Crystallization behaviors in the isotactic polypropylene/graphene composites

Mechanical, Thermal, and Morphological Properties of Graphene Nanoplatelet-Reinforced Polypropylene Nanocomposites: Effects of Nanofiller Thickness

In this work, polypropylene (PP) and graphene nanoplatelet (GNPs) composites are routed through twin screw mixing and injection moulding. Two types of GNPs with a fixed size of 25 µm with surface areas ranging from 50–80 m2/g (H25, average thickness 15 nm) and 120–150 m2/g (M25, average thickness 6–8 nm) were blended with PP at loading rates of 1, 2, 3, 4, and 5 weight%. Mechanical properties such as tensile, flexural, and impact strengths and Young’s modulus (Ε) are determined. The X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), field emission scanning electron microscopy (FESEM), and polarised light microscopy (PLM) techniques are used to understand the crystallisation, thermal, dynamic mechanical, and structural behaviour of the prepared composites. The improvement of mechanical strength is observed with GNP loading for both grades. Decreasing the GNP thickness decreases the impact strength and on the other hand improves the tensile and flexural strengths and Young’s modulus. Maximum tensile (≈33 MPa) and flexural (≈58.81 MPa) strength is found for the composite carrying 5 wt% M25. However, maximum impact strength (0.197 J) is found for PP-5 wt% H25. XRD analysis confirms GNPs have an induction effect on PP’s β phase crystal structure. The PP-GNP composite exhibits better thermal stability based on determining the TD (degradation temperature), T10 (temperature at 10% weight loss), T50 (temperature at 50% weight loss), and TR (temperature at residual weight). Enhancement in melt (Tm) and crystallisation temperatures (Tc) is are observed due to a heterogeneous nucleation effect. The FESEM analysis concludes that the GNP thickness has a significant effect on the degree of dispersion and agglomeration. The smaller the thickness, the better is the dispersion and the lower is the agglomeration. Overall, the use of thinner GNPs is more advantageous in improving the polymer properties.

A Review on Graphene’s Light Stabilizing Effects for Reduced Photodegradation of Polymers

Graphene, the newest member of the carbon’s family, has proven its efficiency in improving polymers’ resistance against photodegradation, even at low loadings equal to 1 wt% or lower. This protective role involves a multitude of complementary mechanisms associated with graphene’s unique geometry and chemistry. In this review, these mechanisms, taking place during both the initiation and propagation steps of photodegradation, are discussed concerning graphene and graphene derivatives, i.e., graphene oxide (GO) and reduced graphene oxide (rGO). In particular, graphene displays important UV absorption, free radical scavenging, and quenching capabilities thanks to the abundant π-bonds and sp2 carbon sites in its hexagonal lattice structure. The free radical scavenging effect is also partially linked with functional hydroxyl groups on the surface. However, the sp2 sites remain the predominant player, which makes graphene’s antioxidant effect potentially stronger than rGO and GO. Besides, UV screening and oxygen barriers are active protective mechanisms attributed to graphene’s high surface area and 2D geometry. Moreover, the way that graphene, as a nucleating agent, can improve the photostability of polymers, have been explored as well. These include the potential effect of graphene on increasing polymer’s glass transition temperature and crystallinity.

Hybrid biocomposites from polypropylene, sustainable biocarbon and graphene nanoplatelets

Polypropylene (PP) is an attractive polymer for use in automotive parts due to its ease of processing, hydrophobic nature, chemical resistance and low density. The global shift towards eliminating non-renewable resource consumption has promoted research of sustainable biocarbon (BioC) filler in a PP matrix, but this material often leads to reduction in composite strength and requires additional fillers. Graphene nano-platelets (GnPs) have been the subject of considerable research as a nanofiller due to their strength, while maleic anhydride grafted polypropylene (MA-g-PP) is a commonly used compatibilizer for improvement of interfacial adhesion in composites. This study compared the thermo-mechanical properties of PP/BioC/MA-g-PP/GnP composites with varying wt.% of GnP. Morphological analysis revealed uniform dispersion of BioC, while significant agglomeration of GnPs limited their even dispersion throughout the PP matrix. In the optimal blend of 3 wt.% GnP and 17 wt.% BioC biocontent, tensile strength and modulus increased by ~19% and ~22% respectively, as compared to 20 wt.% BioC biocomposites. Thermal stability and performance enhancement occurred through incorporation of the fillers. Thus, hybridization of fillers in the compatibilized matrix presents a promising route to the enhancement of material properties, while reducing petroleum-based products through use of sustainable BioC filler in composite structures.

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

Graphene-based materials are a family of carbonaceous structures that can be produced using a variety of processes either from graphite or other precursors. These materials are typically a few layered sheets of graphene in the form of platelets and maintain some of the properties of pristine graphene (such as two-dimensional platelet shape, aspect ratio, and graphitic bonding). In this work we present melt mixed graphene-based polypropylene systems with significantly reduced percolation threshold. Traditionally melt-mixed systems suffer from poor dispersion that leads to high electrical percolation values. In contrast in our work, graphene was added into an isotactic polypropylene matrix, achieving an electrical percolation threshold of ~1 wt.%. This indicates that the filler dispersion process has been highly efficient, something that leads to the suppression of the β phase that have a strong influence on the crystallization behavior and subsequent thermal and mechanical performance. The electrical percolation values obtained are comparable with reported solution mixed systems, despite the use of simple melt mixing protocols and the lack of any pre or post-treatment of the final compositions. The latter is of particular importance as the preparation method used in this work is industrially relevant and is readily scalable.

Millisecond Response of Shape Memory Polymer Nanocomposite Aerogel Powered by Stretchable Graphene Framework

Shape memory polymers (SMPs) change shapes as-designed through altering the chain segment movement by external stimuli, promising wide uses in actuators, sensors, drug delivery, and deployable devices. However, the recovery speed of SMPs is still far slower than the benchmark shape memory alloys (SMAs), originating from their intrinsic poor heat transport and retarded viscoelasticity of polymer chains. In this work, monolithic nanocomposite aerogels composed of bicontinuous graphene and SMP networks are designed to promote the recovery time of SMP composites to a record value of 50 ms, comparable to the SMA case. The integration of a stretchable graphene framework as a fast energy transformation grid with ultrathin polycaprolactone nanofilms (tunable at 2.5-60 nm) enables the rapid phase transition of SMPs under electrical stimulation. The graphene-SMP nanocomposite aerogels, with a density of ∼10 mg cm^-3, exhibit a fast response (175 ± 40 mm s^-1), large deformation (∼100%), and a wide response bandwidth (0.1-20 Hz). The ultrafast response of SMP nanocomposite aerogels confers extensive uses in sensitive fuses, micro-oscillators, artificial muscles, actuators, and soft robotics. The design of bicontinuous ultralight aerogels can be extended to fabricate multifunctional and multiresponsive hybrid materials and devices.

Polyolefin/graphene nanocomposites: a review

The present article is mainly focused on literature studies centred on polyolefin (especially PE and PP) nanocomposites based on graphene and its derivatives.

Graphene oxide induced isotactic polypropylene crystallization: role of structural reduction

Nucleation ability of reduced GO was enhanced by the removal of oxygenic groups and the partial recovery of sp² carbon network.