FLUOROPOLYMER ALLOYS, THEIR PREPARATION AND APPLICATION

Abstract: This invention relates to fluoropolymer alloys made of melt fabricatable extra-high-molecular weight fluorlnated ethylene-propylene copolymer (EHMW-FEP) and one or more other polymers. In fluoropolymer alloys made of EHMW-FEP and polytetrafluoroethylene, weight percentage of the former is 0.1-99.9% and the latter is 99.9-0.1%. The processes for preparing fluoropolymer alloys are blend of dried powder co-mill or wetted powder co-mill. Using the fluoropolymer alloys of this invention, various kinds of articles have been fabricates by melt compression or cold compaction and sintering. These properly fabricated arti­ cales show a great improvement in creep property and also a prolonged service life in comparision with those made from ordinary polytetrafluoroethylene.

Description: This invention relates to fluoropolymer alloys made of melt fabricatable extra-high-molecular weight fluorinated ethylene-propylene copolymer ( EHMW-FEP ) and one or more other polymers, their preparation and application. The fluoropolymer alloys are new materials having different properties from original polymers of which they are made. It has become an important way to prepare new materials with a great variety of properties, because of its advantages of using available polymers, simple process, and short research period. It has become of attracting interest recently, see Sato Kawa, plastics ( Japan ) 32, 69 (1981). The fluoropolymer alloys which have been reported are limited to blending alloys based on polyvinylidene fluoride, as well as on polytetrafluoroethylene ( PTFE ) dispersion and fluorinated ethylene-propylene copolymer (FEP) dispersion GB-A 935, 706, (1960); Japanese patent kokai 12521/62. Polytetrafluoroethylene, commonly named " King of plastics ", has excellent comprehensive properties. It has excellent thermal and chemical stability, and outstanding electrical insulation and anti-stick properties. But it could not be fabricated by melt processing, it can only be fabricated by cold compaction and then sintering. Its creep-resistance is also low. Therefore, its applications have been limited. Fluorinated ethylene-propylene copolymer having good creep-resistance is copolymer of tetrafluoroethylene and hexafluoro-propylene, it can be melt fabricated due to the presence of trifluoromethyl in the copolymer chain. The chemical inertness and outstanding electrical insulating properties of the copolymer are similar to polytetrafluoroethylene, but its thermal stability is not so excellent as PTFE, it can only withstand temperature up to 200°C, and its cost is higher than that of PTFE. The purpose of present invention is to prepare a fluorine-containing material with more perfect properties through blending PTFE and FEP, and obtaining a polymer alloy with enhancing excellent properties and overcoming drawbacks of the two original polymers. There are processes for preparing polymer alloy made of polytetrafluoroethylene and fluorinated ethylene-propylene copolymer in British patent 935, 706 (1960) and Japanese patent kokai 12521/62, by using co-precipitation of these two fluoropolymer dispersions. The process is complicated, and the cost increased. Mechanical properties of the fluoropolymer alloy are worse than that of PTFE and FEP; for example their tensile strength is much lower than that of the two original polymers and only 142-213 bar (142-213 Kg/cm²) under room temperature. An important problem is to match the polytetrafluoroethylene with fluorinated ethylene-propylene copolymer in order to get a good fluoropolymer alloy made of PTFE and FEP. These two raw fluoropolymers have different processing temperatures and different thermal stability. Temperature of melt compression molding of FEP is about 310° C, but sintering temperature after cold compaction of PTFE is about 380°C. The decomposition rate of FEP is much higher than that of PTFE at 380° C. Particularly, when FEP resin having carboxyl end group is prepared by copolymerization using persulfates as initiator, it must be roasted at 380° C in order to stabilized the end group. However, FEP