News

Stability of Instant Coffee Foam by Nanobubbles Using Spray-Freeze Drying Technique

Abstract

Instant coffee with stable foam is considered to be an important parameter for consumer preference and acceptability. For foam sustenance, nanoscale bubbles are more useful compared with microbubbles, due to their high specific area and high stagnation in the liquid phase (without undesirable liquid drainage). The technique that produces nanobubbles in coffee would concomitantly produce and preserve the coffee foam, the best. Spray-freeze drying (SFD) is known to be more effective for the production of instant coffee, compared with conventional spray drying (SD) and freeze drying (FD) techniques. However, its efficiency in the production of nanobubbles has not been explored. To address the issue, in the present study, SFD has been employed to produce instant coffee, and the findings have been compared with SD and FD. The coffee powder obtained with SFD produced a foam with higher stability that also comprised of nanobubbles, in contrast to SD and FD powders. The FE-SEM analysis of SFD foam showed the presence of nanobubbles in the range of 100–200 nm. When the beverage was prepared, the SFD coffee powder dissolved in water at 90 °C produced an excellent foam. The said foam structure was intact up to 2400 s (40 min), and lost only 89.5 ± 2 mm of foam height, during the experiment. Thus, apart from instant coffee, a stable foam in coffee comprising nanobubbles can also be achieved through the SFD.

Keywords

Spray-freeze drying, Nanobubbles, Coffee, Foam stability, Foam structure

Desalination of seawater by spray freezing in a natural draft tower

YangLiu, TingzhenMing, YongjiaWu, Renaudde Richter, YuepingFang, NanZhou

Abstract

The freeze-melting process can be a viable method for the purposes of desalination because of its low energy consumption, ignorable corrosion issues, and without huge pressure or membrane replacement work. Large contact area for heat and mass transfer per unit mass of water between the water and air and low heat resistance results in higher energy efficiency during spray freezing desalination process compared to other freezing desalination methods. A 200 m high desalination tower was proposed in this paper that could generate 27.7 kg/s fresh water in the form of water droplets with 2 mm diameter at an atmospheric temperature of −26°C. This research has founded that the natural convective airflow induced by the heat released by the warm water in the freezing process could generate through the wind turbine mounted in this system approximately one-third of the energy consumed by the water pump of the system. This free energy has never been studied in previous research. The power consumption required to produce 1 m³ fresh water in this system is approximately 1.07 kWh. Compared to traditional desalination methods, the power consumption of our new spray freezing desalination system is much lower than previous systems with the same mass flow rate of fresh water. Only 375.4 kJ cold energy to produce one-kilogram fresh water. Thus, this spray freezing desalination system could be employed in desalination industry if free cold energy (e.g. from the cold atmosphere or the regasification process of LNG) and seawater resources are available.

Keywords

Compressible airflowNatural draft towerSeawater desalinationSpray freezingWater droplet

Inhalable nanoparticulate powders for respiratory delivery

Priya Muralidharan, Monica Malapit, Evan Mallory, Don Hayes Jr., Heidi M. Mansour

Abstract

Nanoparticles are extensively studied for drug delivery and are proving to be effective in drug delivery and the diagnostic field. Drug delivery to lungs has its advantages over other routes of administration. Inhalable powders consisting of nanoparticles are gaining much interest in respiratory research and clinical therapy. Particle engineering technique is a key factor to develop inhalable formulations that can successfully deliver drug with improved therapeutic effect and enhanced targeting. Inhalable nanoparticles in the solid-state dry powders for targeted pulmonary delivery offer unique advantages and are an exciting new area of research. Nasal delivery of inhalable nanoparticulate powders is gaining research attention recently, particularly in vaccine applications, systemic drug delivery in the treatment of pain, and non-invasive brain targeting. Fundamental aspects and recent advancements along with future prospects of inhalable powders consisting of nanoparticles in the solid-state for respiratory delivery are presented.

From the Clinical Editor

The advance in nanotechnology has enabled the design of new drug delivery systems through inhalation, which has many advantages over traditional delivery systems. This comprehensive review describes and discusses the current status, drug design and modification for targeted delivery and challenges of the use of nanoparticles in the respiratory tract.

