PLA-based Nanocomposite

Fig. 9.4 Bright field TEM images of PLA-based nanocomposites prepared with (A) MMT-C1gH3N+, (B) MMT-Clg(CH3)3N+and (C) MMT-2Clg(CH3)2N+. The dark entities are the cross section and/ orfaceofthe intercalated-and-stacked silicate layers and the bright areas are the matrix. Reprinted from [18], 2006, Wiley-VCH.

Fig. 9.11 Flow activation energy of pure PLA and various PLA-based nanocomposites as a function of MMTcontent. Reprinted from [47], 2003 Wiley-VCH Verlag GmbH Co.

As in PP-based nanocomposite systems, the extended Trouton rule, 3r 0 (y t) = r E (so t), also does not hold for PLANC melts, in contrast to the melt of pure polymers. These results indicate that in the case of P LANC, the flow induced internal structural changes also occur in elongation flow [48], but the changes are quite different in shear flow. The strong rheopexy observed in the shear measurements for the PLA-based nanocomposite at very slow shear rate reflects the fact that the shear-induced structural change involved a process with an extremely long relaxation time. 

Recently, Yamada and Okamoto et al. [52-54] first reported the biodegradability of neat PLA and PLA-based nanocomposites prepared with trimethyl octadecylammo-nium-modified MMT (MMT-Ci8(CH3)3N+) with a detailed mechanism. The compost... 

Fig. 9.14 (A) Photographs of biodegradability of neat PLA and PLA-based nanocomposite recovered from compost with time. Initial size of the crystallized samples was 3 x 10 x 0.1 cm3.

Fig. 9.15 (A) Degree of biodegradation (i.e., C02 evolution), and (B) time-dependent change of matrix Mw of neat PLA and PLA-based nanocomposite (syn-FH = 4 wt%) under compost at 58 + 2°C. Reprinted from [53], 2004 WILEY-VCH.

Figure 9.28 shows the relation of the relative modulus (Ktf Kp) to the relative density (Pf/Pp) of neat PLA and PLA-based nanocomposite foams, taken in the directions parallel (A) and perpendicular (B) to the flow. 

Raquez, J.-M., Habibi, Y, Murariu, M., and Dubois, P. (2013) Polylactide (PLA)-based nanocomposites. Prog. Polym. 

Araujo, A., BoteUio, G., Oliveira, M., Machado, A.V. Influence of clay organic modifier on the thermal-stability of PLA based nanocomposites. Appl. Clay Sci. 88-89, 144—150 (2014)... 

Solution casting has been widely used as a nanocomposite processing method since solvent intercalation is the simplest way to prepare PLA/clay nanocomposites. But, a solvent where polymer is soluble and nanofillers are highly dispersible is necessary. The preparation of PLA-based nanocomposites by this method normally results in good dispersion of the nanofillers within the polymer matrix, and consequently in enhanced properties, as has successfully been demonstrated by some authors. 

Table 9.1 Avrami parameters and crystallization half times of PLA-based nanocomposites containing 1 wt% of the nucleating agent.

The dependence of the foam density (p) on the foaming temperature (Tf) under different CO2 pressures (14-30 MPa) was also investigated. Using depressions (corresponding to ATg), master plots of p versus 7> + ATg were constructed using data for both neat PLA and PLA-based nanocomposites [41]. Two distinct behaviors were observed (Figure 17.5). 

FIGURE 17.5 Master plot of density versus Tf + ATg (redueed foaming temperature) using data of both neat PLA and PLA-based nanocomposites foamed under various CO2 pressures (14-30 MPa) [41]. Nanocomposite specimens and PLA type are described in Table 17.3. 

Chang et al. [35, 36] reported the preparation of PLA-based nanocomposites with three different kinds of organo-clays (such as Cloisite 20A, Cloisite 25A, and Cloisite 30B) via a solution intercalation method. They used A,W-dimethylacetamide (DMA) for the preparation of nanocomposites. XRD patterns indicated the formation of intercalated nanocomposites for all the three organoclays tested. TEM images proved that most of the clay layers were dispersed homogeneously in the PLA matrix, although some clusters or agglomerated particles were also detected. 

Petersson and Oksman (2006) compared the properties of PLA-based nanocomposites made of CNC and nonbiodegradable layered sihcate bentonite. At 5 wt % loading, there was more evidence of agglomeration in CNC/PLA composites than betonite/PLA composites, as shown in Fig. 7. The PLA/bentonite nanocomposite showed a 53 % increase in tensile modulus and a 47 % increase in the yield strength compared to neat PLA. The PLA/CNC system on the other hand showed no increase in tensile modulus and only a 12 % increase in yield strength compared to neat PLA. These results were lower than expected. Two factors were ascribed for... 

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