Polyesters for expansion in an autoclave

Abstract

The present invention relates to a biodegradable polyester particularly suitable for use in autoclave expansion, to a process for obtaining foams from those preforms and to biodegradable and recyclable expanded articles obtained therefrom.

Description

[0001] POLYESTERS FOR EXPANSION IN AN AUTOCLAVE

[0002] DESCRIPTION

[0003] The present invention relates to a biodegradable polyester that is particularly suitable for autoclave expansion, its expansion process and the expanded articles comprising it.

[0004] Usually, autoclave expansion refers to a batch expansion process in which polymer material, for example in pellet form, may be suspended in a liquid medium and is exposed to a physical expansion agent at high pressure and temperature. When the pressure decreases abruptly, the expanding agent begins to expand, forming cells that cause the polymer matrix to expand. This results in an expanded pellet that is then moulded into three-dimensional foam articles, for example by the steam-chest moulding process.

[0005] Autoclave expansion technology is a widely practised industrial process in the foam industry. In some cases, it is employed with a polymer matrix in pellet form. Smaller pellets are preferred because they require less time for both gas diffusion during saturation and heat conduction during expansion. During expansion, the expanding agent can escape into the environment through cell-to-cell diffusion before the cell structure of the expanded pellet is fully stabilised. Because of the loss of gas from the surface layer, the gas concentration is therefore typically lower in the latter.

[0006] Consequently, the density of the foam in the surface layer is usually higher than in the core area, and the core area of the expanded pellet has much larger cells. Also, the surface layer that cools first is strongly orientated in the biaxial direction when expansion occurs. Thus, the mechanical properties of the foam are typically not uniform and are better at the surface layer of the pellet.

[0007] An alternative is to expand the polymer matrix in the form of a sheet or preform obtained, for example, by injection moulding.

[0008] Foamed articles obtained by such industrial processes are particularly suitable for the automotive industry, the construction industry, the packaging sector, particularly the electronics protective packaging sector, and the sporting goods sector.

[0009] In order to obtain foam articles with properties suitable for use in the sectors indicated, particularly for the sporting goods sector and footwear, materials such as expanded polystyrene (EPS), ethylene vinyl acetate (EVA), polyurethanes, and polyolefins such as polypropylene (EPP) are conventionally used.

[0010] However, the use of such materials entails limitations in terms of environmental impact as they are not biodegradable or recyclable, while the use of biodegradable materials (such as PLA) , entails limitations in terms of the complexity of the expansion process, that requires e.g. cross- linking using chemical additives to reach properties suitable for use in the areas indicated, such as for expansion from injection moulded preforms.

[0011] It is therefore of particular interest to develop new materials that not only perform similarly to conventional materials in expansion processes, but also do not require necessarily cross-linking by means of chemical additives and are also biodegradable and recyclable.

[0012] A first object of the present invention is therefore a biodegradable preform, obtainable by injection moulding and suitable for autoclave expansion by physical foaming in the absence of chemical expanders and / or cross-linkers, comprising a biodegradable diacid-diol polyester characterised by an enthalpy of fusion (AHm) lower than 18.5 J / g, preferably lower than 18 J / g a shear viscosity of 1500 Pa.s to 150 Pa.s at 190°C, a melt strength of 0.04 N to 0.002 N at 190°C, and a viscoelastic ratio (RVE) of 15,000 to 200,000.

[0013] The Applicant has found that the said combination of thermal and rheological properties results in a reduction of the orientation of the melted polyester in the preform of the invention.

[0014] This reduction of the orientation of the melt allows in turn to obtain a foamed product in autoclave with a final density in the range required for the desired applications and reduces defects such as delamination, and macrobubbles as well as warpage phenomena.

[0015] With “delamination” is meant an uneven density due to non-homogeneous distribution of cells between the external part and the internal part of the expanded material; with “macrobubble” is meant a spherical or oval cavity with an average diameter greater than 0.5 mm enclosing air or another gas. With “warpage phenomena” (or “shrinkage”) is meant the distortion or deformation of a material, such as unevenness or curvature in the material's shape, caused e.g. by anisotropic internal stresses or shrinkage variations.

[0016] According to one aspect of the invention, said biodegradable polyester is branched, being obtained in the presence of a polyfunctional compound.

[0017] Said preform is advantageously recyclable.

[0018] A further object of the present invention is a process for obtaining foams in the presence of expanding gas under supercritical conditions from the biodegradable preform described above. Said process comprises the steps of: a) placing in an autoclave a non-expanded or partially expanded preform comprising a biodegradable polyester characterised by AHm lower than 18.5 J / g, a shear viscosity of 1500 Pa.s to 150 Pa.s at 190°C, a melt strength of 0.04 N to 0.002 N at 190°C, and a viscoelastic ratio (RVE) of 15,000 to 200,000, in contact with an expanding gas; b) reaching a temperature between the softening point and the closing temperature of the melting peak of said polyester, at a pressure sufficient to maintain the expanding gas under supercritical conditions and for a sufficient time to allow adsorption of said gas by the preform material; c) instantaneously reducing the pressure while keeping the temperature above the softening point of said polyester, resulting in foam.

[0019] Said expanding gas is advantageously chosen from CO2, N2, hydrocarbons and mixtures thereof. CO2, N2 and mixtures thereof are preferred; mixtures including nitrogen are particularly preferred.

[0020] According to a preferred embodiment, in step a) of the process the preform is placed in contact with an expanding gas in the presence of a co-expanding agent (or co-expander) chosen from water, C1-C4 alcohols and mixtures thereof, preferably water. Said co-expanding agent has surprisingly been shown to help reduce density and improve cell distribution in the polymer matrix.

[0021] Foamed articles obtained in an autoclave using the polyester according to the invention possess cells having a particular density and dimensional homogeneity, making them particularly suitable for application in the sporting goods sector, particularly in the production of footwear. A third object of the invention is therefore biodegradable and recyclable foam articles comprising the biodegradable polyester described above, in which the density is less than 0.9 g / cm3, preferably less than 0.7 g / cm3and more than 0.05 g / cm3, preferably 0.10 to 0.50, more preferably 0.15 to 0.40 g / cm3, even more preferably 0.18 to 0.3 g / cm3.

[0022] The invention will be described in greater detail below.

[0023] Figure 1 shows the geometry of the mould used in the injection moulding process of Example 1 including the position of the injection gate.

[0024] The preform according to the invention may be obtained by techniques known to those skilled in the art, for example selected from compression moulding, injection moulding, extrusion, including pre-expansions by the use of expansion agents during moulding, injection or extrusion. Said preform may be obtained by shaping the compression, injection or extrusion product, for example by die-cutting. Said preform may also be obtained by sintering granules or pellets of polymer material.

