile substances condensed on glass parts as e.g. the windscreen of a vehicle.

k) Average Fibre Diameter

[0378] The average fibre diameter is determined according to ISO 1888:2006(E), Method B, microscope magnification of 1000.

2. Preparation of the Polypropylenes

a) Preparation of the Single Site Catalyst System 1

Catalyst Complex

[0379] The following metallocene complex has been used as described in WO 2019/179959:

##STR00007##

Preparation of MAO-Silica Support

[0380] A steel reactor equipped with a mechanical stirrer and a filter net was flushed with nitrogen and the reactor temperature was set to 20° C. Next silica grade DM-L-303 from AGC Si-Tech Co, pre-calcined at 600° C. (5.0 kg) was added from a feeding drum followed by careful pressuring and depressurising with nitrogen using manual valves. Then toluene (22 kg) was added. The mixture was stirred for 15 min. Next 30 wt.-% solution of MAO in toluene (9.0 kg) from Lanxess was added via feed line on the top of the reactor within 70 min. The reaction mixture was then heated up to 90° C. and stirred at 90° C. for additional two hours. The slurry was allowed to settle and the mother liquor was filtered off. The catalyst was washed twice with toluene (22 kg) at 90° C., following by settling and filtration. The reactor was cooled off to 60° C. and the solid was washed with heptane (22.2 kg). Finally MAO treated SiO.sub.2 was dried at 600 under nitrogen flow for 2 hours and then for 5 hours under vacuum (−0.5 barg) with stirring. MAO treated support was collected as a free-flowing white powder found to contain 12.2% Al by weight.

Single Site Catalyst System 1 Preparation

[0381] 30 wt.-% MAO in toluene (0.7 kg) was added into a steel nitrogen blanked reactor via a burette at 20° C. Toluene (5.4 kg) was then added under stirring. The metallocene complex as described above under 2a) (93 g) was added from a metal cylinder followed by flushing with 1 kg toluene. The mixture was stirred for 60 minutes at 20° C. Trityl tetrakis(pentafluorophenyl) borate (91 g) was then added from a metal cylinder followed by a flush with 1 kg of toluene. The mixture was stirred for 1 h at room temperature. The resulting solution was added to a a stirred cake of MAO-silica support prepared as described above over 1 hour. The cake was allowed to stay for 12 hours, folled by drying under N.sub.2 flow at 60° C. for 2 h and additionally for 5 h under vacuum (−0.5 barg) under stirring stirring.

[0382] Dried catalyst was sampled in the form of pink free flowing powder containing 13.9% Al and 0.11% Zr.

b) Preparation of the Ziegler-Natta Catalyst System 2

[0383] A Ziegler-Natta catalyst system has been used

Used Chemicals:

[0384] 20% solution in toluene of butyl ethyl magnesium (Mg(Bu)(Et), BEM), provided by Chemtura [0385] 2-ethylhexanol, provided by Amphochem [0386] 3-Butoxy-2-propanol—(DOWANOL™ PnB), provided by Dow [0387] bis(2-ethylhexyl)citraconate, provided by SynphaBase [0388] TiCl.sub.4, provided by Millenium Chemicals [0389] Toluene, provided by Aspokem [0390] Viscoplex® 1-254, provided by Evonik [0391] Heptane, provided by Chevron

Preparation of a Mg Alkoxy Compound

[0392] Mg alkoxide solution was prepared by adding, with stirring (70 rpm), into 11 kg of a 20 wt-% solution in toluene of butyl ethyl magnesium (Mg(Bu)(Et)), a mixture of 4.7 kg of 2-ethylhexanol and 1.2 kg of butoxypropanol in a 20 I stainless steel reactor. During the addition the reactor contents were maintained below 45° C. After addition was completed, mixing (70 rpm) of the reaction mixture was continued at 60° C. for 30 minutes. After cooling to room temperature 2.3 kg of the donor bis(2-ethylhexyl)citraconate was added to the Mg-alkoxide solution keeping temperature below 25° C. Mixing was continued for 15 minutes under stirring (70 rpm).

Preparation of Solid Catalyst Component

[0393] 20.3 kg of TiCl.sub.4 and 1.1 kg of toluene were added into a 20 I stainless steel reactor. Under 350 rpm mixing and keeping the temperature at 0° C., 14.5 kg of the prepared Mg alkoxy compound was added during 1.5 hours. 1.7 I of Viscoplex® 1-254 and 7.5 kg of heptane were added and after 1 hour mixing at 0° C. the temperature of the formed emulsion was raised to 90° C., within 1 hour. After 30 minutes mixing was stopped catalyst droplets were solidified and the formed catalyst particles were allowed to settle. After settling (1 hour), the supernatant liquid was siphoned away. Then the catalyst particles were washed with 45 kg of toluene at 90° C. for 20 minutes followed by two heptane washes (30 kg, 15 min). During the first heptane wash the temperature was decreased to 50° C. and during the second wash to room temperature.

