A critical assessment of techniques for monitoring polymer photodegradation

Abstract

Methods used to assess the extent of polymer photodegradation after exposure to ultraviolet irradiation (UV) are reviewed and compared. Characterization methods reviewed include Fourier transform infrared analysis (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), gel permeation chromatography (GPC), residual stress analysis, and mechanical testing. Emphasis is placed on techniques used in the author's laboratory, especially methods that help to link chemical degradation with engineering failure. The use of FTIR to monitor carbon dioxide emission dynamically while the polymer is under UV exposure is also described: this method gives a very rapid assessment of the photosensitivity of the polymer and of the effectiveness of photostabilizing (or photo-catalytic) additives. Results are compared with those given by FTIR measurements of carbonyl group development during UV exposure. Computer analysis of molecular weight distributions (MWDs) made by GPC to measure scission and crosslinking rates is discussed. Crystallinity measurements made by DSC and XRD are compared. The use of DSC re-heating runs to investigate the type of molecular damage caused by UV exposure is discussed briefly. Measurement of residual stresses and their relationship with mechanical test failures is discussed. © Springer Science+Business Media, LLC 2009.