resins become "bread ruck", after roasted , and could not be blended with PTFE powder. Another important problem is the blend process of preparing a polymer alloy made of PTFE and FEP. In general blending polymers can be carried out by solution blend method, melt blend or dispersion co-precipitate blend method. As there is no any solvent found for PTFE and FEP, they could not be carried out by solution blend. They could not be carried out by melt blend also, because PTFE could not be melt processed. Therefore, the dispersion co-precipitating blent has been the only way used in British patent 935, 706 and Japanese patent kokai 12521/62, although the cost of the polymer alloy should be high, by using expensive fluorine-containing emulsifier in preparing dispersion of PTFE and FEP. Besides, the process of co-precipitating blend is rather complicate. In accordance with the present invention, fluoropolymer alloys are made available comprising melt fabricatable extra-high-molecular weight fluorinated ethylene-propylene copolymer and one or more other polymers selected from the group consisting of polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-ethylene copolymer, polysulfone, polyethylene, polypropylene, polyimide, polycarbonate, polyphenylene oxide and polyphenylene sulfide, wherein the molding powder is extra-high-molecular weight fluorinated ethylene-propylene copolymer which can be melt fabricated, with 12-30 % by weight of hexafluoropropylene, weight-average molecular weight of over 2 x 10⁵ , melt viscosity of 1 x 10⁶ P or more, and melt flow index less than 0.8 gram/10 minutes. As a preferred embodiment the fluoropolymer alloys comprise extra-high-molecular weight fluorinated ethylene-propylene copolymer and polytetrafluoroethylene. As a further preferred embodiment the fluoropolymer alloys have 0.1-60 % by weight extra-high-molecular weight fluorinated ethylene-propylene copolymer and 99.9-40 % by weight polytetrafluoroethylene. As a further embodiment the fluoropolymer alloys contain glass fiber, graphite, molybdenum disulfide, carbon and/or metal powder. Furthermore, according to the present invention, extra-high-molecular weight fluorinated ethylene-propylene copolymer which can be melt fabricated is prepared by solution precipitation polymerization using liquid hexafluoropropylene as a solvent by charging 0.2-0.5 g of tetrafluoroethylene and hexafluoropropylene per 1 ml autoclave capacity into an autoclave, the monomer mixture of tetrafluoroethylene and hexafluoropropylene containing 11-50 % by weight of tetrafluoroethylene, the weight ratio between water and monomers being 3:1 to 1:1, equivalents of initiator diisopropyl peroxydicarbonate based on monomers being 0.001 to 0.05 % by weight, at a polymerization pressure of 20-30 bar (20-30 kg/cm 2 ), a polymerization temperature of 40 to 80° C and a polymerization time of 1-5 hours per batch. In accordance with the present invention, the polytetrafluoroethylene (PTFE) used is a commercial resin, including resins prepared by suspension or dispersion polymerization, and has a tensile strength of more than 270 bar (270 kg/cm²) under room temperature. In accordance with the present invention, the other commercial polymers, such as polychlorotrifluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-ethylene copolymer, polyethylene, polypropylene, polysulfone, polyimide, polycarbonate, polyphenylene oxide, polyphenylene sulfide, can be used to prepare fluoropolymer alloy together with extra-high-molecular weight fluorinated ethylene-propylene copolymer ( EHMW-FEP ). A given weight ratio of EHMW-FEP and one or more other polymers as described above, have been ground by mill separately, and then mixed and ground again until the two or more phases were homogeneously mixed. The mixture is screened by a 0,42-0,84 mm (40-80 mesh) and ready for processing. The mixing and grinding process of two or more polymers, may be mixed and ground either in dried powder form or wet powder form. During wet powder mixing and grinding, the polymers are moistened by water, ethyl alcohol, ethyl acetate or a mixture of these solvents. When the mixing