Natural fibers and polypropylene based part obtained by injection molding

Abstract

Natural fibers and polypropylene based part obtained by injection molding The application relates to an injection molded part comprising (a) at least 15% by weight of a first polypropylene chosen from a polypropylene homopolymer having a melt flow index from 40 g / 10min to 80 g / 10min at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index from 1 g / 10min to 70 g / 10min at 230°C under a load of 2.16 kg, and mixtures thereof; (b) from 3 to 40% by weight of natural fibers having an average length from 1 µm to 4 mm; (c) from 1 to 5% by weight of a second polypropylene, the second polypropylene being grafted with a carboxylic acid, one of its esters or anhydrides, an epoxy and / or a silane and having a melt flow index from 20 g / 10min to 150 g / 10min at 190°C under a load of 2.16 kg, and (d) from 5% to 60% by weight of an elastomer having a melt flow index from 0.5 g / 10min to 10 g / 10min at 190°C under a load of 2.16 kg and to the preparation method thereof.

Description

[0001] Natural fibers and polypropylene based part obtained by injection molding

[0002] Field of the invention

[0003] The present invention relates to a natural fibers based injection molded part, in particular for the automotive field.

[0004] Technological background

[0005] Various composite materials that are useful for the preparation of automotive interior parts are commercially available or described in the literature. For example, the application WO 2012 / 093167 describes a composite material comprising:

[0006] (a) 28 to 95% by weight of a matrix-forming polypropylene-polyethylene copolymer;

[0007] (b) 0 to 10% by weight of a flow agent, in particular a polyolefin such as polyethylene or polypropylene homopolymer;

[0008] (c) 1 to 20% by weight of an impact modifier;

[0009] (d) 1 to 20% by weight of a compatibilizer; and

[0010] (e) 3 to 70% by weight of natural fibers, and its uses in the preparation of interior parts of vehicles.

[0011] Natural fibers based composite materials are lighter than those prepared from a composite material based on glass fibers. However, the parts obtained from a composite material based on natural fibers can be too brittle for use on visible areas.

[0012] Natural fibers based composite parts having improved mechanical properties, and an improved appearance and a reduced carbon dioxide factor are sought.

[0013] For this purpose, according to a first object, the invention relates to an injection molded part, which comprises:

[0014] - (a) at least 15% by weight of a first polypropylene chosen from a polypropylene homopolymer having a melt flow index comprised from 40 g / 10min to 80 g / 10min at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index comprised from 1 g / 10min to 70 g / 10min at 230°C under a load of 2.16 kg, and mixtures thereof,

[0015] (b) from 3 to 40% by weight of natural fibers having an average length comprised from 1 pm to 4 mm,

[0016] (c) from 1 to 5% by weight of a second polypropylene, the second polypropylene being a polypropylene homopolymer or copolymer having a melt flow index comprised from 20 g / 1 Omin to 150 g / 1 Omin at 190°C under a load of 2.16 kg, the second polypropylene being grafted with a carboxylic acid, one of its esters or anhydrides, an epoxy and / or a silane, and

[0017] (d) from 5% to 60% by weight of an elastomer having a melt flow index comprised from 0.5 g / 1 Omin to 10 g / 1 Omin at 190°C under a load of 2.16 kg.

[0018] According to other advantageous aspects of the invention, the injection molded part comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0019] - the natural fibers are derived from miscanthus, flax, hemp hurds, hemp fibers, reed, oyster, vine shoots, olive stone and mixture thereof, preferably from olive stone, vine shoots, oyster, reed, hemps fibers or hemp hurds, more preferably from olive stone, vine shoots or oyster, and even more preferably from olive stone;

[0020] - the injection molded part comprises from 3% to 25% of natural fibers having an average length comprised from 1 pm to 4 mm;

[0021] - the second polypropylene homopolymer or copolymer has a melt flow index comprised from 100 g / 1 Omin to 150 g / 10 min at 190°C ;

[0022] - the second polypropylene copolymer is grafted with maleic anhydride ;

[0023] - the elastomer is chosen from ethylene- 1 -octene elastomer, ethylene-1 -butene elastomer, hydrogenated styrene-isoprene-styrene block copolymers, styrene-ethylene- butylene-styrene and mixtures thereof, and preferably ethylene-octene elastomer;

[0024] - the injection molded part further comprises (e) from 0 to 1% by weight of additives chosen from an antioxidant, a lubricant, an UV light absorber, and mixtures thereof and / or (f) from 0 to 3% by weight of a dye, a pigment and mixtures thereof;

[0025] - the first polypropylene (a) comprises:

[0026] (a1 ) at least one polypropylene copolymer having a melt flow index comprised from 1 to 10 g / 10 min at 230°C under a load of 2.16 kg, and

[0027] (a2) at least one polypropylene copolymer having a melt follow index comprised from 30 to 70 g / 10 min at 230°C under a load of 2.16 kg;

[0028] - the weight ratio of the polypropylene copolymer (a2) versus the polypropylene copolymer (a1 ) is comprised from 3.0 to 25.0; and

[0029] - the injection molded part is a visible interior trim part or a non-visible structural part of a motor vehicle. The invention further relates to a method for the preparation of an injection molded part according to any of the preceding embodiments, the method comprising injecting into a mold a mixture comprising:

[0030] (a) at least 15% by weight of a first polypropylene chosen from a polypropylene homopolymer having a melt flow index comprised from 40 g / 10min to 80 g / 10min at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index comprised from 1 g / 10min to 70 g / 10min at 230°C under a load of 2.16 kg and mixtures thereof,

[0031] (b) from 3 to 40% by weight of natural fibers having a length comprised from 1 pm to 4 mm,

[0032] (c) from 1 to 5% by weight of a second polypropylene, the second polypropylene being a polypropylene homopolymer or copolymer having a melt flow index comprised from 20 g / 1 Omin to 150 g / 1 Omin at 190°C under a load of 2.16 kg, the second polypropylene being grafted with a carboxylic acid, one of its esters or anhydrides, an epoxy and / or a silane,

[0033] (d) from 5% to 60% by weight of an elastomer having a melt flow index comprised from 0.5 g / 1 Omin to 10 g / 1 Omin at 190°C under a load of 2.16 kg, and whereby the injection molded part is obtained.

[0034] The method may comprise preparing the mixture by extruding a composition A comprising components (a), (b), (c), (d) as defined above.

[0035] The method may also comprise: i) extruding a composition B comprising:

[0036] (ai) a polypropylene chosen from a polypropylene homopolymer having a melt flow index comprised from 40 g / 1 Omin to 80 g / 1 Omin at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index comprised from 1 g / 1 Omin to 70 g / 1 Omin at 230°C under a load of 2.16 kg and mixtures thereof, and

[0037] (b) natural fibers having a length comprised from 1 pm to 4 mm, to obtain a composite material B; and ii) extruding a composition C comprising:

[0038] (aii) a polypropylene chosen from a polypropylene homopolymer having a melt flow index comprised from 40 g / 1 Omin to 80 g / 1 Omin at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index comprised from 1 g / 1 Omin to 70 g / 1 Omin at 230°C under a load of 2.16 kg and mixtures thereof, and (d) an elastomer having a melt flow index comprised from 0.5 g / 10min to 10 g / 10min at 190°C under a load of 2.16 kg; to obtain a composite material C, at least one of composition B and composition C further comprising (c) a second polypropylene, the second polypropylene being a polypropylene homopolymer or copolymer having a melt flow index comprised from 20 g / 10min to 150 g / 10min at 190°C under a load of 2.16 kg and being grafted with a carboxylic acid, one of its esters or anhydrides, an epoxy and / or a silane, ill) blending the composite material B and the composite material C to obtain the mixture as defined above, iv) injecting the mixture into a mold.

