Page 205 - IJB-10-6

International Journal of Bioprinting Effect of G/GO on photocurable resin structure

explained in a previous study. In short, G and GO were was used. The ratio signal-to-noise is better than 8000:1
17
sonicated with MMA, and resin was gradually added with (5.4 × 10 noise absorbance). Spectra were recorded with
−5
sonication steps. The resin:MMA ratio was 300:10 v/v. a resolution of 4 cm from 4000 to 400 cm by taking
−1
−1
The frequency range applied was 1985–2050 kHz at a 50% 32 scans.
amplitude for 10 ± 0.5 min—pulses of 10 ± 0.5 s on and 20
± 0.5 s off. This process was followed by degassing to avoid Double bond conversion (DBC) was studied following
the presence of microbubbles that could affect mechanical the peaks corresponding to carbonyl groups (C=O) at 1728
−1
properties. Samples of as-received Clear resin and resin cm and the peak corresponding to acrylate double bond
−1 22
reinforced with 0.05 wt.% of G (R+G) and GO (R+GO) (C=C) located at 810 cm . As reference, liquid resin with
23
were prepared. or without GBN was used, using Equation I.
The printed samples were obtained by stereolithography
with SLA printer Form2 (Formlabs, Somerville, MA, USA).  I ( CC= ) I liquidC O=( ) 
Layer thickness was set at 100 µm and the wavelength used DBC = 1 − I × I  ×100 (I)


was 405 nm. Exposure time was set by the manufacturer  liquidC C=( ) ( CO= ) 
specifications, but it was adapted in the case of R+G
samples since these had shown printability issues, then it 2.2.4. Tensile tests
13
was increased by an 8.9% to achieve enough polymerization To carry out tensile tests, dog bone samples were obtained
degree to obtain parts. The other parameters were already following ISO 527-2:2012 standard (sample 1BA).
24
set by the manufacturer. The samples were cleaned for 3 Printed layers formed 85° with the applied load direction.
min with isopropyl alcohol in FormWash (Formlabs) Tests were conducted using a Universal Testing Machine
equipment. Post-curing was realized in FormCure chamber IBTH/500 (Ibertest, Madrid, Spain) with a load cell of
(Formlabs). During this process, samples were subjected to 5 kN, operating at an elongation rate of 3 mm/min. The
UV and heat. Parameters used were 405 nm of wavelength, tensile strength, Young’s modulus, and elongation at break
a temperature of 80°C, and a duration of 90 min. Samples were calculated using the load and elongation data.
without post-curing (as-printed) and with post-curing
treatment (post) were studied in order to determine the 2.2.5. Dynamic mechanical thermal analysis
effect of the post-curing treatment in the resin properties. Dynamic mechanical thermal analysis (DMTA) of post-
cured samples was performed using DMTA Q800 (TA
2.2.2. Differential scanning calorimetry instrument, DE, USA) with printed rectangular specimens
The differential scanning calorimetry (DSC) measurements 3
were performed using DSC882e differential scanning (15.3 × 5.0 × 1.4 mm ) in tension mode in a temperature
calorimetery, (Mettler-Toledo, Greifensee, Switzerland). range of 30–225°C, at a single frequency of 1 Hz and a
Dynamic scans from 20 to 250°C at 20°C/min were carried heating rate of 2°C/min. As in tensile tests, layers were
out, and STARe software (Mettler Toledo) was used to printed with an angle of 85° with the applied load.
analyze the curves. Samples (5–10 mg) were placed into With the data obtained from DMTA, it was possible
aluminum crucibles with a capacity of 40 µL and 50 µm hole to calculate the molecular weight between crosslinks in
in the lid. Nitrogen was the purge gas and was delivered a thermosetting resin. Firstly, storage modulus had to be
at a rate of 80 mL/min. Two scans were carried out. In measured within the rubbery plateau region (E’ ) and,
rubbery
the first scan, the area of the curing peak was measured from that value and applying Equation II, molecular weight
to determine if the polymer was completely cured and it between crosslinks (M ) could be calculated :
25
could be completely polymerized by the application of c
heat, while in the second scan, glass transition temperature
RT ⋅ ρ
(T ) was determined as the midpoint of the step of the M = 3 ⋅⋅ (II)
g
'
baseline through the endothermal direction. At least, three c E rubbery
samples per condition were tested and averaged.
where R is the universal gas constant, T is the absolute
2.2.3. Fourier-transformed infrared temperature at which the modulus was calculated (448 K),
spectroscopy (FTIR) and ρ is the density of the polymer. Density was obtained
Infrared spectra were obtained with an IRT-5200 FTIR by applying Archimedes’ principle with a Density Kit
spectrometer from Jasco (Jasco Analitica Spain, Madrid, (Mettler Toledo, Greifensee, Switzerland).
Spain), with attenuated total reflectance (ATR) technique.
DuraSample Diamond accessory formed by a diamond, Besides, crosslinking density per unit volume was
with a diameter of 0.5 mm, embedded in a ZnSe crystal calculated using Equation III :
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Volume 10 Issue 6 (2024) 197 doi: 10.36922/ijb.4075