Nylon 6/clay nanocomposite

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... 

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

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]. 

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. 

VanderHart, D.L., Asano, A., and Gilman, J.W. 2001. Solid-state NMR investigation of paramagnetic nylon-6 clay nanocomposites. 1. Crystallinity, morphology, and the direct influence of Fe3+ on nuclear spins. Chemistry of Materials 13(10) 3781-3795. 

Besides melt intercalation, described above, in situ intercalative polymerization of E-caprolactone (e-CL) has also been used [231] to prepare polycaprolactone (PCL)-based nanocomposites. The in situ intercalative polymerization, or monomer exfoliation, method was pioneered by Toyota Motor Company to create nylon-6/clay nanocomposites. The method involves in-reactor processing of e-CL and MMT, which has been ion-exchanged with the hydrochloride salt of aminolauric acid (12-aminodecanoic acid). Nanocomposite materials from polymers such as polystyrene, polyacrylates or methacrylates, styrene-butadiene rubber, polyester, polyurethane, and epoxy are amenable to the monomer approach. 

Since Nylon-6/clay nanocomposites with excellent thermal and mechanical properties were reported by many scientists and polymer/clay nanocomposites have attracted much attention. The improvements in thermal. 

Variations in the preparation of nanocomposites have now been investigated extensively. Liu et al. [202] proposed the preparation of nylon-6/clay nanocomposites by a melt-intercalation process. They reported that the crystal structure and crystallization behaviors of the nanocomposites were different from those of nylon-6. The properties of the nanocomposites were superior to nylon-6 in terms of the heat-distortion temperature, strength, and modulus without sacrificing their impact strength. This is attributed to the nanoscale effects and the strong interaction between the nylon-6 matrix and the clay interface. More recently, nanocomposites of nylon-10,10 and clay were prepared by melt intercalation using a twin-screw extruder [203]. The mechanical properties of the nanocomposites were better than those of the pure nylon-10,10. 

Mathias LJ, Davis RD, Jarrett WL.(1999). Observation of a- and g-crystal forms and amorphous regions of nylon 6-clay nanocomposites using solid-state 15N nuclear magnetic resonance. Macromolecules 32 7958-60. 

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

It is reported that the nylon 6 clay nanocomposite has flame-resistant properties (flammability property). It is thought that a protective layer forms on the surface of this composite and functions to protect the composite from heat. The analysis of this protective layer revealed that it contains an organophilic layer consisting of about 80% clay and 20% graphite [30,31]. 

If the nylon 6 clay nanocomposite is processed in an oxygen plasma, a uniform passivation film is formed. It was found that as the polymers are oxidized, highly oblique composites form, in which the clay concentration increases toward their surfaces, and that the clay layers in these composites function as polymer-protective layers. This indicates that the uniform passivation film may prevent the deterioration of the polymers [32]. 

According to some reports on studies conducted to improve the physical properties of polymer-clay nanocomposites, a small amount of clay was added to a nylon 6-clay nanocomposite and various improvements were achieved higher polymer strength, higher heat resistance, low linear expansion, low gas permeability, and so on. 

Fomes, T. D. and Paul, D. R. Modeling properties of nylon 6/clay nanocomposites using composite theories. Polymer, 44,4993-5013 (2003). 

Studies show that Nylon-6/clay nanocomposites can achieve an OTR (oxygen transmission rate) almost four times lower than unfilled nylon-6 [32]. In the case of Honeywell Aegis OX, the nanoclay layers act as a trap to retain the active oxygen scavengers in the polymer while reducing OTR 100-fold [291]. Imperm , produced by Mitsubishi Gas Chemical Company, has similar results when added to a multilayer PET structure. Imperm s oxygen barrier is two times the standard Nylon MXD6 and its carbon... 

Figure 6.7 Schematic illustration for synthesis of nylon-6/clay nanocomposites/...

