Fused filament fabrication (FFF) notoriously suffers from weak interlayer adhesion, leading to anisotropic mechanical properties in the fabricated parts. The present study addresses this challenge by developing thermoplastic-based vitrimers via reactive extrusion of maleic anhydride-grafted polypropylene (PP-g-MAH) with an epoxy crosslinker and a transesterification catalyst. The vitrimers were further compounded with carbon fibres (CF), processed into filaments, and used for FFF to fabricate specimens for testing interlayer adhesion. Spectroscopic and thermomechanical analyses revealed the formation of a crosslinked network, characterised by β-hydroxyester linkages and a pronounced rubbery plateau. Vitrimers exhibited enhanced mechanical properties, with notched Charpy impact strength increasing by up to 155%. As-printed vitrimeric FFF specimens demonstrated enhanced flexural toughness, indicating that dynamic transesterification reactions during layer deposition promote more consistent interlayer bonding. Vitrimeric specimens exhibited slightly increased flexural strength and preserved toughness upon post-printing thermal annealing at 150 °C, while non-vitrimeric specimens exhibited systematic embrittlement. The results demonstrate that vitrimerisation of thermoplastic polymers is a viable and effective strategy for improving interlayer adhesion in FFF fabricated parts.

To reduce fuel consumption and extend flight time, the aerospace industry has focused on lightweight design. Achieving this without compromising structural integrity has been challenging. However, innovative additive manufacturing offers new opportunities for practical solutions. This study presents two methods: multi-material additive manufacturing (MMAM) and variable infill density additive manufacturing (VIDAM), aimed at reducing structural weight while maintaining mechanical performance. These methods were applied to a wing spar, a test geometry based on stress distribution principles from laminated beam mechanics. The structures produced with these new approaches showed improved mechanical responses compared to those made with traditional additive manufacturing techniques. A maximum increase of 91% in load-carrying capacity and a 34.8% increase in specific energy absorption were observed. scanning electron microscopy analysis revealed that layer bonding and material diffusion greatly influenced the mechanical performance. Although the study was conducted on small-scale models, the design concepts can be adapted to large-scale industrial applications that benefit from lightweight structures, such as the aerospace and automotive.

The study investigates the use of repurposed milled carbon fibre (mCF) as reinforcement for polyamide 66 (PA66) in gear applications, addressing environmental and cost concerns of virgin carbon fibres. Neat PA66 and PA66 composites reinforced with mCF, glass fibres (GF), and carbon fibres (CF), with and without polytetrafluoroethylene (PTFE), were injection moulded and evaluated for microstructure (fibre length), thermal, mechanical, surface, and tribological properties, as well as gear performance under VDI 2736 guidelines. CF reinforced composites showed the highest modulus and tensile strength, followed by mCF and GF. PTFE reduced modulus and strength in binary composites. All reinforced composites significantly lowered the coefficient of friction (COF) and wear rate compared to neat PA66, with mCF showing the most notable improvements. PTFE slightly improved tribological performance only for GF (wear) and CF (COF) composites. In gear testing, binary composites outperformed neat PA66, with CF performing best, followed by mCF and GF. Ternary composites had slightly lower performance than their binary equivalents. Correlation analysis showed that gear performance is closely linked to structural integrity. Failure analysis revealed higher crack susceptibility in mCF reinforced gears due to shorter fibre length. The findings highlight mCF reinforced PA66 as a sustainable, cost-effective material for durable polymer gears.

This study explores the mechanical properties and water resistance of polypropylene (PP) composites reinforced with oil palm trunk (OPT) components, specifically vascular bundles (VB) and parenchyma cells (PC) particles, at 30 and 60 wt% content levels. The research addresses challenges posed by the inherent variability in density and moisture sensitivity of OPT in composite formulation. Utilizing a hot-pressing technique, we examined the effects of OPT type, filler content, and the addition of a maleic anhydride-grafted polypropylene (MAPP) coupling agent. The findings reveal that VB- and PC-reinforced PP composites show enhanced density, moisture resistance, and overall mechanical performance relative to untreated OPT. Notably, while increasing OPT content improves modulus and density, it negatively impacts tensile and flexural strengths due to poor interfacial bonding. The incorporation of MAPP significantly enhances interfacial adhesion between the PP matrix and OPT fillers, leading to reduced moisture uptake and dimensional swelling, particularly at higher filler loadings. These results highlight the potential of VB and PC as sustainable reinforcement materials for wood-plastic composites (WPC), providing critical insights for optimizing composite designs aimed at improving durability and water resistance.

Graphene oxide (GO) nanoplatelets can be used to reinforce neat resin or the matrix phase of fiber composites for improved mechanical properties. Although the oxygen content levels in GO and reduced graphene oxide (rGO) strongly influence the interface with the polymer, experimental-based optimization of the oxygen content for enhanced composite properties is difficult and time-consuming. Fortunately, molecular dynamics (MD) simulation can be used to efficiently predict the interfacial properties of composite on the molecular level and provide physical insight into the effect of the oxygen content of rGO. In this study, MD is used to predict the elastic properties of rGO/epoxy interfaces and the corresponding interfacial shear strength (IFSS) for different oxygen content levels. The results indicate that increasing levels of oxygen in rGO results in interfaces with a reduced in-plane elastic modulus but a substantially higher IFSS. These results are important for the design of rGO/epoxy composites for specific engineering applications.