Process for manufacturing foam

Abstract

The present invention relates to a method for manufacturing a foam comprising a polymer matrix reinforced by a filler. This manufacturing method consists of a continuous, single-step extrusion process using a co-rotating twin-screw extruder (1). The co-rotating twin-screw extruder (1) comprises a screw (2)-barrel (3) assembly having successive zones, in particular: - a first feeding zone (4), in which said screw (2)-barrel (3) assembly is fed with at least one polymer intended to form said polymer matrix, - a second feeding zone (6), in which said screw (2)-barrel (3) assembly is fed with said filler selected from nanocellulose and chitin nanocrystals, - a third feeding zone (8), in which said screw (2)-barrel (3) assembly is fed with at least one blowing agent. Figure for the abstract: 1

Description

Title of the invention: Process for manufacturing a foam Technical field of the invention

[0001] The present invention relates to the technical field of processes for manufacturing a foam. State of the art

[0002] Technological advances in the field of polymer materials have opened the way to new possibilities for reinforcement and structuring, in particular with the emergence of polymer foams whose walls are reinforced by fibers or nanofillers.

[0003] Despite their potential, polymer foams with such characteristics remain largely unexplored.

[0004] Indeed, obtaining foam composites from these nanometric reinforcements remains largely confined to laboratory research.

[0005] In this regard, the matrices used are most often polyurethanes; thermoplastic polymers are also sometimes used (polystyrene, polypropylene, PMMA, polylactide).

[0006] Moreover, the nanofillers are mainly lamellar clays or carbon nanotubes.

[0007] In all cases, nanocomposite foams are currently produced in two distinct stages:

[0008] - the preparation of the nanocomposite, by in situ polymerization or extrusion, then

[0009] - foaming, generally in an autoclave, sometimes by single-screw extrusion or by injection.

[0010] Such polymer foams, and their two-step manufacturing processes, are not entirely satisfactory.

[0011] In this context, there is a need for new technical solutions for the production of nanocomposite foams reinforced by nanofillers, with the objective of simplifying and optimizing manufacturing processes. Presentation of the invention

[0012] In order to remedy the aforementioned drawback of the prior art, the present invention proposes a method for manufacturing a foam comprising a polymer matrix which is reinforced by a filler.

[0013] This manufacturing process consists of a continuous, single-step extrusion manufacturing process using a co-rotating twin-screw extruder,

[0014] which co-rotating twin-screw extruder comprises a screw-barrel assembly which includes successive zones, terminated downstream by a die, namely:

[0015] - a first feeding zone, in which said screw-sheath assembly is powered by at least one polymer intended to form said polymer matrix,

[0016] - a melting zone, at the level of which said at least one polymer undergoes a merger,

[0017] - a second feeding zone, in which said screw-sleeve assembly is powered by said load,

[0018] said at least one filler being chosen from nanocelluloses (for example cellulose nanocrystals or cellulose nanofibrils) and / or chitin nanocrystals,

[0019] - a first dispersion zone, in which said charge is dispersed in said polymer matrix,

[0020] - a third feed zone, in which said screw-sleeve assembly is fueled with at least one blowing agent, and

[0021] - a second dispersion zone, in which said at least one blowing agent is dispersed in said polymer matrix.

[0022] In general, the manufacturing process according to the invention has the advantage of allowing the production of a reinforced foam, continuously and in a single operation, using a co-rotating twin-screw extruder.

[0023] The process according to the invention includes, on the same machine, the dispersion of the nanofillers in the matrix, the decomposition of the blowing agent, the shaping in a die and the obtaining of the final foam.

[0024] Such a process makes it possible to consider an application on an industrial scale.

[0025] Other non-limiting and advantageous features of the process according to the invention, taken individually or in all technically possible combinations, are as follows:

[0026] - said at least one polymer is chosen from polyolefins, preferably the semi-crystalline thermoplastic polyolefins, for example among polyethylene (PE), polypropylene (PP), polybutene (PB); poly(butyl succinate) (PBS); polyamide block and polyether block copolymers (PEBA), preferably PEBAX; aliphatic polyamides, for example polyamide 11 (Pall);

[0027] - said charge also contains lignin;

[0028] - said at least one load is supplied in a dry form, for example under in the form of a powder;

[0029] - said at least one charge is supplied in the form of a premix, advantageously resulting from a preparation phase comprising the following steps: a step of supplying at least one first component chosen from said nanocelluloses and / or said chitin nanocrystals, dispersed in a liquid medium; a step of mixing said at least one first component with a fraction of said at least one micronized polymer dispersed in a liquid medium, to obtain a first premix; a step of evaporating the liquid medium of said first premix; and optionally a step of adding lignin, to obtain a second premix;

[0030] - preferably, for a nonpolar polymer (for example PP), said first premix still contains at least one compatibilizing agent, for example selected from PPgMA and / or a PPO-PEO-PPO copolymer (CP), of which at least one compatibilizing agent is preferably introduced into said fraction of said at least one polymer, during the mixing step;

[0031] - said at least one blowing agent is chosen from among chemical blowing agents, capable of releasing gas by thermal decomposition or physical blowing agents, for example supercritical fluids, for example supercritical CO2;

[0032] - said screw-sheath assembly and said die are separated by a gear pump.

