Epoxy resin Exfoliation

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%. ... 

MMT and EPON-828, the DSC curve (Fig. 17) indicates that the spontaneous clay exfoliation epoxide polymerization occurred at an onset temperature of 229 °C. On the basis of the integrated peak area, the heat of reaction for the composite was 572 J/g. DSC curves for the neat epoxy resin and the pristine [H3N(CH2)n-COOH]+-MMT are shown for comparison in Figs. 18 and 19 respectively. In the absence of a catalyst, self polymerization of the neat resin occurred at a much higher onset temperature of 384 °C but the heat of reaction (611 J/g) was comparable to that observed for the corresponding nanocomposite (572 J/g), when corrected for the presence of clay (572/0.95) or 602 J/g. 

Ale Alessi, S., Conduruta, D., Pitarresi, G., Dispenza, C., Spadaro, G. Accelerated ageing due to moisture absorption of thermally cured epoxy resin/polyethersulphone blends Thermal, mechanical and morphological behaviour. Polym. Degradation Stability 96 (2011) 642-648. llAsi Asif, A., Rao, V. L., Ninan, K. N. Preparation, characterization, thermo-mechanical, and barrier properties of exfoliated thermoplastic toughened epoxy clay ternary nanocomposites. Polym. Adv. Technol. 22 (2011) 437 47. 

A, 135 A, 126 A, respectively. The carbon length of the ammonium cation appears to have no direct effect on the dispersion and exfoliation of nanoclay in the epoxy resin. It appears that the acidic alkyl amnuHiium ions play a key role for the exfoliation of epoxy organoclay nanocomposite (10). 

The functionality of the thermoset polymers also plays a vital role in the formation of exfoliated or intercalated composites [32]. The XRD studies reveal the exfoliation of clay platelets at all clay concentration except 10 wt% when dispersed in bi-functional epoxy resin [32]. Whereas the tri-and tetra-functional epoxy resin results in formation of intercalated nanocomposites only, except at very low clay concentrations. 

Abstract In this chapter, we report the findings of experimental investigations conducted on durability of glass fiber-reinforced polymer (GFRP) composites with and without the addition of montmorillonite nanoclay. First, neat and nanoclay-added epoxy systems were characterized to evaluate the extent of clay platelet exfoliation and dispersion of nanoclay. GFRP composite panels were then fabricated with neat/modified epoxy resin and exposed to six different conditions, i.e. hot-dry/wet, cold-dry/wet, ultraviolet radiation and alternate ultraviolet radiation-condensation. Room temperature condition samples were also used for baseline consideration. 

Therefore in order to understand the degree of exfoliation or intercalation. X-ray diffraction (XRD) analysis was carried out on multiple samples of pure 1-28E nanoclay, cured epoxy resin with and without nanoclay of 2 wt% loading as shown in Fig. 21.3. Intense peaks of 100% and 25% were observed at 26 = 3.8° and 26 = 19.7° for the pure montmorillonite nanoclay, similar to the standard montmorillonite-22A nanoclay available in the directory with a PDF 29-1499 in the Rigaku D/MAX 2200 X-ray diffractometer. However, for 2 wt% epoxy/nanoclay samples, the peak intensity was significantly reduced, and the interplanar spacing was increased, indicating that the platelets were... 

Lu JK, Ke YC, Qi ZN, Yi XS (2001) Studies of intercalation and exfoliation behavior of organoclays in epoxy resin. J Poym Sci Part B Polym Phys 39 115-120 Lotti C, Isaac CS, Branciforti MC, Alves RMV, Liberman S, Bretas RES (2008) Rheological, mechanical and transport properties of blown films of high density polyethylene nanocomposites. Eur Polym J 44 1346-1357... 

Lan, T. Kaviratna, P.D. Pinnavaia, T.J. Mechanism of clay tactoid exfoliation in epoxy-clay nanocomposites. Chem. Mater. 1995, 7, 2144-2150. Wang, M.S. Pinnavaia, T.J. Clay polymer nanocomposites formed from acidic derivatives of montmorillonite and an epoxy-resin. Chem. Mater. 1994, 6, 468-474. Pinnavaia, T.J. Intercalated clay catalysts. Science 1983, 220, 365-371. 

Solar et al. [87] apphed oscillatory measurements to study the durability of nanodispersions in a DGEBA epoxy resin with an organophUic MMT (Nanofil 919) in the presence of vibration or external stress. The dependence of rheological properties on the intercalated/exfoliated structures and the surface characteristics between the polymer chains and clays were then monitored. An increase in both the G and G" moduh was detected as the concentration of nanoclay was increased. A transition from a liquid-hke behavior (G" > G at low temperatures) to a sohd-hke behavior (G > G" at higher temperatures) was also observed, due to the formation of a percolated structure of interconnected tactoids through hydro-phobic interactions (as shown in Figure 4.9). This transition was seen to shift to a lower temperature as the nanoparticle content was increased. 

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