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   Melt Instability Identification Using Unsupervised Machine Learning Algorithms; ; et al in Macromolecular Materials and Engineering (2023) In industrial extrusion processes, increasing shear rates can lead to higher production rates. However, at high shear rates, extruded polymers and polymer compounds often exhibit melt instabilities ... [more ▼] In industrial extrusion processes, increasing shear rates can lead to higher production rates. However, at high shear rates, extruded polymers and polymer compounds often exhibit melt instabilities ranging from stick-slip to sharkskin to gross melt fracture. These instabilities result in challenges to meet the specifications on the extrudate shape. Starting with an existing published data set on melt instabilities in polymer extrusion, we assess the suitability of clustering, unsupervised machine learning algorithms combined with feature selection, to extract and identify hidden and important features from this data set, and their possible relationship with melt instabilities. The data set consists of both intrinsic features of the polymer as well as extrinsic features controlled and measured during an extrusion experiment. Using a range of commonly available clustering algorithms, it is demonstrated that the features related to only the intrinsic properties of the data set can be reliably divided into two clusters, and that in turn, these two clusters may be associated with either the stick-slip or sharkskin instability. Furthermore, using a feature ranking on both the intrinsic and extrinsic features of the data set, it is shown that the intrinsic properties of molecular weight and polydispersity are the strongest indicators of clustering. [less ▲] Detailed reference viewed: 49 (2 UL)Electrospinning Ethanol–Water Solutions of Poly(Acrylic Acid): Nonlinear Viscosity Variations and Dynamic Taylor Cone BehaviorVats, Shameek  ; Lagerwall, Jan in Macromolecular Materials and Engineering (2021) Electrospinning of polymer solutions is a multifaceted process that depends on the careful balancing of many parameters to achieve a desired outcome, in many cases including mixtures of multiple solvents ... [more ▼] Electrospinning of polymer solutions is a multifaceted process that depends on the careful balancing of many parameters to achieve a desired outcome, in many cases including mixtures of multiple solvents. A systematic study of how the solution viscosity 𝜼—a good probe of solvent–polymer interactions—and the electrospinnability change when poly(acrylic acid) (PAA) is dissolved in ethanol–water mixtures at varying mixing ratio is carried out. A pronounced maximum is found in 𝜼 at a water-to-ethanol molar ratio of about 2:1, where the solvent mixture deviates maximally from ideal mixing behavior and partial deprotonation of carboxyl groups by water coincides synergistically with dissolution of the uncharged protonated PAA fraction by ethanol. The PAA concentration is tuned as a function of water–ethanol ratio to obtain a common value of 𝜼 for all solvent mixtures that is suitable for electrospinning. For high PAA content, the Taylor cone grows in volume over time despite minimum solution flow rate, even experiencing surface gelation for ethanol-rich solutions. This is attributed to the hygroscopic nature of PAA, drawing excess water into the Taylor cone from the air during spinning. [less ▲] Detailed reference viewed: 55 (17 UL) Resolving Inclusion Structure and Deformation Mechanisms in Polylactide Plasticized by Reactive Extrusion; ; et al in Macromolecular Materials and Engineering (2017) Detailed reference viewed: 158 (0 UL)Morphology and Core Continuity of Liquid-crystal-functionalized, Coaxially Electrospun Fiber Mats Tuned Via the Polymer Sheath Solution; ; et al in Macromolecular Materials and Engineering (2013), 298(5), 583-589 By electrospinning liquid crystals coaxially inside a polymer sheath, responsive fibers with application potential, e.g., in wearable sensors can be produced. We conduct a combined scanning electron ... [more ▼] By electrospinning liquid crystals coaxially inside a polymer sheath, responsive fibers with application potential, e.g., in wearable sensors can be produced. We conduct a combined scanning electron/polarizing microscopy study of such fibers, concluding that a match between the properties of the sheath solution and that of the core fluid is vital for achieving well-formed and well-filled fibers. Problems that may otherwise arise are fibers that are continuously filled, but partially collapsed; or fibers in which the core breaks up into droplets due to a mismatch in elongational viscosity between inner and outer fluids. [less ▲] Detailed reference viewed: 126 (1 UL) |
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