FIBER REINFORCED POLYPROPYLENE COMPOSITE

Abstract

The present invention relates to a new composite comprising cellulose-based fiber and polymer-based fiber as well as to a process for the preparation of the composite and molded articles made from said composite.

Claims

1. A composite having an elongation at break in the range from 2.5 to 7.5%, the composite comprising: a) 25 to 92.5 wt. %, based on the total weight of the composite, of a polypropylene base material having a melt flow rate MFR.sub.2 (230 C., 2.16 kg) measured according to ISO 1133 in the range of from 3.0 to 140.0 g/10 min, wherein the polypropylene base material is; i) a heterophasic propylene copolymer (HECO) comprising a (semicrystalline) polypropylene (PP) as a matrix in which an elastomeric propylene copolymer (EC) is dispersed; or ii) a propylene homopolymer (hPP); and b) 5 to 50 wt. %, based on the total weight of the composite, of a cellulose-based fiber (CF); and c) 2.5 to 25 wt. %, based on the total weight of the composite, of a polymer-based fiber (PF) having a melting temperature of 210 C., wherein the weight ratio of the cellulose-based fiber (CF) and the polymer-based fiber (PF) [(CF)/(PF)] is in the range of 2.0 to 20.0.

2. The composite according to claim 1, wherein the heterophasic propylene copolymer (HECO) has: a) a melt flow rate MFR.sub.2 (230 C., 2.16 kg) in the range of from 5.0 to 120.0 g/10 min, and/or b) a xylene cold soluble (XCS) fraction (25 C.) of from 15.0 to 50.0 wt. %, based on the total weight of the heterophasic propylene copolymer (HECO), and/or c) a comonomer content of 30.0 mol. %, based on the heterophasic propylene copolymer (HECO).

3. The composite according to claim 1, wherein the amorphous fraction (AM) of the heterophasic propylene copolymer (HECO) has: a) a comonomer content in the range of 30.0 to 60.0 mol. %, based on the amorphous fraction (AM) of the heterophasic propylene copolymer (HECO), and/or b) an intrinsic viscosity (IV) in the range of 1.8 to 4.0 dl/g.

4. The composite according to claim 1, wherein the propylene homopolymer (hPP) has: a) a melt flow rate MFR.sub.2 (230 C., 2.16 kg) in the range of from 5.0 to 120.0 g/10 min, and/or b) a melting temperature measured according to ISO 11357-3 of at least 150 C., and/or c) a xylene cold soluble (XCS) content, below 4.5 wt. %, based on the total weight of the propylene homopolymer (hPP).

5. The composite according to claim 1, wherein the cellulose-based fiber (CF): a) is selected from the group consisting of wood, flax, hem, jute, straw, rice, hardboard, cardboard, paper, pulp, raw cellulose, cellulose, cellulose acetate, cellulose triacetate, cellulose propionate, cellulose acetate propionate, cellulose acetate butyrate, nitrocellulose, methylcellulose, ethylcellulose, ethyl methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose (HPC), hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose (HPMC), ethyl hydoxyethyl cellulose, carboxymethyl cellulose (CMC), and any mixtures thereof, and/or b) has a volume moment mean (D[4.3]) diameter between 1 and 1 200 m.

6. The composite according to claim 1, wherein the polymer-based fiber (PF) is selected from a poly vinyl alcohol (PVA) fiber, a polyethylene terephthalate (PET) fiber, a polyamide (PA) fiber and mixtures thereof.

7. The composite according to claim 1, wherein the polymer-based fiber (PF) has: i) a fiber average diameter in the range of 10 to 30 m, and/or ii) a tenacity of from 3.0 cN/dtex to 17 cN/dtex.

8. The composite according to claim 1, wherein the polymer-based fiber (PF) has a melting temperature Tm according to ISO 11357-3 which is 42 C., above the melting temperature Tm according to ISO 11357-3 of the polypropylene base material.

9. The composite according to claim 1, wherein the weight ratio of the cellulose-based fiber (CF) and the polymer-based fiber (PF) [(CF)/(PF)] is in the range of 2.0 to 10.0.

10. The composite according to claim 1, wherein the composite comprises an adhesion promoter (AP) in an amount from 0.1 to 6.0 wt. %, based on the total weight of the composite.

