WO2011070272A1 - Polylactic acid composition - Google Patents

Abstract

The present invention relates to a polylactic acid (PLA) composition, to the preparation method thereof, to the shaping method thereof, and to the uses thereof, in particular in the manufacture of various objects as common consumer goods such as: electrical, electronic, or motor vehicle devices; surgical material; sporting goods or the packaging thereof; diaphragms for, for example, treating effluents; or fibers and fabrics.

Description

 POLYLACTIC ACID COMPOSITION

The present invention relates to a composition based on poly lactic acid (PLA), to its preparation process, to its shaping process, as well as to its uses, especially in the manufacture of various objects, such as goods consumer goods such as electrical, electronic or automotive equipment, surgical equipment, packaging or sporting goods, membranes for example for the treatment of effluents.

The invention relates more particularly to a composition comprising a lactic acid polyacid, and a block copolymer of which at least one of the blocks is predominantly constituted by poly lactic acid L or lactic polyacid D. This composition has crystallization characteristics allowing advantageous molding, especially at low temperature, but also a particularly high load deflection temperature compared to PLA. This composition is further composed entirely of renewable materials, is biodegradable and contains no catalytic residues of the family of metals which makes it interesting in areas where these residues are undesirable, for example when the use concerns a contact with foodstuffs or living tissues. This composition is also transparent which allows uses in areas where transparency is necessary. PLA is a polymer whose interest continues to grow due to its properties, including mechanical properties but also its compatibility with living tissues. It is also biodegradable and comes from renewable resources.

One of the limitations to the use of PLA is its ability to retain its mechanical properties from a certain temperature, typically above 50 ° C while retaining where necessary good biodegradability and good compatibility with living tissues. Regarding this last point the PLA must generally be purified because it contains metal catalytic residues involving additional costs. Another limitation relates to the molding conditions, in particular the temperature which is not always as low as one would like to minimize the energy consumption necessary for shaping by molding.

Prior art.

Several solutions for improving the temperature of deflection under charges are known from the literature. The so-called stereocomplex technique described in WO2008057214 consists in mixing a poly (lactic acid) homopolymer mainly consisting of one L enantiomer to a lactic acid homopolymer predominantly consisting of one D enantiomer. In this case, the melt temperature of the stereocomplex is 230. ° C against 170 ° C for the PLA from a mixture of enantiomers L and D. Unfortunately the synthesis of PLLA and PDLA is expensive because it supposes to isolate at previously enantiomerically pure monomers and thus synthesize two polymers. It is also necessary to intimately mix the two polymers to obtain the stereocomplex.

In 1990, (Yui et al., Makrol.chem.191: 481) showed that stereocomplexes could be observed on PLLA-PDLA diblock copolymers obtained without metal catalysis, with an associated melting temperature above 200 ° C. However, the use of pure PLLA-PDLA diblock copolymers is expensive and may require precipitation steps.

Another technique for improving the temperature of deflection under charges described in WO 2003016015 consists of heat treatments which improve the crystallinity of the composition and therefore the temperature of deflection under charges. In this application, a nucleating agent is jointly used in the heat treatment. This nucleating agent however disturbs the transparency and can sometimes compromise the compatibility with living tissues or the biodegradability of the composition. Other techniques for improving the temperature of deflection under charges consist of mixing the PLA with another polymer, such as polycarbonate or ABS. Note that these solutions lead to compositions that are not from fully renewable materials. Their biodegradability and their compatibility with living tissues are also generally no longer assured. The application JP2005035134 A2 considers the addition of natural fibers to the PLA and claims by these compositions an improved thermal resistance. These composite compositions, although interesting do not allow the development of transparent materials.

In the journal Polymer, vol 47, 3826-3837 (2006), Tsuji et al show that small amounts of PDLA added to a PLLA lead to a composition having improved crystallization behaviors and a higher melting temperature. But up to 40% of PDLA is required for PLLA / PDLA composition to observe a significantly higher melting temperature than for PLLA.

The Applicant has now shown that a composition comprising a lactic acid polyacid and a block copolymer of which at least one of the blocks is predominantly constituted by lactic polyacid L or poly lactic acid D has crystallization characteristics which allow advantageous molding conditions, in particular at low temperature, but also a particularly high load deflection temperature compared to PLA while remaining transparent.

The object of the present invention is therefore to provide a composition of renewable origin comprising PLA entities, having a high temperature of deflection under load, biodegradable, compatible with living tissue, transparent, and the least expensive possible with respect to its synthesis and its transformation, in particular mild temperature conditions, both for synthesis only during molding conditions (mold temperature).

Summary of the invention.

The present invention relates to a transparent composition comprising a polyacid lactic homopolymer of enantiomeric purity L or D greater than 75% and a block copolymer of which at least one of the blocks is a lactic polyacid of enantiomeric purity greater than 75% and of which 1 ' The majority enantiomer is of enantiomeric form opposite to that constituting the lactic polyacid homopolymer. Detailed description.

 By PLA L is meant a PLA of which the enantiomer L is more than 75% predominant. More particularly, the enantiomer L is greater than 90% and more preferably more than 98%.

By PLA D is meant a PLA of which the enantiomer D is more than 75% majority. More particularly, the enantiomer D is greater than 90% and even more preferably greater than 98%. By PLA (D or L) is meant a PLA L or a PLA D.

The PLA (D or L) homopolymer used in the invention may be a PLA (D or L) synthesized by any synthetic route described in the literature. However, in order to confer good compatibility with living tissues and to minimize the energy required during the synthesis, it will be preferable to prepare it according to a method described in application WO2008104724 of the Applicant, ie mild conditions of temperature and the absence of metals avoiding a polymer washing step. It has the following characteristics:

 Molecular weight, Mw g / mol, greater than or equal to 10000 and preferably greater than 80000, even more preferably greater than 100000. Its polydispersity index is preferably less than 1.5 and even more preferably less than 1.2.

The block copolymer comprising at least one PLA entity (D or L) has the following structure:

PLA (D or L) _n -R, where n is an integer between 1 and 10, preferably 1 and 2, and more particularly 1, R is chosen from the following groups:

-PLA (D or L), of enantiomeric purity greater than 75%, preferably greater than 90% and even more preferably SUpG .L ^" ï Θ Θ cL 98" 6 _{r of} which the majority enantiomer is of opposite configuration to at least one of the PLA blocks (D or L) _n .

-PMMA (polymethyl methacrylate)

-PEG (polyethylene glycol)

 -PTMG (polytetramethylene glycol)

 functionalized polyolefins

 Polybutadiene,

 poly (dimethyl siloxane)

As the PLA synthesis method described in WO2008104724 results in one or more hydroxyl ends depending on the number of hydroxyl groups contained in the initiator, R must contain at least one entity capable of reacting on a hydroxyl function by polycondensation such as acid, anhydride, acid chloride, epoxy, etc.

 When R is not a PLA (L or D). Any method of synthesis known to those skilled in the art may be used to provide this functionality to R such as grafting a functional monomer on a polymer trunk, copolymerization of a functional monomer, telomerization with a telogen carrying the appropriate functionality, oxidation .

When R is not a PLA entity, the PLA block copolymer (D or L) _n -R can be prepared by reacting the two functional entities PLA (D or L) and R separately or during mixing in the state. melted with PLA (D or L) ie "in situ synthesis of the block copolymer". When R is multifunctional (n> 1), the copolymer can be triblock, starred, connected.

In the case of a PLA D-PLA L multiblock copolymer, the synthesis will be carried out in sequential addition of the monomers of the two different enantiomeric configurations according to the method described in WO2008104724.

Preferably, the synthesis and use of diblock copolymer PLA D-PLA L will be considered, but it is not excluded in the context of the invention the synthesis and the use of multiblock copolymers of alternating structure PLA L and PLA D .

The block copolymer is present in the composition in mass proportions ranging from 0.01 to 50%, preferably 0.1 to 15% and more particularly from 0.1 to 10%, inclusive. The compositions of the present invention may further contain one or more additives such as impact modifiers, external or internal lubricants, UV stabilizers, heat, flame retardants. These additives represent less than 50% by weight of the composition, preferably less than 30% by weight. For impact modifiers, external or internal lubricants, and UV stabilizers, heat, the content is less than 20% and preferably less than 10% by weight.

It would not be outside the scope of the invention to add fillers such as talc, chalk, kaolin, mica, carbon black, the content by weight of which will be less than 50% of the composition, preferably less than 50% by weight. 20% and more preferably less than 10%, these fillers may act as a nucleating agent together with the block copolymer.

Finally, the composition of the invention may contain fibers, natural or otherwise, in contents ranging from 1 to 60%, preferably ranging from 5 to 40% and more preferably from 5 to 20%, as well as nanotubes, carbon or not, in proportions ranging from 0.01 to 10%, and more particularly from 0.01 to 5%.

The composition of the invention may be prepared by a tool known to those skilled in the art, operating in the molten state of the polymeric entities in the presence, such as an extruder, or a kneader. The compositions can also be obtained by dissolving the polymeric entities in a suitable solvent such as dichloromethane, chloroform, toluene, aromatic solvents generally, and then precipitated in a non-solvent such as water, heptane, aliphatic solvents in general, or evaporation of the solvent. The invention also includes objects shaped typically by a molding injection method as well as the use of these objects.

 Such objects concern consumer goods such as electrical, electronic or automotive equipment, surgical equipment, packaging, sporting goods or membranes for example for the treatment of effluents. The invention also comprises the fibers obtained by spinning, in the melt or not, of the compositions of the invention, as well as the tissues obtained with these fibers, and using these fabrics derived from these fibers.

EXAMPLES

Example 1 Preparation of a Composition According to the Invention

1A - Preparation of the block copolymer PLA (D) -b-PLA (L)

 The copolymer is prepared according to a method described in the application WO2008104724 of the applicant.

The synthesis is carried out in a 2 L jacketed reactor, inerted and maintained under a nitrogen sweep, provided with mechanical stirring (500 rpm), and connected to a temperature control group allowing regulation between 0 ° C. and 250 ° C. Are successively introduced into the reactor controlled at 80 ° C, under nitrogen, with stirring at 500 rev / min:

 765 g of toluene, previously passed on sieve of alumina to dry it.

 135 g Lactide D (0, 8366 mol) (Puralact D from Purac).

 Then after 30 min:

 6.08 g of anhydrous trifluoromethanesulfonic acid

(0.0405 mol)

 1.76 g of anhydrous n-octanol (0.0135 mol).

The reaction medium is stirred under nitrogen at 80 ° C. until complete conversion of the monomer established from gravimetric measurements by taking samples of the reaction medium over time, ie 4 hours (100% conversion).

After ensuring that the conversion of lactide D to polymer is quantitative, then 135 g of lactide L (0.8366 mol) (Puralact L from Purac) are then added.

 After 2 hours of polymerization, 15.73 g of di-isopropylethylamine (source Aldrich) (0.1215 mol) are then added to the reaction medium to ensure that the reaction is complete.

The toluene is then evaporated and the polymer is washed with 1 L of acetone and then dried under vacuum at 30 ° C for 24 h. The gravimetric measurements to determine the solids content of the reaction medium indicate the amount of polymer present in the medium (the solvent and the monomer being removed by vacuum and temperature). The samples are previously neutralized with Di-isopropylethylamine to block any reaction and introduced into an aluminum cup placed in an oven at 200 ° C for 30 minutes, under 10 mbar.

The resulting polymer is characterized by DSC on a TA Instrument DSC 2910 © equipped with Thermal Advantage and data collection and universal analysis software 2000 for analysis. The TA Instrument DSC 2910 © is connected to a cylinder containing liquid nitrogen which allows the cooling of the DSC oven to -120 ° C. The reference is an empty aluminum capsule.

 The mass of product used to perform the DSC measurement is between 5.0 mg and 20.0 mg. The sample is introduced into an aluminum capsule.

The sample is cooled to -110 ° C. and then heated to 250 ° C. at 10 ° C./min under a flow of air (10 ml / min) and then cooled again to 40 ° C. under air. The method is applied twice successively to each sample to ensure the removal of any traces of residual solvent and to be certain that the transition temperatures obtained are not due to artifacts.

The polymer obtained has a melting temperature of 204 ° C., which is characteristic of a Poly (lactic acid) stereoblock and a degree of crystallinity (area under the melting curve) estimated at 83% (referring to the melting enthalpy of a lactic acid polyactide 100 of 93.1 Jg-1).

1B - Blend of Block Copolymer with Homopolymer of Lactic Acid

The copolymer prepared as described in Example 1A was mixed with polylactic acid (PLA) (2002 D from Nature Works) in a weight ratio copolymer: PLA 40:60, in a 220 BUSS co-kneader. ° C. The mixture is injected in a closed loop on a BILLION injection press with 70 tons of closing force. The injection temperature is 210 ° C and the mold temperature is 20 ° C.

EXAMPLE 2 Evaluation of the Optical and Mechanical Properties of the Composition According to the Invention

2A - Protocols of tests performed

The composition of Example 1B was subjected to various tests carried out under the operating conditions detailed in Table 1 below.

Table 1

Test carried out on the composition PLA / block copolymer

2B - Test results

The results of the tests performed on the composition of Example 1B are given in Tables 2 and 3 below. Table 2

 Mechanical properties of the composition according to the invention

Table 3

 Optical Properties of the Composition According to the Invention

From the point of view of its mechanical properties, the temperature of deflection under load is significantly improved and the optical properties preserved.

Claims

1. Transparent composition comprising a lactic polyacid homopolymer of enantiomeric purity L or D greater than 75% and a block copolymer consisting of the PLA L and PLA D entities. The composition of claim 1 wherein the block copolymer is a triblock copolymer. 3. The composition of claim 1 wherein the block copolymer is a diblock copolymer. 4. Composition according to claim 1 wherein the block copolymer is present in proportions ranging from 0.01 to 50%. 5. Process for shaping by injection of a composition according to claims 1 to 4. 6. Fibers whose composition corresponds to one of claims 1 to 4. 7. Object shaped according to the method of claim 5. 8. Use of an object according to claim 7 as consumer goods such as electrical, electronic or automotive equipment, surgical equipment, packaging, sport or membranes for example for treatment of eff luents.