The present invention relates to biodegradable plastics. More particularly, the present invention relates to biodegradable plastics having enhanced rate of biodegradability due to the presence of powdered fruit waste, such as skin and seeds from rambutan, banana, jackfruit and other tropical fruits.

BACKGROUND OF THE INVENTION Environmentally degradable plastics are increasing in popularity because of environmental issues facing the society. The biodegradable plastics currently developed can be categorized into the following that somewhat overlap: i. natural polymers that use polysaccharides such as starch and the like ii. microbial polyesters that use the biological activity of microorganisms iii. blends with accelerated degradation properties that are regular plastics with degradation accelerator additives

iv. chemical synthetics that include aliphatic polyesters and the like. Depending on the particular properties of the different materials, biodegradable plastics are used as raw materials for disposable products and in products that generally do not have to carry heavy loads. Such applications include: agricultural products such as films, sheets, bottles, pots, and bags; products for daily use and tableware such as trays, cases, and straws; some medical equipment; and sports equipment. Nonetheless, the use of biodegradable plastics is still limited and their effect on the general plastics industry as a whole is limited.

Biodegradable plastic offers promise to solve the problem of the disposal of regular plastic. But there have been several obstacles. Depending on the type and ratios of the components in the biodegradable plastic and depending on the environment where the biodegradable plastic is disposed, the rate of biodegradation may be less than desired. Another obstacle is that as the thickness of the product containing biodegradable plastic increases, the biodegradability property is diminished. Furthermore, the life span of the product containing biodegradable plastic might be detrimentally shortened as a result of insects causing damage. A greater problem still is that many polymers are specifically formulated to serve narrow optimized functions, or to display certain manufacturing process behaviors. Substitution with a biodegradable plastic diminishes the effectiveness of these processes and generates an inferior final product. It would therefore be highly advantageous to formulate a way to improve the biodegradability of all plastics while maintaining each plastic's desirable features.

One possibility for achieving this aim would be through the use of an additive to the plastic, in place of currently used common fillers, that increases the plastic's susceptibility to environmental degradation. Additives to plastics are currently used to obtain desirable properties in the plastic. For example, additives are used to impart such properties as strength, hardness, flexibility, color, etc. An extensive review of properties, applications, and toxicologies of additives for plastics is found in: "Chemical Additives for the Plastics Industry", prepared by Radian Corp., Noyes Data Corp, N.J. (1987), the entirety of which is incorporated herein by reference. One possibility of a plastic additive to increase environmental degradability may be a biomaterial such as plant fiber or wood powder.

Fruit processing industry produces wastes, such as skin and seed, which are discarded in abundance. If not handled and managed properly, the fruit wastes can cause disposal problems that lead to adverse environmental effects. Hence, the productive use of such wastes would certainly solve the disposal problems.

In view of the above, it is desirable to provide the inclusion of fruit wastes into biodegradable polymers to fabricate environmentally friendly plastics having enhanced biodegradability rate.

SUMMARY OF THE INVENTION It is an object of the present invention to increase the biodegradability of conventional biodegradable plastic.

It is another object of the present invention to increase the biodegradability of conventional biodegradable plastic without sacrificing processing properties that lead to good molding, extruding and casting. It is yet another object of the present invention to utilize at an industrial production level the skin waste produced from fruit processing, which has little use and are largely unnecessarily discarded. Briefly, the skin from a processed fruit, such as rambutan, banana and jackfruit and a biodegradable plastic or polymer are blended as an industrial material to provide a biodegradable plastic product made from fruit skin in the form of powder that will return to the environment after disposal. A dry powder is created from the skin of rambutan, banana and jackfruit. A product is created from a raw material that is composed of 8 to 45% by weight of dry skin powder of rambutan, banana and jackfruit mixed with biodegradable plastic or polymer. Plastic additives, standard in the industry, can be added to achieve desired properties. For example, a piasticizer may be added in order to soften the biodegradable plastic by increasing its flexibility; polymerization modifiers such as cross-linkers may be added to enhance the properties of the base plastic, especially tensile properties; and a surfactant may be added to lower the surface tension of the liquid, allowing easier spreading and lowering interfacial tension between liquid and dried skin powder.

