WO2002024753A2

WO2002024753A2 - Water resistant expanded polysaccharide based compositions and processes for making the same

Info

Publication number: WO2002024753A2
Application number: PCT/US2001/042191
Authority: WO
Inventors: Milford Hanna; Vesselin Miladinov
Original assignee: The Board Of Regents Of The University Of Nebraska
Priority date: 2000-09-25
Filing date: 2001-09-18
Publication date: 2002-03-28
Also published as: AU2002211813A1; WO2002024753A3

Abstract

The current invention is directed toward substantially water resistant expanded polysaccharide compositions. The expanded polysaccharide compositions comprise a polysaccharide derivative having a degree of substitution between about 1.5 and about 3.0, and preferably, a nucleating agent and a filler. The addition of the nucleating agent and filler result in an expanded polysaccharide composition with a dramatically improved texture. The invention also relates to processes for producing the expanded polysaccharide composition.

Description

WATER RESISTANT EXPANDED POLYSACCHARIDE BASED COMPOSITIONS AND PROCESSES FOR MAKING THE SAME

Field of the Invention

The current invention is directed toward polysaccharide-based expanded compositions that are both biodegradable and substantially water resistant. In particular, the expanded composition comprises a polysaccharide derivative having a degree of substitution between about 1.5 and about 3.0, and preferably, nucleating agent and a filler. The present invention also relates to a process for producing a substantially water resistant expanded polysaccharide composition.

Background of the Invention

Each year nearly 200 million tons of petrochemicals are used to produce plastics. This is split about evenly between ther osetting resins (e.g., phenol formaldehyde, urea formaldehyde) and thermoplastic products (e.g., polyethylene, polystyrene). These products are not biodegradable. Replacement of even a portion of these materials with a biodegradable substance could have significant environmental effect. One of the prospective materials to replace some of the plastics is starch. Presently about 50 million pounds of starch are utilized annually for both food and industrial applications.

During recent years, considerable effort has been made either to incorporate starch into various synthetic polymers or to replace synthetic polymers. It is known that starch may be heated under pressure to form a melt suitable for the production of various shaped materials. Accordingly, starch has been used as a filler in thermoplastic polymers such as polyethylene, polyethylene acrylic acid and polypropylene to reduce cost and increase biodegradability. In some cases, synthetic polymers have completely been replaced by starch. Exchanging polystyrene packing materials with extruded starch "peanuts" (i.e. loose-fill packaging material) is an example of complete replacement. In fact, several products currently employ starch in the production of loose-fill packaging materials formed by extrusion. However, such starch-based materials generally exhibit the disadvantages of relatively poor physical properties compared to synthetic polymers and are highly water soluble. Thus, when these loose-fill packaging materials are contacted with water or high humidity their structural integrity is compromised, significantly impacting their ability to function as a packaging material.

Attempts to overcome these shortcomings have been made by substituting starch with various hydrophobic groups in order to impart water insolubility to the resulting starch-based composition. These attempts have been generally unsuccessful as the resulting products exhibit only slightly enhanced water insolubility characteristics and have a poor balance of desirable physical properties needed for utilization as a loose- packaging material. Therefore, a need exists for a substantially water resistant starch- based composition that possesses physical characteristics substantially similar to polystyrene and other commercially available foams.

Summary of the Invention

Accordingly, applicants have discovered a substantially water resistant expanded polysaccharide composition comprising a polysaccharide derivative having a degree of substitution between about 1.5 and about 3.0, a nucleating agent and a filler. The addition of the nucleating agent and the filler dramatically improve the texture of the expanded polysaccharide. The expanded polysaccharide is both water resistant and biodegradable. Additionally, the expanded polysaccharide also possesses physical properties similar to polystyrene and other commercially available foams, such as a relatively low unit density with good flexibility and/or rigidity as well as resilience and compressibility. In addition, the expanded polysaccharide composition also maintains these physical properties when contacted with water or high humidity.

Accordingly, an aspect of the invention is to provide substantially water resistant expanded polysaccharide composition comprising polysaccharide derivative having a degree of substitution between about 1.5 and about 3.0, the polysaccharide derivative having a beta linkage or an alpha linkage between linear monosaccharide units, provided if the linkage is alpha and the polysaccharide derivative is an ester, the ester is either substituted or contains greater than 3 carbon atoms.

Another aspect of the invention is to provide a substantially water resistant expanded polysaccharide composition comprising polysaccharide derivative having a degree of substitution between about 1.5 and about 3.0 and nucleating agent.

In yet another aspect of the invention is provided a substantially water resistant expanded polysaccharide composition comprising polysaccharide derivative having a degree of substitution between about 1.5 and about 3.0 and filler.

Another aspect of the invention provides a substantially water resistant expanded polysaccharide composition comprising polysaccharide derivative having a degree of substitution between about 1.5 and about 3.0, nucleating agent, and filler.

In yet a further aspect of the invention is provided a process for the preparation of a substantially water resistant expanded polysaccharide composition comprising a polysaccharide derivative having a degree of substitution between about 1.5 and about 3.0, the polysaccharide derivative having a beta linkage or an alpha linkage between linear monosaccharide units, provided that if the linkage is alpha and the polysaccharide is an ester derivative, the ester is either substituted or contains greater than 3 carbon atoms, the process comprising:

(a) combining the polysaccharide derivative with an organic solvent to form an extrusion mixture; and (b) extruding the mixture to form the substantially water resistant expanded polysaccharide composition.

Another aspect of the invention provides a process for the preparation of a substantially water resistant expanded polysaccharide composition comprising polysaccharide derivative having a degree of substitution between about 1.5 and about 3.0, the process comprising:

(a) combining the polysaccharide derivative with an organic solvent and nucleating agent to form an extrusion mixture; and

(b) extruding the mixture to form the substantially water resistant expanded polysaccharide composition. Other features of the present invention will be in part apparent to those skilled in the art and in part pointed out in the detailed description provided below.

Brief Description of the Drawings

These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying figures where:

Figure 1 is a photograph of a cross section of extrudate from a single screw extruder obtained from extruding starch acetate (DS of 3), ethanol, and talc in mass ratio of 20:5:1 respectively. The temperature of the three sections was 50, 140, and 140 °C.

