RU2584159C1 - Method of producing ultra-high molecular polyethylene, modified with zirconium oxide nanoparticles - Google Patents

Abstract

FIELD: manufacturing technology.

SUBSTANCE: invention relates to a process for preparing ultrahigh molecular weight polyethylene (UHMWPE) modified by nanosized zirconia particles intended for production of ceramics, catalysts, biomedical materials. Method is carried out in several steps. First, organic suspension is obtained by dispersing UHMWPE with vigorous stirring at 80-100 ºC for 4-5 hours in organic solvents, to which is added benzyl alcohol. Then, suspension is added to heated organic solution of zirconium tetrachloride in an amount corresponding to a molar ratio thereof to benzyl alcohol, 1:4.0-4.3, with constant stirring at 80-100 ºC for 5-6 hours after which step for separation of UHMWPE modified with zirconia nanoparticles is carried out. Organic solvents used are acetophenone, acetophenone, or a mixture of xylene.

EFFECT: materials derived from UHMWPE modified with zirconium oxide have high physical-mechanical properties such as tensile strength and modulus.

3 cl, 3 ex

Description

The 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 zirconium oxide, which can be used in various fields, for example, for the manufacture of ceramics, catalysts, biomedical materials.

For example, it is known to use in dentistry polymer polyacrylate composite materials modified with nanoparticles of zirconium and silicon oxides (US 61/105488, A61K 33/24, 2008).

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 has been revealed that the use of metal oxides in the nanodispersed state for polymer modification significantly affects their properties, for example, it reduces the manufacturing temperature of composite materials or leads to a significant increase in abrasion resistance, which is one of the reasons for their widespread use recently for the manufacture of new polymer materials. In composite materials, one of the important parameters characterizing them is the size of the particles included in them, for example, 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, by themselves, have ultra-high activity, which complicates their preparation. 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 this case are subjected to thermal decomposition (thermolysis) directly in the 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 (UHMW) or High - pressure polyethelen (HPPE). Such a polymer having a high molecular weight has a semicrystallen semicrystalline structure 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). Ultra-high molecular weight polyethylene (UHMWPE) is classified as non-polar low-pressure polyethylene, synthesized by the polymerization of ethylene [SA.P. Gubain and G.Yu. Yrcov, Int. J. Materials & Product Technology, vol. 23, nos ½, 2005].

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, B82 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. Changing the wear resistance of plates of ultra-high molecular weight polyethylene with its modification Chemical Technology, 2009, No. 7, p. 422) involves the introduction of mechanically activated ceramic powders in ultra-high molecular weight polyethylene (UHMWPE) with a molecular weight 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 different methods for producing nanodispersed metal oxides 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 rather 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 energy intensive and require special expensive equipment.

To obtain metal nanopowders, including zirconium oxide, the liquid-phase method is also used, which is considered the least labor-intensive and energy-intensive. This also applies to the production of nanodispersed zirconia, carried out, for example, by neutralizing zirconium salts with an alkaline agent and subsequent heat treatment of the obtained zirconium hydroxide to obtain zirconium oxide in the form of a nanopowder. As the initial salts of zirconium, the following are usually used: zirconium oxychloride, zirconium chloride, zirconium nitrate. 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 have shown that the above method for producing UHMWPE modified with metal oxide nanoparticles, including the preliminary stage of obtaining metal oxide nanoparticles, is very laborious and not effective enough to produce UHMWPE modified with zirconia nanoparticles.

For non-polar or weakly polar polymers, which include UHMWPE, as mentioned above, the in situ co-polymerization method is more preferable. By this method, for example, nanocomposites of polyamide-6, polyethylene, including UHMWPE, and polystyrene are obtained (RU 2433082, В82В 3/00, 2012). It was revealed that the introduction of even small amounts of fillers into the UHMWPE matrix allows one to obtain materials with unusual physical properties that are several times higher than the similar properties of unmodified UHMWPE [SA.P. Gubain and G.Yu. Yrcov, Int. J. Materials & Product Technology, vol. 23, nos 54, 2005]. This publication proposes 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 salts of these metals and their metal-containing compounds of the formula: MRn, where M is the above metal, a R = CO, HCOO, CH ₃ COO, C ₂ O ₄ . The use of iron acetate, barium acetate, and strontium acetate is given as specific examples in this article. For example, it is proposed to decompose iron acetate to form iron oxide in a solution of polyethylene in purified oil (bobbin oil) and at a temperature of 250 ° C in the atmosphere. The introduction of precisely nanoscale particles has a significant positive role on 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, in the presence of modifying particles, become more ordered [A. Pomogailo, A. Rosenberg ., Uflyand 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 discussed above, is carried out by the so-called “in-situ” polymerization method.

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 solution of tantalum pentachloride in benzyl alcohol 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 yield of UHMWPE modified with tantalum oxide, based on the initial loaded polyethylene in this method, is 93%, and the content of tantalum pentaxide nanoparticles in UHMWPE is 007 wt.%.

For the present invention, the closest in technical essence is the in situ co-polymerization method, which was previously used 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], as well as for the production of UHMWPE modified with tantalum pentoxide (RU 2532926). Data on the application of this method for the modification of UHMWPE with nanosized particles of zirconium oxide have not been identified.

