Green Approach Toward In Situ Exfoliation and Enhanced Compatibility To Obtain Highly Conductive Polypropylene/Graphene Composites

Abstract

The high-interfacial tension, poor compatibility, low dispersion, and toxic auxiliaries remain a historical challenge in fabricating polymer/graphene functional composites. Herein, an industrially viable and green process of manufacturing polypropylene/few-layer graphene (PP/FLG) composites with enhanced interfacial adhesion was demonstrated by combining planetary ball milling and supercritical CO2 (scCO2). Thus, a PP/FLG composite was obtained in one step without requiring organic solvents and toxic auxiliaries. The PP/FLG composite showed an appreciably enhanced through-plane thermal conductivity and in-plane thermal conductivity up to 6.15 and 4.75 W·m–1 K–1, respectively, at an FLG loading of 15 wt %. Also, the in-plane electrical conductivity (IP-σ) and through-plane electrical conductivity (TP-σ) increased to 4.6 × 10–2 and 2.8 × 10–2 S·m–1, respectively, at 3 wt %. Furthermore, the mechanical performance of the composite also improved. Such significant improvements were attributed to the mechanochemical and plasticizing effects of ball milling and scCO2, respectively, which improved the interfacial compatibility between graphene and the polymer matrix. Also, scCO2 exploited complete exfoliation of bulk graphite into few-layer (≤10) graphene flakes, making continuous randomly oriented and interconnected graphene in the matrix. This process holds great potential to prepare functional polymer–graphene composites for next-generation electronic devices and scale-up opportunities.

Straightforward Strategy Toward In Situ Water-Phase Exfoliation and Improved Interfacial Adhesion to Fabricate High-Performance Polypropylene/Graphene Nanocomposites

“…Furthermore, the tensile strength increases with higher MOG loadings (Figure 7c), which is a practical advantage compared to other reported PP/ graphene hybrid systems, as they normally show a reduced tensile strength due to the aggregation of graphene sheets in the matrix. 11,23,64 This further demonstrates that the excellent dispersibility and interfacial compatibility achieved via the strong hydrogen bonding interactions between the PP-M matrix and the incorporated MOG. The confinement effect via nanoscale MOG fillers in the matrix and the strong interfacial adhesion are also able to restrict the PP chains and consequently increase the stiffness of the nanocomposites.…”

“…3,4 In the last decades, the rise of two-dimensional (2D) materials, 5−7 especially graphene, 5,8 provides a new perspective for modified PP materials, enabling a large variety of functional PP composites to be used in electroactive devices, 9 energy harvesting and storage, 10 and heat and electrostatic dissipation. 11 A challenging issue to be faced with is the poor dispersibility of graphene sheets in polymeric matrices due to their strong self-aggregation inclination and inert surface. 12,13 In conventional composite strategies, graphene or its modified products are synthesized in advance and then mixed with PP by melt blending, 14 solution mixing, 15 or in situ polymerization 16 to optimize graphene dispersibility.…”

“…In recent years, a straightforward one-step approach, that is, the in situ exfoliation of bulk graphitic precursor within the PP matrix, has been proposed. Based on different technological processes, this approach can be divided into three categories: solid-state shearing exfoliation, 11,17,18 melt shearing exfoliation, 19−23 and liquid-phase exfoliation. 24−26 Unfortunately, these techniques currently suffer from a common challenge of inefficient exfoliation, which reduces the intrinsic advantages of graphene and further limits their performance in composites.…”

“…22,24,28 Other studies have shown the improved interfacial affinity between graphene and PP achieved by the mechanochemical and plasticizing effects during the exfoliation process; however, their interfacial energy is still too high to obtain a perfect match, and it carries the risk of lattice structure destruction of graphene and molecular chain scission of PP. 11,21 Herein, we report a MAPP-assisted water-phase exfoliation strategy for producing non-covalently modified graphene. A mild oxidation process is employed to introduce the desired amount of oxygen-containing functional groups onto chemically expanded graphite (CEG), which can serve as active sites for hydrogen bonding with MAPP chains.…”

Improvement of “point‐plane”‐like hetero‐structured fillers on thermal conductivity of poly(vinyl alcohol) composites

“…[3,4] However, the intrinsic thermal conductivity (TC) of neat polymer, in the range of 0.2-0.5 W/(mÁK), cannot fulfill the thermal diffusion requirement of highpower electronic devices. [5,6] In order to obtain exceptionally thermally conductive polymers, several nanofillers, such as carbon-based nanomaterials (graphene, carbon nanotubes), [7][8][9] metal fillers (Ag, Cu, and Fe), [10][11][12] ceramic fillers (Al 2 O 3 , SiC, and BN), [13][14][15] and hybrid fillers [16][17][18] have been introduced in the polymer matrix. Hexagonal boron nitride (h-BN), a typical two-dimensional ceramic material, has received wide attention owing to its unique properties, including electrical insulation, TC with high value and anisotropy, good thermal stability, and mechanical properties.…”