Polymer Processing Additives for Melt Fracture Control

Hatzikiriakos, Savvas G.; Migler, Kalman D.

doi:10.1002/9781118140611.ch2

Cited by 4 publications

(4 citation statements)

References 58 publications

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“…The concentration of the CB for the ShSF was selected at 30 wt.% because sensor fibers with a filler content of 25 wt.% were not conductive, and composites with a higher filler content than 30 wt.% could not be extruded with a constant diameter because of the melt fracture effect. Melt fracture occurs when excessive shear stress is exerted on a melt, leading to roughness in the extrudate [ 45 , 46 ]. This phenomenon is also known as sharkskin, and it was observed at a low shear rate.…”

Section: Methodsmentioning

confidence: 99%

Supramolecular Self-Healing Sensor Fiber Composites for Damage Detection in Piezoresistive Electronic Skin for Soft Robots

et al. 2021

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Self-healing materials can prolong the lifetime of structures and products by enabling the repairing of damage. However, detecting the damage and the progress of the healing process remains an important issue. In this study, self-healing, piezoresistive strain sensor fibers (ShSFs) are used for detecting strain deformation and damage in a self-healing elastomeric matrix. The ShSFs were embedded in the self-healing matrix for the development of self-healing sensor fiber composites (ShSFC) with elongation at break values of up to 100%. A quadruple hydrogen-bonded supramolecular elastomer was used as a matrix material. The ShSFCs exhibited a reproducible and monotonic response. The ShSFCs were investigated for use as sensorized electronic skin on 3D-printed soft robotic modules, such as bending actuators. Depending on the bending actuator module, the electronic skin was loaded under either compression (pneumatic-based module) or tension (tendon-based module). In both configurations, the ShSFs could be successfully used as deformation sensors, and in addition, detect the presence of damage based on the sensor signal drift. The sensor under tension showed better recovery of the signal after healing, and smaller signal relaxation. Even with the complete severing of the fiber, the piezoresistive properties returned after the healing, but in that case, thermal heat treatment was required. With their resilient response and self-healing properties, the supramolecular fiber composites can be used for the next generation of soft robotic modules.

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Section: Methodsmentioning

confidence: 99%

Supramolecular Self-Healing Sensor Fiber Composites for Damage Detection in Piezoresistive Electronic Skin for Soft Robots

et al. 2021

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“…The fluid within the drool layer creeps through the die and accumulates on the die face as drool . Cohesive melt failure has also been observed in conjunction with melt fracture (see Figure 6 and EPAPS online video for Figure 5 in Migler et al, Figure 5.17 of Migler, and section 2.3 of Hatzikiriakos and Migler) . Additives are often used to suppress die drool and to alleviate other processing problems .…”

Section: Introductionmentioning

confidence: 99%

“…[11,13] Cohesive melt failure has also been observed in conjunction with melt fracture (see Figure 6 and EPAPS online video for Figure 5 in Migler et al, [14] Figure 5.17 of Migler, [15] and section 2.3 of Hatzikiriakos and Migler). [16] Additives are often used to suppress die drool and to alleviate other processing problems. [17] These processing aids can intervene at the wall, but may also intervene at the cohesive slip interface.…”

Section: Introductionmentioning

confidence: 99%

Slip heating in die drool

Gilbert

Giacomin

2015

Can J Chem Eng

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When molten plastic is extruded from a die, it can collect on the open die face. Called die drool, this phenomenon costs plastics manufacturers by requiring shutdown for die cleaning. This has been attributed to cohesive failure within the fluid at an internal surface, where the fluid slips on itself; the corresponding isothermal analysis led to an analytical solution for the drool rate (Schmalzer and Giacomin, J. Polym. Eng. 2013, 33, 1). In this paper, we account for the frictional heating at the cohesive slip interface, which we call slip heating. We focus on slit flow, which is used in film casting, sheet extrusion, curtain coating, and in many other chemical engineering unit operations. In slit flow, the magnitude of the heat flux from the slipping interface is the product of the shear stress and the slip speed. We present the solution for the temperature rise in pressure‐driven slit flow subject to constant heat generation at the cohesive slip interface. We solve the energy equation in Cartesian coordinates for the temperature rise, for both the transient and steady temperature profiles, in both the drool layer and the bulk polymer. We then evaluate the effect of this temperature rise on the rate of die drool. For this simplest relevant non‐isothermal problem, we neglect viscous dissipation and convective heat transfer in the melt and we model viscosity as an Arrhenius function of temperature. We conclude with three worked examples showing the relevance of slip heating in determining die drool flow rates. We find that slip heating diminishes die drool. We arrive at two sufficient dimensionless conditions for the accurate use of our results: Br ≪1 or Gi ≪1.

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“…Sharkskin melt fracture is not to be confused with gross melt fracture, a larger scale distortion arising at throughputs higher than the critical throughput for sharkskin melt fracture [1][2][3][4] (see section 2.3.1 of Ref. 5). Sharkskin melt fracture has been attributed to a breakdown of the no slip boundary condition in the extrusion die, that is, to adhesive failure at the die walls, where the fluid moves with respect to the wall and this is called stick-slip [1] (see section 6.2.1 of Ref.…”

Section: Introductionmentioning

confidence: 99%

Wall slip heating

Gilbert

Giacomin

2014

Polym Eng Sci

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When molten plastic is extruded, the upper limiting throughput is often dictated by fine irregular distortions of the extrudate surface. Called sharkskin melt fracture, plastics engineers spike plastics formulations with processing aids to suppress these distortions. Sharkskin melt fracture is not to be confused with gross melt fracture, a larger scale distortion arising at throughputs higher than the critical throughput for sharkskin melt fracture. Sharkskin melt fracture has been attributed to a breakdown of the no slip boundary condition in the extrusion die, that is, adhesive failure at the die walls, where the fluid moves with respect to the wall. In this article, we account for the frictional heating at the wall, which we call slip heating. We focus on slit flow, which is used in film casting, sheet extrusion, curtain coating, and when curvature can be neglected, slit flow is easily extended to pipe extrusion and film blowing. In slit flow, the magnitude of the heat flux from the slipping interface is the product of the shear stress and the slip speed. We present the solutions for the temperature rise in pressure-driven slit flow and simple shearing flow, each subject to constant heat generation at the adhesive slip interface, with and without viscous dissipation in the bulk fluid. We solve the energy equation in Cartesian coordinates for the temperature rise, for steady temperature profiles. For this simplest relevant nonisothermal model, we neglect convective heat transfer in the melt and use a constant viscosity. We arrive at a necessary dimensionless condition for the accurate use of our results: Pé(1. We find that slip heating can raise the melt temperature significantly, as can viscous dissipation in the bulk. We conclude with two worked examples showing the relevance of slip heating in determining wall temperature rise, and we show how to correct wall slip data for this temperature rise. POLYM. ENG.

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Polymer Processing Additives for Melt Fracture Control

Cited by 4 publications

References 58 publications

Supramolecular Self-Healing Sensor Fiber Composites for Damage Detection in Piezoresistive Electronic Skin for Soft Robots

Supramolecular Self-Healing Sensor Fiber Composites for Damage Detection in Piezoresistive Electronic Skin for Soft Robots

Slip heating in die drool

Wall slip heating

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