Keywords

Pulmonary nanomedicine, Solid-state, Dry powder inhaler, Particle engineering design, Inhalation powders, Lung/nasal

Impact of excipient choice on the aerodynamic performance of inhalable spray-freeze-dried powders

Stefan Wanning, Richard Süverkrüp, Alf Lamprecht

Abstract

Spray-freeze-drying (SFD) is a process in which a solution is dispersed into a freezing medium and dried by sublimation, resulting in lyophilized powders with spherical particles. This study aims at screening and evaluating the impact of the excipient choice and spray solution characteristics in SFD on the physico-chemical characteristics of lyospheres and rate their suitability for producing pulmonary applicable powders using a novel SFD method. A monodisperse droplet-stream was injected into a vortex of cold gas for the production of inhalable, uniform spherical lyophilisates with a narrow particle size distribution. Model solutions containing graded contents (0.3%, 1.0%, and 3.0% w/v) of common bulk-forming excipients like mannitol, lactose, poylvinylpyrrolidone (PVP), maltodextrin or hydroyxpropyl methylcellulose (HPMC) and their blends were dispersed using a single 20 μm pinhole diaphragm. Powders were analyzed regarding their geometric particle size, apparent density, mechanical stability and aerodynamic performance. The diameter of the frozen droplets partially correlated with the Ohnesorge number of the spray solutions. The lyosphere powders had median geometric particle diameters ranging from 20 µm to 81 µm. Some powders showed signs of particle shrinkage during the drying step and diameters were reduced down to 30% of their initial size. The apparent particle densities ranged from 0.009 g/cm³ to 0.087 g/cm³. The mechanical stability of the lyospheres depended on the constituents and concentration of the initial spray solution. Mannitol/maltodextrin formulations yielded large porous particles with promising performance in the Next-Generation-Impactor, emitted fractions between 92 and 98% (w/w) and fine-particle-fractions of over 55% (w/w). According to our first steps towards formulations for free-flowing inhalable spray freeze-dried powders the impact of excipient choice on the SFD process is significant and based on the current findings we consider mannitol or mannitol/maltodextrin as best performing formulations.

Keywords

Spray freeze drying, Droplet-stream generator, Protein formulations, Lyophilization, Porous particles, Pulmonary drug delivery, Droplet collision, Lyosphere

A nanoindentation based study to evaluate the effect of carbon nanofibers on the mechanical properties of SiC composites

Shaik Mubina, P Sudharshan Phani, Asit Kumar Khanra, Bhaskar Prasad Saha

Abstract

An advanced high-speed nanoindentation technique is employed to analyze the combined benefit of the particulate and continuous fiber’s reinforcing effect of carbon fibers in the SiC matrix. Spray freeze granulated well-dispersed carbon nanofibers (CNF) containing precursor SiC-CNF (1 wt%) composite powder was used as a base matrix in which continuous carbon fibers were introduced in a systematic laying pattern to produce hybrid composite tubes with 10–12 mm wall thickness. Thin tubes with a wall thickness of 1–2 mm were produced with SiC, SiC-CNF composite powder. The two types of tubes with various lengths were cold isostatically pressed and pressureless sintered at 2150°C/1hour under Argon (Ar). The surface properties of the sintered tubes were further enhanced by coating with a dense SiC layer by adopting a CVD technique. The properties of the fiber-matrix interface and coating-matrix interfaces of the tube samples were evaluated using conventional processes as well as the nanoindentation techniques and compared at different length scales. Attempts have been made to correlate the structure-property relations of complex multi-phase of SiC composites employing high-speed nanoindentation mapping as well as XRD, Digital optical, SEM, and TEM analysis.

Recent progress in structural development and band engineering of perovskites materials for photocatalytic solar hydrogen production: A review

Sehar Tasleem, Muhammad Tahir

Abstract

Photocatalytic water splitting for hydrogen production is a promising technology for the conversion of solar light to clean energy. In this perspective, several semiconductors have been under investigation, but they show less efficiency, selectivity and stability for hydrogen production. Recently, perovskites are most demanding due to their exceptional characteristics such as controlled structure and morphology, adjustable band structure, controlled valence state, adjustable oxidation state and visible light response. This review highlights structural classification of perovskites and band engineering for solar energy assisted photocatalytic hydrogen production. In the main stream, overview and fundamentals of perovskite materials for selective solar to hydrogen conversion are presented. The structural modification and band alteration to stimulate quantum efficiency and stability are specifically demonstrated. Photoactivity enhancement through metals, noble metals, non-metals doping, oxygen vacancies and fermi level adjustments are also deliberated. The role of perovskites with binary semiconductors towards hydrogen production has also been discussed. Up conversion effect of doping luminescent agents (Er, Ho, Eu, Nd) for improved photocatalytic activity by band gap narrowing is also deliberated. Various conventional and non-conventional synthesis methods for perovskites including solid-state, hydrothermal, sol-gel, co-precipitation, spray-freeze drying, microwave assisted, spray pyrolysis, low temperature combustion, pulse laser deposition and wet chemical method for enhanced photocatalytic activity are also demonstrated in this work. Finally, the key challenges and future directions for sustainable energy systems are also included.

