FIELD OF INVENTION: 5
[001] The present invention relates to conducting polymer composite for electromagnetic interference shielding and a process of preparation thereof. The synthesized polymer composite act as a excellent shield against microwave radiations in the frequency range of 8.2 GHz to 12.4 GHz (x-band). Specifically the present invention describes the process of synthesis of conducting polymer composite comprising of 10 polymer matrix and encapsulated with nanofillers like magnetic fillers, dielectric fillers.
BACKGROUND OF INVENTION:
[002] Electromagnetic radiations cause interference in nearby electronic system working and also have adverse effect on human health. World Health Organization (WHO) also raised his concern over the effect of EM radiation on human and 15 environment. So the need of highly absorption based EM shielding material is amplified. Traditionally metal, metallic foams, films and metal composite have been used against EMI pollution. They have certain shortcomings like heavy weight, corrosion, high cost and short life span etc. The present invention relates to the designing and synthesis of alternative material which is fulfills these shortcomings and act as shield against the 20 EMI pollution. In past decades many researchers explore the field of EMI shielding and work on various materials like dielectric fillers and magnetic fillers for the shielding purposes. The shielding effectiveness of the composite depends upon various factors like thickness, magnetic permeability, dielectric permittivity and frequency. Herein in this invention conducting polymer matrix is embedded with the dielectric fillers, 25 conductive materials and magnetic fillers. The combined synergistic effect of these materials exhibits excellent shielding effectiveness.
[003] Following are the works done so far in the field of conductive polymers based materials for protection against electromagnetic Inference.
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[004] US patent- 8847184 B2: Composite film for board level EMI shielding. The patent relates to development of composite film that protects the printed circuit board from electromagnetic interference. It contains basically two layer system; the top layer is conducting in all direction while bottom layer is conductive only in z direction. Both top and bottom layers were thermally compressed. The different layers were composed 5 of thermoset or thermoplastic resin or there combination. Different conducting fillers were loaded in the matrix like silver, nickel, copper, graphite, carbon nanotubes, and core/shell particles. Theses fillers were loaded about 15 volume% or more wrt to the total composition of the top layer. In bottom layer conductive filler loading level is about 2 to 20 volume% wet to the total composition of the bottom layer. Dielectric 10 materials like boron nitride, aluminum oxide, aluminum nitride, were also incorporated in the bottom layer and loading varies from 10 to 80 Wt%. The top layer prevents the electromagnetic radiations to enter in the electronic system and escaping into the environment. The bottom layer interconnects the top and grounding pads and facilitates the release of the radiations. 15
[005] WO 1999057952 A1: Emi shielding enclosures. Present patent relates to the designing of EMI shielding enclosures that comprise of ground plane, shielding cover formed by thermoforming composite sheet. The shielding cover posses a non-porous carrier sheet and fibrous metal mat. The carrier sheet is made up of polymer like polycarbonate, acrylonitrile butadiene styrene copolymers (ABS), styrene acrylonitrile 20 copolymers (SAN), polystyrene, polyvinyl chloride, polyether imide, polypropylene, polyethylene, polybutylene, polyamide, polyethylene terephthalate, etc. These carrier plates have softening point below 150 oC. The fiber coat comprises of thermoplastic polymers, hot melt adhesive polymers and pressure sensitive adhesive polymers. The outer surface has thickness less than 0.15 mm. 25
[006] US 8520406 B2: Electromagnetic interference shielding structure including carbon nanotube or nanofiber films. The patent describes preparation of composite material for electromagnetic interference shielding. The composite material is made up of layer structure that contains two different film layers separated to each other. The two
4
conductive layers were separated by one insulating gap. This stack structure enhances the shielding effectiveness by increasing multiple internal reflections. At least one of the nanoscale fiber films comprises a buckypaper and one of the nanoscale fiber films has a conductivity of at least 5 S/cm. The insulating gap made up of dielectric materials like polyethylene, polyethylene terephthalate, polyetherketone, or a combination of them. 5 The insulating gap thickness ranges from about 200 μm to about 2 mm. This film structure is flexible in nature and has a thickness from about 1 mm to about 2.5 mm. The stack structure provides an electromagnetic interference shielding effectiveness ranging from 5 dB to 100 dB in the frequency range of 4 GHz to 18 GHz.
[007] US 20100311866 A1: Heirarchial polymer-based nanocomposites for emi 10 shielding. The patent deals with the development of polymer based nano-composite for electromagnetic shielding that includes three nanofillers used in a formation of a hierarchy in structure, length, size, and dimension. Three different filler (nickel-coated carbon fibers, carbon nanofibers and multi-walled carbon nanotubes) has been used in this composite. Herein a thermoplastic polymer matrix is used like acrylonitrile-15 butadiene-styrene. The final composition of composite comprises 18 wt % of nickel-coated carbon fibers (NCCB), 7 wt % of carbon nanofibers, and 2 wt % of multi-walled carbon nanotubes incorporated in ABS copolymer matrix of 72 wt %. A suspension of ABS and of all three nanofillers was compressed molded at 225 oC into a sheet of either 12.7×12.7×0.1 cm or 61×61×0.1 cm. The composite material shows the shielding 20 effectiveness of 33 to 73 dB at frequency range 0.8-18 GHz.
[008] US 9469743 B2: Composite material with conductive and ferromagnetic properties and hybrid slurry. The invention relates to a synthesis of conducting polymer composite for EMI shielding. The material prepared by chemical oxidative polymerization of different monomers like aniline, poly(3,4-25 ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), etc. The conducting polymer contain conjugated system like polyacetylene, polypyrrole, polythiophene, polyaniline, poly(p-phenylene sulfide, poly(p-phenylene vinylene, poly(3,4-ethylenedioxythiophene, poly(3,4-ethylenedioxythiophene)-polystyrene sulfonateThe
5
conductive matrix is about 5 to 90 parts by weight and ferromaganetic filler (iron oxide nanorods) is about 0.1 to 40 parts by weight. The iron oxide nanorods comprise of Fe3O4, γ-Fe2O3, or combination. The diameter of nanorods is about 10 to 100 nm and length to diameter ratio is between 5 and 10. This conducting polymer composite is dispersed in adhesive materials like polyvinyl alcohol, polyacrylic acid, polyurethane, 5 epoxy resin, polymethylmethacrylate and acrylonitrile butadiene styrene etc. The resulting slurry is sonicated in vaccum, poured in mold and dreid at 50
oC in oven to yield thin film of dimension 15 cm×15 cm×40 cm. The obtained films can be utilized in EMI shielding, radar/microwave absorption, or electro static discharge (ESD) applications. 10
[009] CN 101525436 A: Polypyrrole/Fe3O4/graphite nanosheets composite material and preparation method thereof. This invention deals with the method of synthesizing Polypyrrole / Fe3O4/ graphite nanosheets composite. Sodium dodecyl benzene sulfonate is used as a surfactant and graphite nanosheets were dispersed in the aqueous medium. Pyrrole used as monomer and adsorbed at Fe3O4 nanoparticles by 15 stirring for 1 hour. FeCl3, 6H20 added to the reaction mixture and stirred for 20~24 hours at room temperature. The resultant product was filtered, washed with distilled water and dried in oven. Thickness of graphite nanosheets is about 30~80nm. Fe3O4 nanoparticles particles size is around 10nm to 15nm. Composite material shows conductivity in the range of 2.8~9.4 S/cm. 20
[0010] CN 103571215 A: High thermal conductivity and EMI sheltering high polymer composite material. This patent describes development of high thermal conductivity and EMI sheltering high polymer composite material. This composite material is synthesized by blending a thermal conduction material with an electromagnetic wave shielding material and a high polymer binder. Polymer composite 25 material, comprises inorganic composite, that have 0.5 wt% to 80wt% of thermally conductive material and 15wt% to 95wt% of the electromagnetic wave shielding material. Thermally conductive material present in the composite materials includes metal, ceramic powder, carbon black, carbon fiber, single-walled or multi-walled carbon
6
nano tubes, graphite, graphene or graphene oxide. The electromagnetic shielding material comprise materials like metal, metal oxide nanoparticles, graphene or ferrite magnets. Conductive matrix includes conductive polymer like: polyacetylene (Polyacetylene), polyphenylene acetylene (polyphenylvinylene), poly-para-phenylene (Poly-p-phenylene), polypyrrole (Polypyrrole), polythiophene (Polythiophene), 5 polyaniline (Polyaniline), polyethylene dioxythiophene Poly (3,4 ~ ethylenedioxythiophene), or derivatives or copolymers thereof. The said composite is synthesized by in-situ intercalation polymerization (in-situ intercalative polymerization). The resultant composite is dispersed in alcohol based dispersants, like a polyvinyl alcohol (Polyvinyl alcohol), polyethylene glycols etc. The composite material shows 15 10 to 48 dB shielding effectiveness in frequency range of 100 KHz ~ 2.45GHz.
