DESC:FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
AND
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
POLYPROPYLENE HAVING IN SITU GENERATED METAL SALTS AND METHOD OF ITS MANUFACTURE

RELIANCE INDUSTRIES LIMITED
an Indian Company of
3rd Floor, Makers Chamber-IV
222, Nariman Point, Mumbai – 400021
Maharashtra, India.

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD
The present disclosure relates to polypropylene having in situ generated metal salts and method of its manufacture.
BACKGROUND
It is a known practice to add nucleating agents to achieve a higher crystallinity in the polymers, more so for polypropylene (PP). These nucleating agents provide nucleation sites for crystal growth during molding or fabrication. Polymers containing such nucleating compounds crystallize at a much faster rate than the virgin polymers and there is an observable increase in the crystallization temperature which further results in reduced cycle times.
Metal salts of various aromatic carboxylic, dicarboxylic or higher polycarboxylic acids, their corresponding anhydrides are known nucleating agents. Various metal salts like sodium benzoate, aluminium p-tert-butyl benzoate, aluminium benzoate and the like are used as nucleating agents for polypropylene. Among the metal salts, sodium benzoate (NaBz) is the most commonly used low cost nucleating agent for compounding polypropylene.
However, while compounding of polypropylene, sodium benzoate is used in combination with calcium stearate that leads to an interchange of calcium ions from stearate with the sodium ions from the nucleating agent, which renders nucleating agent ineffective. Non-ionic acid neutralizers, such as dihydrotalcite used in conjunction with nucleating agents such as sodium benzoate, reduce the interchange of the ions. However, other problems such as dispersion, agglomeration of nucleating agents lead to inconsistent nucleation, stiffness and impact variation in the polypropylene.
The common method of incorporating nucleating agents into the polymer is by mixing finely divided nucleating agents with finely divided solid polymer. Better results can be obtained by dissolving the finely divided nucleating agents in a solvent and adding the solvent containing nucleating agents to the polymer and evaporating the solvent from the intimate mixture of the polymer and the nucleating agents. In spite of all these methods, sodium benzoate has dispersion problems that do not allow sodium benzoates efficient use because of which polypropylene has a marked haze.
Hence, there is a felt need to provide a method of generating metal salts onto polypropylene.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide a method for generating metal salts onto polypropylene in situ.
Another object of the present disclosure is to provide better dispersion of metal salt onto the polypropylene in situ.
Yet another object of the present disclosure is to provide a method of generating polypropylene with a metal salt in situ that prevents any agglomeration of the metal salts in the polymer during processing.
Still another object of the present disclosure is to provide a method of generating polypropylene with a metal salts in situ that produces polypropylene with high crystallization temperatures.
Other objects and advantages of the present disclosure will be more apparent from the following description which is not intended to limit the scope of the present disclosure.

SUMMARY
The present disclosure relates to polypropylene having in situ generated metal salts, wherein the polypropylene is at least one selected from the group consisting of homopolymer, random copolymer, block copolymer, and graft copolymer. In an embodiment of the present disclosure, the polypropylene is in the form of beads, or powder.
In an embodiment of the present disclosure, the metal salts are generated in situ inside the pores, and in situ on the surface of the polypropylene.
In an embodiment of the present disclosure, the metal salts are strong nucleating agents.
In an embodiment of the present disclosure, the polypropylene having in situ generated metal salts is used for providing a polymer composition having high crystallization, low haze, and enhanced mechanical properties.
The present disclosure further relates to a method of synthesizing metal salts in situ onto polypropylene. The method comprises addition of at least one organic acid dropwise to polypropylene to form an acid-polypropylene complex. The acid-polypropylene complex is neutralized with the help of at least one alkali by introducing the alkali dropwise onto the acid-polypropylene complex, followed by sub-atmospheric drying to obtain metal salt generated in the polypropylene in situ.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The present disclosure will now be described with the help of the accompanying drawing, in which:
Figures 1(A), 1(B) and 1(C) depict the SEM micrographs of the porosity in polypropylene spheribeads: 1(A) at the outer surface; 1(B) at the cross section; and 1(C) spheribeads showing furrows;
Figures 2(A) and 2(B) depict the SEM micrographs of in situ generated sodium benzoate polypropylene spheribeads at 50 µm scale and 2 µm scale respectively;
Figures 3(A), 3(B) and 3(C) depict the SEM micrographs of spherical and oval particles of sodium benzoate generated by the method of the present disclosure inside the pores of polypropylene spheribeads;
Figure 4 depicts an SEM micrograph of in situ generated sodium benzoate particles extracted from the polypropylene spheribeads;
Figures 5(A), 5(B), 5(C) and 5(D) depict optical microscope pictures of 5(A) polypropylene and polypropylene compounded with 1000 ppm of metal nucleating agents, 5(B) iNaBz, 5(C) iNaACC, and 5(D) iNaADC;
Figure 6 depicts an EDXA graph of in situ generated Sodium Benzoate;
Figure 7 depicts a DSC thermogram of in situ generated Sodium Benzoate (iNaBz) onto polypropylene homopolymer; and
Figure 8 depicts a DSC thermogram of in situ generated sodium salt of 1-amino-1-cylcohexane carboxylic acid (iNaACC) onto polypropylene homopolymer.
DETAILED DESCRIPTION
Metal salt nucleating agents are a common type of nucleating agents used to compound polypropylene to increase its crystallinity. However, their dispersion into polypropylene is achieved with difficulty. They are also known to agglomerate during compounding which adds to their inefficient dispersion.
The method of the present disclosure aims at providing a better method of dispersion of metal salt nucleating agents onto polypropylene. The disclosure, therefore, envisages preparing metal salts in situ onto polypropylene for an efficient dispersion of the metal salts.
In one aspect of the present disclosure, there is provided a polypropylene having in situ generated metal salts, wherein the polypropylene can be at least one selected from the group consisting of homopolymer, random copolymer, block copolymer, and graft copolymer.
