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Solid state stability of polyphenols from a plant extract after fluid bed atmospheric spray-freeze-drying

Solid state stability of polyphenols from a plant extract after fluid bed atmospheric spray-freeze-drying

Cristiane Cardoso Correia Teixeira, Tatiana Pereira de Freitas Cabral, Luciana, Alves Tacon, Isabel Lemos Villardi, Aurea Donizete Lanchote, Luis Alexandre Pedro deFreitas

Abstract

Dry powder extracts are the most suitable pharmaceutical forms of phytomedicines due to their greater physical and chemical stability in the solid state, in addition to the possibility of easy preparation of tablets and capsules. Recently, Baccharis dracunculifolia D.C. crops have been stimulated in Brazil to obtain the green propolis, which is derived from pollen harvesting of Baccharis by the Apis mellifera, and develop new phytomedicines from this plant. The aim of this work was to obtain stable powdered Baccharis dracunculifolia leaf extracts dried by fluidized-bed atmospheric spray-freeze-drying and study the stability of its chemical markers in the solid state. The drying was performed using D-mannitol, modified corn starch and their mixture as adjuvants. Physical characterization was performed by determining the dried extract powder size, morphology, flow and packing. Their chemical stability was evaluated by high performance liquid chromatography quantification of p-coumaric acid, cinnamic acid, artepillin C and baccharin. The antioxidant activity of the dried extract was determined using the stable free radical 2,2-diphenylpicrylhydrazil. The results showed that the four prenylated compounds are sensitive to drying at freezing temperatures, but D-mannitol could efficiently prevent their loss. The Baccharis spray-freeze-dried extracts showed a high yield, low moisture and excellent pharmacotechnical properties. The stability tests demonstrated a high loss of polyphenols at 40, 60 and 80 °C, especially artepillin C (the main marker) and showed high instability. The kinetics of polyphenols losses were measured, and their rates were used to fit three-dimensional diffusion models and the Arrhenius equation. The results demonstrate that the Baccharis dracunculifolia dried extract, using artepillin C as a reference, could achieve a shelf life as long as 10 years when stored at 4 °C and protected from light. The process of fluid-bed atmospheric spray-freeze-drying was shown to be an attractive alternative for drying of heat-sensitive and high value-added materials such as medicinal plant extracts.

Keywords

Polyphenols, Baccharis dracunculifolia, Fluid bed, Spray-freeze-drying, Degradation

Synthesis of high-performance Li2FeSiO4/C composite powder by spray-freezing/freeze-drying a solution with two carbon sources

Synthesis of high-performance Li2FeSiO4/C composite powder by spray-freezing/freeze-drying a solution with two carbon sources

Yukiko Fujita, Hiroaki Iwase, Kenji Shida, Jinsun Liao, Takehisa Fukui, Motohide Matsuda

Abstract

Li2FeSiO4 is a promising cathode active material for lithium-ion batteries due to its high theoretical capacity. Spray-freezing/freeze-drying, a practical process reported for the synthesis of various ceramic powders, is applied to the synthesis of Li2FeSiO4/C composite powders and high-performance Li2FeSiO4/C composite powders are successfully synthesized by using starting solutions containing both Indian ink and glucose as carbon sources followed by heating. The synthesized composite powders have a unique structure, composed of Li2FeSiO4 nanoparticles coated with a thin carbon layer formed by the carbonization of glucose and carbon nanoparticles from Indian ink. The carbon layer enhances the electrochemical reactivity of the Li2FeSiO4, and the carbon nanoparticles play a role in the formation of electron-conducting paths in the cathode. The composite powders deliver an initial discharge capacity of 195 and 137 mAh g−1 at 0.1 C and 1 C, respectively, without further addition of conductive additive. The discharge capacity at 1 C is 72 mAh g−1 after the 100th cycle, corresponding to approximately 75% of the capacity at the 2nd cycle.

