RU2588622C1 - Method of producing ultra-high molecular polyethylene, modified with nanoparticles of hafnium oxide - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to methods for producing polymer nanocomposite materials and directly relates to production of ultrahigh molecular weight polyethylene (UHMWPE), modified with hafnium oxide nanoparticles, which can be used in different fields, for example, for producing ceramics, catalysts, biomedical materials, and also for producing materials for non-volatile memory elements needed by microelectronics. Method involves stage of dispersion UHMWPE in organic solvents, subsequent stage of introduction organic solution of hafnium tetrachloride into formed UHMWPE organic suspension, and stage of extracting UHMWPE modified with hafnium oxide nanoparticles. At initial stage of process, to initial UHMWPE acetophenone or acetophenone-xylene mixture added under intense stirring, preferably containing 15-50 % xylene relative to total mixture volume. Then benzyl alcohol is added dropwise and mixture is intensely mixed while maintaining temperature at level of 80-100 °C during 4-5 hours. To formed suspension, hafnium tetrachloride solution in acetophenone or in acetophenone and xylene mixture is added dropwise, containing hafnium tetrachloride in amount corresponding to its molar ratio to benzyl alcohol equal to 1:4.0-4.3. After that mixture is intensely mixed at rate of 400-500 rpm, while maintaining the temperature at level of 80-100 °C during 5-6 hours. Obtained suspension is cooled, filtered, washed with chloroform, then solvent is distilled and dried out.

EFFECT: materials obtained based on UHMWPE modified with hafnium oxide have good physical and mechanical properties.

3 cl, 3 ex

Description

The present invention relates to methods for producing polymer nanocomposite materials and directly relates to the production of ultra-high molecular weight polyethylene (UHMWPE) modified with nanosized particles of hafnium oxide, which can be used in various fields, for example, for the manufacture of ceramics, catalysts, biomedical materials, for the manufacture of materials for non-volatile elements memory for the needs of microelectronics.

For example, it is known to use polymeric materials, for example, polycarbonates modified with hafnium oxide nanoparticles, in such fields of medicine as therapy, diagnostics (RU 2447105, A61K 33/24, 2012, MX 2014007131 A61K 33/24, 2014; EP 201101193968, A61K 33 / 24, 2011), in aircraft construction for the manufacture of aircraft structures (RU 2447105, C08L 69/02, 2012).

In practice, it is proved that polymer compositions based on polyolefins, polyamides, modified with nanosized particles of metal oxides, carbides, nitrides, have improved physical and mechanical properties. It was revealed that the introduction of even insignificant amounts of fillers into the matrix of polymeric materials allows one to obtain materials with unusual physical properties that are several times higher than similar properties compared to unmodified polymers. The structure and size of the introduced modifying additive plays an essential role in the preparation of polymeric nanocomposite materials with certain physical and mechanical properties. It was revealed that the use of metal oxides in the nanodispersed state for modification of polymers significantly affects their properties, for example, it allows to reduce the manufacturing temperature of composite materials, significantly increases abrasion resistance, which is one of the reasons for their widespread use recently for the manufacture of new polymeric materials. In composite materials, one of the important parameters characterizing them is the size of the incoming nanoparticles, including oxides. Depending on the particle size, they are divided into nanostructured particles (with a size of 1-10 nm) and microstructured particles (with a size of 50-500 nm). The particle size of metal oxides, as follows from information sources, affects their catalytic activity: the smaller the particle size, the greater their catalytic activity (JP 20100267439, C01G 35/00, 2010, JP 2011140433, 2011).

As practice shows, metal nanoparticles having a diameter of d = 1-10 nm, in themselves, have ultra-high activity, which complicates their preparation as such. Therefore, to facilitate the preparation of these materials, it was proposed to obtain metal nanoparticles introduced into the polymer matrix and to obtain various heterostructures containing nanoparticles. The starting metal-containing compounds in the described process are subjected to thermal decomposition (thermolysis) directly in a polymer matrix, usually a carbon-containing matrix, for example, carbon-rain or polycarbosilanes or oligomers. Of particular interest is the use as a matrix of ultra-high molecular weight polyethylene (SVMHG) or High - pressure polyethelen (HPPE). Such a polymer has a semi-crystalline porous structure (semicrystallen) containing both crystalline and amorphous regions, which plays a key role and determines the properties of materials. The indicators characterizing the porosity are: specific pore surface (S _sp ), pore volume (V ₀ ) and pore radius (r). As you know, ultra-high molecular weight polyethylene (UHMWPE) refers to non-polar low-pressure polyethylene, synthesized as a result of polymerization of ethylene. [SA.P. Gubain and G.Yu. Yrcov, Int. J. Materials & Product Technology, vol. 23, nos ½, 2005]. It was revealed that the introduction of even insignificant amounts of fillers into the UHMWPE matrix allows one to obtain materials with unusual physical properties that are several times higher than those compared to unmodified UHMWPE.

