Method for preparing a 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 of preparing a vehicle part comprising the steps of: (i) heat treating natural lignocellulosic fibers in a chamber 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, wherein water vapor is continuously introduced into the chamber and a gas phase comprising water vapor and volatile organic compounds (VOCs) is continuously extracted from the chamber, (ii) mixing the heat-treated lignocellulosic natural fibers with at least one thermoplastic polymer in a molten state and whose melting point is less than or equal to 230° C., whereby a composite material is obtained, and (iii) injecting the composite material into a mold, whereby the vehicle part is obtained.

2. The method according to claim 1, wherein the natural lignocellulosic fibers are: extracted from seeds or fruit of a plant; extracted from a stem of a plant extracted from plant leaves; extracted from a trunk of a plant; extracted from herbaceous plants; or extracted from a stem of agricultural waste.

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 retted stems, then sieving to separate the lignocellulosic natural fibers from a residues.

4. The method according to claim 1, wherein the natural lignocellulosic fibers have: an average length of between 0.1 and 10 mm, and/or an average diameter of between 40 and 200 μm.

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.

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

7. The method according to claim 1, wherein: water vapor is introduced into the chamber continuously at a temperature of between 100 and 150° C., and the gas phase is extracted continuously, so that a pressure within the chamber is 1 to 50 bar.

8. The method according to claim 1, wherein an atmosphere in which step (i) is carried out has a volume proportion of oxygen of less than 18%.

9. The method according to claim 1, wherein the at least one thermoplastic polymer is selected from: polyolefins, styrenic polymers, halogenated vinyl polymers, biodegradable and/or biosourced polymers, polyamides, and thermoplastic elastomers.

10. The method according to claim 1, wherein the mixture formed in step (ii) comprises: (a) from 40 to 80% by weight of thermoplastic polymer(s); (b) from 0 to 20% by weight of a polymer having a melt index of 500 to 2000 g/10 min at 230° C. under a load of 2.16 kg; (c) from 0 to 20% by weight of an impact modifier; (d) from 0.5 to 10% by weight, of a compatibilizer; and (e)from 10 to 60% by weight of natural lignocellulosic fibers obtained in step (i).

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

12. The method according to claim 1, wherein the at least one thermoplastic polymer is selected from: polyethylenes, polypropylenes, or copolymers of ethylene and propylene, acrylonitrile butadiene styrene (ABS) or polystyrene (PS), polyvinyl chloride (PVC), cellulose acetate, biobased polyethylene, biobased polypropylene, plasticized starch-based mixtures, poly lactic acid (PLA), polyalkanoates (PHAs), or polybutylene succinate, polyamide 11, polyamide 6, polyamide 6-10, or polyamide 12, and polyethylene oxide (POE), polystyrene-b-polybutadiene-b-polystyrene (SBS), polystyrene-b-poly (ethylene-butylene) -b-polystyrene (SEBS), thermoplastic polyurethane polymers (TPU), or polyether-b-amide (PEBA).

13. A method for preparing a composite material, comprising the steps of: (i) heat treating natural lignocellulosic fibers in a chamber 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, wherein water vapor is continuously introduced into the chamber and a gas phase comprising water vapor and volatile organic compounds (VOCs) is continuously extracted from the chamber, (ii) mixing the heat-treated natural lignocellulosic fibers with at least one thermoplastic polymer in a molten state and whose melting point is less than or equal to 230° C., whereby the composite material is obtained.

14. A method for improving injectability of a vehicle part comprising natural lignocellulosic fibers and at least one thermoplastic polymer in the molten state, comprising the steps of: (i) heat treating natural lignocellulosic fibers in a chamber 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, wherein water vapor is continuously introduced into the chamber and a gas phase comprising water vapor and volatile organic compounds (VOCs) is continuously extracted from the chamber, and (ii) mixing the heat-treated natural lignocellulosic fibers with at least one thermoplastic polymer in a molten state and whose melting point is less than or equal to 230° C., whereby a composite material is obtained, and (iii) injecting the composite material into a mold, whereby the vehicle part is obtained.

Description

EXAMPLE

(1) Hemp fibers provided by APM TF (length less than 2 mm and diameters between 40 and 150 μm) 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).

(2) 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.

(3) 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

(4) The mixture was extrusion compounded under the following conditions: Temperature 190° C.;

(5) Pressure: 5 to 30 Bar

(6) The composite material was obtained in the form of granules that could be used for the production of parts by injection.

(7) 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) μg/g 120 70 95

(8) 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).

(9) 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.