Method for manufacturing a foam

Abstract

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

Description

[0001] Description

[0002] Title of the invention: Process for manufacturing a foam

[0003] Technical field of the invention

[0004] The present invention relates to the technical field of processes for manufacturing foam.

[0005] State of the art

[0006] Technological advances in the field of polymer materials have opened the way to new possibilities for reinforcement and structuring, notably with the emergence of polymer foams whose walls are reinforced by fibers or nanofillers.

[0007] Despite their potential, polymer foams with such characteristics remain largely unexplored.

[0008] Indeed, obtaining foam composites from these nanometric reinforcements remains largely confined to laboratory research.

[0009] In this regard, the matrices used are most often polyurethanes; thermoplastic polymers are also sometimes used (polystyrene, polypropylene, PMMA, polylactide).

[0010] Furthermore, the nanofillers are mainly lamellar clays or carbon nanotubes.

[0011] In all cases, nanocomposite foams are currently produced in two distinct stages:

[0012] - the preparation of the nanocomposite, by in situ polymerization or extrusion, then

[0013] - foaming, generally in an autoclave, sometimes by single-screw extrusion or injection.

[0014] Such polymer foams, and their two-step manufacturing processes, are not entirely satisfactory.

[0015] In this context, there is a need for new technical solutions for the production of nanocomposite foams reinforced by nanofillers, with the aim of simplifying and optimizing manufacturing processes.

[0016] Presentation of the invention

[0017] To overcome the aforementioned drawback of the prior art, the present invention proposes 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, which comprises a screw-barrel assembly with successive zones, terminated downstream by a die, namely:

[0018] - a first feeding zone, in which said screw-sleeve assembly is fed by at least one polymer intended to form said polymer matrix,

[0019] - a melting zone, at which said at least one polymer undergoes melting,

[0020] - a second feeding zone, in which said screw-sheath assembly is fed by said charge, said at least one charge being selected from nanocelluloses (for example cellulose nanocrystals or cellulose nanofibrils) and / or chitin nanocrystals,

[0021] - a first dispersion zone, in which said filler is dispersed in said polymer matrix,

[0022] - a third feeding zone, in which said screw-sleeve assembly is supplied with at least one blowing agent, and

[0023] - a second dispersion zone, in which said at least one blowing agent is dispersed in said polymer matrix.

[0024] In general, the manufacturing process according to the invention has the advantage of allowing the production of reinforced foam, continuously and in a single operation, using a co-rotating twin-screw extruder.

[0025] The process according to the invention includes, on the same machine, the dispersion of nanofillers in the matrix, the decomposition of the blowing agent, the shaping in a die and the obtaining of the final foam.

[0026] Such a process makes it possible to consider an application on an industrial scale.

[0027] Other non-limiting and advantageous features of the process according to the invention, taken individually or in all technically possible combinations, are as follows:

[0028] - said at least one polymer is chosen 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 (Pa11);

[0029] - said charge also contains lignin;

[0030] - said at least one charge is supplied in a dry form, for example in the form of a powder;

[0031] - said at least one load 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 selected 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;

[0032] - preferably, for a nonpolar polymer (for example PP), said first premix still contains at least one compatibilizing agent, for example chosen 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;

[0033] - 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;

[0034] - said screw-sheath assembly and said die are separated by a gear pump.

[0035] 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.

[0036] Of course, the different features, variants and embodiments of the invention can be combined with each other in various ways as long as they are not incompatible or mutually exclusive.

[0037] Detailed description of the invention. Furthermore, 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:

[0038] [Fig. 1] is a schematic view of a co-rotating twin-screw extruder, adapted to implement the process according to the invention;

[0039] [Fig. 2] illustrates the evolution of the density of the foams prepared at (a) 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);

[0040] [Fig. 3] represents the structure of the foams (PP + 0.5% blowing agent) prepared at (a) 1 kg / h and (b) 2 kg / h;

[0041] [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);

[0042] [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);

[0043] [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;

[0044] [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 whose formulations are detailed in Table 1;

[0045] [Fig. 8] represents the distribution of bubble radii (expressed as the number of bubbles as a percentage of the radius in pm) in the foams whose formulations are detailed in Table 1;

[0046] [Fig. 9] illustrates the evolution of the oxidation temperature of the foam expressed in °C (OOT) (Oxidation Onset Temperature or initial oxidation temperature) in Figure a) and the oxidative induction temperature expressed in °C (OIT, min.) in Figure b), as a function of its composition, with a progression of the temperature of

[0047] RECTIFIED SHEET (RULE 91) ISA / EP 10°C / min up to 350°C under oxygen; compositions are detailed in Table 1;

[0048] [Fig. 10] illustrates cross-sections of nanocomposite foams containing cellulose nanocrystals and lignin (2000 pm x 2667 pm) observed under an optical microscope (left) and a fluorescence microscope (right). The compositions and mean bubble radius analysis of each formulation (7 to 9) are detailed in Table 1.

[0049] It should be noted that, in these figures, the structural and / or functional elements common to the different variants may have the same references.

[0050] The present invention relates, in general, to a method for manufacturing a foam comprising a polymer matrix which is reinforced by a filler.

[0051] Generally speaking, "foam" is advantageously understood as a porous material consisting of a gaseous phase dispersed in a solid phase (in this case the polymer matrix, also called the "polymer phase").

[0052] The gaseous phase is usually air, but can be another gas.

[0053] Generally speaking, the "polymer matrix" refers to the material that constitutes the continuous phase of the foam. This polymer matrix defines a network of polymers that surrounds the bubbles and provides structure and cohesion to the entire foam.

[0054] More generally, "filler" is advantageously understood to mean the particulate material added to the polymer matrix to modify its properties.

[0055] According to the invention, the manufacturing process consists of a continuous, single-step extrusion manufacturing process using a co-rotating twin-screw extruder.

[0056] In other words, the manufacturing process advantageously consists of a reactive extrusion process, in which the co-rotating twin-screw extruder performs the function of a continuous-type chemical reactor.

[0057] In general, an extrusion manufacturing process advantageously consists of producing an object of constant cross-section continuously and in a single step within a screw / sleeve system. Such an extrusion process according to the invention, due to its versatility, high production capacity, and cost-effectiveness, also aims to promote the industrialization of the materials thus produced.

[0058] 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.

[0059] 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.

[0060] In other words, the manufacturing process includes, on the same machine, the dispersion of fillers in the polymer matrix, the decomposition of the blowing agent, the shaping in a die and the obtaining of the final foam.

[0061] Co-rotating twin-screw extruder

[0062] As schematically illustrated in Figure 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 materials.

[0063] The 2 extrusion screws allow for homogeneous mixing and precise control of temperature and pressure during the extrusion process.

[0064] The term "corotative" indicates 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.

[0065] 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 Treatise Collection - Mechanics and Materials Engineering, published on 12 / 02 / 2014.

[0066] More generally, a twin-screw co-rotating extruder 1 comprises a screw 2 - sleeve 3 assembly.

[0067] Preferably, screws 2 are modular, composed of screw sections with different geometries, assembled to suit the specifics of the reactive system to be treated.

[0068] These screw sections are generally of three types:

[0069] - Direct pitch screw sections for conveying material; different screw pitches allow for modulation of conveying and pressure; - Reverse pitch screw sections, creating a return flow;

[0070] - the sections of mixing screws, allowing the creation of a strong shear force to, for example, break up agglomerates and disperse charges.

[0071] In this case, the screw 2 - sheath 3 assembly comprises successive zones, ending downstream with a die, namely:

[0072] - a first feeding zone 4, in which said screw assembly 2 - sleeve 3 is fed by at least one polymer intended to form the polymer matrix,

[0073] - a melting zone 5, at which said at least one polymer undergoes melting,

[0074] - a second feeding zone 6, in which said screw assembly 2 - sleeve 3 is fed by the load,

[0075] - a first dispersion zone 7, in which the filler is dispersed in the polymer matrix,

[0076] - a third supply zone 8, in which the screw assembly 2 - sleeve 3 is supplied with at least one blowing agent, and

[0077] - a second dispersion zone 9, in which said at least one blowing agent is dispersed in said polymer matrix.

[0078] This feeding sequence, made possible by the design of the co-rotating twin-screw extruder, optimizes the efficiency of the process in a single step, while preserving the functional properties (mechanical, antioxidant, etc.) of the fillers and guaranteeing the structural quality of the foam obtained.

[0079] The various successive zones are terminated downstream by a channel 10.

[0080] According to a preferred embodiment, the screw assembly 2 - sleeve 3 and the die 10 are separated by a gear pump 11.

[0081] By "gear pump" we advantageously mean a positive volumetric pump which uses two gears to transport a fluid.

[0082] Such a gear pump 11 has the particular advantage of ensuring a constant and precise flow rate, the ability to handle high viscosities and low shear.

[0083] Preferably, downstream in the process, the foam is collected by an endless belt. This foam cools advantageously in the open air.

[0084] Polymer(s)

[0085] Preferably, said at least one polymer is chosen from:

[0086] - polyolefins, - poly(butyl succinate) (PBS),

[0087] - copolymers with polyamide and polyether blocks (PEBA),

[0088] - aliphatic polyamides,

[0089] In particular, a polyolefin, sometimes called a "polyalkene", refers to a saturated, synthetic aliphatic polymer resulting from the polymerization of an alkene.

[0090] Preferably, the polyolefins are chosen from semi-crystalline thermoplastic polyolefins (having crystalline and amorphous regions), namely, for example:

[0091] - polyethylene (PE),

[0092] - polypropylene (PP),

[0093] - polybutene (PB).

[0094] Furthermore, polyamide block polyether block copolymers (PEBA) are a family of thermoplastic polymers made up of alternating blocks of polyamide and polyether.

[0095] Among PEBA, PEBAX (registered trademark), developed by the company Arkema, should be mentioned in particular.

[0096] By "polyamide" we advantageously mean a polymer containing amide functions that can result from the polycondensation between carboxylic acid and amine functions.

[0097] The term "aliphatic polyamides" advantageously encompasses polyamides:

[0098] - with an open chain (linear or branched), and

[0099] - comprising one or more non-aromatic rings (alicyclic compounds).

[0100] By "aliphatic polyamide", we mean, for example, polyamide 11 (Pa11 or polyundecanamide).

[0101] Charge

[0102] At least one charge is chosen from:

[0103] - nanocelluloses, including cellulose nanocrystals or cellulose nanofibrils, and

[0104] - chitin nanocrystals, or a combination of at least two of them.

[0105] The mass concentration of said at least one filler, relative to the total mass of the foam, is for example from 0.5 to 3%, preferably from 0.5 to 1.5%. This mass concentration range also encompasses the ranges defined by the following values: 0.5, 1.0, 1.5, 2.0, 2.5, 3.0.

[0106] The charges, also called "nanocharges", here 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.

[0107] In general, the dimensions of these loads can be adjusted by treatments known to those skilled in the art, for example mechanical or chemical.

[0108] Such fillers are described for example in the document Moon et al., 2011, “Cellulose nanomaterials review: structure, properties and nanocomposites”.

[0109] Cellulose is defined as a linear homopolysaccharide derived from biomass (encompassing organic matter of plant origin, including algae, cellulose of animal origin, and cellulose of bacterial origin) and composed 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.

[0110] AGUs have 3 hydroxyl functions: 2 secondary alcohols (on carbons in positions 2 and 3 of the glucose ring) and one primary alcohol (on carbon in position 6 of the glucose ring).

[0111] These polymers combine through intermolecular hydrogen bonds, thus giving cellulose its fibrous structure. In particular, the combination of cellobiose dimers forms a basic cellulose nanofibril (with a diameter of approximately 5 nm). The combination of these basic 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.

[0112] The term "nanocelluloses" refers to the various forms of cellulose with dimensions on the order of nanometers. According to the invention, this term encompasses, in particular, two families of nanocelluloses: cellulose nanocrystals and cellulose fibrils.

[0113] The terms "cellulose fibrils", "cellulose nanofibrils", "cellulose nanofibers", "nanofibrillated cellulose", "cellulose microfibrils", "microfibrillated cellulose", "microfibrillated cellulose", and "cellulose nanofibrils" are used synonymously herein. In the remainder of this application, the term "cellulose nanofibrils" (NFC or CNF) will be used generically.

[0114] 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.

[0115] The elimination of amorphous areas from cellulose nanofibrils makes it possible to obtain cellulose nanocrystals (CNC).

[0116] 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).

[0117] 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.

[0118] In the case of bacterial cellulose, the nanofibrils, or ribbons, of bacterial cellulose are generally several micrometers long and 30 to 60 nm wide, particularly 45 to 55 nm.

[0119] Such nanocelluloses are described for example in the document Moon et al., 2011, “Cellulose nanomaterials review: structure, properties and nanocomposites”.

[0120] 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).

[0121] Chitin nanocrystals are still generally referred to in English as "chitin nano-crystal" or "ChN".

[0122] The chemical name of the chitin molecule is poly N-acetyl-D-glucosamine, [3-(1,4)-2-acetamido-2-deoxy-D-glucose or more simply [N-acetyl-D-glucosamine|3-(1,4) N-acetyl-D-glucosamine]n.

[0123] Chitin advantageously encompasses polysaccharides composed of N-acetyl-[3-D-glucosamine units (from 50 to 100%) and D-glucosamine units (from 0 to 50%). 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] Nanocrystals can also be derived from polysaccharides selected from (3-1,3-glucan, [3-1,3-xylan and [3-1,4-mannan], which share 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. Examples of plant sources for [3-1,3-xylane include certain algae. For [3-1,4-mannan], examples also include certain algae, as well as the endosperm of terrestrial plant seeds. Examples of fungal sources for polysaccharides include certain fungi and yeasts 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 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 polyphenolic macromolecules, which is one of the main components of wood along with cellulose and hemicelluloses. In other words, lignin is the polymer biosynthesized from three monolignols: paracoumaric alcohol, coniferyl alcohol, and sinapyl alcohol.

[0135] The fraction of each monomer varies depending on the plant lineage, species, organ, and tissue.

[0136] Without being limited by any theory, this lignin is associated with the surface of nanofillers by adsorption (or even by grafting).

[0137] This phenomenon is described for example in the document Hambardzumyan et al., Biomacromolecules 2012, 13, 4081-4088.

[0138] 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.

[0139] 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%.

[0140] 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.

[0141] Preferably, the addition of lignin in the formulation of cellulose-based foams leads to a significant increase in the average size of bubbles formed within the polymer matrix.

[0142] More specifically, the presence of lignin advantageously promotes the growth and / or coalescence of bubbles during the foaming phase, resulting in an average bubble radius significantly greater than that observed in equivalent formulations without lignin.

[0143] For example, while the incorporation of cellulose nanocrystals or nanofibrils allows for the formation of small bubbles (typically with a radius of 15 to 45 pm), the addition of lignin (for example, at a rate of 1% by mass) leads to the formation of larger bubbles, with radii of up to 200 to 500 pm, or even 200 to 400 pm depending on the precise composition.

[0144] Without being limited by any one theory, this effect is attributed to the influence of lignin on foam stability and bubble coalescence during expansion. Lignin modifies the interactions at the polymer / filler interface, thus promoting the aggregation of larger gas bubbles. It is also observed that, advantageously, the incorporation of lignin confers fluorescent properties to the foam. Thus, the foam obtained according to the invention, in the presence of lignin, exhibits not only larger bubbles but also a fluorescent property (Figure 10).

[0145] Blowing agent (BA)

[0146] Preferably, at least one of the said blowing agent is chosen from:

[0147] - chemical blowing agents, capable of releasing gas through thermal decomposition or

[0148] - physical blowing agents, for example supercritical fluids, for example supercritical CO2.

[0149] Preparation of the load for the manufacturing process

[0150] 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.

[0151] Preferably, at least one feedstock (and advantageously lignin) is supplied in the form of a premix.

[0152] This could be, for example, a premix chosen from:

[0153] - micronized PP and PPgMA (for example 1%) + CNC or CNF (for example 1%),

[0154] - Micronized PP + CNC or CNF (e.g. 1%) (with 1% copolymer),

[0155] - PP + PPgMA (for example 0.5%) micronized + CNC or CNF 1% (with 0.5% copolymer).

[0156] Micronization is implemented for example by using a mill, for example Retsch ZM100 (Retsch GmbH), under liquid nitrogen.

[0157] In general, micronized powder advantageously has a size ranging from 500 pm to 1 mm.

[0158] More generally, the premix is ​​advantageously produced from a preparation phase comprising the following steps:

[0159] - a step of supplying at least one first component chosen from said nanocelluloses and / or said chitin nanocrystals, dispersed in a liquid medium,

[0160] - 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,

[0161] - an evaporation step of the liquid medium of said first premix, and - possibly a step of adding lignin, to obtain a second premix.

[0162] Preferably, in the case of a nonpolar polymer (for example PP), said first premix still contains at least one compatibilizing agent.

[0163] Preferably, such a compatibilizing agent is intended to be placed at the interface between the polymer and the filler.

[0164] 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.

[0165] Said at least one compatibilizing agent may be chosen for example from PPgMA and / or a PPO-PEO-PPO copolymer.

[0166] PPgMA is the acronym for poly(propylene grafted maleic anhydride).

[0167] 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).

[0168] 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.

[0169] Preferably, the process allows, for example, the use of a cellulose-based premix (NFC or NCC, with different shape factors), with or without lignin, with or without copolymer, combined with an ultra-milled polymer matrix (for example PP), without the use of chemicals, without additional chemical reaction and at room temperature.

[0170] Preferably, this premix is ​​introduced not at the beginning of the extruder, but halfway through, which helps to preserve the intrinsic properties (mechanical, antioxidant, etc.) of the fillers used.

[0171] Manufacturing process

[0172] During the implementation of the manufacturing process, the first feeding zone 4 is supplied with at least one polymer in solid or liquid form, advantageously in solid form (for example in the form of granules or a powder), intended to form the polymer matrix.

[0173] The throughput is, for example, from 1 kg to 10 kg, or even up to 100 kg, by adjusting the screw rotation speed. Then, at least one polymer undergoes melting within the melting zone.

[0174] 5.

[0175] The polymer in question is thus advantageously melted directly within the melting zone 5 of the co-rotating twin-screw extruder, without the need for additional peripheral equipment. This integration of all stages into a single machine is a distinctive feature, simplifying the manufacturing process and optimizing industrial efficiency.

[0176] The screw assembly 2 - sleeve 3 is then fed by the load, within the second feeding zone 6.

[0177] The charge is then dispersed in the polymer matrix, within the first dispersion zone 7.

[0178] Downstream, in the third feed zone 8, the screw assembly 2 - sleeve 3 is supplied with at least one blowing agent.

[0179] In the second dispersion zone 9, said at least one blowing agent is dispersed in said polymer matrix.

[0180] 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).

[0181] 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).

[0182] Without being limited by any theory, the process according to the invention makes it possible to obtain a foam advantageously exhibiting 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.

[0183] Mousse

[0184] 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.

[0185] 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%. Where appropriate, such a foam advantageously contains lignin.

[0186] 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%.

[0187] Within the framework 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").

[0188] Moreover, in general, pores (or bubbles) advantageously have a micrometric size, measured by microscopy and image analysis (ImageJ in particular) for example.

[0189] 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.

[0190] More generally, the said foam advantageously presents at least one of the following properties and applications:

[0191] - low density: for many industrial applications, for example in the transport sector, weight reduction has become a priority to limit the carbon footprint and participate in the fight against global warming;

[0192] - high mechanical properties: the presence of nanofillers in the cell walls will increase the rigidity and final mechanical resistance compared to an unfilled foam;

[0193] - partially or totally bio-based material: CNC / CNF are 100% bio-based;

[0194] - Acoustic and thermal insulation properties: the addition of nanofillers in the walls of the foam improves the acoustic absorption properties and such a foam makes it possible to achieve low thermal conductivities;

[0195] - Oxidation stability properties of the matrix, particularly with respect to thermo-oxidation (notably according to an OOT parameter for Oxidation Oxygen Treatment), are 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 for 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;

[0196] - antioxidant and antimicrobial properties.

[0197] 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.

[0198] 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 in the order of 30°C.

[0199] Preferably, regardless of the filler used, which is 100% bio-based (cellulose alone or cellulose combined with lignin), the density of the final product is preferably maintained at 0.65, thus guaranteeing a lightweight material while retaining its performance.

[0200] The process preferentially imparts antioxidant properties to the foam, ensuring increased stabilization of the matrix against oxidation. Other properties can also be imparted, such as antimicrobial and fluorescent properties, thanks to the natural autofluorescence of lignin.

[0201] Of course, various other modifications can be made to the invention within the scope of the attached claims.

[0202] Examples

[0203] Materials

[0204] Matrices: petroleum-based: polyolefins (PP - polypropylene), possibly made compatible with PP-g-MA or PE-g-MA, or bio-based: PLA, PBS.

[0205] Fillers: cellulose nanocrystals (CNC) and nanofibrils (CNF), possibly dispersed in water in the presence of a PPO-PEO-PPO copolymer.

[0206] 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. A polypropylene (PP) homopolymer was chosen as the matrix (HB12XF, Polychim Industrie, Mardick, France). It has a melting point of 12 g / 10 min (230°C, 2.16 kg) and a density of 0.904 g / cm³.

[0207] To improve compatibility with CNC / CNF, a maleic anhydride grafted PP (PP-g-MA) (Orevac CA100, Arkema) was added to the formulations.

[0208] 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).

[0209] 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.

