Toughened poly(lactic acid)/thermoplastic polyurethane uncompatibilized blends

Poly(lactic acid), PLA, is a biodegradable polymer obtained from renewable sources with similar properties when compared with petroleum-based thermoplastics but with inherent brittleness. In this work, the use of thermoplastic polyurethane (TPU) as toughening agent was evaluated. PLA/TPU blends with 25 and 50 wt% of TPU were produced in an internal mixer without the use of compatibilizers. Their thermal, rheological, and mechanical properties were analyzed and correlated with the developed morphology. Immiscible blends with dispersed droplets morphology were obtained, and it was observed an inversion between the matrix and dispersed phases with the increase of the TPU content. The presence of TPU altered the elasticity and viscosity of the blends when compared to PLA, besides acting as a nucleating agent. Huge increments in impact resistance (up to 365%) were achieved, indicating a great potential of TPU to be used as a PLA toughening agent.

Hot Deformation Behavior of a Beta Metastable TMZF Alloy: Microstructural and Constitutive Phenomenological Analysis

A metastable beta TMZF alloy was tested by isothermal compression under different conditions of deformation temperature (923 to 1173 K), strain rate (0.172, 1.72, and 17.2 s−1), and a constant strain of 0.8. Stress–strain curves, constitutive constants calculations, and microstructural analysis were performed to understand the alloy’s hot working behavior in regards to the softening and hardening mechanisms operating during deformation. The primary softening mechanism was dynamic recovery, promoting dynamic recrystallization delay during deformation at higher temperatures and low strain rates. Mechanical twinning was an essential deformation mechanism of this alloy, being observed on a nanometric scale. Spinodal decomposition evidence was found to occur during hot deformation. Different models of phenomenological constitutive equations were tested to verify the effectiveness of flow stress prediction. The stress exponent n, derived from the strain-compensated Arrhenius-type constitutive model, presented values that point to the occurrence of internal stress at the beginning of the deformation, related to complex interactions of dislocations and dispersed phases.

Study of the conservation properties in two-way coupled dispersed multiphase flows using finite volume methods

In order to simulate dispersed multiphase flows, the coupling level must be determined according to the volume fraction in the system. The volume fraction is the ratio of the total volume of the dispersed phases over the total volume of the flow. In dilute flows, with volume fractions smaller than 10-6, only the influence of carrier phase over the dispersed phase is considered which is known as one-way coupling. Nonetheless, in dispersed flows with higher volume fractions, the effect of the dispersed phase over the continuous one should be taken into consideration, known as two-way coupling. This effect normally is applied as a source term in the conservation equations of the carrier phase. Depending on the numerical method and the discrete operators employed, these source terms can lead to some issues when aiming to preserve physical properties like mass, momentum and energy. Moreover, in order to validate the two-way coupling method, a particle-laden turbulent flow benchmark case with a mass loading of 22% is simulated by means of large eddy numerical simulation (LES). The aim of this work is to study the conservation properties of dispersed multiphase flows like momentum, kinetic energy and thermal energy through two-way coupling between dispersed and continuous phases.

Studies and Research on the Influence of Deposit Parameters on the Characteristics of Composite Coatings Ni-Al2O3 Obtained by Electrochemical Methods

The paper presents the characterization of composite coatings with nickel matrix using as dispersed phases Al2O3 particles, both from the microstructural point of view and from the point of view of the layer thickness, micro-hardness and corrosion behavior in saline fog. The presence of dispersed phase particles led to the finishing of the structure because they acted as nucleus centres, reducing the size of nickel crystallites. The parameters of the deposits influence the structure and properties of the obtained layers.

