TITLE OF THE INVENTION

METHOD FOR PRODUCING HIGH-PERFORMANCE NANOCOMPOSITE TECHNICAL FIELD A polyolefin is an excellent multi-purpose plastic material having a low price, a light weight, a high melting point, good processability, good and widely adjustable mechanical properties, and good recyclability. Since the polyolefin does not generate harmful gas upon its combustion, it is also advantageous in terms of environmental aspects. Especially, polypropylene has a high melting point and high mechanical strength and has been attractive as a substituent for inorganic materials or engineering plastics. In these substitution attempts, the reinforcement and functionalization of the polyolefin by means of compounding with inorganic materials (so-called filler) is an attractive method.

TECHNICAL BACKGROUND

Production of a composite of a filler and a polyolefin is usually conducted by a polymer processing and molding company which melts and kneads a polyolefin pellet supplied by a resin maker with a filler supplied elsewhere. However, it is not easy to disperse the filler to the polyolefin which lacks a polar functional group. Previously, various attempts, such as chemical modification of the filler surfaces and the addition of a compatibilizer, have been proposed for improving the dispersion of the filler in the polyolefin.

PRIOR ART LIST

PATENT DOCUMENT

[Patent Literature 1] Japanese Patent Application Publication 2008-75052 [Patent Literature 2] Japanese Patent Application Publication 2010-174120 [Patent Literature 3] International Patent Application Publication WO 2008/048693 A2 [Patent Literature 4] Japanese Patent Application Publication 2016-124942

Patent Literature 1 discloses a method of blending magnesium hydroxide which is preliminarily surface-modified with pentaerythritol and zinc stearate, into polyolefin. Patent Literature 2 discloses the utilization of a porous material, which consists of particles containing alkoxysilane and magnesium hydroxide, is used as a flame-retardant agent. Patent Literature 3 discloses magnesium hydroxide nanoparticles whose surfaces are modified with an organic dispersant agent (e.g., a hydroxy acid) and an aliphatic compound (e.g., a monofunctional alcohol). It also discloses the magnesium hydroxide nanoparticles exhibit superior fire retarding properties in polymer materials.

According to the conventional methods described in Patent Literatures 1 , 2 and 3, the addition of dispersants such as surface modifiers and compatibilizers is essential to improve the dispersion of the magnesium hydroxide. Unfavorable side effects from these dispersants to the resultant composite finally are unavoidable. Typical side effects known are cost penalty, unfavorable impacts on polymer properties, accelerated degradation, and unfavorable interaction with other additives (anti-oxidants, colorant, and so on), and bleed phenomenon.

In order to solve such problems, the present inventors proposed a method for producing a high-performance nanocomposite that a nano-sized inorganic filler disperses in the polyolefin as fine particles in Patent Literature 4 without the addition of any dispersants. This method begins with mixing with a metal alkoxide, which is a precursor of the inorganic filler, and a polyolefin powder, and thereafter converts the metal alkoxide into metal hydroxide or a metal oxide in the polyolefin. They succeeded in producing new composite materials that the inorganic filler, which is in the form of fine particles whose maximum particle diameter is 500 nm or less are dispersed in the polyolefin. However, the concentration of the inorganic filler, which can be dispersed without an agglomeration of particles in polyolefin, is only about 3 wt% to a polyolefin in the case of metal oxides. In order to increase the content of the inorganic filler, the nanoparticles (commercial fine particles etc.) of the inorganic filler prepared separately need to be added additionally. However, in such an additional addition, the agglomeration of the particles of the inorganic filler in the polyolefin matrix was unavoidable. Furthermore, the problem of the agglomeration of the inorganic filler particle becomes more serious with the increase of the content of the inorganic filler. As a result, with the technique indicated in Patent Literature 4, it was impossible to excellently functionalize the polyolefin by the inorganic filler at a sufficiently high concentration, specifically by dispersing the inorganic filler having 15 wt% or more to the polyolefin, more specifically 20 wt% or more, without particle agglomeration, and maintaining the mechanical properties of the polyolefin.

SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

Then, the present inventors sought for the method of dispersing an inorganic filler, such as AI2O3, to a polyolefin at a high concentration, further in a form of independent fine particles (so-called nanoparticles) whose maximum particle diameter is approximately 500 nm.