[0011] WO 2007101646 A1: Functional papers for the absorption of radiofrequency electrical fields and method for their production. A excellent EMI Shielding system is described in present invention. A improved barrier system is 15 developed to absorbed the microwave radiation. As per invention papers have one or more layers structure, functional layers contain different types of inorganic materials which is evenly dispersed in the matrix. While one of the layers contains ferrite particles like hexaferrites, doped hexaferrites etc ferrite particles were blended with various electromagnetic radiation absorbing materials, like carbonyl iron, iron silicides and / or 20 titanates etc. The present invention claims excellent microwave-absorption and low-reflection properties of paper in the frequency range of from 1 GHz to 100 GHz.
[0012] EP 0781085 A1: Method and arrangement for electromagnetically shielding an electronic means. The invention described the dual barrier property of the film that provides protection against external electromagnetic interference and preventing the 25 electronic devices from interference created by close by electric devices. According to the invention, a shielding film posse’s layer structure that contains one or more layers of intrinsically conductive polymer and insulating films. Conductive film material is an intrinsic conducting polymer like polyaniline with different surfactants like camphor
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sulphonic acid (CSA), dodecylbenzenesulfonic (DBSA). Material used for insulating film is polycarbonate, polyurethane or polyvinyl fluoride etc. various different techniques like heat treatment or a vacuum treatment or the combination of the two is used to attached the composite film to the surface of the electronic devices. The present invention also claims a process for electrically connecting the intrinsic polymers layer to 5 the electronic devices. The invention further claims a process for using the electromagnetic shield to form capacitors and resistors for the electronic devices like mobile communication device.
OBJECTIVE OF THE INVENTION:
[0013] The main objective of the present invention is to design efficient conducting 10 polymer composite encapsulated with dielectric filler and magnetic fillers for EMI shielding application.
[0014] Another object of the present invention is to provide alternative EMI shielding material that has low cost, corrosion resistant, light weight, easily processable and provide effective shield against electromagnetic radiations. 15
SUMMARY OF THE INVENTION:
[0015] The present invention relates to a process for designing of conducting polymer based composite shield against EMI pollution. The polymer matrix is embedded with a hybrid material that contains different dielectric or magnetic or conductive fillers. The method comprising steps of: Synthesis of conducting polymer 20 Polypyrrole/RGO/BST/Fe3O4 composite by a facile chemical oxidative polymerization method in aqueous medium consisting Sodium Lauryl Sulphate. After synthesis, Loading of hybrid materials like magnetic, dielectric, and conductive fillers in the polymer matrix. At the end, testing the Shielding effective of conducting polymer composite by vector network analyzer at frequency range of 8.2-12.4 GHz. 25
[0016] The polymer matrix chosen for the study is polypyrrole. Further, the BRF hybrid material is synthesized by incorporating barium strontium titanate, RGO in the FeCl3 and FeCl2 solution. The resultant solution was co-precipitated by ammonia
8
solution. The BRF hybrid material is homogenized in sodium lauryl sulfate aqueous suspension for 2 hour at 10000-12000 rpm. Further, the BRF hybrid material is loaded in the polymeric matrix with respect to monomer, taken as 1:0.5, 1:1 and 1:2 weight ratios. The monomer is added in reaction medium for polymerization, at room temperature. The oxidation of reaction mixture is carried out by oxidant like ammonium 5 persulphate or potassium persulphate, ferric chloride and the like. The polymerization reaction was stirred for 4-5 hours. The content of monomer to oxidant ratio was maintained between 0.1 mole to 0.2 mole.
[0017] In another embodiment of the invention, Sodium Lauryl Sulphate is used as surfactant and its molar concentration with respect to monomer was maintained between 10 0.1 to 0.4 mole.
[0018] In another embodiment of the invention, the final resultant composite was dried at 50-60 oC in vacuum oven.
[0019] In another embodiment of the invention, the powder composite was pelletized in rectangular shape of dimension 22.8 X 10.03 X 2.5 mm. 15
[0020] In another embodiment of the invention, conducting polymer composite embedded with BRF hybrid were tested for EMI shielding application.
[0021] In order to further understand the characteristics and technical contents of the present subject matter, a description relating thereto will be made with reference to the accompanying drawings. However, the drawings are illustrative only but not used to 20 limit scope of the present subject matter.
BRIEF DESCRIPTIONS OF THE DRAWINGS
[0022] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective 25 embodiments. The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or
9
methods in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[0023] Fig. 1: Schematic of the synthesis of polypyrrole/RGO/BST/Fe3O4 composite by chemical oxidative polymerization process, in accordance with an embodiment of the 5 present subject matter;
[0024] Fig. 2 illustrates process step for manufacturing of PBRF composite, in accordance with an embodiment of the present subject matter;
[0025] Fig 3: SEM micrographs showing morphology of (a) Barium Strontium Titnate, (b) Polypyrrole, (c) & (d) of polypyrrole/RGO/BST/Fe3O4 at magnification scale shows 10 Edax pattern. BRF composite particles embedded inside the polymer matrix are visible in the micrograph, in accordance with an embodiment of the present subject matter;
[0026] Fig. 4: XRD patterns of (a) BRF, (b) Polypyrrole, (c) polypyrrole/RGO/BST/Fe3O4 (PBRF1, PBRF2, and PBRF3), in accordance with an embodiment of the present subject matter; 15
[0027] Fig. 5: FTIR Spectra of (a) BST, (b) BRF, (c) Polypyrrole and (d) polypyrrole/RGO/BST/Fe3O4 (PBRF1,PBRF2, PBRF3), in accordance with an embodiment of the present subject matter;
[0028] Fig. 6: TGA Plots of (a) BRF, (b) Polypyrrole and (c) polypyrrole/RGO/BST/Fe3O4 (PBRF1, PBRF2, and PBRF3), in accordance with an 20 embodiment of the present subject matter;
[0029] Fig. 7 Vibrating Sample Magnetometer plots of the a) BRF, (b) polypyrrole/RGO/BST/Fe3O4 (PBRF1, PBRF2, and PBRF3), in accordance with an embodiment of the present subject matter;
[0030] Fig. 8: Variation of total shielding effectiveness with frequency, in accordance 25 with an embodiment of the present subject matter;
[0031] Fig. 9: Shielding effectiveness due to absorption loss, in accordance with an embodiment of the present subject matter; and
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[0032] Fig 10: Shielding effectiveness due to reflection loss, in accordance with an embodiment of the present subject matter.
[0033] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein 5 may be employed without departing from the principles of the disclosure described herein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
[0034] At the very outset of the detailed description, it may be understood that the ensuing description only illustrates a particular form of this invention. However, such a 10 particular form is only exemplary embodiment, and without intending to imply any limitation on the scope of this invention. Accordingly, the description is to be understood as an exemplary embodiment and teaching of invention and not intended to be taken restrictively.