[0025] The preform according to the invention is preferably obtained by injection moulding. Advantageously, an appropriate position of the injection gates within the mould during the injection moulding process, combined with the thermal and rheological properties of the polyester of the preform of the invention, allows to further reduce sink marks and fountain flow and to increase homogeneity of cooling. An example of design of the mould is shown in Fig. 1. The fewest possible injection gate number is preferred, as a single gate eliminates welding lines.

[0026] Advantageously, as shown below in Example 1, a preform according to the invention expanded in an autoclave (with a preform of 4 x 6 x 10 mm3in a 250 mL autoclave) maintained in static condition at 105°C and lOObar CO2 (e.g. in a thermostatic bath) for 90 minutes, with a releasing time of 3-5 seconds allows to obtain an expanded product having the following characteristics (after a stabilization period of 5 days at 25°C): a density of0.15 + / - 0.01 g / cm3(weigh / volume ratio with volume measured by calliper); a cells’ size of about 110 pm (measured by SEM) and a shrinkage of 10% (variation of density measured immediately after foaming and measured after 5 days stabilization).

[0027] The polyester in the biodegradable preform according to the present invention is advantageously chosen from biodegradable aliphatic and aliphatic-aromatic polyesters.

[0028] In a preferred embodiment, the polyester according to the present invention is a biodegradable aliphatic-aromatic polyester.

[0029] With regard to the aliphatic-aromatic polyesters of the preform according to the invention, they exhibit:

[0030] (a) a di carboxylic component comprising

[0031] (al) units derived from at least one aromatic dicarboxylic acid and

[0032] (a2) units derived from at least one saturated or unsaturated (preferably saturated) aliphatic dicarboxylic acid,

[0033] (b) a diol component comprising units derived from at least one saturated or unsaturated (preferably saturated) aliphatic diol.

[0034] The content of aromatic dicarboxylic acid al) is preferably from 30 to 60%, preferably from 35 to 55%, more preferably from 40 to 48% in moles with respect to the content of total dicarboxylic component a) in moles.

[0035] Said at least one aromatic dicarboxylic acid of component (al) is preferably selected from aromatic dicarboxylic acids of the phthalic acid type, preferably terephthalic acid or isophthalic acid, more preferably terephthalic acid and heterocyclic aromatic dicarboxylic compounds, preferably 2,5-furandicarboxylic acid, 2,4-furandicarboxylic acid, 2,3 -furandicarboxylic acid, 3,4-furandicarboxylic acid, more preferably 2,5-furandicarboxylic acid, their esters, salts and mixtures thereof. Said at least one aliphatic dicarboxylic acid of component a2) is preferably selected from saturated C2-C24, preferably C4-C13, more preferably C4-C11, dicarboxylic acids, their Cl- C24, more preferably C1-C4, alkyl esters, their salts and mixtures thereof.

[0036] According to a preferred aspect, these aliphatic dicarboxylic acids are selected from: succinic acid, 2-ethylsuccinic acid, glutaric acid, 2-methylglutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, hexadecanedioic acid, octadecanedioic acid, their Cl -24 alkyl esters and mixtures thereof. Advantageously said aliphatic dicarboxylic acids comprise succinic acid, adipic acid, azelaic acid, sebacic acid or mixtures thereof. According to one aspect, mixtures of adipic acid and azelaic acid are preferred. According to another aspect, adipic acid is preferred.

[0037] In another embodiment, the biodegradable polyester according to the invention is an aliphatic polyester.

[0038] In this case, the dicarboxylic component comprises units derived from at least one saturated or unsaturated (preferably saturated) aliphatic dicarboxylic acid.

[0039] The said dicarboxylic acid is preferably chosen from saturated C2-C24, preferably C4-C18, more preferably C4-C11, dicarboxylic acids, their C1-C24, preferably C1-C4 alkyl esters, their salts and mixtures thereof.

[0040] Preferably, the aliphatic dicarboxylic acids are selected from: succinic acid, 2-methylsuccinic acid, 2-ethylsuccinic acid, glutaric acid, 2-methylglutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecandioic acid, dodecandioic acid, brassylic acid and their C1-C24 alkyl esters. Preferably said aliphatic dicarboxylic acids are selected from the group consisting of succinic acid, adipic acid, azelaic acid, sebacic acid, undecandioic acid, dodecandioic acid, brassylic acid, hexadecandioic acid, octadecandioic acid and mixtures thereof. Said aliphatic dicarboxylic acids are advantageously chosen from succinic acid, sebacic acid and mixtures thereof.

[0041] The dicarboxylic component of the aliphatic or aliphatic-aromatic polyesters according to the present invention may comprise up to 5% unsaturated aliphatic dicarboxylic acids, preferably selected from itaconic acid, fumaric acid, 4-methylene-pimelic acid, 3,4-bis (methylene) nonandioic acid, 5-methylene-nonandioic acid, their C1-C24, preferably C1-C4, alkyl esters, their salts and mixtures thereof. In a preferred embodiment of the present invention the unsaturated aliphatic dicarboxylic acids comprise mixtures comprising at least 50% by moles, preferably more than 60% by moles, more preferably more than 65% by moles of itaconic acid and / or its C1-C24, preferably C1-C4 esters. More preferably, the unsaturated aliphatic dicarboxylic acids comprise itaconic acid. In the aliphatic or aliphatic-aromatic polyesters according to the present invention diols are understood to mean compounds bearing two hydroxyl groups, preferably selected from 1,2- ethanediol, 1,2-propanediol, 1,3 -propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11 -undecanediol, 1,12- dodecanediol, 1,13 -tri decanediol, 1,4-cyclohexanedimethanol, neopentylglycol, 2-methyl-l,3- propanediol, dianhydrosorbitol, dianhydromannitol, dianhydroiditol, cyclohexanediol 1,4- bis(hydroxymethyl)cyclohexane, dialkylene glycols and polyalkylene glycols of molecular weight 100-4000 such as polyethylene glycol, polypropylene glycol and mixtures thereof. Preferably, the diol component of least 50% in moles comprises one or more diols chosen from 1,2-ethanediol, 1,3 -propanediol, 1,4-butanediol. In a preferred embodiment of the present invention the saturated aliphatic diol is 1,4-butanediol.

[0042] Advantageously, the diol may be obtained from renewable sources, from first- or second- generation sugars.

[0043] The diol component of the aliphatic or aliphatic-aromatic polyesters according to the present invention may comprise up to 5% unsaturated aliphatic diols, preferably selected from cis 2- buten-l,4-diol, trans 2-buten-l,4-diol, 2-butyn-l,4-diol, cis 2-penten-l,5-diol, trans 2-penten- 1 ,5-diol, 2-pentyn-l,5-diol, cis 2-hexen-l,6-diol, trans 2-hexen-l,6-diol, 2-hexyn-l,6-diol, cis 3-hexen-l,6-diol, trans 3-hexen-l,6-diol, 3-hexyn-l,6 diol.

