COMPOSITE MATERIAL MADE FROM NATURAL LIGNOCELLULOSIC FIBERS HAVING IMPROVED RHEOLOGICAL PROPERTIES AND REDUCED EMISSIONS OF ODORS AND VOLATILE ORGANIC COMPOUNDS

Abstract

A method for preparing a composite material that includes the steps of: (i) heat treating natural lignocellulosic fibers at a temperature of 130 to 320 C. for 2 minutes to 24 hours in an atmosphere oxygen-deficient in and in the presence of water vapor, and (ii) mixing the heat treated natural lignocellulosic fibers with at least one thermoplastic polymer in the molten state and whose melting point is less than or equal to 230 C. The method is useful for producing vehicle parts from a composite material having natural lignocellulosic fibers with reduced volatile organic compound odor emissions.

Claims

1. A method for preparing a composite material comprising the steps of: (i) heat treating natural lignocellulosic fibers at a temperature of 130 to 320 C., preferably from 130 to 300 C., for 2 minutes to 24 hours in an atmosphere deficient in oxygen and in the presence of water vapor, and (ii) mixing the heat treated natural lignocellulosic fibers with at least one thermoplastic polymer in the molten state and whose melting point is less than or equal to 230 C.

2. The method according to claim 1, wherein the natural lignocellulosic fibers are: extracted from seeds or fruit of the plant such as cotton, kapok, milkweed, or coconut; extracted from the stem of the plant such as flax, hemp, jute, ramie, or kenaf; extracted from plant leaves such as sisal, Manila hemp or abaca, henequen, raffia or agave; extracted from the trunk of the plant such as wood, or banana; extracted from herbaceous plants, such as switchgrass, miscanthus, bamboo, sorghum, esparto, or sabei communis; or extracted from the stem of agricultural waste, such as rice or wheat.

3. The method according to claim 1, comprising, before step (i), a step of preparation of lignocellulosic natural fibers comprising the substeps of: a) retting stems, then b) defibration of the rusty stems, then sieving to separate the lignocellulosic natural fibers from the residues.

4. The method according to claim 1, wherein the natural lignocellulosic fibers have: an average length of between 0.1 and 10 mm, in particular of 0.1 to 3 mm, preferably of 0.1 to 2 mm, and/or an average diameter of between 40 and 200 m, preferably of between 50 and 150 m.

5. The method according to claim 1, wherein step (i) is carried out at a temperature of 180 to 300 C. for 2 min to 8 h, preferably 240 to 300 C. for 2 to 30 minutes.

6. The method according to claim 1, wherein the pressure in step (i) is 1 to 50 bar, preferably 2 to 50 bar.

7. The method according to claim 1, wherein step (i) is implemented in a heating chamber: in which water vapor is introduced continuously at a temperature of between 100 and 150 C., preferably at a pressure of 1 to 50 bar, in particular from 2 to 50 bar, from which the gaseous phase formed during step (i) is extracted continuously, so that the pressure within the chamber is 1 to 50 bar, especially 2 to 50 bar, preferably 2 to 10 bar, preferably 2 to 5 bar.

8. The method according to claim 1, wherein the atmosphere in which step (i) is carried out has a volume proportion of oxygen of less than 18%, for example less than 15%, preferably less than 10%, especially less than 3%, typically less than 2%, preferably less than 0.5%, wherein an oxygen-free atmosphere is more particularly preferred.

9. The method according to claim 1, wherein the thermoplastic polymer is selected from: polyolefins, for example polyethylenes, polypropylenes or copolymers of ethylene and propylene, styrenic polymers such as acrylonitrile butadiene styrene (ABS) and polystyrene (PS), halogenated vinyl polymers such as polyvinyl chloride (PVC), biodegradable and/or biosourced polymers, such as cellulosic polymers such as cellulose acetate, biobased polyethylene, biobased polypropylene, plasticized starch-based mixtures, biodegradable and/or biobased polyesters such as poly lactic acid (PLA), polyalkanoates (PHAs) and polybutylene succinate, polyamides, in particular polyamides 11, 6, 6-10 and 12, and thermoplastic elastomers (TPE) such as polyethylene oxide (POE), polystyrene-b-polybutadiene-b-polystyrene (SBS), polystyrene-b-poly (ethylene-butylene)-b-polystyrene (SEBS), thermoplastic polyurethane polymers (TPU), polyether-b-amide (PEBA).

