3.4. Fourier Transform Infrared (FTIR) analyses of PKO and PKO
biolubricants
The surface chemistry of the extracted PKO sample and the synthesized
biolubricants samples were analyzed using FTIR spectroscopy in other to
determine the functional groups present in them. The results in Figs. 10
– 12 were analyzed and likened with known signature of identified
materials in the FTIR library [46]. For all the samples, the main
peaks of importance would be highlighted and briefly discussed.
For the PKO sample (Fig. 10), the peak at 1047.5 cm-1is a characteristic of C – O stretching, an indication of the presence
of alcohol and phenol, which are oxygen-containing compounds. Similarly,
the peak at 2020.284 cm-1 is characteristics of
combination N – H stretching, combination O – H stretching, indicating
the presence of organic compounds. Furthermore, the peaks centered at
3002.457 cm-1 and 3289.143 cm-1 are
characteristic of O – H stretching, indicating the presence of
carboxylic acids, which are oxygen-containing compounds and water; as
such the easy biodegradability of the oil sample.
Fig. 11 shows the FTIR spectrum of synthesized biolubricant to confirm
that the transesterification reaction between methyl esters and
trimethylolpropane (TMP) actually occurred. From the spectrum, the peak
at 1773.514 cm−1, which falls in the range of carbonyl
(C=O) group, indicates the absorption for esters [47]. Similarly,
the absorption peaks at 2931 and 2886 cm−1, are within
the absorption range for C – H stretching in the hydrocarbon component
of the biolubricant. Finally, the broad peak at 3340
cm−1, indicates the presence of O – H groups, which
is an indication of the presence of oxygen-containing compounds and
water molecules which appear as impurities in the TMP.
Fig. 12 indicates the FTIR spectrum ranges of the PKO biolubricant
obtained by the epoxidation-esterification of the methyl ester sample.
This spectrum indicates that epoxidation had taken place. For instance,
the appearance of the band peaks of 1100 cm-1 and 1110
– 1290 cm-1, which were not present in the methyl
ester sample, is characteristics of the epoxide. This is because the
functional groups of C – O – C stretching of ethers oxirane ring and
Aliphatic C – O stretching of esters, indicate the presence of
oxygen-containing compounds [46]. The band corresponding to the
carboxylic acid functional group is located at 3509 – 3533
cm-1. The presence of this group is associated with
the ester hydrolysis during epoxidation reaction [22]. Furthermore,
the band corresponding to the alkane group is located at 2850 – 2873
cm-1. The presence of this functional group which was
not present in the raw PKO sample indicates the stability of the
biolubricant sample obtained by epoxidation-esterification. Finally,
predominance of epoxy groups 1100 – 1290 cm-1,
indicates that epoxidation reaction actually occurred.