[0044] The aliphatic or aliphatic-aromatic polyesters according to the present invention may also advantageously comprise repetitive units derived from at least one hydroxy acid in an amount of from 0 to 49%, preferably from 0 to 30% in moles with respect to the total moles of the dicarboxylic component.

[0045] Examples of convenient hydroxy acids are glycolic acid, glycolide, hydroxybutyric acid, hydroxy caproic acid, hydroxy valeric acid, 7-hydroxyheptanoic acid, 8-hydroxycaproic acid, 9-hydroxynonanoic acid, lactic acid or lactide. The hydroxy acids may be inserted into the chain as such or as prepolymers / oligomers, or they may also be previously reacted with diacid diols.

[0046] In a preferred embodiment the polyesters are aliphatic-aromatic and are preferably selected from: poly(l,4-butylene adipate-co-l,4-butylene terephthalate), poly(l,4-butylene sebacate- co-l,4-butylene terephthalate), poly(l,4-butylene azelate-co-l,4-butylene terephthalate), poly(l,4-butylene brassylate-co-l,4-butylene terephthalate), poly(l,4-butylene succinate-co- 1,4-butylene terephthalate), poly(l,4-butylene adipate-co-l,4-butylene sebacate-co-1,4- butylene terephthalate), poly(l,4-butylene azelate-co-l,4-butylene sebacate-co-l,4-butylene terephthalate), poly(l,4-butylene adipate-co-l,4-butylene azelate-co-l,4-butylene terephthalate), poly(l,4-butylene succinate-co-l,4-butylene sebacate-co-l,4-butylene terephthalate), poly(l,4-butylene adipate-co-l,4-butylene succinate-co-l,4-butylene terephthalate), poly(l,4-butylene azelate-co- 1 ,4-butylene succinate-co- 1 ,4-butylene terephthalate). In a particularly preferred embodiment, the aliphatic-aromatic polyester is chosen from poly(l,4-butylene adipate-co-l,4-butylene terephthalate) and poly(l,4-butylene adipate-co-l,4-butylene azelate-co- 1,4-butylene terephthalate).

[0047] In another preferred embodiment the polyesters are aliphatic and preferably chosen from: polybutyl succinate, polybutylene sebacate, polyethylene sebacate.

[0048] The polyester of the preform according to the present invention advantageously has an Mn of from 20000 to 85000, preferably from 30000 to 50000, and an acidity of less than 100 meq / kg, preferably less than 60 meq / kg. The MFR at 19072.16 kg on the dried polyester is advantageously from 1 to 50 g / lOmin.

[0049] Preforms comprising mixtures of the different polyesters according to the invention are also part of the invention.

[0050] Surprisingly, the polyester obtained by the process according to the present invention exhibits improved rheological characteristics in terms of thermal stability of the melt and high Breaking Stretching Ratio.

[0051] The enthalpy of fusion (AHm) of the polyester (or polyester mixture) of the preform of the invention is lower than 18.5 J / g, preferably lower than or equal to 18 J / g, and preferably greater than 1 J / g, more preferably greater than 5 J / g. It is advantageously determined on a sample having a water content of less than 500 ppm by differential scanning calorimetry (DSC) using a Perkin Elmer Pyris Diamond calorimeter under the conditions given below:

[0052] 60 s isotherm at -20°C;

[0053] 1st scan from -20°C to 200°C at 20°C / min.

[0054] The enthalpy of melting (AHm) is measured as the area of the endothermic peak corresponding to the polyester melt found in the first scan using the PyrisTM software from Perkin Elmer, specially designed to process DSC diagrams.

[0055] From a rheological point of view, it is optimal to use a polymer characterised by a suitable combination of melt strength and shear viscosity values. In order to assess the quality of the melt and its possible processing behaviour in industrial expansion processes, it is therefore necessary to consider both properties, by means of the viscoelastic ratio, RVE. This is calculated via the quotient of shear viscosity and melt strength. Shear viscosity is determined at 190°C and shear rate y =103.7s1with a capillary having a diameter of 1 mm and L / D=30 according to ASTM D3835-90 “Standard Test Method for Determining Properties of Polymer Materials by means of a Capillary Rheometer”, while melt strength is measured according to ISO 16790:2021 at 190°C and y =103.7s1using a capillary of 1 mm diameter and L / D=30 at a constant acceleration of 6 mm / sec2and a stretching length of 150 mm.

[0056] According to one aspect the biodegradable polyester from diacid-diol of the invention is branched.

[0057] In this case, this branching is obtained in the presence of a poly functional compound, preferably in an amount of 0.05% to 0.7% in moles with respect to the total moles of the dicarboxylic component, preferably 0.2 to 0.5% in moles. A polyfunctional compound is defined as a molecule comprising at least 3 functional groups capable of forming bonds with dicarboxylic or hydroxyl functional groups, for example hydroxyl groups.

[0058] This polyfunctional compound is preferably chosen from pentaerythritol, dipentaerythritol, ditrimethylolpropane, diglycerol, triglycerol, tetraglycerol, glycerol, sorbitol, mannitol and mixtures thereof.

[0059] According to a preferred aspect said polyfunctional compound comprises at least four acids (COOH) or at least four hydroxyl functional groups (OH), in which at least two of said hydroxyl functional groups are primary and at least two of said hydroxyl functional groups are primary or secondary, provided that, if present, the secondary hydroxyl group is not vicinal to another secondary hydroxyl group. A primary hydroxyl functional group is defined as a functional group in which the carbon atom bound to the hydroxyl group is bound to only one carbon atom. A secondary hydroxyl functional group is a functional group in which the carbon atom bound to the hydroxyl group is bound to two carbon atoms. A neighbouring hydroxyl functional group means two hydroxyl groups bonded to two adjacent carbon atoms.

[0060] According to another aspect, the biodegradable polyester according to the present invention is characterised by branching obtained by means of a preparation process employing a mixture of poly functional compounds comprising at least 50% in moles with respect to the total number of polyfunctional compounds of at least one polyfunctional compound containing at least four COOH and / or OH functional groups, in which preferably at least two of said hydroxyl functional groups are primary and at least two of said hydroxyl functional groups are primary or secondary, provided that, if present, the secondary hydroxyl group is not vicinal to another secondary hydroxyl group.

[0061] This polyfunctional compound is chosen from the group of polyfunctional molecules such as polyacids, polyols and mixtures thereof. Examples of these polyacids are pyromellitic acid, pyromellitic anhydride, ethylenediamine tetraacetic acid, furan-2,3,4,5-tetracarboxylic acid, naphthalene-l,4,5,8-tetracarboxylic acid, naphthal ene- 1 ,4, 5 , 8 -tetracarb oxy li c anhy dri de .

[0062] Examples of these polyols are pentaerythritol, dipentaerythritol, ditrimethylol propane, diglycerol, triglycerol, tetraglycerol and mixtures thereof.

