Case: Read the passage and answer the following questions

A large number of polymers are quite resistant to the environmental degradation processes and are thus responsible for the accumulation of polymeric solid waste materials. These solid wastes cause acute environmental problems and remain undegraded for quite a long time. In view of the general awareness and concern for the problems created by the polymeric solid wastes, certain new biodegradable synthetic polymers have been designed and developed. These polymers contain functional groups similar to the functional groups present in bio-polymers. Aliphatic polyesters are one of the important classes of biodegradable polymers.

Which of the following is not an example of a natural biodegradable polymer?

Polyvinyl alcohol

The correct answer is option 2. Polyvinyl alcohol.

Biodegradable polymers can be broken down by natural processes, typically by microorganisms, into harmless substances such as water, carbon dioxide, and biomass. Natural biodegradable polymers are derived from natural sources. Let's look at each option:

1. Collagen: Collagen is a natural biodegradable polymer found in animal tissues. It is the main structural protein in the extracellular matrix of various connective tissues.

2. Polyvinyl alcohol (PVA): Polyvinyl alcohol is a synthetic polymer, not a natural one. While PVA can be biodegradable under specific conditions, it is not derived from natural sources, and thus it is not a natural biodegradable polymer.

3. Lignin: Lignin is a complex organic polymer found in the cell walls of plants, particularly in wood and bark. It is a natural biodegradable polymer.

4. Natural rubber:Natural rubber, also known as cis-1,4-polyisoprene, is derived from the latex of rubber trees. It is a natural biodegradable polymer.

Hence, collagen, lignin, and natural rubber are all examples of natural biodegradable polymers. Polyvinyl alcohol (PVA) is not a natural biodegradable polymer; it is a synthetic polymer.

Therefore, the correct answer is: Polyvinyl alcohol