Relevance of Dielectric Properties in Microwave Assisted Processes

Microwaves are electromagnetic radiation with wavelength ranging from 1 mm to 1 m in free space with a frequency from 300 GHz to 300 MHz, respectively. International agreements regulate the use of the different parts of the spectrum; the frequencies 915 MHz and 2.45 GHz are the most common among those dedicated to power applications for industrial, scientific and medical purposes (Metaxas & Meredith, 1983). Although microwaves have been firstly adopted for communications scope, an increasing attention to microwave heating applications has been gained since after World War II (Meredith, 1998; Chan & Reader, 2002). Reasons for this growing interest can be found in the peculiar mechanism for energy transfer: during microwave heating, energy is delivered directly to materials through molecular interactions with electromagnetic field via conversion of electrical field energy into thermal energy. This can allow unique benefits, such as high efficiency of energy conversion and shorter processing times, thus reductions in manufacturing costs thanks to energy saving. Moreover, other effects have been pointed out, such as the possibility to induce new structural properties to irradiated materials (development of new materials) and to apply novel strategies in chemical syntheses (green techniques). Crucial parameters in microwave heating are the dielectric properties of matter; they express the energy coupling of a material with electromagnetic microwave field and, thus, the heating feasibility (Metaxas & Meredith, 1983; Schubert & Regier 1995; Tang et al., 2002). On the bases of dielectric properties, microwave devices (applicators) can be adopted in heating operations and optimized working protocols can be used. This chapter is divided into four sections dealing with: i. fundamentals of microwave heating and relevance of dielectric properties of materials; ii. different techniques used in dielectric properties measurements of materials (test fixtures characteristics, technique applicability, advantages and disadvantages); iii. application of the open-ended coaxial-probe method in dielectric properties measurements of food, pharmaceutical ingredients, living materials, to understand specific heating phenomenology and, thus, to optimize thermal treatments / to define safety limits of exposition; iv. basics of heat and mass transfer modeling in microwave assisted processes

Microwaves in Soil Remediation from VOC’s. 1. Heat and Mass Transfer Aspects.

A novel technique presented performs in situ remediation of soils contaminated by volatile organic compounds (VOCs) based on the use of electromagnetic fields for heating operations. Attention is focused on heat and mass transfer occurring in porousmoisturized media like a soil matrix. The microwave induced steam distillation process is investigated. Measurements are reported of temperature, humidity, residual contaminant concentration, and permittivity during the process. The crucial role is elucidated that the changes of the dielectrical properties of the soil matrix play on the electromagnetic field propagation. A mathematical model of the remediation process relating all the parameters above is proposed and validated. doi: 10.1002/aic.69049072

The global operations of European firms - The second EFIGE policy report

This Bruegel blueprint analyses, within the framework of the EFIGE (European Firms in a Global Economy) project, the export and foreign investment performance of European firms. It is based on new cross-country data from 15,000 individual firms never available before. Written by Giorgio Barba Navaretti, Matteo Bugamelli, Gianmarco Ottaviano and Fabiano Schivardi, the report looks at the specific elements that make some European companies more competitive than others in foreign markets, revealing that firm characteristics -mainly size- are the primary determinants of export performance, even more so than country characteristics. Therefore the authors suggest that firm growth and consolidation in all European countries would generate a considerable increase in the value of European exports and thus help lift European growth. These findings will be crucial for policymakers, who, in order to boost the chance of European firmsâ?? on foreign markets, should shift the policy discussion from the current focus on specific sectors and skill groups to structural reforms that allow firms across the board to grow and to develop more sophisticated forms of management. Until now, evidence on European firmsâ?? competitiveness has been based on partial, non-comparable national data. But for the first time this paper is based on detailed results from a new large-scale survey of 15,000 manufacturing companies in seven EU countries (Austria, France, Germany, Hungary, Italy, Spain and the United Kingdom). The survey examines firmsâ?? exporting, importing, outsourcing and foreign investment activities. This survey data has then been combined with structural data about the individual firms taken from their balance-sheets such as governance, profits, number of employees.

