IT202300024147A1 - POLYESTERS FOR AUTOCLAVE EXPANSION - Google Patents

Description

POLYESTERS FOR AUTOCLAVE EXPANSION

DESCRIPTION

The present invention relates to a biodegradable polyester particularly suitable for use in autoclave expansion, to the related expansion process and to the expanded articles comprising it.

Specifically, autoclave expansion refers to a batch expansion process in which the polymer material, for example in the form of pellets, is suspended in a liquid medium and exposed to a physical blowing agent at elevated pressure and temperature. With a sudden decrease in pressure, the blowing agent begins to nucleate and expand, forming cells that cause the polymer matrix to expand. The resulting expanded pellet is then shaped into three-dimensional foamed articles, for example through the steam-chest molding process.

Autoclave expansion technology is a widely used industrial process in the foam industry.

In some cases, it is performed starting from a polymer matrix in the form of pellets. Smaller pellets are preferred because they require less time for both gas diffusion during saturation and heat conduction during expansion. During expansion, the blowing agent can escape into the environment through cell-to-cell diffusion before the cellular structure of the expanded pellet is fully stabilized. Therefore, due to the loss of gas from the surface layer, the gas concentration in the latter is typically lower.

As a result, the foam density of the surface layer is usually higher than that of the core area, and the core area of the expanded pellet has much larger cells. Furthermore, the surface layer, which cools first, is strongly oriented in the biaxial direction when expansion occurs. Therefore, the mechanical properties of the foam are typically non-uniform and are better at the surface layer of the pellet. An alternative is to perform the expansion of the polymer matrix in the form of a sheet or preform obtained, for example, by injection molding.

The expanded articles obtained through these industrial processes are particularly suitable for the protective packaging sector for electronics and in the sporting goods sector.

To obtain expanded articles with properties suitable for use in the indicated sectors, materials such as expanded polystyrene (EPS) and polyolefins such as polypropylene (EPP) are traditionally used.

However, the use of these materials entails limitations in terms of environmental impact as they are not biodegradable or recyclable, while the use of biodegradable materials (such as PLA or unbranched PBTA) with properties suitable for use in the sectors indicated, entails limitations in terms of the complexity of the expansion process which requires cross-linking using chemical additives.

? It is therefore of particular interest to develop new materials that not only guarantee performance similar to conventional materials in expansion processes, but which also do not require cross-linking using chemical additives and are also biodegradable.

A first object of the present invention is therefore a biodegradable preform suitable for expansion in an autoclave by physical foaming, in the absence of chemical expanding agents and/or cross-linkers, comprising a biodegradable polyester from diacid-diol characterised by

- a shear viscosity at 190?C from 1500 Pa.s to 150 Pa.s,

- a melt strength at 190?C of 0.04 N to 0.002 N, and

- a viscoelastic ratio RVE of 15,000 to 200,000.

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

This preform is advantageously recyclable.

A further object of the present invention is a process for obtaining foams in the presence of expanding gas under supercritical conditions starting from the biodegradable preform described above. Said process comprises the following steps:

a) placing in an autoclave a preform, unexpanded or partially expanded and comprising a biodegradable polyester characterized by a shear viscosity at 190°C of 1500 Pa.s to 150 Pa.s, a melt strength at 190°C of 0.04 N to 0.002 N, and a viscoelastic ratio (RVE) of 15,000 to 200,000, in contact with an expanding gas;

b) reach a temperature between the softening point and the melting point closure temperature of said polyester, at a pressure sufficient to maintain the expanding gas in supercritical conditions and for a time sufficient to allow the adsorption of said gas by the material;

c) reduce the pressure while maintaining the temperature above the softening point of said polyester, obtaining a foam.

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

According to a preferred embodiment, in step a) of the process, the preform is placed in contact with a blowing gas in the presence of a co-blowing agent selected from water, C1-C4 alcohols, and mixtures thereof, preferably water. This co-blowing agent has surprisingly been shown to help reduce density and improve cell distribution in the polymer matrix.

The expanded articles obtained in an autoclave using the polyester of the invention have a particular density and dimensional homogeneity of the cells, proving particularly suitable for application in the sporting goods sector, in particular in the production of footwear.

A third object of the invention is therefore biodegradable and recyclable expanded articles comprising the biodegradable polyester described above, in which the density is lower than 0.9 g/cm<3> and higher than 0.1 g/cm<3>, 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/cm<3>.

