The need for biodegradable plastic arosewhen several shortcomings of non-degradable plastic became evident. Non-degradableplastics are carbon based polymers, which are composed of crude oil, cellulose,coal, natural gas and salt. These are all non-renewable resources, which areall available in limited supplies and are becoming increasingly expensive. Anapproximate of eight percent of world oil production is consumed as feedstockfor plastic manufacturing and as energy in the manufacturing process (Johnston,2017).
Moreover, plastic materials such as bags that are used for an average oftwelve minutes by consumers, take about 500-1000 years to decompose. Henceseveral amounts of plastic material are accumulated in landfills or arepolluting the environment. In addition, when plastics encompassing organoch-lor-based substances such as Poly Vinyl Chloride (PVC) are burnt, toxic amountsof dioxins, which are highly hazardous compounds are released into theenvironment (DiGregorio, 2009). Hence, biodegradable plastic was invented as aneffective alternate to plastic.
However, it can be debated whether thisbiodegradable plastic is really a better alternative than traditional plastic.Considering the advantages and disadvantages of biodegradable plastic, it isnot much effective than plastic and it creates more challenges in terms of environmentand waste management. Biodegradableplastics are plastics that can be degraded when exposed to bacteria and willgenerate natural end products such as water and carbon dioxide within apractical period of time. This time taken to decompose varies depending on thetypes of bioplastic material, site of decomposition and environmentalcircumstances such as moisture and temperature. Biodegradable plastics can befurther classified into two types: Oxo-biodegradable plastic andHydro-biodegradable plastic (Fridovich-Keil, 2016).Oxo-biodegradable plastic is manufactured by a process called Oxo-degradation.
Theyare usually made from the by-product of oil refining. They are madebiodegradable by adding a small quantity of pro-degradant additive into themanufacturing procedure. The pro-degradant additive added changes theproperties or conduct of plastic and turns it biodegradable. After a programmedtime period, the additive reduces the molecular structure of the plastic to alevel that allows bacteria to attain the carbon and hydrogen in the plastic.Then the material is degraded to carbon dioxide, water and humus (Kinhal,2015). Hydro-biodegradable plastic’s degradation isinduced by hydrolysis. Hydrolysis refers to a chemical reaction in which bondsof certain substance are broken down with the use of water.
The substances thatare broken down are generally in the form of polymers, which are macromoleculesconstituted of recurring subunits called monomers. Several plastics under thisclassification are composed of large quantities of starch and hence they aremade from renewable sources. However, all the plastics under this category arenot bio based. Some do contain about fifty percentage of synthetic plastic(which is made from oil.) Certain exceptions such as aliphatic polyesters also arecompletely based on crude oil intermediates. Moreover, genetically modifiedcrops such as genetically modified corn is also used to manufacture certainplastics under this category. An example of a plastic under this category is polylactic acid (PLA) (C3H4O2)n (Antoniou,2010).
Polylactic acid is a polymer that is mainlycomposed of corn starch, cassava roots, or sugarcane. They are primarily madethrough two different processes: polymerization and condensation. The mostpredominant polymerization technique that is used to manufacture these polymersis called ring-opening polymerization.
This is a form of chain growth polymerization, which is a method in whichunsaturated monomer molecules are added onto a growing polymer chain one at atime. The ring-opening polymerization process uses metal catalysts along withlactide monomers (OCHCO2) (which is the lactone derived from lactic acid) tomanufacture larger and longer chains of polylactic acid. The condensation processis also quite similar with the exception of a few differences. The process iscarried out at less than 200 degrees Celsius.
Instead of lactide monomers, thisprocess utilizes lactic acid monomers CH3CH(OH)COOH. Lactic acid ismade by fermenting corn or other sources of carbohydrates. The other primarydifference between the two processes are the by-products released at the end ofthe reaction (Rogers, 2017).