WO2003051980A1

WO2003051980A1 - Method of molding a biodegradable article

Info

Publication number: WO2003051980A1
Application number: PCT/CA2002/002005
Authority: WO
Inventors: Doug Harle; Sunmin Wang; Richard C. Green
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-12-19
Filing date: 2002-12-19
Publication date: 2003-06-26
Anticipated expiration: 2004-06-19
Also published as: AU2002351622A1; CA2365505A1

Abstract

A thin walled article, for example a biodegradable tray is formed by a method using a mixture comprised substantially of wheat flour. The mixture is subjected to pressure within a heated mold for cooking the mixture under pressure to produce the article. Water is added to the mixture having a combined weight which is less than 23% of the total weight of the mixture. The mixture thus has the consistency of a moistened powder before being placed in the mold. The mixture is thus readily mixed and handled while permitting various additives to also be readily added to the mixture. These additives may include a powdered dye, a pre-gelatinised starch, a binding agent (for example guar gum), a humectant (for example D-Sorbitol), a cellulose fibre (for example a natural dietary fibre) or a preservative (for example Sodium Benzoate).

Description

M E T H O D O F M O L D I N G A B I O D E G RA D A B L E A R T I C L E

FIELD OF THE INVENTION

The present invention relates to a biodegradable, disposable, thin walled, molded article and more particularly to a method of making an article using flour from an edible crop plant, for example wheat flour, as a main ingredient. BACKGROUND

Environmental friendly and biodegradable containers and packaging materials have received increasing attention and positive feedback from the public during the past decade. Information on related manufacturing technologies and protocols were exchanged and the numbers of biodegradable products available in the market are on the rise.

United States Patent 5,154,982 to Cessna describes biodegradable food trays which are thermoformed from sheets of wood pulp having synthetic pulp, clay and rosin added thereto. The use of synthetic pulp and rosin is required to fuse the sheets together in the thermoforming process.

A review of recent literature showed that renewable agricultural biomasses have been used as the main ingredients to produce disposable trays and packaging containers for various applications. In the work of Frigant et al. (1998), trays were prepared from a formula which comprised wheat starch, pre-gelatinized starch, starch acetate, water and ethanol. The mixture was molded at 250 °C to form a tray with a 1.5 mm thickness.

US Patent 4,125,495 to Griffin reported that trays used to hold fresh meat could be made from a mixture, which included acrylonitrile/ butadiene/ styrene (100 parts by weight), corn Starch (175 parts by weight), ethyl oleate (0.6 parts by weight), oleic acid (0.05 parts by weight), and titanium dioxide pigment (3.0 parts by weight). The mixture was heated by steam at 90 psi and stripped from a 2-roll mill as a smooth hide about 3 mm thick. The hide was subsequently thermoformed, after re-heating to 150 °C, to make shallow dishes. The dishes were very strong and had a matt white appearance and a water repellant surface, but required several steps for forming. The hydrophobic nature of the composition inhibits the absorption of blood from the meat into the body of the dish which would otherwise cause unsightly staining.

Biodegradable trays have also been made from protein-based materials, such as corn gluten meal which is a by-product of ethanol production (Wei et al., 1996- 1998). The trays were used for short term packaging of fresh food and seed planting cups for horticulture. The use of biodegradable polymers to replace conventional synthetic materials reduces consumption of non-renewable resources and decreases waste through biological recycling to the bio-system. Enormous potentials exist for the development and marketing of environmental friendly and biodegradable products.

US Patent 6,461 ,549 to Meeuwsen describes a method of producing a biodegradable product in which an edible crop plant flour is mixed with wood flour, natural wax and water. The mixture is molded at elevated temperature and pressure to produce a molded product. While wood flour provides some structural integrity to the finished molded product, strength of the product is limited because cellulose in wood flour is already networked and bound with other wood components such as resin and hemicellulose which limits bonding of the various ingredients in the molded product. Furthermore, the complex mixture of aliphatic esters and aliphatic higher alcohols in the natural wax may migrate within the structure so that the emulsification and stabilization properties of the tray formulation would be limited. SUMMARY

According to one aspect of the present invention there is provided a method of making a molded article, said method comprising: providing a grouping of dry ingredients including an amount of plant flour, an amount of hydrocolloid, an amount of cellulose fibre, an amount of alcohol sugar and an amount of pre-gelatinised starch; providing an amount of water; mixing said grouping of dry ingredients with said amount of water to form a mixture; providing a mold; filling the mold with the mixture; heating the mold; applying pressure to the mixture within the mold so as to form a thin walled article from the mixture; and releasing the article from the mold after a prescribed cooking time has expired.

The amount of plant flour may have a weight in a range between 50% and 75% of a combined weight of said grouping of dry ingredients, but is preferably in a range between 50% and 60% of said grouping of dry ingredients, and is most preferred to be approximately 55% of a combined weight of said grouping of dry ingredients. The plant flour preferably comprises flour derived from an edible crop plant, for example wheat flour.

The amount of hydrocolloid may have a weight in a range between 5% and 15% of a combined weight of said grouping of dry ingredients, but is preferably in a range between 7% and 13%, and is most preferred to be approximately 10% of a combined weight of said grouping of dry ingredients.

The hydrocolloid is preferably a long-chain, high molecular weight polymer, which may comprise a plant seed gum, for example guar gum.

The amount of cellulose fibre may have a weight in a range between 5% and 15% of a combined weight of said grouping of dry ingredients, but is preferably in a range between 7% and 13%, and is most preferred to be approximately 10% of a combined weight of said grouping of dry ingredients.

The cellulose fibre preferably comprises a dietary fibre which is a pure, refined cellulose, for example Solka-Floc.