The distance between each two notches is 50 micrometers. Figure 2 is a photograph of a cross section of extrudate from a twin screw extruder obtained from extruding starch acetate (DS of 3), ethanol, and talc in mass ratio of 20:5:1 respectively. The temperature of the four sections was 15, 160, 160, and 160 °C. The distance between each two notches is 50 micrometers.

Figure 3 is a photograph of a cross section of extrudate from a single screw extruder obtained from extruding starch acetate (DS of 3), ethanol, and microcrystalline cellulose in mass ratio of 20:5:1 respectively. The temperature of the three sections was

50, 140, and 140 °C. The distance between each two notches is 50 micrometers.

Figure 4 is a photograph of a cross section of extrudate from a single screw extruder obtained from extruding starch acetate (DS of 3), ethanol, starch, water, and talc in mass ratio of 100:20:20:3:6 respectively. The temperature of the three sections was 50,

140, and 140 °C. The distance between each two notches is 50 micrometers. Figure 5 is a photograph of a cross section of extrudate from a single screw extruder obtained from extruding starch acetate (DS of 3), ethanol, starch, water, and talc in mass ratio of 10:2:10:1.5:1 respectively. The temperature of the three sections was 50, 180, and 180 °C. The distance between each two notches is 50 micrometers. Figure 6 is a photograph of a cross section of extrudate from a single screw extruder obtained from extruding starch acetate (DS of 2), ethanol, starch, water, and talc in mass ratio of 10:2:10:1.5:1 respectively. The temperature of the three sections was 50, 180, and 180 °C. The distance between each two notches is 50 micrometers.

Description of the Preferred Embodiments The expanded polysaccharide composition of the invention may be composed of any polysaccharide derivative or any combination of different polysaccharide derivatives. The polysaccharide will preferably comprise a highly linear polymer consisting of monosaccharide units. The monosaccharide units are generally joined by either alpha or beta linkages. Linear polysaccharide are preferred because the resulting expanded composition is more durable compared to an expanded composition composed of a highly branched polysaccharide. However, the expanded composition may be composed of a branched polysaccharide or a mixed branched and linear polysaccharide. In accordance, the polysaccharide may be selected from the group consisting of glycogen, hyaluronic acid, dextran, chitin, starch and cellulose. Preferably, the polysaccharide employed will be chitin, starch or cellulose and even more preferably, the polysaccharide will be starch or cellulose.

If starch or cellulose is used, it may be any starch or cellulose of plant origin. Accordingly, the starch or cellulose may also be isolated from potatoes, rice, tapioca, maize, as well as cereals, such as rye, oats, wheat, barley, millet and mixtures thereof. Additionally, the expanded composition may comprise any combination of starch and cellulose. For example, the polysaccharide of the expanded composition may comprise 100% starch or 100% cellulose. Equally, the polysaccharide may comprise 50% starch and 50% cellulose or any other combination of starch and cellulose.

Starch and cellulose are preferably used due to their highly linear structure. Starch is composed of amylose and amylopectin. Amylose is composed of linear chains of D- glucose in alpha (1>4) glycosidic linkages. Amylopectin is the branched component of starch. The starch used will preferably have a high amylose content due to its preferable linear structure. In addition, starch with a high amylose content is preferable because amylose is the component of starch that causes colloidal starch solutions, sols, and hydrosols to thicken on cooling. Preferably, the starch utilized in the present invention will have an amylose content ranging between about at least 25% and about 70%, more preferably, ranging between about at least 50% and about 70%, and even more preferably, at least about 70%. Cellulose, unlike starch, does not contain a branched component. In addition, unlike starch, cellulose is composed of linear chains of D-glucose in beta (1>4) glycosidic linkages. The polysaccharide utilized preferably imparts water resistance to the expanded composition. The ability of the polysaccharide to confer water resistance to the expanded composition is achieved by substituting the polysaccharide with a hydrophobic group or a combination of different hydrophobic groups. As utilized herein the term "polysaccharide derivative" shall mean the polysaccharide substituted with the indicated hydrophobic group. The degree of water resistance of the expanded composition is determined by both the type of hydrophobic group the polysaccharide is substituted with and the degree of its substitution ("DS").

The ("DS") of the polysaccharide, as stated above, is one factor that determines the degree of water resistance of the expanded composition. The DS indicates the average number of substitutions ( i.e. ester substitution) per anhydroglucose unit in a polysaccharide, such as cellulose or starch. The highest possible DS is 3 since there are three OH groups available per anhydroglucose unit. In general, a polysaccharide having a degree of substitution of 3.0 is more water resistant compared to a polysaccharide having a degree of substitution of 1.0. The DS also impacts the physical properties of the resulting expanded composition. Therefore, an important facet of the present invention is selecting a DS such that the resulting expanded composition is nearly 100% water resistant and yet, possesses a balance of desired physical characteristics. Accordingly, the polysaccharide utilized preferably will have a DS between about 1.5 and about 3.0, more preferably, between about 2.0 and about 3.0, and even more preferably, about 2.5. Additionally, the polysaccharide may be substituted with any hydrophobic group that imparts both water resistance and desired physical properties to the expanded composition. The polysaccharide may be substituted with a hydrophobic group or a combination of different hydrophobic groups. Preferably, the polysaccharide is substituted with an ether, an ester or any combination of ethers and esters and even more preferably, the polysaccharide is substituted with an ester.

In one embodiment, the polysaccharide is preferably esterified with an ester comprising an aliphatic chain containing approximately 2 to about 20 carbon atoms. The esterified polysaccharide will generally be substituted such that a covalent bond is formed between a hydroxyl group of the monosaccharide unit of the polysaccharide and the carboxylic acid portion of the ester. Polysaccharide esterified with shorter aliphatic chains are generally more preferable because the resulting expanded composition is more rigid and has a higher melting temperature compared to polysaccharides esterified with longer aliphatic chains. However, the polysaccharide may be esterified with an aliphatic chain of any length to the extent the expanded composition possesses the desired degree of water resistance and physical properties. In a preferred embodiment, the polysaccharide is esterified with a group selected from substituted or unsubstituted acetate, propionate, butyrate, pentanoates, and hexanoates . Even more preferably, in some embodiments the group will be substituted or unsubstituted acetate.

