Low-carbon halogen-fire-free safe polyolefin material and preparation method thereof
By adding recycled resin and biomass raw materials to polyolefin materials, low-carbon, halogen-free and fire-safe polyolefin materials are prepared, which solves the problem of insufficient flame retardancy and fire protection and achieves flame retardancy and fire protection in a combustion environment.
Patent Information
- Application Number
- CN202511082392.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-04
- Publication Date
- 2025-09-09
AI Technical Summary
Existing polyolefin materials have deficiencies in flame retardancy and fire resistance, especially in that they are easily fragile and fall off during combustion, and cannot effectively prevent the spread of flames.
A low-carbon, halogen-free, fire-safe polyolefin material is prepared by adding recycled resin raw materials and biomass raw materials, combined with surface-modified silicate powder, flux and flame retardant, to form a ceramic shell layer to improve flame retardancy and fire resistance.
It exhibits good flame retardant properties in a short period of time and quickly forms a ceramic shell under long-term flame erosion, achieving long-term fire protection. It is suitable for fire protection of wires and cables and electronic appliances in new energy vehicles.
Smart Images
Figure CN120607757A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of new energy fire safety materials, and in particular to a low-carbon, halogen-free, fire-safe polyolefin material and a preparation method thereof. Background Art
[0002] Due to their excellent electrical insulation properties and good processing properties, polyolefin materials are widely used in wires and cables, electronic and electrical accessories, and casing protection. Therefore, improving the fire safety performance of polyolefin materials is of vital importance. Currently, most common flame-retardant polyolefin composite materials on the market use hydroxides as flame retardants. Hydroxides need to be added in large quantities to ensure the flame retardant properties of the composite materials. In addition, hydroxides mainly rely on absorbing heat and releasing water vapor during the combustion process to achieve the purpose of flame retardancy. Therefore, the residues of such flame-retardant polyolefin composite materials after combustion have a loose structure and are extremely fragile. They will fall off and break under the action of external forces or flame impact, thus failing to achieve the fireproof effect.
[0003] To achieve fireproofing requirements, sintering aids (such as low-melting-point glass powder) and fillers such as silicates can be added to polyolefins. This allows the glass powder to melt and bond with the silicate filler during combustion, forming a dense ceramic shell that can withstand the impact of sustained flames. Currently, common flame-retardant polyolefin materials on the market have good flame retardancy but lack fireproofing properties. Ceramicized polyolefin materials, while somewhat fireproof, lack excellent flame retardancy, and their overall fire safety performance needs further improvement. Summary of the Invention
[0004] The present invention aims to address the deficiencies in the fire safety performance of polyolefin materials in the prior art. By adding recycled resin and biomass raw materials, a method for preparing a low-carbon, halogen-free, fire-safe polyolefin composite material is provided. This composite material exhibits excellent flame retardancy under short-term flame conditions and rapidly forms a ceramic shell under prolonged flame ablation, providing long-term fire protection. The composite material has potential applications in protecting wires and cables, electronic and electrical components, and housings for new energy vehicles. This can ensure that cable harnesses remain functional in a burning environment, and that the housing acts as a flame retardant to prevent the spread of fire in the event of a battery thermal runaway.
[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A low-carbon, halogen-free, fire-safe polyolefin material comprising the following components in parts by weight: 60-100 parts of polyolefin resin, 5-30 parts of compatibilizer, 10-50 parts of surface-modified silicate powder, 10-40 parts of flux, 20-50 parts of flame retardant, 1-5 parts of antioxidant, and 10-20 parts of surface-modified biomass material.
[0006] As a preferred embodiment, the polyolefin resin includes at least one of 20 to 60 parts of polyethylene, 20 to 60 parts of polypropylene, 20 to 50 parts of ethylene-octene copolymer, and 30 to 40 parts of ethylene-vinyl acetate copolymer.
[0007] As a preferred solution, the compatibilizer comprises at least one of 5 to 20 parts of maleic anhydride grafted polyolefin elastomer and 10 to 30 parts of maleic anhydride grafted polyolefin.