[0394] The thus obtained catalyst was used along with triethyl-aluminium (TEAL) as co-catalyst and dicyclo pentyl dimethoxy silane (D-donor) as donor. The ratio used was:

TEAL/Ti: 250 mol/mol
TEAL/Donor: 10 mol/mol

TABLE-US-00001 TABLE 1 Polymerization conditions of HPP1, and HPP3 HPP1 HPP3 Catalyst system 1 2 Prepolymerization Temperature [° C.] 20 30 Pressure [kPa] 5337 5450 Catalyst feed [g/h] 2.5 1.8 C3 feed [kg/h] 48 55 H2 feed [g/h] 0.2 0.0 Residence time [h] 0.37 0.30 Loop (Reactor 1) Temperature [° C.] 75 75 Pressure [kPa] 5376 5325 H2/C3 ratio [mol/kmol] 0.16 7.5 Residence time [h] 0.47 0.45 Loop reactor split [wt.-%] 48 50 MFR.sub.2 [g/10 min] 8.0 75 GPR (Reactor 2) Temperature [° C.] 80 80 Pressure [kPa] 2400 2500 H2/C3 ratio [mol/kmol] 1.5 94 Polymer residence time [h] 3.0 1.9 GPR reactor split [wt.-%] 52 50 MFR.sub.2 total [g/10 min] 7.0 75

c) Visbreaking of the Propylene Homopolymer HPP1 to HPP2

[0395] In a second step the propylene homopolymer HPP2 is produced by visbreaking HPP1 by using a co-rotating twin-screw extruder at 200-230° C. and using (tert.-butylperoxy)-2,5-dimethylhexane (Trigonox 101, distributed by Akzo Nobel, Netherlands) in an appropriate amount to achieve the target MFR.sub.2 as indicated in table 2.

[0396] The properties of the propylenes homopolymers are summarized in table 2.

TABLE-US-00002 TABLE 2 Properties of HPP1, HPP2, and HPP3 HPP1 HPP2 HPP3 Properties Tm [° C.] 156 156 164 MWD [—] 3.2 2.8 4.9 XCS [wt.-%] 0.4 0.4 3.5 MFR.sub.2 [g/10 min] 7.0 72 75 VB ratio [—] 1.0 10.3 1.0 <2.1> defects [%] 0.60 0.60 0

[0397] The inventive examples IE1 and the comparative examples CE1 and CE2 were prepared by compounding on a co-rotating twin-screw extruder (ZSK 40 from Coperion) with an L/D ratio of 43. The following process parameters were used: [0398] throughput of 100 kg/h [0399] screw speed of 100-150 rpm [0400] barrel temperatures of 220-250° C. increasing from the feeding zone and decreasing again towards the die plate [0401] die plate with 4 mm diameter holes and 3 strands

[0402] The polypropylene and the additives different from the short glass fibers were fed to the extruder and melt-kneaded in the 2.sup.nd barrel. A first kneading zone for mixing the polypropylene and the additives is located between the 3.sup.rd and 5.sup.th barrel. The short glass fibers were added in the 6.sup.th barrel using a side feeder. A second kneading zone for glass fibre dispersion is located between the 7.sup.th and 12.sup.th barrel.

[0403] The composites and their properties are summarized in Table 3.

TABLE-US-00003 TABLE 3 Properties of the inventive and comparative composites IE1 CE1 CE2 Composite HPP1 [wt.-%] — 78 — HPP2 [wt.-%] 78 — — HPP3 [wt.-%] — — 78 Glass fibre [wt.-%] 20 20 20 Compatibilizer [wt.-%] 1.5 1.5 1.5 Additives [wt.-%] 0.5 0.5 0.5 Properties Tm [° C.] 156 156 164 MFR.sub.2 [g/10 min] 17 3.2 16 Tensile modulus [MPa] 4986 4977 5256 Impact [kJ/m.sup.2] 48.2 50.4 48.8 HDT [° C.] 152 151 161 VOC [μg/g] <1 7 18 FOG [μg/g] 28 42 196 Fogging [mg] 0.27 0.30 0.46

[0404] As glass fibers the commercial product ECSO3T-480H of Nippon Electric Glass having an average fiber length of 3.0 mm and an average diameter of 10 μm.

[0405] The following combination of additives was used in compounding: 0.2 wt % of Tris (2,4-di-t-butylphenyl) phosphite (CAS-No. 31570-04-4, commercially available as Irgafos 168 from BASF AF, Germany), 0.1 wt % of Pentaerythrityl-tetrakis(3-(3′,5′-di-tert. butyl-4-hydroxyphenyl)-propionate (CAS-No. 6683-19-8, commercially available as Irganox 1010 from BASF AG, Germany) and 0.2 wt % of the carbon black masterbatch “Plasblak PPP6331” of Cabot Corporation, Germany.

[0406] Compatibilizer is the commercial maleic anhydride grafted polypropylene “Sconia TPPP 8112 GA” of BYK of having a maleic anhydrid content of 1.4 wt.-% and an MFR.sub.2 of more than 80 g/10 min.