Title of Invention	"A PROCESS FOR THE PREPARATION OF HOMOPOLYMER FREE PLASMA GRAFTED POLYPROPYLENE-G-POLYACRYLIC ACID COPOLYMER"
Abstract	The present invention relates to a process for the preparation of homopolymer free plasma-grafted polypropylene-g-polyacrylic acid copolymer. More particularly, the present invention relates to a process for the preparation of homopolymer free plasma-grafted polypropylene-g-polyacrylic acid copolymer, wherein the polypropylene monofilament was exposed to oxygen plasma and was subsequently grafted with acrylic acid. Plasma activation of the polypropylene surface needs only few seconds. The graft polymerization of acrylic acid on polypropylene surface has been accomplished where the homopolymer formation is completely inhibited This has been achieved for the first time by using methanol and acetone as the additive. This is an innovative way to modify the materials without the homopolymer formation. Homopolymer free reaction helps in reusing the reaction bath several times making the process highly efficient.

Title of Invention

"A PROCESS FOR THE PREPARATION OF HOMOPOLYMER FREE PLASMA GRAFTED POLYPROPYLENE-G-POLYACRYLIC ACID COPOLYMER"

Abstract

The present invention relates to a process for the preparation of homopolymer free plasma-grafted polypropylene-g-polyacrylic acid copolymer. More particularly, the present invention relates to a process for the preparation of homopolymer free plasma-grafted polypropylene-g-polyacrylic acid copolymer, wherein the polypropylene monofilament was exposed to oxygen plasma and was subsequently grafted with acrylic acid. Plasma activation of the polypropylene surface needs only few seconds. The graft polymerization of acrylic acid on polypropylene surface has been accomplished where the homopolymer formation is completely inhibited This has been achieved for the first time by using methanol and acetone as the additive. This is an innovative way to modify the materials without the homopolymer formation. Homopolymer free reaction helps in reusing the reaction bath several times making the process highly efficient.

