Title of Invention

POLYLACTIC ACID-CLAY NANOCOMPOSITES AND PROCESS FOR PREPARING THEM

Abstract The invention relates to polylactic acid-clay nanocomposite havin molecular weight in the range of around 100000 to 200000, crystallinity in the range of around 75% to 100% polydispersivity index in the rangae of around 1.0 to 2.0, onset degradation temperature in the ranfe of around 200 C to 300 C and melting point in the range of around 100 C to 200C. The invention also relates to a A dispersion of polylactic acid prepolymer and clay, capable of a 2 to 7 fold increase in molecular weight, on polymerization in the solid state, the dispersion having a polydispersivity index in the range of around 1.0 to 1.5, molecular weight in the range of around 1,000 to 60,000 preferably in the range of around 20,000 to 50,000 and crystallinity in the range of around 40% to 60%, the clay being present in the range, 0.5% yo 10%, preferably in the range, 1% to 5% by weight, either in the intercalated or exfoliated form.
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 and process for preparing them
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 ot invention:
The invention relates to polylactic acid-clay nanocomposites and a process for preparing them.
The invention also relates to a dispersion of a lactic acid prepolymer and clay used for preparing the nanocomposites and to a process for preparing such a dispersion.
Background of the invention
Polymer clay nanocomposites have long been known for their advantageous properties arising out of a synergy between the clay and polymer components in the nanocomposites. Because of its biodegradability, polylactic acid is highly desirable and several attempts were 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, high molecular weight and nanocomposite crystallinity are required. Conventionally, high molecular weight polylactic acid-clay nanocomposites are prepared by melt compounding of the polymer clay mixture. 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) of different molecular weight (Mw = 2,000 and 300,000-500,000) were used in this study. It was, however, observed that 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 processing cost and time. To avoid such drawbacks, the polylactic acid-clay nanocomposites need to be prepared starting from monomers/oligomers or lactide and by adding the clay at suitable time, before the melt polymerization is completed. 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
2-

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 could be attained in the process was 14000, 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 synthesis of nanocomposites polylactic acid of increased molecular weight and crystallinity .
Detailed description of the invention
Accordingly, the present invention provides a polylactic acid-clay nanocomposite of high crystallinity and molecular weight. In one embodiment of the invention, the invention provides a polylactic acid-clay nanocomposite with high crystallinity and molecular weight, the molecular weight being in the range of around 100000 to 200000 and crystallinity in the range of around 75% to 100%.
In another embodiment of the invention, there is provided a process for preparing polylactic acid-clay nanocomposite of high molecular weight and crystallinity, the process comprising solid state polymerization of a dispersion of a lactic acid prepolymer and a clay resulting in around 2 to 7 fold increase in the molecular weight.
In a further embodiment of the invention, the invention provides a dispersion of lactic acid prepolymer and a clay, the prepolymer having a molecular weight in the range of 10000 to 60000 and crystallinity in the range of 40 % to 70 % and clay present in the range, 0.5% to 10%, preferably in the range, 1% to 5% by weight, either in the intercalated or exfoliated form, the dispersion being capable of undergoing around 2 to 7 fold increase in molecular weight on further polymerization in the solid state.
In yet another embodiment, the invention provides a process for preparing a dispersion of a lactic acid prepolymer and clay, the process comprising intercalation followed by melt polymerization of a lactic acid oligomer in a clay.
"b

