The invention is in the field of polymeric products such as foams, sheet, film, fibers and the like. In particular, the invention is directed to polymeric foams that are based on biopolymers and have a low open-cell content. The invention is further directed to a method for preparing said polymer products.

Polymeric products are product based on polymers. Accordingly, polymeric foams are foams based on polymeric materials, typically on synthetic polymeric materials. Polymeric products such as foams find several applications as engineering materials. For certain applications, foams, films or sheets can for instance be used in insulation, packaging and structural applications. For these applications, polymeric foams preferably have a low open-cell content. In contrast to open-cell-structured foams, closed-cell-structures foams do not, or only to a limited extent, contain interconnected pores. As such, the closed-cell foams have higher thermal insulation and mechanical properties such as compressive strengths.

In general, low open-cell contents can only be produced from materials which possesses a specific combination of various rheological properties (especially melt strength) in combination with suitable processing conditions. Polymeric foams are based on a resin composition and the resin that is to be foamed must have a specific shear viscosity in combination with a minimal melt strength such that it can be expanded by a blowing agent. However, it must also be able to retain the blowing agent and possesses a minimum strain hardening property such that the blown resin does not collapse during the growth of a foam bubble.

Rheological properties such as melt strength not only play a role in foaming to obtain foams. Melt strength is typically also a relevant parameter for other resin (melt) processing or shaping methods where stretching processes play an important role such as film extrusion ( e.g . film blowing, film casting), fiber spinning, blow molding, injection stretch blow molding, roto molding, 3D-printing techniques, particle foaming,

thermoforming and the like.

The melt processing such as foaming of resins, in particular resins based on bio-based polymers such as poly(lactic acid) (PLA), has proven to be challenging due to the intrinsic rheological properties of PLA. However, due to the favorable biodegradability and sustainability properties of bio based polymers, it is desired to provide closed-cell foams based on these biopolymers.

Attempts for the production of PLA-based foams are for instance described in US2008/0262118. The described foams are based on amorphous PLA and a drawback of this specific family of PLA-based foams is that these foams are not dimensionally stable above 60 °C (i.e. above the glass transition temperature of PLA). A wider range of maximum usage

temperatures is required for a lot of applications.

Alternative efforts, as for instance described in W02008/098888, have been made by providing foams that are based on a blend of PLA with additives such as ahphatic or aromatic polyesters and/or with chain extenders or branching agents like styrene-acrylic multifunctional oligomeric agents, available under the tradename Joncryl (more specifically grade Joncryl 4368 C ). Such additives typically negatively influence the favorable properties of PLA-based foams such as limitations on food contact approvals. Moreover addition of these type of additives result in very high shear viscosities. It is preferred that the presence of such additives is kept to a minimal and that the PLA-based foams are mainly, more preferably essentially entirely based on PLA. Other examples of chain extenders or branching agents include peroxides, carbodiimides and various types of bisoxazolines.

The present inventors have surprisingly found that the melt processability properties such as foamabihty properties of resins and/or the properties of the products such as foams based on these resins comprising polymers can be improved by the presence of a crystalline part that is still present at the foaming temperatures. It was found that by using this combination of polymer states, melt strength of the resin is improved. This may for instance advantageously be used to provide a polymeric foam that has an open-cell content of less than 80% or even lower, such as 50% or less can be obtained.

Accordingly, the present invention is directed to a polymeric product such as a foam, film, sheet or fiber, that is based on a resin composition that comprises at least two phases of polymers that are based on the same monomers and/or isomers thereof. Of these phases, one phase has a higher melting point than another phase. Typically, both polymer phases in the resin composition have at room temperature a semi-crystalline state. Without wishing to be bound by theory, the present inventors believe that the favorable melt processing properties, in particular the foaming properties of the resin and the low open-cell content of the foam is the result of the presence of specific crystalline states of the polymer phases in the resin composition and the difference in melting points between the phases.

In particular, the invention is directed to a polymeric product such as a foam, film, sheet or fiber, preferably a polymeric foam, that is based on a resin composition that comprises a high melting point (T _m ) semicrystalline polymer phase and a low melting point (T _m ) semicrystalline polymer phase, wherein the high T _m and low T _m semicrystalline polymer phases comprise polymers based on the same monomers and/or isomers thereof, and wherein the high T _m semicrystalline polymer phase has a higher melting point than the melting point of the low T _m semicrystalhne polymer phase. It is believed that the difference between the melting points of the high Tm semicrystalline polymer phase and low Tm semicrystalline polymer phase enables the foaming of the resin at a temperature at which the low T _m semicrystalhne polymer phase is melted while the high T _m semicrystalline polymer phase is still semicrystalline, or at least still provided in structure to the molten low T _m semicrystalline polymer phase thereby providing the observed favorable melt processing properties and the favorable foaming.

The difference in melting points between the semicrystalline polymer phases is typically at least partially due to a difference in the degree of crystallinity and/or type of crystals between the phases. Generally, both polymers phases can be considered semicrystalhne, i.e. having a degree of crystallinity between 0% (i.e. fully amorphous) and 100% (i.e. fully crystalline). In practice, a crystallinity of 100% can not be achieved since even the etches of a perfect one-crystal do not have the same crystallinity as the bulk of the perfect one-crystal. In addition, between polymer crystals in a polymer phase having a high degree of crystallinity, generally some amorphous polymer substance is located. Accordingly, the term

semicrystalline is used in the context of the present invention.

