Thermogravimetric Analysis (TGA) of Graphene Nanoparticle Polymer Composite Systems

Thermogravimetric analysis was performed for (a) neat SC-15, (b) 10% EP, (c) 1% SG-Ag, (d) 2% SG-Ag, (e) 5% SG-Ag, (f) 1% SG, (g) 2% SG, (h) 5% SG. (i) 1% CG, (j) 2% SG, and (k) 5% CG to understand the effects of the nanoparticulates

TABLE 6.4

Thermogravimetric Properties

on the decomposition temperature of the modified polymer system. Data analysis from the weight loss curve of the thermogravimetric analysis indicates there is an increase in the degradation onset point in both the SG (f-h) and SG-Ag (c-e) nano- phased samples. Largest improvements were seen in 5% SG (h) (307°C;~ 13%) and 2% SG-Ag (d) (298°C; 10%, respectively. This may be attributed to the larger surface area seen in these two systems, hence improved dispersion within the polymer system. Subsequently, there is an increase in overall decomposition temperature seen in all nanophased systems with the most significant being the 5% SG-Ag (367°C) (e) at ~8%. The increase in decomposition temperature can be attributed to the thermally conductive nature of the particulate systems (Table 6.4).

The ability to conduct heat allows the particles to perform as a throughput carrier for heat, thus increasing the heat capacity of the polymer system producing a slight delay in polymer chain movement.

The derivative weight curves indicate a reduction in thermal stability as the plasticizer is introduced into the system; however, there is continued stability as the nanoparticles were added to the plasticized system.

Dynamic Mechanical Analysis (DMA) of Graphene Nanoparticle Composite Systems

Dynamic mechanical analysis (DMA) was performed on all neat and nanophased plasticized samples. Figure 6.Ю displays the DMA storage modulus curves of (a) neat SC-15, (b) 10% EP, (c) 1% SG-Ag, (d) 2% SG-Ag, (e) 5% SG-Ag, (f) 1% SG, (g) 2% SG, (h) 5% SG, (i) 1% CG, (j) 2% SG, and (k) 5% CG polymer nanocomposites. Data interpretation indicates that there is a fairly linear increase in storage modulus throughout all systems. The 5% SG-Ag (e) (2,788 MPa) showed the highest overall storage modulus improvement at~ 19%, respectively (Table 6.5).

FIGURE 6.10 DMA storage modulus curves of (a) neat SC-15, (b) 10% EP. (c) 1% SG-Ag, (d) 2% SG-Ag. (e) 5% SG-Ag, (f) 1% SG. (g) 2% SG, (h) 5% SG. (i) 1% CG. (j) 2% SG. and (k) 5% CG.

TABLE 6.5

Dynamic Mechanical Analysis

The cross -link density was calculated using the rubber plateau region of the storage modulus curve [39,40]:

FIGURE 6.11 Stress-strain curves of (a) neat SC-15, (b) 10% EP, (c) 1% SG-Ag, (d) 2% SG-Ag, (e) 5% SG-Ag. (f) 1% SG. (g) 2% SG. (h) 5% SG. (i) 1% CG. (j) 2% SG. and (k) 5% CG polymer nanocomposites.

where E,= storage modulus (MPa); R = Avogadro’s number (m'Pa K/mol ); T, = temperature (°K); and v, = cross -link density (molm³).

Therefore, E, = ^V| .

3RT_r

Cross-link density analysis shows 5% CG (h) samples have the highest cross -linkage (1,458mol/m³) within the polymer system. These values directly coincide with the storage modulus values. Oddly, the 5% SG-Ag (e) samples have relatively similar storage modulus values; however, the cross-link density (704 mol/m³) is significantly lower. The CG nanoparticles have a significantly lower density when compared to the SG nanoparticles. The higher density SG is due in part to the remaining Si0₂. Therefore, the cross-link density results can be somewhat misleading due to the increased rubbery plateau, which subsequently increases the cross-link density due to the proportionality. It can then be surmised that the reinforcement capabilities of the SG and SG-Ag nanoparticulate systems exceed those of the CG nanoparticles. This is supported by the flexure results seen in Figure 6.11.

Flexure 3-Point Bending Analysis

Stress-strain analysis gives a clear understanding of the mechanical properties of the polymer nanocomposites under static load. Figure 6. II shows the stress-strain

TABLE 6.6

Cross-Link Density of Polymer Nanocomposites

curves of (a) the neat SC-15, (b) 10% EP, (c) 1% SG-Ag, (d) 2% SG-Ag, (e) 5% SG-Ag, (f) 1% SG, (g) 2% SG, (h) 5% SG, (i) 1% CG, (j) 2% SG. and (k) 5% CG polymer nanocomposites. Data interpretation depicts SG (f-h) nanoparticles outperforming the other constituent materials in overall load capacity (Table 6.6).

This may be attributed to several factors; one could presume a better interfacial interaction between that of the SG nanoparticles with the matrix when compared to the SG-Ag nanoparticles. Based on the morphological variances within the hybrid particle such as hexagonally, and circularly shaped silver when compared to solely multilayer graphene. Adversely, it can be surmised that the CG nanoparticles had an extremely regressive effect on the polymer system shown by the reduction in stress and strain by up to (54.40 MPa) 57% and (4.24 %) 90%, respectively (Table 6.6).

This can be ascribed to the chemical morphology of the spz freestanding orbitals on the commercial graphene as compared to the synthesized graphene (Table 6.7).

The processed graphene has oxide regions that help create a better cross-linkage with the matrix. Also, the density variance may factor into the particulate amount that would have then led to potentially poor dispersion within the matrix.