Natural Ester | Paper | Standard | Temperatures | Duration | Results |
Rapeseed [6] | Not specified | Coulometric determination of alkali blue B6 | 120˚C, 140˚C and 160˚C | 800, 1000, 1200, 1500, 1600 and 2000 h | After 1200 h, increase from an initial value of 0.01 to a final value of 4.158 mg KOH/g for a wet sample, and 1.613 mg KOH/g for a dry sample. |
Rapeseed and palm oils [22] | Kraft paper and pressboard | ASTM D664 | 130˚C | 100, 250, 500, 1000 and 1500 h | Acidity 8 times higher (palm) and 12 times higher (rapeseed) than mineral oil. |
Sunflower [23] | Pressboard | ASTM D974 | 120˚C | 672, 840, 1152, 1488, 1752 and 2016 h | Acidity of the ester was 76 to 43 times higher than that of mineral oil. However, given the very low aging rate of the natural ester-impregnated paper, but also the intact state of the copper used, the acidity index measured remained acceptable, the authors proposed to measure the low molecular acids content, in addition to the measurement of the TAN. |
EnviroTemp FR3 [24] | Kraft paper | ASTM D974 | Yearly average 20˚C; Annual maximum 40˚C | 7 years of service = 62,088 h | Acidity indices of mineral oil 0.003 mg KOH/g and natural ester oil 0.020 mg KOH/g. |