The Raman spectra of carbon black and lignosulfonate-carbon
black hybrid fillers are presented in Fig. 5. The LS-CB hybrid particles
were prepared by dispersing CB in solution of LS in deionized
water followed by evaporation of water. The spectra were deconvoluted
into three peaks [30e32] to produce a composite
curve that fit well with the experimental curve as shown in
Fig. 5(b). The graphitic crystal structures and the amorphous carbon
in carbon black particles contribute to the Raman intensity. The first
high intensity peak at 1580e1600 cm1 is attributed to the G-band
arising from graphitic crystal lattice vibrations in carbon black. The
second high intensity peak (D-band) is located at ~1350 cm1 and is
obtained due to the defects/disorders in graphitic crystal lattices.
The third peak seen at ~1500 cm1 is obtained due to the presence
of amorphous carbon in carbon black [30,33].
The relative intensity of the D-band (ID) to the G-band (IG),
designated as ID/IG in Fig. 5(a) is seen reduced in hybrid particles
(curves 2 and 3); the reduction is greater at higher content of lignin.
It is noted that the D-band or the defect band appears due to the
presence of defects or disorder in the graphitic crystal structures in
carbon black. These defects or disorders in carbon black mostly
occur at the edges of the graphitic crystallites [33,34]. The edges of
the crystallites are regarded as the highest energy sites in carbon
black due to high concentration of p electrons [32]. Thus, a
reduction in intensity of the D-band relative to the G-band in
hybrid particles can be attributed to the interactions between lignin
molecules and carbon black particles via pep stacking. Similar
conclusions were drawn for the interactions of CNTs with sodium
lignosulfonate [20].