MEANS TO SOLVE THE PROBLEM

As a result, in the production method of the high-performance nanocomposite, the present inventors have succeeded in dispersing an inorganic filler, such as AI2O3, at a high concentration in polyolefin by changing the sol-gel reaction process of a metal alkoxide, which was not attained in the past. That is, the present inventions are as follows: (1 ): A method for producing a high-performance nanocomposite containing a polyolefin and a metal oxide, which comprises the following Steps 1-4:

(Step 1 ) a step of impregnating a metal alkoxide which is a precursor of the metal oxide to a polyolefin powder;

(Step 2) a step of removing the solvent by drying the polyolefin powder obtained in Step 1 ; (Step 3) a step of heating the polyolefin powder obtained in Step 2 under a water vapor atmosphere; and

(Step 4) a step of melting and kneading the polyolefin powder obtained in Step 3, wherein the sol-gel reaction from the metal alkoxide as the precursor to the fine particles of the metal oxide is completed. (2): A method for producing a high-performance nanocomposite according to (1), wherein the heating condition of Step 3 is the cooking time of 20 hours or longer at 50 °C.

(3) : A method for producing a high-performance nanocomposite according to (1), wherein the heating condition of Step 3 is the cooking time of 6 hours or longer at 70 °C.

(4) : A method for producing a high-performance nanocomposite according to (1 ), (2) or (3), wherein the metal oxide contained in the high-performance nanocomposite is selected from AI2O3 or

T1O2, and wherein the metal alkoxide used in Step 1 as the precursor is selected from alminium alkoxides or titanium alkoxides.

(5) : A high-performance nanocomposite containing a polyolefin and a metal oxide obtained by the method of (1 ), (2), (3) or (4), wherein the content of the metal oxide is 5 wt% or higher to the polyolefin, and wherein the metal oxide disperses in the polyolefin as fine particles whose maximum particle diameter is 500 nm or less.

(6): A high-performance nanocomposite containing a polyolefin and a metal oxide obtained by the method of (1), (2), (3) or (4), wherein the content of the metal oxide is 20 wt% or higher to the polyolefin, and wherein the metal oxide disperses in the polyolefin as independent fine particles whose maximum particle diameter is 500 nm or less.

(7): A high-performance nanocomposite containing a polypropylene-based polymer and AI2O3 according to (6), wherein the content of AI2O3 is more than 20 wt% or higher to the polypropylene-based polymer, wherein the AI2O3 disperses in the polypropylene-based polymer as independent fine particles whose maximum particle diameter is 500 nm or less, and wherein a thermal conductivity calculated based on the following formula is more than 0.40 Wm 'K ^"1 , λ = or Cp where the said a denotes thermal diffusivity, the said λ denotes thermal conductivity, the said Cp denotes specific Heat capacity, and the said p denotes density.

ADVANTAGEOUS EFFECTS OF THE INVENTION According to the present invention, a novel material, which is a composite in which an inorganic filler whose concentration is 5 wt% or higher, especially higher than 20 wt%, is uniformly dispersed in the polyolefin in a form of independent fine particles whose maximum particle size is 500 nm or less, is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows the IR spectrum of the nanocomposite according to Example 2 (T1O2 content of 10 wt%).

Fig. 2 shows the IR spectrum of the nanocomposite according to Comparative Example 1 (T1O2 content of 10 wt%).

Fig. 3 shows a TEM image of the nanocomposite according to Example 2 (Ti0 ₂ content of 10 wt%). Fig. 4 shows a TEM image of the nanocomposite according to Example 3 (Ti0 ₂ content of 20 wt%).

Fig. 5 shows the IR spectra of neat polypropylene, the nanocomposite according to Example 4 (AI2O3 content of 5 wt%), and the nanocomposite according to Comparative Example 2-1 (AI2O3 content of 5 wt%).

Fig. 6 shows a TEM image of the nanocomposite according to Example 4 (AI2O3 content of 5 wt%). Fig. 7 shows a TEM image of the nanocomposite according to Example 5 (Al ₂ 0 ₃ content of 10 wt%). Fig. 8 shows a TEM image of the nanocomposite according to Example 6 (AI2O3 content of 20 wt%). Fig. 9 shows a TEM image of the nanocomposite according to Example 7 (Al ₂ 0 ₃ content of 30 wt%). Fig.10 shows a TEM image of the nanocomposite according to Comparative Example 2-1 (AI2O3 content of 5 wt%).

