FR3001422A1 - Trimming part, useful in e.g. interior door panel of car, comprises needle punched nonwoven fabric panel with natural fibers and polymer fibers having polylactic acid, where natural fibers are flax fibers and bicomponent polymer fibers - Google Patents

Abstract

The trimming part comprises a panel (9) equipped with natural vegetable fibers and polymer fibers comprising polylactic acid. The panel is a needle punched nonwoven fabric panel. The vegetable natural fibers are flax fibers and bicomponent polymer fibers, and comprise a core formed by a first polylactic acid and an envelope formed by a second polylactic acid. The envelope is placed around the core. The needle punched nonwoven fabric panel comprises 50 mass% of flax fibers and 50 mass% of polymer fibers. A mass crystallinity rate of the polymer fibers is 36%. The trimming part comprises a panel (9) equipped with natural vegetable fibers and polymer fibers comprising polylactic acid. The panel is a needle punched nonwoven fabric panel. The vegetable natural fibers are flax fibers and bicomponent polymer fibers, and comprise a core formed by a first polylactic acid and an envelope formed by a second polylactic acid. The envelope is placed around the core. The first polylactic acid has a first melting point of 155-165[deg] C. The second polylactic acid has a second melting point lower than the first melting point. The needle punched nonwoven fabric panel comprises 50 mass% of flax fibers and 50 mass% of polymer fibers. A mass crystallinity rate of the polymer fibers is 36%. The second melting point is 130[deg] C. The first polylactic acid has a first fusion threshold of 158[deg] C and a second fusion threshold of 165[deg] C. The panel has a tensile strength of 2-25 MPa and an elongation of 5-25%. The trimming part has an acoustic absorption coefficient of 10-90% for a frequency of 200-6000 Hz, and further comprises an aspect layer (6) covering a face of the panel. Independent claims are included for: (1) a needle punched nonwoven fabric panel; and (2) a method for manufacturing a trimming part.

Description

The invention relates to the general field of dressing and soundproofing of vehicles, particularly motor vehicles, and more specifically the trim parts provided with panels for such vehicles. The invention also relates to the needled nonwoven panels for the manufacture of such pieces of gaskets, as well as the processes for producing such gaskets from such needled nonwoven panels. Roof pavilions for motor vehicles formed of a multilayer composite structure are known, which structure is provided with a block of flexible polyurethane foam interposed between two layers of glass fibers, respectively a first layer and a second layer, a coating formed of a nonwoven fabric composed of polyester fibers covering the first layer of glass fibers and a nonwoven web covering the second layer of glass fibers. The block of flexible polyurethane foam comprises a binder element facilitating the adhesion of this block with the layers of glass fibers. Interior panels for motor vehicle doors are also known, comprising kenaf fibers and polylactide fibers, also called poly (acid lactic) or poly (lactic acid) fibers. Kenaf fibers are fibers from so-called bio-sourced materials that are biodegradable. The aim of the invention is to provide a piece of vehicle trim, comprising a panel provided with natural plant fibers and polymer fibers, which is just as biodegradable as the inner panels of the prior art, which is particularly efficient, as well as in terms of sound absorption, rigidity and durability, and which is furthermore particularly simple and convenient to manufacture.

The invention thus provides, in a first aspect, a piece of trim for vehicles, comprising a panel provided with natural plant fibers and polymer fibers comprising polylactic acid, characterized in that said panel is a non-structural board. needled woven, said natural plant fibers are flax fibers and said polymer fibers are bicomponent fibers each having a core formed by a first polylactic acid and a shell formed by a second polylactic acid, which shell is formed around said core; said first polylactic acid has a first melting temperature and said second polylactic acid has a second melting temperature lower than said first melting temperature; said needled nonwoven panel is comprised of from about 15% to about 60%, by weight, of flax fibers and from about 40% to about 85%, by weight, of bicomponent polymer fibers; and said needled nonwoven panel has a mass crystallinity ratio of said two-component polymer fibers of from about 10% to about 40%. The interaction of the different polymer fibers with one another and polymer fibers with the flax fibers which make up the nonwoven needle-punched panel enables the trim piece according to the invention to exhibit the mechanical properties (rigidity, flexibility and flexibility), acoustic and aging (durability) required. The degree of crystallinity measures the proportion of matter in the crystalline state. The mass crystallinity level of the crystallized polymer fibers is defined by the ratio of the mass of the crystalline phases to the total mass of the bicomponent polymer (the non-crystalline part of the material is composed of amorphous fractions). In the same way, the degree of volume crystallinity can be considered. The mass and volume crystallinity rates of the polymers are generally not very different. We will speak later only of the mass crystallinity rate.

