Production of Bioplastic Abstract In order to synthesize bioplastic out of potato starch, we first made some preleminary experiments to determine the adequate proportion of the ingredients. The production of plastic requires a polymer (starch), a plasticizer (glycerin), a solvent (water) and an acid (vinegar). The result of our research is a flexible, dense polymer which can be used for several applications a in daily life. What is Bioplastic? Bioplastic is the universal term for polymers made of renewable biomass sources. As a consquence, bioplastic is biodegradable in about 80 days in oppostion to traditionnal plastics, which remain in the environment for 500 to 000 years. Bioplastics are made of different sources of biomass, such as corn or potato starch and cellulose. These substances are naturally produced by plants. Potato starch We used potato starch for our research because we reflected about a sustainable use of potato peel, which is often degraded to waste and potato starch is easily accessible in every grocery. Plants store starch in special organelles called amyloplasts which are present in the cells in form of granules to save the energy produced by photosynthesis. The glucose produced by photosynthesis forms bonds to grow to a macromolecule following the equation: n C6HO6 => (C6H0O5)n + (n-) HO
There are two products which can form: amylopectine and amylose. For amylopectine n in the above equation can vary between 000 and 00 000, which means that the amylopectine chains are formed by between 000 and 00 000 glucose units, which form branchings every 4 to 0 glucose units. For amylose, n varies between 00 and 000 and there are no branchings in the chain,in contrary to amylopectine, and, as a consequence, amylose is less soluble in water than amylopectine because its molecules do not link to water molecules via hydrogen bonds. In the image below, the structures of amylose and amylopectine are respresented. The branchings of amylopectine are visible. The potato starch we used contains 70 % amylopectine and 0% amylose.
Glycerin (Propan-,, triol) Glycerin is a hygroscopic liquid with a high viscosity. It has hydroxyl groups which make it be soluble in water. The above image shows the structure of glycerin. Glycerin makes the biolastic more flexible. Water Water plays an important role in the production of bioplastic. First, it acts as a solvent to dissolve the starch. Secondly, it helps the starch molecules to stay disrupted after heating. Acid (Vinegar) Vinegar, a 6% in volume solution of acetic acid liberates acetate ions and hydrogen ions in solution. This is important, because ions react with the starch polymers and make them be disordered more easily in the solution. This disorder, resulting from the disruption by the water and the ionization by the acetic acid, makes the resulting cast film more homogenous. Determination of the best water/starch ratio We did some tests to find out in which proportion we have to mix water to starch in order to receive a plastic which conforms to our criteria. The plastic has to be flexible, but not too soft.
The mixture in a beaker glass Solution number Mass of Water in % Mass of Satrch in % 8 7 57 4 60 40 Plastics produced with solution seemed to fit the best to our conditions, so we continued with this proportion for further research. Determination of the temperature of gelation We heated our starch solution to determine the temperature of gelation. After tests, we can conclude that the gelation process begins at a temperature of 60 degrees centigrade. Determination of the amound of acetic acid We made tests to find out which amount of vinegar was necessary to make the plastic homogenous. 4
Homogeneity experiment number Amount of acetic acid in % of total mass 6 9 7.6 The 7.6 % of acetic acid containing mixture gives the plastic with the best homogeneity. The 9 % plastic smells of the acid, which means that there was acid in abundance. Determination of the amount of glycerin Again, we made tests to determine the amount of glycerine necessary to make the plastic flexible. Flexibility experiment number Amount of glycerin in % of total mass 6 0 5.7 Our conclusion of this experiment was, that plastics with less glycerin content made our plastic stiffer but not more breakable. General Conclusion All in all, we can say that our produced plastic satisfied our expectations. Now, we are looking for a practical application of this material. Further, we are going to analyze the biodegradability. Sources: http://www.mhhe.com http://green-plastics.net http://www.thenakedscientists.com blog.trilighthealth.com Le parfum de la Fraise, mystérieuses molécules, Peter Atkins, DUNOD 5