Roles of in situ surface modification in controlling the
growth and crystallization of CaCO3 nanoparticles, and
their dispersion in polymeric materials
Ahmed Barhoum1,2,3*, Luk Van Lokeren1, Hubert Rahier1, Alain Dufresne3,4, Guy Van Assche1
1
Department of Materials and Chemistry, Vrije Universiteit Brussel (VUB), Pleinlaan 2, 1050
Brussels, Belgium
2
SIM vzw, Technologiepark 935,BE-9052 Zwijnaarde, Belgium
3
Université Grenoble Alpes, LGP2, F-38000 Grenoble, France
4
CNRS, LGP2, F-38000 Grenoble, France
Corresponding author: ahmed.abdelrasoul@vub.ac.be
Supplementary Material
1. Preparation and characterization of calcium carbonate
During the preparation of CaCO3, the pH of the slurry varies. The pH of the aqueous CaO slurry
is about 13~14. When the CO2 gas is bubbled in the solution, the pH decreases slowly from 12.4
then it stays stable for a comparatively long time (around 45-100 min). After that the pH
decreases to 9 in a few minutes. Before bubbling of CO2 gas, CaO particles (Figure S1) dissolve
to deliver OH− ions that keep the pH high at 14. When CO2 gas is bubbled in water (Figure S2),
the dissolution of CO2 gas in the solution delivers H2CO3 that reacts with OH− ions equilibrating
1
the pH at 12.4. After complete consumption of CaO (end of the reaction) the pH of the system
decreases suddenly from 12.4 to 9.
Figure S1. SEM image of the commercially CaO powder
Figure S2. Schematic representation of the system used in preparing the CaCO3 nanoparticles
Phase identification, amorphous content (%) and the average crystallite size of the prepared
CaCO3 samples were determined using X–ray diffraction (XRD, Diffractometer Bragg Bantano,
Bruker D500, Germany) with Cu-Kα (λ = 1.5406 Å) radiation and a secondary graphite mono
chromator. Scanning step size was 0.02°. The following slits were applied: divergence slit 0.3°,
receiving slit 0.15° and soller slit 2.3°. The Cu Kα radiation was applied with the tube working
conditions 40 kV and 40 mA. Peak position, area and crystallite size were determined from the
fitted profiles using FP function (fundamental parameter) with the TOPAS software (Bruker).
2
The average crystallite size was determined according to the Debye Scherrer equation using
TOPAS software (Bruker). The amorphous CaCO3 content (crystallintiy %) was calculated by
Diffrac. Suite software (Bruker).
The average particle size and morphology were examined by a high resolution transmission
electron microscopy (HRTEM, Jeol, JEM-2010, Japan). The samples were examined with an
acceleration voltage up to 120 kV, a magnification power up to 600 k, and a resolving power
down to 0.2 nm. A droplet of CaCO3 water suspension was pipetted onto a wholly carbon–coated
TEM grid and allowed to dry before the measurements. The average particle size was measured
from HRTEM photos using the specially written software that determined boundaries of each
crystal on the photo and measured its area in real units.
Raman spectra were recorded in the backscattering configuration on a LabRAM HR Evolution HORIBA spectrometer (1800 grooves/mm) under a confocal microscope with a 50X objectives
focusing the 532 nm line. Measurements were performed using laser output power of 2.5 mW,
pinhole 1000 µm and slit 100 µm. Data acquisition and spectra treatment were carried out with
the commercially available program LabSpec 6 (HORIBA Scientific). For all spectra,
background subtraction and peak analysis were performed with the program Origin-lab 7.5
professional combined with an additional peak-fitting module.
The X-ray photoelectron spectroscopy (XPS) measurements were performed on a PHI 5600
spectrophotometer with an Al-Kα monochromated source operating in a vacuum of 5x10–9 Torr
base pressure was used to identify the core levels of the elements of the synthesized CaCO 3. The
samples were irradiated with 187.86 eV, X-ray flux 200 Watt, takeoff angle of 45°. The highresolution Ca(2p), C(1s) and O(1s) core-levels were obtained at a pass energy of 46.5 eV. The
outcome electrons were analyzed by a spherical capacitor analyzer using the slit aperture of 0.8
3
mm. Sample charging was compensated by using the charge neutralizer, with an additional
mathematical shift relative to the reference (C1s at 285 eV). The spectra acquisition parameters
(channel exposition, number of scans, analyzer parameters, etc.) were selected in order to
provide the best energy resolution and signal/noise ratio. Peak position, peak intensity, and full
width at half–maximum (FWHM) of the samples were calculated using Multipack software
(provided by Physical Electronics).
The water contact angle (WCA) was measured with a Kruss DSA-100 contact angle analyzer.
The measurements were performed on the prepared CaCO3 powders compressed into discs using
5 μL water droplet volume and the contacted angle was determined from the profile of the
droplets that were fully separated from the pump syringe needle tip. The discs were prepared by
compression under controlled conditions: 100 mg of the sample and a pressure of 107 Pa, in a
typical IR die.