This degree of crystallinity, and in particular its evolution, reflects a modification of the microstructure and therefore of the properties of the material (Young's modulus, elongation at break, etc.), and makes it possible to assess the amorphous and crystalline contributions. The mass crystallinity rate is generally measured using differential scanning calorimetry or X-ray diffractometry. Differential Scanning Calorimetry (DSC) quantifies the flow of heat normalized to the mass of the analyzed polymer sample (more precisely to 1 g of polymer analyzed), as a function of temperature. Here, the value range in which the degree of crystallinity characterizing the bicomponent polymer fibers of this needle-punched nonwoven panel is significant is that the first polylactic acid forming the core of these polymer fibers has been less melted than the second polylactic acid forming the shell of the polymer fibers, or even not melted at all; while this second polylactic acid was much more melted than the first polylactic acid, or was completely melted. It is the combination of this first polylactic acid (having a major part of these fibers not bonded to each other) and this second polylactic acid (whose fibers are all or almost all bonded to each other and with their environment) which makes it possible to form mechanical bonds between the polymer fibers and the flax fibers and thus to provide the mechanical properties (rigidity) of the needle-punched nonwoven panel, and consequently of the lining piece. Melting the polymer fibers (especially those of the second polylactic acid) causes them to coat at least some of the flax fibers so as to mechanically bond these flax fibers to the polymer fibers. Thus, the linen fibers form a so-called reinforcing structure of the needle-punched nonwoven panel, which forms a composite material. It is from the synergy between the wool fibers and the fibers of the first and second polylactic acids that the acoustic properties of the needle-punched nonwoven panel originate. In addition, the flax fibers have particularly good aging properties compared to the polymer fibers, and the flax fiber-polymer fiber composition therefore provides the needle-punched nonwoven panel, and therefore the trim piece, with excellent durability. This synergy between the flax fibers and the polymer fibers of the needled nonwoven panel of the lining piece according to the invention is in particular due to the mass proportions of flax fibers and polymer fibers characterizing this lining piece. It should be noted that these mass proportions are detectable and measurable by thermogravimetry. The liner has the required mechanical, acoustic and aging properties, while having a needled nonwoven panel of totally or almost biodegradable composition. Thus the trim piece according to the invention offers the advantage of protecting the environment because of its recyclability. Here, the term "polylactic acid" is used, knowing that it is a polymeric material also called poly (lactic acid) or poly (lactic acid). According to preferred, simple, convenient and economical characteristics of the packing piece according to the invention: said needle-punched nonwoven panel is composed of about 30% to about 55%, by weight, of flax fibers and about 45% from about 70% by weight of bicomponent polymer fibers, and said needled nonwoven panel has a mass crystallinity ratio of said bicomponent polymer fibers of from about 25% to about 40%; said needled nonwoven panel is composed of about 50% by weight of flax fibers and about 50% by weight of bicomponent polymer fibers, and said needled nonwoven panel has a mass crystallinity ratio. said bicomponent polymer fibers equal to about 36%; said first polylactic acid has a first melting temperature of from about 150 ° C to about 170 ° C and said second polylactic acid has a second melting temperature of from about 125 ° C to about 155 ° C; said first polylactic acid has a first melting temperature of from about 155 ° C to about 165 ° C and said second polylactic acid has a second melting temperature of about 130 ° C; said first polylactic acid has a first melting point of about 158 ° C and a second melting point of about 165 ° C; said needled nonwoven panel has a tensile strength of from about 2 MPa to about 25 MPa for an elongation of about 5% to 25%, in length, of said needled nonwoven panel; such measured numerical values being obtained by conventional tensile tests, for example using a tensile test piece and a traction machine; the lining piece has an acoustic absorption coefficient of between about 10% and about 90% for a frequency of about 200 Hz to about 6000 Hz; such measured numerical values being obtained by conventional acoustic tests, for example using an impedance tube (also called "Kundt tube"); and / or - the lining piece further comprises an appearance layer covering a face of said needled nonwoven panel. The invention also provides, in a second aspect, a nonwoven needle-punched panel for vehicle trim parts, characterized in that it comprises natural plant fibers and polymer fibers comprising polylactic acid, said fibers vegetable natural fibers being flax fibers, said polymer fibers being bicomponent fibers each having a core formed by a first polylactic acid and an envelope formed by a second polylactic acid, which envelope is formed around said core; said first polylactic acid has a first melting temperature and said second polylactic acid has a second melting temperature lower than said first melting temperature; and said needled nonwoven panel is comprised of from about 15% to about 60%, by weight, of flax fiber and from about 40% to about 85%, by weight, of bicomponent polymer fibers. The needled nonwoven panel according to the invention has a composition selected herein to obtain, after carrying out a thermoforming process applied to this needle-punched nonwoven panel, a piece of packing as described above. It will be appreciated that said needled nonwoven panel may be preferably composed of from about 30% to about 55% by weight of flax fiber and from about 45% to about 70% by weight of The bicomponent polymer, and / or more preferably, said needled nonwoven panel is composed of about 50% by weight of flax fibers and about 50% by weight of bicomponent polymer fibers. According to preferred features of the needled nonwoven panel according to the invention, said first polylactic acid has a first melting temperature between about 150 ° C and about 170 ° C and said second polylactic acid has a second melting temperature of about 125 ° C and about 155 ° C. It will be appreciated that in said needled nonwoven panel, preferably, said first polylactic acid has a first melting temperature of from about 155 ° C to about 165 ° C and said second polylactic acid has a second melting temperature of about 130 ° C. ° C, and / or more preferably, said first polylactic acid has a first melting point of about 158 ° C and a second melting point of about 165 ° C. According to other preferred characteristics of the needle-punched nonwoven panel according to the invention, said flax fibers have a mean diameter of between about 20ktm and about 20011m and an average length of between about 70mm and 110mm; and said bicomponent polymer fibers have a mean diameter of from about 15 to about 30 μm and an average length of from about 40 mm to about 60 mm.

