The use of plastic is now being limited due to environmental concern. In many countries and regions, uses of plastics are restricted as they pollute the air with toxic gases like carbon dioxide and other greenhouse gases. The greenhouse effect from these from these toxic gases are increasing pollution and rising global warming. Nevertheless the use of plastic continues. 
Plastic are polymers used for application such as packaging, building materials and commodities. There are mainly two types of polymers: one is naturally occurring polymers which are biodegradable and the other is synthetic polymer which is man-made.  Natural polymers are biodegradable and therefore it is observed that it has lesser negative impact on the environment than synthetic polymer.
Definition, Properties and their uses
Synthetic polymers are made artificially from chemical substance in industries. They are non-biodegradable polymers and do not decompose easily. These polymers are produced from non-renewable resources, petroleum by the process polymerization.  They have useful properties as they do not react with alkali and acid and they are light but strong. Its shape and color can be altered easily and it is a good insulator of heat and electricity. Due to its properties and as they are cheap, they are used in place of metal, wood and other materials. They are most commonly used as plastic bags. As they are good insulator of heat and electricity they are used for coating wires, they are also used to make cups, bowls, containers, toys, etc.
Even though synthetic polymers are cheap, its resource, petroleum is becoming more and more limited. And a large amount of energy is required to recycle them. Therefore the process of recycling them is not energy efficient. As its resource it finite and it is expensive to recycle them, and it cannot be easily decomposed, scientist introduced a different type of polymer alternative to them. These polymers are more beneficial to use and less harmful to the environment as they are biodegradable, even though they are more expensive.
Natural polymers are biodegradable. They are formed naturally in all living organism, both in plants and animals.  They can be made from elements such as carbon, hydrogen, nitrogen and oxygen. In animals natural polymers are found in muscles skin, silk, hair, wool and fur. Natural polymers are produced from starch and cellulose from plants and vegetables like potatoes, maize, sugar cane, corn. Complex hydro-carbon polymers can be produced by the help of bacteria and fungi. 
Another type of polymer is synthetic biodegradable polymers. These are chemically derived natural polymers, mainly from plants. They are modified to improve the biodegradability and other properties. They can decompose under natural; condition by bacteria or fungi.  They can also be degraded biologically with enzymes and other living organism. Biodegradation takes place by the process oxidation, photo degradation, hydrolysis or biotic reaction which is followed by bio- assimilation of the polymer fragments by micro-organisms and their mineralization. 
Types of biodegradable polymers:
Natural polymers or biopolymers which exists in plants and animals
Natural polymers from renewable resource monomers synthesized with chemicals
Polymers formed by microorganism and bacteria
Polymers with hydrolysable backbone
Polymer with carbon back bone
There is also petroleum based biodegradable polymer. These are produced from petroleum polymer to increase its biodegradability and to reduce the use of petroleum. These are made by mixing petroleum with starch and other substances so that it can be decomposed by bacteria, light and by other processes where less energy is needed. 
Since 1990, synthetic polymers which are completely biodegradable, for example compounds like poly (lactic acid), polypro lactone and poly (hydroxyl butyrate-valerate), have been available commercially. Polymers produced from starch are useful in cosmetics and pharmaceutical industries. The use of biodegradable polymers is mainly performed in medical application, agricultural fields and for packaging food and other goods.
In medical application the use of biodegradable polymers are needed for surgical sutures, bone fixation devices, vascular grafts, adhesion prevention, and artificial skin and drug delivery systems. 
Polymers are used in agricultural application to improve the condition of the soil and to control the release of pesticides. They are also used for nutrients. 
For packaging the quality and the properties of the polymer depends on the type of good which will be packed.
Advantages and Disadvantages of Synthetic Polymer and Biodegradable Polymer and their Impact on the Environment
Biodegradable synthetic polymers are now being widely replaced by synthetic polymers even though synthetic polymers cost lesser. This is because synthetic polymers are unfavorable to the environment as they are unable to decompose. As a result they remain in the environment for hundreds of years. This polymer wastage pollutes water and block drainage systems and rivers. This causes flash floods. The populations of mosquitoes increase as these plastic wastages are good breeding spot for the mosquitoes. As a result diseases are spread by them which cause people to have malaria and dengue fever. Therefore number of aquatic animals is reducing due to the pollution made by the synthetic polymers.
Used polymers which are petroleum based are often burned in open space producing poisonous that causes acid rain which disrupts the balance of the environment. These also cause greenhouse effect.
Compare to synthetic polymers, biodegradable synthetic polymer are environmentally friendlier. And the demand for biodegradable polymers is increasing as their costs are falling. People prefer biodegradable polymers as they can decompose or decay naturally and biologically, they are found in large range and its resource is renewable.
Biodegradable polymers also improve agriculture by making the soil more fertile. It can be used to minimize the growth of weeds. It can increase the temperature of the soil and keep a constant level of moist in the soil. This increases the growth rate of the plants and vegetables.
Recently the production of biodegradable polymer is increasing as the demand for sustainable packaging is ascending. Consumers are more interested in eco-friendly products. As a result the demand for petroleum base polymers are descending.
Even though a huge range of the area is used to grow plants and vegetables to make polymer we can conclude from the above information and an explanation, biodegradable polymers upsets the environmental far less than synthetic polymers.
Leon P.B.M. Janssen and Leszek Moscicki (Eds), (2009). Thermoplastic Starch. Wiley-VCH.