In another embodiment, the polysaccharide ester may comprise a mixed ester. A mixed ester, as used herein, is an polysaccharide ester having different types of ester groups attached to the same molecule, as are obtained for example by reaction of starch with a mixed acid anhydride or 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.

In yet another embodiment, the polysaccharide may comprise a substituted ester. A substituted ester, as described herein, are ester groups in which a carbon is covalently bonded to at least one heteroatom and optionally with hydrogen, the heteroatom being, for example, a nitrogen, oxygen, silicon, phosphorous, boron, sulfur, or halogen atom.

Accordingly, in a preferred embodiment the expanded composition will comprise a polysaccharide substituted with an ester wherein the polysaccharide has a DS between about 1.5 and 3.0. Even more preferably, the polysaccharide will have a DS between about 2.0 and about 3.0. The polysaccharide will also preferably be starch or cellulose or a combination of starch and cellulose. If starch is utilized, preferably the starch is preferably esterified with a substituted acetate or with an aliphatic chain comprising approximately 3 to about 20 carbon atoms. If cellulose is utilized preferably the cellulose is esterified with an aliphatic chain comprising approximately 2 to about 20 carbon atoms. In one embodiment, the polysaccharide derivative is mixed with an organic solvent prior to expansion. The organic solvent functions to cause expansion of the polysaccharide composition. An organic solvent is preferred as opposed to other types of solvents, such as water, in order to improve the physical properties (as set forth below) of the expanded polysaccharide. Water has a higher boiling point than an organic solvent such as ethanol. At the same temperature, therefore, water generates vapor at a lower pressure than an organic solvent. Thus, water causes less expansion of the polysaccharide than an organic solvent. In addition, organic solvents are more similar in terms of hydrophobicity to polysaccharide derivatives compared to water. Thus, water does not intimately mix with the polysaccharide derivative, but rather forms pockets of water inside the expanded polysaccharide composition. Upon cooling, these water pockets evaporate faster, forming channels in the expanded polysaccharide composition. This causes the expanded composition to have a poor balance of physical properties. For example, the composition tends to be brittle and has a relatively low degree of_. resilience, flexibility and compressibility. Contrastingly, when an organic solvent is employed, the solvent thoroughly mixes with the polysaccharide derivative, resulting in an expanded composition that possesses desirable physical properties such as comprising cells with a closed cell structure, and having a relatively low unit density with good flexibility and/or rigidity as well as resilience and compressibility.

Accordingly, in a preferred embodiment the polysaccharide derivative is mixed with an organic solvent selected from the group consisting of a substituted or unsubstituted C₅ to C₁₀ hydrocarbon, a substituted or unsubstituted C_r to C₅ alcohol, a substituted or unsubstituted to C₅ fatty acid, a substituted or unsubstituted to C₅ fatty acid ester, acetone and tetrahydrofuran. More preferably, the polysaccharide derivative is mixed with a C_t to C₅ alcohol and even more preferably, the organic solvent employed will be ethanol. Additionally, the polysaccharide derivative may be mixed with the organic solvent in a ratio of polysaccharide derivative to organic solvent between about 1 : 1 and about 20: 1 by weight. More preferably, the ratio of polysaccharide derivative to organic solvent is between about 4:1 and about 6:1 by weight. Even more preferably, the ratio of polysaccharide derivative to organic solvent is about 5:1 by weight.

In a preferred embodiment, the polysaccharide derivative and organic solvent are mixed with a nucleating agent. The nucleating agent facilitates the formation of the expanded compound by providing an interface surface wherein the initiation of evaporation of the organic solvent occurs. The use of the nucleating agent dramatically improves physical properties of the expanded polysaccharide composition. In particular, use of a nucleating agent will preferably result in an expanded composition with a more uniform cell size. Thus, addition of the nucleating agent dramatically improves the overall texture of the expanded polysaccharide composition. This is especially helpful when dies of increased and large open areas or cross section are used and particularly improves the cell structures of the expanded composition in this situation.

Various nucleating agents may be utilized in this capacity including any inorganic salts, or mixtures thereof and especially an alkali metal or alkaline earth metal salt such as sodium sulfate and sodium chloride. Other nucleating agents such as the alkali metal or alkaline earth metal salts can be used, however, microcrystalline and magnesium silicate (talc) are preferred. The amount of nucleating agent used will depend on particular processing conditions and desired expanded composition dimensions. Preferably, the nucleating agent is added to the polysaccharide derivative and organic solvent between about 1% and about 15% by weight, more preferably, between about 1% and about 5% by weight, and even more preferably, about 5% by weight. Additionally, preferably the nucleating agent is added prior to the expansion of the composition.

In yet another preferred embodiment, a filler is added to the polysaccharide derivative and organic solvent. Fillers are added to the mixture in place of a portion of the polysaccharide derivative and thereby, dramatically decrease the cost of the expanded composition. Additionally, fillers dramatically reduce static electricity of the expanded composition. Various fillers may be employed in this capacity including, but not limited to native cellulose, ground cellulose, microcrystalline, wood pulp, calcium carbonate, talc, and native starch. Preferably, native starch is used. As used herein, the term "native" means starch or cellulose that has not been modified. The amount of filler added will vary depending upon both the type of filler employed and the desired physical properties of the expanded composition. In general, the filler may be added as a ratio of polysaccharide derivative and organic solvent to filler ranging between about 1:100 and about 1 : 1 by weight, more preferably, between about 1 :20 and about 1 : 10 by weight, and even more preferably, about 1 : 10 by weight. However, if the filler is either native starch or microcrystalline, then the ratio of filler to polysaccharide derivative and organic solvent is preferably between about 1:20 and about 5:1 by weight, and even more preferably, about 1 : 1 by weight. The filler may be added during the expansion process. However, preferably the filler is added prior to the expansion process. In one embodiment, native starch is added to the polysaccharide derivative and organic solvent as a filler. Native starch for use as a filler may be isolated from any plant source. It may be isolated from, for example, potatoes, rice, tapioca, maize, as well as cereals, such as rye, oats, wheat, barley, millet and mixtures thereof . In addition, native starch utilized as a filler will preferably have an amylose content of about 25%. Native starch is preferably first mixed with water as a ratio of native starch to water between about 1:1 and about 10:1 by weight, and more preferably, between about 6:1 and about 8:1 by weight. The native starch mixture is then added to the polysaccharide derivative and organic solvent with a ratio of native starch to polysaccharide derivative and organic solvent preferably between about 1 :20 and about 5 : 1 by weight, and even more preferably, about 1 : 1 by weight.

