Title of Invention

POLYLACTIC ACID - CLAY NANOCOMPOSITES BY LACTIDE POLYMERIZATION IN CLAYS

Abstract The invention relates to process for preparing a polylactic acid-clay nanocomposite the process comprising melt polymerization of the lactide intercalated in an organically modified clay in the presence of a catalyst to form a prepolymer-clay nanocomposite having reactive end groups, the catalyst being in the form of a complex, the complex comprising a lactide, a metal-oxo compound and a lactic acid oligomer and the clay being present in an amount up to approximately 10% by weight, the residual lactide after the melt polymerization being removed by heating the prepolymer-clay nanocomposite in the temperature range of 98°C to a temperature lower than melting point of the prepolymer and solid state polymerization of the prepolymer-clay nanocomposite. The process of the present invention yield polylactic acid-clay nanocomposites having a molecular weight from around 10,000 to 20,000 and crystallinity in the range of 25 to 95%.
Full Text FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Polylactic acid-clay nanocomposites by lactide polymerization in clays APPLICANTS
Name : Indian Institute of Technology, Bombay
Nationality : an autonomous research and educational
institution established in India by a special Act of the Parliament of the Republic of India under the Institutes of Technology Act 1961 Address : Powai, Mumbai 400076, Maharashtra, India
INVENTORS
Names : Nanavati Hemant and Katiyar Vimal
Nationality : both Indian Nationals
Address : both of Indian Institute of Technology, Bombay,
Centre for Environmental Science and Engineering, Powai, Mumbai 400076, Maharashtra, India
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed :

Field of invention
The invention relates to a process for preparing polylactic acid-clay nanocomposites by intercalation followed by polymerization of lactide in a clay. The invention also relates to polylactic acid-clay nanocomposites and to a catalyst for preparing the same.
Background of the invention
The synergistic association of polymer chains and clay layers as in a polymer-clay nanocomposite, result in improved properties. Because of its biodegradability, polylactic acid is highly desirable and several attempts have been made in the past to form nanocomposites of polylactic acid with clay. Polylactic acid-clay nanocomposites are suitable for various applications such as automotive, electronic, film, fiber, biocompatible and biomedical applications, where a combination of mechanical and permeation properties are required. For obtaining- superior mechanical properties, it is required that the molecular weight and crystallinity of the nanocomposite is high. Conventionally, high molecular weight polylactic acid-clay nanocomposites are prepared by melt compounding of the polymer-clay mixture. Tanoue et al., [Tanoue et al, Polymer Composites, 27(3) (2006) 256-263] disclose the preparation of poly (lactic acid) (PLA)/organoclay nanocomposites by melt compounding in a co-rotating twin screw extruder. Two types of commercialized organoclays (di-methyl benzyl stearyl ammonium ion and di- methyl distearyl ammonium ion intercalated between clay platelets) and two grades of poly(ethylene glycol) (PEG) with different molecular weight (Mw = 2,000 and 300,000-500,000) have been used in this study. However it has been observed that the melt compounding often leads to degradation of the polylactic acid polymer accompanied by decrease in molecular weight during the formation of the nanocomposite, resulting in considerable loss, in terms of processing cost and time. To avoid such drawbacks, the polylactic acid-clay nanocomposites need to be prepared starting from monomers/oligomers of lactic acid and clay. Paul et al. {Macromol. Rapid Commun. 24 (2003) 561-566) disclose a process for preparation of polylactide/clay nanocomposite by in situ polymerization of L-lactide. In this study, organically modified clay is directly added into the polymerization reactor to perform bulk in situ polymerization at 120°C for 48 hours using tin octanoate as a catalyst (lactide to catalyst molar ratio = 300). However the maximum molecular weight that has been
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attained in the process is 14,000, which is too low for many practical applications of the nanocomposite. Since high molecular weight and crystallinity are of significance, there is scope for further developments in the synthesis of nanocomposites of polylactic acid of increased molecular weight and clay
Detailed Description of the invention
The present invention provides a process for preparing a polylactic acid-clay nanocomposite the process comprising the steps of intercalation and polymerization of a lactide in a clay.
In one embodiment, the invention provides a process for preparing a polylactic acid-clay nanocomposite, the process comprising melt polymerization of a lactide intercalated in an organically modified clay in the presence of stannous octoate at a temperature range of 120°C to 180°C, the clay being present in an amount up to approximately 10% by weight
In a preferred embodiment of the invention, there is provided a process for preparing a polylactic acid-clay nanocomposite the process comprising the steps of
i) Melt polymerization of a lactide intercalated in an organically
modified clay in the presence of a catalyst to form a prepolymer-clay nanocomposite having reactive end groups, the catalyst being in the form of a complex, the complex comprising a lactide, a metal-oxo compound and a lactic acid oligomer and the clay being present in an amount up to approximately 10% by weight, the residual lactide after the melt polymerization being removed by heating the prepolymer-clay nanocomposite in the temperature range of 98 C to a temperature lower than melting point of the prepolymer and
ii) Solid state polymerization of the prepolymer-clay nanocomposite.
In another embodiment, the invention provides a catalyst for preparing polylactic acid-clay nanocomposite, the catalyst being a complex comprising a lactide, a metal-oxo compound and a lactic acid oligomer, the metal to oligomer ratio in the complex
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being in the range of 0.1 to 10, preferably in the range of 0.5 to 5, more preferably in the range of 0.8 to 1.5
In a further embodiment, there is provided a process of preparing a catalyst for producing polylactic acid-clay nanocomposite, the process comprising dissolving a mixture of a lactide, a lactic acid oligomer and an organic metal-oxo compound in an organic solvent, stirring the mixture and removing the solvent with or without vacuum.
In yet another embodiment, there is provided a polylactic acid-clay nanocomposite wherein the polymer has a molecular weight from around 30,000 to 200,000 and crystallinity in the range of 25 to 95%.
The polymerization process leading to the formation of a polylactic acid nanocomposite comprises melt polymerization of a lactide and a catalyst in an organically modified clay.
In the melt polymerization step, lactide and clay are used as main starting materials, the lactide being polymerized in a molten state via ring opening polymerization. The melt polymerization is carried out at a temperature in the range from 100°C-200°C, preferably from 140°C -180°C, more preferably from 145°C-165°C and the polylactic acid polymer-clay nanocomposite formed has an average molecular weight of from 10,000 to 50,000. The polymerization reaction is carried out by heating the reaction mixture comprising lactides for 0.5 to 5 hours using a amount of catalyst in the range of, preferably, 0.00001- 10% by weight, more preferably 0.001 ~ 2 % by weight. The molecular weight of the final polymer product can be adjusted by adjusting the amount of catalyst added. The reaction is preferably carried out at a reduced pressure or in the presence of inert gasses.
The catalyst of the present invention is either stannous octoate or a catalyst complex. The catalyst complex is formed by the reaction between a lactide, a lactic acid oligomer and an organic metal-oxo compound. For preparing the complex, the lactide, the lactic acid oligomer and the metal-oxo compound, are dissolved in an organic solvent or in a mixture of organic solvents at a temperature less than the