Generally, the melting point of semicrystalline phases can routinely be determined by differential scanning calorimetry (DSC) according to ISO 11357-3. For certain product structures such as foams, the high T _m may be difficult to determine, in particular when the content of the high T _m semicrystalhne polymer phase is low with respect to the low T _m semicrystalline polymer phase. At the other hand, the degree of the crystallinity of the low T _m semicrystalline polymer phase may be very low, e.g. 2 to 3% or less, such that in particular cases the melting point of the low T _m semicrystalhne polymer phase may be difficult to be determined or can not be determined. In such cases, in the context of the present invention, the melting point of the high T _m semicrystalhne polymer phase is considered to be higher than the melting point of the low T _m semicrystalhne polymer phase. To facilitate the determination of the melting points T _m it may be suitable to determine these points of the resin composition in powder form or after an annealing procedure for a specific period of time at a suitable temperature.

For the favorable resin processing properties, in particular in order to foam at a temperature between the melting points of the high T _m and low T _m semicrystalhne polymer phase, it is preferred that there is sufficient difference between said melting points, in particular if the melting of the phases proceeds through a melting range. Accordingly, it is preferred that the melting point of high T _m semicrystalline polymer phase is more than 10 °C, preferably more than 25 °C, more preferably more than 40 °C higher than the melting point of low T _m semicrystalhne polymer phase as determined by differential scanning calorimetry according to ISO 11357-3.

The semicrystalhne polymer phases in accordance with the present invention comprise or essentially consist of the same type of polymers, meaning that the polymers which form the high T _m

semicrystalhne polymer phase are built from or based on the same monomers and/or isomers thereof as the polymers which form the low T _m semicrystalhne polymer phase. With isomer of a monomer is meant a molecule with the same molecular formula as the monomer but with a different chemical structure. Thus, an isomer of a monomer consists of the same number of atoms of each element, but with a different arrangement or orientation of their atoms. The isomers can comprise stereoisomers such as enantiomers, diastereoisomers and cis/trans-isomers (sometimes also referred to as E/Z-isomers), as well as structural isomers that have the same molecular formula but different bonding patterns and atomic organization.

It is preferred that the high and low T _m semicrystalhne polymer phases essentially consist of polymers based on the same monomers and/or stereoisomers thereof. By using different isomers of a particular monomer, the melting point of the polymers concerned can be influenced.

Due to its higher melting point, high T _m semicrystalhne polymer phase can be regarded as being more crystalline, comprising more perfect crystals, and/or comprising other crystal types than the low T _m

semicrystalline polymer phase. However, it may be appreciated that low T _m semicrystalline polymer phase as such may also be considered to have crystalline properties, as long as the melting point is lower than that of high T _m semicrystalline polymer phase. Examples of suitable combinations of various polymers include the combination of syndiotactic polypropylene (st- (poly)propylene) (having a melting point of 125-131 °C) and isotactic polypropylene (having a melting point of 160-170 °C), as well as the combination of polylactic acid based on 95 mol% L-lactic acid and 5 mol% D- lactic acid (having a melting point of about 130 °C) and polylactic acid based on at least 99 mol% L-lactic acid and less than 1 mol% D-lactic acid (having a melting point of about 180 °C). The melting point of semicrystalline polymer phases of the same type can routinely be determined by differenti l scanning calorimetry (DSC) according to ISO 11357-3.

In a particular embodiment of the present invention, the high T _m semicrystalline polymer phase comprises a set of polymers that are capable of forming a stereocomplex. Preferably, said set of polymers is present in the polymeric product as a stereocomplex meaning that the first and the second polymer are at least partially present in the product as a stereocomplex.

Stereocomplex formation of polymers is a physical phenomenon wherein two complementary polymers stoichiometrically interact at the level of monomeric units. The polymers can be seen as forming a complexed pair. Stereocomplex formation is known for several sets, typically pairs, of polymers, including sets of synthetic polymers. Typically, the stereocomplex has a crystalline form of which the melting temperature is higher than that of the individual polymers on which the stereocomplex is based.

In aspects of the invention, the stereocomplex is preferably formed by a pair of polymers in the polymer set, preferably by the first and second polymers, preferably by interaction of monomeric units of the first and second polymers, preferably by stoichiometric interaction involving non- ί covalent forces, including hydrogen bonding, stacking interaction, Van Der Waals interaction, Van der Waals forces, ionic interaction, dipole

interactions, charge-charge interaction and/or electrostatic interactions, optionally stabilized by cations or anions.

In aspects of the invention, the formation of the stereocomplex, at least during preparation of the polymer product, may be the result of all, or, preferably, part of the first and second polymers in the resin composition forming one or more stereocomplexes. The stereocomplexes may be permanent, but may also be temporary. Preferably the stereocomplexes are permanent.