In an embodiment of the present disclosure, the polypropylene can be in the form of beads, or powder.
In an embodiment of the present disclosure, the metal salts are generated in situ inside the pores of the polypropylene.
In an embodiment of the present disclosure, the metal salts are generated in situ on the surface of said polypropylene.
In an embodiment of the present disclosure, the metal salts are strong nucleating agents.
In an embodiment of the present disclosure, the polypropylene is used for providing a polymer composition having high crystallization, low haze, and enhanced mechanical properties.
In another aspect of the present disclosure, a method of synthesizing metal salts in situ onto polypropylene is provided. The method comprising the following steps:
In the first step, at least one organic acid is added dropwise to polypropylene to form an acid-polypropylene complex.
The organic acid is added to the polypropylene in a dropwise manner under continuous stirring at a temperature in the range of 20 °C to 40 °C and the temperature is further raised to 50 °C to 70 °C and stirred for a time period in the range of 10 minutes to 100 minutes to obtain an acid-polypropylene complex. The organic acid added to the polypropylene gets absorbed on the surface and inside the pores of the polypropylene to obtain an acid-polypropylene complex.
The organic acid used to prepare the acid-polypropylene complex can be an organic acid solution prepared by dissolving the organic acid with at least one first fluid medium.
In an embodiment of the present disclosure, the organic acid can be at least one selected from the group consisting of benzoic acid, cyclohexane aminocarboxylic acid, adamantane carboxylic acid, adamantane dicarboxylic acid, adamantane acetic acid, acenapthene carboxylic acid, boronic acid, cyclohexane carboxylic acids, pimelic acid, and azelaic acid.
In an embodiment of the present disclosure, the first fluid medium can be at least one selected from the group consisting of water, ketone, benzene, toluene, xylene, methanol, ethanol, and isopropanol. In accordance with one embodiment of the present disclosure, the first fluid medium can be ethanol.
The polypropylene used in the present disclosure can be in the form of spheribeads and powder. The polypropylene can be at least one selected from the group consisting of homopolymer, random copolymer, block copolymer, and graft copolymer having an average molecular weight in the range of 10,000 Da to 20,00,000 Da, preferably, from 30,000 Da to 3,00,000 Da. The co-monomer used in the random, block, and graft copolymers is at least one belonging to the group of C2-C6 alpha-olefins. The amount of co-monomer can be in the range of 1 mol% to 8 mol% of the copolymer.
In accordance with one embodiment of the present disclosure, the polypropylene is a homopolymer and in the form of spheribeads. The spheribeads have voids, furrows and crevices. When the spheribeads are immersed in the organic acid, the acid creeps into these crevices to obtain acid coated polypropylene. The acid coated polypropylene is further neutralized with a metal hydroxide solution, to form the metal salts in situ in those crevices which results in an efficient dispersion of the metal salts nucleating agent.
In the second step, the acid-polypropylene complex is neutralized with the help of at least one alkali by introducing the alkali dropwise onto the acid-polypropylene complex, followed by sub-atmospheric drying to obtain metal salt generated in said polypropylene in situ.
In an embodiment of the present disclosure, the alkali can be at least one selected from the group consisting of sodium hydroxide, and potassium hydroxide.
The alkali used to neutralize the acid-propylene complex can be an alkali solution prepared by dissolving the alkali with at least one second fluid medium.
The second fluid medium can be at least one selected from the group consisting of water, and ethanol. In accordance with one embodiment of the present disclosure, the second fluid medium can be water.
In an embodiment of the present disclosure, the sub-atmospheric drying can be carried out under sub-atmospheric pressure in the range of 0.05 atm to 0.9 atm, and at a temperature in the range of 50 °C to 110 °C. In accordance with one embodiment of the present disclosure, a rotary evaporator can be used for drying the wet metal salt generated in the polypropylene in situ.
The amount of metal salt generated in the polypropylene in situ is quantitatively measured by gravimetry and qualitatively by Energy-dispersive X-ray spectroscopy (EDXA).
The metal salt generated in the polypropylene in situ contains the amount of metal salt in the range of 50 ppm to 20,000 ppm by weight of the metal salt generated in the polypropylene in situ.
The method of the present disclosure for generating metal salt in the polypropylene in situ further includes at least one additive selected from the group consisting of acid scavengers, stabilizers, lubricants, colorants, and antioxidants.
In accordance with an embodiment of the present disclosure, the acid scavenger can be at least one selected from the group consisting of hydrotalcite, and calcium stearate; the stabilizer can be at least one selected from the group consisting of 2-hydroxybenzophenone UV absorber, hydroxyphenol benzotriazole UV absorber, and meta stearate; the lubricant can be at least one selected from the group consisting of waxes, glycerol stearate, and metallic stearate; and the antioxidant can be at least one selected from the group consisting of Pentaerythritol Tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), octadecyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate, and Tris(2,4-ditert-butylphenyl) phosphite. In accordance with one embodiment of the present disclosure, the acid scavenger can be hydrotalcite.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following laboratory scale experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial/commercial scale.
EXPERIMENTS
EXPERIMENT-1A (Comparative Example)
Synthesis of Sodium Benzoate (REF1)

Sodium Benzoate was synthesized by dissolving 2 g of NaOH (0.05M) in 10 ml of water in a 250 ml round bottom flask and heated to 40 °C while stirring in an oil bath to obtain a sodium hydroxide solution. The pH of the solution was found to be 13. 6.1 g of benzoic acid (0.05 M) was added slowly to the sodium hydroxide solution till the pH came down to 6 due to reaction between the acid and the alkali and the reaction was continued for 2 hours under stirring. Water was then removed under vacuum to yield 8 g of white solid of sodium benzoate. Melting point of sodium benzoate was determined and was found to be >325 °C.
