THERMOPLASTIC BIODEGRADABLE RESINS AND A PROCESS OF PREPARATION THEREOF

Abstract: A thermoplastic biodegradable resin having a number average molecular weight of 25,000 SIMILAR 45,000, which is prepared by polycondensing one or a plurality of dicarboxylic acids represented by formula (I) with one or a plurality of diols represented by formula (II), wherein R and R' are both hydrogen or are both methyl, n is 2 to 8 and m is 2 to 6.

Description: THERMOPLASTIC BIODEGRADABLE A PROCESS OF PREPARATION THEREOF TECHNICAL FIELD: The present invention relates to thermoplastic biodegradable resins having a number average molecular weight of 25,000 to 45,000 and to method for making the same. BACKGROUND ART: Recently, environmental pollution problems have taken on increas¬ ing worldwide concern, especially because the plastics used for all purposes are not degradable. Such undegradabie plastics therefore contribute to the destruction of the natural environment. Attention is therefore now being directed to ways in which the problem of the disposal of waste undegradabie plastics can be solved. An aliphatic polyester is known which is biodegradable! Journal of Macromol , SCI-Chem., A-23(3), 1986, 393-409). It has a variety of uses as medical, agricultural, fishery and packaging material and other applications are being developed. However, because the conventional aliphatic polyester has a low melting point and a high melt index, because of the structure of the main chain and crystal I ini ty, and has low heat-resistance and unsatis- factory mechanical properties, the utility of this polymer mater ial has been limited. (R&D Evaluation Report No. 47 Chart 3). Japanese laid-open patent No. 4-189822 and 4-189823 disclose a process for the preparation of aliphatic polyester. But here, because the polyester has a low melting point and a molecular weight of less than 20,000, the polyester is not used as industrial material. A method is known in which an isocyanate is introduced into the polyester. However, because the method introduces isocyanate, it is not desirable to use the modified substance as an industrial material. Isocyanate is harmful to the human body, and further it is hard to cleave the ester linkage in comparison to the polyester into which the isocyanate is not introduced. Also, the biodegradabi I ity of the isocyanate modified polymer is decreased. A need therefore continues to exist for a biodegradable polyester of improved mechanical properties and heat resistance. DISCLOSURE OF INVENTION Accordingly, one object of the present invention is to provide a biodegradable aliphatic polyester having improved properties by con¬ trolling the reaction mole ratio of dicarboxylic acid and diol, the amount of catalyst and the reaction temperature, and by providing for separate times of catalyst addition to the reaction mixture. Another object of the invention is to provide a polyester product of increased number average molecular weight ranging from 25,000- 45,000 by a polycondensation reaction, while avoiding the addition of an isocyanate or aromatic polyester component. Briefly, these and other objects of the invention as hereinafter will become more readily apparent can be attained by a biodegradable thermoplastic having a number average molecular weight of 25,000- 45,000 which is prepared by polycondensing one or a plurablity of dicarboxylic acids represented by formula ( I ) with one or a plurablity of diols represented by formula! II ) : R O O C — - C H 2 — 7 j C O O R ' ( I ) H O ^ C H ; — ^ O H ( II ) wherein R and R ' are both hydrogen or are both methyl, n is 2 to 8 and m is 2 to 6. BEST MODE FOR CARRING OUT THE INVENTIONS In the present invention, a thermoplastic biodegradable resin having a number average molecular weight of 25,000-45,000 is prepared by polycondensation of a dicarboxylic acid represented by formula ( I ) or mixtures thereof with a diol represented by formula (II) or mixtures thereof: ROOC — X- CH-. — - COOR' ( I ) HO CH, —^ OH (II) wherein R and R' are both hydrogen or are both methyl, n is 2 to 8 and m is 2 to 6. During the course of the esterification or the ester-exchange re¬ action in accordance with the process of the present invention, a di¬ carboxylic acid of 4 to 10 carbon atoms is preferred and one or a plurablity of dicarboxylic acids optionally may be employed. A preferred reactant is succinic acid or dimethyl succinate when using a single reactant of formula ( I ) and is succinic acid or dime¬ thyl succinate as a component acid when using a plurality of dicarboxylic acid reactants. The weight ratio of succinic acid or dimethyl succinate to other alkylene dicarboxylic acid preferably ranges from 70:30-100:0. If the amount of the other alkylene dicarboxylic acid component is more than 30% by weight, the melting point of the product may undesirably decrease. A diol reactant of 2 to 6 carbon atoms is preferred and a repre¬ sentative diol of 2 to 6 carbon atoms