Full Text	Field of the Invention The present invention relates to a process for the preparation of homopolymer free plasma-grafted polypropylene-g-polyacrylic acid coplymer. More particularly, the present invention relates to a process for the preparation of homopolymer free plasma-grafted polypropylene-g-polyacrylic acid copolymer, wherein the polypropylene monofilament was exposed to oxygen plasma and was subsequently grafted with acrylic acid. Background of the Invention Modification of polypropylene by grafting of monomers has been an interesting area for introducing desirable properties into the material. The advantage of radiation grafting is that the modification may be carried out on the polymer existing in any shape and the size. Both the radiation and the plasma induced graft polymerization have been achieved on the polypropylene using a wide range of monomers. On one hand, the radiation induced graft polymerization leads to the bulk modification of the polymer due to high energy of the photons. However, plasma induced grafting leads to surface functionalization due to the low energy of activating species. The gamma radiation induced graft polymerization on polypropylene has been carried out both by pre irradiation and direct radiation grafting method. Abdel-Fattah et al Radiation Physics Chemistry, 1999, 54, 271277 reported the simultaneous grafting method where the polypropylene film was grafted using ferrous sulfate as the inhibitor for the homopolymerization. It is important to note that very high graft levels are achieved in the radiation grafting method. These grafted films have ability to bind the dyes and have been used for radiation dosimetry. The earlier study on acrylic acid grafting on polypropylene indicates that the homopolymer formation is prevented by the use of ferrous salts. However, N. H. Taher et al. Radiation Physics Chemistry, 1990, 36, 785-790, have found that the organic solvents if added to the grafting medium influence the grafting yield. They have found that the homopolymer formation is there in grafting medium comprising of water, DMF, isopropanol/water, methanol/water and benzene. In case of benzene neither polymerization nor grafting took place. The problem of homopolymer formation during the grafting of acrylic acid has been observed in these studies. The plasma grafting on the other hand is milder in the polymer activation due to low energy. The acrylic acid grafting on polypropylene has been reported by Cernakova et al. Plasma Chemistry Plasma Processing, 2005, 24, 427-437, wherein the authors have carried out the nitrogen and air plasma exposure of polypropylene fabric followed by the grafting of acrylic acid using 20% monomer solution at 60°C. The grafting process gave reasonably good yield of 0.72-5.88% under the specified conditions. It is important to mention here that in this investigation, a significant amount of homopolymer is formed and it was separated by extraction in water. The US patent from Demuth et al. US Patent, 5,348,772, describes the use of nitrogen plasma for polypropylene activation to create amino groups for subsequent grafting of an acrylic monomer by impregnating the polypropylene with a bath containing the said monomer. The investigations of Poncin-Epailliard et al. Journal Applied Polymer Science, 1994, 53, 1291-1306, the homopolymer formation has been projected as the major obstacle and has been tackled by the addition of ferrous sulfate. In another investigation of I.L.J. Dogue et al, Journal Applied Polymer Science, 1995, 56, 33-40, on acrylic acid grafting on polypropylene initiated by gamma radiation, homopolymer is reported to overcome buy the addition of ferrous salt. The addition of ferrous sulfate to the grafting medium may inhibit the homopolymer formation. However, the ferrous ions remain bonded to the carboxyl groups. The complete separation of the ferrous ions from the grafted matrix is difficult. This is where there is a need of organic additives which would inhibit the homopolymerization and would provide a metal free grafting system. The US patent (L. Rupp, US Patent 5,451,428) uses two different options for plasma polymerization technique to apply the polymer coating where the medical device is put in a closed, preferably pressure-tight chamber. The gaseous chemical agent consisting of monomer molecules chemically combined with functional groups is then allowed to stream into the chamber through an appropriate opening or valve. Next, a source of radiation energy is switched on. This source may be arranged at a side wall of the chamber or in an annular arrangement around the chamber which preferably has a cylindrical cross section. Other suitable arrangements of the radiation source may be used as well. Because of the high intensity of the radiation, an electrically shielded chamber is preferred. In an advantageous embodiment, the emitted electromagnetic waves are in the radio frequency spectrum. Specifically, a frequency of 13.56 Mhz has been used. The electromagnetic waves are irradiated into the chamber, and the spark discharge causes the gaseous chemical agent to form a "plasma", e.g. a gas with free radicals This allows the monomers with their respective functional groups to form a polymer which covers the surface of the medical device. Alternatively, the so-called plasma grafting technique is used in contrast to the plasma polymerization technique. This technique comprises two basic steps: In the first step, a chemically inert gas such as a noble gas such as argon, helium or neon is applied to the medical device, and the source of electromagnetic radiation is turned on. This creates or induces charge carriers on the surface of the medical device. These charge carriers remain present even when the source of radiation is switched off. In the second step, the medical device is exposed to a chemical agent of the same constitution as in the plasma polymerization technique. If the process is performed in a closed chamber, the inert gas is removed by suction, and the chemical agent is allowed to stream into the chamber. However, in this second step, the source of electromagnetic radiation or the spark discharge is switched off. The charge carriers in the outer layers of the surface of the medical device initiate the polymerization process. F. Basarir et al., Journal Membrane Science, 2005, 260, 66-74, have reported another modification of plasma grafting, acrylic acid was grafted on polypropylene films using the vapour of acrylic acid instead of the monomer solution. This led to the deposition of the polyacrylic acid on the polypropylene surface. Similar investigations have been carried out by Sciarratta et al. Surafce Coating Technology, 2003, 174-175, 805-810, for the functionalization of polypropylene surfaces using hydrogen plasma. However, it may be mentioned here that in this work the coating is the physical interaction of the polyacrylic acid on polypropylene surface and not the covalent one. This structure is bound to be unstable one and therefore a covalent binding is required to produce a stable surface. The published literature does not account for the crystalline behavior, thermal stability and strength of the modified materials. Our investigation is based on the plasma induced grafting of acrylic acid monomer on polypropylene fiber in such a way that the homopolymer formation is inhibited and the modified material retains its inherent physical characteristics while surface morphology is altered. Objectives of the invention The main objective of the present invention is to provide a process for the preparation of homopolymer free plasma-grafted polypropylene-g-polyacrylic acid copolymer. Another object of the invention is to provide a process wherein the Homopolymer free reaction helps in reusing the reaction bath several times making the process highly efficient. Yet another object of the invention is to provide a process wherein the formation of homopolymer during the reaction is completely inhibited. Still another object of the invention is to provide a process wherein the inherent property of the polypropylene mono filament does not altered significantly after the modification process of acrylic acid grafting. Summary of the invention Accordingly, the present invention provides a process for the preparation of homopolymer free plasma-grafted polypropylene-g-polyacrylic acid copolymer, which comprises: modifying the surface of polypropylene by treating it with oxygen plasma, at a plasma power in the range of 40-100 W, under vacuum, at a pressure of 0.5 torr, for a period of 20-500 seconds to obtain the plasma modified polypropylene filament, reacting the above said modified polypropylene with acrylic acid having concentration in the range of 20-60 vol % in a mixture of water and organic solvent, under inert atmosphere, at a temperature in the range of 40-70°C, for a period of 0.5 to 3 hrs, followed by the removal of resultant grafted filament and washing it with water to obtain the desired product. In an embodiment of the present invention the organic solvent used in the mixture of water and organic solvent is selected from the group consisting of methanol, acetone and