Experiment-1B: Direct Addition of Sodium Benzoate to Polypropylene homopolymer (REF2)
100 g of polypropylene homopolymer in the form of spheribeads were taken in a 250 ml three necked round bottom flask equipped with a mechanical stirrer, N2 gas inlet tube and reflux condenser. 1.2 g of sodium benzoate prepared in experiment-1A was dissolved separately in 15 ml of water to obtain a sodium benzoate solution. The so obtained sodium benzoate solution was added in a dropwise manner to the polypropylene homopolymer at room temperature under stirring for 30 minutes to get sodium benzoate solution absorbed on the surface and inside the pores of polypropylene homopolymer spheribeads. The temperature was further increased up to 100 °C of polypropylene solution and stirred for another 3.5 hours to obtain a product mixture comprising sodium benzoate-polypropylene homopolymer complex. The product mixture was transferred to a separate flask and the excess water was removed under vacuum in a rotary evaporator for 2 hours at 90 °C to obtain 101 g of sodium benzoate-polypropylene homopolymer (PPNaBz). The amount of sodium benzoate absorbed was estimated gravimetrically. DSC analysis of the reference sample is given in Table 1.
EXPERIMENT 2
In situ generation of Sodium Benzoate onto Polypropylene homopolymer
In situ generation of sodium benzoate onto polypropylene homopolymer spheribeads was carried out in a 500 ml three necked reaction vessel equipped with a mechanical stirrer, a N2 gas inlet tube and a reflux condenser. The three necked reaction vessel was charged with 200 g of polypropylene homopolymer spheribeads. 1.525 g of benzoic acid (0.0125M) was dissolved separately in 10 ml of ethanol to obtain a benzoic acid solution. The so obtained benzoic acid solution was added dropwise to the polypropylene homopolymer spheribeads to obtain a mixture. Further, the temperature of the so obtained mixture was increased to 60 °C and stirred for 30 minutes to obtain benzoic acid-polypropylene homopolymer complex. 0.5 g of sodium hydroxide (0.0125M) was dissolved separately in 15 ml of demineralized water to obtain sodium hydroxide solution. The so obtained sodium hydroxide solution was added in a dropwise manner to the so obtained benzoic acid-polypropylene homopolymer complex and refluxed at 80 °C for 3.5 hours to complete the neutralization reaction between the acid and alkali to obtain a product mixture comprising sodium benzoate generated onto polypropylene homopolymer in situ. The product mixture was then transferred to a separate reaction vessel and the excess water was removed under vacuum in a rotary evaporator maintained at 90 °C for 2 hours. 201.8 g of white colored in situ generated sodium benzoate (iNaBz) onto polypropylene homopolymer were obtained (PP iNaBz). The amount of sodium benzoate generated in situ was estimated gravimetrically. The iNaBz powder extracted by boiling PP iNaBz in water and drying in vacuum showed a melting point >320 °C confirming the formation of sodium benzoate onto polypropylene in situ. Various master batches of iNaBz onto polypropylene homopolymers were prepared containing 100 ppm to 20,000 ppm in situ generated sodium benzoate. In situ generation of NaBz was carried by using different solvents like benzene, toluene, ethanol, isopropanol, and acetone, and by varying temperature and time of the reaction. Various first fluid fluid mediums used for in situ generation of sodium benzoate and the nucleation efficiency of different iNaBz salts measured by DSC analysis are given in Table 1.
Evaluation of the nucleation efficiency
The nucleation efficiency of the in situ generated metal salts were evaluated by measuring crystallization temperature (Tc) using a differential scanning calorimeter (DSC). All the in situ generated metal salts onto polypropylene homopolymers, copolymers and random copolymers and various polyolefin compositions mentioned below containing them were subjected to nucleation efficiency test. In this test, samples were heated from 50 °C to 220 °C in DSC at a heating rate of 10 °C/minute and then held for 5 minutes at 220 °C and then the samples were cooled at the rate of 10 °C/minute till they reached the room temperature. The peak crystallization temperatures (Tc) and melting temperatures (Tm) were measured. The super cooling temperature ?T (?T = Tm – Tc) i.e., the difference between the melting temperature and crystallization temperature which is a function of overall rate of crystallization was measured. The smaller the difference between these temperatures, the greater is the rate of crystallization and hence the nucleation efficiency. The efficiencies of various in situ generated metal salt master batches were evaluated by measuring their Tm, Tc and ?T and are provided in Tables 1 to 3.
Table 1: Generation of sodium benzoate onto polypropylene (PP) homopolymer
Sr. No. Generation of NaBz onto PP First fluid medium Tm (oC) Tc (oC) ?T = Tm –Tc (oC)
1 PP - 165 119 46
2 PPNaBz(REF2) Water 165 121 44
3 PPiNaBz Water 165 128 37
4 PP iNaBz Ethanol 166 130 36
5 PP iNaBz Toluene 164 125 39
6 PP iNaBz Iso-propanol 166 129 37
7 PP iNaBz Acetone 165 126 39
8 PP iNaBz Iso-propanol + water mixture 166 131 35
9 PP iNaBz Ethanol 166 124 42
10 PP iNaBz Ethanol 166 128 38
Tm – Melting temperature, Tc – Crystallization temperature.
It is evident from table 1 that the super cooling temperature ?T (?T = Tm – Tc) i.e., the difference between the melting temperature and crystallization temperature, of PP iNaBz prepared by the process of the present disclosure is smaller than the PP NaBz prepared by the direct addition of sodium benzoate to polypropylene as given in experiment-1B. The smaller the difference between these temperatures, the greater is the rate of crystallization and hence the higher nucleation efficiency. Therefore, PP iNaBz prepared by the process of the present disclosure has the enhanced rate of crystallization and nucleation efficiency compared to PP NaBz.
In Situ generation of sodium benzoate onto polypropylene homopolymer, polypropylene copolymer, and polypropylene random copolymer
In situ generation of sodium benzoate onto polypropylene homopolymer (PPHP) with 3 melt flow index (MFI) (PPHP) was carried out by the process as given in experiment-2 of the present disclosure by taking 3.05 g of benzoic acid (0.025M), 1 g of sodium hydroxide (0.025M) and 200 g of polypropylene homopolymer to yield 203.9 g of in situ generated sodium benzoate (iNaBz) onto polypropylene homopolymer (PPHP iNaBz) having a peak crystallization temperature of 130 °C as compared to 114 °C for virgin PPHP.
