Mechanical performance and supermolecular morphology of void free polypropylene manufactured by fused filament fabrication

Abstract

It is known from the literature that freedom from macroscopic defects (voids) is an essential prerequisite for good mechanical properties of 3D-printed components manufactured using fused filament fabrication. The present study further shows that the morphology and mechanical properties of void free components are significantly influenced by the choice of process parameters.Components that were printed at low temperatures and high speeds show fair and inhomogeneous supermolecular morphology, clearly visible weld seams and a special flow-induced staggered structure of the individual strands laidup. At higher magnification in the optical microscope, transcrystalline structures are visible starting from the contact area between the strands, that is, crystallization has started at the interface between the strands and is moving forward towards the center of the strands. In contrast, the samples printed at high temperatures and low speeds show a homogeneous supermolecular morphology with overall larger spherulites and a higher degree of crystallinity and compared to the specimens printed with the low temperature/high speed-set much better mechanical properties. A numerical simulation of the temperature at the contact point of the strand emerging from the hot nozzle and the cooled strand neighbor agrees well with the measured behavior. The thermal simulation thus enables the temperature to be calculated at any point in time in the welding contact and thus access to the local thermal conditions during joining, cooling and the formation of the morphology.

Reinforcement‐material effects on the compression behavior of polymer composites

“…FFF is placed layer by layer, which results in poor mechanical characteristics and poor adhesion between the layers 25,34,37 . FFF‐printed products produced of polymer matrix can benefit substantially from fiber reinforcement 5,13,27,30,38 . Polymer composites' fiber orientation and void percentage have significant effect over the functional property of the parts 8,38,39 .…”

“…The low melting point, easy formability, mechanical property versatility, and the ease with which additives can be incorporated into the host polymer have all contributed significantly to reinforced functional parts. [4][5][6][7] Acrylonitrile butadiene styrene (ABS), [8][9][10] polylactic acid (PLA), 6,[11][12][13][14][15][16][17] thermoplastic polyurethane (TPU), 8,18 polyethylene terephthalate (PET), 8,19 glycol modified polyethylene terephthalate (PETG), 12,15,[19][20][21] high-density polyethylene 22 and many more are among the most frequent polymers generated through AM. 2,[23][24][25] Each of these polymers is useful for a variety of purposes due to its unique combination of mechanical strength, thermal qualities, and other characteristics.…”

“…25,34,37 FFF-printed products produced of polymer matrix can benefit substantially from fiber reinforcement. 5,13,27,30,38 Polymer composites' fiber orientation and void percentage have significant effect over the functional property of the parts. 8,38,39 As the process adds layers, the infill pattern gives structural support from the inside out because the material tends to sink over the empty regions of the print in the absence of an infill pattern.…”

“…5,13,27,30,38 Polymer composites' fiber orientation and void percentage have significant effect over the functional property of the parts. 8,38,39 As the process adds layers, the infill pattern gives structural support from the inside out because the material tends to sink over the empty regions of the print in the absence of an infill pattern. 32,40 The Nozzle Diameter (ND) is another crucial factor in the FFF process that determines the extrusion and layer deposition modes.…”

The importance of local process conditions on the properties of fused filament fabrication printed polypropylene components

“…It is generally accepted that the mobility of polymer chains is drastically reduced upon crystallization, as the polymer chains are embedded in the growing crystals. Consequently, it is pivotal to establish sufficiently strong interlayer bonds that the deposited strand be maintained above the crystallization temperature for an adequate time to allow molecular diffusion 10 . In contrast to conventional fabrication, the printed parts are far from homogeneous due to the local flow condition and thermal gradients 15,17,18 .…”