is a single diol or a plurality of diols selected from the group of ethylene glycol, 1 ,3-propanediol , 1 ,4-butanediol , 1,6-hexanediol , and more preferably is 1,4-butane- diol when a single diol is used, and when a plurality of diols is employed, 1 ,4-butanediol is preferably one of the diols. The weight ratio of 1 ,4-butanediol to other diols of the plurality of diols is preferably 50:50-100:0. The amount of other diols in the plurality of diols has an effect on the melting point of the polymer, and if the amount of other diols is more than 50% by weight, the properties of the product may be adversely affected such as the melting point. The mole ratio of the dicarboxylic acid to diol is preferably 1: 1.2-2. If the mole ratio of diol reactant to dicarboxylic acid reactant is less than 1.2, the color of the resin is inferior and the reactivity decreases. If the mole ratio is more than 2, increases in cost of preparation are undesirably incurred for any improvement of reactivity gained. The temperature at which the esterification or ester-exchange reaction is conducted preferably ranges from 190 to 220°C. Tetrabutyl titanate catalyst can be used alone as the catalyst or a mixture of tetrabutyl titanate and one or more other catalysts selected from the group consisting of calcium acetate, zinc acetate, dibutyltinoxide and tetrapropyl titanate which is added to the re¬ action medium at the initiation of esterification or the ester- exchange reaction. The amount of catalyst employed preferably ranges from 0.005 to 2% by weight. If the amount of catalyst is less than 0.005 wt.%, the reaction rate is low. On the other hand, if the amount of catalyst exceeds 2 wt.%, the color of polymer is inferior although the reaction rate is high. At the end of the esterification or ester-exchange reaction or at the start of the polycondensation reaction dibutyltinoxide can be added alone as the catalyst or as a component of plurality of cata¬ lysts, wherein the other catalysts are selected form the group consisting of tetrabutyl titanate, tetrapropyl titanate, calcium acetate and tetraisopropyl titanate. The amount of the dibutyltinoxide catalyst is preferably in the range of 0.2 to 1.5 wt.%. If the amount of catalyst employed is less than 0.2 wt.%, the inherent viscosity and molecular weight of the product do not increase and the reaction rate is low. If the amount of catalyst used exceeds 1.5 wt.%, the color of the product is inferior although the reaction rate is high. A stabi I izer should be added to the reaction medium whi le ta ing the color of the resulting resin product into consideration. Suitable stabilizers include trimethyl phosphate alone or a mixture of trime- thyl phosphate with one or more other stabilizers selected from the group consisting of neopentyl-diaryl-oxytr iphosphate, tr iphenylphos- phine, tr iphenylphosphate and phosphate. The amount of stabilizer employed preferably ranges from 0.1 to 0.8 wt.%. If the amount of stabilizer used is less than 0.1 wt.%, the effect of the stabilizer is not sufficient, and if the amount exceeds 0.8 wt.%, the time required tor the reaction is extended and the properties of the product are adversely affected. A small amount of an adjusting agent of less than 0.015 wt.% can be added to the reaction mixture to prevent the polymer from yel lowing. The polycondensat ion temperature preferably ranges from 240 to 270°C. If the reaction temperature is less than 240°C, the time required for the polycondensat ion reaction is extended. If the temperature exceeds 270°C, the polymer is pyrolyzed and the resin color is bad. The time required for the polycondensat ion reaction preferably ranges from 250 to 360 min and is affected by the amount of catalyst and stabilizer employed. The longer the polycondensation period, the higher the molecular weight. Therefore, the time required for the polycondensation reaction should be controlled according to the molecular weight of the product desi red. In addition, to the resin product of the present invention can be added an inorganic filler such as talc or calcium carbonate in an amount of 5 to 60 wt.%. Such compounded materials provide advantages such as low cost, improved tensile strength and low melt index. Because the so-obtained thermoplastic biodegradable resin exhibits improved biodegradabi I i ty and properties which prevent envir- onmental pollution, it is useful as a resin material for the prepara¬ tion of medical, agricultural, fishery and packaging materials, and also as a raw material for the manufacture of office supply items and electric home -appl iances, as well as other areas including industry where biodegradabi I ity is required. Having now generally described this invention, a further under¬ standing can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified. < EXAMPLE 1 > 146g of dimethylsuccinate, 162g of 1 ,4-butanediol and 0.03g of tetrabutyl titanate as catalyst is added to heat-melting condensation reactor, and the mixture is esterified until the approximate theoretical amount of methanol is produced at the temperature of 200°C. After ester-exchange step is completed, 0.3g of tetrabutyl tita¬ nate, 0.