Thermoplastic polyurethane foam with allophanate and / or isocyanurate functions

Abstract

The invention relates to a thermoplastic polyurethane foam, comprising at least one thermoplastic polyurethane comprising at least 90 wt.-% aliphatic units relative to the total weight of the thermoplastic polyurethane and comprising functions selected from allophanate functions, isocyanurate functions or a combination of both. The invention also relates to a method for preparing such a foam, as well as to an article comprising such a foam.

Description

[0001] Thermoplastic polyurethane foam with allophanate and / or isocyanurate functions

[0002] Field of invention

[0003] The present invention relates to thermoplastic polyurethane (TPU) foams, usable in particular for the manufacture of sports shoe soles, as well as methods for preparing them.

[0004] Technical background

[0005] Various polymer foams are used in particular in the field of sports equipment, such as soles or sole components, gloves, rackets or golf balls, personal protective equipment particularly for sports (vests, interior parts of helmets, shells, etc.).

[0006] Such applications require a set of specific physical properties that ensure rebound ability, low compression set and the ability to withstand repeated impacts without deforming and returning to its original shape.

[0007] Document EP 4050063 A1 describes a high flatness thermoplastic polyurethane foam having a density of 0.08 to 0.8 g / cm 3 , this foam comprising a TPU having a melting point of 90 to 160°C.

[0008] CN 115873396 A describes a composite material-based foam suitable for use in shoe soles, comprising an ethylene-vinyl acetate copolymer, an aliphatic TPU composite elastomer, a polyborosiloxane, a foaming agent, an active agent, a bridging agent, a coupling agent, and zinc oxide.

[0009] There is a need to provide thin and homogeneous polymer foams, which can have a low density and have good mechanical properties, particularly in terms of rebound resilience and compression set.

[0010] Summary of the invention

[0011] The invention relates firstly to a thermoplastic polyurethane foam, comprising at least one thermoplastic polyurethane comprising at least 90% by mass of aliphatic units relative to the total mass of the thermoplastic polyurethane and comprising functions chosen from allophanate functions, isocyanurate functions or a combination thereof.

[0012] In embodiments, the at least one thermoplastic polyurethane comprises a content of allophanate and / or isocyanurate functions, relative to the urethane functions, of from 0.01 to 1 mol%, preferably from 0.05 to 0.5 mol%.

[0013] In embodiments, the at least one thermoplastic polyurethane comprises allophanate functionalities.

[0014] In embodiments, the foam comprises at least 80% by mass, preferably at least 90% by mass, more preferably at least 95% by mass, even more preferably at least 99% by mass, of thermoplastic polyurethane relative to the total mass of the foam.

[0015] In embodiments, the at least one thermoplastic polyurethane is a rigid block and soft block copolymer, wherein:

[0016] - the flexible blocks are chosen from polyether blocks, polyester blocks, polycarbonate blocks and a combination thereof, preferably the flexible blocks are polyether blocks; and

[0017] - the rigid blocks comprise units derived from at least one aliphatic polyisocyanate and at least one diol chain extender.

[0018] In embodiments, the flexible blocks are polyether blocks comprising repeating units having at least 4 carbon atoms, preferably polytetrahydrofuran blocks.

[0019] In embodiments, the at least one aliphatic polyisocyanate is a linear aliphatic diisocyanate, preferably having between the isocyanate functions a linear chain comprising from 5 to 10 carbon atoms, and is more preferably selected from the group consisting of 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate, nonamethylene diisocyanate, decamethylene diisocyanate and combinations thereof.

[0020] In embodiments, the at least one diol chain extender comprises a carbon number less than or equal to 8, preferably the at least one diol chain extender is selected from 1,3-propanediol, 1,4-butanediol and / or 1,6-hexanediol. In embodiments, the foam has a density less than or equal to 800 kg / m 3 , preferably less than or equal to 400 kg / m 3 , more preferably from 50 to 300 kg / m 3 .

[0021] The invention also relates to a process for preparing a thermoplastic polyurethane foam comprising at least one thermoplastic polyurethane comprising at least 90% by mass of aliphatic units relative to the total mass of the thermoplastic polyurethane and comprising functions chosen from allophanate functions, isocyanurate functions or a combination thereof, comprising the following steps:

[0022] - the provision of at least one thermoplastic polyurethane comprising at least 90% by mass of aliphatic units relative to the total mass of the thermoplastic polyurethane;

[0023] - mixing said at least one thermoplastic polyurethane with a blowing agent; and

[0024] - foaming the mixture of thermoplastic polyurethane and blowing agent, wherein, in at least one of these steps, the thermoplastic polyurethane is in the molten state.

[0025] In embodiments, the thermoplastic polyurethane foam is as defined above.

[0026] In embodiments, the thermoplastic polyurethane comprising at least 90% by mass of aliphatic units relative to the total mass of the thermoplastic polyurethane is subjected, in at least one of the steps of the method, to a temperature greater than or equal to 160°C, preferably greater than or equal to 180°C, more preferably greater than or equal to 200°C, for a duration greater than or equal to 30 s, preferably greater than or equal to 1 min, more preferably greater than or equal to 1.5 min.

[0027] In embodiments, the blowing agent is mixed with the at least one thermoplastic polyurethane in the molten state, the foaming of the mixture being preferably carried out in a mold.

[0028] In embodiments, the step of providing the at least one thermoplastic polyurethane comprising at least 90% by mass of aliphatic units relative to the total mass of the thermoplastic polyurethane comprises preparing a preform from the thermoplastic polyurethane comprising at least 90% by mass of aliphatic units relative to the total mass of the thermoplastic polyurethane in the molten state, preferably by extrusion, injection molding, compression molding, lamination or 3D printing, more preferably by extrusion or injection molding, the mixing of the at least one thermoplastic polyurethane with the blowing agent preferably being carried out by impregnating the preform with the blowing agent, the foaming of the mixture preferably being carried out in an autoclave.

[0029] In embodiments, the preparation of a preform from the thermoplastic polyurethane in the molten state is carried out at a temperature greater than or equal to 160°C, preferably greater than or equal to 180°C, more preferably greater than or equal to 200°C, applied for a duration greater than or equal to 30 s, preferably greater than or equal to 1 min, more preferably greater than or equal to 1.5 min.

[0030] In embodiments, the step of providing the at least one thermoplastic polyurethane comprises preparing the thermoplastic polyurethane by reacting at least one polyol, preferably at least one polyether polyol, with at least one polyisocyanate and with at least one diol chain extender, wherein the molar ratio of the isocyanate functions of the polyisocyanate relative to the sum of the hydroxyl functions of the at least one polyol and the at least one diol chain extender is from 0.98 to 1.05, preferably from 0.995 to 1.02.

[0031] The invention also relates to an article made of a foam as described above or comprising at least one element made of a foam as described above, preferably chosen from soles of sports shoes, balls, gloves, personal protective equipment, soles for rails, automobile parts, construction parts and parts of electrical and electronic equipment.

[0032] The present invention makes it possible to meet the need expressed above. More particularly, it provides a thermoplastic polyurethane foam having a homogeneous and fine cellular structure and having a low density. The foam according to the invention also has a high rebound resilience as well as a low compression set.

[0033] This is achieved through the use in the foam of a thermoplastic polyurethane comprising allophanate and / or isocyanurate functions. Indeed, a TPU comprising such functions exhibits a higher viscosity at low frequency in oscillatory rheometry, which results in a better capacity of the TPU to contain the blowing agent during foam formation, as well as viscosification under uniaxial stretching in elongational rheology, which results in better foamability due to a greater capacity of the TPU to limit cell growth during foaming. These properties thus lead to a finer and more homogeneous foam, with better mechanical properties. Furthermore, the foam according to the invention can be prepared by a simple process.