[0033] The present invention further relates to a foam comprising a matrix polymer, which is reinforced by a filler, obtained by the manufacturing process according to the invention.

[0034] Of course, the various features, variants, and embodiments of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. Detailed description of the invention

[0035] In addition, various other features of the invention become apparent from the attached description made with reference to the drawings which illustrate non-limiting embodiments of the invention and where:

[0036] [Fig-1] is a schematic view of a co-rotating twin-screw extruder, adapted for the setting implementation of the process according to the invention;

[0037] [Fig.2] illustrates the evolution of the density of the foams prepared at (b) 1 kg / h and (b) 2 kg / h, with different rates of blowing agent (expressed as mass percentage), for two cooling conditions: in air (solid circle) and in water (empty circle);

[0038] [Fig.3] represents the structure of the foams (PP + 0.5% blowing agent) prepared at (a) 1 kg / h and (b) 2 kg / h;

[0039] [Fig.4] illustrates the distribution of bubble radii in foams with 0.5% blowing agent at (a) 1 kg / h and (b) 2 kg / h, for two cooling conditions: water (empty bar) and air (solid bar); legend: number of bubbles (as a percentage) according to the radius (in pm);

[0040] [Fig.5] illustrates the evolution of the density of the foam, depending on its composition: PP (1), PP+AG (2), PP+PPgMA+AG (3), PP+PPgMA+NFC+AG (4), PP+PPgMA +NFC+CP+AG (5), PP+NFC+CP+AG (6);

[0041] [Fig.6] illustrates the structure of foams prepared at 1 kg / h, observed with the Axio Zoom macroscope (Zeiss, Germany), according to sections of the material 30 pm thick (Image in the visible, magnification 50X) and according to the formulations detailed in Table 1;

[0042] [Fig.7] represents the distribution of bubble radii (expressed as a percentage of the number of bubbles as a function of the radius in pm), in the foams for the following formulations: Histogram A: PP+AG (first bar), PP+PPgMA+AG (second bar), PP+PPgMA+CNC+AG (third bar), PP+PPgMA+CNC+CP+AG (fourth bar), PP+CNC+CP+AG (fifth bar), Histogram B: PP+AG (first bar), PP+PPgMA+AG (second bar), PP+PPgMA+CNF+AG (third bar), PP+PPgMA+CNF+CP+AG (fourth bar), PP+CNF+CP+AG (fifth bar);

[0045] [Fig.8] represents the distribution of bubble radii in the PP+PPgMA +CNC+CP+AG foam (expressed as the number of bubbles as a percentage of the radius in pm), without and with lignin (respectively first bar and second bar, by each radius);

[0046] [Fig.9] illustrates the evolution of the oxidation temperature of the foam expressed in °C (OOT) (Oxidation Onset Temperature or initial oxidation temperature), depending on its composition (if applicable with 1% lignin), with an increase in temperature from 10°C / min up to 350°C under oxygen; Legend: PP+AG (1), PP+PPgMA+AG (2), PP+PPgMA+CNC+AG (3), PP+PPgMA+CNC+lignin+AG (4), PP+PPgMA+CNC+CP+AG (5), PP+PPgMA+CNC+lignin+AG (6), PP +CNC+CP +AG (7), PP+CNC+lignin+CP+AG (8).

[0047] It should be noted that, in these figures, the structural and / or functional elements common to the different variants may have the same references.

[0048] The present invention relates, in general, to a method for manufacturing a foam comprising a polymer matrix which is reinforced by a filler.

[0049] Generally speaking, "foam" is advantageously understood to mean a porous material consisting of a gaseous phase which is dispersed in a solid phase (in this case the polymer matrix, also called "polymer phase").

[0050] The gaseous phase is generally air, but may be another gas.

[0051] Generally speaking, the "polymer matrix" advantageously refers to the material which constitutes the continuous phase of the foam. This polymer matrix defines a network of polymers that envelop the bubbles and provide structure and cohesion to the whole foam.

[0052] More generally, "filler" advantageously means the particulate material added to the polymer matrix to modify its properties.

