Direct evidence of interfacial crystallization preventing weld formation during fused filament fabrication of poly(ether ether ketone)

Collinson, David W.; Windheim, Natalia von; Gall, Ken; Brinson, L. Catherine

doi:10.1016/j.addma.2022.102604

Cited by 9 publications

(5 citation statements)

References 58 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…An initial interpretation for this phenomenon was densification of the long-annealed monoliths due to an increasing crystallinity. Thermal annealing is often utilized to increase the crystallinity of polymers to augment mechanical strength. ,− Furthermore, crystalline regions are inherently denser than amorphous polymer due to the close packing of chains on a crystalline lattice . The use of an annealing temperature very close to the PEEK melting temperature ( T m ≈ 343 °C) should primarily promote the growth of spherulites, supporting the densification of the sample through increased crystallinity as the source of the contraction.…”

Section: Resultsmentioning

confidence: 99%

Multiple Molecular-Level Processes in the Evolution of Residual Strain in 3D Printed Poly(ether ether ketone)

Riggins,

Dadmun

2024

ACS Appl. Polym. Mater.

View full text Add to dashboard Cite

The processing that occurs during material extrusion (ME) 3D printing imparts residual stress in printed parts, which is released during annealing and manifests as an irreversible thermal strain. Our group seeks material-based solutions that control the release of residual stress through molecular-level processes, decrease the magnitude of observed strain, and produce structures that can be annealed without loss of structural fidelity. This work describes an examination of the release of residual stress in 3D printed monoliths made from poly(ether ether ketone) (PEEK) filaments using nanographene sheets as an additive, in situ illumination with an appropriate wavelength light source, and thermal annealing close to the melting temperature. The extent of strain release of the PEEK monoliths is far suppressed relative to that of those made from poly(lactic acid) for all formulations. Moreover, there is a consistent pattern of a transition from positive-to-negative residual strains with annealing time that is independent of the annealing temperature and material formulation. This is interpreted to indicate that multiple competing processes drive the development of residual stress in the ME-printed PEEK samples. Short time relaxation of molecular alignment compels macroscopic expansion, while increased polymer crystallization at longer times forces macroscopic contraction due to densification. These results, therefore, provide crucial insight into molecular-level processes that guide macroscopic structural changes and will inform the development of PEEK annealing protocols to form robust structures by ME without sacrificing structural integrity.

show abstract

Section: Resultsmentioning

confidence: 99%

Multiple Molecular-Level Processes in the Evolution of Residual Strain in 3D Printed Poly(ether ether ketone)

Riggins,

Dadmun

2024

ACS Appl. Polym. Mater.

View full text Add to dashboard Cite

show abstract

“…TPUs exhibit a great layer-to-layer adhesion [16]. For semi-crystalline polymers such as PEEK, surface crystallization between printed layers takes place, leading to poor weld strength [17]. However, DSC investigations (not included in this contribution) showed a mostly amorphous behaviour, with no crystallization peaks even for varying cooling rates, and no apparent melting, i.e., low crystallinity content.…”

Section: Part Bmentioning

confidence: 94%

The influence of printing parameters on the mechanical properties of 3D printed TPU-based elastomers

et al. 2023

View full text Add to dashboard Cite

Additive Manufacturing (AM) becomes more and more focus of studies in the scientific community. Nevertheless, elastomers in 3D printing are still a relatively understudied topic despite their extensive use in machine components. The further understanding of the technologies and knowledge acquirement are fundamental steps towards the improvement of the printing process and the broadening of feasible applications of 3D printed elastomers. This work focused on thermoplastic polyurethanes printed with Fused Filament Fabrication (FFF) and investigated the effect of infill deposition angle and contour lines on the tensile and the stress relaxation behaviour. Samples were printed in alternating as well as unidirectional infill orientations, the latter without and with outlines. Tensile tests revealed that alternating orientations of 0°–90° and 45°–135° have a similar behaviour and benefit the integrity of the part. The fully unidirectional orientation at 90° hindered the tensile strength due to the absence of outlines and consequent delamination. All comparative analyses displayed a low influence of the raster angle at lower strains. Stress relaxation results showed similar behaviour for samples with outlines, without a clear effect of the infill orientations. In summary, contour lines are essential and an alternating orientation is recommended for better part integrity.

show abstract

“…A commonly applied criterion for the fluidity of polymeric filaments for FFF is to have a zero shear viscosity η 0 of about 10 2 to 10 3 Pa·s, at relevant printing temperatures close to the nozzle. − This criterion gives a reasonable guideline for the successful processing of related polymers but neglects the shear rate dependence of the fluidity of the polymeric melt. Since shear rates γ̇ in the range of about 10 2 to 10 3 s –1 occur in the nozzle, , this is a relevant restriction that has been included in more detailed studies. , The importance of crystallization, shear viscosity, and an applied printing program for the interlayer/welding strength and the formation of voids in 3D-printed components has also been explicitly considered in special studies. − …”

Section: Introductionmentioning

confidence: 99%

“… 30 , 31 The importance of crystallization, shear viscosity, and an applied printing program for the interlayer/welding strength and the formation of voids in 3D-printed components has also been explicitly considered in special studies. 32 − 34 …”

Section: Introductionmentioning

confidence: 99%

Influence of Crystallization Kinetics and Flow Behavior on Structural Inhomogeneities in 3D-Printed Parts Made from Semi-Crystalline Polymers

Sattler,

Zhang,

Gupta

et al. 2024

Macromolecules

View full text Add to dashboard Cite

We report the results of a study focusing on the influence of crystallization kinetics and flow behavior on structural inhomogeneities in 3D-printed parts made from polyamide 12 (PA12) and poly(lactic acid) (PLA) by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), fast scanning calorimetry (FSC), and wide-angle X-ray diffraction (WAXD). Temperature-dependent WAXD measurements on the neat PLA filament reveal that PLA forms a single orthorhombic α phase during slow cooling and subsequent 2nd heating. The PA12 filament shows a well pronounced polymorphism with a reversible solid–solid phase transition between the (pseudo)hexagonal γ phase near room temperature and the monoclinic α′ phase above the Brill transition temperature T B = 140 °C. The influence of the print bed temperature T b on structure formation, polymorphic state, and degree of crystallinity χc of the 3D-printed parts is investigated by height and depth-dependent WAXD scans and compared with that of 3D-printed single layers, used as a reference. It is found that the heat transferred from successive layers has a strong influence on the polymorphic state of PA12 since a superimposed mixture of γ and α phases is present in the 3D-printed parts. In the case of PLA, a single α phase is formed. The print bed temperature has, in comparison to PA12, a major influence on the degree of crystallinity χc and thus the homogeneity of the 3D-printed parts, especially close to the print bed. By comparing the obtained results from WAXD, DMA, DSC, and FSC measurements with relevant printing times, guidelines for 3D-printed parts with a homogeneous structure are derived.

show abstract

Direct evidence of interfacial crystallization preventing weld formation during fused filament fabrication of poly(ether ether ketone)

Cited by 9 publications

References 58 publications

Multiple Molecular-Level Processes in the Evolution of Residual Strain in 3D Printed Poly(ether ether ketone)

Multiple Molecular-Level Processes in the Evolution of Residual Strain in 3D Printed Poly(ether ether ketone)

The influence of printing parameters on the mechanical properties of 3D printed TPU-based elastomers

Influence of Crystallization Kinetics and Flow Behavior on Structural Inhomogeneities in 3D-Printed Parts Made from Semi-Crystalline Polymers

Contact Info

Product

Resources

About