In this work we have prepared ceramic-polybenzoxazine composites based on poly(P-ddm) as matrix reinforced by 0, 3, 5, 7, 10, 15, and 20 wt.% of GX-540 silane-treated nano-Cr2O3 filler via a solution blending method in THF. These nanocomposites are used as new organic coating materials. The effect Cr2O3 nanofillers inclusion on the viscoelastic properties of poly(P-ddm) is studied using dynamic mechanical analysis (DMA). Figure 76 illustrates the change in the storage modulus at 50oC and Tg (measured from tan δ) of the pure poly(P-ddm) and its poly(P-ddm)/Cr2O3 nanocomposites. The DMA properties reveal that the nanocomposites exhibit higher storage modulus at the glassy state than that of the neat poly(P-ddm) and it is firstly enhanced
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The microhardness values for the nanocomposites increase with increasing the nano-Cr2O3 content in the matrix, due to the higher microhardness of the nanofillers (29.5 GPa) compared to the pure poly(P-ddm) thermoset (367 MPa). The highest microhardness values is measured for the nanocomposite containing 20 wt.% of nano-Cr2O3 fraction by 413 MPa. Moreover, the good dispersion of nano-Cr2O3 fillers in the poly(P-ddm) matrix can also contribute to the improved microhardness values. Similar polybenzoxazine-ceramic systems also exhibited improved microhardness, such as poly(BA-a)-Si3N4, and poly(BA-a)-SiO2 nanocomposites [24, …show more content…
As it is seen from Figure 80, the low frequency modulus value for the uncured P-ddm resin coating is detected at 4.54 x 1010 Ω cm2, while that of the cured poly (P-ddm) reached only 4.37 x 108 Ω cm2. This discrepancy was also reported for the poly(BA-a) and BA-a resins [108]. The addition of nano-Cr2O3 particles gradually increased the initial impedance modulus values to reach a maximum value by 8.46 x 1012 Ω cm2 at 20 wt.% of nano-Cr2O3 content. This result implies that the poly(ddm)/Cr2O3 nanocomposites are more effective than the neat poly(P-ddm). These interesting results are mainly attributed to the hydrophobicity of poly(P-ddm) resin and high crosslink density which isolates the substrate from the solution leading to better anti-corrosion properties. Moreover, the nano-Cr2O3 reduced the water diffusion channels that are the main cause of the organic coating failure [109].
FIGURE 80 Evolution of the impedance modulus at the initial immersion stages for the uncured and cured P-ddm resin and its cured nanocomposites various nano-Cr2O3 contents. By analyzing data from Figure 81, it seems that a prolonged contact of the prepared coatings severe form decrease a slight in the high frequency modulus is noticed for all the nanocomposites after 6 days of immersions. Cr3+ ions and OH− groups can react to form passive film of Cr(OH)3 deposits
The microhardness values for the nanocomposites increase with increasing the nano-Cr2O3 content in the matrix, due to the higher microhardness of the nanofillers (29.5 GPa) compared to the pure poly(P-ddm) thermoset (367 MPa). The highest microhardness values is measured for the nanocomposite containing 20 wt.% of nano-Cr2O3 fraction by 413 MPa. Moreover, the good dispersion of nano-Cr2O3 fillers in the poly(P-ddm) matrix can also contribute to the improved microhardness values. Similar polybenzoxazine-ceramic systems also exhibited improved microhardness, such as poly(BA-a)-Si3N4, and poly(BA-a)-SiO2 nanocomposites [24, …show more content…
As it is seen from Figure 80, the low frequency modulus value for the uncured P-ddm resin coating is detected at 4.54 x 1010 Ω cm2, while that of the cured poly (P-ddm) reached only 4.37 x 108 Ω cm2. This discrepancy was also reported for the poly(BA-a) and BA-a resins [108]. The addition of nano-Cr2O3 particles gradually increased the initial impedance modulus values to reach a maximum value by 8.46 x 1012 Ω cm2 at 20 wt.% of nano-Cr2O3 content. This result implies that the poly(ddm)/Cr2O3 nanocomposites are more effective than the neat poly(P-ddm). These interesting results are mainly attributed to the hydrophobicity of poly(P-ddm) resin and high crosslink density which isolates the substrate from the solution leading to better anti-corrosion properties. Moreover, the nano-Cr2O3 reduced the water diffusion channels that are the main cause of the organic coating failure [109].
FIGURE 80 Evolution of the impedance modulus at the initial immersion stages for the uncured and cured P-ddm resin and its cured nanocomposites various nano-Cr2O3 contents. By analyzing data from Figure 81, it seems that a prolonged contact of the prepared coatings severe form decrease a slight in the high frequency modulus is noticed for all the nanocomposites after 6 days of immersions. Cr3+ ions and OH− groups can react to form passive film of Cr(OH)3 deposits