[0035] The present subject matter relates to a polymer based composite for EMI 15 shielding, the said polymer based composite comprises Pyrrole encapsulated with dielectric material like barium strontium titanate or magnetic materials like Fe3O4 or conductive material like RGO in presence of aqueous suspension of like sodium lauryl sulfate.
[0036] In another embodiment of the present subject matter relates to a process for 20 synthesizing polymers based composite for EMI shielding application. The process comprising steps of: Synthesizing of Barium strontium titanate (BST) and Synthesizing of Reduced Graphene Oxide (RGO) from natural graphite powder. After synthesizing of BST and RGO, BRF composite is prepared by synthesizing of Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 composite (BRF composite) by co-25 precipitation of FeCl2 and FeCl3. At the end PBRF composite is prepared by mixing Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 composite (BRF composite) in polypyrrole matrix in different weight ratio (BRF:PPY). The mixture the
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Barium strontium titanate/ Reduced Graphene oxide/ Fe
3O4 composite (BRF composite) and polypyrrole (PBRF) is polymerized by adding 0.2 M FeCl3 drop by drop at room temperature with continuous stirring for 4-5 hours.
[0037] It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that 5 conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also be appreciated by those skilled in the art that by devising various arrangements that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its spirit and 10 scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present 15 subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures.
[0038] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the 20 description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[0039] The present subject matter relates generally to electromagnetic (EM) radiation 25 absorbing composites containing conducting polymer and carbon allotropes. These prepared composites found enormous applications as EM shielding materials, for example, EM-sensitive electronic equipment, stealth vehicles, aircraft, etc., having low radar profiles, protection of electronic components from interference from one another
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on circuit boards, protection of computer equipment from emitting RF radiation causing interference to navigation systems, medical life support systems, etc. Without being bound by theory, it is believed that in composites of this invention, EM shielding is achieved through absorption of radiation rather than reflection.
[0040] Figure 1 describes the process of synthesizing and designing of conducting 5 polymers based composite for EMI pollution. Further, the each step as shown in the figure 1 is illustrates and explained in the method figure 2. Therefore, the figure 1 and figure 2 should be considered together for better illustration and understanding of the present subject matter. The figure 2 illustrates the steps of the figure 1. As shown in the figure 2 at step 202, Barium strontium titanate is synthesized. Further, the Synthesis of 10 Barium strontium titanate is explained in the example 2.
[0041] At step 204, Synthesizing of Reduced Graphene Oxide (RGO) from natural graphite powder is explained. Further, detailed explanation of the synthesized is explained in the example 3.
[0042] At step 206, the Synthesizing of Barium strontium titanate/ Reduced Graphene 15 oxide/ Fe3O4 composite (BRF composite) by co-precipitation of FeCl2 and FeCl3 is explained. Whereas detailed explanation is given in the example 4.
[0043] At step 208, Mixing Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 composite (BRF composite) in polypyrrole matrix in different weight ratio (BRF:PPY) is explained. The mixture the Barium strontium titanate/ Reduced Graphene oxide/ 20 Fe3O4 composite (BRF composite) and polypyrole (PBRF) is polymerized by adding 0.2 M FeCl3 drop by drop at room temperature with continuous stirring for 4-5 hours. Further more detailed explanation is given in the example 5-7.
[0044] At the end, EMI shielding measurements of the final PBRF composite is crushed in mortar and pestle. The PBRF composite pellets of dimension (22.8 X 10.03 X 2.5 25 mm) are made with help of hydraulic press and various shielding parameters were measured on Agilent E8362B VNA in the 8.2-12.4 GHz (X-band) microwave range. Further, all test results and comparisons are given in the table 1.
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[0045] The following examples are given to illustrate the process of the present invention and should not be construed to limit the scope of the present invention:
Example 1: Synthesis of Polypyrrole
[0046] Synthesis of polypyrrole has been carried out by the chemical oxidative polymerization of pyrrole monomer. Herein 0.2 M Sodium Lauryl Sulphate aqueous 5 solution is homogenized at 10000 rpm. 0.1 M pyrrole monomer is added to this slurry and stirred for 1 hour. FeCl3 (0.2M) is used as oxidant and added to the reaction mixture in drop wise manner to polymerize the reaction. The reaction mixture was stirred for 4-5 hour. The solution is then filtered and washed with distilled water. The resultant product is dried at 60 °C in the vacuum oven. 10
Example 2: Synthesis of Barium strontium titanate
[0047] Modified polymerized citrate precursor method was used for the synthesis of BST nanoparticles. In a typical reaction, 0.1 mol of titanium tetrabutoxide and 2 mol of ethylene glycol were dissolved and stirred until it results into transparent and yellow solution. Citric acid (CA) was added with small amount of water to this reaction 15 mixture. The resultant slurry was stirred for 30 min, and the solution became transparent. Barium carbonate (BaCO3) 0.07 mol and Strontium carbonate (SrCO3) 0.03 mol were added to this solution. Few drops of nitric acid (HNO3) was added to the reaction mixture to initiates the catalysis of samples dissolved in reaction mixture. The reaction mixture was stirred till solution colour turns to transparent and pale brown. 20 Further reaction mixture was dipped in hot silicon oil (50–60 oC) and stirred for 12 h. Excess solvent was removed by drying into an oven at 150 oC. Viscosity of resin increases due to the continuous heating and its colour changes from pale brown to deep brown. The obtained resin was charred at 300 oC for 2h in an electric furnace, yields black solid mass. The charred precursor was calcined at 800–900 oC at rate of 10 oC/min 25 for eight hours in a muffle furnace yields white BST powder.
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Example 3: Synthesis of Reduced Graphene Oxide
[0048] Improved hummers method is used to synthesize Reduced Graphene oxide (RGO) from natural graphite powder. A homogeneous mixture was prepared by adding sulphuric acid (H2SO4 (360 ml) and o-phosphoric acid (H3PO4 (40 ml) by vigorous stirring and immersed in an ice bath to maintain the low temperature for reaction. To 5 this mixture 3 gm (1 wt eq.) natural graphite powder was added and stirred till uniform dispersion of graphite is achieved. With the slow addition of 18 gm (6 wt eq.) of KMnO4 there is rise in temperature (about 35–40 oC) of reaction mixture. The resultant mixture was stirred for 20 hours at 50 oC. 400 ml ice cold distilled water was added to the solution. Subsequently 10 ml H2O2 is added to the reaction, there is change in the 10 suspension colour from dark brown to yellow. The obtained suspension is washed with HCl, followed by DI water, till pH 7 was attained. Graphene oxide was recovered with ethanol and dried at 80 oC in a vacuum oven. 1 gm of graphene oxide is dispersed in 1l of distilled water and ultrasonicated for 1hour. 10 mL of hydrazine was added to the ultrasonicated solution, and stirred for 4hours at 80 oC. The final product is filtered and 15 dried in vacuum oven at 60 oC.
Example 4: Synthesis of Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 composite (BRF composite)
[0049] Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 hybrid material was 20 prepared by co-precipitation of FeCl2 and FeCl3 in the presence of Barium strontium titanate (BST), reduced graphene oxide (RGO). 1.0 M FeCl2 and 0.2 M FeCl3 were mixed in an appropriate quantity of HCl. RGO and BST (1:2 weight ratios wrt to Fe3O4) were added to the above solution and stirred for 1 hour. 0.1 M aqueous NH3 solution was added drop by drop to the reaction solution. Brownish black precipitate was 25 observed in reaction and solution is stirred for 2 hours. The suspension was filtered and washed with DI water till pH 7 is attained. The final product is obtained after drying the filtrate in vacuum oven at 60 oC.
