QUALITY-CONTROL OF PAINTS - PYROLYSIS-MASS SPECTROMETRY AND CHEMOMETRICS

The thermal degradation of a standard (sample 1) and five resin-modifi ed paints has been investigated by pyrolysis-field ionization mass spe ctrometry (Py-FIMS). The modifications simulate possible industrial di sturbances: cross-linker modification (omission of methyl melamine: sa mple 2, replacement by benzoguanamine: sample 3), resin-reduction (acr ylic resin: sample 4, polyester: sample 5) and resin-exchange (epoxy r esin: sample 6). For the investigated resins, the following marker sig nals have been assigned: melamine (m/z 126) and methyl melamine (m/z 1 40); benzoguanamine (m/z 187); propenal (m/z 57) and styrene (m/z 104) for the acrylic resin; adipic (m/z 129) and phthalic acid (m/z 149) f or the polyester; bisphenol A diglycidyl ether monomer (m/z 340) and d imer (m/z 624) for the epoxy resin. Apart from these resin marker sign als, major pyrolysis products of the polymer backbone, like eaters of trimethylolpropane units with phthalic (m/z 413, 561, 807) and adipic acid (mit 541, 727 and homologues), and cross-linking products, e.g. b etween methyl melamine and trimethylolpropane ester fragments (m/z 785 , 805, 825), have been identified. Using these signals, all six sample s were differentiated and the origins of the modifications specified. The data were interpreted by principal component (PCA) and discriminan t analysis (DA). Chemometric evolution as a means of visualizing the d ata enabled the reproducibilty of the measurements to be estimated and the samples to be differentiated according to the influence of their modifications. The most intense effects were assigned to the cross-lin ker modifications. They affected several resin signals, while other mo difications showed minor effects mainly on their own marker peaks.