The amount of alcohol sugar may have a weight in a range between 2% and 10% of a combined weight of said grouping of dry ingredients, but is preferably in a range between 3% and 7%, and is most preferred to be approximately 5% of a combined weight of said grouping of dry ingredients.

The alcohol sugar preferably comprises a sugar which does not undergo carmelization, and which includes a plurality of hydroxyl groups which are available for bonding.

The amount of pre-gelatinised starch may have a weight in a range between 10% and 30% of a combined weight of said grouping of dry ingredient, but preferably is in a range between 15% and 25%, and is most preferred to be approximately 20% of a combined weight of said grouping of dry ingredients.

The amount of water may have a weight in a range between 5% and 85% of a combined weight of said grouping of dry ingredients, but preferably is in a range between 10% and 20% of a combined weight of said grouping of dry ingredients, and is most preferred to be approximately 15% of a combined weight of said grouping of dry ingredients.

The method may include adding a preservative to the grouping of dry ingredients, for example sodium benzoate. The amount of sodium benzoate may have a weight which is in a range between 0.1 % and 0.9% of a combined weight of said grouping of dry ingredients, but is preferred to be approximately 0.5% of a combined weight of said grouping of dry ingredients.

At least one of the amount of plant flour, the amount of hydrocolloid, the amount of cellulose fibre, the amount of alcohol sugar and the amount of pre-gelatinised starch, preferably includes between 3 and 6 hydroxyl groups per molecule which are available for bonding.

With few biodegradable additives to the flour and water, various improvements to strength and appearance can be readily achieved. The use of pressure provides reasonable results with very low water content to eliminate the usual additional steps of drying, conditioning or additional forming processes normally required when forming a disposable molded article. By permitting low water content, reasonable results using flour from an edible crop plant, for example wheat flour, can be achieved because excessive steam pockets are unlikely to develop which would normally reduce the strength and reduce the uniformity of the appearance of the article. The pressure applied during cooking allows partial gelatinization of the starch to occur using the low water content.

The pressure is preferably applied to the mixture in the range of 59 psi to 946 psi. An ideal pressure is between 236 and 355 psi, but variation within the preferred range still provides reasonable results.

The mold is preferably heated to a temperature in the range of 100 degrees Celsius to 150 degrees Celsius. An ideal surface temperature of the dies of the mold is between 120-130 degrees Celsius.

The water in the mixture preferably has a combined weight which is less than 23% of the total weight of the mixture. The weight of water noted herein preferably includes the water content of the wheat flour added to the mixture.

The mixture preferably has a powder like consistency when it is placed in the mold. The water content added to the flour is sufficiently low to only slightly moisten the flour, thus producing a moistened powder consistency which is easily mixed and handled unlike dough when too much water is added.

The prescribed cooking time is preferably in the range of 6 minutes to 12 minutes.

The flour may comprise either whole wheat flour or white refined wheat flour, as well as a variation of other flours derived from edible crop plants which have similar characteristics.

The mold is preferably preheated before being filled with the mixture.

Water contained in the article released from the mold preferably has a combined weight which is substantially less than 23% of a combined weight of the article.

Pressure applied to the mixture preferably has a substantially constant magnitude throughout the prescribed cooking time. Variation of the pressure applied to the mixture may be required to accommodate for variation in the dimensions of the mixture as it is cooked.

The mold preferably comprises a pair of mating dies which are urged towards one another when applying pressure to the mixture. The method may include moving the dies towards one another during the prescribed cooking time so as to apply a substantially constant pressure on the mixture as water is released from the mixture.

The powder like consistency of the mixture enables various powdered additives to be easily mixed into the mixture without extra water being required. These additives may include a powdered dye, a pre-gelatinised starch (preferably corn starch), a binding agent (preferably guar gum), a humectant (preferably D-Sorbitol), a cellulose fibre (preferably a dietary fibre) and/or a preservative (preferably Sodium Benzoate).

According to a second aspect of the present invention there is provided a method of making a molded article, said method comprising: providing a grouping of dry ingredients including an amount of plant flour and an amount of hydrocolloid; providing an amount of water; mixing said grouping of dry ingredients with said amount of water to form a mixture; providing a mold; filling the mold with the mixture; heating the mold; applying pressure to the mixture within the mold so as to form a thin walled article from the mixture; and releasing the article from the mold after a prescribed cooking time has expired.

According to a third aspect of the present invention there is provided a method of making a molded article, said method comprising: providing a grouping of dry ingredients including an amount of plant flour and an amount of cellulose fibre; providing an amount of water; mixing said grouping of dry ingredients with said amount of water to form a mixture; providing a mold; filling the mold with the mixture; heating the mold; applying pressure to the mixture within the mold so as to form a thin walled article from the mixture; and releasing the article from the mold after a prescribed cooking time has expired.

According to a fourth aspect of the present invention there is provided a method of making a molded article, said method comprising: providing a grouping of dry ingredients including an amount of plant flour and an amount of alcohol sugar; providing an amount of water; mixing said grouping of dry ingredients with said amount of water to form a mixture; providing a mold; filling the mold with the mixture; heating the mold; applying pressure to the mixture within the mold so as to form a thin walled article from the mixture; and releasing the article from the mold after a prescribed cooking time has expired.

According to a fifth aspect of the present invention there is provided a method of making a molded article, said method comprising: providing a grouping of dry ingredients including an amount of plant flour and an amount of pre-gelatinised starch; providing an amount of water; mixing said grouping of dry ingredients with said amount of water to form a mixture; providing a mold; filling the mold with the mixture; heating the mold; applying pressure to the mixture within the mold so as to form a thin walled article from the mixture; and releasing the article from the mold after a prescribed cooking time has expired.