θg of dibutyltinoxide as catalyst, 0.4g of trimethyl phos- phate as stabilizer and 0.01g of cobalt acetate as adjusting agent slurried in 1 ,4-butanediol is added thereto and mixed for 10 min at the temperature of 230°C and then the temperature is elevated to 250 °C and polycondensation is allowed to proceed for 5 hrs under o.3 m Hg pressure. The product is then removed from the reactor. < EXAMPLE 2-15 > The same procedure as described in Example 1 is conducted with the amounts of components shown in Table 1. The reaction mixture is esterified until the approximate theoretical amount of water is produced in the case of using succinic acid. < COMPARATIVE EXAMPLE 1 > 118g of succinic acid and 127.5g of 1 ,4-butanediol are added to a heat-melting condensation reactor and mixed under an atmosphere of nitrogen, and esterified until the appromixate theoretical amount of water is produced at the temperature of 210°C. After esterification is completed, 0.6g of tetrabutyl titanate slurried in 1,4-butanediol is added thereto under an atmosphere of ni trogen. The above mixture is mixed for 10 min at the temperature of 200°C and the temperature is elevated to 220°C and allowed to polycondense for 5 hrs under 0.3 mmHg pressure. The product is then removed from the reactor. < COMPARATIVE EXAMPLE 2 > 118g of succinic acid and 85g of ethyIenegIycoI are added to a heat-melting condensation reactor and mixed under an atmosphere of nitrogen and esterified until the approximate theoretical amount of water is produced at a temperature of 210°C. After esteri fication is completed, 0.5g of tetrabutyl titanate slurried in ethylene glycol is added thereto under an atmosphere of ni trogen. The above ingredients are mixed for 10 min at the temperature of 220°C and the temperature is elevated to 220°C and allowed to poly¬ condense for 5 hrs under 0.3 mmHg pressure. The product is then removed from the reactor. The amounts of components of the reaction and the properties of the prepared resin are provided in Table 1. The various properties in the examples and comparative examples were measured in accordance with the following procedures. Measuring Methods 1. Intrinsic viscosity measured at 30°C in o-chlorophenol . 2. Melting point measured using a Differential Scanning Cal¬ orimeter (DSC) 3. Molecular weight measured in a mixed solvent of o-chloro¬ phenol and chloroform using gel-chromato- graphy 4. Biodegradabi I ity measured using the procedure of ASTM-D4300. After 100mg of 40μm thickness of aliphatic polyester film was added to 100 μmole of phosphoric acid buffer solution (pH 7.0), 0.2mg of Aspergillus Niger was added thereto to make 1 ( volume of total reaction solution. After this reaction solution was stirred at 150 rpm for 60 days at a temperature of 37°C, the sample was extracted and biodegrad¬ abi I ity was estimated by change of molecular weight. Wi - Wf Percentage of weight reduction x 100 Wi (wherein Wi is the initial weight, Wf is the weight after 60 days) The resin products of the comparative examples, because of their low molecular weights and viscosities, are not suited for the forma¬ tion of molded articles. Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifi¬ cations can be made thereto without departing from the spirit or scope of the invention as set forthe herein.

Claims: WHAT IS CLAIMED IS; 1. A thermoplastic biodegradable resin having a number average molecular weight of 25,000-45,000, which is prepared by polyconden¬ sing one or a plurality of dicarboxylic acids represented by formula ( I ) with one or a plurality of diols represented by formula (II): ROOC —(—CH- — h COOR' (I) HO (-CH ! — OH (II) wherein R and R ' are both hydrogen or are both methyl, n is 2 to 8 and m is 2 to 6. 2. A method of preparing a biodegradable thermoplastic resin by reacting a dicarboxylic acid of 4 to 10 carbon atoms and a diol of 2 to 6 carbon atoms in a reaction medium in a first stage of a ester- ification or an ester-exchange reaction and a final stage of a poly¬ condensation reaction, wherein, from 0.005 to 2 wt.% of a catalyst is present in the first stage of esterification or ester-exchange reaction and wherein from 0.2 to 1.5 wt.% of a catalyst, 0.1 to 0.8 wt.% of a stabilizer and less than 0.015 wt.% of an adjusting agent are added to the reaction medium at the end of the esterification or ester-exchange reaction or at the start of polycondensation. 3. The method of Claim 2, wherein said carboxylic acid re- actant is succinic acid or dimethyl succinate or a mixture of dicar- boxyI ic acid reactants containing succinic acid or dimethyl succinate. 4. The method of Claim 2, wherein said diol is one or more diols selected from the group consisting of ethylene glycol, 1,3- propane diol, 1,4-butanediol , and 1,6-hexanediol . 5. The method of Claim 2, wherein the mole ratio of said di- carboxylic acid to said diol ranges from 1:1.2-2. 6. The method of Claim 2, wherein said catalyst added to the reaction medium at the initiation of esterification or ester- exchange is tetrabutyltitante or a mixture of tetrabutyltitanate and one or more catalysts selected from the group consisting of calcium acetate, zinc acetate, dibutyltinoxide and tetrapropyl titanate. 7. The method of Claim 2, wherein said catayst added to the reaction medium at the conclusion of the esterification or ester- exchange reaction or at the initiation of polycondensation is tetra- butyltinoxide or tetrabutyltinoxide and one or more other catalysts selected from the group consisting of tetrabutyl titanate, tetrapropyl titanate, calcium acetate and tetraisopropyl titanate. 8. The method of Claim 2, wherein said stabilizer is tri- methylphosphate or mixture of trimethylphosphate and one or more stabilizers selected from the group consisting of neopentyl-diaryl- oxytriphosphate, triphenyl phosphine, triphenyl phosphate and phos¬ phate. 9. The method of Claim 2, wherein said adjusting agent is cobalt acetate. 10. The method of Claim 2, wherein the temperature of said polycondensation reaction is 240~270°C. 1 1. The method of Claim 2, wherein the time of said polycon¬ densation reaction ranges from 250-360 min. AMENDED CLAIMS [received by the International Bureau on 25 May 1994 (25.05.94); original claim 3 cancelled; original claims 1, 2, 4-7 amended; other claims unchanged (3 pages)] 1. A biodegradable thermoplastic resin characterized by naving a number average molecular weight of 25,000-45,000, which is prepared by poly-condensing the compound of following formula(la) or a mixtur ' e of the compound of following formula(la) and one or more selected from compounds of following formula(lb) with one or more selected from compounds of following formula(II). ROOC- ( CH 2 ) 2 -COOR —(la) ROOC- ( CH- ) -COOR —(lb) HO- ( CH 2 )m -OH —( II) Wherein R is hydrogen or methyl, m is 2 to 6 and n is 3 to 8 2. A method of preparing a biodegradable thermoplastic resin characterized by reacting the compound of following formula (la) or a mixture of the compound of following formula (la) and one or more selected from compounds of the following formula (lb) with one or more selected from compounds of following formula (II) in a reaction medium in a first stage of a esterif ication or an ester-exchange reaction and a final stage of a polycondensation reaction, wherein, from 0.005 to 2wt.% of a catalyst is present in the first stage of ester i fication or ester-exchange reaction and wherein from 0.2 to 1.5wt.% of a catalyst, 0.1 to 0.8wt.% of a stabilizer and less than 0.015wt.% of an adjusting agent is added to the reaction medium at the end of the ester i f ication or ester-exchange reaction or at the start of polycondensation. ROOC- ( CH 2 ) 2 -COOR —(la) ROOC- ( CH 2 ) n -COOR —(lb) HO- ( CH_ )m -OH —(II) Wherein R is hydrogen or methyl, m is 2 to 6 and n is 3 to 8 3. (deleted) 4. The method of Claim 2, wherein said formular( II ) is one or more diols selected from the group consisting of ethylene glycol, 1 ,3-propanediol , 1 ,4-butanediol , and 1 ,6-hexanediol . 5. The method of Claim 2, wherein the mole ratio of said formular(la) or formular(la) and formular(lb) to said tormuIar( II ) ranges from 1 :1.2-2. 6. The method of Claim 2, wherein said catalyst added to the reaction medium at the initiation of esterification or ester- exchange is tetrabutyl titanate or a mixture of tetrabutyltitanate and one or more catalysts selected from the group consisting of calcium acetate, zinc acetate, dibutyltinoxide and tetrapropyl titanate. 7. The method of Claim 2, wherein said catalyst added to the reaction medium at the conclusion of the esterification or ester- exchange reaction or at the initiation of polycondensation is tetra¬ butyltinoxide or tetrabutyltinoxide and one or more other catalysts selected from the group consisting of tetrabutyl titanate, tetrapropyl titanate, calcium acetate and tetraisopropyI titanate. 8. The method of Claim 2, wherein said stabilizer is tri¬ methylphosphate or mixture of trimethylphosphate and one or more stabilizers selected from the group consisting of neopentyl-diaryl- oxytriphosphate, triphenyl phosphine, triphenyl phosphate and phos¬ phate. 9. The method of Claim 2, wherein said adjusting agent is cobalt acetate. l 0. The method of Claim 2, wherein the temperature of said polycondensation reaction is 240-270°C. 1 1. The method of Claim 2, wherein the time of said polycon¬ densation reaction ranges from 250-360 min.

Inventors: CHAE HOON, CHO SOO IL, HWANG KI HO, JUN JUNG NAM, KIM HYO YEOL, CHAE, HOON, CHO, SOO, IL, HWANG, KI, HO, JUN, JUNG, NAM, KIM, HYO, YEOL
Applicants: SUNKYONG IND LTD, SUNKYONG INDUSTRIES
Application year: 1993
Main classification: C08G63
IPC codes: C08G63, C08L101