WO2007086623A1

WO2007086623A1 - Biodegradable nanocomposite resin composition

Info

Publication number: WO2007086623A1
Application number: PCT/KR2006/000440
Authority: WO
Inventors: Jae Sik Lee; Yeon Suk Jang
Original assignee: Sk Networks Co., Ltd.
Priority date: 2006-01-27
Filing date: 2006-02-07
Publication date: 2007-08-02
Also published as: KR100655914B1

Abstract

The present invention relates to a biodegradable nanocomposite resin composition. More particularly, the present invention relates to a novel biodegradable nanocomposite resin composition having mechanical, physical and thermal properties comparable to those of general plastics, while maintaining biodegradability, by applying an inorganic material prepared by dispersing powder of specifically selected layered inorganic silicate in oil to a biodegradable resin.

Description

BIODEGRADABLE NANOCOMPOSITE RESIN COMPOSITION

Technical Field

The present invention relates to a biodegradable nanocomposite resin

composition, more particularly to a novel biodegradable nanocomposite resin

composition having mechanical, physical and thermal properties comparable to

those of general plastics, while maintaining biodegradability, by applying an

inorganic material prepared by dispersing powder of specifically selected layered

inorganic silicate in oil to a biodegradable resin.

Background Art

Nano-crystalline materials refer to the materials having a crystal size of 100

nm or smaller which are prepared by various physical, chemical and mechanical

processes. Since Professor Gleiter of Germany prepared a nano-crystalline

material by gas-condensation/ vacuum compaction, intensive researches have been

performed on these materials.

Because the nano-crystalline materials show unique physical properties not

offered by micro-sized materials as the crystal size decreases to the nanometer scale,

they can be utilized in a variety of fields. Composite materials refer to a combination of two or more materials that

offers physically or chemically better capabilities. Nanocomposite materials are

new materials developed by controlling atoms or molecules in the nanometer scale.

Biodegradable resins refer to the resins that can be degraded by

microorganisms living in the earth. They are advantageous in that they are

degraded without sunlight and are combusted perfectly without producing toxic

gases. Because of superior physical properties, processing property and

bioavailability, biodegradable resins are widely used for controlled drug release

system, artificial bone, etc. in the medical field.

Despite superior biodegradability, most of currently available biodegradable

resins are disposable products and are thus uneconomical. Also, products

produced from the biodegradable resins do not have sufficient mechanical

properties comparable to those of general plastics.

A method of using a variety of inorganic fillers has been proposed to

improve mechanical property of biodegradable resins.

However, when such commonly used nonmetals as talc are used in the form

of powder, such mechanical properties as impact strength, flexural strength, etc.

may worsen or water absorptivity may increase, so that degradation by

microorganisms may be accelerated, depending on the particular biodegradable

resin, making it difficult for them to be used as general plastics. Disclosure of the Invention

The present inventors worked to solve the afore-mentioned problems.

In doing so, they found that a nanocomposite resin composition obtained by mixing

an inorganic material prepared by dispersing finely ground powder of a specially

selected layered inorganic silicate, which does not negatively affect the physical

properties of a biodegradable resin, in an oil, which is selected based on the

properties of the layered inorganic silicate powder and the biodegradable resin, with

a biodegradable resin, considering the temperature and stirring condition, has

improved mechanical, physical and thermal properties while maintaining

biodegradability.

Accordingly, it is an object of the present invention to provide a novel

biodegradable nanocomposite resin composition that has improved mechanical,

physical and thermal properties as well as biodegradability and can be used in a

variety of industrial fields, replacing general plastics.

Best Mode for Carrying Out the Invention

The present invention is characterized by a biodegradable nanocomposite

resin composition comprising 5-30 wt% of an inorganic material, wherein powder of

layered inorganic silicate selected from muscovite, phlogopite or a mixture thereof is

dispersed in oil, and 70-95 wt% of a biodegradable resin.

Hereunder is given a more detailed description of the present invention. The present invention relates to a novel biodegradable nanocomposite resin

composition having mechanical, physical and thermal properties comparable to

those of general plastics, while maintaining biodegradability, by applying an

inorganic silicate in oil to a biodegradable resin.

Hereinafter, each constituent of the biodegradable nanocomposite resin

composition the present invention is described in detail.