According to a further aspect of the present invention there is provided a thin walled molded article formed of a mixture including an amount of plant flour, an amount of hydrocolloid, an amount of cellulose fibre, an amount of alcohol sugar, an amount of pre-gelatinised starch and water.

The article preferably has a thickness approximately in a range of 3 millimetres to 4 millimetres.

The low water content in a tray formed substantially of flour from an edible crop plant provides a biodegradable tray which maintains a reasonable consistency even when exposed to water for an given period of time. Trays produced from a high pressure molding process, even when formed substantially of wheat flour, have a high capacity to resist water absorption. BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which illustrate an exemplary embodiment of the present invention:

Figure 1 is a top plan view of a tray.

Figure 2 is a sectional view of the tray along the line 2-2 of Figure 1.

Figure 3 is a front elevational view of the hydraulic press and mold.

Figure 4 is a sectional view of the mold along the line 4-4 of Figure 3. DETAILED DESCRIPTION

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are now described. All documents and publications mentioned hereunder are incorporated herein by reference.

Referring to Figures 1 and 2 there is illustrated a tray 12. The tray 12 is a biodegradable, thin walled, molded article which can be formed using various ingredients in combination with flour from an edible crop plant as described herein. The tray 12 illustrated herein in Figures 1 and 2 is only one example of a molded article which can be formed according to the present invention.

The tray 12 has a flat bottom 14 which is circular in shape with sides 16 extending at an incline upwardly and outwardly from a periphery of the bottom 14 to an annular upper flange 18 about a top end of the tray 12. The bottom sides and upper flange have an even thickness of approximately 3 to 4 mm. The selection of the thickness depends upon the desirability of strength as well as the desirability of ease of manufacturing by reducing cooling time and raw materials used. The tray 12 being molded, has an even surface with a slight texture resulting from the texture of the particles used as ingredients, for example the particles in whole wheat flour. The tray 12 is hard with a somewhat water resistant surface as a result of the processes to be described herein in which starches in the raw ingredients are partially gelantinized. A. MATERIALS AND METHOD

1. Tray Ingredients

The tray 12 is formed from a mixture having the following ingredients:

Wheat flour and whole wheat flour: The flours were used as main tray ingredients. Commercial all purpose refined wheat flour and whole wheat flour were purchased from a local supermarket. Wheat flour can be used to obtain reasonable results with water when using a thermo-molding process. The addition of few additives provides improved results. Other flours from edible crop plants having similar characteristics could be effectively used in place of wheat flour.

Pre-qelatinized corn starch: Pre-gelatinized corn starch was used as structure/strength builder. The pre-gelatinized starch assists in resisting cracks by adding strength and some flexibility to the finished tray. It was supplied by Charles Tennant & Company (Weston, Ontario, Canada).

D-Sorbitol: D-Sorbitol is a humectant which was used as a softner or moisture holder. By retaining some moisture, the finished tray has reduced brittleness. It was supplied by Fisher Scientific (Fairlawn, NJ, USA).

Fibre: A natural dietary fibre (Solka-Floc) was used as a structure/strength element to increase strength by providing some increased flexibility and thereby reduce brittleness. It was supplied by Canada Colors and Chemical Limited (Don Mills, Ontario, Canada).

Guar gum: Guar gum was used as a binder and water barrier for added strength and reduced flexibility. It was supplied by Hercules Inc. (Wilmington, DE, USA).

Sodium Benzoate: Sodium benzoate was used as a preservative and applied at 0.5% in the tray formula. Colorants: Three food grade colorants (red, orange, and purple) were added separately to the tray formula at 0.14% (weight of colorant/ weight of dry ingredients, x100%).

Water: Water was used to mix with tray ingredients. It was also used to dissolve colorants in some embodiments.

2. Development of A Baking Method

Pre-weighed dry ingredients were mixed with water in a Hobart Food Mixer (Model: N-50, Hobart Canada, Inc., Don Mills, Ontario, Canada) for 5 min. The dough developed was allowed to sit for 1 h before it was manually sheeted to 3-4 mm in thickness. The dough sheet was placed between two 9" pie pans, which were then clamped. Trays were baked at 110-170 °C for 1-2 h. After the baking, tray and the pans were cooled to room temperatures before the tray was released.

The tray formula was studied. Baked trays were evaluated for uniformity in shape and color, and surface smoothness. Baking temperatures (110-170 °C) and baking time (1-2 h) were investigated.

The baking study was designed to determine optimum tray formula and baking protocol. It formed a basis for development of press thermo-molding method.

3. Development of A Thermo-Molding Method

The thermo-molding method suits the purpose for low cost and mass production of trays with consistent quality. The thermo-molding method uses a hydraulic press 30, as shown in Figures 3 and 4, for forming the trays 12 under heat and pressure.

The hydraulic press 30 includes a frame 32 having an upper support member 34 spanning laterally across a top end thereof and a lower support member 36 spanning laterally across the frame 32 spaced below the upper support member 34. A mold is provided on the press 30 which includes a lower female die 38 and an upper male die 40. The lower female die 38 is fixed on the lower support 36 of the frame and includes a recessed molding surface 42 in a top side thereof which mates with a lower surface of the molded article.

The upper male die 40 is mounted above the lower female die 38 for vertical sliding movement in relation to the lower female die. The upper male die 40 is supported at respective corners on shafts 44 extending upwardly from the lower female die and slidably mounting the upper die thereon. The upper male die 40 includes a protruding molding surface 46 in a bottom side thereof which is arranged to fit within the recessed molding surface 42 of the lower female die. The protruding molding surface 46 is arranged to mate with the upper surface of the molded article.

A plurality of stops 48 are provided about a periphery of the male die 40 for engaging between the upper and lower dies to prevent the dies from moving closer than 3 mm away from one another. The distance between the dies as prescribed by the stops 48 is predetermined based upon the desired final thickness of the molded article.