[0039] In any of the above embodiments of the method, the mixture may further comprise a dye, a pigment or mixtures thereof and / or additives.

[0040] According to other advantageous aspects of the invention, the method comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0041] - composition B comprises from 35% to 70% by weight of natural fibers;

[0042] - the blending of the composite material B and the composite material C is performed in an injection molding press;

[0043] - the mixture further comprises a dye, a pigment or mixtures thereof and / or additives.

[0044] Detailed description of the invention

[0045] In the present invention, the weight percentages of the constituents of the part are given in relation to the total weight of the part.

[0046] In the application, melt indexes (Melt Flow Indexes (MFI)) are as measured according to ISO 1133-2 (201 1 ).

[0047] First polypropylene

[0048] The part, as well as the mixture to be injected to form said part, comprises at least 15% by weight, preferably at least 19 % by weight, preferably at least 25% by weight, preferably at least 30% by weight, preferably at least 35% by weight, more preferably at least 40% by weight, of a first polypropylene chosen from a polypropylene homopolymer having a melt flow index from 40 g / 10min to 80 g / 10min at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index from 1 g / 10min to 70 g / 10min, preferably from 10 g / min to 70 g / 10 min, at 230°C under a load of 2.16 kg and mixtures thereof.

[0049] The polypropylene homopolymer has a melt flow index at 230°C under a load of 2.16 kg comprised from 40 to 80 g / 10 min, preferably from 45 to 70 g / 10min, more preferably from 50 to 60 g / 10min.

[0050] The polypropylene homopolymer having a melt flow index comprised from 40 g / 1 Omin to 80 g / 1 Omin at 230°C under a load of 2.16 kg can comprise recycled polypropylene.

[0051] Preferably, less than 70%, more preferably less than 40 %, even more preferably less than 30 %, by weight of the polypropylene homopolymer having a melt flow index comprised from 40 g / 1 Omin to 80 g / 1 Omin at 230°C under a load of 2.16 kg is recycled polypropylene.

[0052] The term « copolymer », as opposed to the term « homopolymer », means a polymer derived from the copolymerization of a least two types of monomers, chemically different, called comonomers. The copolymer is therefore formed of at least two repeating units. Depending on the manner in which the repeating units are distributed in the macromolecular chains, a distinction is made between copolymers with random, alternate or statistical sequence distribution, and block copolymers. Also, copolymers are known that are derived from the grafting of pendant groups.

[0053] The polypropylene copolymer is preferably a copolymer of propylene and of ethylene.

[0054] The polypropylene copolymer has a melt flow index at 230°C under a load of 2.16 kg comprised from 1 g / 1 Omin to 70 g / 1 Omin, preferably from 1 to 50 g / 1 Omin, preferably from 1 to 40 g / 1 Omin, preferably from 1 to 30 g / 1 Omin, notably from 1 to 20 g / 1 Omin, notably from 1 g to 10g / 1 Omin, more preferably from 2 g / 1 Omin to 8 g / 1 Omin, even more preferably from 2 g / 1 Omin to 6 g / 1 Omin, even more preferably from 2 g / 1 Omin to 4 g / 1 Omin, even more preferably approximately 3 g / 1 Omin.

[0055] The polypropylene copolymer having a melt flow index comprised from 1 g / 1 Omin to 70 g / 1 Omin at 230°C under a load of 2.16 kg can comprise recycled polypropylene.

[0056] Preferably, less than 70%, more preferably less than 60 %, even more preferably less than 50 %, by weight of the polypropylene copolymer having a melt flow index comprised from 1 g / 1 Omin to 70 g / 1 Omin at 230°C under a load of 2.16 kg is recycled polypropylene.

[0057] The first polypropylene may comprise:

[0058] (a1) at least one polypropylene copolymer having a melt flow index comprised from 1 to 10 g / 10 min at 230°C under a load of 2.16 kg, preferably comprised from 1 to 6 g / 1 Omin, and (a2) at least one polypropylene copolymer having a melt flow index comprised from 30 to 70 g / 10 min at 230°C under a load of 2.16 kg, preferably from 40 to 65 g / 1 Omin at 230°C under a load of 2.16 kg, more preferably from 40 to 60 g / 1 Omin at 230°C under a load of 2.16 kg.

[0059] The first polypropylene may comprise a plurality of polypropylene copolymers (a1 ) having different melt flow indexes.

[0060] The weight ratio of the polypropylene copolymer (a2) versus the polypropylene copolymer (a1 ) may be comprised from 3.0 to 25.0, preferably from 3.0 to 15.0, more preferably from 3.0 to 10.0.

[0061] If the part comprises a mixture of a polypropylene homopolymer and of a polypropylene copolymer, the sum of the proportion of the polypropylene homopolymer having a melt flow index comprised from 40 g / 1 Omin to 80 g / 1 Omin at 230°C under a load of 2.16 kg and of the proportion of the polypropylene copolymer having a melt flow index comprised from 1 g / 1 Omin to 70 g / 1 Omin at 230°C under a load of 2.16 kg may be at least 30% by weight.

[0062] Preferably, less than 70% by weight, more preferably less than 60 % by weight, of the mixture of polypropylene homopolymer having a melt flow index comprised from 40 g / 1 Omin to 80 g / 1 Omin at 230°C under a load of 2.16 kg and of polypropylene copolymer having a melt flow index comprised from 1 g / 1 Omin to 70 g / 1 Omin at 230°C under a load of 2.16 kg is recycled polypropylene.

[0063] Preferably, the first polypropylene is not grafted with a carboxylic acid, one of its esters or anhydrides, an epoxy and / or a silane, most preferably not grafted at all.

[0064] Natural Fibers

[0065] The part, as well as the mixture to be injected to form said part, comprises from 3 to 40% by weight, notably from 5 to 25%, in particular from 10 to 23% by weight, preferably from 17 to 23% by weight, more particularly 20% of natural fibers.

[0066] The term "natural fibers" refers to fibrous materials derived from materials of plant or animal origin or grinded animal inorganic shells. They typically bring mechanical reinforcement. The natural fibers are preferably derived from:

[0067] - seeds or fruit of a plant, such as olive stone, cotton, kapok, milkweed and / or coconut,

[0068] - the stem of the plant, such as flax, hemp (hemp hurds or hemp fibers), palm, jute, ramie and / or kenaf,

[0069] - leaves of the plant such as sisal, Manila hemp, abaca, henequen, raffia and / or agave, - the trunk or branches of the plant, such as vine shoots, wood (softwood or hardwood) and / or banana,

[0070] - herbaceous plants such as reed, miscanthus, switchgrass, palm, bamboo, sorghum, esparto and / or sabei communis,

[0071] - the waste agricultural stalks such as rice, wheat, coffee ground and / or corn,

[0072] - hair, secretion or feathers of animals, such as oyster shell, scallop shell, mussels shell, eggshell, wool, alpaca, mohair, cashmere, angora, goose feathers, silk, Tussah or wild silk and / or spider silk, and mixtures thereof.