is finished, the mixture of polymers must be dried, and then screened. In the fluoropolymer alloy made of EHMW-FEP and PTFE, the weight of EHMW-FEP is 0.1-99.9% and the weight of PTFE is 99.9-0.1%. In a preferred embodiment the weight ratios have 0.1-60% of EHMW-FEP and 40-99.9% of PTFE. The fluoropolymer alloys made of EHMW-FEP and PTFE can be melt pressed into articles under temperature of 300-350° C and pressure of 50-200 bar (50-200Kg/cm²) like FEP. They can also be cold compressed under pressure of 50-200 bar (50-200 Kg/cm²) and then sintered under temperature of 300-390°C like PTFE. The temperatures of melt pressing or sintering fluoropolymer alloys described above depend on the amount of PTFE in them. The higher the amount of PTFE, the higher the temperature. The fluoropolymer alloys made of EHMW-FEP and PTFE of present invention have not only creep-resistance like FEP, but also high tensile strength under high temperature like PTFE. It exhibits a tensile strength of 200-400 bar (200-400 Kg/cm²) and an elongation of 300-700% under room temperature, and correspondingly 50-200 bar (50-200 Kg/cm²) and 300-700% under 200° C. Extra-high-molecular weight fluorinated ethylene-propylene copolymers have a good compatibility with polytetrafluoroethlene in the fluoropolymer alloys described above. Fluoropolymer alloy, e.g. , made of 10% of EHMW-FEF and 90% of PTFE, has nearly only one peak of melting and one peak of crystallizing in its DSC spectrum. All kinds of the fluoropolymer alloys described above can be reinforced and improved by adding glass fiber, graphite, molybdenum disulfide, carbon and various metal powders. The fluoropolymer alloys made of EHMW-FEP and PTFE of the present invention are a kind of materials having excellent thermal stability, chemical inertness and outstanding electrical insulating properties. Taking this kind of fluoropolymer alloys as material, various diaphragm, seals, linings for valves, pipes, pumps , various components of pumps , such as shells, wheels, wind wrap wires, can be fabricated. The articles made of fluoropolymer alloys have better creep-resistance than that of PTFE and consequently have a rather long operating life. The fluoropolymer alloys described above can be used in powder coating by either static electricity method or flow-bed method, and can also be fabricated into complex articles using ram-extruding a paste consisting of fluoropolymer alloy and petroleum ether or kerosene. The invention is more specifically described and explained by means of the following examples . In the examples all parts and percentages are by weight except as otherwise noted. Example 1 20 grams of EHMW-FEP with an melt flow index of 0 gram/10min., and 180 grams PTFE were successively moistened by a mixture of ethyl alcohol and ethyl acetate, milled, filtered, dried and passed through a 40 mesh screen. The resulting powder was cold compressed into a 2 mm thick sheet under pressure of 80 bar (80 Kg/cm²), and sintered in a over for 1 hour at 350° C. After cooling, its tensile strength is 277 bar (277 Kg/cm²) under room temperature. Example 2 EHMW-FEP and PTFE were mixed in weight ratios of 1/9 ,1/3, 1/1, 3/1 and 9/1 respectively, the resulting mixture milled to pass through a 0,42 mm (40 mesh) screen, cold compressed under 80 bar (80 Kg/cm²) and sintered separately. The properties of the resulting fluoropolymer alloys are shown in Table 1. Physical properties of alloys made of EHMW-FEP/PTFE Composition (EHMW-FEP/PTFE) 1/0 9/1 3/1 1/1 1/3 1/9 0/1 sintering temp. (°C) 300 300 300 320 340-365 340-365 365 room tensile strength temp. (Kg/cm²) bar 265 210 250 290 260 280 320 elongation (%) 330 310 370 500 520 520 650 200°C tensile strength (Kg/cm²) bar 46 87 84 82 89 104 89 elongation (%) 340 340 500 450 500 680 480 Example 3 EHMW-FEP was mixed with tetrafluoroethylene-ethylene copolymer (F40) in weight ratio showed in Table 2 by blending dried powder or wetted powder, the resulting fluoropolymer alloys were fabricated by cold compression under pressure of 70-150 bar (Kg/cm²) and then sintered, or by melt pressing. Physical properties of alloys made of EHMW-FEP and F40 