butanone. In yet another embodiment the ratio of organic solvent to water in the water-organic solvent mixture used is in the range of 50: 50 to 80 :20 (V%). A process as claimed in claim 1, wherein the concentration of acrylic acid used is in the range of 20-60 (V%). In yet another embodiment the concentration of acrylic acid used where maximum grafting of polypropylene obtained is in the range of 40-50%(V%). In yet another embodiment the reaction temperature used for maximum grafting of polypropylene is in the range of 50-55 °C. In yet another embodiment the reaction bath used for grafting of polypropylene is reusable for further reactions. In yet another embodiment the plasma grafted polypropylene-g-polyacrylic acid copolymer obtained has a tensile strength, elongation, melting point and crystallinity similar to the parent polypropylene. In still another embodiment the plasma grafted polypropylene-g-polyacrylic acid copolymer obtained is useful for dying with basic dyes selected from the group consisting of Toluidine Blue, Crystal Violet, Rhodamine B and Bismark Brown XLR. Brief description of the drawings Fig. 1. Schematic representation of the plasma unit. Fig. 2. Variation of the degree of grafting with the solvent composition in the grafting medium. Plasma exposure- 100s; grafting temperature 50°C; monomer concentration- 30%; organic solvent- water ratio- 55:45. Fig. 3. Variation of contact angle with the degree of grafting. Fig. 4. Variation of degree of grafting with the monomer concentration. Plasma exposure- 100s; grafting temperature 50°C; monomer concentration- 50%; acetone-water ratio- 55:45. Fig. 5. Scanning electron micrographs of polypropylene filaments prepared in different organic additives. Detail description of the invention The plasma induced modification of polypropylene is carried out in such a way that the process is completely devoid of homopolymerization during the graft polymerization reaction. This has been achieved by the addition of organic solvents to the grafting medium. The plasma treatment of polypropylene is carried out in the plasma chamber consisting of radio frequency plasma of 13.56MHz where the reactor consists of two cylindrical electrodes of 13cm diameter and 2.2 cm apart in a cylindrical vacuum vessel. The lower electrode and the reactor walls is grounded. The polypropylene filament is placed on the grounded electrode and the system is evacuated to 10-4 torr and oxygen is introduced into the chamber at the specified flow rate and the pressure is maintained to 0.05 torr. The plasma was generated at specific power for a precise period. After the plasma treatment, the chamber is filled with atmospheric air and sample was removed from the reactor. In the second step, grafting is carried out in glass ampoules of 2x10 cm2 size with B-24 joints. A weighed amount of plasma treated monofilament (~500 mg) is placed into ampoules containing monomer and the solvent. Nitrogen is purged into the ampoule to remove air trapped inside the reaction mixture and the ampoule was subsequently placed in a water bath maintained at 50°C. After a desired period, the ampoule is removed and is washed with water. The samples are dried in an oven at 50°C under vacuum and the degree of grafting is estimated. The following are the key features of the process (1) Plasma activation of the polypropylene surface needs only few seconds. (2) The graft polymerization of acrylic acid on polypropylene surface has been accomplished where the homopolymer formation is completely inhibited This has been achieved for the first time by using methanol and acetone as the additive. This is an innovative way to modify the materials without the homopolymer formation. (3) Homopolymer free reaction helps in reusing the reaction bath several times making the process highly efficient. (4) The graft modification does not alter crystallinity, melting point, and tensile properties of the inherent filament. (5) Moisture absorption is introduced in the filament up to 0.63%. (6) The dyeability of the modified fibre may be achieved even at ambient condition (25°and above). The following examples are given by the way of illustration and therefore should not be construed to limit the scope of the invention. Example 1 0.5g PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 30% monomer concentration at 60°C for 2.5h. The medium was methanol-water. The homopolymer formation was completely inhibited at 55% methanol concentration (methanol:water- 55:45 vol%). The degree of grafting is 16µg/cm2. Example 2 0.5g PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 30% monomer concentration at 50°C for 2.5h. The medium was methanol-water mixture. The homopolymer formation was completely inhibited at 55% methanol concentration (methanol:water- 55:45 vol%). The degree of grafting varied between 28µg/cm2. Example 3 0.5g PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 30% monomer concentration at 50°C for 2.5h. The medium was acetone-water mixture. The homopolymer formation was completely inhibited at 55% acetone concentration. The degree of grafting was 10µg/cm2. Example 4 0.5g PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 50% monomer concentration at 50°C for 2.5h. The medium was acetone-water mixture.The homopolymer formation was completely inhibited at 55% acetone concentration (acetone:water- 55:45 vol%). The degree of grafting was 42µg/cm2. Example 5 0.5g PP filament was exposed to oxygen plasma for 300s. The grafting was carried out using 50% monomer concentration at 50°C for 2.5h. The medium was acetone-water mixture. The homopolymer formation was completely inhibited at 55% acetone concentration. The degree of grafting varied between 64µg/cm2. Example 6 0.5g PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 50% monomer concentration at 50°C for 2.5h. The medium was butanone-water mixture. The homopolymer formation was completely inhibited at 60% butanone concentration. The degree of grafting was 16µg/cm2. Example 7 0.5 gm of PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 30% monomer concentration at 50°C for 2.5h. The medium was methanol-water mixture (methanohwater- 55:45 vol%). The Crystallinity of the filament remains unchanged at 48%. The melting point remained unchanged at 166°C. Example 8 0.5 gm of PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 30% monomer concentration at 50°C for 2.5h. The medium was methanol-water mixture (methanol:water- 55:45 vol%). The tenacity of the filament remained unchanged at 4.1gpd. The elongation also remained unchanged at 22%. Example 9 0.5 gm of PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 30% monomer concentration at 50°C for 2.5h. The medium was methanol-water mixture (methanol:water- 55:45 vol%). The moisture absorption has increased from 0% for unmodified PP to 0.63% for modifies filament at graft level of 22 µg/cm2. Example 10 0.5 gm of PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 30% monomer concentration at 50°C for 2.5h. The medium was methanol-water mixture (methanohwater- 55:45 vol%). The dyeability with Rhodamine B (Basic Dye) is 6 (K/S value). Example 11 0.5 gm of PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 30% monomer concentration at 50°C for 2.5h. The medium was methanol-water mixture (methanol:water- 55:45 vol%). The maximum dyeability with Toluidine Blue, Crystal Violet and Bismark Brown XLR (Basic Dyes) was 8.9, 7.6 and 7.0 respectively (K/S value). We Claim: 1. A process for the preparation of homopolymer free plasma-grafted polypropylene-g-polyacrylic acid copolymer, which comprises modifying the surface of polypropylene by treating it with oxygen plasma, at a plasma power in the range of 40-100 W, under vacuum, at a pressure of 0.5 torr, for a period of 20-500 seconds to obtain the plasma modified polypropylene filament, reacting the above said modified polypropylene with acrylic acid having concentration in the range of 20-60 vol % in a mixture of water and organic solvent, under inert atmosphere, at a temperature in the range of 40-70°C, for a period of 0.5 to 3 hrs, followed by the removal of resultant grafted filament and washing it with water to obtain the desired product. 2. A process as claimed in claim 1, wherein the organic solvent used in the mixture of water and organic solvent is selected from the group consisting of methanol, acetone and butanone. 3. A process as claimed in claims 1 & 2, wherein the ratio of organic solvent to water in the water-organic solvent mixture used is in the range of 50: 50 to 80 :20 (V%). 4. A process as claimed in claim 1, wherein the concentration of acrylic acid used for maximum grafting of polypropylene obtained is in the range of 40-50%(V%). 5. A process as claimed in claim 1, wherein the reaction temperature used for maximum grafting of polypropylene is in the range of 50-55°C. 6. A process as claimed in claim 1, wherein the reaction bath used for grafting of polypropylene is reusable for further reactions. 7. A process as claimed in claim 1, wherein the plasma grafted polypropylene-g-polyacrylic acid copolymer obtained is useful for dying with basic dyes selected from the group consisting of Toluidine Blue, Crystal

