Nylon nanocomposites

In the case of mica-type layered silicates it has been recently demonstrated that nanocomposites (both intercalated and delaminated) can be synthesized by direct melt intercalation even with high molecular weight polymers [7-18]. This synthetic method is quite general and is broadly applicable to a range of commodity polymers from essentially non-polar polystyrene, to weakly polar polyethylene terephthalate), to strongly polar nylon. Nanocomposites can, therefore, be processed using currently available techniques such as extrusion, thus lowering the barrier towards commercialization. 

Choi et al. reported y-irradiation-induced preparation of Ag/poly(ester) and Ag/nylon nanocomposites (Choi et al. 2003b). Ag NPs were dispersed into poly(ester) or nylon via condensation of polymerization and those nanocomposites were expected to be used as antibacterial fibers or electromagnetic inference (EMI) shielding materials. Ag NPs existed as aggregates in the poly(ester) matrix, whereas the Ag NPs were dispersed in the nylon matrix. 

Although enrichment of silicate at the surface occurred, coloration of the sample, and thus increased solar-absorbtivity, occurred. Optical micrographs in Figure 11 show a 2.5wt% nylon nanocomposite sample before (a) and after exposure (b) in the SCEPTRE facility. After the space simulated exposure, the... 

Nanoclays. Nanocomposites are materials that contain nanofillers, or fillers of nanometer dimensions. The successful synthesis of nylon-clay nanocomposites (57-59) ushered in nylon nanocomposites that could attain high modulus, heat distortion temperature, dimensional stabiUty, impermeabiUty, and strength with only a few percent modified clay nanofillers. Although it has been long known that poljuners could be mixed with appropriately modified clay minerals and synthetic clays, the field of polymer-layered silicate nanocomposites has gained... 

The last paper in this series [15] focused on the measurement of the mechanical properties of the nylon 6-montmorillonite nanocomposites prepared above. The control nylon 6 (1013B, Ube Industries) was reported to have a = 13 000. The montmorillonite content in the nylon 6 polymer nanocomposites varied from 1.9% to 7.1%. In the previous article, the montmorillonite content at 1.5% in the nylon 6 nanocomposite produced M = 62000 the nylon 6 nanocomposite at 6.8% produced M = 29 000. The influence of molecular weight on the Young s modulus was not compensated for in the comparisons of the pure nylon with the nylon nanocomposites. The Young s modulus values were measured at 23 °C and 120 °C. The modulus values at 120 °C increased from about 0.19 GPa for pure nylon to about 0.7 GPa for the nylon 6 nanocomposite with 6.8% montmorillonite content. The heat distortion temperature climbed from approximately 65 °C to approximately 150 °C for the polymer nanocomposite with a 6.8% montmorillonite content. The authors argue the applicability of the mixing law (Equation 5.3) coupled with a constrained polymer region associated with the montmorillonite as the mechanism for reinforcement. Identification of the proper mechanism for reinforcement of nylon 6-montmorillonite is provided above by Paul et al. [5j. 

L. S. Schadler, K. O. Laul, R. W. Smith, E. Petrovicova (1997) Microstructure and mechanical properties of thermally sprayed silica/nylon nanocomposites, J. Therm. Spray Technol. 6,475. 

The process of organizing clay using ammonium ions has a considerable impact on production cost. In order to omit this expensive process, silicate layers of clay (sodium-type montmorillonite) were uniformly dispersed in a water slurry and mixed with a molten resin. This method is shown schematically in Fig. 1.16. The clay slurry was injected into a twin-screw extruder by a pump, and water was removed under reduced pressure. In this process, a nylon nanocomposite with uniformly dispersed silicate layers was fabricated successfully. This method simplified the clay organization process, allowing nanocomposites to be obtained at low cost. Table 1.8 shows the mechanical properties of this nanocomposite. The heat distortion temperature was somewhat lowered because the bonding between clay and nylon was not ionic bonding. 

A variety of polyamide (nylon) nanocomposites have been developed and many of diese now have practical applications. Nylon-clay nanocomposite materials containing small amounts of clay minerals exhibit high performance and robust gas barrier properties and have attracted attention worldwide from major chemical manufacturing companies in this field. There are a number of expected applications ... 

Schadler L S, Laul K O, Smith R W and Petrovicova E, Microstructure and mechanical properties of thermally sprayed siUca/nylon nanocomposites , J Therm Spray Tech 1997 6(4) 475-85. 

The first nanocomposite prepared by Toyota Group of Japan was based on nylon 6. In situ polymerization of caprolactum inside the gallery of 5% MMT resulted in the first nylon 6-clay nanocomposite. Besides nylon, polypropylene (PP) is probably the most thoroughly investigated system. Excepting the study of the various properties, theoretical aspects and simulations have also... 

This is a highly polar polymer and crystalline due to the presence of amide linkages. To achieve effective intercalation and exfoliation, the nanoclay has to be modified with some functional polar group. Most commonly, amino acid treatment is done for the nanoclays. Nanocomposites have been prepared using in situ polymerization [85] and melt-intercalation methods [113-117]. Crystallization behavior [118-122], mechanical [123,124], thermal, and barrier properties, and kinetic study [125,126] have been carried out. Nylon-based nanocomposites are now being produced commercially. 

PP is probably the most thoroughly investigated system in the nanocomposite field next to nylon [127-132]. In most of the cases isotactic/syndiotactic-PP-based nanocomposites have been prepared with various clays using maleic anhydride as the compatibilizer. Sometimes maleic anhydride-grafted PP has also been used [127]. Nanocomposites have shown dramatic improvement over the pristine polymer in mechanical, rheological, thermal, and barrier properties [132-138]. Crystallization [139,140], thermodynamic behavior, and kinetic study [141] have also been done. 

Tian et al. [56] have studied poly(G-caprolactone)-silica and Sengupta et al. [57] have investigated nylon 66-silica hybrid systems and have observed that the phase separation started when Si/H20 mole ratio is increased above 2 and the resultant hybrid films become opaque. Gao [11] has reported similar observations on sol-gel-derived ionomeric polyethylene-silica system. A wide range of literatures is not available on this topic of mbber-silica hybrid nanocomposites, though Bandyopadhyay et al. [34,35] have reported the hybrid formation with different TEOS/H2O mole ratios from ACM and ENR and also demonstrated detailed structure-property correlation in these systems. The hybrids have been prepared with 1 1, 1 2, 1 4, 1 6, 1 8, and 1 10 TEOS/H2O mole ratios. Figure 3.14 shows the morphology of the ACM-silica hybrid composites prepared from different TEOS/H2O mole ratios. 

TABLE 1 Mechanical and Thermal Properties of Nylon-6 and Nylon-6-Clay Nanocomposites... 

Epoxy-clay nanocomposites from epoxide precursors have been investigated by research groups at Michigan State University [34-40], Cornell University [41], and Case Western Reserve University [42,43]. In general, the synthesis is similar to that of Nylon-6 and PS... 

Nylon-6-clay nanocomposites were also prepared by melt intercalation process [49]. Mechanical and thermal testing revealed that the properties of Nylon-6-clay nanocomposites are superior to Nylon. The tensile strength, flexural strength, and notched Izod impact strength are similar for both melt intercalation and in sim polymerization methods. However, the heat distortion temperature is low (112°C) for melt intercalated Nylon-6-nanocomposite, compared to 152°C for nanocomposite prepared via in situ polymerization [33]. 

Most nanocomposite researchers obdurately believe that the preparation of a completely exfoliated structure is the ultimate target for better overall properties. However, these significant improvements are not observed in every nanocomposite system, including systems where the silicate layers are near to exfoliated [29]. While, from the barrier property standpoint, the development of exfoliated nanocomposites is always preferred, Nylon 6-based nanocomposite systems are completely different from other nanocomposite systems, as discussed [3,8]. 

The rheological properties of insitu polymerized nanocomposites with end-tethered polymer chains were first described by Krisnamoorti and Giannelis [33]. The flow behavior of PCL- and Nylon 6-based nanocomposites differed extremely from that of the corresponding neat matrices, whereas the thermorheological properties of the nanocomposites were entirely determined by the behavior of the matrices [33]. The slope of G (co) and G"(co) versus flxco is much smaller than 2 and 1, respectively. Values of 2 and 1 are expected for linear mono-dispersed polymer melts, and the large deviation, especially in the presence of a very small amount of layered silicate loading, may be due to the formation of a network structure in the molten... 

To date, the melt state linear dynamic oscillatory shear properties of various kinds of nanocomposites have been examined for a wide range of polymer matrices including Nylon 6 with various matrix molecular weights [34], polystyrene (PS) [35], PS-polyisoprene (PI) block copolymers [36,37], poly(e-caprolactone) (PCL) [38], PLA [39,40], PBS [30,41], and so on [42],... 

Layered silicates, in nylon-clay nanocomposites, 77 313 Layer-lattice solids, 75 246 Layers, in landfill design, 25 878-879 Lazurite, 79 406... 

Nylon blends, dyeing, 9 204 Nylon block copolymer, 19 762 Nylon carpet fibers, stain-resistant, 19 764 Nylon-clay nanocomposites, 11 313-314 Nylon extrusion, temperatures for, 19 789t Nylon feed yarns, spin-oriented, 19 752 Nylon fiber(s), 24 61 production of, 19 740 world production of, 19 7654 Nylon fiber surfaces, grafting of polymers on, 19 763-764... 

F. J. Medellin-Rodriguez, C. Burguer, B. S. Flsiao, B. Chu, R. Vaia, S. Phillips, Time-resolved shear behavior of end tethered nylon 6-clay nanocomposites followed by non-isothermal crystallization, Polymer, vol. 42, pp. 9015-2023, 2001. 

Polymer-clay nanocomposites (PCN) are a class of hybrid materials composed of organic polymer matrices and organophilic clay fillers, introduced in late 1980s by the researchers of Toyota (Kawasumi, 2004). They observed an increase in mechanical and thermal properties of nylons with the addition of a small amount of nano-sized clays. This new and emerging class of pol miers has found several applications in the food and non-food sectors, such as in constmction, automobiles, aerospace, military, electronics, food packaging and coatings, because of its superior mechanical strength, heat and flame resistance and improved barrier properties (Ray et al., 2006). 

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