[0063] Preferably the multifunctional compound is pentaerythritol.

[0064] Advantageously, a branched polyester according to the invention is obtained by adding the above described polyfunctional compound together with the monomers during the polymer synthesis. Surprisingly, the branched polyester thus obtained exhibits improved rheological characteristics in terms of high Breaking Stretching Ratio (i.e. the ratio between drawing velocity at break and initial drawing velocity during the melt strength determination test) with respect to a polyester obtained by reactive extrusion, i.e. adding a cross-linking or chain extending agent after polymerization.

[0065] A further object of the present invention is the use of the preform comprising polyester having improved rheological characteristics obtained according to the process of the present invention for autoclave and / or gas expansion processes under supercritical conditions.

[0066] The polyester of the preform according to the present invention is characterised by a shear viscosity of less than 1500 Pa.s, preferably 1200 Pa.s, more preferably less than 1000 Pa.s, and preferably greater than 150 Pa.s, determined at 190°C and with a flow gradient y =103.7s1with a capillary having a diameter of 1 mm and L / D=30 according to ASTM standard D3835- 90 “Standard test method for determining the properties of polymer materials by means of a capillary rheometer”.

[0067] It is also characterised by a melt strength of more than 0.002 N, preferably more than 0.005 N, more preferably more than 0.01 N, and preferably less than 0.04 N, more preferably less than 0.03 N, measured according to ISO 16790:2021 at 190°C and y =103.7s1using a capillary of 1 mm diameter and L / D=30 at a constant acceleration of 6 mm / sec2and a stretching length of 150 mm.

[0068] The polyester preform according to the present invention is also characterised by a ratio of viscosity to melt strength, i.e. the viscoelastic ratio (RVE), of less than 200000, preferably less than 100000, more preferably less than 80000, even more preferably less than 70000 and preferably greater than 15000.

[0069] Such rheological characteristics ensure good expansion of polyester according to the present invention using common industrial autoclave expansion processes. The preform and biodegradable polyesters according to the invention are biodegradable according to EN 13432.

[0070] The biodegradable polyester from diacid-diol according to the invention is obtained by a polyester synthesis process known in the art.

[0071] The biodegradable polyester of the preform according to the invention has a carbon content of biological origin greater than or equal to 40%, determined according to Standard EN16640 - Annex E- Method B.

[0072] The polyester of the preform according to the present invention may further optionally comprise 0 - 5% by weight, more preferably 0.05 - 4% by weight, even more preferably 0.05 - 3% by weight of the total mixture, of at least one cross-linking agent and / or chain extender. Said cross-linking agent and / or chain extender improves stability to hydrolysis and is selected from di- and / or poly-functional compounds bearing isocyanate, peroxide, carbodiimide, isocyanurate, oxazoline, epoxy, anhydride, divinyl ether groups and mixtures thereof. Preferably, the cross-linking agent and / or chain extender comprises at least one di- and / or polyfunctional compound bearing epoxy or carbodiimide groups.

[0073] Preferably, the cross-linking agent and / or chain extender comprises at least one di- and / or polyfunctional compound bearing isocyanate groups. More preferably, the cross-linking agent and / or chain extender comprises at least 25% by weight of one or more di- and / or polyfunctional compounds bearing isocyanate groups. Especially preferred are mixtures of di- and / or polyfunctional compounds bearing isocyanate groups with di- and / or polyfunctional compounds bearing epoxy groups, even more preferably comprising at least 75% by weight of di- and / or polyfunctional compounds bearing isocyanate groups.

[0074] Preferably, the di- and polyfunctional compounds bearing isocyanate groups are selected from p-phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4- diphenylmethane diisocyanate, l,3-phenylene-4-chloro diisocyanate, 1,5 -naphthalene diisocyanate, 4,4-diphenylene diisocyanate, 3,3'-dimethyl-4,4-diphenylmethane diisocyanate, 3-methyl-4,4'-diphenylmethane diisocyanate, diphenylether diisocyanate, 2,4-cyclohexane diisocyanate, 2,3 -cyclohexane diisocyanate 1 -methyl 2,4-cyclohexyl diisocyanate, 1 -methyl 2,6-cyclohexyl diisocyanate, bis(isocyanate cyclohexyl) methane, 2,4,6-toluene triisocyanate, 2,4,4-diphenylether triisocyanate, polymethylene-polyphenyl-polyisocyanates, methylene diphenyl diisocyanate triphenylmethane triisocyanate, 3,3'dithiolylene-4,4-diisocyanate, 4,4'- methylenebis(2-methyl-phenyl isocyanate), hexamethylene diisocyanate, 1,3-cyclohexylene diisocyanate, 1,2-cyclohexylene diisocyanate and mixtures thereof. In a preferred embodiment, the compound bearing isocyanate groups is 4,4-diphenylmethane-diisocyanate. With regard to di- and polyfunctional compounds bearing peroxide groups, these are preferably selected from benzoyl peroxide, lauroyl peroxide, isononanoyl peroxide, di-(t- butylperoxyisopropyl)benzene, t-butyl peroxide, dicumyl peroxide, alpha, alpha'-di(t- butylperoxy)diisopropylbenzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butyl cumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hex-3-yne, di(4-t- butylcyclohexyl)peroxy dicarbonate di cetyl peroxydicarbonate, dimyristyl peroxydicarbonate, 3,6,9-triethyl-3,6,9-trimethyl-l,4,7-triperoxonane, di(2-ethylhexyl) peroxydicarbonate and mixtures thereof. The di- and polyfunctional compounds bearing carbodiimide groups which are preferably used in the mixture according to the present invention are chosen from poly(cyclooctylene carbodiimide), poly(l,4-dimethylcyclohexylene carbodiimide), poly(cyclohexylene carbodiimide), poly(ethylene carbodiimide), poly(butylene carbodiimide), poly(isobutylene carbodiimide), poly(nonylene carbodiimide), poly(dodecylene carbodiimide), poly(neopentylene carbodiimide), poly(l,4-dimethylene phenylene carbodiimide), poly(2, 2', 6, 6', tetraisopropyldiphenylene carbodiimide) (Stabaxol® D), poly(2,4,6-triisolpropyl-l,3-phenylene carbodiimide) (Stabaxol® P-100), poly(2,6- diisopropyl-l,3-phenylene carbodiimide) (Stabaxol® P), poly(tolyl carbodiimide), poly(4, d'diphenylmethane carbodiimide), poly(3,3'-dimethyl-4,4'biphenylene carbodiimide), poly(p- phenylene carbodiimide), poly(m -phenylene carbodiimide), poly (3,3 '-dimethyl-4, d'diphenylmethane carbodiimide), poly(naphthylene carbodiimide), poly(isophorone carbodiimide), poly(cumene carbodiimide), p-phenylene bis(ethyl carbodiimide), 1,6- hexam ethylene bis(ethylcarbodiimide), 1,8-octam ethylene bis(ethylcarbodiimide), 1,10- decamethylene bis(ethylcarbodiimide), 1,12-dodecam ethylene bis(ethylcarbodiimide) and mixtures thereof.

[0075] Examples of di- and poly functional compounds bearing epoxy groups which may be advantageously used in the mixture according to the present invention are all polyepoxides from epoxidised oils and / or styrene - glycidyl ether-methyl methacrylate, glycidyl ethermethyl methacrylate, included in a molecular weight range from 1000 to 10000 and with a number of epoxides per molecule in the range from 1 to 30 and preferably from 5 to 25, and epoxides selected from the group comprising: diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, 1,2-epoxybutane, poly glycerol polyglycidyl ether, isoprene di epoxide, and cycloaliphatic di epoxides, 1,4- cyclohexanedimethanol diglycidyl ether, glycidyl 2-methylphenyl ether, glycerol propoxylatotri glycidyl ether, 1,4-butanediol diglycidyl ether, sorbitol polyglycidyl ether, glycerol diglycidyl ether, tetraglycidyl ether of meta-xylenediamine and diglycidyl ether of bisphenol A and mixtures thereof.

[0076] In a particularly preferred embodiment of the invention the cross-linking agent and / or chain extender comprises compounds bearing isocyanate groups, preferably 4,4- diphenylmethanodiisocyanate, and / or bearing carbodiimide groups, and / or bearing epoxy groups, preferably of the styrene-glycidyl-ether-methylmethacrylate type. In a particularly preferred embodiment of the invention, the cross-linking agent and / or chain extender comprises compounds bearing epoxy groups of the styreneglycidylether-methylmethacrylate type.

[0077] Along with the di- and polyfunctional compounds bearing isocyanate, peroxide, carbodiimide, isocyanurate, oxazoline, epoxy, anhydride or divinylether groups, catalysts may also be used to increase the reactivity of the reactive groups. In the case of polyepoxides, fatty acid salts are preferably used, even more preferably calcium and zinc stearates.

[0078] The biodegradable branched polyester of the preform according to the invention may be mixed with other polymers of synthetic or natural origin, whether biodegradable or not. Compositions comprising the polyester according to the present invention are also an object of the present invention.

[0079] With regard to polymers of synthetic or natural origin, whether biodegradable or not, these are advantageously selected from the group consisting of polyhydroxyalkanoates, vinyl polymers, diacid diol polyesters, polyamides, polyurethanes, polyureas, polycarbonates and mixtures thereof. In a particularly preferred form, said polymers may be blended in amounts up to 80% by weight with the biodegradable polyester according to the invention.

[0080] As far as polyhydroxyalkanoates are concerned, these may be present in quantities of from 30 to 80% w / w, preferably from 40 to 75% w / w, even more preferably from 45 to 70% w / w, of the total composition.

[0081] Said polyhydroxyalkanoates are preferably selected from the group consisting of the polyesters of lactic acid, poly-8-caprolactone, polyhydroxybutyrate, polyhydroxybutyrate-valerate, polyhydroxybutyrate-propanoate, polyhydroxybutyrate-hexanoate, polyhydroxybutyratedecanoate, polyhydroxybutyrate-dodecanoate, polyhydroxybutyrate-hexadecanoate, polyhydroxybutyrate-octadecanoate, poly-3 -hydroxybutyrate-4-hydroxybutyrate. Preferably, the polyhydroxyalkanoate of the composition comprises at least 80% w / w of one or more polyesters of lactic acid. In a preferred embodiment, lactic acid polyesters are selected from the group consisting of poly L-lactic acid, poly D-lactic acid, poly D-L lactic acid stereo complex, copolymers comprising more than 50% by moles of said lactic acid polyesters or mixtures thereof.

[0082] Particularly preferred are lactic acid polyesters containing at least 95% w / w of repetitive units derived from L-lactic or D-lactic acid or combinations thereof, with a molecular weight Mw greater than 50000 and with shear viscosity from 50 to 700 Pa.s preferably from 80 to 500 Pa.s (measured according to ASTM D3835 standard at T=190 °C, shear rate=1000s-l, D=lmm, L / D=10).

[0083] In a particularly preferred embodiment of the present invention, the lactic acid polyester comprises at least 95% w / w of units derived from L-lactic acid, < 5% w / w of repetitive units derived from D-lactic acid, exhibits a Melting Temperature in the range 135-175°C, a Glass Transition Temperature (Tg) in the range 55-65°C and an MFR (measured according to ASTM-D1238 standard at 190°C and 2.16kg) in the range 1-50 g / 10 min.

[0084] Commercial examples of lactic acid polyesters with these properties include the Ingeo™ Biopolymer brand products 4043D, 325 ID, 6202D, and the Luminy® brand product L105. Preferred vinyl polymers include polyethylene, polypropylene, their copolymers, polyvinyl alcohol, polyvinyl acetate, polyethylene vinyl acetate and polyethylene vinyl alcohol, polystyrene, chlorinated vinyl polymers, polyacrylates.

[0085] Chlorinated vinyl polymers include, in addition to polyvinyl chloride, polyvinylidene chloride, polyethylene chloride, poly(vinylchloride-vinylacetate), poly(vinylchloride-ethylene), poly(vinylchloride-propylene), poly(vinylchloride-styrene), poly(vinylchloride-isobutylene) as well as copolymers in which polyvinyl chloride accounts for more than 50% by moles. Such copolymers may be random, block or alternating.

[0086] With regard to the polyamides of the composition according to the present invention, these are preferably selected from the group consisting of polyamide 6 and 6,6, polyamide 9 and 9,9, polyamide 10 and 10,10, polyamide 11 and 11,11, polyamide 12 and 12,12 and their combinations of the 6 / 9, 6 / 10, 6 / 11, 6 / 12 type, mixtures thereof and copolymers both random and block.

[0087] Preferably, the polycarbonates of the composition according to the present invention are selected from the group consisting of polyalkylene carbonates, more preferably polyethylene carbonates, polypropylene carbonates, polybutylene carbonates, mixtures thereof and both random and block copolymers. Among the polyethers, those preferred are selected from the group consisting of polyethylene glycols, polypropylene glycols, polybutylene glycols, their copolymers and their blends with molecular weights from 70000 to 500000.

[0088] As for the diacid diol polyesters, these preferably include:

[0089] (a) a di carboxylic component comprising, with respect to the total dicarboxylic component:

[0090] (al) 20-100% in moles of units derived from at least one aromatic di carboxylic acid,

[0091] (a2) 0-80% in moles of units derived from at least one saturated aliphatic dicarboxylic acid,

[0092] (a3) 0-5% in moles of units derived from at least one unsaturated aliphatic dicarboxylic acid;

[0093] (b) a diol component comprising, in relation to the total diol component:

[0094] (bl) 95-100% in moles of units derived from at least one saturated aliphatic diol;

[0095] (b2) 0-5% in moles of units derived from at least one unsaturated aliphatic diol.

[0096] Preferably, aromatic di carboxylic acids al, saturated aliphatic dicarboxylic acids a2, unsaturated aliphatic dicarboxylic acids a3, saturated aliphatic diols bl and unsaturated aliphatic diols b2 for said polyesters are selected from those described above for the polyester according to the present invention.

[0097] As for polymers of natural origin, these are advantageously selected from starch, chitin, chitosan, alginates, proteins such as gluten, zein, casein, collagen, gelatin, natural gums, cellulose (also in nanofibrils) and pectin.

[0098] The term starch is understood here to mean all types of starch, i.e. flour, native starch, hydrolysed starch, destructured starch, gelatinised starch, plasticised starch, thermoplastic starch, biofillers comprising complexed starch or mixtures thereof. Particularly suitable according to the invention are starches such as potato, maize, tapioca and pea starch. Particularly advantageous are starches capable of being easily deconstructed and having high initial molecular weights, such as potato or maize starch. The starch may be present both as such and in a chemically modified form, such as in the form of starch esters with a degree of substitution from 0.2 to 2.5, hydroxypropyl starch, and modified starch with fat chains.

[0099] By destructured starch, reference is made herein to the teachings contained in Patents EP-0 118240 and EP-0 327 505, starch processed in such a way that it does not substantially show the so-called “maltese crosses” under the optical microscope in polarised light and the so- called “ghosts” under the optical microscope in phase contrast. Advantageously, starch is destructured by an extrusion process at temperatures between 110-250 °C, preferably 130- 180 °C, pressures between 0.1-7 MPa, preferably 0.3-6 MPa, preferably providing, during said extrusion, a specific energy greater than 0.1 kWh / kg. The destructuring of starch preferably takes place in the presence of 1 to 40% w / w, relative to the weight of the starch, of one or more plasticisers chosen from water and polyols having 2 to 22 carbon atoms. As far as water is concerned, this may also be the water naturally present in starch. Among the polyols, polyols with 1 to 20 hydroxyl groups containing 2 to 6 carbon atoms, their ethers, thioethers and organic and inorganic esters are preferred.

[0100] Examples of these polyols are glycerol, diglycerol, polyglycerol, pentaerythritol, ethoxylated polyglycerol, ethylene glycol, polyethylene glycol, 1,2-propanediol, 1,3 -propanediol, 1,4- butanediol, neopentylglycol, sorbitol, sorbitol monoacetate, sorbitol diacetate, sorbitol monoethoxylate, sorbitol diethoxylate, and mixtures of these.

[0101] In a preferred embodiment, the starch is destructured in the presence of glycerol or a plasticiser mixture comprising glycerol, more preferably comprising from 2 to 90% w / w glycerol. Preferably, the destructured and cross-linked starch according to the present invention comprises between 1-40% w / w, relative to the weight of the starch, of plasticisers.

[0102] The biodegradable polyester of the preform according to the invention may also optionally be mixed with one or more additives selected from the group consisting of plasticisers, UV stabilisers, lubricants, nucleating agents, surfactants, antistatic agents, pigments, compatibilising agents, lignin, silymarin organic acids, antioxidants, anti-mould agents, waxes, process aids and polymer components preferably selected from the group consisting of vinyl polymers and diacid diol polyesters other than or the same as the aliphatic and / or aliphatic- aromatic polyesters described above.

[0103] Each additive is present in quantities preferably less than 10% by weight, more preferably less than 5% by weight, less than 3% or even more preferably less than 1% by weight of the total weight of the mixture.

[0104] As far as plasticisers are concerned, in addition to the plasticisers preferably used for the preparation of destructured starch described above, these are selected from the group consisting of trimellitates, such as trimellitic acid esters with C4-C20 mono-alcohols preferably selected from the group consisting of n-octanol and n-decanol, and aliphatic esters having the following structure:

[0105] Rl-O- C(O)-R4-C(O)-[-O-R2-O-C(O)-R5-C(O)-]m-O-R3 where:

[0106] R1 is selected from one or more of the groups formed by H, linear and branched alkyl residues, saturated and unsaturated of the C1-C24 type, polyol residues esterified with C1-C24 monocarboxylic acids; R2 comprises -CH2-C(CH3)2-CH2- and C2-C8 alkylene groups, and consists of at least 50% in moles of said -CH2-C(CH3)2-CH2- groups;

[0107] R3 is selected from one or more of the groups formed by H, linear and branched, saturated and unsaturated alkyl residues of polyols esterified with C1-C24 monocarboxylic acids;

[0108] R4 and R5 are the same or different, comprise one or more C2-C22, preferably C2-C11, more preferably C4-C9 alkenes, and consist of at least 50% by moles of C7 alkenes; m is a number between 1-20, preferably 2-10, more preferably 3-7.

[0109] Preferably, in said esters at least one of groups R1 and / or R3 comprises, preferably in an amount of > 10% in moles, more preferably > 20%, even more preferably > 25% in moles, with respect to the total amount of groups R1 and / or R3, of polyol residues esterified with at least one C1-C24 monocarboxylic acid selected from the group consisting of stearic acid, palmitic acid, 9-ketostearic acid, 10-ketostearic acid and mixtures thereof. Examples of such aliphatic esters are described in Italian patent application MI2014A000030 and international patent applications WO 2015 / 104375 and WO 2015 / 104377.

[0110] Preferably, the lubricants are chosen from esters and metal salts of fatty acids such as, for example, zinc stearate, calcium stearate, aluminium stearate and acetyl stearate. Preferably, the composition according to the present invention comprises up to 1% by weight of lubricants, more preferably up to 0.5% by weight, relative to the total weight of the composition.

[0111] Examples of nucleating agents include saccharin sodium salt, calcium silicate, talc, kaolin, clay, carbon nanofiber, nanosilica, sodium benzoate, calcium titanate, boron nitride, polymers such as isotactic polypropylene, low molecular weight PLA.

[0112] Pigments may also be added, if necessary, for example titanium dioxide, clays, copper phthalocyanine, titanium dioxide, silicates, iron oxides and hydroxides, carbon black, and magnesium oxide.

[0113] Process aids such as gliding and / or releasing agents include, for example, biodegradable fatty acid amides such as oleamide, erucamide, ethylene-bis-stearylamide, fatty acid esters such as glycerol oleates or glycerol stearates, saponified fatty acids such as stearates, inorganic agents such as silicas or talc. Process aids are preferably present in quantities of less than 10% by weight, more preferably less than 5% by weight, and even more preferably less than 2% by weight of the total weight of the mixture.

[0114] It is also an object of the present invention to use the preform for the production of expanded products, preferably expanded products obtained in autoclave. In particular, the polyester described above is particularly suitable for application in a process for obtaining foams in the presence of expanding gas under supercritical conditions comprising the steps of: a) place said non-expanded or partially expanded preform in an autoclave, in contact with expanding gas; b) reaching a temperature between the softening point and the closing temperature of the polyester's melting peak, at a pressure sufficient to maintain the expanding gas under supercritical conditions and for a sufficient time to allow it to be adsorbed by the preform material; c) instantaneously reducing the pressure while maintaining the temperature above the softening point of said polyester, resulting in foam.

[0115] This expanding gas is chosen from CO2, N2, hydrocarbons and mixtures thereof. N2, CO2 and mixtures thereof are particularly preferred.

[0116] According to a particularly advantageous embodiment, during step a) the polyester is placed in contact with expanding gas in the presence of a co-expanding agent chosen from water, C1-C4 alcohols and mixtures thereof. Said co-expanding agent is preferably water; it is preferably used when the expanding gas is N2.

[0117] The ratio of the volume of this co-expander to the total volume of the autoclave is from 0.01 to 0.25.

[0118] Preferably, the ratio of the weight of preform to the weight of co-expander or conductive medium (e.g. water) is below 0.2 g preform / g co-expander. Preferably the conductive medium is the gas or gas mixture.

[0119] The softening temperature may be determined, for example, by the change in slope of the curve (onset) of the melting peak in DSC analysis.

[0120] During step b), the polyester is impregnated with said expanding agent at a temperature around its melting point (Tm) for a sufficient time for it to diffuse into its softened state, for example, 90 minutes. When measured by DSC, the Tm is the maximum of the endothermic peak corresponding to melting of the polyester.

[0121] Step c) is carried out in a time of less than 25 seconds, preferably less than 20 seconds, more preferably less than 10 seconds, even more preferably less than 5 seconds.

[0122] Preferably, during step c) the temperature is reduced.

[0123] Foamed articles, prepared from the preform according to the present invention, obtained by physical expansion without cross-linking by chemical additives, are an object of the present invention. Such articles include protective packaging for the electronics sector such as separators or films, sporting articles such as technical equipment and footwear and articles for the footwear sector.

[0124] Foamed articles comprising the biodegradable polyester described above advantageously have a density < 0.9 g / ml, preferably < 0.7 g / ml, more preferably < 0.3 g / ml, and preferably >0.005 g / ml.

[0125] In these articles, the cell wall, measured as the shortest distance between two adjacent cells by SEM microscopy, is advantageously less than 30pm thick, preferably <20pm, even more preferably <15 pm, and more than 1pm.

[0126] In addition, the average cell size is advantageously greater than or equal to 25 microns, preferably greater than or equal to 30 microns, more preferably from 50 to 200 or 250 microns. EXAMPLES

[0127] Example 1 : preform preparation by injection moulding

[0128] A Poly(l,4-butylene adipate-co-l,4-butylene terephthalate) was prepared as follows. The synthesis process was carried out in a 3 1 6L stainless steel reactor with a geometric volume of 25 litres and equipped with: a mechanical stirring system, a distillation line consisting of a packed-fill column and a shell-and-tube cooler equipped with a condensate collection barrel, a polymerisation line equipped with a high-boil abatement system, cold traps and a mechanical vacuum pump, and an inlet for nitrogen. The reactor was loaded with: terephthalic acid 2653g (15.98 mol), adipic acid 2631g (18.02 mol), 1,4-butanediol 4284g (47.6 mol), branching agent 13.9g of Pentaerythritol (0,3% by mol), 1.78g of diisopropyl triethanolamine titanate (Tyzor TE, equal to 250ppm by weight of catalyst and 21ppm of metal to final polymer). The temperature was raised to 235°C over 90 min and held at 235°C until an esterification conversion of more than 95% was achieved, as calculated from the mass of reaction water distilled from the system. At the end of the esterification step a first gradual vacuum ramp was applied up to a pressure of 100 mbar in 20 min to complete esterification, then the pressure was restored with nitrogen and the polycondensation catalyst was added: a mixture of tetrabutyltitanate (TnBT) and tetrabutylzirconate (NBZ) consisting of 2.97g TnBT (amounting to 417ppm catalyst and 58ppm metal) and 7.08g NBZ (amounting to 994ppm catalyst and 206ppm metal). The pressure in the reactor was reduced to below 3 mbar over 30 min and the temperature was raised to 245°C and maintained until the desired molecular mass, estimated from the consumption of the stirring motor, was reached. At the end of the reaction the vacuum was neutralized with nitrogen and the material was extruded through a die in the form of filaments. The filaments were cooled in a water bath, dried with a stream of air and granulated with a cutter. The obtained (PBTA) granules showed:

[0129] - an enthalpy of fusion of 15,0 J / g and a Melting Temperature of 123°C (determined as described above);

[0130] - a shear viscosity of 640 Pa.s at 190°C (as described above according to ASTM D3835-90);

[0131] - a melt strength of 0.031 N at 190°C (as described above according to ISO 16790:2021), and

[0132] - a viscoelastic ratio (RVE) of 20700.

[0133] The PBTA granules have been fed to an injection molding machine model Engel Victory 120 equipped with a mould described in Figure 1 (i.e. having a single injection gate in the center of the mould) for the production of the preforms.

[0134] The operating conditions for the production of the preform are described below:

[0135] Injection T°C = 40°C;

[0136] Approx, filling pressure = 500 bar

[0137] Approx, filling time = 40 cm3 / sec

[0138] Holding or packing pressure = 750 bar

[0139] Holding time under packing pressure = 25 sec;

[0140] Cooling time = 50 sec;

[0141] Approx, cycle time = 85 sec;

[0142] Screw speed = 0.3m / s;

[0143] The obtained preform showed a medium thickness of 6 mm and a density of 1.19 g / cm3.

[0144] Example 2: expansion process of the preform of example 1

[0145] The preform prepared as described in Example 1 was cut using a saw into a reduced preform of dimension 4 x 6 x 10 mm3to adapt it to the dimension of the autoclave.

[0146] The obtained reduced preform was located in an Autoclave (Roth) with Volume of 250 mL. The autoclave was pressurized at room temperature with CO2 to reach the final pressure of 100 bar after heating.

[0147] The autoclave was heated by immersing it in a thermostatic bath at a temperature of 105 °C and maintained in static condition (105°C and lOObar) for 90 minutes. The pressure was then released in 3-5 seconds.

[0148] The autoclave was cooled down immersing in ice bath, then opened and the expanded product removed for characterizations.

[0149] The expanded product has been left for 5 days at 25°C and then characterized. The expanded product was weighted and its volume measured with a calliper obtaining a density of 0.145 g / cm3; the cells’ size was of 110pm (measured by SEM) and a shrinkage of 10% was measured (in terms of variation of density measured immediately after foaming and measured after 5 days stabilization).

[0150] Example 3 : expansion process of the preform of example 1

[0151] The preform prepared as described in Example 1 was cut using a saw into a reduced preform of dimension 4 x 6 x 10 mm3to adapt it to the dimension of the autoclave.

[0152] The obtained reduced preform was located in an Autoclave (Roth) with Volume of 250mL. The autoclave was pressurized at room temperature with a partial pressure of 80% of CO2 and 20% of N2 to reach the final pressure of 200 bar after heating.

[0153] The autoclave was heated by immersing it in a thermostatic bath at a temperature of 105 °C and maintained in static condition (105°C and 200bar) for 60 minutes. The pressure was then released in 3-5 seconds.

[0154] The autoclave was cooled down immersing in ice bath, then opened and the expanded product removed for characterizations.

[0155] The expanded product has been left for 5 days at 25°C and then characterized. The expanded product was weighted and its volume measured with a calliper obtaining a density of 0.12g / cm3; The cells’ size measured by SEM was 80pm; the shrinkage, measured in terms of variation of density after foaming and after 5 days was 9%.

Claims

CLAIMS1. Biodegradable preform, obtainable by injection moulding and suitable for autoclave expansion by a physical foaming process in the absence of chemical expansion and / or cross-linking agents, comprising a biodegradable polyester from diacid-diol characterised by an enthalpy of fusion (AHm) lower than 18.5 J / g, a shear viscosity of 1500 Pa.s to 150 Pa.s at 190°C, a melt strength of 0.04 N to 0.002 N at 190°C, and a viscoelastic ratio (RVE) of 15,000 to 200,000.

2. Biodegradable preform according to claim 1 in which said polyester is branched and preferably obtained in the presence of a polyfunctional compound in an amount from 0.05% to 0.7% in moles with respect to the total dicarboxylic component, preferably from 0.2 to 0.5% in moles.

3. Biodegradable preform according to claim 2 in which said polyfunctional compound is selected from pentaerythritol, dipentaerythritol, ditrimethylolpropane, diglycerol, triglycerol, tetraglycerol, glycerol, sorbitol, mannitol and mixtures thereof.

4. Biodegradable preform according to each of claims 1-3 in which said polyester comprises:(a) a dicarboxylic component comprising(al) units derived from at least one aromatic dicarboxylic acid and(a2) units derived from at least one saturated or unsaturated (preferably saturated) aliphatic dicarboxylic acid,(b) a diol component comprising units derived from at least one saturated or unsaturated (preferably saturated) aliphatic diol.

5. Biodegradable preform according to claim 4 in which the aromatic content is from 35 to 55%, preferably from 40 to 48% in moles in relation to total dicarboxylic component a).

6. Biodegradable preform according to any one of claims 4-5, in which the aromatic dicarboxylic acids of component al) are selected from aromatic dicarboxylic acids of the phthalic acid type, preferably terephthalic acid or isophthalic acid, more preferably terephthalic acid and heterocyclic dicarboxylic aromatic compounds, preferably 2,5- furandicarboxylic acid, 2,4-furandicarboxylic acid, 2,3-furandicarboxylic acid, 3,4- furandicarboxylic acid, more preferably 2,5-furandicarboxylic acid, their esters, salts and mixtures thereof.

7. Biodegradable preform according to any one of claims 4-6, in which the aliphatic dicarboxylic acid of component a2) is selected from C2-C24, preferably C4-C13, more preferably C4-C11, saturated dicarboxylic acids, their C1-C24, more preferably C1-C4, alkyl esters, their salts and mixtures thereof.

8. Biodegradable preform according to claim 7 in which said at least one aliphatic dicarboxylic acid is selected from: succinic acid, 2-ethylsuccinic acid, glutaric acid, 2- methylglutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecandioic acid, dodecandioic acid, brassylic acid, hexadecandioic acid, octadecandioic acid and Cl -24 alkyl esters thereof.

9. Biodegradable preform according to claim 8 in which said at least one aliphatic dicarboxylic acid include succinic acid, adipic acid, azelaic acid, sebacic acid or mixtures thereof.

10. Biodegradable preform according to any one of claims 1 to 3, in which said biodegradable diacid-diol polyester is an aliphatic polyester.

11. Biodegradable preform according to claim 10 in which said aliphatic polyester comprises units derived from saturated C2-C24, preferably C4-C18, more preferably C4-C11, dicarboxylic acids, their C1-C24, more preferably C1-C4, alkyl esters, their salts and mixtures thereof.

12. Biodegradable preform according to any of claims 1-11 in which said polyester has a carbon content of biological origin greater than or equal to 40%, determined according to Standard EN 16640 - Annex E- Method B.

13. Process for obtaining foams in the presence of expanding gas under supercritical conditions comprising the steps of: a) place the preform according to claim 1 un-expanded or partially expanded, in an autoclave, in contact with expanding gas; b) reaching a temperature between the softening point and the closing temperature of the melting peak of the polyester of said preform, at a pressure sufficient to maintain the expanding gas in supercritical conditions for a sufficient time to allow adsorption of said gas by the preform material; c) instantaneously reducing the pressure while maintaining the temperature above the softening point of said polyester, resulting in foam.

14. Process according to claim 13 in which said expanding gas is chosen from CO2, N2, hydrocarbons and mixtures thereof, preferably N2.

15. Process according to any of claims 13-14 in which, in step a), said preform is placed in contact with expanding gas in the presence of a co-expander comprising water.

16. Process according to any one of claims 13-15, in which the ratio of the volume of said co-expander to the total volume of the autoclave is from 0.01 to 0.25.

17. Process according to any of claims 13-16, in which step c) is performed in a time of less than 20 seconds, preferably less than 10 seconds.

18. Process according to each of claims 13-17 in which during step c) the temperature is reduced.

19. Biodegradable and recyclable foam article obtained from the preform according to claim 1 having a density of less than 0.9 g / cm3, preferably less than 0.7 g / cm3and more than 0.05 g / cm3, preferably more than 0.1 g / cm3, preferably from 0.10 to 0.50, more preferably from 0.15 to 0.40 g / cm3, even more preferably from 0.18 to 0.3 g / cm3.

20. Biodegradable and recyclable foam article according to claim 19 having a hardness of less than 55 determined according to ASTM D2240-15 on the Asker C scale with a load of 1 kg.

21. Biodegradable and recyclable foam article according to any one of claims 19-20 in which the cell wall, measured as the average distance between two adjacent cells by SEM microscopy, has a thickness of less than 30pm and more than 1 pm, preferably less than 20pm and even more preferably less than or equal to 15 pm.

22. Biodegradable and recyclable foam article according to any one of claims 19-21, in which the average cell size is greater than or equal to 25 microns, preferably greater than or equal to 30 microns, more preferably from 50 to 250 microns.

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