[0053] According to the invention, the manufacturing process consists of a continuous, single-step extrusion manufacturing process using a co-rotating twin-screw extruder.

[0054] In other words, the manufacturing process advantageously consists of a reactive extrusion process, in which the co-rotating twin-screw extruder performs a continuous chemical reactor function.

[0055] Generally speaking, an "extrusion" manufacturing process advantageously consists of manufacturing an object of constant cross-section, continuously and in a single step, within a screw / sleeve system.

[0056] Such an extrusion process according to the invention, due to its versatility, its large production capacities and its profitability, also aims to promote the industrialization of the materials thus produced.

[0057] By "a single step", it is advantageously understood that the manufacturing process according to the invention is carried out within the co-rotating twin-screw extruder.

[0058] In other words, the manufacturing process according to the invention is adapted to ensure the dispersion of at least one charge and the foaming of a polymer matrix, within the same co-rotating twin-screw extruder.

[0059] In other words, the manufacturing process includes, on the same machine, the dispersion of the fillers in the polymer matrix, the decomposition of the blowing agent, the shaping in the die and the obtaining of the final foam. Co-rotating twin-screw extruder

[0060] As schematically illustrated in [Fig.1], a co-rotating twin-screw extruder 1 is a machine equipped with two extrusion screws 2 which rotate in the same direction, to mix and shape the materials.

[0061] The extrusion screws 2 allow for homogeneous mixing and precise control of temperature and pressure during the extrusion process.

[0062] The term "corotative" specifies that the two screws 2 of the corotative twin-screw extruder 1 rotate in the same direction and at the same speed. This ensures uniform mixing of the materials and consistent foam distribution throughout the extrusion process.

[0063] In general, such corotative twin-screw extruders 1 (also called "corotative twin-screw extruder") are described for example in the following document: Polymer Extrusion, by Pierre Lafleur et al., MIM-Mechanics and Materials Engineering Treatise Collection, published on 12 / 02 / 2014.

[0064] In general terms, a co-rotating twin-screw extruder 1 comprises a screw 2 - sleeve 3 assembly.

[0065] Preferably, the screws 2 are modular, composed of screw sections which have different geometries, assembled in a way according to the specificities of the reactive system to be treated.

[0066] These screw sections are generally of three types:

[0067] - Direct-pitch screw sections for conveying material; different screw pitches allow for modulation of the conveying and pressurization;

[0068] - reverse thread screw sections, creating a return flow;

[0069] - the sections of mixing screws, allowing the creation of a strong shear force to, by for example, breaking up agglomerates and dispersing charges.

[0070] In this case, the screw 2 - sheath 3 assembly comprises successive zones, terminated downstream by a die, namely:

[0071] - a first feed zone 4, in which said screw assembly 2 - sleeve 3 is powered by at least one polymer intended to form the polymer matrix,

[0072] - a melting zone 5, at which said at least one polymer undergoes a merger,

[0073] - a second feed zone 6, in which said screw assembly 2 - sleeve 3 is powered by the load,

[0074] - a first dispersion zone 7, in which the charge is dispersed in the polymer matrix

[0075] - a third feed zone 8, in which the screw assembly 2 - sleeve 3 is fueled with at least one blowing agent, and

[0076] - a second dispersion zone 9, in which said at least one blowing agent is dispersed in said polymer matrix.

[0077] The various successive zones are terminated downstream by a channel 10.

[0078] According to a preferred embodiment, the screw assembly 2 - sleeve 3 and the die 10 are separated by a gear pump 11.

[0079] By "gear pump" advantageously means a positive volumetric pump which uses two gears to transport a fluid.

[0080] Such a gear pump would notably combine the interest of ensuring a constant and precise flow rate, the ability to handle high viscosities and low shear.

[0081] Preferably, downstream of the system, the foam is collected by an endless belt. This foam advantageously cools in the open air. Polymer(s)

[0082] Preferably, said at least one polymer is chosen from:

[0083] - polyolefins,

[0084] - poly(butyl succinate) (PBS),

[0085] - polyamide block and polyether block copolymers (PEBA),

[0086] - aliphatic polyamides,

[0087] In particular, a polyolefin, sometimes called a "polyalkene", refers to a saturated, synthetic aliphatic polymer, obtained from the polymerization of an alkene.

[0088] Preferably, the polyolefins are chosen from semi-crystalline thermoplastic polyolefins (having crystalline and amorphous regions), namely, for example:

[0089] - polyethylene (PE),

[0090] - polypropylene (PP),

[0091] - polybutene (PB).

[0092] Furthermore, polyamide block and polyether block copolymers (PEBA) are a family of thermoplastic polymers made up of alternating blocks of polyamide and polyether.

