PL219419B1 - Modified composition comprising a polymer of lactide and a process for its preparation - Google Patents

Description

The present invention relates to a modified lactide polymer composition and a method for its production, which consists in mixing the lactide polymer composition with a biodegradable copolyester which is a copolymer of butylene terephthalate and at least 2 out of 3 monomers selected from the group consisting of butylene succinate, butylene glutarate and butylene adipate.

Polylactide is a biodegradable polymer composed of repeating units - units with the chemical formula: [-CH (CH3) -C (O) -O-]. Due to the presence of an asymmetric carbon atom in the meter, polylactide can exist in the form of homochiral poly (L-lactide), poly (D-lactide), or copolymers containing units of different chirality. The characteristics of polylactide depend on the stereochemical composition of the repeat units and their distribution along the polymer chain. Homochiral poly (L-lactide) and poly (D-lactide) are stereoregular, isotactic polymers with good crystallinity and a degree of crystallinity up to 60%. The crystalline phase melts at about 180 ° C [A. Duda, S. Penczek, Polylactide [poly (lactic acid)]: synthesis, properties and applications, Polymers 48, 16-27 (2003)]. The presence of mers of different chirality in the polymer chain significantly reduces the ability of the polylactide to crystallize, which is manifested by slower crystallization, a decrease in the degree of crystallinity and a decrease in melting point.

The glass transition temperature of the amorphous polylactide phase, T _g , is about 55-60 ° C. This makes polylactide at room temperature a brittle and stiff polymer with a modulus of elasticity of about 3-3.5 GPa.

A known method of modifying the properties of polylactide is plasticization, consisting in mixing the polymer with a plasticizer - a substance with a much lower glass transition temperature [E. Piórkowska, Z. Kuliński, K. Gadzinowska, Polylactide plasticization, Polimery 54, 83-90 (2009); M. Baiardo, G. Frissoni, M. Scandola, M. Rimelen, D. Lips, K. Ruffieux, E. Wintermantel, Thermal and Mechanical Properties of Plasticized Poly (L-lactic acid), J. Appl. Polym. Sci. , 90, 1731-1738 (2003)]. Mixing polylactide with a plasticizer at the molecular level lowers the glass transition temperature, T _g . Plasticized polylactide exhibits lower elastic modulus, lower yield stress, and higher elongation to break than unplasticized polylactide, and may also exhibit greater impact strength. The disadvantageous effect of plasticization is to reduce the temperature range in which the material can be used. Moreover, the plasticized polylactide may undergo aging processes related to the migration of the plasticizer to the surface and / or phase separation of polylactide and plasticizer, and also polylactide crystallization and plasticizer crystallization may take place, which deteriorate the toughness of the material [Y.Hu, M. Rogunova, V. Topolkaraev, A. HiItner, E. Baer, Aging of poly (lactide) / poly (ethylene glycol) blends. Part 1. Poly (lactide) with low stereoregularity, Polymer 44, 5701-5710 (2003); Y.Hu, YSHu, V. Topolkaraev, A. Hiltner, E. Baer, Aging of poly (lactide) / poly (ethylene glycol) blends. Part 2. Poly (lactide) with high stereoregularity. Polymer 44, 5711-5720 (2003)].

Another known method of modifying polylactide is mixing it with a second polymer which is incompatible or only partially miscible with the polylactide at the molecular level, e.g. poly (butylene succinate). In such materials, both polymers exist as separate phases. The presence of the second polymer modifies the mechanical properties of the material, increasing its ductility. Elongation to break increases and toughness improves. A significant advantage of these materials is the unchanged or slightly lowered glass transition temperature of the polylactide.

