Abstract:
Biodegradable thermoplastic materials made of blends of starch esters and polyalkylene glycols with additions of polybasic aliphatic carboxylic acids and oxycarboxylic acids are improved with respect to water stability and mechanical characteristics and barrier properties by admixing to the blends aliphatic polycarbonates at levels of from 5:95 to 95:5 with the optional addition of ecologically compatible plasticizers and fillers. 
     These materials can be used for all goods which are to be packaged in films, in particular tobacco products, but also soap, paper tissues, toilet articles, and the like. In addition to biodegradability, said materials are characterized in that they may be fed to a special recycling process, but also to conventional recycling processes without adversely affecting them.

Description:
FIELD OF THE INVENTION 
     The invention relates to thermoplastic materials made of biodegradable polymer blends in the form of granule, molded parts, extrudates, films, etc. based on a blend consisting of starch esters, polyalkylene glycols and other biocompatible additives, the use thereof, and a package made of said biodegradable thermoplastic materials. 
     BACKGROUND OF THE INVENTION 
     As environmental problems continue to grow, there is an increased need for ecologically compatible materials on the polymer market. Attempts to take account thereof have resulted in the use of products from fermentatively produced polyesters, polyvinyl alcohols, starch and starch derivatives with a low degree of substitution, cellulose and cellulose derivatives as well as blends of these with conventional plastics, such as polyethylene. Those materials have a drawback in that they have insufficient durability, inferior mechanical properties, and, especially in the case of blends with conventional plastics, they are but incompletely biodegradable. Using derivatized starch, especially with a higher degree of substitution and modified with appropriate biodegradable plasticizers (DE 41 14 185), materials were achieved which are readily processed thermoplastically and are useful for injection molding, melt-spinning or the preparation of films. However, these materials are known to become brittle again rather soon. 
     According to the German Laid-Open No. 43 26 118, such brittleness can be prevented by modifying starch esters with a degree of substitution of &lt;3, preferably from 1.8 to 2.6, using polyethylene glycol (PEG). According to the German Laid-Open No. 44 18 678, it is possible to increase melt stabilization of blends from starch esters with a degree of substitution of &lt;3 and polyalkylene glycols and to improve their biodegradability by the addition of aliphatic, saturated or unsaturated, dicarboxylic acids and/or oxydicarboxylic acids and/or oxytricarboxylic acids. 
     However, such blends have insufficient water stability and mechanical properties, in particular elongation at break, impact resistance, and barrier characteristics, particularly in the case of molding compositions which are to be processed by injection molding, deep drawing, melt-spinning and extruding, especially into films. 
     Packages for cigarettes and other tobacco products are known in a variety of designs and made of a number of rather different materials, such as pouches, cans and hinged-lid boxes made of aluminum, tin, cardboard or plastic. The most widely spread package for cigarettes is the hinged-lid box according to DEP 34 14 214 (U.S. Pat. No. 5,379,889). This package achieves the required protection of its contents by a multi layer combination of different materials. It frequently consists of an inner layer of backed or printed aluminum foil, a cardboard or paper layer which in most cases is printed with specifications, and an outer closed wrapping of a thermally weldable film, e.g. of polypropylene (German Laid-Open Nos. 30 27 448 and 28 44 238). Other packages for cigarettes achieve the required protection of their contents from deformation, flavor and humidity losses by the combination of other materials, such as tin (i.e. metal sheet) and paper according to EP 087 483. 
     However, packages have also been described which exclusively consist of films of thermoplastics (German Laid-Open No. 42 26 640). 
     In order to improve the mechanical properties and the gas and water vapor permeability of thermoplastic films used for cigarette packages, plastic films of polypropylene or polyalkylene terephthalate are used which have been oriented by biaxial stretching and may be metallized (German Laid-Open No. 36 32 276, EP 454 003, EP 317 818). 
     All these solutions have drawbacks in that protection of the contents as well as water vapor and gas tightness can only be achieved if materials are selected comprising at least one aluminum foil, tin foil, or biaxially stretched plastic film. The necessary specifications are printed mostly onto a cardboard, tin or paper wrapping used in said combination. These complex packages require considerable expenditures for their preparation as well as for the packing material employed in order to maintain the quality of the packaged goods and to ensure the appeal of the package. 
     After use, the packages usually go to the waste and therefore contribute to the existing environmental problems. They decompose but very slowly or not at all when under weathering actions on dumping grounds and in nature. Their being reprocessed in the usual recycling processes requires that the materials be first separated. Such separation can be performed but incompletely in general. Moreover, these processes are adversely affected, e.g. by contamination of the process water. Reuse of the packages is out of the question for food law reasons. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to embody the features of the German Laid-Open Nos. 43 26 118 and 44 18 678 to greater advantage by improving the water stability, mechanical characteristics and barrier properties of the blends and to develop packages for good of various kinds consisting of one or more layers of films of thermoplastic materials which can be prepared without great technical expenditures, are light-weighted, have good barrier properties with respect to water vapor and gases without additional finishing or treatment, can be printed, and in addition are completely biodegradable, can be fed to a technical recycling process and will not adversely affect usual recycling processes. 
     This is solved by the invention which is defined by the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a cigarette package with an inner cardboard package and an outer wrapping consisting of the film according to the invention; 
     FIG. 2 shows a cigarette package made of one-layer material; 
     FIG. 3 shows a cigarette package made of cardboard material backed with the material according to the invention; and 
     FIG. 4 shows a sectional view of the material of the package of FIG. 3. 
    
    
     DESCRIPTION OF THE INVENTION 
     The blends according to the invention comprise starch esters, mainly starch acetate, with a degree of substitution of &lt;3, preferably from 1.8 to 2.6, and polyethylene glycols (PEGs) having molar masses of from 200 to 1000 g/mol, preferably from 200 to 600 g/mol, with or without addition of saturated dicarboxylic acids and/or oxydicarboxylic acids and/or oxytricarboxylic acids containing from 2 to 10 carbon atoms in a ratio of starch ester to polyfunctional carboxylic acid of from 100:2 to 1000:1, compounded with aliphatic polycarbonates and plasticizers as well as conventional additives, especially fillers. 
     Said aliphatic polycarbonates are polymers containing carbonic ester groups and having the formula ##STR1## wherein R 1  and R 2  are hydrogen or straight or branched chain C 1  to C 4  alkyl groups and may be the same or different or may be linked to one another, and n equals 250-10,000, preferably 350-3000. The use of polyethylene and polypropylene carbonates is particularly preferred. Aliphatic polycarbonates may also be polyalkylene copolymers or terpolymers. 
     As plasticizers, biocompatible compounds are preferably considered, i.e., polyethylene glycols, monoesters and diesters of polyethylene glycols with C 1  to C 10  carboxylic acids, such as triethyleneglycol diacetate, glycerol triacetate, and citric acid trialkylester. Further, esters of phthalic acid with C 1  -C 10  n-alkanols may be used, such as dimethyl phthalate, diethyl phthalate, or dibutyl phthalate. The ratio of starch acetate blend to aliphatic polycarbonates may be 5:95 to 95:5, preferably 30:70 to 70:30. The content of additives or plasticizers is from 0 to 30%, preferably from 0 to 15%. 
     These additives do not adversely affect the barrier properties and strength of the blends for packing materials. 
     For thermoplastic processing, it is particularly advantageous to premix starch acetate with a degree of substitution of &lt;3 with polyalkylene glycol with the addition of dicarboxylic acids and/or oxydicarboxylic acids and/or oxytricarboxylic acids, to extrude this premix and make it into granules and then to process the granules with appropriate aliphatic polycarbonates and additives. 
     In this way, thermoplastically processable molding compositions for all of the usual processing methods, for example, injection molding, deep drawing, melt-extrusion etc., may be produced. These molding compositions are completely biodegradable and have increased water stability, good mechanical properties, especially with films, increased elongation at break, and good barrier properties with respect to gas and water vapor. 
     For surface design in terms of promotional appealing prints, up to 35%, based on the total mass, of suitable fillers, such as chalk, talcum, anhydrite or kaolin, may be admixed to the films. The concentration of fillers is preferred to be from 1 to 30% by weight. 
     Due to the good barrier properties of the films with respect to water vapor and gases, especially air, without additional treatment by biaxial stretching or metal vapor deposition, one-layer packages, in particular, may be advantageously realized. This may be common selling packages, additional outer packages, shipping packages, or even refilling packages for a system of reusable selling packages. The one-layer embodiment of the package saves high expenditures in terms of preparation costs and packing materials while still ensuring the whole protection of the quality of the packaged good. For packages which have to meet especially high mechanical demands, however, multi layer film cuts may also be employed which may have different compositions according to their position within the ensemble. The biodegradability and compostability of the claimed packing films is excellent such that they are completely decomposed upon storing under rotting conditions for several weeks. 
     When known processes for recycling these articles are used, no failures will occur. 
     The following examples illustrate the benefits of the blends according to the invention. The solid starting components of the respective composition were briefly premixed in a high-speed mixer. Then, the liquid plasticizers were added to give a powdery dry blend. This was processed into granules using an extruder which were subsequently either injection-molded into ISO bars (80 mm×10 mm×4 mm) or extruded into films. 
     
