Processing–morphology–property relationships of polypropylene–graphene nanoplatelets nanocomposites

Abstract

Polypropylene (PP) nanocomposites reinforced with graphene nanoplatelets (GNPs) were prepared via melt extrusion. A special sheet die containing with two shunt plates was designed. The relationships among the flow field of the special die, exfoliation, and dispersion morphology of the GNPs in PP and the macroscopic properties of the nanocomposites were analyzed. Flow field simulation results show that the die with shunt plates provided a high shear stress, high pressure, and high velocity. The differential scanning calorimetry, X-ray scattering, and electron microscopy results reveal that the nanocomposites prepared by the die with the shunt plates had higher crystallinity values and higher exfoliation degrees of GNPs. The orientation of the GNPs parallel with the extrusion direction was also observed. The nanocomposites prepared by the die with shunt plates showed a higher electrical volume conductivity, thermal conductivity, and tensile properties. This indicated that the high shear stress exfoliated the GNPs effectively to a thinner layer and then enhanced the electrical, thermal, and mechanical properties.

Melt-Mixed 3D Hierarchical Graphene/Polypropylene Nanocomposites with Low Electrical Percolation Threshold

“…However, it could be associated with the existence of a multi-step percolation behavior where a tunneling mechanism dominates the current flow between the conductive particles [46,55]. Most importantly, the percolation threshold reported in this study is significantly lower than those reported previously for polypropylene [40,41,56] using melt mixing methods [27] and other similar polymers [57]. An overview of the reported electrical percolation values for a number of different polypropylene/graphene systems prepared with various melt mixing protocols is presented in Table 1.…”

“…That can be seen by relatively high values of the electrical percolation Nanomaterials 2019, 9,1766 3 of 19 threshold 3 . In previous studies on PP the electrical percolation threshold for melt mixed systems using a variety of mixing protocols and pre/post mixing procedures has been reported in the range 6-15 wt.% [27,[39][40][41]. These values are significantly higher than theoretical predictions [47] and values obtained for near perfect dispersion of graphene in a variety of matrices using solvents and sonication protocols [2].…”

“…Polypropylene (PP) is one of the most commonly-used polyolefins with a myriad of application uses ranging from everyday items like trays and bottles to high performance compounds suitable for medical, automotive, energy transport and storage, and pipe products [38]. Due to its commercial importance a number of studies have been undertaken on PP/graphene nanocomposites focusing mainly on electrical [27,[39][40][41], thermal [42], and mechanical [43][44][45] performance. Electrical conductivity and especially the electrical percolation threshold is directly linked to the level of dispersion of the filler in the matrix [46].…”

Thermal, Mechanical, and dielectric properties of Injection Molded Graphene Nanocomposites Based on ABS/PC and ABS/PP Blends

“…Liang et al found that Young's modulus of the composites increased, whereas the values of tensile yield strength and tensile fracture increased slightly with increasing the GNP weight fraction. Zhang et al observed that the tensile strength increased after the incorporation of 4 wt % GNPs and that the tensile strength was higher when the nanocomposites had prepared by the die with shunt plates indicating that the high shear stress exfoliated the GNPs effectively to a thinner layer. A significant increase in the Young's modulus by graphene nanoplatelets from around 1.3 GPa to over 2.0 GPa was reported by Ahmad et al and an increase of more than 380% of the Young's modulus by Caradonna et al .…”

Effect of oxygen functional groups of reduced graphene oxide on the mechanical and thermal properties of polypropylene nanocomposites

“…With a decrease of oxygen functional groups on the surface of rGO, the compatibility and interfacial adhesion between rGO and PP matrix increases gradually, which facilitates the load transfer from PP to rGO and improves the mechanical properties of PP nanocomposites . On the other hand, the addition of rGO with higher C/O ratio can increase the degree of crystallinity of PP, which is also beneficial for improving the tensile strength of PP nanocomposites …”