EP4257743A1 - Method for the mechanical treatment of hemp for obtaining a moulding paste - Google Patents

Abstract

The process for preparing a cellulosic pulp suitable for molding uses hemp as the sole raw material. After fragmentation by grinding (50) of the hemp straw (10), typically including the leaves, a crushed raw material (1) is obtained with the unit fibers and the mixed hemp pieces. The raw material is wetted, and preferably steamed, so as to circulate a moistened hemp ground material (1'), with the fibers and pieces of hemp loaded with hot water, in a twin-screw extrusion line. Mechanical treatment, including extrusion (53), makes it possible to increase the quantity of fibers with the advantageous obtaining of fibers from hemp that are comparatively longer than the fibers already present in the crushed raw material. The transformation is mechanical, that is to say without chemical additives. The paste is structural, uniquely biosourced, and is used for molding (58) three-dimensional containers or products.

Description

Technical area

The present disclosure relates to the field of hemp valorization by mechanical treatment of industrial hemp. The invention relates more particularly to a mechanical process for preparing a paste whose constituents come from the whole hemp plant. It also relates to a paste directly obtained by this process, as well as a use of paste to manufacture a molded container suitable for food contact.

Prior art

The production of biosourced packaging too often uses fibers obtained from wood, which involves energy-intensive transport phases. Alternative productions can reduce this impact, in particular when it is possible to produce the raw plant material closer to the final place of marketing.

We know, from the document WO 9858119 , a process for the continuous preparation of paper pulp from lignocellulosic textile fibers and using a twin-screw extrusion line. During treatment, it is planned to separate the textile fibers and the rest of the plant, which amounts to a separation step to preserve the long fibers. This type of process thus generates a significant quantity of waste.

Generally in the field of paper production, it is known to produce a long fiber pulp by separating, during an extraction/separation step, the constituents of certain harvested plants having a heterogeneous composition. However, the prior isolation of long fibers, called defibration, generates a large amount of waste. In the case of hemp, the core (chènevotte) is considered waste, not recycled on the processing site in question. Furthermore, when wood is not used but a plant stem (such as hemp straw), the treatments involve chemical reactions.

The document FR 3015529 plans to optimize the use of lignocellulose material, including short fibers, for the production of paper pulp, through chemical-mechanical treatment, which involves in particular an alkaline hydroxide type additive, added during processing by a twin-screw extruder.

Furthermore, there are methods using plant fibers such as hemp which form constituents used in the composition of an underlayer of a plastic container. It is thus known, from the document CA 2947636 , to produce biodegradable food packaging, for example in the form of food trays, comprising a base, interior and exterior coating layers to ensure the required rigidity, using natural fibers and chemical additives. He is also known to perform injected plastic parts reinforced with flax or hemp plant fibers. Here too, only a specific part of the plant is used.

Conventional methods of producing relatively rigid molded articles require the use of exogenous polymer components, that is to say polymer components not originating from plant material containing cellulose fibers.

There is therefore a need for purely mechanical (thermo-mechanical) treatment methods, respectful of the environment and which minimize waste, to obtain a paste having good structural quality, allowing optimal valorization of annual plants.

Summary

• ladite matière brute consiste en de la paille de chanvre, avec les feuilles sans les racines, incluant ainsi la chènevotte ;
• la transformation est mécanique (purement de type thermo-mécanique), c'est-à-dire sans additif chimique, la matière étant introduite et mise à circuler dans une ligne d'extrusion.

In order to improve the situation, a process is proposed for transforming a biosourced fibrous raw material, to form a cellulosic pulp suitable for molding, with the particularity that:

• said raw material consists of hemp straw, with the leaves without the roots, thus including hemp;
• the transformation is mechanical (purely of the thermo-mechanical type), that is to say without chemical additives, the material being introduced and allowed to circulate in an extrusion line.

Almost the entire plant is used (the roots are usually not taken into account because they are left at the time of harvest), which makes it possible to avoid a leaf separation phase or a separation between layers of the stem. For example. The material to be processed according to this process is a raw material, so that the process requires neither the use of hemp exclusively in the form of hemp nor the exclusive use of hemp in the form of fibers (already individualized/flexible). The extrusion phase is adapted to obtain a single-source mechanical cellulosic pulp (coming only from hemp as harvested), which limits the material selection steps at the start and which avoids the use of chemistry during processing.

• un transfert du matériau brut broyé (par exemple à l'aide d'un doseur), dans la ligne d'extrusion, sachant que ledit matériau est humidifié pendant une étape d'humidification ;
• un traitement mécanique du matériau broyé et humidifié (intrant) pour augmenter la quantité de fibres, au cours duquel on peut réaliser simultanément un chauffage permettant un échauffement et/ou une vaporisation de l'eau contenue dans des pores des morceaux (décompactés) et une réduction des morceaux (décompactés), qui sont réduits entre deux vis parallèles de la ligne d'extrusion servant à faire circuler le matériau broyé et humidifié ; et
• une collecte, à une sortie de la ligne d'extrusion, d'une pâte défibrée (extrant).

After breaking up the entire hemp plant to obtain a crushed raw material including three mixed fractions consisting of a first fraction composed of fibers, a second fraction composed of dust, and a third fraction composed of pieces of hemp, the process comprises the following steps:

• a transfer of the crushed raw material (for example using a doser), into the extrusion line, knowing that said material is humidified during a humidification step;
• a mechanical treatment of the crushed and humidified material (input) to increase the quantity of fibers, during which heating can be carried out simultaneously allowing heating and/or vaporization of the water contained in the pores of the (decompacted) pieces and a reduction of (decompacted) pieces, which are reduced between two screws parallel to the extrusion line used to circulate the crushed and moistened material; And
• a collection, at an exit from the extrusion line, of a defibrated pulp (output).

The process advantageously combines grinding and humidification which makes it possible to limit the size of the pieces and to decompact them without chemical action. The pieces are for example crushed to limit their maximum length below a threshold, for example with a maximum length of one or a few centimeters: the different constituents are mixed in the crushed material and are suitable for extrusion. The humidification is carried out for a sufficient duration to decompact the pieces of hemp using water vapor, the humidification step being preferably carried out before introduction into the extrusion line.
The crushed/shredded material can be 100% biosourced.

According to one particular feature, the humidification step (52) uses water vapor after a prior wetting phase, the humidification step (52) being carried out before introduction into the extrusion line (4). ).

With such chemical-free pre-treatment, it is possible to avoid effluent management (without unwanted discharges), while the defibration yield in the extrusion line is significant/increased. A better compromise can be reached between obtaining fibers that are not too short (not too cut) and reducing the small pieces of hemp, capable of providing long fibers (> 0.8 mm after extrusion) . The heating induced by the mechanical action of the screws of the extrusion line, possibly supplemented by a thermal transfer in a sheath housing these screws, can also effectively soften the pieces of hemp to facilitate the progressive release of fibers on the edges. pieces, with the rise in water temperature (typically vaporized). Softening and the decompaction effect allow the fibers to be less linked together before the mixing, shearing and compression phases when such pre-treatment has been carried out upstream of extrusion and at least upstream of the sections of mechanical action allowing fibrillation of the pieces of the third fraction.

According to one particular feature, the water vapor is used to decompact the pieces of hemp already loaded with water during a soaking step (penetration phase already carried out by this soaking), so as to achieve degradation of hydrophilic components such as pectins of the plant (start of steam degumming effect) to initiate extraction and separation of the unitary hemp fibers from the pieces of hemp. Concretely, pretreatment by contact with water then with water vapor makes it possible to decompose and/or extract pectic substances binding the fibers to the plant. Such pretreatment contributes to the beginning of progressive separation of the fiber bundles from the tissues of the stem and the cohesion between the fibers is reduced. Mechanical treatment can then finalize this separation, by removing the fibers from the blocks/pieces.

It is for example planned to steam the crushed and quenched material with water vapor, typically for more than approximately 5 or 10 minutes, for example for a period of less than 60 or 90 minutes, in order to avoid degrading the mechanical properties of fibers by hydrolysis and/or dissolving too much material (loss of mass).

It has been observed experimentally that humidification and the absence of chemicals (absence of sodium hydroxide for example or similar alkaline hydroxide) can correspond to a controlled pre-treatment in order to obtain individualized fibers from unitary fibers of the first fraction. In addition, this control can allow the use of water vapor at a limited temperature, close to 100°C and not exceeding 130°C, so that any phenomenon of steam explosion is avoided: by preventing this phenomenon (exacerbated when using a chemical product), we limit the appearance of pieces playing a negative role on the distribution of fiber lengths.