11. (canceled)

12. A process for the preparation of a composite according to claim 1, comprising the steps of: a) providing a polypropylene base material, b) providing a cellulose-based fiber (CF), c) providing a polymer-based fiber (PF), d) melt-blending the cellulose-based fiber (CF) of step b) with the polypropylene base material of step a) such as to obtain a cellulose-based fiber reinforced polypropylene base material, e) impregnating the polymer-based fiber (PF) of step c) with the polypropylene base material of step a) such as to obtain a polymer-based fiber reinforced polypropylene base material, f) blending the cellulose-based fiber reinforced polypropylene base material obtained in step d) and the polymer-based fiber reinforced polypropylene base material obtained in step e), and g) injection molding the blend obtained in step f), wherein step e) is carried out by pultrusion.

13. The process according to claim 12, wherein process step d) is carried out by extrusion and/or the polymer-based fiber (PF) of step c) is a continuous fiber.

14. The process according to claim 12, wherein process step e) comprises impregnating and coating the polymer-based fiber (PF) of step c) with the polypropylene base material (PBM) of step a), wherein impregnating and coating is carried out with the same or different polypropylene base material (PBM).

15. A molded article comprising a composite according to claim 1.

16. The molded article according to claim 15 being an automotive article.

Description

EXAMPLES

1. Definitions/Measuring Methods

[0361] 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.

Quantification of Microstructure by NMR Spectroscopy

[0362] 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 optimised 10 mm extended temperature probehead at 125 C. using nitrogen gas for all pneumatics. Approximately 200 mg of material was dissolved in 3 ml o f1,2-tetrachloroethane-d.sub.2 (TCE-d2) 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).

[0363] 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.

[0364] 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.

[0365] 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(S+S+S+0.5 (S+S))

[0366] Through the use of this set of sites the corresponding integral equation becomes:

E=0.5(I.sub.H30 I.sub.G+0.5(I.sub.C+I.sub.D))

[0367] 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.

[0368] The mole percent comonomer incorporation was calculated from the mole fraction:

E[mol %]=100*fE

[0369] The weight percent comonomer incorporation was calculated from the mole fraction:

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

[0370] The comonomer sequence distribution at the triad level was determined using the analysis method of Kakugo et al. (Kakugo, M., Naito, Y., Mizunuma, K., Miyatake, T. Macromolecules 15 (1982) 1150). This method was chosen for its robust nature and integration regions slightly adjusted to increase applicability to a wider range of comonomer contents.

[0371] DSC analysis, melting temperature (T.sub.m) and heat of fusion (H.sub.f), crystallization temperature (T.sub.c) and heat of crystallization (H.sub.c): measured with a TA Instrument Q2000 differential scanning calorimetry (DSC) on 5 to 7 mg samples. DSC is run according to ISO 11357/part 3/method C2 in a heat/cool/heat cycle with a scan rate of 10 C./min in the temperature range of 30 to +225 C. Crystallization temperature and heat of crystallization (H.sub.c) are determined from the cooling step, while melting temperature and heat of fusion (H.sub.f) are determined from the second heating step.

[0372] Density is measured according to ISO 1183-1-method A (2004). Sample preparation is done by compression moulding in accordance with ISO 1872-2:2007.

[0373] MFR.sub.2 (230 C.) is measured according to ISO 1133 (230 C., 2.16 kg load).

[0374] MFR.sub.2 (190 C.) is measured according to ISO 1133 (190 C., 5 kg or 2.1 kg load).

[0375] The xylene cold solubles (XCS, wt.-%): Content of xylene cold solubles (XCS) is determined at 25 C. according to ISO 16152; first edition; 2005-07-01

[0376] The amorphous content (AM) is measured by separating the above xylene cold soluble fraction (XCS) and precipitating the amorphous part with acetone. The precipitate was filtered and dried in a vacuum oven at 90 C.

[00001]$\mathrm{AM}.Math..Math.\%=\frac{100*m.Math..Math.1*v.Math..Math.0}{m.Math..Math.0*v.Math..Math.1}$

wherein
AM% is the amorphous fraction,
m0 is initial polymer amount (g)
m1 is weight of precipitate (g)
v0 is initial volume (ml)
v1 is volume of analyzed sample (ml)

[0377] Intrinsic viscosity is measured according to DIN ISO 1628/1, October 1999 (in Decalin at 135 C.).