As the first constituent, the biodegradable nanocomposite resin composition

of the present invention comprises an inorganic material in which powder of

specially selected layered inorganic silicate is dispersed in oil.

For the powder of layered inorganic silicate, one which has an average

particle size in the range of 0.01 to 5 μm is used. If the particle size is smaller

than the above range, fracture toughness may be reduced. In contrast, if it is

larger than the above range, adhesivity of the inorganic material with the

biodegradable resin may decrease.

A variety of layered inorganic silicates exist in nature, but in the present

invention, muscovite, phlogopite or a mixture thereof is used considering various

physical properties, compatibility with the biodegradable resin and chemical

properties of the biodegradable resin.

Muscovite is a hexagonal mineral belonging to the monoclinic group. It

has a perfect cleavage at the bottom and the cleaved piece is given with superior elasticity. The mineral has structural stability by nature. Muscovite has a

hardness of 2-2.5 and a specific gravity of 2.7-3. It forms fine fibrous crystals.

Muscovite has superior fire resistance, insulating property and plasticity.

With large dry strength and green strength, it has good mechanical strength.

Since it is thin and strong, it has superior flexibility and elasticity. When melted,

muscovite in the glassy phase has a large viscosity and a high softening temperature

under load. Therefore, when added to a biodegradable resin with poor thermal

property, it may improve the thermal property of the biodegradable resin.

Muscovite is resistant to almost all acids, excluding fluoric acid and strong

sulfuric acid and does not react with alkalis, common organic solvents or oils.

When processed into powder, the surface becomes rough and without luster and it

has a high aspect ratio since it is cleaved to form very thin layers. Thus, when

applied to a biodegradable resin having weak mechanical property along the

longitudinal direction, particularly polylactic acid, it may make up for the weak

mechanical property.

Since muscovite is weakly acidic with pH 5-7, it reduces water absorptivity

of a biodegradable resin, particularly polylactic acid, compared with conventional

alkaline fillers with pH 8-9.5, such as talc, and thus, it may reduce biodegradability.

For example, polylactic acid is a biodegradable resin having relatively good

thermal property and mechanical property. However, when conventional

alkaline nonmetal minerals such as talc, calcium carbonate (CaCOa), limestone and titanium dioxide (Tiθ2) are added as a filler or a modifier, water absorptivity of

polylactic acid increases abruptly, thereby accelerating biodegradation of polylactic

acid, making it inappropriate for a long-term use.

Although it depends on the molecular weight and crystallinity of polylactic

acid, the problem of accelerated biodegradation caused by addition of an alkaline

filler or modifier cannot be completely solved.

As described above, muscovite does not chemically react with acids, alkalis,

common organic solvents, oils, etc., has superior plasticity, mechanical property and

structural stability and is an ideal insulator with good fire resistance. Especially,

muscovite, due to its weak acidity, can solve the problem of accelerated

biodegradation caused by abrupt increase in water absorptivity, when used in

biodegradable resins.

Because muscovite can prevent the biodegradable resin from absorbing

water too fast and being degraded by microorganisims too quickly, it can offer water

repellency, antibacterial property and sterilizing property to a biodegradable resin.

Thus, muscovite, phlogopite or a mixture thereof is preferred to conventional

alkaline nonmetal minerals to be used along with biodegradable resins.

Phlogopite is a monoclinic mineral with a hardness of 2.5-3 and a specific

gravity of 2.78-2.85. It contains a lot of fluorine and little iron. Typically, it

forms a plate crystal, but sometimes a columnar crystal is obtained. Phlogopite

has a perfect cleavage at the bottom and has strong elasticity and fire resistance. Thus, it is frequently used as fire-resisting material and electrical insulator. For

the similar reason as mentioned in the above muscovite, it is preferable to be used in

a biodegradable resin.

Whereas muscovite is dehydrated at 500 ⁰C or above to experience structure

destruction, phlogopite is stable even at about 1000 ⁰C. Therefore, it can further

make up for the thermal property of biodegradable resins.

The present invention is also characterized in that the layered inorganic

silicate, which is selected from muscovite and phlogopite, is finely ground and

dispersed in oil.

