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.
NamGJYooJHLeeJW.Effect of long-chain branches of polypropylene on rheological properties and foam-extrusion performances. J Appl Polym Sci2005;
96: 1793–1800.
2.
StangeJMunstedtH.Effect of Long-chain branching on the foaming of polypropylene with azodicarbonamide. J Cell Plastics2006;
42: 445–467.
3.
LiSXiaoMGuanY, et al.
A novel strategy for the preparation of long chain branching polypropylene and the investigation on foamability and rheology. Eur Polym J2012;
48: 362–371.
4.
MohebbiAMighriFAjjiA, et al.
Current issues and challenges in polypropylene foaming: a review. Cell Polym2015;
34: 299–338.
5.
XuZZhangZGuanY, et al.
Investigation of extensional rheological behaviors of polypropylene for foaming. J Cell Plastics2013;
49: 317–334.
6.
LiaoRYuWZhouC.Rheological control in foaming polymeric materials: I. Amorphous polymers. Polymer2010;
51: 568–580.
7.
LiaoRYuWZhouC.Rheological control in foaming polymeric materials: II. Semi-crystalline polymers. Polymer2010;
51: 6334–6345.
8.
LiYYaoZChenZ, et al.
Numerical simulation of polypropylene foaming process assisted by carbon dioxide: Bubble growth dynamics and stability. Chem Eng Sci2011;
66: 3656–3665.
9.
GotsisAZeevenhovenBHogtA.The effect of long chain branching on the processability of polypropylene in thermoforming. Polym Eng Sci2004;
44: 973–982.
10.
LagendijkRPHogtAHBuijtenhuijsA, et al.
Peroxydicarbonate modification of polypropylene and extensional flow properties. Polymer2001;
42: 10035–10043.
11.
RuinaardH.Elongational viscosity as a tool to predict the foamability of polyolefins. J Cell Plast2006;
42: 207–220.
12.
BahreiniEAghamiriSFWilhelmM, et al.
Infuence of molecular structure on the foamability of polypropylene: linear and extensional rheological fingerprint. J Cell Plast2018;
54: 515–543.
13.
HuegunAFernándezMMuñozME, et al.
Rheological properties and electrical conductivity of irradiated MWCNT/PP nanocomposites. Comp Sci Tech2012;
72: 1602–1607.
14.
FernandezMHuegunASantamariaA.Relevance of rheology on the properties of PP/MWCNT nanocomposites elaborated with different irradiation/mixing protocols. Fluids2019;
4: 7.
15.
ItohMKabumotoA.Effects of crystallization on cell morphology in microcellular polyphenylene sulfide. Furukawa Review2005;
28: 32–38.
16.
WenJChenLCaoX, et al.
The interaction between crystallization behavior and foaming performance in the foamed polypropylene. J Polym Mater2017;
34: 513–524.
17.
WangWZhouSXinZ, et al.
Preparation and foaming mechanism of foamable polypropylene based on self-assembled nanofibrils from sorbitol nucleating agents. J Mater Sci2016;
51: 788–796.
18.
SuhKWParkCPMaurerMJ, et al.
Lightweight cellular plastics. Adv Mater2000;
12: 1779–1789.
19.
DemoriRBischoffEAzeredoAP, et al.
Morphological, thermo-mechanical and thermal conducivity properties of halloysite nanotube-filled polypropylene nanocomposite foam. J Cell Plast2018;
54: 217–233.
20.
DuttaASankarpandiSGhoshAK.Evaluation of polypropylene/clay nanocomposite foamability based on their morphological and rheological aspects. J Cell Plast2018;
54: 829–850.
21.
da SilvaABMariniJGelvesG, et al.
Synergic effect in electrical conductivity using a combination of two fillers in PVDF hybrids composites. Eur Polym J2013;
49: 3318–3327.
22.
da SilvaABArjmandMSundararajU, et al.
Novel composites of copper nanowire/PVDF with superior dielectric properties. Polymer2014;
55: 226–234.
23.
SantosJPFda SilvaABSundararajU, et al.
Novel electrical conductive hybrid nanostructures based on PA6/MWCNTCOOH electrospun nanofibers and anchored MWCNTCOOH.Polym Eng Sci2015;
55: 1263–1272.
24.
SantosJPFArjmandMMeloGHF, et al.
Electrical conductivity of electrospun nanofiber mats of polyamide 6/polyaniline coated with nitrogen-doped carbon nanotubes. Mater Design2018;
141: 333–341.
25.
SantosJPFMeloGHFGonçalvesAM, et al.
Flexible conductive poly (styrene-butadiene-styrene)/carbon nanotubes nanocomposites: self-assembly and broadband electrical behavior. J Appl Polym Sci2018;
135: 46650–46659.
26.
VerdejoRStampfliRAlvarez-LainezM, et al.
Enhanced acoustic damping in flexible polyurethane foams filled with carbon nanotubes. Comp Sci Tech2009;
69: 1564–1569.
27.
AmeliAKazemiYWangS, et al.
Process-microstructure-electrical conductivity relationships in injection molded polypropylene/carbon nanotube nanocomposite foams. Composites: Part A2017;
96: 28–36.
28.
AmeliANofarMParkCB, et al.
Polypropylene/carbon nanotube nano/microcellular structures with high dielectric permittivity, low dielectric loss and low percolation threshold. Carbon2014;
71: 206–217.
