RU2505379C1 - Production method of nanopowder of zinc oxide with surface modification for use in building sealers - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: modified powder of zinc oxide is obtained by sedimentation from salt solution. Obtained powder is treated in polymer diluted solution in non-polar solvent. Then heat treatment is performed for obtained cover polymerisation.

EFFECT: increasing ultimate tensile strength and building sealers deformation degree.

6 dwg, 2 tbl, 1 ex

Description

This invention relates to the field of creating nanosized powders based on zinc oxide, used as fillers to improve the performance of various types of sealing polymer materials used in construction.

A known method of using ultrafine ceramic powders in the modification of polytetrafluoroethylene. (RF patent No. 2160697, IPC C08J 5/16, priority December 20, 1997). The process of grinding the material and applying it on the surface of revolution is interesting, however, the development does not imply the creation of a modifying coating on their surface.

A method is also proposed for controlling the shape of synthesized particles (RF patent No. 2179270, IPC B22F 9/30, priority 11.09.1998) and devices containing oriented anisotropic structures and nanostructure particles. The method provides the ability to control the size of the nanoparticles and obtain extended linear nanostructures. An interesting approach is to organize a method for controlling the process of changing the size of nanostructures. However, data on the possibility of surface modification of nanostructured inorganic components are not specified in the development.

In particular, there is a known method for producing nanoscale fillers used to create composites with functional properties, which includes grinding the fraction of layered minerals and exposure to thermal shock with a given temperature gradient (RF patent No. 2269554, IPC C09C 03/04, priority 13.07.2004), as a result, it is possible to obtain dispersed powders with a dimension of not more than 100 nm. Of interest is the process of grinding finely divided fillers. The disadvantage of the prototype is the lack of the possibility of applying nanosized polymer coatings on the surface of the filler in the process of its preparation.

The author's development according to the patent of the Russian Federation No. 2179270, IPC F16C 33/14 relates to a method of forming a coating on rubbing surfaces by grinding the initial mixture of minerals with the addition of a surfactant and obtaining a solid lubricant composition, which is then subjected to mechanical activation with a binder and placing the resulting composition between the rubbing surfaces. The method is characterized by the possibility of coating the surface of the inorganic coating, however, it is not possible to control the thickness of the applied coating.

A method of obtaining a composite material containing metal nanoparticles dispersed in a polymer matrix (French patent 2850661, priority 04.02.2003), provides for the preparation of these nanoparticles, their introduction into the monomers after treatment with the appropriate substances, emulsification of the obtained organic suspension in water and polymerization of the emulsion obtained. Of interest is the method of processing a polymer material to obtain a uniform distribution of components in the matrix medium, however, a limitation of the technology is the possibility of producing only metallic nanoparticles.

The present invention proposed a material that is a nanostructured powder filler based on zinc oxide for building sealants, significantly improving the mechanical characteristics.

A new technical result achieved by using the proposed method for producing filler material for sealants is to increase the uniformity of the filler distribution over the volume of the sealant and increase the elastic modulus while maintaining high deformability.

To obtain the proposed material using the method of deposition of alkali from solutions of metal salts, followed by treatment in a dilute solution of the polymer in a non-polar solvent and heat treatment to polymerize the resulting coating. In contrast to the known methods for producing nanosized fillers, it is not required to carry out joint mechanical activation treatment of ceramic and polymer material.

A method of obtaining a nanoscale filler from zinc oxide is illustrated as follows. The initial solutions of zinc chloride and alkali are mixed in the reaction vessel, maintaining a constant pH of the solution. In this case, a chemical reaction occurs in the volume of the Solution, accompanied by the formation of nanosized particles of insoluble zinc hydroxide by the reaction

ZnO: ZnCl ₄ + 4NaOH + Zn (OH) ₂ ↓ + 4NaCl.

The precipitate thus obtained is washed from the anions by decantation, centrifugation, washing filtration and other necessary amounts of water. After complete washing from the anions, the suspension obtained is washed from water in a polar or non-polar organic solvent, depending on what type of polymer coating will be applied. The last washing in a non-polar solvent is carried out in the presence of a given dissolved amount of polymer material, intended to modify the surface of the nanoscale filler. In this case, the process of chemical and physical adsorption of the additive on the surface of the metal hydroxide nanoparticles takes place. After that, the obtained modified nanopowder of metal hydroxide is separated on a filter or centrifuge. Then the precipitate is dried in air at a temperature of from 50 to 150 ° C, depending on the type of material. In the drying process, adsorbed water is removed and the metal hydroxide is dehydrated by the reaction according to the reaction:

The process of drying the hydroxide and its decomposition to oxide can be represented by the following scheme: an analysis of the latter can be represented as a sequence of transformations:

where Me _p (OH) _n is hydroxide; Me _x O _y - oxide; H ₂ O _d - water released during dehydration.

The process of water removal at elevated temperature occurs in parallel with the polymerization of the modifying coating. The thickness of the polymer coating will be determined by the amount and concentration of the modifying component at the last stage of processing. It is proposed to use organosilicon compounds - silanes as a polymer for creating a coating.