The invention also relates, in a third aspect, to a method of manufacturing a piece of packing as described above, comprising the following steps: - providing a needle-punched nonwoven panel composed of about 15% to 5% about 60% by weight of flax fiber and from about 40% to about 85% by weight of bicomponent polymer fibers each having a first polylactic acid having a first melting temperature and a second acid polylactic having a second melting temperature, which second melting temperature is lower than said first melting temperature; heating said needled nonwoven panel for a first predetermined period until the latter reaches a predetermined temperature of between about 130 ° C and about 150 ° C; so as to completely or almost completely melt said second polylactic acid of said bicomponent polymer fibers and to keep said first second polylactic acid of said bicomponent polymer fibers unmelted or nearly unmelted; and compressing said prewired, needled nonwoven panel to a predetermined pressure of from about 50 bar to about 200 bar for a second predetermined period; whereby said needled nonwoven panel is thermoformed and has a mass crystallinity ratio of said bicomponent polymer fibers of from about 10% to about 40%. It should be noted that the steps implemented by this method of manufacturing the lining piece, and more specifically the thermoforming steps, are particularly simple, convenient and economical. It will further be noted that it is the characteristics relating to the selected heating temperature range, the predetermined time and pressure, together with the characteristics (the composition) of the needle-punched nonwoven panel, which make it possible to obtain a piece of trim comprising a nonwoven needle-punched panel having such a crystallinity level and more generally a trim piece with improved performance both in terms of rigidity and sound absorption and durability, while being totally or almost biodegradable. According to preferred, simple, convenient and economical characteristics of the manufacturing method according to the invention: said first predetermined period of heating said needled nonwoven panel is between about 30s and about 60s and said pressure at which said nonwoven panel is compressed; pre-heated needle punch is from about 50 bar to about 100 bar; and / or - said step of heating said needled nonwoven panel is performed using heating trays in contact with said needled nonwoven panel and said compressing step of said needled nonwoven panel is performed using cold molds; or - said step of heating said needled nonwoven panel is carried out using an infrared ray lamp and said step of compressing said needled nonwoven panel is performed using cold molds. We will now continue the description of the invention by the description of an exemplary embodiment, given below by way of illustration and not limitation, with reference to the accompanying drawings in which: - Figure 1 illustrates a piece of packing complies to the invention, here a pavilion for garnishing a roof of motor vehicles; - Figure 2 is a partial view showing in detail the lining piece said flag of Figure 1; - Figure 3 is a partial sectional view of a flax fiber; - Figure 4 is a schematic sectional view of a bicomponent polymer fiber; - Figure 5 illustrates different steps of the manufacturing process of the lining piece of Figure 1; FIG. 6 diagrammatically illustrates an infrared lamp making it possible to implement one of the steps of the method of FIG. 5, according to an alternative embodiment; and FIGS. 7 to 11 are graphs showing various properties, in particular mechanical and acoustic properties, of a lining piece such as that of FIG. 1, according to various compositions of the latter. Figure 1 schematically and partially illustrates a lining piece, here called flag 1, mounted under a roof 2 of a motor vehicle (not shown), in the passenger compartment of the vehicle. This flag 1 is arranged facing and away from the roof 2 so as to leave a free space 3 between them. The space 3 allows the circulation of fluids and waves, for example the noise coming from the outside of the vehicle as well as the noise coming from inside the vehicle and also the air coming as well from inside as from the outside of the vehicle. The roof 2 is conventionally made of metal material, for example sheet steel.