The preparation of polylactic acid-clay nanocomposite with high molecular weight and crystallinity essentially involves the following steps.
A. First, lactic acid is oligomerized under stepwise increase in vacuum, to yield an
oligomer with average degree of polymerization not less than 5.
B. Then, a dispersion of lactic acid prepolymer and clay (PrePLA-CNC) is formed
by polymerization of the oligomer using tin chloride dihydrate and p-
toluenesulphonic acid as catalysts, in an organically modified clay. The
polymerization temperature may vary in the range of 120°C to 200°C.
C. In the third step, the PrePLA-CNC is further polymerized in the solid state, at
temperature(s) lower than its melting point, resulting in several-fold increase in
molecular weight, within a period of around 10 hours.
Lactic acid used for preparing the dispersion of the present invention is used either in the form of L-lactic acid , D-Lactic acid or as a combination of both (i.e., as a racemic mixture) in solution with a hydroxylic medium such as water or other solvent such as methanol, ethanol, propanol, butanol, isopropanol, or the like, or mixtures thereof. The source of lactic acid could be an ester of lactic acid, such as methyl lactate, ethyl lactate, propyl lactate, butyl lactate, isopropyl lactate, or the like or mixture thereof. Polymerization of lactic acid is optionally carried out in a mixture with one or more other hydroxycarboxylic acid. Exemplary hydroxycarboxylic acids include lactic acid, glycolic acid, 3-hydroxybutyric acid, 4-hydroxy butyric acid, 3-hydroxyvaleric acid, 5-hydroxyvaleric acid or the like.
The lactic acid used in the present invention may generally be defined by the formula:
o
H || HO—C—C—OR
CH3
wherein R can be H, C1-C4 linear or branched alkyl.
k

Initially, the lactic acid is converted to an oligomer. During the oligomerisation process, the linear or branched alkoxy or/and hydroxyl group leaves from one end of the lactic acid and/or lactate molecule, while a hydrogen is cleaved from the hydroxyl group at the opposite end of another lactate molecule and/ or growing polymer chain. The overall oligomerization process can be represented as follows:
0
H II
n HO—C—C—OR ► 0 CH30 O
I H || / I || \ ||
c H3 HO—C—C-hO—C—C-fO—CH—C—OR
Lactic acid (R=H) | \ H / ? I
Ester of lactic acid (R=C,-C4) CH3 " CH3 +n-lROH
The condensation reaction by-products of the oligomerisation process include water and compounds of the general formula ROH wherein R is either hydrogen or a C1-C4 linear or branched alkyl. In the oligomerization reactor, sufficient water or solvent and condensation byproducts such as water, ethanol, methanol, propanol and the like are removed and collected into the receiver at a temperature near 4°C, during the course of which the lactic acid oligomerizes to form low molecular weight lactic acid oligomer. Oligomerization begins in inert atmosphere in the temperature range 100°C to 180°C, preferably in the range of 130°C to 160°C. During the oligomerization process, pressure is reduced in steps from 1000 mm Hg up to 0.0001 mm Hg, preferably from 1000 mm up to 0.01 mmHg. The oligomer has an average molecular weight, less than around 5000, preferably around 200 to 3000, and more preferably around 400 to 2500.
The lactic acid oligomer is utilized to prepare a dispersion of a lactic acid prepolymer and clay. For this, the clay is added under inert atmosphere and stirred with the oligomer. The mixture of oligomer and clay (the clay being present in the range, 0.5% to 10%, preferably in the range, 1% to 5% by weight) is melt polymerized in presence of a catalyst, in the temperature range of 120°C to 200°C, preferably in the range of 150°C to 180°C. During the process, pressure is reduced in steps from 1,000 mm Hg up to 0.0001 mm Hg, preferably from 1,000 mm Hg up to 0.01 mm Hg. PrePLA-CNC so formed has
6

