Biodegradability of Plastics


[1]According to the Blue Recycling Association in Ontario, an average household produces 8.88 kilograms of plastic bags per year. [2]In 2008, the population of Canada was about 34 million. Therefore total amount of plastic bags produced in that year will be about 30 million kilograms averagely. If this large figure is just for the amount of plastic bags for that year, what of plastic cups, plastic bowls and all other plastic materials? How much plastic would have been dumped altogether in that year? I would probably say enough to cover the Vatican City, the smallest city in the world.

Canada is not alone in this mass production of plastics. According to the National Geographic Magazine, Europeans lead in the use of plastic bottled water. People in general are drinking more water and this has increased the global demand from 28 to 47 million gallons between 2000 and 2006. All this consumption of plastic means that landfills will be full within a very short time and alternative ways of producing plastics would have to be thought of if we want to save our planet from imminent pollution and extinction.


The following analysis below shows the top ten markets of plastic bottled water consumption, by litres per person in 2006





United Arab Emirates
















United States


Source: National Geographic Magazine. July 2007

It is widely known that plastics are bad for our environment and with all these plastics being produced, a problem springs up which is the problem of dumping these plastics. Plastics are non-biodegradable and cannot be fully recycled. So, they are dumped in landfills which has an adverse effect on the ecosystem in that landfill because plastics contain a deadly chemical called Polyvinylchloride (PVC).

So, a solution in the form of biodegradable plastics was proposed and accepted. Interest inbiodegradable plasticsfor packaging, medical, agricultural, and fishery applications has increased in recent years. Therefore, questions to be asked are what biodegradation is and what is a biodegradable plastic?

[3]Biodegradation is chemical degradation caused by the action of naturally occurring micro-organisms such as bacteria and a biodegradable plastic is one in which degradation results from the same microorganisms that cause biodegradation.

There are two types of bio-degradable plastics namely: hydro-biodegradable plastics and oxo-biodegradable plastic. [4]Both these plastics initially undergo oxidation or hydrolysis to reduce molecular weights and cause disintegration followed by a biological process.

a) Hydro-biodegradable plastics:

These plastics are formed from renewable resources such as crops e.g. maize, or non-renewable resources, or a mixture of both of them. Due to their dydrolysable ester bonds, polyesters such as polyhydroxylalkanoates play a major role in the manufacture of HBP's.

HBP's tend to degrade faster than OBP's but it all doesn't matter because in the end, both of the plastics are converted into carbon dioxide, water and biomass.

b) Oxo-biodegradable plastics:

[5]This is a two-step process in which additives have been added to ordinary polyolefin plastics to speed up oxidation and eventually lead to biodegradation.

This process works in a way that in the presence of certain environmental conditions e.g. air, sunlight and naturally occurring micro-organisms e.g. bacteria, biodegradation occurs.

This plastic can also be recycled and do not release harmful chemicals even when they are thrown deep into the landfills.




Can be made from recycled plastics

Cannot be made from recyclable plastics

Harmless deep within a landfill

Can release methane in a landfill

Cost of production is minimal

Costs up to 4 times more than normal plastics

Can degrade in any given condition

Requires certain environment to degrade

Are as strong as normal plastics

Weaker than normal plastics


From this table, it can be noted that oxo-biodegradable plastics are more economically and environmentally sound than hydro-biodegradable plastics.

Biodegradable plastics are one of the major ways in which we can ensure a cleaner and greener planet Earth. Some people know the importance of this discovery and are researching ways in which the potential of biodegradable plastics can be fully maximized.

One such research is the role of starch and cassava in the production of biodegradable plastics in Thailand. This experiment reviews the role of starch and cassava in the production of biodegradable plastics in the country above. Types of biodegradable plastics and their manufacturing process are described.

It also focuses on cassava starch incorporation into biodegradable plastics. The world production of plastic is about 100 million tonnes per year. This shows the high demand for “traditional plastics” and this is majorly because of its unique properties such as light weight, processability and resistance to chemical reactions. As said earlier in this report, these plastics have a negative effect on our environment; scientists are concentrating on ways to develop plastic use more efficiently.


Starch is a natural polymer and is biodegradable and is used in this research because it is renewable and cheap. Also, it is pure and can be blended with other polymers to make cheap biodegradable plastic.


There are two methods from which biodegradable plastics can be gotten from starch namely:

a) Starch puff.

In this method, starch is expanded through the action of high temperature and water vapour and under extrusive conditions. Due to its low bulk density, certain modifications have to be made to the starch to increase moisture level.

[6]The starch can also be moulded and expanded into different shapes after it has been heated with a temperature within 200-240 degree Celsius for about 1-3 minutes. Some additives including calcium carbonate are added to the starch to make it more processable. Products made from this method e.g. package utensils, bowls.

Special machinery is required for production of plastics using this method and demand for this product is limited due to its rigidity and short shelf life.

b) Polymer Blends

In this method, biodegradable polymers such as polylactic acid are produced when starch is blended with a polymer. This leads to copolymerization which results in a high molecular compound with thermoplastic properties.

These blends are then moved to normal plastic converters which process the blends to normal plastic products.


There are four ways in which plastics can be blended with polymers:

a) Starch in granular form:

When starch is blended with limited moisture content, [7]it causes less loss of structure of the starch granule. So, the intermolecular bonds of the starch are broken in the presence of water and heat so that the starch can absorb more water.

[8]When the polymers are blended with granular starch, the resulting structure consists of a continuous polymer with starch granules. This increases the strength, water absorption and permeability and this reduces cost of production.

b) Gelatinized starch:

Starch granule can be completely melted at the same time with the polymer; therefore, both of them are blended together. This enables some modifications to the polymer.

c) Thermoplastic starch:

[9]A thermoplastic is one that is constantly melted by heating and hardened by cooling. In its softened state, the thermoplastic can be shaped by moulding or extrusion. So, thermoplastic starch is a kind of starch that has been alternately softened and hardened by changes in temperature.

When the starch has been melted under severe extrusion methods, it can then be blend with the polymer.

d) Modified starch:

In this method, the entire structure of the starch is modified to enable it blend effectively with the polymer. Starch can be modified by adding chemicals such as ethers or esters to reduce gelatinization time and increase heat resistibility.

In this way the chemical properties of the starch would be modified to suit the polymer used therefore leading to a blend between the starch and the polymer.

Modified starch could be also used as a food additive. It could also be added to frozen products to keep them from leaking after been defrosted.



The images above show different types of plastics. The first one shows a landfill in Mexico filled with non-biodegradable plastics and the second one just illustrates how biodegradable packaging plastic gets decomposed in the soil and mixes with it.


There is an abundance of cassava starch in Thailand and in a time where people are trying to save the planet, biodegradable polymers would be one of the keys to a safer Earth. Since it is cheaper than conventional plastics, it could reduce production cost and increase profit for the economy.

Apart from the economical benefits, cassava starch can help in the production of biodegradable plastics in the future through the following ways:

a) Starch can serve as the carbon source in the fermentation process leading to the formation of high M.W plastics or organic compounds such as lactic acid which can undergo direct condensation to produce plastics.

b) As the blended material, starch can be altered in many ways so as to give the best possible result. This would fully maximize production cost.

Although conventional plastics have certain characteristics that make them ‘special', biodegradable plastics are going to be demanded in bulk in the near future and all methods of production would be used maximally.

Therefore, major companies are increasing their research and development in this area. One breakthrough in the research of biodegradable plastics is a new plastic made from plants called Ingeo.

[10]This plastic was produced by Nature Works, a leading manufacturer in biodegradable plastics. This new plastic reduces CO2 emissions by about sixty percent and requires thirty percent less energy than any other bioplastics to produce. Using Ingeo to produce PET (polyethylene terephthalate) requires 0.75 kilograms of CO2 per kilogram of resin produced which is relatively small in contrast to the 3.4 kilograms of CO2 emitted by the traditional plastics to produce the same PET.

Ingeo can be used to make normal plastic products e.g. packaging plastics, textile production and house wares. The U.S government invested 25 million into this research and it seems to prove very


Fenichell, Stephen. Plastic: The Making Of A Synthetic Century. New York: Harper Business, 1996.

Klanarong Sriroth, Rungsima Chollakup, Kuakoon Piyachomkwan and Christopher G. Oates. "Biodegradable Plastics From Cassava Starch In Thailand." (n.d.): 16.

National Geographic Society. "Malaria: Stopping A Global Killer." Bottled Water Backwash (2007): 154.

Palmisano, Anna C., and Charles A. Pettigrew. "Biodegradability of Plastics." (1992): 2.

Stevens, E.S. Green Plastics . New Jersey: Princeton University Press, 2002.



[3] Green Plastics by E.S. Stevens





[8] ibid

[9] Green Plastics by E.S. Stevens


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