Pavilion 1 is itself multi-layered and comprises in particular a biodegradable structure 4 formed of so-called bio-sourced materials, a non-woven 5 here polyester and an appearance coating here also polyester. The structure 4, which forms the body of the lining piece, hereinafter referred to as lining 1, is sandwiched between the nonwoven 5 and the appearance liner 6. The nonwoven 5 forms a so-called rear layer arranged opposite roof 2 while the appearance coating 6 forms a so-called front layer disposed opposite the passenger compartment of the vehicle. Figure 2 shows in detail a sample of flag 1, 25 here with the different layers making up this flag 1 which are shown exploded. The structure 4 centrally comprises a needled nonwoven panel 9 composed here of natural plant fibers 10 (Figure 3) and polymer fibers (Figure 4). The structure 4 further comprises two weaves 7 and 8 sandwiching the needled nonwoven panel 9, which woven 7 and 8 are each composed of natural plant fibers 10 and polymer fibers 12, as is the needled nonwoven panel 9 The natural plant fibers 10 that make up both the needle-punched nonwoven panel 9 and the fabrics 7 and 8 of the structure 4 are flax fibers 10. FIG. This flax fiber 10 is here a red flax fiber (i.e., which has undergone a retting step) which has a plurality of unit fibers 11 arranged in a bundle, which bundle is surrounded by a fibrous shell Here, the flax fibers used have an average diameter of between about 20 μm and about 200 μm, and an average length of between 70 mm and 110 mm, and preferably an average length of about 100 μm. mm. It will be noted that the flax fiber 10 illustrated in FIG. 3 is a flax fiber which has not undergone a combing step but that this step is generally necessary for the production of the structure 4, so that the structure 4 of the Pavilion 1 is made of combed linen. The polymer fibers 12 used to form the structure 4 are here polymer fibers comprising polylactic acid (abbreviated as "PLA"). FIG. 4 shows such a polymer fiber 12 which is here bicomponent so that it comprises two polylactide acids. This bicomponent polymer fiber 12 is provided with a core 13 and an envelope 14 formed around the core 13. The core 13 is formed by a first polylactic acid, also called first PLA, while the envelope 14 is formed by a second polylactic acid, also called second PLA. The bicomponent polymer fiber 12 is circular and has a mean diameter of between about 15 μm and about 30 μm and an average length of between about 40 mm and about 60 mm, and preferably here the bicomponent polymer fiber 12 has an average length of 20 μm. about 51mm, plus or minus 3mm. The first PLA forming the core 13 has a first melting temperature and the second PLA forming the casing 14 has a second melting temperature distinct from the first melting temperature, and more particularly here below this first melting temperature. Here, the first PLA has a first melting temperature of from about 155 ° C to about 165 ° C and the second PLA has a second melting temperature of about 130 ° C. As will be seen in more detail below with reference to FIGS. 7 and 8, the first PLA actually has a first melting point equal to about 158 ° C. and a second melting threshold equal to about 165 ° C. vs. It will be noted more generally that the first PLA has a first melting temperature between about 150 ° C and about 170 ° C while the second PLA has a second melting temperature of between about 125 ° C and about 155 ° C (all respecting the aforementioned constraint of inferiority of the second melting temperature). The bicomponent polymer fiber 12 has at its core, ie at the core 13, a first PLA said to have a high melting point, while in sheath, that is to say at level of the envelope 14, the second PLA is said to low melting point. The bicomponent polymer fiber 12 shown in FIG. 4 (i.e. used to form the structure 4) has a crystallinity level of about 44%, which means that it has a crystal phase of about 44% and therefore an amorphous phase of about 56%. This is the mass crystallinity rate, measured by differential scanning calorimetry ("Differential Scanning Calorimetry" or "DSC") or by X-ray diffractometry. These are flax fibers and bicomponent polymers. 12 as described above which make up the reinforcing structure 4 and in particular the needled nonwoven panel 9 as well as the woven fabrics 7 and 8.

The needled nonwoven panel 9 of Hall 1 of Figures 1 and 2 here is composed of about 50% by weight of flax fibers 10 and about 50% by weight of bicomponent polymer fibers 12. This panel The nonwoven needle 9 also has a mass crystallinity ratio of the bicomponent polymer fibers 12 of about 36%. Such a degree of crystallinity means that the bicomponent polymer fibers 12 of the needled nonwoven panel 9 have about 36% crystalline phase and therefore about 64% amorphous phase. This degree of mass crystallinity is, as indicated above, measured by differential scanning calorimetry with a measuring machine called a differential calorimeter. This measurement makes it possible to provide, as will be seen hereinafter with reference to FIGS. 7 and 8, a thermogram called "DSC thermogram". It will also be appreciated that this needled nonwoven panel 9 has a maximum tensile strength of about 25 MPa for elongation of the needled nonwoven panel 9 to about 20% of its length. This measurement is carried out conventionally by tensile effects, for example by means of a tensile test piece and a traction machine. Note further that the needled nonwoven panel 9 of the flag 1 has an acoustic absorption coefficient of between about 10% and 90% for a frequency between about 200Hz and about 6000Hz. This is due to the fact, as will be seen below in more detail, that the second PLA has been completely melted or almost completely melted while the first PLA has been kept unmelted or almost unmelted. The needled nonwoven panel 9 is more generally composed of about 30% to about 55%, or even about 15% to about 60%, by weight, of flax fiber 10; and from about 45% to about 70%, or even about 40% to about 85%, by weight of bicomponent polymer fibers 12. This nonwoven, needle-bonded panel 9 therefore more generally has a mass crystallinity bicomponent polymer fibers 12 from about 25% to about 40% or even from about 10% to about 40%. It will be noted that this nonwoven, needle-punched panel 9 thus has, more generally, a tensile strength of between approximately 2 MPa and approximately 25 MPa for an elongation of approximately 5% to 25%, in length, of this panel 9. woven 7 and 8, the latter have a composition similar to that of the nonwoven needle-punched panel 9. These woven 7 and 8 form an outer envelope to the nonwoven needle-punched panel 9 and can protect or even strengthen slightly, the opposite major faces of this needle-punched nonwoven panel 9 that these woven 7 and 8 cover. The nonwoven 5 is applied to the structure 4 so as to also cover one of the faces of the nonwoven needle-punched panel 9, the woven 7 15 being interposed between this nonwoven 5 and this face of the nonwoven needle-punched panel 9; while the appearance coating 6 is itself configured to cover the other side of the nonwoven needle board 9, with the woven 8 which is interposed between the appearance coating 6 and the other side of the nonwoven needle board 9 Referring now to FIG. 5, the manufacturing process of the horn 7, starting from different elements, namely from nonwoven needles of identical composition to the composition of the panel 9 described above, of woven fabrics similar to the woven fabrics, will now be described with reference to FIG. 7 and 8 described above, nonwoven similar to the nonwoven 5 described above and coating of similar appearance to the appearance coating 6 described above. As illustrated in FIG. 5, the various elements 5 to 9 mentioned above are packaged in roll and define the raw material used in the process described below. The method of manufacturing the so-called lining piece 1 is here a thermoforming process implemented on a production line schematically visible in FIG. 5.