an average molecular weight, less than around 70,000, preferably around 1,000 to 60,000, and more preferably around 20,000 to 50,000.
The average molecular weight of the PrePLA-CNC obtained by the process of this invention varies, depending on the kind and amount of the catalysts, clay loading, reaction temperature, reaction time, type of modifier present in the clay and the method of treatment of clay with the modifier. PrePLA-CNC can also be synthesized in the absence of a catalyst. However, the reaction rate is increased by the use of a catalyst.
The catalysts which are used include metals of group II, III, IV or V in the periodic table, oxides of these metals or salts of these metals. Exemplary catalysts include zinc powder, tin powder, aluminum, magnesium and other metals; tin oxide, antimony oxide, zinc oxide, aluminum oxide, magnesium oxide, titanium oxide, and other metal oxides; stannous chloride, stannous bromide, antimony fluoride, zinc chloride, magnesium chloride, aluminum chloride and other metal halides; tin sulfate, zinc sulfate, aluminum sulfate and other metal sulfates; zinc carbonate, magnesium carbonate and other metal carbonates; zinc acetate, tin lactate, zinc lactate, and other metal organic carboxylates; tin trifluoromethanesulfonate, zinc trifluoromethanesulfonate, tin methanesulfonate, tin p-toluenesulfonate and other metal organic sulfonates, p-toluenesulfonic acid with metal halides, titanium isopropoxide and other metal alkoxides; or ion exchange resins such as Amberlite. The amount of catalyst used for polymerization is preferably around 0.00001 to 10% by weight, more preferably around 0.001 to 2% by weight, of the hydroxycarboxylic acid or oligomer thereof.
The clays 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 is selected from a group that includes montmorillonite, nontronite, beidellite, volkonskoite, Laponite, synthetic hectorite, natural hectorite, saponite, sauconite, magadite, hydrotalcite and kenyaite.
6

The cationic clay materials used in the present invention are those treated with at least one quarternary ammonium ion of the formula:
+N*RiR2R3R4 or ^RJlbRcRd wherein:
Ri, R2, R3 and R4 are independently selected from a group consisting of a saturated or unsaturated Ci to C22 hydrocarbon, substituted hydrocarbon and branched hydrocarbon. Ri and R2 optionally form an N,N-cyclic ether. Examples of groups represented by Ri, R2, R3 and R4 include saturated or unsaturated alkyls, including alkylenes; 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 Ri, R2, R3 and R4 is hydrogen. Ra, Rb and Re are hydrogens (H) and Rd includes a carboxylic acid moiety. The treatment of clay, is preferably from about 30 milliequivalents/lOOg clay to about 200 milliequivalents/lOOg clay.
The dispersion of the present invention optionally includes various components which are additives commonly employed with polymers. Such 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 dispersion of polylactic acid prepolymer and clay 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 nanocomposite, in the range between glass transition temperature and melting point of pre poly lactic acid nanocomposite, 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
7

temperature may be kept constant during the reaction, or alternately, a stepwise change in temperature may be carried out. Vacuum is maintained in the range of 100 mm Hg to 0.0001 mm Hg, preferably from 10 mm to 0.001 mm Hg. The dispersion is capable of a 2 to 7 fold increase in molecular weight, on polymerization in the solid state, and has a polydispersivity index in the range of around 1.0 to 1.5, molecular weight in the range of around 1,000 to 60,000, preferably in the range of around 20,000 to 50,000 and crystallinity in the range of around 40 % to 60 %. The dispersion contains the clay in the range, 0.5% to 10%, preferably in the range, 1% to 5% by weight, either in the intercalated or exfoliated form. Solid state polymerization may be performed for long reaction times, as high as 48 hours, or for reaction times less than 20 hours. The reaction is preferably performed for 10 hours.
The Polylactic acid-clay nanocomposites of the present invention have molecular weight in the range of around 100000 to 200000, crystallinity in the range of around 75% to 100%, polydispersivity index in the range of around 1.0 to 2.0, onset degradation temperature in the range of around 200°C to 300 °C and melting point in the range of around 100°C to 200 °C.
The clays used in the following examples were Cloisite 15A, Cloisite 20A and Cloisite 30B purchased from Southern Clay Product Inc. (Texas, U.S.A.). All the three clays were quarternary ammonium salt modified natural montmorrilonite, the modifier concentration being 125 meq/lOOg clay, 95 meq/lOOg clay and 90 meq/lOOg clay and the interlayer spacing (dooi) of the clay being 31.5A, 24.2A and 18.5A, respectively. In the examples 2 to 7, the clay was used in an amount in the range, 0.5% to 10%, preferably in the range, 1% to 5% by weight. Also the reactions in examples 1 to 7 were continued till 100% conversion was reached.
The molecular weight determination of the polymers and the nanocomposites in the following examples was carried out by a Waters GPC (Waters 2414 RI Detector) with
$