[0008] As a preferred embodiment, the surface-modified silicate powder includes at least one of surface-modified mica, surface-modified wollastonite, surface-modified montmorillonite, and surface-modified kaolin.
[0009] As a preferred embodiment, the flux comprises: at least one of low melting point glass powder and zinc borate; The flame retardant comprises at least one of piperazine pyrophosphate, ammonium polyphosphate, melamine cyanurate and melamine phytate.
[0010] As a preferred solution, the antioxidant includes: at least one of antioxidant 1010, antioxidant 1076, antioxidant 168, and antioxidant 300.
[0011] As a preferred embodiment, the surface-modified biomass material includes at least one of surface-modified Sichuan pepper seed shells, surface-modified coffee grounds, and surface-modified straw.
[0012] A preparation method of a low-carbon, halogen-free, fire-safe polyolefin material comprises the following steps: S1. Pre-weighing and preparing materials: weighing the following parts by weight: 60-100 parts of polyolefin resin, 5-30 parts of compatibilizer, 10-50 parts of surface-modified silicate powder, 10-40 parts of flux, 20-50 parts of flame retardant, 1-5 parts of antioxidant and 10-20 parts of surface-modified biomass material; S2. Banbury mixing: Add the polyolefin matrix, compatibilizer, and antioxidant into a banbury mixer at 130-200° C. and mix for 2-10 minutes; Then add silicate powder, flux, flame retardant and biomass material, mix at 150-200°C for 3-10 minutes, stop mixing and obtain a mixture; S3. Tablet forming: The mixed material is tableted by a flat-plate tablet press to obtain a low-carbon, halogen-free, and fire-safe polyolefin material. The tableting temperature is 150-200° C., the pressure is 5-15 MPa, and the tableting time is 2-10 min.
[0013] As a preferred embodiment, the surface-modified silicate powder in S1 is prepared by dispersing the silicate powder in a metal ion-containing aqueous solution, slowly adding a phytic acid solution dropwise, stirring for a certain period of time, filtering and washing the product with distilled water, and drying in an oven for later use; Wherein: the metal ion aqueous solution includes: one of: manganese acetate solution, zinc acetate solution, nickel acetate solution, and calcium acetate; the phytic acid concentration is 0.015 mol / L, and the stirring time is 2 hours.
[0014] As a preferred embodiment, the preparation method of the surface-modified biomass material in S1 is to grind and sieve the biomass raw material, then mix, react or coat it with the flame retardant component under certain conditions, filter and wash the product with distilled water, and dry it in an oven for later use; The biomass material comprises: one of: pepper seed shells, coffee grounds and straw; The flame retardant component includes at least one of ammonium meta-phenylenediamine phosphate (MAP), ammonium phosphatidyl arginine (ATTPMA), and 1-ethyl-3-methylimidazolium hexafluorophosphate ([EMIM][PF6]) ionic liquids.
[0015] The reaction and coating conditions are as follows: adding dicyandiamide to a mixed solution of the biomass material and the flame retardant component, and stirring under condensation reflux at 50-90° C. for 4 hours, then filtering the mixed solution and washing it three times with distilled water, and finally drying it in an oven at 90° C. for 4 hours.
[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The preparation method proposed in the present invention has relatively simple steps, low cost, and uses conventional polymer processing equipment without the need for special processing equipment. It has the feasibility of industrial mass production, and the prepared polyolefin surface modified material has the characteristics of safety, environmental protection, flame retardancy, and fire resistance.
[0017] 2. The polyolefin surface modified material proposed in the present invention is halogen-free and free of heavy metals, meets the green material standards, is harmless to the environment and human body, and has the characteristics of safety, environmental protection, flame retardancy and fire prevention. In a burning environment, it can be flame retardant in the early stage, and during continuous flame ablation, a ceramic shell can be formed on the outer layer of the material to play a fire prevention role, and the overall material has a fire safety function.
[0018] 3. The metal ions loaded on the surface of the silicate powder in the present invention can further cooperate with the silicate powder to improve the flame retardant properties of the material by catalyzing the metal ions into carbon; the flame retardant components grafted or coated on the surface of the biomass material can also further improve the continuous flame retardant properties of the material on the basis of improving the dispersion performance of the biomass material. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 The present invention provides a flow chart of a method for preparing a low-carbon, halogen-free, fire-safe polyolefin material. DETAILED DESCRIPTION
[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.
