Continued from page 28 .
eventual outcome is the formation of organic acids . The current ASTM standard which defines biodiesel as a blend stock , provides a limit of TAN , or total acid number of 0.5 maximum , down from initial industry specifications of 1.2 and the first ASTM D6751 specification of 0.8 . To evaluate the potential impact which severely degraded fuel might have on the target elastomer , some tests were done in which biodiesel samples with high acid numbers were used . These high acid numbers were achieved by adding decanoic acid to the fuel samples to achieve TAN levels far higher than the allowed limit . All of these elevated
Figure 1-2 . Type M Durometer used for hardness measurements of the nitrile samples before and after exposure to fuels . acid number tests were done using just biodiesel ( B100 ).
Decanoic acid was selected for use in this study because it is highly soluble in biodiesel and fuel oil and it was the organic acid used to produce biodiesel at the limit of acidity in the UL study of B5 blends . Hardness Samples were tested per the ASTM D2240 Durometer Hardness test . A Type M durometer ( Checkline RX-1600-M attached to a Checkline OS-3 test frame , Figure 1 ) was used which lowers a hardened steel pin into contact with the sample , measuring deformation and determining Durometer ( M ) rating on a scale of 0 to 100 . The instrument was calibrated using Type M standard materials prior to each set of samples tested . For each specimen 10 durometer measurements were made and then averaged for a group of specimens . Measurements were made at the center of the dog bone sample base , and the disc sample centers . Durometer hardness is reported as a function of conditioning protocol .
Volume Swell Samples were measured for volume swell per ASTM 471 Fluid Aging test . All specimens , dogbone and discs , were weighed both in air and while submerged in water , using a specimen sling , before and after oil immersion . Specimens were dipped in acetone and blotted with lint free lab paper prior to measurements to remove residual surface water or oil . Archimedes principle is used to calculate the percent change in volume from the mass values , as the body ’ s density ( and
32 FEBRUARY 2019 | FUEL OIL NEWS | www . fueloilnews . com