Plastic and nonmetallic article shaping or treating: processes – Vacuum treatment of work
Patent
1995-03-15
1996-06-11
Thurlow, Jeffery R.
Plastic and nonmetallic article shaping or treating: processes
Vacuum treatment of work
127 32, 127 34, 264564, 26421111, 26421124, 264330, 428532, B29C 4776
Patent
active
055252818
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for preparing biodegradable films from plant-based raw materials. Such methods are gaining more and more importance, for example, in the production of environmentally compatible packing material. The object is to produce films having sufficient strength that can easily be disintegrated or dissolved into their original natural components.
BACKGROUND OF THE INVENTION
Methods for preparing thermoplastic granules by using starches have been disclosed previously (U.S. Pat. Nos. 4,133,784, 4,021,388, DE-A-23 22 440). Such granules are processed to films in a second procedural step. In so doing, the starch is used as filler material in synthetic polymers. Furthermore, methods for preparing and modifying destructured thermoplastic starch have been disclosed (EP-A-378 646, EP-A-397 819).
WO 90/05161 A1 shows thermoplastically processable starch as well as a method for preparing it. In the process aggregates and, if desired, various further additives are added to raw starch material to reduce the melting temperature of the starch to a level below its decomposition temperature. This is to improve the structure of the starch melt so as to facilitate handling in preparing and processing thermoplastic starch.
EP-A1-0 474 095 discloses a process of preparing biodegradable articles, such as dishes, cups, cardboard boxes, etc. using plant-based raw material, such as starch, as starting material. This material is supplemented with additives, plastified and converted in a first extruder to an intermediate to form a billet or granules. Then the intermediate is molded in a second extruder into the desired article.
Similarly, conventional film preparation from plant-based raw materials proceeds in two completely separate steps. The biopolymer melt destructured and plastified in the extrusion process is cooled at the end of the first step, forced through a die under high pressure and granulated. In order to avoid biopolymer foaming, it is required to cool the melt. The resulting high shear stress causes damage to the molecular structure of the starch while various molecule fragments are split off. The polymer chains of the starch are shortened and the molecular weight is reduced. The obtained starch granules are then processed to films in a further extrusion process subject to similar conditions. In the process the biopolymer is again decomposed as the molecular weight is reduced and the chains are shortened. The two-fold damage to the molecular structure, especially the shortening of the amylose chains, causes immediate deterioration of the properties (tensile strength, elasticity, etc.) of the thus obtained films. What is more, the two-fold extrusion is time-, energy- and cost-consuming.
By contrast, the object underlying the present invention is to provide a cost-efficient method for preparing biodegradable films from plant-based raw materials while avoiding the drawbacks of the prior art, improving the quality of the obtained films and achieving, for instance, high tensile strength and elasticity.
This object is achieved by providing the features indicated in the claims.
SUMMARY OF THE INVENTION
In achieving the object, the invention is based on the concept of optionally disintegrating and modifying plant-based raw materials, e.g., in the form of carbohydrates, in a continuous and one-step process without involving intermediates and without interruption, of plastifying as well as of compressing and molding them into films. A suitable configuration of a screw-type extruder to transport the film materials and suitable temperature conditions ensure careful processing of the biopolymers.
The plant-based raw materials can include carbohydrates, e.g., flour or native starch in natural or hybrid form-derived, for example, from potatoes, manioc, peas, beans, corn, wax corn, corn with high amylose content, grain such as wheat and fractions prepared therefrom, barley or sorghum, starch derivatives consisting of physically and/or chemically modified starch, cellulose deriv
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Heuer Joachim
Klenke Kurt
Lorcks Jurgen
Pommeranz Winfried
Schmidt Harald
Biotec Biologische Naturverpackungen GmbH & Co.
Rauchfuss, Jr. George W.
Thurlow Jeffery R.
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