The strengths of additive manufacturing (AM), especially the tool-less manufacturing paradigm and rapid production of low-volume products, are well-aligned with the needs of manufacturing of expensive, high-temperature resistant, engineering thermoplastic polymers. High temperature polymer parts made with AM for either tooling or end-use applications have been implemented in the aerospace, automotive, and biomedical fields. However, parts made from these polymers using traditional manufacturing processes are generally high-value parts in low-quantity production runs. Moreover, AM processing of these polymers present significant challenges due to limitations associated with large thermal gradients, residual stress buildup, and interlayer adhesion as well as the inability of the printers to consistently maintain required high processing temperatures. This review highlights the current state of the art for processing high-temperature (i.e., traditional processing temperatures exceeding 250°C) thermoplastic polymers by the melt-based, AM processes of material extrusion (MatEx) and laser powder bed fusion (PBF). The authors address common challenges to AM of high-temperature polymers and gaps in fundamental understanding of the process-structure-property relationships needed to identify the machine design, process parameter selection, and synthetic modifications to enable processing.

Current understanding and challenges in high temperature additive manufacturing of engineering thermoplastic polymers

This review provides a comprehensive analysis of available peer-reviewed literature in which graphene and/or its derivatives are incorporated into a polymer matrix in order to enhance the final properties and functionalities of the three dimensional (3D) printed structure. Research in which graphene derivatives have been incorporated into plastic 3D printing technologies such as Fused deposition modeling (FDM), Stereolithography (SLA), Selective laser sintering, Inkjet 3D printing, Extrusion-based printing and Binder-jet printing is presented. For certain design requirements and applicability of the material, great care needs to be taken to select the appropriate printing method. Factors which play a key role in final performance of the printed parts are identified, including dispersion of graphene or its derivatives in matrix, interfacial interaction between graphene or its derivatives and matrix, printing orientation, nanofiller's aspect ratio, reduction of graphene oxide and ink viscosity. In fact, the multifunctional applications of the 3D printed structures based on graphene or graphitic filler composites open up the countless possibilities of current research. Although great progress has been made in exploring the mechanical, electrical, optical and thermal, characteristics of these materials, significant research and development need to be done to fully fetch their inherent potential. This article serves the purpose to researchers to improve latest research outcomes and explore new graphene–based nanocomposites for different applications.

Recent progress and multifunctional applications of 3D printed graphene nanocomposites

Polymer nanocomposites with enhanced performances are becoming a trend in the current research field, overcoming the limitations of bulk polymer and meeting the demands of market and society in tribological applications. Polytetrafluoroethylene, poly(ether ether ketone) and ultrahigh molecular weight polyethylene are the most popular polymers in recent research on tribology. Current work comprehensively reviews recent advancements of polymer nanocomposites in tribology. The influence of different types of nanofiller, such as carbon-based nanofiller, silicon-based nanofiller, metal oxide nanofiller and hybrid nanofiller, on the tribological performance of thermoplastic and thermoset nanocomposites is discussed. Since the tribological properties of polymer nanocomposites are not intrinsic but are dependent on sliding conditions, direct comparison between different types of nanofiller or the same nanofiller of different morphologies and structures is not feasible. Friction and wear rate are normalized to indicate relative improvement by different fillers. Emphasis is given to the effect of nanofiller content and surface modification of nanofillers on friction, wear resistance, wear mechanism and transfer film formation of its nanocomposites. Limitations from the previous works are addressed and future research on tribology of polymer nanocomposites is proposed.

Effect of Nanofillers on Tribological Properties of Polymer Nanocomposites: A Review on Recent Development.

Impact behavior of nanoengineered, 3D printed plate-lattices

Energy absorption and self-sensing performance of 3D printed CF/PEEK cellular composites

The study is focused on multifunctional performance of carbon nanotubes (CNT) and Graphene nanoplatelets (GNP) reinforced PEEK composites enabled via fused filament fabrication (FFF) additive manufacturing (AM) utilizing in-house nanoengineered filaments. Thermo-physical, mechanical and wear characteristics of electro-conductive PEEK nanocomposites are reported. The coefficient of thermal expansion (CTE) is found to decrease by 26% and 18% with the incorporation of 5 wt% GNP and 3 wt% CNT into PEEK polymer, respectively. The decrease in CTE provides better dimensional stability to resulting nanocomposite structures. Due to uniform dispersion of CNT and GNP in the PEEK matrix, the crystallization temperature and degree of crystallinity are both increased. The 3D printed PEEK nanocomposites reveal interfacial voids between the beads and intra-bead pores and thus exhibit lower density compared to that of the 3D printed neat PEEK. Young's and storage moduli are found to increase by 20% and 66% for 3 wt% CNT loading and by 23% and 72% for 5 wt% GNP loading respectively. However, the PEEK nanocomposites exhibit similar tensile strength to that of neat PEEK. The coefficient of friction obtained from fretting wear tests is found to decrease by 67% and 56% for 1 wt% CNT and 3 wt% GNP loaded PEEK nanocomposites, respectively and the decrease is attributed to reduced hardness and increased porosity. Multifunctional performance of carbon nanostructures reinforced AM-enabled PEEK composites demonstrated here makes them suitable for a range of applications such as orthopedics, oil and gas, automotive, electronics and space.

H. Alhashmi

Papers

Multifunctional performance of carbon nanotubes and graphene nanoplatelets reinforced PEEK composites enabled via FFF additive manufacturing