[0378] Charpy notched impact strength is determined according to ISO 179/1eA at 23 C. and at 20 C. by using injection moulded test specimens of 80104 mm.sup.3 prepared in accordance with EN ISO 19069-2.

[0379] Charpy unnotched impact strength is determined according to ISO 179/1eU at 23 C. by using injection moulded test specimens of 80104 mm.sup.3 prepared in accordance with EN ISO 19069-2.

[0380] Tensile Modulus is measured according to ISO 527-3 (cross head speed=1 mm/min; 23 C.) using injection molded specimens as described in EN ISO 1873-2 (dog bone shape, 4 mm thickness).

[0381] Elongation at yield is measured according to ISO 527-3 (cross head speed=50 mm/min; 23 C.) using injection molded specimens as described in EN ISO 1873-2 (dog bone shape, 4 mm thickness). Tensile strength is measured according to ISO 527-2 (cross head speed=50 mm/min; 23 C.) using injection molded specimens as described in EN ISO 1873-2 (dog bone shape, 4 mm thickness).

[0382] Elongation at break is measured according to ISO 527-4 (cross head speed=50 mm/min; 23 C.) using injection molded specimens as described in EN ISO 1873-2 (dog bone shape, 4 mm thickness).

[0383] Average fiber diameter and average fiber length were determined by using a light microscopy. Samples were embedded in Struers CaldoFix resin under vacuum.

[0384] Abrasion/polishing was performed on a Struers LaboPol-5 machine, employing grinding media with particles sizes down to 0.04 m. The samples thus prepared were analyzed using an Olympus optical microscope in brightfield mode. The dimensions of the fiber cross-sections of the fibers in the matrix were measured to get the average fiber-diameter (typically around 30 individual fibers were measured and the shortest dimension of the fiber cross-section was used to get the fiber diameter). In contrast, the average fiber length was measured on around 30 individual pellets and the longest dimension of the pellet was used to get the average fiber length.

[0385] The particle size and particle size distribution of the cellulose-based fibers (CF), like wood flour fibers were determined by a Horiba Partica LA 950 V2 (Horiba Co., Japan) laser diffraction particle size analyzer equipped with an automated dry powder dispersion unit. Three parallel measurements were carried out and the result given is their average. The volume moment mean (D[4.3]) was calculated and used as mean particle size of cellulose-based fibers (CF), like the wood flour fibers.

[0386] The aspect ratio of the cellulose-based fibers (CF), like wood flour fibers was determined with the help of scanning electron microscopy (SEM). The SEM micrographs were taken by a Jeol JSM 6380 LA apparatus. The particles on the SEM micrographs were measured with the help of image analysis software (Image Pro Plus) and the length and diameter of the particles were measured individually by hand. At least 500 particles were analyzed on several micrographs in order to lower the standard deviation of the evaluation and aspect ratio was calculated thereof. Heat deflection temperature (HDT) A is determined according to ISO 75-2 at 0.45 MPa.

2. Examples

[0387] Composites were prepared using the components in the amounts as indicated in table 1 below and as explained further below. Pellets of the cellulose-based fiber (CF) composition DIL1 were prepared by compounding in a parallel, co-rotating twin screw extruder Brabender DSE20, coupled to an ECON EUP50 underwater pelletizer (UP). The DSE20 has a screw diameter (d) of 20 mm, and a length of 800 mm (40d). Pellets of the polymer-based fiber (PF) compositions DIL2, DIL3 and DIL4 were prepared by impregnating and coating endless multifilament fibers in a pultrusion process. The impregnating and coating is carried out at a temperature not exceeding 210 C.

