Individual fibers were mounted on paper tabs for tensile
tests, and nominally 25 samples per group of fibers were
tested using a gage length of 10 mm. Fig. 4 displays modulus
and strength of various carbon fibers as a function of fiber
extension-during-carbonization (EDC). As expected, carbon fi-
bers with larger EDC displayed better tensile properties, due
to a higher molecular orientation. After compliance correction
for modulus (using shorter and longer gage lengths of 5
and 25 mm, per ASTM D-3379-5), carbon fibers displayed a
tensile modulus, strength, and strain-to-failure values of
52 ± 2 GPa, 1.04 ± 0.10 GPa, and 2.0 ± 0.2%, respectively. The
largest individual filament tensile strength recorded was
1.3 GPa. In contrast to the doubly-convex crenulations
observed for current fibers (shown schematically in Fig. 2c)
that result in sharp notches, fibers with smoother crenulations
(Fig. 2d) will likely possess better mechanical properties.
Thus, further dry-spinning studies will address the role of
spinning conditions in attaining an optimum level/shape of
crenulations.
In conclusion, the tensile strength of present carbon fibers
produced from dry-spinning of partially acetylated lignin is
amongst the highest values reported in the literature. It is also
noted that crenulated carbon fibers obtained in this study
from dry-spinning of ACE-SKL have 35% larger surface area
as compared with equivalent circular fibers that are typically
obtained by melt-spinning. Further, due to the lack of graphitic
crystallinity in these lignin-derived carbon fibers, their
surface is expected to be more reactive than that of carbon
fibers possessing graphitic structure (such as those from
mesophase pitch precursor) that tends to be rather inert
due to the stable crystalline form. Therefore, such lignin-derived
carbon fibers could possess an intrinsically higher