Particular attention in the preparation of polymers modified with nanoparticles is given to the development of techniques for their mixing. Three main methods of mixing polymers with nanoparticles are distinguished: 1) dispersion in solutions; 2) joint in situ polymerization; 3) melt mixing (RU 2433082, B82Y 3/00, 2012). As you know, the choice of a method is determined by the type of polymer. For example, for polar polymers, all three of these methods are applied. For non-polar or weakly polar polymers, which include UHMWPE, the in situ co-polymerization method is more preferred. Ready-made nanopowders of metal oxides, which are then mixed with a polymer (UHMWPE) and the mixture are subjected to appropriate processing, can be used as initial products for obtaining modified UHMWPE. Thus, the known method (G.E. Selyutin et al. Changes in the wear resistance of ultra-high molecular weight polyethylene plates during its modification. Chemical Technology, 2009, No. 7, p. 422) involves the introduction of mechanically activated ceramic powders into ultra-high molecular weight polyethylene (UHMWPE) with molecular weighing up to 8 × 10 ⁶ . For this, the initial mixture is subjected to processing in planetary activators on a plant with a capacity of about 1000 W / g, mixed in a mixer and then subjected to the hot pressing method. This process, as can be seen, involves an additional step in the preparation of a modifier — metal oxide nanoparticles, which can be preliminarily obtained by various methods.

Several methods for producing metal oxide nanoparticles are known: mechanochemical, plasma chemical, liquid-phase chemical precipitation from solutions, hydrothermal synthesis.

The mechanochemical method, which includes the stage of grinding a pre-dispersed metal oxide in planetary or ball mills. The method is quite laborious and not effective enough. To obtain nanodispersed metal oxides, the plasma chemical method is also used (RU 2071678, C01G 31/02, 1994); hydrothermal synthesis (CN 1636932, C01G 25/02, 2005); solid-phase synthesis (CN 101844807, B82B 3/00, C01G 27/02, 2010; CN 101823766, B82B 3/00, C01G 27/02, 2010), carried out at a temperature of about 500-800 ° C. All of these methods are quite energy intensive and require sophisticated special equipment.

To obtain metal nanopowders, including hafnium oxide, the liquid-phase method is also used, which is considered the least labor-intensive and energy-intensive. In this method, as in the solid-phase method, hafnium chloride and, less commonly, hafnium oxychloride are usually used as the starting hafnium salts. However, nanopowders obtained by this method have a high degree of aggregation and agglomeration, which makes them unsuitable for obtaining dense high-strength ceramics (Shabanova N.A. et al. Chemistry and Technology of Nanodispersed Oxides. M .: Akademkniga, 2006, 309). To prevent aggregation, additional steps have to be used, for example, spraying and quick freezing with liquid nitrogen, vacuum sublimation and subsequent calcination (US 5004710) or sedimentation in an ultrasonic field (from 20-50 kHz), followed by drying and calcination (RU 2058939, C01G 25 / 02, 2000), drying under the influence of microwave radiation in the frequency range 500-2000 MHz with a continuous power of 3-50 kW. (Konstantinova T.E. et.al. The mechanisms of particle formation in Y-doped ZrO ₂ // Int / J / Nanotechnology, 2006, vol. 3, No. 1, p. 29-38).

Additional studies showed that the above method for producing UHMWPE modified with nanoparticles of metal oxides, including the preliminary stage of obtaining nanoparticles of metal oxides, is very laborious and not effective enough to produce UHMWPE modified with nanoparticles of hafnium oxide.