TABLE-US-00001 TABLE 1 Examples Example DIL1 DIL2 DIL3 DIL4 hPP [wt.-%] 66.9 75.1 62.3 86.6 CF [wt.-%] 30.4 PF1 [wt.-%] 24.9 37.7 PF2 [wt.-%] 13.4 AP [wt.-%] 2.7 Density [kg/m.sup.3] 1010 990 1040 950 Tensile modulus [MPa] 3734 2254 2470 3394 Tensile strength [MPa] 39.8 51.5 47.4 41.0 Tensile Elongation at yield [%] 2.9 24.4 22.5 5.9 Tensile Elongation at [%] 3.2 25.7 23.5 6.0 break NIS (23 C.) [kJ/m.sup.2] 2.4 70.6 94.6 51.5 NIS (20 C.) [kJ/m.sup.2] 1.8 66.4 38.5 42.4 UNIS (23 C.) [kJ/m.sup.2] 12.3 105.4 186.4 61.9 HDT A (0.45 Mpa) [ C.] 106.1 79.1 90.0 72.7 hPP is the commercial polypropylene homopolymer HJ120UB containing nucleating and antistatic additives, provided by Borealis. This polymer is a CR (controlled rheology) grade with narrow molecular weight distribution, density of 905 kg/m.sup.3 (ISO1183) and an MFR.sub.2 of 75 g/10 min (230 C.; 2.16 kg; ISO 1133); XCS of 2.2 wt.-% and melting temperature of 164 C. and a Charpy Notched Impact Strength at 23 C. of 1.0 kJ/m.sup.2. CF is the commercial cellulosic product Arbocel C320 of Rettenmaier und Shne having a volume moment mean (D[4.3]) diameter of 467 m and an aspect ratio of 4. PF1 is the commercial endless multifilament yarn on bobbins PET T715 11000 dtex, tenacity of 7.45 cN/dtex, elongation at break 13%, with a specific surface-treatment for PP, supplied by DuraFiber Technologies. PF2 is the commercial endless multifilament yarn on bobbins PVA-fiber Mewlon AB (P100), tenacity of 10 cN/dtex, Young Modulus of 21.5 N/tex, melting temperature Tm of 240 C. with a specific surface-treatment for PP, supplied by Unitika, Japan. AP is the ethylene polypropylene copolymer (functionalized with maleic anhydride) TPPP6102 GA of BYK Co. Ltd, Germany, having a MFR.sub.2 (190 C.) of 20-40 g/10 min and a maleic anhydride content of >0.9 wt.-%. NIS is the notched impact strength. UNIS is the unnotched impact strength. HDT is the heat deflection temperature A.

[0388] The compositions DIL1 to DIL4 were dry-blended for preparing inventive examples IE1, IE2 and IE3 as outlined in table 2. Comparative example CE1 was prepared by conventional compounding in a parallel, co-rotating twin screw extruder Brabender DSE20, coupled to an ECON EUP50 underwater pelletizer (UP). The DSE20 has a screw diameter (d) of 20 mm, and a length of 800 mm (40d). Injection molding of CE1, IE1, IE2 and IE3 was carried out on a Battenfeld HM 1300/350 injection molding machine. IE1, IE2 and IE3 were prepared by blending DIL1 and DIL3 or DIL2 or DIL4 in a weight ratio of about 3:1.

TABLE-US-00002 TABLE 2 Examples IE1 IE2 IE3 (DIL1 + (DIL1 + (DIL1 + Example CE1 DIL3) DIL2) DIL4) hPP [wt.-%] 75.8 65.8 69.0 71.8 CF [wt.-%] 22.2 22.8 22.8 22.8 PF1 [wt.-%] 9.4 6.2 PF2 [wt.-%] 3.4 AP [wt.-%] 2.0 2.0 2.0 2.0 Density [kg/m.sup.3] 980 1020 1010 990 Tensile modulus [MPa] 3094 3619 3424 3753 Tensile strength [MPa] 35.4 40.8 39.1 42.3 Tensile Elongation at yield [%] 3.1 3.4 3.4 3.2 Tensile Elongation at [%] 3.6 3.8 3.9 3.3 break NIS (23 C.) [kJ/m.sup.2] 2.2 21.9 15.9 4.5 NIS (20 C.) [kJ/m.sup.2] 1.2 21.7 16.3 4.0 UNIS (23 C.) [kJ/m.sup.2] 11.3 25.1 20.4 14.3 HDT A (0.45 Mpa) [ C.] 91.9 102.3 101.7 95.1

[0389] From table 2, it can be gathered that the inventive examples exhibit improved impact strength combined with high stiffness.