Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1995-02-06
1996-12-24
Nutter, Nathan M.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
536107, 536110, C08B 3302
Patent
active
055874126
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to degradable polymer compositions capable of being formed by heat and pressure into articles having good dimensional stability and physical properties. These compositions comprise an esterified starch preferably having a degree of substitution of at least about 1.5 and preferably an amylose content of at least about 50%.
BACKGROUND TO THE INVENTION
It is known that starch may be heated under pressure to form a melt suitable for the production of shaped articles. Such starch-based shaped articles may exhibit the disadvantages of relatively poor physical properties under high relative humidity conditions and a relatively high tendency to embrittlement under relatively low humidity conditions.
Attempts to overcome these problems by the replacement of the above mentioned starch by maize starch esters having a low degree of substitution, as commonly found in the starch industry, have generally been unsuccessful, often resulting in weak, brittle, hydrophilic materials having a poor balance of physical properties. It is an object of the present invention to overcome, at least in part, the above mentioned disadvantages.
SUMMARY OF THE INVENTION
According to the present invention there is provided a composition as obtained from a melt comprising esterified starch having a degree of substitution of at least about 1.5.
The esterified starch may be selected from the group consisting C.sub.2 to C.sub.22 -starch esters preferably from the group consisting of starch acetates, starch propionates, starch butyrates, starch pentanoates, and starch hexanoates, and mixtures thereof.
The starch ester may be a mixed ester, i.e. having different kinds of ester groups attached to the same molecule, as are obtained for example by reaction of starch with a mixed acid anhydride or a mixture of different acid anhydrides. Such a mixed acid anhydride may be for example an acid anhydride made from acetic acid and propionic acid; a mixture of different acid anhydrides may be for example a mixture of acetic acid anhydride and propionic acid anhydride.
The esterified starch as used in this invention may be made from a starch as obtained from potatoes, rice, tapioca, corn, pea, rye, oats, and wheat with the respective known amylose content. However, the amylose content of the starch is preferably at least about 50% by weight with respect to that of the starch.
The composition may further include one or more members selected from the group consisting of extenders; fillers; wood derived materials; oxides of magnesium, aluminum, silicon, and titanium; lubricants; mold release agents; plasticisers; stabilisers; colouring agents; flame retardants; boron-containing compounds; alkali and alkaline earth metal salts; thermal stabilisers; and melt flow accelerators; and mixtures thereof.
The invention further provides the composition according to this invention when shaped into articles, for example bottles, strands, sheets, films, packaging materials, pipes, cups, rods, laminated films, sacks, bags, pharmaceutical capsules, foams, granulates and powders by a process including injection molding, compression molding, filming, blow molding, vacuum forming, thermoforming, extrusion, extrusion moulding, co-extrusion, foaming, profile extrusion and combinations thereof.
The invention still further provides the composition of the present invention in the form of a melt.
The invention still further provides a process for forming said melt comprising heating an esterified starch having a degree of substitution of at least about 1.5, optionally in the presence of a plasticiser to an elevated temperature and plastifying the thus heated composition until a uniform melt is obtained.
The present invention still further provides the use of an esterified starch having a degree of substitution of at least about 1.5, and preferably also an amylose content of at least about 50% by weight with respect to that of the starch, as a component in a thermoplastic melt.
The present invention will be further apparent
REFERENCES:
patent: 5314754 (1994-05-01), Knight
Wolff et al "Mixed Esters of Amylose" Industrial and Engineering Chemistry, vol. 49, No. 8, Aug. 1957, pp. 1247-1248.
Borchers Gerd
Dake Ingo
Dinkelaker Albrecht
Loomis Gary
Mauzac Olivier
National Starch and Chemical Investment Holding Corporation
Nutter Nathan M.
Zagarella, Jr. Eugene
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