Interlaboratory study on the degradation of poly(vinyl chloride), nitrocellulose and poly(tetrafluoroethylene) by x-rays in XPS

In XPS, it is often observed that the x-ray flux causes changes in the surface structure and chemistry in the surface region of organic materials. However, at present, there is no standard guide to estimate the relationship between the degradation rate and x-ray source flux. To investigate this relationship, we conducted an interlaboratory study on the degradation of three kinds of polymers - poly(vinyl chloride) (PVC), nitrocellulose + cellulose acetate (NC + CA) and poly(tetrafluoroethylene) (PTFE) -by x-ray irradiation as Project A5 of the VAMAS Technical Working Area 2 on Surface Analysis; 40 laboratories participated in this study. From this interlaboratory study, it was concluded that the rate constant of the degradation for PVC and NC + CA could be obtained from the peak intensity changes of CI 2p and N 1s photoelectrons, respectively, assuming first-order reaction with photons. There is a fairly good correlation between the rate constants of the degradation for PVC and that of NC + CA, and, if the analysis was carried out using achromatic x-ray sources only, a better correlation was obtained than that by a monochromatic source. Therefore, PVC and NC + CA will be good specimens for the indicators of x-ray source flux. The degradation behaviour of PTFE is more complicated and does not follow a first-order reaction. The rate constant of the degradation for PTFE obtained at the initial stage of the irradiation was compared with that of NC + CA. However, there is a poor correlation between them. Copyright (C) 2002 John Wiley Sons, Ltd.