[0093] Among PEBA, PEBAX (registered trademark), developed by the company Arkema, will be mentioned in particular.

[0094] By “polyamide”, advantageously means a polymer containing amide functions that can result from the polycondensation between carboxylic acid and amine functions.

[0095] The term "aliphatic polyamides" advantageously includes polyamides:

[0096] - with an open chain (linear or branched), and

[0097] - comprising one or more non-aromatic rings (alicyclic compounds).

[0098] By "aliphatic polyamide", we mean, for example, polyamide 11 (Pal 1 or poly undecanamide). Charge

[0099] Said at least one charge is chosen from:

[0100] - nanocelluloses, including cellulose nanocrystals or nanofibrils of cellulose, and

[0101] - chitin nanocrystals,

[0102] or a combination of at least two of them.

[0103] The mass concentration of said at least one filler, relative to the total mass of the foam, is for example 0.5 to 3%, preferably 0.5 to 1.5%.

[0104] This mass concentration range also includes the ranges defined by the following values: 0.5, 1.0, 1.5, 2.0, 2.5, 3.0.

[0105] The charges, also called "nanocharges", advantageously have a size ranging from 3 nm to 70 nm in diameter (d) and from 50 nm to more than 1 pm in length (L), i.e. form factors (L / d) ranging from 17 to 40.

[0106] In general, the dimensions of these charges can be adjusted by treatments known to those skilled in the art, for example mechanical or chemical.

[0107] Such fillers are described for example in the document Moon et al., 2011, “Cellulose nanomaterials review: structure, properties and nanocomposites”.

[0108] By "cellulose" is meant a linear homopolysaccharide derived from biomass (encompassing organic matter of plant origin, including algae, cellulose of animal origin, and cellulose of bacterial origin) and consisting of glucose units (or cycles) (D-Anhydroglucopyranose - AGU for "Anhydro glucose unit") linked together by [3-(1-4) glycosidic bonds. The repeating unit is a glucose dimer, also called a cellobiose dimer.

[0109] The AGUs have 3 hydroxyl functions: 2 secondary alcohols (on the carbons in positions 2 and 3 of the glucose ring) and one primary alcohol (on the carbon in position 6 of the glucose ring).

[0110] These polymers associate through intermolecular hydrogen bonds, thus conferring a fibrous structure to the cellulose. In particular, the association of cellobiose dimers forms an elementary cellulose nanofibril (with a diameter of approximately 5 nm). The association of elementary nanofibrils forms a nanofibril (with a diameter generally ranging from 50 to 500 nm). The arrangement of several of these nanofibrils then forms what is generally called a cellulose fiber.

[0111] The term “nanocelluloses” refers to the various forms of cellulose having a dimension on the order of a nanometer. This term encompasses in particular, according to the invention, two families of nanocelluloses: cellulose nanocrystals and cellulose fibrils.

[0112] The terms “cellulose fibrils”, “cellulose nanofibrils”, “cellulose nanofibers”, “nanofibrillated cellulose”, “cellulose microfibrils”, “microfibrillated cellulose”, “microfibrillated cellulose”, “microfibrillated cellulose”, “cellulose nanofibrils” are used synonymously herein. In the remainder of this application, the term “cellulose nanofibrils” (NFC or CNF) will be used generically.

[0113] Each cellulose nanofibril contains crystalline parts stabilized by a strong network of inter- and intra-chain hydrogen bonds. These crystalline regions are separated by amorphous regions.

[0114] Eliminating amorphous areas from cellulose nanofibrils allows cellulose nanocrystals (CNC) to be obtained.

[0115] NCCs advantageously comprise at least 50% crystalline portion, preferably at least 55% crystalline portion. They generally have a diameter ranging from 5 to 50 nm (preferably less than 15 nm, for example ranging from 3 to 10 nm), and a length ranging from 40 nm to about 1 pm, preferably ranging from 40 nm to 500 nm (i.e., an L / d aspect ratio advantageously ranging from 17 to 40).

[0116] The terms “cellulose nanocrystals”, “nanocrystalline cellulose”, “cellulose whiskers”, “microcrystals” or “cellulose nanocrystal” are used synonymously herein for the sake of simplicity. In the remainder of this application, the term “cellulose nanocrystals” (NCCs) will be used generically.

[0117] In the case of bacterial cellulose, the nanofibrils, or ribbons, of bacterial cellulose generally have a length of several micrometers and a width ranging from 30 to 60 nm, in particular from 45 to 55 nm.

[0118] Such nanocelluloses are described for example in the document Moon et al., 2011, “Cellulose nanomaterials review: structure, properties and nanocomposites”.