                       TABLE 1______________________________________summarizes the base formulations selected for illustrating the results:  Stac    PPC    PEC         Oxalic   mass    mass   mass                      PEG 400                             Acid  mass                                     Plast. IIExample  %!      %!     %!    mass %!                             %!       mass %!______________________________________1 (comp.)  83.0.sup.(3)          --     --   16.6   0.41    --2 (inv.)  68.6.sup.(3)          13.7   --   17.2   0.48    --3 (inv.)  45.3.sup.(3)          --     45.3 9.1    0.32    --4 (inv.)  39.8.sup.(3)          --     39.8 16.0   0.40    4.0.sup.(1)5 (inv.)  66.4.sup.(4)          13.3   --   16.6   0.33    3.4.sup.(2)6 (inv.)  30.7.sup.(4)          20.0   40.0 6.1    0.20    3.0.sup.(2)______________________________________ Plast. II is .sup.(1) dimethyl phthalate. .sup.(2) triethylene glycol diacetate. The degree of acetylation of the starch was .sup.(3) 2.26 and .sup.(4) 2.24. Stac = starch acetate PEC = polyethylene carbonate PPC = polypropylene carbonate PEG = polyethylene glycol 
    
     One particular advantage of the blends according to the invention is that fillers are readily incorporated and, in addition to the advantage in expenses, certain mechanical characteristics can be improved. 
     
                       TABLE 2______________________________________Base Formulations with Fillers    Base formulationExample  according to example                    added fillers                              percent______________________________________ 7 (como.)    1               chalk     10                    TiO.sub.2 0.5 8 (inv.)    6               talcum    11.3                    TiO.sub.2 0.8 9 (inv.)    6               talcum    13.0                    TiO.sub.2 0.510 (inv.)    6               chalk     12.9                    TiO.sub.2 0.9______________________________________ 
    
     From compositions 1, 2, 3, 4, and 8, ISO bars were made and examined for mechanical characteristics. 
     
                       TABLE 3______________________________________Mechanical Characteristics of ISO Bars              Flex-              ural Tensile                          TensileEx-  IR,           Mod- Strength                          Strength at                                 Elongationam-  kg/    FS,    ulus,                   at Break,                          Break, at Break,                                        BIHple  m.sup.2       Mpa    Mps  Mpa    Mpa    Mpa    Nimm.sup.2______________________________________1     3.2   35.1   1455 19.9   19.6   1.3    642     8.5   35.5   1140 29.6   15.1   13     483    16.8   17.7    666 17.8   7.1    20.5   154    *      3.6     137 6.5    4.3    700     75    35.4   20.7   1157 24.8   8.9    107    75______________________________________ *100% unbroken, IR impact resistance, FS flexural strength (at conventional deflection), BIH ball indentation hardness 30 
    
     It can be clearly seen that the characteristics may be varied within broad ranges, wherein especially composition 4 is not useful for injection molding. Such compositions are more useful for film applications. 
     
                                           TABLE 4__________________________________________________________________________Mechanical Characteristics of Extruded FilmsTensile Strength       Tensile             Direction (?)                        PermcationElongation       Strength at             elongation,                   thickness,                        H.sub.2 O vapor,                              pentanc,Ex.   dir.Mpa  % Break, MPa             %     mm   g/m.sup.2 d                              g/m.sup.2 d__________________________________________________________________________1  1 7.2  7.2       5.1   67.0  0.03 60.5  12.1   t 5.3  4.27  1 10.7 5.1       5.3   31.5  0.03 55.9  10.8   t8  1 29.5 3.4       12.0  30.0  0.08 46.8  7.0   t9  1 11.2 3.7       69    291.7 0.14 31.6  5.7   t10 1 10.5 5.1       4.2   294.0 0.08 39.3  3.8   t__________________________________________________________________________ 
    
     Measuring conditions 
     Width: 15 mm 
     Direction with respect to film feeding: 1 longitudinal, t transversal 
     Measuring length: 50 mm 
     Test speed: 100 mm/min 
     initial force: 0.1 N 
     Examples of applications as packing materials 
     One-layer cigarette packages were prepared from different film cuts whose compositions of materials are listed in Table 5. 
     
                       TABLE 5______________________________________Compositions of Materials      1        2          3______________________________________starch acetate        48%        30%        26.1%(degree of subst. = 2.4)polypropylene carbonate 37.5%      34.8%(degree of polym. = 950)polyethylene carbonate        32%        12.5%      17.4%(degree of polym. =1100)plasticizers/aids        20%        20%        21.7%        polyalkylene                   polyethylene                              Dioctyl        glycol     glycol dioctate                              phthalate______________________________________ 
    
     Dry blends of the components for examples 1 to 3 of Table 5 were processed into granules on an extruder and subsequently extruded or blown into films. In Table 6, the measured mechanical values and the permeation properties of the films are given. 
     
                       TABLE 6______________________________________Mechanical Values and Permeation PropertiesExample         1         2      3______________________________________Film thickness (mm)           0.04      0.08   0.060Tensile strength (Mpa)           13.1      32.0   17.2Tensile strength at Break           4.8       12.1   6.9(Mpa)Elongation at break (in           100.7     22.9   29.1film feeding direction, %)Permeation of H.sub.2 O vapor           34        7.4    25.5(g/m.sup.2 d)Permeation of pentane           9.0       1.1    5.7(g/m.sup.2 d)Permeation of air           15.8      6.4    9.8(cm.sup.3 /m.sup.2 d)______________________________________ 
    
     Film cuts from composition of materials according to examples 1 to 3 can be readily welded. The measured strength properties of the films demonstrate that the films are excellently suitable for tobacco products, especially for cigarette packages, and will protect the package contents from shipping damage and damage from storage and handling. The permeation values measured have been achieved without biaxial stretching of the films. For examining the biodegradability, empty packages having the above mentioned compositions were disposed in an industrial composting plant under rotting conditions. The condition of the packages was monitored weekly and the time was established after which the morphology of the film cut could no longer be recognized (Table 7). 
     
                       TABLE 7______________________________________Rotting time (weeks)Example        1            2     3______________________________________Rotting time (weeks)          8           14    12______________________________________ 
    
     In the following, examples of packages prepared from the material according to the invention are explained in more detail with reference to the drawings, taking cigarette packages as an example. 
     In the example of FIG. 1, an inner package 10 in the form of a conventional cigarette box made of cardboard material is provided. The cardboard material consists of a cellulose containing material, in particular the usual cardboard. Such material has a relatively high vapor permeability. The inner package 10 completely encloses the cigarettes contained therein. It has a conventional separation seam 12 or cutting seam in order that the lid 13 embodied as an upper cap may be lifted off. 
     Inner package 10 is enclosed by an outer package 11 made of the material according to the invention as set forth above. The outer package 11 consists of a thin, preferably transparent film which is wrapped around the inner package 10 and forms a fold along one narrow side. At the front faces, outer package 11 is sealed by folding 15. Further, a ripping strip 16 which runs once around the outer package 11 is provided which is bounded by two weakening lines 17. After ripping off said ripping strip 16, the upper cap part of said outer package 11 can be removed such that said inner package 10 is exposed for opening the lid. All seams and folds of the outer package 11 may be sealed vapor-tight. 
     In the example of FIG. 2, the cigarette package as a whole is embodied as a one-material package 20 consisting of the material according to the invention having a thickness of at least 100 μm, in particular 120 μm. Said one-material package 20 also has a rectangular shape. The material of the package overlaps at a longitudinal weld seam 21 at which the overlapping parts are sealed. At the front faces, the packing material is laid on top of itself by folding 22, the overlapping plies being sealed. Further, an integrated ripping strip 23 is provided which is bounded by weakening lines 24 and runs once around the package near one of the front walls. 
     Thus, the package according to FIG. 2 consists of one ply of a vapor-tight material in which the cigarettes are contained without a further inner package. After ripping off the ripping strip 23, the ends of the cigarettes are immediately exposed. 
     In the example of FIGS. 3 and 4, the package 30 is also a one-material package which is embodied as two plies, though, and has a cardboard material 31 which is backed with the film 32 according to the invention. The outer shape of package 30 is the same as that of one-material package 20 of the example of FIG. 2. 
     The packaging material of the invention can be used to package a wide variety of materials, including, but not limited to, foods, cosmetics, detergents, paper tissues and toilet articles. This packaging film is useful for packaging any article that has requirements similar to the packaging of cigarettes, such as the need for protection of the package contents, and water vapor and gas tightness requirements. 
     Although certain presently preferred embodiments of the present invention have been specifically described herein, it will be apparent to those skilled in the art to which the invention pertains that variations and modifications of the various embodiments shown and described herein may be made without departing from the spirit and scope of the invention. Accordingly, it is intended that the invention be limited only to the extend required by the appended claims and the applicable rules of law.