Keywords

Photo-catalysis, Hydrogen production, Perovskites, Structural classification, Synthesis methods, Binary semiconductors

Microstructure of spray freezing dried powders affected by the presence of inert particles

Fan Zhang, Linsong Wang, Xiaoyu Ma, Qing Xu, Wei Tian, Zhanyong li

Abstract

Spray freeze-drying is a process to directly produce high quality powders with short drying time. The difference of microstructures has a great influence on the physical properties of powders. However, during the spray freeze-drying process, the freezing degree of droplets in the drying chamber will change the product structure and affect the powder quality. In this study, the surface structure and morphology of dry powders were observed using scanning electron microscopy. The formation mechanism of droplet morphology during spray freeze-drying was analyzed. The results show that the rapid freezing process can produce finer microstructures.

Nacre-like alumina composites based on heteroaggregation

Mariana Muňoz, Manuella Cerbelaud, Arnaud Videcoq, Hassan Saad, Alexandre Boulle, Sylvain Meille, Sylvain Deville, Fabrice Rossignol

Abstract

High strength and high toughness are usually mutually exclusive in materials. Among all material classes, ceramics exhibit a high stiffness and strength, but they present a limited plastic deformation, which results in a moderate toughness. However, tough ceramics have been obtained using anisotropic particles organized in a ‘brick and mortar’ microstructure, inspired by the structure of the natural nacre. Here, we propose to build nacre-like ceramic composites from colloidal suspensions using heteroaggregation of particles. Two different shaping processes are used: direct settling of suspensions or freeze-granulation. After sintering, in both cases, the platelets alignment is very good, close to that of platelets in natural nacre, with a slightly better one noted for direct settling. Despite a better platelet alignment, the toughness is lower than in previous studies showing that further improvement of the interfacial phases present in the material must now be considered to reinforce its mechanical behavior.

Keywords

Nacre-like composite, Heteroaggregation, Platelet alignment, Settling, Freeze-granulation

Dynamical in-situ observation of the lyophilization and vacuum-drying processes of a model biopharmaceutical system by an environmental scanning electron microscope

Abstract

The paper discusses the real-time monitoring of the changing sample morphology during the entire lyophilization (freeze-drying) and vacuum-drying processes of model biopharmaceutical solutions by using an environmental scanning electron microscope (ESEM); the device’s micromanipulators were used to study the interior of the samples in-situ without exposing the samples to atmospheric water vapor. The individual collapse temperatures (Tc) of the formulations, pure bovine serum albumin (BSA) and BSA/sucrose mixtures, ranged from −5 to −29 °C. We evaluated the impact of the freezing method (spontaneous freezing, controlled ice nucleation, and spray freezing) on the morphologies of the lyophiles at the constant drying temperature of −20 °C. The formulations with Tc above −20 °C resulted in the lyophiles’ morphologies significantly dependent on the freezing method. We interpret the observations as an interplay of the freezing rates and directionalities, both of which markedly influence the morphologies of the frozen formulations, and, subsequently, the drying process and the mechanical stability of the freeze-dried cake. The formulation with Tc below −20 °C yielded a collapsed cake with features independent of the freezing method. The vacuum-drying produced a material with a smooth and pore-free surface, where deep cracks developed at the end of the process.

Keywords

Bovine serum albumin, Freeze-drying, Vacuum-drying, Environmental scanning electron microscopy

Sintering investigations of a UO₂-PuO₂ powder synthesized using the freeze-granulation route

Marion Le Guellec, Florent Lebreton, Laure Ramond, Abibatou Ndiaye, Thierry Gervais, Guillaume Bernard-Granger

Abstract

Sintering investigations of a UO₂-PuO₂ powder, integrating 11 wt% of PuO₂ and synthesized by freeze-granulation, were completed at temperatures up to 1700°C, in an atmosphere of Ar/4 vol% H₂ and 1200 vpm H₂O. Analyzing the “grain size versus relative density” trajectory enabled to propose that densification was controlled by volume diffusion and grain growth by the grain boundaries. An activation energy around 630 kJ/mol was obtained for densification, which was close to the value reported for volume diffusion of plutonium cations in U_1-xPu_xO₂ polycrystals. The sintered microstructure appeared homogeneous regarding the plutonium and uranium cations distribution.

Keywords

Sintering, Ceramics, Oxides, Microstructure, MOX