Tensile modulus, polymer clay nanocomposites

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 physical properties of a number of other polymer nanocomposites made with clays have been measured. Table 33.3 contains a selection of reported values for some of the most common polymers. Poly(ethylene terephthalate) (PET) and Poly(butylene terephthalate) (PBT) are the most commOTi commercial engineering polymers. The average increase in tensile modulus for most of the PET nanocomposites [21,22,24] is in the range of 35%. This is well below the prediction of a 95% increase for a 5% by weight nanocomposite utilizing Halpin-Tsai theory. The only exception was PET produced by in situ polymerization and tested as fibers [20]. In each one of these references it was acknowledged that full exfoliation had not been reached in the composite. It is reasonable to expect that substantial improvement in properties could be seen if full exfoliation were achieved. The reported increase in tensile modulus for PBT nanocomposites is only in the 36% range [23,24]. 

Polymer/clay nanocomposites exhibit remarkable improvement in material properties relative to unfilled polymers or conventional composites. These improvements can include increased tensile modulus, mechanical strength, and heat resistance and reduced gas permeability and flammability [1], There are various methods of preparing polymer/clay nanocomposites (i) in situ polymerization, (ii) solution intercalation, (iii) melt intercalation, and (iv) in situ template synthesis [2],... 

Fertig, R.S. and Garnich, M.R. (2004) Influence of constituent properties and mi-crostructural parameters on the tensile modulus of a polymer/clay nanocomposite. 

Polymer/clay nanocomposites were first prepared by Carter, Hendricks, and Bolley (1950), bnt only at the end of the 1980s was there the development of a great tnrning point in the polymer-clay nanocomposite technology by Toyota, using polyamide 6 and organophilic clays especially prepared for this nanocomposite (Kawasnmi et al., 1989 Okada et al., 1988). They developed this nanocomposite to be applied in timing belt covers of Toyota vehicles, in collaboration with the UBE Indnstries, a Japanese polyamide 6 indnstry. This nanocomposite had only 5 wt% special clay, which sensibly improved the final material properties as compared with pnre polyamide 6. The nanocomposite formation provided an increase of 40% in the rnptnre tension, 60% of the tensile modnlns, and 126% in the flexion modulus, in addition to the increase in the thermal distortion temperature from 65 to 152°C as compared to the pure polymer. 

Polymer-clay nanocomposites have become a popular topic in both industrial and academic fields dne to their remarkable enhancement of the matrix properties at low loading levels (1-5 wt %) conpared with the standard micro-composites, which contain high levels of reinforcement loading (30-50 wt %). The reinforced properties include tensile modulus, tensile strength, dimensional stability, thermal stability, flame retardanQr, gas and liqttid transport properties [3,4]. 

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. 

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). 

Corn oil-based polymer resin, prepared by the cationic polymerisation of conjugated corn oil, styrene and divinylbenzene, using boron trifluoride diethyl etherate modifled by Norway fish oil as the initiator with 4-vinylbenzyl triethylammonium cation modified montmorillonite clay (VMMT) nanocomposites were reported. The resultant nanocomposites with 2-3 wt% VMMT exhibited significant around two-fold improvements in tensile modulus, tensile strength and toughness when compared to the pristine polymer. There is an improvement in thermal stability up to 400°C in the nanocomposites. ... 

Because of their nanometer size, mbber clay nanocomposites exhibit markedly improved properties when compared to the pure polymers or their traditional composites. Most notable properties are increased tensile strength, tear strength, modulus, gas barrier properties, thermal stability. 

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