Intensifying the microencapsulation process: Ultrasonic atomization as an innovative approach

In this review, new approaches to the microencapsulation processes, widely used in the manufacturing of pharmaceutical products, are discussed focusing the attention on the emerging ultrasonic atomization technique. Fundamentals and novel aspects are presented, and advantages of ultrasonic atomization in terms of intensification and low energy requests are emphasized

Single-Pot Semicontinuous Bench Scale Apparatus To Produce Microparticles

This work presents both the design of a novel process to produce microparticles with a shell−core structure and a bench scale apparatus purposely realized. The developed process was designed to respond to mandatory needs of process intensification. It involved the coupling of two emergent technologies: atomization assisted by ultrasonic energy and microwave heating. The former was used to atomize polymeric solutions; the latter was applied to stabilize the produced droplets by drying. Both operations were performed in the same vessel with the aim to have a single-pot process chamber and were carried out by a semicontinuous procedure. Basic design criteria and advantages of the ultrasonic−microwave coupled operations in the realized apparatus are presented and discussed. Results of testing and of operating runs to produce shell−core microparticles are also reported, emphasizing the main features of the produced particles

In vitro dissolution of pH sensitive microparticles for colon-specific drug delivery

Objective: The objective of this work is to prepare oral dosage systems based on enteric materials in order to verify their possible use as Colon-Specific Drug Delivery Systems (CSDDSs). Methodology: In particular, three different copolymers of methyl-methacrylate (MMA) - acrylic acid (AA) are synthesized with increasing percentage of MMA (from 70% to 73%) and they are used to produce microparticles by the double-emulsion solvent evaporation method. The microparticles, loaded using theophylline as model drug, are then tested for drug release under varying pH to reproduce what happens in the human GI tract. Results: All the investigated systems have shown an effective pH sensitiveness: they show a good gastro-resistance, releasing the model drug only at higher pH, small intestine or colon, depending on the kind of used copolymer. Conclusion: The results confirm the usefulness of both the materials and the methods proposed in this study for colon-specific delivery applications

Microencapsulation effectiveness of small active molecules in biopolymer by ultrasonic atomization technique

A method to produce biopolymeric (alginate) microparticles by ultrasonic assisted atomization, previously developed, has been applied to the production of microparticles loaded with a small active molecule (theophylline). Fine loaded alginate droplets have been cross-linked with divalent ions to produce microparticles. Once produced, the particles have been separated by centrifugation or filtration and then they have been dried. Drug release has been evaluated by dissolution tests, dissolving the dried particles in acidic solution at pH 1 for a given time and then at pH 7 to simulate the stomach and intestinal environment, respectively. The encapsulation efficiency and the drug loading have been investigated and the operating conditions have been changed to clarify the role of the transport phenomena on the overall process. To increase the drug loading, shorter separation time and better network’s structure were identified as the key operating parameters to allow the process to gain interest from a practical point of view

Intensification of biopolymeric microparticles production by ultrasonic assisted atomization

In this work ultrasonic atomization process is applied to produce biopolymer microparticles with potential applications in pharmaceutical and nutraceutical fields. Natural polymer (alginate)/water solution is atomized by ultrasonic assisted process and the droplets spray is reticulated using a solution of copper sulfate, where the Cu2+ ions cause the formation of a network structure (hard porous gel). Several operating parameters (solution concentration, flow rate, atomization power) are changed to study their effects on the produced microparticles. Literature correlations able to predict the features of the droplets as functions of process parameters are optimized using a statistical approach. Furthermore, the energy requirement for the drops production is compared with the energy required by traditional techniques to evaluate the intensification effect of the ultrasonic on the atomization process. doi:10.1016/j.cep.2009.08.00

Pharmaceutical Applications of Biocompatible Polymer Blends ontaining Sodium Alginate

Biocompatible polymer blends, such as alginate blends, have a widespread use in pharmaceutical and medical applications due to their specific features, such as biodegradation, adhesiveness, and thermo- and pH sensitivity and that can be obtained from the mixture composition. In this work, the use of alginate blends was tested in a novel production methodology of therapeutic dosage forms based on polymeric chain reticulation phenomena induced by exposure to bivalent ions. Two kinds of sodium alginate were used to obtain gel films (structured films) in blends with Pluronic F127®. The blends were considered for applications in gel paving of drug-eluting stents. Sodium alginate was also used in shell–core particle production (structured particles) to obtain shell-barrier reducing drug release in the preparative steps (see wash operations). Both structures, films and particles, were obtained using Cu2+ and Ca2+ ions, respectively. Film/shell barrier properties were tested in dissolution experiments using vitamin B12 as an active molecule model. Experimental work demonstrated that the alginate composition is a crucial point in defining reticulated structures