In yet another preferred embodiment, polysaccharide derivative, organic solvent, nucleating agent and filler (filler and water) are mixed. The polysaccharide derivative is preferably starch ester or cellulose ester with a degree of substitution between about 2.0 and about 3.0, but may be any polysaccharide derivative set-forth above. The organic solvent may also be any organic solvent set-forth above, but is preferably ethanol. In addition, the nucleating agent may be any such agent described above, but is preferably microcrystalline cellulose or talc. The filler may be any such filler described above, but is preferably native starch. This mixture preferably comprises a ratio between polysaccharide derivative, organic solvent, native starch, water and talc between about 100:20:20:3:6 and about 100:20:100:15:10 by weight, respectively. Even more preferably, the mixture comprises a ratio between polysaccharide derivative, organic solvent, native starch, water and talc of about 10:2:10:1.5:1 by weight, respectively. However, any of the ranges set-forth above for polysaccharide derivatives, organic solvents, nucleating agents, and fillers may be employed in this mixture.

In a further embodiment, a colorant may be added to the mixture. The colorant is added to the mixture preferably between about 0.5% and about 5% by weight, and more preferably about 1 % by weight.

In yet another embodiment, the extrusion mixture is conditioned prior to being expanded. In general this mixture comprises all components, for example, including but not limited to polysaccharide derivative, organic solvent, nucleating agent, filler and colorant, that are mixed together to form the substantially water resistant expanded polysaccharide composition. As used herein conditioning means that the extrusion mixture is placed in an air tight container and allowed to equilibrate between about 1 and about 24 hours at approximately 25° C. Preferably, the extrusion mixture is conditioned between about 8 and about 12 hours and more preferably, for about 12 hours prior to being expanded. Although the extrusion mixture may be extruded immediately upon its formation, conditioning is preferred because it allows the organic solvent more time to penetrate the polysaccharide derivative composition. This penetration is preferable because it causes the polysaccharide derivative to melt more uniformly when subjected to the expansion process, resulting in an expanded composition that is more uniform with improved physical properties such as a relatively low unit density with good flexibility and/or rigidity as well as resilience and compressibility.

The substantially water resistant composition of the invention is preferably expanded by an extrusion process. The apparatus used in carrying out the extrusion process is not a critical feature of the invention and may be any screw-type extruder. While the use of a single or twin screw extruder may be employed, it is preferred to use a twin-screw extruder. Such extruders will typically have rotating screws in a horizontal cylindrical barrel with an entry port mounted over one end and a shaping die mounted at the discharge end. When twin screws are used, they may be co-rotating and intermeshing or non-intermeshing. Each screw will comprise a helical flight or threaded sections and typically will have a relatively deep feed section followed by a tapered transition section and a comparatively shallow constant-depth meter section. The motor driven screws, generally fit snugly into the cylinder or barrel to allow mixing, heating and shearing of the material as it passes through the extruder. In carrying out the extrusion process, temperatures in the extruder will vary depending on the particular material, desired properties, and application. Control of the temperature along the length of the extruder barrel is important and is accomplished in zones along the length of the screw. Heat exchange means, typically a passage such as a channel, chamber or bore located in the barrel wall, for circulating a heated media such as oil, or an electrical heater such as calrod or coil type heaters, are often used. Additionally, heat exchange means may also be placed in or along the shaft of the screw device. In a preferred embodiment the temperatures of the feeding, metering and die sections are maintained at approximately between about 15° C and about 50° C, between about 130° C and about 160° C and between about 130° C and about 140° C, respectively.

Additionally, it is preferable to maintain extruder barrel at proper temperature to ensure that the resulting expanded composition possesses desirable physical properties. For example, if the barrel temperature is too high, the expanded composition will degrade, and will have compromised structural integrity. However, the temperature is preferably sufficiently high so that the viscosity of the extrudate is decreased. This decreased viscosity enables the extrudate to expand more upon leaving the die nozzle. In addition, at higher extrusion temperature the volatiles in the extrudate are heated more so they have a higher pressure, which translates into higher driving forces for the expansion of extrudates. At the lower temperatures, however, the extrudate has a high viscosity and thus, is subjected to higher shear forces. The higher shear forces at the lower extrusion temperature may cause a significant loss of substituted groups from the extrudate resulting in an expanded composition with diminished water resistance. Hence, the extrusion temperature is preferably high enough to facilitate formation of an expanded composition possessing desired physical characteristics, but is preferably not too high so as to not cause degradation of the extrudate. Accordingly, the extruder barrel temperature is preferably maintained between about 120° C and about 220° C, and still more preferably, between from about 140° C and about 180° C throughout the extrusion process.

Different dies and die configurations may be employed in the extruder depending on the particular form and/or shape of the expanded composition that is desired. Annular or tubular dies are one suitable type that can be used.

Additionally coupled extrusion may be employed to extrude any of the various extrusion mixtures set-forth above. The term coupled extrusion, as used herein, shall mean an extrusion process employing two extruders whereby a first extruder is extruding its extrudate through an injection port directly in the middle of the second extruder. The injection port of the second extruder is located after the compression section. The use of a coupled extrusion process results in a better mixing of components. For example, when native starch is mixed with polysaccharide derivative and organic solvent, as described above, coupled extrusion may be employed. The native starch mixture is preferably fed into the first extrusion hopper and the polysaccharide derivative and organic solvent mixture is fed into the second extrusion hopper in accordance with the various ratios set-forth above. The native starch mixture is then extruded into the second extruder containing the ester mixture where both molten masses are blended together. The resulting composite is then extruded to form an extrudate comprising the water resistant polysaccharide composition of the present invention. Alternatively, the polysaccharide derivative and organic solvent mixture may be added to the first extrusion hopper and the native starch mixture may be added to the second extrusion hopper. The polysaccharide derivative mixture is then extruded into the second extruder containing the native starch mixture and the resulting composite is then extruded to form an extrudate comprising the water resistant expanded polysaccharide composition. The extrusion is carried out in accordance with the operating parameters set-forth above. Variations in any of the operating parameters used in the extruder may be made as desired in accordance with conventional design practices. For example, one reasonably skilled in the art may modify operating parameters such as temperature, pressure, and/or residence time (the time that material stays in the extruder) depending on the particular material, desired properties and type of application. A further description of extrusion and typical design variations can be found in "Encyclopedia of Polymer Science and Engineering^,,, Vol. 6, 1986, pp. 571 to 631.

Preferably, the expanded polysaccharide composition produced by the process of the invention will possess physical properties similar to polystyrene or other commercially available foams, but will have the added advantage of being biodegradable. These physical properties, as set-forth in detail below, include a relatively low unit density with good flexibility and/or rigidity as well as resilience and compressibility. The expanded polysaccharide composition will also preferably maintain these physical properties when subjected to water or high humidity.

Therefore, the expanded composition will preferably comprise between about 30% and about 95% by weight of polysaccharide derivative. More preferably, the expanded composition will comprise between about 50% and about 95% by weight of polysaccharide derivative and even more preferably, will comprise between about 90% and about 95% by weight of polysaccharide derivative.

In addition, the expanded polysaccharide composition preferably comprises uniform cells having a closed cell structure. A closed cell structure is defined as one having largely non-connecting cells, as opposed to open cells which are largely interconnecting or defined as two or more cells interconnected by broken, punctured or missing cell walls. The uniform closed cell structure of the expanded composition results in preferable physical properties such as resilience and compressibility (as described in detail below). Additionally, the composition preferably comprises cells that have a small diameter. In general, an expanded composition with more cells that are smaller in diameter is preferable because the resulting expanded composition is more flexible at the same density relative to an expanded composition with fewer cells that are larger in diameter. Accordingly, preferably the expanded composition will comprise cells, the cells having a closed cell structure and a cell diameter between about 50 and about 1000 micrometers. More preferably, the cell diameter will be between about 100 and about 300 micrometers.

The substantially water resistant expanded polysaccharide composition will also preferably have a relatively low unit density. Unit density is determined by dividing the volume of the expanded composition by the mass of the expanded composition and is one of the most important physical properties. This is particularly true when the expanded composition is utilized as a loose-fill packaging material. Low unit density is preferable because it results in lower manufacturing costs due to reduced polymer cost and has more consumer appeal due to reduced freight costs. In accordance, the unit density of the expanded composition of the invention is preferably between about 0.5 lb/ft³ and about 15 lb/ft³, more preferably, between about 0.5 lb/ft³ and about 10 lb/ft³, and even more preferably, between about 0.5 lb/ft³ and about 2 lb/ft³.

The expanded polysaccharide composition will also preferably be highly resilient and compressible. Resilience and compressibility of the expanded composition are significant characteristics because together they determine the number of objects that may be cushioned by the expanded composition of the invention. These properties may be expressed in terms of an expanded composition's spring index. Spring index is an indirect measure of a composition's ability to absorb energy and refers to the ability of a material to recover its original shape after it has been deformed. Briefly, the spring index may be determined by compressing a sample of the expanded composition with a weight to deform it to 90% of its original diameter. The weight is removed and the sample is recompressed after approximately 1 minute. The amount of compression may be determined using an Instron Universal Testing Machine or any other generally known apparatus. The spring index may then be determined by dividing the re-compressing force by the original force of compression. The spring index may be expressed as a coefficient from 0 to 1. A value of 1 is the highest possible spring index and is indicative of a material that recovers 100% of its original shape after it has been deformed. The closer the value is to 1, the more elastic is the expanded composition. A composition with a low spring index has a relatively low degree of elasticity. Accordingly, the spring index of the expanded composition of the invention is preferably between about 0.90 and about 1.0, and more preferably, between about 0.95 and about 1.0.

The expanded polysaccharide composition of the present invention is also preferably substantially water resistant. As stated above, the degree of substitution of the polysaccharide derivative confers water resistance to the expanded composition of the present invention. As utilized herein, substantially water resistant means that the composition substantially maintains its physical properties, as set forth above, when subjected to water or high humidity. For example, when the expanded composition of the present invention is subjected to water or high humidity it retains good flexibility and/or rigidity as well as resilience and compressibility.

In addition to being substantially water resistant, the expanded polysaccharide composition is preferably also substantially water insoluble. Water insolubility may be determined by any known method, including for example, a water solubility index ("WSI") may be determined by measuring the amount of polysaccharide derivative which stays permanently in the water phase when the ester is submerged in water according to the method of Dubois ( Dubois et al., (1956) Anal. Chem. 28:350). In general, preferably the expanded polysaccharide composition is between about 80% and about 100% water insoluble, more preferably, between about 90% and about 100% water insoluble and even more preferably, about 100% water insoluble. Accordingly, the expanded polysaccharide composition will preferably be substantially water resistant with a relatively low unit density with good flexibility and/or rigidity as well as resilience and compressibility. In particular, the composition will preferably comprise a substantially water resistant expanded polysaccharide composition wherein the physical properties of the composition comprise an unit density between about 0.5 lb/ft³ and about 10 lbs/ft³, comprises cells, the cells having a closed cell structure and a cell diameter between about 50 micrometers and about 1000 micrometers, a spring index between about 0.90 and about 1.0, and between about 80% and about 100% water insoluble. More preferably, the composition will comprise a substantially water resistant expanded composition wherein the composition has an unit density between about 0.5 lbs/ft³ and about 2 lbs/ft³, comprises cells, the cells having a closed cell structure and a cell diameter between about 100 micrometers and about 300 micrometers, a spring index between about 0.95 and is about 1.0, and is about 100% water resistant.

The expanded polysaccharide composition of the present invention is both substantially water resistant and biodegradable. In addition the expanded composition possesses physical characteristics comparable to polystyrene and other commercially available foams, such as a relatively low density with good flexibility and/or rigidity as well as resilience and compressibility. The compound also maintains these physical properties when subjected to water or high humidity. Accordingly, the expanded composition of the invention may be utilized in any application that employs the use of polystyrene or other commercially available foams. These applications include but are not limited to loose-fill packaging material, containers for food such as claim shells, and thermoformed into plates or bowls. In addition, the expanded composition may also be utilized as an insulating material in construction and other applications.

The detailed description set-forth above is provided to aid those skilled in the art in practicing the present invention. Even so, this detailed description should not be construed to unduly limit the present invention as modifications and variation in the embodiments discussed herein can be made by those of ordinary skill in the art without departing from the spirit or scope of the present inventive discovery.

All publications, patents, patent applications and other references cited in this application are herein incorporated by reference in their entirety as if each individual publication, patent, patent application or other reference were specifically and individually indicated to be incorporated by reference.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

Examples

Example 1

Starch acetate prepared as described by Mark, A.M.; Mehltretter C.L. Facile Preparation of Starch Triacetates. Starch 1972, 24,73. Starch acetate (200 grams) with DS of 3 was mixed with 40 grams ethanol. After mixing the sample was placed in an airtight plastic container to equilibrate for 12 h at 25 °C and then extruded. Immediately before extrusion 10 grams of talc was added. Extrusion processing was carried out in a single screw C.W. Brabender (Model 2003 GR-8) laboratory extruder. The barrel diameter was 19 mm with L:D ratio of 20:1, the screw had a compression ratio of 3:1 and the cylindrical die nozzle had diameter of 3 mm. The drive system was a Plasti-Corder with controlling units type FE-2000 and FE-2000A. Temperatures of the feeding, metering and die sections were maintained at 50, 140 and 140 °C, respectively. Screw speed was maintained at 140 rpm. The die nozzle had a diameter of 3 mm. The ethanol was 20% on a dry basis (db). The sample was fed manually as much as the extruder would process (approximately 30 g per min). The material had physical properties very similar to polystyrene foam (Fig. 1). It was water insoluble and resistant and was building static electricity charge when mechanically agitated. Upon cooling the extrudates collapsed resulting in higher than the original unit density. After airing and steaming or hot air re-expanding the foam several times the original volume was recovered.

Example 2 A sample (500 g of starch acetate with DS of 3) mixed with 100 grams of ethanol and 25 grams of talc as in Example 1 was extruded in a twin screw extruder (Brabender laboratory twin screw extruder Model CTSE-V with conical intermeshing co-rotating screws). The screws had decreasing diameter from 43 mm to 28 mm along its length of 365 mm. The revolution speed of 140 rpm was constant during the processing. The die nozzle had diameter of 3 mm. The barrel temperature could be independently varied in three zones. During this experiment the temperatures of the first, the second, the third, and the die zones were fixed at 15, 160, and 160, 160°C, respectively. The sample was fed manually as much as the extruder would process (approximately 90 g per min). The extrudate had physical properties very similar to polystyrene foam (Fig.2). It was water insoluble and water resistant and was building static electricity charge when mechanically agitated. Upon cooling the extrudates were collapsing resulting in higher than the original unit density. After airing and steaming or hot air re-expanding the foam several times the original volume was recovered. It had a lower itnit density than the foam from Example 1. Extruded foam pieces 20 mm long with about 18 mm average diameter, were submerged in water in a beaker open to the air at room temperature. The level of the water was adjusted daily by addition of distilled water. After one week the foam lost buoyancy as a result of displacement of the air out of the foam. In three months pieces started chipping off and in six months the piece lost its original shape. In one year there were still small non-degraded pieces of the foam. The compostability of the foam was tested in laboratory compost chambers. The temperature inside the compost chambers was maintained at 50 °C. Identically sized pieces of foam as above were subjected to the conditions in the compost pile (high temperature, high moisture content and high microbial load). After two months in the compost chamber, the foam was structurally intact with some discoloration on the surface.

Example 3

Starch acetate (500 grams) with DS of 3 was mixed and conditioned with 100 grams of ethanol as in Example 1. Immediately before extrusion 25 grams of microcrystalline cellulose (MCC) was added. Extrusion processing was carried out in a single screw C.W. Brabender (Model 2003 GR-8) laboratory extruder at the same conditions as in Example 1. The material had physical properties very similar to polystyrene foam (Fig. 3). It was water insoluble and water resistant, but was building less static electricity charge when mechanically agitated compared to the foam of examples 1 and 2. It had a slightly higher unit density than the foam from Example 1.

Example 4

Starch acetate with DS of 3 (500 grams) prepared, mixed and conditioned as in Example 3, was blended with 100 grams of 25% amylose content corn starch conditioned with 15 grams of water for 12 hours in a separate container. Immediately before extrusion 30 grams of microcrystalline cellulose (MCC) was added. Extrusion processing was carried out in a single screw C.W. Brabender (Model 2003 GR-8) laboratory extruder at the same conditions as in Example 1. The material was water insoluble and water resistant, but was not building any noticeable static electricity charge when mechanically agitated. It had slightly higher unit density than the foam from Example 3 (Fig. 4) and possessed physical properties similar to polystyrene.

Example 5

Starch acetate with DS of 3 (250 grams) mixed with 50 grams of ethanol and conditioned as in Example 3 was blended with 250 grams of 25% amylose content corn starch conditioned with 37.5 grams of water for 12 hours in a separate container. Immediately before extrusion 25 grams of talc was added. Extrusion processing was carried out in a single screw C.W. Brabender (Model 2003 GR-8) laboratory extruder at the same conditions as in Example 1, except the temperature profile. The barrel temperature in the first, the second and the die sections were 15, 180 and 180°C respectively. The material was water insoluble and water resistant, but was not building any noticeable static electricity charge when mechanically agitated. It had a higher unit density than the foam from Example 4 (Fig 5) and possessed physical properties similar to polystyrene.

Extruded pieces 20 mm long with approximately 12 mm average diameter, were submerged in water at the same conditions as the foam from Example 1. The water displaced the air out of the foam in only 24 hours. The fast water penetration is easily explained by the larger number open cells as compared to the foam from Example 1 that was exclusively closed cell foam. Surprisingly it took about 4 months before any significant amount of degradation was noticed and about 8 months to have the foam degraded to smaller pieces. This foam contained 50% native starch and was expected to loose structural integrity faster than the foam from Example 1. Most likely this was due to the good blending between the two types of starch and the less available surface. As it can be noticed from the pictures the cell walls of the foam from this example were thicker than the foam from Example 1, thus the surface to mass ratio was smaller. In addition the good blending as a result of the extrusion process made the regular starch less available to the action of water and microorganisms.

Example 6

Starch acetate with DS of 2 (250 grams) prepared by the method from Example 1 was mixed and conditioned with 50 grams of ethanol as in Example 1 and blended with 250 grams of 25% amylose content corn starch conditioned with 37.5 grams of water for 12 hours in a separate container. Immediately before extrusion 25 grams of talc was added. Extrusion processing was carried out in a single screw C.W. Brabender (Model

2003 GR-8) laboratory extruder at the same conditions as in Example 5. The material was water insoluble and water resistant, but was not building any noticeable static electricity charge when mechanically agitated. It had a higher unit density than the foam from Example 5 (Fig 6) and possessed physical properties similar to polystyrene.

Claims

ClaimsWHAT IS CLAIMED IS:

1. A substantially water resistant expanded polysaccharide composition comprising polysaccharide derivative having a degree of substitution between about 1.5 and about 3.0, the polysaccharide derivative having a beta linkage or an alpha linkage between linear monosaccharide units, provided if the linkage is alpha and the polysaccharide derivative is an ester, the ester is either substituted or contains greater than 3 carbon atoms.

2. A composition of claim 1 wherein the polysaccharide derivative is an ester derivative selected from the group consisting of starch esters, cellulose esters, chitin esters, glycogen esters, hyaluronic acid esters, and dextran esters.

3. A composition of claim 2 wherein the starch ester is selected from the group consisting of starch acetate, starch propionate, starch butyrate, starch pentanoate, and starch hexanoate.

4. A composition of claim 2 wherein the cellulose ester is selected from the group consisting of cellulose acetate, cellulose propionate, cellulose butyrate, cellulose pentanoate, and cellulose hexanoate.

5. A composition of claim 1 wherein the composition has a degree of substitution between about 2.0 and about 2.5.

6. A composition of claim 1 wherein the composition has a degree of substitution of about 2.5.

7. A composition of claim 1 wherein the polysaccharide is selected from the group consisting of potatoes, rice, tapioca, maize, rye, oats, and wheat.

8. A composition of claim 2 wherein the starch ester has an amylose content between about 25% and about 70% by weight.

9. A composition of claim 2 wherein the starch ester has an amylose content between about 50% and about 70% by weight.

10. A composition of claim 1 wherein the composition has a density between about 0.5 lbs/ft³ and about 10 lbs/ft³.

11. A composition of claim 10 wherein the composition comprises cells, the cells having a closed cell structure.

12. A composition of claim 11 wherein the composition has a cell diameter between about 50 micrometers and about 1000 micrometers.

13. A composition of claim 12 wherein the composition has a spring index between about 0.90 and about 1.0.

14. A substantially water resistant expanded polysaccharide composition comprising polysaccharide derivative having a degree of substitution between about 1.5 and about 3.0 and nucleating agent.

15. A composition of claim 14 wherein the polysaccharide derivative is an ester derivative selected from the group consisting of starch esters, cellulose esters, chitin esters, glycogen esters, hyaluronic acid esters, and dextran esters.

16. A composition of claim 15 wherein the starch ester is selected from the group consisting of starch acetate, starch propionate, starch butyrate, starch pentanoate, and starch hexanoate.

17. A composition of claim 15 wherein the cellulose ester is selected from the group consisting of cellulose acetate, cellulose propionate, cellulose butyrate, cellulose pentanoate, and cellulose hexanoate.

18. A composition of claim 14 wherein the composition has a degree of substitution between about 2.0 and about 2.5.

19. A composition of claim 14 wherein the composition has a degree of substitution of about 2.5.

20. A composition of claim 14 wherein the polysaccharide is selected from the group consisting of potatoes, rice, tapioca, maize, rye, oats, and wheat.

21. A composition of claim 15 wherein the starch ester has an amylose content between about 25% and about 70% by weight.

22. A composition of claim 15 wherein the starch ester has an amylose content between about 50% and about 70% by weight.

23. A composition of claim 14 wherein the composition has a density between about 0.5 lbs/ft³ and about 10 lbs/ft³.

24. A composition of claim 23 wherein the composition comprises cells, the cells having a closed cell structure.

25. A composition of claim 24 wherein the composition has a cell diameter between about 50 micrometers and about 1000 micrometers.

26. A composition of claim 25 wherein the composition has a spring index between about 0.90 and about 1.0.

27. A composition of claim 14 wherein the composition comprises between about 1% and about 15% by weight of the nucleating agent.

28. A composition of claim 14 wherein the composition comprises between about 1% and about 5% by weight of the nucleating agent.

29. A composition of claim 28 wherein the nucleating agent is selected from the group consisting of magnesium silicate, calcium phosphate, and magnesium phosphate.

30. A composition of claim 28 wherein the composition further comprises between about 1% and about 50% by weight the filler.

31. A composition of claim 30 wherein the composition comprises between about 30% and about 50% by weight the filler

32. A composition of claim 31 wherein the filler is native starch.

33. A composition of claim 30 wherein the filler is selected from the group consisting of cellulose, ground cellulose, microcrystalline, wood pulp, calcium carbonate, talc, and native starch.

34. A process for the preparation of a substantially water resistant expanded polysaccharide composition comprising a polysaccharide derivative having a degree of substitution between about 1.5 and about 3.0, the polysaccharide derivative having a beta linkage or an alpha linkage between linear monosaccharide units, provided that if the linkage is alpha and the polysaccharide is an ester derivative, the ester is either substituted or contains greater than 3 carbon atoms, the process comprising:

(a) combining the polysaccharide derivative with an organic solvent to form an extrusion mixture; and

(b) extruding the mixture to form the substantially water resistant expanded polysaccharide composition.

35. The process of claim 34 wherein the polysaccharide derivative is an ester derivative selected from the group consisting of starch esters, cellulose esters, chitin esters, glycogen esters, hyaluronic acid esters, and dextran esters.

36. The process of claim 35 wherein the starch ester is selected from the group consisting of starch acetate, starch propionate, starch butyrate, starch pentanoate, and starch hexanoate.

37. The process of claim 35 wherein the cellulose ester is selected from the group consisting of cellulose acetate, cellulose propionate, cellulose butyrate, cellulose pentanoate, and cellulose hexanoate.

38. The process of claim 34 wherein the composition has a degree of substitution between about 2.0 and about 2.5.

39. The process of claim 34 wherein the composition has a degree of substitution of about 2.5.

40. The process of claim 34 wherein the polysaccharide is selected from the group consisting of potatoes, rice, tapioca, maize, rye, oats, and wheat.

41. The process of claim 35 wherein the starch ester has an amylose content between about 25% and about 70% by weight.

42. The process of claim 35 wherein the starch ester has an amylose content between about 50% and about 70% by weight.

43. The process of claim 34 wherein the organic solvent is selected from the group consisting of a C₅ to C₁₀ hydrocarbon, a C_j to C₅ alcohol, a C_j to C₅ fatty acid, a C_x to C₅ fatty acid ester, acetone and tetrahydrofuran.

44. The process of claim 43 wherein the extrusion mixture comprises a ratio of polysaccharide derivative to organic solvent between about 1:1 and about 20:1.

45. The process of claim 43 wherein the ratio of polysaccharide derivative to organic solvent is between 4: 1 and about 6: 1 by weight.

46. The process of claim 45 wherein the organic solvent is ethanol.

47. The process of claim 34 wherein the extrusion mixture further comprises between about 1% and about 15% by weight of a nucleating agent.

48. The process of claim 34 wherein the extrusion mixture comprises between about 1% and about 5% by weight of a nucleating agent.

49. The process of claim 48 wherein the nucleating agent is selected from the group consisting of magnesium silicate, calcium phosphate, and magnesium phosphate.

50. The process of claim 49 wherein the nucleating agent is magnesium silicate.

51. The process of claim 48 wherein the extrusion mixture further comprises between about 1% and about 50% by weight of a filler.

52. The process of claim 51 wherein the filler is selected from the group consisting of cellulose, ground cellulose, microcrystalline, wood pulp, calcium carbonate, talc, and native starch.

53. The process of claim 52 wherein the filler is native starch.

54. The process of claim 53 wherein the extrusion mixture further comprises between about 25% and about 50% by weight of a filler.

55. The process of claim 54 wherein the nucleating agent is magnesium silicate and the filler is native starch.

56. The process of claim 34 wherein the extruder barrel temperature is maintained from about 140° to about 180°C.

57. The water insoluble expanded product produced by the process of claim 55.

58. The process of claim 34 wherein the process further comprising conditioning the extrusion mixture between about 1 hour and about 24 hours prior to the mixture being extruded.

59. The process of claim 34 wherein the extrusion mixture is conditioned between about 8 hours and about 12 hours prior to being extruded.

60. A process for the preparation of a substantially water resistant expanded polysaccharide composition comprising polysaccharide derivative having a degree of substitution between about 1.5 and about 3.0, the process comprising:

61. The process of claim 60 wherein the polysaccharide derivative is an ester derivative selected from the group consisting of starch esters, cellulose esters, chitin esters, glycogen esters, hyaluronic acid esters, and dextran esters.

62. The process of claim 61 wherein the starch ester is selected from the group consisting of starch acetate,' starch propionate, starch butyrate, starch pentanoate, and starch hexanoate.

63. The process of claim 61 wherein the cellulose ester is selected from the group consisting of cellulose acetate, cellulose propionate, cellulose butyrate, cellulose pentanoate, and cellulose hexanoate.

64. The process of claim 60 wherein the composition has a degree of substitution between about 2.0 and about 2.5.

65. The process of claim 60 wherein the composition has a degree of substitution of about 2.5.

66. The process of claim 60 wherein the polysaccharide is selected from the group consisting of potatoes, rice, tapioca, maize, rye, oats, and wheat.

67. The process of claim 61 wherein the starch ester has an amylose content between about 25% and about 70% by weight.

68. The process of claim 61 wherein the starch ester has an amylose content between about 50% and about 70% by weight.

69. The process of claim 60 wherein the organic solvent is selected from the group consisting of a C₅ to C₁₀ hydrocarbon, a to C₅ alcohol, a to C₅ fatty acid, a Cj to C₅ fatty acid ester, acetone and tetrahydrofuran.

70. The process of claim 69 wherein the extrusion mixture comprises a ratio of polysaccharide derivative to organic solvent between about 1:1 and about 20:1.

71. The process of claim 70 wherein the ratio of polysaccharide derivative to organic solvent is between 4:1 and about 6:1 by weight.

72. The process of claim 71 wherein the organic solvent is ethanol.

73. The process of claim 60 wherein the extrusion mixture comprises between about 1% and about 15% by weight of the nucleating agent.

74. The process of claim 60 wherein the extrusion mixture comprises between about 1% and about 5% by weight of the nucleating agent.

75. The process of claim 74 wherein the nucleating agent is selected from the group consisting of magnesium silicate, calcium phosphate, and magnesium phosphate.

76. The process of claim 75 wherein the nucleating agent is magnesium silicate.

77. The process of claim 60 wherein the extrusion mixture further comprises between about 1% and about 50% by weight of a filler.

78. The process of claim 77 wherein the filler is selected from the group consisting of cellulose, ground cellulose, microcrystalline, wood pulp, calcium carbonate, talc, and native starch.

79. The process of claim 77 wherein the filler is native starch.

80. The process of claim 74 wherein the extrusion mixture further comprises between about 25% and about 50% by weight of a filler.

81. The process of claim 80 wherein the nucleating agent is magnesium silicate and the filler is native starch.

82. The method of claim 60 wherein the extruder barrel temperature is maintained from about 140° to about 180°C.

83. The water insoluble expanded product produced by the process of claim 81.

84. The process of claim 60 wherein the process further comprising conditioning the extrusion mixture between about 1 hour and about 24 hours prior to the mixture being extruded.

85. The method of claim 60 wherein the extrusion mixture is conditioned between about 8 hours and about 12 hours prior to being extruded.