The polymer set is preferably selected from the group consisting of a set of lactic acid polymers, a set of propylene succinate polymers, a set of i-butylthiirane polymers, a set of methyl-a-chloro acrylate polymers, a set of g-benzyl-glutamate polymers, a set of methyl methacrylate polymers, a set of poly(si-methyl methacrylate) and poly i-butyl methacrylate), a set of a-methylbenzyl methacrylate polymers, set of it -polypropylene and si- polypropylene, and a set of a-ethyl-a-methyl-6-propiolactone polymers. For these sets, stereocomplex formation is known as is i.a. described in Joseph C. Salamone, Concise Polymeric Materials Encyclopedia, 1998 by CRC Press and in Elwin Schomaker, Thesis on The Process of Stereocomplexation between it- and si-PMMA, 1998.

For instance, stereocomplex formation of the set of polypropylene succinate) is known for poly((S)-propylene succinate) and poly((R)-propylene succinate) (see Longo et al, J. Am. Chem. Soc. 136(2014), 15897-15900); stereocomplex formation of the set of a-ethyl-a-methylpropiolactone polymers is known for isotactic (it-) (R)-a-ethyl-a-methylpropiolactone and ii-(S)-a-ethyl-a-methylpropiolactone; stereocomplex formation of the set of t- butylthiirane polymers is known for it- (R) - i-butylthiir ane and it-(S)-t- butylthiirane; stereocomplex formation of the set of methyl-a-chloro acrylate polymers is known for i t -p oly (m e thyl - a -chlor o acrylate) and syndiotactic ( st -) poly(methyl-a-chloro acrylate); stereocomplex formation of the set of (y- benzyl-glutamate) polymers is known for poly(y-benzyl-D-glutamate) and poly(y-benzyl-L-glutamate); stereocomplex formation of the set of methyl methacrylate polymers is known for ii-poly(methyl methacrylate) and st- poly(methyl methacrylate); stereocomplex formation of the set of

poly(methyl methacrylate) and polyO-butyl methacrylate) is known for it- poly(methyl methacrylate) and s/-polyO-butyl methacrylate); stereocomplex formation of the set of polypropylene polymers is known for ii-polypropylene and si-polypropylene; stereocomplex formation of the set of a-methylbenzyl methacrylate polymers is known for (R) -ct -m e thylb enzyl methacrylate and ii-(S)-a-methylbenzyl methacrylate; and stereocomplex formation for the set of lactic acid polymers is known for poly(L-lactic acid) and poly(D-lactic acid). These sets of polymers are accordingly preferred for the present invention.

Unless it is specifically indicated otherwise, with polymers being based on monomers is herein meant that the polymers at least comprise those monomers referred to and that optionally additional monomers or molecular units may be present. For instance, the polymers of the present invention may include block-co-polymers, of which one or more blocks are formed by the monomers referred to, while other blocks may be formed by other monomers. Similarly, when polymers are named after certain monomers, the presence of other monomers or units in the polymers is not excluded. For instance, lactic acid polymers may include block-co-polymers of which one or more blocks consist of poly(lactic acid), star-shaped polymers comprising a core ( vide infra ) of which one or more arm consist of poly(lactic acid), and the like. The polymer may also essentially consist or consist of the monomers referred to. With essentially consist of is meant that units such as cores ( e . for star-shape or hyperbranched architectures) or backbones (e.g. for brush- or comb-shape architectures) may be present. The low and high T _m semicrystalline polymer phases may at least partially comprise the same polymers, in particular in the embodiments wherein the high T _m semicrystalline polymer phase comprises a set of polymers capable of forming a stereocomplex. For instance, in the

embodiments wherein the high T _m semicrystalline polymer phase comprises a set of the first and second polymers, the low T _m semicrystalline polymer phase may comprise, preferably consist of, the first polymer as well. This means that the low T _m semicrystalline polymer phase may consist of the first polymer and that this first polymer is capable of forming a

stereocomplex with a second polymer. Accordingly, the high T _m

semicrystalline polymer phase comprises a combination of the first and the second polymers. In other words, the resin composition may comprise the first and second polymers as the sole polymers, the first polymer being in excess with the respect to the second polymer.

In a preferred aspect of the present invention, the low and high T _m semicrystalline polymer phase consist of poly(lactic acid) polymers. As such, the low and high T _m semicrystalline polymer phase are both based on L-lactic acid, D -lactic acid or a combination thereof.

In a particular preferred embodiment, the low T _m semicrystalline polymer phase comprises a poly(L-lactic acid) polymer that is mainly based on L-lactic acid and the high T _m semicrystalline polymer phase comprises a combination of said poly(L-lactic acid) polymer that is mainly based on L- lactic acid and a poly(D-lactic acid) polymer that is mainly based on D-lactic acid. As such, in this embodiment, the combination of said poly(L-lactic acid) and poly(D-lactic acid) are capable of forming a stereocomplex having a melting point of higher than 200 °C, such as about 210 °C or 230 °C, while the said poly(L-lactic acid) has a melting point of about 140 to 180 °C

(depending on the amount of D-lactic acid). Such combination of polymers in the resin result in a high melt strength at processing temperature such as foaming temperatures, which is advantageous for the process and the process or the particular foam obtainable by this process. Accordingly, the present invention is particularly directed to a poly(lactic acid)-based product, preferably a polymeric foam, based on a resin composition comprising a poly(L-lactic acid) (PLLA) polymer that is mainly based L- lactic acid, and a poly(D-lactic acid) (PDLA) polymer that is mainly based on D -lactic acid.