[0034] Detailed description

[0035] The invention is now described in more detail and in a non-limiting manner in the following description.

[0036] Unless otherwise stated, all percentages are by mass.

[0037] In this text, the quantities indicated for a given species may apply to this species according to all its definitions (as mentioned in this text), including the more restricted definitions.

[0038] The invention relates to a thermoplastic polyurethane foam. The foam comprises at least one thermoplastic polyurethane comprising functions selected from allophanate functions, isocyanurate functions or a combination thereof.

[0039] Thermoplastic polyurethane (TPU) with allophanate and / or isocyanurate functions

[0040] The thermoplastic polyurethane with allophanate and / or isocyanurate functions according to the invention is an essentially aliphatic or, more particularly, aliphatic thermoplastic polyurethane. For the purposes of the present invention, the term "essentially aliphatic thermoplastic polyurethane" means a TPU essentially comprising aliphatic units, i.e. a TPU comprising at least 90% by mass, preferably at least 95% by mass, more preferably at least 97% by mass, more preferably at least 99% by mass, of aliphatic units (relative to the total mass of the TPU). In other words, the TPU according to the invention may comprise up to 10% by mass of aromatic units, preferably up to 5% by mass, more preferably up to 3% by mass, more preferably up to 1% by mass, of aromatic units.Even more preferably, the TPU according to the invention is a (totally) aliphatic TPU, that is to say that it comprises only aliphatic units. The term “aliphatic unit / residue” means any unit or residue which is not aromatic, this unit / residue being able to be, in general, saturated or unsaturated, cyclic or acyclic, linear or branched.

[0041] The thermoplastic polyurethane according to the invention is a copolymer with rigid blocks and soft blocks.

[0042] Generally, in this text, a "rigid block" means a block that has a melting point above 50°C. The presence of a melting point can be determined by differential scanning calorimetry, according to ISO 11357-3 Plastics - Differential scanning calorimetry (DSC) Part 3. A "soft block" means a block with a glass transition temperature (Tg) less than or equal to 0°C. The glass transition temperature can be determined by differential scanning calorimetry, according to ISO 11357-2 Plastics - Differential scanning calorimetry (DSC) Part 2.

[0043] Thermoplastic polyurethanes result from the reaction of at least one polyisocyanate with at least one isocyanate-reactive compound, preferably having two isocyanate-reactive functional groups, more preferably a polyol, and with a chain extender, optionally in the presence of a catalyst. The rigid blocks of the TPU are blocks consisting of units derived from polyisocyanates and chain extenders, while the flexible blocks mainly comprise units derived from isocyanate-reactive compounds preferably having a molar mass of between 0.2 and 100 kg / mol, preferably polyols.

[0044] The polyisocyanate used to prepare the TPU according to the invention comprises at least one aliphatic polyisocyanate, preferably consists of at least one aliphatic polyisocyanate. The aliphatic polyisocyanate may be acyclic aliphatic, cycloaliphatic and / or araliphatic. Preferably, the polyisocyanate is acyclic aliphatic (or linear aliphatic). Preferably, the polyisocyanate is a diisocyanate. Advantageously, the polyisocyanate, preferably the diisocyanate, is linear.

[0045] The polyisocyanate may in particular be selected from the group consisting of tri-, tetra-, penta-, hexa-, hepta- octa-, nona- and / or decamethylene diisocyanate, 2-methyl-pentamethylene 1,5-diisocyanate, 2-ethyl-butylene-1,4-diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane (isophorone diisocyanate, IPDI), 1,4-bis(isocyanatomethyl)cyclohexane, 1,3-bis(isocyanatomethyl)cyclohexane (HXDI), 4,4'-, 2,4'- and / or 2,2'-dicyclohexylmethane diisocyanate (H12 MDI), 1,4-cyclohexane diisocyanate, 1-methyl-2,4- and / or 1-methyl-2,6-cyclohexane diisocyanate, methylene bis(4-cyclohexylisocyanate) (HMDI) and mixtures thereof.

[0046] More particularly, the polyisocyanate may be selected from the group consisting of tri-, tetra-, penta-, hexa-, hepta- and / or octamethylene diisocyanate and mixtures thereof.

[0047] Preferably, the polyisocyanate comprises between the terminal isocyanate functions a linear chain having from 5 to 10 carbon atoms, more preferably from 5 to 8 carbon atoms; for example a linear chain having 5, or 6, or 7, or 8, or 9, or 10, carbon atoms.

[0048] More preferably, the polyisocyanate is selected from the group consisting of penta-, hexa-, hepta-, octa-, nona- and / or decamethylene diisocyanate and mixtures thereof.

[0049] Even more preferably, the polyisocyanate is 1,5-PDI (1,5-pentamethylene diisocyanate), 1,6-HDI (1,6-hexamethylene diisocyanate), nonamethylene diisocyanate, decamethylene diisocyanate or a mixture thereof. Even more preferably, the polyisocyanate is chosen from 1,5-pentamethylene diisocyanate, nonamethylene diisocyanate, decamethylene diisocyanate and mixtures thereof. Advantageously, the polyisocyanate is biosourced; mention may be made, as biosourced polyisocyanates, in particular, of 1,5-pentamethylene diisocyanate, nonamethylene diisocyanate and decamethylene diisocyanate. Generally, the term "biosourced compound" means a compound comprising 14 C; preferably the biosourced compounds according to the invention comprise at least 0.2x10' 10 % by mass of 14C relative to total carbon (corresponding to a biomass carbon content of at least approximately 20% by mass relative to the total carbon mass). The content of 14 C can be determined by mass spectrometry according to ASTM D6866-06.

[0050] The isocyanate-reactive compound(s) preferably have an average functionality between 1.8 and 3, more preferably between 1.8 and 2.6, more preferably between 1.8 and 2.2. The average functionality of the isocyanate-reactive compound(s) corresponds to the number of isocyanate-reactive functions of the molecules, calculated theoretically for a molecule from a quantity of compounds. Preferably, the isocyanate-reactive compound has, according to a statistical average, a Zerewitinoff active hydrogen number in the above ranges.

[0051] Preferably, the isocyanate-reactive compound (preferably a polyol) has a number-average molar mass of 500 to 100,000 g / mol. The isocyanate-reactive compound may have a number-average molar mass of 500 to 8,000 g / mol, more preferably 700 to 6,000 g / mol, more preferably 800 to 4,000 g / mol.In embodiments, the isocyanate-reactive compound has a number average molar mass of 500 to 600 g / mol, or 600 to 700 g / mol, or 700 to 800 g / mol, or 800 to 1000 g / mol, or 1000 to 1500 g / mol, or 1500 to 2000 g / mol, or 2000 to 2500 g / mol, or 2500 to 3000 g / mol, or 3000 to 3500 g / mol, or 3500 to 4000 g / mol, or 4000 to 5000 g / mol, or 5000 to 6000 g / mol, or 6000 to 7000 g / mol, or 7000 to 8000 g / mol, or from 8000 to 10000 g / mol, or from 10000 to 15000 g / mol, or from 15000 to 20000 g / mol, or from 20000 to 30000 g / mol, or from 30000 to 40000 g / mol, or from 40000 to 50000 g / mol, or from 50000 to 60000 g / mol, or from 60000 to 70000 g / mol, or from 70000 to 80000 g / mol, or from 80000 to 100000 g / mol. The number average molar mass can be determined by GPC, preferably according to ISO 16014-1:2012.

[0052] Advantageously, the isocyanate-reactive compound has at least one reactive group selected from hydroxyl group, amine group, thiol group and carboxylic acid group. Preferably, the isocyanate-reactive compound has at least one hydroxyl reactive group, more preferably several hydroxyl groups. Thus, particularly advantageously, the isocyanate-reactive compound comprises or consists of a polyol.

[0053] Preferably, the polyol is selected from the group consisting of polyester polyols, polyether polyols, polycarbonate diols, polysiloxane diols, polyalkylene diols, and mixtures thereof. More preferably, the polyol is a polyether polyol, a polyester polyol, and / or a polycarbonate diol, such that the flexible blocks of the thermoplastic polyurethane are polyether blocks, polyester blocks, and / or polycarbonate blocks, respectively. More preferably, the flexible blocks of the thermoplastic polyurethane are polyether blocks and / or polyester blocks (the polyol being a polyether polyol and / or a polyester polyol). More preferably, the flexible blocks of the thermoplastic polyurethane are polyether blocks (the polyol being a polyether polyol).

[0054] As polyester polyol, mention may be made of polycaprolactone polyols and / or copolyesters based on one or more carboxylic acids chosen from adipic acid, succinic acid, pentanedioic acid and / or sebacic acid and one or more alcohols chosen from 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol and / or polytetrahydrofuran. More particularly, the copolyester may be based on adipic acid and a mixture of 1,2-ethanediol and 1,4-butanediol, or the copolyester may be based on adipic acid, succinic acid, pentanedioic acid, sebacic acid or mixtures thereof, and polytetrahydrofuran (tetramethylene glycol), or the copolyester may be a mixture of these copolyesters.

[0055] As polyether polyol, polyether diols (i.e., aliphatic α,α-dihydroxylated polyoxyalkylene blocks) are preferably used. The polyether polyol may, in particular, be a polyether diol based on ethylene oxide, propylene oxide, and / or butylene oxide, a block copolymer based on ethylene oxide and propylene oxide, a polyethylene glycol (PEG), a polypropylene glycol (PPG), a polybutylene glycol, a polytetrahydrofuran (PTMG), or a mixture thereof. More particularly, the polyether polyol may be a polytetrahydrofuran (flexible blocks of thermoplastic polyurethane therefore being blocks of polytetrahydrofuran) and / or a polypropylene glycol (flexible blocks of thermoplastic polyurethane therefore being blocks of polypropylene glycol) and / or a polyethylene glycol (flexible blocks of thermoplastic polyurethane therefore being blocks of polyethylene glycol).

[0056] Advantageously, the polyether polyol comprises repeating units having at least 4 carbon atoms, for example repeating units having 4, or 5, or 6, carbon atoms.

[0057] Preferably, the polyether polyol is a polytetrahydrofuran, preferably having a number average molar mass of 500 to 15000 g / mol, preferably 1000 to 3000 g / mol. The polyether polyol may be a polyether diol which is the reaction product of ethylene oxide and propylene oxide; the molar ratio of ethylene oxide to propylene oxide is preferably 0.01 to 100, more preferably 0.1 to 9, more preferably 0.25 to 4, more preferably 0.4 to 2.5, more preferably 0.6 to 1.5 and is most preferably 1.

[0058] The polysiloxane diols usable in the invention preferably have a number-average molar mass of 500 to 15000 g / mol, preferably of 1000 to 3000 g / mol. The number-average molar mass can be determined by GPC, preferably according to ISO 16014-1:2012. Advantageously, the polysiloxane diol is a polysiloxane of formula (I): [Chem.

[0059] HO-[R- in which R is preferably a C2-C4 alkylene, R' is preferably a C1-C4 alkyl and each of n, m and p independently represents an integer preferably between 0 and 50, m being more preferably from 1 to 50, even more preferably from 2 to 50. Preferably, the polysiloxane has the following formula (II):

[0060] [Chem. 2] in which Me is a methyl group, or the following formula (III):

[0061] [Chem. 3]

[0062] The polyalkylene diols which can be used in the invention are preferably based on butadiene.

[0063] The polycarbonate diols that can be used in the invention are very preferably aliphatic polycarbonate diols. The polycarbonate diol is preferably based on alkanediol. Preferably, it is strictly bifunctional. The preferred polycarbonate diols according to the invention are those based on butanediol, pentanediol and / or hexanediol, in particular 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methylpentane-(1,5)-diol, or mixtures thereof, more preferably based on 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, or mixtures thereof. In particular, the polycarbonate diol may be a polycarbonate diol based on butanediol and hexanediol, or based on pentanediol and hexanediol, or based on hexanediol, or may be a mixture of two or more of these polycarbonate diols.The polycarbonate diol advantageously has a number average molar mass of 500 to 4000 g / mol, preferably 650 to 3500 g / mol, more preferably 800 to 3000 g / mol. The number average molar mass can be determined by GPC, preferably according to ISO 16014-1:2012.

[0064] Advantageously, the compound reactive with the isocyanate, preferably the polyol, is biosourced.

[0065] One or more polyols may be used as the isocyanate-reactive compound. Particularly preferably, the flexible TPU blocks are polyether blocks comprising repeating units having at least 4 carbon atoms, even more preferably polytetrahydrofuran blocks.

[0066] A chain extender is used for the preparation of thermoplastic polyurethane, in addition to polyisocyanate and isocyanate-reactive compound.

[0067] The chain extender is aliphatic. The chain extender may be acyclic aliphatic, araliphatic, and / or cycloaliphatic. Preferably, the chain extender is linear. It advantageously has a number-average molar mass of 50 to 499 g / mol. The number-average molar mass may be determined by GPC, preferably according to ISO 16014-1:2012. The chain extender preferably has two isocyanate-reactive groups (also called "functional groups"). A single chain extender or a mixture of two or more chain extenders may be used.

[0068] The chain extender is preferably bifunctional. Examples of chain extenders are diamines and diols, and more particularly alkanediols having from 2 to 10 carbon atoms. Preferably, the chain extender is a diol. In particular, the chain extender may be selected from the group consisting of 1,2-ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanediol, 1,4-dimethanol cyclohexane, neopentyl glycol, hydroquinone bis(beta-hydroxyethyl)ether (HQEE), di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona- and / or deca-alkylene glycol, their respective oligomers, polypropylene glycol and mixtures thereof.Preferably, the chain extender according to the invention is a diol chain extender comprising at most 8 carbon atoms, more preferably at most 6 carbon atoms; for example a diol chain extender comprising 2, or 3, or 4, or 5, or 6, or 7, or 8, carbon atoms. More preferably, the chain extender is chosen from the group consisting of 1,2-ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and mixtures thereof, and more preferably it is chosen from 1,3-propanediol, 1,4-butanediol and / or 1,6-hexanediol. Even more preferably, the chain extender is 1,4-butanediol. The chain extender may also be a mixture of 1,4-butanediol and 1,6-hexanediol, particularly in a molar ratio of 6:1 to 10:1.Preferably, the chain extender is bio-sourced; bio-sourced chain extenders that may be mentioned include, for example, 1,4-butanediol, 1,3-propanediol and 1,6-hexanediol.

[0069] The TPU according to the invention preferably has a number average molar mass greater than or equal to 10,000 g / mol, preferably greater than or equal to 40,000 g / mol and more preferably greater than or equal to 60,000 g / mol. Preferably, the number average molar mass of the TPU is less than or equal to 80,000 g / mol. In embodiments, the number average molar mass of the TPU is from 10,000 to 25,000 g / mol, or from 25,000 to 40,000 g / mol, or from 40,000 to 50,000 g / mol, or from 50,000 to 60,000 g / mol, or from 60,000 to 70,000 g / mol, or from 70,000 to 80,000 g / mol. Number-average molar masses can be determined by gel permeation chromatography (GPC).

[0070] The content of rigid blocks in the TPU is preferably less than or equal to 90% by mass and more preferably less than or equal to 80% by mass (relative to the total mass of the TPU). More advantageously, the content of rigid blocks in the TPU is from 30 to 60% by mass (the amount of flexible blocks being from 40 to 70% by mass).More particularly, the content of rigid blocks in the TPU may be 10 to 20% by mass (the amount of soft blocks being 80 to 90% by mass), or 20 to 30% by mass (the amount of soft blocks being 70 to 80% by mass), or 30 to 40% by mass (the amount of soft blocks being 60 to 70% by mass), or 40 to 50% by mass (the amount of soft blocks being 50 to 60% by mass), or 50 to 60% by mass (the amount of soft blocks being 40 to 50% by mass), or 60 to 70% by mass (the amount of soft blocks being 30 to 40% by mass), or 70 to 80% by mass (the amount of soft blocks being 20 to 30% by mass). mass), or 80 to 90% by mass (the amount of soft blocks being 10 to 20% by mass). These amounts result in a foam with a lower density, greater flexibility and better rebound resilience.The rigid block content, expressed as a percentage, is defined as follows: [(mass fraction of polyisocyanates + mass fraction of chain extender) / (mass fraction of polyisocyanates + mass fraction of chain extender + mass fraction of compounds reactive with isocyanate)] x 100.

[0071] It can be measured by proton NMR in a solvent chosen from DMSO D6, tetrachloromethane and deuterated chloroform (CDCIs), preferably DMSO D6, in particular at 298 K. Advantageously, the TPU is semi-crystalline. Its melting temperature Tm is preferably between 100°C and 230°C, more preferably between 120°C and 200°C. The melting temperature can be measured according to ISO 11357-3 Plastics - Differential scanning calorimetry (DSC) Part 3.

[0072] The TPU may be a recycled TPU. Advantageously, the TPU may be a partially or, preferably, completely bio-sourced TPU. In particular, the TPU may be prepared from at least one bio-sourced diisocyanate (for example chosen from 1,5-pentamethylene diisocyanate, nonamethylene diisocyanate, decamethylene diisocyanate and their mixture), at least one bio-sourced diol chain extender (for example 1,4-butanediol) and at least one bio-sourced polyol.

[0073] Advantageously, the TPU has a hot melt flow index (or MFI) of 1 to 200 g / 10 min, in particular 10 to 100 g / 10 min, preferably 25 to 80 g / 10 min, more preferably 35 to 65 g / 10 min. In particular, the melt flow rate of TPU can be 10 to 25 g / 10 min, or 25 to 35 g / 10 min, or 35 to 45 g / 10 min, or 45 to 55 g / 10 min, or 55 to 65 g / 10 min, or 65 to 80 g / 10 min, or 80 to 100 g / 10 min, or 100 to 150 g / 10 min, or 150 to 200 g / 10 min. The melt flow rate is measured at 200°C under a load of 10 kg, according to ASTM D1238.

[0074] Preferably, the TPU has a Shore D hardness of less than or equal to 75, more preferably less than or equal to 65. In particular, the TPU used in the invention may have a hardness of 65 Shore A to 70 Shore D, preferably of 75 Shore A to 60 Shore D. The hardness measurements may be carried out according to the ISO 7619-1 standard.

[0075] Advantageously, the TPU according to the invention has a concentration as an OH function of 0.002 meq / g to 0.6 meq / g, preferably of 0.01 meq / g to 0.4 meq / g, more preferably of 0.03 meq / g to 0.2 meq / g. In embodiments, the TPU according to the invention has an OH-dependent concentration of 0.002 to 0.005 meq / g, or 0.005 to 0.01 meq / g, or 0.01 to 0.02 meq / g, or 0.02 to 0.04 meq / g, or 0.04 to 0.06 meq / g, or 0.06 to 0.08 meq / g, or 0.08 to 0.1 meq / g, or 0.1 to 0.2 meq / g, or 0.2 to 0.3 meq / g, or 0.3 to 0.4 meq / g, or 0.4 to 0.5 meq / g, or 0.5 to 0.6 meq / g. The concentration in OH function can be determined by proton NMR in a solvent chosen from DMSO D6, tetrachloromethane or deuterated chloroform (CDCh), preferably DMSO D6, in particular at 298 K.

[0076] Very advantageously, the TPU is not crosslinked. The TPU in the foam according to the invention comprises at least functions chosen from allophanate functions, isocyanurate functions or a combination thereof. By "allophanate" is meant the group (or function) formed by the reaction of an isocyanate function with a urethane function. By "isocyanurate" is meant the group (or function) formed by the reaction of three isocyanate functions with each other. More preferably, the TPU comprises at least allophanate functions. In particular, the TPU may comprise allophanate functions and optionally isocyanurate functions. In other embodiments, the TPU comprises at least isocyanurate functions. In other embodiments, the TPU comprises allophanate functions and isocyanurate functions.

[0077] Advantageously, the TPU comprises a content of allophanate and isocyanurate functions (i.e. the sum of the allophanate functions and the isocyanurate functions), relative to the urethane functions, of 0.01 to 1 mol%, preferably of 0.05 to 0.5 mol%. In particular, the content of allophanate and isocyanurate functions, relative to the urethane functions, may be from 0.01 to 0.05 mol%, or from 0.05 to 0.1 mol%, or from 0.1 to 0.2 mol%, or from 0.2 to 0.3%, or from 0.3 to 0.4 mol%, or from 0.4 to 0.5 mol%, or from 0.5 to 0.6 mol%, or from 0.6 to 0.8 mol%, or from 0.8 to 1 mol%. The content of allophanate functions and the content of isocyanurate functions may be, independently or together, measured by proton NMR, for example in a solvent chosen from DMSO D6, tetrachloromethane and deuterated chloroform (CDCIs), preferably DMSO D6, in particular at 298 K., via the integration of peaks corresponding to CH2 in position a of urethane, allophanate and / or isocyanurate functions.

[0078] The TPU in the foam according to the invention may comprise a content of allophanate functions of 0.01 to 1 mol%, preferably 0.05 to 0.5 mol%, relative to the urethane functions. In particular, the content of allophanate functions relative to the urethane functions may be 0.01 to 0.05 mol%, or 0.05 to 0.1 mol%, or 0.1 to 0.2 mol%, or 0.2 to 0.3%, or 0.3 to 0.4 mol%, or 0.4 to 0.5 mol%, or 0.5 to 0.6 mol%, or 0.6 to 0.8 mol%, or 0.8 to 1 mol%.

[0079] The TPU in the foam according to the invention may comprise a content of isocyanurate functions of, relative to the urethane functions, 0.01 to 1 mol%, preferably 0.05 to 0.5 mol%. In particular, the content of isocyanurate functions relative to the urethane functions may be 0.01 to 0.05 mol%, or 0.05 to 0.1 mol%, or 0.1 to 0.2 mol%, or 0.2 to 0.3%, or 0.3 to 0.4 mol%, or 0.4 to 0.5 mol%, or 0.5 to 0.6 mol%, or 0.6 to 0.8 mol%, or 0.8 to 1 mol%.

[0080] TPU foam

[0081] The TPU foam according to the invention advantageously comprises at least 60% by mass of thermoplastic polyurethane (total) relative to the total mass of the foam. Preferably, the foam comprises at least 80% by mass, more preferably at least 90% by mass, more preferably at least 95% by mass, of thermoplastic polyurethane relative to the total mass of the foam. In particular, the foam may comprise from 60 to 70% by mass, or from 70 to 80% by mass, or from 80 to 85% by mass, or from 85 to 90% by mass, or from 90 to 95% by mass, or from 95 to 97% by mass, or from 97 to 99% by mass, or from 99 to 100% by mass, of thermoplastic polyurethane (total) relative to the total mass of the foam. In embodiments, the polymer of the foam consists of one (or more) TPUs.

[0082] Preferably, the foam according to the invention comprises at least 60% by mass, more preferably at least 80% by mass, more preferably at least 90% by mass, more preferably at least 95% by mass, of essentially aliphatic thermoplastic polyurethane comprising allophanate and / or isocyanurate functions, relative to the total mass of the foam; for example from 60 to 70% by mass, or from 70 to 80% by mass, or from 80 to 85% by mass, or from 85 to 90% by mass, or from 90 to 95% by mass, or from 95 to 97% by mass, or from 97 to 99% by mass, or from 99 to 100% by mass, of essentially aliphatic thermoplastic polyurethane comprising allophanate and / or isocyanurate functions relative to the total mass of the foam. Advantageously, the polymer of the foam consists of at least one essentially aliphatic TPU comprising allophanate and / or isocyanurate functions.

[0083] Advantageously, the TPU of the foam consists of at least one essentially aliphatic thermoplastic polyurethane comprising allophanate and / or isocyanurate functions (i.e. the essentially aliphatic TPU(s) comprising allophanate and / or isocyanurate functions are the only TPUs of the foam), or consists essentially of at least one essentially aliphatic thermoplastic polyurethane comprising allophanate and / or isocyanurate functions (i.e. the essentially aliphatic TPU(s) comprising allophanate and / or isocyanurate functions represent at least 95% by mass of the TPU of the foam).

[0084] Alternatively, the TPU of the foam may comprise one or more additional TPUs, for example one or more aromatic TPUs, preferably in an amount less than or equal to 30% by mass, more preferably less than or equal to 20% by mass, more preferably less than or equal to 15% by mass, more preferably less than or equal to 10% by mass, even more preferably less than or equal to 5% by mass, even more preferably less than or equal to 2% by mass, relative to the total mass of the TPU of the foam.

[0085] The foam matrix may consist essentially of, or consist of, the at least one essentially aliphatic TPU comprising allophanate and / or isocyanurate functionalities. The foam may also comprise degradation products of a blowing agent (particularly in its matrix), particularly when a chemical blowing agent has been used to form the foam.

[0086] Alternatively, the foam may comprise one or more additives, for example ethylene and vinyl acetate copolymers or EVA (for example those marketed under the name Evatane® by SK Chemical), or ethylene and acrylate copolymers, or ethylene and alkyl(meth)acrylate copolymers, for example those marketed under the name Lotryl® by SK Chemical. These additives may make it possible to adjust the hardness of the foamed part, its appearance and its comfort. The foam according to the invention may also comprise one or more polyamide block and polyether block copolymers or “PEBA” (for example, those marketed under the name Pebax® by Arkema, under the name Vestamid® by Evonik®, under the name Grilamid® by EMS and / or under the name Pelestat® by Sanyo).Other additives suitable for the invention include pigments (such as TiO2 and other compatible colored pigments), adhesion promoters (to improve the adhesion of the foam to other materials), fillers (e.g., calcium carbonate, barium sulfate and / or silicon oxide), nucleating agents (particularly in pure or concentrated form, e.g., CaCOs, ZnO, SiO2, or combinations of two or more thereof), rubbers (to improve rubbery elasticity, such as natural rubber, SBR, polybutadiene and / or ethylene propylene terpolymers), stabilizers (e.g., antioxidants, UV absorbers and / or flame retardants), processing aids (e.g., stearic acid), antioxidants, including phenolic antioxidants such as IRGANOX from Ciba Geigy Inc.The additives may be present in a content of 0 to 30% by mass, preferably 0.1 to 20% by mass, more preferably 0.2% to 10% by mass, relative to the total mass of the foam.

[0087] Preferably, the foam according to the invention is at least 50% thermoplastic by mass, preferably at least 60% thermoplastic by mass, more preferably at least 70% thermoplastic by mass, more preferably at least 80% thermoplastic by mass, more preferably at least 90% thermoplastic by mass, even more preferably at least 95% thermoplastic by mass, even more preferably 100% thermoplastic by mass. The thermoplastic proportion of the foam (in mass percentage) can be determined by measuring the solubility of the foam in DMSO D6 (in mass percentage).

[0088] The foam according to the invention preferably has a density less than or equal to 800 kg / m3 , preferably still less than or equal to 600 kg / m 3 , more preferably less than or equal to 400 kg / m 3 , even more preferably less than or equal to 300 kg / m 3 . For example, it can have a density of 25 to 600 kg / m 3 , and more particularly preferably from 50 to 300 kg / m 3 The density of the foam can range from 25 to 100 kg / m 3 , or from 100 to 200 kg / m 3 , or 200 to 250 kg / m 3 , or 250 to 300 kg / m 3 , or 300 to 400 kg / m 3 , or 400 to 500 kg / m 3 , or 500 to 600 kg / m 3 , or 600 to 800 kg / m 3 Density control can be achieved by adapting the manufacturing process parameters. Density can be measured at 23°C according to ISO 1183-1.

[0089] Preferably, the foam according to the invention has an Asker C hardness of 20 to 90, preferably 25 to 70. In particular, the Asker C hardness of the foam may be 20 to 25, or 25 to 30, or 30 to 40, or 40 to 50, or 50 to 60, or 60 to 70, or 70 to 80, or 80 to 90. The Asker C hardness may be determined at 23°C, after 3 seconds, according to ISO 48-4:2018.

[0090] Preferably, the foam has a rebound resilience greater than or equal to 50%, more preferably greater than or equal to 60%, more preferably greater than or equal to 70%. The rebound resilience is measured according to ISO 8307:2007 but using an 18.8 g ball.

[0091] Preferably, this foam has a compression set of less than or equal to 70%, more preferably less than or equal to 65%, more preferably less than or equal to 50%, for example less than or equal to 45%, or less than or equal to 40%, or less than or equal to 35%. The compression set (CS) is measured according to the following method: a foam sample is compressed to a strain rate of 50%, at a temperature of 50°C and for a holding time of 6 hours, then the stress is released. The residual deformation after a recovery time of 30 minutes is measured according to a method adapted from the ISO1856 standard. The residual deformation after compression, expressed as a percentage, is given by the formula: dO — dr DRC = - — xlOO du — de in which dO is the initial thickness of the specimen, de is the thickness of the compressed specimen and dr is the thickness of the specimen after the recovery time.

[0092] Preferably, this foam also exhibits excellent fatigue resistance and damping properties.

[0093] Preferably, this foam also has good resistance to tearing, crack initiation and propagation.

[0094] The foam according to the invention can be used to manufacture sports equipment, such as soles of sports shoes, ski boots, midsoles, insoles, or even functional components of soles, in the form of inserts in different parts of the sole (heel or arch of the foot for example), or even components of the uppers of shoes in the form of reinforcements or inserts in the structure of the upper of the shoe, in the form of protections.

[0095] It can also be used to make balls, sports gloves (e.g. football gloves), golf ball components, rackets, protective elements (vests, interior elements of helmets, shells, etc.).

[0096] The foam according to the invention has interesting anti-shock, anti-vibration and anti-noise properties, combined with haptic properties suitable for capital goods. It can therefore also be used for the manufacture of railway rail bases, or various parts in the automotive industry, in transport, in electrical and electronic equipment, in construction or in the manufacturing industry.

[0097] According to advantageous embodiments, the foam objects according to the invention can be easily recycled, for example by melting them in an extruder equipped with a degassing outlet (optionally after having cut them into pieces).

[0098] TPU preparation

[0099] Advantageously, a catalyst is used to synthesize the thermoplastic polyurethane. The catalyst accelerates the reaction between the NCO groups of the polyisocyanate and the isocyanate-reactive compound (preferably with the hydroxyl groups of the isocyanate-reactive compound) and with the chain extender.

[0100] The catalyst is preferably a tertiary amine, more preferably selected from triethylamine, dimethylcyclohexylamine, N-methylmorpholine, N,N'-dimethylpiperazine, 2-(dimethylaminoethoxy)ethanol and / or diazabicyclo-(2,2,2)octane. Alternatively, or additionally, the catalyst is an organic metal compound such as a titanium acid ester, an iron compound, preferably ferric acetylacetonate, a tin compound, preferably those of carboxylic acids, more preferably tin diacetate, tin dioctoate, tin dilaurate or dialkyl tin salts, preferably dibutyltin diacetate and / or dibutyltin dilaurate, a bismuth carboxylic acid salt, preferably bismuth decanoate, or a mixture thereof.

[0101] More preferably, the catalyst is selected from the group consisting of tin dioctoate, bismuth decanoate, titanium acid esters and mixtures thereof. More preferably, the catalyst is tin dioctoate.

[0102] When preparing thermoplastic polyurethane, the molar ratios of the isocyanate-reactive compound and the chain extender can be varied to adjust the hardness and melt flow rate of the TPU. Indeed, as the proportion of chain extender increases, the hardness and melt viscosity of the TPU increase while the melt flow rate of the TPU decreases. For the production of soft TPU, preferably TPU having a Shore A hardness of less than 95, more preferably 75 to 95, the isocyanate-reactive compound and the chain extender may be used in a molar ratio of 1:1 to 1:5, preferably 1:1.5 to 1:4.5, preferably such that the mixture of isocyanate-reactive compound and chain extender has a hydroxyl equivalent mass of greater than 200, more preferably 230 to 650, even more preferably 230 to 500.For the production of a harder TPU, preferably a TPU having a Shore A hardness greater than 98, preferably a Shore D hardness of 55 to 75, the isocyanate-reactive compound and the chain extender may be used in a molar ratio of 1:5.5 to 1:15, preferably 1:6 to 1:12, preferably such that the mixture of isocyanate-reactive compound and chain extender has a hydroxyl equivalent mass of 110 to 200, more preferably 120 to 180.

[0103] Preferably, to prepare the TPU, the polyisocyanate is added to the reaction medium comprising at least the isocyanate-reactive compound and preferably the chain extender. Even more preferably, the polyisocyanate is added to the reaction medium comprising the isocyanate-reactive compound so as to create locally at the point of addition of the polyisocyanate a high concentration of polyisocyanate. This high local concentration of polyisocyanate can in particular be formed by adapting the rate of addition of the polyisocyanate and / or the stirring of the reaction medium (in particular at the point of addition of the polyisocyanate), for example by adding the polyisocyanate rapidly and / or by stirring slowly (or not stirring) the reaction medium.The creation of a high local concentration of polyisocyanate in the reaction medium, at the point of addition of the polyisocyanate, makes it possible to promote the formation of allophanate and / or isocyanurate functions in the TPU.

[0104] Advantageously, to prepare the TPU, the polyisocyanate, the isocyanate-reactive compound, and the chain extender are reacted, preferably in the presence of a catalyst, in amounts such that the equivalent ratio of the NCO groups of the polyisocyanate to the sum of the hydroxyl groups of the isocyanate-reactive compound and the chain extender is from 0.95:1 to 1.10:1, preferably from 0.98:1 to 1.08:1, more preferably from 1:1 to 1.05:1. Very advantageously, the equivalent ratio of the NCO groups of the polyisocyanate to the sum of the hydroxyl groups of the isocyanate-reactive compound and the chain extender is from 0.98:1 to 1.05:1, preferably from 0.995:1 to 1.02:1; such ratios help to aid the formation of allophanate and / or isocyanurate functions in the TPU.

[0105] The catalyst is advantageously present in an amount of 0.0001 to 0.1 parts by mass per 100 parts by mass of the TPU synthesis reagents. Very advantageously, no external branching agent is added during the preparation of the TPU (it being understood that the term "external branching agent" designates the branching agents other than the polyisocyanate, the isocyanate-reactive compound, and the chain extender). Thus, preferably, the prepared TPU consists solely of residues derived from the polyisocyanate, the isocyanate-reactive compound, and the chain extender.

[0106] Preparation of the mousse

[0107] The foam according to the invention can be prepared by mixing at least one essentially aliphatic TPU (or a polymer composition comprising at least one essentially aliphatic TPU) with a blowing agent (and optionally with one or more additives), then carrying out a foaming step.

[0108] The essentially aliphatic TPU which is mixed with the blowing agent may comprise functions selected from allophanate functions, isocyanurate functions or a combination thereof, or may be devoid of such functions (the TPU may be devoid of allophanate functions, or devoid of isocyanurate functions or, more particularly, devoid of allophanate and isocyanurate functions, the TPU may in particular be linear).

[0109] The blowing agent may be a chemical or physical agent, or may also consist of any type of hollow object or any type of expandable microsphere. Preferably, it is a physical agent, such as, for example, nitrogen or carbon dioxide, or a hydrocarbon, chlorofluorocarbon, hydrochlorocarbon, hydrofluorocarbon or hydrochlorofluorocarbon (saturated or unsaturated) or a mixture thereof. For example, butane or pentane may be used. Also preferably, it may also be a chemical agent, such as, for example, azodicarbonamide or mixtures based on citric acid and sodium hydrogen carbonate (NaHCOs) (such as the product from the Clariant Hydrocerol® range).

[0110] According to the invention, very preferably, the essentially aliphatic TPU undergoes at least one passage in the molten state before its mixing with the blowing agent (for example during its preparation, or after, such as during a possible step of shaping the TPU or during a possible step of adding additives to the TPU), and / or in the step of mixing with the blowing agent and / or in the foaming step.Advantageously, the essentially aliphatic TPU is subjected, during at least one passage in the molten state, to a temperature greater than or equal to 160°C, preferably greater than or equal to 170°C, more preferably greater than or equal to 180°C, more preferably greater than or equal to 190°C, more preferably greater than or equal to 200°C (for example at a temperature of 160°C to 250°C, preferably from 180°C to 230°C, more preferably from 200°C to 220°C), preferably for a duration greater than or equal to 30 s, preferably greater than or equal to 1 min, more preferably greater than or equal to 1.5 min. In embodiments, the temperatures mentioned above are applied for a duration of at least 3 min, preferably at least 5 min. Applying such temperatures to the TPU for the durations indicated above helps to aid the formation of allophanate and / or isocyanurate functions in the TPU.