To extend the range of composite materials with improved physical and mechanical properties a process for preparing ultra high molecular weight polyethylene (UHMWPE), modified nanoparticles zirconia comprising UHMWPE dispersing step in organic solvents, the subsequent step of introducing into the resulting organic suspension UHMWPE organic solution of zirconium tetrachloride and allocation step UHMWPE, modified zirconium oxide nanoparticles, characterized in that at the initial during the process step, acetophenone or acetophenone-xylene mixture is added to the initial UHMWPE with vigorous stirring and then benzyl alcohol is added dropwise, after which the reaction mixture is stirred vigorously for 4-5 hours, maintaining the temperature at 80-100 ° C, and the solution is added dropwise to the resulting suspension zirconium tetrachloride in acetophenone or acetophenone-xylene mixture containing zirconium tetrachloride in an amount corresponding to its molar ratio to benzyl alcohol equal to 1: 4-4.3 after which the mixture is intensively changed ivayut for 5-6 h, maintaining the temperature at 80-100 ° C, and then the resulting suspension was cooled, treated with chloroform, distilling off the solvent therefrom, 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 zirconium 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 zirconium chloride at the next stage of the process under consideration

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

A necessary condition for carrying out this stage of the proposed method is the choice of zirconium tetrachloride as the initial zirconium-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 zirconium chloride, unlike, for example, benzene, which is known to be used in the preparation of UHMWPE modified tantalum oxide nanoparticles ((RU 2532926, C08L 213/06, 2014). It is known that upon dissolution of zirconium chloride in acetophenone and xylene intermediate complex compounds are formed that affect the efficiency of hydrolysis process.

Zirconium tetrachloride is used in an amount corresponding to its molar ratio to benzyl alcohol equal to 1: 4.0-4.3, which is determined experimentally. 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 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 UHMWPE, modified by zirconia nanoparticles, from the solvent (acetophenone, xylene) and unreacted starting products by known methods: filtration, processing of the product with chloroform and subsequent distillation of the solvents and drying.

Below the invention is illustrated by the following examples.

Example 1. Dispersion of UHMWPE

In a four-necked flask with a capacity of 2000 cm ³ , 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 UHMWPE suspension, the previously prepared zirconium chloride solution is added in an amount corresponding to a molar ratio of benzyl alcohol to zirconium tetrachloride equal to 4: 1. The added solution is obtained from zirconium chloride (72 mmol; 16.8 g) and an acetophenone-xylene mixture containing 15% xylene (50 ml). To prepare the solution, a flat-bottomed flask with a capacity of 250 cm ^{3 is} taken, zirconium tetrachloride is added using a glass funnel, then the solvent. The resulting solution was added through a dropping funnel to the UHMWPE suspension with constant stirring and heating at 90 ° C for 6 h, then the resulting suspension was cooled, filtered, extracted with chloroform, vacuum distilled off solvents and dried.

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 the magnetic stirrer of 500 rpm. Immediately after adding the solvent, 33.8 g of benzyl alcohol (32.3 ml, 311 mmol) are added dropwise into the flask, stirred at a speed of 500 rpm at a temperature of 80 ° C for 4 hours.

A pre-prepared solution of zirconium chloride (molar ratio of benzyl alcohol to zirconium chloride 4.3: 1) is added to the suspension. A solution of zirconium chloride is obtained from zirconium chloride (72 mmol; 16.8 g) and acetophenone (50 ml). To prepare the solution, a flat-bottomed flask with a capacity of 250 cm ^{3 is} taken, zirconium 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 and heating at 90 ° C for 5 hours, the resulting suspension is cooled, filtered, extracted with chloroform, vacuum distilled solvents and dried.

Example 3

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 the magnetic stirrer of 500 rpm. Immediately after adding the solvent, 39.4 g of benzyl alcohol (37.5 ml, 362 mmol) are added dropwise to the flask. 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

After adding benzyl alcohol to the UHMWPE suspension, the previously prepared zirconium chloride solution is added in an amount corresponding to a molar ratio of benzyl alcohol to zirconium tetrachloride equal to 4: 1. The added solution is obtained from zirconium chloride (72 mmol; 16.8 g) and an acetophenone-xylene mixture containing 15% xylene (50 ml). To prepare the solution, a flat-bottomed flask with a capacity of 250 cm ^{3 is} taken, zirconium tetrachloride is added using a glass funnel, then the solvent.

The resulting solution is added through a dropping funnel to the UHMWPE suspension with constant stirring and heating at 90 ° C for 6 hours, then the resulting suspension is cooled, filtered, extraction is purified by chloroform, vacuum distillation of solvents and drying.

As additional studies show, materials based on UHMWPE modified with zirconium 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 wt.%, 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 samples of UHMWPE modified with nanoparticles of zirconium oxides, which indicates a change in the morphological properties of the samples, in particular, on the character of 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.

Confirmation that the sample really contains zirconium oxide nanoparticles are micrographs of its surface made using a HITACHI SU1510 scanning electron microscope.

Claims (3)

1. A method of producing ultra-high molecular weight polyethylene (UHMWPE) modified with nanosized particles of zirconium oxide, comprising the step of dispersing UHMWPE in organic solvents, the subsequent step of introducing an organic solution of zirconium tetrachloride into the resulting organic suspension of UHMWPE, and the step of isolating UHMWPE modified with zirconia nanoparticles, which is characterized by at the initial stage of the process, acetophenone or acetophenonexy is added to the initial UHMWPE with vigorous stirring benzene alcohol, 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 ° C, after which a solution of zirconium tetrachloride in acetophenone or in acetophenone-xylene is added dropwise to the resulting suspension. a mixture that contains zirconium 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 about the resulting suspension is cooled, filtered, treated with chloroform, distilled off the solvent and dried. 2. The method according to p. 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 p. 1, characterized in that the mixing is carried out preferably at a speed of 400-500 rpm