Sugar – starch – and carbohydrates – Products – Modified starches
Patent
1996-02-05
2000-10-24
Bell, Mark L.
Sugar, starch, and carbohydrates
Products
Modified starches
127 67, 127 71, 1062061, 1062155, 426516, 536102, C08B 3012, C08B 3000, C68L 3500, A01J 110
Patent
active
06136097&
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for producing biopolymeric, thermoplastic starch on the basis of renewable raw materials by extrusion in the form of a strip, threads or in other geometrical shapes. This extrudate can be further processed into a granulate.
In the prior art granulates from thermoplastic starches and other modified starches are obtained by extrusion in such a manner that directly at the outlet of the extruder the hot modified starch is cut to granular pieces by a rotating blade. During the extrusion step the starch is disintegrated under pressure and temperature. Normally the natural water content of 10 to 20% is sufficient and optionally solvents, additives and plasticizers can be added. The plastic hot starch mass is subject to mechanical and/or physico-chemical damage by the reaction conditions in the extruder and the high shearing stress, i.e. as undesired side-effect an unavoidable molecular decomposition of the starch polymer is accepted. As a result, the binding strength and film strength of the extruded starch deteriorate as the film strength of the starch is reduced in dependence of the molecular weight. The twin-screw extruder experiences an above-average wear due to the high viscosity and stickiness of the destructurized starch. Therefore, either very expensive, wear-resisting machine parts must be used for the extruder casing and the screw material or the respective components are subject to an over-proportional wear entailing both high costs and non-constant quality of the produced thermoplastic starch. Due to the wear and tear problems of the extruder and the quality problems of the starch thermoplastics this process, which is for instance disclosed in GB-A-2 208 652, has so far not been widely accepted.
It is the object of the present invention to provide an improved process for producing a starch extrudate, preferably in granulate or fibrous form, such that the quality of the product is improved, the mechanical wear of the extruder equipment is reduced while increasing its capacity.
This object is achieved with the features of the patent claims.
The present invention is based on the following concept:
Thermoplastic starch is disintegrated with low viscosity and low shearing strength and is chemico-physically modified in the extrusion process. The highly viscous liquid thermoplastic starches leave the extruder in the form of a strip, filaments or in other geometrical shapes and are then conditioned to compact, stabilize and carefully after-treat them. Subsequently, the solidified starch may be granulated or further processed into fibers and adjusted in a further conditioning step to the desired residual moisture and packaged.
The invention exhibits the following advantages: protection of the thermoplastic starch, no molecular decomposition, considerably improved quality, protection of the extruder equipment, no wear as the inner friction is considerably minimized, and in particular higher yields at lower torques and energy input. For example, the process according to the present invention yields thrice the amount of the nominal output of the twin-screw extruder than currently known processes.
The invention is illustrated by way of a working example.
The pertaining drawing shows in
FIG. 1 the inventive principle of the process for producing granulated thermoplastic starch.
As shown in FIG. 1, according to the process for producing thermoplastic starch the starting materials are mixed in a mixer 1. The mixture of raw materials from renewable raw materials such as polymeric carbohydrates from corn, wheat, potatoes, tapioca, hybrid corn or other cereal or starch containing roots or tubers is used and additional suitable emulsifiers such as glycerin monostearate are added to the mixture. After mixing the homogenous mass is added to a buffer container 2 which always carries a sufficient amount of mixture for a continuous process. From said container a feed screw 3 transports the mixture to a dosage device 4 which provides a twin-screw extruder 6 with a predetermined amount of mixt
REFERENCES:
patent: 3265509 (1966-08-01), Wurzburg et al.
patent: 4076846 (1978-02-01), Nakatsuka et al.
Patent Abstracts of Japan--English Abstract of Japanese Patent Publication No. 4-210222, Jul. 1992.
Heuer Joachim
Klenke Kurt
Lorcks Jurgen
Pommeranz Winfried
Schmidt Harald
Bell Mark L.
Biotec Biologische Naturverpackungen GmbH & Co., Forschungs- und
Hailey Patricia L.
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