It is therefore here firstly to provide a nonwoven needle-like panel 9 as described above, which is packaged in roll, woven 7 and 8 as described above also packaged in roll and a nonwoven 5 as described above and also rolled.

The nonwoven needle-punched panel 9, the two woven fabrics 7 and 8 and the non-woven fabric 5 are unwound until they pass into a first roller system 20 provided here with two rollers so as to form a first assembly grouping these elements 5 and 7 together. 9, this first assembly being conveyed to a second roller system 21, here provided with a single roller, so as to stretch this first assembly. This first set is then conveyed to a third roller system 22 provided here with two rollers that allow to clamp the first set before its introduction into a heating system 23 here formed by two heating plates 24 arranged facing one of the other.

These two heating plates 24 are configured to sandwich and come into contact, or almost, with the nonwoven needle-punched panel 9 and more generally with the first assembly thus formed so that this first assembly, and consequently the non-woven panel Needled woven fabric 9, reaches a predetermined temperature of about 150 ° C.

More generally, the heating trays are configured so that this first set and in particular this nonwoven needle board 9 reaches a predetermined temperature of between about 130 ° C and about 150 ° C. This heating step is carried out for a first predetermined period here equal to about 50s, and more generally between about 30s and about 50s. The fact that the heating plates 24 come into contact with the first set generates a relatively moderate or negligible pressure of the order of a few MPa (for example less than 20 MPa). This heating step is configured to completely or almost completely melt the second PLA of the bicomponent polymer fibers 12 of the panel 9, or even the weaves 7 and 8, and to keep the first PLA This heating step therefore makes it possible to modify the first assembly, which first modified assembly is then conveyed to a compression system 26 formed here by two mobile compression molds 27 arranged in FIGS. facing each other. Before entry into this compression system 26, the first modified assembly is joined by the aspect coating 6 which is unwound and then stretched at a third roller system 25 here provided with a single roll, to form a second assembly comprising the first modified assembly and this aspect coating 6. This second assembly formed of the first modified assembly, that is to say of the first set and therefore of the previously heated nonwoven needle board 9, as well as the appearance coating 6, is therefore compressed by the molds 27 which are said to be cold (in fact at room temperature) at a predetermined pressure here equal to about 100 bars for a second predetermined period here equal to about 50s. More generally, the second set, and therefore the needled nonwoven panel 9, is compressed to a predetermined pressure of between about 50bar and about 200bar for a second predetermined period of time between about 30s and 60s. The second assembly thus compressed by the compression system 26 thus forms a third so-called thermoformed assembly which has a mass crystallinity ratio of the bicomponent polymer fibers 12 which it comprises here equal to approximately 36% and more generally between approximately 10%. and about 40% according to the particular composition of the needled nonwoven panel 9 (see the different weight percentages of the flax fibers 10 and bicomponent polymer fibers 12 mentioned above). This third thermoformed assembly is then conveyed to a cutting system 28 to be cut, and thus form a lining piece having the form here of a horn 1 configured to garnish from below (interior of the passenger compartment) the roof 2 of a motor vehicle.

Here, the cutting system 28 is a water jet cutting machine provided with a support 30 and a nozzle 29 configured to provide a water jet 31 capable of cutting the third thermoformed assembly. In a variant illustrated in FIG. 6, the heating system 23 formed of heating plates 24 illustrated in FIG. 5 is replaced by a heating system 123 formed of an infrared ray lamp. Here, the mass crystallinity rate which characterizes the bicomponent polymer fibers 12 of the needle-punched nonwoven panel 9 thus thermoformed, and more generally of the flag 1 thus formed, is significant because the first PLA forming the core 13 of these fibers polymer 12 has been less melted than the second PLA forming the envelope 14 of these polymer fibers 12, or has not been melted at all; while this second PLA has been much more melted than the first PLA, or has been completely melted. This allows an interaction of the different polymer fibers 12 with each other and polymer fibers 12 with the flax fibers 10 which make up the needle-punched nonwoven panel 9 and more generally the structure 4 and even more generally the pavilion 1. This interaction is representative of the fact that the polymer fibers 12, in particular those of the second PLA, have melted and at least partly coated with the flax fibers 10 so as to mechanically bond these flax fibers 10 to the polymer fibers 12. Thus, the Linen fibers 10 form a so-called reinforcing structure of the needle-punched nonwoven panel 9, and more generally of the roof 1 thus forming a composite material. It is this synergy between the PLA and linen fibers that allows the trim piece, here flag 1, to present the mechanical properties 25 (rigidity, flexibility and flexibility), acoustics and aging (durability) required. In the above description of the roof 1, the nonwoven needle-punched panel 9 forms the body of the structure 4 and more generally of the lining piece referred to as liner 1. In fact, this needle-punched nonwoven panel 9 here has a thickness equal to about 8.5mm for a roof thickness 1 equal to about 10mm so that this needle-punched nonwoven panel 9 forms a major part of the roof 1 and therefore the mechanical, acoustic and aging properties of the roof are substantially provided by those of the panel 9. The properties of bicomponent polymer fibers 12 before and after thermoforming of the so-called lining piece 1, as well as the mechanical and acoustic properties of two lodges 1 having compositions will now be described with reference to FIGS. 7 to 11. as a percentage by weight of bicomponent polymer fibers 12 and flax fibers 10.