Biodegradable mixtures of polylactide with poly (hydroxyalkanoates) are known [I. Noda, M.M. Satkowski, A.E. Dowrey, C. Marcott, Polymer Alloys of Nodax Copolymers and Poly (lactic acid), Macrom. Biosci. 4, 269-275 (2004)] and urethane polyether [Y. Li, H. Shimizu, Toughening of Polylactide by Melt Blending with a Biodegradable Poly (ether) urethane Elastomer. Macrom Biosci. 7, 921-928 (2007)]. In addition, the literature describes mixtures of polylactide with biodegradable aliphatic polyesters, e.g. with poly (ethylene succinate) [J.Lu, Z.Qiu, W Yang, Fully biodegradable blends of poly (L-lactide) and poly (ethylene succinate): Miscibility , crystallization, and mechanical properties. Polymer, 48, 4196-4204 (2007)] and with poly (butylene succinate) [M. Shibata, Y. lonue, M. Miyoshi, Mechanical properties, morphology, and crystallization behavior of blends of poly (L-lactide) with and poly (butylene succinate). Polymer 47, 3557-3564 (2006)]. The latter publication also describes mixtures of polylactide with a copolyester of butylene succinate and butylene lactate.

Biodegradable aliphatic polyesters with the [-O- (CH ₂ ) _n1 -OC (O) - (CH ₂ ) _n2 -C (O-)] _n mer structure are formed by the reaction of dicarboxylic acid esters and diols. In the case of poly (succinate

Of butylene) n1 = 4 and n2 = 2, and for poly (ethylene succinate) n1 = 2 and n2 = 2. For n2 = 3 or n2 = 4 the above formula describes copolyesters of glutaric acid or adipic acid, respectively. The combination of esters of different dicarboxylic acids leads to the formation of biodegradable copolyesters.

Moreover, biodegradability is also demonstrated by aliphatic-aromatic copolyesters which contain in the chain the units resulting from esterification of terephthalic acid of the formula [-O- (CH ₂ ) _{n 1} -OC (O) -C6H4-C (O)] n. The literature describes mixtures of polylactide with a copolymer of butylene adipate and butylene terephthalate (poly (adipate-co-terephthalate)) [L. Jiang, MP Wolcott, J.Zhang, Study of Biodegradable Polylactide / Poly (butylene adipate-co-terephthalate) Blends, Biomacromolecules 7, 199-207 (2006)]. Examples of commercially produced biodegradable polyesters and copolyesters are Ecoflex - poly (butylene adipate-co-terephthalate) produced by BASF, and aliphatic polyesters and copolyesters of the Bionolle series, e.g. poly (butylene succinate) and poly (butylene succinate-co-adipate) , produced by Showa Highpolymers Co Ltd.

Also known are [US Patent 5,883,199] biodegradable mixtures comprising a lactic acid polymer or copolymer as a first component and one or more homopolymer or random copolymer polyesters which are polyesters of one or more aliphatic dicarboxylic acids as a second component. As aliphatic polyesters mentioned are polymers or copolymers selected from the group consisting of poly (butylene succinate), poly (butylene adipate), butylene succinate and ethylene adipate copolymer, poly (ethylene succinate), poly (ethylene adipate) and ethylene adipate copolymer of ethylene adipate. The second component of the mixture can also be a copolyester of an aliphatic polyester and an aromatic polyester, especially polyethylene terephthalate. Patent US5883199 [US Patent 5,883,199] discloses mixtures of polylactide with biodegradable polyesters or copolyesters in which the second component of the mixture forms a co-continuous phase and at least the first component or the second component is present in the continuous phase of the mixture .

The phase structure is very important due to its influence on the mechanical properties of the mixture. In the case of polymers that are immiscible at the molecular level, the components can form co-continuous blends with high impact strength [P. Potschke, D.R.Paul, Formation of Co-continous Structures in Melt-Mixed Immiscible Polymer Blends, J. Macromol. Sei. C. Polym. Rev. C43, 87-141 (2003)]. Obtaining such a structure in a mixture is not always possible, and moreover, it requires an appropriate mixture composition, appropriate melt properties and interactions between them, as well as appropriate processing conditions. The formation of such a structure is favored by: high viscosity of the polymer matrix, high shear rates during mixing and low interfacial tension between the components. Co-continuous structures are generally non-equilibrium structures that arise when two polymers are mixed in the melt and begin to change as the mixture leaves the mixing device. This can only be prevented by the rapid solidification of the mixture, which requires intensive cooling. Typically, in the case of polymers that are incompatible at the molecular level, one component forms the continuous phase and the other is dispersed in the form of generally spherical inclusions.

