Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Shaping by extrusion
Patent
1992-05-18
1994-01-04
Thurlow, Jeffery
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Shaping by extrusion
106211, 106213, 127 32, 26421111, 2643282, 264330, 264101, B29C 4700, B29C 4500, B29K 100
Patent
active
052757749
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for treating starch by extrusion or injection moulding and, in particular to a process for producing thermoplastic starch products by extrusion.
The processing of starch in an extruder has been known for many years and there are articles in the literature describing various aspects of the process e.g. Cereal Chemistry 54(3):436-443. In the extruder the starch is subjected to a shearing effect at an elevated temperature resulting in gelatinisation of the starch granules and some degradation of the starch molecules.
Recently, descriptions have appeared in the literature e.g. in European patent 118240 of a process for the injection moulding of starch in which the starch is injected into a mould to produce a shaped starch article. The process described in EP 118240 includes (a) maintaining a composition comprising a starch and water at a water content in the range of from 5 to 30% by weight based on the weight of the composition and heating the composition at elevated pressure to form a melt (b) further heating and plasticising the melt into a molecularly dispersed form (c) injecting the plasticised melt into a mould while maintaining the water content in the 5-30% by weight range (d) cooling down the mould and (e) ejecting the moulded article. This process is suitably carried out in injection moulding equipment.
The starch used in the process of EP 118240 may be chosen from a wide range of commercially available starches e.g. maize, wheat, potato, rice or tapioca starch, the only proviso being that the starch is not chemically modified. The thermomechanical properties of the product of the process are said to be strongly dependent on its water content, the lower limit being defined by a maximum processing temperature of 240.degree. C., which cannot be exceeded if degradation of the starch is to be avoided. The upper limit is determined by the stickiness and distortion of the finished products. Since natural starches generally contain an equilibrium amount of water of about 12% to 20% by weight the use of an untreated starch may fall, depending upon the quantity of substances other than starch in the composition, within the range specified in EP 118240 of 5 to 30% without the need to add more water. We have now found however that a product of improved clarity is obtained if the starting material for the process is a so-called super-dry starch containing less than 8% by weight water and particularly less than 5% by weight. The production of a clear product is especially important for film production.
The invention is applicable to a process in which a starch-containing composition is extruded to produce pellets for subsequent processing as a thermoplastic e.g. by injection moulding, compression moulding or film extrusion or to a process in which the starch-containing composition is processed in an injection moulding machine followed by direct injection into a mould.
According to the present invention a process for extruding or injection moulding a starch-containing composition by feeding the composition either to an extruder which extrudes the composition through a die or to an injection moulding machine which injects the composition into a mould is characterised in that a substantially transparent product is produced by providing that. the starch. injection moulding machine is controlled so as to be in the range 5 to 20% preferably 7 to 15% by weight of the starch and composition leaves the barrel of the extruder or the injection moulding machine so that the water content of the composition passing through the die and/or entering the mould is less than 3% by weight of the starch.
For the sake of convenience, the invention will be described in the remainder of this specification by referring to an extruder although it should be understood that this description applies equally as well to an injection moulding machine.
Preferably, the starch which is fed to the extruder contains less than 5 weight % water and suitably contains 2 to 3 weight % water. Starch containing thi
REFERENCES:
patent: 3117014 (1964-01-01), Klug
patent: 3137592 (1964-06-01), Protzman et al.
patent: 3243308 (1966-03-01), Barger et al.
patent: 3265509 (1966-08-01), Wurzburg et al.
patent: 3891624 (1975-06-01), Boonstra et al.
patent: 4454268 (1984-06-01), Otey et al.
patent: 4673438 (1987-06-01), Wittwer et al.
patent: 5043196 (1991-08-01), Lacourse et al.
Cereal Chemistry, The American Association of Cereal Chemists, vol. 54, No. 3, ISSN 0009-0352 pp. 436-443, B. Y. Chiang et al. Gelatinization of Starch in Extruded Products, May-Jun. 1977.
Chimia, Association of Swiss Chemists, vol. 41, Injection Moulding of Natural Hydrophilic Polymers in the Presence of Water, R. F. T. Stepto et al, pp. 76-81, Mar. 1987.
Bahr Kark-Heinz
Fitton Michael G.
Koch Helmut
Cerestar Holdings B.V.
Thurlow Jeffery
Vargot Mathieu
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