The structural diagram of a molecule of organosilicon compounds (silanes) located on the surface of a ceramic particle is presented in figure 1.

The silicon atom is located in the center of the silane molecule, contains an organic functional group R (for example, amino, vinyl, chloro, epoxy) and inorganic (X) (methoxy, ethoxy). The functional group R is attached to an organic resin, while the functional group (X) is attached to an inorganic material, for example, particles of a ceramic filler. As a result, the organic material and inorganic material tightly bind together after heating to temperatures of 80-120 ° C.

It should be noted that silane molecules are able to attach to the surface only as a monomolecular layer. Therefore, to calculate the required amount of modifying component, the following formula can be used:

Silane amount = {filler amount * specific surface area of ceramic filler} / {silane molecule area}.

In the process of drying hydroxide particles, water vapor is released as a result of the removal of structural and adsorbed water and the conversion of metal hydroxide to oxide. Silane alcohol groups react with water and form covalent bonds during dehydration and condensation.

In this work, an idin of the most accessible types of silanes, aminopropyltriethoxysilane with the structural formula, was used as a surface modifier for nanosized zinc oxides:

The properties of the obtained modified nanodispersed materials will be determined on the one hand by the degree of dispersion, on the other hand, by the thickness and composition of the polymer shell. The dispersion (particle size) of the material can be determined by microscopy, low-temperature nitrogen adsorption, and the composition of the polymer and the degree of polymerisation of the polymer coating by spectrometric methods, in particular, infrared spectrometry.

Studies have shown that by changing the conditions for obtaining nanodispersed materials, such as the feed rate of solutions, temperature, and the level of pH, the shape and particle size of the resulting fillers based on zinc oxide can be controlled.

Experimental studies have shown the high efficiency of the proposed method for producing various nanodispersed modified fillers for polymers. Using the proposed technology can significantly reduce the cost of the production process, since the processes of their production are carried out at low temperatures, it is not necessary to conduct mechanical activation of mixtures and the use of special equipment. On the other hand, the materials obtained due to the presence of a modifying layer on the surface are characterized by a set of useful characteristics that allow their effective use to increase the operational characteristics of polymeric materials and products.

The possibility of industrial applicability of the proposed method and the materials obtained with its use is confirmed by the following implementation examples.

Example

Obtaining precipitation of zinc hydroxides was carried out from solutions of the corresponding salts with alkali. The essence of the method is as follows: salt solutions are fed into the reaction vessel by peristaltic pumps, which are controlled by a system ensuring a constant pH of the reaction medium, including a pH meter and a power control system for peristaltic pumps. If the pH value deviates, the reagent supply automatically turns off. An alkali solution was supplied from another vessel. In this case, the following reactions proceed in the reaction vessel:

ZnO: ZnCl ₄ + 4NaOH = Zn (OH) ₂ ↓ + 4NaCl.

Microphotographs of nanodispersed fillers based on ZnO are presented in figure 2. Microphotographs allow us to conclude that their size does not exceed 100 nm. The obtained data on zinc oxide do not contradict the results of the specific surface analysis presented in Table 1. The particle shape is close to spherical, which indicates the applicability of the assumptions made when estimating the average particle size from low-temperature nitrogen adsorption. According to one of the developed methods, organosilicon compounds (silanes) were used as a material for surface modification. The obtained samples of modified nanodispersed fillers were intended to improve the operational characteristics of thiocol-based building sealants.

Table 1 The results of the analysis of the specific surface area of zinc oxide nanopowders before and after modification Sample Density g / m ³ Ssp, m ² / g Dcp, nm Zno 5,6 17,2 62 ZnO modified 5,6 21.3 fifty

As can be seen from table 1, the modified zinc oxide sample is characterized by a slightly larger value of the specific surface area in comparison with the initial nanopowder. Such a change in properties is quite typical during the treatment of nanopowders with silanes, since it allows one to stabilize the disperse system and prevent particle aggregation.

For the application of modifying coatings on zinc oxide nanoparticles, 0.2% (wt.) Solutions of aminopropyltriethoxysilane in ethanol were used. The consumption of the modifier was 3 grams per 100 grams of nanopowder, which, according to the analysis of the specific surface of materials and the calculations performed, corresponded to the formation of a monolayer of the modifier on the surface of each particle. Zinc hydroxide nanopowders previously washed in alcohol were added to a container with a solution of silane in ethanol with continuous stirring. Then, within 10 minutes, the solutions with fillers were processed using an ultrasonic homogenizer, due to which a uniform distribution of the modifier over the particle surface was ensured. Next, the powder was separated from the liquid by centrifugation. Modified powders were dried for 3 hours at 120 ° C, with the conversion of zinc hydroxide to oxide and coating polymerization. The obtained samples were studied by electron microscopy, low-temperature nitrogen adsorption, and IR Fourier spectroscopy.

