Tensile modulus nanocomposites

The effect of the microstructure of acrylic copolymer/terpolymer on the properties of silica-based nanocomposites prepared by the sol-gel technique using TEOS has been further studied by Patel et al. [144]. The composites demonstrate superior tensile strength and tensile modulus with increasing proportion of TEOS up to a certain level. At a particular TEOS concentration, the tensile properties improve with increasing hydrophilicity of the polymer matrix and acrylic acid modification. 

Figure 2.9. (a) and (b) Tensile modulus and strength of PAN nanocomposites. Curves a and c represent theoretical values of hot stretched and original electrospun composites, whereas curves b and d represent the experimental values of these composites. Reproduced from reference 47 with permission from American Chemical Society. 

Du et al. (50) reported the synthesis of butadiene styrene rubber nanocomposites with halloysite nanotubes. The tensile properties of the composites containing various amounts of nanotubes are depicted in Table 2.2. The tensile properties were observed to significantly increase as a function of increasing amount of nanotubes in the composites. For the maximum loading of the nanotubes, a tensile modulus of 5.56 MPa was observed as compared to 1.52 MPa for the pure polymer. 

Eitan et al. (1) reported the synthesis of polycarbonate nanocomposites with untreated (as received) and epoxide treated nanocomposites. A 70% increase in the tensile modulus in the nanocomposites as compared to pure polymer with 5 wt% of the untreated nanotubes was observed as shown in Figure 2.12. However, this increase was increased to 95%, when same amount of epoxide treated nanotubes were used thus indicating the significance of interfacial interactions on the composite properties. 

In the epoxy nanocomposites containing untreated as well as maleic anhydride grafted nanotubes (51), the tensile strength was observed to increase by 50% at 1 wt% of the modified nanotubes, whereas the untreated nanotubes led to only a slight increase in the tensile strength which subsequently decreased on further addition of these pristine nanotubes. The tensile modulus of the nanocomposites was observed... 

Figure 2.12. Enhancement of the tensile modulus of the polycarbonate nanocomposites as a function of nanotube content in the composites, while using as received (AR) and epoxide treated (EP) multi walled nanotubes. Reproduced from reference 1 with permission from Elsevier.

Deng et al. (8) investigated the tensile properties of PEEK/MWCNTs, and found increases in the elastic modulus and yield strength at temperatures above and below Tg at 25°C, the tensile modulus increased by -90% for composites including 15 wt% MWCNTs, and the increment reached -160% at 200°C. According to those results, the improvement of MWCNTs in the mechanical behaviour of the matrix is more effective at higher temperatures. Experimental results do confirm that the overall mechanical performance of PEEK/CNT nanocomposites is well above the required for potential aircraft applications. 

In one example, the tensile strength of polyamide 6 was increased by 55% and the moduli by 90%, with the addition of only 4wt% of delaminated clay. The enhanced tensile property of PCN suggests that nanocomposite performance is related to the degree of clay delamination, which increases the interaction between the clay layers and the polymers. Several explanations, based on the interfacial properties and the mobility of the polymer chains, have been given for this reinforcement. Kojima et al. reported that the tensile modulus improvement for polyamide 6-clay hybrid originated from a constrained region, where the polymer chains have reduced mobility. The dispersion and delamination of the clay were the key factors for the reinforcement. The delaminated nanocomposite structure produces a substantial increase in modulus. 

Figure 16.24 shows the schematic representation of dispersed clay particles in a polymer matrix. Conventionally dispersed clay has aggregated layers in face-to-face form. Intercalated clay composites have one or more layers of polymer inserted into the clay host gallery. Exfoliated polymer/clay nanocomposites have low clay content (lower than intercalated clay composites which have clay content -50%). It was found that 1 wt% exfoliated clay such as hectorite, montmorillonite, or fluorohectorite increases the tensile modulus of epoxy resin by 50-65%. ... 

The procedure to obtain nanocomposites based on unsaturated polyester resins leads to improvements in the order of 120% in the flexural modulus, 14% in flexural strength and 57% increase in tensile modulus with 4.7% of clay slurry content. Thermal stability augments and the gelation temperature increases to 45 °C, as compared to that of the resin (Fig. 31.6). It seems that adding water to the MMT allows better intercalation of polymer chains into the interlamellar space. Because clay is first suspended in water, this improves dispersion and distribution of the particles in the resin matrix. Longer gelation times lead to more uniform and mechanically stronger structures and to yield stresses (Fig. 31.7). Enhanced polymer-clay interactions are revealed by XPS in this case (Fig. 31.8). 

Hoffmann et al. [2000] demonstrated that the low-frequency modulus of exfoU-ated PS-based nanocomposites was higher than for intercalated nanocomposites. This conclusion was confirmed by Mohanty and Nayak [2007], who studied the effect of the MMT exfoliation in PA-6-based CPNCs. The large increase in contact surface between the two phases resulted in improved mechanical properties. The high aspect ratio, p = 200 to 1000, the high tensile modulus of the inorganic filler E 170 GPa), and the large specific surface area (Asp 150 m /g) all play a role in the confinement of the polymer chain—hence in mobility under stress [Yasmin et al., 2006 Utracki, 2009],... 

Okamoto et al. [2000, 2001a] investigated the dispersed structures in PNC with PMMA or its copolymers (MMA with polar monomers) as the matrix. The PNC was prepared by in situ polymerization with 10 wt% of organically modified smectic clay, obtaining intercalated nanocomposites. The storage tensile modulus E and tan 5 of PMMA-clay and PMMA-intercalant were similar. However, when copolymers were used as the matrix, the E of PNC increased over the entire temperature range, but tan 5 peaks shifted to lower T. 

Liao et al. [261] reported biodegradable nanocomposites prepared from poly(lactic acid) (PLA) or acrylic acid grafted poly(lactic acid) (PLA-g-AA), titanium tetraisopropylate, and starch. Arroyo et al. [262] reported that thermoplastic starch (TPS) and polylactic acid (PLA) were compounded with natural montmorillonite (MMT). The TPS can intercalate the clay structure and that the clay was preferentially located in the TPS phase or at the blend interface. This led to an improvement in tensile modulus and strength, but a reduction in fracture toughness. 

Nanocomposites containing CNC filler loading levels of up to 20 wt% were prepared by film-casting 7-1-8 from a DMF suspension of CNCs. The tensile modulus was found to increase with increasing CNCs loading levels, ranging... 

Fig. 12 Relation between N-NMR chemical shifts of model compoimds and tensile modulus of nylon 6 clay nanocomposites at 120 °C...

The desirable properties of polymer nanocomposites which are obtained by the incorporation of small amounts of nanomaterials make them of signihcant value to the scientihc community. Properties such as tensile strength, tensile modulus, thermal and barrier properties, flame retardancy and chemical resistance of vegetable oil-based polymer matrices are improved signihcantly without affecting the light weight characteristics and flexibility of the pristine polymer system. 

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