[0210] Preparing the mousse

[0211] Foams can be prepared by chemical foaming (with blowing agent, AG) or physical foaming (for example with supercritical CO2).

[0212] Process optimization

[0213] 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.

[0214] 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.

[0215] A flat die was attached to the end of the extruder.

[0216] 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.

[0217] At the exit of the process, two cooling conditions were tested: either in a water bath or in ambient air.

[0218] For composite foams, a second screw profile was used. In this case, a larger mixing zone 7 was implemented to disperse the nanofillers that were introduced into the feeding zone 6.

[0219] PP alone (without filler) A decrease in density from 0.9 to 0.6 is observed, for a concentration of 0.5% in blowing agent (figure 2).

[0220] This decrease is not very dependent on operating conditions (speed, flow rate) and the cooling method.

[0221] The average radius of the bubbles varies from 45 to 60 pm (figures 3 and 4).

[0222] PP + NFC or CNC

[0223] The foams were made with 0.5% AG, with 1% CNC or CNF, with or without copolymer (CP).

[0224] Adding a blowing agent to a PP or PP / PPGMA matrix reduces the material density by 33%, with a bubble size distribution in radius ranging from 45 to 60 pm.

[0225] The addition of nanofillers does not significantly change the density of the foams (figure 5).

[0226] The average radius of the bubbles varies from 15 to 30 pm for cellulose-based foams, as illustrated in Figure 6 in relation to the formulations specified in Table 1.

[0227] [Table 1]

[0228] Table 1: Composition (%) of premixes before extrusion

[0229] Adding CNC or NFC fillers up to 1% (w / w) reduces bubble size by 15 to 30 µm while maintaining the same density. Adding lignin (1%) to the PP + PPgMA + CNC + CP + AC mixture (foam 3) increases the average bubble radius to between 295 and 350 µm (Figure 8). These bubbles tend to collapse during the process (foam 7) (Figure 6).

[0230] This technical effect is further demonstrated in relation to Table 2, which presents the average radius of bubbles in cellulose-based nanocomposite foams, determined by image analysis carried out on ten sections, each containing between 450 and 600 bubbles.

[0231] [Table 2]

[0232] Table 2: Average radius of bubbles in cellulose-based nanocomposite foams (image analysis on ten sections with between 450 and 600 bubbles).

[0233] In connection with formulation 7, the addition of lignin (1%) improves the stability of the PP matrix with respect to thermo-oxidation: increase of the OOT (Oxidation Onset Temperature) of the order of 30°C (figure 9).

[0234] 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.

[0235] This technical effect is also demonstrated in relation to Table 3, which presents the oxidation onset temperature (OOT, °C) and the oxidative induction temperature (OIT, min.) of nanocomposite foams based on cellulose nanocrystals (CNC, 1 wt%).

[0236] [Table 3]

[0237] Table 3: Oxidation onset temperature (OOT, °C) and oxidative induction temperature (OIT, min.) of cellulose nanocrystal-based nanocomposite foams (CNC, 1 wt %).

[0238] In addition, cross-sections of nanocomposite foams containing cellulose nanocrystals and lignin (dimensions: 2000 pm x 2667 pm) were made and observed both by optical microscope and fluorescence microscope (Figure 10).

[0239] Observation under an optical microscope allows visualization of the cellular structure and the distribution of bubbles within the polymer matrix, while observation under a fluorescence microscope highlights the fluorescent property conferred by the presence of lignin in the foam.

Claims

Demands

1. A method for manufacturing a foam comprising a polymer matrix which is reinforced by a filler, characterized in that said manufacturing method consists of a continuous, single-step extrusion manufacturing process using a co-rotating twin-screw extruder (1), which co-rotating twin-screw extruder (1) comprises 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) - sleeve (3) assembly is fed by at least one polymer intended to form said polymer matrix, - a melting zone (5), at which said at least one polymer undergoes melting, - a second feeding zone (6), in which said screw (2) - sleeve (3) assembly is fed by said charge, said at least one charge 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 supply 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 among polyethylene (PE), polypropylene (PP), polybutene (PB), - poly(butyl succinate) (PBS), - copolymers with polyamide and polyether blocks (PEBA), preferably PEBAX, - aliphatic polyamides, for example polyamide 11 (Pa11).

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 method according to any one of claims 1 to 4, characterized in that said at least one feed 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 nano-cellulose 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, - an evaporation step of the liquid medium of said first premix, and - possibly 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 method 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 through 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 (2) - sleeve (3) assembly 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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