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boiling point of the solvent or of the mixture of solvents. The reaction mixture is stirred for a period of 15 minutes to 24 hours. After formation of the catalyst complex, the solvent is removed by evaporation or filtration process, with or without vacuum. The metal to oligomer ratio in the complex is in the range of 0.1 to 10, preferably in the range of 0.5 to 5 and more preferably in the range of 0.8 to 1.5. The catalyst is used in an amount of 0.00001 to 10% by weight, preferably in an amount of 0.001 to 2 % by weight.
The metals used for the formation of the complex are selected from groups II, III, IV or V of the periodic table. Alternately, oxides of these metals or salts of these metals are also used. The metals/metallic compounds are selected from the group consisting of zinc powder, tin powder, aluminum and other metals; tin oxide, zinc oxide, aluminum oxide, magnesium oxide, titanium oxide, and other metal oxides; stannous chloride, stannic chloride, stannous bromide, antimony fluoride, zinc chloride, magnesium chloride, aluminum chloride and other metal halides; tin lactate, zinc lactate, tin octanoate, and other metal organic carboxylates; titanium isopropoxide, aluminium isopropoxide and alkoxides of other metals having at least one terminal hydroxy 1 group.
Organic solvents used in the preparation of the catalyst complex include hydrocarbon solvents such as benzene, toluene, xylene and mesitylene; halogenated hydrocarbon solvents such as chlorobenzene, bromobenzene, dichlorobenzene; halogenated solvents such as chloroform, dichloro methane; ether solvents such as tetra hydrofuran, dibutyl ether 3-methoxy toluene. These solvents are used either individually or as a mixture.
The polymerization of lactide is preferably carried out in the presence of the catalyst complex. When the catalyst complex is used, the melt polymerization results in a polylactic acid prepolymer-clay nanocomposite. The prepolymer-clay nanocomposite may contain lactides in an amount of from 0.001 to 10% by weight. Residual lactides after melt polymerization are removed by heating the prepolymer-clay nanocomposite in the preferred range of 98° C to below the melting point of the polylactic acid prepolymer nanocomposite, under reduced pressure.
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The polylactic acid prepolymer-clay nanocomposite of the present invention optionally include various components which are additives commonly employed with polymers. Such optional components include surfactants, nucleating agents, coupling agents, fillers, impact modifiers, chain extenders, plasticizers, compatibilizers, colorants, mold release lubricants, antistatic agents, pigments, fire retardants, and the like. Suitable examples of fillers include carbon fiber, glass fiber, kaolin clay, wollastonite, mica and talc. Suitable examples of compatibilizers include lactone copolymers.
The lactides used for the process of the present invention is selected from the group consisting of D-Lactide, L-lactide, DL lactide or a mixture of D- and L-lactides The lactides are optionally copolymerized with various lactones selected from the group consisting of b-propiolactone, d-valerolactone and S-caprolactone glycolide, and the like.
The clays used for the preparation of the nanocomposite is selected from a group consisting of anionic and cationic clays including montmorillonite, nontronite, beidellite, volkonskoite, laponite, synthetic hectoritea, natural hectorite, saponite, sauconite, magadite, hydrotalcite or kenyaite.
The polylactic acid prepolymer-clay nanocomposite has a molecular weight in the range of 20,000 to 70,000. It may be formed into a desired shape, such as granular, film, fiber and pelletized forms, using a forming machine and further polymerization in the solid state when carried out, is carried out, atleast maintaining its approximate shape. For this, the polylactic acid prepolymer nanocomposite may be cooled to a temperature lower than the crystallization temperature of the polymer, for 0.25 hour to 10 hours, preferably for 1 hour to 4 hours, and then further polymerized, at the temperature of the solid state polymerization.
The polylactic acid prepolymer-clay nanocomposite is further polymerized in the solid state. Solid state polymerization is carried out under reduced pressure as well as in inert gas flow, at a temperature below the melting point of the polylactic acid prepolymer, in the range between glass transition temperature and melting point of
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poly lactic acid prepolymer, preferably in the range of about 100°C to about 180°C, more preferably in the range of about 140°C to about 170°C. The reaction temperature is either kept constant during the reaction or alternately a stepwise change in temperature is carried out. Vacuum is maintained in the range of 100 mm Hg to 0.0001 mm Hg, preferably in the range of 10 mm to 0.001 mmHg. Solid state polymerization may be performed for long reaction times, as high as 20 hours. The reaction is preferably performed for 10 hours.
The temperature of solid state polymerization is desirably set at a temperature higher than the melting point of the lactide and lower than the melting temperature of the prepolymer-clay nanocomposite.
During solid state polymerization, solid-solid reactions of prepolymer chains occurs resulting in high molecular weight highly crystalline polylactic acid nanocomposite. The solid state polymerization time is normally from 1 to 20 hours, preferably from 5 to 10 hours. In order to shorten the reaction time, the reaction temperature may be raised with the progress of the solid state polymerization. The melting point of the final polymer product increases with higher reaction temperature, and can be increased up to a temperature near 185°C. The solid state polymerization may be performed with or without crystallizing the polylactic acid prepolymer-clay nanocomposite. A catalyst may be further added just after melt polymerization.
Polylactic acid nanocomposite formed during the solid state polymerization has a molecular weight from around 10,000 to 200,000 and crystallinity, in the range of 25 to 95%.
The catalysts used for the polymerization process are added in one or more separate portions during the polymerization process. Further, the various components of the catalyst complex of the present invention are added either individually or added in the form of the complex of the lactide, metal octoate and the lactic acid oligomer.