The specific surface area (S _beats ) of the final and initial products was measured on a specific surface and porosity analyzer Quantachrome Noval200 by the BET method for low-temperature nitrogen adsorption. The error in measuring the specific surface area is 5%. The device allows you to measure pressure from 13.3 Pa to 133.3 KPa with an error of 0.3%.

According to measurements of the specific surface area of the samples, the mean particle size D _{cp was} determined:

where ρ is the density of the material, kg / m ³ ;

S is the specific surface, m ² / kg.

IR spectra were taken on a Then-no Nicolet 380 IR Fourier spectrometer in the mode of irregular internal reflection with a Smart Performer attachment equipped with a ZnSe crystal.

The mechanical characteristics of the samples were studied on an INSTRON 150LX universal testing machine with a deformation rate of 0.1 mm per second.

As can be seen from table 1, the modified zinc oxide sample is characterized by a slightly larger value of the specific surface area in comparison with the initial nanopowder. Such a change in properties is quite typical during the treatment of nanopowders with silanes, since it allows one to stabilize the disperse system and prevent particle aggregation.

Figure 3 presents the IR spectra of zinc oxide.

From the spectra shown in Fig.3, it was possible to determine the presence of silane on the surface of zinc oxide nanoparticles. No more changes in the spectra of these substances as a result of surface modification were detected.

The obtained modified nanopowders were intended for use as modifiers of thiokol sealants used for sealing in various technologies of the construction industry. The main requirements for these types of building sealants are a high tensile strength and high ability to reversible deformation.

The samples were prepared for tensile strength tests by adding nanodispersed pure and aired zinc oxides in a weight ratio of zinc oxide to thiocol of 1: 1. Mixing of the components was carried out using a mechanical stirrer for 10 minutes. Further, the sample, which is a viscous light gray mastic, was poured into a glass mold pretreated with a release compound to ensure ease of its separation after hardening. Then the sealant was cured at room temperature for 3 days. Further, blades for tensile tests according to GOST 21751-76 were cut from the obtained plates with a thickness of 2 mm.

Two types of manganese oxide nanopowders were introduced into the samples of urethane sealants - modified and unmodified. Powders were introduced into a liquid urethane prepolymer with continuous stirring with a mechanical stirrer for 10 minutes. Samples were cured in air at room temperature for 3 days.

Before the tests, a study was conducted on the possibility of curing thiocol sealants with zinc oxide without any additives. Mixing of zinc oxide with liquid thiocol was carried out using a mechanical stirrer for 10 minutes, then the samples were poured into a mold and cured at room temperature for 72 hours. Thus, 3 samples were prepared for curing, where the curing agents were: 1) Industrial zinc oxide (specific surface Ssp = 6 m ² / g); 2) Zinc oxide nanopowder obtained by chemical precipitation (specific surface Ssp = 16 m ² / g); 3) Modified zinc oxide nanopowder (specific surface Ssp = 20 m ² / g).

After 72 hours, only samples 2 and 3 fully hardened, sample 1, where industrial zinc oxide was used, characterized by a low specific surface area remained in the state of liquid mastic. Photos of samples 2 and 3 are presented in figure 4.

As can be seen in Fig. 4, in the sample containing the modified zinc oxide nanopowder, there is not such a large number of inclusions as compared to the cured unmodified zinc oxide nanopowder sample, which may indicate better dispersion of the zinc oxide nanopowder in the thiocol at the sample preparation stage and is explained by the direct effect modifying coating. Thus, modifying the surface of the fillers has significantly improved the uniformity of the distribution of the ceramic phase over the volume of the polymer material.

The mechanical properties of cured thiocol sealants were investigated according to GOST 21751-76. For research samples were prepared (figure 5). Tension diagrams are presented in Fig.6.

The results, averaged over five tests, for samples of thiocol sealants are presented in table 2.

table 2 Test results of samples of thiocol sealants with nanosized fillers based on zinc oxide Sample Sample Thickness (mm) Sample Width (mm) Starting Length (mm) Final length (mm) Tensile strength (MPa) Relates. elongation,% Elongation at Pmax (mm) one ZnO uncoated 2,50 6.30 40.50 49.20 0.88 21.48 8.37 2 ZnO coated 2,50 6.30 40.50 67.90 1.30 51.90 22.02

Samples for the curing of which a modified zinc oxide nanopowder was used are characterized by significantly greater elongation (21.5 and 51.9% for unmodified and modified nanopowders, respectively) and higher tensile strengths of 0.88 and 1.30 MPa, respectively. This is due to several factors: a more uniform distribution of particles of zinc oxide with a modified surface throughout the polymer; a decrease in the average size of ceramic inclusions; increasing the bond strength of polymer molecules with the surface of the filler particles. Thus, experimental studies have shown that obtained by the present method, nanoscale fillers for polymers, provide improved performance properties of polymer compounds, in particular, increase the tensile strength and tensile modulus.

Claims (1)

A method of producing a surface-modified zinc oxide nanopowder used in building sealants, including producing zinc oxide nanopowder by alkali deposition from a salt solution, processing in a dilute polymer solution in a non-polar solvent, and subsequent heat treatment to polymerize the resulting coating.

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