[0021] Reference Figure 1 , a low-carbon, halogen-free, fire-safe polyolefin material, comprising the following components in parts by weight: 60-100 parts of polyolefin resin, 5-30 parts of compatibilizer, 10-50 parts of surface-modified silicate powder, 10-40 parts of flux, 20-50 parts of flame retardant, 1-5 parts of antioxidant, and 10-20 parts of surface-modified biomass material.
[0022] The polyolefin resin comprises at least one of 20 to 60 parts of polyethylene, 20 to 60 parts of polypropylene, 20 to 50 parts of ethylene-octene copolymer, and 30 to 40 parts of ethylene-vinyl acetate copolymer.
[0023] The compatibilizer comprises at least one of 5 to 20 parts of maleic anhydride grafted polyolefin elastomer and 10 to 30 parts of maleic anhydride grafted polyolefin.
[0024] The surface-modified silicate powder includes at least one of surface-modified mica, surface-modified wollastonite, surface-modified montmorillonite, and surface-modified kaolin.
[0025] The flux comprises: at least one of low melting point glass powder and zinc borate; The flame retardant includes at least one of piperazine pyrophosphate, ammonium polyphosphate, melamine cyanurate, and melamine phytate.
[0026] The antioxidant includes at least one of antioxidant 1010, antioxidant 1076, antioxidant 168, and antioxidant 300.
[0027] The surface-modified biomass material includes at least one of surface-modified pepper seed shells, surface-modified coffee grounds, and surface-modified straw.
[0028] A method for preparing a low-carbon, halogen-free, fire-safe polyolefin material comprises the following steps: Step 1: Weigh the following parts by weight: 60-100 parts of polyolefin resin, 5-30 parts of compatibilizer, 10-50 parts of surface-modified silicate powder, 10-40 parts of flux, 20-50 parts of flame retardant, 1-5 parts of antioxidant and 10-20 parts of surface-modified biomass material; Step 2: Add the polyolefin matrix, compatibilizer, and antioxidant into an internal mixer at 130-200°C and mix for 2-10 minutes; Then add silicate powder, flux, flame retardant and biomass material, mix at 150-200°C for 3-10 minutes, stop mixing and obtain a mixture; Step 3: The mixture is pressed into a tablet by a flat-plate tablet press to obtain a low-carbon, halogen-free, and fire-safe polyolefin material. The tableting temperature is 150-200° C., the pressure is 5-15 MPa, and the tableting time is 2-10 min.
[0029] Furthermore, in step 2, the polyolefin matrix, compatibilizer, and antioxidant are added to an internal mixer at 130-200° C. and kneaded for 2-10 minutes, preferably at 190° C. for 3 minutes.
[0030] Furthermore, in step 2, silicate powder, flux, flame retardant and biomass material are added, and the mixture is banburying at 150-200° C. for 3-10 minutes, and the banburying is stopped, preferably at 190° C. for 5 minutes.
[0031] The surface-modified silicate powder is prepared by dispersing the silicate powder in a metal ion-containing aqueous solution, slowly adding a phytic acid solution, stirring for a certain period of time, filtering and washing the product with distilled water, and drying in an oven for later use. The metal ion aqueous solution includes one of manganese acetate solution, zinc acetate solution, nickel acetate solution, and calcium acetate solution; the phytic acid concentration is 0.015 mol / L, and the stirring time is 2 hours.
[0032] The surface modified biomass material is prepared by crushing and sieving the biomass raw material, then mixing or coating it with the flame retardant component under certain conditions, filtering and washing the product with distilled water, and drying it in an oven for later use; The biomass material includes one of: pepper seed shells, coffee grounds and straw; The flame retardant component includes at least one of ammonium meta-phenylenediamine phosphate (MAP), ammonium phosphatidyl arginine (ATTPMA), and 1-ethyl-3-methylimidazolium hexafluorophosphate ([EMIM][PF6]) ionic liquids.