Full Text

Field of the Invention
The present invention relates to a process for the preparation of homopolymer free plasma-grafted polypropylene-g-polyacrylic acid coplymer. More particularly, the present invention relates to a process for the preparation of homopolymer free plasma-grafted polypropylene-g-polyacrylic acid copolymer, wherein the polypropylene monofilament was exposed to oxygen plasma and was subsequently grafted with acrylic acid.
Background of the Invention
Modification of polypropylene by grafting of monomers has been an interesting area for introducing desirable properties into the material. The advantage of radiation grafting is that the modification may be carried out on the polymer existing in any shape and the size. Both the radiation and the plasma induced graft polymerization have been achieved on the polypropylene using a wide range of monomers. On one hand, the radiation induced graft polymerization leads to the bulk modification of the polymer due to high energy of the photons. However, plasma induced grafting leads to surface functionalization due to the low energy of activating species.
The gamma radiation induced graft polymerization on polypropylene has been carried out both by pre irradiation and direct radiation grafting method. Abdel-Fattah et al Radiation Physics Chemistry, 1999, 54, 271277 reported the simultaneous grafting method where the polypropylene film was grafted using ferrous sulfate as the inhibitor for the homopolymerization. It is important to note that very high graft levels are achieved in the radiation grafting method. These grafted films have ability to bind the dyes and have been used for radiation dosimetry. The earlier study on acrylic acid grafting on polypropylene indicates that the homopolymer formation is prevented by the use of ferrous salts. However, N. H. Taher et al. Radiation Physics Chemistry, 1990, 36, 785-790, have found that the organic solvents if added to the grafting medium influence the grafting yield. They have found that the homopolymer formation is there in grafting medium comprising of water, DMF, isopropanol/water, methanol/water and benzene. In case of benzene neither polymerization nor grafting took place. The problem of homopolymer formation during the grafting of acrylic acid has been observed in these studies.