The foam typically has a product density that is lower than the material density of the material on which the foam is based, due to the presence of cells. A typical foam density may be 20% less than the material density or less, and may for instance be 1000 g/L or less, and for example even as low as 30 g/L.

Without wishing to be bound by theory, the present inventors believe that the combination of said PLLA and said PDLA form a PLA stereocomplex (PLA SC) in the resin and that said stereocomplex results in overall improved rheological characteristics of the resin. The formation of stereocomplexes by PLLA/PDLA combinations as such is known (see for instance Ikada et al., Macromolecules , 1987, 20 (4), pp 904-906). PLA SC typically has a higher melting temperature than the individual PLA polymers on which the stereocomplexes are based. Typically the difference in the melting temperature can be 40 °C or more. The presence of

stereocomplexes such as PLA SC in the resin of the present invention can be determined by analytical techniques such as differential scanning

calorimetry (DSC).

The combination of said lactic acid based polymers comprising PLLA and PDLA in the resin composition can thus result in that the resin composition comprises a stereocomplex such as PLA SC of said PLLA and PDLA. Differences between PLA homocrystals and PLA stereocomplex crystals can be distinguished by DSC and or X-ray (more specific WAXS; see figure 1). It was found that for the present invention, it is not required that the resin composition comprises an equal amount of the low T _m semicrystalline polymer phase and high T _m semicrystalline polymer phase. In general, it is sufficient if high T _m semicrystalhne polymer phase is present in an amount of less than 30%, preferably in the range of 0.05 to 25%, more preferably in the range of 0.1 to 20%, based on the total weight of the resin composition. These amounts were found particularly applicable to PLLA and PDLA. Thus in a preferred embodiment, the resin composition comprises 0.05 to 10% PDLA and 80 to 95% PLLA, based on the total weight of the resin composition.

For the amount of the high T _m semicrystalhne polymer phase are to be considered all polymers in the resin composition that are part of the phase having the higher melting point. Thus, in the embodiments wherein the low T _m semicrystalhne polymer phase comprises or consists of the first polymer, while the high T _m semicrystalline polymer phase comprises a combination of the first and second polymers capable of forming a

stereocomplex, the amount of high T _m semicrystalhne polymer phase is regarded to comprise the combined amount of the first and second polymers that can form said stereocomplex, while the remainder of the first polymer is to be considered to be part of the total amount of the low T _m

semicrystalhne polymer phase. For instance, if the low T _m semicrystalhne polymer phase consists of the first polymer, while the high T _m

semicrystalhne polymer phase consists of the first and second polymers which form a stereocomplex in a 1:1 ratio, the amount of high T _m

semicrystalhne polymer phase can also be regarded as twice the amount of second polymers, while the amount of low T _m semicrystalhne polymer phase can be considered as the total amount of the first polymer minus the amount of the second polymer.

A particular advantage of the present invention is that the amount of the low T _m semicrystalhne polymer phase polymer in the resin composition is typicahy in the range of 70% or higher, preferably 85% or higher, more preferably 90% or higher, based on the total weight of the resin composition. This means that the resin and the resulting product may consist essentially entirely of the low and high T _m semicrystalline polymer phases. As such the product can retain the favorable properties that are known for the low and high T _m semicrystalline polymer phases, i.e. the biodegradabihty and sustainability. It may be appreciated that one or more additives may be present ( e.g . a nucleation agent, vide infra), but it is preferred that these additives are of a natural source and/or biodegradable such that the product remains environmentally benign. Accordingly, with the resin and the polymeric product based thereon consisting essentially entirely of the low and high T _m semicrystalline polymer phases is meant that the combined amount of the low and high T _m semicrystalline polymer phases is at least 90 wt%, preferably at least 95%, more preferably at least 98 wt% of respectively the resin and the polymeric product based thereon.

The terms PLLA and PDLA as used herein are meant to include all types of poly(lactic acid) polymers that have crystalline character and a glass transition or melting temperature. PLLA and PDLA in accordance with the present invention may be based entirely on L- or D-lactic acid respectively. However, it was found for the present invention that this is not required. In accordance with the invention, PLLA may comprise small amounts of D-lactic acid with respect to L-lactic acid and/or PDLA may comprise small amounts of L-lactic acid with respect to D-lactic acid.

Accordingly, PLLA is mainly based on L-lactic acid and PDLA is mainly based on D-lactic acid. Amorphous PLA that does not have a crystalline character is not considered PLLA or PDLA in accordance with the present invention.

In a preferred embodiment, the poly(L-lactic acid) polymer is based on less than 13 mol%, preferably less than 10 mol%, D-lactic acid and essentially entirely complemented with L-lactic acid. In yet another preferred embodiment, the poly(D-lactic acid) polymer is based on less than 13 mol%, preferably less than 10 mol%, L-lactic acid and essentially entirely complemented with D-lactic acid. In certain embodiments of the present invention, the PLLA and/or PDLA may be based on an initiator ( e.g . a polyalcohol, vide infra) that is not PLLA and/or PDLA. Accordingly, with essentially entirely complemented is meant that the complementing monomers of PLLA and PDLA are based on L- or D-lactic acid respectively, while the core or initiator may be of a different origin.

Particularly good results in terms of melt strength and open-cell content were obtained in case the PDLA is a branched polymer (herein also referred to as branched PDLA). PLA polymers are generally linear polymers, but branched PLA polymers can be provided by using chain extenders or branching agents that result in cross-linking or branching of the PLA polymers. Alternatively, or additionally, branched PLA polymers can be obtained by using a multifunctional initiator for initiating the PLA polymerization reaction. In a particularly preferred embodiment, the PDLA is a multi-arm polymer (herein also referred to as multi-arm PDLA or star shaped PDLA) of which each arm comprises a poly(D-lactic acid) segment that is mainly based on D-lactic acid - similar to the PDLA as such.

Multi-arm PDLA can be obtained by initiating the polymerization reaction with a multi-functional initiator. Examples of multi-functional initiators include polyalcohols such as glycerol, trimethylolpropane, pent aery thritol, dipentaerythritol, hexaglycerol and tripentaerythritol. The multi-arm PDLA thus accordingly may comprise a core that is based on an poly-alcohol such as glycerol, trimethylolpropane, pentaerythritol, dipentaerythritol, hexaglycerol and tripentaerythritol. By selecting the appropriate multi-functional initiator, the multi-arm polymer may comprise up to 25 arms. Preferably the multi-arm PDLA comprises 8 or less arms, more preferably 3 to 6 arms, such as 4 arms. The multi-arm polymer is a branched polymer which can have various structures, shapes or

architectures. For instance, the polymer may be star-shaped, comb-shaped, brush-shaped, dendrimeric, or hyperbranched (see e.g. Nouri et al., Journal of Polymer Science, Part B: Polymer Physics (2015), 53, 522-531, which is incorporated herein in its entirety, for a variety of architectures). As such, a multiplicity of arms can be present. The multi-arm polymers may also be obtained by reactive extrusion (see e.g. Corre et a.L, Rheology Acta (2011) 50:613-629, which is incorporated herein in its entirety).

A particular advantage of the branched PDLA, and especially of the multi-arm PDLA is that these PDLA polymers in said PLA based formulations result in a particularly low open-cell content. It was found possible to provide the poly(lactic acid)-based foam with an open-cell content of less than 10%, even less than 5%.

As such, in general, branched or multi-arm properties of the polymers have a positive effect on the open-cell content of the foam. A particular embodiment of the present invention is therefore the foam, in particular the poly(lactic acid)-based foam, having an open-cell content of less than 80%, preferably less than 50%, more preferably less than 25%, most preferably less than 10% as determined by a method as described in DIN ISO 4590.

The present inventors have further surprisingly found that the weight- average molecular weight (absolute molecular weight determined with help of GPC and HexaFluoroIsoPropanol (HFIP) as solvent) of the PDLA is preferably less than 150 x 10’' g/mol, more preferably less than 130 x 10 ³ g/mol, even more preferably less than 100 x 10 ³ g/mol, most preferably less than 50 x 10 ³ g/mol, even more preferably less than 45 x 10 ³ g/mol. A low average molecular weight of the PDLA results in improved rheological properties and a low cell content of the foam. A combination of the multi arm PDLA and the indicated average molecular weights have shown particular good results.

Foaming processes typically i.a. rely on the presence of a nucleation agent. Accordingly, the foam in accordance with the present invention, preferably further comprises a nucleation agent. It is preferred that the nucleation agent, if present, is present in an amount of less than 10%, preferably less than 5% based on the total weight of the resin

composition. Too much nucleation agent would diminish the favorable properties of the foam due to the very high cell density, while too less nucleation agent may result in poor mechanical properties. The nucleation agent may comprise an organic and/or an inorganic nucleating agent.

Examples of preferred inorganic nucleation agents include a lamellar clay mineral such as talc.

The resin composition of the present invention may further comprise UV stabilizers, heat stabilizers, anti-oxidants, flame retardants, impact modifiers, plasticizers, rheology modifiers, antistatic agents, mold release agents, lubricants, colorants (pigments) or biodegradable and/or biobased thermoplastic blend components like poly-butylene-adipate-(co)- terephtalate (PBAT), poly-butylene-succinate (PBS) and its copolymers like poly-butylene-succinate-(co)-adipate (PBSA), poly-hydroxy-alkanoate (PHA), poly-caprolactone (PCL), Poly-vinyl acetate (PVAc), Poly-vinyl-alcohol (PVOH) and carbohydrate based components like (thermoplastic) starch and (thermoplastic) cellulose.

A further aspect of the present invention is a method for the production of the polymeric product, which method comprises processing the resin composition at a temperature between the melting point of the low T _m semicrystalline polymer phase and the melting point of the high T _m semicrystalline polymer phase to obtain the polymeric product. The type of processing of the resin depends on the desired product. Typically, the processing comprises shaping the resin into the shape of the product. In general, the processing may comprise melt stretch processing such as film extrusion ( e.g . film blowing, film casting), fiber spinning, blow molding, injection stretch blow molding, roto molding, 3D-printing techniques

(additive manufacturing), particle foaming, expanded beads forming, thermoforming, or the like, and combinations thereof. Preferably the processing comprise foaming, since the present invention is particularly suitable for providing foams having a low open-cell content ( vide supra).

Surprisingly, the foam product that is obtainable by the present invention is particularly suitable for thermoforming. It was found that the cell size and open-cell content do not notably reduce upon thermoforming, which is indicative of a highly stable foam product. As such, a preferred embodiment of the present invention comprises providing the polymeric foam, preferably a polymer foam sheet (e.g. by foam extrusion) and thermoforming said sheet to form a product of a desired shape. This product may for instance be used for packaging of food.

The resin composition can be made using typical methodologies known to the skilled person. For example, the polymers forming the high T _m semicrystalline polymer can be added as an additive to the polymers forming the low T _m semicrystalline polymer phase. The additive can consist essentially of only one of polymer of the set forming the stereocomplex, but the additive may also comprise both polymers of the set of polymers forming the stereocomplex. Such additive comprising both polymers is herein also referred to as a masterbatch. The polymers of the set of polymers forming the stereocomplex can be present in a 1: 1 ratio in the masterbatch, but other ratios are also well possible. For example, a masterbatch comprising about 1 to 10%, e.g. about 5%, of one type of polymer, based on the total weight of the masterbatch, can typically be used for the present invention.

As described above, the degree of the crystallinity of the low T _m semicrystalline polymer phase may be very low, e.g. 2 to 3% or less such that the melting point of the low T _m semicrystalline polymer phase may be difficult to be determined or can not be determined. In the context of the production of the product as described above, the melting point can be considered as the processing temperature. The processing temperature of a semicrystalline polymer phase such as the low T _m semicrystalline polymer phase can be determined by using viscosity/shear rate relations. Viscosity/shear rate relations can be analyzed using a Rosand RH7 Dual Bore Advanced Capillary Extrusion Rheometer. Speeds of the piston can be set from lmm/min to 150mm/min. When equipped with e.g. a capillary of 16x1 mm, viscosities in the shear rate range of 40 to 3000 s ¹ can be determined. Viscosity itself can be deduced by help of a pressure transducer placed just before the entrance of the capillary. Prior to the analysis, the machine has to be filled with about 50 grams of material, next the sample needs to be heated/melted at the measuring temperature for 6 minutes.

After this the analysis can start. Preferably, the thermoplastic composition has a viscosity of at least 100, 1000, 10 ⁴ or even 10 ⁵ , 10 ⁶ mPa.s and/or at most 10 ⁵ , 10 ⁶ , 10 ⁷ 10 ⁸ or 10 ⁹ mPa.s at processing conditions such as temperature and shear rate.

Foaming such as extrusion foaming in general is known in the art, for instance from the aforementioned US2008/262118.

For the present invention, the method to provide the foam can be carried out by using a twin-screw extruder (both co-rotating and counter rotating versions are possible) with a die connected to the extruder.

Preferably, a melt cooler and/or a melt mixer is/are located between the extruder and die. Alternatively, a single screw extruder with a die connected to the extruder can be used. Also for the single screw extruder, it is preferred that between extruder and die, the melt cooler and/or melt mixer is/are located. In yet another alternative setup, the present method to provide the foam can be carried out in a tandem extrusion setup wherein two extruders attached to each other. Alternative extruder setups may also be possible to carry out the present method.

In a preferred embodiment of the method to provide the foam, the foaming comprises extrusion foaming and the steps of:

1) heating said resin composition to a temperature at or above its lowest melting point, preferably to a temperature of 140 to 215 °C, preferably 140 to 210 °C, more preferably 150 to 200 °C to provide a heated resin composition;

2) adding a blowing agent to the heated resin composition such that a foamable resin composition is provided; and

3) optionally adjusting the temperature of the foamable resin composition to a temperature of 90 to 160 °C, preferably 100 to 145 °C;

4) passing the foamable resin composition through an extrusion die and allowing said foamable resin composition to expand such that the foam is obtained.

In a preferred embodiment, the extrusion foaming comprises the preparation of extrusion expanded beads that can be used for further processing, e.g. in a molding process to produce 3-dimensional shaped products. In the present invention, the resin composition is heated and at least partially expanded according the procedure as described above. The beads prepared according to this process have a density typically of less than 100 g/L, for instance in the range of 10 to 60 g/L, preferably 15 to 50 g/L.

In the method of the present invention, the resin composition is heated to a temperature at or above the melting point of the low T _m semicrystalline polymer phase. In particular for PLA-based products as described herein, it was found to be preferable not to exceed a temperature of 215 °C, more preferable not to exceed 210 °C, most preferably not to exceed 200 °C. Without wishing to be bound by theory, the inventors believe that at a temperature of 200 °C or lower, the PLA SC remains intact which explains the improved melt strength as provided by the present invention. The temperature is preferably between 140 °C and 200 °C. At temperatures in this range, the heated resin composition has a similar appearance as molten PLA while maintaining some of the structure of crystalline PLA. This is believed to be the result of the presence of PLA SC. Particular good results were obtained at a temperature in the range of 150 to 200 °C. After heating the resin composition to the indicated temperature to provide the heated resin, the blowing agent is added for the foaming. The blowing agent may comprise a physical blowing agent, preferably one or more physical blowing agents selected from the group consisting of nitrogen, carbon dioxide, fluorocarbons, hydrofluorocarbons, hydrocarbons such as isobutane and pentane, hydrochlorofluorocarbons, lower alkanols, alkyl chlorides and alkyl ethers. Isobutane and carbon dioxide are particularly preferred. Alternatively, or additionally to the physical blowing agent, the blowing agent may comprise a chemical blowing agent, preferably one or more chemical blowing agents selected from the group consisting of nitrogen- or carbon-dioxide-generating agents such as sodium bicarbonates and mixtures thereof with citric acid.

Preferably, the blowing agent comprises carbon dioxide. Carbon dioxide can be added to the heated resin in any physical phase: solid, liquid, gaseous and/or supercritical. In a most preferred embodiment, the blowing agent comprises supercritical carbon dioxide. Using supercritical carbon dioxide is particularly advantageous. This blowing agent can be fed to the extruder as liquid, but changes into the supercritical state when it enters the extruder. After introduction, the supercritical liquid can be maintained under supercritical conditions (i.e. pressure and temperature conditions to prevent the supercritical hquid from a phase transition to gas) until the foamable resin composition passed through the die, resulting in a better mixing with the resin. Carbon dioxide is for instance a supercritical fluid at a temperature and pressure simultaneously at or above 31.1 °C and 72.9 bar. Inter alia for reasons of ease of operation and reliability, it is preferred that supercritical conditions are maintained throughout the extrusion process, i.e. during steps 2-3 of the present method.

In the embodiments wherein the blowing agent comprises CO2, the blowing agent is typically added in an amount of at least 1 wt%, preferably up to 12 wt%, more preferably up to 11 wt%, most preferably 4 to 10.5 wt%, based on the weight of the polymer composition.

Generally, the heated resin and the blowing agent added are mixed or blended in the melt mixer (the basic mixing process happens in the extruder; homogenizing the resin temperature is the main goal of the melt mixer) to obtain a homogeneous distribution of the blowing agent in the foamable resin composition. This can be carried out before or after the temperature adjustment in step 3 that is, optionally but typically carried out. It may be appreciated that mixing in the melt mixer may also be carried out without the temperature adjustment being carried out. It has been found that preferred foaming temperatures (i.e. temperatures at the die in step 4) are lower than the heating temperatures (i.e. the temperature of step 1). Accordingly, the temperature adjustment of step 3 is preferred. It is particularly preferred to adjust the temperature in step 3 to a temperature between 90 and 160 °C, more preferably between 100 and 145 °C to give the best foam properties, in particular of the PLA-based foams as described herein. The temperature adjustment can be carried out in the melt cooler that can be part of the extruder setup as described herein -above.

The present invention can be illustrated by the following non- limiting examples.

Example 1: preparation of three-, four- or six-armed PDLA

Various multi-armed PDLA polymers were prepared as described in S. Nouri, C. Dubois, and P.G. Lafleur, Polymer 67 (2015) 227-239.

Three different initi tors were used:

• Trimethylolpropane, for three armed PDLA

• Pentaerythritol, for four armed PDLA

• Dip ent aery thritol, for six armed PDLA

and with different molar ratios ((D)-lactide/initiator) to realize different arm lengths: • 1.0 / 0.0090 for‘extra short’ arms (XS)

• 1.0 / 0.0036 for short arms (S)

• 1.0 / 0.0018 for long arms (L)

Several PDLA polymers were accordingly obtained as indicated in Table 1.

The linear PDLA polymers D070 (Mw = 59 kg/mol; Mw/Mn = 1.7) and PDLA D 120 (Mw = 86 kg/mol; Mw/Mn = 1.7) are commercially available and were obtained from Total Corbion.

Table 1: PDLA polymers

Example 2: preparation of PDLA masterbatch

compositions

To add PDLA to the final foam composition it is for practical reasons preferred to have master batches consisting of PLLA and PDLA: a mixture of PLLA (a poly(L-lactic acid) polymer based on 95% L-lactide and 5% D-lactide having a molecular weight of 137 kg/mol named BF1505 and supplied by BEWiSynbra RAW b.v., Etten-Leur, The Netherlands) was mixed with the various PDLA polymer materials (5 wt%) of Table 1. This mixture was extruded on a Berstorff ZE 25 CE * 40 D into a homogeneous strand at a melt temperature of about 190 °C and 300 rpm. After cooling the strand with help of a water bath, the strand was pelletized into cylindrical shaped pellets.

Pellets were analyzed with help of a Rosand twin bore capillary rheometer equipped with a haul off device for determination of the melt strength. An overview of the melt strength properties, analyzed at 160 °C, of some of the master batches can be found in Figure 2. A clear positive effect of adding short chain branched PDLA structures to PLLA on melt strength when compared to the reference material can be seen from Figure 3. A typical DSC spectrum of the masterbatch containing 3S is shown in Figure 4.

Example 3: extrusion foaming of resin compositions

Foaming experiments were performed on three extrusion foam lines. Line 1 comprised a Leistritz ZSE 27 maxx - 48 L/D twin-screw extruder setup (commercially available from Leistritz AG), equipped with a promix Z400 CO2 dosing station, melt pump and a rod die with diameter of 2 mm.

Resin compositions based on a PLLA (a PLLA polymer based on 95.5% L-lactide and 4.5% D-lactide having a molecular weight of 148 kg/mol named BF2004 and supplied by BEWiSynbra RAW B.V., Etten-Leur, The Netherlands), a talc masterbatch (Talc MB Na BIO L 6951 (30% filler content) and supplied by Polyone Corporation, Assesse, Belgium) and the master batches as described in Example 2. Dry blend mixtures as given in Table 2 were subjected to extrusion foaming using different amount of the blowing agent supercritical CO2 (6 or 8%, based on the weight of the resin composition) to provide poly (lactic acid)-based extrusion foams. Table 2: Resin compositions foamed in line 1

Processing conditions were:

• Temperatures extruder (hopper to die):

cold/160/160/160/140/140/140/130/125/125/125/125/125 °C

• Temperatures melt pump: 125/125 °C

• Temperatures die: 125/125 °C

• Screw speed extruder: 60 rpm The open-cell content of each foam was determined according to

DIN ISO 4590. The results are provided in figure 3.

Typically, foam densities in the range of 20 to 100 g/L were obtained. Significant differences in open-cell content could be remarked when 8% of CO2 is added to the foam formulation. With linear PDLA D070 and PDLA 6L high open-cell contents could be determined. When PDLA 3XS or 6S are added to the foam formulation very low open-cell contents could be determined (< 10%). Example 4: thermoforming of sheet extruded foams

Line 2 comprised a Sulzer’s extruder foaming system that consists of a combination of dosing devices, an inter-meshing co-rotating twin screw extruder, a melt conditioning section including melt cooler, melt mixer and die (Figure 7). The Sulzer pilot plant used in this work, consisted of a 45 mm corotating twin-screw extruder (L/D 42) with a screw configuration designed for foaming process. Attached to this extruder are subsequently a melt cooler (type 425‘Torpedo’), a melt mixer (type SMB Plus DN40) and at the end an adjustable annular sheet die. Extruder is provided with 6

gravimetric feeders and a gas dosing station capable of feeding 3 different blowing agents. In Table 3, critical foaming and thermoforming process conditions are provided.

A masterbatch containing 5 wt.% 3S PDLA polymer (see Table 1) complemented with a mixture of PLLA (a poly(L-lactic acid) polymer based on 95% L-lactide and 5% D-lactide having a molecular weight of 137 kg/mol named BF1505 and supplied by BEWiSynbra RAW B.V., Etten-Leur, The Netherlands was processed with peroxide (0.2 % DCP) -treated 700 ID (per) PLA (obtainable from NatureWorks LLC) and 1 wt.% talc using the blowing- agent isobutane (6%, based on the weight of the resin composition) to form a foamed sheet.

Next, the foamed sheet was thermoformed to form a bowl (as exemplified with a photo in Figure 5). Thermoforming experiments were performed on a small scale Illig thermoforming machine equipped with a salad bowl mould with dimensions (l*w*d = 147*77*41 mm). A special shaped pre-stretcher was used. For thermoforming, foamed sheets were preheated in an oven at a temperature of 450 °C during 3 seconds, molding took place in a mould of 30 °C for 4 seconds.

In Table 3, foaming and thermoforming process conditions are provided. As a comparative example, a resin composition solely based on peroxide-treated 700 ID (per) PLA (obtainable from NatureWorks LLC) with 1% talc was similarly processed to form a foamed sheet and thermoformed afterwards using the same settings described above.

Table 3: Thermoforming of foamed sheets

In Figure 6, typical scanning electron microscopy (SEM) images before and after thermoforming are shown.

It was found that the resin composition including the 5 wt.% 3S PDLA polymer allows for much less critical process conditions making the process much more stable and reliable. As a consequence, as shown by the SEM images, the cells of the foam, in particular at the bottom, of the bowl of the reference sample are stretched and disrupted. This is detrimental to the packaging properties of the foam product. Example 5: expanded bead production

A masterbatch containing 5 wt.% 3S PDLA polymer (see Table 1) complemented with a mixture of PLLA (a poly(L-lactic acid) polymer based on 95% L-lactide and 5% D-lactide having a molecular weight of 137 kg/mol named BF1505 and supplied by BEWiSynbra RAW B.V., Etten-Leur, the Netherland was processed with PLLA (BF1505) and 1 wt.% talc using the blowing agent CO2 (8%, based on the weight of the resin composition).

Processing was carried out in the Sulzer extrusion foaming system, line 3. This system comprised a corotating twin screw extruder (diameter 45mm and L/D = 42) with a screw configuration designed for foaming processes. Attached to this extruder are subsequently a melt cooler (type 425‘Torpedo’), a melt pump, a melt screen and at the end a die plate and an underwater pelletizer system. Water temperature could be regulated. CO2 was fed to the extruder via a Sulzer designed gas dosing system. The beads expand just after leaving the die.

In Table 4, process conditions are provided.

It was found that particular foamed beads with very low open-cell content could be obtained using the 5 wt.% 3S PDLA masterbatch under various processing conditions. By adding 3S PDLA masterbatch we can prove that there is a bigger process window in which low open cell contents can be realized.

Table 4: Expanded bead production