Characterizing Biaxially Stretched Polypropylene / Graphene Nanoplatelet Composites

Abstract

In this work, polypropylene (PP) nanocomposites containing different weight concentration of graphene nanoplatelets (GNP) were prepared by melt-mixing using an industrial-scale, co-rotating, intermeshing, twin-screw extruder. The materials were then compression moulded into sheets, and biaxially stretched at different stretching ratios (SRs) below the PP melting temperature. The effects of GNP content and biaxial stretching on the bulk properties of unfilled PP and PP/GNP nanocomposites have been investigated in details. Results show that the addition of GNP (>5wt%) can lead to electrically conductive composites due to the formation of percolation network. The GNP have led to increased polymer crystallinity and enhanced materials stiffness and strength. Biaxial stretching process further enhances the materials mechanical properties but has slightly decreased the composites electrical conductivity. The PP/GNP nanocomposites were also processed into 3D demonstrator parts using vacuum forming, and the properties of which were comparable with biaxially stretched composites.

Biaxial Stretching of Polymer Nanocomposites: A Mini-Review

“…Compared to conventional methods, the biaxial stretching process results in a high degree of orientation and regular alignment of chains by intermolecular friction (Li et al, 2020). The structure, orientation degree, and surface morphology of polymers can be changed by adjusting the stretching ratio (SR) of biaxial stretching to enhance strength and tensile modulus in the oriented direction (Soon et al, 2012;Mayoral et al, 2021). Molecular alignment of amorphous polymer chains in the oriented direction and strain-induced crystallization are also influenced by biaxial tension (Delpouve et al, 2012;Ouchiar et al, 2016;Van Berkel et al, 2018).…”

“…Molecular alignment of amorphous polymer chains in the oriented direction and strain-induced crystallization are also influenced by biaxial tension (Delpouve et al, 2012;Ouchiar et al, 2016;Van Berkel et al, 2018). Generally, the degree of molecular orientation, amount of strain-induced crystallization, and extent of amorphous chain confinement all affect the barrier performance and thermomechanical properties of polymer nanocomposites (Delpouve et al, 2012;Mayoral et al, 2021). Another benefit of biaxial stretching is the ability to disperse nanofillers in the polymer matrix without using compatibilizers (Xiang et al, 2015).…”

“…Biaxial tension is not only an advanced composite manufacturing process, but also a deformation mode in other processing methods, such as blow film extrusion (Espinosa et al, 2016) and thermoforming (Mayoral et al, 2021). Moreover, the use of biaxial stretching in changing the structure, dispersion, and orientation of neat polymer materials to enhance performance has been widely studied for polymers including biaxially oriented polypropylene (Xing et al, 2019), biaxially oriented polyethylene (Chen et al, 2020), and biaxially oriented polyethylene terephthalate (Onyishi and Oluah, 2020).…”

Mechanical properties of in situ modified graphene nanosheets‐reinforced polypropylene

“…Compared with pristine PP, the nonisothermal crystallization temperature (T c ) of the composite gradually increases with increasing graphene content (Figure 10), indicating that graphene nanoplatelets act as seeds for faster nucleation. [ 45 ] In addition, the crystallinity (X c ) of the graphene‐doped composites is higher than that of pure PP. Graphene could play a role in heterogeneous nucleation, and several nuclei are generated simultaneously during the crystallization process; thus, crystallization can be achieved at high temperatures.…”

Enhanced sensing performance of flexible strain sensors prepared from biaxially stretched carbon nanotubes/polydimethylsiloxane nanocomposites

“…So far, only flexible strain sensors, mainly based on the sequential biaxial stretching of a thermoplastic elastomer (such as thermoplastic polyurethane [TPU]) (stretching in the x-direction, then in the y-direction), have been reported. [21][22][23][24][25] In comparison, simultaneous biaxial stretching has a higher production efficiency and possible structural changes, including the orientation and dispersion of nanofillers. The impact of simultaneous biaxial stretching on the structure and sensing properties of sensors has yet to be investigated in detail.…”