Fig.11 shows a TEM image of the nanocomposite according to Comparative Example 2-2 (AI2O3 content of 5 wt%). Fig.12 shows a comparison of TEM images of the nanocomposites according to Examples 4-6 (precursor: AI(OiPr) ₃ ) and Examples 8-10 (precursor: AI(OEt) ₃ ).

DESCRIPTION OF THE EMBODIMENTS

(Step 1) Step 1 is a step of impregnation of a metal alkoxide which is a precursor of the metal oxide to a polyolefin powder. As the polyolefin powder, the polyolefin obtained as a result of polymerization, so-called a reactor powder or a reactor granule, can be used without any restriction. There is no restriction over olefin polymerization methods. Typical olefins such as ethylene and a- olefin which has the carbon numbers 3 to 10 can be used for polymerization as itself (homopolymer) and as mixture (copolymer). Small amounts of branched olefins, aromatic olefins, and dienes can be also added to the monomer or the monomer mixture. As a method for producing polyethylene, a high-pressure radical polymerization method, and a coordination polymerization method in the presence of either of Ziegler-Natta, Phillips, and metallocene catalysts are common. As a method for producing polypropylene, a coordination polymerization method in the presence of either Ziegler- Natta or metallocene catalysts are common. There is no restriction for a radical initiator and a type of catalysts used for the said polymerization methods. Preferable polyolefin according to the present invention is polyethylene- or polypropylene-based polymer. In the present invention, this means polymer which is obtained by polymerizing ethylene or propylene as itself, otherwise in the presence of a small amount of other olefins.

The metal oxide meant in the present invention is not restricted if it is a metal oxide which has a positive effect on improving the properties of the polyolefin. For instance, a metal oxide selected from Al ₂ 0 ₃ , T1O2, Si0 ₂ , ZnO, Zr0 ₂ , MgO, and a ternary oxide or a complex oxide from the two of more of those can be used as such the metal oxide. In Step 1 , an alkoxide of Al, Ti, Si, Zn, Zr, Mg represented by a formula M(OR) _n ("M" denotes a metal atom, "R" denotes an alkyl group having the carbon number of 1 or larger, and "n" denotes an integer corresponding to the valence of the metal atom) is used as a precursor of the metal oxide.

In the case that the metal alkoxide is solid at an ordinary temperature, a solution, which dissolves the metal alkoxide to a solvent having a high affinity to the polyolefin, can be used as a metal alkoxide solution. As such a solvent, for example, one or more sorts are available from alcohols such as methanol and ethanol, aromatics such as toluene, xylene and benzene, hydrocarbons such as hexane and heptane, ketones such as acetone and diethyl ketone, and chlorinated solvents such as dichloromethane and dichlorobenzene. In the case that the metal alkoxide is liquid at an ordinary temperature, a solution consisting of the metal alkoxide itself, or a metal alkoxide and the above-mentioned solvent are available as a metal alkoxide solution. However, when using the metal alkoxide itself, the metal alkoxide needs to be a volatile liquid at the conditions of the impregnation. For instance, titanium alkoxides, which are the precursors of ΤΊΟ2, such as Ti(OEt) ₄ , Ti(OnPr) ₄ , Ti(OiPr) ₄ , Ti(OnBu) and Ti(OiBu) ₄ , are available as it is, or used by diluting to an appropriate concentration with the above-mentioned solvent. Aluminium alkoxides, which are the precursors of AI2O3, such as AI(OEt) ₃ , AI(OnPr) ₃ , AI(OiPr) ₃ , AI(OnBu) ₃ , and AI(OiBu) ₃ , are preferably used by diluting to an appropriate concentration with the above-mentioned solvent.

