Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-03-13
2001-11-27
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
Reexamination Certificate
active
06323265
ABSTRACT:
DESCRIPTION
1,4-&agr;-D-Polyglucan-based thermoplastic mixture, process for the preparation and use thereof.
The invention relates to 1,4-&agr;-D-polyglucan-based thermoplastic mixtures, to the preparation of such mixtures and to the use of these mixtures for producing biodegradable moldings such as molded parts or sheets. The present invention particularly relates to those thermoplastic mixtures where the 1,4-&agr;-D-polyglucan employed has been produced biocatalytically.
The use of materials based on renewable raw materials has increased in importance and extent in recent years because of various advantages. Such biopolymers such as, for example, starch or protein etc. are, in contrast to petroleum-based polymers such as, for example, polyethylene, polypropylene or polystyrene etc., biodegradable. In addition, biopolymers can be obtained without restriction, whereas petroleum-based polymers are available to only a finite extent because of the limited availability of petroleum.
Biopolymers often result as by-products or waste products of the production of other products, for example in the vegetable kingdom as skeletal substances in plants and in production of foodstuffs.
In addition, biopolymers are CO
2
-neutral, i.e. breakdown thereof does not result in harmful by-products contributing to the greenhouse effect.
During the increase in the use of biopolymers, especially starch, as natural and thus physiologically tolerated and degradable materials for a wide range of applications, processes have been developed to make it possible to process starch by known plastic processing techniques such as, for example, injection molding and extrusion.
Thus, for example, EP 0 599 535, WO90/05161 and WO92/04408 describe processes for producing thermoplastic starch from native, i.e. naturally occurring, starch and derivatives thereof with the addition of water, plasticizers and, where appropriate, other additives with exposure to heat and mechanical energy, and the use thereof for producing moldings.
Inter alia, the use of thermoplastic starch for producing sausage casings (EP 0 709 030) and casings for processing meat (U.S. Pat. No. 2,729,565) is known. Native starches employed in these cases too.
Despite these considerable advantages of biopolymers compared with conventional synthetic polymers, unrestricted application thereof has not been possible. A significant reason for this is that biopolymers, like all naturally occurring substances, show considerable variations in constitution and structure, and therefore the required reproducibility and thus constant product quality is not ensured.
Thus, starch, as one of the promising representatives of the renewable raw materials, shows an exceptionally inhomogeneous constitution and composition. Depending on the origin (natural source) of the starch, its content of its constituents amylose and amylopectin varies considerably.
In addition, wide molecular weight distributions may be shown by amylose, a linear 1,4-linked poly-&agr;-D-glucan which has a molecular weight of about 50,000-150,000 dalton, and amylopectin, a highly branched 1,4- and 1,6-linked polyglucan which has a molecular weight of about 300,000-2,000,000 dalton.
There is no fixed boundary between highly branched and linear and therefore a plant may have a wide range of variation of the branching in the starch, which makes a sharp differentiation virtually impossible.
The ratio of amylose to amylopectin varies depending on plant origin. For example, starch from potatoes contains 20% by weight amylose and about 80% by weight amylopectin, whereas starch from corn comprises about 50% by weight amylose and 50% by weight amylopectin. In addition, the ratio within one plant varies depending on the soil characteristics, fertilizer uptake, seasonal climatic differences etc.
Besides this pronounced structural inhomogeneity, which may be expressed, as described, by wide molecular weight distributions or mixtures of polymers differing in spatial arrangement, biopolymers contain other constituents such as low molecular weight compounds, for example fats and oils, which can be removed from the biopolymers only with difficulty and have disadvantageous effects on further processing.
Attempts have therefore been made to produce biopolymers, for example polysaccharides and starches, by fermentation using microorganisms (WO95/31553).
However, the biopolymers obtained in this way likewise have a wide variation in molecular weight and defined reproduction thereof is impossible.
In addition, after this process the biopolymers are obtained in a mixture with the microorganisms used or residues thereof, and the residues of the nutrient medium required for the fermentation. The removal, especially when the resulting product is inside the cells and disruption of the microorganism is first necessary, is very elaborate, and in some cases impurities cannot be completely eliminated.
In addition, only limited amounts of biopolymer can be produced by fermentation, a very low space-time yield inter alia being responsible for this.
Attempts have also been made to optimize starches or other biopolymers by genetic manipulation of the plants from which the biopolymers are obtained. Thus, for example, WO94/03049 describes the production and use of a starch which has a high amylose content and can be obtained from genetically manipulated corn. In spite of this, the described disadvantages concerning the homogeneity of the natural polymers and concerning the contaminations with other natural components remain.
However, it is known from polymer processing by conventional plastics processing techniques that the reproducibility and quality depend crucially on the homogeneity and purity of the starting materials. To ensure products of high quality, it must be possible clearly to define and characterize these starting materials.
It is therefore an object of the present invention to provide a thermoplastic mixture based on biopolymers which does not have the abovementioned disadvantages and with which moldings of constant quality can be produced reproducibly.
It is particularly intended that the moldings producible in this way have improved properties such as excellent mechanical properties and good barrier properties toward gases and liquids.
This object is achieved by a mixture having the features of claim
1
. The dependent claims relate to preferred embodiments.
The provision of a thermoplastic mixture obtainable by mixing 100 parts by weight of a biocatalytically produced 1,4-&agr;-polyglucan (A), up to 400 parts by weight of a melt-processable polymeric material (B) different from (A), where the water content of (A) and (B) is corrected to zero percent by calculation, water (C) in an amount sufficient for plastification, at least one plasticizer (D) in an amount in the range from 10 parts by weight up to half the total of the parts by weight of (A) and (B), and, where appropriate, up to (A)+(B) parts by weight of other conventional additives makes it possible to produce, in a way which was not directly predictable, to produce a melt-processable mixture based on biopolymers which has excellent melt-processing properties, can be obtained reproducibily and in constant quality, and can thus be processed to molded parts likewise of constant quality.
A process for producing a thermoplastic mixture for extrudates or granules, and the use of the thermoplastic mixture, was also an object of the invention.
The 1,4-&agr;-D-polyglucan employed according to the invention as component (A) is produced biocatalytically.
1,4-&agr;-Polyglucan is, like amylose, constituted from 1,4-&agr;-glycosidically linked glucose units and is linear.
In contrast to amylose, which is very soluble in water even in the high molecular weight state, corresponding biocatalytically produced 1,4-&agr;-D-polyglucan is insoluble in water.
Unlike starch and amylose from native starch, which vary greatly in quality depending on the plant variety, location of origin, cultivation conditions etc., biocatalytically produced 1,4-&agr;-polyglucan is of constant un
Bengs Holger
Böhm Gitte
Grande Jürgen
Aventis Research & Technologies GmbH & Co KG
Connolly Bove & Lodge & Hutz LLP
Michl Paul R.
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