## 3 Results and Discussion
### Before Aging: Paints Characterization
#### 3.2.2 Alkyd-Based Samples  
ATR-FTIR and \(\upmu\)-Raman analyses of alkyd paints (Alk_V) show the characteristic bands of both the oil and phthalate components. The IR spectrum (Supplementary Figure S3 and Table S4) identifies a strong C=O _stretching_ peak (1722 cm\({}^{-1}\)) that is common to both components [22]. The phthalate component can be detected by the bands of the C=C _stretching_ (1600-1581 cm\({}^{-1}\)), C-O _stretching_ (1261-1115-1069 cm\({}^{-1}\)), and C-H _bending_ (742-710 cm\({}^{-1}\)) [22]. The oil component is characterized by the CH\({}_{2}\) and CH\({}_{3}\) symmetric and asymmetric _stretching_ at 2925 and 2854 cm\({}^{-1}\); and CH\({}_{3}\)_bending_ at 1462, 1447, and 1388 cm\({}^{-1}\)[22; 25]. Raman analysis (Figure 5a) identifies the following characteristic bands of alkyd resin: the C=O _stretching_ vibration at 1727 cm\({}^{-1}\), the C=C _stretching_ at 1601 cm\({}^{-1}\), the C-O _stretching_ at 1163 cm\({}^{-1}\), the _ring breathing_ at 1041 and 1003 cm\({}^{-1}\), and the C=O _wagging_ at 650 cm\({}^{-1}\)[51].  
THM-Py-GC/MS analyses allowed the identification of the polybasic acid and the polyol constituting the binder and provided further information on the oil component present.  
Supplementary Figure S4 shows the TIC pyrogram obtained for the alkyd samples, and in Supplementary Table S5, all the compounds detected are listed. Polyol has been identified as pentaerythnt (PE), a five-carbon tetraol widely used in commercial formulations since the 1960s, as it allows the resin to dry faster [52]. The identification was possible due to the presence of PE dissociation products obtained from the TMAH derivatization and pyrolysis, such as pentaerythntol tetramethyl ester at RT 8.23 min and pentaerythntol trimethyl ester at RT 8.78 min. The identification of phthal acid (as dimethyl ester) can indicate that  
Figure 5: \(\upmu\)-Raman spectra acquired before accelerating aging and obtained with a 785 nm laser. The green circles indicate the peaks corresponding to the binder. (**a**) Alk_V sample, (**b**) Acr_V (red), and Sty_V (blue) samples.  
the type of polybasic acid present is phthalic anhydride. This pyrolysis product was detected at RT 10.64 min. However, the presence of phthalic anhydride at RT 9.61 min was also detected, although in a lower concentration. This may be due to the incomplete derivatization of phthalic anhydride.  
Regarding the oil fraction, peaks related to saturated monocarboxylic acids (myristic, palmitic, stearic, and arachidonic acids), dicarboxylic saturated acids (suberic, azelaic, and sebaic acids), and unsaturated fatty acids (oleic and linoleic acids) were detected. These fatty acids are the most commonly detected to characterize siccative oils [48]. Moreover, according to the calculated molar ratio between palmitic and stearic acids (P/S = 1.48), the oil component was identified as linseed oil [49; 50]. Considering the ratio of azelaic and suberic acids (A/Sub = 7.17), it appears that the oil had not undergone any pre-heating processes [49; 50]. There are also two peaks at RT 17.33 min and RT 17.78 min that are related to the oxirane octanoic acid 3-octyl-methyl ester and hexadecanoic acid 9,10,16-trimethoxy-methyl ester, respectively. These two compounds can be considered oxidation products of unsaturated fatty acids formed during drying and curing [48]. The most intense peak is the benzoic acid (BA) at RT 7.54 min. Considering its high concentration, it was likely added in the formulation as a stopping agent rather than being a pyrolysis product of polybasic acid [25]. Additionally, a phthalate-based additive, i.e., allyl methyl phthalate (\(m/z\) 220, 163, 164, and 104), is present which is often added to commercial formulations as a plasticizer [25]. Finally, as for oil samples and the commercial samples, peaks related to [2-(N,N-dimethyl)]-1,2-propane-diamine and phosphoric acid (as trimethyl ester) were detected.