[0033] The reaction and coating conditions are as follows: dicyandiamide is added to the mixed solution of biomass material and flame retardant component, and condensed and refluxed at 50-90 ° C for 4 hours, then the mixed solution is filtered and washed three times with distilled water, and finally dried in a 90 ° C oven for 4 hours. The surface modified silicate powder is based on the principle of electrostatic adsorption, and phytic acid metal salt is deposited on the surface of the silicate powder with negative surface charge. The metal phytate includes one of: manganese phytate, zinc phytate, nickel phytate, and calcium phytate.
[0034] Surface modified biomass materials are based on the principle that the surface of biomass materials is rich in hydroxyl groups, and components with flame retardant functions are grafted or coated onto the surface of biomass materials; The flame retardant component includes at least one of ammonium meta-phenylenediamine phosphate (MAP), ammonium phosphatidyl arginine (ATTPMA), and 1-ethyl-3-methylimidazolium hexafluorophosphate ([EMIM][PF6]) ionic liquids.
[0035] Example 1: A low-carbon, halogen-free, fire-safe polyolefin composite material. The specific components of the surface-modified material are shown in Table 1: Table 1 Components Number of copies Polyethylene (containing 50% recycled resin raw materials) 30 Ethylene vinyl acetate copolymer 31 Ethylene-octene copolymer 18 Maleic anhydride grafted polyethylene 11 Manganese phytate surface modified montmorillonite 10 Wollastonite 32 Low melting point glass powder 24 zinc borate 16 Piperazine pyrophosphate 28 Antioxidant 1010 2 MAP surface modified biomass materials 10 The preparation method of the surface modified material of this embodiment 1 is as follows: (1) Add ethylene-vinyl acetate copolymer, ethylene-octene copolymer, polyethylene, maleic anhydride grafted polyethylene and antioxidant 1010 into an internal mixer at 170°C and mix for 3 minutes; (2) Add surface-modified montmorillonite, wollastonite, low-melting-point glass powder, zinc borate, piperazine pyrophosphate and surface-modified biomass materials and knead them at 170°C for 5 minutes, then stop kneading.
[0036] (3) The mixture obtained in step 2 was hot pressed on a flat plate press at 170°C and a pressure of 10 MPa for 5 min to obtain a low-carbon, halogen-free, fire-safe polyolefin composite material sheet sample.
[0037] Example 2: A low-carbon, halogen-free, fire-safe polyolefin composite material. The specific components of the surface-modified material are shown in Table 2: Table 2 Components Weight (g) Polyethylene (containing 50% recycled resin raw materials) 50 Ethylene-octene copolymer 26 Maleic anhydride grafted polyethylene 14 Montmorillonite 10 Wollastonite surface modified with zinc phytate 32 Low melting point glass powder 24 zinc borate 16 Ammonium polyphosphate 28 Antioxidant 1010 1.5 ATTPMA surface modified biomass materials 20 The preparation method of the surface modified material of this embodiment 2 is as follows: (1) Add polyethylene, ethylene-octene copolymer, maleic anhydride grafted polyethylene and antioxidant 1010 into an internal mixer at 170°C and mix for 3 minutes; (2) Add montmorillonite, surface-modified wollastonite, low-melting-point glass powder, zinc borate, ammonium polyphosphate and surface-modified biomass materials and knead them at 170°C for 5 minutes, then stop kneading.
[0038] (3) The mixture obtained in step 2 was hot pressed on a flat plate press at 170°C and a pressure of 10 MPa for 5 min to obtain a low-carbon, halogen-free, fire-safe polyolefin composite material sheet sample.
[0039] Example 3: A low-carbon, halogen-free, fire-safe polyolefin composite material. The specific components of the surface-modified material are shown in Table 3: Table 3 Components Weight (g) Polypropylene (containing 50% recycled resin raw materials) 50 Ethylene-octene copolymer 26 Maleic anhydride grafted polypropylene 14 Nickel phytate surface modified wollastonite 25 Low melting point glass powder 25 Piperazine pyrophosphate 40 Antioxidant 1010 1.5 Surface modification of biomass materials using ionic liquids 15 The preparation method of the surface modified material of this embodiment 3 is as follows: (1) Add polypropylene, ethylene-octene copolymer, maleic anhydride grafted polypropylene and antioxidant 1010 into an internal mixer at 190°C and mix for 3 minutes; (2) Add surface-modified wollastonite, low-melting-point glass powder, piperazine pyrophosphate, and surface-modified biomass material and knead at 190°C for 5 minutes, then stop kneading.