[0111] To facilitate the creation of allophanate and / or isocyanurate functions in the TPU of the foam, one can:

[0112] - increasing the local concentration of polyisocyanate when it is added to the reaction medium, during the synthesis of TPU, in particular by increasing the rate of addition of the polyisocyanate to the reaction medium and / or by reducing the stirring rate of the reaction medium;

[0113] - increasing the equivalent ratio of NCO groups in the polyisocyanate to the sum of the hydroxyl groups in the isocyanate-reactive compound and the chain extender during TPU synthesis; and

[0114] - increase the temperature applied to the TPU and / or its application time, during the preparation of the TPU and / or during the manufacture of the foam.

[0115] Thus, by adjusting the various parameters above (addition rate of the polyisocyanate; stirring rate of the reaction medium; ratio of NCO groups / OH groups; temperature applied to the TPU; duration of application of this temperature) in a combined manner, the person skilled in the art is able to form foam of allophanate and / or isocyanurate groups in the TPU, and to adjust the content of allophanate and isocyanurate functions in this TPU.

[0116] In embodiments, the blowing agent is blended with the substantially aliphatic TPU (or the polymer composition comprising the at least one substantially aliphatic TPU) in a molten state. Preferably, the blowing agent is a physical blowing agent. The physical blowing agent may be in liquid or supercritical form and is then converted to the gas phase during the foaming step. Foaming may be caused by a pressure drop, for example resulting from the exit of an extruder.

[0117] Advantageously, the mixture of essentially aliphatic TPU and the blowing agent and / or the foaming of the mixture (regardless of the method for preparing the foam used) is carried out at a temperature greater than or equal to 160°C, preferably greater than or equal to 170°C, more preferably greater than or equal to 180°C, more preferably greater than or equal to 190°C, more preferably greater than or equal to 200°C, for example at a temperature of 160°C to 250°C, preferably 180°C to 230°C, more preferably 200°C to 220°C. This temperature is preferably applied for a duration greater than or equal to 30 s, preferably greater than or equal to 1 min, more preferably greater than or equal to 1.5 min. In embodiments, this temperature is applied for a duration of at least 3 min, preferably at least 5 min (for example, in foam injection processes).

[0118] In advantageous embodiments, the mixture of essentially aliphatic TPU and the blowing agent is injected into a mold and foaming is carried out in the mold. Foaming can be caused by under-dosing, by opening the mold, by removing gas counter-pressure or by a mold equipped with a Variotherm® system. These techniques make it possible to directly produce three-dimensional foamed objects with complex geometries.

[0119] In advantageous alternative embodiments, the essentially aliphatic TPU is processed, preferably in a molten state, to create a preform. A blowing agent, in particular a chemical blowing agent, may be mixed with the TPU during its processing to form the preform, or before. The preform may be prepared by compression molding, extrusion, injection molding, lamination or 3D printing processes. Preferably, the preform is produced by extrusion or injection molding.Very advantageously, the preparation of the preform, preferably by extrusion or injection molding, is carried out at a temperature greater than or equal to 160°C, preferably greater than or equal to 170°C, more preferably greater than or equal to 180°C, more preferably greater than or equal to 190°C, more preferably greater than or equal to 200°C, for example at a temperature of 160°C to 250°C, preferably 180°C to 230°C, more preferably 200°C to 220°C, this temperature preferably being applied for a duration greater than or equal to 30 s, more preferably greater than or equal to 1 min, for example greater than or equal to 1.5 min, or for a duration of at least 3 min. The preform, in the solid state, may be contacted with a physical blowing agent in gaseous or supercritical form (in particular, in embodiments in which no blowing agent has been added during, or before, the production of the preform).The physical expansion agent impregnates the solid preform, preferably by applying overpressure. Preferably, the foaming is carried out in an autoclave. Preferably, the pressure within the autoclave is maintained between 0.20 and 50 MPa during foaming. Preferably, the temperature during foaming is in the range from (Tf - 5°C) to (Tf + 40°C), Tf being the melting temperature of the TPU (which can in particular be measured according to the ISO 11357-3:2011 standard). Advantageously, the foaming of the preform is contained in a mold.

[0120] Other foaming techniques that can be used include batch foaming, extrusion foaming, such as single-screw or twin-screw extrusion foaming, and microwave foaming.

[0121] In embodiments, the method of preparing the foam is not a foaming method by producing and then melting expanded particles (or beads).

[0122] In particular, the foam preparation process can be an injection foaming process, extrusion foaming, or preform foaming, particularly in an autoclave. These are relatively simple techniques to implement, particularly compared to certain expanded particle fusion processes: in fact, filling the mold with foamed polymer granules and then melting the particles to ensure mechanical strength of the parts without destroying the structure of the foam are complex operations.

[0123] Examples

[0124] The following examples illustrate the invention without limiting it.

[0125] Two TPUs were prepared: - TPU No. 1: TPU with rigid blocks based on 1,6-HDI and 1,4-BDO (1,4-butanediol) and with soft PTMG blocks, with a hardness of 95 Shore A and a melting point of 148°C. This TPU does not include any allophanate or isocyanurate function.

[0126] - TPU No. 2: TPU with rigid blocks based on 1,6-HDI and 1,4-BDO (1,4-butanediol) and with soft PTMG blocks, with a hardness of 95 Shore A and a melting point of 147°C. This TPU comprises 0.15 mol% of allophanate function compared to the urethane functions of the TPU.

[0127] The content of allophanate and isocyanurate functions (in molar percentage relative to the urethane functions) was measured by proton NMR at 600 MHz and 298 K, in DMSO D6, via the integration of the peaks corresponding to CH2 in the a position of the urethane, allophanate and isocyanurate functions.

[0128] The TPUs were prepared as shown below.

[0129] TPU No. 1: TPU No. 1 was synthesized from the following reagents:

[0130] - 22.9% by mass of 1,6-hexamethylene diisocyanate (1,6-HDI);

[0131] - 5.9% by mass of 1,4-butanediol; and

[0132] - 71.2% by mass of PTMG polyol having a molar mass of 1000 g / mol and a functionality of 2.

[0133] TPU was obtained by adding the diisocyanate 1,6-HDI to the mixture of 1,4-butanediol and PTMG initially placed in a stainless steel reactor equipped with a stirrer under nitrogen flushing.

[0134] The initial temperature of the mixture is 90°C. The addition of 1,6-HDI is carried out over 25 minutes with stirring set at 300 rpm. At the end of the 25-minute addition, the temperature of the reaction mixture is 173°C.

[0135] The reaction mixture was kept at this temperature for 5 minutes under stirring and nitrogen flushing. The TPU thus synthesized was then extruded and pelletized.

[0136] TPU No. 2: TPU No. 2 was synthesized from the following reagents:

[0137] - 22.9% by mass of 1,6-hexamethylene diisocyanate (1,6-HDI);

[0138] - 5.9% by mass of 1,4-butanediol; and

[0139] - 71.2% by mass of PTMG polyol having a molar mass of 1000 g / mol and a functionality of 2.

[0140] TPU was obtained by adding the diisocyanate 1,6-HDI to the mixture of 1,4-butanediol and PTMG initially placed in a stainless steel reactor equipped with a stirrer under nitrogen flushing.

[0141] The initial temperature of the mixture is 90°C. The addition of 1,6-HDI was carried out in 10 minutes with stirring set at 300 rpm. At the end of the 10 minutes of addition, the temperature of the reaction mixture is 191°C.

[0142] The reaction mixture was kept at this temperature for 5 minutes under stirring and nitrogen flushing. The TPU thus synthesized was then extruded and pelletized.