Polymer/clay nanocomposites (PCN)are a new class of nanocomposite that makes use of clay materials, which are cheap and well known fillers for polymer materials. The research on polymer-clay intercalation has been reported before 1980s [10]. However, these works were not taken in the history of polymer/clay nanocomposites as these did not result in a dramatic improvement in the physical and engineering properties of the polymers. The researchers at Toyota, Japan demonstrated for the first time that clay (so called filler) can do miracles in 1993 [11,12]. While searching for a lightweight material for automotive applications they successfully developed a nylon-6/clay nanocomposite, which resnlts in a dramatic improvement in properties compared to the pristine polymer. Subseqnently, the technique was extended to thermoset resins leading to the formation of thermoset nanocomposites. 

D.L. VanderHart, A. Asano, J.W. Gilman, NMR measurements related to clay-dispersion quality and organic-modifier stabihty in nylon-6/clay nanocomposites. Macromolecules 34 (2001) 3819-3822. 

The new class of polymer materials, organic- inorganic (clay) nanocomposites, was also reported as an excellent FR composition [234]. Nylon-6 clay nanocomposites, first developed by Toyota Central Research and Development Laboratories, are materials with unique properties. The nylon- 6 clay nanocomposites (clay mass fraction from 2%-70%) are synthesized by ring - opening polymerization of e-caprolactam in the presence of cation exchanged montmorillonite clay [235]. 

This process creates a polymer-layered silicate nanocomposite with the either a delaminated hybrid structure or an intercalated one. The intercalated structure, which forms when the mass fraction of clay is greater than 20%, is characterized by a well ordered multilayer with spacing between the silicate layers of only a few nanometers. The delaminated hybrid structure, which forms when the mass fraction of clay is less than 20%, contains the silicate layers individually dispersed in the polymer matrix. The thermal, mechanical and FR properties of nylon-6 clay nanocomposite with only 5% of clay fraction show excellent improvements over nylon 6. In the paper by Gilman it was pointed out that cone calorimeter data show the reduction of RHR (max.) by 63% in a nylon,6/clay nanocomposite containing a clay mass fraction of only 5% [233]. This nanocomposite has the same heat of combustion as the pure nylon-6. 

T. D. Fornes, P. J. Yoon, and D. R. Paul, Polymer matrix degradation and color formation in melt processed nylon 6/clay nanocomposites. Polymer, 44 (2003), 7545-56. 

Figure 9.7 (a) Comparison of the HRR plot for nylon 6 and nylon-6 silicate nanocomposites (mass fraction 5%) at 35 KW/m heat flux (b) the mass loss rate data for nylon 6 and nylon-6 clay nanocomposites [78]. Reproduced from [78] by permission of Elsevier Science Ltd., UK. 

Processing operations such as injection and compression moulding, extrusion, fibre spuming, etc. are likely involved for the preparation and commercialization of polymer/clay nanocomposites. The flow applied during processing play a decisive role in crystallization kinetics and in the morphology obtained. For neat polymers, it has been demonstrated that the flow accelerates crystallization kinetics when compared with the quiescent melts (Keller and Kolnaar 1997 Kumaraswamy et al. 1999) and some crystallization mechanism has been proposed (Somani et al. 2000 Seki et al. 2002), whereas for polymer/clay nanocomposites, studies are still lacking and most of results have been reported for iPP and nylon 6/clay nanocomposites. 

In contrast with the above results, Zhang et al. (2003) reported a decreased orientation of iPP in iPP/PP-MA/o-MMT nanocomposites during dynamic packing injection moulding as compared to that of neat iPP solidified under the same conditions. Similarly, Medellin-Rodriguez et al. (2001) found that the overall molecular orientation of the crystals was found to decrease with the clay content in Nylon 6/clay nanocomposites subject to uniaxial deformation, with some clay platelets oriented perpendicular to the film surface and the molecular axis of the Nylon 6 crystals parallel to the stretching direction. This was explained by the presence of the clay platelets as well as the rotation of the clay platelets during deformation, which hindered the orientation of the nylon crystals. 

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