The XRD profile of the clay and the nanocomposite are given in figure 1. XRD peaks corresponding to neat clay, disappear in case of nanocomposite, and shift towards lower 20 values. The SAXS profiles of the nanocomposites are given in figure 2.
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SAXS peaks corresponding to the nanocomposite appear at 20 values between 2° and 4°.
The clay materials used in the present invention are layered materials, selected from the group consisting of fibrous, chain-like minerals, for example, sepiolite, attapulgite and sipiolite. The clay can be an anionic or a cationic clay. The clay used can be one or more of montmorillonite, nontronite, beidellite, volkonskoite, laponite, synthetic hectorite, natural hectorite, saponite, sauconite, magadite, hydrotalcite and kenyaite. The cationic clay materials used in the present invention, are those treated with at least one quarternary ammonium ion of the formula:
+N*R1R2R3R4 or +NRaRbRcRd wherein:
R1, R2, R3 and R4 are independently selected from a group consisting of a saturated or unsaturated C1 to C22 hydrocarbon, substituted hydrocarbon and branched hydrocarbon. R1 and R2 optionally forms an N,N-cyclic ether. Examples of groups represented by R1, R2, R3 and R4 include saturated or unsaturated alkyls, including alkylenesa; substituted alkyls such as hydroxyalkyls, alkoxyalkyl, alkoxys, amino alkyls, acid alkyls, halogenated alkyls, sulfonated alkyls, nitrated alkyls and the like; branched alkyls; aryls and substituted aryls, such as alkylaryls, alkoxyaryls, alkylhydroxyaryls, alkylalkoxyaryls and the like. Optionally, one of R1, R2, R3 and R4 is hydrogen. Ra, Rb and Re are hydrogens (H) and Rd includes a carboxylic acid moiety. The treatment, is preferably from about 30 milliequivalents/l00g clay to about 200 milliequivalents/l00g clay.
The clays used in the following examples were Cloisite Na+, modified clays Cloisite 20A Cloisite 30B purchased from Southern Clay Product Inc. (Texas, U.S.A.), CDMB2C and CHMB1.2C (in-house modified from Cloisite Na+, using DODMAB (Dioctyldimethyl ammonium bromide) and HDTMAB (Hexa-Dexyl-Tri-Methyl-Ammonium Bromide) modifiers repectively, using standard procedures). Clays 20A and 30B are quarternary ammonium salt modified natural montmorrilonite, the modifier concentration being 125 meq/l00g clay, 95 meq/l00g clay and 90 meq/l00g
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clay and the interlayer spacing (doo1) of the clay being 31.5A, 24.2A and 18.5A, respectively.
The molecular weight determination of the polymers and the nanocomposites in the following examples has been carried out by a Waters GPC (Waters 2414 RI Detector) with PL-gel,5m Mixed-D (2x300mm) column, with polystyrene standards in chloroform that cover a molecular weight range of 160 to 4x10 .
The melting temperature (Tm) and crystallinity (Xc) of neat poly lactic acid nanocomposite have been determined by a NETZSCH STA 409PC Luxx Differential Scanning Calorimeter in the temperature range of 20 - 300°C at the rate of 10°C/minute.
Optical purity (% L- content) has been measured using Jasco DPI-370 digital polarimeter, calibrated with 5% fructose solution [a] 589nm= -89°.
WAXD (Wide angle X-ray Diffraction) analyses have been performed for the pristine clays and organoclays by using X' pert pro PANalytical X-ray diffractometer, which has an X-ray generator operated at 40 kV/30 mA, with a nickel filter, and Cu Ka radiation of wavelength (k), 0.154 nm. The samples have been scanned in continuous mode with a scan step size (29) of 0.017 and scan step time of 5.08s in the range of 2-25°. SAXS analyses have been performed for neat PLLA and its nanocomposites by using Anton Paar GmbH SAXS compact slit camera, PANalytical X-ray generator with Packard Imaging-Plate reader in line collimation mode. The X-ray generator is operated at 40 kV/30 mA, Cu Ka radiation of wavelength (A,) 0.1542 nm and for a sample exposure time of 15 minutes.
The Transmission Electron Microscope (TEM) images of poly lactic acid nanocomposites have been obtained by performing bright field imaging using Tecnai G2 12 TEM optimized for cryo - TEM work. The microscope was operated at an accelerating voltage of 80 kV. Ultra thin sections of nanocomposites (80nm thickness) were prepared by ultramicrotomy at room temperature using Leica EM KM R2 model ultramicrotome equipped with a glass knife.
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Preparation of nanocomposite in the presence of stannous octoate catalyst
EXAMPLE 1
Mixtures of any of the organically modified clays (CHMB1.2C, CDMB2C, C20A or C30B) and L-Lactide, were prepared by dispersion of clays (1, 2 or 4 % by wt.) into a solution of L-lactide in dichloromethane at room temperature, allowing vigorous stirring for two hours to ensure proper dispersion. The solvent was removed at room temperature and the mixture is dried at 50°C under high vacuum. This mixture preparation procedure enabled intercalation of the L-lactide within the clay galleries.
ROP (Ring Opening Polymerisation) of clay-L-lactide mixture was carried out in vacuum-sealed glass ampoules. First, the glass ampoule was charged with the dried clay-L-lactide mixture and subsequently, the catalyst, stannous octoate in toluene, was added according to the L-lactide to catalyst molar ratio of 1000. The ampoule was sealed under high vacuum and immersed in an oil bath. Polymerizations were carried out in the temperature range of 160°C. After a predetermined time (~2 hours), the glass ampoule was removed and subsequently, the molten reactive polymer mixture was cooled at room temperature, and the product was analysed. The analyses were performed on the crude reaction mixture, without precipitation.
Preparation of catalyst complex
EXAMPLE 2
72 mg of dry L-lactide was taken in 50 mg round bottomed flask with 10 ml toluene under a nitrogen atmosphere, and was stirred for 30 min. This solution was transferred into another round bottomed flask which already contained 200 mg of tin octanoate (manufactured by Sigma Aldrich). Subsequently, 500 mg lactic acid oligomer was added into the reaction mixture, which was further diluted with 10 ml toluene. The reaction mixture was stirred at room temperature for 5 hours. Toluene was finally removed from the reaction mixture under vacuum at room temperature. Dry tin octanoate-oligomer-lactide catalyst complex so formed was utilized for the ROP of L-lactide.
in