The concentration of the metal alkoxide contained in the metal alkoxide solution can suitably be set according to the saturated concentration of the metal alkoxide in the solvent. The amount of the metal alkoxide to the reactor powder can suitably be set according to the final content of the metal oxide which is dispersed in the polyolefin. In Step 1 according to the present invention, the metal alkoxide can be impregnated to the polyolefin powder at the corresponding content of the metal oxide to the polyolefin of 60 wt% at maximum, generally 50 wt% or less. In the viewpoint of the functionalization through the addition of the metal oxide, the amount of the metal alkoxide used in Step 1 is set so that the content of the metal oxide to a polyolefin finally becomes 1 wt% or more, preferably 5 wt% or more. When the amount of the metal oxide used in Step 1 is set so that the content of the metal oxide to the polyolefin finally becomes 15 wt% or more, especially 20 wt% or more, unique properties of the metal oxide can be attached to the polyolefin, and remarkable functionalization of the polyolefin is realized. There is no restriction for the method for mixing the reactor powder and the metal alkoxide solution as long as the reactor powder and the metal alkoxide solution are uniformly mixed with each other. Various mixers are available as a mixing apparatus. Preferably, the mixing is performed at a temperature lower than the softening point of the polyolefin. In Step 1 , it is preferable to add an anti-oxidant in order to prevent the thermooxidative degradation of the polyolefin in Step 4. As such the anti-oxidant, any of anti-oxidants for polyolefin publicly known is available. For instance, phenolic antioxidants are available such as

1 , 3, 5-tris (3, 5-di-t-butyl-4-hydroxybenzyl) - 1 , 3, 5-triazine -2, 4, 6 (1 H, 3H, 5H) - trione,

4, 4', 4"-(1 -methyl propanil-3-ylidene) tris (6-t-butyl-m-cresol), 6, 6'- di-butyl-4, 4'-butylidenedi-m-cresol, octadecyl 3-(3, 5-di-t-butyl-4-hydroxyphenyl) propionate, pentaerythritoltetrakis [3-(3, 5-di-t-butyl-4-hydroxyphenyl) propionate],

3, 9-bis {2-[3-(3-t-butyl-4-hydroxy- 5-methylphenyl) propionyloxy]-1 , 1-dimethylethyl}-2, 4, 8, 10- tetraoxaspiro [5.5] undecane, 1 , 3, 5-t tris(3, 5-di-t-butyl-4-hydroxyphenyl methyl)-2, 4, 6-trimethylbenzene, etc.

In Step 1 , a promoter of the sol-gel reaction can be used together with the metal alkoxide solution as needed. As such the promoter, basic compounds such as bis (1 , 2, 2, 6, 6-pentamethyl 4-piperidyl) sebacate and tetrakis (1 , 2, 2, 6, 6-pentamethyl 4-piperidyl), butane 1 , 2, 3, 4-tetra-carboxylate, tetrakis (2, 2, 6, 6-tetramethyl 4-piperidyl), butane 1 , 2, and 3, 4-tetracarboxylate, bis (2, 2, 6, 6-tetramethyl-4-piperidyl) sebacate, bis (1-undecanoxies-2, 2, 6, 6-tetramethylpiperidine-4-yl) carboxylate, 1 , 2, 2, 6, 6-pentamethyl-4- piperidylmethacrylate, 2, 2, 6, 6-tetramethyl-4-piperidylmethacrylate, and acidic compounds such as citric acid, maleic anhydride modified polyolefin, can be used. Among these, bis (1 , 2, 2, 6, 6-pentamethyl 4-piperidyl) sebacate and tetrakis (2, 2, 6, 6-tetramethyl-4-piperidyl) butane-1 , 2, and 3, -tetra-carboxylate, which have a high compatibility with the polyolefin as well as a light stabilizing ability, are preferable.

(Step 2) Step 2 is a step of removing the solvent by drying the polyolefin powder obtained in Step 1. There is no restriction for methods of the drying. For instance, a vacuum drying, a lyophilization, and a flash drying are available. As a result of removing the solvent, the powder, which is filled by the metal alkoxide, is obtained. (Step 3) Step 3 is a step of heating the polyolefin powder obtained in Step 2 under a water vapor atmosphere. There is no restriction of temperature and time of the heating. The cooking time of 20 hours or longer at 50 °C, and the cooking time of 6 hours or longer at 70 °C are typical conditions for the heating.

