Method of modification of properties of poly lac tide or compositions containing polylactide.

The subject of the invention is a method of modification of polylactide or compositions containing polylactide by means of blending with polypropylene glycol) .

Polylactide is a biodegradable polymer, stiff and brittle, having modulus of elasticity around 3-3.5GPa; exhibiting stiffness and brittleness at ambient temperature. Glass transition temperature of amorphous phase, T _g , is about 55-6O ⁰ C.

The known method of modification of polylactide properties, plasticization, involves blending of a polymer with a substance having much lower glass transition temperature. L. V. Labreque, R.A.Kumar, V.Dave, R.A. Gross, S. P. McCarthy: Citrate Esters as Plastidzers for Polyβactid add), J.Appl.Polym.Sci, 66, 1507-1513 (1997); N. Ljungberg, B.Wesslen: The effect of Plastidzers on the Dynamic Mechanical and Thermal Properties of Polyβactic add). J.Appl.Polym.Sci., 86, 1227-1234 (2002)- S. Jacobsen, H. G. Fritz: Plastidzing Polylactide - The Effect of Different Plastidzer on the Mechanical Properties. Polym.Eng.Sci., 39, 1303-1310 (1999); M.Baiardo, G.Frissoni, M.Scandola, M.Rimelen, D. Lips, K.Ruffieux, E.Wintermantel, Thermal and Mechanical Properties of Plastidzed Poly(L-lactic add). J.Appl.Polym.Sci., 90, 1731-1738 (2003); M.Sheth, R.A.Kumar, V.Dave, R.A.Gross, S. McCarthy: Biodegradable Polymer Blends of Polyβactic add) and Polyfethylene glycol). J.Appl.Polym. Sd., 66, 1495-1505 (1997); Y. Hu, M.Rogunova, V.Topolkareaev,

A.Hiltner, E.Baer: Aging of polyβactide)/ poly (ethylene glycol) blends. Part I. Polyβactide) with low stereoregularity, Polymer 44, 5701-5710 (2003). The blend obtained in this way exhibits the glass transition temperature lower than that of neat polylactide. The blend has different physical properties like lower modulus of elasticity, larger elongation at break and, in addition, may exhibit larger impact strength.

In the description of US Patent No 5 424 346 oligomers of lactic acid, oligomers of lactide, and mixtures thereof, lactic acid, D-lactide, L- lactide, D,L-lactide, racemic D,L-lactide and mixtures thereof were listed as plasticizers. In the description of US Patent No 5 756 651 polyethylene glycol), poly (ethylene oxide), polycaprolactone and oligomer of lactic acid were listed as impact modifiers of polylactide. In the description of US Patent No 5 908 918 the following plasticizers of a blend of polylactide and an impact modifier were described: citrate esters, adipate esters, epoxidized soy oil, acetylated coconut oil, linseed oil, and mixtures thereof. In the description of US Patent No 6 117 928 carboxylic acid esters, polymeric polyesters, polyalkyl ethers, glycerol esters, glycol esters and mixtures thereof were listed as plasticizers for polylactide.

Widely investigated plasticizer for polylactide is poly(ethylene glycol) [S. Jacobsen, H.G.Fritz: Plasticizing Polylactide - The Effect of Different Plasticizer on the Mechanical Properties. Polym.Eng.Sci.,39, 1303-1310 (1999); 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); M.Sheth, R.A.Kumar, V.Dave, R.A. Gross, S. McCarthy: Biodegradable Polymer Blends of Poly (lactic acid) and Poly (ethylene glycol). J.Appl.Polym. Sci., 66, 1495-1505 (1997); Y. Hu, M.Rogunova, V.Topolkareaev, A.Hiltner, E.Baer: Aging of polyβactide)/ poly (ethylene glycol) blends. Part I. Polyβactide) with low stereoregularity., Polymer 44, 5701-5710 (2003)].

Admixture of poly(ethylene glycol) to polylactide decreases the glass transition temperature of polylactide, decreases the modulus of elasticity and increases the ability to plastic deformation dependent on a

content and molecular mass. A disadvantage of poly(ethylene glycol) is its ability to crystallize. In a blend of polylactide and poly(ethylene glycol) crystallization of polyethylene glycol) can occur, leading to worsening of mechanical properties of the blend [[Y. Hu, M.Rogunova, V.Topolkareaev, A.Hiltner, E.Baer: Aging of poly (lactide)/ poly (ethylene glycol) blends. Part I. Polyβactide) with low stereoregularity., Polymer 44, 5701-5710 (2003)].

Attempts are known to apply polypropylene glycol) as a modifier of properties of a biodegradable polymer: poly( 3-hydroxybutyrate)-poly(3- hydroxyvalerate) [V. P. Cyras , N. G. Fernandez, A. Vazquez Biodegradable films from PHB-8HV copolymers and polyalcohols blends: crystallinity, dynamic mechanical analysis and tensile properties. Polymer International, 48, 705-712 (1999)]. Polypropylene glycol) was found to be immiscible with this polymer.

The subject of the invention is plasticization of polylactide with oligomers and polymers of propylene glycol and propylene oxide. Applications of oligomers and polymers of propylene glycol and propylene oxide are not known.

A method of modification of properties of polylactide or compositions containing polylactide with known additives, in accordance to the invention, comprises mixing of polylactide or compositions of polylactide and known additives with 0.2 to 30 wt. parts of polypropylene glycol) or poly(propylene oxide) per 100 wt. parts of the composition.

The method of modification of a composition containing polylactide in accordance to the invention preferably comprises mixing in the molten state or in a solution.

According to the invention, poly(propylene glycol) or poly(propylene oxide) is added to the composition before, during or after mixing of polylactide with known additives.

According to the invention, preferably, known organic or mineral fillers are applied, selected from the group comprising starch, cellulose fibers and cellulose flakes, chitosan, calcium carbonate, montmorillonite and bentonite are applied as admixtures.

According to the invention, preferably, other polymers or oligomers selected from the group comprising poly(ethylene oxide), polycaprolactone, poly(hydroxybutyrate) and polybutadiene are applied as admixtures.

According to the invention, preferably, a chemical compound with a small molecular mass selected from the group comprising pigments, stabilizers and antioxidant is applied as an admixture.

According to the invention, preferably, poly (propylene glycol) with molecular mass ranging from 100 to 20 000 g/mol is used.

According to the invention, preferably, the content of poly(propylene glycol) or poly(propylene oxide) in the composition is in the range from 0.5 to 30 wt. parts.

According to the invention, preferably, poly(L-lactide), poly(D- lactide), copolymers of L-lactide with D-lactide or mixture thereof are used instead of a polylactide.

According to the invention, preferably, copolymers of L-lactide, copolymers of D-lactide or copolymers of L-lactide and D-lactide with other polymers selected from the group comprising poly(ethylene oxide), poly (ethylene glycol), poly(propylene glycol), ρoly(propylene oxide) and polycaprolactone are used instead of polylactide.

According to the invention copolymer of ethylene oxide and propylene oxide is used instead of polypropylene glycol) or poly(propylene oxide).

The invention is explained below with the help of the following examples.

Example I.

For blend preparation, polypropylene glycol) and polylactide produced by Hycail, denoted as HMlOlO, with mass M _w of 108 kg/mol and residual monomer content of 0.5%, were used. This polylactide contains 98% of L-lactide and 2% of D-lactide. Two poly(propylene glycol) s were used: 1: with molecular mass of 425 g/mol and 2. with molecular mass of lOOOg/mol. Blends containing 7.5, 10 and 12.5 wt.% of poly(propylene

glycol) were prepared by blending of the components in a Brabender mixer at temperature of 190 ⁰ C for 20 min. Neat polylactide was subjected to the same treatment for comparison. Samples for further investigations, in the form of 0.3mm thick films, were compression moulded in a hydraulic press at the temperature of 180 ⁰ C for 3 min. and quenched to room temperature. Oar shaped specimens, with the gauge length of 9.53 mm were cut out from the films for studies of mechanical properties. Ability to plastic deformation was investigated after one day, during uniaxial drawing in an Instron tensile testing machine at the rate of 5%/min, at 25°C.

Comparison of properties of neat polylactide and polylactide plasticized with poly(propylene glycol) is shown in Table 1.

Table 1.

Example II.

Films for the studies, of neat polylactide produced by Hycail, and also a blend of polylactide and poly(propylene glycol) with molecular mass of 425 g/mol, containing 10wt.% of poly(propylene glycol), obtained as it is described in the Example I, were annealed in order to crystallize polylactide. The film of blend of polylactide and poly (propylene glycol) was annealed for lhr at temperature 9O ⁰ C, whereas the film of neat polylactide at temperature 100 ⁰ C for 2 hrs. Oar shaped specimens, with

gauge length of 9.53mm were cut out from the films. Ability for the plastic deformation was investigated after one day, during uniaxial drawing in an Instron testing machine at the rate of 5%/min, at 25 ⁰ C.

For the film of blend of polylactide and polypropylene glycol) the elongation at break of 62% was reached, whereas for the neat polylactide only 9%.

Example III.

Polylactide produced by Hycail, poly(propylene glycol) and a pigment named as methyl blue were used for composition preparation. A composition containing polylactide produced by Hycail, poly(propylene glycol) with molecular mass of 425g/mol and methyl blue in the weight proportions: 88.2:9.8:2 was obtained by mixing all of the components in a Brabender mixer at 19O ⁰ C for 20min. For comparison, a composition of polylactide and methyl blue in weight proportions: 98:2, was prepared using the same route. Specimens for studies of mechanical properties were prepared following the protocol described in the Example I. Ability to the plastic deformation were studied as in the Example I. For the composition of polylactide with methyl blue the elongation at break of 10% and the stress at break of 36MPa were reached, whereas for the composition of polylactide, methyl blue and poly(propylene glycol) an elongation at break and stress at break were 470% and 19MPa, respectively.

Example IV.

Polylactide produced by Hycail, poly(propylene glycol) with molecular mass of 425g/mol and a filler in the form of grounded cellulose flakes were used for composition preparation. A composition containing polylactide produced by Hycail, polypropylene glycol) with molecular mass of 425g/mol and cellulose flakes in the weight proportions: 72:8:20 was obtained by mixing of all the components in a Brabender mixer at 19O ⁰ C for 20min. For comparison, a composition of polylactide and cellulose flakes in weight proportions: 80:20, was prepared using the

same route. Specimens for studies of mechanical properties were prepared following the protocol described in the Example I. Ability to plastic deformation were studied as in the Example I. For the composition of polylactide with cellulose flakes the elongation at break of 3% and the stress at break of 32MPa were reached, whereas for the composition of polylactide, cellulose flakes and poly(propylene glycol) an elongation at break and stress at break were 38% and 9 MPa, respectively.

Example V.

Polylactide produced by Hycail, poly(propylene glycol) with molecular mass of 425g/mol and montmorillonite filler were used for composition preparation. A composition containing polylactide produced by Hycail, poly(ρropylene glycol) with molecular mass of 425g/mol and montmorillonite in the weight proportions: 85.5:9.5:5 was obtained by mixing of all the components in a Brabender mixer at 19O ⁰ C for 20min. For comparison, a composition of polylactide and montmorillonite in weight proportions: 95:5, was prepared using the same route. Specimens for studies of mechanical properties were prepared following the protocol described in the Example I. Ability to plastic deformation were studied as in the Example I. For the composition of polylactide with montmorillonite the elongation at break of 3% and the stress at break of 44 MPa were reached, whereas for the composition of polylactide, montmorillonite and poly(propylene glycol) an elongation at break and stress at break were 241% and 16 MPa, respectively.

Example VI.

Polylactide produced by Hycail, poly(propylene glycol) with molecular mass of 425g/mol and ρoly(ethylene oxide) with M _w =100kg/mol were used for blend preparation. A blend containing polylactide produced by Hycail, poly(propylene glycol) with molecular mass of 425g/mol and poly(ethylene oxide) in the weight proportions: 81:9: 10 was obtained by mixing all of the components in a Brabender mixer at 190 ⁰ C for 20min.

For comparison, a blend of polylactide and poly(ethylene oxide) in weight proportions: 90: 10, was prepared using the same route. Specimens for studies of mechanical properties were prepared following the protocol described in the Example I. Ability to the plastic deformation were studied as in the Example I. For the blend of polylactide with polyethylene oxide) the elongation at break of 495% and the stress at break of 22 MPa were reached, whereas for the composition of polylactide, ρoly(ethylene oxide) and poly(propylene glycol) an elongation at break and stress at break were 772% and 19 MPa, respectively.

Example VII.

Blends of polylactide produced by Hycail and poly(propylene glycol) with molecular mass of 425g/mol, containing 5, 7.5, 10 and 12.5 wt% of poly(ρropylene glycol) were prepared according to the route described in the Example I. Neat polylactide was subjected to the same treatment for comparison. Films for studies were prepared using the protocol described in the Example I. From the films, specimens with the diameter of 5mm were cut out, for studies by a differential scanning calorimetry method during heating at the rate of 10K/min. Temperature corresponding to a midpoint of specific heat increment was taken as temperature of the transition from the glassy state to the rubbery state, Tg. The results obtained are shown in Table 2.

Table 2.

Example VIIL

Poly(L-lactide) with molecular mass M _w of 104kg/mol, obtained by thermal polymerization in bulk, and poly(propylene glycol) with mass M _w of 425g/mol were used for blend preparation.

2 % solution of poly(L-lactide) in methylene chloride was prepared in two pots. Polyfpropylene glycol) was added to one of the pots, in the proportion: 10 weight parts of poly(propylene glycol) to 90 weight parts of poly(L-lactide) and the solution was stirred for 20 min. After another day from the solution of poly(L-lactide) and from the solution of blend of poly(L-lactide) and poly(propylene glycol) films were cast, which were dried for 4hrs, in vacuum at temperature of 75 ⁰ C. From the films specimens having mass of 7 mg were prepared for studies by a differential scanning calorimetric method. The temperature of the transition from the glassy state to the rubbery state was determined during heating at the rate of 10K/ min as the temperature corresponding to a midpoint of specific heat increment during heating. Poly(L-lactide) without admixture of poly(propylene glycol) exhibited the temperature of the transition from the glassy state to the rubbery state of 43°C, whereas the corresponding temperature for the blend of poly(L-lactide) and poly(propylene glycol) was 31.5 ⁰ C.

An advantage of the method according to the invention is a composition with lower temperature of glass transition and better ability to the plastic deformation than those of neat polylactide.

An advantage of the method according to the invention is easiness of admixing of poly(propylene glycol) or poly(propylene oxide) to polylactide.

An advantage of the method according to the invention is that poly(propylene glycol) and poly(propylene oxide) are not crystallizable, therefore neither the crystallization of poly(propylene glycol) in a blend of polylactide with poly(propylene glycol) nor crystallization of poly(propylene oxide) in a blend of polylactide with poly(propylene oxide) occurs.