Tensile modulus, polymer clay

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). 

PNC have been prepared with virtually all polymers, from water-soluble macromolecules to polyolefins and high-temperature specialty resins such as polyimide (PI). Elastomer-based PNCs with large clay platelets have been commercialized for improved barrier properties in automotive tires or sport balls. Elastomeric epoxy resins with clays demonstrate substantial improvement in mechanical properties (e.g., tensile modulus and strength) [Varghese and Karger-Kocsis, 2005 Utracki, 2008]. In this chapter we focus primarily on clay-containing PNCs, the CPNCs. 

Galgali, G., Agarwal, S., and Lele, A., Effect of clay orientation on the tensile modulus of polypropylene-nanoclay composites, Polymer, 45, 6059-6069 (2004). 

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. ... 

It was reported that the compatibilizer normally gets adsorbed on the surface of the clay platelets and alters the interphase [92]. The tensile strength and tensile modulus are always good for CPN compared with PP. The nano-level dispersion of clay in PP plays a vital role in such an improvement. The stiffness of the silicate layers contributes to the presence of immobilized (or) partially immobilized polymer phases [93]. The orientation of the silicate layer and molecular orientation also play a vital role in the improvement of the stiffness. 

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]. 

The addition of fillers to polymers is to obtain an increase in the modulus or stiffness by reinforcement mechanisms. Stiffness of the material can be increased by proper dispersion of aligned clay platelets. This can be seen by the increase in the tensile modulus of the material with the addition of the filler to the product. Increase of modulus by a factor of two is accomplished using montmorillonite, with one third... 

In order to assess the benefit of clay exfoliation in the epoxy matrix, the tensile stren s and moduli for the amine-cured epoxy-clay nanocomposites have been determined for loadings in the range 1 - 2 wt %. For the pristine amine-cured epoxy matrix, the tensile strength is 90 MPa and the tensile modulus is 1.1 GPa. Comparing the mechanical properties of the exfoliated and intercalated nanocomposite in Figure 6, we find that the exfoliated nanocomposites show improved performance, especially in the modulus, relative to the pristine polymer. 

Different approaches have been investigated to improve properties of PBAT/PLA blends to meet specific requirements. Reinforcing the blends with cellulose fiber, limestone, and/or clay led to an increase in tensile modulus but decreases in tensile strength and elongation at break [195]. The drawback of reinforcement techniques is the weak adhesion between fibers and the polymer/clay matrix [195]. Plasticization of PBAT/PLA blends (comprised of 10-25 wt % PBAT) with acetyl tributyl citrate (ATBC) (from 5-30 wt %) decreased Tg, 7)., and and increased the degree of... 

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],... 

Polycaprolactone can increase the tensile strength and impact strength but reduce the ultimate elongation, tensile modulus, and shrinkage of the thermoplastic starch (TPS) polymer (Avemous et al. 2000). Montmorillonite clay can improve the properties of TPS and create a biobased nanocomposite (Bordes et al. 2009 Aouada et al. 2011). 

In order to improve the tensile properties of low-density polyethylene. Mead and Porter [100] added high density polyethylene fibers and film strips. This resulted in an increase in the extensional viscosity and consequently, the tensile modulus of the composite was increased by a factor of 10. The effect of different mineral fillers (e.g. talc, mica, clay, dolomite) on the rheological properties of low density polyethylene films was studied by Arina et al. [17]. It was found that the fillers increased the extensional viscosity of a polymer matrix in concurrence with the earlier observations of Han and Kim [86] as well as Mead and Porter [100]. 

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