10. The method according to claim 1, wherein the mixture formed in step (ii) comprises: (a) from 40 to 80% by weight, in particular from 55 to 75% by weight of thermoplastic polymer(s), preferably having a melt index of 25 to 150 g/10 min, in particular from 25 to 150 g/10 min, preferably 45 to 125 g/10 min, at 230 C. under a load of 2.16 kg; (b) from 0 to 20% by weight, preferably from 0.1 to 20% by weight, especially from 3 to 12% of a polymer having a melt index of 500 to 2000 g/10 min at 230 C. under a load of 2.16 kg, preferably 500 to 1500 g/10 min; (c) from 0 to 20% by weight, preferably from 1 to 20% by weight, especially from 3 to 15% by weight, of an impact modifier; (d) from 0.5 to 10% by weight, especially from 0.5 to 5% by weight, of a compatibilizer; and (e) from 10 to 60% by weight, preferably from 10 to 57.9% by weight, in particular from 10 to 30% by weight of natural lignocellulosic fibers obtained in step (i).

11. A composite material obtained by the method of claim 1.

12. A vehicle part comprising the composite material set forth in claim 11.

13. A method of preparing a vehicle part comprising the steps of: heat treating natural lignocellulosic fibers at a temperature of 130 to 320 C., preferably from 130 to 300 C., for 2 minutes to 24 hours in an oxygen-deficient atmosphere and in the presence of water vapor, mixing the heat-treated lignocellulosic natural fibers with at least one thermoplastic polymer in the molten state and whose melting point is less than or equal to 230 C., whereby a composite material is obtained, and injecting the composite material into a mold, whereby the vehicle part is obtained.

14. A vehicle part made by the method of claim 13.

15. A method for: reducing emissions of odors and volatile organic compounds, and/or improving rigidity, of a composite material comprising lignocellulosic natural fibers and at least one thermoplastic polymer, comprising the steps of: (i) heat treating natural lignocellulosic fibers at a temperature of 130 to 320 C. for 2 minutes to 24 hours in an oxygen-deficient atmosphere and in the presence of water vapor, and (ii) mixing the heat-treated natural lignocellulosic fibers with at least one thermoplastic polymer in the molten state and whose melting point is less than or equal to 230 C.

16. A method for improving the injectability of a composite material comprising natural lignocellulosic fibers and at least one thermoplastic polymer in the molten state, comprising the steps of: (i) heat treating natural lignocellulosic fibers at a temperature of 130 to 320 C. for 2 minutes to 24 hours in an oxygen-deficient atmosphere and in the presence of water vapor, and (ii) mixing the heat-treated natural lignocellulosic fibers with at least one thermoplastic polymer in the molten state and whose melting point is less than or equal to 230 C.

Description

EXAMPLE

[0124] Hemp fibers provided by APM TF (length less than 2 mm and diameters between 40 and 150 m) derived from fibers which have undergone minimal retting have been heat-treated in a heating chamber at 260 C. for 10 min in an oxygen-deficient atmosphere and in the presence of water vapor injected under pressure (2 bar) and 150 C. step (i).

[0125] In a Buss Kneader-type extruder, 51.5 kg of the propylene-ethylene copolymer (Borealis BH345M0), MFI 45 g/10 min as thermoplastic polymer, 10 kg of polypropylene homopolymer (Borflow HL508FB) were introduced through a first Borealis hopper) of MFI 800 g/10 min as high MFI polymer, 11 kg of the ethylene-octene copolymer impact modifier (Exact 8201 from Exxon Mobil Chemical) and 2.5 kg of the maleic anhydride grafted polypropylene compatibilizer (Orevac CA100 from Arkema) then 25 kg of heat-treated hemp fibers according to the conditions defined above, half of which is introduced by means of a second hopper located downstream.

TABLE-US-00001 TABLE 1 Composition of the composite material Component Proportion [% by weight] Propylene-Ethylene Copolymer 51.5 Homopolymer (high MFI polymer) 10 Impact modifier 11 Compatibilizer 2.5 Heat-treated hemp fibers 25

[0126] The mixture was extrusion compounded under the following conditions: Temperature 190 C.;

Pressure: 5 to 30 Bar

[0127] The composite material was obtained in the form of granules that could be used for the production of parts by injection.

TABLE-US-00002 TABLE 2 Mechanical, thermal, and rheological properties profile Composite material Material composite with Composite material with heat-treated hemp fibers which were with hemp fiber not hemp fibers in the heat-treated but in the heat treated presence of water absence of water vapor Properties Unit (Comparative) vapor (comparative) Modulus of elasticity MPa 2 975 3 275 3 100 at 23 C. (ISO 527) Spiral flow length cm 57 68 65 (T C.: 185 C.) Odor (VDA 270) 3.8 2.9 3.5 VOC (VDA 278) g/g 120 70 95

[0128] As demonstrated by the results in Table 2, the composite material prepared from thermally treated hemp fiber in the presence of water vapor is 10% more rigid, 20% more injectable, with 20% to 30% lower emissions, than that obtained with the same composition except to use heat-treated hemp fibers (without step (i)comparative).

[0129] By virtue of the heat treatment of the fibers, the composite material obtained is injectable at 220 C., with a flow length of 110 cm. This composite material is therefore particularly suitable for the preparation of large automotive parts.