In situ generation of sodium benzoate onto polypropylene copolymer (PPCP) powder containing 3 wt% ethylene with MFI 3.5 was carried out was carried out by the process as given in experiment-2 of the present disclosure by taking 200 g of PPCP, 200 ml of ethanol, 0.1525 g of benzoic acid (0.00125M) and 0.05 g of sodium hydroxide (0.00125M) to yield an in situ generated sodium benzoate (iNaBz) onto polypropylene copolymer (PPCP iNaBz) having a crystallization temperature of 128 °C against 115 °C for virgin PPCP.
In situ generation of sodium benzoate onto polypropylene random copolymer (PPRCP) powder with an ethylene content of 1.5 to 3 wt% and MFI 10 was carried out by the process as given in experiment-2 by taking 250 g of PPRCP, 185 ml of ethanol, 1.89 g of benzoic acid (0.0155M), 0.621 g of NaOH (0.0155M) which resulted in 252.05 g of in situ generated sodium benzoate (iNaBz) onto polypropylene random copolymer (PPRCP iNaBz) having a peak crystallization temperature of 118 °C against virgin PPRCP having a peak crystallization temperature of 110 °C.
Nucleation efficiency measured for in situ generated sodium benzoate onto polypropylene homopolymers, in situ generated sodium benzoate onto polypropylene copolymers and in situ generated sodium benzoate onto polypropylene random copolymers are given in Table 2.
Further, the reference samples PPHP NaBz (REF3) and PPRCP NaBz (REF4) were prepared with commercial NaBz samples by physical addition of sodium benzoate to polypropylene homopolymer, and polypropylene random copolymer as given in experiment-1B.
Table 2: Generation of sodium benzoate onto polypropylene homopolymer, polypropylene copolymer and polypropylene random copolymer
Sr. No. Generation NaBz PPHP / NaBz PPCP / NaBz PPRCP Tm (oC) Tc
(oC) Tm –Tc (oC)
1 PPHP3 165 114 51
2 PPHP NaBz (REF3) 165 123 42
3 PPHP iNaBz 165 130 35
4 PPCP 162 115 47
5 PPCP – iNaBz 164 128 36
6 PPRCP 148 110 38
7 PPRCP NaBz (REF4) 149 115 34
8 PPRCP iNaBz 148 118 30

It is evident from table 2 that the PPHP iNaBz, PPCP iNaBz, and PPRCP iNaBz prepared by the process of the present disclosure shows enhanced rate of crystallization and nucleation efficiency compared to PPHP NaBz, PPCP, and PPRCP NaBz.
Further, formation of in situ generated sodium benzoate onto polypropylene was established by extracting the in situ generated sodium benzoate by heating the in situ generated sodium benzoate onto polypropylene with water at 80 °C for 1 hour. After extraction, some amount of sodium benzoate remained on the polypropylene and some amount was extracted as a white powder which had a melting point of >320 °C compared to 124 °C for benzoic acid.
Analysis of the extracted in situ generated sodium benzoate white powder by EDXA, as depicted in Figure 6, indicated prominent Na peaks clearly indicating that sodium benzoate was generated in situ onto polypropylene by using the method of the present disclosure. Figure 7 shows a DSC analysis of iNaBz. The DSC thermogram showed sharp single melting and crystallization peak confirming the formation of iNaBz.
Scanning Electron Microscopic (SEM) studies of virgin polypropylene showed high porosity with pores, furrows and grooves on the surface and inside of polypropylene. The pores are not very deep as the pores can be seen in Figures 1(A), Figures 1(B), and Figures 1(C).
Figures 2(A) and Figures 2(B) depict sodium benzoate generated in situ on the surface, inside the pores, grooves, and furrows of polypropylene, which filled the polypropylene spheribeads with sodium benzoate. The sodium benzoate appears in the form of round smooth spherical balls without any pores. Figures 3(A), Figures 3(B), and Figures 3(C) depict the formation of the in situ generated sodium benzoate in the form of small spherical or flake-like particles inside the pores of polypropylene. Figure 4 shows the in situ generated sodium benzoate in the form of rod-like particles. Polarized optical micrographs in Figure 5B for iNaBz (1000 ppm) showed small spherulites compared to virgin polypropylene (Figure 5A).

EXPERIMENT-3 (Comparative experiment)
Synthesis of sodium-1-amino–1-cyclohexane carboxylate (NaACC) (REF5)
0.8 g of sodium hydroxide (0.02M) was taken in a 250 ml reaction vessel and dissolved in 20 ml of water and heated to 50 °C to obtain sodium hydroxide solution. To this sodium hydroxide solution, 2.86 g of 1-amino-1-cyclohexane carboxylic acid (0.02M) was added, followed by stirring for 2 hours while maintaining the temperature at 50 °C. Water was removed by drying under vacuum in a rotary evaporator to obtain 2.7 g of sodium salt of 1-amino-1-cylcohexane carboxylic acid.
The sodium salt of 1-amino-1-cyclohexane carboxylic acid was also prepared using a surfactant i.e., CTAB (Hexadecyl trimethyl ammonium bromide). A reaction vessel was charged with 5.369 g (0.0375M) of 1-amino -1-cyclohexane carboxylic acid in 375 ml of water on a hot plate and heated to 50 °C under stirring. 500 mg of CTAB as a surfactant was added and stirred for another 10 minutes to obtain a mixture. 1.5 g of NaOH (0.0375M) dissolved separately in 15ml of water was added to the mixture under stirring and the reaction was continued for 2 hours. After the reaction, water was removed slowly by evaporation which gave a fine powder of sodium salt of 1-amino-1-cyclohexane carboxylic acid with a yield of 6.75 g.
