Cure kinetics of epoxy nanocomposites affected by MWCNTs functionalization: A review

The current paper provides an overview to emphasize the role of functionalization of multiwalled carbon nanotubes (MWCNTs) in manipulating cure kinetics of epoxy nanocomposites, which itself determines ultimate properties of the resulting compound. In this regard, the most commonly used functionalization schemes, that is, carboxylation and amidation, are thoroughly surveyed to highlight the role of functionalized nanotubes in controlling the rate of autocatalytic and vitrification kinetics. The current literature elucidates that the mechanism of curing in epoxy/MWCNTs nanocomposites remains almost unaffected by the functionalization of carbon nanotubes. On the other hand, early stage facilitation of autocatalytic reactions in the presence of MWCNTs bearing amine groups has been addressed by several researchers. When carboxylated nanotubes were used to modify MWCNTs, the rate of such reactions diminished as a consequence of heterogeneous dispersion within the epoxy matrix. At later stages of curing, however, the prolonged vitrification was seen to be dominant. Thus, the type of functional groups covalently located on the surface of MWCNTs directly affects the degree of polymer-nanotube interaction followed by enhancement of curing reaction. Our survey demonstrated that most widespread efforts ever made to represent multifarious surface-treated MWCNTs have not been directed towards preparation of epoxy nanocomposites, but they could result in property synergism

Evolution of Co-continuous Morphology along the Screw Length in a Co-rotating Twin-screw Extruder and Its Effect on Impact Strength of Compatibilized PA6/ABS Blend

An ultra-glide twin screw extruder is employed to allow the quick and easy removal of the screws from the fixed processing section within few seconds, probing the current degree of the melting state, the dispersive anddistributive processing steps and finally the level of morphology development along extruder screws. For morphological studies the molten samples, collected from different points along the screw length, were quickly frozen in liquid nitrogen and observed under a scanning electron microscope. The morphology development along screws was studied for the compatibilized PA6/ABS blends with different ABS contents. It was observed that the co-continuous morphology was formed in an initial stage of mixing, which then transformed into a refined co-continuous structure and developed along the extruder. The level of co-continuity decreased at higher ABS content. In addition the effect of processing condition on morphology development was studied. In view of the mechanical properties, the effect of morphology on the impact strength could be elucidated. It was found that not only the co-continuous morphology but also the level of co-continuity plays an important role in determination of ultimate impact properties. The impact strength was lowered to 35 kJ/m2 from initial value of 47 kJ/m2  by increasing the ABS content from 60 to 70 wt%

Assessment of Melt Rheological Behavior of PTT/PE and PTT/PA 12 Blends by Emulsion and Micromechanical Models

To describe the rheological behavior of polymer blends using emulsionbased (Palierne theory) as well as micromechanical models (Coranapproach), two immiscible polymeric blend systems of poly(trimethylene terephthalate) (PTT)/polyamide-12 (PA12) and PTT/polyethylene (PE) having different levels of molecular interactions were investigated as model systems. The role of interfacial interactions, viscosity ratio, composition, and shear rate were also explored with respect to the aforementioned theories. For both systems no reasonable agreement was noticed between the experimental data and Palierne model predictions, which was related to high viscosity ratio and high dispersed phase content. Nevertheless, the PTT/PE blend, having almost a zero interfacial thickness due to the absence of intermolecular interaction, exhibited a seemingly better correlation with experimental data compared to PTT/PA12 system. Moreover a better agreement between experimental and theoretical data was obtained in the blend where the viscosity of dispersed phase was higher than that of matrix. Also, in both model systems, the values predicted from Palierne were closer to empirical data at higher frequencies most likely due to breakdown in physical network structure. Coran analysis due to its micromechanical origin could give outputs in good agreement with the experimental results in both model systems

A numerical study on deformation of Newtonian droplets through converging cylindrical dies

In this work, the dynamic deformation of a viscose Newtonian droplet passing through cylindrical converging dies has been studied. The changes in the interfacial area between two immiscible Newtonian fluids have been considered as a variable representing the time-dependent deformation of a circular droplet along converging dies. To do so, a surface tracking method has been incorporated into a finite element code, developed by the authors, which quantifies the deformation of the droplet through the converging path, and where the surface area of the deformed drop has been consequently chosen as a criterion for a two-phase interface. In this study, it has been revealed that by changing both rheological and geometrical parameters it is possible to manage the value of interface area between two phases. Ultimately, a unique curve is developed for each droplet to primary phase viscosity ratio which can correlate drop deformation with geometrical parameters

A numerical study on deformation of Newtonian droplets through converging cylindrical dies

In this work, the dynamic deformation of a viscose Newtonian droplet passing through cylindrical converging dies has been studied. The changes in the interfacial area between two immiscible Newtonian fluids have been considered as a variable representing the time-dependent deformation of a circular droplet along converging dies. To do so, a surface tracking method has been incorporated into a finite element code, developed by the authors, which quantifies the deformation of the droplet through the converging path, and where the surface area of the deformed drop has been consequently chosen as a criterion for a two-phase interface. In this study, it has been revealed that by changing both rheological and geometrical parameters it is possible to manage the value of interface area between two phases. Ultimately, a unique curve is developed for each droplet to primary phase viscosity ratio which can correlate drop deformation with geometrical parameters

Review of Bioprinting in Regenerative Medicine: Naturally Derived Bioinks and Stem Cells

Regenerative medicine offers the potential to repair or substitute defective tissues by constructing active tissues to address the scarcity and demands for transplantation. The method of forming 3D constructs made up of biomaterials, cells, and biomolecules is called bioprinting. Bioprinting of stem cells provides the ability to reliably recreate tissues, organs, and microenvironments to be used in regenerative medicine. 3D bioprinting is a technique that uses several biomaterials and cells to tailor a structure with clinically relevant geometries and sizes. This technique's promise is demonstrated by 3D bioprinted tissues, including skin, bone, cartilage, and cardiovascular, corneal, hepatic, and adipose tissues. Several bioprinting methods have been combined with stem cells to effectively produce tissue models, including adult stem cells, embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and differentiation techniques. In this review, technological challenges of printed stem cells using prevalent naturally derived bioinks (e.g., carbohydrate polymers and protein-based polymers, peptides, and decellularized extracellular matrix), recent advancements, leading companies, and clinical trials in the field of 3D bioprinting are delineated. © 2021 American Chemical Society