Recently, Kuruma et al. [64] reported the development of new-generation PU
composite materials containing surface-modified MoS 2 nanosheets. Nanostructured
MoS 2 was synthesized using a hydrothermal method. To improve their compatibility with the PU matrix, the synthesized MoS 2 nanosheet surface was modified
with melamine, an eco-friendly and non-corrosive organic compound containing a
high nitrogen number.
In a typical synthesis process, the poly(ethylene glycol) (PEG) polyol (18.4 g)
was first fed into a round bottom flask and stirred for 1 h under N 2 atmosphere at
85 °C. After that, excess methylene diphenyl diisocyanate (MDI) was dissolved in
30 mL of solvent mixture dimethyl acetamide (DMAc): tetrahydrofuran
(THF) = 3:2 v/v ratio) separately, and then slowly added to the polyol together with
3 drops of dibutyl tindilaurate (DBTDL) catalyst. Then, the reaction was continued
for 2 h to obtain the “–NCO” terminated PU polymer. Afterwards, a calculated
amount of 3-amino-propyl-trimethoxy silane (APTMS) (0.9 mL) was added to the
mixture to react with the remaining “–NCO” by forming the urethane urea bonds.
The stoichiometric ratio –NCO/–OH of 1 was maintained in all cases. The reaction
was allowed to continue until “–NCO” was completely converted to urethane, as
monitored by IR spectra until the complete disappearance of –NCO peak at
2270 cm
−1 [65]. Into the reaction mixer, M-MoS 2 at a calculated weight percentage
with respect to the polyol was added, and the reaction continued for another 3 h.
Finally, the obtained homogeneous and viscous solution was poured into a Teflon
mold and kept in an oven overnight (14 h) at 80 °C, and then kept in a vacuum
oven for one day (24 h) at 60 °C for complete drying. The same procedure was
carried out for the synthesis of PU/MoS 2 composite, except using varying weight
percentages of MoS 2 nanosheets. The reaction conditions and step-by-step chemical
reactions are schematically presented in Fig. 7.4. The formation of MoS 2 ,
melamine-functionalized MoS 2 , and their PU composites was confirmed by
Fourier-transform infrared (FT-IR) spectroscopy. X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy
(XPS) were used to study the structure and morphology of the various samples.
Cone calorimetry tests were carried out to evaluate the flammability of pure PU
and its MoS 2 -containing composites. Figure 7.5 reports the heat release rate
(HRR) (Fig. 7.5a), total heat release rate (THR) (Fig. 7.5b), total smoke release
(TSR) (Fig. 7.5c), and mass loss rates (MLR) (Fig. 7.5d) with time. In addition,
important parameters for the complete analysis of FR activity, such as the time to
ignite (TTI), peak heat releasing rate (PHRR), total smoke release (TSR), time to
PHRR (t PHRR ), fire growth index (FGI), and fire performance index (FPI), were
calculated from Fig. 7.5 and summarized in Table 7.1. After the pristine PU
ignition, it exhibited PHRR and THR values of 477.4 kW m
−2 and 16.9 MJ m
−2 ,
respectively. After the addition of MoS 2 and M-MoS 2 to the PU, the TTI values of
the composites slightly decreased, since the MoS 2 nanosheets catalyze polymer
degradation as explained in the previous section. Moreover, MoS 2 nanosheets in the
polymer matrix increase the viscosity and rapidly increase the surface temperature
with the physical barrier effect of the nanosheets, and therefore, the polymer
decomposes sooner than neat PU. In other words, it burns in the early stage to form
90
7 Polymer Nanocomposites for Fire Retardant Applications
composite materials containing surface-modified MoS 2 nanosheets. Nanostructured
MoS 2 was synthesized using a hydrothermal method. To improve their compatibility with the PU matrix, the synthesized MoS 2 nanosheet surface was modified
with melamine, an eco-friendly and non-corrosive organic compound containing a
high nitrogen number.
In a typical synthesis process, the poly(ethylene glycol) (PEG) polyol (18.4 g)
was first fed into a round bottom flask and stirred for 1 h under N 2 atmosphere at
85 °C. After that, excess methylene diphenyl diisocyanate (MDI) was dissolved in
30 mL of solvent mixture dimethyl acetamide (DMAc): tetrahydrofuran
(THF) = 3:2 v/v ratio) separately, and then slowly added to the polyol together with
3 drops of dibutyl tindilaurate (DBTDL) catalyst. Then, the reaction was continued
for 2 h to obtain the “–NCO” terminated PU polymer. Afterwards, a calculated
amount of 3-amino-propyl-trimethoxy silane (APTMS) (0.9 mL) was added to the
mixture to react with the remaining “–NCO” by forming the urethane urea bonds.
The stoichiometric ratio –NCO/–OH of 1 was maintained in all cases. The reaction
was allowed to continue until “–NCO” was completely converted to urethane, as
monitored by IR spectra until the complete disappearance of –NCO peak at
2270 cm
−1 [65]. Into the reaction mixer, M-MoS 2 at a calculated weight percentage
with respect to the polyol was added, and the reaction continued for another 3 h.
Finally, the obtained homogeneous and viscous solution was poured into a Teflon
mold and kept in an oven overnight (14 h) at 80 °C, and then kept in a vacuum
oven for one day (24 h) at 60 °C for complete drying. The same procedure was
carried out for the synthesis of PU/MoS 2 composite, except using varying weight
percentages of MoS 2 nanosheets. The reaction conditions and step-by-step chemical
reactions are schematically presented in Fig. 7.4. The formation of MoS 2 ,
melamine-functionalized MoS 2 , and their PU composites was confirmed by
Fourier-transform infrared (FT-IR) spectroscopy. X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy
(XPS) were used to study the structure and morphology of the various samples.
Cone calorimetry tests were carried out to evaluate the flammability of pure PU
and its MoS 2 -containing composites. Figure 7.5 reports the heat release rate
(HRR) (Fig. 7.5a), total heat release rate (THR) (Fig. 7.5b), total smoke release
(TSR) (Fig. 7.5c), and mass loss rates (MLR) (Fig. 7.5d) with time. In addition,
important parameters for the complete analysis of FR activity, such as the time to
ignite (TTI), peak heat releasing rate (PHRR), total smoke release (TSR), time to
PHRR (t PHRR ), fire growth index (FGI), and fire performance index (FPI), were
calculated from Fig. 7.5 and summarized in Table 7.1. After the pristine PU
ignition, it exhibited PHRR and THR values of 477.4 kW m
−2 and 16.9 MJ m
−2 ,
respectively. After the addition of MoS 2 and M-MoS 2 to the PU, the TTI values of
the composites slightly decreased, since the MoS 2 nanosheets catalyze polymer
degradation as explained in the previous section. Moreover, MoS 2 nanosheets in the
polymer matrix increase the viscosity and rapidly increase the surface temperature
with the physical barrier effect of the nanosheets, and therefore, the polymer
decomposes sooner than neat PU. In other words, it burns in the early stage to form
90
7 Polymer Nanocomposites for Fire Retardant Applications