For the present invention, the closest in technical essence is the method of co-polymerization "in situ", this method is obtained, for example, nanocomposites of polyamide-6, polyethylene, including UHMWPE, and polystyrene (RU 2433082, B82 3/00, 2012). ]. The in-situ method is also proposed for introducing into the UHMWPE nanoparticles of transition metal oxides selected from the group: M = Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, Mn, Mo, Nd, Ni, Pt, Re , Ti, Pb, Sr, Sm, W, Zn ([SA.P. Gubain and G. Yu. Yrcov, Int. J. Materials & Product Technology, vol. 23, nos ½, 2005], and also for the production of UHMWPE, modified tantalum pentoxide (RU 2532926, C08L 213/06, 2014). In the publication cited above, it is proposed to introduce into the UHMWPE matrix nanoparticles of transition metal oxides selected from the group: M = Ba, Be, Ca, Cd, Co, Cr, Cu, Fe , Mn, Mo, Nd, Ni, Pt, Re, Ti, Pb, Sr, Sm, W, Zn, for which it is proposed to use a wide group of inorganic Olay these metals and metal containing compounds of the formula:. MRn, where M - above metal, a R = CO, HCOO, CH ₃ COO, C ₂ O ₄ As specific examples in this article the use of iron acetate, barium acetate, acetate strontium For example, decomposition of iron acetate to form iron oxide is proposed to be carried out in a solution of polyethylene in purified oil (bobbin oil) and at a temperature of 250 ° C in the atmosphere. The introduction of nanosized particles plays a significant role in the properties of modified UHMWPE, which is explained by the high surface energy of such particles and their ability to influence the formation of supramolecular aggregates of UHMWPE macromolecules, which become more orderly in the presence of modifying particles [Pomogailo AD, Rosenberg AS Ufland I.E. Metal nanoparticles in polymers. - M. Chemistry, 2000].

It is also known to obtain ultra-high molecular weight polyethylene (UHMWPE) modified with nanosized particles of tantalum pentoxide (RU 2532926, C08L 213/06, 2014). This known method as well as the above, carry out the so-called method of joint polymerization "in situ". This method is carried out in several stages: receive a UHMWPE benzene solution; benzyl alcohol is added to it; mix the resulting reaction mass at a speed of 400-500 rpm at boiling for 5.0-6.0 hours; filtered, washed with benzene, distilled off the solvent; add to the resulting reaction mass a benzene solution of tantalum pentachloride in an amount corresponding to a molar ratio of tantalum pentachloride to benzyl alcohol equal to 1: 5-5.3; the resulting reaction mass is stirred at a speed of 400-500 rpm at boiling for 3-4 hours, cooled; the target product is isolated by filtration, washing, extraction with chloroform and vacuum distillation of the solvent.

The output of UHMWPE modified with tantalum oxide, calculated on the initial loaded polyethylene in this case is 93%.

The content of tantalum pentoxide nanoparticles in this polymer is 0.07 wt. %

To expand the range of composite materials with improved physicomechanical properties, a method for producing ultrahigh molecular weight polyethylene (UHMWPE) modified with hafnium oxide nanoparticles is proposed. modified nanoparticles of hafnium oxide, characterized in that at the initial stage In the process, acetophenone or acetophenone-xylene mixture is added to the initial UHMWPE with vigorous stirring and then benzene alcohol is added dropwise, after which the reaction mass is intensively stirred for 4-5 hours, maintaining the temperature at 80-100 ° C, and a tetrachloride solution is added dropwise to the resulting suspension. hafnium in acetophenone or acetophenone-xylene mixture containing hafnium tetrachloride in an amount corresponding to its molar ratio to benzyl alcohol equal to 1: 4.3, after which the mixture is intensively mixed for 5-6 hours, maintaining the temperature at 80-100 ° C, and then the resulting suspension is cooled, treated with chloroform, the solvent is distilled from it and dried.

The acetophenone-xylene mixture used as a solvent preferably contains 15-50% xylene of the total mixture volume.

Stirring is preferably carried out at a speed of 400-500 rpm.

As can be seen from the brief description of the process, the proposed method includes three main stages.

The first stage consists in dispersing UHMWPE in acetophenone or acetophenone-xylene mixture with heating and stirring, followed by the addition of the required amount of benzyl alcohol. The necessary conditions for this stage are:

the introduction of the required amount of benzyl alcohol (based on the molar ratio of benzyl alcohol to hafnium chloride equal to 4-4.3: 1);

dispersing UHMWPE with vigorous stirring, preferably at a speed of 400-500 rpm (for example, using a magnetic stirrer);

maintaining certain temperature and time conditions (80-100 ° C for 4-5 hours), which are directly dependent on the selected solvents;

the choice of acetophenone or acetophenone-xylene mixture as a solvent for dispersing UHMWPE, in which the xylene content is preferably 15-50% of the total volume of the solvent mixture.

