Patent Grant
7745513
The present invention relates to fluoropolymers having improved elastic modulus, “storage modulus” G′ and yield stress at room temperature and even at high temperatures, higher than 100° C., maintaining the good chemical and thermal resistance properties typical of fluoropolymers.
In the case of thermoprocessable fluoropolymers the addition of reinforcing fillers does not bring any substantial improvement of the polymer tensile properties (see the comparative Examples).
Thermoplastic fluorinated polymers having improved elastic modulus at room temperature containing lamellar silicate particles having nanometric sizes, are known from U.S. Pat. No. 5,962,553. Said polymers are obtained by adding thereto various types of layered silicates modified with intercalating compounds that allow their exfoliation into lamellar particles having a nanometric thickness. Said intercalating compounds are organophosphonium compounds capable to substitute the Na cations of the silicate leading to a modified layered silicate. Said modified silicate in powder form is mixed with the fluoropolymer in powder and the mixture is melted under mechanical stress, obtaining the exfoliation of the modified silicate inside the fluoropolymer matrix. However the above process shows the drawback of requiring the presence of high amounts of organic intercalating compounds in the fluoropolymer, causing a reduced chemical and/or thermal resistance thereof.
The need was felt to have available fluoropolymers having improved elastic modulus, “storage modulus” G′ and yield stress at room temperature and especially at high temperatures, higher than 100° C., contemporaneously maintaining the good chemical and thermal resistance properties of fluoropolymers.
The Applicant has unexpectedly and surprisingly found that it is possible to prepare fluoropolymers having the above properties.
An object of the present invention is a polymeric composition comprising:
In particular b) is formed by lamellar particles having a thickness lower than 100 nm, preferably lower than 50, more preferably lower than 10, and the other two dimensions lower than 10,000 nm, preferably lower than 2,000, more preferably lower than 500 nm.
As fluoropolymers a) it can be mentioned, for example:
The fluoropolymer a) is preferably a semicrystalline fluoropolymer having a second melting temperature lower than 310° C., more preferably selected in classes 3) and 4).
The lamellar inorganic particles b) are preferably formed by silicates, more preferably aluminum-silicates and/or magnesium-silicates containing other metals such as sodium, potassium, iron or lithium. As inorganic precursor of particle b) having a layered lamellar morphology can be mentioned: smectic clays formed by silicates, more preferably aluminum-silicates and/or magnesium-silicates containing other metals such as sodium, potassium, iron or lithium. Examples of smectic clays are natural minerals called montmorillonite, sauconite, vermiculite, hectorite, saponite, nontronite, or synthetic clays, for example, fluorohectorite, laponite (magnesium-silicate).
Preferably the lamellar inorganic particles b) have at least one dimension lower than 50 nm, more preferably lower than 10 nm.
The polymeric composition preferably contains from 0.3 to 6% by weight of said lamellar inorganic particles b).
A further object of the invention is the process for obtaining the above composition, comprising:
In step 2) the stirring is preferably a strong mechanical stirring and/or an ultrasound treatment.
The latex 1) is prepared by aqueous emulsion polymerization of fluorinated monomers, preferably in the presence of a surfactant or of an aqueous microemulsion based on (per)fluoropolyethers.
When the concentration of the latex prepared in 1) is lower than 30% it is possible to directly add to said latex the inorganic component having a layered lamellar morphology, thus avoiding step 2).
With “microemulsion” it is meant a thermodynamically stable oil/water (O/W) system formed by a mixture of water, a fluorinated surfactant and an oil phase based on (per)fluoropolyether, which appears as a clear solution. See for example U.S. Pat. No. 4,864,006, U.S. Pat. No. 5,498,680, U.S. Pat. No. 5,959,026 and U.S. Pat. No. 6,103,843.
The latex fluoropolymer particles have dimensions comprised between 20 and 300 nm, preferably between 50 and 150 nm. Said latexes are obtained by controlling the surfactant amount used in the polymerization and/or the monomer conversion. For example, at equal conversion, by reducing the surfactant, latex particles having larger dimensions are obtained; at equal surfactant content, a conversion decrease leads to a reduction of the particle size of the latex.
As inorganic components having a layered lamellar morphology are used those previously defined.
The invention process leads to a fluoropolymer powder in which the lamellar inorganic particles are homogeneously dispersed.