When the layered inorganic silicate is added to a biodegradable resin after

being ground and made into powder, the biodegradable resin becomes more viscous

and the melt index decreases. Then, higher temperature and pressure are

required to process the mixture of the biodegradable resin and the layered inorganic

silicate by injection, extrusion, etc. Increased temperature and pressure may result

in increase of mechanical load in injector, extruder, etc. or pyrolysis of the

biodegradable resin during injection or extrusion.

In addition, because the powder of layered inorganic silicate, an inorganic

material, is not highly compatible with the biodegradable resin, an organic material,

it is difficult to attain uniform dispersibility and uniform physical properties. Accordingly, the present invention offers the followings to enable uniform

dispersion of the powder of layered inorganic silicate in a biodegradable resin and

solve the problem of increased fluidity.

That is, the present invention is characterized in that an inorganic material in

which the powder of layered inorganic silicate is dispersed in oil is added to a

biodegradable resin in order to solve the above-mentioned problems, improve

compatibility of the powder of layered inorganic silicate with the biodegradable

resin and make up for mechanical and thermal properties, while maintaining

biodegradability.

In the present invention, the selected layered inorganic silicate is ground by

various methods to an average particle size of 0.01-5 μm, considering miscibility

with oil, stability and the modification of physical properties of the biodegradable

resin, and is dispersed in oil.

For the oil, one having 12-20 carbon atoms, preferably natural oil, more

preferably plant oil, is used. For example, at least one oil selected from olive oil,

palm oil, coconut oil, etc., may be used.

Selection of the oil is made considering compatibility with the powder of the

selected layered inorganic silicate, stability of the prepared inorganic material,

compatibility with the biodegradable resin, various properties of the biodegradable

nanocomposite resin to be prepared, including biodegradability, commercial

applicability and economicity. Besides, it may solve the environmental pollution problem related with the use of synthetic processing oils in the preparation

of conventional nanocomposite resins or composite resins.

The inorganic material comprises 90-93 wt% of the powder of layered

inorganic silicate and 7-10 wt% of the oil having 12-20 carbon atoms.

The inorganic material may be prepared as follows.

7-10 wt% of oil and 90-93 wt% of powder of layered inorganic silicate are

mixed by stirring at 1,000-2,000 rpm. If the content of oil is smaller than the above

range, increase in the relative content of the powder of layered inorganic silicate

makes stirring difficult and improvement of the surface property of the powder of

layered inorganic silicate by the nonpolar oil decreases. Also, reduced

adsorption between the oil and the layered inorganic silicate lowers pore swelling in

the layered inorganic silicate. In contrast, if the oil content is larger than the above

range, binding force of the biodegradable resin with the powder of layered inorganic

silicate is reduced, interfering with improvement in mechanical and physical

properties.

As the stirring continues, temperature becomes increased because of the heat

generated by the friction between the oil and the powder of layered inorganic

silicate. The stirring is continued until the temperature reaches about 90 ⁰C,

preferably 80-100 ⁰C. In general, it takes about 10-30 minutes to reach the

above-mentioned temperature. In addition to improvement of dispersibility of the powder of layered

inorganic silicate in the biodegradable resin, use of the oil facilitates injection of the

powder of layered inorganic silicate into the biodegradable resin, as pores swell and

interlayer spacing increases with the injection of oil into the fine pores. Also,

increased reaction heat further increases the interlayer spacing due to thermal

expansion of the oil in the pores or between the layers.

The inorganic material being comprised in the biodegradable nanocomposite

resin composition of the present invention may be prepared by the common

dispersion method.

As the second constituent, the biodegradable nanocomposite resin

composition of the present invention comprises a biodegradable resin.

For the biodegradable resin, at lest one selected from polylactic acid (PLA),

polyglycolic acid (PGA), polycaprolactone (PCL), aliphatic polyester resin,

polyhydroxybutyric acid (PHB), D-3-hydroxybutyric acid, etc., may be used. In

particular, polylactic acid is preferred to be used.

Of the above-mentioned biodegradable resins, polylactic acid has a

coefficient of tensile elasticity comparable to that of polyethyleneterephtalate (PET),

which is one of general use plastic resins, and superior bending rigidity.

Polylactic acid melts at 171 °C, higher than other biodegradable resins, but it is

inappropriate for use in injection molding products because has low impact strength and is oxidized quickly by absorbing moisture in the air. These problems can be

solved by using the nanocomposite material presented by the present invention.

Aliphatic polyesterr, another biodegradable resin, shows low crystallinity

because of its structural characteristic and softens in the temperature range of

60-70 ⁰C. Thus, it is generally used as film products rather than injection

molded products. This problem can also be solved by using the nanocomposite

material of the present invention.

The biodegradable nanocomposite resin of the present invention comprises

5-30 wt % of an inorganic material in which the powder of layered inorganic silicate

is dispersed in oil and 70-95 wt% of a biodegradable resin. If the content of the

inorganic material is smaller than the above range, mechanical, physical and thermal

properties of the biodegradable resin cannot be sufficiently improved. In

contrast, if the content of the inorganic material is larger than the above range,

compatibility of the inorganic material with the biodegradable resin may decrease.

In addition to the afore-mentioned constituents, common additives may be

added in the range not negatively affecting the physical properties of the

biodegradable nanocomposite resin of the present invention. For example, such

additives as talc, calcium carbonate, titanium dioxide, etc. may be added in 0.1-10

parts by weight per 100 parts by weight of the combined inorganic material and the

biodegradable resin. It is apparent that selection of the additive does not limit

the scope of the present invention. After dispersing the powder of layered inorganic silicate in oil, the inorganic

material of the present invention may be used as dried under the condition not

negatively affecting the constituents or as prepared into pellet or film comprising the

biodegradable resin comprised in the biodegradable nanocomposite resin. If it

is prepared into pellet or film in advance, the inorganic material is better to be used

in the industrial field because stability, storage property, etc. are improved.

That is, when a predetermined amount of a biodegradable resin is added to

the powder of layered inorganic silicate to form a pellet or a film, reaction heat

generated during the dispersion of the powder of layered inorganic silicate and the

oil enables the oil adsorbed in the pores of the powder of layered inorganic silicate to

swell, making the biodegradable resin be introduced into the expanded interlayer

space and pores. The biodegradable resin introduced into the interlayer space

or pores of the powder of layered inorganic silicate directly bond with the powder of

layered inorganic silicate, thereby enhancing fracture toughness of the

nanocomposite material, which has been the problem of conventional

nanocomposite materials.

In the preparation of the pellet or film, improvement of physical properties

may be attained if drying is performed by natural cooling, rather than water cooling,

because crystallization of the biodegradable resin proceeds rapidly.

The amount of the biodegradable resin may be determined within the range

required for the preparation of the biodegradable nanocomposite resin. The biodegradable nanocomposite resin composition of the present invention

can be prepared into a variety of forms for use. Specifically, it can be prepared

into dried powder, film, pellet, etc.

Hereinafter, the method for preparing the biodegradable nanocomposite

resin of the present invention is described in detail.

In the first step, 90-93 wt% of powder of layered inorganic silicate

comprising muscovite, phlogopite or a mixture thereof, which has been ground to an

average particle size of 0.01-5 μm is added to 7-10 wt% of oil having 12-20 carbon

atoms and the mixture is stirred at 1,000-2,000 rpm to prepare an inorganic material.

In the first step, the stirring is performed until the temperature of the

reaction mixture reaches about 90 ⁰C, preferably 80-100 ⁰C. The reaction heat is

generated bv the friction of the powder of layered inorganic silicate with the oil.

In general, it takes 10-30 minutes to reach the temperature range, although it is not

necessarily so. The dispersion of the powder of layered inorganic silicate in oil

improves dispersibility with the biodegradable resin and enables penetration of the

oil into the pores in between the layers of the powder of layered inorganic silicate,

thereby further expanding the pores or interlayer spacing.

If the stirring rate is lower than the above range, the oil is not easily

dispersed and a long stirring time is required. In contrast, if the stirring rate is

higher than the above range, the oil is not adsorbed well in the pores or interlayer

spacing of the powder of layered inorganic silicate. The inorganic material may be used in the form of dried powder or as

prepared into pellet or film by adding a biodegradable resin, if required. The

drying condition is controlled so that the constituents of the inorganic material may

not be deteriorated. The biodegradable resin used for the preparation may be

that used for preparation of the biodegradable nanocomposite resin of the present

invention. Preferably, 8-12 parts by weight of a biodegradable resin may be

added per J OO parts by weight of the muscovite, phlogopite or a mixture thereof

used in the preparation.

The biodegradable resin may be added in the first step mentioned above

after the temperature of the reaction mixture reaches 80-100 ⁰C.

In the second step, 5-30 wt% of the inorganic material prepared in the first

step and 70-95 wt% of a biodegradable resin is stirred at 1,000-2,000 rpm until the

temperature of the reaction mixture reaches 180-200 ⁰C. As the temperature of the

reaction mixture increases, the oil comprised in the inorganic material expands and,

consequently, the pores or interlay er spacing of the layered inorganic silicate

increases further, enabling introduction of the biodegradable resin into the pores or

interlayer spacing.

If the temperature of the reaction mixture is lower than the above range, the

biodegradable resin is not introduced well into the pores or interlayer spacing of the

layered inorganic silicate. In contrast, if the temperature of the reaction mixture

is higher than the above range, the oil and the biodegradable resin may be oxidized or decomposed by the heat. If the stirring rate is below the above-mentioned range,

the oil may flow out of the pores or interlayer spacing of the layered inorganic

silicate, interfering with the introduction of the biodegradable resin.

In the third step, the reaction mixture is prepared into pellet and extruded.

If necessary, commonly used additives may be added in the second step

within the range not negatively affecting the physical properties of the

biodegradable nanocomposite resin of the present invention. For example, talc,

calcium carbonate, limestone, carbon, etc. may be added in 0.01-10 parts by weight

per 100 parts by weight of the combined inorganic material and the biodegradable

resm.

Thus prepared biodegradable nanocomposite resin of the present invention

has mechanical, physical and thermal properties comparable to those of general

plastics, while maintaining biodegradability.

Further, since the injection or extrusion processing property of the

biodegradable nanocomposite resin is improved, it is expected to be used in a

variety of industrial fields, replacing general plastics.

Brief Description of the Drawing

FlG. 1 is a flow diagram illustrating the method for preparing a

biodegradable nanocomposite resin in accordance with the present invention. Examples

Hereinafter, the present invention is described in further detail through

examples. However, the following examples are only for the understanding of

the present invention and they should not be construed as limiting the scope of the

present invention.

Example 1: Preparation of an inorganic material

90 g of muscovite powder ground to an average particle size of 0.1 μm was

mixed with 10 g of palm oil. The mixture was dispersed by stirring at about

1,500 rpm for 25 minutes. Temperature (^r-Sr) of the reaction mixture was about

90 ⁰C and the obtained inorganic material had an average particle size of about 0.12

μm.

Example 2: Preparation of an inorganic material in the form of pellet

90 g of muscovite powder ground to an average particle size 0.1 μm was

mixed with 10 g of palm oil. The mixture was dispersed by stirring at about

1,500 rpm for 25 minutes. Temperature of the reaction mixture was about 90 ⁰C.

10 g of polylactic acid having a glass transition temperature of 57 ⁰C was added and

the mixture was stirred at about 1,500 rpm until the temperature of the mixture

reached about 190 ⁰C. Then, the mixture was extruded at about 180 ⁰C and 30 kg/ cm² to obtain an inorganic material in the form of pellet having an average

particle size of 4 mm.

Example 3: Preparation of biodegradable nanocomposite resin (polylactic acid)

30 g of the inorganic material prepared in Example 1 was mixed with 70 g of

polylactic acid and the mixture was stirred at about 1,000 rpm until the temperature

of the mixture reached about 90 ⁰C. The mixture was further stirred until the

temperature reached about 190 ⁰C and extruded at about 190 ⁰C and 70 kg/ cm² to

obtain a biodegradable nanocomposite resin in the form of pellet having an average

particle size of 4 mm.

Example 4: Preparation of biodegradable nanocomposite resin (polylactic acid)

30 g of the inorganic material in the form of pellet prepared in Example 2

was mixed with 70 g of polylactic acid and the mixture was stirred at about 1,000

rpm until the temperature of the mixture reached about 90 ⁰C. The mixture was

further stirred until the temperature reached about 190 ⁰C and extruded at about

190 ⁰C and 65 kg/ cm² to obtain a biodegradable nanocomposite resin in the form of

pellet having an average particle size of 4 mm.

Comparative Example 1 The same polylactic acid used in Example 3 was used to compare physical

properties.

Comparative Example 2

A composite resin was prepared by stirring 30 g of muscovite powder

ground to an average particle size of 0.1 μm and 70 g of the polylactic acid of

Comparative Example 1 at 1,000 rpm.

Experimental Example: Physical property measurement

Samples were prepared from the biodegradable nanocomposite resins of

Examples 3 and 4 and the composite resins of Comparative Examples 1 and 2.

Physical properties were measured as follows. The result is given in Table 1

below.

1. Specific gravity: Measured in accordance with ASTM D 792.

2. Impact strength: Measured in accordance with ASTM D 256.

3. Tensile strength: Measured in accordance with ASTM D 633.

4. Flexural strength: Measured in accordance with ASTM D 790.

5. Water absorptivity: Measured in accordance with ASTM D 570.

6. Chemical resistance: Measured in accordance with ASTM D 543.

7. Heat deflection temperature: Measured in accordance with ASTM D 648.

As seen in Table 1, the biodegradable nanocomposite resins of the present

invention show 14-24 times better impact strength than conventional biodegradable

resin. I hey also show 3-4 % reduced water absorptivity, and thus are expected

to be used in the air replacing general plastics.

Industrial Applicability

As apparent from the above description, the present invention enables

preparation of a biodegradable nanocomposite resin having mechanical, physical

and thermal properties comparable to those of general plastics while maintaining

biodegradability. The biodegradable nanocomposite resin of the present invention also has

improved injection or extrusion processing property, and thus can be applied in a

variety of industrial fields where conventional biodegradable resins cannot be used.

While the present invention has been described in detail with reference to the

preferred embodiments, those skilled in the art will appreciate that various

modifications and substitutions can be made thereto without departing from the

spirit and scope of the present invention as set forth in the appended claims.

Claims

1. A biodegradable nanocomposite resin composition comprising:

(a) 5-30 wt % of an inorganic material, wherein powder of layered inorganic

silicate comprising muscovite, phlogopite or a mixture thereof is dispersed in oil,

and

(b) 70-95 wt % of a biodegradable resin.

2. 1 he biodegradable nanocomposite resin composition of Claim 1, wherein

said oil has 12-20 carbon atoms.

3. 1 he biodegradable nanocomposite resin composition of Claim 1, wherein

said powder of layered inorganic silicate has an average particle diameter of 0.01-5

μm.

4. I he biodegradable nanocomposite resin composition of Claim 1, wherein

said biodegradable resin is at least one selected from polylactic acid, polyglycolic

acid, polycaprolactone, aliphatic polyester resin, polyhydroxybutyric acid (PHB) and

D-3-hydroχγ butyric acid.

5. The biodegradable nanocomposite resin composition of any of Claims 1 to

4, which is i n the form selected from dried powder, film and pellet.

6. A method for preparing a biodegradable nanocomposite resin comprising:

a) adding 90-93 wt% of powder of layered inorganic silicate ground to an

average particle size of 0.01-5 μm, which comprises muscovite, phlogopite or a

mixture thereof, to 7-10 wt% of oil having 12-20 carbon atoms and stirring the

mixture at 1 ,000-2,000 rpm to prepare an inorganic material;

b) stirring a mixture of 5-30 wt% of the inorganic material prepared in step 1)

with 70-95 \vt% of a biodegradable resin at 1,000-2,000 rpm until the temperature of

the reaction mixture reaches 180-200 ⁰C; and

c) processing said mixture into pellet and injecting or extruding said pellet.

7. 1 he method of Claim 6, wherein the stirring in step 1) is carried out until

the temperature of the reaction mixture reaches 80-100 ⁰C.

8. The method of Claim 6, wherein 8-12 parts by weight of the biodegradable

resin is further added per 100 parts by weight of the powder of layered inorganic

silicate when the temperature of the reaction mixture reaches 80-100 ⁰C in step 1)

and the resulting mixture is prepared into pellet.

9. 1 lie method of Claim 6, wherein 0.01-10 parts by weight of an additive is

further added per 100 parts combined weight of the inorganic material and the

biodegradable resin in step 2).