Ultrasound-Assist Extrusion Methods for the Fabrication of Polymer Nanocomposites Based on Polypropylene/Multi-Wall Carbon Nanotubes.

Carlos Ávila-Orta,Erika Rivera-Paz,José Mata-Padilla,Miguel Waldo-Mendoza,Víctor Cruz-Delgado,Pablo González-Morones,Zoe Quiñones-Jurado,Ronald Ziolo

doi:10.3390/ma8115431

Carlos Ávila-Orta, Erika Rivera-Paz + Show 6 more

Open Access

https://doi.org/10.3390/ma8115431

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Abstract

Isotactic polypropylenes (iPP) with different melt flow indexes (MFI) were used to fabricate nanocomposites (NCs) with 10 wt % loadings of multi-wall carbon nanotubes (MWCNTs) using ultrasound-assisted extrusion methods to determine their effect on the morphology, melt flow, and electrical properties of the NCs. Three different types of iPPs were used with MFIs of 2.5, 34 and 1200 g/10 min. Four different NC fabrication methods based on melt extrusion were used. In the first method melt extrusion fabrication without ultrasound assistance was used. In the second and third methods, an ultrasound probe attached to a hot chamber located at the exit of the die was used to subject the sample to fixed frequency and variable frequency, respectively. The fourth method is similar to the first method, with the difference being that the carbon nanotubes were treated in a fluidized air-bed with an ultrasound probe before being used in the fabrication of the NCs with no ultrasound assistance during extrusion. The samples were characterized by MFI, Optical microscopy (OM), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), electrical surface resistivity, and electric charge. MFI decreases in all cases with addition of MWCNTs with the largest decrease observed for samples with the highest MFI. The surface resistivity, which ranged from 1013 to 105 Ω/sq, and electric charge, were observed to depend on the ultrasound-assisted fabrication method as well as on the melt flow index of the iPP. A relationship between agglomerate size and area ratio with electric charge was found. Several trends in the overall data were identified and are discussed in terms of MFI and the different fabrication methods.

Highlights

Carbon nanotube/polymer nanocomposites [1,2,3,4,5,6] have been studied for over a decade due to their outstanding properties, which result from the combination of a soft phase and a functional phase
Given the paucity of data and difficulty in comparing different ultrasound extrusion fabrication studies, we focused on a model system to determine the effects of ultrasound-assist methodology on the properties of nanocomposites formed by the extrusion process
The four fabrication methods are designated as W-U for fabrication without ultrasound, F-U for fixed-frequency ultrasound fabrication, variable frequencies in the molten state (V-U) for variable-frequency ultrasound fabrication and PT for pretreated carbon nanotubes, where the carbon nanotubes were treated in a fluidized air-bed with an ultrasound probe before being used in the fabrication of the nanocomposites (NCs), with no ultrasound assistance during the extrusion

Summary

Introduction

Carbon nanotube/polymer nanocomposites [1,2,3,4,5,6] have been studied for over a decade due to their outstanding properties, which result from the combination of a soft phase (polymer matrix) and a functional phase (dispersed nanomaterials). Polymers, as well as CNTs, are often subjected to treatments prior to nanocomposite fabrication in order to reduce the free energy difference between the components. In this sense, the application of high-frequency sound waves during pretreatment, as well as during fabrication, could provide an effective energy source to improve the dispersion of the functional CNTs in the polymer matrix

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