Therefore the invention powders are obtainable by mixing a fluoropolymer latex with an aqueous dispersion of the lamellar inorganic component (step 2), and then by carrying out the further process steps. In process step 2) the inorganic particles are exfoliated as it can be seen by the AFM analysis (see the characterization method of the Examples). The thickness can reach the monolamellar level or there can be overlapping of some lamellas. By AFM analysis thicknesses from 1 to 2 nm are noticed. The largest particle dimension is about 400 nm for the montmorillonite and about 50 nm for the laponite. By AFM analysis the skilled man in the art is able to determine the inorganic particle dimensions.
The invention composition powders can be compression moulded or extruded to give shaped articles as sheets, pipes, films.
A further object of the present invention is an aqueous mixture comprising from 5% to 90% by weight of:
Said aqueous mixture is obtainable according to the sequence of steps 1), 2) and 3) of the invention process. Said aqueous mixture can be used to obtain a continuous and homogeneous polymeric film or coatings by water evaporation.
Some Examples follow for illustrative purposes and are not limitative of the present invention.
The following characterizations carried out on the components of the Examples are hereinafter listed:
A PCTFE homopolymer latex has been prepared according to patent EPA 1,067,146;
In an enamelled autoclave equipped with enamelled baffles and stirrer working at 300 rpm there were introduced in sequence:
Then the autoclave was heated to the reaction temperature of 60° C. and the radical initiator under the form of a solution of 19 g of potassium persulphate dissolved in 800 g of demineralized water was introduced.
When the working pressure decreased by 50% with respect to its initial value, i.e. after 290 minutes of reaction, the autoclave was vented and the latex discharged at room temperature.
The obtained latex was diluted with demineralized water to a concentration of 215.2 g of polymer for kg of latex. The latex particles average diameter, measured by DLLS, was 84 nm.
A montmorillonite dispersion was prepared by using a sodium montmorillonite (MMT), sold as Cloisite Na+ (CAS No. 1318-93-0) by the Southern Clay company, having the following particle distribution:
27.7%>600 micron,
31.8% in the range 500-250 micron,
36.6% in the range 250-106 micron,
3.9%<75 micron.
10 g of MMT were dispersed in 200 g of demineralized water under strong mechanical stirring and subsequent ultrasound treatment.
The lamellar inorganic particles have an average thickness of about 2 nm and an average length of 400 nm measured by AFM (Atomic Force Microscopy).
In a 2 litre flask 1.5 kg of the PCTFE latex prepared in A) and the MMT dispersion prepared in B) were mixed. After stirring an aqueous mixture containing 19.5% by weight of solid was obtained. Then the solid phase was precipitated by cooling at a temperature of −20° C., separated by filtration and dried at 175° C. for 16 hours obtaining a powder.
The powder is constituted by 97% by weight of PCTFE and by 3% by weight of MMT, and has a Melt Flow Index (MI), determined at 265° C. with a 10 kg load, equal to 2.7 g/10′.
A compression moulded specimen from said powder has a modulus G′ at 150° C. as reported in Table 1, and TmII and Txx, determined with a scanning rate of 40° C./min, as reported in Table 2.
1.5 kg of the PCTFE latex of Example 1 were precipitated by cooling at temperature of −20° C., the product has been separated and dried at 175° C. for 16 hours obtaining a powder.
The obtained product has a Melt Flow Index (MI), determined at 265° C. with a 10 kg load, equal to 41.5 g/10′.
A compression moulded specimen from said powder has a modulus G′ at 150° C. as reported in Table 1, and TmII and Txx, determined with a scanning rate of 40° C./min, as reported in Table 2.
48.5 g of PCTFE powder of Example 2 (comparative) were mixed with 1.5 g of MMT powder, thus obtaining a blend formed by 97% by weight of PCTFE and 3% by weight of MMT.
A compression moulded specimen from said powder has a modulus G′ at 150° C. as reported in Table 1, and TmII and Txx, determined with a scanning rate of 40° C./min, as reported in Table 2.
It is possible to notice visually or by optical microscope the presence of MMT particles having the same dimension of the used MMT powder.
In an enamelled autoclave equipped with enamelled baffles and stirrer working at 300 rpm there were introduced in sequence:
Then the autoclave was heated to the reaction temperature of 60° C. and ethylene was introduced up to a pressure of 21.4 absolute bar. The radical initiator under the form of a solution of 4.8 g of potassium persulphate dissolved in 800 g of demineralized water was then introduced in the autoclave.
The pressure was maintained constant during the whole polymerization by continuously feeding ethylene in the reactor up to a consumption of 230 g. Then the autoclave was vented and the latex discharged at room temperature.
The obtained latex was diluted with demineralized water to a concentration of 160.1 g of polymer for kg of latex. The latex particles average diameter, determined by DLLS, was 94 nm.
A synthetic hectorite dispersion was prepared by using a hectorite, sold as Laponite RD by the LAPORTE company, having the following particle distribution:
0.7%>600 micron,
7.3% in the range 500-250 micron,
52.6% in the range 250-106 micron,
39.4%<75 micron.
51 g of Laponite were dispersed in 5.1 kg of demineralized water under strong mechanical stirring obtaining a transparent dispersion.
The lamellar inorganic particles have an average thickness of about 1 nm and an average length of 50 nm measured by AFM (Atomic Force Microscopy).
In a 10 litre flask 5 kg of the ECTFE latex prepared in A) and the Laponite dispersion prepared in B) were mixed.
After stirring an aqueous mixture containing 8.5% by weight of solid was obtained. Then the solid phase was precipitated by cooling at a temperature of −20° C., separated by filtration and dried at 120° C. for 16 hours obtaining a powder.
The powder is constituted by 94% by weight of ECTFE and 6% by weight of Laponite, and has a Melt Flow Index (MI), measured at 210° C. with a 10 kg load, equal to 0.36 g/10′.
A compression moulded specimen from said powder has modulus G′ values at 23° C., 100° C. and 125° C. as reported in Table 3, and TmII and Txx, measured with a scanning rate of 10° C./min, as reported in Table 4.
The mechanical properties measured at 100° C. are reported in Table 6.
The X ray analysis on a compression moulded specimen from said powder shows that the dimensions of the inorganic particles are lower than 50 nm.
The ECTFE latex of Example 4 was used.
The sodium montmorillonite (MMT) of Example 1 was used.
25 g of MMT were dispersed in 2.5 kg of demineralized water by strong mechanical stirring.
The lamellar inorganic particles have an average thickness of about 2 nm and an average length of 400 nm measured by AFM (Atomic Force Microscopy).
In a 10 litre flask 5 kg of the ECTFE latex and the MMT dispersion prepared in B) were mixed.
After stirring, an aqueous mixture containing 11% by weight of solid was obtained. Then the solid phase was precipitated by cooling at a temperature of −20° C., separated by filtration and dried at 120° C. for 16 hours obtaining a powder.
The powder is constituted by 97% by weight of ECTFE and 3% by weight of MMT, and has a Melt Flow Index (MI), measured at 210° C. with a 10 kg load, equal to 1.0 g/10′.
A compression moulded specimen from said powder has modulus G′ values at 23° C., 100° C. and 125° C. as reported in Table 3, and TmII and Txx, measured with a scanning rate of 10° C./min, as reported in Table 4.
The mechanical properties measured at 23° C. and at 100° C. are respectively reported in Tables 5 and 6.
5 kg of the ECTFE latex of Example 4 were precipitated by cooling at a temperature of −20° C., the compound was separated by filtration and dried at 120° C. for 16 hours obtaining a powder.
The obtained powder has a Melt Flow Index (MI), measured at 210° C. with a 10 kg load, equal to 8.2 g/10′.
A compression moulded specimen from said powder has modulus G′ values at 23° C., 100° C. and 125° C. as reported in Table 3, and TmII and Txx, determined with a scanning rate of 10° C./min, as reported in Table 4.
The mechanical properties measured at 23° C. and at 100° C. are respectively reported in Tables 5 and 6.
The aqueous mixture containing 8.5% by weight of solid obtained in Example 4 C), was used to obtain a film by “spin coating” on a mica surface. The film, after drying, is continuous and uniform.
A powder of an ethylene/chlorotrifluoroethylene copolymer having molar composition 50/50 (ECTFE), having a Melt Flow Index (MI), measured at 275° C. with a 2.16 kg load, equal to 7.0 g/10′ and a TmII of 240° C., determined with a scanning rate of 10° C./min, was compression moulded obtaining a specimen. The mechanical properties measured at 23° C. are reported in Table 7.
The powder of the same ECTFE polymer was mixed with mica powder (coated with titanium oxide) IRIODIN® 123 by MERCK, having a particle size in the range 5-25 micron, obtaining a mixture of powders formed by 97% by weight of ECTFE and by 3% of mica, from which a specimen was compression moulded.
The mechanical properties measured at 23° C. compared with those of ECTFE not filled with mica, are reported in Table 7.
As it is shown in Table 7, the filled ECTFE does not show an improvement of the tensile properties compared with the non-filled ECTFE, except for a slight increase of the elastic modulus. In general a worsening of the tensile properties of the filled ECTFE with respect to the non-filled ECTFE is noticed.
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