[0119] In the context of the invention, cellulose nanocrystals are for example extracted from spruce, comprising crystalline cellulose associated with sulfate esters on the surface in position C6 (approximately 1% w / w of sulfur).

[0120] Chitin nanocrystals are still generally referred to in English as "chitin nano-crystal" or "ChN".

[0121] The chemical name of the chitin molecule is poly N-acetyl-D-glucosamine, [3-(l,4)-2-acetamido-2-deoxy-D-glucose or more simply [N-acetyl-D-glucosamine [3-(1,4) N-acetyl-D-glucosamine]n.

[0122] Chitin advantageously encompasses polysaccharides composed of N-acetyl-[3-D-glucosamine units (from 50 to 100%) and D-glucosamine units (from 0 to 50%).

[0123] In the context of the invention, acicular crystalline objects formed from an association of copolymer chains of glucosamine and N-acetyl-D-glucosamine linked by a [3, (1-4) bond will advantageously be called "chitin nanocrystals".

[0124] Chitin nanocrystals can be of animal or fungal origin. Examples of animal sources include crustaceans (crabs, shrimp, lobsters, etc.) and certain insects (cockchafers, beetles, etc.). Examples of fungal sources of chitin include fungi and yeasts.

[0125] The nanocrystals can also be derived from polysaccharides selected from [3-1,3-glucan, [3-1,3-xylan and [3-1,4-mannan, which have in common a fibrillar structure similar to that of chitin. Thus, these polysaccharides can also be in the form of nanocrystals.

[0126] These nanocrystals can be of plant or fungal origin. As an example of a plant source, certain algae can be cited for [3-1,3-xylane]. For [3-1,4-mannan], certain algae can also be cited, as well as the endosperm of terrestrial plant seeds. As an example of a fungal source of the polysaccharides, certain fungi and yeasts can be cited for [3-1,3-glucan].

[0127] Advantageously, chitin nanocrystals have an elongated anisotropic shape.

[0128] Chitin nanocrystals generally have the following dimensional characteristics:

[0129] - an average length between 150 and 600 nm, and

[0130] - a width between 5 and 50 nm.

[0131] In general, the morphology and dimensions of the charges can be determined using different imaging techniques such as transmission electron microscopy (TEM) or atomic force microscopy (AFM).

[0132] In general, nanofillers are advantageously native. They can also be modified by lignins.

[0133] According to an advantageous embodiment, the filler further contains lignin.

[0134] Lignin is a biomolecule, more precisely a family of macromolecules polyphenols, which are one of the main components of wood along with cellulose and hemicelluloses.

[0135] In other words, lignin is the polymer biosynthesized from three monolignols: paracoumaric alcohol, coniferyl alcohol and sinapyl alcohol.

[0136] The fraction of each monomer varies according to the plant line, species, organ and tissue.

[0137] Without being limited by any theory, this lignin is associated with the surface of the nanocharges by adsorption (or even by grafting).

[0138] This phenomenon is described for example in the document Hambardzumyan et al., Biomacromolecules 2012, 13, 4081-4088.

[0139] In general, the lignin used is advantageously Protobind 1000 lignin, described for example in the document Gerbin et al., 2021, International Journal of Biological Macromolecules, Volume 181, 30 June 2021, Pages 136-149.

[0140] In general terms, the mass concentration of lignin, relative to the total mass of the foam, is for example 0.5 to 5%, preferably 0.5 to 3%.

[0141] This mass concentration range also includes the ranges defined by the following values: 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0. Blowing agent (BA)

[0142] Preferably, said at least one blowing agent is selected from:

[0143] - chemical blowing agents, capable of releasing gas by thermal decomposition Or

[0144] - physical blowing agents, for example supercritical fluids, for example supercritical CO2 again.

[0145] Preparation of the load for the manufacturing process

[0146] At the level of the second feeding zone 6, the screw assembly 2 - sleeve 3 is fed by the charge, preferably in a dry form, for example in the form of a powder.

[0147] Preferably, said at least one feedstock (and advantageously lignin) is supplied in the form of a premix.

[0148] This is, for example, a premix chosen from:

[0149] - micronized PP and PPgMA (for example 1%) + CNC or CNF (for example 1%),

[0150] - Micronized PP + CNC or CNF (for example 1%) (with 1% copolymer),

[0151] - PP + PPgMA (e.g. 0.5%) micronized + CNC or CNF 1% (with copolymer) 0.5%).

[0152] Micronization is for example carried out by the use of a mill, for example Retsch ZM100 (Retsch GmbH), under liquid nitrogen.

[0153] In general, the micronized powder advantageously has a size ranging from 500 pm to 1 mm.

