Types+of+polymers

Based on degradation patterns, there are three different types of polymers:


 * 1) Nondegradable polymers:**

These polymers are extremely stable and do no degrade in any environment. These types of polymers are strong, water resistant and do not undergo microorganism degradation. Such types of polymers are currently used in common plastics and some examples of them are polyethylene, polypropylene and poly(vinyl chloride).



Figure 1: The degradation curve of a nondegradable polymer. PI represents the "Performance-Integrity" index which indicates how resistant is the polymer to degradation
 * 2) Readily Degradable Polymers:**

Such types of polymers degrade rapidly after their useful life has ended.These polymers simply self-destruct and then they are assimilated by microorganisms. The time of degradation depends on the type of disposal environment and application; however it usually is in the order of days or weeks. Such types of polymers are used in detergents and other applications where a rapid degradation is required. Some examples of these polymers are poly (vinyl alcohol), poly(glycolytic acid) and polycaprolactone.

Figure 2: The degradation curve of a readily degradable polymer. PI represents the "Performance-Integrity" index which indicates how resistant is the polymer to degradation.
 * 3) Programmed Degradable Polymers:**

These types of polymers degrade only under specific conditions. Therefore, these polymers have a controlled degradation and have controlled life spans.

One of the ways it is possible to make these kinds of polymers is to attach a photo-sensitizing group to the resin of conventional polymers. The resultant polymer would be photodegradable in natural sunlight, because the photo-sensitive group would absorb radiation of light and cause the entire polymer to breakdown. An example of this, the the copolymer of carbon monoxide (photo-sensitizer) and polyethylene. A polymer containing 1% carbon monoxide degrades about after 3 week's exposure to sunlight.

Advances in these kinds of polymers have resulted in newer polymers that do not need light for their degradation. Chemical processes such as oxidation and hydrolysis are used in order to degrade the polymers. Oxidative degradation can be initiated by by light, heat or mechanical stress. Furthermore, the fragments formed after oxidative degradation are wettable and therefore, more susceptible to hydrolytic degradation

Figure 3: The degradation curve of a programmed degradable polymer in one stage. PI represents the "Performance-Integrity" index which indicates how resistant is the polymer to degradation.



Figure 4: The degradation curve of a programmed degradable polymer in two stages. PI represents the "Performance-Integrity" index which indicates how resistant is the polymer to degradation.