COMPOSITION COMPRISING A MIXTURE OF POLYESTERS AND THERMOPLASTIC STARCH, HAVING IMPROVED FILM-FORMING ABILITY

Abstract

The invention relates to a thermoplastic composition comprising: at least one mixture of polyesters (A) including at least one polylactic acid (A1) and at least one aliphatic polyester (A2) or a semi-aliphatic polyester other than polymer (A1); at least one starch (B); at least one organic plasticiser (C) for starch. The composition is characterised in that: the weight percentage of (A1) in relation to the weight of (A1) and (A2), expressed as dry weight, varies between 2 and 70%, advantageously between 10 and 50%, preferably between 18 and 30%; at least 50% of the weight of the polylactic acid (A1) is formed by semi-crystalline polylactic acid; and in that the weight ratio of starch (B)/organic plasticiser (C), expressed as dry weight, varies between 90/10 and 40/60.

Description

FIELD OF THE INVENTION

A subject of the invention is a thermoplastic composition comprising thermoplastic starch, a semi-crystalline polylactic acid and at least one aliphatic polyester different than said polylactic acid. Another subject of the invention is a process for manufacturing this composition and also a process for manufacturing a film by film blowing using this composition.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

As a result of their numerous advantages, plastics have become indispensable in the mass manufacture of objects. Indeed, because of their thermoplastic nature, it is possible to manufacture objects of any type from these polymers, at a high rate. To manufacture these objects, small pieces of these thermoplastic polymers are used, generally in the form of granules, that are melted by providing heat and mechanical stresses in forming machines. For example, it is possible to manufacture film by introducing these granules into a blown film extruder or a flat die extruder (cast extrusion) or else to manufacture bottles by introducing said granules into a blow-molding extruder.

These objects are generally made of non-biodegradable thermoplastics, such as polyolefins or polyamides. However, these plastics are still today not recycled a great deal. Thus, this causes environmental problems since they are generally incinerated and this incineration can cause toxic gases to be given off. Thus, one of the important preoccupations today in the polymer field is to provide polymers which are biodegradable or at least compostable.

Among the biodegradable and/or compostable polymers, mention may be made of aliphatic polyesters, such as poly(butylene succinate) (PBS), poly(butylene succinate-co-adipate) (PBSA), poly-ε-caprolactone (pCAPA), polylactic acid (PLA) and also polyhydroxyalkanoates of polyhydroxybutyrate (PHB) or poly(hydroxy butyrate-co-valerate) (PHVB) type. Aliphatic polyesters generally have melting points close to those of polyolefins, thereby allowing, inter alia, their use in the fields of films and packaging, the biodegradability of which is an obvious advantage for single-use applications.

However, one of the problems of these polyesters is that they are relatively expensive. One of the solutions envisioned for providing biodegradable compositions which are more economical is to manufacture compositions based on thermoplastic starch, this consisting of starch and of a plasticizer for this starch, such as glycerol. Specifically, the manufacture of these compositions is advantageous since starch is one of the biosourced polymers that is naturally the most widespread in the environment. However, these thermoplastic starches have insufficient properties, in particular in terms of water resistance. Furthermore, transforming starch into thermoplastic starch is not easy since it requires the use of substantial constraints and/or temperatures during the thermomechanical mixing, which has a tendency to degrade the thermoplastic starch thus formed.

To counter these drawbacks, compositions based on aliphatic polyesters and plasticized starch have been developed. In these compositions, the thermoplastic starch phase is generally dispersed in the polyester phase. These compositions have numerous advantages, for instance that of being able to be compostable and/or biodegradable and of having water resistance that is very much improved relative to thermoplastic starch. These compositions are generally manufactured by extrusion. A rod of intimate blend of the two polymers is then obtained, this rod then being passed through a granulator so as to form granules.

The applicant has been able to note that one of the problems of the compositions based on thermoplastic starch and aliphatic polyesters such as PBS or PBSA is that these compositions can be converted into the form of a film by film blowing only at very reduced rates compared, for example, with polyethylenes. This phenomenon is particularly important when the amount by weight of organic plasticizer in the thermoplastic starch is high, that is to say when the organic plasticizer/starch weight ratio, expressed by dry weight, is equal to or exceeds 10/90. In the context of industrial processes, this results in an unsatisfactory productivity and thus in production costs that are too high.

Compositions 7A, 8A and 9A of U.S. Pat. No. 7,820,276 describes compositions comprising an aliphatic-aromatic polyester, a semi-crystalline polylactic acid and thermoplastic starch. The properties of the films obtained, and in particular the elongation at break thereof, are not satisfactory.

Application WO 2013/073402, having been the subject of a European application published under number EP 2 781 546 A1, describes a composition comprising a starch (a1), a biodegradable resin (a2) different than a polylactic acid and also an amorphous polylactic acid (b), in which the (b)/(a2) weight ratio ranges from 20/80 to 50/50 and the (constituents other than (b))/(b) weight ratio is between 95/5 and 50/50. This composition is converted by film blowing. It has improved tensile strength, elongation at break, impact strength, thermosealing resistance and tearing strength properties. However, the applicant has been able to note that these compositions do not make it possible to manufacture films by blowing film extrusion, at a high rate. Comparative compositions have also been manufactured, in which the amounts of plasticizer are very low (3 parts of plasticizer per 40 parts of starch) and semi-crystalline polylactic acid is used in place of amorphous polylactic acid. The properties of the films obtained, and in particular the tensile strength and the elongation at break, are not satisfactory, thus giving reason not to use semi-crystalline polylactic acid in thermoplastic compositions for the purpose of manufacturing films.