The invention will be described in greater detail below.

The preform according to the invention can be obtained using techniques known to those skilled in the art, for example, compression molding, injection molding, extrusion, including pre-expansion through the use of blowing agents during the molding, injection, or extrusion process. This preform can be obtained by shaping the compression, injection, or extrusion product, e.g., by die-cutting. This preform can also be obtained by sintering polymeric material in granules or pellets.

The polyester contained in the biodegradable preform according to the present invention is advantageously selected from aliphatic and aliphatic-aromatic biodegradable polyesters.

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

As regards the aliphatic-aromatic polyesters of the preform according to the invention, they present:

a) a dicarboxylic component comprising

a1) 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.

The content of aromatic dicarboxylic acid a1) is preferably between 30 and 60%, preferably between 35 and 55%, more preferably between 40 and 48% by moles with respect to the content by moles of the total dicarboxylic component a).

Said aromatic dicarboxylic acids of component a1) are 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, their salts and mixtures thereof.

Said aliphatic dicarboxylic acids of component a2) are preferably selected from saturated dicarboxylic acids C2-C24, preferably C4-C13, more preferably C4-C11, their alkyl esters C1-C24, preferably C1-C4, their salts and mixtures thereof.

According to a preferred embodiment, said 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 and their C1-24 alkyl esters.

Advantageously, said aliphatic dicarboxylic acids include succinic acid, adipic acid, azelaic acid, sebacic acid, or mixtures thereof. In one aspect, mixtures of adipic acid and azelaic acid are preferred. In another aspect, adipic acid is preferred. In another embodiment, the biodegradable polyester according to the invention is an aliphatic polyester.

In this case the dicarboxylic component is preferably selected from saturated dicarboxylic acids with a chain length of C2-C24, preferably C4-C18, more preferably C4-C11, their alkyl esters of C1-C24, preferably C1-C4, their salts and mixtures thereof.

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, undecanedioic acid, dodecanedioic 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, undecanedioic acid, dodecanedioic acid, brassylic acid, hexadecanedioic acid, octadecanedioic acid, and mixtures thereof. Said aliphatic dicarboxylic acids are advantageously selected from succinic acid, sebacic acid, and mixtures thereof.

The dicarboxylic component of the aliphatic or aliphatic-aromatic polyesters according to the present invention may comprise up to 5% of unsaturated aliphatic dicarboxylic acids, preferably selected from itaconic acid, fumaric acid, 4-methylene-pimelic acid, 3,4-bis(methylene)nonanedioic acid, 5-methylene-nonanedioic 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 Preferably, unsaturated aliphatic dicarboxylic acids consist of itaconic acid.

In the aliphatic or aliphatic-aromatic polyesters according to the present invention, diols are understood to be 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-tridecanediol, 1,4-cyclohexanedimethanol, neopentylglycol, 2-methyl-1,3-propanediol, dianhydrosorbitol, dianhydromannitol, dianhydroiditol, cyclohexanediol, 1,4-bis(hydroxymethyl)cyclohexane, dialkylene glycols and polyalkylene glycols with molecular weights of 100-4000, such as polyethylene glycol, polypropylene glycol, and mixtures thereof. Preferably, the diol component comprises at least 50 mol% of one or more diols selected from 1,2-ethanediol, 1,3-propanediol, and 1,4-butanediol. In a preferred embodiment of the present invention, the saturated aliphatic diol is 1,4-butanediol.

Advantageously, the diol can be obtained from renewable sources, starting from first or second generation sugars.

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

The aliphatic or aliphatic-aromatic polyesters of the present invention can also advantageously comprise repeating units deriving from at least one hydroxyacid in an amount between 0 - 49%, preferably between 0 - 30%, by moles with respect to the total moles of the dicarboxylic component.

Examples of suitable hydroxy acids are glycolic acid, glycolide, hydroxybutyric acid, hydroxycaproic acid, hydroxyvaleric acid, 7-hydroxyheptanoic acid, 8-hydroxycaproic acid, 9-hydroxynonanoic acid, lactic acid, or lactide. Hydroxy acids can be inserted into the chain as such or as prepolymers/oligomers, or they can also be reacted with diacid diols beforehand.

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

In another preferred embodiment, the polyesters are aliphatic and preferably selected from: polybutyl succinate, polybutylensebacate, polyethylensebacate.