The temperature can be controlled, at the level of the introduction of crushed material and/or by a sheath housing the two screws, so that the temperature remains below 125 or 130°C. For example, a set temperature of between 105 and 115°C can be set for the thermoregulated sheath.

The increase in the number of individual fibers corresponds to the reduction, in number and size, of hemp pieces containing cellulosic material. Additionally, it may be permitted to increase an average fiber length. Heating makes the process in the extrusion line effective in improving the structural characteristics of the water-laden hemp pulp. With such a process, it is possible to produce a structural paste, resulting from a thermo-mechanical treatment only, which makes it possible to avoid the use of chemicals and the treatment of liquid effluents without discarding a significant quantity of biomass from the treatment.

Surprisingly, extrusion transforms the heterogeneous mixture of fibers (already individualized) and pieces of millimeter or centimeter sized hemp into a mixture of fibers which can become entangled in an interconnected three-dimensional structure. Thanks to the improvement in the strength and stability of this paste, it can be used to mold a three-dimensional packaging unit, such as a tray, a bowl, an egg packaging unit or any other packaging.

The humidification step makes it possible to wet the raw material (for example with a diffuser), and the elimination of the water takes place without entrainment of exogenous compounds (not from the plant) such as chemical agents. . The humidification step (wetting/steaming), whether carried out entirely before extrusion or at least partly during extrusion, serves to obtain a material with a humidity level greater than 60 or 70%, for example example of the order of 75%, at the entrance to the active sections of the extrusion line (active sections for shearing, accumulation, compression, mixing or mechanical action). In variants, an addition of water, for example proportional to the hemp flow dry ground, can be produced in a feed part towards the extrusion line. Optionally, a steaming effect can be achieved at such a location.

• une zone d'accumulation du matériau humidifié ; et
• une zone de compression du matériau humidifié, adjacente à la zone d'accumulation.

According to a particular feature, all of the moistened ground material circulates between the two screws, co-rotating (that is to say rotating in the same direction of rotation), which belong to a twin-screw extruder, the two screws delimiting between they several treatment sections, of which at least one section has:

• a humidified material accumulation zone; And
• a compression zone of the humidified material, adjacent to the accumulation zone.

The mechanical treatment may include an extrusion step using a twin-screw extruder, in a sheath which is temperature regulated. This type of extrusion can allow a regular supply and flow rates can thus be increased. Mixing is much more efficient than with single-screw extrusion, and the homogeneity of the dough is ensured.

• le broyage est réalisé à une vitesse inférieure ou égale à 150 ou 200 tours/min.
• la vitesse de l'élément de contact (appartenant au broyeur) en contact avec la paille peut être de 100 à 200 mètres par minute ; c'est une vitesse qui ne génère pas trop de poussières (sachant que le diamètre du rotor du broyeur peut être optionnellement de 50 à 60 cm).
• compte tenu de l'hétérogénéité des parties constitutives de la plante de chanvre et la présence de poussières, le broyage est contrôlé en évitant de générer des effets de poussières/effets destructeurs des fibres, ce qui peut impliquer de limiter la durée de broyage et/ou la vitesse de rotation d'un arbre de contact avec le matériau, appartenant au broyeur (limitation de la vitesse de rotation de broyeur à couteaux/déchiqueteuse ou appareil similaire de réduction de la taille des composants du matériau brut).
• le morcellement/broyage est contrôlé pour s'opposer à une dégradation des fibres de la première fraction, en limitant une vitesse de rotation d'un arbre d'un broyeur en dessous d'un seuil prédéterminé, qui est de préférence inférieur ou égal à 200 tours/min (ou moins de 200 mètres par minute à une extrémité radiale du rotor du broyeur).
• le broyage est paramétré pour limiter la réduction excessive engendrant de la perte de matières (par exemple, on peut éviter un broyage à couteaux à vitesse élevée comme 1000 ou 1500 tours/min, générateur de poussières).
• le broyage/déchiquetage est réalisé, optionnellement par un broyeur ou déchiqueteur à recycler du plastique, ce déchiquetage étant du type à basse vitesse (par exemple 80 tours/min).
• une vitesse de rotation pendant l'étape de broyage et/ou coupe est comprise entre 55 et 100 tours/min.

In pretreatment options, a ground raw material can be obtained using one or more of the following measures:

• grinding is carried out at a speed less than or equal to 150 or 200 rpm.
• the speed of the contact element (belonging to the crusher) in contact with the straw can be 100 to 200 meters per minute; it is a speed which does not generate too much dust (knowing that the diameter of the crusher rotor can optionally be 50 to 60 cm).
• taking into account the heterogeneity of the constituent parts of the hemp plant and the presence of dust, the grinding is controlled by avoiding generating dust effects/destructive effects of the fibers, which may involve limiting the grinding duration and/or or the rotation speed of a material contact shaft belonging to the crusher (limiting the rotation speed of a knife mill/shredder or similar device for reducing the size of components of the raw material).
• the fragmentation/grinding is controlled to prevent degradation of the fibers of the first fraction, by limiting a rotation speed of a shaft of a crusher below a predetermined threshold, which is preferably less than or equal to 200 rpm (or less than 200 meters per minute at one radial end of the mill rotor).
• the grinding is configured to limit the excessive reduction causing loss of materials (for example, we can avoid grinding with knives at high speeds such as 1000 or 1500 rpm, which generates dust).
• the grinding/shredding is carried out, optionally by a crusher or shredder to recycle plastic, this shredding being of the low speed type (for example 80 rpm).
• a rotation speed during the grinding and/or cutting step is between 55 and 100 rpm.

• une étape d'extraction et évacuation d'eau et de composants extractibles dissous dans l'eau, séparément de la pâte défibrée, lors du traitement mécanique dans la ligne d'extrusion (des substances pectiques et la lignine, présente en faible quantité dans la mesure où le chanvre est une plante pauvre en lignine, font typiquement partie des composant extractibles/extrais avec l'eau évacuée).
• les vis sont co-rotatives, par exemple interpénétrantes au moins dans certaines parties, en ayant des profils conjugués (au moins dans la ou les zones de compression).
• l'étape de traitement mécanique, dans la ligne d'extrusion est adaptée pour faire passer la masse de fibres individualisées issues de la chènevotte d'un pourcentage en masse sèche inférieur à 3 ou 5% (en référence à la masse totale de fibres individualisées), dans le matériau brut broyé humidifié et soumis à un étuvage (avant ce traitement mécanique), à un pourcentage en masse sèche supérieur ou égal à 35%, de préférence supérieur ou égal à 45% (par exemple entre 48 et environ 60%) ; ainsi, le traitement augmente la quantité de fibres, sachant que la chènevotte représente généralement entre 50 et 60% de la masse sèche de paille de chanvre formant le matériau brut de départ, et apporte en outre une amélioration qualitative dans la mesure où les fibres initialement contenues dans la troisième fraction peuvent constituer des fibres individualisées plus longues.
• une température de consigne inférieure ou égale à 115 ou 120°C (et typiquement supérieure à 100°C) est utilisée pour un fourreau thermorégulé qui enveloppe/loges les deux vis.
• l'étape d'extrusion est réalisée sans adjonction d'eau ou de vapeur (ceci peut permettre d'éviter des effet de hausse locale de température).
• une même vitesse de rotation des axes est paramétrée, avec un même sens de rotation, la vitesse étant choisie par exemple entre 300 et 750 ou 1000 tours/min, plus particulièrement entre 350 et 700 tours/min.
• l'étape de traitement mécanique utilise des contre-filets dans les vis de l'extrudeuse, par exemple avec une taille caractéristique de rainure, dans les contre-filets, qui se réduit en passant d'un premier tronçon à contre-filets à un deuxième tronçon à contre-filets.
• les contrefilets sont disposés de façon interpénétrante dans chaque tronçon à contrefilets.
• le deuxième tronçon est séparé du premier tronçon par une section de convoyage ou par plusieurs sections intermédiaires dont une section de convoyage.
• il est prévu un troisième tronçon séparée du deuxième tronçon par une autre section de convoyage ou par plusieurs sections intermédiaires dont une autre section de convoyage.
• les deux vis de la ligne d'extrusion peuvent inclure chacune un ou plusieurs organes malaxeurs (par exemple de type monolobe ou bilobe par exemple).
• les organes malaxeurs sont disposés chacun en aval (par exemple moins de 10 ou 15 cm plus en aval), suivant le sens de circulation de la matière dans la ligne d'extrusion, d'un tronçon à contre-filets.