In the context of its research, the applicant has succeeded in providing novel compositions which make it possible to overcome these problems.

SUMMARY OF THE INVENTION

A subject of the invention is thus a thermoplastic composition comprising at least one blend of polyesters (A) comprising at least one polylactic acid (A1) and at least one aliphatic polyester (A2) other than the polymer (A1), at least one starch (B) and at least one organic plasticizer for starch (C), characterized in that:

• • the weight percentage of (A1), relative to the weight of (A1) and (A2), expressed by dry weight, ranges from 2% to 70%;
  • at least 50% of the weight of polylactic acid (A1) consists of semi-crystalline polylactic acid;
  • and in that the starch (B)/organic plasticizer (C) weight ratio, expressed by dry weight, ranges from 90/10 to 40/60, for example from 85/15 to 40/60.

The applicant has been able to note that these compositions can be easily made into films by blown film extrusion, despite the high amount of organic plasticizer used in the thermoplastic starch. Surprisingly in the light of the teaching of document EP 2 781 546 A1, the applicant has succeeded in obtaining, using semi-crystalline polylactic acid it and not using amorphous polylactic acid, thermoplastic compositions which allow the manufacture of films which have mechanical properties that are entirely satisfactory and which have the advantage of being able to be converted at high rates. From an industrial point of view, this is particularly important with a view to being able to rapidly manufacture films of compositions of this type.

The invention will now be described in detail in the description hereinafter.

DETAILED DESCRIPTION OF THE INVENTION

A subject of the invention is a thermoplastic composition based on a blend of polyesters (A) comprising at least one polylactic acid (A1) and at least one aliphatic polyester (A2) different than (A1), on starch (B) and on plasticizer (C).

A thermoplastic composition is a composition which, reversibly, softens under the action of heat and hardens on cooling to ambient temperature. It has at least one glass transition temperature (Tg) below which the amorphous fraction of the composition is in the brittle vitreous state, and above which the composition may undergo reversible plastic deformations. The glass transition temperature or at least one of the glass transition temperatures of the starch-based thermoplastic composition of the present invention is preferably between −150° C. and 40° C. This starch-based composition may, of course, be formed via processes conventionally used in plastics engineering, such as extrusion, injection, molding, blow-molding and calendering. Its viscosity, measured at a temperature from 100° C. to 200° C., is generally between 10 and 10⁶ Pa·s.

The composition according to the invention is based on a blend of polyester which comprises polylactic acid (A1), said polylactic acid being at least 50% constituted of semi-crystalline polylactic acid. Polylactic acid is generally obtained by polymerization of lactide, by ring opening. The lactide can be in the form of D-lactide, of L-lactide or else in the form of meso-lactide. The crystallinity of the polylactic acid is mainly controlled by the amount of D-lactide and of L-lactide and to a lesser extent by the type of catalyst used. Thus, the polymerization of a racemic mixture of L-lactide and D-lactide generally leads to the synthesis of an amorphous polylactic acid, whereas the polymerization of pure D-lactide or of pure L-lactide leads to the synthesis of a semi-crystalline polylactic acid. A synthesis process using a racemic mixture can also lead to a heterotactic PLA exhibiting crystallinity by using stereospecific catalysts. Preferably, the polylactic acid exhibits a crystallinity (or a degree of crystallinity) ranging from 30% to 75%, most preferentially from 40% to 60%.

The degree of crystallinity of the PLA can be determined by differential scanning calorimetry analysis on the basis of the calculation of the ratio of the Cp jump values at Tg of the semi-crystalline product that it is sought to characterize and of the same product made completely amorphous.

For example, a sample of approximately 10 mg of the material that it is sought to characterize is subjected to a heating gradient from −20° C. to 200° C. at a rate of 10° C./min. The value of the jump in Cp at Tg of this sample (called ΔCp_sample) is measured on this cycle. At the end of this first heating, the sample is completely melted. It is then subjected to rapid cooling at a rate of 30° C./min down to −20° C. The aim of this second step is to make the sample completely amorphous. It is possible to be sure of the non-recrystallization of the sample during cooling by monitoring the signal measured by the apparatus. Finally, once the sample has been made 100% amorphous, it is reheated again to 200° C. at a rate of 10° C. per minute. The value of the jump in Cp at Tg of this 100% amorphous sample (called ΔCp_sample) is measured on this third cycle. The degree of crystallinity (χ) is determined in the following way: χ=(1−ΔCp_sample/ΔCp_amorphous)×100.

According to one variant of the invention, the polylactic acid (A1) comprises an amorphous polylactic acid, that is to say that (A1) is a blend of amorphous polylactic acid and of semi-crystalline polylactic acid. According to this variant, the amount of amorphous polylactic acid, relative to the total polylactic acid, does not exceed 50%, advantageously does not exceed 20%, preferentially does not exceed 10%. More particularly, the polylactic acid can advantageously consist of a blend of 55% to 90% of semi-crystalline polylactic acid and of 10% to 45% of amorphous polylactic acid, the amounts being expressed by dry weight of polylactic acid.