The polyester of the preform according to the present invention advantageously has a Mn between 20,000 and 85,000, preferably between 30,000 and 50,000, an inherent viscosity between 0.3 and 1.1 dl/g, preferably between 0.5 and 1.0 dl/g, and an acidity lower than 100 meq/kg, preferably lower than 60 meq/kg. The MFR at 190?/2.16 kg, on the dried polyester, is advantageously between 1 and 50 g/10 min.

The invention also includes preforms comprising mixtures of the different polyesters of the invention.

Surprisingly, the polyester obtained with the process of the present invention presents improved rheological characteristics in terms of thermal stability of the melt and high breaking stretching ratio.

From a rheological point of view, the optimal choice is a polymer characterized by a suitable combination of melt strength and shear viscosity values. To evaluate the quality of the melt and its possible processing behavior in industrial expansion processes, it is therefore necessary to consider both properties using the viscoelastic ratio, RVE. This is calculated by calculating the quotient between the shear viscosity and the melt strength. The shear viscosity is determined at 190°C and with a flow gradient of ? = 103.7 s?1 with a capillary tube having a diameter of 1 mm and L/D = 30 according to the ASTM D3835-90 standard "Standard Test Method for Determination of Properties of Polymeric Materials by Means of a Capillary Rheometer", while the melt strength is measured according to ISO 16790:2021 at 190°C and ? =103.7s- l using a capillary with a diameter of 1 mm and L/D=30 at a constant acceleration of 6 mm/sec2 and a draw length of 150 mm. According to one aspect, the biodegradable diacid-diol polyester of the invention is branched. In this case, it is obtained in the presence of a polyfunctional compound, in an amount preferably from 0.05% to 0.7% by moles with respect to the total moles of the dicarboxylic component, preferably from 0.2 to 0.5% by moles. A polyfunctional compound is understood to be a molecule comprising at least 3 functional groups capable of forming bonds with the dicarboxylic or hydroxyl functionalities, for example hydroxide groups.

Said multifunctional compound is preferably selected from pentaerythritol, dipentaerythritol, ditrimethylolpropane, diglycerol, triglycerol, tetraglycerol, glycerol, sorbitol, mannitol and mixtures thereof.

According to a preferred aspect, said polyfunctional compound comprises at least four acids (COOH) or at least four hydroxyl functional groups (OH), wherein 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. By primary hydroxyl functionality is meant a functionality in which the carbon atom bonded to the hydroxyl group is bonded to only one carbon atom. By secondary hydroxyl functionality is meant a functionality in which the carbon atom bonded to the hydroxyl group is bonded to two carbon atoms. By vicinal hydroxyl functionality is meant two hydroxyl groups bonded to two adjacent carbon atoms. According to another aspect, the biodegradable polyester according to the present invention is characterized by branches obtained by a preparation process using a mixture of polyfunctional compounds, comprising at least 50% mol with respect to the total polyfunctional compounds of at least one polyfunctional compound containing at least four COOH and/or OH functionalities, wherein 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 proximal to another secondary hydroxyl group.

This polyfunctional compound is chosen from the group of polyfunctional molecules such as polyacids, polyols, and their mixtures.

Examples of such polyacids are: pyromellitic acid, pyromellitic anhydride, ethylenediamine tetraacetic acid, furan-2,3,4,5-tetracarboxylic acid, naphthalene-1,4,5,8-tetracarboxylic acid, naphthalene-1,4,5,8-tetracarboxylic anhydride.

Examples of such polyols are: pentaerythritol, dipentaerythritol, ditrimethylolpropane, diglycerol, triglycerol, tetraglycerol and mixtures thereof.

Preferably the multifunctional compound is pentaerythritol.

Surprisingly, the use of polyester according to the present invention in autoclave expansion processes allows for improved properties in terms of thermal stability of the melt and breaking stretching ratio.

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

The polyester of the preform according to the present invention is characterized 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 rate ? =103.7s<?1 >with a capillary having a diameter of 1 mm and L/D=30 according to the ASTM D3835-90 standard "Standard Test Method for Determination of Properties of Polymeric Materials Using a Capillary Rheometer".

It is also characterized by a melt strength greater than 0.002 N, preferably greater than 0.005 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 ? =103.7s- l using a capillary of 1 mm diameter and L/D=30 at a constant acceleration of 6 mm/sec2 and a draw length of 150 mm.

The polyester preform according to the present invention is further characterized by a ratio between the viscosity and the melt strength, viscoelastic ratio (RVE), less than 200,000, preferably less than 100,000, more preferably less than 80,000, even more preferably less than 70,000 and preferably greater than 15,000.

These rheological characteristics are such as to guarantee good expansion of the polyester according to the present invention using common industrial processes for autoclave expansion.

The preform and the biodegradable polyesters according to the invention are biodegradable according to the EN13432 standard.

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

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.

The polyester of the preform according to the present invention may also optionally comprise 0 - 5% by weight, more preferably 0.05 - 4% by weight, even more preferably 0.05 - 3% by weight based on the total mixture, of at least one crosslinking agent and/or chain extender.

Said cross-linking agent and/or chain extender improves hydrolysis stability and is selected from di- and/or polyfunctional compounds bearing isocyanate, peroxide, carbodiimide, isocyanurate, oxazoline, epoxide, anhydride, divinylether groups, and mixtures thereof. Preferably, the cross-linking agent and/or chain extender comprises at least one di- and/or polyfunctional compound bearing epoxide or carbodiimide groups.

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. Particularly preferred are mixtures of di- and/or polyfunctional compounds bearing isocyanate groups with di- and/or polyfunctional compounds bearing epoxide groups, even more preferably comprising at least 75% by weight of di- and/or polyfunctional compounds bearing isocyanate groups.

The di- and polyfunctional compounds bearing isocyanate groups are preferably selected from pphenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4-diphenylmethane diisocyanate, 1,3-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, diphenyl ester diisocyanate, 2,4-cyclohexane diisocyanate, 2,3-cyclohexane diisocyanate, 1-methyl 2,4-cyclohexyl diisocyanate, 1-methyl 2,6-cyclohexyl diisocyanate, bis(cyclohexyl isocyanate) methane, 2,4,6-Toluene triisocyanate, 2,4,4-diphenyl ether triisocyanate, polymethylene polyphenyl polyisocyanates, methylene diphenyl diisocyanate, triphenylmethane triisocyanate, 3,3-ditolylene-4,4-diisocyanate, 4,4-methylenebis(2-methylphenyl 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.

As for 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-2,5di(t-butylperoxy)hexane, t-butylcumyl peroxide, di-t-butylperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hex-3-yne, di(4-t-butylcyclohexyl)peroxy dicarbonate, dicetyl peroxydicarbonate, dimyristyl peroxydicarbonate, 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane, di(2-ethylhexyl) peroxydicarbonate and their mixtures. The di- and polyfunctional compounds bearing carbodiimide groups which are preferably used in the mixture according to the present invention are selected from poly(cyclooctylene carbodiimide), poly(1,4-dimethylenecyclohexylene carbodiimide), poly(cyclohexylene carbodiimide), poly(ethylene carbodiimide), poly(butylene carbodiimide), poly(isobutylene carbodiimide), poly(nonylene carbodiimide), poly(dodecylene carbodiimide), poly(neopentylene carbodiimide), poly(1,4-dimethylene phenylene carbodiimide), poly(2,2',6,6',tetraisopropyldiphenylene carbodiimide) (Stabaxol ? D), poly(2,4,6-triisolpropyl-1,3-phenylene carbodiimide) (Stabaxol ? P-100), poly(2,6 (Stabaxol ? P), poly(tolyl carbodiimide), poly(4,4'-diphenylmethane carbodiimide), poly(3,3'-dimethyl-4,4'biphenylene carbodiimide), poly(p-phenylene carbodiimide), poly(m-phenylene carbodiimide), poly(3,3'-dimethyl-4,4'-diphenylmethane carbodiimide), poly(naphthylene carbodiimide), poly(isophorone carbodiimide), poly(cumene carbodiimide), p-phenylene bis(ethylcarbodiimide), 1,6-hexamethylene bis(ethylcarbodiimide), 1,8-octamethylene bis(ethylcarbodiimide), 1,10-decamethylene bis(ethylcarbodiimide), 1,12-Dodecamethylene bis(ethylcarbodiimide) and mixtures thereof.

Examples of di- and poly-functional compounds bearing epoxide groups that can be advantageously used in the mixture according to the present invention are all polyepoxides from epoxidized oils and/or from styrene - glycidyl ether methyl methacrylate, glycidyl ether methyl methacrylate, 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 the epoxides selected from the group comprising: diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, 1,2-epoxybutane, polyglycerol polyglycidyl ether, isoprene diepoxide, and cycloaliphatic diepoxides, 1,4-cyclohexanedimethanol diglycidyl ether, glycidyl 2-methylphenyl ether, glycerol propoxylated triglycidyl ether, 1,4-butanediol diglycidyl ether, sorbitol polyglycidyl ether, glycerol diglycidyl ether, meta-xylenediamine tetraglycidyl ether and bisphenol A diglycidyl ether and mixtures thereof.

In a particularly preferred embodiment of the invention, the crosslinking agent and/or chain extender comprises compounds bearing isocyanate groups, preferably 4,4-diphenylmethanediisocyanate, and/or bearing carbodiimide groups, and/or bearing epoxide groups, preferably of the styrene-glycidyl ether-methyl methacrylate type. In a particularly preferred embodiment of the invention, the crosslinking agent and/or chain extender comprises compounds bearing epoxide groups of the styrene-glycidyl ether-methyl methacrylate type. In addition to the di- and polyfunctional compounds bearing isocyanate, peroxide, carbodiimide, isocyanurate, oxazoline, epoxide, anhydride, and divinylether groups, catalysts can 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.

The branched, biodegradable polyester of the preform according to the invention can be mixed with other polymers of synthetic or natural origin, whether biodegradable or not. The present invention also covers compositions comprising the polyester according to the present invention.

As for polymers of synthetic or natural origin, biodegradable or not, these are advantageously selected from the group consisting of polyhydroxyalkanoates, vinyl polymers, diacid diol polyesters, polyamides, polyurethanes, polyethers, polyureas, polycarbonates, and mixtures thereof. In a particularly preferred form, these polymers can be mixed in quantities of up to 80% by weight with the biodegradable polyester according to the invention.

As regards polyhydroxyalkanoates, these can be present in quantities between 30 and 80% by weight, preferably between 40 and 75% by weight, even more preferably between 45 and 70% by weight, with respect to the total composition.

Said polyhydroxyalkanoates are preferably selected from the group consisting of polyesters of lactic acid, poly-?-caprolactone, polyhydroxybutyrate, polyhydroxybutyrate valerate, polyhydroxybutyrate propanoate, polyhydroxybutyrate hexanoate, polyhydroxybutyrate decanoate, polyhydroxybutyrate dodecanoate, polyhydroxybutyrate hexadecanoate, polyhydroxybutyrate octadecanoate, poly3-hydroxybutyrate 4-hydroxybutyrate. Preferably, the polyhydroxyalkanoate of the composition comprises at least 80% by weight of one or more polyesters of lactic acid.

In a preferred embodiment, the lactic acid polyesters are selected from the group consisting of poly L-lactic acid, poly D-lactic acid, poly D-L lactic stereocomplex, copolymers comprising more than 50 mol % of said lactic acid polyesters or mixtures thereof.

Particularly preferred are lactic acid polyesters containing at least 95% by weight of repeating units derived from L-lactic or D-lactic acid or combinations thereof, with a molecular weight Mw greater than 50000 and with a shear viscosity between 50 and 700 Pa*s, preferably between 80 and 500 Pa*s (measured according to the ASTM D3835 standard at T=190°C, shear rate=1000s-1, D=1mm, L/D=10).

In a particularly preferred embodiment of the present invention, the lactic acid polyester comprises at least 95% by weight of L-lactic acid derived units, ≥ 5% of D-lactic acid derived repeating units, 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 the ASTM-D1238 standard at 190°C and 2.16kg) in the range 1-50 g/10 min. Commercial examples of lactic acid polyesters having these properties are, for example, the products branded Ingeo® Biopolymer 4043D, 3251D, 6202D, the product branded Luminy® L105.

Among the vinyl polymers, preferred are: polyethylene, polypropylene, their copolymers, polyvinyl alcohol, polyvinyl acetate, polyethylene vinyl acetate and polyethylene vinyl alcohol, polystyrene, chlorinated vinyl polymers, polyacrylates.

Chlorinated vinyl polymers include, in addition to polyvinyl chloride, polyvinylidene chloride, polyethylene chloride, poly(vinyl chloride-vinyl acetate), poly(vinyl chloride-ethylene), poly(vinyl chloride-propylene), poly(vinyl chloride-styrene), poly(vinyl chloride-isobutylene), as well as copolymers in which polyvinyl chloride represents more than 50% by mole. These copolymers may be random, block, or alternating.

As for 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 combinations thereof such as 6/9, 6/10, 6/11, 6/12, their mixtures and copolymers, both random and block. 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, their mixtures and copolymers, both random and block.

Among polyethers, preferred are those selected from the group consisting of polyethylene glycols, polypropylene glycols, polybutylene glycols, their copolymers and mixtures thereof with molecular weights from 70,000 to 500,000.

For diacid diol polyesters, these preferably comprise: a) a dicarboxylic component comprising, in relation to the total dicarboxylic component:

a1) 20-100 mol % of units derived from at least one aromatic dicarboxylic acid, a2) 0-80 mol % of units derived from at least one saturated aliphatic dicarboxylic acid, a3) 0-5 mol % of units derived from at least one unsaturated aliphatic dicarboxylic acid; b) a diol component comprising, with respect to the total diol component: b1) 95-100 mol % of units derived from at least one saturated aliphatic diol;

b2) 0-5 mol% of units derived from at least one unsaturated aliphatic diol.

Preferably, aromatic dicarboxylic acids a1, saturated aliphatic dicarboxylic acids a2, unsaturated aliphatic dicarboxylic acids a3, saturated aliphatic diols b1 and unsaturated aliphatic diols b2 for said polyesters are selected from those described above for the polyester according to the present invention.

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 (including nanofibrils) and pectin.

The term "starch" herein refers to all types of starch, namely: flour, native starch, hydrolyzed starch, destructured starch, gelatinized starch, plasticized starch, thermoplastic starch, biofillers comprising complexed starch or mixtures thereof. Starches such as potato, corn, tapioca, and pea starches are particularly suitable according to the invention. Starches that can be easily destructured and have high initial molecular weights, such as potato or corn starch, are particularly advantageous. Starch can be present either as such or in chemically modified form, such as starch esters with a degree of substitution between 0.2 and 2.5, hydroxypropylated starch, or starch modified with fatty chains.

By destructured starch, reference is made here to the teachings contained in Patents EP-0118240 and EP-0 327 505, meaning starch processed in such a way as to substantially eliminate the so-called "Maltese crosses" under a polarized light microscope and the so-called "ghosts" under a phase-contrast optical microscope. Advantageously, the destructuring of the starch is carried out through 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 supplying, during said extrusion, a specific energy greater than 0.1 kWh/kg.

Starch destructurization preferably occurs in the presence of 1-40% by weight, based on the weight of the starch, of one or more plasticizers selected from water and polyols with 2 to 22 carbon atoms. Water may also be that naturally present in starch. Among polyols, preferred are those with 1 to 20 hydroxyl groups containing 2 to 6 carbon atoms, their organic and inorganic ethers, thioethers, and esters.

Examples of such polyols are glycerin, diglycerol, polyglycerol, pentaritritol, 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 thereof.

In a preferred embodiment, the starch is destructured in the presence of glycerol or a mixture of plasticizers comprising glycerol, more preferably comprising between 2 and 90% by weight of glycerol. Preferably, the destructured and cross-linked starch according to the present invention comprises between 1 and 40% by weight, based on the weight of the starch, of plasticizers.

When present, the starch in the composition according to the present invention is preferably in the form of particles having a circular, elliptical or in any case elliptical cross-section having an arithmetic mean diameter, measured taking into consideration the major axis of the particle, of less than 1 micron and more preferably less than 0.5 μm in mean diameter.

The biodegradable polyester of the preform according to the invention may also be optionally mixed with one or more additives selected from the group consisting of plasticizers, UV stabilizers, lubricants, nucleating agents, surfactants, antistatic agents, pigments, compatibilizing agents, lignin, silymarin, organic acids, antioxidants, anti-mold agents, waxes, processing aids and polymeric components preferably selected from the group consisting of vinyl polymers and diacid-diol polyesters different from or identical to the aliphatic and/or aliphatic-aromatic polyesters described above.

Each additive is present in a quantity preferably less than 10% by weight, more preferably less than 5% by weight, even more preferably less than 1% by weight with respect to the total weight of the mixture.

