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3D Printing of a Graphene-Modified Photopolymer Using SLA
GBN on the polymerization separately from the effect to R. These differences in accuracy could be explained
on UV absorption. Hence, it was studied to find out if by GBN dispersion. Viscosity results suggested that the
nanofillers influence the polymerization reaction by dispersibility of GoxNP was slightly better that GO.
avoiding the polymer chain growth or terminating the Perhaps, the presence of agglomerates could diffract
polymerization process. The obtained results suggested the light affecting to the accuracy of the printed cross-
that the incorporation of nanofillers did not influence section. To the best of our knowledge, this effect has not
the thermal polymerization process. Some studies [46,47] been previously reported; however, some studies using
[59]
explored the capability of G to act as free radical other 3D printing technologies found that functionalized
scavengers, which, in this study, could result in the capture G nanoplatelets did not affect printing accuracy, except
of free radicals formed during polymerization leading to when the layer thickness was large. Besides, this study
a slowdown of this process. However, in this study, GBN shows the good accuracy of SLA compared to other 3D
did not impede polymerization reaction acting as free printing techniques. For example, Zhou et al. found a
[51]
radical scavengers. maximum accuracy of 85.68% using powder-based ink-
In terms of UV polymerization, the results of this jet 3D printing.
study have demonstrated that the incorporation of GBN Our results suggest that there was a relation between
has a significant impact on UV polymerization since printability, dimensional stability and roughness. It was
the presence of these nanoparticles could affect the UV- observed that the greater the effect of GBN on printability
visible light absorption. This effect could decrease the and dimensional stability, the higher the surface roughness.
energy caught by the photoinitiator resulting in a lower R+G showed the worst printability and printing accuracy
polymerization degree. It was more noticeable with and it presented the highest values of roughness, followed
the addition of G than GO and GoxNP, which could by R+GO. R+GoxNP had similar roughness and printing
be attributed to the darker color of G nanoparticles . accuracy than R.
[58]
The higher is the light absorption, the lower is the In relation to nanoparticle dispersion, the differences
polymerization degree because the light that actually observed between G, GO and GoxNP could be better
reaches the photoinitiator is reduced. G, GO and GoxNP understood from a chemical point of view. Both GO and
showed different color, and therefore, they hamper GoxNP had oxygenated groups in their composition.
the light absorption of the photoinitiator in different These groups were responsible for the better interaction
extents. G was the darkest, followed by GoxNP and between the nanomaterial and the matrix thanks to
finally, GO with a brownish color. All of them presented the polarity of the nanomaterial, which increases the
a decrease in polymerization degree at low exposure stability of the dispersion . It was seen in viscosity,
[60]
times; however, for high exposures times (> 5 min), glass transition temperature, and thermal conductivity
G only achieved 87.3% compared to 96.7% in pristine measurements.
resin. Conversely, GoxNP achieved a 95% and GO was It has been reported that an increase in viscosity is
similar to pristine resin. It was found that GBN does expected when nanofillers are well-dispersed since more
not change polymerization energy when this process is surface area is available for interaction with the matrix .
[61]
conducted by heating. For this reason, it seems that GBN Therefore, an increase of GO and GoxNP viscosity could
does not affect polymerization energy when light is not suggest a homogenous dispersion of the nanofiller, which
involved in the process. Therefore, GBN avoid light to is probably improved due to the presence of the oxygenated
reach the photoinitiator and this is why differences in groups on their surface. Conversely, the addition of G
polymerization degree appeared. decreased the viscosity, suggesting a poor dispersion of
The extent of the polymerization reaction determined these nanoparticles within the polymer matrix. Similar
the printability of the samples. If polymerization degree findings were reported in other studies [54,62,63] .
is not adequate, curing depth decreases, leading to lack This decrease in the viscosity caused by
of adhesion between layers. GO and GoxNP allowed the the nanoparticles addition was attributed to some
printing process with the same parameters than pristine physicochemical phenomena. Jain et al. postulated
[62]
resin, whilst G did not allow to obtain satisfactory printed that the decrease in viscosity could be due to a selective
structures. This negative effect on the printability suggests physisorption of the highest molecular weight polymer
that the G resin did not present enough polymerization chains on the nanoparticle surface, leaving low molar
degree to achieve the minimum adhesion between layers mass in the surrounding molten matrix. Conversely,
to obtain a printed structure. Merkel et al. explained the decrease in viscosity by the
[54]
In terms of printing accuracy, GoxNP showed excluded free volume induced around the nanoparticles,
higher accuracy than GO and similar to R. Besides, the which was accompanied by a reduction in the T .
g
study of surface roughness revealed that the smoothest Therefore, since a decrease in T of G samples
g
surface was obtained with R+GoxNP and it was similar was found, it could be concluded that the addition of G
192 International Journal of Bioprinting (2022)–Volume 8, Issue 1