MWCNT/PS nanocomposites

Park and co-workers presented a surface TLIRP to synthesize PS-functionalized MWCNTs in toluene at 100 °C for 24 h. FTIR spectroscopy, XPS, SEM and TEM measurements were employed to investigate the as-prepared core-shell nanostructure hybrid nanocomposites. The MWCNT-PS nanocomposites possess good dispersibility in common organic solvents. 

Figure 9.19 Frequency dependence of (a) dielectric constant (cO and real permeability ip. ), (b) dielectric loss (e")> and magnetic loss (p") of PANI-MWCNT/PS nanocomposites with increasing loading (10, 20, and 30 wt.%) of PANl-MWCNT filler. Reprinted from Ref [11] with permission from Elsevier.

Figure 5.3 [resp. Figure 5.4]. Upon further CNT addition, the conductivity levels off around 70 S/m (resp. 7 S/m] at 2 wt% of MWCNTs (resp. SWCNTs], irrespective of the type of matrix. Note, however, that the same CNTs dispersed in a PS matrix, following the same experimental procedure, exhibit significantly higher percolation threshold values than in the CNT/iPP-g-MA series, namely, of the order of 0.55 wt% for SWCNT/PS systems and 0.81 wt% for MWCNT/PS nanocomposites.

Figure 5.3 Conductivity (four-point measurements) as a function of MWCNT concentration for MWCNT/iPP-g-MA and MWCNT/PS nanocomposites.

MWCNT/PP nanocomposites were prepared by melt blending at 200°C with a rotor speed of 60 rpm using an internal batch mixer. SEM images of the fracture surface in the composites demonstrated that PS-grafted MWCNTs were dispersed well in... 

As shown in Table 5.1, the percolation thresholds in both SWCNT-and MWCNT-based nanocomposites of iPP-g-MA and PS roughly... 

Figure 5.8 SEM micrograph of the surfece of a MWCNT/PPO/PS nanocomposite containing 0.75 wt% of MWCNTs. Scale bar 1 pm.

Figure 5.9 shows the electrical conductivity of the MWCNT/ PPO/PS nanocomposites as a function of the weight fraction of the MWCNTs. The percolation threshold is already reached at about 0.3 wt% MWCNT. As for the other series of nanocomposites studied, the conductivity is in the range of several tens of S/m at higher MWCNT concentrations [i.e., higher than 1 wt%]. 

Figure 5.9 Results of four-point conductivity measurements as a function of the MWCNT concentration for MWCNT/PPO/PS nanocomposites.

Here, an alternative approach based on masterbatches is presented in order to prepare CNT/PPO/PS nanocomposites. Instead of directly mixing a surfactant-CNT dispersion with a PPO/ PS polymer in the form of a latex, the nanocomposite was prepared in two steps. The first step consisted of producing a MWCNT/ PS masterbatch with a relatively high, well-dispersed MWCNT... 

Figure 5.10 Two-point measurements of the conductivity of MWCNT/PPO/ PS nanocomposites as a function of the MWCNT concentration for 2 and 5 min of mixing in the extruder. The symbol ( ), at 6.7 wt% MWCNTs, corresponds to the conductivity of the pure masterbatch (MWCNT /PS before extrusion).

Two series ofMWCNT/PS nanocomposites were prepared, both by using the same latex-based technology, with two kinds of MWCNTs, in order to study the influence of the characteristics of the CNTs on the overall conductivity of the final nanocomposites, without varying other important parameters like the type of polymer matrix used and the dispersion and aggregation state of the conductive fillers. It... 

Polymer-linked MWCNT nanocomposites were prepared by reversible addition fragmentation chain transfer (RAFT). The RAFT reagent was successfully grafted on to the surface of MWCNTs and PS chains were grafted from MWCNTs via RAFT polymerization [192], By covalently linking acyl chloride functions of functionalized MWCNTs with living polystyryllithium, Huang et al. succeeded in the preparation of polystyrene-functionalized MWCNTs (Scheme 1.32) [193],... 

Another important property - wettability was followed by SEM analysis on PS/MWCNTs nanocomposite prepared by in-situ bulk-suspension polymerization (54). Figure 8.7 presents a micrograph of fracture surface of the prepared nanocomposite. The picture very clearly evidences that the nanotubes are covered by a thick layer of polystyrene. Parts of original nanotubes can be identified at the end of the fracture noteworthy is also the smaller diameter at the end of tubes. 

Other nano-fillers have also investigated. Cao et al. [253] reported the utilization of multiwalled carbon nanotubes (MWCNTs) as filler-reinforcement to improve the performance of plasticized starch (PS). The PS/MWCNTs nanocomposites were prepared by a simple method of solution casting and evaporation. The results indicated that the MWCNTs dispersed homogeneously in the PS matrix and formed strong hydrogen bonding with PS molecules. Besides the improvement of mechanical properties, the incorporation of MWCNTs into the PS matrix also led to a decrease in the water sensitivity of the PS-based materials. 

For carbon nanotubes, organosoluble PS-SWCNT nanocomposites [292] have been prepared that could be efficiently transformed to highly hydrosoluble, pH-responsive materials via direct sulfonation of the grafted PS chains [296]. In another approach, MWCNT-C H was clicked with azide-functionalized poly(glycerol methacrylate) and the final hairy MWCNTs were used for the in situ synthesis and immobilization of monodisperse 3 nm-sized palladium nanoparticles. The final heterostructure had a high catalytic activity (77%) for the C-C coupling Suzuki reaction between 4-bromobenzene and phenyl boronic acid [293],... 

As an additional factor, the lower melt viscosity at the compression molding temperature of the iPP-g-MA matrix in comparison with the PS system (about 50 Pa s at 170°C for the former in non-emulsified form vs. well-above 10 Pa s at 180°C for the latter) certainly favors the lowering of the experimental percolation threshold, both for SWCNT and MWCNT nanocomposites (see Table 5.1). A lower melt viscosity of the matrix, indeed, reduces the average CNT-CNT distance and was... 

Alternative route to prepare PPO/PS/MWCNT nanocomposites the masterbatch approach... 

Figure 7.3 Four-point conductivity ofMWCNT/PS composite as a function of MWCNT content VGCNT2s fo) IPCNTs ( ]. Each point of the curve is the average of several measurements performed several times on several locations on both sides of the nanocomposite films.

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