[0073] Natural fibers derived from miscanthus, flax, hemp hurds, hemp fibers, reed, oyster, vine shoots, olive stone, and mixtures thereof are preferred.

[0074] Natural fibers derived from olive stone, for example olive stone powder, or vine shoots, oyster, in particular oyster shell, and mixtures thereof are more particularly preferred.

[0075] Natural fibers derived from olive stone, for example olive stone powder, are more particularly preferred.

[0076] In an embodiment, the natural fibers comprise a mixture of hemp hurds and hemp fibers, for example from 10 to 20% by weight of hemp fibers and from 5 to 15% by weight of hemp hurds versus the weight of the part.

[0077] In an embodiment, the natural fibers comprise a mixture of fibers derived from oyster and from reed, for example from 5 to 15% by weight of fibers derived from oyster and from 1 to 10% by weight of fibers derived from reed versus the weight of the part.

[0078] In an embodiment, the natural fibers comprise a mixture of fibers derived from olive stone, for example olive stone powder, and fibers derived from reed, vine shoots or hemp hurds, for example from 15 to 25% by weight of fibers derived from olive stone and from 5 to 15% of fibers derived from hemp, vine shoots or reed versus the weight of the part.

[0079] The average length of the natural fibers ranges from 1 pm to 4 mm, preferably from 1 pm to 2 mm, more preferably from 100 pm to 3 mm, and even more preferably from 500 pm to 2 mm.

[0080] The average length is typically measured by Scanning Electron Microscopy (SEM), Hi-Res, MorFI or Metso morphological.

[0081] By “length” is meant in the present description the average of the greatest dimensions of the fibers. Typically, the greatest dimension of at least 100 fibers is measured, for example by SEM, and an average length is determined. Said fibers are typically obtained by grinding followed by dynamic selection to obtain the desired average length.

[0082] Incorporating fibers of greater length into a composition to be extruded for forming the part, and thus into the part, is generally more difficult to incorporate.

[0083] Fibers weight proportions of less than 15% generally result in a part of insufficient rigidity.

[0084] The presence of natural fibers allows increasing the thermal resistance of the part.

[0085] Even in the presence of these natural fibers, it is possible to obtain large parts such as dashboard inserts by injection molding. However, optimum injection behavior is observed when the mixture to be injected to form the part contains less than 35% by weight, in particular less than 30% by weight or even less than 25% by weight, of natural fibers.

[0086] Second polypropylene

[0087] The part, as well as the mixture to be injected, comprises from 1 to 5% by weight, preferably from 2% to 4% by weight, more preferably 3% by weight of a second polypropylene.

[0088] The second polypropylene is a polypropylene homopolymer or copolymer grafted with a carboxylic acid (such as maleic acid), one of its esters or anhydrides (such as maleic anhydride), an epoxy (such as an oxirane, typically a polyolefin obtained using glycidyl methacrylate as comonomer) and / or a silane.

[0089] The second polypropylene has a melt flow index at 190°C under a load of 2.16 kg comprised from 20 g / 1 Omin to 150 g / 1 Omin, preferably from 100 g / 1 Omin to 150 g / 1 Omin, more preferably from 1 10 g / 1 Omin to 130 g / 1 Omin, still more preferably of approximately 120 g / 1 Omin.

[0090] The second polypropylene is advantageously grafted with maleic anhydride.

[0091] The second polypropylene acts as a compatibilizing agent. In other words, the second polypropylene ensures good affinity between the fibers and the other components of the mixture to be injected and thus makes it possible to obtain a homogeneous mixture at the injection stage.

[0092] Elastomer

[0093] The part, as well as the mixture to be injected, further comprises from 5% to 60% by weight, preferably from 8% to 55% by weight, preferably from 8% to 40% by weight, preferably from 15% to 35% by weight, more preferably from 15% to 25% by weight, of an elastomer, the elastomer having a melt flow index from 0.5 g / 10min to 10 g / 10min at 190°C under a load of 2.16 kg.

[0094] The elastomer is advantageously chosen from ethylene-1 -octene elastomer, ethylene-1 -butene elastomer, hydrogenated styrene-isoprene-styrene block copolymers, styrene-ethylene-butylene-styrene (SEBS) and mixtures thereof, and is preferably ethylene-1 - octene elastomer.

[0095] The elastomer acts as an impact modifier. The elastomer improves the properties of impact resistance of the part. More particularly, the elastomer forms a multiphase system with the polypropylene matrix, thus improving its resilience.

[0096] Such a proportion of elastomer allows to increase the impact energy absorption thanks to the plastic deformation of the polymer matrix. Such high proportion of elastomer compensates the higher rigidity given by the natural fibers compared to classic micronized fillers like talc.

[0097] The elastomer has a melt flow index from 0.5 g / 1 Omin to 10 g / 1 Omin at 190°C under a load of 2.16 kg, preferably from 2 g / 1 Omin to 5 g / 1 Omin.

[0098] The low melt flow index of the elastomer is related to the molecular weight of the elastomer and provides the impact energy absorption and the balanced flowability for the injection molding process, considering the proportion of natural fibers in the composition.

[0099] Additional compounds

[0100] The part may also comprise less than 20% by weight of a mineral reinforcement filler, in particular talc (Si4Mg3Oio(OH)2), preferably micronized talc.

[0101] The combination of talc and natural fibers allows to balance the rigidity and impact resistance according to the part requirement. A prior art talc reinforced PP compound has good impact resistance but does not present high rigidity, whereas the natural fiber reinforced PP part according to the invention present simultaneously good impact resistance and high rigidity

[0102] The part may also comprise a dye, a pigment or mixtures thereof.

[0103] The part comprises preferably from 0 to 3% by weight of dye, pigment or mixtures thereof.

[0104] The part may also comprise one or more additives, preferably chosen among:

[0105] - an antioxidant, for example a state-of-the-art hindered phenol in combination with phosphite hydroxylamine, for example for melt processing stability, or a thiosynergist in combination with a phenol, in particular when long term thermal stability is required. The antioxidant is preferably chosen among pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate and tris(2,4-di(2,4-di-tert-butylphenyl)phosphite and mixtures thereof;

[0106] - a UV stabilizer, for example hindered amine light stabilizer (HALS), in particular to inhibit the degradation of the polymer. Preferably, the UV stabilizer is a mixture of high molecular weight HALS comprising hindered amine 2,2,6,6-tetramethyl-4-piperidinol;

[0107] - a lubricant such as a demolding agent;

[0108] - an acid scavenger; and mixtures thereof.

[0109] Preferably, the total proportion of additives is from 0 to 1% by weight.

[0110] In an embodiment, the part consists of:

[0111] (a) at least 40% by weight of the first polypropylene chosen from a polypropylene homopolymer having a melt flow index comprised from 40 g / 10min to 80 g / 10min at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index comprised from 1 g / 10min to 70 g / 10min at 230°C under a load of 2.16 kg, and mixtures thereof,

[0112] (b) from 3 to 40% by weight of the natural fibers having an average length comprised from 1 pm to 4 mm,

[0113] (c) from 1 to 5% by weight of the second polypropylene, the second polypropylene being a polypropylene homopolymer or copolymer grafted with a carboxylic acid, one of its esters or anhydrides, an epoxy and / or a silane and having a melt flow index comprised from 20 g / 1 Omin to 150 g / 1 Omin at 190°C under a load of 2.16 kg,

[0114] (d) from 5 to 40% by weight of the elastomer having a melt flow index comprised from 0.5 g / 1 Omin to 10 g / 1 Omin at 190°C under a load of 2.16 kg,

[0115] (e) from 0 to 1% by weight of an additive chosen among an anti-oxidant, a UV stabilizer, a lubricant, such as a demolding agent, an acid scavenger and mixtures thereof, and

[0116] (f) from 0 to 3 % by weight of a dye, a pigment or mixtures thereof.