Experiment-4: In situ generation of sodium- 1-amino-1-cyclohexane carboxylate (iNaACC) onto polypropylene
In situ generated sodium salt of 1-amino-1-cyclohexane carboxylic acid was prepared by taking 200 g of polypropylene homopolymer spheribeads in a reaction vessel equipped with a mechanical stirrer, a N2 gas inlet tube and a reflux condenser. Further, 1.72 g of 1-amino-1-cyclohexane carboxylic acid (0.0120M) was dissolved separately in 70 ml of water to obtain 1-amino-1-cyclohexane carboxylic acid solution. The so obtained 1-amino-1-cyclohexane carboxylic acid solution was added in a dropwise manner to polypropylene spheribeads at 90 °C for 2 hours to obtain a 1-amino-1-cyclohexane carboxylic acid-polypropylene homopolymer complex. Further, 0.48 g of sodium hydroxide (0.012M) was dissolved separately in 5 ml of water to obtain sodium hydroxide solution. The so obtained sodium hydroxide solution was added in a dropwise manner to 1-amino-1-cyclohexane carboxylic acid-polypropylene homopolymer complex and stirred for 2 hours while maintaining the temperature at 90 °C to obtain a product mixture comprising in situ generated sodium salt of 1-amino-1-cylcohexane carboxylic acid onto polypropylene homopolymer. The product mixture was then transferred to a reaction vessel and dried under vacuum in a rotary evaporator at 90 °C to yield 202.2 g of in situ generated sodium salt of 1-amino-1-cylcohexane carboxylic acid (iNaACC) onto polypropylene homopolymer. DSC peak crystallization temperature of in situ generated sodium salt of 1-amino-1-cylcohexane carboxylic acid (iNaACC) onto polypropylene homopolymer was found to be 133 °C as shown in Figure 8. Polarized optical microscope photographs of the in situ generated sodium salt of 1-amino-1-cylcohexane carboxylic acid (1000 ppm) (as shown in Figure 5C) depicts small and uniform spherulites as compared to virgin polypropylene (Figure 5A), iNaBz (Figure 5B) and iNaADC (in situ generated sodium salt of adamantane-1-carboxylic acid) (Figure 5D).
In situ generated sodium salt of 1-amino-1-cyclohexane carboxylic acid onto polypropylene random copolymer was prepared by the process of experiment-4 of the present disclosure by taking 100 g of polypropylene random copolymer powder and adding 0.859 g of 1-amino-1-cyclohexane carboxylic acid (0.006M), 0.24 g of NaOH (0.006M) to yield 101.5 g of the in situ generated sodium salt of 1-amino-1-cyclohexane carboxylic acid onto polypropylene random copolymer with a peak crystallization temperature of 116 °C.
In situ generated sodium salt of 1-amino-1-cyclohexane carboxylic acid (ACCA) onto polypropylene copolymer was prepared by the process of experiment-4 of the present disclosure by taking 200 g of polypropylene copolymer powder, 200 ml of ethanol, 0.157 g (0.0011M) of 1-Amino-1-cyclohexane carboxylic acid, and 0.04 g of NaOH (0.0011M) to yield 200.17 g of in situ generated sodium salt of 1-amino-1-cyclohexane carboxylic acid onto polypropylene copolymer with a peak crystallization temperature of 119 °C.
EXPERIMENT-5
In situ generation of sodium-1-amino-1-cyclopentane carboxylate onto polypropylene
In situ generated sodium salt of 1-amino-1-cyclopentane carboxylic acid was prepared by the process of experiment-4 of the present disclosure by taking 100 g of polypropylene homopolymer, 0.774 g of 1-amino-1-cyclopentane carboxylic acid (0.006M) and 0.24 g of sodium hydroxide (0.006M) which resulted in 108.4 g of in situ generated sodium salt of 1-amino-1-cyclopentane carboxylic acid onto propylene homopolymer. The in situ generated sodium salt of 1-amino-1-cyclopentane carboxylic acid onto propylene homopolymer was found to have a peak crystallization temperature of 116 °C.
EXPERIMENT-6
In situ generation of sodium adamantane -1-carboxylate onto polypropylene
3.3184 g of adamantane-1-carboxylic acid (0.0046M) was dissolved in 10 ml of ethanol to obtain adamantane-1-carboxylic acid solution. The so obtained adamantane-1-carboxylic acid solution was added to 200 g of polypropylene spheribeads in a reaction vessel to obtain adamantane-1-carboxylic acid-polypropylene complex. The so obtained adamantane-1-carboxylic acid-polypropylene complex was stirred for 1 hour under N2, followed by refluxing at 80 °C. Further, 0.736 g of sodium hydroxide (0.0046M) was dissolved separately in 10 ml of water/ethanol mixture (1:9) to obtain sodium hydroxide solution. The sodium hydroxide solution was added to adamantane-1-carboxylic acid-polypropylene complex in a dropwise manner and stirred for 3 hours at 65 °C to obtain a product mixture. The product mixture was dried using rotary vacuum drier to obtain 200.92 g of in situ generated sodium adamantane -1-carboxylate (iNaADC) onto polypropylene. The iNaADC salt was found to have a melting point >325 °C. The peak crystallization temperature of the polypropylene having in situ generated sodium adamantane-1-carboxylate was found to be 129 °C. Figure 5D depicts polarized optical microscope photograph of iNaADC wherein iNaADC appears as small spherulites as compared to virgin polypropylene (Figure 5A) and iNaBz (Figure 5B).
In situ generation of adamantane-1-carboxylic acid onto polypropylene random copolymer powder was also carried by the process of experiment-4 of the present disclosure by taking 100 g of polypropylene random copolymer powder, 90 ml of ethanol, 0.901 g of adamantane-1-carboxylic acid (0.005 M), and 0.200 g of sodium hydroxide (0.005M) which yielded 101.1 g of in situ generated adamantane-1-carboxylic acid onto polypropylene random copolymer having a peak crystallization temperature of 112 °C.
