PMMA Nanocomposite Foam Preparation

Typically, physical foaming is a three-step process (1) mixing a blowing gas is dissolved in the polymer to form a homogeneous solution (2) bubble nucleation subsequent pressure release or temperature increase induces phase separation due to the thermodynamic instability, and gas starts to form nuclei and (3) bubble growth and stabilization. 

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FIGURE 1.12 Bimodal cell size distribution observed in PMMA-lwt% CNT nanocomposite foams prepared at 13.8 MPa and different temperatures (a) 100°C (b) 120°C. 

FIGURE 1.12 Continued) Bimodal cell size distribution observed in PMMA-lwt% CNT nanocomposite foams prepared at 13.8 MPa and different temperatures (c) 140°C. Scale bars 10 pm in all micrographs. (Reprinted with permission fromZeng C. et al.. Polymer 2010,51, 655-664. Copyright 2010, Elsevier.)... 

Yeh et al. (2009) investigated the effect of nanoclay on the dielectric and thermal transport properties of PMMA nanocomposite foams. As shown in Figure 1.18, the nanocomposite foams showed lower dielectric constants than the neat PMMA foam. And the effect is more prominent when the clay nanoparticles were better dispersed (CCLMA clay) and when the clay concentration was increased. The effect on thermal conductivity (Figure 1.19) was slightly more complicated. While the nanocomposite foams with better dispersion, that is, CCLMA nanocomposites with an exfoliated-intercalated mixed morphology, showed a deaease in thermal conductivity, the thermal conductivity of the intercalated ACLMA nanocomposite foam was higher than that of neat PMMA foam. They have also prepared PMMA M WCNT nanocomposite foams and measured their insulation property. Interestingly, they noticed a decrease in both dielectric constant (22.6%) and thermal conductivity (19.7%) in the nanocomposite foams with 0.3 wt% carboxyl-multi-walled carbon nanotubes (c-MWNTs). 

Poly(methyl methacrylate) (PMMA) was also used in MMT nanocomposite foam preparation (Fu and Naguib, 2006 Weickmann et al, 2010). Organomodified MMT was used in its preparation by in situ bulk polymerization and batch foaming process with N2. The MMT acted as a heterogeneous nucleation agent in polymer matrix that reduced cell size and increased cell density. Moreover, MMT addition decreased dielectric constant and slightly increased the thermal conductivity as well as the mechanical strength due to the well-dispersed clay mineral platelets (Yeh et al., 2009). 

Retrograde foaming of PMMA nanocomposites have been studied. Zeng etal. (2003) prepared clay nanocomposite foam by retrograde foaming of PMMA-5%. MHABS nanocomposite and submicron cellular foams were prepared (Figure 1.6). 

Chen et al. (2011) prepared PMMA-CNT nanocomposite foams by retrograde foaming and identified two additional complications that might occur. First, as will be discussed in great detail in Section 1.4.1.2, the exceptionally high nucleation rates... 

Later, Goren et al. (2010) eonducted a more systanatic study on the size effect using nanoparticles with the same base geometrical shape (spherical). They prepared PMMA silica nanocomposite foams using two nanosilica of different sizes... 

Yeh JM, Chang KC, Peng CW, Chand BG, Chiou SC, Huang HH, et al. Preparation and insulation property studies of thermoplastic PMMA-silica nanocomposite foams. Polym Compos 2009 30 715-22. 

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