The plasma grafting on the other hand is milder in the polymer activation due to low energy. The acrylic acid grafting on polypropylene has been reported by Cernakova et al. Plasma Chemistry Plasma Processing, 2005, 24, 427-437, wherein the authors have carried out the nitrogen and air plasma exposure of polypropylene fabric followed by the grafting of acrylic acid using 20% monomer solution at 60°C. The grafting process gave reasonably good yield of 0.72-5.88% under the specified conditions. It is important to mention here that in this investigation, a significant amount of homopolymer is formed and it was separated by extraction in water. The US patent from Demuth et al. US Patent, 5,348,772, describes the use of nitrogen plasma for polypropylene activation to create amino groups for subsequent grafting of an acrylic monomer by impregnating the polypropylene with a bath containing the said monomer. The investigations of Poncin-Epailliard et al. Journal Applied Polymer Science, 1994, 53, 1291-1306, the homopolymer formation has been projected as the major obstacle and has been tackled by the addition of ferrous sulfate. In another investigation of I.L.J. Dogue et al, Journal Applied Polymer Science, 1995, 56, 33-40, on acrylic acid grafting on polypropylene initiated by gamma radiation, homopolymer is reported to overcome buy the addition of ferrous salt. The addition of ferrous sulfate to the grafting medium may inhibit the homopolymer formation. However, the ferrous ions remain bonded to the carboxyl groups. The complete separation of the ferrous ions from the grafted matrix is difficult. This is where there is a need of organic additives which would inhibit the homopolymerization and would provide a metal free grafting system.
The US patent (L. Rupp, US Patent 5,451,428) uses two different options for plasma polymerization technique to apply the polymer coating where the medical device is put in a closed, preferably pressure-tight chamber. The gaseous chemical agent consisting of monomer molecules chemically combined with functional groups is then allowed to stream into the chamber through an appropriate opening or valve. Next, a source of radiation energy is switched on. This source may be arranged at a side wall of the chamber or in an annular arrangement around the chamber which preferably has a cylindrical cross section.
Other suitable arrangements of the radiation source may be used as well. Because of the high intensity of the radiation, an electrically shielded chamber is preferred. In an advantageous embodiment, the emitted electromagnetic waves are in the radio frequency spectrum. Specifically, a frequency of 13.56 Mhz has been used. The electromagnetic waves are irradiated into the chamber, and the spark discharge causes the gaseous chemical agent to form a "plasma", e.g. a gas with free radicals This allows the monomers with their respective functional groups to form a polymer which covers the surface of the medical device. Alternatively, the so-called plasma grafting technique is used in contrast to the plasma polymerization technique. This technique comprises two basic steps: In the first step, a chemically inert gas such as a noble gas such as argon, helium or neon is applied to the medical device, and the source of electromagnetic radiation is turned on. This creates or induces charge carriers on the surface of the medical device. These charge carriers remain present even when the source of radiation is switched off. In the second step, the medical device is exposed to a chemical agent of the same constitution as in the plasma polymerization technique. If the process is performed in a closed chamber, the inert gas is removed by suction, and the chemical agent is allowed to stream into the chamber. However, in this second step, the source of electromagnetic radiation or the spark discharge is switched off. The charge carriers in the outer layers of the surface of the medical device initiate the polymerization process.
F. Basarir et al., Journal Membrane Science, 2005, 260, 66-74, have reported another modification of plasma grafting, acrylic acid was grafted on polypropylene films using the vapour of acrylic acid instead of the monomer solution. This led to the deposition of the polyacrylic acid on the polypropylene surface. Similar investigations have been carried out by Sciarratta et al. Surafce Coating Technology, 2003, 174-175, 805-810, for the functionalization of polypropylene surfaces using hydrogen plasma. However, it may be mentioned here that in this work the coating is the physical interaction of the polyacrylic acid on polypropylene surface and not the covalent one. This structure is bound to be unstable one and therefore a covalent binding is required to produce a stable surface.
The published literature does not account for the crystalline behavior, thermal stability and strength of the modified materials. Our investigation is based
on the plasma induced grafting of acrylic acid monomer on polypropylene fiber in such a way that the homopolymer formation is inhibited and the modified material retains its inherent physical characteristics while surface morphology is altered. Objectives of the invention
The main objective of the present invention is to provide a process for the preparation of
homopolymer free plasma-grafted polypropylene-g-polyacrylic acid copolymer.
Another object of the invention is to provide a process wherein the Homopolymer free
reaction helps in reusing the reaction bath several times making the process highly
efficient.
Yet another object of the invention is to provide a process wherein the formation of
homopolymer during the reaction is completely inhibited.
Still another object of the invention is to provide a process wherein the inherent property of the polypropylene mono filament does not altered significantly after the modification process of acrylic acid grafting.
Summary of the invention
Accordingly, the present invention provides a process for the preparation of homopolymer free plasma-grafted polypropylene-g-polyacrylic acid copolymer, which comprises: modifying the surface of polypropylene by treating it with oxygen plasma, at a plasma power in the range of 40-100 W, under vacuum, at a pressure of 0.5 torr, for a period of 20-500 seconds to obtain the plasma modified polypropylene filament, reacting the above said modified polypropylene with acrylic acid having concentration in the range of 20-60 vol % in a mixture of water and organic solvent, under inert atmosphere, at a temperature in the range of 40-70°C, for a period of 0.5 to 3 hrs, followed by the removal of resultant grafted filament and washing it with water to obtain the desired product.
In an embodiment of the present invention the organic solvent used in the mixture of
water and organic solvent is selected from the group consisting of methanol, acetone and
butanone.
In yet another embodiment the ratio of organic solvent to water in the water-organic
solvent mixture used is in the range of 50: 50 to 80 :20 (V%).
A process as claimed in claim 1, wherein the concentration of acrylic acid used is in the range of 20-60 (V%).