The zeta potential of CaCO3 particles in suspension was measured at 25°C using a Zeta meter 3.0
equipped with a microprocessor unit (Malvern Instrument Zetasizer 2000). The prepared samples
contain 1 mg of CaCO3 dispersed in 100 g monodistilled water. The samples were treated by
ultrasonic-horn for 30 min and magnetically stirred for 10 min. The unit automatically calculates
the electrophoretic mobility of the particle and converts it into zeta potential using the
Smoluchowski equation.
Thermogravimetric analysis was performed on a TGA Q5000 (TA Instruments, USA). The
samples were dried isothermally at 60 °C for 20 min before heating from 60 to 1000 °C at a
heating rate of 10 °C·min–1 under 50 mL·min–1 N2 gas flow. High temperature platinum pans
were used and sample mass was approximately 5 mg. The temperature at the maximum rate of
decomposition was determined using universal analysis software provided by TA.
4
Thermal degradation of the surfactants on the surface of the prepared modified CaCO3 was
performed using differential scanning calorimetry (TA Instruments, Q2920 DSC, USA).
Differential scanning calorimetry was used to determine thermal transitions of the synthesized
crystals in the temperature range 60–500 ºC. Temperature and enthalpy calibration were
performed using an indium standard. Around 0.5 mg of sample was used. Each sample was
heated from 60 to 500 °C at a heating rate of 10 K·min–1 under 25 mL·min–1 gas flow.
2. Preparation and characterization of PCL nanocomposite
The CaCO3-PCL composites were prepared by melt mixing at 130 °C using a batch-operated
lab-scale twin-screw DSM Xplore Micro-Compounder 15 cc (Figure 2s). The CaCO3 dispersion
state was characterized by means of scanning electron microscopy (SEM) using a Jeol JSM7000F equipped with a field emission gun and operating at 10 mm working distance and 5 keV
electron beam energy. The SEM was performed on the set of samples with a CaCO3 loading of 3
wt%. Prior to SEM, the samples were microtomed at –100 °C to create a perfect plane face using
a Leica Ultracut UCT ultra-cryomicrotome with a glass knife. The sample preparation (ultra–
cryomicrotome) for SEM is time-consuming and cutting the sample, handling and storage,
making the surface of the cross section rough and hence difficult to distinguish the NPs from the
rough surface. Thus, the microtomed samples are stored in a bottle contains liquid nitrogen until
the samples were characterized by SEM.
Thermogravimetric analysis equipment (TA Instruments, TGA Q5000, USA) was employed to
examine the thermal degradation of the samples and CaCO3 content. The samples were dried
isothermally at 60 °C for 10 min before heating from 60 to 700 °C at a heating rate of 10 K·min–1
under air atmosphere (25 mL·min–1). High temperature platinum pans were used and sample
mass was approximately 5 mg. The CaCO3 content in the composite samples was calculated
5
from the mass loss % for filled samples at 550 °C. The temperature of 550 °C is chosen as at that
temperature the polymeric part of the nanocomposite samples completely decomposed while the
decarbonation of the carbonate did not start yet.
Thermal characterization using differential scanning calorimetry (TA Instruments, Q2000 DSC,
USA) was performed using a nitrogen-purged 25 mL·min‒1; the instrument is equipped with a
refrigerated cooling system (RCS). Around 6 mg of samples were placed in a DSC cell. Each
sample was heated from –90 to 90 °C at a heating rate of 10 °C·min–1 under nitrogen atmosphere
with a flow rate of 25 mL·min‒1. The crystallization temperature, Tc, was taken as the peak
temperature of the crystallization exotherm. Second heating cycles were used to obtain onset,
peak temperatures, as well as melting enthalpies. The isothermal crystallization was performed
using modulated-temperature differential scanning calorimetry (MTDSC). The selected
temperature modulation conditions during quasi-isothermal experiments were amplitude of 0.5 K
and a period of 60 s. Measurements were initiated by erasing the thermal history of the samples
during one hour at 130 °C. Thereafter, the sample was kept quasi-isothermal at 50 °C using the
modulated temperature program during 1000 min to ensure that a steady-state condition (i.e.,
equal exothermic and endothermic contributions) is attained. This steady-state is attained after
the heat flow signal has reached its baseline level, thus after the main crystallization process of
the PCL samples.
For tensile strength measurements, tensile strength bars (sample dimensions 90×5×1.5 mm3)
were prepared using DSM Xplore Micro-Injection Molding Machine 5.5 mL (Figure 3s
supplementary information). The granulated compounds were injection-molded into test bars
(DIN 53455) on. The flow direction coincided with the longitudinal direction of the bar. The
conditions of nozzle temperature 85 °C, injection pressure 4.5 bars, mould temperature 35 °C
6
and cooling time 2 min, were used. The tensile strength measurements carried out by Instron
5900 R at a cross-head speed of 5 mm·min–1. Each sample was measured three times, the data
shown being averages over three measurements. All tensile strength measurements were
performed 7 days after compression molding to ensure full crystallization of the PCL
nanocomposites.
Water contact angle (WCA) of the composite polymer was measured with a Kruss DSA-100
contact angle analyzer. The contact angle of water on the substrate was calculated based on a
numerical solution of the full Young–Laplace equation by a computer program from the
equipment supplier. All contact angle measurements were carried out at 25 °C from the profile of
the droplets that were fully separated from the pump syringe needle tip. The droplet volume was
5 µL and at least three parallel measurements were recorded.
Figure S3. Batch-operated lab-scale twin-screw DSM Xplore Micro-Compounder
7
Figure S4. DSM Xplore Micro-Injection Molding 5 mL
8
3. Results
Figure S5. XPS spectra of pure CTAB and sodium oleate
Figure S6. Thermogram of pure CTAB and sodium oleate; (a) TGA mass loss curve; (b) DTG
derivative mass loss; (c) DSC curve
9
Figure S7. Derivative weight curves by TGA of pure PCL (BK) and PCL loaded with the
prepared CaCO3 fillers
10
Figure S8. Data as calculated from TGA and DSC curves of pure PCL (BK) and CaCO3-PCL
composites; (a) TGA maximum decomposition temperature; (b) DSC melting temperature at
peak maximum; (c) DSC melting enthalpy; (d) DSC crystallization enthalpy
11
Table S1. XPS data of the prepared calcium carbonates
Calcium carbonate core levels
Sample
Ca 2p
C 1s
O 1s
Ca 2p1/2
Ca 2p2/3
CO3
*CxHy
Peak position (eV)
MC
347.0
350.7
289.7
285
531.5
NC
346.9
350.6
289.5
285
531.5
CC
346.8
350.5
289.4
285
531.3
OC
346.7
350.4
289.4
285
531.2
Peak relative intensity (%)
MC
45.20
19.4
12.60
12.60
100
NC
38.22
14.52
11.11
10.68
100
CC
39.1
15.38
11.5
12.67
100
OC
43.2
17.69
12.9
21.7
100
Atomic concentration (%)
MC
16
36.2
47.8
NC
13.3
33.4
53.3
CC
14.7
35.1
50.2
OC
14.3
43.3
42.3
* C 1s (CxHy) is due to carbon of surfactant and carbon of contamination
from the environment i.e. CO2
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Table S2. TGA data of the prepared calcium carbonates
Sample
Temperature range
Temperature range
100 ºC – 500 ºC
500 ºC – 1000 ºC
compound
W1 [%]
Td [°C]
TR [°C]
W2 [%]
MC
H2 O
1.7
752
183
41.3
NC
H2 O
1.9
745
199
41.5
CC
H2O + CTAB
2.2
729
210
41.6
OC
H2O + oleate
3.3
712
228
41.9
W1, mass change due to loss of crystalline water and surfactant; Td, decomposition
temperature of decarbonation and losing CO2; TR, decomposition temperature interval
of decarbonation process; W2, mass change due to loss of CO2
Table S3. DSC data of the prepared calcium carbonates
decomposition enthalpy
Sample
[°C]
[J.g-1]
MC
356
8
NC
330
20
CC
325
99
OC
361
311
13
Table S4. Thermo-mechanical properties of pure PCL and the prepared CaCO3-PCL NCs
Sample
Pure PCL
PCL
filled
MC
PCL
filled
NC
PCL
filled
CC
PCL
filled
OC
content
Td
To
Tm
Hm
Tc
Hc
[wt%]
[ºC]
[ºC]
[ºC]
[J.g-1]
[ºC]
[J.g-1]
E
[Mpa]
0.00
328
294
56.5
67.7
35.4
64.5
345
0.70
333
303
56.9
69.0
35.9
64.0
349
2.50
346
313
56.7
69.3
36.2
64.0
417
4.40
335
318
56.9
68.6
35.9
63.1
458
5.40
323
303
56.6
67.4
36.2
63.0
485
0.60
337
303
56.7
69.3
35.5
63.1
437
2.70
324
296
56.6
69.5
35.7
63.3
379
4.20
326
294
56.5
68.1
36.1
63.1
424
5.50
312
288
56.4
68.8
36.2
63.9
436
0.60
353
335
56.8
68.7
35.4
62.9
432
2.40
357
332
56.8
69.9
36.0
63.4
433
4.20
339
325
56.5
68.9
35.8
63.1
451
5.70
332
317
57.0
67.2
35.9
63.3
474
0.70
342
315
56.8
68.4
36.0
64.1
397
2.20
330
308
56.7
68.9
36.1
64.3
409
4.10
393
292
56.4
70.4
36.0
64.2
421
5.80
326
283
56.6
69.8
36.5
64.7
457
To, onset decomposition temperature; Td, decomposition temperature at inflection point;
Tm, melting temperature at inflection point; Hm, melting enthalpy; Tc, onset
crystallization temperature; Hc, crystallization enthalpy; E, elastic modulus
14