Surprisingly, it turned out that mixtures of lactide polymers with aliphatic-aromatic copolyesters, being copolymers of butylene succinate, butylene glutarate, butylene adipate and butylene terephthalate, obtained by the process according to the invention, in which the copolyester is dispersed in the form of inclusions, show very good ductility and toughness. On cooling the mixture, only the butylene terephthalate sequences crystallize in the copolyester and the aliphatic sequences remain in the amorphous phase. This leads to a low degree of crystallinity, below 20% by weight, which results in a high content of the amorphous phase characterized by a low glass transition temperature, below -20 ° C. Due to the high content of the amorphous phase in the rubber-like state, the copolyester inclusions effectively modify the mechanical properties of the mixture.

So far, there are no known or used mixtures of lactide polymers with copolymers that are copolymers of at least 3 out of 4 monomers selected from the group consisting of butylene succinate, butylene glutarate, butylene adipate and butylene terephthalate, in which the lactide polymer would form a continuous phase and the copolyester was dispersed therein. inclusion form.

The modified composition containing lactide polymers according to the invention is characterized in that it is a mixture of lactide polymers containing from 5 to 50 percent by weight of a copolyester being a copolymer of butylene terephthalate and at least 2 of 3 monomers selected from the group consisting of butylene succinate, butylene glutarate, butylene adipate, being used

The copolyester is dispersed as inclusions in the polylactide matrix or polylactide composition with known additives.

The composition according to the invention preferably comprises a copolyester which is a copolymer of 4 monomers: butylene succinate, butylene glutarate, butylene adipate and butylene terephthalate.

The method of obtaining a modified composition containing lactide polymers according to the invention consists in blending the lactide polymer with 5 to 50 percent by weight of a copolyester being a copolymer of butylene terephthalate and at least 2 of 3 monomers selected from the group consisting of butylene succinate, butylene glutarate and adipate. of butylene until the copolyester is dispersed as inclusions in the mixture.

The method of obtaining the modified composition containing lactide polymers according to the invention is preferably carried out by melt blending or in solution with a copolyester being a copolymer of 4 monomers: butylene succinate, butylene glutarate, butylene adipate and butylene terephthalate.

In the modification process of the invention, preferably, the copolyester is added to the lactide polymer after the lactide polymer is mixed with the additive or before the lactide polymer is mixed with the additive.

In the modification process of the invention, preferably, the additive is a low molecular weight chemical selected from the group consisting of pigments, stabilizers and antioxidants.

In the modification process according to the invention, it is preferable to use a copolyester with a molecular weight of 1,000 to 500,000 g / mol, with a molar composition of at least 50% aliphatic groups.

In the modification process according to the invention, preferably poly (L-lactide), poly (D-lactide), poly (meso-lactide), copolymers of L-lactide and D-lactide or a mixture of these polymers are used as the lactide polymers.

In the process according to the invention, preferably, the copolyester is a mixture consisting of a copolymer of butylene terephthalate and at least 2 of 3 monomers selected from the group consisting of butylene succinate, butylene glutarate, butylene adipate, and one or more aliphatic or aliphatic-aromatic copolyesters.

In the process of the invention, preferably, mixing is performed using conventional mixing devices, mixers or extruders.

In the process according to the invention, the mixture is preferably processed by extrusion, injection or blow molding.

The invention is illustrated below with the aid of exemplary embodiments.

P r z x l a d I.

The mixtures were prepared with polylactide (PLA) by Hycail, marked with HM1011 symbol, and polylactides by NatureWorks, marked with 2002D, 4060D and 3251D symbols. The molecular weight distribution of these polymers was determined by gel permeation chromatography, while the content of L-lactide and D-lactide by measuring the optical specific rotation. The characteristics of polylactides are presented in Table 1.

In addition, aliphatic-aromatic copolyesters were used, synthesized from a mixture of terephthalic acid dimethyl ester, dimethyl esters of aliphatic dicarboxylic acids (succinic, aric gluten, adipic) and 1,4-butanediol, with the addition of a small amount of tetrabutylorthothitanate, marked as PAT2 and PAT1, PAT3.

The molecular weight distribution of these copolyesters was determined by gel permeation chromatography. Moreover, the flow index was determined at 190 ° C under a load of 2.16 kg. The characteristics of copolyesters are presented in Table 2.

T a b e l a 1

Characteristics of the polylactides used. Mw - weight average molecular weight, Mw / Mn - molecular weight ratio; weight average to number average

PLA symbol Mw [kg / mol] Mw / Mn D-lactide content [%] L-lactide content [%] HM1011 104 1.5 4.6 95.4 2002D 104 1.4 2.5 97.5 3251D 55 1.3 0.65 99.35 4060D 119 1.4 18.0 82.0

PL 219 419 B1

T a b e l a 2

Characteristics of the copolyesters used. Mw - weight average molecular weight,

Mw / Mn - ratio of molecular weights: weight average to number average, mFr - melt flow index

Symbol copolyester Mw [kg / mol] Mw / Mn MFR [g / 10 min] (190 ° C, 2.16 kg) Content of dimethyl esters of dicarboxylic acids in the mixture [mol%] succinate dimethyl glutarate dimethyl adipate dimethyl terephthalate dimethyl PAT1 55 1.6 thirty 7 27 21 45 PAT2 53 2.0 74 11 39 twenty thirty PAT3 47 1.8 45 9 33 18 40

Blends containing 5, 10, 15, 25 and 35 wt% copolyesters were prepared by melt blending the ingredients in a Brabender mixer at 190 ° C for 10 min at 60 rpm. For comparison, pure polylactides were subjected to the same procedure. The structure of mixtures of polylactides with copolyesters was examined by scanning electron microscopy with the use of a Jeol 5500 LV scanning electron microscope. The test specimens, in the form of 0.5 or 1 mm thick films, were prepared by pressing in a hydraulic press at 180 ° C for 3 minutes and cooling to room temperature.

Paddle-shaped specimens for testing mechanical properties with a measuring length of 9.53 mm were cut from the 0.5 mm thick foil. Plastic deformability was tested with an Instron testing machine, during uniaxial stretching at a rate of 5% / min and 50% / min at room temperature. From 3 to 5 samples of each composition were tested. Moreover, samples of the shape defined by the ISO 8256 standard were cut from the 0.5 mm thick foil for the measurement of tensile impact strength. Measurements were made using a CEAST, RESIL5.5 device at a temperature of 23 ° C, with a maximum hammer energy of 1 J and a speed of 2.9 m / s. From 8 to 10 samples of each composition were tested.

The test specimens for the dynamic mechanical thermal analysis (DMTA) method, cuboid in shape and dimensions 10x30x1 mm, were cut from 1 mm thick foil. The tests, by the method of three-point bending with the fixed ends of the sample (dual cantilever bending), were carried out with the DMTA Mk III apparatus, Rheometric Scientific Ltd. at a frequency of 1 Hz, while heating from -100 to 100 ° C at a rate of 2 ° C / min.

Tables 3 and 4 show a comparison of the properties of pure polylactides and modified polylactides. Table 3 describes the mechanical properties of polylactides and mixtures with PAT1 copolyester, determined during uniaxial stretching at 50% / min and during the impact test. In contrast, Table 4 shows the properties of mixtures of polylactide 4060D with different copolyesters tested during uniaxial stretching at 5% / min.

T a b e l a 3

Mechanical and impact properties of mixtures of polylactides with PAT1 copolyester

Symbols ingredients mixtures Content of copolyester in the mixture [wt.%] Stress at yield [MPa] Elongation to break [%] Stress at break [MPa] Impact breaking strength [kJ / m ² l 1 2 3 4 5 6 HM1011 0 65 14 38 57 PAT1 5 63 49 38 55 15 56 150 38 82 25 44 300 35 138 35 36 110 29 137 2002D 0 61 6 59 56 PAT1 5 62 16 40 56 15 54 79 38 98 25 44 156 37 138 35 34 95 thirty 137

Table 3 continues

1 2 3 4 5 6 3251D 0 61 9 53 58 PAT1 5 54 18 29 63 15 44 59 29 98 25 37 105 26 140 35 32 107 23 115 4060D 0 62 11 55 48 PAT1 5 57 11 43 47 15 51 75 33 116 25 39 208 33 142 35 29 28 24 135

T a b e l a 4

Mechanical and impact properties of mixtures of polylactide 4060D with various copolyesters