The choice of acetophenone or acetophenone-xylene mixture as solvents for dispersion of UHMWPE is explained by the fact that these solvents were chosen as solvents of solid hafnium chloride at the next stage of the process under consideration

The second stage, which takes place with the formation of hafnium dioxide nanoparticles in UHMWPE macromolecules, involves adding to the heated suspension formed after adding benzyl alcohol to UHMWPE the corresponding amount of hafnium chloride, which in polymer macromolecules (UHMWPE) reacts with benzyl alcohol according to the reaction chemistry given below , and as a result of hydrolysis, hafnium dioxide is formed:

A necessary condition for carrying out this stage of the proposed method is the selection of hafnium tetrachloride as the initial hafnium-containing product, which is introduced into the reaction with benzyl alcohol in the form of a solution in acetophenone or in an acetophenone-xylene mixture,

The choice of acetophenone or acetophenone-xylene mixture as dispersion solvents for UHMWPE is explained by the fact that these solvents have the best dissolving ability with respect to solid hafnium chloride, unlike, for example, benzene, which is known to be used in the preparation of modified UHMWPE tantalum oxide nanoparticles (RU 2532926, C08L 213/06, 2014). It is known that upon dissolution of hafnium chloride in acetophenone and xylene, intermediate complex compounds are formed that affect the efficiency of the hydrolysis process.

Hafnium tetrachloride (solid product) is used in an amount corresponding to its molar ratio to benzyl alcohol equal to 1: 4.0-4.3. A necessary condition for carrying out this stage of the process is temperature and time conditions, namely, intensive mixing of the resulting reaction mass for 5-6 hours, maintaining the temperature at 80-100 ° C, namely, carrying out the process at the boiling point of the solvent or close to the boiling point. In the case of an increase in temperature, undesired gelation of UHMWPE occurs.

The third stage is the purification of the final product from the solvent (acetophenone, xylene) and unreacted starting materials, for which the known purification methods are used: filtration, processing of the product with solvent (chloroform), and subsequent distillation of the solvents and drying.

Below the invention is illustrated by the following examples.

Example 1

In a four-necked flask with a capacity of 2000 cm, equipped with a magnetic stirrer, a thermometer, a reflux condenser with a calcium chloride tube, and also a dropping funnel, 150 g of UHMWPE are charged. 400 ml of solvent (a mixture of acetophenone and xylene in an equal volume ratio) are added to the same flask in small portions at a stirring speed of a magnetic stirrer of 400 rpm. Immediately after adding the solvent, 31.5 g of benzyl alcohol (30 ml, 290 mmol) was added to the flask through a dropping funnel and, after the addition of benzyl alcohol, the mixture was intensively stirred at a speed of 500 rpm at 100 ° C for 5 hours using magnetic mixers.

After adding benzyl alcohol to the suspension of UHMWPE, the previously prepared hafnium chloride solution is added in an amount corresponding to a molar ratio of benzyl alcohol to hafnium tetrachloride equal to 4: 1. The added solution was prepared from hafnium chloride (72 mmol; 23.11 g) and an acetophenone-xylene mixture containing 50% xylene (50 ml). To prepare the solution, a flat-bottomed flask with a capacity of 250 cm is taken, hafnium tetrachloride is added using a glass funnel, then the solvent. The resulting solution was added through a dropping funnel to the suspension of UHMWPE with constant stirring at a speed of 400 rpm and heating at 90 ° C for 6 hours. Then the resulting suspension is cooled to room temperature, after which cooling is continued in a water bath. The resulting suspension is filtered under vacuum of a water-jet pump, treated with chloroform for 3 hours at 100 ° C. The solvent is distilled off on a rotary evaporator (20-30 mm Hg 110 rpm). A white powder weighing 142.5 g is obtained. The product yield, based on the initial loaded polyethylene, is 95%. The powder obtained after filtration is poured into 100 ml of chloroform, stirred and again filtered on a Schott filter in a vacuum of a water-jet pump. For complete and thorough washing of the product from unreacted starting materials, the resulting powder is placed in a Soxhlet apparatus. 300 ml of chloroform are poured into an Soxhlet extraction flask. Extraction is carried out with chloroform for 3 hours. After distillation of the solvent, a white powder weighing 142.5 g is obtained. The product yield, based on the initial loaded polyethylene, is 95%.

Example 2

150 g of UHMWPE are charged and 400 ml of acetophenone are added to the same flask in small portions at a stirring speed of a magnetic stirrer of 500 rpm. 33.8 g of benzyl alcohol (32.3 ml, 311.75 mmol) are added dropwise to the flask immediately after the addition of solvent. Upon completion of the addition of benzyl alcohol, the mixture is stirred at a speed of 500 rpm at a temperature of 80 ° C for 4 hours.

