XPS and ToF-SIMS study of freeze-dried and thermally cured melamine-formaldehyde resins of different molar ratios

The surface chemical characterization of melamine-formaldehyde (MF) resins by x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) is examined in this study. Melamine-formaldehy de resins with different molar ratios of formaldehyde to melamine are synth esized and thermally cured. From XPS measurements, quantitative information is obtained and atomic chemical concentrations show the effect of the mola r ratio for the freeze-dried resins, However, the thermally cured resins di splay a rather similar surface elemental composition, Moreover, because the binding energy values of the main N-C-N and N-C-O groups are too close, XP S does not help to identify changes in chemical structure after curing. The main ToF-SIMS negative and positive mass fragments of the MF resins are id entified. Principal component analysis (PCA) is shown to be useful to deter mine and explain the main differences between all of the ToF-SIMS spectra, It allows us to distinguish the effect of the bulk chemical composition on the respective surface compositions of not only the uncured but also the cu red MF resins, Moreover, extended interpretation leads to the identificatio n of peaks characteristic of methylol groups and methylene ether bridges, b ut their absolute quantification is not straightforward. However, this resu lt indicates that surface analysis helps to characterize the poorly defined chemical structure of MF resins, This is important for understanding the i nfluence of surface chemistry on macroscopic surface properties such as che mical durability under exterior exposure, Copyright (C) 2000 John Wiley & S ons, Ltd.