Effect of MWCNT carboxyl functionalization on the shear rheological and electrical properties of HMS-PP/MWCNT foams

Abstract

Different concentrations of multiwall carbon nanotubes (MWCNT) and carboxyl functionalized MWCNT (MWCNT-COOH) were added to a high melt strength polypropylene (HMS-PP) to produce foams with high dielectric constants, using azodicarbonamide (AZO) as blowing agent. The AZO foaming behavior and the crystallization, thermal properties, steady state and oscillatory shear rheological properties of the nanocomposites were analyzed by polarized light optical microscopy (PLOM), differential scanning calorimetry (DSC), thermogravimetry analyses (TGA) and parallel plate rheometry. The morphology, the dielectric and dynamic mechanical properties (DMTA) of the foams were also studied by scanning electron microscopy (SEM), impedance spectroscopy and bending method, respectively. A decrease in crystallite size and an increase in the HMS-PP overall crystallinity promoted by the presence of both types of MWCNTs was observed, as well as an increase in the crystallization temperatures. From these results and from the analyses of the rheological properties, it was possible to predict that the 5 wt.% MWCNT foam would have the lowest bubble growth rate, the 1.5 wt.% MWCNT-COOH the highest, while the 3 wt.% MWCNT-COOH composition would have the slowest bubble stability (and consequently the highest cellular density) and the 1.5 wt.% MWCNT-COOH the fastest. Also, it was possible to predict that only the 5 wt.% MWCNT-COOH foam would have a percolated and electrically conductive structure. All these predictions were confirmed by the resultant morphology and impedance spectroscopy results. The highest mechanical damping was displayed by the 3 wt.% MWCNT-COOH foam, while the lowest by the 5 wt.% MWCNT-COOH foam. Regarding the dielectric properties, the 1.5 wt% MWCNT-COOH foam was found to be the most suitable to be used as a capacitor material; this foam was also the less dense of all the samples.

A strategy for extending the processing temperature for polypropylene in foam extrusion and its theoretical validation

“…Figure 9 indicates that when the HIPS content increases, the temperature range of the blends foaming expands, and by manipulating the temperature, foaming samples with variable foaming multiplicity/density can be obtained. At 156°C, the expansion ratio of pure PP foam samples can reach, 20 but the structure of cell is not satisfactory. By incorporating HIPS, foam samples with volume expansion rates ranging from 8 to 18 can be produced by adjusting the temperature.…”

“…The viscoelastic properties of the sample also strongly influence the cell shape and structure during the extrusion foaming process. 19,20 Therefore, it is highly important to study the variations of the elastic modulus, viscous modulus and loss tangent of the blends with frequency. Figure 4 presents graphs showing the storage modulus, loss modulus and loss tangent as a function of frequency for different samples as obtained at 160°C by dynamic thermodynamic analysis and at 180°C using a rotational rheometer.…”

Effect of reduction time of functionalized graphene oxide on the morphology and properties of epoxy composite foams

“…[1][2][3][4] Further making these CPCs into the porous structure will bring added advantages, including savings in materials and stronger microwave-absorbing ability, which is of great significant for electronic devices, especially those applied in aircraft, watercraft, and automobiles. [4][5][6] Among these conductive nanofillers, carbon nanomaterials like carbon nanotubes and graphene have outstanding structural and electrical properties, thereby having been extensively reported for the preparation of conductive polymer foams. 4,[6][7][8] Since Novoselov et al 9 first obtained graphene by stripping graphite using adhesive tape, graphene has emerged as an attractive option for conductive composite materials due to its unique two-dimensional structure and excellent electrical and mechanical properties.…”

“…[4][5][6] Among these conductive nanofillers, carbon nanomaterials like carbon nanotubes and graphene have outstanding structural and electrical properties, thereby having been extensively reported for the preparation of conductive polymer foams. 4,[6][7][8] Since Novoselov et al 9 first obtained graphene by stripping graphite using adhesive tape, graphene has emerged as an attractive option for conductive composite materials due to its unique two-dimensional structure and excellent electrical and mechanical properties. However, due to the large surface area and high surface energy, graphene tends to agglomerate in the polymer matrix, thus reducing the composites'mechanical and electrical performances.…”

“…1-4 Further making these CPCs into the porous structure will bring added advantages, including savings in materials and stronger microwave-absorbing ability, which is of great significant for electronic devices, especially those applied in aircraft, watercraft, and automobiles. 4-6…”