[0154] More generally, the premix is ​​advantageously obtained from a preparation phase comprising the following steps:

[0155] - a step of supplying at least one first component chosen from said nanocellulose and / or said chitin nanocrystals, dispersed in a liquid medium,

[0156] - a step of mixing said at least one first component with a fraction of said at least one micronized polymer dispersed in a liquid medium, to obtain a first premix,

[0157] - an evaporation step of the liquid medium of said first premix, and

[0158] - possibly a step of adding lignin, to obtain a second premix.

[0159] Preferably, in the case of a nonpolar polymer (for example PP), said first premix still contains at least one compatibilizing agent.

[0160] Preferably, such a compatibilizing agent is intended to be placed at the interface between the polymer and the filler.

[0161] Such compatibilizing agents are described for example in the document Nagalakshmaiah et al., The Royal Society of Chemistry, 2016, or the document Li et al., 2011, ACS Appl. Mater. Interfaces 2011, 3, 2349-2357.

[0162] Said at least one compatibilizing agent may for example be chosen from PPgMA and / or a PPO-PEO-PPO copolymer.

[0163] PPgMA is the acronym for poly(propylene grafted maleic anhydride).

[0164] The PPO-PEO-PPO copolymer is a triblock copolymer composed of three blocks in which PPO corresponds to poly(propylene oxide) and PEO corresponds to poly(ethylene oxide).

[0165] In practice, said at least one compatibilizing agent is preferably introduced into the fraction of said at least one polymer, during the aforementioned mixing step. Manufacturing process

[0166] During the implementation of the manufacturing process, the first feeding zone 4 is supplied with at least one polymer, advantageously in liquid form, intended to form the polymer matrix.

[0167] The throughput is for example from 1 kg to 10 kg, or even up to 100 kg, by adapting in particular the rotation speed of the screws.

[0168] Next, said at least one polymer undergoes melting within the melting zone 5.

[0169] The screw assembly 2 - sleeve 3 is then fed by the load, within the second feeding zone 6.

[0170] The charge is then dispersed in the polymer matrix, within the first dispersion zone 7.

[0171] Downstream, in the third feed zone 8, the screw assembly 2 - sleeve 3 is supplied with at least one blowing agent.

[0172] In the second dispersion zone 9, said at least one blowing agent is dispersed in said polymer matrix.

[0173] A foaming phase is obtained at the outlet of the die 10. Expansion is obtained by depressurization at the outlet of the die 10 (for example a flat die 10 for extruding expanded plates).

[0174] During this foaming phase, the higher viscosity of the polymer matrix limits coalescence and the nanofillers advantageously play the role of nucleating agent, not only for the foaming itself but also for the crystallization of the polymer matrix (which marks the end of bubble growth).

[0175] Without being limited by any theory, the process according to the invention makes it possible to obtain a foam advantageously having small cells, with a homogeneous distribution, thus leading to better properties, for a foam incorporating said filler compared to a foam devoid of said filler. Foam

[0176] The present invention further relates to a foam comprising a polymer matrix, which is reinforced by a filler, obtained by the manufacturing process according to the invention.

[0177] Preferably, in this foam, the mass concentration of said at least one filler, relative to the total mass of the foam, is for example 0.5 to 3%, preferably 0.5 to 1.5%.

[0178] Where appropriate, such a foam advantageously contains lignin.

[0179] The mass concentration of lignin, relative to the total mass of the foam, is for example 0.5 to 5%, preferably 0.5 to 3%.

[0180] In the context of the present invention, it is observed that lignin participates in stabilizing the polymer matrix against oxidation (improvement of the OOT parameter for "Oxidation Oxygen Treatment").

[0181] Moreover, in general, pores (or bubbles) advantageously have a micrometric size, measured by microscopy and image analysis (ImageJ in particular) for example.

[0182] The term "micrometer size" advantageously encompasses a radius of less than 1 mm, preferably less than 500 pm. For example, the radius is advantageously less than 100 pm, for example ranging from 15 to 45 pm, in the absence of lignin; the radius is advantageously greater in the presence of lignin, for example from 200 to 500 pm, preferably from 200 to 400 pm.