FIG. 7 shows a so-called DSC thermogram derived from the differential calorimetric analysis of the bicomponent polymer fiber 12 described above, in particular with reference to FIG. 4. This DSC thermogram characterizes this bicomponent polymer fiber 12 by indicating the flow of normalized heat, in W / g, as a function of the temperature, in ° C, of this bicomponent polymer fiber 12. FIG. 7 shows a glass transition region, corresponding to an endothermic jump, at around 60 ° C. C - 70 ° C, which is representative of a glass transition temperature Tg of the bicomponent polymer fiber 12 equal to about 62 ° C. FIG. 7 also shows an endothermic peak whose maximum is at about 130 ° C. corresponding to the melting temperature, called the second melting temperature, characterizing the second PLA forming the envelope 14. This second melting point is represented in FIG. 7 by the reference Tfmax1. Another endothermic phenomenon is observed in FIG. 7, different from the first because this other endothermic phenomenon here illustrates a second melting between about 150 ° C. and about 170 ° C. This second fusion concerns the first PLA at the core 13 of the bicomponent polymer fibers 12. It is observed here that this second fusion can characterize the passage from a first crystalline form to a second crystalline form, for example here at a about 158 ° C, represented by Tfmax2, and then melting this second crystalline form, for example, here at a temperature of about 165 ° C, shown in Figure 7 by the reference Tfmax3. These temperatures correspond to the first melting threshold (equal to about 158 ° C. equivalent to Tf max 2) and the second melting threshold (equal to about 165 ° C. equivalent to Tf max 3) of the second PLA described above. It is from such a DSC thermogram that the mass crystallinity level is determined. The degree of specific crystallinity is more specifically determined, in particular by calculating the area under the endothermic peaks visible in FIG. 7, and by normalizing by means of a theoretical value of the enthalpy of fusion of a 100% crystalline PLA. This level is here equal to approximately 44%, and therefore the amorphous phase of the bicomponent polymer fiber 12 is thus deduced, which is here approximately equal to 56%. It will be further noted that in the example described, the mass crystallinity level of about 44% is provided by the first PLA at about 7% and the second PLA at about 37%. We will now describe some properties of a lining piece called flag 1 whose composition is, in a first example, about 50%, by weight, of flax fibers 10 and about 50%, by mass, of Bicomponent polymer fibers 12, and in a second example, about 20% by weight of flax fiber 10 and about 80% by weight of bicomponent polymer fibers 12. It will be appreciated that bicomponent polymer 12 have the aforementioned melting temperatures as well as an average length and a mean diameter as indicated with reference to FIG. 4; while the flax fibers 10 have a mean diameter and an average length identical to those described with reference to FIG. 3. For these two examples of composition of the nonwoven needle 9 panel of the roof 1, the heating step has been carried out using heating trays such as those depicted in Fig. 5 for a first predetermined period of time of about 50s to achieve a temperature of the needled nonwoven panel 9 of 150 ° C; and the compression step was carried out using molds such as those described in Figure 5, at room temperature, for a second predetermined period equal to 50s and a predetermined pressure equal to 100 bars. FIG. 8 shows the normalized heat flux in W / g as a function of the temperature in ° C of the bicomponent polymer fibers 12 of the nonwoven, needle-punched panel 9 and more generally of the thermoformed louver 1 (i.e. has undergone the steps of the manufacturing process illustrated in Figure 5). After heating at 150 ° C. and compression at 100 bars during the predetermined periods mentioned above, the bicomponent polymer fibers 12 have different properties than they initially had and in particular the degree of crystallinity has changed. It is observed in FIG. 8 that there is no endothermic peak at around 130.degree. C. since the heating temperature is about 150.degree. C., which means that the second PLA in sheath is ie at the envelope 14, has been completely melted, or nearly so. This means that at room temperature, the second sheath PLA is completely amorphous or nearly so. A digital microscope analysis of the nonwoven panel 9 thus thermoformed makes it possible to distinguish a fibrous structure since the core, that is to say the core 13 of the bicomponent polymer fiber 12, 20 has not been melted, as shown in FIG. 8. The fibrous structure is particularly compact since the melting of the second PLA creates a greater cohesion between the PLA fibers 12 and the flax fibers 10. The DSC thermogram of FIG. the degree of crystallinity of the panel 9 (by calculating the area under the endothermic peaks) which is now about 36%. This degree of crystallinity is obtained because, after the heating and compression steps, the cooling of the material of the panel 9 and more generally of the horn 1 is too fast ("quenching with ambient air") so that the second PLA which It has been melted to reform a crystalline phase (such as spherolites formed during slow cooling). The second PLA is therefore completely amorphous and the percentage of this amorphous phase is now about 64% in the bicomponent polymer fibers 12. What is described with reference to FIG. 8 is true regardless of the fiber composition of Linen 10 and bicomponent polymer fibers 12 of the needled nonwoven panel 9 since Fig. 8 characterizes the bicomponent polymer fiber 12 itself. FIG. 9 shows the resistance, in MPa, of the needled nonwoven panel 9 and therefore, more generally, of the roof 1, as a function of the elongation, in%, of this panel 9, for the two composition examples described above. The graph of FIG. 9 is the result of a tensile test which makes it possible to visualize the mechanical behavior of the needled nonwoven panel 9. It can be seen in FIG. 9 that the higher the mass percentage of bicomponent polymer fibers 12 increases, the more the maximum stresses increase and the curve deviates from a conventional bell curve diagram. This is significant because the nonwoven needle-punched panel 9 and more generally the roof 1 approaches the mechanical behavior of a conventional composite material with an elastic and then plastic domain representative here of a clear rupture of the material at about 25 MPa, in the case of the second example of composition (80% by mass of PLA). For the first example of composition (50% PLA), the mechanical behavior is similar to that of the second example except that the break is not clear. Indeed, there is a decrease in stress due to disentanglement of bicomponent polymer fibers 12 and flax fibers 10 (end of the curve which takes a substantially bell shape). In the case of this first example, the maximum resistance is of the order of about 10 MPa. As regards the elongation of the nonwoven needle-punched panel 9, it can be seen that the maximum strengths for the two examples of composition are established for a similar elongation of about 20%.

