Volume 40, Issue 2

Conducting polymers and polymer-based nanocomposites has occupied significant importance in the scientific field as well as engineering research and applications. Among all different applications, conducting polymers as a corrosion resistive coating on steel have developed a lot of research interest and success for the last four decades. This paper provides an extensive review on the corrosion resistive conducting organic polymer coating systems over steel substrates. It mainly discusses different mechanisms of corrosion provided by different conducting polymer coatings over steel. The corrosion resistance mechanisms of coatings based on polyaniline (PANI) and polypyrrole (PPy) and their nanocomposites, which are considered very promising conducting polymers in different fields, are reviewed here. PANI provides corrosion resistance via different mechanisms. PANI in oxidised form can offer effective anodic corrosion resistance to steel surface due to its higher oxidising ability than in reduced form. It can provide a good extent of barrier protection to steel as well. PPy also can provide both the barrier and anodic protection. The mechanism of intelligent release of doped corrosion inhibitive anions from the conducting polymer coating and its contribution to corrosion protection mechanism of steel is also focused in this article. The limitations of conducting polymer coating are briefly discussed.

In this study, compatibilized thermoplastic elastomers (TPE) based on recycled high-density polyethylene (HDPE) and high ground tire rubber (GTR) content (70, 80 and 90 wt%) were prepared by twin-screw extrusion followed by injection molding. The main objective of the work was to use three different compatibilizers and to compare their efficiency: ethylene-octene copolymer (Engage 8180), styrene-ethylene-butylene-styrene grafted with maleic anhydride (SEBS-g-MA) (Kraton FG1901X) and a trans-polyoctenamer (Vestenamer 8012). A morphological analysis showed that the addition of a compatibilizer produced more homogeneous structures, significantly improving mechanical performance compared with their uncompatibilized counterparts. This modification had a direct effect on all the properties, especially the tensile properties which were evaluated at different crosshead speeds (10, 50, 100 and 500 mm/min) to better see differences in the interfacial state. High elongations at break exceeding 100 % for highly filled recycled blends (up to 90 wt% of GTR) with Kraton FG1901X were obtained, highlighting superior compatibility efficiency. In general, adding GTR to recycled PE produced a more elastic TPE. Increasing the GTR concentration led to lower modulus (from 300 MPa for R-PE to 50 MPa for 70 % GTR). The main conclusion of the work was that injection molding of TPE with high GTR content (above 70 %) was only possible by adding compatibilizers. Nevertheless, the best performance to produce high GTR content TPE was obtained using Kraton FG1901X probably due to its grafted functionality (maleic anhydride, MA) leading to better interfacial interactions between the phases.

Additive manufacturing techniques have made it possible to create lighter and stronger lattice structures with intricate repeating geometric patterns which can be utilized for various industrial applications. Although several studies have reported on the effects of lattices with varying geometry on mechanical properties, fewer studies have investigated the effects of post-processing parameters on mechanical properties of these lattices. As such, this study investigates the effects of solid fraction of octet truss-based lattices and the effect of heat treatment on the mechanical properties of 3D printed octet truss lattices. Experimental findings revealed that Young’s Modulus and strength of lattices were enhanced upon heat treatment where tensile strength and stiffness of lattices with 40 % solid fraction improved by 20.55 % and 29.11 % respectively. Besides, it was found that the lattices without and with heat treatment obeyed the Ashby’s classic scaling law reasonably well for both modulus-density and strength-density relationship.

Thermoplastic starch (TPS)/polyethylene glycol (PEG)/polyvinyl acetate (PVAc) blends were prepared through melt blending, in which PEG content was fixed at 5 wt% and PVAc content ranged from 10 wt% to 20 wt%, with increments of 5 wt%. For comparison, a TPS/PEG blend was also prepared. All the blends were subsequently characterized using various techniques. Differential scanning calorimetry (DSC) results showed that the melt temperatures ( T m ) of TPS and PEG in all blends remained independent, indicating immiscibility of TPS and PEG. Notably, T m of TPS weakened upon the addition of PVAc, and the effect was particularly pronounced in the blend containing 15 wt% PVAc, whose T m disappeared and a cold crystallization temperature ( T cc ) emerged, suggesting a crystal hindering effect exerted by PVAc on TPS. X-ray diffraction (XRD) results further supported this finding, showing that PVAc primarily inhibited the formation of V A -type crystals in TPS and slightly increased starch retrogradation. Scanning electron microscopy (SEM) images revealed that starch plasticization increased with higher PVAc content, and TPS particles agglomerated into larger nodules. Tensile testing demonstrated that the ternary blends exhibited enhanced strength, while PEG did not contribute to the toughness of the system. Additionally, the thermal resistance, equilibrium moisture adsorption, and biodegradation stability of the ternary blends improved with the incorporation of PVAc. It is evident that in TPS/PEG/PVAc ternary blends, PVAc retained its reinforcing and crystallinity-reducing effect, whereas the toughening effect of PEG was absent.

