PMMA/CNTs nanocomposites

Figure 10.19 Variation of the microhardness of PMMA-CNTs nanocomposites with CNTs content. Reprinted from [91] Copyright 2005, with permission from Elsevier.

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... 

FIGURE 1.14 Effects of MWCNT surface functionalization on the bubble density of PMMA CNT nanocomposite foams, (a) Surface functionalization scheme, in which oxidized CNTs (M20 and MlOO) were surface grafted with glycidyl phenyl ether (P20 and PlOO). 20, 100 in the notation refer to the CNT aspect ratio, (b) A comparison of the bubble nucleation density of MlOO, PlOO, M20, and P20 nanocomposites foamed, saturated at various pressures, and foamed at 65°C for 5 minutes. Error bars represent the standard deviations of bubble nucleation density data of four samples under each condition. (Reprinted with permission from Chen L. et al.. Composites Science and Technology 2012, 72, 190-196. Copyright 2012, Elsevier.)... 

McClory C, McNally T, Baxendale M, Potschke P, Blau W and Ruether M (2010) Electrical and rheological percolation of PMMA/MWCNT nanocomposites as a function of CNT geometry and functionality, Eur Polym J 46 854-868. 

For bulk materials, Jin et al fabricated poly (methylmethacrylate) (PMMA)/MWNT nanocomposites by melt mixing. MWNTs were well dispersed in the matrix [90]. Melt compounding is also widely used for the fabrication of composite fibers. Sandler et al mixed polyamide-12 pellets and CNTs in a twin-screw micro-extruder and then the extrudate was chopped and fed into a capillary rheometer with 1 mm die. The CNTs in the spun fibers were uniformly dispersed [91]. Not only can thermoplastic polymers be melt-compounded, polyimide, a thermoset plastic, can be also prepared by mixing the imide oligomer at 320 °C on a steel plate and then cured at 370°C. It was found that the dispersion of CNTs in... 

A large amount of research has been reported on the mechanical properties of CNT reinforced plastic materials. In the early days, pristine CNTs were mostly used to fabricate CNT nanocomposites. The PMMA nanocomposites were prepared by melt blending, and the nanotubes were well dispersed in the matrix with no apparent damage or breakage. The storage modulus of the PMMA matrix is significantly increased by the incorporation of pristine MWNTs, particularly at high temperatures [90]. 

Du, Fischer, and Winey (2003) and Zeng et al. (2010) used both methods in attempts to produce the PMMA/carbon nanotube (CNT) nanocomposites. They found ASP resulted in better CNTs dispersion. Unlike the solvent casting process where nanoparticles may agglomerate during solvent evaporation, in ASP, the rapid precipitation of PMMA-CNTs very effectively lock down the well-dispersed structure. 

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.)... 

FIGURE 1.15 Failure surfaces of PMMA (a) and (b) PMMA-0.5% CNT nanocomposite foams. The PMMA foam showed brittle failure while the nanocomposite foam exhibited ductile failure with extensive deformation contributing to the improvement in tensile toughness. (Reprinted with permission from Zeng C. et al., Composites Science and Technology 2013, 82, 29-37. Copyright 2013, Elsevier.)... 

Early, in situ radical polymerization was used for the synthesis of poly(methyl methacrylate) (PMMA)-CNT composites [82]. In situ polymerization was performed using the radical initiator 2,2-azobisisobutyronitrile(AIBN). In this reaction, p-bonds in CNTs were initiated by AIBN, and therefore nanotubes could participate in PMMA polymerization to form a strong interface between the CNT and the PMMA matrix. PA6/CNT composites have been prepared by in situ polymerization of e-caprolactam in the presence of pristine and carboxylated CNTs. The e-caprolactam monomer was found to form an electron-transfer complex with CNTs and result in a homogeneous, polymerizable solution. The final composites can be spun into PA6/CNT fibers (Fig. 7) with excellent mechanical and electrical properties [83].This method is also suitable for the fabrication of thermosetting polymer composites with nanofillers. Bauhofer et al. [84] dispersed CNTs in an epoxy solution system based on a bisphenol-A epoxy resin and an amine hardener During nanocomposite curing, electric fields were used to induce the formation of aligned conductive nanotube networks. Recently, the in situ polymerization method... 

Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have a chemically inert surface and it is difficult to carry out surface modification. Acid treatment is usually used to introduce carboxylic groups at the defects of the CNT and CNF surface, which can improve particle dispersion. However, the acid treatment may damage the nanoparticles causing a reduction of mechanical properties. Park et al. prepared PMMA-MWCNT nanocomposites via suspension polymerization. Acid-treated MWCNTs were dispersed in MMA by ultrasonication, then an initiator (AIBN) was dissolved in the MMA-MWCNT mixture which was later poured into a solution with a stabilizer (PVA) to carry out polymerization at 95 °C for 3.5 h. After polymerization, the PS-MWCNT nanocomposite particles were collected by filtration. 

Benoit et al. (41) obtained electrically conductive nanocomposites by dispersing SWCNT and PMMA in toluene, followed by drop casting the mixture on substrates. Thin films of SWCNT-PMMA composites for different CNT concentration were produced by spin casting by Chapelle et al. (54) and Stephan et al. (55). They characterized these nanocomposites by Raman spectroscopy to study interactions between nanotubes and PMMA and found that PMMA tends to intercalate between the CNTs thereby increasing the distance between the nanotubes in the film. 

Chen et al. (67) reported the use of trifluoroacetic acid (TFA) as a cosolvent with tetrahydrofuran (THF) to improve dispersion and processability of the nanocomposites. They prepared MWCNT-PMMA composite films with varying CNT content by solvent casting method using 10 vol % TFA as a co-solvent with tetrahydrofuran (THF). SEM and optical microscopy revealed a good dispersion of nanotubes in solvent and PMMA. The composites showed low percolation... 

Many studies have used these methods for processing of both thermosetting and thermoplastic polymers. Y. Liao (53) dissolved epoxy in a well-dispersed, ultra-sonicated CNT suspension. The solvent was evaporated, and the epoxy was subsequently cured to form a nanocomposite in which the good CNT dispersion was achieved. Jin et al. (54) produced various types of polymer-coated and polymer-grafted MWNT solutions, in some cases evaporating the solvent and subsequently melt-mixing with another polymer. Yudasaka et al. (55) used a mixture of SWNTs and PMMA in monochlorobenzene (MCB) for dispersion, purification and subsequent spin-casting of the material. 

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