The study aims to produce biodegradable plastic using cassava starch as its main component. Cassava starch was mixed with water, epoxydized soya bean oil (ESBO), glycerol, and polyvinyl alcohol (PVA). The mixture was then compressed and tested. Three preparations were made from the mixture. The first preparation contained 50 grams starch, 50 grams water, 50 grams PVA, 2.5 grams ESBO, and 2.5 grams glycerol. The second preparation contained 65 grams starch, 65 grams water, 50 grams PVA, 2.5 grams ESBO, and 2.5 grams gycerol. The third preparation contained 80 grams starch, 80 grams water, 50 grams PVA, 2.5 grams ESBO, and 2.5 grams gycerol. The first preparation exhibited the most desirable mechanical properties. The material produced was proven to be biodegradable.
There is an increasing demand for plastic, from the highly technological fields of electronics, fiber optics, and pharmaceuticals to the basic necessities such as sandwich wrappers and garbage bags. This high demand for plastics, however, has been a major contributor to the world's present garbage problems. The researches _ AZ1 aimed at developing biodegradable plastics is one big step to lessen, if not total eliminate, this global concern. The use of biodegradable plastics has already started in the United States. Some plastics use cornstarch as an additive. This additive helps in the natural decomposition of the plastic materials. Cassava is basically composed of starch. Cassava starch is composed of two components: amylose and amylopectin. An amylose is a long straight chain of polymer of anhydroglucose units. An amylopectin is a branched chain compound, also of anhydroglucose units.
Because plastics are made of polymers, starch is a very favorable raw material in plastic-making. The study was limited to one species of cassava, Manihot esculenta. The plastic produced was treated with different amounts of starch, polyvinyl alcohol (binder), epoxidized soya bean oil (stabilizer), and glycerol(plasticizer). The finished product was expected to be comparable to commercial plastics in terms of clarity, reaction to acids and bases, water absorption, tensile stress and tensile strain, electrical conductivity and flammability.
REVIEW OF RELATED LITERATURE
The word plastic came from the Greek word plastikos, meaning capable of being molded. Plastics can be as hard as metal or as soft as silk. They can take any shape in almost any form due to the versatility of the carbon, the most common backbone of polymer chains. Plastics can be conveniently divided into two categories: semi-synthetic, in which the basic chain structure is derived from a natural product, such as cellulose; and synthetic, which is built up chemically from small units or monomers. Despite the various applications of plastics, drawbacks have been encountered in three major points. Firstly, there are certain chemicals used in the manufacture of .plastics that may cause allergic reactions. Three is a need man from these threat. Secondly, since cellulose films are biodegradable; they are readily attacked by bacteria. Films and packaging materials from synthetic polymers are normally attacked at a very low rate. New polymers such is nylon, polyvinyl chloride and Polystyrene have replaced cellulose, the pioneer plastic material. As a result, these plastic materials have become permanent wastes.
There 'are various methods in making biodegradable plastics. The simplest is the production of plastic from the extraction of casein from milk. Casein is obtained in two ways by souring, with the use of lactic acid, arid by boiling together with an additive, such as acetic acid.
Starch is a natural organic polymer manufactured by green plants through photosynthesis s to serve as metabolic reserve It occurs in the form of grains in many 'parts of the plant, principally in embryonic tissues such as seeds, fruits, roots and tubers.
Polyvinyl alcohol is a colorless, odorless, tasteless, thermoplastic synthetic resin. It is usually used for grease-proofing paper, in adhesives, in gas- and oil-impervious films and Coatings. This substance, although soluble in water, is insoluble in Common organic solvents.
Glycerol is the simplest trihydric alcohol. In commercial form, it is called glycerin. It is a colorless odorless and viscous liquid with a sweet taste. It is completely soluble in water and alcohol but is only slightly soluble in many common solvents, such as ether, ethyl acetate and dioxane. It is widely used in coatings and paints, pharmaceuticals and cosmetics.
Plastic production is relatively new technology. Experiments are being conducted to relieve the negative effects 'of overproducing plastics. By changing its raw materials and additives, commercial plastic may be improved so that it will become degradable while retaining its good quality.
In order to determine the right combination, three batches with different proportions were prepared.
Batch 1 is made of 50 grams .PVA (1:4 ratio Of PVA to water). 50 grams water; 50 grams starch; 2.5 grams ESBO; and 2.5 grams glycerol. Batch II is composed of 50 grams PVA (1:4 ratio of PVA to water); 65 grams water; 80 grams starch; 2.5 grams ESBO; and 2.5 grams glycerol.; 2.5 grams ESBO; and 2.5, grams glycerol.Measured amounts of water and starch were mixed and boiled, using a hot plate (at 80 degrees Centigrade), until a sticky paste was formed. After removing the starch-water mixture from the hot plate, the rest of the materials were added. After mixing all the materials, the mixture was passed through a roll-mill with a temperature of 118 to 120 degrees Centigrade. Then, it was compressed, using a compressor with a temperature of 130 degrees Centigrade for seven minutes.
The samples produced were cut into strips (1 inch by 2 inches dimension) for testing. Several tests were conducted to determine the mechanical properties of the samples. The plastics were inspected to determine their opacity, translucency and transparency. To determine the effects of strong acids, the plastic strips were immersed in concentrated hydrochloric acid (HC1) for thirty minutes. Changes in length, width and appearance were noted. A tensile test was also conducted. Strips were hooked to a spring balance and were pulled until they tore apart. The readings on the balance when the strips broke were recorded. To test the samples for flammability, strips with the same dimensions were burned using Bunsen burners. Burning time was noted. An organic solvent test was also conducted using Bunsen burners. Burning time was noted. An organic solvent test was also conducted by immersing the material in ethanol for 48 hours. Changes in length, width and appearance were also noted. The samples also underwent biodegradability tests. The strips were stapled to a piece of cardboard and buried in a can of soil. The strips were unearthed after a week and their final dimensions were recorded. To determine the effects of water, the samples were immersed in a bottle of chlorinated water. The bottle was sealed so as to isolate its contents from the external environment. After a week, their final dimensions were noted. In conducting the air test, the strips were exposed to open air for a week. Changes in the dimensions were also noted.
RESULTS AND DISCUSSIONS
The quality of plastic produced greatly depends on the proportion of additives used. Any difference in the formulation may bring about changes in terms of flexibility, color, transparency and texture. The difference in the amount of starch had an effect in the texture and transparency of the samples (see Table 1). The different proportions were formulated to test which of the samples from the different formulations would exhibit the best properties. The rest of the formula was kept at a constant amount to test the effect of variations in starch content.
Commercial plastic served as the control. All the preparations, except for Preparation I which is the only sample that underwent the Tensile Stress Test, were subjected to the same tests. The tests were conducted to find out which among the samples is comparable with the control.The strong acids had unfavorable effects on the samples, unlike the control which did not manifest any change. It was observed in the strong base test that instead of being dissolved, the samples absorbed the liquid. No significant difference was observed in the dimensions of the three preparations and the control. When tested for flammability, the samples completely burned. It was also observed that the samples produced resisted heat better since they took longer to burn.The soil biodegradability test showed that there was a significant reduction in the size of the samples when burned in the soil for a week.
The samples dissolved in water. This may be because the binder (PVA) used is water-soluble. However, the samples would not dissolve in ethanol since the binder (PVA) used is insoluble to organic solvents. Exposure to air did not have any effect on the samples.
SUMMARY AND CONCLUSIONS
Favorable results were obtained in the Strong Acid Test, Strong Base Test, and Flammability Test. The samples were found to be water-soluble. However, the samples would not dissolve in ethanol, an organic solvent. All the samples were biodegradable.
The samples dissolved in water because the binder (PVA) used is water-soluble. In order to solve this problem, an alternate binder may be used. A water-proof, biodegradable coating may be used to solve this problem. Antioxidants may also be used to make the product more transparent.