Mechanism of the degradation of polyamides

Abstract

Films of polyamides were exposed to heat, ultraviolet radiant energy, and different atmospheric conditions. The degradation products were collected in some cases and an-alyzed by mass spectrometric techniques. The unexposed and exposed specimens were examined by the following techniques to obtain information concerning the changes in chemical and physical structure of the polymer: infrared absorption, ultraviolet absorption , viscosity of solutions, measurement of dielectric constant and dissipation factor, photo-micrography, X-ray diffraction, electron microscopy, electron diffraction, and effect of organic liquids. In addition, pyrolysis studies were made and some physical properties were determined. The results of the investigation show clearly that no single method gives a complete picture but that the results from several of the methods give an insight into the mechanism of degradation of poly ami des. Polyamide molecules are relatively unaffected by exposure to moderate temperature (60 0 C). However, loss of water and other volatile materials may cause changes in physcial properties. The effects of exposure to ultraviolet radiant energy are more pronounced, and degradation of the polyamide molecule occurs with accompanying loss of water and other volatile materials that act as plasticizers. The results of this inves tigation show that the general course of the degradation of poly-amides is as follows : 1. The polymer mol ecules break at the C -N bond of the peptide group creating smaller polymer molecules with the same unit of chemical structure. The fragments broken out are evolved as carbon dioxide, carbon monoxide, water, and hydrocarbons. 2. The degree of crystallinity or local order changes, including alterations in hydro-carbon packing, dipole rearrangement, and hydrogen bridging. 3. The amount of strongly bound water and/or organic liquids changes. These mate-rials are probably bound by hydrogen bridging to the oxygen of the peptide group. They act as plasticizers for the polyamides.