EXPERIMENT-7
In situ generation of sodium salt of 1,3-adamantane dicarboxylate (NaADL) onto polypropylene spheribeads
Sodium salt of 1,3–adamantane dicarboxylic acid was generated in situ onto polypropylene spheribeads by charging 50 g of polypropylene spheribeads in a reaction vessel. 0.392 g of 1,3-adamantane carboxylic acid (0.00175M) was dissolved in 35 ml of ethanol to obtain 1,3-adamantane carboxylic acid solution. The so obtained 1,3-adamantane carboxylic acid solution was added to polypropylene spheribeads under nitrogen to obtain 1,3-adamantane carboxylic acid-polypropylene complex. The so obtained 1,3-adamantane carboxylic acid-polypropylene compex was stirred for 1 hour at 65 °C. Further, 0.14 g of sodium hydroxide (0.0035M) was dissolved in 10 ml of water/ethanol mixture (1:9) to obtain sodium hydroxide solution. The so formed sodium hydroxide solution was added slowly to the 1,3-adamantane carboxylic acid-polypropylene complex in a dropwise manner and heated for 3 hours at 65 °C to obtain a product mixture. The product mixture was dried using rotary vacuum drier to obtain 50.87 g of in situ generated sodium salt of 1, 3-adamantane dicarboxylic acid onto polypropylene. The NaADL had a melting point of >325 °C. The DSC peak crystallization temperature of the in situ generated sodium salt of 1,3-adamantane dicarboxylic acid onto polypropylene was found to be 119 °C.
EXPERIMENT-8
In situ generation of sodium-1-adamantane acetate onto polypropylene
0.8742 g of adamantane acetic acid (0.0045M) was dissolved in 10 ml of ethanol to obtain adamantane acetic acid solution. The so obtained adamantane acetic acid was added to 100 g of polypropylene spheribeads charged in a reaction vessel under nitrogen and mixed well for 1 hour at room temperature to obtain a mixture. The so obtained mixture was heated to 65 °C and stirred for 1 hour to obtain adamantane acetic acid-polypropylene complex. Further, 0.18 g of sodium hydroxide (0.0045 M) was dissolved in 10 ml of water/ethanol mixture (1:9) to obtain sodium hydroxide solution. The so obtained sodium hydroxide solution was added in a dropwise manner to adamantane acetic acid-polypropylene complex and refluxed for 3 hours at 90 °C to obtain a product mixture comprising in situ generated sodium salt of 1-adamantane acetic acid onto polypropylene spheribeads. The product mixture was dried using rotary vacuum drier to yield 100.9 g of in situ generated sodium salt of 1-adamantane acetic acid onto polypropylene spheribeads having a DSC peak crystallization temperature of 121 °C.
EXPERIMENT-9
In situ generation of sodium 4-carboxyphenyl borate (Na4CB) onto polypropylene
Sodium salt of 4-carboxyphenyl boronic acid was prepared in a reaction vessel. The method used for preparation of in situ generated sodium 4-carboxyphenyl borate (Na4CB) onto polypropylene was similar to the process of experiment-6 of the present disclosure by taking 100 g of polypropylene spheribeads, 0.83 g of 4-carboxyphenyl boronic acid (0.005M), and 0.2 g of sodium hydroxide (0.005M) to yield 100.9 g of in situ generated sodium salt of 4-carboxyphenyl boronic acid onto polypropylene spheribeads having a DSC peak crystallization temperature of 116 °C.
EXPERIMENT-10
In situ generation of Sodium 5-Acenaphthene carboxylate onto polypropylene
0.892 g of 5-acenaphthene carboxylic acid (0.0045M) was dissolved in 45 ml of ethanol and heated to 60 °C for the acid to dissolve to obtain a 5-acenaphthene carboxylic acid solution. The so obtained 5-acenaphthene carboxylic acid solution was then added slowly to 100 g of polypropylene spheribeads charged in a reaction vessel to obtain a mixture. The mixture was heated at 80 °C and stirred for 1 hour to obtain 5-acenaphthene carboxylic acid-polypropylene complex. Further, 0.18 g of sodium hydroxide (0.0045M) was dissolved in 5 ml of water and added to 5-acenaphthene carboxylic acid-polypropylene complex and stirred for 3 hours at 80 °C to obtain a product mixture comprising in situ generated sodium salt of 5-acenaphthene carboxylic acid onto polypropylene. The product mixture was then dried to yield 101 g of in situ generated sodium salt of 5-acenaphthene carboxylic acid onto polypropylene having a DSC peak crystallization temperature of 118 °C.
EXPERIMENT-11
In situ generation of sodium and potassium cyclohexane carboxylate onto polypropylene
In situ generated Sodium salt of cyclohexane carboxylic acid (iNaCHC) was prepared in a reaction vessel. The method of preparation of iNaCHC was similar to experiment-6 of the present disclosure. 100 g of polypropylene spheribeads, 0.769 g of cyclohexane carboxylic acid (0.006M), and 0.24 g of sodium hydroxide (0.006 M) were taken and reacted in a same way similar to experiment-6 to yield 100.9 g in situ generated Sodium salt of cyclohexane carboxylic acid onto polypropylene. A potassium salt was also prepared using 0.308 g of potassium hydroxide (0.0055M), 0.854 g of cyclohexane carboxylic acid (0.0055M) which yielded 101.16 g of in situ generated potassium salt of cyclohexane carboxylic acid onto polypropylene having a peak crystallization of 122 °C.
In situ generated sodium salt of cyclohexane carboxylic acid onto polypropylene random copolymer was prepared by using a method similar to the experiment-6 of the present disclosure by taking 100 g of polypropylene random copolymer, 90 ml of ethanol, 0.769 g of cyclohexane carboxylic acid (0.006M), and 0.240 g of sodium hydroxide (0.006M) to yield 100.86 g of in situ generated sodium salt of cyclohexane carboxylic acid onto polypropylene random copolymer having a DSC peak crystallization temperature of 107 °C.
