NATURAL FIBERS AND POWDERY POLYPROPYLENE HOMOPOLYMER BASED COMPOSITION

Abstract

A composition that includes: (a) from 65 to 85% by weight of polypropylene homopolymer in powder form, the average particle size of which is micrometric, (b) from 14 to 30% by weight, preferably 14 to 25% by weight, of natural fibers less than or equal to 2 mm in length, and (c) from 1 to 3% by weight of compatibilizer, its uses for the preparation of a composite material by extrusion, wherein this composite material is useful for preparing a part by injection, in particular a vehicle part whose rigidity is improved.

Claims

1. A composition comprising: (a) from 65 to 85% by weight of polypropylene homopolymer; (b) from 14 to 30% by weight of natural fibers less than or equal to 2 mm in length, and (c) from 1 to 3% by weight of compatibilizer, wherein the polypropylene homopolymer is in the form of a powder whose average particle size measured by scanning electron microscopy is micrometric.

2. The composition according to claim 1, wherein the polypropylene homopolymer is in the form of a powder whose average particle size measured by scanning electron microscopy is from 1 to 1000 m.

3. The composition according to claim 2, wherein the polypropylene homopolymer is in the form of a powder whose average particle size measured by scanning electron microscopy is from 300 to 1000 m.

4. The composition according to claim 1, comprising from 14 to 25% of natural fibers less than or equal to 2 mm in length.

5. The composition according to claim 1, in which the natural fibers are derived from: seeds or fruit of plants, the stem of the plant, leaves of the plant, the trunk of the plant; herbaceous plants the stem of agricultural waste, hair, secretion or feathers of animals, and mixtures thereof.

6. The composition according to claim 5, in which the natural fibers are derived from: cotton, kapok, milkweed and/or coconut, flax, hemp, jute, ramie and/or kenaf, sisal, Manila hemp, abaca, henequen, raffia and/or agave, wood and/or banana; switchgrass, mismaythus, bamboo, sorghum, esparto and/or sabei communis rice, wheat and/or corn, wool, alpaca, mohair, cashmere, angora, goose feathers, silk, Tussah or wild silk and/or yarn spider, and mixtures thereof.

7. The composition according to claim 1, in which the compatibilizing agent is chosen from polyolefins grafted with a carboxylic acid, with one of the esters thereof, with one of the anhydrides thereof, with an epoxy, or with a silane.

8. The composition according to claim 1, comprising from 0.1 to 15% by weight, of an impact modifier selected from the group consisting of the ethylene-propylene-diene monomer (EPDM), ethylene-propylene monomer (EPM), ethylene-propylene rubber (EPR), polyolefin elastomers (POE), copolymers and terpolymers based on ethylene, propylene, butene and octene, nitrile-butadiene rubber (NBR), isobutylene (IB), chlorinated rubber, poly (styrene-butadiene-styrene) (SBS), styrene-ethylene-butene-styrene copolymer (SEBS), isobutylene-isoprene rubber (IIR), styrene-isoprene-styrene copolymer (SIS), chlorinated polyethylene (CM), isoprene polymers, ethylene-butylene copolymers, mixtures thereof and derivatives thereof grafted with maleic acid and/or maleic anhydride.

9. The composition according to claim 8, comprising from 3 to 11% by weight of the impact modifier.

10. The composition according to claim 1, wherein the polypropylene homopolymer has a melt index at 230 C. under a load of 2.16 kg greater than 30 g/10 min.

11. The composition according to claim 10, comprising from 0.1 to 15% by weight of a polypropylene homopolymer having a melt index at 230 C. under a load of 2.16 kg greater than 400 g/10 min.

12. A method for preparing a composite material comprising extruding a composition according to claim 1 to obtain the composite material, optionally followed by granulation to obtain the composite material in the form of pellets.

13. A composite material obtainable by the method according to claim 12.

14. A method for the preparation of a part by injection of the composite material according to claim 13.

15. A part obtainable by the method of claim 14.

16. The part according to claim 15, which is a vehicle part.

17. The part according to claim 16, which is an automotive part.

18. A method for improving the rigidity of a part comprising the steps of: extrusion of a composition comprising: (a) from 65 to 85% by weight of polypropylene homopolymer, (b) from 14 to 30% by weight of natural fibers less than or equal to 2 mm in length, and (c) from 1 to 3% by weight of compatibilizer to obtain a composite material, then optionally granulation to obtain the composite material in the form of pellets, then injection of the composite material to obtain the part, in which the homopolymer polypropylene used in the extrusion is in the form of a powder whose average particle size measured by scanning electron microscopy is micrometric.

19. The method according to claim 18, wherein the polypropylene homopolymer is in the form of a powder whose average particle size measured by scanning electron microscopy is from 1 to 1000 m.

20. The method according to claim 18, wherein the composition which is extruded comprises from 14 to 25% by weight of natural fibers of length less than or equal to 2 mm.

Description

EXAMPLE

[0069] In a twin-screw extruder were introduced through a first hopper: 70 kg of powdery polypropylene homopolymer (particle size between 300 and 800 m), such as Icorene N4450 from A. Schulman, 2 kg of compatibilizer, Orevac CA100 from Arkema, and 20 kg of ret hemp fiber of lengths less than 2 mm provided by APM TF, half of which is introduced by means of a second hopper located downstream, 5 kg of an ethylene-octene copolymer impact modifier, Exact 8201 supplied by ExxonMobil Chemical, and 3 kg of a metallocene homopolymer with a MFI of 800 g/10 min Borflow HL508FB supplied by Borealis. The components and their proportions are shown in the table below:

TABLE-US-00001 TABLE 1 Composition of the composition used to prepare the composite material Component Proportion [% by weight] Polypropylene homopolymer powder 70 Compatibilizer 2 Hemp fibers 20 Impact modifier 5 Homopolymer of high MFI 3

[0070] The mixture was extrusion-compounded under the following conditions:

[0071] Temperature 180 C.

[0072] Pressure: 5 to 30 bar

[0073] The composite material was obtained in the form of pellets that could be used for the production of parts by injection.

[0074] Injectability was measured by the spiral flow test, which is a measure of the viscosity of the resins in a spiral-shaped mold (e.g. an AIM Insert Spiral Flow Axxicon mold (3 mm)) having a specified section thickness and a circular flow path length (sample sizes: 115053 mm). The cross-section of the mold is constant. Composite materials are evaluated under typical injection molding conditions. The length of the flow in the mold is a function of the viscosity of the composite material, the injection pressure, the degree of filling, and the injection temperature. To compare the injectability of two composite materials, therefore, comparative tests should be performed at the same injection pressures, fill rates, and injection temperatures. The injection conditions used determine the final length of the spiral formed by the composite material injected into the mold. There is no holding phase because there is no end in the mold. As the cross-section of the mold is constant, the flow rate is constant. The composite material is melt-injected at a maximum pressure value, which is determined by the fact that the material must reach all the sensors in the mold. The test was carried out under the following conditions: maximum injection temperature (end of screw): 185 C., injection rate: 30 cm.sup.3/s, injection pressure: 115 bar.

[0075] This composite material makes it possible to obtain a 34% more rigid part than a composite material obtained from the same composition, except wherein the powdery PP homopolymer was replaced by a granulated PP homopolymer (HJ325MO Borealis). The table below lists the key properties of composite materials prepared.

TABLE-US-00002 TABLE 2 Mechanical, thermal, and rheological properties profile Improvement Form of the homopolymer PP in the due to the composition replacement Pellets powder of the pellets Properties Unit (comparative) (invention) by powder Modulus of MPa 2950 3950 34% elasticity at 23 C. (ISO 527) Load C. 137 145 deflection temperature (HDT B) (0.45 MPa) (ISO 75) Spiral flow Cm 65 80 23% length