(Step 4) Step 4 is a step of melting and kneading the polyolefin powder obtained in Step 3. The sol-gel reaction of the metal alkoxide proceeds in Step 4, and the metal alkoxide impregnated to the polyolefin is converted into the metal oxide. After the sol-gel reaction is completed in Step 4, the high-performance nanocomposite according to the present invention, in which the metal oxide is dispersed to the polyolefin in the form of the independent fine particles, is obtained. The temperature of the melting and kneading is equal to or above the melting point of the polyolefin, while below the temperature to promote the thermal degradation of the polyolefin. The temperature 150-250 °C is common when using polyethylene. The temperature 180-280 °C is common when using polypropylene. There is no restriction of an apparatus used for the melting and kneading. Various mixers and extruders are available.

In Step 4, the high-performance nanocomposite according to the present invention can be granulated or pelletized, following the melting and kneading. Various additives or other resin ingredients can also be added at the time of the melting and kneading. The high-performance nanocomposite according to the present invention is processible into various molding products by methods, such as an extrusion and an injection molding, following Step 4. The high-performance nanocomposite according to the present invention which is pelletized in Step 4 can be also used as a masterbatch.

(Dispersion) In the high-performance nanocomposite according to the present invention, it can be confirmed that the metal oxide uniformly disperses in the polyolefin in the form of so-called nano-sized fine particles by the transmission electron microscopy (TEM) image of the high- performance nanocomposite.

(High performance) In the method for producing the high-performance nanocomposite according to the present invention, approximately 60 wt% at maximum, generally 50 wt% or less of the metal oxide to the polyolefin can be compounded without the addition of dispersants at the nano level as described above. Therefore, in the high-performance nanocomposite obtained by the method according to the present invention, the mechanical properties of the polyolefin is maintained or even improved, and properties of the metal oxide are remarkably attached to the polyolefin. As a result, a new property which could not be expected in a conventional polyolefin composite containing the metal oxide can be realized. For instance, when more than 20 wt% of AI2O3 is dispersed to the polypropylene based on the present invention, the thermal conductivity of the polypropylene can be improved greatly while maintaining the mechanical properties.

EXAMPLES

(Materials) The following materials were used in the following Examples and Comparative Examples.

- Polypropylene Powder

A reactor granule of isotactic polypropylene which was produced by propylene polymerization in the presence of a MgC -based Ziegler-Natta catalyst was used. It possessed the weight average molecular weight (M _w ) of 2.6 x 10 ⁵ , the molecular weight distribution (MJM _n ) of 5.69, the meso pentad (mmmm) of 98 mol%, the average particle diameter (D50) of 480 μηι, and the pore volume of 40-50%.

- Metal Alkoxide (Precursor) Ti(OiPr)4 provided by Sigma-Aldrich was used as the precursor of ΤΊΟ2. AI(OiPr) ₃ and AI(OEt)3 provided by Sigma-Aldrich were used as the precursors of AI2O3.

- Antioxidant

Antioxidant commercial product supplied by ADEKA Corporation named AO-50 (n-Octdecyl-3-(3', 5'- di-t-butyl-4'-hydroxyphenyl)-propionate), and an amine promoter, and LA-77 (Bis (1 , 2, 2, 6, and 6- pentamethyl-4-piperidyl) sebacate) were used.

(Example 1 : Example for producing the high-performance nanocomposite containing 5 wt% of ΤΊΟ2) The high-performance composite according to the present invention was produced through the following Steps 1 to 4. (Step 1) Ti(OiPr) ₄ was impregnated to the polypropylene powder by mixing 30 g of the polypropylene powder and 60 ml of a heptane solution of Ti(OiPr) ₄ , whose concentration was adjusted so as to meet 5 wt% of T1O2 produced in the polypropylene, in a flask at 50 °C under nitrogen atmosphere. (Step 2) The mixture obtained in Step 1 was vacuum dried to remove the solvent. (Step 3) The polypropylene powder through Step 2 was treated in an oven at a relative humidity 100% and 80 °C for 24 hours. (Step 4) The polypropylene powder through Step 3 was melted and kneaded by a Labo Plastomill provided by Toyo Seiki for 15 minutes at 180 °C and at the rotation speed of 100 rpm. The obtained product was compression molded for 6 minutes at 230 °C and 10 MPa, and cooled down at 100 °C for 5 minutes and at 0 °C for 1 minute to form a sample film having 100 pm thickness for analytical purposes. (Example 2: Example for producing the high-performance nanocomposite containing 10 wt% of T1O2) The concentration of the heptane solution of Ti(OiPr) ₄ used in Step 1 according to Example 1 was changed so that the content of T1O2 corresponded to 10 wt% to the polypropylene. Other conditions were the same as those in Example 1 , and the high-performance composite according to the present invention was obtained.