In injection molding, ensuring consistent optical part quality, in particular achieving identical color across the parts produced, is crucial. In the context of processing recycled materials, variations in the input material streams can pose challenges, requiring color masterbatch content to be adapted inline if a predefined reference color is to be achieved. This study presents a color assistance system that uses a sensor to measure the color of injection molded parts and to determine the optimal amount of masterbatch to be added for achieving a specified color for a defined material input stream. Testing of the system focused on post-industrial recyclate which had a color in the second color quadrant in the CIELAB color space. The system proved effective in regulating masterbatch contents to improve color consistency and can be employed for quality assurance in the injection molding process, particularly when using recycled materials.

Fused deposition modeling (FDM) has emerged as the preferred method for creating three-dimensional (3D) models with minimal waste. To enhance the mechanical strength of the 3D-printed models using FDM, researchers have explored composite filaments. This study aims to advance electronic waste (EW) recycling for effective waste management by fabricating a composite filament by incorporating EW as a filler particle for FDM application. The composite filament merges polylactic acid with printed circuit board (PCB) particles sourced from EW. Physical properties like flexural and compression strength were evaluated. The samples were printed following ASTM D790 and ASTM D695 standards, using default parameters such as a 100 % infill rate, rectilinear pattern, and a layer thickness of 0.2 mm. The optimal printing temperature of 200 °C for the samples was determined through flowability testing. Subsequently, the dimensional stability and surface roughness of the printed samples were assessed, demonstrating that the inclusion of filler particles enhanced dimensional stability and decreased surface roughness. The results of this study show that a composite filament containing 3 wt% EW-PCB exhibits enhanced flexural strength and a notable increase in flexural modulus. Similarly, the filament containing 3 wt% EW-PCB exhibited a 35 % increase in bulk modulus compared to the filament without EW, attributed to the presence of metals in the PCBs. The micromorphological analysis was performed on the tested samples using field emission scanning electron microscopy.

This study explores the development of electrically conductive co-continuous polyvinylidene fluoride/polyethylene terephthalate (PVDF/PET) nanocomposites incorporating graphite (GR) and reduced graphene oxide (rGO) for potential use in proton exchange membrane fuel cell (PEMFC) bipolar plates. The influence of GR particle size, concentration (20–60 wt%), and hybrid GR/GR and GR/GR/rGO combinations on electrical, thermal, mechanical, and water absorption properties was systematically investigated. Scanning electron microscopy revealed GR localization within the PET phase and the formation of a dense conductive network. The optimal composition, a hybrid G2/G3 (45/15 wt%) system, achieved low through-plane (0.93 Ω cm) and in-plane (0.71 Ω cm) resistivities, further reduced with 2 wt% rGO (0.89 Ω cm through-plane and 0.62 Ω cm in-plane). This formulation also exhibited superior thermal stability (onset degradation at ∼490 °C) and mechanical properties, with a flexural strength of 44.4 MPa and modulus of 16.4 GPa. Additionally, water absorption decreased significantly to 0.05 %. These findings demonstrate the potential of hybrid GR/rGO nanocomposites for enhanced durability and performance in PEMFC applications, offering a balance between electrical conductivity, mechanical strength, and environmental resilience.

