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US5227415.Pdf ||||||||||||| US00522745A United States Patent (19) 11) Patent Number: 5,227,415 Masuda et al. 45) Date of Patent: Jul. 13, 1993 (54) BIODEGRADABLE PLASTIC 56 References Cited COMPOSITON U.S. PATENT DOCUMENTS 75) Inventors: Takashi Masuda, Abiko; Akio 4,841,968 6/1989 Dunn et al. ......................... 606/231 Matsuda, Kashiwa; Kazuhisa 4,863,472 9/1989 TSrmala .... ... 626/66 Murata, Tsukuba; Shinsuke 4,968,317 11/1990 Törmala ........ ... 606/76 Yamazaki, Ibaraki, all of Japan 5,076,983 2/1991 Loomis et al. ...................... 528/359 73) Assignee: Director-General of Agency of Primary Examiner-John Kight, III Industrial Science and Technology, Assistant Examiner-Jeffrey Culpeper Mullis Japan Attorney, Agent, or Firm-Lorusso & Loud (21) Appl. No.: 668,153 (57) ABSTRACT (22) Filed: Mar. 12, 1991 A biodegradable plastic composition for use in produc tion of shaped articles includes polyglycolide and a high (30) Foreign Application Priority Data molecular weight substance selected from poly(3- hydroxybutyric acid), a copolymer of 3-hydroxybutyric Apr. 6, 1990 JP Japan .................................... 2-92816 acid and 3-hydroxyvaleric acid, polycaprolactone, Apr. 6, 1990 (JP Japan .................................... 2-92.817 polyglutamic acid, polyolefin, polyvinyl alcohol, poly 51) Int. Cl.......................... C08J 3/00; C08L 67/04; alkylene oxide, cellulose acetate and mixtures thereof, C08G 63/02; C08G 63/08 the amount of the polyglycolide being 5-60% based on 52 U.S. C. ........................................ 524/17; 524/18; the total weight of the polyglycolide and the high mo 524/306; 524/315; 524/317; 528/354; 528/359 lecular weight substance. 58) Field of Search ................... 524/17, 18, 306, 315, 524/317; 562/553; 528/354, 359 5 Claims, No Drawings 5,227,415 2 lide may be obtained by a method including the steps of BIODEGRADABLE PLASTIC COMPOSITION adding water or a lower alcohol to ordinary polyglyco lide to cause depolymerization reaction to form glycolic BACKGROUND OF THE INVENTION acid or a lower alcohol ester thereof, and heating, it to This invention relates to a biodegradable plastic com cause polymerization (U.S. Pat. No. 2,668,162 issued to position. More particularly, this invention relates to a C. E. Lowe). Such a high molecular weight polyglyco biodegradable plastic composition containing poly lide is suitably used for the purpose of the present inven glycolide and one or more specific high molecular tion because of its excellent moldability. In the present weight substances. invention, however, a polyglycolide having a relatively Plastics are widely utilized in daily life as various 10 low molecular weight obtained by reacting carbon shaped articles such as films, bags and containers. As monoxide and formaldehyde in the presence of an the majority of plastics is not decomposed in natural acidic catalyst can also be used as the starting material. environment, however, a serious problem of environ It is without saying that polyglycolides produced by mental destroy or pollution due to waste plastics has any known methods other than those described above now been raised with increase in the amount of plastics 15 may be used for the purpose of the present invention. In used. For example, a movement of prohibiting or limit general, a polyglycolide having a number average mo ing the use of plastics as packaging materials is being lecular weight higher than 500, preferably within the encouraged in recent years in Europe and America. range from 800 to 200,000 can advantageously be used Accordingly, the development of plastics decompos in the present invention. able (biodegradable) by microorganisms or enzymes in 20 The high molecular weight substances to be used in the soil is now being carried out widely. the present invention as the other constituent of the In the past, polyglycolide was known to be one of the composition, i.e. the poly(3-hydroxybutyric acid), a biodegradable high molecular compounds. This com copolymer of 3-hydroxybutyric acid and 3-hydroxyval pound has a high melting point and so is excellent in eric acid, polycaprolactone, polyglutamic acid, polyole heat-resistance, but has high crystallinity and is brittle. 25 fin, polyvinyl alcohol, polyalkylene oxide and cellulose Accordingly, this compound alone has not yet been acetate, are all commercially available. Accordingly, used practically as a plastic material. these commercially available high molecular weight SUMMARY OF THE INVENTION substances can be used as such for the other constituent It is an object of the present invention to provide a 30 of the present invention. biodegradable plastic composition practically useful as The molecular weight of the high molecular weight a material for shaped plastic articles. substance varies with the kind of the substance but is In accordance with one aspect of the present inven generally in the range of 2,000-5,000,000, preferably tion, there is provided a biodegradable plastic composi 10,000-1,000,000. More particularly, in case poly(3- tion comprising polyglycolide and a high molecular 35 hydroxybutyric acid) is used, a preferable molecular weight substance selected from the group consisting of weight is within the range of 20,000-1,000,000, more poly(3-hydroxybutyric acid), a copolymer of 3-hydrox preferably 300,000-900,000. In case of a copolymer of ybutyric acid and 3-hydroxyvaleric acid, polycaprolac 3-hydroxybutyric acid and 3-hydroxyvaleric acid, the tone, polyglutamic acid, polyolefin, polyvinyl alcohol, proportion of both components is preferably within the polyalkylene oxide, cellulose acetate and mixtures range of 1:0.05 to 1:0.3 and the molecular weight thereof, said polyglycolide being present in an amount thereof is preferably within the range of of 5-60% based on the total weight of said polyglyco 10,000-1,000,000, more preferably 300,000-900,000. In lide and said high molecular weight substance. case of polycaprolactone, the molecular weight is pref. In another aspect, the present invention provides a erably within the range of 20,000-100,000, more prefer shaped article obtained by a method comprising the 45 ably 30,000-60,000. In the case of polyglutamic acid, steps of providing the above biodegradable plastic com the molecular weight is preferably within the range of position, heating said composition to a temperature 20,000-80,000, more preferably 30,000-70,000. Illustra sufficient to melt said composition, and molding said tive of polyolefins suitably utilizable in the present in melted composition into a desired shape. vention are homopolymers of lower olefins and copoly Other objects, features and advantages of the present 50 mers of lower olefins themselves or with other mono invention will become apparent from the detailed de mers, such as polyethylene, polypropylene, polybutyl scription of the invention to follow. ene, ethylene/propylene copolymer and ethylene/vinyl DETAILED DESCRIPTION OF THE acetate copolymer. The molecular weight of the poly PREFERRED EMBODIMENTS OF THE olefin used is preferably within the range of 55 20,000-1,000,000, more preferably 30,000-200,000. In INVENTION case of polyvinyl alcohol, the preferable molecular The polyglycolide to used in the present invention as weight is within the range of 15,000-100,000, more one of the constituents is a crystalline polymer obtained, preferably 20,000-90,000. Illustrative of suitable polyal for example, by heating glycolic acid, an ester thereof, kylene oxides are polyethylene oxides, polypropylene sodium chloroacetate or glycolide (U.S. Pat. No. oxides and the like lower polyalkylene oxides. The 2,585,427 issued to M. L. Beck; Chujo, K. et al, Mak molecular weight of the polyalkylene oxide is prefera romolekulare Chem., 100, 262(1967); and Hirono, H. et bly within the range of 2,000-5,000,000, more prefera al, Kogyo Kagaku Zasshi, 67, 604(1964)). Polyglycolide bly 10,000-1,000,000. In case cellulose acetate is used in is advantageously prepared by reacting carbon monox the present invention as the starting material, its molec ide with formaldehyde or paraformaldehyde in the 65 ular weight is preferably within the range of presence of an acidic catalyst to form a polyglycolide 10,000-200,000. (Masuda, T. et al, Japanese patent (Tokkyo Kokoku) The molecular weights of polyglycolide and the high No. 56-34,205) Very high molecular weight polyglyco molecular weight substance are suitably selected ac 5,227,415 3 4. cording to the kind of the high molecular weight sub This invention will now be illustrated in more detail stance and the desired properties (biodegradability and by way of example and comparative example. moldability) of the composition. If the high molecular weight substance by itself shows poor moldability, the EXAMPLE 1 polyglycolide is desired to have a molecular weight of 5 In carbon monoxide atmosphere, a stainless steel at least 20,000. autoclave was charged with 10.0 g of trioxane, 30 ml of It is of interest that other various plastic substances dichloromethane and 4 mmol of chlorosulfonic acid. such as polyvinyl chloride and polystyrene are ex The autoclave was then charged with carbon monoxide tremely poor in blend performance with the polyglyco under pressure until the inner pressure became 55 lide, and a biodegradable plastic shaped article cannot O kg/cm2, and the mixture was reacted together for 2 be obtained practically from a blend of these substances hours while stirring the mixture and elevating the tem and the polyglycolide. perature up to 180' C. After completion of the reaction, The biodegradable plastic composition of this inven unreacted carbon monoxide was discharged and the tion can easily be obtained by blending the polyglyco content of the autoclave was washed out with acetone lide with one or more of the high molecular weight 15 whereby 8.6 g of an acetone-insoluble polymer (poly substances under fusion. The resulting molten blend can glycolide having a molecular weight of about 1200 or then be processed by the aid of a conventional heat higher) and 4.3 g of an acetone-soluble polymer (poly molding machine to manufacture molded articles of a clycolide having a molecular weight less than about desired shape.
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