[0143] An oscillatory rheometry analysis was performed on both TPUs. For this, the complex viscosity (q*) of TPUs No. 1 and 2 was determined by oscillatory rheometry according to ISO 6721-10 with a plane-plane geometry of diameter 25 mm and a gap of 1 mm. The measurement was carried out in the linear domain under nitrogen sweeping, at 180°C (melting point of TPU + 30°C) so that the samples were completely melted.

[0144] The results obtained are as follows. Over the low angular frequency range between 0.135 and 1.35 rd / s, the complex viscosity of TPU No. 1 reaches a so-called Newtonian plateau, while that of TPU No. 2 experiences a rise in viscosity at low gradients. The complex viscosity of TPU No. 2 as measured at the angular frequency of 0.135 rd / s is at least 25% higher than that of TPU No. 1.

[0145] This viscosification at low angular frequencies reflects a greater ability of TPU No. 2 to contain the expansion of the gas (used as a blowing agent) during the foaming phase when used for the formation of a foam, compared to TPU No. 1.

[0146] Foams were prepared from TPUs No. 1 and 2 described above according to the following protocol.

[0147] These foams were manufactured using an Arburg Allrounder 320 S injection molding machine, with a Mucell injection system. The operating parameters are as follows:

[0148] - Barrel temperature (from hopper to nozzle): 70 to 180°C.

[0149] - Injection speed: 70 cm 3 / s.

[0150] - Holding time before opening the mold: 30 to 40 s.

[0151] - Applied pressure: 27.5 MPa.

[0152] - Mold temperature: 45°C.

[0153] - Mold opening length: 12 mm.

[0154] - Mold opening speed. 20 mm / s.

[0155] - Mold: plate mold with dimensions 145 x 100 x 3 mm. The foaming agent (or expansion agent) used is nitrogen which was introduced at a rate of 0.8% by mass, relative to the total mass of the polymer.

[0156] Foam No. 1, prepared from TPU No. 1, corresponds to a comparative foam, foam No. 2, prepared from TPU No. 2, is a foam according to the invention.

[0157] Due to the viscosification capacity at low angular frequencies of the TPU composing it, foam No. 2 according to the invention (prepared from a TPU comprising allophanate functions) is finer and more homogeneous than comparative foam No. 1 (prepared from a TPU without allophanate and isocyanurate functions), and has improved mechanical performance.

Claims

Claims 1. Thermoplastic polyurethane foam, comprising at least one thermoplastic polyurethane comprising at least 90% by mass of aliphatic units relative to the total mass of the thermoplastic polyurethane and comprising functions chosen from allophanate functions, isocyanurate functions or a combination thereof.

2. Foam according to claim 1, in which the at least one thermoplastic polyurethane comprises a content of allophanate and / or isocyanurate functions, relative to the urethane functions, of from 0.01 to 1 mol%, preferably from 0.05 to 0.5 mol%.

3. Foam according to claim 1 or 2, in which the at least one thermoplastic polyurethane comprises allophanate functions.

4. Foam according to one of claims 1 to 3, comprising at least 80% by mass, preferably at least 90% by mass, more preferably at least 95% by mass, even more preferably at least 99% by mass, of thermoplastic polyurethane relative to the total mass of the foam.

5. Foam according to one of claims 1 to 4, in which the at least one thermoplastic polyurethane is a copolymer with rigid blocks and soft blocks, in which: - the flexible blocks are chosen from polyether blocks, polyester blocks, polycarbonate blocks and a combination thereof, preferably the flexible blocks are polyether blocks; and - the rigid blocks comprise units derived from at least one aliphatic polyisocyanate and at least one diol chain extender.

6. Foam according to claim 5, wherein the flexible blocks are polyether blocks comprising repeating units having at least 4 carbon atoms, preferably polytetrahydrofuran blocks.

7. Foam according to claim 5 or 6, in which the at least one aliphatic polyisocyanate is a linear aliphatic diisocyanate, preferably having between the isocyanate functions a linear chain comprising from 5 to 10 carbon atoms, and is more preferably chosen from the group consisting of 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate, nonamethylene diisocyanate, decamethylene diisocyanate and combinations thereof.

8. Foam according to one of claims 5 to 7, in which the at least one diol chain extender comprises a carbon number less than or equal to 8, preferably the at least one diol chain extender is chosen from 1,3-propanediol, 1,4-butanediol and / or 1,6-hexanediol.

9. Foam according to one of claims 1 to 8, having a density less than or equal to 800 kg / m 3 , preferably less than or equal to 400 kg / m 3 , more preferably from 50 to 300 kg / m 3 .

10. Process for preparing a thermoplastic polyurethane foam comprising at least one thermoplastic polyurethane comprising at least 90% by mass of aliphatic units relative to the total mass of the thermoplastic polyurethane and comprising functions chosen from allophanate functions, isocyanurate functions or a combination thereof, comprising the following steps: - the provision of at least one thermoplastic polyurethane comprising at least 90% by mass of aliphatic units relative to the total mass of the thermoplastic polyurethane; - mixing said at least one thermoplastic polyurethane with a blowing agent; and - foaming the mixture of thermoplastic polyurethane and blowing agent, wherein, in at least one of these steps, the thermoplastic polyurethane is in the molten state.

11. A method according to claim 10, wherein the thermoplastic polyurethane foam is as defined in one of claims 2 to 9.

12. Method according to claim 10 or 11, in which the thermoplastic polyurethane comprising at least 90% by mass of aliphatic units relative to the total mass of the thermoplastic polyurethane is subjected, in at least one of the steps of the method, to a temperature greater than or equal to 160°C, preferably greater than or equal to 180°C, more preferably greater than or equal to 200°C, for a duration greater than or equal to 30 s, preferably greater than or equal to 1 min, more preferably greater than or equal to 1.5 min.

13. Method according to one of claims 10 to 12, in which the blowing agent is mixed with the at least one thermoplastic polyurethane in the molten state, the foaming of the mixture being preferably carried out in a mold.

14. Method according to one of claims 10 to 12, wherein the step of providing the at least one thermoplastic polyurethane comprising at least 90% by mass of aliphatic units relative to the total mass of the thermoplastic polyurethane comprises the preparation of a preform from the thermoplastic polyurethane comprising at least 90% by mass of aliphatic units relative to the total mass of the thermoplastic polyurethane in the molten state, preferably by extrusion, injection molding, compression molding, lamination or 3D printing, more preferably by extrusion or injection molding, the mixing of the at least one thermoplastic polyurethane with the blowing agent preferably being carried out by impregnating the preform with the agent expansion, the foaming of the mixture being preferably carried out in an autoclave.

15. Method according to claim 14, in which the preparation of a preform from the thermoplastic polyurethane in the molten state is carried out at a temperature greater than or equal to 160°C, preferably greater than or equal to 180°C, more preferably greater than or equal to 200°C, applied for a duration greater than or equal to 30 s, preferably greater than or equal to 1 min, more preferably greater than or equal to 1.5 min.

16. Method according to one of claims 10 to 15, in which the step of providing the at least one thermoplastic polyurethane comprises the preparation of the thermoplastic polyurethane by reacting at least one polyol, preferably at least one polyether polyol, with at least one polyisocyanate and with at least one diol chain extender, in which the molar ratio of the isocyanate functions of the polyisocyanate relative to the sum of the hydroxyl functions of the at least one polyol and of the at least one diol chain extender is from 0.98 to 1.05, preferably from 0.995 to 1.

02.

17. Article made of a foam according to one of claims 1 to 9 or comprising at least one element made of a foam according to one of claims 1 to 9, preferably chosen from soles of sports shoes, balls, gloves, personal protective equipment, soles for rails, automobile parts, construction parts and parts of electrical and electronic equipment.

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