(Example 3: Example for producing the high-performance nanocomposite containing 20 wt% of T1O2) The concentration of the heptane solution of Ti(OiPr) used in Step 1 according to Example 1 was changed so that the content of ΤΪΟ2 corresponded to 20 wt% to the polypropylene. Other conditions were the same as those in Example 1 , and the high-performance composite according to the present invention was obtained.

(Comparative Example 1 : Example for producing a conventional nanocomposite containing 10 wt% of Ti0 ₂ without treatment under the water vapor atmosphere) The nanocomposite for the reference was produced by using the same procedures and the conditions as Example 2 except for omitting Step 3.

(Infrared spectroscopy (IR)) Fig.1 shows the IR spectrum of the film product prepared in Example 2. Fig.2 shows the IR spectrum of the film product prepared in Comparative Example 1 is analyzed. The IR spectrum of neat polypropylene (PP) is also shown in Fig.1 and Fig.2. In Comparative Example 1 , although the precursor solution was impregnated to the polyolefin powder, the treatment under the water vapor atmosphere (Step 3) was omitted before the melting and kneading of Step 4. As a result, in Comparative Example 1 , only a fraction (approximately 3 wt%) of the metal alkoxide was converted into the titanium oxide, in contrast to the addition corresponding to 10 wt%. This fact proved that, in the conventional methodology, a large amount of the metal oxide was not able to be fabricated and dispersed in the polyolefin.

On the other hand, in Example 2, after applying Step 3 of heating the polypropylene powder containing the precursor under the water vapor atmosphere, the melting and kneading of Step 4 were performed. As shown in Fig. 1 , the adsorption bands derived from the metal alkoxide was not anymore detected in the product obtained by the method according to the present invention. This fact indicates that, in the method according to Example 2, the precursor was completely converted into the metal oxide and dispersed in the polyolefin.

Based on the results according to Example 2 and Comparative Example 1 , it is found that Step 3 in the method for producing the high-performance nanocomposite according to the present invention is significant to achieve the full conversion of the precursor, especially at a high content of the metal oxide.

(Conversion into Ti0 ₂ ) The high-performance composites obtained in Examples 1 , 2 and 3 were incinerated at 600 °C, and the actual content of Ti0 ₂ was evaluated as the remaining ash content. The result is shown in Table 1. Based on Table 1 , it can be confirmed that in Examples 1 , 2, and 3, most of the Ti(OiPr) ₄ precursor was changed into T1O2. This result is consistent with the IR results mentioned above.

[Table 1]

(Dispersion) Fig.3 shows a TEM image of the high-performance nanocomposite according to Example 2. Fig.4 shows a TEM image of the high-performance nanocomposite according to Example 3. As shown in Fig.3 and Fig.4, T1O2 is uniformly dispersed in the polypropylene as independent fine particles whose particle diameter is smaller than 500 nm. These high-performance nanocomposites containing T1O2 according to the present invention have a potential application as substrates for buildings, electronics, and packaging in which UV absorption is requested.

(Example 4: Example for producing the high-performance nanocomposite containing 5 wt% of AI2O3) The high-performance nanocomposite according to the present invention was produced through the following Steps 1 to 4.

(Step 1) AI(OiPr) ₃ was impregnated to the polypropylene powder by mixing 30 g of the polypropylene powder and 80 ml of a toluene solution of AI(OiPr)3, whose concentration was adjusted so as to meet 5 wt% of Al ₂ 0 ₃ produced in the polypropylene, in a flask at 50 °C under nitrogen atmosphere. (Step 2) The mixture obtained in Step 1 was vacuum dried to remove the solvent. (Step 3) The polypropylene powder through Step 2 was treated in an oven at a relative humidity 100% and 80 °C for 24 hours. (Step 4) The polypropylene powder through Step 3 was melted and kneaded by a Labo Plastomill provided by Toyo Seiki for 15 minutes at 180 °C and at the rotation speed of 100 rpm. The obtained product was compression molded for 6 minutes at 230 °C and 10 MPa, and cooled down at 100 °C for 5 minutes and at 0 °C for 1 minute to form a sample film having 100 μητι thickness for analytical purposes.

