Starch derived shaped articles - Patent Review 5314754

I claim:

1. A method of manufacturing a starch derived shaped article comprising the steps of:

(1) preparing a hot melt by heating a composition comprising (a) a high amylosic material, or a derivative thereof, said derivative being selected from the group consisting of amylosic ethers, amylosic esters and combinations thereof and (b) water, the water being present in an amount of less then 24% by weight, at an elevated temperature and pressure below the temperature and pressure at which the material or derivative decomposes to provide a homogeneous melt;

(2) extruding the hot melt from an extruder to form a shaped article; and

(3) subjecting the hot melt to a subatmospheric pressure prior to issue from the extruder whereby to remove water from the shaped article.

2. A method according to claim 1 wherein the subjecting of step (3) is at a pressure of 0 to 200 mbar.

3. A method according to claim 1 wherein the high amylosic material is derived from maize plants.

4. A method according to claim 1, wherein the derivative is selected from the group consisting of carboxymethylated, hydroxypropylated and acetylated derivatives.

5. A method according to claim 1 wherein the composition for preparing a hot melt comprises 0 to about 9.0% by weight of added water.

6. A method according to claim 5 wherein said composition comprises from about 3% to about 8% by weight of added water.

7. A method according to claim 6 wherein said composition comprises about 5.5% by weight of added water.

8. A method according to claim 5 wherein the composition for preparing a hot melt comprises an amylosic composition containing from about 9% to about 15% of moisture and no added water.

9. A method according to claim 1 wherein the composition for preparing a hot melt comprises a plasticizer in an amount of about 0 to 30% by weight of the composition.

10. A method according to claim 1 wherein the composition for preparing a hot melt comprises stabilizers selected from the group consisting of carbon black, alumina and calcium carbonate, coloring agents, preservatives, bactericides or a combination thereof.

11. A method according to claim 1 wherein the high amylosic material comprises plasticizer in an amount of about 0 to 30% by weight of the high amylosic material, said composition being in the form of free flowing particles prior to being formed into the hot melt.

12. A method according to claim 11 wherein the high amylosic material further comprises stabilizers selected from the group consisting of carbon black, alumina and calcium carbonate, coloring agents, preservatives, bactericides or a combination thereof.

13. A method according to claim 9 wherein the plasticizer is selected from the group consisting of polyethylene glycol, glycerol and glycerol acetate.

14. A method according to claim 1 wherein the hot melt is formed by subjecting the composition to a temperature in the range of about 120.degree. C. to about 210.degree. C.

15. A method according to claim 14 wherein the hot melt is extruded through a die having a temperature in the range of 60.degree. C. to 130.degree. C.

16. A method according to claim 1 wherein the shaped article is a rod.

17. A method according to claim 1 wherein the shaped article is a film.

18. A method according to claim 17 wherein the film is extruded by blown film techniques.

19. A method according to claim 17 wherein the film is co-formed with at least one layer of a first polymeric material so as to form a laminate comprising the starch derived film and a layer of the first polymeric material coating on at least one face thereof.

20. A method according to claim 17 wherein the film is co-formed with a first and second polymeric material to form a laminate comprising a tie layer intermediate the film and the layer of the first polymeric material, said tie layer consisting of the second polymeric material.

21. A method according to claim 17 wherein the first polymeric material is selected from the group comprising polypropylene, polyethylene, or co-polymers thereof; polyvinylchloride, polycarbonate, polystyrene, polyester, ionomer resins, acrylates and nylons.

22. A method according to claim 17 wherein the second polymeric material is a blend of modified or functionalized polymers selected from the group of the first polymeric materials.

23. A method according to claim 19 wherein the starch derived film is co-extruded with the polymeric material.

24. A method according to claim 17 wherein the starch derived film is extruded into a solution of the polymeric material.

25. A method according to claim 17 wherein the film is subsequently heated and stretched.

26. A starch derived shaped article produced by the process according to claim 1.

27. A method according to claim 17 wherein the starch derived film is coated immediately after extrusion with the polymeric material by way of spraying.

28. A method according to claim 17 wherein the starch derived film is coated immediately after extrusion with the polymeric material by way of brushing.

29. A method according to claim 17 wherein the film is co-formed with at least one layer of a hydrophobic polymeric material so as to form a laminate comprising the starch-derived film and a layer of hydrophobic polymeric material coating on at least one face thereof.

30. A method according to claim 1 wherein the high amylosic material used in step (1) is itself the product of a method according to claim 1.

