PMMA/CNTs nanocomposites mechanical properties

Gleason and coworkers have demonstrated that the surface coating of carbon nanotubes (CNTs) by hot filament CVD of tetrafluoroethylene and by plasma enhanced CVD of MMA provide surface-modified CNTs having a stable/ superhydrophobic surface and good compatibility with PMMA, respectively [91, 92]. The superhydrophobic CNT indicated superior water repellency, whereby essentially spherical and micrometer-sized water droplets were suspended on top of the nanotube forest. The multiwall-CNT/PMMA nanocomposites were dispersed into PMMA via melt mixing. The orientation of CNT in the blend was achieved by melt drawing. The dispersed CNT in the blend indicated a significant effect on mechanical properties of the blend even at a 1% concentration of CNT. 

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]. 

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. 

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