(Example 5: Example for producing the high-performance nanocomposite containing 10 wt% of AI2O3) The concentration of the heptane solution of AI(OiPr) ₃ used in Step 1 according to Example 4 was changed so that the content of Al ₂ 0 ₃ corresponded to 10 wt% to the polypropylene. Other conditions were the same as those in Example 4, and the high-performance composite according to the present invention was obtained.

(Example 6: Example for producing the high-performance nanocomposite containing 20 wt% of AI2O3) The concentration of the heptane solution of AI(OiPr) ₃ used in Step 1 according to Example 4 was changed so that the content of AI2O3 corresponded to 20 wt% to the polypropylene. Other conditions were the same as those in Example 4, and the high-performance composite according to the present invention was obtained.

(Example 7: Example for producing the high-performance nanocomposite containing 30 wt% of AI2O3) The concentration of the heptane solution of AI(OiPr) ₃ used in Step 1 according to Example 4 was changed so that the content of A 0 ₃ corresponded to 30wt% to the polypropylene. Other conditions were the same as those in Example 4, and the high-performance composite according to the present invention was obtained.

(Comparative Example 2-1 : Example for producing a conventional nanocomposite by blending 5 wt% of pre-formed AI2O3 nanoparticles) The polypropylene powder was melted and kneaded with a commercial fine grade of AI2O3 at its content of 5wt%, according to the procedures and conditions of Step 4 in Example 4.

(Comparative Example 2-2: Example for producing a conventional nanocomposite containing 5 wt% of AI2O3 without treatment under the water vapor atmosphere) The nanocomposite for the reference was produced by using the same procedures and the conditions as Example 4 except for omitting Step 3.

(IR) Fig. 5 shows the IR spectra of the film samples according to Example 4 and Comparative Example 2-1 and that of neat polypropylene (PP). In Fig. 5, it is found that a peak relevant to the AI-0 bond of aluminum oxide is detected at 560cm ^"1 . In Example 4, the peaks relevant to the original metal alkoxide are absent. This fact corresponds to the full conversion of the precursor into the corresponding metal oxide. Furthermore, all the peaks relevant to the polypropylene are maintained in Example 4, suggesting no degradation in the molecular structure of the polypropylene along with the compounding.

(Conversion into AI2O3) The high-performance composites obtained in Examples 4, 5, 6 and 7 were incinerated at 600 °C, and the actual content of AI2O3 was evaluated as the remaining ash content. The result is shown in Table 2. Based on Table 2, it can be confirmed that in Examples 4, 5, 6 and 7, most of the AI(OiPr) ₃ precursor was converted into AI2O3.

[Table 2]

(Dispersion) Figs. 6, 7, 8, and 9 shows a TEM image of the high-performance nanocomposite according to Examples 4, 5, 6, and 7, respectively, As shown in Figs. 6 to 9, AI2O3 is uniformly dispersed in the polypropylene as independent fine particles whose particle diameter is smaller than 500 nm in a wide range of the AI ₂ 0 ₃ content.

Fig. 10 shows a TEM image of the conventional nanocomposite according to Comparative Example 2-1. Fig. 11 shows a TEM image of the conventional nanocomposite according to Comparative Example 2-2. Based on Fig.10 and Fig.11 , agglomerations of AI2O3 are identified when pre-formed nanoparticles are melt mixed or when the pretreatment under water vapor atmosphere is omitted.

As mentioned above, although the content of Al ₂ 0 ₃ in Fig. 6 (Example 4), Fig. 9 (Comparative Example 2-1) and Fig. 10 (Comparative Example 2-2) is equal to 5 wt%, AI2O3, which is properly dispersed in the polypropylene in the form of independent nanoparticles, is observed only in Fig. 6 (Example 4) corresponding to the present invention.

(Example 8: Example for producing the high-performance nanocomposite containing 5 wt% of AI2O3) The high-performance composite according to the present invention was produced based on the same procedures and conditions of Example 4 except for the usage of AI(OEt)3 instead of AI(OiPr) ₃ in Step 1.

