Nanocomposites of PLA

Table 8.2 Reported reductions (%) in 0)ygen and water vapour permeability for nanocomposites of PLA compared with the virgin resin.

Fukushima K, Tabuani D, Camino G (2009) Nanocomposites of PLA and PCL based on montmorillonite and sepiolite. Mater Sci Eng C Biomimetic Supramol Syst 29 1433-1441... 

Gorrasi et al. [280] improved water vapor barrier properties by creating bio-nanocomposites of PLA and MMT modified with a functionalized ammonium. 

Figure 5.1 WAXS patterns of CLO30B, NAN804 and nanocomposites of PLA and PCL with (a) 5% CLO30B and (b) 5% NAN804. Reproduced from K. Fukushima et al. by permission of Elsevier Science Ltd., UK.

In subsequent research, Sinha Ray et al. prepared PLACNs with organically modified synthetic fluorine mica (OMSFM). For the characterization of structure and morphology of prepared nanocomposites they first used XRD and conventional TEM (CTEM), and then CTEM and high resolution TEM (HRTEM), they examined the final structure of PLACNs. The compositions of nanocomposites of PLA with OMSFM are summarized in Table 3.1. The XRD... 

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.

Except for the PBS/SAP-qC16 (n-hexadecyl tri-n-butyl phosphonium cation modified saponite) system, the degree of degradation is the same for other samples. This indicates that MMT or alkylammonium cations, and at the same time other properties, have no effect on the biodegradability of PBS. The accelerated degradation of PBS matrix in the presence of SAP-qC16 may be due to the presence of alkylpho-sphonium surfactant. This kind of behavior is also observed in the case of PLA/MMT-based nanocomposite systems. 

For both foam systems, the calculated distribution functions of the cell size from the SEM images are presented in Figure 9.20. The nanocomposite foams nicely obeyed a Gaussian distribution. In the case of PLA/ODA foamed at 150 °C under a high pressure of 24 MPa, we can see that the width of the distribution peaks, which indicates the dispersity for cell size, became narrow, accompanied by a finer dispersion of silicate particles. 

This chapter first presents a brief discussion on the synthesis of PLA, then, it gives an overview of various processing techniques used to fabricate PLA nanocomposites, with a special focus on the microcellular technology. Lastly, the chapter discusses various viscoelastic, thermal, mechanical, thermal degradation, electrical... 

Among the applications discussed in this chapter, the most prominent in recent years is CNT-reinforced polymer nanocomposites. The use of CNTs in polymers can provide superior mechanical properties (60). For instance, the addition of 1% CNTs might increase the stiffness of polymers by 10% and increase their resistance to fracture however, improvements in the properties of CNT-reinforced polymers largely depend on the dispersion of CNTs within the polymer matrix and the polymer-CNT interfacial properties. The following section highlights several studies regarding the processing of PLA-CNT nanocomposites. 

Wu et al. (73) studied the viscoelastic properties, viz. storage modulus (GO and complex viscosity (r 0 with respect to frequency (co) of PLA-carboxylic-acid-functionalized MWCNTs nanocomposites using a rheometer (HAAKE RS600, Thermo Electron Co., USA). The dynamic frequency sweep measurements were carried out at the pre-strain level of 1%. They observed that the addition of carboxylic-acid-functionalized MWCNTs weakened the dependence of G on go, especially at higher loading levels (Figure 9.12). This indicates... 

Figure 9.15. Effect of MWCNTs contents on the surface resistance of PLA-MWCNTs nanocomposites. Reprinted with permission from C-F. Kuan et al.. Journal of Physics and Chemistry of Solids, Vol. 69, p. 1395,2008, 2008, Elsevier Science Ltd.

The correct balance has to be found between the durability of the packaging needed for the preservation of packed food during its shelf-life, and the expected biodegradability at the end of the life cycle. Addition of nanocomposites in PLA can improve barrier properties for food applications and increase degradation in compost conditions [217]. On the other hand, plasticizers are commonly added to promote flexibility of PLA but degradation increases, and food shelf life is often negatively affected by increasing plasticizer content [89]. 

The TEM image of the MN-270-Pt nanocomposite after incorporation of pla-tinic acid is presented in Fig. 3.15. One can see that the material contains nanoparticles with a diameter exceeding 0.7 nm (the estimated resolution of the microscope). The mean particle diameter calculated from a particle size histogram is 1.6nm and standard deviation is 0.6 nm. Evidently, since HPS is a very hydrophobic matrix, Pt species do not dissipate within a polymer matrix but form well defined clusters. light colored areas in the TEM image indicate macropores. The XRD profile of this sample confirms the absence of the Pt-containing crystaUine phase, but suggests the presence of Pt amorphous scatterers. 

In the second part of this chapter, an illustrative example of PARAFAC analysis for three-way data obtained in an actual laboratory experiment is presented to show how PARAFAC trilinear model can be constructed and analyzed to derive in-depth understanding of the system from the data. Thermal deformation of several types of poly lactic add (PLA) nanocomposites xmdergoing grass-to-rubber transition is probed by cross-polarization magic-angle (CP-MAS) NMR spectroscopy. Namely, sets of temperature-dependent NMR spectra are measured under varying clay content in the PLA nanocomposite samples. While temperature strongly affects molecular dynamics of PLA, the clay content in the samples also influences the molecular mobility. Thus, NMR spectra in this study become a three-way... 

A pertinent example for PARAFAC analysis based on NMR spectra of PLA nanocomposites is provided here to show how certain useful information can be effectively extracted from an actual laboratory experiment. 

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