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Example 5: Synthesis of Polypyrrole/Barium strontium titanate/Reduced Graphene oxide/ Fe3O4 (PBRF1)
[0050] In typical reaction PBRF composite was synthesized by using emulsion polymerization technique. A aqueous solution of 0.2 M Sodium Lauryl Sulphate is homogenized at 10000 rpm for 2 hours. 3.39 gm (0.5:1 weight ratio wrt to monomer 5 (pyrrole)) of BRF hybrid material, followed by 0.1 M pyrrole monomer was added to the slurry and homogenized for 2 hours at 10000 rpm. 0.2 M FeCl3 solution was added to the reaction in drop wise manner at room temperature. The reaction mixture was stirred for 4-5 hours. The obtained product was filtered in G2 filtration funnel and washed with DI water. Black powder was obtained after drying at 60 oC in vacuum 10 oven.
[0051] For EMI shielding measurements PBRF composite was crushed in mortar & pestle. PBRF composite pellets of dimension (22.8 X 10.03 X 2.5 mm) were made with help of hydraulic press and various shielding parameters were measured on Agilent E8362B VNA in the 8.2-12.4 GHz (X-band) microwave range. 15
Example 6: Synthesis of Polypyrrole/Barium strontium titanate/Reduced Graphene oxide/ Fe3O4 (PBRF2)
[0052] PBRF composite was synthesized by a facile method of in-situ emulsion polymerization using FeCl3 as a oxidant. 0.1M pyrrole monomer was dispersed in 0.2 M 20 Sodium Lauryl Sulphate aqueous suspension. 6.79 gm (1:1 weight ratio wrt to monomer (pyrrole)) of BRF hybrid material is added to this suspension and homogenized for 2 hour at 10000 rpm. The reaction mixture was polymerized by adding 0.2 M FeCl3 drop by drop. The solution is stirred for 4-5 hour at room temperature. The resultant precipitate was filtered using G2 funnel and washed with DI water. The filtered PBRF 25 composite was dried in vacuum oven at 60 o C.
[0053] Agilent E8362B VNA is used for EMI shielding measurement in the 8.2-12.4 GHz (X-band) microwave range. The resultant composite was grinded by using mortar & pestle, PBRF composite was pelletized in dimension (22.8 X 10.03 X 2.5 mm) with
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help of hydraulic press. The maximum shielding effectiveness of 44 (dB) was obtained with PBRF2 at 8.2 GHz frequency.
Example 7: Synthesis of Polypyrrole/Barium strontium titanate/Reduced Graphene oxide/ Fe3O4 (PBRF3)
[0054] Polypyrrole/Barium strontium titanate/Reduced Graphene oxide/Fe3O4 5 composite were synthesized by polymerizing 0.1 M pyrrole in a aqueous suspension of 0.2 M of Sodium Lauryl Sulphate. BRF hybrid material 13.5 gm (1:2 weight ratio wrt to monomer (pyrrole)) was added to the reaction solution and homogenized for 2 hours at 10000 rpm. The above solution was polymerized at room temperature through emulsion polymerization by using 0.2 M FeCl3 as an oxidant. The reaction mixture was 10 continuously stirred for the 4 hours and yields blackish solution. The final composite solution was filtered and washed with distilled water. The obtained composite was dried at 60 oC in a vacuum oven and grinded into fine powder using mortar and pestle. This fine powder was pelletized in dimension of (22.8 X 10.03 X 2.5 mm). PBRF3 composite act as a barrier against EMI pollution and shows shielding effectiveness of 48 (dB) at 15 8.2 GHz frequency.
[0055] Fig 3: SEM micrographs showing morphology of (a) Barium Strontium Titnate, (b) Polypyrrole, (c) & (d) of polypyrrole/RGO/BST/Fe3O4 at magnification scale shows Edax pattern. BRF composite particles embedded inside the polymer matrix are visible in the micrograph, in accordance with an embodiment of the present subject matter. 20
[0056] Fig. 4: XRD patterns of (a) BRF, (b) Polypyrrole, (c) polypyrrole/RGO/BST/Fe3O4 (PBRF1, PBRF2, and PBRF3), in accordance with an embodiment of the present subject matter.
[0057] Fig. 5: FTIR Spectra of (a) BST, (b) BRF, (c) Polypyrrole and (d) polypyrrole/RGO/BST/Fe3O4 (PBRF1,PBRF2, PBRF3), in accordance with an 25 embodiment of the present subject matter.
[0058] Fig. 6: TGA Plots of (a) BRF, (b) Polypyrrole and (c) polypyrrole/RGO/BST/Fe3O4 (PBRF1, PBRF2, and PBRF3), in accordance with an embodiment of the present subject matter.
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[0059] Fig. 7 Vibrating Sample Magnetometer plots of the a) BRF, (b) polypyrrole/RGO/BST/Fe3O4 (PBRF1, PBRF2, and PBRF3), in accordance with an embodiment of the present subject matter.
[0060] Fig. 8: Variation of total shielding effectiveness with frequency, in accordance with an embodiment of the present subject matter. 5
[0061] Fig. 9: Shielding effectiveness due to absorption loss, in accordance with an embodiment of the present subject matter.
[0062] Fig 10: Shielding effectiveness due to reflection loss, in accordance with an embodiment of the present subject matter.
[0063] EMI shielding data of various combinations of BRF composite incorporated in 10 Polypyrrole matrix
TABLE 1
SI No.
Sample
Pyrrole
BRF
SET
SEA
SER
1.
BRF
-----
----
14.06
12.22
1.84
2.
PBRF1
6.79 g
3.35g
44.44
38.47
5.97
3.
PBRF2
6.79 g
6.79g
44.56
41.36
3.20
4
PBRF3
6.79g
13.58
48.58
42.75
5.83
EMBODIMENT OF THE PRESENT SUBJECT MATTER:
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[0064] In an embodiment of the present subject matter, the conducting polymer is used as matrix is chosen from polymers of pyrrole and the like. The monomer have nitrogen group in cyclic ring structure.
[0065] Another embodiment, the dielectric fillers is barium titanate, Barium Strontium titanate, and the like. 20
[0066] Another embodiment, magnetic fillers is Fe3O4, Y-Fe2O3, and the like.
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[0067] Another embodiment, conducting polymer matrix posse’s conductive material like reduced graphene oxide and the like. Further, the surfactant like sodium lauryl sulfate (SLS), dodecylbenzenesulfonic acid (DBSA) and the like has been used for emulsion polymerization.
[0068] In another embodiment of the present process, 0.1 M pyrrole and filler materials 5 is added in aqueous suspension of 0.2 M sodium lauryl sulfate and homogenized for 2 hours at 10000 rpm. Further, 0.2 M FeCl3 is added to the reaction mixture in drop-wise manner with continuous stirring for 4-5 hours. The conductive polymer composite samples were investigated for EMI shielding application. The powder composite was pelletized in rectangular shape of dimension 22.8 X 10.03 X 2.5 mm. The conducting 10 polymer composite embedded with BRF hybrid were tested for EMI shielding application.
[0069] Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific 15 features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/component of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter.

Claims:We claim:
1. A polymer based composite for EMI shielding, the said polymer based composite comprises Pyrrole encapsulated with dielectric material like barium strontium titanate or magnetic materials like Fe3O4 or conductive material like RGO in presence of aqueous suspension of like sodium lauryl sulfate.
2. A process for synthesizing polymers based composite for EMI shielding application, the process comprising steps of:
a) Synthesizing of Barium strontium titanate (BST);
b) Synthesizing of Reduced Graphene Oxide (RGO) from natural graphite powder;
c) Synthesizing of Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 composite (BRF composite) by co-precipitation of FeCl2 and FeCl3; and
d) Mixing Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 composite (BRF composite) in polypyrrole matrix in different weight ratio (BRF:P), wherein the mixture the Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 composite (BRF composite) and polypyrrole (PBRF) is polymerized by adding 0.2 M FeCl3 drop by drop at room temperature with continuous stirring for 4-5 hours.

3. The process as claimed in claim 2, wherein the process further comprising obtaining final composite solution after washing and filtering, wherein the obtained composite powder is dried in vacuum oven at 60oC.

4. The process as claimed in claim 2, wherein the different weight ratio of BRF:PPY are 0.5:1, 1:1, 1:2.
5. The process as claimed in claim 2, wherein the conducting polymer is used as matrix is selected from polymers of pyrrole and the like, wherein the polymer has a nitrogen group in cyclic ring structure.

6. The process as claimed in claim 2, wherein the dielectric fillers is barium titanate, Barium Strontium titanate, and the like.

7. The process as claimed in claim 2, wherein the magnetic fillers is Fe3O4, Y-Fe2O3, and the like.
8. The process as claimed in claim 2, wherein the Sodium Lauryl Sulfate is used as surfactant and its molar concentration with respect to monomer was maintained between 0.1 to 0.4 mole.

9. The process as claimed in claim 2, wherein the Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 composite and polypyrrole (PBRF composite) are synthesized by polymerizing 0.1 M pyrrole and filler materials is added in aqueous suspension of 0.2 M sodium lauryl sulfate and homogenized for 2 hours at 10000 -12000 rpm.

10. The process as claimed in claim 2, wherein the step (b) Synthesizing of Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 composite (BRF composite) comprises: mixing RGO and BST in 1:2 weight ratios wrt to Fe3O4 in solution of 1.0 M FeCl2 and 0.2 M FeCl3 and stirred for 1 hour, and adding 0.1 M aqueous NH3 solution drop by drop to the reaction solution to obtain BRF composite.
, Description:CONDUCTING POLYMER COMPOSITE FOR ELECTROMAGNETIC INTERFERENCE SHIELDING AND A PROCESS OF PREPARATION THEREOF
FIELD OF INVENTION:
[001] The present invention relates to conducting polymer composite for electromagnetic interference shielding and a process of preparation thereof. The synthesized polymer composite act as a excellent shield against microwave radiations in the frequency range of 8.2 GHz to 12.4 GHz (x-band). Specifically the present invention describes the process of synthesis of conducting polymer composite comprising of polymer matrix and encapsulated with nanofillers like magnetic fillers, dielectric fillers.
BACKGROUND OF INVENTION:
[002] Electromagnetic radiations cause interference in nearby electronic system working and also have adverse effect on human health. World Health Organization (WHO) also raised his concern over the effect of EM radiation on human and environment. So the need of highly absorption based EM shielding material is amplified. Traditionally metal, metallic foams, films and metal composite have been used against EMI pollution. They have certain shortcomings like heavy weight, corrosion, high cost and short life span etc. The present invention relates to the designing and synthesis of alternative material which is fulfills these shortcomings and act as shield against the EMI pollution. In past decades many researchers explore the field of EMI shielding and work on various materials like dielectric fillers and magnetic fillers for the shielding purposes. The shielding effectiveness of the composite depends upon various factors like thickness, magnetic permeability, dielectric permittivity and frequency. Herein in this invention conducting polymer matrix is embedded with the dielectric fillers, conductive materials and magnetic fillers. The combined synergistic effect of these materials exhibits excellent shielding effectiveness.
[003] Following are the works done so far in the field of conductive polymers based materials for protection against electromagnetic Inference.
[004] US patent- 8847184 B2: Composite film for board level EMI shielding. The patent relates to development of composite film that protects the printed circuit board from electromagnetic interference. It contains basically two layer system; the top layer is conducting in all direction while bottom layer is conductive only in z direction. Both top and bottom layers were thermally compressed. The different layers were composed of thermoset or thermoplastic resin or there combination. Different conducting fillers were loaded in the matrix like silver, nickel, copper, graphite, carbon nanotubes, and core/shell particles. Theses fillers were loaded about 15 volume% or more wrt to the total composition of the top layer. In bottom layer conductive filler loading level is about 2 to 20 volume% wet to the total composition of the bottom layer. Dielectric materials like boron nitride, aluminum oxide, aluminum nitride, were also incorporated in the bottom layer and loading varies from 10 to 80 Wt%. The top layer prevents the electromagnetic radiations to enter in the electronic system and escaping into the environment. The bottom layer interconnects the top and grounding pads and facilitates the release of the radiations.
[005] WO 1999057952 A1: Emi shielding enclosures. Present patent relates to the designing of EMI shielding enclosures that comprise of ground plane, shielding cover formed by thermoforming composite sheet. The shielding cover posses a non-porous carrier sheet and fibrous metal mat. The carrier sheet is made up of polymer like polycarbonate, acrylonitrile butadiene styrene copolymers (ABS), styrene acrylonitrile copolymers (SAN), polystyrene, polyvinyl chloride, polyether imide, polypropylene, polyethylene, polybutylene, polyamide, polyethylene terephthalate, etc. These carrier plates have softening point below 150 oC. The fiber coat comprises of thermoplastic polymers, hot melt adhesive polymers and pressure sensitive adhesive polymers. The outer surface has thickness less than 0.15 mm.
[006] US 8520406 B2: Electromagnetic interference shielding structure including carbon nanotube or nanofiber films. The patent describes preparation of composite material for electromagnetic interference shielding. The composite material is made up of layer structure that contains two different film layers separated to each other. The two conductive layers were separated by one insulating gap. This stack structure enhances the shielding effectiveness by increasing multiple internal reflections. At least one of the nanoscale fiber films comprises a buckypaper and one of the nanoscale fiber films has a conductivity of at least 5 S/cm. The insulating gap made up of dielectric materials like polyethylene, polyethylene terephthalate, polyetherketone, or a combination of them. The insulating gap thickness ranges from about 200 µm to about 2 mm. This film structure is flexible in nature and has a thickness from about 1 mm to about 2.5 mm. The stack structure provides an electromagnetic interference shielding effectiveness ranging from 5 dB to 100 dB in the frequency range of 4 GHz to 18 GHz.
[007] US 20100311866 A1: Heirarchial polymer-based nanocomposites for emi shielding. The patent deals with the development of polymer based nano-composite for electromagnetic shielding that includes three nanofillers used in a formation of a hierarchy in structure, length, size, and dimension. Three different filler (nickel-coated carbon fibers, carbon nanofibers and multi-walled carbon nanotubes) has been used in this composite. Herein a thermoplastic polymer matrix is used like acrylonitrile-butadiene-styrene. The final composition of composite comprises 18 wt % of nickel-coated carbon fibers (NCCB), 7 wt % of carbon nanofibers, and 2 wt % of multi-walled carbon nanotubes incorporated in ABS copolymer matrix of 72 wt %. A suspension of ABS and of all three nanofillers was compressed molded at 225 oC into a sheet of either 12.7×12.7×0.1 cm or 61×61×0.1 cm. The composite material shows the shielding effectiveness of 33 to 73 dB at frequency range 0.8-18 GHz.
[008] US 9469743 B2: Composite material with conductive and ferromagnetic properties and hybrid slurry. The invention relates to a synthesis of conducting polymer composite for EMI shielding. The material prepared by chemical oxidative polymerization of different monomers like aniline, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), etc. The conducting polymer contain conjugated system like polyacetylene, polypyrrole, polythiophene, polyaniline, poly(p-phenylene sulfide, poly(p-phenylene vinylene, poly(3,4-ethylenedioxythiophene, poly(3,4-ethylenedioxythiophene)-polystyrene sulfonateThe conductive matrix is about 5 to 90 parts by weight and ferromaganetic filler (iron oxide nanorods) is about 0.1 to 40 parts by weight. The iron oxide nanorods comprise of Fe3O4, ?-Fe2O3, or combination. The diameter of nanorods is about 10 to 100 nm and length to diameter ratio is between 5 and 10. This conducting polymer composite is dispersed in adhesive materials like polyvinyl alcohol, polyacrylic acid, polyurethane, epoxy resin, polymethylmethacrylate and acrylonitrile butadiene styrene etc. The resulting slurry is sonicated in vaccum, poured in mold and dreid at 50 oC in oven to yield thin film of dimension 15 cm×15 cm×40 cm. The obtained films can be utilized in EMI shielding, radar/microwave absorption, or electro static discharge (ESD) applications.
[009] CN 101525436 A: Polypyrrole/Fe3O4/graphite nanosheets composite material and preparation method thereof. This invention deals with the method of synthesizing Polypyrrole / Fe3O4/ graphite nanosheets composite. Sodium dodecyl benzene sulfonate is used as a surfactant and graphite nanosheets were dispersed in the aqueous medium. Pyrrole used as monomer and adsorbed at Fe3O4 nanoparticles by stirring for 1 hour. FeCl3, 6H20 added to the reaction mixture and stirred for 20~24 hours at room temperature. The resultant product was filtered, washed with distilled water and dried in oven. Thickness of graphite nanosheets is about 30~80nm. Fe3O4 nanoparticles particles size is around 10nm to 15nm. Composite material shows conductivity in the range of 2.8~9.4 S/cm.
[0010] CN 103571215 A: High thermal conductivity and EMI sheltering high polymer composite material. This patent describes development of high thermal conductivity and EMI sheltering high polymer composite material. This composite material is synthesized by blending a thermal conduction material with an electromagnetic wave shielding material and a high polymer binder. Polymer composite material, comprises inorganic composite, that have 0.5 wt% to 80wt% of thermally conductive material and 15wt% to 95wt% of the electromagnetic wave shielding material. Thermally conductive material present in the composite materials includes metal, ceramic powder, carbon black, carbon fiber, single-walled or multi-walled carbon nano tubes, graphite, graphene or graphene oxide. The electromagnetic shielding material comprise materials like metal, metal oxide nanoparticles, graphene or ferrite magnets. Conductive matrix includes conductive polymer like: polyacetylene (Polyacetylene), polyphenylene acetylene (polyphenylvinylene), poly-para-phenylene (Poly-p-phenylene), polypyrrole (Polypyrrole), polythiophene (Polythiophene), polyaniline (Polyaniline), polyethylene dioxythiophene Poly (3,4 ~ ethylenedioxythiophene), or derivatives or copolymers thereof. The said composite is synthesized by in-situ intercalation polymerization (in-situ intercalative polymerization). The resultant composite is dispersed in alcohol based dispersants, like a polyvinyl alcohol (Polyvinyl alcohol), polyethylene glycols etc. The composite material shows 15 to 48 dB shielding effectiveness in frequency range of 100 KHz ~ 2.45GHz.

[0011] WO 2007101646 A1: Functional papers for the absorption of radiofrequency electrical fields and method for their production. A excellent EMI Shielding system is described in present invention. A improved barrier system is developed to absorbed the microwave radiation. As per invention papers have one or more layers structure, functional layers contain different types of inorganic materials which is evenly dispersed in the matrix. While one of the layers contains ferrite particles like hexaferrites, doped hexaferrites etc ferrite particles were blended with various electromagnetic radiation absorbing materials, like carbonyl iron, iron silicides and / or titanates etc. The present invention claims excellent microwave-absorption and low-reflection properties of paper in the frequency range of from 1 GHz to 100 GHz.
[0012] EP 0781085 A1: Method and arrangement for electromagnetically shielding an electronic means. The invention described the dual barrier property of the film that provides protection against external electromagnetic interference and preventing the electronic devices from interference created by close by electric devices. According to the invention, a shielding film posse’s layer structure that contains one or more layers of intrinsically conductive polymer and insulating films. Conductive film material is an intrinsic conducting polymer like polyaniline with different surfactants like camphor sulphonic acid (CSA), dodecylbenzenesulfonic (DBSA). Material used for insulating film is polycarbonate, polyurethane or polyvinyl fluoride etc. various different techniques like heat treatment or a vacuum treatment or the combination of the two is used to attached the composite film to the surface of the electronic devices. The present invention also claims a process for electrically connecting the intrinsic polymers layer to the electronic devices. The invention further claims a process for using the electromagnetic shield to form capacitors and resistors for the electronic devices like mobile communication device.
OBJECTIVE OF THE INVENTION:
[0013] The main objective of the present invention is to design efficient conducting polymer composite encapsulated with dielectric filler and magnetic fillers for EMI shielding application.
[0014] Another object of the present invention is to provide alternative EMI shielding material that has low cost, corrosion resistant, light weight, easily processable and provide effective shield against electromagnetic radiations.
SUMMARY OF THE INVENTION:
[0015] The present invention relates to a process for designing of conducting polymer based composite shield against EMI pollution. The polymer matrix is embedded with a hybrid material that contains different dielectric or magnetic or conductive fillers. The method comprising steps of: Synthesis of conducting polymer Polypyrrole/RGO/BST/Fe3O4 composite by a facile chemical oxidative polymerization method in aqueous medium consisting Sodium Lauryl Sulphate. After synthesis, Loading of hybrid materials like magnetic, dielectric, and conductive fillers in the polymer matrix. At the end, testing the Shielding effective of conducting polymer composite by vector network analyzer at frequency range of 8.2-12.4 GHz.
[0016] The polymer matrix chosen for the study is polypyrrole. Further, the BRF hybrid material is synthesized by incorporating barium strontium titanate, RGO in the FeCl3 and FeCl2 solution. The resultant solution was co-precipitated by ammonia solution. The BRF hybrid material is homogenized in sodium lauryl sulfate aqueous suspension for 2 hour at 10000-12000 rpm. Further, the BRF hybrid material is loaded in the polymeric matrix with respect to monomer, taken as 1:0.5, 1:1 and 1:2 weight ratios. The monomer is added in reaction medium for polymerization, at room temperature. The oxidation of reaction mixture is carried out by oxidant like ammonium persulphate or potassium persulphate, ferric chloride and the like. The polymerization reaction was stirred for 4-5 hours. The content of monomer to oxidant ratio was maintained between 0.1 mole to 0.2 mole.
[0017] In another embodiment of the invention, Sodium Lauryl Sulphate is used as surfactant and its molar concentration with respect to monomer was maintained between 0.1 to 0.4 mole.
[0018] In another embodiment of the invention, the final resultant composite was dried at 50-60 oC in vacuum oven.
[0019] In another embodiment of the invention, the powder composite was pelletized in rectangular shape of dimension 22.8 X 10.03 X 2.5 mm.
[0020] In another embodiment of the invention, conducting polymer composite embedded with BRF hybrid were tested for EMI shielding application.
[0021] In order to further understand the characteristics and technical contents of the present subject matter, a description relating thereto will be made with reference to the accompanying drawings. However, the drawings are illustrative only but not used to limit scope of the present subject matter.
BRIEF DESCRIPTIONS OF THE DRAWINGS
[0022] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[0023] Fig. 1: Schematic of the synthesis of polypyrrole/RGO/BST/Fe3O4 composite by chemical oxidative polymerization process, in accordance with an embodiment of the present subject matter;
[0024] Fig. 2 illustrates process step for manufacturing of PBRF composite, in accordance with an embodiment of the present subject matter;
[0025] Fig 3: SEM micrographs showing morphology of (a) Barium Strontium Titnate, (b) Polypyrrole, (c) & (d) of polypyrrole/RGO/BST/Fe3O4 at magnification scale shows Edax pattern. BRF composite particles embedded inside the polymer matrix are visible in the micrograph, in accordance with an embodiment of the present subject matter;
[0026] Fig. 4: XRD patterns of (a) BRF, (b) Polypyrrole, (c) polypyrrole/RGO/BST/Fe3O4 (PBRF1, PBRF2, and PBRF3), in accordance with an embodiment of the present subject matter;
[0027] Fig. 5: FTIR Spectra of (a) BST, (b) BRF, (c) Polypyrrole and (d) polypyrrole/RGO/BST/Fe3O4 (PBRF1,PBRF2, PBRF3), in accordance with an embodiment of the present subject matter;
[0028] Fig. 6: TGA Plots of (a) BRF, (b) Polypyrrole and (c) polypyrrole/RGO/BST/Fe3O4 (PBRF1, PBRF2, and PBRF3), in accordance with an embodiment of the present subject matter;
[0029] Fig. 7 Vibrating Sample Magnetometer plots of the a) BRF, (b) polypyrrole/RGO/BST/Fe3O4 (PBRF1, PBRF2, and PBRF3), in accordance with an embodiment of the present subject matter;
[0030] Fig. 8: Variation of total shielding effectiveness with frequency, in accordance with an embodiment of the present subject matter;
[0031] Fig. 9: Shielding effectiveness due to absorption loss, in accordance with an embodiment of the present subject matter; and
[0032] Fig 10: Shielding effectiveness due to reflection loss, in accordance with an embodiment of the present subject matter.
[0033] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
[0034] At the very outset of the detailed description, it may be understood that the ensuing description only illustrates a particular form of this invention. However, such a particular form is only exemplary embodiment, and without intending to imply any limitation on the scope of this invention. Accordingly, the description is to be understood as an exemplary embodiment and teaching of invention and not intended to be taken restrictively.
[0035] The present subject matter relates to a polymer based composite for EMI shielding, the said polymer based composite comprises Pyrrole encapsulated with dielectric material like barium strontium titanate or magnetic materials like Fe3O4 or conductive material like RGO in presence of aqueous suspension of like sodium lauryl sulfate.
[0036] In another embodiment of the present subject matter relates to a process for synthesizing polymers based composite for EMI shielding application. The process comprising steps of: Synthesizing of Barium strontium titanate (BST) and Synthesizing of Reduced Graphene Oxide (RGO) from natural graphite powder. After synthesizing of BST and RGO, BRF composite is prepared by synthesizing of Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 composite (BRF composite) by co-precipitation of FeCl2 and FeCl3. At the end PBRF composite is prepared by mixing Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 composite (BRF composite) in polypyrrole matrix in different weight ratio (BRF:PPY). The mixture the Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 composite (BRF composite) and polypyrrole (PBRF) is polymerized by adding 0.2 M FeCl3 drop by drop at room temperature with continuous stirring for 4-5 hours.
[0037] It should be noted that the description and figures merely illustrate the principles of the present subject matter. It should be appreciated by those skilled in the art that conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present subject matter. It should also be appreciated by those skilled in the art that by devising various arrangements that, although not explicitly described or shown herein, embody the principles of the present subject matter and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the present subject matter and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. The novel features which are believed to be characteristic of the present subject matter, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures.
[0038] These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
[0039] The present subject matter relates generally to electromagnetic (EM) radiation absorbing composites containing conducting polymer and carbon allotropes. These prepared composites found enormous applications as EM shielding materials, for example, EM-sensitive electronic equipment, stealth vehicles, aircraft, etc., having low radar profiles, protection of electronic components from interference from one another on circuit boards, protection of computer equipment from emitting RF radiation causing interference to navigation systems, medical life support systems, etc. Without being bound by theory, it is believed that in composites of this invention, EM shielding is achieved through absorption of radiation rather than reflection.
[0040] Figure 1 describes the process of synthesizing and designing of conducting polymers based composite for EMI pollution. Further, the each step as shown in the figure 1 is illustrates and explained in the method figure 2. Therefore, the figure 1 and figure 2 should be considered together for better illustration and understanding of the present subject matter. The figure 2 illustrates the steps of the figure 1. As shown in the figure 2 at step 202, Barium strontium titanate is synthesized. Further, the Synthesis of Barium strontium titanate is explained in the example 2.
[0041] At step 204, Synthesizing of Reduced Graphene Oxide (RGO) from natural graphite powder is explained. Further, detailed explanation of the synthesized is explained in the example 3.
[0042] At step 206, the Synthesizing of Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 composite (BRF composite) by co-precipitation of FeCl2 and FeCl3 is explained. Whereas detailed explanation is given in the example 4.
[0043] At step 208, Mixing Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 composite (BRF composite) in polypyrrole matrix in different weight ratio (BRF:PPY) is explained. The mixture the Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 composite (BRF composite) and polypyrole (PBRF) is polymerized by adding 0.2 M FeCl3 drop by drop at room temperature with continuous stirring for 4-5 hours. Further more detailed explanation is given in the example 5-7.
[0044] At the end, EMI shielding measurements of the final PBRF composite is crushed in mortar and pestle. The PBRF composite pellets of dimension (22.8 X 10.03 X 2.5 mm) are made with help of hydraulic press and various shielding parameters were measured on Agilent E8362B VNA in the 8.2-12.4 GHz (X-band) microwave range. Further, all test results and comparisons are given in the table 1.
[0045] The following examples are given to illustrate the process of the present invention and should not be construed to limit the scope of the present invention:
Example 1: Synthesis of Polypyrrole
[0046] Synthesis of polypyrrole has been carried out by the chemical oxidative polymerization of pyrrole monomer. Herein 0.2 M Sodium Lauryl Sulphate aqueous solution is homogenized at 10000 rpm. 0.1 M pyrrole monomer is added to this slurry and stirred for 1 hour. FeCl3 (0.2M) is used as oxidant and added to the reaction mixture in drop wise manner to polymerize the reaction. The reaction mixture was stirred for 4-5 hour. The solution is then filtered and washed with distilled water. The resultant product is dried at 60 ?C in the vacuum oven.
Example 2: Synthesis of Barium strontium titanate
[0047] Modified polymerized citrate precursor method was used for the synthesis of BST nanoparticles. In a typical reaction, 0.1 mol of titanium tetrabutoxide and 2 mol of ethylene glycol were dissolved and stirred until it results into transparent and yellow solution. Citric acid (CA) was added with small amount of water to this reaction mixture. The resultant slurry was stirred for 30 min, and the solution became transparent. Barium carbonate (BaCO3) 0.07 mol and Strontium carbonate (SrCO3) 0.03 mol were added to this solution. Few drops of nitric acid (HNO3) was added to the reaction mixture to initiates the catalysis of samples dissolved in reaction mixture. The reaction mixture was stirred till solution colour turns to transparent and pale brown. Further reaction mixture was dipped in hot silicon oil (50–60 oC) and stirred for 12 h. Excess solvent was removed by drying into an oven at 150 oC. Viscosity of resin increases due to the continuous heating and its colour changes from pale brown to deep brown. The obtained resin was charred at 300 oC for 2h in an electric furnace, yields black solid mass. The charred precursor was calcined at 800–900 oC at rate of 10 oC/min for eight hours in a muffle furnace yields white BST powder.

Example 3: Synthesis of Reduced Graphene Oxide
[0048] Improved hummers method is used to synthesize Reduced Graphene oxide (RGO) from natural graphite powder. A homogeneous mixture was prepared by adding sulphuric acid (H2SO4 (360 ml) and o-phosphoric acid (H3PO4 (40 ml) by vigorous stirring and immersed in an ice bath to maintain the low temperature for reaction. To this mixture 3 gm (1 wt eq.) natural graphite powder was added and stirred till uniform dispersion of graphite is achieved. With the slow addition of 18 gm (6 wt eq.) of KMnO4 there is rise in temperature (about 35–40 oC) of reaction mixture. The resultant mixture was stirred for 20 hours at 50 oC. 400 ml ice cold distilled water was added to the solution. Subsequently 10 ml H2O2 is added to the reaction, there is change in the suspension colour from dark brown to yellow. The obtained suspension is washed with HCl, followed by DI water, till pH 7 was attained. Graphene oxide was recovered with ethanol and dried at 80 oC in a vacuum oven. 1 gm of graphene oxide is dispersed in 1l of distilled water and ultrasonicated for 1hour. 10 mL of hydrazine was added to the ultrasonicated solution, and stirred for 4hours at 80 oC. The final product is filtered and dried in vacuum oven at 60 oC.

Example 4: Synthesis of Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 composite (BRF composite)
[0049] Barium strontium titanate/ Reduced Graphene oxide/ Fe3O4 hybrid material was prepared by co-precipitation of FeCl2 and FeCl3 in the presence of Barium strontium titanate (BST), reduced graphene oxide (RGO). 1.0 M FeCl2 and 0.2 M FeCl3 were mixed in an appropriate quantity of HCl. RGO and BST (1:2 weight ratios wrt to Fe3O4) were added to the above solution and stirred for 1 hour. 0.1 M aqueous NH3 solution was added drop by drop to the reaction solution. Brownish black precipitate was observed in reaction and solution is stirred for 2 hours. The suspension was filtered and washed with DI water till pH 7 is attained. The final product is obtained after drying the filtrate in vacuum oven at 60 oC.

Example 5: Synthesis of Polypyrrole/Barium strontium titanate/Reduced Graphene oxide/ Fe3O4 (PBRF1)
[0050] In typical reaction PBRF composite was synthesized by using emulsion polymerization technique. A aqueous solution of 0.2 M Sodium Lauryl Sulphate is homogenized at 10000 rpm for 2 hours. 3.39 gm (0.5:1 weight ratio wrt to monomer (pyrrole)) of BRF hybrid material, followed by 0.1 M pyrrole monomer was added to the slurry and homogenized for 2 hours at 10000 rpm. 0.2 M FeCl3 solution was added to the reaction in drop wise manner at room temperature. The reaction mixture was stirred for 4-5 hours. The obtained product was filtered in G2 filtration funnel and washed with DI water. Black powder was obtained after drying at 60 oC in vacuum oven.
[0051] For EMI shielding measurements PBRF composite was crushed in mortar & pestle. PBRF composite pellets of dimension (22.8 X 10.03 X 2.5 mm) were made with help of hydraulic press and various shielding parameters were measured on Agilent E8362B VNA in the 8.2-12.4 GHz (X-band) microwave range.

Example 6: Synthesis of Polypyrrole/Barium strontium titanate/Reduced Graphene oxide/ Fe3O4 (PBRF2)
[0052] PBRF composite was synthesized by a facile method of in-situ emulsion polymerization using FeCl3 as a oxidant. 0.1M pyrrole monomer was dispersed in 0.2 M Sodium Lauryl Sulphate aqueous suspension. 6.79 gm (1:1 weight ratio wrt to monomer (pyrrole)) of BRF hybrid material is added to this suspension and homogenized for 2 hour at 10000 rpm. The reaction mixture was polymerized by adding 0.2 M FeCl3 drop by drop. The solution is stirred for 4-5 hour at room temperature. The resultant precipitate was filtered using G2 funnel and washed with DI water. The filtered PBRF composite was dried in vacuum oven at 60 o C.
[0053] Agilent E8362B VNA is used for EMI shielding measurement in the 8.2-12.4 GHz (X-band) microwave range. The resultant composite was grinded by using mortar & pestle, PBRF composite was pelletized in dimension (22.8 X 10.03 X 2.5 mm) with help of hydraulic press. The maximum shielding effectiveness of 44 (dB) was obtained with PBRF2 at 8.2 GHz frequency.
Example 7: Synthesis of Polypyrrole/Barium strontium titanate/Reduced Graphene oxide/ Fe3O4 (PBRF3)
[0054] Polypyrrole/Barium strontium titanate/Reduced Graphene oxide/Fe3O4 composite were synthesized by polymerizing 0.1 M pyrrole in a aqueous suspension of 0.2 M of Sodium Lauryl Sulphate. BRF hybrid material 13.5 gm (1:2 weight ratio wrt to monomer (pyrrole)) was added to the reaction solution and homogenized for 2 hours at 10000 rpm. The above solution was polymerized at room temperature through emulsion polymerization by using 0.2 M FeCl3 as an oxidant. The reaction mixture was continuously stirred for the 4 hours and yields blackish solution. The final composite solution was filtered and washed with distilled water. The obtained composite was dried at 60 oC in a vacuum oven and grinded into fine powder using mortar and pestle. This fine powder was pelletized in dimension of (22.8 X 10.03 X 2.5 mm). PBRF3 composite act as a barrier against EMI pollution and shows shielding effectiveness of 48 (dB) at 8.2 GHz frequency.
[0055] Fig 3: SEM micrographs showing morphology of (a) Barium Strontium Titnate, (b) Polypyrrole, (c) & (d) of polypyrrole/RGO/BST/Fe3O4 at magnification scale shows Edax pattern. BRF composite particles embedded inside the polymer matrix are visible in the micrograph, in accordance with an embodiment of the present subject matter.
[0056] Fig. 4: XRD patterns of (a) BRF, (b) Polypyrrole, (c) polypyrrole/RGO/BST/Fe3O4 (PBRF1, PBRF2, and PBRF3), in accordance with an embodiment of the present subject matter.
[0057] Fig. 5: FTIR Spectra of (a) BST, (b) BRF, (c) Polypyrrole and (d) polypyrrole/RGO/BST/Fe3O4 (PBRF1,PBRF2, PBRF3), in accordance with an embodiment of the present subject matter.
[0058] Fig. 6: TGA Plots of (a) BRF, (b) Polypyrrole and (c) polypyrrole/RGO/BST/Fe3O4 (PBRF1, PBRF2, and PBRF3), in accordance with an embodiment of the present subject matter.
[0059] Fig. 7 Vibrating Sample Magnetometer plots of the a) BRF, (b) polypyrrole/RGO/BST/Fe3O4 (PBRF1, PBRF2, and PBRF3), in accordance with an embodiment of the present subject matter.
[0060] Fig. 8: Variation of total shielding effectiveness with frequency, in accordance with an embodiment of the present subject matter.
[0061] Fig. 9: Shielding effectiveness due to absorption loss, in accordance with an embodiment of the present subject matter.
[0062] Fig 10: Shielding effectiveness due to reflection loss, in accordance with an embodiment of the present subject matter.
[0063] EMI shielding data of various combinations of BRF composite incorporated in Polypyrrole matrix
TABLE 1
SI No. Sample Pyrrole BRF SET SEA SER
1. BRF ----- ---- 14.06 12.22 1.84
2. PBRF1 6.79 g 3.35g 44.44 38.47 5.97
3. PBRF2 6.79 g 6.79g 44.56 41.36 3.20
4 PBRF3 6.79g 13.58 48.58 42.75 5.83

EMBODIMENT OF THE PRESENT SUBJECT MATTER:

[0064] In an embodiment of the present subject matter, the conducting polymer is used as matrix is chosen from polymers of pyrrole and the like. The monomer have nitrogen group in cyclic ring structure.
[0065] Another embodiment, the dielectric fillers is barium titanate, Barium Strontium titanate, and the like.
[0066] Another embodiment, magnetic fillers is Fe3O4, Y-Fe2O3, and the like.
[0067] Another embodiment, conducting polymer matrix posse’s conductive material like reduced graphene oxide and the like. Further, the surfactant like sodium lauryl sulfate (SLS), dodecylbenzenesulfonic acid (DBSA) and the like has been used for emulsion polymerization.
[0068] In another embodiment of the present process, 0.1 M pyrrole and filler materials is added in aqueous suspension of 0.2 M sodium lauryl sulfate and homogenized for 2 hours at 10000 rpm. Further, 0.2 M FeCl3 is added to the reaction mixture in drop-wise manner with continuous stirring for 4-5 hours. The conductive polymer composite samples were investigated for EMI shielding application. The powder composite was pelletized in rectangular shape of dimension 22.8 X 10.03 X 2.5 mm. The conducting polymer composite embedded with BRF hybrid were tested for EMI shielding application.
[0069] Although embodiments for the present subject matter have been described in language specific to structural features, it is to be understood that the present subject matter is not necessarily limited to the specific features described. Rather, the specific features and methods are disclosed as embodiments for the present subject matter. Numerous modifications and adaptations of the system/component of the present invention will be apparent to those skilled in the art, and thus it is intended by the appended claims to cover all such modifications and adaptations which fall within the scope of the present subject matter.