[0117] In another embodiment, the part consists of:

[0118] (a) at least 15% by weight of the first polypropylene chosen from a polypropylene homopolymer having a melt flow index comprised from 40 g / 1 Omin to 80 g / 1 Omin at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index comprised from 1 g / 1 Omin to 70 g / 1 Omin at 230°C under a load of 2.16 kg, and mixtures thereof, (b) from 3 to 40% by weight of the natural fibers having an average length comprised from 1 pm to 4 mm,

[0119] (c) from 1 to 5% by weight of the second polypropylene homopolymer or copolymer, the second polypropylene being polypropylene homopolymer or copolymer grafted with a carboxylic acid, one of its esters or anhydrides, an epoxy and / or a silane and having a melt flow index comprised from 20 g / 10min to 150 g / 10min at 190°C under a load of 2.16 kg,

[0120] (d) from 50 to 60% by weight of the elastomer having a melt flow index comprised from 0.5 g / 10min to 10 g / 10min at 190°C under a load of 2.16 kg,

[0121] (e) from 0 to 1% by weight of an additive chosen among an anti-oxidant, a UV stabilizer, a lubricant, such as a demolding agent, an acid scavenger and mixtures thereof, and

[0122] (f) from 0 to 3 % by weight of a dye, a pigment or mixtures thereof.

[0123] The part is preferably a vehicle part, preferably a car part, including an automotive visible interior part, for example an interior trim part, such as a dashboard, a dashboard insert, a center console, a glove box or a door panel element such as a door panel carrier or a map pocket.

[0124] The part may have large dimensions, wherein at least one of the dimensions is greater than 50 cm, preferably more than 100 cm, sometimes more than 150 cm. One may mention a dashboard, which typically has a dimension of about 1600 cm long.

[0125] As the part comprises natural fibers, it is more eco-friendly and lighter, usually 6.5 to 7% lighter, than a part having an identical composition except the replacement of the natural fibers by glass fibers.

[0126] The part has improved mechanical properties compared to a part prepared from a composite material based on glass fibers. Thus, it is possible to prepare a reduced-size part, typically of reduced thickness, compared to a part comprising glass fibers while maintaining the mechanical properties, in particular of rigidity, relative to a part based on glass fibers.

[0127] On this basis, by combining the weight reduction associated with the use of lighter natural fibers and the weight reduction related to the reduction of the thickness of the part, the part according to the invention is typically 10 to 25% lighter than a part having identical mechanical properties (and therefore thicker) and having an identical composition except the replacement of the natural fibers by glass fibers.

[0128] Thanks to the synergy between the natural fibers and the ethylene-octene elastomer at the specific proportions of the composition of the part, the part has improved yield strength (measured according to ISO 527), and hence higher impact resistance, compared to a part free of natural fibers and / or of ethylene-octene elastomer.

[0129] The ductility of the part, characterized by the elongation at break (measured according to ISO 527) and / or the deformation at maximum strength (measured according to ISO 6603-2), the energy at maximum strength (measured according to ISO 6603-2) and / or the energy at puncture (measured according to ISO 6603-2 and ISO 180 (UN / N-IZOD) is also improved thanks to the synergy between the different components.

[0130] Among the natural fibers, olive stone, vine shoots and oyster, preferably olive stone or vine shoots, more preferably olive stone, allow obtaining a particularly satisfactory ductile behavior of the part.

[0131] Further, the specific composition of the part confers a so-called “green appearance”. The green appearance allows the user to understand that the part is obtained from eco-friendly materials. In particular, the natural fibers are evenly dispersed in the part but visible at the visible surface thereof.

[0132] Moreover, some natural fibers, in particular fibers derived from miscanthus or from olive stone, allow coloring the part in dark tones as well as in light colors. By way of an example, natural fibers derived from vine shoots are suitable for light colors and natural fibers derived from oyster are suitable for darker tones colored part.

[0133] Hence, the part can be a visible trim part of a motor vehicle.

[0134] According to a second object, the invention relates to a method for the preparation of an injection molded part as defined above. The embodiments described above for the part may be applied for the method.

[0135] The method comprises injecting in a mold a mixture comprising:

[0136] (a) at least 15% by weight of the first polypropylene chosen among a polypropylene homopolymer having a melt flow index comprised from 40 g / 10min to 80 g / 10min at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index comprised from 1 g / 10min to 70 g / 10min at 230°C under a load of 2.16 kg, and mixtures thereof,

[0137] (b) from 3 to 40% by weight of the natural fibers having a length comprised from 1 pm to 4 mm,

[0138] (c) from 1 to 5% by weight of the second polypropylene, the second polypropylene being a polypropylene homopolymer or copolymer having a melt flow index comprised from 20 g / 1 Omin to 150 g / 1 Omin at 190°C under a load of 2.16 kg, the second polypropylene being grafted with a carboxylic acid, one of its esters or anhydrides, an epoxy and / or a silane, and (d) from 5 to 60% by weight of the elastomer having a melt flow index from 0.5 g / 10min to 10 g / 1 Omin at 190°C under a load of 2.16 kg, whereby an injection molded part is obtained.

[0139] The mixture may also comprise from 0 to 3 %, by weight of a dye, a pigment or mixtures thereof preferably in a color masterbatch. The color masterbatch typically comprises up to 60% by weight of one or more dye and a carrier resin, typically low density polyethylene. Other carrier resins may be used, like high density polyethylene or polypropylene homopolymer or copolymer.

[0140] The mixture may also comprise one or more additives, preferably chosen among:

[0141] - an anti-oxidant, for example of hindered phenols in combination with phosphite hydroxylamine, in particular for melt processing stability or a thiosynergist in combination with a phenol, in particular when long term thermal stability is required. The antioxidant is preferably chosen among pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and tris(2,4-di(2,4-di-tert-butylphenyl)phosphite and mixtures thereof;

[0142] - a UV stabilizer, for example hindered amine light stabilizer (HALS), in particular to inhibite the degradation of the polymer. Preferably, the UV stabilizer is a mixture of high molecular weight HALS comprising hindered amine 2,2,6,6-tetramethyl-4-piperidinol;

[0143] - a lubricant such as a demolding agent;

[0144] - an acid scavenger;

[0145] - and mixtures thereof.

[0146] Preferably, the total proportion of additives is from 0 to 1% by weight.

[0147] Advantageously, the mixture comprises from 0 to 1% by weight of an additive chosen among an antioxidant, a lubricant, an UV light absorber and mixtures thereof and from 0 to 3% by weight of a dye, a pigment or mixtures thereof.

[0148] The mixture may consist of:

[0149] (a) at least 15% by weight of the first polypropylene chosen among a polypropylene homopolymer having a melt flow index comprised from 40 g / 1 Omin to 80 g / 1 Omin at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index comprised from 1 g / 1 Omin to 70 g / 1 Omin at 230°C under a load of 2.16 kg, and mixtures thereof,

[0150] (b) from 3 to 40% by weight, preferably form 3 to 25% by weight, of the natural fibers having a length comprised from 1 pm to 4 mm,

[0151] (c) from 1 to 5% by weight of the second polypropylene homopolymer or copolymer, the second polypropylene being grafted with a carboxylic acid, one of its esters or anhydrides, an epoxy and / or a silane, and having a melt flow index comprised from 20 g / 10min to 150 g / 10min at 190°C under a load of 2.16 kg,

[0152] (d) from 5% to 60% by weight of the elastomer, having a melt flow index comprised from 0.5 g / 10min to 10 g / 10min at 190°C under a load of 2.16 kg,

[0153] (e) from 0 to 1% by weight of an additive chosen among an anti-oxidant, a UV stabilizer, a lubricant (like a demolding agent), an acid scavenger and mixtures thereof, and

[0154] (f) from 0 to 3% by weight of a dye, a pigment or mixtures thereof preferably in a color masterbatch.

[0155] The first polypropylene may comprise:

[0156] (a1) at least one polypropylene copolymer having a melt flow index comprised from 1 to 10 g / 10 min at 230°C under a load of 2.16 kg, preferably comprised from 1 to 6 g / 10 min, and (a2) at least one polypropylene copolymer having a melt flow index comprised from 30 to 70 g / 10 min at 230°C under a load of 2.16 kg, preferably from 40 to 65 g / min at 230°C under a load of 2.16 kg, more preferably from 40 to 60 g / min at 230°C under a load of 2.16 kg.

[0157] The first polypropylene may comprise a plurality of polypropylene copolymers (a1) having different melt flow indexes.

[0158] The weight ratio of the polypropylene copolymer (a2) versus the polypropylene copolymer (a1 ) may be comprised from 3.0 to 25.0, preferably from 3.0 to 15.0, more preferably from 3.0 to 10.0.

[0159] When the first polypropylene comprises both at least one polypropylene copolymer (a1) and at least one polypropylene copolymer (a2), the first polypropylene has a broad molecular weight distribution. Such first polymer lowers the melt viscosity of a mixture comprising it, and leads to satisfactory flow length and processability.

[0160] According to a first alternative, the method may comprise, prior to injecting, preparing the mixture by extruding a composition A comprising:

[0161] (a) at least 15% by weight of the first polypropylene chosen among a polypropylene homopolymer having a melt flow index comprised from 40 g / 10min to 80 g / 10min at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index comprised from 1 g / 10min to 70 g / 10min at 230°C under a load of 2.16 kg, and mixtures thereof,

[0162] (b) from 3 to 40% by weight, preferably from 3 to 25% by weight, of the natural fibers having a length comprised from 1 pm to 4 mm,

[0163] (c) from 1 to 5% by weight of the second polypropylene, the second polypropylene being a polypropylene homopolymer or copolymer grafted with a carboxylic acid, one of its esters or anhydrides, an epoxy and / or a silane and having a melt flow index comprised from 20 g / 1 Omin to 150 g / 1 Omin at 190°C under a load of 2.16 kg, and

[0164] (d) from 5% to 60% by weight of the elastomer having a melt flow index from 0.5 g / 1 Omin to 10 g / 1 Omin at 190°C under a load of 2.16 kg, to obtain the mixture.

[0165] The second polypropylene may have a melt flow index comprised from 20 g / 10 min to 150 g / 10 min at 190°C under a load of 2.16 kg.

[0166] The obtained mixture is thus in the form of an extruded composition, which is then injected in a mold to form the injection molded part.

[0167] Generally, the first polypropylene forms the matrix of the extruded composition.

[0168] The extrusion is preferably carried out in a screw extruder, such as a twin-screw, single-screw, planetary extruder, and preferably a co-kneader type single-screw extruder which limits shearing and is used at low temperature (< 200°C), thus advantageously avoiding the degradation of natural fibers and ensuring very good dispersion of the fibers in the polypropylene matrix.

[0169] The extruded composition is typically in the form of pellets, which are used in the subsequent step of injection molding.

[0170] Typically, pellets of the extruded composition are brought into contact with a heated and temperature-controlled plasticizing screw. The pellets are softened under the combined action of the screw and the temperature to reach a viscous state at the front of the screw, and constituting the supply of material ready to be injected. The mixture present at the front of the plasticizing screw is then injected under high pressure into a mold (or cavity) having the desired shape for the part. Then, the part is cooled for a few seconds, before being ejected.

[0171] According to a second alternative, the method may comprise, prior to injecting, i) extruding a composition B comprising:

[0172] (ai) a polypropylene chosen from a polypropylene homopolymer having a melt flow index comprised from 40 g / 1 Omin to 80 g / 1 Omin at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index comprised from 1 g / 1 Omin to 70 g / 1 Omin at 230°C under a load of 2.16 kg and mixtures thereof, and

[0173] (b) the natural fibers having a length comprised from 1 pm to 4 mm, to obtain a composite material B; ii) extruding a composition C comprising: (aii) a polypropylene chosen from a polypropylene homopolymer having a melt flow index comprised from 40 g / 10min to 80 g / 10min at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index comprised from 1 g / 10min to 70 g / 10min at 230°C under a load of 2.16 kg and mixtures thereof, and

[0174] (d) the elastomer having a melt flow index comprised from 0.5 g / 1 Omin to 10 g / 1 Omin at 190°C under a load of 2.16 kg, to obtain a composite material C; at least one of composition B and composition C further comprising (c) the second polypropylene, the second polypropylene homopolymer or copolymer being grafted with a carboxylic acid, one of its esters or anhydrides, an epoxy and / or a silane and having a melt flow index from 20 g / 1 Omin to 150 g / 1 Omin at 190°C under a load of 2.16 kg, ill) blending the composite material B and the composite material C to obtain the mixture as defined above, iv) injecting the mixture into a mold.

[0175] In a particular embodiment, any one or both of compositions B and C may comprise (a1 ) the at least one polypropylene copolymer having a melt flow index comprised from 1 to 10 g / 10 min at 230°C under a load of 2.16 kg, preferably comprised from 1 to 6 g / 10 min, and (a2) the at least one polypropylene copolymer having a melt flow index comprised from 30 to 70 g / 10 min at 230°C under a load of 2.16 kg, preferably from 40 to 65 g / min at 230°C under a load of 2.16 kg, more preferably from 40 to 60 g / min at 230°C under a load of 2.16 kg.

[0176] The extrusion is preferably carried out in a screw extruder, such as a twin-screw, single-screw, planetary extruder, and preferably a co-kneader type single-screw extruder which limits shearing and is used at low temperature (< 200°C), thus advantageously avoiding the degradation of natural fibers and ensuring very good dispersion of the fibers in the polypropylene matrix.

[0177] The composite material B is generally extruded in the form of pellets, as well as the composite material C.

[0178] The blend of composite materials B and C, for example in form of pellets, is typically brought into contact with a heated and temperature-controlled plasticizing screw. The pellets are softened under the combined action of the screw and the temperature to reach a viscous state at the front of the screw, and constituting the supply of material ready to be injected, whereby the mixture to be injected is obtained, and then injected under high pressure into a mold (or cavity) having the desired shape for the part. The part is then cooled for a few seconds and then ejected.

[0179] In a particular embodiment, the blending of the composite material B and the composite material C is performed in an injection molding press.

[0180] Composite material B may have a high natural fiber content, for example composite material B may comprise from 35% to 70% by weight of the natural fibers. The flowability of composite material C and / or the weight ratio of the composite material B versus composite material C can be adjusted depending on the wished mechanical properties of the part to be obtained.

[0181] The method according to this second alternative generally allows an improved dispersion of the natural fibers in the part and a better impact resistance of the part compared to the one according to the first alternative.

[0182] The method according to this second alternative generally also allows the blending of a large variety of proportions of composition B and composition C.

[0183] The invention also relates to the part obtained by the any of the methods described above.

[0184] The invention is illustrated by the following examples and figure.

[0185] Figure 1 shows the tensile modulus and the unnotched Izod measured for compositions B, C, B80C20, B60C40, B40C60 and B20C80 of Table 3.

[0186] Example 1 : Preparation and mechanical properties of the part

[0187] In a twin-screw extruder, six different mixtures were formed by introducing through a first hopper:

[0188] - 2,2 kg of polypropylene heterophasic copolymer (PPC 12642 from Total (Melt Flow Index (2.16 kg-230°C): 70 g / 10min) ;

[0189] - 2 kg of natural fibers of lengths o Expl A (comparative example): no natural fibers; o Expl B: Olive stone powder <100 pm from BioPowder o Expl C: Vine shoots fibers (Sarment) <530 pm from Vitis Valoren o Expl D: Vine shoots fibers (Sarment) 0 - 4 mm from Vitis Valoren o Expl E: Miscanthus <500 pm from FRD Lab o Expl F: flax shives 223 pm from the Flax Company o Expl G: hemp hurds 1 mm from APM (Automotive Performance Materials);

[0190] - 5,5 kg of an ethylene-octene copolymer (MFI 5.0 g / 10min at 190°C under a load of 2.16 kg, AFFINITI EG 8200 from DOW);

[0191] - 0,3 kg of Maleic Anhydride Modified polypropylene copolymer (MFI 100 g / 10min at 190°C under a load of 2.16 kg, Bondyram 1001 CN from Polyram)

[0192] The components and their proportions are shown in Table 1 below:

[0193] [TABLE 1]

[0194] The mixture was extrusion-compounded under the following conditions:

[0195] Temperature 180°C

[0196] Pressure: 5 to 30 bar

[0197] The mixture was obtained in the form of pellets that were used for the production of specimens by injection molding in a Kraus Maffei 130 machine, with a profile of temperatures from 165 to 185°C to prevent the degradation of the natural fiber and natural fillers. The yield strength of a part obtained by injection molding of each of the six mixtures was measured according to UNE-EN ISO 527-2.

[0198] The yield strength is higher with natural fibers (expl B to G) than without natural fibers (comparative expl A), and of at least 16.0 MPa.

[0199] The elongation at break of a part obtained by injection molding of each of the six mixtures was measured according to UNE-EN ISO 527-2. Except for expl D (vine shoots 0-4 mm) and G (hemp hurds), the elongation at break is improved by the natural fibers, and strongly improved (14%) for expl B (natural fibers derived from olive stone).

[0200] The deformation at maximum strength and the deformation at puncture of a part obtained by injection molding of each of the five composite materials comprising natural fibers was measured according to ISO 6603-2. The highest deformation at maximum strength and deformation at puncture are obtained for expl A (natural fibers derived from olive stone).

[0201] The energy at maximum strength and the energy at puncture of a part obtained by injection molding of each of the six composite materials comprising natural fibers was measured according to ISO 6603-2. The highest energy at maximum strength and the energy at puncture are obtained for expl B (natural fibers derived from olive stone).

[0202] The results of the measurements can be observed in Table 2.

[0203] [TABLE 2]

[0204] Mechanical properties of the parts of examples A to G

[0205] Example 2: impact of the proportion of ethylene-octene elastomer

[0206] In a twin-screw extruder, two different mixtures were produced: Composition B:

[0207] - 74% by weight of a nucleated, heterophasic polypropylene copolymer produced in reactor, having a melt flow index from 50 to 60 g / 10min at 230°C under a load of 2.16 kg (polypropylene copolymer (a2)), tensile modulus of 1450 MPa and notched Izod of 7 kJ / m2;

[0208] - 23% by weight of natural hemp fibers having particle size up to 4 mm; and

[0209] - 3% by weight of a maleic anhydride-grafted polypropylene copolymer having a melt flow index from 20 g / 10min to 50 g / 10min at 190°C under a load of 2.16 kg (second polypropylene).

[0210] The extrusion process was conducted in a twin-screw extruder Coperion ZSK30, intermeshing co-rotating. It was applied during the extrusion process a specific energy of 0,2 kWh / kg for the melting and dispersing of the natural fibers and fillers in the polypropylene matrix, with a profile of temperatures not higher than 180°C to control the melt temperature range from 180 to 190°C.

[0211] Composition C:

[0212] - 33% by weight of a polypropylene copolymer having a melt flow index from 45 to 60 g / 10min at 230°C under a load of 2.16 kg (polypropylene copolymer (a2));

[0213] - 15% by weight of a polypropylene copolymer having a melt flow index from 3 to 5 g / 10min at 230°C under a load of 2.16 kg (polypropylene copolymer (a1 ));

[0214] - 3% by weight of a polypropylene copolymer having a melt flow index from 40 to 50 g / 10min at 230°C under a load of 2.16 kg (polypropylene copolymer (a2));

[0215] - 45% of ethylene- 1 -octene elastomer having a melt flow index from 2 to 3 g / 10min at 190°C under a load of 2.16 kg;

[0216] - 3% by weight of a high-density polyethylene having a melt flow index from 5 to 8 g / 1 Omin at 190°C under a load of 2.16 kg; and

[0217] - 1% by weight of a combination of additives antioxidant, lubricant and UV light absorber.

[0218] The extrusion process was conducted in a twin-screw extruder Coperion ZSK30, intermeshing co-rotating. It was applied during the extrusion process a specific energy of 0,3 kWh / kg for the melting and dispersing of the elastomers and the polypropylenes in the composition. A temperature profile from 150 to 200°C was applied to control the melt temperature range from 200 to 220°C. The composition B and composition C in pellet form were blended in four different ratios, prior to injection molding of specimens in a Kraus Maffei 130 machine, with a profile of temperatures from 165 to 185°C to prevent the degradation of the natural fiber and natural fillers.

[0219] The specimens made of such blended composition B and composition C were tested according to the following test methods:

[0220] Spiral flow - Determined according to a spiral mold insert Axxicon ISO standard, 4 mm width and 3 mm thick, the mold temperature of 30°C and injection molding temperature profile from 165 to 185°C. The injection pressure of 2000 bars and injection speed of 19 mm / s, the injection and cooling time of 26 s, then the total injection cycle of 34 s. The dosage for the spiral flow of 34 cm3follows from the predetermined length of the testing material. The spiral flow length is the total length of solidified material from the injection gate to the end of flow, as the average of 10 molded spiral flows at stable injection molding process, presenting flow length variation lower than 0,5 mm. The spiral flow determines the molten material flow until it solidifies in a specified thermodynamic injection molding process, allowing to compare the samples with a reference material.

