Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
1999-08-19
2002-04-09
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S102000, C536S107000, C536S110000, C536S124000
Reexamination Certificate
active
06369215
ABSTRACT:
This application is the national phase under 35 U.S.C. §371 of prior PCT International Application No. PCT/FI97/00836 which has an International filing date of Dec. 31, 1997 which designated the United States of America.
The present invention relates to a hydroxyalkylated starch ester which is a hydroxypropyl starch ester, comprising an ester group derived from acetic acid, propionic acid or butyric acid or from a mixture thereof, the molar substitution of the hydroxypropyl group being 1.4 at the most and the degree of substitution of the ester group at least 1.
The invention also relates to a thermoplasticized starch component containing 90 to 60% by weight of a hydroxypropyl starch ester whose hydroxypropyl group has a molar substitution of up to 2 and whose ester group has a degree of substitution of at least 1, and 10 to 40% by weight of a plasticizer. This thermoplasticized starch may also have additives known as such within the fields of polymer and plastics technology. The invention also relates to a process for preparing a hydroxyalkylated starch ester wherein the starch-containing base is hydroxypropylated and esterified, characterized in that the hydroxypropylation is performed in an aqueous alkanol medium containing 10 to 95% by weight of a lower alkanol, 5 to 90% by weight of water and 0.1 to 10% by weight of a catalyst.
The current emphasis on an environmentally friendly attitude and green values is opening up new markets for products based on renewable natural resources. Such trends can be seen within the sectors of, e.g. the packaging industry, the sanitary industry and the glue industry, where recyclability, reuse, compostability, biodegradability and lack of environmental strain are demands of today. The trend of replacing products based on petrochemistry by processed biopolymer products is also emphasized. Starch and its derivatives constitute a particularly interesting initial material for the preparation of biodegradable polymer products.
Of industrially usefull starch derivatives, particularly starch esters and ethers may be mentioned, as well as mixed ester-ethers of starch, containing both ester and ether groups. The latter are represented by hydroxyalkylated starch esters which have been described, among others, in U.S. Pat. Nos. 4,997,581, 4,193,989, 4,041,179, 4,035,572 3,883,666, 5,360,845, 4,383,988, 4,067,824, 4,035,572 and 3,824,085.
The most important among hydroxyalkylated starch esters are hydroxypropylated derivatives because they can be prepared in room temperature using a liquid material, propylene oxide (1,2 epoxy propane) which reacts easily with the hydroxy groups of starch whereby an ether of starch and 1- and 2-propoxy groups is formed. Other hydroxyalkylated derivatives can be prepared from other corresponding epoxy alkane compounds. Unreacted hydroxyl groups can be esterified further by means of an esterifying agent whereby the corresponding acyl groups are obtained. As the alkylene oxide groups in connection with alkoxylation easily react with one another forming an oligomer, several alkylene oxide residues may be attached to each etherified hydroxyl group. Therefore, the number of hydroxy alkyl groups is given as the molar substitution degree (MS) of the glucose unit, the MS typically varying between 3 and 6. The number of starch ester groups in the glucose unit, that is, the degree of substitution (DS), is 3 at the most.
In the prior art, hydroxypropyl starch acetate has mainly been used as a basic material for chewing gum (e.g., U.S. Pat. No. 4,041,179, U.S. Pat. No. 4.035.572 and U.S. Pat. No. 3,883,666) and as a gelling agent or, rather, an agent which increases the viscosity of the blend in suntan lotions, perfumes, antiperspirants or in organic solvents in general (e.g. U.S. Pat. No. 3,824,085, U.S. Pat. No. 4,067,824, U.S. Pat. No. 4,383,988 and U.S. Pat. No. 4,193,989). Typically, hydroxypropyl starch acetate can be used as a basic material for chewing gum, the DS thereof being 0.5-0.92 and its MS=3-6 (U.S. Pat. No. 4,041,179), or DS=1 -2.5 (1.3-1.65) and MS=3-6 (4.4-4.5) (U.S. Pat. No. 3,883,666).
In the above-described uses the hydroxypropyl starch acetate is typically prepared by allowing the starch dispersed in an organic solvent (preferably toluene) to react with propylene oxide in the presence of NaOH, whereafter the reaction is continued with an acetic acid anhydride. Next, excess toluene is removed by distillation from the toluene/rubber blend, the final product is dissolved in chloroform or ethanol and the purified rubber is precipitated from hexane or water and dried.
By way of summarizing the prior art solutions it can be observed that known hydroxy-alkylated starch esters are not suitable for use as raw materials of compostable starch bioplastics; for that use, they are too glutinous and difficult to mould. In addition, the above-described methods for preparing hydroxypropyl starch acetate are not particularly environmentally friendly, among other reasons because carcinogenic organic solvents are used.
The present invention aims at removing the drawbacks of the prior art and at achieving a new starch derivative as a raw material for starch plastics. A further aim of the invention is new starch derivative as a raw material for starch plastics. A further aim of the invention is to provide a new method for the preparation thereof and to achieve new thermoplasticized starch components and compositions. The invention also relates to the use of these products.
The invention is based on the concept of hydroxyalkylating the starch to a relatively low molar substitution degree and esterifying it to as high a substitution degree as possible, whereby a thermoplasticizable hydroxyalkyl starch ester is obtained which behaves in the manner of plastics. According to the invention, the MS of a hydroxyalkylated starch ester is smaller than 2 and its DS is greater than 1; thus, the MS of hydroxypropyl starch acetate is typically 0.05 to 1.2 and its DS is 1.5 to 3. The hydroxyalkylated starch esters can be mixed with plasticizers whereby a thermoplasticized starch component is obtained containing 90 to 60% by weight of a starch derivative and 10 to 40% by weight of a plasticizer. A useful composition may be formed of the starch component by admixing it with auxiliaries and additives known as such.
By means of the invention, it is possible to obtain a new process for preparing an esterified starch ether used as a raw material for starch-based bioplastics. It is characteristic of the process that starch is etherified in an aqueous alkanol medium in the presence of a catalyst, whereafter the product is filtered and the alcohol is evaporated. After the evaporation of alcohol the hydroxypropyl starch is esterified, washed and dried.
In more detail, the thermoplasticized starch derivative according to the invention is a hydroxypropyl starch ester, comprising an ester group derived from acetic acid, propionic acid or butyric acid or from a mixture thereof, the molar substitution of the hydroxypropyl group being 1.4 at the most and the degree of substitution of the ester group at least 1.
The thermoplasticized starch component according to the invention then, is characterized as containing 90 to 60% by weight of a hydroxypropyl starch ester whose hydroxypropyl group has a molar substitution of 2 at the most and whose ester group has a degree of substitution of at least 1, and 10 to 49% by weight of a plasticizer. This thermoplasticized starch may also have additives known as such within the fields of polymer and plastics technology.
The process according to the invention for preparing a starch derivative is a process for preparing a hydroxyalkylated starch ester wherein the starch-containing base is hydroxypropylated and esterified, characterized in that the hydroxypropylation is performed in an aqueous alkanol medium containing 10 to 95% by weight of a lower alkanol, 5 to 90% by weight of water and 0.1 to 10% by weight of a catalyst.
Considerable benefits are provided by the invention. Thus, the above-described raw m
Happonen Harri
Peltonen Soili
Tiitola Pertti
Törmälä Pertti
Vuorenp{umlaut over (aa)} Jani
Birch & Stewart Kolasch & Birch, LLP
Geist Gary
Valtion teknillinen tutkimuskeskus
White Everett
LandOfFree
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