[0183] More generally, said foam advantageously possesses at least one of the following properties and applications:

[0184] - low density: for many industrial applications, for example in In the transport sector, weight reduction has become a priority to limit the carbon footprint and participate in the fight against global warming;

[0185] - high mechanical properties: the presence of nanofillers in the walls of the cells will increase the rigidity and final mechanical resistance compared to an unfilled foam;

[0186] - partially or totally bio-based material: CNC / CNF are 100% bio-based;

[0187] - Acoustic and thermal insulation properties: the addition of nanofillers in the The walls of the foam improve the sound absorption properties and such a foam makes it possible to achieve low thermal conductivities;

[0188] - oxidation stability properties of the matrix, particularly with respect to the thermo-oxidation (particularly according to an OOT parameter for Oxidation Oxygen Treatment), being significantly improved by combining nanocellulose with another aromatic structural component derived from biomass, such as lignin; this combination, achieved by adsorption and / or grafting onto the surface of the nanofillers, provides additional functionalities such as antioxidant and antimicrobial properties; this incorporation allows a shift in the oxidation temperature of several tens of degrees Celsius, thus increasing the thermal resistance of the material; this means that the resulting foam has better durability and increased stability when exposed to oxidizing environments;

[0189] - antioxidant and antimicrobial properties.

[0190] More generally, the addition of CNC or NFC type fillers, advantageously up to 1% (w / w), makes it possible to reduce the size of the bubbles (advantageously from 15 to 30 pm) while keeping the same density.

[0191] Furthermore, the addition of lignin (advantageously up to 1% (w / w)) in a PP / PPgMA / CNC mixture improves the stability of the PP / PPgMA matrix against thermo-oxidation, advantageously by about 30°C.

[0192] Of course, various other modifications can be made to the invention within the scope of the annexed claims. Examples Materials

[0193] Matrices: petroleum-based: polyolefins (PP - polypropylene), possibly made compatible with PP-g-MA or PE-g-MA, or bio-based: PLA, PBS.

[0194] Fillers: cellulose nanocrystals (CNC) and nanofibrils (CNF), optionally dispersed in water in the presence of a PPO-PEO-PPO copolymer.

[0195] A technical lignin, Protobind (PB1000) produced from a mixture of wheat straw and Sarkanda grass bagasse via a soda process by GreenValue Enterprises LLC (USA) (Gerbin et al., 2021) is used in powder form.

[0196] A polypropylene (PP) homopolymer was chosen as the matrix (HB12XF, Polychim Industrie, Mardick, France). It has a melting index of 12 g / 10 min (230°C, 2.16 kg) and a density of 0.904 g / cm3.

[0197] To improve compatibility with CNC / CNF, a maleic anhydride grafted PP (PP-g-MA) (Orevac CA100, Arkema) was added to the formulations.

[0198] The triblock copolymer PPO25-PEO7-PPO25 (Sigma-Aldrich, Mw 3300 g mol-1, 12% PEO) (Hambardzumyan et al., 2003) is added to the cellulosic suspension to make the surface of the nanofibrils more hydrophobic after adsorption of the latter, and thus increase their affinity with the PP polymer matrix (Nagalakshmaiah et al., 2016).

[0199] The chemical blowing agent (GA) is Palmarole MB.BA.18 (Adeka Palmarole, Mulhouse, France). It contains 30% by weight of blowing agent, the decomposition of which above a temperature of 190°C produces CO2. Preparing the mousse

[0200] Foams can be prepared by chemical foaming (with blowing agent, GA) or physical foaming (for example with supercritical CO2). Process optimization

[0201] The foams were prepared on a laboratory-scale twin-screw extruder (Leistritz ZSE 27 MAXX, Nuremberg, Germany), with a screw diameter of 27 mm and a total length of 990 mm.

[0202] The PP and PP-g-MA granules were introduced into a first feeding zone 4, melted in a melting zone 5; the blowing agent was introduced into the third feeding zone 8 and mixed with the melted polymer in the last mixing disc block.

[0203] A flat die was fixed to the end of the extruder.

[0204] The experiments were carried out at 200 rpm and at a total flow rate of 1 and 2 kg / h, for different contents of blowing agent: 0.5, 1, 1.5 and 2% by weight.

[0205] At the outlet of the die, two cooling conditions were tested: either in a water bath or in ambient air.

[0206] For composite foams, a second screw profile was used. In this case, a larger mixing zone 7 was set up to disperse the nanofillers that were introduced into the feed zone 6. PP only (without charge)

[0207] A decrease in density from 0.9 to 0.6 is observed, for a concentration of 0.5% in blowing agent ([Fig.2]).

[0208] This decrease is little dependent on operating conditions (speed, flow rate) and the cooling method.

[0209] The average radius of the bubbles varies from 45 to 60 pm (figures 3 and 4). PP + NFC or CNC

[0210] The foams were made with 0.5% AG, with 1% CNC or CNF, with or without copolymer (CP).

[0211] Adding a blowing agent to a PP or PP / PPGMA matrix reduces the material density by 33%, with a radius bubble size distribution ranging from 45 to 60 pm.