Composition (EHMW-FEP/F40) 1/0 99/1 9/13/1 1/1 1/3 1/9 1/99 0/1 fabrication temp. (°C ) 310-380 300-350 300-340 300-330 300-320 300-320 300-320 280-330 280-340 tensile strength (Kg/cm²) bar 300 310 315 320 325 330 340 350 400 elongation (%) 300 300 280 260 200 150 100 100 100 Example 4 A mixture of 40 grams of EHMW-FEP, 40 grams of PTFE and 10 grams of polysulfone, was moistened with acetone, mixed homogeneously by high speed stirring, milled, dried, 40 mesh screened, cold compressed under 80 bar (Kg/cm²) and then sintered for one hour at 320° C. The hardness (Rockwell) of the fluoropolymer alloy obtained is D50. Example 5 EHMW-FEP was mixed with polychlorotrifluoroethylene (CTFE) in weight ratio showed in Table 3 by blending dried powder or wetted powder, the resulting fluoropolymer alloys were fabricated by cold compression under pressure of 70-150 bar (Kg/cm²) and then sintered, or by melt pressing. Physical properties of alloys made of EHMW-FEP and CTFE Composition (EHMW-FEP/CTFE) 1/0 99/1 9/1 3/1 1/1 1/3 1/9 1/99 0/1 fabrication temp. (°C ) 310-380 310-330 300-330 270-300 250-300 250-300 250-300 250-300 250-320 tensile strength (Kg/cm²) bar 300 280 200 220 300 305 320 300 350 elongation (%) 350 300 40 100 250 180 200 150 150 Example 6 EHMW-FEP was mixed with polyvinylidene fluoride (PVDF) in weight ratio showed in Table 4 by blending dried powder or wetted powder (including using diisobutyl acetone as a moistener), the resulting fluoropolymer alloys were fabricated by cold compression under pressure of 70-150 bar (Kg/cm²) and then sintered, or by melt pressing. Physical porperties of alloys made of EHMW-FEP and PVDF Composition (EHMW-FEP/PVDF) 1/0 99/1 9/1 3/1 1/1 1/3 1/9 1/99 0/1 fabrication temp. (°C ) 310-380 280-320 280-330 280-330 250-330 240-300 220-250 200-250 200-250 tensile strength (Kg/cm²) bar 310 330 350 300 300 350 400 450 500 elongation (%) 320 250 200 150 150 100 60 60 50 Example 7 EHMW-FEP was mixed with polysulfone (PS) in weight ratio showed in Table 5 by blending dried powder or wetted powder (including using chloroform as a solvent), the resulting flyoropolymer alloys were fabricated by melt compression under pressure of 70-150 bar (Kg/cm².). Physical properties of alloys made of EHMW-FEP and PS Composition (EHMW-FEP/PS) 1/0 99/1 9/1 3/1 1/1 1/3 1/9 1/99 0/1 fabrication temp. (°C) 310-380 280-320 250-310 220-300 250-290 250-290 270-280 200-270 200-280 tensile strength (Kg/cm²) bar 300 270 250 220 200 250 360 700 800 elongation (%) 320 250 200 100 4 5 5 40 50 Example 8 EHMW-FEP was mixed with polyethylene (PE) in weight ratio showed in Table 6 by blending dried powder or wetted powder (including using xylene as a solvent), the resulting fluoropolymer alloys were fabricated by melt compression under pressure of 70-150 bar (Kg/cm²). Physical propreties of alloys made of EHMW-FEP and PE Composition (EHMW-FEP/PE) 1/0 99/1 9/1 3/1 1/1 1/3 1/9 1/99 0/1 fabrication temp. (°C) 310-380 280-350 250-300 200-300 170-250 150-200 160-170 150-170 150-200 tensile strength (Kg/cm²) bar 300 280 250 180 100 150 190 200 200 elongation 1% 350 300 200 100 50 400 600 210 250 Example 9 EHMW-FEP was mixed with polypropylene (PP) in weight ratio showed in Table 7 by blending dried powder or wetted powder (including using decalin as a solvent), the resulting fluoropolymer alloys were fabricated by melt compression under pressure of 70-150 bar (Kg/cm²). Physical properties of alloys made of EHMW-FEP and PP Composition (EHMW-FEP/PP) 1/0 99/1 9/1 3/1 1/1 1/3 1/9 1/99 0/1 fabrication temp. (°C) 310-380 300-330 280-320 250-300 230-300 220-280 220-250 220-260 230-300 tensile strength (Kg/cm²) bar 310 300 280 200 180 200 240 310 350 elongation (%) 340 300 350 200 300 350 500 250 200 Example 10 EHMW-FEP was mixed with polycarbonate (PC) in weight ratio showed in Table 8 by blending dried powder or wetted powder (including using chloroform as a solvent), the resulting fluoropolymer alloys were fabricated by melt compression under pressure of 70-150 bar (Kg/cm²). Physical properties of alloys made of EHMW-FEP and PC Composition (EHMW-FEP/PC) 1/0 99/1 9/1 3/1 1/1 1/3 1/9 1/99 0/1 fabrication temp. (°C) 