A series of three electric heating elements 50 are mounted within each of the dies 38 and 40 evenly spaced apart from one another so as to be arranged to heat the respective dies with a substantially even molding surface temperature. Separate controls 52 including respective thermostats are provided for controlling the temperature of the respective dies within a preset range of temperatures or at a specific prescribed temperature for each die.

A hydraulic piston cylinder 54 is provided being coupled at a cylinder end on the upper support 34 of the frame and being coupled at a piston and on the upper male die 40 for controlling the relative position of the upper male die in relation to the lower female die as the hydraulic piston cylinder is extended and contracted. Extension of the hydraulic piston cylinder urges the upper male die 40 downwardly towards the lower female die for applying pressure to a mixture located between the dies. A gauge 56 is coupled to the hydraulic piston cylinder 54 for determining the amount of pressure exerted on the mixture within the mold by the hydraulic piston cylinder. A pressure control element 58 is provided for controlling the amount of pressure exerted on the mold in response to readings from the gauge 56.

The gauge 56 records the actual pressure of fluid within the hydraulic piston cylinder 54. Due to the difference in cross sectional area of the chamber within the piston cylinder and the cross sectional area of the upper and lower dies, the actual pressure on the mixture between the dies will only be a fraction of the pressure recorded by the gauge 56. For example, in the illustrated embodiment, the cylinder has a radius of approximately 2.25 inches while the upper and lower dies have a radius of approximately 4.625 inches. By calculating the cross sectional areas of each, the dies are determined to have a cross sectional area which is approximately 4.23 times greater than that of the piston cylinder and thus the pressure of fluid in the piston cylinder as measured by the gauge will be 4.23 times greater than the actual pressure acting on the mixture between the dies.

The hydraulic press 30 (Princess Auto Ltd. Winnipeg, MB) used for the thermo-molding has a maximum 30 T force load. The mold has a heating capability and was designed for use in the press 30. As noted above, the mold comprises basically of two parts, an upper male die and a lower female die, both of which are made from aluminum metal. Both dies are tray shaped, and measure 160-240 mm in diameter and 25 mm in depth. The mold and associated connections for the press were manufactured at AJ Machine & Manufacturing Ltd. (Saskatoon, SK). Also as noted above, three electrical heaters each are housed in the upper and lower die, which allow die surface temperatures to reach 150 °C or higher. Die temperatures are displayed and can be adjusted through a control box. The lower die is stationary, while the upper die is able to travel downward or upward. A minimum gap of 3 mm between the two dies is ensured when they are completely closed.

The tray preparation procedures are described as follows. Both dies were pre-heated to pre-determined surface temperatures, which were between 100-140 °C. A pre-determined amount of tray formula (275 g) was placed into the lower plate lined with an aluminum foil, and was spread evenly. Then another sheet of aluminum foil was placed on the top of the evenly spread formula. The use of aluminum foil was to prevent the tray from sticking to the dies when the tray was released after molding. The upper plate was then gradually lowered to compress the formula to a pre-determined pressure, which ranged from 59 to 473 psi. Simultaneous actions of compression, cooking and formation were thus exerted on the formula. Following 6-15 min holding period, the tray was released by slowly raising the upper die.

A sufficient amount of the mixture for forming the tray is placed within the mold so as to produce a tray having a thickness in the order of 3 to 4 millimeters. Thinner and thicker trays can be molded, however thinner trays will be less strong and thicker trays will require more cooling time and more raw material. 4. Characterization of Trays

Trays produced from both baking and thermo-molding methods were evaluated subjectively for their physical appearance, uniformity, color, flexibility, and overall quality. An overall rating was assigned to each tray, which was categorized as "Good", "Fair", "Fair to Poor", "Poor", and "Very Poor". In addition to the subjective evaluations, trays were also characterized for strength and water absorption/resistance. 4.1 Tray strength:

A Texture Test System (model TMS-90, Food Technology Corp., Rockville, MD) was used. The flat bottom components of the trays were cut into four 7.5x4 cm rectangular pieces, which were then placed horizontally onto a cylinder-type round testing cell (diameter: 6.5 cm). A round plunger having 1.9 cm diameter travelled at a speed of 20 mm/min to hit the piece until it was broken. Maximum breaking forces were recorded, and a mean maximum breaking force, following four repetitive tests, was used to characterize the strength of trays.

4.2 Water absorption and resistance:

Trays were floated in a sink filled with water at room temperature. Trays were evaluated for deformation for a period of 24 h. With another set of trays, 50 ml of water was poured into each tray. The trays were placed on the lab counter for a period of 24 h, during which trays were evaluated for deformation and water uptake.

Tray water absorption and resistance was characterized. B. RESULTS AND DISCUSSION 1. Baking Method

Tests were carried out to determine appropriate levels of ingredients, water content, and baking conditions.

1.1. Effect of Dough Water Content

Doughs made from whole wheat flour having various water concentrations were sheeted and baked at 140 °C for 1.5 h, as previously described. Trays were evaluated for uniformity and surface smoothness. The results are summarized in Table 2. It was found that an appropriate water content in the dough was essential in order to produce even surfaced and homogeneous trays. Tray uniformity was not obtained if water content in the dough was 40% or less. Water content higher than 50% resulted in air embedded trays. Optimum water content for whole wheat flour was determined to range between 42-45%. At the optimum water level, dough was fully developed and non-sticky during handling and sheeting. The resulting trays generally had a smooth surface and were homogeneous overall.

Table 1 — Effect of water content on tray quality³

^aTrays were made from whole wheat flour and water only. Tray thickness ranged from 3-4 mm. bdough water content was calculated by including initial water in whole wheat flour.