According to an embodiment of the present invention, a biodegradable plastic product comprises from about 40 to 75% by weight of a biodegradable plastic or polymer, and from about 8 to 45% by weight of a dried powder, the dried powder including fine skin of rambutan, banana and jackfruit.

According to another embodiment of the present invention, a biodegradable plastic product comprises from about 40 to 75% weight of a biodegradable plastic or polymer, from about 8 to 45% by weight of a dried powder, the dried powder including fine skin of rambutan, banana and jackfruit, and from about 10 to 25% by weight of at least one member selected from the group consisting of a piasticizer, a cross-linking agent and a surfactant.

The piasticizer may be, for example glycerol, sorbitol and polyethylene glycol.

The cross-linking agent may be, for example hexamethylenetetramine, glutadehyde, formaldehyde and boric acid. The surfactant is a non-ionic surfactant and may be, for example polysorbate 80, polyoxyethylene glycol and fatty alcohol.

According to another embodiment of the present invention, a method of making a biodegradable plastic product comprises the steps of:

separating a skin component from a fruit that includes rambutan, banana and jackfruit;

cleaning and sanitizing the skin to remove contaminant components from the skin;

soaking the cleaned and sanitized skin component in sodium metasulfit solution to prevent browning;

washing the soaked skin component with water;

slicing the washed skin component to a thickness of 5 to 10 mm;

drying the sliced skin component at 60°C to 80°C to remove moisture;

grinding the dried and sliced skin component to produce a fine powder having a particle size of about 25 to 60 μιη;

making a mixture of from about 8 to 45% by weight of the fine powder, from about 40 to 75% by weight of a biodegradable plastic/polymer, and from about 10 to 25% by weight of at least one additive member selected from the group consisting of a plasticizer, a cross-linking agent and a surfactant; and

forming the biodegradable plastic product.

The biodegradable plastic product of the present invention can also be used as agricultural materials, construction materials, electronic appliance parts, automobile parts, and stationery. The material of the present invention breaks down by biodegradation in landfills to water and carbon dioxide, thereby minimizing the space taken up and extending the life of the landfill. Furthermore, the present invention may be easily composted or incinerated. The present invention produces little smoke, no foul odors, and no toxic gases upon incineration. The present invention can be used in the form of a film, such as in compost bags, garbage bags, and the like.

The above and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 is a schematic diagram of the reaction flask for the formation of biodegradable polymer solution at controlled temperature, according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

The biodegradable plastic product in accordance with the present invention is constituted of a biodegradable plastic blended with the skin of fruits in powder form, the fruits include rambutan, banana and jackfruit, and at least one additive member selected from the group consisting of a plasticizer, a cross-linking agent and a surfactant.

The amounts of each constituent are as follows: i. about 40 to 75% weight percent of biodegradable plastic;

ii. about 8 to 45% weight percent of fruit skin in powder form;

iii. about 10 to 25% weight percent of at least one additive member selected from the group consisting of a plasticizer, a cross-linking agent and a surfactant.

Specifically, the preferred amounts of each of the additive member are as follows: i. about 8.2 to 12.3 weight percent of plasticizer;

ii. about 0.8 to 4.1 weight percent of cross-linking agent; and

iii. about 3.3 to 6.6 weight percent of surfactant.

The method of producing the biodegradable plastic according to the present invention involves the following stages: processing of fruit skin into fine powder;

mixing about 8 to 45% by weight of the fine powder with about 40 to 75% by weight of a biodegradable plastic/polymer and about 10 to 25% by weight of at least one additive member selected from the group consisting of a plasticizer, a cross-linking agent and a surfactant; and

forming the biodegradable plastic product.

As an example of processing the fruit skin, tropical fruit waste, for example rambutan skin, banana skin, jackfruit skin, and the like, are rinsed under running tap water to remove dirt and then are soaked in a disinfectant agent for 30 minutes for sanitization purpose. The fruit waste is further soaked with sodium metasulfit solution for about 30 minutes to present browning and then washed with distilled water. The cleaned fruit waste is then sliced to a thickness of 5-10 mm by using a slicer. The sliced fruit is then dried in a vacuum at 60-80°C for 12 hours to remove moisture. The sliced dried fruit waste is then grinded using a grinder to produce a flour powder in finer particle size.

As an example of mixing the constituents, the range of materials composition used in the blending step is shown in Table 1. A biodegradable polymer, the selected and processed fruit waste in powder form and a plasticizer are physically pre-mixed in deionized water and the mixture is refluxed at a temperature ranging from 85°C to 95°C for 30 minutes. A steady stirring speed is set at an optimum value ranging from 1000 to 1100 rpm in order to enhance the mixing operation. Next, a cross-linking agent is added and the mixture is refluxed at a temperature of 95°C for 40 minutes. This is followed by the addition of a non-ionic surfactant and the mixture is refluxed at a temperature of 95°C for 10 minutes to remove air bubbles trapped and formed during the stirring process. Throughout the mixing and blending step, the stirring speed is maintained at 1000 to 1 100 rpm. A schematic diagram of the reaction flask used to mix and blend the constituents as mentioned above is shown in Figure 1. As can be seen in the figure, the flask is a round bottom flask equipped with a mechanical stirrer. The resulting biodegradable polymer solution is then collected and placed under vacuum condition to remove remaining air bubbles. As an example of forming the biodegradable plastic product, the vacuumed biodegradable polymer solution is immediately poured onto a leveled glass plate framed four glass bars, and spread evenly with a glass rod. After that, a fully dried film is peeled off from the glass plate and then cured in a thermosetting oven to induce a cross-linking reaction. The cast film is then ready to be used for packaging application.

Table 1 Formulation of biodegradable polymer film

In the biodegradable plastic of the present invention, plastic additives, standard in the industry, can be added to achieve desired properties. For example, a cross- linking agent may be added in order to improve interaction between biodegradable polymer and dried skin powder, thereby the properties, especially tensile properties that meet the requirement for the commercial plastic film. Plasticizers and non-ionic surfactant are normally added to plastics at the appropriate stage in the process to improve the blending of the components and to improve the mold release.

In the biodegradable plastic product of the present invention, a suitable amount of the constituents is used as the raw material. Depending on the type of product, and its shape, film thickness, and the like, the biodegradable plastic of the present invention can be used in agriculture or fishing, products for daily use, construction, medical hygiene, or sports and the like, as films, sheets, boards, molded goods, wrapping material, or covering material. Production is by any convenient forming means such as for example, injection molding, extrusion molding, calendar molding, cast processing, blow molding, vacuum molding, and lining processing. After use, the biodegradability of the product of the present invention is dramatically increased, as compared to a pure biodegradable plastic alone, when left in soil, sludge, compost, or in water. The biodegradability of the biodegradable plastic film of the present invention was tested by cutting into dumbbell shaped specimen and buried in the natural soil for a period of 3 months. The buried specimens were collected at a regular time interval (7 days) from the soil and washed gently with distilled water. The specimens were dried at 50°C until a constant weight was obtained. Weight loss of the specimen with time was used to determine the degradation rate of the specimen by following Equation. Tensile test and surface characterization were also done on the buried specimens.

Degradation % =— ' ^a x 100

1 where Wj is the initial dry weight of the specimen and W _d is the dry weight of the specimen after soil burial test. The weight loss of unfilled PVOH film, as a control sample was also determined. As anticipated, the waste fruit skin powder was more rapidly biodegraded compared to PVOH. Based on the results, the weight loss of blended film was significantly changed and rapidly increased from 20% up to 60% with an increase of waste fruit skin powder content (0 wt% to 40 wt%) in PVOH matrix within 12 weeks in natural soil condition. The present invention of the biodegradable plastic product made from the skin of fruits in powder mixture utilizes fast degrading waste materials obtained from rambutan skin, banana skin and/or jackfruit skin that are produced in large quantity in the tropics. Such waste materials are generally discarded because they have not yet been found useful for industry.

By mixing a biodegradable plastic with the fruit skin powder, the present invention discovered that biodegradability and processability is heightened. As a result, products can be made thicker. Furthermore, because the fruit fibre has a high degree of hardness, resiliency, and water absorption, the present invention can result in a product with a strong mechanical rigidity. The present invention furthermore makes the technical innovative demonstration that regular plastic which is non-biodegradable can be very advantageously used as a degradation rate modulator. Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope of the invention as defined in the appended claims.