EXPERIMENT-12
In situ generation of potassium pimelate onto polypropylene
In situ generated potassium salt of pimelic acid onto PP spheribeads was prepared by using a method similar to experiment-6 of the present disclosure by taking 100 g of PP spheribeads, 0.8 g of pimelic acid (0.005M), and 0.280 g of potassium hydroxide (0.005M). The method resulted in 100.31 g of in situ generated potassium salt onto polypropylene having a peak crystallization temperature of 119 °C.
EXPERIMENT-13
In situ generation of sodium azelate onto polypropylene
In situ generated sodium salt of azelaic acid was prepared using a method similar to experiment-6 of the present disclosure by taking 100 g of polypropylene spheribeads, 0.7458 g of azelaic acid (0.007M), and 0.28 g of sodium hydroxide (0.007M) to yield 100.2 g of in situ generated sodium salt of azelaic acid onto polypropylene having a DSC peak crystallization temperature of 116 °C.
Maximum crystallization temperatures obtained for different in situ generated metal salt are provided below in Table 3.
Table 3: Crystallization temperatures of in situ generated metal salts onto polypropylene homopolymer
Sr.
No. In situ generation of metal salts onto polypropylene homopolymer Tm (oC) Tc
(oC) Tm –Tc (oC)
1 PP14 165 119 46
2 PP NaBz - Commercial Sodium Benzoate (REF) 165 121 44
3 PP iNaBz - Sodium Benzoate (in situ) 166 131 35
4 PP iNaACC - Sodium-1-Amino-1-cyclohexane carboxylate (in situ) 166 133 33
5 PP NaADC - Sodium Adamantane-1-carboxylate (in situ) 166 129 37
6 PP iNaCHC - Sodium Cyclohexane-1-carboxylate (in situ) 166 126 40
7 PP iKCHC - Potassium cyclohexane carboxylate (in situ) 164 122 42
8 PP iNaADAc - Sodium Adamantane acetate (in situ) 164 121 43
9 PP iNaADDC - Sodium 1, 3-Adamantane dicarboxylate (in situ) 165 119 46
10 PP iNaCBPB - Sodium 4-carboxyphenyl borate (in situ) 166 116 50
11 PP iKPim - Potassium Pimelate (in situ) 149 119 30
12 PP iNaAze - Sodium Azelate (in situ) 163 116 47

It is evident from table 3 that the in situ generated sodium benzoate, in situ generated sodium-1-Amino-1-cyclohexane carboxylate, in situ generated sodium adamantane-1-carboxylate, and in situ generated potassium pimelate has enhanced rate of crystallization and nucleation efficiency compared to commercial sodium benzoate. Among the in situ generated metal salts PP iNaACC gave highest nucleating efficiency.
EXPERIMENT-14
Polypropylene homopolymer compositions with in situ generated sodium benzoate and other additives
Polypropylene homopolymer compositions with in situ generated sodium benzoate (iNaBz – 1000 ppm) were prepared by taking 3000 g of polypropylene homopolymer, 3 g of B-230 (mixture of primary and secondary antioxidant), and 1.5 g of calcium stearate and mixed thoroughly in a high speed mixer for 10 minutes. Similar experiments were carried out by replacing calcium stearate with 300 ppm of hydrotalcite.
Polypropylene random copolymer compositions with in situ generated sodium benzoate and other additives
Polypropylene random copolymer compositions with in situ generated sodium benzoate metal salt (iNaBz - 1000 ppm) were prepared by taking Pentaerythritol Tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), Tris(2,4-ditert-butylphenyl)phosphite, hydrotalcite, glycerol monostearate and dry blended in a high speed ribbon mixer for 10 minutes. Typical composition is given in Table 4.

Table 4: Polypropylene random homopolymer composition
S. No. Additives / polypropylene Weight
(g) PPM
1 Polypropylene random copolymer 3500 -
2 Pentaerythritol Tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), Primary antioxidant, (Ciba Geigy Ltd) 1.75 500
3 Tris(2,4-ditert-butylphenyl)phosphite, Secondary Antioxidant (from Ciba) 3.5 1000
4 Hydrotalcite 0.875 250
5 Glycerol Monostearate, 1.75 500
6 Inventive Nucleating agents ( 50 – 1K ) ppm 0.875 250

Polypropylene random copolymer compositions with other in situ generated metal salts
In situ generated sodium metal salts of 1-amino-1-cyclohexane carboxylic acid (iNaACC), adamantane carboxylic acid (iNaADC), cyclohexane carboxylic acid (iNaCHC) in a quantity in the range of 250 to 500 ppm on polypropylene homopolymer and random copolymer (3500 g) were mixed separately with 250 ppm hydrotalcite (0.875 g), Pentaerythritol Tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (1.75 g) and Tris(2,4-ditert-butylphenyl)phosphite (3.5 g) and compounded in a high speed mixer as above. All the above compositions were extruded in Buss-co-kneader with a temperature profile of 140-150-210-240-230 °C, with a screw RPM of 1st screw – 7.5 and 2nd screw of 8. All the extrudates were passed through a trough of water and cut into granules of 3 mm size and dried at 80 °C for 3 hours in an air circulating oven. The dried granules were injection molded into ASTM test specimens in an injection molding machine with the temperature profile of 180-190-200-210 °C. All the test specimens were conditioned for 48 hours and their thermo mechanical and optical properties were measured. The values are tabulated in Tables 5-7. Polarized optical microscope photographs given in Figures 5A-5D of PP (Figure 5A) and PP compounded with 1000 ppm of iNaBz (Figure 5B), iNaACC (Figure 5C) and iNaADC (Figure 5D) showed small and uniform spherulites in Figure 5B, Figure 5C & Figure 5D as compared to bigger spherulites in Figure 5A.
Table 5: Thermo-mechanical and Optical properties of polypropylene homopolymer and in situ generated sodium benzoate compositions
Sr. No. PP$ /
Nucleating agent iNaBz (ppm) FM
(Kg/cm2) TS
(Kg/cm2) Tc#
(oC) Tc (oC) % Haze
1 mm
1 Virgin PPHP 0 12450 328 123 119 67
2 PP /iNaBz 50 14110 370 124 121 65
3 PP/iNaBz 100 14120 370 125 123 65
4 PP/iNaBz 250 15710 371 128 122 65
5 PP/iNaBz 500 16960 382 131 123 59
6 PP/iNaBz 1000 18330 401 132 128 47
7 PP/NA21 1000* 16300 392 127 127 34
8 PP/NABz 1000 16449 389 125 125 54
FM: Flexural modulus; TS: Tensile strength; Tm: Melting temperature;
Tc: Crystallization temperature; $ 500 ppm Ca (St)2; # 300 ppm of hydrotalcite;
Sr No 7 * PP with 1000 ppm of commercial NA21 – Bis (2,4,8,10-tetra-tert-butyl-6-hydroxy-12H-dibenzo[d,g][1,3,2]dioxaphosphocin-6-oxide)aluminum hydroxide and Sr No 8 with Commercial NaBz.

It is evident from table 5 of the present disclosure that the flexural modulus (FM) and crystallization temperature (Tc) increased with increase in concentration of in situ generated iNaBz metal salt from 50 to 1000 ppm in polypropylene homopolymer.
Table 6: Thermo-mechanical and Optical properties of polypropylene random copolymer and in situ generated sodium benzoate compositions
Sr. No RCP# / Nucleating agent (ppm) FM Kg/cm2)
TS Kg/cm2)
Gloss (%) Tm (oC) Tc (oC) % Haze at 1mm
Ca (St)2 Talcite
1 RCP 10870 313 93 149 112 57 85
2 RCP/iNaBz (250) 10050 314 93 151 118 40 40
3 RCP/iNaBz (500) 11060 323 93 151 119 44 44
4 RCP/iNaBz (1000) 11250 317 91 154 122 48 48
5 RCP/NA21-(1000)* 11860 331 94 152 122 21 21
FM: Flexural modulus; TS: Tensile strength; Tm: Melting temperature;
Tc: Crystallization temperature; #: with 500 ppm Ca (St)2; * RCP with 1000 ppm NA21

It is evident from table 6 of the present disclosure that with increase in iNaBz concentration from 250 to 1000 ppm in PP random copolymer (PPRCP) the FM and Tc values increased as observed in Table 5.
Table 7: Thermo – mechanical and optical properties polypropylene random copolymer and in situ generated metal salts compositions
S No RCP / in situ generated metal salts (ppm) Haze (%) at 1mm DSC (o C) Mechanical Properties
Tc Tm TM FM
1 RCP 57 112 149 9060 10736
2 RCP/iNaBz (250) 40 118 151 9105 10870
3 RCP/iNaBz (500) 44 119 149 9305 11060
4 RCP/iNaACC (250) 20 119 151 9939 11058
5 RCP/iNaACC (500) 64 121 151 9979 11112
6 RCP/iNaADC (250) 55 119 151 9039 10902
7 RCP/iNaADC (500) 56 119 151 9653 11415
8 RCP/iNaCHC (250) 57 116 150 9229 10487
9 RCP/iNaCHC (500) 48 120 151 9441 11118
FM: Flexural modulus; Tm: Melting temperature; Tc: Crystallization temperature; TM: Tensile modulus
iNaACC, iNaADC, iNaCHC and iNaBz are in situ generated sodium salts of 1-amino-1-cyclohexane carboxylic acid, adamantane carboxylic acid, cyclohexane carboxylic acid and benzoic acid respectively.
It is evident from table 7 of the present disclosure that the tensile modulus, flexural modulus and Tc values increased with increase in in situ generated different metal salts concentration from 250 – 500 ppm compared to virgin PPRCP.

TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of:
? a method of generating metal salts onto polypropylene in situ;
? a method of generating metal salts onto polypropylene in situ that prevents any agglomeration of the metal salts in the polymer during processing; and
? a method of generating metal salts onto polypropylene in situ that produces polypropylene with high crystallization temperature.
The foregoing description of the specific embodiments so fully reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, is understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
,CLAIMS:WE CLAIM:
1. Polypropylene having in situ generated metal salts, wherein said polypropylene is at least one selected from the group consisting of homopolymer, random copolymer, block copolymer, and graft copolymer.
2. The polypropylene as claimed in claim 1, wherein said polypropylene is in the form of beads, or powder.
3. The polypropylene as claimed in claim 1, wherein said metal salts are generated in situ inside the pores of said polypropylene.
4. The polypropylene as claimed in claim 1, wherein said metal salts are generated in situ on the surface of said polypropylene.
5. The polypropylene as claimed in claim 1, wherein said metal salts are strong nucleating agents.
6. The polypropylene as claimed in claim 1 is used for providing a polymer composition having high crystallization, low haze, and enhanced mechanical properties.
7. A method of synthesizing metal salts in situ onto polypropylene as claimed in claim 1, said method comprising the following steps:
(a) adding at least one organic acid dropwise to polypropylene to form an acid-polypropylene complex; and
(b) neutralizing said acid-polypropylene complex with the help of at least one alkali by introducing the alkali dropwise onto said acid-polypropylene complex, followed by sub-atmospheric drying to obtain metal salt generated in said polypropylene in situ.
8. The method as claimed in claim 1, wherein said organic acid is at least one selected from the group consisting of benzoic acid, cyclohexane aminocarboxylic acid, adamantane carboxylic acid, adamantane dicarboxylic acid, adamantane acetic acid, acenapthene carboxylic acid, boronic acid, cyclohexane carboxylic acids, pimelic acid, and azelaic acid.

9. The method as claimed in claim 1, wherein said alkali is at least one selected from the group consisting of sodium hydroxide, and potassium hydroxide.
10. The method as claimed in claim 1, wherein said sub-atmospheric drying is carried out under sub-atmospheric pressure in the range of 0.05 atm to 0.9 atm, and at a temperature in the range of 50 °C to 110 °C.