EXAMPLE 3
Dry L-lactide was taken in 100 mg round bottom flask with 30 ml toluene under a nitrogen atmosphere, and was stirred for 30 min. This solution was transferred into another round bottomed flask which already contained aluminium isopropoxide (manufactured by Sigma Aldrich). Subsequently, 1.000 g lactic acid oligomer was added into the reaction mixture and further diluted with 20 ml toluene and was stirred at room temperature for 5 hours. Appropriate quantities of each ingredient were added in order to maintain lactide to aluminium ration of 20. Toluene was finally removed from the reaction mixture under vacuum at room temperature. Dry aluminium isopropoxide-oligomer-lactide catalyst complex so formed was utilized for the ROP of L-lactide.
EXAMPLE 4
To a 3-necked tubular reactor, equipped with a condenser and receiver at one end, and with mechanical stirrer having screw type impeller, was added 375 g of lactic acid (90% w/w solution in water). The solution was stirred at 30 rpm and heated to 150°C by temperature control tubular heater for two hours under nitrogen flow. Thereafter, stirring and heating were continued and the pressure was gradually reduced by a vacuum pump over two hours. The molten reaction mixture was then allowed to cool to room temperature to give 300g of lactic acid oligomer with weight average molecular weight of 522 Dalton. 13g of this oligomer was taken into another 100ml three necked tubular reactor and stirred with 5.22gm zinc powder having particle size of 200 mesh, for 8 hours at 120°C. Thereafter, the reaction mixture was dissolved in hot water and the filtrate was recovered and further dried to yield a zinc oligomer catalyst complex.
Preparation of polylactic acid prepolymer-clay nanocomposite
EXAMPLE 5
2g of L-lactide was placed in a round bottomed flask and dissolved in 20 ml dichloromethane. Subsequently, 1 wt % clay (C20A) was introduced into the lactide
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solution and stirred for 2 hours and thereafter, solvent was removed under reduced pressure to obtain dry lactide-clay mixture. In this mixture, the catalyst complex prepared by example 2, was added in an amount of 30 mg into reaction mixture and immersed in an oil bath to heat the mixture at a temperature of 160°C under reduced pressure for 2 hours. The reaction time was measured after all L-lactide has melted and the set temperature was reached. The obtained polylactic acid prepolymer-clay mixture had an average molecular weight of 45,000 and a crystallinity of 61%. Polylactic prepolymer-clay mixture was further heated at 110°C for 2 hours under high vacuum to obtain lactide-free polylactic acid prepolymer-clay nanocomposite.
EXAMPLE 6
2g of L-lactide was placed in a round bottomed flask and dissolved in 20 ml dichloromethane. Subsequently, 2 wt % clay (C20A) was introduced into the lactide solution and stirred for 2 hours and thereafter, solvent was removed under reduced pressure to obtain dry lactide-clay mixture. In this mixture, the catalyst complex prepared by example 2 was added in an amount of 30 mg and immersed in an oil bath to heat the mixture at a temperature of 160°C under reduced pressure for 2 hours. The reaction time was measured after all L-lactides were melted and the set temperature was reached. The obtained polylactic acid nanocomposite had an average molecular weight of 41,000 and a crystallinity of 60%. Polylactic prepolymer-clay mixture was further heated at 110°C for 2 hours under high vacuum to obtain lactide free polylactic acid prepolymer-clay nanocomposite.
EXAMPLE 7
2g of L-lactide was placed in a round bottomed flask and dissolved in 20ml dichloromethane. Subsequently, 4 wt % clay (C20A) was introduced into the lactide solution and stirred for 2 hours and thereafter, solvent was removed under reduced pressure to obtain dry lactide-clay mixture. In this mixture, the catalyst complex prepared in example 2 was added in an amount of 30 mg and immersed in an oil bath to heat the mixture at a temperature of 160°C under reduced pressure for 2 hours. The
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reaction time was measured after all L-lactides were melted and the set temperature was reached. The obtained polylactic acid nanocomposite had an average molecular weight of 28,000 and a crystallinity of 53%. Polylactic prepolymer-clay mixture was further heated at 110°C for 2 hours under high vacuum to obtain lactide-free poly lactic acid prepolymer-clay mixture.]
Solid State Polymerization of polylactic acid prepolymer-clay nanocomposite
EXAMPLE 8
Solid State Polymerization was performed for 10 hours at 150°C and 160°C on the polylactic acid prepolymer-clay nanocomposite synthesized by methods, illustrated in example 5, example 6 and example 7. Molecular weights and crystallinity were determined before and after solid state polymerization. The nanocomposite samples were found to increase in molecular weight and crystallinity.