310-380 300-350 290-340 290-330 280-320 280-310 280-310 250-320 220-350 tensile strength (Kg/cm²) bar 310 300 280 260 200 300 360 550 700 elongation (%) 350 300 200 100 50 10 5 80 100 Example 11 EHMW-FEP was mixed with polyphenylene oxide (PPO) in weight ratio showed in Table 9 by blending dried powder or wetted powder (including using chloroform as a solvent), the resulting fluoropolymer alloys were fabricated by melt compression under pressure of 70-150 bar (Kg/cm²). Physical properties of alloys made of EHMW-FEP and PPO Composition (EHMW-FEP/PPO) 1/0 99/1 9/1 3/1 1/1 1/3 1/9 1/99 0/1 fabrication temp. (°C) 310-380 300-320 300-320 300-320 300-320 300-320 305-310 300-320 300-350 tensile strength (Kg/cm²) bar 305 280 250 200 150 50 110 250 650 elongation (%) 330 250 200 100 10 4 5 40 50 Example 12 EHMW-FEP was mixed with polyphenylene sulfide (PPS) in weight ratio showed in Table 10 by blending dried or wetted powder, the resulting fluoropolymer alloys were fabricated by melt compression under pressure of 70-150 bar (Kg/cm²). Physical properties of alloys made of EHMW-FEP and PPS Composition (EHMW-FEP/PPS) 1/0 99/1 9/1 3/1 1/1 1/3 1/9 1/99 0/1 fabrication temp. (°C) 310-380 300-350 300-350 300-350 300-350 300-350 300-350 300-350 290-360 tensile strength (Kg/cm²) bar 300 290 280 250 200 300 400 850 900 elongation (%) 320 300 250 200 100 50 5 15 10 Example 13 EHMW-FEP was mixed with polyimide (PI) in weight ratio showed in Table 11 by blending dried powder or wetted powder, the resulting fluoropolymer alloys were fabricated by melt compression under pressure of 70-150 bar (Kg/cm²) or cold compaction under pressure of 70-150 bar (Kg/cm²) and sintered. Physical properties of alloys made of EHMW-FEP and PI Composition (EHMW-FEP-PI) 1/0 99/1 9/1 3/1 1/1 1/3 1/9 1/99 0/1 fabrication temp. (°C) 310-380 300-320 300-320 300-320 300-320 300-320 310-320 250-300 150-300 tensile strength (Kg/cm²) bar 320 310 300 250 200 300 400 800 900 elongation (%) 330 300 280 250 100 80 50 10 5 Example 14 10 grams of EHMW-FEP were mixed with 90 grams molding powder or dispersion powder of PTFE, and then the resulting mixture was milled, 0,42 mm (40 mesh) screened. The resulting dried powder of fluoropolymer alloy were moistened by 200E gasoline, cold compressed and sintered. This fluoropolymer alloy product can be used for linings for valves and pipes. Example 15 40 grams of fluoropolymer alloy made of EHMW-FEP and PTFE were mixed with glass fiber in its weight ratio of 10%, 20% and 30% respectively. The resulting mixture was cold compressed under pressure of 80 bar (Kg/cm²) and sintered for 2 hours at 320° C separatly. The date of tensile strength of these reinforced fluoropolymer alloy are 250, 220 and 150 bar (Kg/cm²), respectively, under room temperature. Example 16 Fluoropolymer alloy made of 50 grams of EHMW-FEP and 50 grams of PTFE was mixed with glass fiber in its weight ratio of 20% and graphite in its weight ratio of 3%, the resulting mixture was milled to pass through 0,42 mm (40 mesh) screen, cold compressed under pressure of 80 bar (Kg/cm²) and then sintered for 2 hours at 320° C. The tensile strength, elongation and hardness (Rockwell) of the reinforced fluoropolymers alloys are 150 bar (Kg/cm²,), 220% and 58, respectively. Example 17 Process for preparing extra-high-molecular weight fluorinated ethylene-propylene copolymer, e.g. in a stainless-steel autoclave having a capacity of 130 liters are charged 60 liters of deionised water, 45 Kg of initial monomers containing hexafluoropropylene weight ratio of 86.6%. The contents were heated to 55-57° C with a pressure of 22.0 bar (Kg/cm²), then 25 ml of diisopropyl peroxydicarbonate were added. The copolymerization was carried on for three hours. 7.5 Kg of dried copolymer powder having a hexafluropropylene weight ratio of 14.5%, a melt viscosity of 1.8 x 10⁶ P (poises) and a melt flow index of 0.3 g/10 min could been obtained. A sample of the copolymer powder was molded into sheet with a thickness of 2 mm at 310° C, which showed the tensil strength 290 bar (Kg/cm²) elongation 320%; and flex fatigue life more than 2 x 10⁵ cycle under room temperature.