PL-gel, 5(i Mixed-D (2> The melting temperature (Tm) and crystallinity (Xc) of neat poly lactic acid
nanocomposite were determined by a NETZSCH STA 409PC Luxx Differential
Scanning Calorimeter in the temperature range of 20°C to 300°C at the rate of
10°C/minute.
Optical purity (% L- content) was measured using Jasco DPI-370 digital polarimeter, calibrated with 5% fructose solution [a] 589nm = -89°.
XRD analyses was performed for the clays 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 (X), 0.154 nm. The samples have been scanned in continuous mode with a scan step size (20) of 0.017 and scan step time of 5.08 s in the range of 2° to 25°. SAXS analyses were performed for neat polylactic acid and its nanocomposites by using Anton Paar GmbH SAXS compact slit camera and PANalytical X-ray generator with Packard Imaging-Plate reader in line collimation mode. The X-ray generator was operated at 40 kV/30 mA. The samples were irradiated by Cu Ka radiation of wavelength (X) 0.154 nm for a sample exposure time of 15 minutes.
The Transmission Electron Microscope (TEM) images of poly lactic acid nanocomposites were obtained by performing bright field imaging using Tecnai G 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 a Leica EM KM R2 model ultramicrotome equipped with a glass knife.
°I

Preparation of lactic acid oligomer
Example 1
To a 3-necked tubular reactor, equipped with a condenser at one end, a receiver at the other end and a mechanical stirrer having screw type impeller, was added 374 g of lactic acid (90 % w/w solution in water). The solution was stirred at 30 rpm and heated to 150°C by temperature controlled tubular heater for two hours under nitrogen flow. Thereafter, stirring and heating were continued and the pressure was gradually reduced by applying vacuum over four hours. The molten reaction mixture was allowed to cool to room temperature to give 275 g of lactic acid oligomer with weight average molecular weight of 1477 Dalton and polydispersity index of 1.06.
Preparation of a dispersion of polylactic acid prepolymer and clay
Example 2
To a 3-necked tubular reactor, equipped with a condenser at one end, a receiver at the other end and a mechanical stirrer having screw type impeller, was added around 26 g of the oligomer, obtained in Example 1. The solution was stirred at 35 rpm and heated to 180°C by temperature controlled tubular heater for 15 minutes under nitrogen flow. Subsequently, 133 mg /?-toluenesulfonic acid and 158 mg tin chloride dehydrates were added. Thereafter, stirring and heating was continued and the pressure was gradually reduced over two hours. Furthermore, 263.5 mg C20A clay along with 20 mg p-toluenesulfonic acid and 23 mg tin chloride dehydrate and another 263.5 mg C20A clay were added, and further, polymerization was carried out for two hours under reduced pressure. The molten reaction mixture was then allowed to cool to room temperature to give 22 g of PrePLA-CNC with weight average molecular weight of 21,000 Dalton and polydispersity index of 1.38.
Fig 1 is the TEM image of the PrePLA-CNC prepared by example 2. The dark lines in the TEM image correspond to the clay layers and bright lines correspond to the prepolymer. It could be seen that the in most regions of the picture, the dark and bright