In yet another embodiment the concentration of acrylic acid used where maximum grafting of polypropylene obtained is in the range of 40-50%(V%).
In yet another embodiment the reaction temperature used for maximum grafting of polypropylene is in the range of 50-55 °C.
In yet another embodiment the reaction bath used for grafting of polypropylene is reusable for further reactions.
In yet another embodiment the plasma grafted polypropylene-g-polyacrylic acid copolymer obtained has a tensile strength, elongation, melting point and crystallinity similar to the parent polypropylene.
In still another embodiment the plasma grafted polypropylene-g-polyacrylic acid copolymer obtained is useful for dying with basic dyes selected from the group consisting of Toluidine Blue, Crystal Violet, Rhodamine B and Bismark Brown XLR.
Brief description of the drawings
Fig. 1. Schematic representation of the plasma unit.
Fig. 2. Variation of the degree of grafting with the solvent composition in the
grafting medium. Plasma exposure- 100s; grafting temperature 50°C; monomer
concentration- 30%; organic solvent- water ratio- 55:45.
Fig. 3. Variation of contact angle with the degree of grafting.
Fig. 4. Variation of degree of grafting with the monomer concentration. Plasma
exposure- 100s; grafting temperature 50°C; monomer concentration- 50%;
acetone-water ratio- 55:45.
Fig. 5. Scanning electron micrographs of polypropylene filaments prepared in
different organic additives.
Detail description of the invention
The plasma induced modification of polypropylene is carried out in such a way that the process is completely devoid of homopolymerization during the graft polymerization reaction. This has been achieved by the addition of organic solvents to the grafting medium. The plasma treatment of polypropylene is carried out in the plasma chamber consisting of radio frequency plasma of 13.56MHz
where the reactor consists of two cylindrical electrodes of 13cm diameter and 2.2 cm apart in a cylindrical vacuum vessel. The lower electrode and the reactor walls is grounded. The polypropylene filament is placed on the grounded electrode and the system is evacuated to 10-4 torr and oxygen is introduced into the chamber at the specified flow rate and the pressure is maintained to 0.05 torr. The plasma was generated at specific power for a precise period. After the plasma treatment, the chamber is filled with atmospheric air and sample was removed from the reactor.
In the second step, grafting is carried out in glass ampoules of 2x10 cm2 size with B-24 joints. A weighed amount of plasma treated monofilament (~500 mg) is placed into ampoules containing monomer and the solvent. Nitrogen is purged into the ampoule to remove air trapped inside the reaction mixture and the ampoule was subsequently placed in a water bath maintained at 50°C. After a desired period, the ampoule is removed and is washed with water. The samples are dried in an oven at 50°C under vacuum and the degree of grafting is estimated. The following are the key features of the process
(1) Plasma activation of the polypropylene surface needs only few seconds.
(2) The graft polymerization of acrylic acid on polypropylene surface has been
accomplished where the homopolymer formation is completely inhibited
This has been achieved for the first time by using methanol and acetone
as the additive. This is an innovative way to modify the materials without
the homopolymer formation.
(3) Homopolymer free reaction helps in reusing the reaction bath several
times making the process highly efficient.
(4) The graft modification does not alter crystallinity, melting point, and
tensile properties of the inherent filament.
(5) Moisture absorption is introduced in the filament up to 0.63%.
(6) The dyeability of the modified fibre may be achieved even at ambient
condition (25°and above).
The following examples are given by the way of illustration and therefore should not be construed to limit the scope of the invention.
Example 1
0.5g PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 30% monomer concentration at 60°C for 2.5h. The medium was methanol-water. The homopolymer formation was completely inhibited at 55% methanol concentration (methanol:water- 55:45 vol%). The degree of grafting is 16µg/cm2.
Example 2
0.5g PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 30% monomer concentration at 50°C for 2.5h. The medium was methanol-water mixture. The homopolymer formation was completely inhibited at 55% methanol concentration (methanol:water- 55:45 vol%). The degree of grafting varied between 28µg/cm2.
Example 3
0.5g PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 30% monomer concentration at 50°C for 2.5h. The medium was acetone-water mixture. The homopolymer formation was completely inhibited at 55% acetone concentration. The degree of grafting was 10µg/cm2.
Example 4
0.5g PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 50% monomer concentration at 50°C for 2.5h. The medium was acetone-water mixture.The homopolymer formation was completely inhibited at 55% acetone concentration (acetone:water- 55:45 vol%). The degree of grafting was 42µg/cm2.
Example 5
0.5g PP filament was exposed to oxygen plasma for 300s. The grafting was carried out using 50% monomer concentration at 50°C for 2.5h. The medium was acetone-water mixture. The homopolymer formation was completely inhibited at 55% acetone concentration. The degree of grafting varied between 64µg/cm2.
Example 6
0.5g PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 50% monomer concentration at 50°C for 2.5h. The medium was butanone-water mixture. The homopolymer formation was completely inhibited at 60% butanone concentration. The degree of grafting was 16µg/cm2.
Example 7
0.5 gm of PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 30% monomer concentration at 50°C for 2.5h. The medium was methanol-water mixture (methanohwater- 55:45 vol%). The Crystallinity of the filament remains unchanged at 48%. The melting point remained unchanged at 166°C.
Example 8
0.5 gm of PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 30% monomer concentration at 50°C for 2.5h. The medium was methanol-water mixture (methanol:water- 55:45 vol%). The tenacity of the filament remained unchanged at 4.1gpd. The elongation also remained unchanged at 22%.
Example 9
0.5 gm of PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 30% monomer concentration at 50°C for 2.5h. The medium was methanol-water mixture (methanol:water- 55:45 vol%). The moisture absorption has increased from 0% for unmodified PP to 0.63% for modifies filament at graft level of 22 µg/cm2.
Example 10
0.5 gm of PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 30% monomer concentration at 50°C for 2.5h. The medium was methanol-water mixture (methanohwater- 55:45 vol%). The dyeability with Rhodamine B (Basic Dye) is 6 (K/S value).
Example 11
0.5 gm of PP filament was exposed to oxygen plasma for 100s. The grafting was carried out using 30% monomer concentration at 50°C for 2.5h. The medium was methanol-water mixture (methanol:water- 55:45 vol%). The maximum dyeability with Toluidine Blue, Crystal Violet and Bismark Brown XLR (Basic Dyes) was 8.9, 7.6 and 7.0 respectively (K/S value).