Claims: Fluoropolymer alloys comprising melt fabricatable extra-high-molecular weight fluorinated ethylene-propylene copolymer and one or more other polymers selected from the group consisting of polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-ethylene copolymer, polysulfone, polyethylene, polypropylene, polyimide, polycarbonate, polyphenylene oxide and polyphenylene sulfide, wherein the molding powder is extra-high-molecular weight fluorinated ethylene-propylene copolymer which can be melt fabricated, with 12-30 % by weight of hexafluoropropylene, weight-average molecular weight of over 2 x 10⁵ , melt viscosity of 1 x 10⁶ P or more, and melt flow index less than 0.8 gram/10 minutes. Fluoropolymer alloys as claimed in claim 1, which comprises extra-high-molecular weight fluorinated ethylene-propylene copolymer and polytetrafluoroethylene. Fluoropolymer alloys as claimed in claim 2 characterized by having 0.1-60 % by weight extra-high-molecular weight fluorinated ethylene-propylene copolymer and 99.9-40% by weight polytetrafluoroethylene. Fluoropolymer alloys as claimed in any of the preceding claims containing glass fiber, graphite, molybdenum disulfide, carbon and/or metal powder. Process for preparing the fluoropolymer alloys as claimed in any of the preceding claims, using either dried powder co-mill or wetted powder co-mill. Process of dried powder co-mill for preparing fluoropolymer alloys as claimed in claim 5, characterized by milling extra-high-molecular weight fluorinated ethylene-propylene copolymer and one or more the other polymers, separately, and then mixing the polymers in a given weight ratio and milling the mixture again until it is homogeneous and passing through a 0.42 to 0.84 mm (40 to 80 mesh) screen. Process of wetted powder co-mill for preparing fluoropolymer alloys as claimed in claim 5, characterized by moistening a given amount of extra-high-molecular weight fluorinated ethylene-propylene copolymer and at least one or more other of the polymers, with water, ethyl alcohol, ethyl acetate or mixed solvent of them and then milling and blending until it is homogeneous, filtering, drying and finally passing it through a 0.42 to 0.84 mm (40 to 80 mesh) screen. Process by preparing extra-high-molecular weight fluorinated ethylene-propylene copolymer suitable for melt fabrication as claimed in any of the claims 1 to 4, which comprises a solution precipitation polymerization using liquid hexafluoropropylene as a solvent by charging 0.2-0.5 g of tetrafluoroethylene and hexafluoropropylene per 1 ml autoclave capacity into an autoclave, the monomer mixture of tetrafluoroethylene and hexafluoropropylene containing 11-50 % by weight of tetrafluoroethylene, the weight ratio between water and monomers being 3:1 to 1:1, equivalents of initiator diisopropyl peroxydicarbonate based on monomers being 0.001 to 0.05 % by weight, at a polymerization pressure of 20-30 bar (20-30 kg/cm ² ), a polymerization temperature of 40 to 80° C and a polymerization time of 1-5 hours per batch.

Inventors: JIN, SUN, SHANRONG, JI, TINGCHUN, HUANG, XIONGYING, YU, YOULU, DUAN
Applicants: SHANGHAI INSTITUTE OF ORGANIC CHEMISTRY ACADEMIA SINICA
Application year: 1986
Main classification: C08L27
IPC codes: C08L23, C08L27, C08F214