scope:

Introduction

The research project was initiated with a literature search to better understand the degradation mechanisms of different non-metallic materials exposed to UVC. In particular, the literature search focused on the degradation mechanisms of the materials and nonmetallic components typically subjected to long-term UVC exposure in HVAC systems. Identified research papers involving 254 nm photodegradation studies that were not discussed in Task 1 are listed at the end of the report as additional background.

Two books published by J. Rabek in 1995 and 1996 were the basis for the conducted literature search and contain thousands of references on research performed to study polymer photodegradation mechanisms using a wide range of experimental UV methods. Although the majority of the reported UV studies were performed with UVA (320-400 nm) and UVB (280 - 320 nm), a significant number of the studies explored the effects of UVC (254 nm) on polymer degradation. The results of the conducted literature search were broken down into the following subcategories for discussion.

1. UVC absorption by the fresh polymeric surface

2. Photodegradation reaction mechanism

3. Effects of UV wavelength on degradation products

4. Effects of contaminants and additives on degradation rate

5. Effects of UV irradiance on degradation rate (Reciprocity Law)

6. Detection of photodegradation