In the process options, one or more of the following features can be used:

• a step of extraction and evacuation of water and extractable components dissolved in water, separately from the defibrated pulp, during mechanical treatment in the extrusion line (pectic substances and lignin, present in small quantities in the since hemp is a plant poor in lignin, are typically part of the extractable components/extracted with the water evacuated).
• the screws are co-rotating, for example interpenetrating at least in certain parts, having combined profiles (at least in the compression zone(s).
• the mechanical treatment step, in the extrusion line, is adapted to pass the mass of individualized fibers from hemp with a dry mass percentage of less than 3 or 5% (with reference to the total mass of individualized fibers ), in the crushed raw material moistened and subjected to steaming (before this mechanical treatment), at a percentage by dry mass greater than or equal to 35%, preferably greater than or equal to 45% (for example between 48 and approximately 60% ) ; thus, the treatment increases the quantity of fibers, knowing that hemp generally represents between 50 and 60% of the dry mass of hemp straw forming the raw starting material, and also provides a qualitative improvement to the extent that the fibers initially contained in the third fraction can constitute longer individualized fibers.
• a set temperature less than or equal to 115 or 120°C (and typically greater than 100°C) is used for a thermoregulated sheath which envelops/houses the two screws.
• the extrusion step is carried out without the addition of water or steam (this can help avoid local temperature rise effects).
• the same speed of rotation of the axes is configured, with the same direction of rotation, the speed being chosen for example between 300 and 750 or 1000 rpm, more particularly between 350 and 700 rpm.
• the mechanical processing step uses counter-threads in the screws of the extruder, for example with a characteristic groove size, in the counter-threads, which reduces when passing from a first section with counter-threads to a second section with strip fillets.
• the sirloins are arranged interpenetratingly in each sirloin section.
• the second section is separated from the first section by a conveyor section or by several intermediate sections including a conveyor section.
• a third section is provided separated from the second section by another conveying section or by several intermediate sections including another conveying section.
• the two screws of the extrusion line can each include one or more mixing members (for example of the monolobe or bilobe type for example).
• the mixing members are each arranged downstream (for example less than 10 or 15 cm further downstream), following the direction of circulation of the material in the extrusion line, of a section with counter-threads.

According to one particular feature, the humidification step has a sufficient duration to decompact the pieces of hemp using water vapor, the humidification step being preferably carried out before introduction into the extrusion line. The duration of humidification can be broken down into a first duration for soaking, greater than 200 minutes for example, and a second duration for a steaming stage (by controlling the temperature so that it is as close as possible of 100°C, for example below 105°C or 110°C).

The humidification step can pass the ground material from a drying state corresponding to a first dryness, for example between 75 and 95%, to a humidified state corresponding to a second dryness of less than 40%, preferably comprised between 20 and 35%. The humidification step can pass through a first stage/humidified state without heating effect, for example at the end of a soaking step in a diffuser, before reaching the final humidified state with the second dryness, in a steam heated state.

• l'étape d'humidification inclut une phase de trempage suivie d'une phase d'étuvage, et/ou une mise en contact du matériau broyé avec de l'eau de trempage pendant une durée d'au moins 200 minutes, de préférence comprise entre 250 et 1000 minutes, dans un diffuseur incluant une cuve équipée d'un filtre, de préférence sous la forme d'une grille.
• un obturateur est déplacé d'une position de fermeture à une position d'ouverture d'un passage d'évacuation prévu dans une partie de fond de la cuve, afin de permettre une évacuation de l'eau de trempage en retenant ledit matériau dans la cuve à l'aide du filtre.
• l'étuvage peut être réalisée après une phase d'élimination d'eau, éventuellement par évacuation de cette eau via une sortie de drainage prévue dans la cuve de trempage (diffuseur). Après trempage, en ouvrant l'accès la sortie/l'évacuation, il est permis d'éliminer l'eau et récupérer les particules sans perte solide (ou tout du moins sans perte significative dans le but recherché, la matière dissoute n'étant d'aucune utilité par exemple).
• l'air présent dans les particules/morceaux peut être chassé lors de l'étape d'humidification, par exemple lors de l'étuvage.
• l'étape d'humidification est réalisée pour permettre une imprégnation en eau homogène dans le mélange à traiter mécaniquement dans l'étape ultérieure utilisant la ligne d'extrusion.
• la cuve peut être équipée d'une grille très fine, dont la taille des mailles de passage est inférieure ou égale à 10 micromètres.

In implementation options, the humidification step may have one or more of the following particularities:

• the humidification step includes a soaking phase followed by a steaming phase, and/or bringing the ground material into contact with soaking water for a period of at least 200 minutes, preferably comprised between 250 and 1000 minutes, in a diffuser including a tank equipped with a filter, preferably in the form of a grid.
• a shutter is moved from a closed position to an open position of an evacuation passage provided in a bottom part of the tank, in order to allow evacuation of the soaking water by retaining said material in the tank using the filter.
• the steaming can be carried out after a water elimination phase, possibly by evacuating this water via a drainage outlet provided in the soaking tank (diffuser). After soaking, by opening access to the outlet/evacuation, it is possible to eliminate the water and recover the particles without solid loss (or at least without significant loss for the intended purpose, the dissolved material not being of no use for example).
• the air present in the particles/pieces can be expelled during the humidification step, for example during steaming.
• the humidification step is carried out to allow homogeneous water impregnation in the mixture to be treated mechanically in the subsequent step using the extrusion line.
• the tank can be equipped with a very fine grid, the size of the passage mesh of which is less than or equal to 10 micrometers.

In the present description, the term diffuser is designated here as any equipment allowing hemp to be soaked with water by blocking an orifice or outlet access (for liquid) while having a filter for drainage. One or more tanks can be part of a diffuser. Optionally, the diffuser can be part of a transfer part to an oven or steaming equipment.

Typically, the humidification step and the extrusion step follow one after the other. More generally, there is no intermediate drying between the end of the humidification step, for example at the end of steaming, and introduction into the extrusion line. Optionally, a humidity maintenance phase, for example in a confined state limiting the circulation of air likely to dry the material, can be planned if the crushed and humidified (steamed) material is placed on hold for several hours before the introduction into the extrusion line.

According to one particular feature, a refining step is carried out from the material having undergone the mechanical treatment step (treatment in the extrusion line), in order to obtain more fibers.

• pâte défibrée est introduite dans un raffineur incluant au moins une paire de disques,
• le raffineur est utilisé lors d'une étape de raffinage au cours de laquelle une vitesse de rotation relative entre deux disques appariés dans le raffineur (pour permettre un raffinage) est comprise entre 1000 et 5000 tours/minute.
• le type raffineur utilisé est sélectionné pour un effet de fibrillation (le raffinage est réalisé en vue d'obtenir la fibrillation des fibres tout en minimisant la coupe des fibres).
• le raffinage est limité de façon à obtenir un indice d'égouttage du standard CSF supérieur à 200 mL, de préférence compris entre 230 et 460 mL.
• le traitement mécanique est réalisé, sans additif chimique, de façon qu'au moins 98% ou 99% des particules ou morceaux résiduels de chènevotte contenus dans la pâte défibrée collectée, qui ne constituent pas des fibres flexibles/individualisées, ont une longueur maximale inférieure ou égale à 2 mm. Typiquement, la pâte collectée peut ne plus contenir de morceaux de chènevotte de taille supérieure au millimètre.
• préférentiellement dans la pâte collectée, les particules rigides et/ou plus épaisses que des fibres de chanvre individualisées (particules ne constituant pas des fibres flexibles) sont toutes de taille submillimétrique ou ne dépassant pas 2 mm.

In the options for the refining stage, one or more of the following features are provided:

• defibrated pulp is introduced into a refiner including at least one pair of discs,
• the refiner is used during a refining step during which a relative rotational speed between two paired discs in the refiner (to allow refining) is between 1000 and 5000 rpm.
• the type of refiner used is selected for a fibrillation effect (refining is carried out with a view to obtaining fibrillation of the fibers while minimizing fiber cutting).
• the refining is limited so as to obtain a freeness index of the CSF standard greater than 200 mL, preferably between 230 and 460 mL.
• the mechanical treatment is carried out, without chemical additives, so that at least 98% or 99% of the particles or residual pieces of hemp contained in the collected defibrated pulp, which do not constitute flexible/individualized fibers, have a lower maximum length or equal to 2 mm. Typically, the collected paste may no longer contain pieces of hemp larger than a millimeter.
• preferably in the collected paste, the rigid particles and/or thicker than individualized hemp fibers (particles not constituting flexible fibers) are all of submillimeter size or not exceeding 2 mm.