29.
AntunesMGedlerGVelascoJI.Multifunctional nanocomposite foams based on polypropylene with carbon nanofillers. J Cell Plastics2013;
49: 259–279.
30.
DolomanovaVKumarVPyrzR, et al.
Foaming of microcellular PP-MWCNT nanocomposite in a sub-critical CO2 process. Cell Polym2013;
32: 1–20.
31.
AmeliANofarMSanieiM, et al. Electrical and dielectric properties of foam injection molded polypropylene/multiwalled carbon nanotube composites. In: Proceedings of PPS-30, AIP Conference Proceedings 1664 (ed SC Jana), Cleveland, USA, 6–12 June 2015. pp.110002-1–110002-5. New York: AIP.
32.
LiZChenMMaW.Polypropylene/hydroxyl-multiwall carbon nanotubes composites: crystallization behavior, mechanical properties and foaming performance. J Mater Sci2016;
51: 4566–4579.
TranM-PThomassinJ-MAlexandreM, et al.
Nanocomposite foams of polypropylene and carbon nanotubes: preparation, characterization and evaluation of their performance as EMI absorbers. Macromol Chem Phys2015;
216: 1302–1312.
MariniJBretasR.Influence of shape and surface modification of nanoparticle on the rheological and dynamic-mechanical properties of polyamide 6 nanocomposites. Polym Eng Sci2013;
53: 1512–1528.
38.
AvilesFCauich-RodriguezJVMoo-TahL, et al.
Evaluation of mild acid oxidation treatments for MWCNT functionalization. Carbon2009;
47: 2970–2975.
39.
TrulliMGSardellaEPalumboF, et al.
Towards highly stable aqueous dispersions of multi-walled carbon nanotubes: the effect of oxygen plasma functionalization. J Colloid Interface Sci2017;
491: 255–264.
40.
WangZShirleyMDMeikleST, et al.
The surface acidity of acid oxidized multi-walled carbon nanotubes and the influence of in-situ generated fulvic acids on their stability in aqueous dispersions. Carbon2009;
47: 73–79.
41.
BauhoferWKovacsJZ.A review and analysis of electrical percolation in carbon nanotube polymer composites. Comp Sci Tech2009;
69: 1486–1498.
42.
SeoMKParkSJ.Electrical resistivity and rheological behaviors of carbon nanotubes-filled polypropylene composites. Chem Phys Letters2004;
395: 44–48.
43.
ShenJChampagneMFGendronR, et al.
The development of conductive carbon nanotube network in polypropylene-based composites during simultaneous biaxial stretching. Eur Polym J2012;
48: 930–939.
44.
AntunesMRealinhoVVelascoJI.Foaming behavior, structure and properties of polypropylene nanocomposites foams. J Nanomaterials2010;
2010: 1–11.
45.
TianJYuWZhouC.Crystallization kinetics of linear and long chain branched polypropylene. J Macrom Sci, Part B: Physics2006;
45: 969–985.
46.
ZhangZYuFYuW, et al.
Non-isothermal crystallization behavior of dynamically vulcanized long chain branched polypropylene/ethylene-propylene-diene monomer blends. J Polym Res2015;
22: 198–213.
47.
ZhangZYuFZhangH.Isothermal and non-isothermal crystallization studies of long chain branched polypropylene containing poly(ethylene-co-octene) under quiescent and shear conditions. Polymers2017;
9: 236–254.
48.
MarinelliALBretasR.Blends of polypropylene resins with a liquid crystalline polymer. I. Isothermal crystallization. J Appl Polym Sci2003;
87: 916–930.
49.
SoaresFANachtigallS.Effect of chemical and physical foaming additives on the properties of PP/wood flour composites. Polym Testing2013;
32: 640–646.
50.
Reyes-LabartaJAMarcillaA.Kinetic study of the decompositions involved in the thermal degradation of commercial azodicarbonamide. J Appl Polym Sci2008;
107: 339–346.
51.
TiwaryPParkCBKontopoulouM.Transition from microcellular to nanocellular PLA foams by controlling viscosity, branching and crystallization. Eur Polym J2017;
91: 283–296.
52.
ZhangYParentJSKontopoulouM, et al.
Foaming of reactively modified polypropylene: effects of rheology and coagent type. J Cell Plast2015;
51: 505–522.
53.
AlokuGOYuanXF.Numerical simulation of polymer foaming process in extrusion flow. Chem Eng Sci2010;
65: 3749–3761.
54.
PrashanthaKSoulestinJLacrampeMF, et al.
Masterbatch-based multi-walled carbon nanotube filled polypropylene nanocomposites: assessment of rheological and mechanical properties. Comp Sci Tech2009;
69: 1756–1763.
55.
MariniJPolletEAverousL, et al.
Elaboration and properties of novel biobased nanocomposites with halloysite nanotubes and thermoplastic polyurethane from dimerized fatty acids. Polymer2014;
55: 5226–5234.
56.
ZhaoJMorganABHarrisJD.Rheological characterization of polystyrene-clay nanocomposites to compare the degree of exfoliation and dispersion. Polymer2005;
46: 8641–8660.
57.
AmeliAWangSKazemiY, et al.
A facile method to increase the charge storage capability of polymer nanocomposites. Nano Energy2015;
15: 54–65.