Table 1: Properties of polylactic acid-clay nanocomposites prepared by Example 1
Polymer/Nanocomposite Clay % Mw %xc Onset Degradation (°C)
PLA — 113,200 29.6 219
PLA-C20A 1 131,300 52.7 262
PLA-C20A 2 127,000 54.3 267
PLA-C20A 4 121,500 54.3 270
PLA-C30B 1 127,100 44.7 242
PLA-C30B 2 92,000 54.3 254
PLA-C30B 4 84,800 34.8 257
PLA-CDMB2C 1 168,800 50.9 251
PLA-CDMB2C 2 78,800 50.0 262
PLA-CDMB2C 4 73,800 47.6 252
PLA-CHMB1.2C 1 102,300 47.9 249
PLA-CHMB1.2C 2 85,600 53.7 267
PLA-CHMB1.2C 4 82,400 43.3 254
f PLA is Polylactic acid; C20A, C30B, CDMB2C and CHMB1.2C are organically modified clays; PLA-C20A, PLA-C30B etc represents nanocomposites formed by

polylactic acid with the respective clays. Mw is weight average molecular weight and %XC is percentage crystallinity.
The properties of polylactic acid-clay nanocomposites prepared by example 1 are given in table 1. It can be observed that, in general, polylactic acid-clay nanocomposites have higher molecular weight, crystallinity and onset degradation temperature as compared to the polylactic acid polymer.
The properties of polylactic acid-clay nanocomposites prepared by example 8 are given in table 2. It can be seen that polylactic acid-clay nanocomposites of high molecular weight and crystallinity are formed. Moreover, there is significant increase in the molecular weight and crystallinity on solid state polymerization of the polylactic acid prepolymer-clay nanocomposite. Solid state polymerization is preferably carried out for obtaining nanocomposites for applications requiring high crystallinity.

