Temperature Effects on Polymer Degradation

A polymer is a chain of identical molecules attached to one another, typically in a long line. Each individual unit is known as a "mer," and each mer has between five and 500 atoms in its structure. The minimum number of mers in a row is about 50 for the chemical to be a polymer. Various plastics are polymers, but fossil fuels and other naturally occurring substances can also be polymers. Although polymers, such as plastics, can be very resistant to forms of degradation, such as biological degradation, other polymers, like those in fats, breakdown at quicker rates. Thermal degradation from the effects of heat on a polymer can act in several different ways on a polymer to break it up into pieces and, thereby, affect the structure of the polymer.

Breakdown

• The basic reason by which thermal energy breaks down polymers is because each mer attaches on to the next mer through a chemical bond. This chemical bond holds the two neighboring molecules together with energy. Temperature is a measure of heat energy, and if the heat energy can overcome the energy held in the bond, it can break the two molecules apart and split the polymer strand. This alters the structure of the polymer and the item that the polymer is part of begins to breakdown.

Single Degradation

• A polymer chain is like a string. Temperature effects can change the structure of either end of the string or can act on the middle part. Random initiation is a situation where the polymer breaks in the middle of the chain, at a random point. Terminal initiation describes when one mer at the end of a polymer breaks off and becomes what is known as a monomer. If this process continues, and more monomers break off, then this type of degradation is called depropogation. If a relatively short polymer splits up into all of its individual constituents, this process is called unimolecular termination.

Multiple Degradations

• One single polymer strand may breakdown without interacting with other polymers in the environment, or it may interact with them. Termination by recombination describes a situation where one polymer attaches to another to form a stable product. Another possibility is termination by disproportionation, where two polymers join and then break up into two separate polymers. Alternatively, intermolecular transfer can result if one polymer and one free molecule (a radical that has enough energy to alter other molecules) in the environment interact and produce two polymers and one free molecule.

Radicals

• Many of the degraded strings or monomers that the initial temperature degradation causes can themselves be damaging to the remainder of the polymers in the environment and adversely affect the structure of other, previously unaffected, polymers. The term "radical" applies to these chemicals.

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