Independently or in combination of the above, the mechanical treatment step can be an extrusion step carried out by setting a useful length and/or a rotation speed of the two parallel screws in order to obtain, for the collected defibrated dough, a drainage index of the CSF standard of between 200 mL and 500 mL (between 230 and 460 mL for example).

In the case of refining, the latter can be carried out to lower the freeness index of the CSF standard by a reduction value of between 40 and 200 mL, for example between 60 and 150 mL. Regardless of the lowering of this index, the refining can be light to avoid cutting the fibers already obtained which have satisfactory quality/aptitude for inter-fiber bonds.

• des bûchettes de taille submillimétrique (fins morceaux allongés/en forme de micro-bâtonnets, à base de chènevotte) sont présentes dans la pâte défibrée collectée et/ou la pâte se caractérise par la présence de fibres et de morceaux fibreux de chènevotte de taille caractéristique submillimétrique.
• le procédé comprend une étape de classage pour séparer des bûchettes restant dans la pâte collectée et/ou une étape de raffinage, permettant de transformer les bûchettes en fibres.
• l'étape de classage permet optionnellement d'éliminer, dans la pâte défibrée collectée, les bûchettes issues de la chènevotte et de les retourner à l'extrudeuse/ligne d'extrusion en vue de les réduire.
• l'étape de classage peut permettre de fibriller les fibres déjà individualisées. Des fibres de longueur supérieure ou égale à 2,5 mm sont présentes dans la pâte défibrée collectée.
• la pâte récupérée/collectée à la sortie de la ligne d'extrusion ou sortant d'une étape de classage est soumise à au moins une étape de raffinage.
• une étape de séparation de morceaux peut être réalisée, par classage ou par sélection adaptée, afin de rejeter des particules de taille supérieure à une limite prédéterminée, de préférence de taille supérieure à 3 mm.
• le procédé peut inclure une étape de remise en circulation, dans la ligne d'extrusion par introduction dans le doseur, optionnellement après une étape additionnelle de coupe et/ou broyage, de morceaux de la troisième fraction récupérées dans la ligne d'extrusion après ladite étape de traitement mécanique.

In the options for carrying out the process, one or more of the following aspects can be provided:

• submillimeter-sized logs (thin elongated/micro-stick-shaped pieces, made from hemp) are present in the collected defibrated dough and/or the dough is characterized by the presence of fibers and fibrous pieces of hemp of characteristic size submillimeter.
• the process comprises a classification step to separate the logs remaining in the collected pulp and/or a refining step, making it possible to transform the logs into fibers.
• the classification step optionally makes it possible to eliminate, in the collected defibrated dough, the logs from the hemp and return them to the extruder/extrusion line in order to reduce them.
• the classification step can make it possible to fibrillate the already individualized fibers. Fibers of length greater than or equal to 2.5 mm are present in the collected defibrated pulp.
• the paste recovered/collected at the exit of the extrusion line or leaving a classification step is subjected to at least one refining step.
• a step of separating pieces can be carried out, by classification or by adapted selection, in order to reject particles of size greater than a predetermined limit, preferably of size greater than 3 mm.
• the process can include a step of recirculating, in the extrusion line by introducing into the dispenser, optionally after an additional step of cutting and/or grinding, pieces of the third fraction recovered in the extrusion line after said mechanical processing stage.

In embodiments limiting the total number of operations, the humidification step and the extrusion step follow one after the other (without intermediate drying for example), and these two consecutive steps allow to produce a quality structural pulp, so that an additional processing step that would reduce fiber length is not necessary. If it is necessary to eliminate logs, a simple classification is sufficient: classifying the paste makes it possible to separate the large elements (here the pieces/logs from the third fraction), also eliminating heavy impurities (sand, solid dust) in a purification line.

According to one particular feature, the collected defibred pulp is used, preferably after a purification step by rinsing and/or filtration, as pulp in a molding step in a mold in order to obtain a three-dimensional container. The molding step may involve heating (to more than 50°C) which does not degrade the pulp, for example brief heating (less than 5 or 10 minutes) and/or not exceeding 190°C or 220°C, preferably below 170°C. This molding can be carried out in a mold with a mobile pressing member or in an injection mold.

According to one aspect of the present disclosure, the fiber pulp obtained by the process can be used as a molding material, this material being able to flow hot without structural alteration of the fibers below a temperature threshold, for example at a molding temperature between 50 and 170°C.

In an example of application, a plate layer, for example of substantially constant thickness, is obtained by a first shaping of a pasty material consisting of the collected defibrated pulp or of a purified paste obtained from the collected defibrated dough. The purified paste can optionally be obtained after a classification step and/or a refining step.

During a second shaping, the plate layer can be deformed/modified, for example by compression and/or stretching in a mold to obtain all or part of a three-dimensional container, preferably forming a food package.

In an example of application, a pasty material consisting of the collected fiber pulp or of a purified pulp obtained from the collected fiber pulp, after a classification step and/or a refining step, is injected into a mold to obtain all or part of a three-dimensional container, preferably forming a food package.

In options without recourse to refining, the collected defibrated pulp can be subjected to a classification operation in one or more classification devices. Optionally, the rejects from the classification operation are subjected to additional mechanical treatment allowing defibration. For example, these rejects are subjected to defibration in at least one mechanical action device chosen from a refiner, a crusher or equivalent system, or the extrusion line. A hammer mill or a knife mill can be used (if a grinder without recycling is used in the extrusion line, the grinding provides additional defibrated material which can be recycled upstream of the processing device(s). ranking).

According to one particular feature, a step of sterilization of the collected defibrated dough is provided, during a forming step, for example by thermoforming at a temperature between 130 and 160°C, for example around 140°C.

The process provides for heating above 100°C, for example without exceeding a threshold of 121°C, both during the humidification step and during the mechanical treatment step in the extrusion line.

According to another aspect, a hemp paste obtained by the process according to the invention is proposed. The paste collected at the exit of the extruder, possibly after mechanical post-treatment such as classification and/or refining, is advantageously usable/used for the production of a three-dimensional part, for example a container, during a shaping step with heating/cooking of the dry material. The shaping may consist, by way of non-limiting example, of injection molding, molding by pressing, or an additive technique (3D printing, for example by depositing the paste in the form of a filament).

Brief description of the drawings

• La Figure 1 illustre un diagramme d'étapes utilisables dans un procédé conforme à un mode de réalisation.
• La Figure 2 montre schématiquement des sections d'une extrudeuse utilisable dans la mise en oeuvre du procédé d'obtention d'une pâte structurelle de chanvre.
• La Figure 3 illustre un détail d'un tronçon de traitement mécanique au sein d'une extrudeuse participant à une étape de traitement mécanique, contribuant au défibrage de morceaux de chènevotte humidifiés qui font partie du matériau broyé introduit dans l'extrudeuse.
• La Figure 4A et la Figure 4B illustrent, respectivement et de façon schématique, des stades de mise en forme pour la production d'un contenant moulé en trois dimensions, à partir d'une pâte défibrée obtenue par un procédé conforme à l'invention, la pâte ayant subi éventuellement un raffinage.
• La Figure 5A et la figure 5B illustrent deux vues, respectivement avant et après une opération de mise en forme, représentatives d'une opération de moulage utilisant une plaque mince pouvant être constituée de la pâte obtenue selon un procédé conforme à l'invention.
• La Figure 6 et une vue en perspective d'un raffineur, utilisable pour un raffinage à haute consistance ou à basse consistance, et permettant ainsi de transformer, dans la pâte collectée en sortie d'extrudeuse, certains morceaux en fibres, en fibrillant en outre les fibres déjà individualisées.

Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the appended drawings, in which:

• There Figure 1 illustrates a diagram of steps usable in a method according to one embodiment.
• There Figure 2 schematically shows sections of an extruder usable in the implementation of the process for obtaining a structural hemp paste.
• There Figure 3 illustrates a detail of a mechanical treatment section within an extruder participating in a mechanical treatment step, contributing to the defibration of moistened hemp pieces which form part of the crushed material introduced into the extruder.
• There Figure 4A and the Figure 4B illustrate, respectively and schematically, shaping stages for the production of a three-dimensional molded container, from a defibrated pulp obtained by a process according to the invention, the pulp having optionally undergone refining .
• There Figure 5A and the Figure 5B illustrate two views, respectively before and after a shaping operation, representative of a molding operation using a thin plate which can be made up of the paste obtained according to a process according to the invention.
• There Figure 6 and a perspective view of a refiner, usable for high consistency or low consistency refining, and thus making it possible to transform, in the paste collected at the extruder outlet, certain pieces into fibers, by further fibrillating the fibers already individualized.