As regards plasticizers, in addition to the plasticizers preferably used for the preparation of destructured starch described above, these are selected from the group consisting of trimellitates, such as for example the esters of trimellitic acid with C4-C20 monoalcohols preferably selected from the group consisting of n-octanol and n-decanol, and aliphatic esters having the following structure:

R1-O- C(O)-R4-C(O)-[-O-R2-O-C(O)-R5-C(O)-]m-O-R3

in which:

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, residues of polyols esterified with C1-C24 monocarboxylic acids;

R2 comprises -CH2-C(CH3)2-CH2- and C2-C8 alkylene groups, and is constituted by at least 50% by moles of said -CH2-C(CH3)2-CH2- groups;

R3 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, residues of polyols esterified with C1-C24 monocarboxylic acids;

R4 and R5 are the same or different, comprise one or more C2-C22 alkylenes, preferably C2-C11, more preferably C4-C9, and consist of at least 50 mol % C7 alkylenes;

m is a number between 1-20, preferably 2-10, more preferably 3-7.

Preferably, in said esters at least one of the groups R1 and/or R3 comprises, preferably in an amount of ? 10 mol %, more preferably ? 20 mol %, even more preferably ? 25 mol %, with respect to the total amount of groups R1 and/or R3, 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 aliphatic esters of this type are described in Italian patent application MI2014A000030 and in international patent applications WO 2015/104375 and WO 2015/104377.

The lubricants are preferably selected from esters and metal salts of fatty acids, such as zinc stearate, calcium stearate, aluminum 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, based on the total weight of the composition.

Examples of nucleating agents include sodium saccharin, calcium silicate, sodium benzoate, calcium titanate, boron nitride, isotactic polypropylene, and low molecular weight PLA. Pigments can also be added if necessary, such as titanium dioxide, clays, copper phthalocyanine, titanium dioxide, silicates, iron oxides and hydroxides, carbon black, and magnesium oxide.

Processing aids such as slip and/or release agents include, for example, biodegradable fatty acid amides such as oleamamide, erucamide, ethylene-bis-stearylamide, fatty acid esters such as glycerol oleates or glycerol stearates, saponified fatty acids such as stearates, and inorganic agents such as silica or talc. Processing aids are present in quantities preferably 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.

The present invention also relates to the use of the preform for the production of expanded products, preferably expanded products obtained by extrusion or injection molding.

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 following phases:

a) placing the said unexpanded or partially expanded preform in an autoclave, in contact with expanding gas;

b) reach a temperature between the softening point and the melting point of the polyester, at a pressure sufficient to maintain the expanding gas in supercritical conditions and for a time sufficient to allow the adsorption of said gas by the material;

c) instantly reduce the pressure while maintaining the temperature above the softening point of said polyester, obtaining a foam.

Said expanding gas is chosen from CO2, N2, hydrocarbons, and their mixtures. N2, CO2, and their mixtures are particularly preferred.

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

The ratio between the volume of said co-expander and the total volume of the autoclave is between 0.01 and 0.25.

The softening temperature can be determined, for example, from the variation in slope of the melting peak curve (onset) in DSC analysis.

During step b), the polyester is impregnated with the said blowing agent at a temperature around the melting point (Tm) for a period of time sufficient for it to diffuse inside it in the softened state, for example 90 minutes.

Phase c) is performed in less than 20 seconds, preferably less than 10 seconds. Preferably, the temperature is reduced during phase c).

The subject of this invention are expanded articles, prepared from the preform according to the present invention, obtained by physical expansion, without cross-linking using chemical additives. These articles include protective packaging for the electronics sector, such as separators or films, sporting goods such as technical equipment and footwear, and articles for the footwear sector.

Expanded 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.

In said articles, the cell wall, measured as the minimum distance between two adjacent cells by SEM microscopy, has a thickness advantageously less than 30?m, preferably <20?m, even more preferably <15?m, and greater than 1?m.

Furthermore, the average cell size is advantageously greater than or equal to 25 microns, preferably greater than or equal to 30 microns, more preferably between 50 and 200 microns.

Claims (22)

1. Biodegradable preform suitable for expansion in an autoclave by means of a physical foaming process, in the absence of chemical blowing agents and/or cross-linkers, comprising a biodegradable diacid-diol polyester characterised by - a shear viscosity at 190?C from 1500 Pa.s to 150 Pa.s, - a melt strength at 190?C of 0.04 N to 0.002 N, and - a viscoelastic ratio RVE of 15,000 to 200,000. 2. Biodegradable preform according to claim 1 wherein said polyester is branched and preferably obtained in the presence of a polyfunctional compound in quantities between 0.05% and 0.7% by moles with respect to the total dicarboxylic component, preferably between 0.2 and 0.5% by moles. 3. Biodegradable preform according to claim 2 wherein said polyfunctional compound is selected from pentaerythritol, dipentaerythritol, ditrimethylolpropane, diglycerol, triglycerol, tetraglycerol, glycerol, sorbitol, mannitol and mixtures thereof. 4. Biodegradable preform according to any of claims 1-3 wherein said polyester comprises: a) a dicarboxylic component comprising a1) 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 wherein the aromatic content is between 30 and 60%, preferably between 35 and 55%, more preferably between 40 and 48% by moles with respect to the total dicarboxylic component a). 6. Biodegradable preform according to any of claims 4-5 wherein the aromatic dicarboxylic acids of component a1) are 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, their salts and mixtures thereof. 7. Biodegradable preform according to any of claims 4-6 wherein the aliphatic dicarboxylic acids of component a2) are selected from saturated dicarboxylic acids C2-C24, preferably C4-C13, more preferably C4-C11, their C1-C24, preferably C1-C4 alkyl esters, their salts and mixtures thereof. 8. A biodegradable preform according to claim 7 wherein said 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 and their C1-24 alkyl esters. 9. Biodegradable preform according to claim 8 wherein said aliphatic dicarboxylic acids comprise succinic acid, adipic acid, azelaic acid, sebacic acid or mixtures thereof. 10. Biodegradable preform according to any of claims 1-3 wherein said diacid-diol biodegradable polyester is characterized by an aliphatic dicarboxylic component. 11. Biodegradable preform according to claim 10 wherein said dicarboxylic component is preferably selected from saturated dicarboxylic acids C2-C24, preferably C4-C18, more preferably C4-C11, their C1-C24, preferably C1-C4 alkyl esters, their salts and mixtures thereof. 12. Biodegradable preform according to any of claims 1-11 wherein said polyester has a carbon content of biological origin greater than or equal to 40%, determined according to Standard EN16640 - Annex E- Method B. 13. Process for obtaining foams in the presence of expanding gas under supercritical conditions comprising the following phases: a) placing the preform according to claim 1 unexpanded or partially expanded in an autoclave, in contact with expanding gas b) reach a temperature between the softening point and the melting point closure temperature of the polyester of said preform at a pressure sufficient to maintain the expanding gas in supercritical conditions for a time sufficient to allow the adsorption of said gas by the material c) instantly reduce the pressure while maintaining the temperature above the softening point of said polyester, obtaining a foam. 14. Process according to claim 13 wherein said expanding gas is selected from CO2, N2, hydrocarbons and mixtures thereof, preferably N2. 15. Process according to any of claims 13-14 wherein, in step a) said preform is placed in contact with expanding gas in the presence of a co-expanding agent comprising water. 16. Process according to any of claims 13-15 wherein the ratio between the volume of said co-expander and the total volume of the autoclave is between 0.01 and 0.25. 17. Process according to any of claims 13-16 wherein step c) is carried out in a time of less than 20 seconds, preferably less than 10 seconds. 18. Process according to any of claims 13-17 wherein during step c) the temperature is reduced. 19. Biodegradable and recyclable foamed article obtained from the preform according to claim 1 having a density lower than 0.9 g/cm<3> and higher than 0.1 g/cm<3>, 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/cm<3>. 20. Biodegradable and recyclable foam article according to claim 19 having a hardness less than 55 determined according to the ASTM D2240-15 standard with Asker C scale with a load of 1 kg. 21. Biodegradable and recyclable expanded article according to any of claims 19-20 wherein the cell wall, measured as the average distance between two adjacent cells by SEM microscopy, has a thickness of less than 30 μm and more than 1 μm, preferably less than 20 μm and even more preferably less than or equal to 15 μm. 22. Biodegradable and recyclable expanded article according to any of claims 19-21 wherein the average cell size is greater than or equal to 25 microns, preferably greater than or equal to 30 microns, more preferably between 50 and 200 microns.