31. A method according to claim 1 further comprising the steps of:

(4) preparing a hot melt by heating at an elevated temperature and pressure the shaped article from stage (2) and less than 24% by weight water to provide a homogenous melt;

(5) extruding the hot melt of step (4) to form a shaped article; and

(6) subjecting the hot melt of step (4) to a subatmospheric pressure prior to issue from the extruder whereby to remove water from the hot melt prior to formation of an extrudate.

32. A method according to claim 1 wherein the high amylosic material has less amylopectin and more amylose than typical high amylose starches derived from U.S. cultivars.

33. A starch based shaped film obtained by extruding in an extrusion direction a composition comprising a high amylosic material and an amount of water, said film having an average tensile strength parallel to the extrusion direction in the range of from about 1000 psi to about 1300 psi and an average elongation before failure of from about 80% to about 240%.

34. A method according to claim 33 being incorporated in a laminate structure wherein a layer of a first polymeric material is coated on at least one face of the film.

35. A method of agriculture comprising the step of covering a tract of land with a biodegradable mulch film prepared by

(1) preparing a hot melt by heating a composition comprising (a) a high amylosic material, or derivative thereof, said derivative being selected from the group consisting of amylosic esters, amylosic ethers and combinations thereof and (b) water, said water being present in an amount of less than 24% by weight, at an elevated temperature and pressure below the temperature and pressure at which the material or derivative decomposes to provide a homogeneous melt;

(2) extruding the hot melt from an extruder to form a film; and

(3) subjecting the hot melt to a subatmospheric pressure prior to issue from the extruder, whereby to remove water from the film.

36. A method of agriculture comprising the step of covering a tract of land with a biodegradable starch derived mulch film, said film having an average tensile strength parallel to the extrusion axis in the range of from about 1000 psi to about 1300 psi and an average elongation before failure of from about 80% to about 240%.

Description Submit all comments and votes

TECHNICAL FIELD

The present invention relates to a method of producing starch derived shaped articles and in particular, a method of producing films derived from high amylose starch. The invention also relates to shaped articles produced by this method and applications of these articles.

BACKGROUND ART

It has long been known that amylosic films may be cast on a surface from a solution of amylosic materials in a solvent, the resultant film being peeled from the surface. However, that method is unsuitable for mass production of amylosic films or for the production of shapes other than films.

In the 1960's various attempts were made to provide more practical methods of manufacture of amylosic films.

U.S. Pat. No. 3,117,014 describes a method of manufacture of shaped articles by forming a hot melt from a mixture of amylaceous material, plasticizer and water. It was shown that plastic flow increased with water content and that it was necessary to retain moisture during extrusion using an unvented extruder.

U.S. Pat. No. 3,243,308 showed that strong flexible edible films could be made by confining amylosic mixtures at high temperatures and under super atmospheric pressures prior to extrusion.

GB Patent No. 965,349 showed that it was advantageous to add from 10% to 50% by weight of water to the amylosic substance prior to extrusion and subsequently to heat and stretch the extruded film.

Notwithstanding the above developments in the early 1960's, and notwithstanding the low cost of amylosic raw materials, the resulting materials have not found widespread acceptance and the extrusion of starch hot melts has not been adopted commercially to any significant extent.

One reason is that although amylose films prepared by the above methods have some useful properties they lack others, in particular mechanical strength and sufficient ability to stretch. The films tend to be hygroscopic and if desired to have a shelf life require to be dried and then lacquered by brush, spray or dipping which is impractical for mass production.

A second reason is that amylose films produced to date have been unsuitable for lamination with other polymers with the result that amylose films have been unable to compete in terms of versatility, or properties with modern co-extruded laminated plastics films in which a plurality of layers each of different polymeric composition, and each layer selected to contribute specific properties, are purpose designed for particular end uses.

Because the elongation before failure of known amylosic films has typically been from about 4% to 20%, the films have not been suitable for use with techniques such as blow moulding, and have been of limited utility in other applications where a greater capacity for elongation is desired.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide an improved method for the manufacture of starch derived shaped articles which avoids or at least ameliorates the above discussed deficiencies of prior art.

It is an object of preferred embodiments of the invention to provide an amylosic film suitable for combination with other extruded polymers as laminates.

It is an object of highly preferred embodiments of the invention to provide films which are of improved elongation before failure in comparison with prior amylosic films.

According to one aspect, the invention consists in a method of manufacturing a starch derived shaped article comprising the steps of:

(1) preparing a hot melt by heating under pressure a composition comprising a high amylosic material, or derivative thereof and sufficient water to provide a homogeneous melt,

(2) Extruding the hot melt from an extruder to form a shaped article, and

(3) Subjecting the hot melt to an atmospheric or sub-atmospheric pressure prior to issue from the extruder or to a sub-atmospheric pressure after issue from the extruder, whereby to remove water from the hot melt.

