Crystallization behavior nanocomposites

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. 

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. 

Nam et al. [44] studied the detailed crystallization behavior and morphology of pure PLA and one representative PLA/C18-MMT nanocomposites. They concluded that the overall crystallization rate of neat PLA increases after nanocomposite preparation with C18-MMT. These behaviors indicate dispersed MMT particles act as a nucleating agent for PLA crystallization in the nanocomposites. Lee and co-workers ([45]) who investigated the thermal and mechanical characteristics of PLA nanocomposite scaffold, reported that the recrystallization temperature (Tc) of quenched PLA and its nanocomposite systems decreased by the addition of MMT clay. The nanosized layered MMT platelets provide large surface area due to their small size and thus it is reasonable to consider that the MMT particles could act as effective nucleating sites of PLA crystallization. The increased nucleating sites are likely to facilitate the PLA crystallization process in the nanocomposite systems. 

Nam, J.Y., Ray, S.S., Okamoto, M. Crystallization behavior and Morphology of biodegradable polylactide/layered silicate nanocomposite. Mactomolecules 36, 7126-7131 (2003)... 

Krikorian, V. and Pochan, D.J. (2005) Crystallization behavior of poly(L-lactic acid) nanocomposites nucleation and growth probed by infrared spectroscopy. Macromolecules, 38,6520-6527. 

Pan, R, Zhu, B., Dong, T. and Inoue, Y. (2008) Poly(L-lactide)/layered double hydroxides nanocomposites Preparation and crystallization behavior. Journal of Polymer Science Part B Polymer Physics, 46, 2222-2233. 

In the same manner, the crystallization behavior of SiO -PET nanocomposites is evaluated by means of DSC studies [33]. Basically polyethylene terephthalate is a crystalline polymer. The endothermic peak of the pure PET appears at 225°C and corresponds to melting temperature. The endothermic peak appears at high temperature for SiO -PET nanocomposite system. The data collected through DSC thermal analysis are given in Table 9.3. 

Table 9.4 Crystallization behavior of H-PP and its nanocomposites. Reprinted from [40] with permission from Elsevier.

Kim, Y. C. 2006. Effect of maleated jxjlyethylene on the crystallization behavior of LLDPE/clay nanocomposites. Polymer Journal 38 250-257. 

Xie, Y., Yu, D., Kong, J., Fan, X., and Qiao, W. 2006. Study on morphology, crystallization behaviors of highly filled maleated polyethylene-layered silicate nanocomposites. Journal of Applied Polymer Science 100 4004-4011. 

Montmorillonite (MMT), a smectite clay, is probably the most extensively studied nanomaterial in terms of mechanical, thermal, fire retardant or crystallization behavior of polylactide, especially when these nanoparticles are organically modified allowing the achievement of intercalated and exfoliated nanocomposites.These nanocomposites show enhanced properties as compared to microcomposites and pristine polymer. However, biodegradation and hydrolytic degradation of PLA in the presence of nanoclays has been investigated to a small extent. 

J. Seyfi, 1. Hejazi, G.M. Mohamad Sadeghi, S.M. Davachi, S. Ghanbar, Thermal degradation and crystallization behavior of blend-based nanocomposites role of clay network formation. Journal of Applied Polymer Science 123 (4) (2012) 2492-2499. 

L. Li, C. Y. Li, C. Ni, L. Rong and B. Hsiao, Structure and crystallization behavior of nylon 6,6/multi-walled carbon nanotube nanocomposites at low carnon nanotube contents. Polymer, 48 3452-3460,2007. 

S. F. Hsu, T. M. Wu, and C. S. Liao, Nonisothermal crystallization behavior and crystalline stmcture of poly(3-hydroxybutyrate)/layered double hydroxide nanocomposites. Journal of Polymer Science, Part B Polymer Physics, 45 (2007), 995-1002. 

Lee S, Hong J-Y, Jang J (2003) The effect of graphene nanofiller on the crystallization behavior and mechanical properties of poly(vinyl alcohol). Polym Int 62 901-908 Lele A, Mackley M, Galgali G, Ramesh C (2002) In situ rheo-x-ray investigation of flow-induced orientation in layered silicate-syndiotactic polypropylene nanocomposite melt. J Rheol 46 1091-1110... 

Lim JY, Kim J, Kim S, Kwak S, Lee Y, Seo Y (2015) Nonisothermal crystallization behaviors of nanocomposites of poly(vinylidene fluoride) and multiwalled carbon nanotubes. Polymer 62 11-18... 

In a more fundamental vein, Zhang et al. [157] studied the confined crystallization behavior of PLA/acetylated BC nanocomposites prepared by compression molding. The results indicated that acetylated BC favored the crystallization of PLA at higher temperatures. In a similar mode, Quero et al. [158] investigated the micromechanical properties of laminated BC/PLA nanocomposites by Raman spectroscopy as a mean to understand the fundamental stress-transfer processes in these nanocomposites and as a tool to select appropriate processing and volume fraction of the fibers. Results showed that Young s modulus and stress at failure of PLA films were foimd to increase by 100 and 315%, respectively, for 18% volume fraction of BC and BC membranes cultured for 3 days exhibited enhanced interaction with PLA because of their higher total surface area. 

Streller RC, Thomann R, Tomo O, Mulhaupt R (2009) Morphology, crystallization behavior, and mechanical properties of isotactic poly(propylene) nanocomposites based on organophilic boehmites. Macromol Mater Eng 294 380-388... 

Wu H-D, Tseng C-R, Chang F-C (2001) Chain conformation and crystallization behavior of the syndiotactic polystyrene nanocomposites studied using fourier transform infrared analysis. Macromolecules 34(9) 2992-2999... 

Morales et al. [323] prepared bionanocomposites of PEA (derived from glycohc acid and 6-aminohexanoic add by in situ polymerization) reinforced with OMMTs. The most dispersed structure was obtained by addition of C25A organoclay. Evaluation of thermal stability and crystallization behavior of these samples showed significant differences between the neat polymer and its nanocomposite with C25A. Isothermal and nonisothermal calorimetric analyses of the polymerization reaction revealed that the kinetics was highly influenced by the presence of the silicate particles. Crystallization of the polymer was observed to occur when the process was isothermally conducted at temperatures lower than 145 °C. In this case, dynamic FTIR spectra and WAXD profiles obtained with synchrotron radiation were essential to study the polymerization kinetics. Clay particles seemed to reduce chain mobility and the Arrhenius preexponential factor. 

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