Table 2 Assignment of the main spectral changes observed in linseed oil aging and summary of the observed changes
Functional group | Peak position (cm−1) | Assignment | Observed changes in linseed oil and BaSO4 | Observed changes in TiO2 |
|---|---|---|---|---|
C=O stretch | 1776 | Peracids, perester, γ-lactones, and anhydrides | Small increase in visible and UV–vis light | Small increase in visible and UV–vis light |
| Â | 1736 | Ester | Used for normalization | Used for normalization |
|  | 1710 | saturated ketones, COOH acid, and aldehydes | Minimal increase in linseed oil and BaSO4 samples in UV–vis and visible light; No changes in dark | Large increase in UV–vis and visible light; Slight increase in dark, final point for anatase UV–vis shows large increase |
C=C | 1670–1610 | ν (C=C) of β-unsaturated carbonyl compounds | Small increase in linseed oil only samples in visible and UV–vis light | Strong increase in anatase and rutile pigmented samples in visible and UV–vis light; minimal increase in dark |
ν (C–O) Triglycer-ide ester linkage | 1000–1300 (main peak at 1168) | ν(C–O) in triglyceride ester linkage + νas (C–O) of C–C(O)–O | Slight increase followed by decrease in linseed oil only samples, N/A in BaSO4 samples | Decrease in TiO2 containing samples in UV–vis and visible light.; No clear change in dark |