[0221] The tensile Modulus was determined according to ISO R 527.

[0222] The Izod impact strength was determined according to ISO 180 / 1 .

[0223] The obtained properties of blended compositions B and C are shown in Table 3, with the consequent content in percentage by weight of natural hemp fibers coming from the composition B and the percentage by weight of elastomer Ethylene-Octene from the composition C selected in Example 2:

[0224] [TABLE 3]

[0225] In the examples, the mixture of compositions B and C comprises polypropylene copolymers having melt flow index from 2 to 60 g / 10min at 230°C under a load of 2.16 kg, which results in a broader molecular weight distribution (BMWD) than composition B having a single polypropylene of MFI from 50 to 60 g / 10min at 230°C under a load of 2.16 kg. Despite the higher MFI of the single polypropylene copolymer of composition B compared to the ones from the composition C, this BMWD is enough for the injection molding at a temperature lower than 200°C. This temperature is chosen to prevent the natural fiber degradation during the transformation process, unlike the recommended injection molding temperature range of 230°C ± 30°C for the prior art polypropylene compounds impact modified and reinforced with micronized talc.

[0226] The molecular weight, indicated by the melt flow index (MFI), influences the processability in the molten state: a higher MFI provides a higher flow length.

[0227] Further, example 2 shows that using a first polypropylene comprising polypropylene copolymers (a1 ) and (a2), and hence having a broad molecular weight distribution (BMWD or high Polydispersity Index) leads to a mixture having a lower melt viscosity. Thanks to their BMWD, mixture samples B80C20, B60C40 and B40C60 present a spiral flow at comparable to the one of reference composition B. The flow length is maintained up to 60% by weight of composition B dispersed in the composition C.

[0228] The higher flow length of 65 cm presented by the mixture sample B80C20 compared to the flow length of composition B of 63 cm is well correlated with the broader molecular weight distribution of B80C20 compared to composition C.

[0229] As the content of elastomer ethylene-octene from the composition C increases to 36% by weight (mixture sample B20C80), the flow length decreases to 61 cm. This can be explained by the influence of the higher melt viscosity of the composition C, which has a flow length of 55 cm.

[0230] Hence, the flow length is satisfactory up to 36% by weight of elastomer ethylene-octene in Example 2.

[0231] Furthermore, the tensile modulus of mixture samples B60C40 and B40C60 is suitable for most of the interior car applications, mixture sample B60C40 being particularly preferred due to its tensile modulus of 1690 MPa.

[0232] This rigidity can be associated with the content of natural hemp fibers of 13.8% by weight. Generally speaking, figure 1 shows a linear correlation between the tensile modulus and the weight percentage of natural fibers in combination with the percentage by weight of elastomer ethylene-octene.

[0233] As shown in figure 1 , a high linear correlation factor (R2= 0,93) between the tensile modulus and the contents of elastomer ethylene-octene from the composition C and of natural hemp fibers from the composition B is measured. This demonstrates a good dispersion and the compatibility of the elastomer phase and the natural fibers with the polypropylene matrix, through the injection molding process at controlled lower temperature than 200°C.

[0234] The improvement of impact resistance, represented by the unnotched Izod impact test, is demonstrated by mixture sample B60C40, which has a significantly higher value of 35 kJ / m2compared to the reference value of 16 kJ / m2of mixture sample B.

[0235] It is important to note the failure mode improvement from complete break, i.e. brittle failure mode not showing plastic deformation, of mixture sample B to partial break, i.e. plastic deformation with crack formation and propagation, of mixture sample B60C40, thanks to its high content of elastomer ethylene-octene of 18% by weight.

[0236] Figure 1 also shows a high linear correlation factor (R2= 0,97) for unnotched Izod impact resistance obtained values, with the content of elastomer ethylene-octene from composition C. This further proves the good dispersion and compatibility of the elastomer phase with the polypropylene matrix, through the injection molding process controlled lower temperature than 200 °C.

[0237] Compared to mixture sample B60C40, mixture sample B40C60 presents an even higher unnotched Izod impact resistance of 51 kJ / m2. This can be due to the higher content of elastomer ethylene-octene of 27% by weight. The tensile modulus is simultaneously reduced to 960 MPa, probably because of the lower content of natural hemp fibers of 9.2% by weight compared to mixture sample H60J40.

[0238] Mixture sample B40C60 is of interest for interior or exterior automotive applications for which impact resistance is more important than rigidity.

[0239] Example 3:

[0240] Two injection molded parts were prepared with respectively a mixture “Mix E” according to the invention and a comparative mixture “Mix L”. The compositions of mixtures Mix E and Mix L and the mechanical properties of the parts are described in Table 4 hereafter, in which the MFIs are expressed in g / 10 min under a load of 2.16kg.

[0241] Table 4 shows that Mix L differs from Mix E in the length of the natural fibers.

[0242] The part obtained with Mix E according to the invention shows improved mechanical properties compared to Mix L, in terms of unnotched Izod impact, energy at puncture, and deformation at puncture, while having satisfactory tensile modulus.

[0243] The MFI of the different polymers are chosen to match with a good injectability, especially for natural fibers-based materials. Indeed the injection temperature is here 185°C, and not 230°C as it is the case for traditional automotive polypropylene talc or polypropylene glass fiber materials.

[0244] [Table 4]

[0245] Example 4:

[0246] Two injection molded parts were prepared with respectively a mixture “Mix D” according to the invention and a comparative mixture “Mix P”. The compositions of mixtures Mix D and Mix P and the mechanical properties of the parts are described in Table 5 hereafter, in which the MFIs are expressed in g / 10 min under a load of 2.16kg.

[0247] Table 5 shows that Mix P differs from Mix D in that mix P does not comprise the second polypropylene c) but a grafted polypropylene copolymer having a lower MFI. The part obtained with Mix D according to the invention shows improved mechanical properties compared to Mix P, in terms of unnotched Izod impact, energy at puncture, and deformation at puncture, while having satisfactory tensile modulus.

[0248] The MFI of the different polymers are chosen to match with a good injectability, especially for natural fibers-based materials. Indeed the injection temperature is 185°C, and not 230°C as for traditional automotive polypropylene talc or polypropylene glass fiber materials.

[0249] [Table 5]

[0250] Example 5:

[0251] Two injection molded parts were prepared with respectively a mixture “Mix B” according to the invention and a comparative mixture “Mix V”. The compositions of mixtures Mix B and Mix D and the mechanical properties of the parts are described in Table 6 hereafter, in which the MFIs are expressed in g / 10 min under a load of 2.16kg.

[0252] Table 6 shows that Mix V differs from Mix B in that mix V does not comprise the elastomer d) but an elastomer having a higher MFI.

[0253] The part obtained with Mix B according to the invention shows improved mechanical properties compared to Mix V, in terms of unnotched Izod impact, energy at puncture, and deformation at puncture, while having satisfactory tensile modulus.

[0254] The MFI of the different polymers are chosen to match with a good injectability, especially for natural fibers-based materials. Indeed the injection temperature is 185°C, and not 230°C as for traditional automotive polypropylene talc or polypropylene glass fiber materials.

[0255] [Table 6]

[0256] Example 6:

[0257] Two injection molded parts were prepared with respectively a mixture “Mix A” according to the invention and a comparative mixture “Mix Abis”. The compositions of mixtures Mix A and Mix Abis and the mechanical properties of the parts are described in Table 7 hereafter, in which the MFIs are expressed in g / 10 min under a load of 2.16kg.

[0258] Table 7 shows that Mix Abis differs from Mix A in that mix Abis does not comprise the first polypropylene a) but a polypropylene having a higher MFI.

[0259] The part obtained with Mix A according to the invention shows improved mechanical properties compared to Mix Abis, in terms of unnotched Izod impact, energy at puncture, and deformation at puncture, while having satisfactory tensile modulus, and injectability.

[0260] The MFI of the different polymers are chosen to match with a good injectability, especially for natural fibers-based materials. Indeed the injection temperature is 185°C, and not 230°C as for traditional automotive polypropylene talc or polypropylene glass fiber materials.

[0261] [Table 7] Examples 3, 4, 5 and 6 show that all the specific MFIs of the first polypropylene a), the second polypropylene c), the elastomer d) and the specific fiber length of the fibers b) contribute simultaneously and synergistically to the obtaining of improved mechanical properties of the injection molded part. In particular, all the parts according to the invention have:

[0262] - an energy at puncture improved of at least 100%;

[0263] - a deformation at puncture improved of at least 50%; and

[0264] - an impact strength improved of at least 30%, compared to those of the comparative parts.

Claims

CLAIMS1 . Injection molded part comprising:(a) at least 15% by weight of a first polypropylene chosen from a polypropylene homopolymer having a melt flow index comprised from 40 g / 10min to 80 g / 10min at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index comprised from 1 g / 10min to 70 g / 10min at 230°C under a load of 2.16 kg, and mixtures thereof,(b) from 3 to 40% by weight of natural fibers having an average length comprised from 1 pm to 4 mm,(c) from 1 to 5% by weight of a second polypropylene, the second polypropylene being a polypropylene homopolymer or copolymer having a melt flow index comprised from 20 g / 1 Omin to 150 g / 1 Omin at 190°C under a load of 2.16 kg, the second polypropylene being grafted with a carboxylic acid, one of its esters or anhydrides, an epoxy and / or a silane, and(d) from 5% to 60% by weight of an elastomer having a melt flow index comprised from 0.5 g / 1 Omin to 10 g / 1 Omin at 190°C under a load of 2.16 kg.

2. Injection molded part according to claim 1 , in which the natural fibers are derived from miscanthus, flax, hemp hurds, hemp fibers, reed, oyster, vine shoots, olive stone and mixture thereof, preferably from olive stone, vine shoots, oyster, reed, hemps fibers or hemp hurds, more preferably from olive stone, vine shoots or oyster, and even more preferably from olive stone.

3. Injection molded part according to any one of the preceding claims, comprising from 3 to -25% by weight of the natural fibers having an average length comprised from 1 pm to 4 mm.

4. Injection molded part according to any one of the preceding claims, in which the second polypropylene homopolymer or copolymer has a melt flow index comprised from 100 g / 1 Omin to 150 g / 10 min at 190°C under a load of 2.16 kg.

5. Injection molded part according to any one of preceding claims, in which the elastomer is chosen from ethylene- 1 -octene elastomer, ethylene-1 -butene elastomer,hydrogenated styrene-isoprene-styrene block copolymers, styrene-ethylene-butylene-styrene and mixtures thereof, and preferably ethylene-octene elastomer.

6. Injection molded part according to any one of the preceding claims further comprising: (e) from 0 to 1 % by weight of additives chosen from an antioxidant, a lubricant, an UV light absorber, and mixtures thereof and / or (f) from 0 to 3% by weight of a dye, a pigment and mixtures thereof.

7. Injection molded part according to any one of the preceding claims, wherein the first polypropylene (a) comprises:(a1 ) at least one polypropylene copolymer having a melt flow index comprised from 1 to 10 g / 1 Omin at 230°C under a load of 2.16 kg, and(a2) at least one polypropylene copolymer having a melt follow index comprised from 30 to 70 g / 1 Omin at 230°C under a load of 2.16 kg.

8. Injection molded part according to the preceding claim, wherein the weight ratio of the polypropylene copolymer (a2) versus the polypropylene copolymer (a1 ) is comprised from 3.0 to 25.0.

9. Injection molded part according to any one of the preceding claims, which is a visible interior trim part or a non-visible structural part of a motor vehicle.

10. Method for the preparation of an injection molded part according to any of claims 1 to 9, comprising injecting into a mold a mixture comprising:(a) at least 15% by weight of a first polypropylene chosen from a polypropylene homopolymer having a melt flow index comprised from 40 g / 1 Omin to 80 g / 1 Omin at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index comprised from 1 g / 1 Omin to 70 g / 1 Omin at 230°C under a load of 2.16 kg and mixtures thereof,(b) from 3 to 40% by weight of natural fibers having a length comprised from 1 pm to 4 mm,(c) from 1 to 5% by weight of a second polypropylene, the second polypropylene being a polypropylene homopolymer or copolymer having a melt flow index comprised from 20 g / 1 Omin to 150 g / 1 Omin at 190°C under a load of 2.16 kg, the second polypropylene being grafted witha carboxylic acid, one of its esters or anhydrides, an epoxy and / or a silane,(d) from 5% to 60% by weight of an elastomer having a melt flow index comprised from 0.5 g / 10min to 10 g / 10min at 190°C under a load of 2.16 kg, and whereby the injection molded part is obtained.1 1 . Method according to claim 10, comprising, prior to injecting, preparing the mixture by extruding a composition A comprising components (a), (b), (c), (d) as defined in claim 10.

12. Method according to claim 10 comprising, prior to injecting : i) extruding a composition B comprising:(ai) a polypropylene chosen from a polypropylene homopolymer having a melt flow index comprised from 40 g / 10min to 80 g / 10min at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index comprised from 1 g / 10min to 70 g / 10min at 230°C under a load of 2.16 kg and mixtures thereof, and(b) natural fibers having a length comprised from 1 pm to 4 mm, to obtain a composite material B; and ii) extruding a composition C comprising:(aii) a polypropylene chosen from a polypropylene homopolymer having a melt flow index comprised from 40 g / 10min to 80 g / 10min at 230°C under a load of 2.16 kg, a polypropylene copolymer having a melt flow index comprised from 1 g / 1 Omin to 70 g / 1 Omin at 230°C under a load of 2.16 kg and mixtures thereof, and(d) an elastomer having a melt flow index comprised from 0.5 g / 1 Omin to 10 g / 1 Omin at 190°C under a load of 2.16 kg; to obtain a composite material C, at least one of composition B and composition C further comprising (c) a second polypropylene, the second polypropylene being a polypropylene homopolymer or copolymer having a melt flow index comprised from 20 g / 1 Omin to 150 g / 1 Omin at 190°C under a load of 2.16 kg and being grafted with a carboxylic acid, one of its esters or anhydrides, an epoxy and / or a silane, ill) blending the composite material B and the composite material C to obtain the mixture as defined in claim 10, iv) injecting the mixture into a mold.

13. Method according to claim 12, wherein composition B comprises from 35% to 70% by weight of natural fibers.

14. Method according to any of claims 12 to 13, wherein the blending of the composite material B and the composite material C is performed in an injection molding press.

15. Method for obtaining an injected molded part according to any one of claims 10 to 14, wherein the mixture further comprises a dye, a pigment or mixtures thereof and / or additives.

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