(Example 9: Example for producing the high-performance nanocomposite containing 10 wt% of AI2O3) The concentration of the heptane solution of AI(OEt)3 used in Step 1 according to Example 8 was changed so that the content of Al ₂ 0 ₃ corresponded to 10 wt% to the polypropylene. Other conditions were the same as those in Example 8, and the high-performance composite according to the present invention was obtained.

(Example 10: Example for producing the high-performance nanocomposite containing 20 wt% of AI2O3) The concentration of the heptane solution of AI(OEt)3 used in Step 1 according to Example 8 was changed so that the content of AI2O3 corresponded to 20 wt% to the polypropylene. Other conditions were the same as those in Example 8, and the high-performance composite according to the present invention was obtained.

(Dispersion) Fig. 12 shows a comparison of TEM images of the high-performance nanocomposites according to Examples 4 to 6 (precursor: Al(OiPr)s) and Examples 8 to 10 (precursor: AI(OEt)3). Based on Fig. 12, it is found that the difference of precursors hardly influences to the final dispersion of AI2O3.

(Thermal Conductivity) Thermal conductivities of the high-performance nanocomposites obtained in Examples 4 to 7 were calculated by the following equations. λ = a Cp p

(a denotes thermal diffusivity, λ denotes thermal conductivity, Cp denotes specific Heat capacity, and p denotes density.) In the formula, or denotes thermal diffusivity, λ denotes thermal conductivity, Cp denotes specific heat capacity, and p denotes density. The thermal diffusivity (a) was measured using "ai- Phase Mobile 1 u/2" provided by Hitachi high-tech science. The specific heat capacity (Cp) was determined by differential scanning calorimeter (DSC, Mettler Toledo DSC-822), where the temperature was swept in the range of 0-50 °C at 20 °C/min under nitrogen flow of 200 ml/min. The results are summarized in Table 3 together with the result for neat polypropylene (denoted as Comparative Example 3).

[Table 3]

Based on Table 3, it is found that, in the method for producing the high-performance nanocomposite according to the present invention, the thermal conductivity of the polypropylene was improved in proportion to the content of AI2O3 disposed in the polypropylene. Moreover, in the present invention, it is possible to easily produce the polypropylene nanocomposite having more than 0.40 Wm ¹ K ^"1 of the thermal conductivity calculated by the above formula. (Mechanical Strength)

Table 4 shows the tensile strength and Young's modulus of the high-performance nanocomposite obtained in Examples 4 to 6, together with the results for neat polypropylene (Comparative example 3). These tensile properties were acquired using a tensile tester (Abecks Inc., Abe Dat-100) at a crosshead speed of 1.0 mm/min. Sample films were die-cut into dumbbell-shaped specimens with the overall length of 23 mm and the gage length of 5 mm. Tensile properties such as tensile strength and Young's modulus were determined as an average value of 10 measurements. [Table 4]

In the present invention, since AI2O3 disperses in the polypropylene as independent nano- sized particles, deterioration of the mechanical properties of the polypropylene, which is mostly the case when pre-formed nanoparticles are added at a high content, does not occur. As shown in Table 4, surprisingly according to the present invention, even if the theoretical content of AI2O3 was increased up to 20 wt%, the tensile strength and Young's modulus of the nanocomposite were even better than those of the comparative example 3(neat polypropylene). As mentioned above, according to the method of the present invention for producing the high-performance nanocomposite, a new polypropylene-based material, which contains dispersed AI2O3 nanoparticles at a high content, is obtained to significantly improve both the mechanical properties and the thermal conductivity of the polypropylene.

INDUSTRIAL AVAILABILITY

According to the present invention, a nano-sized metal oxide filler can properly be dispersed up to a high content in the polyolefin without the addition of any dispersants. The present invention is believed as a breakthrough for producing a highly value-added polyolefin-based material at low cost. The high-performance nanocomposite obtained by the present invention has outstanding properties, which was not able to be expected to the conventional polyolefin-based nanocomposites in the past, although the raw materials are the same cheap resin ingredients and additives as conventional ones. The high-performance nanocomposite according to the present invention is expected as novel materials which can substitute for conventional polyolefin-based materials and masterbatches, engineering plastics, and inorganic materials, which are used in the fields of automobiles, construction, electronics, machineries, and resin additives.