Table 2: Proper ties of polylactic acid-clay nanocomposite prepared by example 8
Prepolymer-Clay nanocomposite used for SSP Solid state polymerization of Example 5, 6 and 7
PrePLA-NC of Mw / PDI %xc SSPTime(Hrs) Post-SSP polymer Mw /PDI %xc
150°C 160°C 150°C 160°C
Example 5 45,000/1.31 61 5 61,100/1.51 67,254/1.7 80
10 120,000/1.43 127,000/1.34 88 90
Example 6 41,000/1.52 60 5 59,000/1.33 89,500/1.51 83
10 71,500/1.38 109,000/1.43 88 90
28,000/1.57 53 5 37,500/1.38 41,800/1.51 65
Example 7 10 54,000/1.41 61,000/1.57 76 80
10 153,000/1.76 96
f PrePLA-NC PDI is polydisp s Prepolyme ersivity index r-Clay nanocon lposite; SSP i s Solid state I 'olyme risation;

The above description is illustrative only and is not limiting. Various of the above-discussed and other features, or alternatives thereof, may be desirably combined and various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims
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WE CLAIM:
1) A process for preparing a polylactic acid-clay nanocomposite the process
comprising the steps of
i) Melt polymerization of a lactide intercalated in an organically modified clay in the presence of a catalyst to form a prepolymer-clay nanocomposite having reactive end groups, the catalyst being in the form of a complex, the complex comprising a lactide, a metal-oxo compound and a lactic acid oligomer and the clay being present in an amount up to approximately 10% by weight, the residual lactide after the melt polymerization being removed by heating the prepolymer-clay nanocomposite in the temperature range of 98 C to a temperature lower than melting point of the prepolymer and
ii) Solid state polymerization of the prepolymer-clay nanocomposite
2) A process for preparing a polylactic acid-clay nanocomposite the process comprising melt polymerization of a lactide intercalated in an organically modified clay in the presence of stannous octoate at a temperature range of 120°C to 180°C, the clay being present in an amount up to approximately 10% by weight
3) The process as claimed in any one of the above claims wherein the process is carried out in the presence of a catalyst present in an amount of 0.00001 to 10% by weight, preferably in an amount of 0.001 to 2 % by weight.
4) The process as claimed in any one of the above claims wherein the lactide used is a D-Lactide, L-lactide, DL lactide or a mixture of D- and L-lactides
5) The process as claimed in any one of the above claims wherein the lactide is copolymerized with various lactones selected from the group consisting of P-propiolactone, 5-valerolactone and s-caprolactone glycolide, and the like.
6) The process as claimed in any one of the above claims wherein the clay is selected from a group consisting of anionic and cationic clays including montmorillonite, nontronite, beidellite, volkonskoite, laponite, synthetic hectorite, natural hectorite, saponite, sauconite, magadite, hydrotalcite or kenyaite.
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7) A polylactic acid prepolymer-clay nanocomposite having a molecular weight in the range of 20,000 to 70,000 formed by the melt polymerization step of the process as claimed in claim 1.
8) A polylactic acid-clay nanocomposite prepared by a process as claimed in any one of the claims 1 to 6 wherein the nanocomposite has a molecular weight from around 10,000 to 200,000 and crystallinity in the range of 25 to 95%.
9) A catalyst for preparing polylactic acid-clay nanocomposite, the catalyst being a complex comprising a lactide, a metal-oxo compound and a lactic acid oligomer, the metal to oligomer ratio in the complex being in the range of 0.1 to 10, preferably in the range of 0.5 to 5, more preferably in the range of 0.8 to 1.5
10) The catalyst as claimed in claim 9 wherein the organic metal-oxo compound
comprises metals of group II, Group III, Group IV or Group IV of the periodic table.
11) A process of preparing a catalyst for producing polylactic acid-clay
nanocomposite, the process comprising dissolving a mixture of a lactide, a lactic acid
oligomer and an organic metal-oxo compound in an organic solvent, stirring the
mixture and removing the solvent with or without vacuum.
Dated this 4th day of April 2007