[0040] (3) The mixture obtained in step 2 was hot-pressed on a flat-plate tablet press at 190°C and a pressure of 10 MPa for 5 min to obtain a low-carbon, halogen-free, fire-safe polyolefin composite material sheet sample.
[0041] Example 4: A low-carbon, halogen-free, fire-safe polyolefin composite material. The specific components of the surface-modified material are shown in Table 4: Table 4 Components Weight (g) Polypropylene (containing 50% recycled resin raw materials) 60 Ethylene-octene copolymer 16 Maleic anhydride grafted polypropylene 14 Calcium phytate surface modified wollastonite 25 Low melting point glass powder 25 Piperazine pyrophosphate 40 Antioxidant 1010 1.5 Surface modification of biomass materials using ionic liquids 20 The preparation method of the surface modified material of this embodiment 4 is as follows: (1) Add polypropylene, ethylene-octene copolymer, maleic anhydride grafted polypropylene and antioxidant 1010 into an internal mixer at 190°C and mix for 3 minutes; (2) Add surface-modified wollastonite, low-melting-point glass powder, piperazine pyrophosphate, and surface-modified biomass material and knead at 190°C for 5 minutes, then stop kneading.
[0042] (3) The mixture obtained in step 2 was hot pressed on a flat plate press at 190°C and a pressure of 10 MPa for 5 min to obtain a low-carbon, halogen-free, fire-safe polyolefin composite material sheet sample.
[0043] Comparative Example 1: A commercially available ceramic polyolefin A was used as a comparative sample. This commercially available product was directly used in the following performance tests for comparison with the examples of the present invention.
[0044] The pellets were hot-pressed on a flat-plate tablet press at 190°C and a pressure of 10 MPa for 5 min to obtain sheet samples.
[0045] Comparative Example 2: The calcium phytate-surface-modified wollastonite in Example 4 was replaced by wollastonite, while the other components and preparation methods remained unchanged.
[0046] The performance tests were conducted on the samples prepared in Examples 1 to 4 and Comparative Examples 1 to 2. The results are shown in Table 5: Table 5: Test items Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 <![CDATA[Density (g / cm 3 ).]]> 1.55 1.54 1.61 1.59 1.54 1.59 Tensile strength (MPa) 9.5 12.1 25.9 26.3 9.4 19.2 Flexural strength (MPa) 20.2 23.5 38.6 33.1 19.4 30.7 Oxygen index (%) 27.8 28.2 28.7 28.6 27.1 26.8 Vertical Burning (Grade) V-1 V-1 V-0 V-0 NR V-1 Heat deformation temperature (℃) 78 84 121 117 76 112 1000℃ muffle furnace, flexural strength after 30min (MPa) 1.70 1.67 1.75 1.63 1.61 1.52 From the test results of the above embodiments and comparative examples, it can be seen that the present invention provides a method for preparing a low-carbon, halogen-free, fire-safe polyolefin composite material, which has relatively simple steps, low cost, and industrial feasibility. The prepared polyolefin surface modified material has the characteristics of safety, environmental protection, flame retardancy, and fire resistance. The prepared material has excellent performance in all aspects and has good application prospects.
[0047] The low-carbon, halogen-free, fire-safe polyolefin composite material of the present invention has excellent comprehensive performance. Compared with commercially available products, it has more excellent flame retardant properties and flame ablation resistance, i.e., fireproof properties, ensuring the fire safety performance of the material in fire scenarios.
[0048] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.
Claims
1. A low-carbon, halogen-free, fire-proof and safe polyolefin material, characterized in that: The composition comprises the following components in parts by weight: 60-100 parts of polyolefin resin, 5-30 parts of compatibilizer, 10-50 parts of surface-modified silicate powder, 10-40 parts of flux, 20-50 parts of flame retardant, 1-5 parts of antioxidant, and 10-20 parts of surface-modified biomass material.
