Three-dimensional (3D) printing has been successfully applied for the fabrication of polymer components ranging from prototypes to final products. An issue, however, is that the resulting 3D printed parts exhibit inferior mechanical performance to parts fabricated using conventional polymer processing technologies, such as compression moulding. The addition of fibres and other materials into the polymer matrix to form a composite can yield a significant enhancement in the structural strength of printed polymer parts. This review focuses on the enhanced mechanical performance obtained through the printing of fibre-reinforced polymer composites, using the fused filament fabrication (FFF) 3D printing technique. The uses of both short and continuous fibre-reinforced polymer composites are reviewed. Finally, examples of some applications of FFF printed polymer composites using robotic processes are highlighted.

This chapter details how plasma treatments can be used to tailor the wettability of polymers. A plasma is an excited gas, and exposure of a polymer to a plasma discharge generally results in an enhancement in surface energy and associated with this is an increase in wettability. The effect however can be short lived due to hydrophobic recovery. In this review the use of both low and atmospheric plasmas for the activation of polymers will be discussed, as will the use of these plasmas for the deposition of plasma polymerised coatings. The latter can be used to produce polymer surfaces with tailored functionalities, thus achieving stable water contact angles ranging from superhydrophilic to superhydrophobic, as required.This review briefly introduces plasmas and plasma processing and includes an overview of typical plasma treatment sources. This is followed by a review of the use of plasma discharges to treat polymers and in particular to enhance their surface energy, which is important for example in achieving enhanced adhesive bond strength. The final section of this chapter focuses on the deposition of plasma polymerised coatings and how these can be used to tailor both surface chemistry and morphology. Thus the wettability of polymer surfaces can be controlled.

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This study evaluates the use of a barrel atmospheric plasma system for the treatment of acrylonitrile butadiene styrene and polylactic acid polymer particles. Treatments were carried out in a helium discharge with either oxygen or nitrogen addition. The plasma activated polymer particles were then used to prepare filaments, which in‐turn were then used to fabricated parts by additive manufacturing. The resultant dog bone polymer parts exhibited up to a 22% increase in tensile strength, compared to parts fabricated using unactivated polymer particles. The explanation for the increased mechanical strength is the enhanced activation of the treated polymer particles, as well as the removal of contaminations from the polymer surface.

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The objective of this study is to investigate the use of an air atmospheric plasma jet for the treatment of sized basalt fibers, used in the fabrication of continuous fiber‐reinforced polypropylene filaments. The plasma treatments were carried out both at a laboratory scale, as well as in‐line during the production of fiber‐reinforced filaments. The latter was carried out at a fiber processing speeds of approximately 15 m/s, just immediately before the polymer coating of the fiber by extrusion. After the air plasma treatment, the water contact angle of the sized basalt fiber decreased from 86° to <10°. X‐ray photoelectron spectroscopy analysis demonstrated that the treatment yielded enhanced levels of oxygen functionality on the fiber surface. After coating with polypropylene, it was observed that there was consistently more homogeneous polymer layer deposited onto the plasma‐activated fiber, compared with that on the unactivated control fiber. The resulting polymer filament with embedded basalt fiber was used to fabricate mechanical test specimens by three‐dimensional printing (fused filament fabrication method). Both three‐point bending tests and short beam strength tests were performed. A comparison study was carried out between test specimens fabricated using sized basalt fiber, with and without the plasma pretreatment. The flexural modulus and maximum shear stress were found to increase by 12% and 13%, respectively, for composite's fabricated using the plasma pretreated basalt fibers. This increased mechanical strength is likely to be due to an increase in interfacial bond strength between the polymer and fiber, with an associated reduction in the level of air incorporation around the basalt filaments as demonstrated using computed tomography analysis.

This work studied the effects of adding short basalt fibers (BFs) and multiwalled carbon nanotubes (MWCNTs), both separately and in combination, on the mechanical properties, fracture toughness, and electrical conductivity of an epoxy polymer. The surfaces of the short BFs were either treated using a silane coupling agent or further functionalized by atmospheric plasma to enhance the adhesion between the BFs and the epoxy. The results of a single fiber fragmentation test demonstrated a significantly improved BF/epoxy adhesion upon applying the plasma treatment to the BFs. This resulted in better mechanical properties and fracture toughness of the composites containing the plasma-activated BFs. The improved BF/epoxy adhesion also affected the hybrid toughening performance of the BFs and MWCNTs. In particular, synergistic toughening effects were observed when the plasma-activated BFs/ MWCNTs hybrid modifiers were used, while only additive toughening effects occurred for the silane-sized BFs/MWCNTs hybrid modifiers. This work demonstrated a potential to develop strong, tough, and electrically conductive epoxy composites by adding hybrid BF/MWCNT modifiers.

This study reports the development and performance of a pilot-scale barrel atmospheric plasma reactor for the atmospheric plasma activation treatment of polymer particles. The polymer particles treated included acrylonitrile butadiene styrene (ABS) and polypropylene (PP). These particles had diameters in the range of 3–5 mm. The initial studies were carried out using a laboratory-scale barrel reactor designed to treat polymer particle batch sizes of 20 g. A pilot-scale reactor that could treat 500 g particle batch sizes was then developed to facilitate pre-industrial-scale treatments. The effect of operating pulse density modulation (PDM) in the range 10%–100% and plasma treatment time on the level of activation of the treated polymers were then investigated. ABS revealed a larger decrease in water contact angle compared with PP after plasma treatment under the same conditions. The optimal treatment time of ABS (400 g of polymer particles) in the pilot-scale reactor was 15 min. The plasma-activated polymer particles were used to fabricate dog-bone polymer parts through injection molding. Mechanical testing of the resulting dog-bone polymer parts revealed a 10.5% increase in tensile strength compared with those fabricated using non-activated polymer particles.