The composition according to the invention also comprises an aliphatic polyester other than the polylactic acid (A1).

An aliphatic polyester is a polyester which comprises exclusively non-aromatic monomers. The term “comprises monomers” is intended to mean that the polyester can be obtained by polycondensation of these monomers. For example, if the polyester comprises succinic acid and 1,4-butanediol, this means that the polyester can be obtained by polycondensation of monomers comprising succinic acid and 1,4-butanediol. It is also specified that, when the polyester comprises x % of a monomer (X), this means that it can be obtained from a mixture of monomers comprising, relative to the total weight of the monomers, x % of monomer (X).

An aliphatic polyester is a polyester that can be obtained using non-aromatic monomers, said monomers being chosen from polyols, polyacids and monomers bearing at least one carboxylic acid function and at least one alcohol function. These non-aromatic monomers may be linear, cycloaliphatic or branched. It is also possible to obtain these polyesters via enzymatic or fermentation routes, as in the case of the polyhydroxyalkanoates.

These polyols are generally aliphatic diols, preferably saturated linear aliphatic diols. As linear aliphatic diol, mention may be made of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, or a mixture of aliphatic diol units comprising at least one of these units, preferentially ethylene glycol and 1,4-butanediol or a mixture of these diols, most preferentially 1,4-butanediol.

The polyacids are generally aliphatic diacids, preferably saturated aliphatic diacids. By way of example, these diacids may be succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid or a mixture of these diacids. Preferably, the aliphatic diacid is chosen from succinic acid and adipic acid or a mixture of these acids. The polyesters can also be obtained from esters, anhydrides or chlorides of these polyacids.

The monomers bearing at least one carboxylic acid function and at least one alcohol function are generally hydroxy acids. By way of example, the hydroxy acids may be glycolic acid, hydroxybutyric acid, hydroxycaproic acid, hydroxyvaleric acid, 7-hydroxyheptanoic acid, 8-hydroxyoctanoic acid, 9-hydroxynonanoic acid, or a mixture of these hydroxy acids. The polyesters may also be obtained from dilactone such as glycolide, or lactone such as caprolactone.

Preferably, the polyester (A2) is an aliphatic polyester chosen from the polymers (A2) from condensation of ethylene glycol and/or of 1,4-butanediol and of succinic acid and/or of adipic acid.

Relative to the total weight of the polyester, the total weight of ethylene glycol, of 1,4-butanediol, of succinic acid and of adipic acid advantageously exceeds 90%.

Preferably, the aliphatic polyester (A2) comprises 1,4-butanediol and succinic acid and/or adipic acid. The polyester (A2) is most preferentially chosen from PBS and PBSA. The invention is particularly advantageous when the aliphatic polyester (A2) is amorphous.

According to the invention, the weight percentage of (A1), relative to the weight of (A1) and (A2), expressed by dry weight, ranges from 2% to 70%. Preferably, this weight percentage ranges from 10% to 50%, most preferentially from 18% to 30%. In these preferred variants, the compositions can be converted into the form of a film by extrusion blow molding at a faster speed, these films also having mechanical properties that are entirely suitable for use in bag manufacture. According to another embodiment, the weight percentage of (A1) relative to the weight of (A1) and (A2) is low, that is to say that this weight percentage, expressed by dry weight, ranges from 2% to 20%, advantageously according to this mode from 3% to 15%, for example from 4% to 10%.

It is possible to manufacture films from this composition, by blown film extrusion, using particularly high production rates, this being in particular in the preferred range above.

It is specified that, according to the invention, the proportions by weight of each constituent are expressed by dry weight. Thus, when the proportions of a constituent are given relative to the total weight of the composition, this is intended to mean the dry weight of this constituent relative to the dry weight of the composition.

Preferably, the polyesters (A) have a flow index ranging from 0.1 to 50 g/10 min, advantageously from 0.5 to 15 g/10 min (ISO 1133, 190° C., 2.16 kg).

The composition according to the invention also comprises starch (B) and an organic plasticizer for starch (C), the two forming thermoplastic starch.

With regard to the starch (B), it may be of any type. If it is desired to obtain a less expensive composition, the starch preferentially used for the manufacture of the composition is a granular starch, preferably a native starch.

The term “granular starch” is intended to mean herein a native or physically, chemically or enzymatically modified starch, which has conserved, within the starch granules, a semicrystalline structure similar to that revealed in the starch grains naturally present in the storage organs and tissues of higher plants, in particular in cereal grains, legume grains, potato or cassava tubers, roots, bulbs, stalks and fruit. In the native state, starch grains generally have a degree of crystallinity that ranges from 15% to 45%, and which depends essentially on the botanical origin of the starch and on the possible treatment that it has undergone.

Granular starch, placed under polarized light, has a characteristic black cross, known as the Maltese cross, typical of the granular state.

According to the invention, the granular starch may come from any botanical origin, including a granular starch rich in amylose or, conversely, rich in amylopectin (waxy). It may be native starch of cereals such as wheat, maize, barley, triticale, sorghum or rice, tubers such as potato or cassava, or legumes such as pea and soybean, and mixtures of such starches.

The starch may also be modified, chemically or physically.

The function of the organic plasticizer for starch (C) is to make the starch thermoplastic.

It may be an organic plasticizer chosen from diols and polyols such as glycerol, polyglycerols, sorbitans, sorbitol, mannitol, and hydrogenated glucose syrups, urea, polyethers with a molar mass below 800 g/mol, and any mixtures of these products, preferably glycerol, sorbitol or a mixture of glycerol and sorbitol.

According to the invention, the composition comprises relatively high amounts of plasticizer, that is to say that the starch (B)/organic plasticizer (C) weight ratio, expressed by dry weight, is less than or equal to 90/10. More specifically, the starch (B)/organic plasticizer (C) weight ratio, expressed by dry weight, ranges from 90/10 to 40/60, advantageously from 85/15 to 50/50, for example from 80/20 to 60/40. The range from 90/10 to 40/60 can be broken down into two sub-ranges: a sub-range from 90/10 to 85/15 (85/15 limit excluded) and a sub-range from 85/15 to 40/60. According to another preferred embodiment, the starch (B)/organic plasticizer (C) weight ratio, expressed by dry weight, ranges from 90/10 to 80/20, or even from 90/10 to 85/15 (85/15 limit excluded). According to these modes, the weight percentage of (A1) relative to the weight of (A1) and (A2) is preferably low. The compositions of this preferred mode make it possible to be subsequently converted, for example in the form of a film, without any fumes being given of during the conversion. Moreover, the films obtained exhibit excellent mechanical properties, in particular when the amount of (A1) is low.

Even when the amounts of plasticizer are high, the composition according to the invention can be converted into the form of films by blown film extrusion, this being even using high production rates.

According to the invention, the composition may comprise relatively high amounts of thermoplastic starch. The composition according to the invention may thus comprise a total amount by weight of polyester (A) included in the range of from 35 to 75 parts. It may comprise a total amount by weight of polyester (A) included for example in the range of from 40 to 70 parts, advantageously ranging from 45 to 60 parts, preferably ranging from 48 to 58 parts, these amounts by weight being expressed relative to 100 parts of the total dry weight of the constituents (A1), (A2), (B) and (C). Preferably, the composition according to the invention is characterized by a morphology which is in the form of co-continuous domains of thermoplastic starch and of polyester. The morphology of the composition can be observed by scanning electron microscopy.

Even when the amounts of thermoplastic starch are high, the composition according to the invention may be in the form of granules, without said granules forming beads. In certain proportions such as those defined above, the morphology of the composition exhibits co-continuous domains of polyester and of thermoplastic starch. These compositions exhibit improved biodegradability compared with compositions in which the thermoplastic starch is dispersed in a continuous phase of polyester.

According to another preferred mode, the composition comprises a total amount by weight of polyester (A) included in the range of from 60 to 75 parts, preferentially from 62 to 72 parts, these amounts by weight being expressed relative to 100 parts of the total dry weight of the constituents (A1), (A2), (B) and (C). Generally, this composition is characterized by a morphology which is in the form of thermoplastic starch domains dispersed in a polyester matrix. According to this mode, the films obtained from these compositions exhibit better tear strength properties.

The composition according to the invention may also comprise additives or additional polymers, termed additional constituents, or a mixture thereof.

The composition according to the invention can thus also comprise a bonding agent bearing several functions capable of reacting with the polyester and/or the starch and/or the organic plasticizer for starch, it being possible for this function to be chosen from carboxylic acid, carboxylic acid ester, isocyanate or epoxy functions.

This bonding agent, in particular citric acid, can be present in an amount by weight ranging from 0.01 to 0.45 part, these amounts by weight being expressed relative to 100 parts of the dry weight of the various constituents of (A1), (A2), (B) and (C). Advantageously, the composition comprises from 0.05 to 0.3 part of citric acid, preferentially from 0.06 to 0.20 part, most preferentially from 0.07 to 0.15 part, relative to 100 parts of the dry weight of the various constituents of (A1), (A2), (B) and (C). The presence of citric acid in the composition makes it possible to improve the homogeneity thereof and thus to improve the properties of the composition. In the citric acid proportions selected and particularly in the preferred proportions, the composition is easy to granulate, in comparison with the compositions based on polyester and thermoplastic starch comprising larger amounts of citric acid.

The composition according to the present invention can also comprise, as other additive or additional constituent, fillers or fibers of organic or inorganic nature, which are optionally nanometric and optionally functionalized. They may be silicas, zeolites, glass fibers or beads, clays, mica, titanates, silicates, graphite, calcium carbonate, talc, carbon nanotubes, wood fibers, carbon fibers, polymer fibers, proteins, cellulose-based fibers, lignocellulosic fibers and non-destructured granular starch. These fillers or fibers can make it possible to improve the hardness, the rigidity or the water- or gas-permeability. Preferably, the composition comprises from 0.1 to 200 parts of fillers and/or fibers, for example from 0.5 to 50 parts, this amount being expressed relative to 100 parts of the total dry matter of the constituents (A1), (A2), (B) and (C). The composition may also be of composite type, i.e. may comprise large amounts of these fillers and/or fibers.

The additive that is of use in the composition according to the invention may also be chosen from opacifiers, dyes and pigments. They may be chosen from cobalt acetate and the following compounds: HS-325 Sandoplast® Red BB (which is a compound bearing an azo function, also known under the name Solvent Red 195), HS-510 Sandoplast® Blue 2B which is an anthraquinone, Polysynthren® Blue R, and Clariant® RSB Violet.

The composition may also comprise, as additive, a processing aid, for reducing the pressure in the processing tool. These aids can also have the function of demolding agents making it possible to reduce the adhesion to the materials for forming the composition, such as molds or calendering cylinders. These aids may be selected from fatty acid esters and fatty acid amides, metal salts, soaps, paraffins and hydrocarbon-based waxes. Particular examples of these aids are zinc stearate, calcium stearate, aluminum stearate, stearamides, erucamide, behenamide, beeswax or candelilla wax. Preferably, the composition also comprises a monoester of a fatty acid and of glycerol, for example glyceryl monostearate. According to this preferred variant, this composition allows the manufacture of films that are less tacky than compositions free of this constituent. Preferably, the amount by weight of processing aid, and in particular of monoester of a fatty acid and of glycerol, ranges from 0.05 to 1.7 parts, for example from 0.3 to 1.65 parts, advantageously from 0.5 to 1.5 parts, preferentially from 0.65 to 1.3 parts, these amounts being expressed relative to 100 parts of the dry weight of the various constituents (A1), (A2), (B) and (C).

The composition according to the invention may also comprise other additives, such as stabilizers, for example light stabilizers, UV stabilizers and heat stabilizers, fluidizers, flame retardants and antistatic agents. It may also comprise primary and/or secondary antioxidants. The primary antioxidant may be a sterically hindered phenol, chosen from the compounds Hostanox® 0 3, Hostanox® 0 10, Hostanox® 0 16, Ultranox® 210, Ultranox®276, Dovernox® 10, Dovernox® 76, Dovernox® 3114, Irganox® 1010 or Irganox® 1076. The secondary antioxidant may be chosen from trivalent phosphorus compounds such as Ultranox® 626, Doverphos® S-9228, Hostanox® P-EPQ or Irgafos® 168.

The composition may also comprise an additional polymer, different than the polyester according to the invention. This polymer may be chosen from polyamides, polystyrene, styrene copolymers, styrene-acrylonitrile copolymers, styrene-acrylonitrile-butadiene copolymers, poly(methyl methacrylate)s, acrylic copolymers, poly(ether-imide)s, poly(phenylene oxide)s, such as poly(2,6-dimethylphenylene oxide), poly(phenylene sulfate)s, poly(ester-carbonate)s, polycarbonates, polysulfones, polysulfone ethers, polyether ketones, and mixtures of these polymers.

The composition may also comprise, as additional polymer, a polymer for improving the impact properties of the polymer, in particular functional polyolefins such as functionalized ethylene or propylene polymers and copolymers, core-shell copolymers or block copolymers.

The compositions according to the invention may also comprise polymers of natural origin, such as cellulose, chitosans, alginates, carrageenans, agar-agar, proteins such as gluten, pea proteins, casein, collagen, gelatin or lignin, these polymers of natural origin possibly being physically or chemically modified.

According to one variant of the invention, the composition comprises by dry weight:

• • from 1 to 55 parts of at least one polyester (A1);
  • from 5 to 65 parts of at least one polyester (A2);
  • from 5 to 50 parts of at least one starch (B), preferably from 20 to 40 parts;
  • from 5 to 50 parts of at least one organic plasticizer (C) for starch, preferably from 10 to 35 parts;
    the sum of the amounts of the constituents (A1), (A2), (B) and (C) coming to 100 parts and in which:
  • the weight percentage of (A1), relative to the weight of (A1) and (A2), expressed by dry weight, ranges from 2% to 70%;
  • at least 50% of the weight of polylactic acid (A1) consists of semi-crystalline polylactic acid;
  • and the starch (B)/organic plasticizer (C) weight ratio, expressed by dry weight, ranges from 90/10 to 40/60;
    the composition possibly also comprising from 0.01 to 200 parts of additional constituent(s) chosen from the additives and polymers, different than (A1), (A2), (B) and (C).

The composition according to the invention can be manufactured using a process for manufacturing a composition as claimed in one of the preceding claims, characterized in that it comprises:

• • a step a) of introducing into a mixing system constituents comprising a blend of polyesters (A) comprising at least one polylactic acid (A1) and at least one aliphatic polyester (A2) other than the polymer (A1), at least one starch (B) and at least one organic plasticizer for starch (C), and optionally water;
  • a mixing step b) in which the constituents are thermomechanically mixed so as to obtain the thermoplastic composition;
  • a step c) of recovering the thermoplastic composition.

The amounts of the various constituents can obviously be varied in such a way as to obtain the compositions described above. In the case where constituents comprising moisture are used, those skilled in the art can easily, in order to carry out the process, determine the amounts by weight of the various constituents by wet weight to be introduced into the mixing system, by measuring beforehand the moisture content in each constituent, for example by carrying out an assay using the Karl-Fisher method, this being in order to obtain the compositions in the proportions described above. By way of illustration, the Examples section contains the description of compositions expressed by dry weight, with the amounts of each of the constituents used during the process which are, for their part, expressed by wet weight.

With regard to the mixing system, it may involve internal blade or rotor mixers, external mixers, or single-screw or co-rotating or counter-rotating twin-screw extruders. However, it is preferred to prepare this mixture by extrusion, in particular using a co-rotating twin-screw extruder. In the case of an extruder, the various constituents of the composition may be introduced by means of feed hoppers located along the extruder.

The process described in WO 2010/010 282 A1 may in particular be used to prepare the composition.

The mixing system may comprise a drying system, for example a system for extracting the volatile compounds, such as a vacuum pump. In this case, the moisture content of the composition at the end of the process may be reduced in comparison with the total moisture content in the constituents introduced in step a).

Preferably, the moisture content of the composition is adjusted so as to be between 2.5% and 9% relative to the total weight (thus wet weight) of the constituents introduced in step a).

Advantageously, the process comprises at least one drying step, such that the moisture content of the composition is between 0.2% and 1.4%. Preferably, the mixing of step b) is carried out simultaneously with the drying step, for example by connecting a vacuum pump to the reactor. The process may also comprise a distinct drying step, which takes place subsequent to the recovering step c).

According to the invention, the mixing temperature during step b) advantageously ranges from 90 to 210° C., preferentially from 110 to 190° C.

The mixing of the constituents of the composition may take place under an inert atmosphere.

With regard to the mixing system, it may involve internal blade or rotor mixers, external mixers, or single-screw or co-rotating or counter-rotating twin-screw extruders. Preferably, the mixing step b) takes place in an extruder, in particular using a co-rotating twin-screw extruder. When it is by extrusion, the step a) of introducing the various constituents of the composition can be carried out by means of feed hoppers located along the extruder.

When the mixing is carried out by extrusion, the composition recovered in step c) is in the form of a rod of polymer.

Preferably, the manufacturing process also comprises a step d) of granulating the composition recovered in step c). At the end of this granulating step d), granules of composition are obtained.

This granulating step can be carried out by means of any type of granulator, for example a water ring granulator, an underwater granulator or a rod granulator. The composition recovered can be very easily granulated, this being without bead formation.

The invention also relates to granules of the composition according to the invention. The invention also relates to an article comprising the composition according to the invention. This article may be of any type and may be obtained using conventional transformation techniques.

It may be, for example, fibers or threads that are of use in the textile industry or other industries.

These fibers or threads may be woven so as to form fabrics, or else nonwovens.

The article according to the invention may also be a film or a sheet. These films or sheets may be manufactured by calendering, cast film extrusion or blown film extrusion techniques.

The invention relates in particular to a process for manufacturing a film by film blowing, comprising

• • a step of extruding the composition or granules according to the invention so as to form a molten composition;
  • a step of forming a blown tube by blowing the molten composition obtained in the following step;
  • a step of drawing the blown tube;
  • and a step of recovering a film.

The composition according to the invention can have, when it is in the form of a film 50 μm thick, a Young's modulus greater than 100 MPa, advantageously ranging from 200 to 1000 MPa, preferably ranging from 300 to 550 MPa. It can also have an elongation at break greater than 150%, for example greater than 200%. In these ranges, and in particular in the preferred ranges, these films make it possible to be advantageously used in bag manufacture.

The film thus obtained can have a thickness ranging from 5 to 200 μm, preferably from 10 to 100 μm. Advantageously, the drawing speed is greater than 5 m/s, preferably greater than 10 m/s. The compositions according to the invention, in particular in the preferred variants, make it possible to keep excellent production rates and to obtain high drawing speeds.

The article according to the invention may also be a container for transporting gases, liquids and/or solids. The containers concerned may be bottles, for example sparkling or still water bottles, juice bottles, soda bottles, carboys, alcoholic drink bottles, small bottles, for example small medicine bottles, small bottles for cosmetic products, dishes, for example for ready meals, microwave dishes, or lids. These containers may be of any size. They may be produced by extrusion-blow molding, thermoforming or injection-blow molding.

The articles may also be multilayer articles, at least one layer of which comprises the composition according to the invention. These articles may be produced via a process comprising a coextrusion step in the case where the materials of the various layers are placed in contact in the molten state. By way of example, mention may be made of the techniques of tube coextrusion, profile coextrusion, coextrusion blow-molding of a bottle, a small bottle or a tank, generally collated under the term “coextrusion blow-molding of hollow bodies”, coextrusion blow-molding also known as film blowing, and cast coextrusion.

They may also be manufactured according to a process comprising a step of applying a layer of molten composition onto a layer based on organic polymer, paper, metal or adhesive composition in the solid state. This step may be performed by pressing, by overmolding, stratification or lamination, extrusion-lamination, coating, extrusion-coating or spreading.

The invention will now be illustrated in the examples hereinafter. It is pointed out that these examples do not in any way limit the present invention.

Manufacture of Compositions According to the Invention and Comparative Compositions

Constituents

The constituents of the various compositions illustrated are presented below.

Aliphatic Polyesters

A2:

Aliphatic polyester from condensation of succinic acid, of adipic acid and of 1,4-butanediol (PBSA), melting point of 95° C., flow index equal to 1.2 g/10 min.

A1:

Semi-crystalline polylactic acid (PLA) produced by Natureworks LLC
L-Lactic acid content: 95.7 mol %
D-Lactic acid content: 4.3 mol %
Melting point=150° C.; Flow index MFI=2.6 g/10 min; crystallinity=51%
Amorphous polylactic acid (PLA) produced by Natureworks LLC
L-Lactic acid content: 88 mol %
D-Lactic acid content: 12 mol %
Melting point=no melting; Flow index MFI=6.0 g/10 min

Starch

(B)=Wheat Starch (containing 12.5% of water)

Plasticizer

(C)=Glycerol

Additives

Compatibilizing agent=Citric acid (CA)
Processing aid=Glyceryl monostearate (GMS)

Composition Manufacturing Process

The examples of this invention were performed on a Leistritz brand extruder, ZSE27MAXX60D, diameter 28, length L/D=60, for a throughput of: 20 kg/h

• • Temperature profile (fifteen heating zones Z1 to Z15, temperature in ° C.): 20/60/60/80/90/110/130/130/180/160/180/150/130/130/130 with a variable screw speed of 200 rpm to 400 rpm.

Physical mixing of the granules of polyester is carried out prior to the introduction into the extruder. In the context of this process, the following are introduced into the extruder:

• • the blend of the polyesters in the main hopper of the extruder, following which said blend passes through all of the heating zones of the extruder,
  • the plasticizer for starch in zone Z3 (9 to 12 D),
  • the starch, the compatibilizing agent and also optionally processing aids in zone Z4 (13 to 16 D),
  • degassing is performed by applying a partial vacuum at Z9 (33-36 D) and at zone 11 (41-44 D) (vacuum of 100 mbar) allowing the volatile compounds such as water to be removed.
  • The granules are obtained by means of a conventional underwater granulation system.

Details of the Compositions

The compositions (examples 1 to 9) were prepared using the process described above. The amounts of the various constituents of the compositions are given in Table 1. The proportions of all the constituents are given relative to the wet weight of the sum of the constituents (A1), (A2), (B) and (C).

TABLE 1
Proportion of the constituents of the compositions by
wet weight introduced into the extruder
	PBSA	PLA
Composition	(A2)	(A1)	(B)	(C)	GMS	CA
Example 1	45.89	0	35.17	18.94	0.95	0.1
Example 2	44.74	1.15	35.17	18.94	0.95	0.1
Example 3	43.6	2.29	35.17	18.94	0.95	0.1
Example 4	41.3	4.59	35.17	18.94	0.95	0.1
Example 5	39.01	6.88	35.17	18.94	0.95	0.1
Example 6	36.71	9.18	35.17	18.94	0.95	0.1
Example 7	32.12	13.77	35.17	18.94	0.95	0.1
Example 8	36.71	9.18*	35.17	18.94	0.95	0.1
Example 9	32.12	13.77*	35.17	18.94	0.95	0.1
*amorphous PLA

The compositions obtained were granulated and these granules were dried for 2 hours at 80° C. Table 2 expresses the proportions by weight of the various constituents of the composition recovered in the form of dried granules, these amounts being expressed relative to 100 parts of the total dry matter of (A1), (A2), (B) and (C).

TABLE 2
Proportion of the constituents of the dry compositions
	PBSA	PLA					% (A1)/
Composition	(A2)	(A1)	(B)	(C)	GMS	CA	(A2 + A1)
Example 1	48	0	32.19	19.81	1	0.1	0
Example 2	46.80	1.20	32.19	19.81	1	0.1	2.5
Example 3	45.6	2.4	32.19	19.81	1	0.1	5
Example 4	43.20	4.8	32.19	19.81	1	0.1	10
Example 5	40.80	7.20	32.19	19.81	1	0.1	15
Example 6	38.40	9.60	32.19	19.81	1	0.1	20
Example 7	33.6	14.4	32.19	19.81	1	0.1	25
Example 8	38.40	9.6*	32.19	19.81	1	0.1	0
Example 9	33.6	14.4*	32.19	19.81	1	0.1	0
*amorphous PLA

The granules of the compositions were converted into films 50 microns thick on a blow-molding extruder of the Collin brand (Diameter 20, Length UD=18, five heating zones Z1 to Z5) using the following temperature profile (160° C./160° C./160° C./160° C./160° C.) and a screw speed of 60 revolutions per minute.

Characterization of the Compositions and Films Obtained from Compositions 1 to 9

Examples 1 to 9 demonstrate the benefits of the composition according to the invention: various compositions, which differ solely by the choice of the amount and of the type of polylactic acid used, are thus compared. The properties were obtained for a thickness of 50 μm.

TABLE 3
Effect of the amount and of the type of polylactic acid (A1)
on the properties of the compositions
		Processing
		speed
		(% max	Overall
	Processing	speed of the	film-		Elongation	Tensile
	speed	blow-molding	forming	Modulus	at break	strength
Composition	(m/min)	extruder)	ability	(MPa)	(%)	(MPa)
Example 1 (CP)	Film formation not possible
Example 2 (EX)	3.5	27	+	61	623	14.4
Example 3 (EX)	4	31	+	67	558	13.6
Example 4 (EX)	4	31	+	100	461	15.6
Example 5 (EX)	7.5	58	+	148	326	16.3
Example 6 (EX)	13	100	++	173	257	14.4
Example 7 (EX)	13	100	++	249	268	15.3
Example 8 (CP)	4.8	37	+	104	288	10.5
Example 9 (CP)	2.4	18	+	195	284	12.5
Film-forming ability grading
++: No bubble stability problem
+: No stability problem after reduction of the processing speed

It is noted that, when the amount of plasticizer in the thermoplastic starch is high (as is the case in example 1), it is not possible to convert this composition into the form of a film by extrusion blow-molding. The use of semicrystalline PLA (examples 2 to 7 according to the invention) makes it possible to obtain a composition with film-forming ability, this being even though the amount of plasticizer in the thermoplastic starch is identical to that of example 1.

It is noted that the Young's modulus increases proportionally to the amount of PLA and is accompanied by a decrease in the elongation at break.

The processing speed reaches the maximum for the compositions comprising 20% or more of semi-crystalline PLA, this amount being expressed by dry weight of the total amount of polyester (A1) and (A2). Furthermore, the appearance of the films is much better in these proportions (no micro-holes). It should however be noted that the applicant was able to observe, by means of additional tests not reported herein, that when this content exceeds 30%, the mechanical properties can be slightly inferior, in particular with regard to the elongation at break, which can decrease to values of less than 150%, or even less than 100%. The films formed for these compositions are then more rigid and more brittle. On the other hand, the use of amorphous PLA is not favorable: whatever the content used, the film pierces, even when the drawing speed is low. Furthermore, the addition of this polymer does not make it possible to improve the drawing speeds in the same proportions as the addition of the semi-crystalline PLA of use in the invention.

Claims

1. A thermoplastic composition comprising at least one blend of polyesters (A) comprising:

at least one polylactic acid (A1) and at least one aliphatic polyester (A2) other than the polymer (A1), wherein at least 50% by weight of said polylactic acid (A1) is semi-crystalline polylactic acid, and a weight percentage range of (A1) from 2% to 70, relative to a weight of (A1) and (A2), expressed by dry weight;

at least one starch (B); and,

at least one organic plasticizer for starch (C),

wherein the starch (B)/organic plasticizer (C) weight ratio, expressed by dry weight, ranges from 90/10 to 40/60.

2. The composition according to claim 1, wherein said polyester (A) content is in a range of from 35 to 75 parts, by weight relative to 100 parts of the total dry weight of the constituents (A1), (A2), (B) and (C).

3. The composition according to claim 1, wherein said semi-crystalline polylactic acid content is in the range of from 30% to 75%.

4. The composition according to claim 1, wherein said polylactic acid comprises a blend of 55% to 90% of semi-crystalline polylactic acid and of 10% to 45% of amorphous polylactic acid, expressed by dry weight of polylactic acid.

5. The composition according to claim 1, wherein said starch/plasticizer weight ratio, expressed by dry weight, ranges from 85/15 to 50/50.

6. The composition according to claim 1, further comprising, a bonding agent bearing several functional moieties capable of reacting with the polyester and the starch, said moieties comprising carboxylic acid, for example citric acid, carboxylic acid ester, isocyanate, or epoxy functions.

7. The according to claim 1, further comprising a processing aid including one of monoesters of a fatty acid and glycerol and glyceryl monostearate.

8. The composition according to claim 1, wherein said organic plasticizer comprises diols and polyols, including glycerol, polyglycerols, sorbitans, sorbitol, mannitol, and hydrogenated glucose syrups, urea, polyethers with a molar mass below 800 g/mol, and mixtures thereof.

9. The composition according to claim 1, wherein the aliphatic polyester (A2) is a polymer from condensation of ethylene glycol and/or of 1,4-butanediol and of succinic acid and/or of adipic acid.

10. A process for manufacturing a composition according to claim 1, comprising

introducing into a mixing system constituents comprising a blend of polyesters (A) comprising at least one polylactic acid (A1) and at least one aliphatic polyester (A2) other than the polymer (A1), at least one starch (B), at least one organic plasticizer for starch (C), and optionally water;

a mixing the constituents thermomechanically to obtain the thermoplastic composition;

recovering the thermoplastic composition.

11. The process according to claim 10, further comprising, adding and adjusting the amount of water to maintain a moisture content of the introduced constituents between 2.5% and 9%; and

the mixing and drying said constituents to produce and recover a thermoplastic composition with a moisture content between 0.2% and 1.4%.

12. The process according to claim 1, wherein the mixing is conducted at a temperature that ranges from 90 to 210° C.

13. The process according to claim 10 wherein the thermomechanical mixing is performed in a twin-screw extruder.

14. The process according to claim 10, wherein the introduced polyester (A) comprises a flow index ranging from 0.1 to 50 g/10 min according to ISO1133 at 190° C. and 2.16 kg).

15. A process for manufacturing a film by film blowing

comprising extruding the composition of claim 1 to form a molten composition;

forming a blown tube from the molten composition comprising,

drawing the blown tube;

and recovering a film.

16. The process according to claim 15, comprising drawing the blown tube at a speed greater than 5 m/s.