Development of extrudate distortions in poly(dimethyl siloxane) and its suspensions with rigid particles

Birinci, Elvan; Kalyon, Dilhan M.

doi:10.1122/1.2184312

Cited by 26 publications

(13 citation statements)

References 34 publications

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“…The PDMS of our investigation did not exhibit wall slip, consistent with the general understanding that PDMS resins generally exhibit wall slip when molecular weights >500 kDa (and typically when the wall shear stress exceeds 70 KPa [73, 75,76] The volume fraction ratios of large, medium and small size particles were kept constant for all  at 9:3:1 to generate a relatively high maximum packing fraction, ϕ m .…”

Section: Methodssupporting

confidence: 81%

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Shear viscosity and wall slip behavior of dense suspensions of polydisperse particles

Lee

Kalyon

2018

Journal of Rheology

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Shear viscosity and wall slip of dense suspensions of a silicone polymer incorporated with polydisperse particles were investigated. Three types of particles with low aspect ratios were used to achieve a relatively high maximum packing fraction,  m =0.86.Such a high  m allowed the preparation of suspensions with a wide range of solid volume fractions, , i.e., 0.62  0.82. The wall slip velocities of the suspensions in steady torsional and capillary flows were characterized and determined to be fully consistent with the mechanism of apparent slip layer formation at the wall. Upon wall slip corrections it was found that at shear stresses which are significantly above the yield stress the relative shear viscosity of the suspensions obeys well the Krieger-Dougherty relationship that links the relative shear viscosity behavior of dense suspensions solely to / m . However, at lower shear stresses that are in the vicinity of the yield stresses the relative shear viscosity becomes functions of both / m and the shear stress. It is clearly demonstrated that without wall slip analysis the accurate characterization of the relative shear viscosity of dense suspensions is not possible. 3 I.

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Section: Methodssupporting

confidence: 81%

“…Figure 15 shows some typical comparisons of the predictions of Equation (19) versus the experimental / s QQ data for =0. 76. Similar results obtained for other  are shown in the supplemental figure, Fig.…”

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confidence: 87%

Shear viscosity and wall slip behavior of dense suspensions of polydisperse particles

Lee

Kalyon

2018

Journal of Rheology

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“…For multicomponent feedstocks such as the one employed in this study, the pressure oscillations appear only at high concentrations of powder and become more irregular as the powder concentration increases [ 60 , 61 ]. The fact that the oscillations start for all the nozzles at a shear stress of approximately 0.25 MPa could indicate the existence of critical shear stress after which slip of the material in the capillary wall starts [ 62 ], leading to the slip-stick effect [ 59 ]. Therefore, it can be said that high-shear rates can negatively affect the extrusion process of this material due to flow instabilities.…”

Section: Discussionmentioning

confidence: 99%

Influence of the Infill Orientation on the Properties of Zirconia Parts Produced by Fused Filament Fabrication

et al. 2020

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The fused filament fabrication (FFF) of ceramics enables the additive manufacturing of components with complex geometries for many applications like tooling or prototyping. Nevertheless, due to the many factors involved in the process, it is difficult to separate the effect of the different parameters on the final properties of the FFF parts, which hinders the expansion of the technology. In this paper, the effect of the fill pattern used during FFF on the defects and the mechanical properties of zirconia components is evaluated. The zirconia-filled filaments were produced from scratch, characterized by different methods and used in the FFF of bending bars with infill orientations of 0°, ±45° and 90° with respect to the longest dimension of the specimens. Three-point bending tests were conducted on the specimens with the side in contact with the build platform under tensile loads. Next, the defects were identified with cuts in different sections. During the shaping by FFF, pores appeared inside the extruded roads due to binder degradation and or moisture evaporation. The changes in the fill pattern resulted in different types of porosity and defects in the first layer, with the latter leading to earlier fracture of the components. Due to these variations, the specimens with the 0° infill orientation had the lowest porosity and the highest bending strength, followed by the specimens with ±45° infill orientation and finally by those with 90° infill orientation.

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“…4 that wall slip velocity increases with shear stress, which is similar to the behavior of other systems exhibiting slip. 9 Addition of 1 wt% TPSE to the 50 wt% wood-filled mPP leads to a significant increase in the wall slip velocity, more pronounced at low-wall shear stresses. This is an important result since wood-plastics composites are usually extruded as thick profiles at relatively low-shear rates, probably less than 50 s −1 at customary production speeds in industrial installations.…”

Section: Capillary Rheometry and Wall Slip Analysismentioning

confidence: 99%

Thermoplastic silicone elastomer lubricant in extrusion of polypropylene wood flour composites

Hristov

Vlachopoulos

2007

Adv Polym Technol

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ABSTRACT:A possibility of using a thermoplastic silicone elastomer (TPSE) for reduction of surface defects in the extrusion of wood-filled metallocene polypropylene (mPP) has been investigated in this work. A capillary rheometer and a single-screw extruder have been utilized to study the effect of the additive on the extrudate distortions. Maleated syndiotactic metallocene polypropylene was also used as an adhesion promoter in mPP/wood flour composites. At loadings of 50 wt% wood flour in the mPP, the extrudates come out of the die with significant tearing and surface roughness. The surface rupture mechanism is similar to that of sharkskin in neat polymers; however, the defect is much more exaggerated in the case of wood fiber-filled composites. It was found that TPSE at low concentrations (1 wt%) was able to reduce or even completely eliminate extrudate surface tearing. Increasing the extrusion speed yielded better results. Addition of a coupling agent also provides improvement in the extrudate appearance.

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Development of extrudate distortions in poly(dimethyl siloxane) and its suspensions with rigid particles

Cited by 26 publications

References 34 publications

Shear viscosity and wall slip behavior of dense suspensions of polydisperse particles

Shear viscosity and wall slip behavior of dense suspensions of polydisperse particles

Influence of the Infill Orientation on the Properties of Zirconia Parts Produced by Fused Filament Fabrication

Thermoplastic silicone elastomer lubricant in extrusion of polypropylene wood flour composites

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