Enhanced thermal conductivity of rheologically percolated carbon nanofiber reinforced polypropylene composites

Abstract

Three different types of carbon nanofibers (CNF) were incorporated in the same polypropylene (PP) matrix by twin-screw extrusion. The rheological and thermal properties were investigated. The rheological characterization of CNFs/PP composites as function of their volume fraction shows different microstructures: percolated and non-percolated behaviors of their CNF's networks. In this work, the laser flash technique is employed in the experimental determination of the thermal diffusivity and conductivity of composites at room temperature. The ultimate aim is to correlate microstructure described by rheological analysis with final thermal properties. The results show that thermal diffusivity and conductivity are clearly higher for rheologically percolated composites suggesting that above certain critical content of nanofibers thermal transport is mainly controlled by percolated structures caused by interconnected CNFs' networks. Finally, thermal conductivity results are described by means of percolation theory from which an intrinsic thermal conductivity for the CNFs' network of approximately 6.5 W/ m K, i.e. close to three times lower than some values reported in literature for SWCNTs' networks, was calculated.

Rheological and Mechanical Properties of Ultra-fine Cellulose-Filled Thermoplastic Epoxy Composites

“…In contrast, the neat TPER composites were predominantly viscous in the terminal region. Similar results were also reported for high viscosity (hv-PP)-expanded graphite (EG) composites, high density polyethylene (HDPE)-fumed silica composites, and polypropylene-carbon nanofiber (CNF-PS-XT grade) composites (Nandi et al 2013;Paleo et al 2015;Piontech et al 2015).…”

“…The deviation from 75° in Fig. 3d shows an elastic response of UFC-filled composites, owing to the creation of a percolated structure in the melt sample (Paleo et al 2015). The UFC-filled composites of 2.5, 5.0, and 10 wt.% were highly elastic, and the 20 wt.% UFC-filled composite was slightly elastic.…”

“…The phase angle (δ) results versus the complex modulus (G*) are shown in the Van Gurp-Palmen plot, which identifies the rheological percolation for the UFC-filled composites (Fig. 3d) (Nandi et al 2013;Paleo et al 2015;Piontech et al 2015). Figure 3d shows that the polymer chains were entirely relaxed at approximately 75° for δ in the low G* region, and a continuous reduction in δ occurred with increasing G* for neat TPER and UFC-filled composites.…”

Negative thermoelectric power of melt mixed vapor grown carbon nanofiber polypropylene composites

“…% of CNF, which is comparable with values reported in meltprocessed PP with 0.8 wt % of CNT [12], but it is very far from PF reported in studies based on solution processed CPC, where values of 1825 μW m -1 K -2 were attained [40]. 3 (measured by using the flash diffusivity method and reported in a previous work for the same PP/CNF composites [41]), the highest figure of merit zT at room temperature for PP composites filled with 2.4 vol. % of CNF was 4.1 x 10 -9 , which is close to the best values of 7.9 × 10 -9 reported in melt mixed PC filled with functionalized carboxyl MWCNT after addition of cyclic butylene terephthalate (CBT) oligomer [42], four order of magnitude lower than the work based on melt-processed PLA/CNT composites for 18 vol.…”

Poly dimethylsiloxane/carbon nanofiber nanocomposites: fabrication and characterization of electrical and thermal properties

“…Due to the depolymerization of PDMS in presence of amine functionalities, pristine CNFreinforced PDMS nanocomposite showed higher decomposition temperature compared to amine-modified CNF-reinforced nanocomposites. More complicated theories, such as the role of tube-end transport and Kapitza contact resistances, have been reported in literature [9].…”