1.2. Effect of Baking Temperature and Duration

Using the optimum water content of 42.5%, doughs made from whole wheat flour and water were sheeted and baked at 100, 140, 170 °C, for 1.0, 1.5, and 2.0 h, respectively. The results indicated that low baking temperature of 100 °C, and/or short baking period of 1 h was insufficient to fully gelatinize the starch and resulted in under- cooked trays. Conversely, high baking temperature (170 °C), and/or prolonged baking periods (2.0 h) resulted in over-cooked trays, which were partially burnt. Baking temperatures at 140+10 °C, coupled with a baking period of 1.5 h were found to be optimum to produce trays with the best external appearance and uniformity.

Following the determination of optimum water content and baking conditions, the effect of individual ingredients on tray physical properties were evaluated. 1.3 Effect of Ingredients

The effect of individual ingredients on the physical appearance of the trays was evaluated after they were baked for 1.5 h at 140 °C. Table 3 shows that trays made from whole wheat flour alone was very brittle. Brittleness was reduced when a strong binding agent (guar gum), humectant (D-sorbital), or fibrous material (Solka-Floc) was introduced. Inclusion of pre-gelatinized starch lightened the color of tray. It may also enhance tray strength. It was concluded that incorporation of ingredients other than whole wheat flour and water were essential in order to produce homogeneous, even surfaced and less brittle trays.

A Tray formula was therefore proposed. It included 50-75% whole wheat flour, 10-30% pre-gelatinized starch, 5-10% guar gum, 5-10% D-sorbitol, 5-10% Solka- Floc, 0.1-0.5% sodium benzoate (as preservative), and an optimum amount of water. Following more baking tests, the optimum tray formula was determined as follows: whole wheat flour (55%), Pre-gelatinized starch (20%), Guar gum (10%), D-sorbitol (5%), Solka- Floc (10%), Sodium Benzoate (0.5%) and Water (85%). The weight of each ingredient is expressed in parentheses as a percentage of the total dry ingredients combined. Trays baked using the above formula were smooth in surface, homogeneous overall, and less brittle. Overall ratings obtained from the optimum trays were between "Fair" and "Good", which exceeded the best ratings obtained on trays with only one extra ingredient incorporated (Table 2).

Table 2 — Effect of Ingredients on Physical Properties of Baked Trays

2. Press Thermo-Molding Method

Preliminary trials were carried out in order to apply the optimum tray formula determined from the baking method to that of thermo-molding method. These trials were also designed to determine thermo-molding conditions, which included die temperature, pressure and cooking time.

2.1. Effect of Water Concentration

It was found that the optimum baking formula determined from the baking method was not applicable for the press thermo-molding method due to its high moisture content. It was observed that during the molding, the dough sheet was completely enclosed within the two heated dies, preventing moisture from escaping. When the dies were opened after molding, sudden release of pressurized moisture instantly destroyed tray integrity. Water content in the dough therefore had to be reduced.

Following preliminary molding trials, the optimum water content as well as optimum tray formula for thermo-molding method was determined to be as follows: whole wheat flour (55%), pre-gelatinized starch (20%), Guar gum (10%), D-sorbitol (5%), Solka- Floc (10%), Sodium Benzoate (0.5%) and Water (14.7%). The weight of each ingredient is expressed in parentheses as a weight percentage of the total ingredients combined (excluding added water), on an as is basis.

With such low water addition, the formula prepared for the molding method was essentially a moistened flour mixture. No sheeting and sheeting related equipment was necessary. The formula could be accurately weighed, divided and spread. 2.2. Effect of Thermo-molding Conditions

Thermo-molding conditions, such as die temperatures, pressure, and cooking time would affect overall tray quality and appearance.

Table 3 — Effect of Thermo-Molding Conditions On Tray Quality

A 275 g (as is) of the optimum tray formula was used for one molding trial. Trays produced were evaluated for uniformity and surface smoothness (Table 3). It was found that die temperatures lower than 120 °C (Tray #1 , Table 3), and/or cooking time less than 8 min (Tray #4, Table 3) resulted in unevenly cooked trays. The trays produced were not uniform or homogeneous in terms of color and shape. However, prolonged cooking time resulted in over cooked trays, especially at the bottom part of the tray (Tray #1 , Table 3). Excessive pressure, coupled with high die temperature resulted in partially burnt trays (Tray #4, Table 3).

The optimum thermo-molding conditions were concluded as follows: die temperatures between 120 and 130 degrees Celsius, pressure between 118 and 355 psi and cooking time between 8 and 10 minutes.

Trays produced based on the optimum conditions had the highest ratings upon evaluation (Tray #2-3, Table 3). The trays were evenly cooked and homogeneous in shape and color.

3. Characterization of Trays

3.1 Trays Produced From Baking and Molding Method

Trays produced by the press thermo-molding method (product "C", "C1 ", "C2", "C3", and "A" were generally consistent in uniformity, shape and color (see their formulae and production conditions in Table 4). These trays were strong enough to hold 5 kg of weight without bending. Maximum breaking forces described previously ranged between 18.8-21.8 N, regardless of added colorants (Table 4). However, it was difficult to produce trays with consistent uniformity and shape by using the baking method ( Table 4). The baked tray also had a low maximum breaking force of 10.2 N (Table 4).

Tray "A" is light brown in color compared to that of tray "C". This is the result of replacing whole wheat flour with all purpose white wheat flour (Table 4). Color uniformity of the tray "C" would be improved if the bran in the commercial whole wheat flour were milled, instead of being blended as large pieces.

Table 4 — Tray Formula and Production Method

3.2 Colored Trays

Trays incorporating the three food grade colorants are described in the above table. These trays were produced by the thermo-molding method using the optimum formula and molding conditions (Table 4). It was possible to incorporate colorants into the tray formula. Colorants could be added directly into the dry ingredients, or pre-dissolved in water followed by mixing.

Addition of colorants offers variety to the products. It makes the external appearance of the tray more attractive.

3.3 Tray Water Absorption/Resistance

The water flotation test described previously showed that trays produced from the molding method basically retained their original shape after a 24 h period, although the lower surface of the trays were partially swollen.

Adding 50 ml of water into trays showed that trays were able to absorb all the water and to keep the original shape within a 24 h period.

Based on the above tests and observations, it was concluded that trays produced from the molding method had a higher capacity to resist water absorption.

High strength and high water resistance exhibited on the trays produced from the molding method could be explained as follows: a) water content in the molding formula was low. b) under the thermo-molding conditions, more than 2/3 of the starch in wheat flour were gelatinized. It resulted consequently in high tray strength. c) tray surface was better "sealed" with the molding method due to a combination of high die temperatures and pressure. It resulted in highly water resistant trays.

3.4. Economics Assessment On Large Scale Production

The current work has assessed the feasibility to produce biodegradable trays made from wheat flour based materials.

The press thermo-molding method requires fewer steps, which would include mixing, weighing and molding. It presents a much shorter and compact tray production cycle, thereby saving costs on labor and energy consumption.

Trays produced by the molding method had higher qualities, which were reflected by product (trays) consistency, uniformity, surface smoothness, strength, and water resistance. The molding method was concluded to be more suitable for low cost, mass produced trays having consistent qualities.

The information and the technologies developed from this project are not restricted to making trays. They can be applied to other product development involving various application potentials. When using the thermal molding method, a mixture is first prepared using wheat flour, either whole wheat flour or white refined wheat flour and water. A low water content is included so as to achieve a moistened powder in which the mixture has a powder-like consistency. The combined weight of the water content of the mixture including the water content in the flour used in the mixture is less than 23% of the total weight of the mixture. Desired additives noted above including colourant, can be mixed into the mixture as a dry powder so that the mixture is easy to mix and handle. The use of each additive provides considerable improvements to the quality of the molded article as noted above but flour from an edible crop plant and water with only one or a few additives is sufficient to achieve reasonable results.

Once the mixture is prepared, the dies of the mold are preheated and separated so that the mold may be filled with a prescribed amount of the prepared mixture which is spread evenly within the lower female die 38. The thickness of the powder used as raw material is greater than the prescribed minimum separation of the dies before the cooking operation begins. The dies are then urged together with pressure being applied to the mixture in the order of approximately 236 psi. The dies are continued to be moved towards one another during the cooking process to maintain a consistent 236 psi pressure as the mixture is compressed during cooking. The prescribed duration of the cooking time is between 8-10 minutes.

Once the cooking time has expired pressure is gradually released over an elapsed period of time to allow steam to escape from the mold while maintaining the form of the molded article between the lower and upper dies. Once the dies are separated, the article may be released from the mold for cooling. After cooling, the molded article has a hard smooth surface with minimal texture and a water content which is less than the starting water content of the mixture which was less than 23% of the weight of the mixture.

Additional trials were conducted using a mixture consisting solely of wheat flour and water. Trials for both whole wheat flour and refined white wheat flour were conducted using a die temperature of 120 to 130 degrees Celsius under pressure of 189 to 284 psi for approximately 9 minutes. The levels of starch gelatinized in these trials were then analysed.

The optimum water content for the trials using flour and water was determined to be a combined weight of water (including water content in the flour itself) which was between 20% and 23% of the combined weight of the overall mixture. Water content less than 20% resulted in trays that were too dry and therefore not completely integral, while water content greater than 23% resulted in air pockets formed in the trays due to excess steam being produced during the thermo-molding process. Greater than two thirds of the starch in the flour was determined to be gelatinized as a result of the molding conditions of temperature and pressure applied to the mixture. In further embodiments, the use of a mechanism to release steam while maintaining pressure on the mixture would permit more water to be added for greater gelatinization without the formation of pockets within the molded article.

The use of pressure during the heated cooking time allows a low water content while still maintaining a sufficient degree of gelatinization of the starches of the wheat flour so as to provide a strong and hard finished molded article, so that little or no pregelatinized starch is required even with the low water content described above.

The purpose of cellulose fibre, for example Solka-Floc, is to impart a structural integrity to the mixture. The main advantage of using cellulose fibre is that it is a refined cellulose fibre which is pure and thus, will react more effectively with the starch and provide greater structural integrity to the mixture.

The hydroxyl ( H) groups on the cellulose molecule will form hydrogen bonds with the amylose fraction of the starch. This provides a stronger and more stable network in the tray.

Hydrocolloids or hydrophilic colloids which are used herein are more commonly referred to as gums and are long-chain, high-molecular-weight polymers that dissolve or disperse in water to give a thickening and sometimes gelling effect. The hydrocolloids which are useful in the present formulation and which are intended to be designated generally herein by the term hydrocolloids, include non-starch hydrocolloids including modified starches but not natural starches. The particular hydrocolloid used in this patent formulation was guar gum but could be selected from a variety of natural and modified natural hydrocolloids as defined by Glicksman (1982). The natural gums may include plant exudates such a gum Arabic, gum tragacanth and gum ghatti; seaweed extracts such as agar, carrageenan and alginates; plant seed gums such as guar gum, locust bean gum and psyllium and fermentation gums such as xanthan gum. Modified natural gums may include carboxymethylcellulose, methylcellulose, modified starches and low methoxyl pectin. Though different hydrocolloid gums may have different levels of association with starch due to the variation in carbohydrate composition and configuration of the gum molecules among the different gums, variations to the amounts used in the mixture can be used to obtain effective results with numerous different gums. Functional properties that the hydrocolloids play in this formulation are adhesiveness and emulsifying properties, prevention of syneresis (loss of moisture due to re-association of the starch) and binding properties.

The incorporation of gums into the formulation may provide an environment that promotes stablility by hydrogen bonding of the carbohydrates of the hydrocolloid gum (ie. guar) with amylose in the starch (Glicksman, 1982; Miller, et al., 1973). The result is the entanglement of the gum carbohydrates with the soluble starch and with the swollen starch granules and thus, a stable polymer network is formed.

The presence of gums in the formulation also provides stability to storage of the formulation by binding amylose and preventing retrogradation (re-forming of the starch granule and loss of water) of the starch that would lead to brittleness of the biodegradable tray.

Water proofing of the tray may occur as a result of the high heat and pressure applied to the surface of the tray during forming. The heat causes drying and some carmelization of the carbohydrates on the surface of the tray. Carmelized sugars are hardened and act as a water barrier for the carbohydrate polymer network in the tray.

Hydrogen bonding, among the guar gum, starch, and cellulose carbohydrates results in effective emulsification of the tray ingredients. Each of the guar gum, starch, cellulose and alcohol sugar include plural hydroxyl groups available for bonding, typically in the range of 3 to 6 available hydroxyl groups.

Sugar alcohol is a simple compound which will not migrate and thus, is relatively stable. Sorbitol is a humectant that helps stabilize the water content of the tray formulation. The sugar alcohols do not undergo Maillard browning and caramelization like other sugar substitutes.

The effect of hydrogen bonding between the hydroxyl groups on sorbitol and those on the surrounding carbohydrate ingredients (starch, guar gum and cellulose) results in a stable, stronger tray with a longer shelf-life compared to known formulations using flour.

Although some carmelization is beneficial on the surface of the tray to impart water barrier properties, the internal moisture of the tray needs to be stabilized in order to prevent brittleness of the product.

Sorbitol is a sugar alcohol or acyclic polyol (Emodi, 1982). The sugar alcohols are produced by reduction of sugars (glucose in the case of sorbitol). Each of the dry ingredients added to the flour, including the cellulose fibre (e.g. Solka-Floc) , the hydrocolloid (e.g. guar gum), the alcohol sugar (e.g. D-Sorbital) or the pre-gelatinised starch (e.g. corn starch) provides some improved quality over the use of flour and water alone, and accordingly can be used alone or in combination depending upon the desired results.

While various embodiments of the present invention have been described in the foregoing, it is to be understood that other embodiments are possible within the scope of the invention. The invention is to be considered limited solely by the scope of the appended claims. REFERENCES

1 ) Frigant, O, Rinaudo, M., Gontard, N., Guilbert, S., and Derradji, H. 1998. A biodegradable starch based coating to waterproof hydrophilic materials. Starch/Starke, No.50, 292-296.

2) Wei et al., 1996-1998, Pilot-plant production and evaluation of novel co-product derived plastics, Contact Dr.Wei, Dep. Food Sci/Human Nutr , Univ. Illinois, Phone: 217-333-9338.

3) Emodi, A. 1982. Polyols: Chemistry and Applications. In: Food Carbohydrates, Lineback, D.R. and Inglett, G.E., (eds.), AVI Publishing Company, Inc., Westport, CT.

4) Glicksman, M. 1982. . Food Applications of Gums. In: Food Carbohydrates, Lineback, D.R. and Inglett, G.E., (eds.), AVI Publishing Company, Inc., Westport, CT.

5) Miller, B.S., Derby, R.I. and Trimbo, H.B. 1973. A pictorial explanation for the increase in viscosity of a heated wheat starch water suspension. Cereal Chem. 50 : 271 - 280.

Claims

CLAIMS:

1. A method of making a molded article, said method comprising: providing a grouping of dry ingredients including an amount of plant flour, an amount of hydrocolloid, an amount of cellulose fibre, an amount of alcohol sugar and an amount of pre-gelatinised starch; providing an amount of water; mixing said grouping of dry ingredients with said amount of water to form a mixture; providing a mold; filling the mold with the mixture; heating the mold; applying pressure to the mixture within the mold so as to form a thin walled article from the mixture; and releasing the article from the mold after a prescribed cooking time has expired.

2. The method according to Claim 1 wherein the amount of plant flour has a weight in a range between 50% and 75% of a combined weight of said grouping of dry ingredients.

3. The method according to Claim 1 wherein the amount of plant flour has a weight which is approximately 55% of a combined weight of said grouping of dry ingredients.

4. The method according to Claim 1 wherein the plant flour comprises flour derived from an edible crop plant.

5. The method according to Claim 1 wherein the plant flour comprises wheat flour.

6. The method according to Claim 1 wherein the amount of hydrocolloid has a weight in a range between 5% and 15% of a combined weight of said grouping of dry ingredients.

7. The method according to Claim 1 wherein the amount of hydrocolloid has a weight which is approximately 10% of a combined weight of said grouping of dry ingredients.

8. The method according to Claim 1 wherein the hydrocolloid comprises a long-chain, high molecular weight polymer.

9. The method according to Claim 1 wherein the hydrocolloid comprises a plant seed gum.

10. The method according to Claim 1 wherein the hydrocolloid comprises guar gum.

11. The method according to Claim 1 wherein the amount of cellulose fibre has a weight in a range between 5% and 15% of a combined weight of said grouping of dry ingredients.

12. The method according to Claim 1 wherein the amount of cellulose fibre has a weight which is approximately 10% of a combined weight of said grouping of dry ingredients.

13. The method according to Claim 1 wherein the cellulose fibre comprises a dietary fibre.

14. The method according to Claim 1 wherein the cellulose fibre comprises a pure, refined cellulose.

15. The method according to Claim 1 wherein the cellulose fibre comprises Solka-Floc.

16. The method according to Claim 1 wherein the amount of alcohol sugar has a weight in a range between 2% and 10% of a combined weight of said grouping of dry ingredients.

17. The method according to Claim 1 wherein the amount of alcohol sugar has a weight which is approximately 5% of a combined weight of said grouping of dry ingredients.

18. The method according to Claim 1 wherein the alcohol sugar is a sugar which does not undergo carmelization.

19. The method according to Claim 1 wherein the alcohol sugar includes hydroxyl groups which are available for bonding.

20. The method according to Claim 1 wherein the amount of pre- gelatinised starch has a weight in a range between 10% and 30% of a combined weight of said grouping of dry ingredient.

21. The method according to Claim 1 wherein the amount of pre- gelatinised starch has a weight which is approximately 20% of a combined weight of said grouping of dry ingredients.

22. The method according to Claim 1 wherein the amount of water has weight in a range between 5% and 85% of a combined weight of said grouping of dry ingredients.

23. The method according to Claim 1 wherein the amount of water has a weight which is less that 20% of a combined weight of said grouping of dry ingredients.

24. The method according to Claim 1 wherein the amount of water has a weight which is approximately 15% of a combined weight of said grouping of dry ingredients.

25. The method according to Claim 1 including adding a preservative to the grouping of dry ingredients.

26. The method according to Claim 1 including adding an amount of sodium benzoate to the grouping of dry ingredients.

27. The method according to Claim 26 wherein the amount of sodium benzoate has a weight which is in a range between 0.1 % and 0.9% of a combined weight of said grouping of dry ingredients.

28. The method according to Claim 26 wherein the amount of sodium benzoate has a weight which is approximately 0.5% of a combined weight of said grouping of dry ingredients.

29. The method according to Claim 1 wherein at least one of the amount of plant flour, the amount of hydrocolloid, the amount of cellulose fibre, the amount of alcohol sugar and the amount of pre-gelatinised starch, includes plural hydroxyl groups per molecule which are available for bonding.

30. The method according to Claim 1 wherein at least one of the amount of plant flour, the amount of hydrocolloid, the amount of cellulose fibre, the amount of alcohol sugar and the amount of pre-gelatinised starch, includes between 3 and 6 hydroxyl groups per molecule which are available for bonding.

31. The method according to Claim 1 wherein pressure is applied to the mixture in the range of 59 psi to 946 psi.

32. The method according to Claim 1 including heating the mold to a temperature in the range of 100 degrees Celsius to 150 degrees Celsius.

33. The method according to Claim 1 wherein the water in the mixture has a combined weight which is less than 23% of the total weight of the mixture.

34. The method according to Claim 1 wherein the water in the mixture, including water content of the flour added to the mixture, has a combined weight which is less than 23% of a total weight of the mixture.

35. The method according to Claim 1 wherein the mixture has a powder like consistency when it is placed in the mold.

36. The method according to Claim 1 wherein the prescribed cooking time is in the range of 6 minutes to 12 minutes.

37. The method according to Claim 1 wherein the mold is preheated before being filled with the mixture.

38. The method according to Claim 1 wherein water contained in the article upon release from the mold has a combined weight which is substantially less than 23% of a combined weight of the article.

39. The method according to Claim 1 wherein pressure applied to the mixture has a substantially constant magnitude throughout the prescribed cooking time.

40. The method according to Claim 39 wherein the mold includes a pair of mating dies and wherein the method includes moving the dies towards one another during the prescribed cooking time so as to apply a substantially constant pressure on the mixture.

41. The method according to Claim 1 including adding a powdered dye to the mixture before filling the mold with the mixture.

42. A method of making a molded article, said method comprising: providing a grouping of dry ingredients including an amount of plant flour and an amount of hydrocolloid; providing an amount of water; mixing said grouping of dry ingredients with said amount of water to form a mixture; providing a mold; filling the mold with the mixture; heating the mold; applying pressure to the mixture within the mold so as to form a thin walled article from the mixture; and releasing the article from the mold after a prescribed cooking time has expired.

43. A method of making a molded article, said method comprising: providing a grouping of dry ingredients including an amount of plant flour and an amount of cellulose fibre; providing an amount of water; mixing said grouping of dry ingredients with said amount of water to form a mixture; providing a mold; filling the mold with the mixture; heating the mold; applying pressure to the mixture within the mold so as to form a thin walled article from the mixture; and releasing the article from the mold after a prescribed cooking time has expired.

44. A method of making a molded article, said method comprising: providing a grouping of dry ingredients including an amount of plant flour and an amount of alcohol sugar; providing an amount of water; mixing said grouping of dry ingredients with said amount of water to form a mixture; providing a mold; filling the mold with the mixture; heating the mold; applying pressure to the mixture within the mold so as to form a thin walled article from the mixture; and releasing the article from the mold after a prescribed cooking time has expired.

45. A method of making a molded article, said method comprising: providing a grouping of dry ingredients including an amount of plant flour and an amount of pre-gelatinised starch; providing an amount of water; mixing said grouping of dry ingredients with said amount of water to form a mixture; providing a mold; filling the mold with the mixture; heating the mold; applying pressure to the mixture within the mold so as to form a thin walled article from the mixture; and releasing the article from the mold after a prescribed cooking time has expired.

46. A thin walled molded article formed of a mixture including an amount of plant flour, an amount of hydrocolloid, an amount of cellulose fibre, an amount of alcohol sugar, an amount of pre-gelatinised starch and water.