Peculiar Morphologies Obtained for 80/20 PLA/PA11 Blend with Small Amounts of Fumed Silica

This work highlights the possibility of obtaining peculiar morphologies by adding fumed silica into 80/20 polylactic acid/polyamide11 (PLA/PA11) blends. Two kinds of fumed silica (A200 and trimethoxyoctylsilane modified R805 fumed silica) were dispersed (by twin-screw extrusion, TSE) at a weight amount of 5% in neat PLA, neat PA11 and a 80/20 PLA/PA11 blend. Thermal Gravimetric Analysis (TGA) was used to verify this 5 wt % amount. Oscillatory shear rheology tests were conducted on all the formulations: (1) on neat polymer nanocomposites (PLASi5, PLASiR5, PA11Si5, PA11SiR5); and (2) on polymer blend nanocomposites (PLA80Si5 and PLA80SiR5). Scanning Electron Microscope (SEM), Scanning Transmission Electron Microscope (STEM), Atomic Force Microscopy (AFM) characterizations and laser granulometry were conducted. Microscopic analysis performed on polymer blend nanocomposites evidenced a localization of A200 silica in the PA11 dispersed phase and R805 silica at the PLA/PA11 interface. Frequency sweep tests on neat polymer nanocomposites revealed a pronounced gel-like behavior for PLASi5 and PA11SiR5, evidencing a high dispersion of A200 in PLA and R805 in PA11. A yield behavior was also evidenced for both PLA80Si5 and PLA80SiR5 blends. For the blend nanocomposites, PA11 dispersed phases were elongated in the presence of A200 silica and a quasi-co-continuous morphology was observed for PLA80Si5, whereas PLA80SiR5 exhibits bridges of silica nanoparticles between the PA11 dispersed phases.

3D-Printed Microfluidic Droplet Generator with Hydrophilic and Hydrophobic Polymers

Droplet generation has been widely used in conventional two-dimensional (2D) microfluidic devices, and has recently begun to be explored for 3D-printed droplet generators. A major challenge for 3D-printed devices is preventing water-in-oil droplets from sticking to the interior surfaces of the droplet generator when the device is not made from hydrophobic materials. In this study, two approaches were investigated and shown to successfully form droplets in 3D-printed microfluidic devices. First, several printing resin candidates were tested to evaluate their suitability for droplet formation and material properties. We determined that a hexanediol diacrylate/lauryl acrylate (HDDA/LA) resin forms a solid polymer that is sufficiently hydrophobic to prevent aqueous droplets (in a continuous oil flow) from attaching to the device walls. The second approach uses a fully 3D annular channel-in-channel geometry to form microfluidic droplets that do not contact channel walls, and thus, this geometry can be used with hydrophilic resins. Stable droplets were shown to form using the channel-in-channel geometry, and the droplet size and generation frequency for this geometry were explored for various flow rates for the continuous and dispersed phases.

Water-in-Oleogel Emulsions—From Structure Design to Functionality

The development of water-in-oleogel (W/Og) emulsions is highlighted, with focus placed on the key properties dictating the structuring ability of both the continuous oleogelled and dispersed phases present. The gelling ability of oleogelators is distinguished by the formation of crystalline structures, polymeric strands, or tubules. Once a dispersed aqueous phase is introduced, droplet stabilization may occur via oleogelator adsorption onto the surface of the dispersed droplets, the formation of a continuous gel network, or a combination of both. Surface-active species (added or endogenous) are also required for effective W/Og aqueous phase dispersion and stabilization. Processing conditions, namely temperature-time-shear regimes, are also discussed given their important role on dispersed droplet and oleogel network formation. The effects of many factors on W/Og emulsion formation, rheology, and stability remain virtually unknown, particularly the role of dispersed droplet size, gelation, and clustering as well as the applicability of the active filler concept to foods. This review explores some of these factors and briefly mentions possible applications of W/Og emulsions.

The effect of added high-iron slag on the frost resistance of cement compositions

Currently, it is of particular importance to study the possibility of increasing the durability of composite building materials by regulating the chemical and mineralogical composition. In this aspect, it is rational to consider the issues of increasing the frost resistance of cement concrete. It is known that to improve this property in concrete, it is necessary to create the correct structure of the hardened cement stone. The work aims to study the process of clogging the pores of a cement stone due to the formation of finely dispersed phases - ferrihydrite - in the process of hydration of composite Portland cement with the addition of high-iron slag of the established chemical composition. The paper analyzes the chemical and phase composition of concretes obtained based on of slag-containing binders with high values of frost resistance. It is shown that, based on this slag, concrete with frost resistance of 500 cycles has been obtained. Analysis of the hydration products showed that finely dispersed ferrihydrite of ferric iron are formed in the cement stone, which increases the density of concrete, plugging the defects in the microstructure of the C-S-H gel.