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ABSTRACT
The invention relates to process for preparing a polylactic acid-clay nanocomposite the process comprising melt polymerization of the lactide intercalated in an organically modified clay in the presence of a catalyst to form a prepolymer-clay nanocomposite having reactive end groups, the catalyst being in the form of a complex, the complex comprising a lactide, a metal-oxo compound and a lactic acid oligomer and the clay being present in an amount up to approximately 10% by weight, the residual lactide after the melt polymerization being removed by heating the prepolymer-clay nanocomposite in the temperature range of 98 C to a temperature lower than melting point of the prepolymer and solid state polymerization of the prepolymer-clay nanocomposite. The process of the present invention yield polylactic acid-clay nanocomposites having a molecular weight from around 10,000 to 200,000 and crystallinity in the range of 25 to 95%

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679-mum-2007-abstract.pdf

679-MUM-2007-CANCELLED PAGES(29-1-2010).pdf

679-MUM-2007-CLAIMS(AMENDED)-(29-1-2010).pdf

679-mum-2007-claims(granted)-(25-6-2010).pdf

679-mum-2007-claims.doc

679-mum-2007-claims.pdf

679-MUM-2007-CORRESPONDENCE(17-12-2008).pdf

679-mum-2007-correspondence(8-12-2008).pdf

679-mum-2007-correspondence(ipo)-(11-2-2009).pdf

679-mum-2007-correspondence(ipo)-(7-7-2010).pdf

679-mum-2007-correspondence-received.pdf

679-mum-2007-description (complete).pdf

679-mum-2007-description(granted)-(25-6-2010).pdf

679-MUM-2007-DRAWING(29-1-2010).pdf

679-mum-2007-drawing(granted)-(25-6-2010).pdf

679-mum-2007-drawings.pdf

679-mum-2007-form 1(27-6-2007).pdf

679-MUM-2007-FORM 1(29-1-2010).pdf

679-mum-2007-form 18(8-7-2007).pdf

679-mum-2007-form 2(granted)-(25-6-2010).pdf

679-mum-2007-form 2(title page)-(granted)-(25-6-2010).pdf

679-mum-2007-form 26(27-6-2007).pdf

679-MUM-2007-FORM 3(29-1-2010).pdf

679-mum-2007-form 8(3-7-2007).pdf

679-mum-2007-form-1.pdf

679-mum-2007-form-2.doc

679-mum-2007-form-2.pdf

679-mum-2007-form-3.pdf

679-MUM-2007-PUBLICATION REPORT(17-12-2008).pdf

679-MUM-2007-REPLY TO EXAMINATION REPORT(29-1-2010).pdf


Patent Number 241277
Indian Patent Application Number 679/MUM/2007
PG Journal Number 27/2010
Publication Date 02-Jul-2010
Grant Date 25-Jun-2010
Date of Filing 04-Apr-2007
Name of Patentee INDIAN INSTITUTE OF TECHNOLOGY, BOMBAY
Applicant Address POWAI, MUMBAI 400 076,
Inventors:
# Inventor's Name Inventor's Address
1 NANAVATI HEMANT Indian Institute of Technology,Bombay, Department of chemical Engineering, Powai,Mumbai 400076
2 KATIYAR VIMAL Indian Institute of Technology,Bombay, Deportment of chemical Engineering, Powai,Mumbai 400076
PCT International Classification Number C08K3/04
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA