AU2010200315A1 - Biodegradable resin composition, method for production thereof and biodegradable film therefrom - Google Patents

Abstract

The invention is concerned with a biodegradable resin composition having a good biodegradability, a good mechanical 5 property and a good compatibility with starch, includes 40 to 80wt% of an aliphatic/aromatic copolyester resin, 8 to 40wt% of a polylactic acid(PLA), 0.1 to 1.0 wt% of a peroxide type high-temperature initiator, 10 to 40wt% of starch, 1 to lOwt% of a starch plasticizer, 0.1 to 5wt% of a starch structure 10 destroying agent, and 0.8 to 3.Owt% of a compatibilizer, based on 100wt% of the resulting biodegradable resin composition. The invention is also concerned with a method of manufacturing the biodegradable resin composition includes 15 steps of mixing 40 to 80wt% of an aliphatic/aromatic copolyester, 10 to 40wt% of a polylactic acid and 0.01 to 1.0 wt% of peroxide type high-temperature initiator, based on 100wt% of the resulting biodegradable resin composition in a mixer for 5 to 15 minutes, extruding the resulting mixture in 20 a twin screw extruder under the vacuum of 10torr or less at a temperature ranging from 150 to 200 0 C, and pelletizing the extruded material using a pelletizer after cooling.

Description

Regulation 3.2 AUSTRALIA 5 Patents Act 1990 10 COMPLETE SPECIFICATION STANDARD PATENT 15 APPLICANT: Green Chemical Co., Ltd NUMBER: FILING DATE: 28 January 2010 20 INVENTION TITLE: BIODEGRADABLE RESIN COMPOSITION, METHOD FOR PRODUCTION THEREOF AND BIODEGRADABLE FILM THEREFROM The following statement is a full description of this invention, including the best method of performing it known to us: 1 BIODEGRADABLE RESIN COMPOSITION, METHOD FOR PRODUCTION THEREOF AND BIODEGRADABLE FILM THEREFROM Technical Field 5 The present invention relates to a biodegradable resin composition having a good biodegradability, a good mechanical property and a good processability. Background Art 10 Since plastic has many strong points, such as its lightness, good processability capable of mass production, a good durability, a good chemical resistance and mechanical property, it has been used as an essential material in our daily life. However, the environmental pollution is getting 15 more serious due to plastic waste all over the world these days. As plastic waste, especially disposable waste becomes the main cause of environmental pollution, biodegradable resins have been applied to disposable products and these have also been developed widely. Further, a polylactic acid 20 is produced, which discharges relatively small amounts of carbon dioxide, compared to plastic produced from petroleum. Therefore, the polylactic acid is preferred as an environmental friendly resin. A biodegradable resin is a limitless resource capable 25 of continuous production. This is because it is 2 inexhaustible compared to petroleum based resins, and therefore the usage of the products using it is greatly enlarged every year. Examples of the biodegradable resins developed so far include: a polylactide synthesized through a 5 ring-opening reaction of a lactic acid or lactide with a chemical catalyst or an enzyme, a polycaprolactone synthesized chemically by starting from e-caprolactone monomer, a diol-diacid type aliphatic polyester, and polyhydroxybutylate (PHB) synthesized in vivo by 10 microorganisms, etc. Biodegradable resins are usually expensive and have poor physical properties to be used compared to the conventional plastic products. On the other hand, a polylactic acid is inexpensive compared to other 15 biodegradable resins, but it has a low heat resistance temperature and a weak impact strength. A polycaprolactone has a low melting point that reduces processability. When diol-diacid type aliphatic polyester is used in making a film, its storage stability and heat sealing is too weak to be 20 produced for practical use. Although the aliphatic/aromatic copolyester, produced by adding an aromatic monomer, has a supplemented physical property, its biodegradability is reduced. Aliphatic/aromatic copolyesters have been used as adhesives or elastomers in various fields. Hence, their 25 preparation methods consist of a first step of producing an 3 oligomer which is produced through an ester exchange process occurring between a bifunctional carboxylic acid and a glycol, and a second step of condensation polymerizing the reactants at a high temperature under reduced pressure. These 5 preparation methods of aliphatic/aromatic copolyester resin were already known several decades ago. Since the preparation method of an aliphatic/aromatic copolyester resin, disclosed in the US Patent US4328059, uses a titanium catalyst, the reaction temperatures of the ester exchange 10 process and condensation are low and therefore it takes a long time to finish the reaction. The US Patent US4094721 discloses the preparation method of an aliphatic/aromatic copolyester resin using at least two kinds of glycol, which causes a rise in price due to recycling of excess glycol. 15 The US Patent US620225 discloses almost the same resin composition, and their preparation methods are as in the US Patent US4328059. The only differences between these patents are the changes of molecular weights and viscosities, which is obvious to those in the industry. The US Patent US3763079 20 discloses a method for production of an aliphatic/aromatic copolyester resin composition using sulfonate, isocyanate and general multi-functional groups in order to increase the molecular weight, with overlooking the function of a catalyst. As a catalyst generally used in these reactions, 25 antimony compound is widely used due to its promotion effect 4 of polymerization. However, the polymer produced by the antimony compound has a problem that its color is gray. Germanium compound, of which color is good, can be used as a catalyst instead of antimony compound. However, germanium 5 compound is not easily dissolved in a reactor, and its promotion effect of polymerization is low. Therefore, A lot of germanium compound must be added to the polymer, and then there remains germanium compound nonreacted, which degradates transparency. As methods of solving this problem, the 10 Japanese Patent Publication So47-11831 discloses using amorphous germanium compound, and the Japanese Patent Publication So49-43396 discloses a method consisting of dissolving germanium dioxide into water, adding ethylene glycol to the resulting solution, removing the water, and 15 using the resulting ethylene glycol solution. However, since germanium compound should be treated for a long time at a high temperature, these methods have problems that activities of catalysts become reduced and the production time is elongated. On the other hand, there have been a lot of 20 studies to improve the biodegradability and reduce the production costs by mixing starch, as a natural material, to an aliphatic/aromatic copolyester resin. However, in the case of applying starch to a biodegradable resin, the starch has a peculiar hydrophilicity and a reduced processability. 25 Therefore, the amount of starch that can be added is limited. 5 As a result, the quality of the resulting products is deteriorated. To solve the above-mentioned problems and also to impart the thermoplasticity to the starch, a glycerin, a 5 sorbitol, or a glucose is used as a starch plasticizer with water (see USP 3,949,145, EP 32802A1); and some plasticizers other than the above known plasticizer, such as a butane diol, propane diol and others, are used to plasticize the starch (see Korean Patent Laid-open No. 93-701529). Further, starch 10 is changed into a thermoplastic starch through a separate device or process and is then compounded into a biodegradable resin (see Korean Patent registration No. 10-0339789) . An aliphatic polyester based resin, having good biodegradability, and starch are used as main ingredients, and furthermore a 15 starch plasticizer and a starch structure destroying agent are added (see Korean Patent Registration No. 10-0465980). A biodegradable aliphatic polyester resin and a polylactic acid are used with a chain extender in a twin screw extruder (see Korean Patent Registration No. 10-0642289). Here, an acrylic 20 acid or a methacrylic acid is used as a commercial catalyst between a thermoplastic starch and the biodegradable resin (see Korean Patent Laid-open No. 97-42813). However, these biodegradable resin compositions, produced by the conventional methods, lead to high production 25 costs due to the deterioration of processability, a 6 carbonation of starch, and the deterioration of physical properties. In particular, when the plasticizer treating process that gives starch thermoplasticity and the chemical modifying process that improves a physical property are 5 conducted separately, the production costs is greatly increased and the process becomes more complicated. Alternatively, when 7 to 60wt% of polybuthylenesuccinate (includes polybuthylenesuccinate-co buthyleneadipate) type aliphatic polyester is mixed to a 10 polylactic acid (or its copolymer) (see Japanese Patent Laid open No. 1997-111107), the resulting products, shaped by using the resin obtained, show that the physical property of the products becomes significantly lowered upon passing time. As a prior art process to improve the weakness of these 15 biodegradable resins, Korean Patent Laid-open No.2001-0032052 discloses that 30 to 70wt% of a polybuthylenesuccinate type copolymer, produced through a condensation polymerization by using a adipic acid and a succinic acid as a dicarboxylic acid and 1,4-buthane diol as an aliphatic diol, which is 20 Japanese Showa Polymer Product Bionolle 3001, is added to polylactic acid (or its copolymer) . This is based on 100 wt% of the polylactic acid, and then these two ingredients are compounded using an extruder to improve the physical property. Korean Patent Registration No. 10-428687 discloses that a 25 composition containing 3 to 65wt% of a polylactic acid, based 7 on 100wt% of an aliphatic polyester and an aliphatic/aromatic copolyester, is compounded using a twin screw extruder to produce a biodegradable resin composition. In this case, during the compounding process of a polylactic acid (or its 5 copolymer) and a polybuthylenesuccinate (or its copolymer), a high melting point of the polylactic acid leads to a significant reduction of the thermal stability of the resin produced when it is extruded at a high temperature as well as a reduction of its mechanical properties. 10 Technical Problem The present invention has been made to solve the foregoing problems with the prior art, and therefore an aspect of this invention is to provide a biodegradable resin 15 composition that has a good biodegradability, a good mechanical property and a good compatibility with starch, and a method for production of it. Brief Description of the Invention 20 We, the inventors, have made efforts to improve the physical property of an aliphatic/aromatic copolyester, which is used as a main ingredient of the biodegradable resin, and its compatibility with the starch. This is achieved by using a mixed solution, as a catalyst, that is formed by dissolving 25 germanium compound and potassium compound in ethylene glycol, 8 and then reacting bifunctional carboxylic acid or its derivatives with diol ingredients. The aliphatic/aromatic copolyester, produced by the above stated method, is mixed with starch and polylactic acid, and extruded in a twin screw 5 extruder to produce a biodegradable resin composition. During the extrusion process, the thermoplasticity of the starch and the physical properties of the polylactic acid are improved simultaneously upon additives. In particular, an aspect of the present invention is to 10 provide a method for the production of a biodegradable resin composition comprising preparing an aliphatic/aromatic copolyester that has good physical properties and compatability with the starch, as a main ingredient, adding the starch and the polylactic acid to the copolyester, and 15 extruding the resulting mixture in a twin screw extruder. Here, the plasticizing of the starch and the chemical modification process for improving the physical properties of the polylactic acid are simultaneously conducted. These processes are simple and inexpensive to carry out. 20 According to an aspect of the present invention, a composition comprises 40 to 80wt% of an aliphatic/aromatic copolyester resin, 8 to 40wt% of a polylactic acid, 0.1 to 1.0 wt% of a peroxide type high-temperature initiator, 10 to 40wt% of starch, 1 to lOwt% of a starch plasticizer, 0.1 to 25 5wt% of a starch structure destroying agent, and 0.8 to 9 3.Owt% of a compatibilizer, based on 100wt% of the resulting biodegradable resin composition. More particularly, this invention relates to a biodegradable resin composition comprising an 5 aliphatic/aromatic copolyester resin, a polylactic acid (PLA), a peroxide type high-temperature initiator, starch, a starch plasticizer, a starch structure destroying agent, and compatibilizer, a method for production of it and resulting in a biodegradable film. 10 Here, the aliphatic/aromatic copolyester resin is prepared by reacting bifunctional carboxylic acid or its derivatives with diol ingredients under a synthetic catalyst, the catalyst is formed as a mixed solution by dissolving germanium compound and potassium compound in ethylene glycol, 15 and this composition is extruded in a twin screw extruder. Since the biodegradable resin compound of this invention contains an aliphatic/aromatic copolyester resin, as a main ingredient, having a good mechanical property and a good compatibility with starch and contains a certain amount 20 of plastisized starch and modified polylactic acid, this invention can produce a film that has good processibility and an improved heat adhesion strength. Further, during the compounding process of the production of the resin composition, the polylactic acid is modified by a peroxide 25 type high-temperature initiator. The process of plastization 10 of starch with a starch plasticizer is carried out simultaneously. As a result, the preparation process is so simple that the production method can save production costs. According to another aspect of the present invention, a 5 method of manufacturing the biodegradable resin composition comprises mixing 40 to 80wt% of an aliphatic/aromatic copolyester, 10 to 40wt% of a polylactic acid and 0.01 to 1.0 wt% of peroxide type high-temperature initiator, based on 100wt% of the resulting biodegradable resin composition in a 10 mixer for 5 to 15 minutes, extruding the resulting mixture in a twin screw extruder under the vacuum of 10torr or less at a temperature ranging from 150 to 200 0 C, and pelletizing the extruded material using a pelletizer after cooling. The method of the present invention can be achieved by 15 preparing an aliphatic/aromatic copolyester that uses a mixed solution, as a catalyst, that is formed by dissolving germanium compound and potassium compound in ethylene glycol, mixing the resulting aliphatic/aromatic copolyester, polylactic acid and the starch, and then compounding the 20 resulting mixture in a twin screw extruder. Here, a peroxide type high-temperature initiator as a modifier of the polylactic acid is added, and at the same time, starch, a starch plasticizer, a starch structure destroying agent, and a compatibilizer are added to provide a resulting 11 biodegradable resin composition that contains the plasticized starch. The term "comprise" and variants of the term such as "comprises" or "comprising" are used herein to denote the 5 inclusion of a stated integer or stated integers but not to exclude another integer or any other integers, unless in the context or usage an exclusive interpretation of the term is required. Any reference to publications or prior art in this 10 specification is not an admission that the disclosures constitute common general knowledge in Australia or in any other country. Advantageous Effects As set forth above, since the biodegradable resin 15 composition of the present invention and the biodegradable film of it have a good tensile strength, a good tear strength, and a good heat adhesion strength, compared to the resin film made of the conventional biodegradable resin, the present invention has the effect of overcoming problems due to its 20 low physical property, and therefore contributes to an overall environmental improvement by biodegrading completely into a natural state. 25 12 Best Method of Performing the Invention -Best Mode In accordance with the method of the present invention, the aliphatic/aromatic copolyester, which is a main ingredient of the biodegradable resin composition, is prepared by reacting 5 bifunctional carboxylic acid or its ester derivatives with diol ingredients to produce a polymer, and condensing the polymer at high temperature under reduced pressure. A mixed solution that is formed by dissolving germanium compound and potassium compound in ethylene glycol is used as a catalyst. 10 Here, the weight ratio of potassium compound to germanium compound ranges from 0.1 to 1.0 to be dissolved easily in ethylene glycol. If the weight ratio is less than 0.1, germanium compound is not dissolved enough. If the weight ratio is larger than 1.0, the resulting aliphatic/aromatic 15 copolyester has the color of yellow. The amount of germanium compound added ranges from 0.01 to 1.0 wt% based on the resulting polyester. If the amount of germanium compound added is less than 0.01 wt%, the polyester can not be obtained due to its poor condensation polymerization effect. 20 If the amount is more than 1.0 wt%, the condensation polymerization effect is enough, but it has insoluble materials that cause problems when it is formed. Examples of the germanium compound, used in this invention, include germanium dioxide, germanium alkoxide, germanium 25 tetrachloride, etc. Examples of the potassium compound, 13 dissolved with the germanium compound, include potassium acetate, potassium hydroxide, potassium iodide, etc. Addition of a solution, of which germanium compound and potassium compound are dissolved in ethlylene glycol, is the 5 first step occurring of ester exchange reaction or direct esterification. A catalyst can be added any time of the condensation polymerization as the second step. However, Addition of the catalyst in the first step is preferable to increase the effect of the catalyst. The weight ratio of 10 potassium compound to germanium compound is 10 to 100. If the weight ratio is less than 10, the germanium compound is not dissolved enough to cause scattering of germanium compound. If the weight ration is larger than 100, the degree of the polymerization is reduced and therefore the 15 physical property of the resulting polyester is deteriorated. Examples of the catalysts, other than those used in this invention, include magnesium, manganese, zinc, etc. Examples of phosphorous compound, as a stabilizer, include phosphoric acid, phosphorous acid, trimethylphosphate, 20 triethylphosphate, triphenylphosphate, etc. Terephthalic acid or dimethylterephtalate, as bifunctional carboxylic acid or its ester derivatives, ranges from 0.45 to 0.55 mole%, an adipic acid or its ester derivatives, as the remaining ingredients, ranges from 0.45 to 0.55 mole%. 1,4-butane 25 alone or a mixture of it can be used as a diol ingredient. 14 Here, the content amount of 1,4-butane ranges from 80 to 100 more%, the remaining aliphatic glycol is used at the amount of less than 20 mole%. Examples of glycol include diethylene glycol, cyclohexanedimethanol, etc. 5 Since this invention uses a mixed solution whose germanium compound and potassium compound dissolved in ethylene glycol as a synthetic catalyst, it solves the problem that the conventional germanium compound is not easily dissolved to cause the deterioration of the 10 transparency. Furthermore, the reaction time is shortened due to the maximizing of the effect of the catalyst. The biodegradable resin composition of this invention is produced by mixing 40 to 80wt% of an aliphatic/aromatic copolyester resin, 8 to 40wt% of a polylactic acid (PLA), 15 0.1 to 1.0 wt% of a peroxide type high-temperature initiator, 10 to 40wt% of starch, 1 to lOwt% of a starch plasticizer, 0.1 to Swt% of a starch structure destroying agent, and 0.8 to 3.Owt% of a compatibilizer, based on 100wt% of the resulting biodegradable resin composition in a mixer for 5 20 to 15 minutes, and compounding the mixture via a twin screw extruder. The compounding is conducted under the vacuum of 10torr or less at a temperature ranging from 150 to 200'C to remove water from the starch and the plasticizer. If the amount of the aliphatic/aromatic copolyester is 25 less than 40wt%, the tear strength of the film can be reduced 15 significantly. Also, if the amount is more than 80wt%, the cooling effect of the film can be reduced significantly leading to a lowered productivity which will result in a rise of the price of the products. 5 If the amount of the polylactic acid is less than 8wt%, the strong points of the polylactic acid, such as a good tensile strength, a cooling effect, and an improved transparency, can not be expected. If the amount is more than 40wt%, the tear strength and ductility of the polylactic 10 acid can be reduced to deteriorate the film. A polylactic acid has isomers, which are polymers having L-, D- or DL formed lactic acid units as main ingredients, and the polylactic acid, used in this invention, can be a homopolymer of D-lactic acid or a copolymer of L- and D-lactic acids. 15 If the amount of the starch, as one of constituting ingredients of the resulting biodegradable resin composition, is more than 40wt%, the tensile strength of the film can be reduced leading to a lowered productivity and poor formability. If the amount is less than lOwt%, the heat 20 adhesion strength and the biodegradability of the film can be reduced. One of the characteristics of the present invention is to use a peroxide type high-temperature initiator, which is able to increase the tensile strength and the cooling effect 25 of the polylactic acid, to improve its compatibility with 16 other resins and, and to improve its viscoelasticity. The high-temperature initiator forms a radical very quickly at a high temperature of more than 150 0 C , and induces the radical reaction of a polylactic acid to extend the length of the 5 chain. This in turn improves the viscoelasticity (melt elasticity) of the resin ultimately increasing the physical property of the film, and in particular the tear strength of the polylactic acid. Examples of the high-temperature initiator include a di-tertiary 10 buthylperoxyhexahydroterephthalate, a di-tertiary buthylperoxy-3,3,5-trimethylcyclohexane, a tertiary buthylperbenzoate, a di-tertiary-buthylperoxide, etc. The amount of the initiator can be added within a range from 0.1 to 1.0 wt%, based on 100wt% of the resulting biodegradable 15 resin composition. Further, examples of the starch used to improve the heat adhesion strength and the biodegradability of the film include corn starch, potato starch, tapioca starch, wheat starch, rice starch, and the modified starches alone or a mixture of 2 or more of them. Examples of the 20 modified starches, used in this invention, include alpha starch, acid-treated starch, acetyladipic acid starch, oxidized starch, octenyl succinatestarch, etc. A starch plasticizer such as a glycerin, a diglycerin, an ethyleneglycol, a prophyleneglycol, a 1,4-buthane diol, a 25 sorbitol, a sorbitolacetate, an aminosorbitol, and a 17 sorbitoldiacetate can be used. The content of the plasticizer can be 1 to lOwt%, based on 100wt% of the resulting biodegradable resin composition. If the amount of the plasticizer is less than lwt%, the plasticization of the 5 starch can not be enough. If the amount is more than lOwt%, the tackiness of the film can be increased to cause a poor processability. A starch structure destroying agent such as urea, sodium, potassium, potassium hydroxide, alum compound can be 10 used. The content of the starch structure destroying agent can be 0.1 to 5wt%, based on 100wt% of the resulting biodegradable resin composition. If the amount of the starch structure destroying agent is less than 0.lwt%, the degree of the destruction the starch can not be enough and therefore 15 the physical property will also be deteriorated. If its amount is more than 5wt%, the physical property of the aliphatic polyester resin can be decreased to cause the strength of the film to be weak. As the Starch is a hydrophilic material, it has little 20 compatibility with an aliphatic/aromatic copolyester which is hydrophobic. To complement this, a compatibilizer which has both hydrophilic and hydrophobic groups, such as a glycidylmethacrylate, an ethylenevinylalcohol, a polyvinylalcohol, and an ethylenevinylacetate, can be used. 25 The content of the compatibilizer can be within a range from 18 0.8 to 3.Owt%. If the amount is less than 0.8wt%, the role as a compatibilizer is not enough. If the amount is more than 3.Qwt%, the deterioration of the biodegradability may happen. 5 Further, to prevent the physical property from decreasing, commonly used additives in the art can be mixed. Examples of the additives include a heat stabilizer, an antioxidant, an ultraviolet stabilizer, a lubricant, a slip agent, a hydrolizable inhibitor, an inorganic filler, etc. 10 A heat stabilizer such as a triphenyl phosphate, a trimethylphosphate, etc. can be used, and the content of the heat stabilizer can be within a range from 0.1 to 1.0wt%, based on 100wt% of the resulting biodegradable resin composition. 15 An antioxidant includes a phenol-based antioxidant, and therefore anything in the Adekastab AO series and Irgafos series can be used within a range from 0.1 to 1.0 wt%, based on 100wt% of the resulting biodegradable resin composition. An ultraviolet stabilizer includes a HALS type compound 20 having an amine group, and it can be used within a range from 0.1 to 0.8 wt%, based on 100wt% of the resulting biodegradable resin composition. A lubricant includes a PE wax of amide series, and it can be used within a range from 0.1 to 1.0 wt%, based on 25 100wt% of the resulting biodegradable resin composition. 19 A slip agent includes Erucamide, Oleamide, etc. of the amide series, and it can be used within a range from 0.01 to 1.0 wt%, based on 100wt% of the resulting biodegradable resin composition. 5 An inhibitor of the hydrolysis includes the polycarbodiimide series, and it can be used within a range from 0.1 to 1.0 wt%, based on 100wt% of the resulting biodegradable resin composition. Inorganic filler includes talc, potassium carbonate, 10 clay, barium sulfate, titanium dioxide, carbon black, mica etc., and the inorganic filler having the average particle size of less than 20 gi can be used within a range from 0.1 to 30 wt%, based on 100wt% of the resulting biodegradable resin composition. 15 The extruding process is conducted at a temperature ranging from 150 to 200'C, by adding raw materials that have the above-mentioned composition to a twin screw extruder. If the extrusion temperature is less than 150 0 C, the degradation rate of the high-temperature initiator becomes slowed down, 20 and the reaction activity is reduced. As a result, the physical property of the aliphatic/aromatic copolyester and the polylactic acid can not be improved. Furthermore, the viscosity of the resin can be increased, and the dispersity of the starch can be reduced to cause the physical property 25 to deteriorate. If the extrusion temperature is more than 20 200 0 C, the discoloring and carbonation of the starch may happen by this heat, and therefore the physical property of the film can be reduced when it is formed. During compounding process, it is important to remove the moisture 5 from the starch and to remove the gas occurred from the additives by applying the vacuum of 10 torr or less to the starch. Otherwise, the foaming phenomenon of the resin may occur, resulting in the productivity and the physical property to decrease. The biodegradable resin film can be 10 provided, which is made of the biodegradable resin composition of the present invention. The biodegradable film of the present invention can be formed into garbage bags, shopping bags, industrial packing film, agricultural film, disposable table cloth and rollbacks. Moreover, it can be 15 completely biodegraded into carbon dioxide and water by microorganisms in natural states. This in turn will contribute to the prevention of an environmental pollution. Next, the following non-limiting examples and 20 comparative examples are used to further describe or illustrate the invention. These examples are given for illustration of the invention and are not intended to be limiting thereof. 25 21 EXAMPLES Example 1 In this example, 100L of reactor was purged by nitrogen, 19.42kg of a dimethylterephthalate, 21.62kg of a 1,4-buthane 5 diol, 3.72kg of ethyleneglycol and 20g of a manganese acetate as a catalyst were added and reacted under the nitrogen flow for 2 hours to drain the calculated amount of methanol. At this time, the temperature was maintained at 2050C. After the methanol was completely drained, 14.61kg of a dipic acid 10 was added, and the reaction temperature was fixed at 2000C and the water was drained. Then, 20g of ethyleneglycol solution of which 0.03 parts of crystalline germanium oxide and 0.5 parts of potassium acetate were dissolved in 2 parts of ethyleneglycol were added as a catalyst, and 40g of a 15 trimethylphosphate was added as a stabilizer. After the calculated amount of water was drained, the temperature was continuously raised up to 2450C . At this temperature, the condensation polymerization was conducted under the reduced pressure of 0.ltorr for 190 minutes. The number average 20 molecular weight of the sample collected was 38,230, and the weight average molecular weight was 105,590. Next, 10g of a tertiary-buthylperbenzoate as a high-temperature initiator, 2kg of a corn starch, 200g of a glycerin as a starch plasticizer, 8g of alum as a starch structure destroying 25 agent, and 80g of ethylenevinyl acetate as a compatibilizer 22 were added to 6kg of the aliphatic/aromatic copolyester resin, which was prepared by the above-mentioned method, and 2kg of polylactic acid 2002D (Natureworks), and all were mixed for 10 minutes using a super mixer. This was at the temperature 5 of 180 0 C whereby the mixture was extruded using a twin screw extruder, having a screw with a diameter of p 7 5 , at a rotation rate of 200rpm under the vacuum of less than 10 torr to produce the pellets. The pellets obtained were dried with a hot air dryer for 12 hours and produced to a film with the 10 thickness of 20 pm, using the blown film forming machine. The resulting film was tested for mechanical properties such as tensile strength, tear strength, and adhesion strength. The results were shown in Table 1. Example 2 15 In this example, 12g of a tertiary-buthylperbenzoate as a high-temperature initiator, 40g of PE-wax as a lubricant, 4g of oleamide as a slip agent, 2kg of a corn starch, 200g of a glycerin as a starch plasticizer, 8g of alum as a starch structure destroying agent, and 80g of ethylenevinyl acetate 20 as a compatibilizer were added to 5kg of the aliphatic/aromatic copolyester resin, which was prepared by the method of Example 1, and 3kg of polylactic acid 2002D (Natureworks), and all were mixed for 5 minutes using a super mixer. This was at the temperature of 160 0 C whereby the 25 mixture was extruded using a twin screw extruder, having a 23 screw with a diameter of p75, at a rotation rate of 180rpm under the vacuum of less than 10 torr to produce the pellets. The pellets obtained were dried with a hot air dryer for 12 hours and produced to a film with the thickness of 20 yim, 5 using the blown film forming machine. The resulting film was tested for mechanical properties such as tensile strength, tear strength, and adhesion strength. The results were shown in Table 1. Example 3 10 In this example, 14g of a tertiary-buthylperbenzoate as a high-temperature initiator, 40g of PE-wax as a lubricant, 4g of oleamide as a slip agent, 2kg of a corn starch, 200g of a glycerin as a starch plasticizer, 8g of alum as a starch structure destroying agent, and 80g of ethylenevinyl acetate 15 as a compatibilizer were added to 5kg of the aliphatic/aromatic copolyester resin, which was prepared by the method of Example 1, and 3kg of polylactic acid 2002D (Natureworks), and all were mixed for 5 minutes using a super mixer. This was at the temperature of 160 0 C whereby the 20 mixture was extruded using a twin screw extruder, having a screw with a diameter of p 7 5 , at a rotation rate of 180rpm under the vacuum of less than 10 torr to produce the pellets. The pellets obtained were dried with a hot air dryer for 12 hours and produced to a film with the thickness of 20 gm, 25 using the blown film forming machine. The resulting film was 24 tested for mechanical properties such as tensile strength, tear strength, and adhesion strength. The results were shown in Table 1. Comparative Example 1 5 In this comparative example, 100L of reactor was purged by nitrogen, 19.42kg of a dimethylterephthalate, 21.62kg of a 1,4-buthane diol, 3.72kg of ethyleneglycol and 20g of a manganese acetate as a catalyst were added and reacted under the nitrogen flow for 2 hours to drain the calculated amount 10 of methanol. At this time, the temperature was maintained at 205 0 C . After the methanol was completely drained, 14.61kg of a dipic acid was added, and the reaction temperature was fixed at 200 0 C and the water was drained. Then, 20g of a trimethylphosphate was added as a stabilizer. After the 15 calculated amount of water was drained, the temperature was continuously raised up to 245'C. At this temperature, the condensation polymerization was conducted under the reduced pressure of 0.ltorr for 190 minutes. The number average molecular weight of the sample collected was 32,000, and the 20 weight average molecular weight was 88,550. Next, 40g of PE wax as a lubricant, 4g of oleamide as a slip agent, 10g of a tertiary-buthylperbenzoate as a high-temperature initiator, 2kg of a corn starch, 200g of a glycerin as a starch plasticizer, 6g of alum as a starch structure destroying 25 agent, and 70g of ethylenevinyl acetate as a compatibilizer 25 were added to 6kg of the aliphatic/aromatic copolyester resin, which was prepared by the above mentioned method, and 2kg of polylactic acid 2002D (Natureworks), and all were mixed for 7 minutes using a super mixer. This was at the temperature of 5 200 0 C whereby the mixture was extruded using a twin screw extruder, having a screw with a diameter of p 7 5, at a rotation rate of 220rpm under the vacuum of less than 10 torr to produce the pellets. The pellets obtained were dried with a hot air dryer for 12 hours and produced to a film with the 10 thickness of 20 gn, using the blown film forming machine. The resulting film was tested for mechanical properties such as tensile strength, tear strength, and adhesion strength. The results were shown in Table 1. Comparative Example 2 15 In this comparative example, 5kg of the aliphatic/aromatic copolyester resin, which was prepared by the method of Comparative Example 1, 3kg of a polylactic acid 2002D (Natureworks), 2kg of a corn starch, 60g of PE-wax as a lubricant, 8g of oleamide as a slip agent, 50g of a glycerin 20 as a starch plasticizer, Sg of alum as a starch structure destroying agent, and 300g of an ethylenevinyl acetate as a compatibilizer all were mixed enough for 5 minutes using a super mixer, at the temperature of 180'C . The mixture was extruded at a rotation rate of 200rpm under the vacuum of 10 26 torr or less using the twin screw extruder, having a screw with a diameter of cp 75 to produce the pellets. The pellets obtained were dried with a hot air dryer for 12 hours and produced to a film with the thickness of 5 20 gm, using the blown film forming machine. The resulting film was tested for mechanical properties such as tensile strength, tear strength, and adhesion strength. The results were shown in Table 1. Comparative Example 3 10 In this comparative example, 4kg of the aliphatic/aromatic copolyester resin, which was prepared by the method of Example 1, 4kg of a polylactic acid 2002D (Natureworks), 50g of PE-wax as a lubricant, and 5g of oleamide as a slip agent all were mixed enough for 3 minutes 15 using a super mixer, at the temperature of 180 0 C. The mixture was extruded at a rotation rate of 200rpm under the vacuum of 10 torr or less using the twin screw extruder, having a screw with a diameter of p 7 5 to produce the pellets. The pellets obtained were dried with a hot air dryer 20 for 12 hours and produced to a film with the thickness of 20 pm, using the blown film forming machine. The resulting film was tested for mechanical properties such as tensile strength, tear strength, and adhesion strength. The results were shown in Table 1. 25 27 Table 1 Tensile strength Tear strength (kgf/cm 2 ) (kgf/cm 2 ) Adhesion strength (kgf/15mm) TD MD TD MD Example 1 510 580 300 340 1.30 Example 2 500 570 290 330 1.20 Example 3 490 550 310 320 1.25 comparative 450 460 250 270 1.13 example 1 comparative 430 440 200 230 0.97 example 2 comparative 480 500 260 280 0.87 example 3 TD: Vertical direction of the blown film 5 MD: Horizontal direction of the blown film In this example, the tensile strength was measured according to the KS M 3509 testing method, and the tear strength was measured by using a universal testing machine according to the KS M 3509 at the temperature of 230C, and 10 the relative humidity of 50%. The tensile strength was measured at a rate of 500mm/minute, and the adhesion strength was measured according to the KS M7132 method. As can be seen in Table 1, it is confirmed that the biodegradable resin compositions (Examples 1 to 3) containing 15 an aliphatic/aromatic copolyester as a main ingredient, which 28 was produced by using a mixed solution of ethylene glycol as a catalyst, a polylactic acid, starch, and a high-temperature initiator, show good mechanical properties (tensile strength, tear strength, adhesion strength) compared to the resins of 5 Comparative Examples 1 to 3 which were prepared without a catalyst, and a high-temperature initiator. Test Example 1 The physical properties of the film made of the biodegradable resin composition change depending upon the 10 contents of a high-temperature initiator To check the optimal content range of the high temperature initiator, the amount of the high-temperature initiator was added variously as in Table 2. The ratio of the aliphatic/aromatic copolyester(50%) to polylactic 15 acid(30%) starch(20%) was fixed and constant. The sample of the film was prepared as in Example 1, and tested for the physical properties such as tensile strength, tear strength, and adhesion strength. The results were shown in Table 2. 20 25 29 Table 2 Physical property Tensile Adhesion Content of high- Tear strength strength k strength temperature (kgf/cm 2 ) (kgf/cm 2 ) (kgf/15mm) initiator TD MD TD MD 0.05% 450 470 240 230 1.0 0.1% 480 500 230 220 1.1 0.2% 490 510 240 230 1.0 0.5% 500 540 300 280 1.2 0.8% 530 570 350 310 1.3 1.0% 520 565 340 320 1.27 As can be seen in Table 2, it was confirmed that, if the content of the high-temperature initiator was less than 5 0.lwt%, the physical property of the film became little improved, and if the content was 1.Owt% or more, the physical property was not improved, proportional to the content increase. Test Example 2 10 To check the biodegradability of the samples prepared in Examples 1 to 3 and Comparative examples 1 to 3, the film having a thickness of 20 gi was tested by the weight loss method through burying it in soil for 3 months. The samples were collected at a certain period after burying, and the 30 foreign substances were removed with water and alcohol. The biodegradability was measured by dividing the weight after burying by the weight before burying. The burying was carried out to a depth of 30 cm in a hill, which invited the 5 coexistence of aerobic microorganisms and anaerobic microorganisms. The measuring results are as follows. Table 3 Biodegradability Classification (rate of weight loss %) Example 1 97.3 Example 2 98.1 Example 3 96.2 comparative example 1 97.9 comparative example 2 93.5 comparative example 3 84.0 10 As can be seen in Table 3, the films containing starch from Example 1 to Comparative example 2 showed that all the samples were completely degraded after 3 months of burying. The film without starch in Comparative example 3 showed that the sample had slowly degraded. 15 Using the method of the present invention, the process is simple and production costs are reduced. Further, the 31 biodegradable film with improved mechanical and chemical properties is effectively obtained compared to conventional methods. 5 32

Claims (12)

1. A biodegradable resin composition, comprising: 40 to 80wt% of an aliphatic/aromatic copolyester, 8 to 40wt% of a polylactic acid, 5 0.1 to 1.0 wt% of a peroxide type high-temperature initiator, 10 to 40wt% of starch, 1 to 10wt% of a starch plasticizer, 0.1 to 5wt% of a starch structure destroying agent, and 10 0.8 to 3.Owt% of a compatibilizer, based on 100wt% of the resulting biodegradable resin composition.

2. The biodegradable resin composition according to claim 1, wherein the aliphatic/aromatic copolyester is prepared by 15 using a synthetic catalyst formed as a mixed solution by dissolving germanium compound and potassium compound in ethylene glycol.

3. The biodegradable resin composition according to claim 20 1, wherein, among ingredients of the aliphatic/aromatic copolyester, a dimethylterephtalate ranges from 0.45 to 0.55 mole, an adipic acid ranges from 0.45 to 0.55 mole per 1 mole of acid ingredient, 1 mole of glycol ingredient is 1,4-butane alone or a mixture ingredient of 0.8 mole or more of 1,4 25 butane. 33

4. The biodegradable resin composition according to claim 1, the germanium compound is added at an amount ranging from 0.01 to 1.0 wt% per the resulting polyester, the potassium compound is added at an amount ranging from 0.1 to 1.0 wt% 5 per the germanium compound, and the ethylene glycol is added at an amount ranging from 10 to 100 wt% per the germanium compound and the potassium compound.

5. The biodegradable resin composition according to claim 10 1, wherein the peroxide type high-temperature initiator is one selected from the group consisting of a di-tertiary-buthylperoxide, a di-tertiary-buthylperoxyhexahydroterephthalate, a di-tertiary-buthylperoxy-3,3,5-trimethylcyclohexane 15 and a tertiary-buthylperbenzoate.

6. The biodegradable resin composition according to claim 5, wherein the peroxide type high-temperature initiator is 20 contained at an amount ranging from 0.1 to l.Owt% based on 100wt% of the resulting biodegradable resin composition.

7. The biodegradable resin composition according to claim 1, wherein the starch is one selected from the group 25 consisting of cornstarch, tapioca starch, potato starch, 34 wheat starch, rice starch, modified starch, such as alpha starch, oxidized starch, acid-treated starch, acetyladipic acid starch, octenylsuccinate starch, and a mixture of these two or more. 5

8. The biodegradable resin composition according to claim 1, wherein the compatibilizer is one selected from the group consisting of a glycidylmethacrylate, an ethylenevinylalcohol, a polyvinylalcohol, and an ethylene vinylacetate. 10

9. A method of manufacturing the biodegradable resin composition according to claim 1, the method comprising: mixing 40 to 80wt% of an aliphatic/aromatic copolyester, 10 to 40wt% of a polylactic acid and 0.01 to 1.0 wt% of 15 peroxide type high-temperature initiator, based on 100wt% of the resulting biodegradable resin composition in a mixer for 5 to 15 minutes, extruding the resulting mixture in a twin screw extruder under the vacuum of 10 torr or less at a temperature 20 ranging from 150 to 200 0 C, and pelletizing the extruded material using a pelletizer after cooling.

10. A biodegradable film made up of the biodegradable resin 25 composition according to claim 1, wherein the film is one 35 selected from the group consisting of garbage bags, shopping bags, food packing film, industrial packing film, agricultural film, disposable table cloth and rollbacks. 5

11. A biodegradable resin composition substantially as hereinbefore described with reference to any one of the examples.

12. A method of manufacturing a biodegradable resin 10 composition substantially as hereinbefore described with reference to any one of the examples. 36