For the purpose of this specification the term "high amylosic mateiral" means any material having the film forming properties characteristic of amylose. The term includes pure amylose, starch mixtures of amylose with amylopectin containing more than 50% of amylose, and modification of those amylose and starches.

"Derivatives" of high amylosic materials include compositions formed during hot melting or during extruding high amylosic material alone or in combination with plasticizers, cross-linking agents or the like.

Extrusion to form a shaped article includes the formation of films, rods, sheets or the like and includes, as the context admits, extrusion in a blow moulding machine.

It will be understood that high amylosic material such as high amylose starch may contain, as normally dried during preparation, from 9% to 15% by weight of water. The amount of water sufficient to form a homogenous hot melt may be as little as 1% or 2% on a dry starch basis so that no water need be added to perform the invention if sufficient water is present in the high amylosic material as prepared. Reference herein to "high amylose material" and to "starch" unless otherwise specified is a reference to "as prepared" material.

In preferred embodiments of the invention a mixture of a high amylose starch, plasticizer and, if required to produce a homogeneous hot melt added water, are first heated to from 120.degree. C. to 210.degree. C. at a pressure of from 150 to 250 psi, to form a hot melt.

The hot melt is then subjected to a reduced pressure of for example 200 mbar, whereby water is removed to produce a low moisture glassy thermoplastic which is subsequently extruded.

The extrudate is desirably pelletized and the above steps repeated, using the pellets as a high amylosic material derivative. The pellets are formed into a second hot melt which is conveniently subjected to low pressure by use of a vented extruder and is extruded, for example, as a film. The resulting film typically has an elongation before failure in excess of 80% and in some embodiments greater than 200%. If preferred, pellets can be formed into a film by blow moulding. In addition, because of its low water content, the film may be formed into laminates with other polymers, for example by co-extrusion, to produce novel laminates having advantageous properties.

It is highly preferred to select as the high amylosic material a starch derived from maize hybrid 55/77 or 65/88 or derivatives of such starch available from Goodman Fielder Mills Pty. Limited.

Hitherto it has been taught that it was advantageous to have water present in starch during the extruding step and that added water contents of 10% to 50% were preferable. It has also been taught that subjecting the hot melt to high (super atmospheric) pressures is advantageous and that extrusion should be carried out in unvented machines of the kind used for processing starch and rubber products.

The present invention arises from the surprising discovery that it is advantageous to subject the hot melt to an atmospheric or sub-atmospheric pressure prior to extrusion. The sub-atmospheric pressure is advantageously applied at the vent of a vented extruder. It is believed that this flashes off water prior to formation of the product resulting in an extrudate of differing structure from prior art. The resulting extrudate has a high degree of thermoplasticity, is compatible with polymer films (presumably because of its low water content) and is able to be co-extruded with other polymers to form novel laminates.

It has also been found surprisingly, that selection of the preferred high amylose maize starch, which has characteristics differing from similar U.S. high amylose maize starches, results in an extrudate having a higher elongation before failure. The invention extends to include novel products made by the method and to novel uses for those products.

BRIEF DESCRIPTION OF DRAWINGS

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings wherein:

FIG. 1 is a typical Brabender viscograph showing Brabender units on the Y axis and time in minutes on the X axis for a high amylose maize starch slurry comprising 8% starch on a dry solid basis (dsb) in water, said starch being typical of those derived from maize hybrids 55/77 and 65/88;

FIG. 2 is a corresponding viscograph typical of high amylose maize starch derived from a U.S. cultivar;

FIG. 3 is a molecular weight profile for a typical high amylose maize starch derived from maize hybrids 55/77 and 65/88 showing response on the Y axis and the log of the molecular weight on the X-axis; and

FIG. 4 is a corresponding molecular weight profile typical of a high amylose maize starch derived from a U.S. cultivar.

BEST MODES FOR CARRYING OUT INVENTION

In preferred embodiments of the invention, the high amylosic material used is high amylosic maize starch comprising at least 50% by weight of amylose or a modified derivative of this starch. It is highly desirable to select a high amylosic maize starch or modified starch derived from the Goodman Fielder Mills Pty Ltd maize hybrids 55/77 or 65/88 described in detail in "Development of High Amylose Maize Production in Australia" by K. S. McWhirter and C. F. Dunn, Paper 17 No. 5 N. Z. Agronomy Special Publication DSIR Plant Breeding Symposium 1986.

Preferred starches for use in the present invention have been characterised according to two physical properties, rheological behaviour, in particular viscous flow, and their distribution of molecular weights.

The rheological property of viscous flow was measured by determining the change in flow of a dispersion of starch derived from maize hybrids 55/77 and 65/88 in water as a function of temperature. This was done using a Bra