A pre-prepared hafnium chloride solution is added to the suspension (molar ratio of benzyl alcohol to hafnium chloride 4.3: 1). A hafnium chloride solution is prepared from hafnium chloride (72 mmol; 23.11 g) and acetophenone (50 ml). To prepare the solution, a flat-bottomed flask with a capacity of 250 cm ^{3 is} taken, hafnium tetrachloride is added using a glass funnel, then the solvent. The resulting solution is added via a dropping funnel to the UHMWPE suspension with constant stirring at a speed of 500 rpm and heating at 90 ° C for 5 hours, the resulting suspension is further processed as in example 3: it is cooled, filtered, extracted with chloroform, vacuum distilled solvents and drying (analogous to example 1).

Example 3

150 g of UHMWPE are charged and 400 ml of acetophenone-xylene mixture containing 15% by volume of xylene are added in small portions to the same flask at a stirring speed of the magnetic stirrer of 500 rpm. Immediately after adding the solvent, 31.5 g of benzyl alcohol (30 ml, 290 mmol) are added dropwise through a dropping funnel and, after the addition of benzyl alcohol, the mixture is stirred at a speed of 500 rpm at 80 ° C for 4 hours.

After adding benzyl alcohol to the suspension of UHMWPE, the previously prepared hafnium chloride solution is added in an amount corresponding to a molar ratio of benzyl alcohol to hafnium tetrachloride equal to 4: 1. The added solution is obtained from hafnium chloride (72 mmol; 23.11 g) and acetophenone - a xylene mixture containing 15% xylene (50 ml). To prepare the solution, a flat-bottomed flask with a capacity of 250 cm ^{3 is} taken, hafnium tetrachloride is added using a glass funnel, then the solvent. The resulting solution was added via a dropping funnel to the suspension of UHMWPE with constant stirring and heating at 90 ° C for 6 hours.

Then the resulting suspension is cooled to room temperature, after which cooling is continued in a water bath. The resulting suspension is filtered under vacuum of a water-jet pump, treated with chloroform for 3 hours at 100 ° C. The solvent is distilled off on a rotary evaporator (20-30 mm Hg 110 rpm). A white powder weighing 142.5 g is obtained. The product yield, based on the initial loaded polyethylene, is 95%.

The data below show that ultra-high molecular weight polyethylene modified with hafnium oxide nanoparticles is a white powder with a particle size in the region of 50-200 microns.

As additional studies show, materials based on UHMWPE modified with hafnium oxide have high physical and mechanical properties. In the study of samples of the modified UHMWPE obtained by the described method by DSC, an increase in the temperature of the onset of melting by 5 ° C was detected with an oxide nanoparticle content of 0.1% by weight, which indicates a significant effect of the added additive on the crystallinity of the polymer. Also, the data obtained by the DLS method indicate a significant change in the dielectric constant of the samples modified by nanoparticles of hafnium oxides UHMWPE, which indicates a change in the morphological properties of the samples, in particular, on the nature of the packing of polymer macromolecules in crystallites. The tensile strength and elastic modulus of the obtained samples are 10-20% higher than that of the initial UHMWPE.

The fact that the sample really contains hafnium oxide nanoparticles is confirmed by micrographs of its surface made using a HITACHI SU 1510 scanning electron microscope.

This product can be used for the manufacture of insulators operating in the high and ultra-high frequency range, insulator supports, conduits and other electrical devices, in the chemical industry for lining containers, pipes, and for transporting liquids.

Claims (3)

1. A method of producing ultra-high molecular weight polyethylene (UHMWPE) modified with nanosized particles of hafnium oxide, comprising the step of dispersing UHMWPE in organic solvents, the subsequent step of introducing into the resulting organic suspension of UHMWPE an organic solution of hafnium tetrachloride and the step of isolating UHMWPE modified by nanoparticles of hafnium oxide, characterized in at the initial stage of the process, acetophenone or acetophenone-xylene is added to the initial UHMWPE with vigorous stirring mixture, and then benzyl alcohol is added dropwise, after which the reaction mass is stirred vigorously for 4-5 hours, while maintaining the temperature at 80-100 ° С, then a solution of hafnium tetrachloride in acetophenone or in acetophenone-xylene mixture is added dropwise to the resulting suspension. , which contains hafnium tetrachloride in an amount corresponding to its molar ratio to benzyl alcohol equal to 1: 4.0-4.3, and the resulting reaction mass is intensively stirred for 5-6 hours at a temperature of 80-100 ° C, after which The resulting suspension is cooled, filtered, treated with chloroform, distilled off the solvent and dried. 2. The method according to claim 1, characterized in that in the acetophenone-xylene mixture, the xylene content is preferably 15-50% of the total volume of the mixture. 3. The method according to claim 1, characterized in that the mixing is carried out preferably at a speed of 400-500 rpm