Description of embodiments

Several examples of non-limiting embodiments are presented below in detail. In the different figures, identical references indicate identical or similar elements.

As illustrated on the figure 1 , a certain number of steps can take place to transform the hemp plant, here in the form of a stem with leaves, into structural paste. The treatment process, mechanical and without the use of chemical additives, makes it possible to prepare a malleable and formable paste, which can be used as a molding substance in packaging applications or other applications using the strength of the cellulosic fibers obtained from hemp, for example in the textile field, construction, the automotive or aeronautics field (if necessary by being combined with other materials), and certain other fields by replacing polymer structures of fossil origin.

It should be noted, as visible on the figure 1 , that apart from the water used in a humidification step 52, the dough capable of being shaped uses only hemp, here hemp straw 10, as raw material. The supply of this hemp (also called industrial hemp) corresponds to a harvested product, typically after drying (possibly natural in the field): the raw material is thus purely from agriculture. In practice, this material can decompose into fibers, dust and hemp: these components thus form three respective fractions present in the hemp used in the transformation/preparation process described here. The fibers typically represent 20 to 35% by weight of the hemp straw 10, while the hemp can represent 55 to 60% by weight of this straw. The dust contained in the plant can correspond to the complement (between 10 to 15% of the weight).

• une réduction mécanique en taille de la paille (ce qui implique la coupe ou morcellement des tiges) afin d'obtenir des morceaux de taille n'excédant pas un seuil, par exemple ne dépassant pas une dimension maximale de 2, 3, 5 ou 10 centimètres pour au moins 99% en poids de la matière solide, cette réduction formant un pré-traitement mécanique incluant au moins une étape (50, 51) de broyage et/ou découpe de la paille de chanvre 10 ; et
• un traitement mécanique, sans addition de produit chimique, pour augmenter la quantité de fibres, avec conversion au moins partielle des morceaux de chènevotte en fibres, dans une ligne d'extrusion 4.

The transformation/preparation process for obtaining a paste, in accordance with the invention, comprises in particular two main stages:

• a mechanical reduction in size of the straw (which involves cutting or breaking up the stems) in order to obtain pieces of size not exceeding a threshold, for example not exceeding a maximum dimension of 2, 3, 5 or 10 centimeters for at least 99% by weight of the solid material, this reduction forming a mechanical pre-treatment including at least one step (50, 51) of grinding and/or cutting the hemp straw 10; And
• a mechanical treatment, without the addition of a chemical product, to increase the quantity of fibers, with at least partial conversion of the pieces of hemp into fibers, in an extrusion line 4.

The process is typically thermo-mechanical, allowing heating of the crushed raw material 1 which includes the three mixed fractions. The extrusion line 4 intervenes during a dough production phase. Heating can be carried out during this production phase but also, for example in a context of wetting and/or steaming, before this production phase, in particular in order to make the pieces of hemp hemp easier to defiber.

Humidification of the ground material or raw material reduced to pieces is carried out, which can make it easier to convert the pieces of hemp into fibers, when passing through the extrusion line 4, in combination with maintaining a temperature beyond a threshold, for example greater than or equal to 100°C, in the circulation zone of the humidified ground material 1' within the extrusion line 4.

In all that follows, the crushed material before humidification is called crushed raw material 1. No chemical additive is used in obtaining the crushed raw material 1, so that the mass composition of the solid part of the crushed raw material 1 can be the same as in straw 10. In other words, there is no loss of solid material nor need for a component selection step. And, preferably, there is no need for mixing with an additional component either.

Obtaining crushed raw material

Step 50 of grinding the hemp plant can be carried out in such a way as to preserve the structural quality of the fibers (first fraction) already present. A knife mill or similar grinder operating in a dry manner, suitable for a fibrous product, can be used in this step 50, in order to fragment the starting material (by reducing the size of the constituents) without generating crushing and without modifying the composition . In the crushed raw material 1, the hemp is thus fragmented into multiple pieces of hemp. The crushed raw material is more easily used in subsequent stages such as the humidification stage 52 and the extrusion stage 53 carried out using an extrusion line 4 with two screws 14, 15, as in the non-limiting case shown on the Figure 3 .

In reference to the figure 1 , after step 50 which can optionally be carried out as close as possible to the harvest site, there is for example a step of verifying that the constituent elements of the crushed hemp do not contain elements whose length exceeds a threshold, for example going beyond 20 or 30 mm. A measurement or detection, where appropriate using a camera or a similar analyzing device, can make it possible to detect such elements longer than the predefined or configured threshold.

If such elements considered too long are detected, an additional reprocessing step can be carried out, without loss of material. For example, the material to be reprocessed is introduced into a crusher equipped with a grid preventing the passage of large elements, for example a grid with holes whose size is chosen close to or equal to the following values: 0.25 / 0.50 / 0.75 / 1.0 / 1.50 cm. The holes can be round, oblong, trapezoidal, rectangular, square or polygonal in section. More generally, we understand that the optional reprocessing can correspond to a cutting phase or step 51, making it possible in particular to cut and thus reduce the length of the longest elements in the raw material which brings together the three aforementioned fractions.

In general, the dryness of crushed and/or cut hemp at this stage (crushed raw material 1) can be in the range between 75 and 94%. The crushed raw material 1 in this form can, if necessary, be packaged in a compact manner and transported to a production site, including in particular an extrusion line 4, in particular a twin-screw extruder during a phase of production which will be described below.

Experimental example : Preparation of a sufficiently crushed raw material

Here, the lignocellulosic material comes only from hemp, more precisely from the harvested part 10 (without the roots) excluding hemp or hemp seeds, called here hemp straw and which includes the leaves of the plant. In this example, a batch of 80 kg of crushed hemp 1 was prepared using a knife grinder. This hemp constitutes a raw material, having a dryness of 85.1%.

A preliminary step may consist of checking that the constituent elements of the batch of crushed hemp do not contain elements whose length exceeds a threshold, for example example a threshold greater than or equal to 20 or 30 mm. In the example considered, the crushed hemp received had elements considered too long. This hemp was therefore reprocessed with a Pallman ^® knife mill equipped with a grid of holes, for example 10 mm in diameter. This reprocessing can correspond to step 51 as illustrated in the embodiment of the figure 1 .

Other processing before production

• une phase de trempage ;
• puis une phase d'étuvage.

The process uses water and involves heating the humidified raw material 1'. In one embodiment option, it is possible to plan to subject the crushed raw material 1 to a humidification step 52 or any type of water addition, which can take place in two phases:

• a soaking phase;
• then a steaming phase.

In an embodiment compatible with the case illustrated in the figure 1 , the soaking phase consists of bringing the crushed raw material 1 into contact with soaking water for a relatively long period, for example comparatively longer than the grinding step 50 and longer than the step 53 of extrusion, for a given quantity of material to be processed. This soaking duration is possibly greater than a suitable threshold, preferably between 250 and 1000 minutes.

The soaking phase can be carried out in a diffuser which is suitable for preserving solid materials of plant origin (from the hemp plant). For this, the diffuser can include a tank equipped with a filter, preferably in the form of a grid. Using a movable shutter, for example moved from a closed position to an open position to free an evacuation passage provided in a bottom part of the tank, it is permitted (at the end of the soaking) to evacuate the soaking water by retaining the material in the tank, using the filter.

The humidification step 52 typically has a duration sufficient to decompact the pieces of hemp. This can be facilitated with heat, using water vapor, for example formed during the steaming phase. In the non-limiting case of the figure 1 , we have illustrated a humidification step 52 carried out before introduction into the extrusion line 4. In variants, the use of liquid water and/or water vapor can continue or can begin during the extrusion step 53.

The humidification step 52 can pass the ground material from a drying state corresponding to a first dryness, between 75 and 95%, to a humidified state corresponding to a dryness less than 40%, for example between 20 and 35%. In embodiment options, the humidification step 52 can be provided at the stage of harvesting and packaging the raw material. For example, step 52 can be provided before or during a step 50 and/or 51 allowing the reduction in size to constitute the humidified raw material.

In a variant embodiment, compatible with or independent of prior humidification, an addition of water can be carried out during dosing in an extruder and/or during the extrusion step 53 in order to obtain suitable dryness, for example less than 40 or 50%. Typically, as detailed below, the extrusion step 53 is applied by heating a ground material loaded with water, therefore by heating the water in this material.