FIG. 10 illustrates a graph for observing the maximum load that may be admitted by the nonwoven needle-punched panel 9 and, more generally, the horn 1 as a function of temperature, for the two examples of composition of this panel 9. that the shape of the curves is substantially identical and that at 150 ° C, the heating temperature of the needle-punched nonwoven panel 9 and more generally of the first assembly described with reference to FIG. 5, the maximum permissible load is here equal to about 300N for the first composition example (50% PLA) and equal to about 600N for the second composition example (80% PLA). It is observed that after this temperature of about 150 ° C., the maximum load drops for the two examples of composition. FIG. 11 illustrates, for its part, the acoustic properties of the nonwoven needle-punched panel 9 and, more generally, the roof panel 1 for a composition of this panel 9 corresponding to the first example (50% of PLA and therefore 50% of linen). FIG. 11 more particularly illustrates the sound absorption coefficient, in%, as a function of frequency, in Hz, which sound absorption coefficient is compared with a sound absorption limit reference. It is observed that the sound absorption coefficient is between about 10% and about 90% for a frequency ranging from 200Hz to about 6000Hz; and that the representative curve of the sound absorption of the panel 9 and more generally of the horn 1, between the aforementioned frequencies, is always above the limit reference (corresponding to the lower limit). In non-illustrated variants: the needle-punched nonwoven panel does not have exactly the same compositions, in mass percentage of flax fibers and in mass percentage of bicomponent polymer fibers, as those described above but different compositions as long as they remain in the intervals mentioned; Woven fabrics 7 and 8 sandwiching the needled nonwoven panel of the structure forming the body of the trim piece does not have quite the same composition as the needle-punched nonwoven panel itself (for example it is not not the same polymer fibers); - The structure forming the body of the trim piece is devoid of the woven 7 and 8 sandwiching the needle-punched nonwoven panel; the elements forming the raw material of the manufacturing method described with reference to FIG. 5 are not packaged in rolls but, for example, in strips; and / or - the lining piece is not a so-called louver piece configured to cover the roof of a motor vehicle, in the passenger compartment, but rather it is a piece of trim for a vehicle door or even for the dashboard. It is recalled more generally that the invention is not limited to the examples described and shown.

Claims (16)

REVENDICATIONS1. A trim piece for vehicles comprising a panel provided with natural plant fibers and polymer fibers comprising polylactic acid, characterized in that said panel is a needle-punched nonwoven panel (9), said natural plant fibers being lin (10) and said polymer fibers are bicomponent fibers (12) each having a core (13) formed by a first polylactic acid and a shell (14) formed by a second polylactic acid, which envelope is formed around said core (13); said first polylactic acid has a first melting temperature and said second polylactic acid has a second melting temperature lower than said first melting temperature; said needled nonwoven panel (9) is comprised of from about 15% to about 60%, by weight, of flax fibers (10) and from about 40% to about 85%, by weight, of bicomponent polymer fibers ( 12); and said needled nonwoven panel (9) has a mass crystallinity ratio of said bicomponent polymer fibers of from about 10% to about 40%. A lining piece according to claim 1, characterized in that said needled nonwoven panel (9) is composed of about 30% to about 55%, by weight, of flax fibers (10) and about 45% at about 70%, by weight, bicomponent polymer fibers (12), and said needled nonwoven panel (9) has a mass crystallinity ratio of said bicomponent polymer fibers (12) of from about 25% to about 40%. 3. Packing piece according to claim 2, characterized in that said needle-punched nonwoven panel (9) is composed of about 50% by weight of flax fibers (10) and about 50% by weight, bicomponent polymer fiber (12), and said needled nonwoven panel (9) has a mass crystallinity ratio of said bicomponent polymer fibers of about 36%. 4. lining piece according to any one of claims 1 to 3, characterized in that said first polylactic acid has a first melting temperature of between about 150 ° C and about 170 ° C said second polylactic acid has a second temperature of melting range from about 125 ° C to about 155 ° C. 5. Packing piece according to claim 4, characterized in that said first polylactic acid has a first melting temperature between about 155 ° C and about 165 ° C and said second polylactic acid has a second melting temperature equal to about 130 ° C. 6. Packing piece according to claim 5, characterized in that said first polylactic acid has a first melting point of about 158 ° C and a second melting point of about 165 ° C. Packing piece according to any one of claims 1 to 6, characterized in that said needle-punched nonwoven panel (9) has a tensile strength of between about 2 MPa and about 25 MPa for an elongation of about 5% at 25%, in length, of said needled nonwoven panel (9). 8. lining piece according to any one of claims 1 to 7, characterized in that it has an acoustic absorption coefficient of between about 10% and about 90% for a frequency of about 200Hz to about 6000Hz. 20 9. lining piece according to any one of claims 1 to 8, characterized in that it further comprises an appearance layer covering a face of said needled nonwoven panel (9). 10. Non-woven needle-punched panel for trim parts (1) for vehicles, characterized in that it comprises natural plant fibers and polymer fibers comprising polylactic acid, said natural plant fibers being flax fibers ( 10), said polymer fibers being bicomponent fibers (12) each having a core (13) formed by a first polylactic acid and a shell (14) formed by a second polylactic acid, which shell (14) is formed around said soul 30 (13); said first polylactic acid has a first melting temperature and said second polylactic acid has a second melting temperature lower than said first melting temperature; and said needled nonwoven panel (9) is comprised of from about 15% to about 60%, by weight, of flax fiber and from about 40% to about 85%, by weight, of bicomponent polymer fibers (12). The needled nonwoven panel according to claim 10, characterized in that said first polylactic acid has a first melting temperature of between about 150 ° C and about 170 ° C and said second polylactic acid has a second melting temperature of between at about 125 ° C and about 155 ° C, and / or preferably, said first polylactic acid has a first melting temperature of about 155 ° C to about 165 ° C and said second polylactic acid has a second equal melting temperature. at about 130 ° C, and / or more preferably, said first polylactic acid has a first melting point of about 158 ° C and a second melting point of about 165 ° C. 15 12. A nonwoven needle-punched panel according to one of claims 10 and 11, characterized in that said flax fibers (10) have an average diameter of between about 201.1m and about 200pm and an average length of between about 70mm and 110mm; and said bicomponent polymer fibers (12) have a mean diameter of from about 15ktm to about 30mm and average length from about 40mm to about 60mm. 13. A method of manufacturing a piece of packing according to any one of claims 1 to 9, characterized in that it comprises the following steps: - provide a needle-punched nonwoven panel (9) composed of about 15% at about 60%, by weight, of flax fibers (10) and from about 40% to about 85%, by weight, of bicomponent polymer fibers (12) each provided with a first polylactic acid having a first melting and a second polylactic acid having a second melting temperature, which second melting temperature is lower than said first melting temperature; - heating said needled nonwoven panel (9) for a first predetermined period of time; the latter reaches a predetermined temperature of between about 130 ° C and about 150 ° C; so as to completely or almost completely melt said second polylactic acid of said two-component polymer fibers (12) and to keep said first second polylactic acid of said two-component polymer fibers (12) unmelted or nearly unmelted; and compressing said prewoven nonwoven panel (9) preheated to a predetermined pressure of between about 50 bar and about 200 bar for a second predetermined period; whereby said needled nonwoven panel (9) is thermoformed and has a mass crystallinity ratio of said bicomponent polymer fibers (12) of between about 10% and about 40%. The method of claim 13, characterized in that said first predetermined period of heating said needled nonwoven panel (9) is between about 30s and about 60s and said pressure at which said needled nonwoven panel is compressed (9). preheated is between about 50bars and about 100bars. 15. Method according to one of claims 13 and 14, characterized in that said step of heating said needled nonwoven panel (9) is performed using heating platens (24) in contact with said needled nonwoven panel (9) and said step of compressing said needled nonwoven panel (9) is performed using cold molds (27). 16. Method according to one of claims 13 and 14, characterized in that said step of heating said needled nonwoven panel (9) is performed using an infrared lamp (123) and said step of compression of said needled nonwoven panel (9) is performed using cold molds (27).