lines alternate, indicating a well interspersed mixture of the clay and polymer in an intercalated morphology.
Example 3
To a 3-necked tubular reactor, equipped with a condenser at one end, a receiver at the other end and a mechanical stirrer having screw type impeller, was added around 20 g of oligomer, obtained by a method of Example 1. The solution was stirred at 30 rpm and heated to 180°C by temperature controlled tubular heater for 15 minutes under nitrogen flow. Subsequently, 102.5 mgj?-toluenesulfonic acid and 121.8 mg tin chloride dehydrate were added. Thereafter, stirring and heating was continued and the pressure was gradually reduced over two hours. Subsequently, 203 mg C30B clay along with 21 mgp-toluenesulfonic acid and 23 mg tin chloride dehydrate and another 203 mg C20A clay were added, and and further polymerization was carried out for two hours under reduced pressure. The molten reaction mixture was then allowed to cool to room temperature to give 16g of a dispersion of prepolymer and clay having an exfoliated morphology, weight average molecular weight of 34,900 Dalton and polydispersity index of 1.46.
Fig 2 is the TEM image of PrePLA-CNC prepared by example 3. The dark regions in the TEM image correspond to the clay while bright regions correspond to the prepolymer. It could be seen from the figure that the dark and bright regions, indicate an effective dispersion of the clay and polymer, and that the clay platelets are exfoliated.
Example 4
To a 3-necked tubular reactor, equipped with a condenser at one end, a receiver at the other end and a mechanical stirrer having screw type impeller, was added around 21.3 g. of oligomer, obtained method of Example 1. The solution was stirred at 30 rpm and heated to 180°C by temperature controlled tubular heater for 15 minutes under nitrogen flow. Subsequently, 107.8 mg/>-toluenesulfonic acid and 128 mg tin chloride dehydrate were added. Thereafter, stirring and heating were continued and the pressure was gradually reduced over two hours. Then, 213.5 mg C15A clay was added twice and
U

further polymerization was carried out for two hours under reduced pressure. The molten reaction mixture was allowed to cool to room temperature to give 17 g of PrePLA-CNC having weight average molecular weight of 44,000 Dalton and polydispersity index of 1.40.
Solid state polymerization (SSP) of a dispersion of polylactic acid prepolymer and clay
Example 5
Solid state polymerization was performed for 10 hours at 150°C using PrePLA-CNC, prepared by the method illustrated in examples 2, 3 and 4. The molecular weights, crystallinity, etc., were determined before and after solid state polymerization. The properties of the material before and after solid state polymerization, are given in tables 1 and 2.
Example 6
Solid state polymerization was performed for 5 hours at 150°C using PrePLA-CNC, prepared by the method illustrated in examples 2, 3 and 4. The molecular weights, crystallinity, etc., were determined before and after solid state polymerization. The properties of the material before and after solid state polymerization, are given in tables 1 and 2.
Fig 3 shows the XRD peaks corresponding to the clay (C30 B) and the corresponding peaks of the PrePLA-CNC formed in example 3. The XRD graph of polylactic acid-clay nanocomposite formed in example 6 is also shown. It could be observed that in the XRD graph of Pre-PLA-CNC as well as that of polylactic acid - nanocomposite (PLA-NC), the peaks corresponding to the clay have disappeared, while new peaks corresponding to the nanocomposite have appeared at a lower 2D.
/ 2-

Example 7
Solid state polymerization was performed for 10 hours at 160°C using PrePLA-CNC, prepared by the method illustrated in examples 2, 3 and 4. The molecular weights, crystallinity, etc., were determined before and after solid state polymerization. The properties of the material before and after solid state polymerization, are given in tables 1 and 2.
Fig 4 (a) shows the SAXS graphs corresponding to polylactic acid-clay nanocomposites (PLA-NC) with different clays (CI5A, C20A, C30B). The SAXS graphs show that the nanocomposites prepared from clays C15A and C20A, have an intercalated morphology, while the nanocomposite prepared from clay C30B, has an exfoliated morphology. Fig 4 (b) shows the XRD graphs for the nanocomposites as well as the XRD graphs of the clays used to prepare the nanocomposites. Fig 4(c) compares the SAXS graph of the clay C15A with that of the corresponding nanocomposite. The disappearance of the clay peaks (especially those at lower angles) and the appearance nanocomposite peaks (at still lower angles) in the XRD and SAXS graphs (Fig 4 (b) and Fig 4(c)) are indicative of nanocomposite formation.
The molecular weight and crystallinity before and after SSP of PrePLA-CNC prepared in examples 2, 3 and 4 are given in the following Table 1.
I?