Symbols ingredients Content of copolyester in the mixture [wt.%] The yield stress [MPa] Elongation to break [%] Stress at break [MPa] Impact breaking strength [kJ / m ² ] 4060D 0 58 17 52 48 PAT1 5 58 60 39 47 15 48 283 34 116 25 38 366 32 142 35 27 12 23 135 4060D 0 58 17 52 48 PAT2 5 54 twenty 38 49 15 48 186 35 70 25 38 121 thirty 136 35 24 21 21 138 4060D 0 58 17 52 48 PAT3 5 54 17 49 50 15 47 119 33 101 25 35 35 28 142 35 27 16 22 135

The obtained results show that in all cases the addition of copolyester to polylactide caused an increase in elongation to break and / or an increase in impact strength at break.

Exemplary micrographs of mixtures are presented in the figures. In all cases, the copolyester formed spherical-shaped inclusions dispersed in the polylactide matrix that formed the continuous phase.

Fig. 1 shows SEM micrographs of mixtures of polylactides with copolyesters: a - a mixture of polylactide 4060D with 5 wt. PAT3 copolyester, b - mixture of polylactide 4060 with 25 wt. PAT3 copolyester, c - mixture of polylactide 4060D with 25 wt. of PAT2 copolyester, d - mixture of polylactide 3251D with 5 wt. PAT1 copolyester, e - mixture of 3251D polylactide with 35 wt. PAT1 copolyester, f - mixture of HM1011 polylactide with 35 wt. copolyester PAT1.

Dynamic mechanical thermal analysis (DMTA) studies have shown that all mixtures exhibit two maxima of the loss modulus, one in the range of 54 to 58 ° C, corresponding to the glass transition in the polylactide matrix, and the other in the range of -25 to -21 ° C, corresponding to the glass transition in the dispersed phase - in the copolyester. The glass transition temperatures defined as the temperatures of the Loss Modulus E ”maximums of these materials are summarized in Table 5.

PL 219 419 B1

T a b e l a 5

Glass transition temperatures of mixtures of polylactides with copolyester PAT1

Symbols ingredients Content of copolyester in the mixture [wt.%] Tg of copolyester [° C] Tg of polylactide [° C] PAT 1 100 -21 - HM 1011 0 - 57 PAT 1 5 -21 58 15 -23 57 25 -24 57 35 -23 55 4060 D. 0 - 54 PAT 1 5 -25 54 15 -25 54 25 -25 54 35 -22 54

Moreover, from the data provided in Table 5, it can be seen that only slight and insignificant changes in the glass transition temperatures of the components occur in the mixtures.

P r z x l a d II

0.5 mm and 1 mm thick films of polylactide 3251D and its mixtures with PAT1 copolyester, prepared as described in Example 1, were annealed to crystallize the polylactide. For this purpose, the films were heated at a rate of 10 ° C / min to a temperature of 120 ° C, where they were annealed for 5 minutes, and then cooled to room temperature. After annealing, the film samples were examined by Differential Scanning Calorimetry, while being heated at a rate of 10 ° C / min. There was no exotherm of cold crystallization in the thermograms, which means that the polylactide crystallization was completed during annealing. The melting enthalpy of pure polylactide was 42 J / g and of polylactide in mixtures from 42 to 44 J per gram of polylactide. If the heat of fusion of the crystalline phase was assumed to be 106 J / g, the degree of crystallinity of the 3251D polylactide was from 40 to 42% by weight. Shapes were cut from the annealed films and the mechanical properties were tested as described in Example I. The results of the testing of the mechanical properties during uniaxial stretching at 50% / min are shown in Table 6.

T a b e l a 6

Mechanical properties of annealed mixtures of 3251D polylactide with PAT1 copolyester

Symbols ingredients Content of copolyester in the mixture [wt.%] The yield stress [MPa] Elongation to break [%] Stress at break [MPa] 3251 D 0 - 4 55 PAT 1 5 54 4 52 15 47 6 44 25 37 7 35 35 32 7 29

The data in Table 6 indicate that the presence of the copolyester in the crystallized 3251D polylactide causes a slight increase in elongation to break.

P r x l a d III

For mixtures of 3251D polylactide with 25 wt. A PAT1 copolyester, prepared as described in Example 1, was made by injection molding a sample for testing mechanical properties. The laboratory injection molding machine had a temperature of 180 ° C and the injection mold conforming to ISO 537-2 type A was kept at 41 ° C. The injection time was 10 s. Also performed for comparison

Samples of pure 3251D polylactide under the same conditions. The properties of the injection specimens were tested by uniaxial stretching at a rate of 5% / min at room temperature using an Instron testing machine. The test results are presented in Table 7.

T a b e l a 7

Mechanical properties of samples obtained by injection method from a mixture of 3251D polylactide with 25 wt. copolyester PAT1

Content Stress at the boundary Elongation Tension copolyester PAT 1 plasticity to break up to break up [%] [MPa] [%] [MPa] 0 56 5 55 25 40 15 24

The data in Table 7 show that the addition of 25 wt. of copolyester to polylactide 3251D increased the elongation to break in the injection samples.

P r x l a d IV.

A mixture of polylactide 4060D with 15 wt. copolyester PAT1. The head temperature was 204 ° C, the temperatures of the heating zones: 180, 190, 200, 200, 195 ° C. Screw rotation speed was set at 200 rev ^min-1, the torque was 16-17 Nm and the plastic pressure in the head of 9-11 bar.

Samples for impact tests were prepared from the prepared mixture and the same mixture prepared using a Brabender mixer. The sample preparation and testing procedures were the same as those described in Example I. The impact strength _{2 of} the mixture obtained with the extruder was found to be 71 kJ / m ² and higher than for pure 4060D polylactide.

The advantage of the solution according to the invention is to obtain a composition with better plastic deformability than pure polylactide.

An advantage of the solution according to the invention is to obtain a composition with a better impact breaking strength than for polylactide.

The advantage of the solution according to the invention is the ease of adding the biodegradable copolyester to the polylactide.

The advantage of the solution according to the invention is to obtain a composition in which the biodegradable copolyester is a dispersed phase in the polylactide matrix, which can be easily obtained by using conventional mixing devices.

The advantage of the solution according to the invention is to obtain a composition in which the component forming the continuous phase does not show a significant reduction in the glass transition temperature compared to pure poly

Claims (10)

A modified composition containing lactide polymers, characterized in that it is a mixture of a lactide polymer with from 5 to 50 percent by weight of a copolyester being a butylene terephthalate copolymer and at least 2 of 3 monomers selected from the group consisting of butylene succinate, butylene glutarate and butylene adipate. 2. A composition according to claim 1 The method of claim 1, wherein the copolyester is a copolymer of 4 monomers: butylene succinate, butylene glutarate, butylene adipate and butylene terephthalate. Method for preparing a modified composition containing lactide polymers, characterized in that the lactide polymer is mixed with 5 to 50 percent by weight of a copolyester being a copolymer of butylene terephthalate and at least 2 of 3 monomers selected from the group consisting of butylene succinate, butylene glutarate and butylene adipate until the copolyester is dispersed as inclusions in the mixture. 4. The method according to p. The process of claim 3, characterized in that a copolymer of 4 monomers: butylene succinate, butylene glutarate, butylene adipate and butylene terephthalate is used as the copolyester. 5. The method according to p. The process of claim 3, characterized in that mixing is performed by mixing in the molten state or in solution. PL 219 419 B1 6. The method according to p. The process of claim 3, wherein the copolyester has a molecular weight of 1,000 to 500,000 g / mol, containing at least 50 mol% aliphatic groups. 7. The method according to p. The method of claim 3, wherein the lactide polymer is poly (L-lactide), poly (D-lactide), poly (meso-lactide), copolymers of L-lactide and D-lactide, or a mixture of these polymers. 8. The method according to p. The process of claim 3, wherein the copolyester is a mixture of butylene terephthalate copolymer and at least 2 of 3 monomers selected from the group consisting of butylene succinate, butylene glutarate, butylene adipate and one or more aliphatic or aliphatic-aromatic copolyesters. 9. The method according to p. The process of claim 3, characterized in that the mixing is performed using conventional mixing devices, mixers or extruders. 10. The method according to p. Process according to claim 3, characterized in that the mixture is processed by extrusion, injection or blow molding.