[0212] The addition of nanofillers does not significantly change the density of the foams ([Fig.5]).

[0213] The average radius of the bubbles varies from 15 to 30 pm for cellulose-based foams, as illustrated in [Fig.6] in relation to the formulations specified in Table 1.

[0214] [Tables 1] Formulations PP PP-g-MA CNC CNF Copolymer PB 1000 (lignin) 1 98 1 1 0 0 0 2 98 1 0 1 0 0 3 98 0.5 1 0 0.5 0 4 98 0.5 0 1 0.5 0 5 98 0 1 0 1 0 6 98 0 0 1 1 0 7 97 0.5 1 0 0.5 1 8 97 0 1 0 1 1 9 97 0 1 0 1 1

[0215] Table 1: Composition (%) of premixes before extrusion

[0216] Adding CNC or NFC type fillers up to 1% (w / w) reduces the size of bubbles by 15 to 30 pm, while maintaining the same density.

[0217] The addition of lignin (1%) in the PP + PPgMA + CNC + CP + AC mixture (foam 3) increases the average radius of the bubbles between 295 and 350 pm ([Fig.8]), bubbles which tend to collapse between each other during the process (foam 7) ([Fig.6]).

[0218] In relation to formulation 7, the addition of lignin (1%) improves the stability of the PP matrix with respect to thermo-oxidation: increase in OOT (Oxidation Onset Temperature or initial oxidation temperature) of the order of 30°C ([Fig.9]).

[0219] In particular, the addition of lignin up to 1% (w / w) in the PP / PPgMA / CNC mixture improves the stability of the PP / PPgMA matrix against thermo-oxidation at around 30°C.

Claims

Demands

1. A method for manufacturing a foam comprising a polymer matrix reinforced by a filler, characterized in that said manufacturing method consists of a continuous, single-stage extrusion manufacturing process using a co-rotating twin-screw extruder (1), said co-rotating twin-screw extruder (1) comprising a screw (2) - barrel (3) assembly having successive zones, terminated downstream by a die (10), namely: - a first feeding zone (4), in which said screw (2) - barrel (3) assembly is fed with at least one polymer intended to form said polymer matrix, - a melting zone (5), in which said at least one polymer undergoes melting, - a second feeding zone (6), in which said screw (2) - barrel (3) assembly is fed with said filler, said at least one filler being selected from nanocellulose and / or chitin nanocrystals,- a first dispersion zone (7), in which said filler is dispersed in said polymer matrix, - a third feeding zone (8), in which said screw (2) - sleeve (3) assembly is supplied with at least one blowing agent, and - a second dispersion zone (9), in which said at least one blowing agent is dispersed in said polymer matrix.

2. A manufacturing process according to claim 1, characterized in that said at least one polymer is selected from: - polyolefins, preferably semi-crystalline thermoplastic polyolefins, for example from polyethylene (PE), polypropylene (PP), polybutene (PB), - poly(butyl succinate) (PBS), - polyamide block and polyether block copolymers (PEBA), preferably PEBAX, - aliphatic polyamides, for example polyamide 11 (Pall).

3. A manufacturing process according to any one of claims 1 or 2, characterized in that said charge further contains lignin.

4. A manufacturing method according to any one of claims 1 to 3, characterized in that said at least one charge is fed in a dry form, for example in the form of a powder.

5. A manufacturing process according to any one of claims 1 to 4, characterized in that said at least one feedstock is supplied in the form of a premix, advantageously from a preparation phase comprising the following steps: - a step of supplying at least one first component selected from said nanocellulose and / or said chitin nanocrystals, dispersed in a liquid medium, - a step of mixing said at least one first component with a fraction of said at least one micronized polymer dispersed in a liquid medium, to obtain a first premix, - a step of evaporating the liquid medium of said first premix, and - optionally a step of adding lignin, to obtain a second premix.

6. A manufacturing process according to claim 5, characterized in that, for a nonpolar polymer (for example PP), said first premix still contains at least one compatibilizing agent, for example selected from PPgMA and / or a PPO-PEO-PPO copolymer, which at least one compatibilizing agent is preferably introduced into said fraction of said at least one polymer, during the mixing step.

7. A manufacturing process according to any one of claims 1 to 6, characterized in that said at least one blowing agent is selected from: - chemical blowing agents, capable of releasing gas by thermal decomposition or - physical blowing agents, for example supercritical fluids, for example supercritical CO2.

8. A manufacturing method according to any one of claims 1 to 7, characterized in that said screw assembly (2) - sleeve (3) and said die (10) are separated by a gear pump (11).

9. Foam comprising a polymer matrix, which is reinforced by a filler, obtained by the manufacturing process according to any one of claims 1 to 8.

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