Table 1: Molecular weight (Mw) and crystallinity (%Xc) before and after SSP
ExampleNo. PrePLA-CNC of exampleNo SSP (hrs) time SSP temp (°C) Mw before Mw after %xcbefore SSP %xcafter SSP
5 Example 2 10 150 21000 137700 45 78
5 Example 3 10 150 34900 99400 49 86
5 Example 4 10 150 44000 123100 51 88
6 Example 2 5 150 21000 107500 45 81
6 Example 3 5 150 34900 77500 49 81
6 Example 4 5 150 44000 72000 51 76
7 Example 2 10 160 21000 136,500 45 94
7 Example 3 10 160 34900 93,000 49 83
7 Example 4 10 160 44000 99990 51 84
It can be seen from Table 1 that there is considerable enhancement of molecular weight (2 to 7 times increase) and crystallinity of PrePLA-CNC on solid state polymerisation. The weight average molecular weight (Mw), crystallinity (% Xc), polydispersivity index (PDI), onset degradation temperature (ODT) and melting point (MP) of the polylactic acid-clay nanocomposites are given in the following Table 2.
"t

Table 2: Properties of polylactic acid-clay nanocomposite (PLA-NC)

ExampleNo. PrePLA-CNCof SSP (hrs) SSP temp (°C) Mw %xc PDI ODT (°C) MP (°Q
5 Example 2 10 150 137700 78 1.46 252 181
5 Example 3 10 150 99400 86 1.39 248 176
5 Example 4 10 150 123100 88 1.23 260 177
6 Example 2 5 150 107500 81 1.41 251 178
6 Example 3 5 150 77500 81 1.36 248 172
6 Example 4 5 150 72000 76 1.23 255 166
7 Example 2 10 160 136,500 94 1.48 244 180
7 Example 3 10 160 93,000 83 1.39 232 174
7 Example 4 10 160 99990 84 1.47 246 175
The high values of molecular weight (Mw), crystallinity (% Xc), onset degradation temperature (ODT) and melting point (MP), are indicative of the high quality of the polymer-clay nanocomposite. The improved properties of the nanocomposite may be attributed to the enhanced dispersion of the polymer and clay achieved by carrying out polymerization inside the clay galleries and further polymerizing the dispersion so formed in the solid state.
Having described the preferred embodiments of the invention, it is to be understood that the invention is not limited to those precise embodiments and various changes and
|5

modifications could be effected by one skilled in the art without departing from the spirit or scope of the present invention, as defined in the claims given below.

WE CLAIM:
1. Polylactic acid-clay nanocomposite having molecular weight in the range of around 100000 to 200000, crystallinity in the range of around 75% to 100%, polydispersivity index in the range of around 1.0 to 2.0, onset degradation temperature in the range of around 200°C to 300 °C and melting point in the range of around 100°C to 200 °C.
2. A process for preparing the nanocomposite as claimed in claim 1, the process comprising solid state polymerization of an effective dispersion of lactic acid prepolymer and clay at a temperature in the range of around 100°C to 180°C, preferably in the range of around 140°C to 170°C, in the presence of a metal based catalyst and preferably for a period of not greater than 20 hours, the dispersion being capable of 2 to 7 fold increase in molecular weight on solid state polymerization
3. A dispersion of polylactic acid prepolymer and clay, capable of a 2 to 7 fold increase in molecular weight, on polymerization in the solid state, the dispersion having a polydispersivity index in the range of around 1.0 to 1.5, molecular weight in the range of around 1,000 to 60,000, preferably in the range of around 20,000 to 50,000 and crystallinity in the range of around 40 % to 60 %, the clay being present in the range, 0.5%) to 10%>, preferably in the range, 1%> to 5% by weight, either in the intercalated or exfoliated form.
4. The dispersion as claimed in claim 3 optionally comprising additional components selected from the group consisting of comonomers, surfactants, nucleating agents, coupling agents, fillers, impact modifiers, chain extenders, plasticizers, compatibilizers, colorants, mold release lubricants, antistatic agents, pigments, and fire retardants.
17

5. A process for preparing an effective dispersion of polylactic acid prepolymer and clay, the process comprising both, intercalation and exfoliation of the clay with a lactic acid oligomer and a metal based catalyst followed by melt polymerization at around 120°C to 200°C of the lactic acid oligomer in the clay.
6. The process as claimed in claim 5 wherein the oligomer is formed from monomers selected from the isomers D- Lactic acid, L-lactic acid and a racemic mixture of the isomers.
7. The process as claimed in any one of the claims 5 to 6 wherein the catalyst is present in an amount of 0.00001 to 10 % by weight, preferably in an amount of 0.001 to 2 % by weight.
8. The process as claimed in any one of the claims 5 to 7, wherein a metal exists preferably in the form its oxide or salt, optionally along with p-toluenesulfonic acid, the metal being selected from group II, group III, group IV or group V of the periodic table.
9. The process as claimed in any one of the claims 5 to 8 wherein the dispersion has a polydispersivity index in the range of around 1.25 to 1.5, molecular weight in the range of around 1000 to 60000, preferably in the range of around 20000 to 50000 and crystallinity in the range of around 40 % to 60 %, the clay being present in the range, 0.5% to 10%, preferably in the range, 1% to 5% by weight, either in the intercalated or exfoliated form.
IF

10. The process as claimed in any one of the claims 2, 5, 6, 7, 8 or 9, 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. Dated this 4th day of April 2007

(Jose M A)
ofKhaitan&Co
Agent for the Applicants
II

Documents:

677-mum-2007-abstract(4-4-2007).pdf

677-mum-2007-abstract(granted)-(12-1-2011).pdf

677-mum-2007-cancelled pages(10-11-2010).pdf

677-MUM-2007-CLAIMS(AMENDED)-(10-11-2010).pdf

677-mum-2007-claims(granted)-(12-1-2011).pdf

677-MUM-2007-CLAIMS(MARKED COPY)-(10-11-2010).pdf

677-mum-2007-claims.doc

677-mum-2007-claims.pdf

677-MUM-2007-CORRESPONDENCE(24-1-2011).pdf

677-MUM-2007-CORRESPONDENCE(27-10-2009).pdf

677-mum-2007-correspondence(27-6-2007).pdf

677-MUM-2007-CORRESPONDENCE(6-4-2009).pdf

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

677-mum-2007-correspondence(ipo)-(24-1-2011).pdf

677-mum-2007-correspondence-received.pdf

677-mum-2007-corresponesce(3-7-2007).pdf

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

677-mum-2007-description(granted)-(12-1-2011).pdf

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

677-mum-2007-form 18(3-7-2007).pdf

677-mum-2007-form 2(granted)-(12-1-2011).pdf

677-mum-2007-form 2(title page)-(amended)-(3-7-2007).pdf

677-mum-2007-form 2(title page)-(complete)-(4-4-2007).pdf

677-mum-2007-form 2(title page)-(granted)-(12-1-2011).pdf

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

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

677-mum-2007-form-1.pdf

677-mum-2007-form-2.doc

677-mum-2007-form-2.pdf

677-mum-2007-form-3.pdf

677-MUM-2007-OTHER DOCUMENT(10-11-2010).pdf

677-MUM-2007-REPLY TO EXAMINATION REPORT(10-11-2010).pdf


Patent Number 245297
Indian Patent Application Number 677/MUM/2007
PG Journal Number 02/2011
Publication Date 14-Jan-2011
Grant Date 12-Jan-2011
Date of Filing 04-Apr-2007
Name of Patentee INDIAN INSTITUTE OF TECHNOLOGY,BOMBAY
Applicant Address Powai, Mumbai.
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 400 076
PCT International Classification Number C0843/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA