Degradation of Polymers: Radiative

Course Module for ME 5XX - The Degradation of Polymers

Types of Degradation - Radiative

Radiatiative degradation can affect polymers in two ways, chain scisson and crosslinking. Photochemical radiation, such as light at 2800angstroms, has the ability to break C-C bonds and instigate both scission and crosslinking. Stronger radiation, such as high-energy electrons, X-rays, and gamma rays can initiate the formation of radicals which can unsaturate the chemical bonding and lead to both chain scission and crosslinking. The predominance of a hugely crosslinkined mass or a jumble of low-molecular-weight fragments depends mostly upon the rate of crosslinking, a function of the polymer.

There are two types of radiative degradation, photolysis, and radiolysis. Photolysis occurs under the influence of photochemical radiation, light in the wavelength of 100 to 10,000angstroms which imparts energy in the range of 100 to 1000 kcal/mole. Degradation of the polymer chain by this method is due to the absorption of energy in discrete energy units by specific functional groups that are on the chain.

Radiolysis occurs under the influence of ionizing radiation, which is X-rays, electron beams, and gamma rays.
Radicals form by a random ray striking a particular atom and initiating an energy transfer. The presence of a radical initiates unsaturation in chemical bonding, chain scission, and crosslinking, as well as volatile fragements that initiate the formation of more radicals, perpetrating the reactions.

Check out this research on UV-degraded HDPE.

The use of polymers in radiative environments is discussed in depth at UMaryland's Laboratory for Radiation and Polymer Science.

This page prepared by Kimberly Farrell for Professor Sisson of WPI, for use in ME XXX, Corrosion and assorted fun times.