2. A low-carbon, halogen-free, fire-safe polyolefin material according to claim 1, characterized in that: The polyolefin resin includes at least one of polyethylene, polypropylene, ethylene-octene copolymer, and ethylene-vinyl acetate copolymer.
3. The low-carbon, halogen-free, fire-safe polyolefin material according to claim 1, characterized in that: The compatibilizer comprises at least one of 5 to 20 parts of maleic anhydride grafted polyolefin elastomer and 10 to 30 parts of maleic anhydride grafted polyolefin.
4. The low-carbon, halogen-free, fire-safe polyolefin material according to claim 1, characterized in that: The surface-modified silicate powder includes at least one of surface-modified mica, surface-modified wollastonite, surface-modified montmorillonite and surface-modified kaolin.
5. The low-carbon, halogen-free, fire-safe polyolefin material according to claim 1, characterized in that: The flux comprises: at least one of low melting point glass powder and zinc borate; The flame retardant comprises at least one of piperazine pyrophosphate, ammonium polyphosphate, melamine cyanurate and melamine phytate.
6. The low-carbon, halogen-free, fire-safe polyolefin material according to claim 1, characterized in that: The antioxidant includes at least one of antioxidant 1010, antioxidant 1076, antioxidant 168, and antioxidant 300.
7. The low-carbon, halogen-free, fire-safe polyolefin material according to claim 1, characterized in that: The surface-modified biomass material comprises at least one of surface-modified pepper seed shells, surface-modified coffee grounds and surface-modified straw.
8. A method for preparing a low-carbon, halogen-free, fire-safe polyolefin material according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Pre-weighing and preparing materials: weighing the following parts by weight: 60-100 parts of polyolefin resin, 5-30 parts of compatibilizer, 10-50 parts of surface-modified silicate powder, 10-40 parts of flux, 20-50 parts of flame retardant, 1-5 parts of antioxidant and 10-20 parts of surface-modified biomass material; S2. Banbury mixing: Add the polyolefin matrix, compatibilizer, and antioxidant into a banbury mixer at 130-200° C. and mix for 2-10 minutes; Then add silicate powder, flux, flame retardant and biomass material, mix at 150-200°C for 3-10 minutes, stop mixing and obtain a mixture; S3. Tablet forming: The mixed material is tableted by a flat-plate tablet press to obtain a low-carbon, halogen-free, and fire-safe polyolefin material. The tableting temperature is 150-200° C., the pressure is 5-15 MPa, and the tableting time is 2-10 min.
9. A preparation method according to claim 8, characterized in that, The surface-modified silicate powder in S1 is prepared by dispersing the silicate powder in a metal ion-containing aqueous solution, slowly adding a phytic acid solution dropwise, stirring for a certain period of time, filtering and washing the product with distilled water, and drying in an oven for later use; Wherein: the metal ion aqueous solution includes: one of: manganese acetate solution, zinc acetate solution, nickel acetate solution, and calcium acetate; the phytic acid concentration is 0.015 mol / L, and the stirring time is 2 hours.
10. A preparation method according to claim 8, characterized in that: The preparation method of the surface-modified biomass material in S1 is to crush and sieve the biomass raw material, then mix, react or coat it with the flame retardant component under certain conditions, filter and wash the product with distilled water, and dry it in an oven for later use; The biomass material comprises: one of: pepper seed shells, coffee grounds and straw; The flame retardant component includes at least one of ammonium meta-phenylenediamine phosphate (MAP), ammonium phosphatidyl arginine (ATTPMA), and 1-ethyl-3-methylimidazolium hexafluorophosphate ([EMIM][PF6]) ionic liquids; The reaction and coating conditions are as follows: adding dicyandiamide to a mixed solution of the biomass material and the flame retardant component, and stirring under condensation reflux at 50-90° C. for 4 hours, then filtering the mixed solution and washing it three times with distilled water, and finally drying it in an oven at 90° C. for 4 hours.