The aim of this research is to develop thermoplastic olefin (TPO) composites containing polypropylene (PP), an elastomeric ethylene-octene copolymer (EOC) and graphene nanoplatelets (GNPs), suitable for material extrusion (MEX). A PP functionalized with amino-pyridine (PP-g-Py) was used as a compatibilizer. The composite blends had droplet-matrix morphology at compositions as high as 40 wt% EOC. Imaging by Transmission Electron Microscopy showed that the GNPs resided at the interface between the blend components. This microstructure promoted higher thermal conductivity of the TPO/GNP composite blends, as compared to the PP/GNP composite (1.54 W/m K, vs 1.3 W/m K respectively). PP/GNP composites processed by MEX exhibited inadequate interfacial fusion between the deposited strands, which resulted in severe delamination during tensile and flexural testing, and consequently poor mechanical properties. In the TPO/GNP composites containing 40 wt% EOC, the slower crystallization of the elongated EOC domains promoted interfacial adhesion between the strands, resulting in better part consolidation, more consistent mechanical properties and improved ductility compared to the PP/GNP composites.

Discontinuous-long-fibre (DLF) composites fabricated from pre-impregnated unidirectional (UD) fibre chips are susceptible to structural deficiency. The in-plane highly anisotropic mechanical properties of the chips combined with the random nature of fibre orientation causes local weaknesses within the material when fibres are perpendicular to the load. Recent experimental results have shown that using woven-fibre chips could improve the performance of DLF composites by increasing their average mechanical properties and reducing their variability. To better understand the underlying phenomenon giving an advantage to the woven chips, a finite element model was developed to predict the mechanical properties obtained from a standard tensile test. DLF chips were modelled based on a voxel method where random chip positions were generated by an algorithm developed in this work. ANSYS® software was utilized to model the non-linear response associated with progressive damage of the composite. The maximum stress and the Puck failure criteria were employed to define damage initiation for the woven and UD fibres, respectively. Tensile modulus predictions for both types of chips showed good results when compared to experimental data. Strength predictions for the UD fibres also showed good correlation with experimental results, but the model overestimated the strength of the woven-fibre DLF composite. It appeared that the failure of the UD-fibre composites was associated with matrix failure (transverse tension and in-plane shear). Woven-fibre composites, however, showed damage modes linked to both fibre failure (longitudinal tension) and matrix failure (transverse tension and in-plane shear).

This work investigates the properties of different types of regenerated recycled rubbers (RR and RR) to produce thermoplastic elastomers (TPE) based on recycled high-density polyethylene (RHD) as the matrix. The higher regeneration degree of RR (24%) compared to RR (15%) was able to better restore the plasticity and processability of the ground tire rubber (GTR). So better entanglement between RR free chains and the thermoplastic macromolecules was obtained inducing stronger interfacial interaction leading to higher elongation at break (159%) and impact strength (342 J/m) of the blends filled with 80 wt.% RR. To further improve the adhesion and achieve rubber-like properties, ethylene vinyl acetate (EVA) was used as a compatibilizer. The microstructure analysis showed that uniform dispersion of the particles and ground tire rubber encapsulation by EVA increased the resistance to crack propagation and failure of the compatibilized blends. The swelling, mechanical and physical properties of the ternary blends (RHD/GTR/EVA) showed that EVA improved the interfacial interactions between GTR and RHD which was confirmed by enhanced elongation at break (203%) and impact strength (379 J/m) by the addition of 10 wt.% EVA.

Discontinuous long-fibre (DLF) composites can be made with randomly oriented unidirectional pre-impregnated composite chips. High fibre volume fraction unidirectional fibre chips provide good mechanical properties to the DLF composite architecture, which enables this material to contribute to bridging the gap between continuous-fibre and randomly-oriented short-fibre composites. However, it is well known that unidirectional fibres have highly anisotropic in-plane behaviour, which causes weak points in the parts when chips are oriented at unfavourable angles. This can be problematic since chips are randomly oriented in DLF composites. To overcome this problem, this research utilizes woven fibre chips instead of unidirectional fibre chips to fabricate DLF composites. Woven fibres diminish the potential for weak points due to their more homogenized in-plane mechanical properties. For comparison purposes, compression moulded carbon/PEI samples were made from both unidirectional chips and 5HS woven chips. Bending and tensile tests following ASTM guidelines were performed to compare both types of fibre arrangement. The results show that woven fibre chips increase the mechanical properties of the DLF composites and reduce their variability.

In-situ manufacturing of thermoplastic composites using Hot Gas Torch (HGT)-assisted Automated Fiber Placement (AFP) has the potential to produce laminates in an efficient manner by avoiding a secondary process, like autoclave consolidation. One of the advantages of AFP technique is its capability to steer fiber path and to manufacture Variable Angle Tow (VAT) laminates which have shown to have improved mechanical performance. This study investigates the process parameters that affect steering of carbon fiber reinforced thermoplastic tapes (AS4/polyether ether ketone) using an HGT-assisted AFP machine. The effect of the steering radius, laydown speed, number of repasses, and substrate angle on the geometry and bond strength of steered tape was investigated through observation and testing. A modified lap shear test was devised and used to study the bond strength between the steered tape and the substrate and the results were compared with autoclave treated samples which served as a reference. It was found that with a decrease in the steering radius of the tape, there was a decrease in the tape width and an increase in the tape thickness. A significant reduction in the steering-induced defects was observed at higher laydown speeds where the defects were intermittent unlike in the case of lower laydown speeds. Performing a repass over the steered tape smoothed some of the tape defects caused by steering. Furthermore, the lap shear strengths of the steered tapes were found to be functions of laydown speed and substrate angle.