The main research objective is to enhance the functional properties of epoxy hybrid nanocomposite laminates made with various sequences of jute (J), glass (G), and kenaf fibers (K) embedded with 1–3 wt% of nanographene particles. This is achieved using a hand layup technique combined with compression moulding. Epoxy resin serves as the adhesive agent, resulting in superior bonding between the fibers and nanographene. The study evaluates the effects of nanographene loading and fiber sequence on X-ray diffraction, mechanical properties, water absorption, thermal behaviour, and intensity peaks of the composites. The results are compared to identify the optimal for high performance for structural applications. According to the findings, the hybrid nanocomposite layered with the sequence glass/jute/jute/kenaf/kenaf/kenaf/kenaf/jute/jute/glass (G/J/J/K/K/K/K/J/J/G) containing 3 wt% nanographene particles demonstrates optimal tensile (110 MPa) and flexural strength (132 MPa), improved microhardness (82 HV), better fracture toughness (2.55 MPa m 0.5 ), and reduced water absorption (2.6 % after six weeks). Additionally, the degradation temperature shows improvements for all hybrid combinations when nanographene is incorporated.

Depending on the conditions of polymer synthesis, polyethylene can exhibit various molecular structures, such as long and short-chain branching, which influence its molecular weight and molecular weight distribution. The molecular structure of polyethylene in the blend significantly impacts its properties, making it essential to study these effects on the blend’s final properties. Based on the above, this work aims to investigate the effects of 1-hexene short chain branching (SCB) of linear low-density polyethylene (LLDPE) and long chain branching (LCB) of low-density polyethylene (LDPE) polymers on the rheological properties and processing of blends with high-density polyethylene (HDPE). LDPE showed higher complex viscosity at low frequencies and stronger shear thinning behavior than HDPE and LLDPE-H polymers. The strong shear thinning behavior of LDPE may be related to its higher molecular weight and presence of LCB. Capillary rheometry tests demonstrated a shear-thinning behavior for both the pure polymers and the blends, with the results for the blends being lower than those for the pure polymers, following the direct mixing rule. LDPE exhibited lower viscosity compared to HDPE, LLDPE-H, and all the blends, corroborating the observed results in complex viscosity at high deformation values. As for the flow instabilities, the occurrence of these instabilities at high shear rates was observed for all the polymers investigated in this study. Two methods were used to measure the swell of the extrudate (in-line and off-line), and both methods were efficient in describing the swell behavior as a function of shear rate. The elongational viscosity of the LDPE was found to exhibit “strain hardening” behavior, i.e., an increase in elongational viscosity with increasing strain and time.

In the present study, the effects of hybridization of Basalt and Kevlar fibers in conjunction with the incorporation of Graphene nanoplatelets (GnPs) on the performance under low-velocity impact were experimentally examined. Two different hybrid structural configurations, reinforced with Basalt and Kevlar composites, were fabricated utilizing a hand lay-up technique followed by vacuum bag molding, with variations that included and excluded GnPs. The synergistic effects of hybridization coupled with the modification by GnPs on the impact characteristics of the Basalt/Kevlar hybrid composites were analyzed under an impact energy of 30 J while varying the GnPs loading. The optimal enhancement observed in the peak load and absorbed energy of the specimens was recorded as a 9.4 % and 45.7 % improvement, respectively, when Kevlar fibers were positioned in the outer layers; conversely, the specimens demonstrated enhancements of 13.35 % and 20.36 % in peak load and absorbed energy with the incorporation of 1 wt% and 3 wt% GnPs when Basalt fibers were situated in the outer layers. The increase of the impact properties of the hybrid structures was ascribed to the robust interfacial interactions established among the fibers, epoxy, and GnPs nanoparticles, which facilitated a notable enhancement in performance and optimal stress transfer from the fibers and nanoparticles to the matrix.

The rationale for recycling in the rotational molding community is arguably stronger than other sectors of the polymer industry since the process is more likely to produce extremely large parts and regardless of whether scrap is generated from an end-of-life situation or from off-spec production, this material is often too much and too valuable for diversion to landfill. It is therefore important for the community to establish test methods and knowledge on how to keep these polymeric materials within a circular economy. There is unfortunately little experimental data on recycling by rotomolding for processors to understand the feasibility of reclaiming scrap material in their production, for which this study aims to address. The molded parts of a commercial-grade and reactor-grade polyethylene were examined over several repeated molding cycles, in each case with between 10 and 50 % reclaim content, and then examined for quality indicators based on mechanical and rheological properties, part color and surface void content. The stabilized resin showed negligible changes over four recycle passes, except for yellowness, while the unstabilized resin showed minor signs of change on the second recycle pass. A narrow examination followed to understand the contributions of antioxidants versus UV stabilizers in the performance witnessed in the recycling trials. Overall, the study shows that robust recycling is very possible for the rotational molding industry with polyethylene grades, especially those intended for this process.