Production of a dough

In reference to the figure 2 , a defibrated paste 3 is obtained after mechanical treatment phases, in an extrusion line 4. After a transfer and a step 41 of feeding the crushed raw material, for example using a doser, into the extrusion line 4, these phases are carried out to convert the pieces of hemp into fibers. The material, which feeds an extruder, can be a moistened raw material 1' resulting from a treatment which allows a sufficient level of wetting of the pieces of hemp. This wetting can typically be controlled during the humidification step 52, in particular by controlling a soaking duration and a steaming duration in options. The wetted material is freed from air (for example by driving out more than 50% of this air) filling porous areas of the material components.

The extrusion line 4 can consist of a twin-screw extruder, comprising two parallel screws 14, 15 actuated in rotation and made co-rotating, therefore rotating in the same direction F as illustrated in the Figure 3 For example. The extrusion line 4 may present means of controlling and maintaining a heating temperature which exceeds a threshold of 100°C, allowing partial/progressive evaporation of the water contained in humidified raw material 1'. As a non-limiting example, the extrusion line 4 can be a twin-screw extruder. In the extruder, the rotating shafts of the screws 14, 15 allow the removable assembly of members capable of composing mechanical treatment sections. An alternation of sections is thus provided, for example designed separately, to obtain different effects.

Alternatively, the extruder is single-screw and different processing sections are also provided.

With reference to figures 2 And 3 , the two screws 14, 15 can delimit between them passage zones for the crushed material. The succession of sections makes it possible to carry out a movement (from left to right for example in the case of the Figure 3 ) and mechanical treatment of the crushed and moistened material 1', in order to increase the quantity of fibers. The wet pieces of hemp which pass regularly between the two screws 14, 15 are reduced and converted at least partially into individualized fibers. More generally, the extrusion line 4 is configured to carry out a reduction of the small pieces of the hemp by separating the moistened and heated fibers initially contained in these pieces from each other.

In the option of figure 2 , the extrusion line 4 alternately presents conveying sections 42, 44, 46, 48 and sections 43, 45, 47 provided with counter-threads with passage grooves 16. Here, a conveying section 49 is provided adjacent to or making it possible to form an extruder outlet. In the counterthreaded processing sections 43 45 47, the extension or size d of the groove (measured perpendicular to the axes of the screws) can be between 6 and 10 mm. Optionally, in a first section 43 with counterthreads among the sections 43, 45, 47, this size d may be greater than the size provided for the groove in one in at least one other of the sections (example, a groove of approximately 8 mm can be provided in this first section, and a groove of approximately 6 mm can be provided at least in the last section 47 having counterthreads).

• une région pourvue de contrefilets répartis sur les deux vis 14, 15 ;
• une zone d'accumulation du matériau humidifié pouvant inclure la région à contrefilets, les rainures 16 correspondantes participant à l'effet d'accumulation en limitant la section de passage pour la circulation du matériau vers la zone suivante ;
• une zone de compression du matériau broyé humidifié, adjacente à la zone d'accumulation (typiquement en aval de la zone d'accumulation).

The extrusion line 4 can admit all of the moistened crushed material 1', which itself includes all the solid components of the crushed raw material 1 obtained at harvest and/or before a humidification step 52. Among the processing sections 42, 43, 44, 45, 46, 47, 48, 49 of the extrusion line 4, at least one section T may present, as visible for example on the Figure 3 :

• a region provided with counterthreads distributed over the two screws 14, 15;
• an accumulation zone for the humidified material which may include the region with cross-threads, the corresponding grooves 16 participating in the accumulation effect by limiting the passage section for the circulation of the material towards the next zone;
• a compression zone of the moistened crushed material, adjacent to the accumulation zone (typically downstream of the accumulation zone).

Mixing members 18 can be arranged downstream of at least one of the sections 43, 45, 47 with counterthreads. The different parts of the extruder are mounted, in the twin-screw structure, so as to obtain combined profiles. The screws are screws 14, 15 can be interpenetrating to compress the material

The succession of phases of compression, shearing, mixing and transport tends to homogenize the mixture containing the three fractions, to the extent that the pieces (non-defibrated) of the third fraction are increasingly reduced, typically to go from one size centimeter or a few millimeters to a submillimeter size (length). These reduced pieces (typically more than 75 microns wide) from the woody part are called logs in all that follows. We thus obtain a defibrated dough 3, collected at the outlet of the extrusion line 4.

In what follows, we designate the bast fibers (bast part) of the hemp plant as fibers of the first fraction. Dusts are non-fibrous, volatile particles of an organic nature.

The pulp contains cellulosic fibers, for example at least 3 or 4 million per gram of pulp, for example containing more than 4.5 million fibers per gram of pulp, this number possibly being between 5 and 12 million, for example gram of dough. By fibers we mean constituents having a sufficiently long length, for example greater than or equal to 200 micrometers

The arithmetic average fiber length, determined by morphological analysis, may be greater than 400 micrometers, while the length-weighted average length may exceed 650 micrometers. The average width of the fibers can be between 20 and 30 micrometers.

The content of logs, forming fibrous pieces of submillimeter size or less than 2 mm, can be less than 0.1 or 0.2 million, per gram of dough. Typically the ratio between the quantity of fibers and the quantity of logs can be greater than 20 to 1, preferably greater than or equal to 40 to 1 to 50 to 1. Counting of fibers and logs, confirming this distribution and the quantitative information associated, can be carried out by a MorFi type analyzer (with image analysis with microscopic resolution), marketed by the company Techpap. This analyzing device (for example such as those designed by the Center Technique du Papier CTP and TechPap) is suitable for the morphological and behavioral characterization of fibers.

The measurements can be carried out in the natural environment of the fibers on a fibrous suspension passing through a measuring vein where an optical system composed of a high-resolution DTC (or CCD in English) camera and a light source allows the acquisition. images immediately processed by a computer. The measurement is a reliable statistical representation of fiber characteristics.

In the case of mechanical treatment of the material prepared according to the experimental example, after a humidification step 52 ending with placing the soaked/wet material in the oven (wet material steamed with steam at 100°C for 20 minutes) , a mechanical treatment in the Clextral Evolum 32 twin-screw extruder was carried out, after introduction of the re-humidified and steamed crushed hemp into the extruder via a doser equipped with a feed screw.

The twin-screw extruder is configured with three compression zones with interlocks having openings of 8 - 6 - 6 mm. The raw material flow rate is set at 8.5 kg/h (dry equivalent) and a rotation speed of the two axes of 500 rpm. A set temperature of 110°C is given for all the extruder sheaths, which breaks down schematically as illustrated on the figure 2 . The rotation speed(s) in the extruder can vary between 300 and 1000 rpm. The raw material flow rate can be adapted, for example between 5 and 8 kg/h or planned between 8 and 9 kg/h or more, by way of non-limiting example.

Still according to the experimental example, the defibration of crushed whole hemp (and rehumidified) in the twin-screw extruder made it possible to produce a paste having a drainage index of 430 ml CSF. This is a low drainage index and it turns out that we obtained a mixture of long cellulosic fibers and hemp fibers. The energy consumption of the extruder is 675 kWh/t, significantly lower than wood chips. The fiber pulp produced is composed of fibers of 0.676 mm of average length (average weighted in length), fines and logs. MorFi analysis shows that fibers longer than 2.5 mm are present in dough 3.

The quantity of logs, even if it remains significant here, is low: 17.3% in surface area with an average length of only 4.7 micrometers. These logs come from hemp which has not been sufficiently/completely defibrated. Of course, the cellulosic fibers are particularly long, taking the direction of extension of the fibers as the direction of length, relative to the short fibrous pieces (logs) forming the hemp residue. For example, we note for the fibers a difference of the order of 100 to 1 compared to the logs (for example 460 micrometers on average for the fibers, compared to 4.7 micrometers for the residual fibrous logs/pieces of hemp) taking as length direction the direction of extension of the fibers. Conversely, the logs are of course thicker/wider with a width typically 10 times greater than a fiber width (the width being a transverse dimension relative to the extension length of the individual fibers).

Fine elements (fines), present in the dough, do not interfere with the molding abilities of the dough 3. The behavior of this defibrated dough, rich in long cellulosic fibers and very good resistance (fibers from hemp) is fully compatible with/suitable for the manufacture of molded cellulose objects.

More generally, the process makes it possible to obtain a defibrated pulp 3 because it is rich in long fibers, for example reaching or exceeding half a millimeter or a millimeter, this pulp being suitable for molding. A start of shaping can be carried out at the exit of the extrusion line 4, by choosing a specific section shape for the opening provided at the exit of a bore or similar extruder channel.

Optional additional treatment(s) of the dough

In reference to the figure 1 , the defibrated pulp 3 can optionally undergo additional treatment, of a non-chemical nature. Optionally, the dough can be classified during a classification step 54, in order to limit or eliminate logs or similar pieces of hemp which may be considered annoying in certain types of molding or similar shaping applications. The classification step 54 can be implemented using rotary sieve classifiers under pressure with low consistency. This makes it possible to reject or separate the coarse fibrous parts, forming a block that is too thick (for example with a width greater than a threshold, possibly of the order of 300 or 500 micrometers). A separation of these coarse fibrous parts can be followed by a reintroduction of these parts in a step (for example step 52 or 53) further upstream of the process. In addition or as an alternative, the paste can undergo a refining step 56, a non-limiting example of which will be detailed below.

Alternatively, the dough 3 collected directly at the end of the extrusion step 53 can constitute a dough ready for molding to form containers, for example for food use (plates, trays) or utensils.

Paste 3 can be obtained with an energy consumption of less than 800 or 900 kWh/t, for example of the order of 675 kWh/t (totally, here including steps 50 to 53). This is low, especially in a process without the slightest use of chemical additives. The temperature may not exceed 115 or 120°C.

Refining option

Before being sent to a molding machine or other shaping machine making it possible to obtain a container 36, the paste 3 can first undergo refining, with purification preceding or succeeding this refining. In reference to the figure 1 , the purification step 55 can be carried out by circulating the paste, possibly mixed with water to form a suspension, by removing for example the residual pieces or sticks as well as the dust (at least in part).

At stage 56 of refining, it is allowed, by mechanical action on the fibers in aqueous environments, to modify their characteristics, in particular their aptitude for interfiber bonds and therefore for the resistance of the hemp paste (more structural paste). After step 56, the fibrous suspension can undergo further treatment, for example to adjust the water content (for example between 10 and 90%).

Refining step 56 is optional. Such a refining step can be carried out at high concentration. The refiner equipment/device 7 can operate hot, for example at 120°C under 1 bar pressure, with a rotation speed of the refiner disks of several thousand revolutions per minute, for example 3000 rpm, as used in a high yield process. This type of step 56 can make it possible to obtain a refined paste with a CSF drainage index of 200-250 ml or between 250 and 450 ml.

To improve the quality of the fibers of the pulp 3 obtained by extrusion and develop the inter-fiber bonds (which structures the material during the manufacture of molded cellulose, here derived only from hemp), the refining step 56 can be carried out with a refiner device 7 which can operate at low consumption (no more than 100 kWh/t for example). In embodiments, the refiner 7 may be a pilot refiner with rotating disks or plate elements each preferably having the same external diameter. Such a refiner 7 can be equipped with a mechanical treatment compartment or pulper, associated with a feed screw or any suitable feed means (a pump can typically be provided), with a parameterization unit (if applicable). with an electrical cabinet or similar unit) and a motor. The body of the refiner 7 and all parts in contact with the hemp paste 3 can be made of stainless steel. Each plate or disc 71, 72, 73, 74 can result from the assembly of different parts, each constituting an angular sector of the disc (for example between 15 and 120 or 180°).

• Vitesse de 2750 tours/min pour la rotation relative entre deux disques ;
• Température d'environ 120°C ;
• Pression environ 1 bar ;
• Vitesse de la vis d'alimentation : 10 tours/min ;
• Débit massique d'environ 13 kg/h, en équivalent sec.

The refining step 56 can be done in a single pass through the refiner 7, optionally under the following conditions:

• Speed of 2750 rpm for relative rotation between two discs;
• Temperature around 120°C;
• Pressure approximately 1 bar;
• Feed screw speed: 10 rpm;
• Mass flow rate of approximately 13 kg/h, in dry equivalent.

In reference to the Figure 6 , the refiner 7 can have a frame on which a shaft X is mounted to rotate. In the refiner casing 75 including a raw material inlet and a raw material outlet, the paste 3 admitted via the inlet can flow towards the outlet. The refiner 7 may have one or more non-rotating discs 71, 72 and one or more rotating discs 73, 74.

By way of non-limiting example, the refiner 7 may present a first non-rotating disk 71 mounted on a first plate or fixed structure forming part of the casing 75, a second non-rotating disk 72 mounted on a second plate or support structure arranged spaced and parallel to the first non-rotating disk 71. The second plate can be part of a movable part, possibly mounted on a hinge/articulated relative to the rest of the casing 75. A certain movement or degree of freedom in sliding of the second non-rotating disk 72 towards the first non-rotating disk 71 can be provided in certain options. The refiner 7 here further comprises a rotor 70 mounted on the shaft , in an operational state mounted and installed, parallel to the respective non-rotating disks 71, 72. The shaft X transmits the rotational movement to the rotor 70; and one or more chambers of the refiner 7 can be formed, into which the pulp to be enriched with structural fibers can flow.

Of course, the refiner 7 can be presented in other forms than that illustrated, for example by allowing rotations of discs in the opposite direction. As an option, the refiner 7 can be of the type marketed by the Austrian company Andritz, for example using discs of 30 cm in diameter. In options/variants, the refiner 7 can be with conical packing.

Optionally, the temperature of the paste 3 can be controlled, for example in the range between 110 and 135°C, for example of the order of 120°C, under 1 bar of pressure. In order to maintain the quality of the fibers of the pulp 3, the hydraulic pressure required for the refining step 56 can be kept less than or equal to 3 or 4 bars, for example less than 2 bars. The relative rotational speed between a pair of disks (71, 73; 72, 74) which face each other can be between 1000 and 5000 rpm. Where applicable, for discs rotating in opposite direction, rotation at 1200 rpm in one direction can be associated with rotation at 1800 rpm in the other direction (which corresponds to a relative speed of 3000 rpm).

The energy consumption in the refining stage 56 can amount to less than 100 kWh/ton of pulp. Optionally, at least 5% of the total energy consumption is supplied to refining.

Molding a container

The defibrated paste 3 obtained using the process can make it possible to produce containers 36 of varying thickness, by molding typically carried out at a temperature which exceeds 100 or 121°C. For example, the molding temperature can be greater than or equal to 130°C, in particular typically greater than the maximum temperature reached during the mechanical treatment which made it possible to obtain paste 3.

• on dispose, dans un bac/ réservoir 8, d'un bain liquide 30 de pulpe fibreuse (pulpe contenant les fibres de la pâte 3 ou 3'), de l'eau pouvant être ajoutée directement dans ce réservoir 8 ;
• une mise en forme préalable (façonnage) est réalisée, en immergeant dans le bain 30 une portion rigide de moule 33, mobile, qui inclut ou qui peut correspondre à une portion mâle (permettant de définir une face intérieure du contenant 36 à mouler), de sorte que les fibres sont rassemblées en une couche brute C30 déposée sur la portion rigide de moule 33 ; un effet d'aspiration par un système 19 d'aspiration/vide du moule filtrant peut être prévu, de préférence pour l'agglutination/accolement de la couche C30 déposée, avec un effet de moulage contre la portion rigide de moule 33 ;
• optionnellement, après le préformage/façonnage et en ayant sorti du bain 30 la portion rigide de moule 33 recouverte de la couche brute C30, on peut réaliser un pré-pressage participant à réduire la fraction de liquide, passant par exemple de 65-80% à 50-69% ; un tel pré-pressage utilise une autre portion de moule complémentaire, éventuellement sans chauffage, en rapprochant entre elles cette portion femelle et la portion mâle recouverte de la couche C30, en recouvrant par le dessus cette couche pour fermer le moule de pré-pressage. On obtient une pièce moulée C3 qui contient typiquement encore une grande quantité d'eau.

In embodiments, the paste 3 or 3' is used in a molding process using a pulp consisting of this paste 3 or 3' with optionally added water, for example with a mass content of 65%-80% in water. A fibrous suspension tank can be provided in association with a vacuum filter mold. In reference to the figure 4A , the paste 3 or the paste 3' having undergone a refining step 56 can constitute all of the fibers of the bath and which will form the solid part of the layer C30 recovered on a portion of the mold. The molding process may include, for example, the following successive steps:

• we have, in a tray/reservoir 8, a liquid bath 30 of fibrous pulp (pulp containing the fibers of the pulp 3 or 3'), water can be added directly to this reservoir 8;
• a preliminary shaping (shaping) is carried out, by immersing in the bath 30 a rigid portion of mold 33, movable, which includes or which may correspond to a male portion (making it possible to define an interior face of the container 36 to be molded), so that the fibers are gathered into a raw layer C30 deposited on the rigid mold portion 33; a suction effect by a suction/vacuum system 19 of the filter mold can be provided, preferably for the agglutination/adherence of the deposited layer C30, with a molding effect against the rigid portion of mold 33;
• optionally, after preforming/shaping and having removed from the bath 30 the rigid portion of mold 33 covered with the raw layer C30, pre-pressing can be carried out helping to reduce the liquid fraction, for example from 65-80% at 50-69%; such pre-pressing uses another complementary mold portion, possibly without heating, by bringing together this female portion and the male portion covered with the C30 layer, covering this layer from above to close the pre-pressing mold. A C3 molded part is obtained which typically still contains a large quantity of water.

Then, hot molding is carried out, for example with a single press in the same mold or preferably in a specific hot pressing station 20 (different from the mold previously used) after transfer of part C3. Station 20 shown on the Figure 4B can receive part C3 on the lower part or tool 21, before obtaining a pressure with the relative movement of the upper/covering tool 35 and heating, for example at a temperature between 125 or 130 and 150°C, optionally of the order of 140°C. Hot pressing of the C3 molded part having undergone pre-pressing has a drying effect and makes it possible to refine the wall thickness, with hot pressing pressure. It is understood that hot molding is carried out with a second forming pressurization greater than a first forming pressurization used during pre-pressing.

• l'outil/élément inférieur de pressage à chaud 21, par exemple maintenu fixe, avec un côté de pressage à chaud 21a adapté à un contour (par exemple la cavité interne) de la pièce moulée formant le contenant 36 ; et
• l'outil/élément supérieur de pressage à chaud 35, pouvant former une portion femelle pour le contact de formage d'une partie externe du contenant 36.

The hot pressing station 20 may include:

• the lower hot pressing tool/element 21, for example held fixed, with a hot pressing side 21a adapted to a contour (for example the internal cavity) of the molded part forming the container 36; And
• the upper hot pressing tool/element 35, capable of forming a female portion for the forming contact of an external part of the container 36.

The molded part C3 being placed or inserted on the lower element 21 during the transfer and in the hot pressing, the upper element here movable hot pressing 35 is pressed thereon to obtain the hot pressing of the part C3 interposed. Optionally, the lower hot pressing tool 21 also comprises channels 21c on its hot pressing side 21a, through which the liquid solution can be at least partially discharged during hot pressing.

Thus, the final molded part forming the container 36 is shaped with a further reduction in the proportion of the liquid (water), for example below 10%, preferably to about 7%, whereby the container 36 is then sufficiently strong and dimensionally stable.

Of course, numerous forming methods can be used to produce a three-dimensional container 36, which can constitute food packaging, for example a tray. The forming temperature can exceed a sterilization threshold temperature, for example 121°. The mechanically treated paste, once hot formed, can make it possible to create an interior surface of the container suitable for food contact. No coating layer or spray is required in options for producing the container 36 from the paste 3, 3'.

With reference to Figures 5A and 5B , a molding option is illustrated which uses a plate layer 30 formed for example exclusively from paste 3 or 3'. The plate layer 30 is illustrated here with a substantially constant thickness. In options of this type, a first shaping of the pasty material consisting of the collected defibrated dough 3 or the purified dough 3' is carried out. As illustrated on the figure 1 , a purified paste 3' having undergone a classification step 54 (after the extrusion step 53) and/or a refining step 55 can be immediately used in a molding application. When a first shaping has been carried out, possibly by a passage between two rigid rotating rollers, obtaining a container 36 can result from a second shaping, by compression and/or stretching in a mold 20 to obtain all or part of a container 36 in three dimensions.

The paste makes it possible to create an interior surface of the container compatible with food contact. In the case of figures 5A-5B , the internal face of the container 36 takes the shape of a punch 20c or similar male/penetrating part of the mold 20. No coating layer or spray is required in options for producing such a container 36.

Whatever the forming method, a ready-to-use container 36 can be molded, which comes out of the mold 20 by separating the different parts 20a, 20b thereof. Optionally, only the mold part 20b which includes the punch 20c can be mobile, the other part 20 which can be hollow remaining fixed.

The present disclosure is not limited to the embodiments described above, only by way of example, but it encompasses all the variants that those skilled in the art may consider in the context of the protection sought.

Claims (11)

Process for transforming a biosourced fibrous raw material to form a cellulosic pulp suitable for molding, characterized in that : - said raw material consists of hemp straw (10), with the leaves without the roots, thus including hemp; - the transformation is mechanical, that is to say without chemical additive, the material being introduced and allowed to circulate in an extrusion line (4); and in that, after breaking up the hemp straw (10) to obtain a crushed raw material (1) including three mixed fractions consisting of a first fraction composed of fibers, a second fraction composed of dust, and a third fraction composed of pieces of hemp, the process includes the following steps: - a transfer of the crushed raw material, using a doser (41), into the extrusion line (4), knowing that said material is humidified during a humidification step (52); - a mechanical treatment of the crushed and moistened material (1') to increase the quantity of fibers, with at least partial conversion of the pieces of wet hemp into fibers, the pieces of hemp being reduced between two parallel screws (14, 15) of the extrusion line (4) used to circulate the crushed and moistened material (1'); And - a collection, at an outlet of the extrusion line (4), of a defibrated paste (3). Method according to claim 1, in which the humidification step (52) is of sufficient duration to decompact the pieces of hemp using water vapor, the humidification step (52) being preferably carried out before introduction into the extrusion line (4);
and in which, during the mechanical treatment, heating or reheating is carried out simultaneously allowing heating and/or vaporization of the water contained in the pores of the decompacted pieces and a reduction of the decompacted pieces. Method according to claim 1 or 2, in which all of the moistened ground material (1') circulates between the two co-rotating screws (14, 15), which belong to a twin-screw extruder, the two screws (14, 15) delimiting between them several treatment sections (42, 43, 44, 45, 46, 47, 48, 49), of which at least one section (T) has: - an accumulation zone of the humidified material; And - a compression zone for the moistened crushed material (1'), adjacent to the accumulation zone. A method according to any one of the preceding claims, wherein the wetting step (52) changes the ground material from a drying state corresponding to a first dryness, between 75 and 95%, to a humidified state corresponding to a dryness less than 40%, preferably between 20 and 35%, and in which the humidification step (52) includes: - a soaking phase followed by a steaming phase; - and/or bringing the crushed material (1) into contact with soaking water for a period of at least 200 minutes, preferably between 250 and 1000 minutes, in a diffuser including a tank equipped with a filter, preferably in the form of a grid, a shutter being moved from a closed position to an open position of an evacuation passage provided in a bottom part of the tank in order to allow evacuation of soaking water by retaining said material in the tank using the filter. Method according to any one of the preceding claims, in which the defibrated pulp (3) is introduced into a refiner (7) including at least one pair of disks, during a refining step (56) during which a speed relative rotation between two discs (71, 72; 73, 74) matched to allow refining is between 1000 and 5000 rpm. Method according to any one of the preceding claims, in which the mechanical treatment step is an extrusion step (53) carried out by parameterizing a useful length and/or a rotation speed of the two parallel screws (14, 15) so as to to obtain, for the collected defibrated dough, a drainage index of the CSF standard of between 200 mL and 500 mL, preferably between 230 and 460 mL. Method according to any one of the preceding claims, in which logs of submillimeter size are present in the collected defibrated dough (3), the method further comprising a classification step (54) for separating logs remaining in the collected dough and /or a refining step (56), making it possible to transform the logs into fibers. Method according to any one of the preceding claims, in which the collected defibrated pulp (3) is used, preferably after a purification step by rinsing and/or filtration, as pulp in a molding step (58) in a mold , (20) in particular in a mold with a movable pressing member (20c) or in an injection mold, in order to obtain a container (36) in three dimensions. Method according to any one of claims 1 to 6, in which a plate layer (30), preferably of substantially constant thickness, is obtained by a first shaping of a pasty material consisting of the collected defibrated dough ( 3) or a purified pulp obtained from the defibrated pulp collected after a classification step (54) and/or a refining step (55),
and in which the plate layer (30) is deformed, during a second shaping, by compression and/or stretching in a mold (20) to obtain all or part of a container (36) in three dimensions, preferably forming a food packaging. Method according to any one of claims 1 to 6, in which a pasty material consisting of the collected fiber pulp or of a purified pulp obtained from the collected fiber pulp, after a classification step and/or a refining step , is injected into a mold (20) to obtain all or part of a container (36) in three dimensions, preferably forming a food package. Method according to any one of the preceding claims, in which the fragmentation is controlled to prevent degradation of the fibers of the first fraction, by limiting a rotational speed of a shaft of a crusher below a threshold. predetermined, which is preferably less than or equal to 200 rpm.

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