We Claim:
1. A process for the preparation of homopolymer free plasma-grafted polypropylene-g-polyacrylic acid copolymer, which comprises modifying the surface of polypropylene by treating it with oxygen plasma, at a plasma power in the range of 40-100 W, under vacuum, at a pressure of 0.5 torr, for a period of 20-500 seconds to obtain the plasma modified polypropylene filament, reacting the above said modified polypropylene with acrylic acid having concentration in the range of 20-60 vol % in a mixture of water and organic solvent, under inert atmosphere, at a temperature in the range of 40-70°C, for a period of 0.5 to 3 hrs, followed by the removal of resultant grafted filament and washing it with water to obtain the desired product.
2. A process as claimed in claim 1, wherein the organic solvent used in the mixture of water and organic solvent is selected from the group consisting of methanol, acetone and butanone.
3. A process as claimed in claims 1 & 2, wherein the ratio of organic solvent
to water in the water-organic solvent mixture used is in the range of 50: 50
to 80 :20 (V%).
4. A process as claimed in claim 1, wherein the concentration of acrylic acid used for maximum grafting of polypropylene obtained is in the range of 40-50%(V%).
5. A process as claimed in claim 1, wherein the reaction temperature used for maximum grafting of polypropylene is in the range of 50-55°C.
6. A process as claimed in claim 1, wherein the reaction bath used for grafting of polypropylene is reusable for further reactions.
7. A process as claimed in claim 1, wherein the plasma grafted polypropylene-g-polyacrylic acid copolymer obtained is useful for dying with basic dyes selected from the group consisting of Toluidine Blue, Crystal

Documents:

1687-DEL-2006-Abstract-(18-05-2012).pdf

1687-DEL-2006-Claims-(18-05-2012).pdf

1687-del-2006-claims.pdf

1687-DEL-2006-Correspondence Others-(18-05-2012).pdf

1687-del-2006-correspondence-others.pdf

1687-DEL-2006-Description (Complete)-(18-05-2012).pdf

1687-del-2006-description (complete).pdf

1687-del-2006-drawings.pdf

1687-del-2006-form-1.pdf

1687-del-2006-form-2.pdf

1687-DEL-2006-Form-3-(18-05-2012).pdf

1687-del-2006-form-3.pdf

1687-del-2006-form-5.pdf

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Patent Number

253551

Indian Patent Application Number

1687/DEL/2006

PG Journal Number

31/2012

Publication Date

03-Aug-2012

Grant Date

31-Jul-2012

Date of Filing

24-Jul-2006

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

ANUSANDHAN BHAWAN, RAFI MARG, NEW DELHI - 110016, INDFIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	GUPTA BHUVANESH	DEPT. OF TEXTILE TECHNOLOGY INDIAN INSTITUTE OF TECHNOLOGY NEW DELHI - 110016.
2	SAXENA SHALINI	DEPT. OF TEXTILE TECHNOLOGY INDIAN INSTITUTE OF TECHNOLOGY NEW DELHI - 110016.

PCT International Classification Number

C08F2/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA