WO2000031166A1

WO2000031166A1 - Biophotodegradable plastic film and plastic filler composition therefor and method of preparing the composition

Info

Publication number: WO2000031166A1
Application number: PCT/KR1999/000405
Authority: WO
Inventors: Young Kwan Ko
Original assignee: Uni Chem Co., Ltd.
Priority date: 1998-11-19
Filing date: 1999-07-26
Publication date: 2000-06-02
Also published as: AU5068399A

Abstract

The plastic filler composition according to the present invention comprises: (i) 60-90 % by weight of inorganic oxide powder made of at least two materials selected from the group consisting of kieselguhr, clay, quartz, feldspat, dolomite, pearlite, pumice and benthonite, thereby containing 60-90 % by weight of silicon oxide, 1-7 % by weight of iron oxide, 2-10 % by weight of aluminium oxide, 1-5 % by weight of manganese oxide, 1-5 % by weight of magnesium oxide, 2-6 % by weight of titanium oxide, and 1-5 % by weight of sodium chloride, and (ii) 40-10 % by weight of a polymer resin. The plastic filler composition is prepared in pellets by mixing the inorganic oxide powder and polymer resin, and extruding the mixture. The plastic film according to the present invention is prepared from the mixture of: (a) 10-50 % by weight of the plastic filler composition and (b) 90-50 % by weight of the polymer resin. The plastic film is biodegradable to microorganisms and photodegradable upon exposure to the ultraviolet lights, and does not discharge contaminants during incineration.

Description

Biophotodegradable Plastic Film and Plastic Filler Composition Therefor and Method of Preparing the Composition

Field of the Invention

The present invention relates to plastic film which is photodegradable and biodegradable, and which does not discharge contaminants during incineration. More particularly, the present invention relates to a plastic filler composition for preparing the plastic film being biophotodegradable and not discharging contaminants during combustion. The present invention also includes a method of preparing the plastic filler composition.

Background of the Invention

Plastic material has advantages of its light weight and good molding processability, and therefore has been widely used for manufacturing various goods in industry as well as general consumer goods nowadays. Also, the plastic has good durability, since it is relatively stable to heat, does not become rusty, and is not degraded by light and moisture. The use of plastic material expands and in particular, the amount of the plastic wasted after having been used as packaging materials, greenhouse films, disposable goods, etc. increases dramatically. Consequently, the environmental pollution problems have arisen because the plastic wastes are not degraded in the natural ecosystem. To solve such problems, there have been many efforts to develop plastic films which can be corroded or degraded either by itself or by other affects in the natural state.

Usually, there are two types of the degradable plastic. The first type is a biodegradable plastic which is degraded by microorganisms in the nature, and the second type is a photodegradable which is degraded by the solar ultra-violet (UN) lights.

The biodegradable plastic material is prepared employing a natural polymer such as starch, cellulose, etc. which have an intrinsic biodegradability under the natural environment. U.S. Patent No. 4,021,388 to Griffin discloses a biodegradable composition including a polymer having carbon linkages and dispersed therein starch granules, the surface of said granules being modified by reaction with a compound which reacts with hydroxyl groups to form an ether or an ester. However, the biodegradable plastic has a drawback that while the starch in the composition is degraded, the other remaining plastic component is not degraded in the environmental system.

Korean Patent Laid-Open No. 97-43399 teaches a process for preparing microorganism-degradable aliphatic polyester multifilaments by esterification of aliphatic dicarboxylic acid with glycol and polymerization of the compound by adding tetrabutyltitanate as catalyst and magnesium oxide or zinc oxide as coupling agent. However, the polyester multifilaments do not have good biodegradability, sufficient strength and elongation, and economic manufacturing cost.

U.S. Patent No. 5,407,979 to Wu et al. discloses a biodegradable thermoplastic film comprising an alkanoyl polymer, a destructured starch and an ethylene copolymer, which can be stretched providing breathability and enhancing its biodegradability. And U.S. Patent No. 5,461,094 to Yoo et al. discloses a biodegradable polyethylene composition chemically bonded with starch, which comprises polyethylene, starch, coupling agent, acid catalytic comonomer, radical initiator, autoxidizing agent and plasticizer.

Biodegradable plastic films should be easily degraded by microorganisms and have good heat- stability and mechanical strength. The photodegradable plastic material are prepared in two ways. The first method is to synthesize a polymer having a structure to form easily cleavage at the main chain upon exposure to UN lights, thereby providing the plastic film with good photodegradability. The second method is to use additives which can form radicals upon exposure to UN lights in order to degrade the plastic film.

U.S. Patent No. 3,860,538 to Guillet et al. discloses polymer compositions photodegradable upon exposure to UN lights comprising a blend of a synthetic polymer and a ketone copolymer, containing from about 0.01 to about 5 weight percent carbonyl groups. U.S. Patent No. 4,337,181 to Otey et al. teaches film-forming formulations comprising starch, ethylene acrylic acid copolymer, and optionally polyethylene, which can be blown into films upon neutralization of a portion of the copolymer acid functionality.

The present inventor has developed a plastic filler composition which is used for preparing a plastic film being biophotodegradable and not discharging contaminants during combustion, and a method of preparing the plastic filler composition.

Objects of the Invention

An object of the present invention is to provide a plastic film which is biodegardable to microorganisms and photodegradable upon exposure to the ultraviolet lights.

Another object of the present invention is to provide a plastic film which does not discharge contaminants during incineration.

A further object of this invention is to provide a plastic filler composition which is used for preparing a plastic film being biophotodegradable and not discharging contaminants during combustion. A further object of this invention is to provide a method of a plastic filler composition which is used for preparing a plastic film being biophotodegradable and not discharging contaminants during combustion. The above and other objects and advantages of this invention will be apparent from the ensuing disclosure and appended claims.

Summary of the Invention

The plastic filler composition according to the present invention comprises (i) 60 — 90 % by weight of inorganic oxide powder made of at least two materials selected from the group consisting of kieselguhr, clay, quartz, feldspar, dolomite, pearlite, pumice and benthonite, thereby containing 60 — 95 % by weight of silicon oxide, 1 — 7 % by weight of iron oxide, 2 — 10 % by weight of aluminium oxide, 1 — 5 % by weight of manganese oxide, 1 — 5 % by weight of magnesium oxide, 2 — 6 % by weight of titanium oxide, and 1 — 5 % by weight of sodium chloride, and (ii) 40— 10 % by weight of a polymer resin. The plastic filler composition is prepared in pellets by mixing the inorganic oxide powder and polymer resin, and extruding the mixture. The plastic film according to the present invention is prepared from the mixture of (a) 10 — 50 % by weight of the plastic filler composition and (b) 90 — 50 % by weight of the polymer resin. The plastic film is biodegardable to microorganisms and photodegradable upon exposure to the ultraviolet lights, and does not discharge contaminants during incineration.

Brief Description of the Drawings

Fig. 1 is a graph showing the tensile strengths depending on the ratio of the plastic filler in the plastic filler/L DPE films of both the machine direction and the transverse direction;

Fig. 2 is a graph showing the elongations depending on the ratio of the plastic filler in the plastic filler/LLDPE films of both the machine direction and the transverse direction;

Fig. 3 is a graph showing the tearing strengths depending on the ratio of the plastic filler in the plastic filler/LLDPE films of both the machine direction and the transverse direction;

Fig. 4 is a graph showing the tensile strengths of the plastic films of Example 3 (plastic filler content: 20 %) and of calcium carbonate/LLDPE (calcium carbonate content: 30 %) depending on the exposure time to UN lights; and

Fig. 5 is a graph showing the elongations of the plastic films of Example 3 (plastic filler content: 20 %) and of calcium carbonate/LLDPE (calcium carbonate content: 30 %) depending on the exposure time to UN lights.

Detailed Description of the Invention The present invention relates to a plastic filler composition for preparing a plastic film having biodegradability and photodegradability and not discharging contaminants during incineration. The plastic filler composition comprises (i) 60 — 90 % by weight of inorganic oxide powder made of at least two materials selected from the group consisting of kieselguhr, clay, quartz, feldspar, dolomite, pearlite, pumice and benthonite, and (ii) 40 — 10 % by weight of a polymer resin. The inorganic oxide powder contains 60 — 95 % by weight of silicon oxide, 1 ~ 7 % by weight of iron oxide, 2 — 10 % by weight of aluminium oxide, 1 — 5 % by weight of manganese oxide, 1 — 5 % by weight of magnesium oxide, 2 — 6 % by weight of titanium oxide, and 1 —5 % by weight of sodium chloride. The plastic filler composition is prepared in pellets by mixing the inorganic oxide powder and polymer resin, and extruding the mixture. Thus, the plastic filler composition is prepared as masterbatch. The plastic film according to the present invention is prepared from the mixture of (a) 10 — 50 % by weight of the plastic filler composition and (b) 90 — 50 % by weight of the polymer resin. The plastic film is biodegardable to microorganisms and photodegradable upon exposure to the ultraviolet lights, and does not discharge contaminants during incineration. The inorganic oxide powder is prepared from the raw materials selected from the group consisting of kieselguhr, clay, quartz, feldspar, dolomite, pearlite, pumice and benthonite. To the inorganic oxide powder, synthesized inorganic oxide powder is added in the amount of about from 2 to 3 % by weight per the plastic filler. The synthesized inorganic oxide powder is made of at least two components selected from the group consisting of AI2O3, Si0₂, Ti0₂, MnO, MgO, Fe₂0₃ and NaCl.

The plastic filler according to the present invention is prepared by calcining the raw materials selected from the group consisting of kieselguhr, clay, quartz, feldspar, dolomite, pearlite, pumice and benthonite, pulverizing the incinerated materials, mixing the pulverized inorganic oxide powder with a polymer resin, and extruding the mixture. The plastic filler is prepared in pellets.

As polymer resin usable for preparing the plastic filler, there are thermoplastic and thermosetting resins. Examples of the thermoplastic resin are vinyl resins such as polyethylene, polystyrene and polyvinyl chloride; polyester resin; polyamide(nylon) resin; acryl(polymethacrylate) resin; ABS (acrylonitryl-butadiene-styrene) resin and the like. Examples of the thermosetting resin are alkyd resin, epoxy resin, phenol resin, urea resin, melamine resin, aniline resin and the like.

The step of calcining the raw materials is carried out at temperature of 600 to 800 °C for 4 to 10 hours under oxidation atmosphere. During this calcination, the raw materials become oxide compounds. To speak clearly, the raw materials become peroxide compounds. To produce peroxide compounds, air is directly blown at the calcination step or oxygen gas is fed. It is preferable that the calcination step is conducted at temperature of about 700 °C for 6 to 7 hours under the condition of blowing air. The step of pulverizing or milling the calcined oxide compounds forms inorganic oxide powder having particle sizes of from 500 to 800 mesh. The calcined oxide compounds are milled with a ball mill or a jet mill. The milling step composes of two courses, coarse milling and fine milling. The coarse milling continues for from three to five hours, and the fine milling for from five to ten hours. The inorganic oxide powder contains 60 — 95 % by weight of silicon oxide, 1 — 7 % by weight of iron oxide, 2 — 10 % by weight of aluminium oxide, 1 — 5 % by weight of manganese oxide, 1 — 5 % by weight of magnesium oxide, 2 — 6 % by weight of titanium oxide, and 1 — 5 % by weight of sodium chloride. The inorganic oxide powder of 60 — 90 % by weight and a polymer resin of 40 — 10 % by weight are mixed in a conventional mixer. Preferably, the inorganic oxide powder of 70 — 80 % by weight and a polymer resin of 30 — 20 % by weight may be blended. To the mixture are additives such as autoxidizing agent, degradation initiator, dyes, pigments, etc added. The additives are easily understood by an ordinary skilled person in the art. Also, to the mixture, synthesized inorganic oxide powder may be added in the amount of about from 2 to 3 % by weight per the plastic filler. The synthesized inorganic oxide powder is made of at least two components selected from the group consisting of AI2O3, SiO₂, TiO₂, MnO, MgO, Fe₂0 and NaCl.

The plastic film according to the present invention is prepared from the mixture of (a) 10 — 50 % by weight of the plastic filler composition and (b) 90 — 50 % by weight of a polymer resin. The plastic film is biodegardable to microorganisms and photodegradable upon exposure to the ultraviolet lights, and does not discharge contaminants during incineration.

The polymer resin is the same resin as it is used in the plastic filler. The process of preparing plastic films from the plastic filler masterbatch and a polymer resin is easily worked by an ordinary skilled person in the art to which this invention pertains.

The plastic filler of the present invention is a porous material which has a particular molecular structure. This porous, particular molecular structure of the plastic filler serves to absorb ultraviolet lights and to preserve sufficient amount of energy of the lights therein. The UN lights having a wavelength band at 290-320 nm has enough energy to cleave the carbon-carbon or hydrogen-hydrogen bonds of the polymer. The plastic filler functions to degrade the polymer of the plastic film. It is believed that the surface of the polymer is gradually broken by the dissolved oxygen and UN lights energy which are preserved in the porous, particular molecular structure.

Fig. 4 shows the tensile strengths of the plastic films of Example 3 (plastic filler content: 20 %) and of calcium carbonate/LLDPE (calcium carbonate content: 30 %) depending on the exposure time to UN lights, and Fig. 5 shows the elongations of the plastic films of Example 3 (plastic filler content: 20 %) and of calcium carbonate/LLDPE (calcium carbonate content: 30 %) depending on the exposure time to UN lights.

In Figs. 4 and 5, the tensile strengths and elongations decrease from the initial value 100 in which the test samples are not exposed to ultraviolet lights. The time reached up to the half of the initial properties is important. Figs. 4 and 5 show that the plastic filler/LLDPE films according to the present invention are faster in photodegradation than the conventional calcium carbonate/LLDPE film. In the conventional plastic films, UN light stabilizer, heat stabilizer, and photoactivator such as photodegradation initiator or accelerator can result in a second contamination. However, the plastic film of the present invention does not cause the second contamination, because the plastic filler is photodegraded by the inorganic oxides therein.

As shown in Figs. 4 and 5, it takes certain time to degrade the plastic films so that the physical properties are drastically varied. Because the various oxides in the plastic filler functions as a stabilizing agent until the UN lights energy is stored in the molecules of the plastic film and prevents degradation and lowering the physical properties. After about thirty hours exposed to UN lights, the polymer is rapidly oxidized by inorganic oxides, dissolved oxygen, light energy, impurities, etc, resulting that the tensile strength is completely weakened after about 200 hours of exposure to UN lights and that the elongation after 60 hours. These degradations are explained as follows:

Firstly, the UN lights energy and inorganic oxides produce free radicals in the polymer molecules. The ultraviolet lights have a wavelength band of 290-320 nm, and the degradation energy is 80-85 kcal/mol. Among inorganic oxides, ferric oxide serves as a photoactivator. Depending on the exposure time, the polymer is rapidly transferred from a stable region to a decomposition region.

Secondly, photochemical reactions are initiated by the UN lights and free radicals. The free radicals are reacted with the polymer by the UN lights energy to produce carbonyl groups. Thirdly, due to the dissolved oxygen in the polymer molecules, the photochemical reaction continues to the thermochemical reaction. The carbonyl groups accelerate lowering the physical properties of the polymer and degradation of the plastic film.

Fourth, the molecular weight of the polymer becomes smaller and the deterioration of physical properties of the polymer is accelerated.

The plastic fillers has characteristics of various molecular structures and types. The plastic film prepared by blending the plastic filler masterbatch and a polymer resin shows good physical properties such as tensile strength, elongation, tearing strength and the like. Futhermore, the plastic filler composition is porous to have large surface area. Upon exposure to UN lights, the inorganic oxides in the plastic filler result in the decrease of physical properties. The dissolved oxygen and water contained in the pores and the oxides generate more carbonyl groups

(C=O) which break the plastic polymer chains. It is also believed that the porous plastic fillers of this invention can provide an environment in which microorganisms can survive and grow, and it is expected that the high molecular weight decreases significantly, thereby the plastic fillers being absorbed and digested by microorganisms.

The plastic fillers according to the present invention result in complete combustion during incineration at low temperature and under low oxygen circumstance. Environmental pollution, terrestrial warming and acidic rain can be prevented because of the small amount of nitrogen and dioxin generated during incineration at high temperature and under high oxygen circumstance. It is believed that the polymer chains of the plastic film are broken by dissolved oxygen, subterranean heat, subterranean moisture and autoxidizing agent in the plastic filler, and turn out to be feed of microorganisms. The plastic films has a good antislipness because of the inorganic materials and keep a good cleanness because of the good dispersion. The plastic filler plastic films gain the weight as much as the plastic filler is used, which will be usually 20-30% and more.

As aforementioned, the plastic fillers of this invention are applicable to the plastic films for various purposes because they do not discharge any contaminants when incinerated, while maintaining the excellent physical properties as well as photodegradability and biodegradability. The plastic fillers can be used in packaging industry, agricultural -horticultural field and medical sanitary field in the form of film, and it can be widely used in containers, sanitary medical supplies, cosmetics, children supplies and the like.

The present invention will be described in more detail by the following Example and Comparative Example. The Example is given only to illustrate the present invention and not intended in any way to limit the scope of the invention.

Example 1: Preperation of Plastic Filler Composition

Natural kieselguhr of 5 kg, pearlite of 2 kg, feldspar of 1 kg and pumice of 2 kg were calcined at temperature of 700 ^°C for 6 hours. Organic impurities were removed from the calcined materials. The calcined materials were cooled and were milled with a ball mill for 8 hours to obtain inorganic oxide powder having size of 500 to 800 meshes. To the oxide powder was 3 kg of polyethylene added, then the mixture was blended in a conventional mixer. The mixture was extruded through an extruder to form the plastic filler in pellets.

Example 2 : Preparation of Plastic Film Having 10 wt % of Plastic Filler

The plastic filler masterbatch prepared in Example 1 was mixed in ' the amount of 10 % by weight with low density polyethylene powder of 90 % by weight. The mixture were melted at temperature of 170 ^°C to prepare plastic film having a thickness of 0.05 mm.

Example 3 : Preparation of Plastic Film Having 20 wt % of Plastic Filler

Plastic film was prepared in the same manner as in Example 1 except that the plastic filler masterbatch was employed in the amount of 20 % by weight with low density polyethylene powder of 80 % by weight.

Example 4 : Preparation of Plastic Film Having 30 wt % of Plastic

Filler

Plastic film was prepared in the same manner as in Example 1 except that the plastic filler masterbatch was employed in the amount of 30 % by weight with low density polyethylene powder of 70 % by weight.

Example 5 : Preparation of Plastic Film Having 40 wt % of Plastic

Filler

Plastic film was prepared in the same manner as in Example 1 except that the plastic filler masterbatch was employed in the amount of 40 % by weight with low density polyethylene powder of 60 % by weight.

Example 6 : Preparation of Plastic Film Having 20 wt % of Plastic Filler

Plastic film was prepared in the same manner as in Example 2 except that the plastic filler masterbatch was employed in the amount of 20 % by weight with high density polyethylene (HDPE) powder of 80 % by weight.

Comparitive Example 1: Preparation of 100 % Polyethylene Plastic

Film

With no use of the plastic filler, low density polyethylene powder of 100 % by weight was melted at temperature of 170 ^°C to prepare plastic film having a thickness of 0.05 mm.

Measurement of Properties

(1) Mechanical Properties

For the plastic films of Examples 2-5 and Comparative Example 1, tensile strength, elongation and tearing strength were measured. The test result are shown in Table 1. The more a plastic filler is used, the weaker the mechanical properties are. However, the plastic film of Example 5 has a sufficient mechanical properties which are better than those of Korean Standard Regulations. The mechanical properties were measured in accordance with KSM 3001 at the cross head speed of 500 mm min. The mechanical properties of Korean Standard Regulations are shown by KSM 3503.

Table 1

Plastic Filler Tensile Strength (kg/cm') Elongation(%) Tearing Strength(g/cm) (wt%) MD^" TD" MD TD MD TD

Comp.Ex. 1 0 350 330 550 800 100 100

Example 2 10 320 300 550 800 100 100

Example 3 20 300 280 550 750 105 90

Example 4 30 280 270 540 750 110 85

Example 5 40 260 240 540 750 105 80

KS Regulations 200 up 200 up 350 up 350 up 75 up 75 up

Notes) * : MD means a plastic film which was tested in the machine direction.

** : TD means a plastic film which was tested in the transverse direction.

The increase of the plastic filler causes the decrease of the mechanical properties. However, the plastic film of Example 5 has a 10 sufficient mechanical properties which are better than those of Korean

Standard Regulations. Tensile strengths, elongations and tearing strengths of Table 1 are shown in Fig. 1, 2 and 3, respectively.

(2) Incineration Property

15

For plastic films of LDPE having a melt index of 6.0, LLDPE having a melt index of 2.0, and HDPE having a melt index of 7.0, and a plastic film of Example 4, the total calories for incineration up to 150 ^°C were measured using DSC (differential scanning calorimeter). The test results are shown in Table 2. It is appreciated that the total calory of Example 4 is lowered by 16 to 36% compared with 100% polyethylene films.

Table 2

Plastic Film Total Calory for Incineration up to 150 °C (J/g)

LDPE (6.0 MI) 360

LLDPE (2.0 MI) 410

HDPE (7.0 MI) 470

Example 4 300

The plastic film of Example 4 does not include additives such as autoxidant, degradation initiator, degradation promotor, etc. Through a test with a pyrolyer, the plastic film of Example 4 did not generate any toxic gases such as dioxin when it was incinerated at the temperatures of 10 700 °C and 1,000 °C , respectively.

(3) Photodegradability

Figs. 4 and 5 show that the plastic filler/LLDPE films according to 15 the present invention are faster in photodegradation than the conventional calcium carbonate/LLDPE film. In the conventional plastic films, UV light stabilizer, heat stabilizer, and photoactivator such as photodegradation initiator or accelerator can result in a second contamination. However, the plastic film of the present invention does not cause the second 20 contamination, because the plastic filler is photodegraded by the inorganic oxides therein. As shown in Figs. 4 and 5, it takes certain time to degrade the plastic films so that the physical properties are drastically varied. Because the various oxides in the plastic filler functions as a stabilizing agent until the UN lights energy is stored in the molecules of the plastic film and prevents degradation and lowering the physical properties. After about thirty hours exposed to UN lights, the polymer is rapidly oxidized by inorganic oxides, dissolved oxygen, light energy, impurities, etc, resulting that the tensile strength is completely weakened after about 200 hours of exposure to UN lights and that the elongation after 60 hours.

(4) Biodegradability

The plastic fillers has characteristics of various molecular structures and types. The plastic film prepared by blending the plastic filler masterbatch and a polymer resin shows good physical properties such as tensile strength, elongation, tearing strength and the like. Futhermore, the plastic filler composition is porous to have large surface area. Upon exposure to UN lights, the inorganic oxides in the plastic filler result in the decrease of physical properties. The dissolved oxygen and water contained in the pores and the oxides generate more carbonyl groups (C=O) which break the plastic polymer chains. It is also believed that the porous plastic fillers of this invention can provide an environment in which microorganisms can survive and grow, and it is expected that the high molecular weight decreases significantly, thereby the plastic fillers being absorbed and digested by microorganisms.

(5) Moisture Permeability of Plastic Filler Film

The moisture permeability of plastic film of Example 4 was conducted at the temperature of 40 ^°C and relative humidity of 70 % in accordance with ASTM E96-80. The test showed 500g/m².day in case that the thickness of the plastic film was 18 m. This moisture permeability is very high compared to that of conventional PE or PP films.

(6) Molecular Weight Distribution after UV Lights Exposure For 100 % LLDPE film and plastic film of Example 6, the molecular weights and distributions thereof were obtained after the UN lights were exposed for 0, 5 and 20 hours, respectively. The data are shown in Table 3.

Table 3

Plastic Film Exposure Time Molecular Weight Distibution

(hrs) Mn Mw

100% LLDPE 0 31727 228785 7.2

LLDPE 5 31518 228204 7.2

LLDPE 20 30841 233039 7.6

Example 6 0 10888 531794 49

Example 6 5 10302 439346 43

Example 6 20 11522 369114 32

In case of 100 % LLDPE film, it was shown that even if it was exposed to UV lights up to 20 hours, there was no big ■ differences in molecular weights and distribution thereof. However, in case of the plastic film of Example 6, it was shown that there was a big change of molecular weights, and if UN lights were exposed thereto, there was a high variation of molecular weight distribution. That is, it is shown that the plastic film of this invention seems to tend to be gradually degraded.

In the above, the present invention was described based on the preferred embodiment of the present invention, but it should be apparent to those ordinarily skilled in the art that various changes and modifications can be added without departing from the spirit and scope of the present invention. Such changes modifications should come within the scope of the present invention.

Claims

What is claimed is:

1. A plastic filler composition being photodegradable and biodegradable, which comprises:

(i) 60 — 90 % by weight of inorganic oxide powder made of at least two materials selected from the group consisting of kieselguhr, clay, quartz, feldspar, dolomite, pearlite, pumice and benthonite; and

(ii) 40 — 10 % by weight of a polymer resin.

2. The plastic filler composition of claim 1 in which said inorganic oxide powder comprises 60 — 95 % by weight of silicon oxide, 1 — 7 % by weight of iron oxide, 2 — 10 % by weight of aluminium oxide, 1 — 5 % by weight of manganese oxide, 1 — 5 % by weight of magnesium oxide, 2 ~ 6 % by weight of titanium oxide, and 1 —5 % by weight of sodium chloride.

3. The plastic filler composition of claim 1, which further comprises about from 2 to 3 % by weight of synthesized inorganic oxide powder as per the plastic filler.

4. The plastic filler composition of claim 3 in which said synthesized inorganic oxide powder is made of at least two components selected from the group consisting of Al₂O₃, Si0₂, Ti0₂, MnO, MgO, Fe₂0 and NaCl.

5. The plastic filler composition of claim 1 in which said polymer resin is selected from the group consisting of polyethylene, polystyrene, polyvinyl chloride, polyester resin, polyamide (nylon) resin, acryl(polymethacrylate) resin and ABS (acrylonitryl-butadien-styrene) resin.

6. The plastic filler composition of claim 1, which further comprises autoxidizing agent, degradation initiator, dyes and/or pigments.

7. A method of preparing a plastic filler composition being photodegradable and biodegradable, which comprises: calcining the raw materials selected from the group consisting of kieselguhr, clay, quartz, feldspar, dolomite, pearlite, pumice and benthonite at temperature of 600 to 800 ^°C for 4 to 10 hours under oxidation atmosphere; pulverizing the calcined materials to form inorganic oxide powder having particle sizes of from 500 to 800 mesh; mixing the pulverized inorganic oxide powder with a polymer resin; and extruding the mixture.

8. The method of claim 7 in which said inorganic oxide powder comprises 60 — 95 % by weight of silicon oxide, 1 —7 % by weight of iron oxide, 2 — 10 % by weight of aluminium oxide, 1 — 5 % by weight of manganese oxide, 1 —5 % by weight of magnesium oxide, 2 — 6 % by weight of titanium oxide, and 1 — 5 % by weight of sodium chloride.

9. The method of claim 1 in which said inorganic oxide powder further comprises about from 2 to 3 % by weight of synthesized inorganic oxide powder as per the plastic filler.

10. The method of claim 9 in which said synthesized inorganic oxide powder is made of at least two components selected from the group consisting of AI2O3, Si0₂, Ti0₂, MnO, MgO, Fe₂0₃ and NaCl.

11. The method of claim 7 in which said polymer resin is selected from the group consisting of polyethylene, polystyrene, polyvinyl chloride, polyester resin, polyamide (nylon) resin, acryl(polymethacrylate) resin and ABS

( aery lonitry 1 - butadien - sty rene ) resin .

12. The method of claim 7 in which said plastic filler further comprises autoxidizing agent, degradation initiator, dyes and/or pigments.

13. The method of claim 7 in which said calcining step is conducted at temperature of about 700 ^°C for 6 to 7 hours under the condition of blowing air.

14. A plastic film composition which is photodegradable and biodegradable, and which does not discharge contaminants during incineration, which comprises:

(a) 10 — 50 % by weight of a plastic filler composition comprising (i)

60 — 90 % by weight of inorganic oxide powder made of at least two materials selected from the group consisting of kieselguhr, clay, quartz, feldspar, dolomite, pearlite, pumice and benthonite; and (ii) 40 — 10 % by weight of a polymer resin; and

(b) 90 — 50 % by weight of the polymer resin.

15. The plastic film composition of claim 14 in which said inorganic oxide powder comprises 60 — 95 % by weight of silicon oxide, 1 — 7 % by weight of iron oxide, 2 — 10 % by weight of aluminium oxide, 1 —5 % by weight of manganese oxide, 1 — 5 % by weight of magnesium oxide, 2 — 6 % by weight of titanium oxide, and 1 — 5 % by weight of sodium chloride.

16. The plastic film composition of claim 14 in which said the plastic filler composition further comprises about from 2 to 3 % by weight of synthesized inorganic oxide powder as per the plastic filler.

17. The plastic film composition of claim 16 in which said synthesized inorganic oxide powder is made of at least two components selected from the group consisting of A1₂0₃, Si0₂, Ti0₂, MnO, MgO, Fe₂0 and NaCl.

18. The plastic film composition of claim 14 in which said polymer resin is selected from the group consisting of polyethylene, polystyrene, polyvinyl chloride, polyester resin, polyamide (nylon) resin, acryK poly methacry late) resin and ABS (acrylonitryl-butadien-styrene) resin.

19. The plastic film composition of claim 14, which further comprises autoxidizing agent, degradation initiator, dyes and/or pigments.

20. A plastic film prepared by extruding the plastic film composition according to claim 14.