Keywords

Lithium-ion battery, Cathode material, Li2FeSiO4/C, Spray-freezing/freeze-drying, Nanoparticle, Composite powder

ECerS2017 Fourth Day

Fourth day at the 15th Conference & Exhibition of the European Ceramic Society (ECerS2017), 13th of July, 2017. Discussions on the applications of Freeze Granulation on the processing of high performance ceramics.

ECerS2017 Fourth day

ECerS2017 Third day

ECerS2017 Third day

Third day at ECerS2017 in Budapest with good meetings on how to apply Freeze Granulation for new challenges within processing of Ceramic powders, like diamonds and graphene, and also powder micro encapsulation.

ECerS2017 Third day

Anisotropy of functional properties of SiC composites with GNPs, GO and in-situ formed graphene

Anisotropy of functional properties of SiC composites with GNPs, GO and in-situ formed graphene

Ondrej Hanzel, Richard Sedlák, Jaroslav Sedláček, Valéria Bizovská, Roman Bystrický, Vladimír Girman, Alexandra Kovalčíková, Ján Dusza, Pavol Šajgalík

Abstract

This paper reports on anisotropy of functional properties of different silicon carbide-graphene composites due to preferential orientation of graphene layers during sintering. Dense silicon carbide/graphene nanoplatelets (SiC/GNPs) and silicon carbide/graphene oxide (SiC/GO) composites were sintered in the presence of yttria (Y2O3) and alumina (Al2O3) sintering additives at 1800 °C in vacuum by the rapid hot pressing (RHP) technique. It is found that electrical conductivity of SiC/GNPs and SiC/GO composites increases significantly in the perpendicular direction to the RHP pressing axis, reached up to 1775 S/m in the case of SiC/GO (for 3.15 wt.% of rGO). Also, thermal diffusivity was found to increase slightly by the addition of GNPs in the SiC/GNPs composites in the perpendicular direction to the RHP pressing axis. But, in the parallel direction, the addition of GNPs showed a negative effect. The formation of graphene domains was observed in reference sample SiC-Y2O3-Al2O3 sintered by RHP, without any addition of graphene. Their presence was confirmed indirectly by increasing electrical conductivity about three orders of magnitude in comparison to the reference sample sintered by conventional hot press (HP). Raman, SEM and TEM analysis were used for direct evidence of presence of graphene domains in RHP reference sample.

Keywords

Graphene nanoplatelets; Graphene oxide; Silicon carbide; Functional properties; Anisotropy

Mechanical and tribological properties of alumina-MWCNTs composites sintered by rapid hot-pressing

Mechanical and tribological properties of alumina-MWCNTs composites sintered by rapid hot-pressing

Ondrej Hanzel, František Lofaj, Jaroslav Sedláček, Margita Kabátová, Monika Tatarková, Pavol Šajgalík

Abstract

Alumina – MWCNTs composites were prepared using a novel approach. This process comprises functionalization of MWCNTs and stabilization of alumina-MWCNTs dispersion with subsequent freezing, which resulted in formation of granulated powders with homogeneous distribution of MWCNTs. The granulated powders were sintered by rapid hot pressing (RHP) at 1550 °C. Relative densities, microstructural analysis, tribological properties, fracture toughness and bending strength of prepared composites were investigated to reveal the effect of MWCNTs. Compared to pure alumina, bending strength and fracture toughness of dense alumina-5 vol.% MWCNTs composites decreased about 37% and 18%, respectively. At higher MWCNT contents, strength remained almost constant and fracture toughness slightly increased. Thus, the positive effect of CNTs on fracture toughness was demonstrated despite their counteracting effect on the refinement of the microstructure.

Keywords

Al2O3 – MWCNT composites; Rapid hot pressing; Tribological properties; Mechanical properties

Machinability analysis of multi walled carbon nanotubes filled alumina composites in wire electrical discharge machining process

Machinability analysis of multi walled carbon nanotubes filled alumina composites in wire electrical discharge machining process

Meinam Annebushan Singh, Deba Kumar Sarma, Ondrej Hanzel, Jaroslav Sedláček, Pavol Šajgalík

Abstract

The approach of machining ceramics with electrical discharge machining process is a great challenge till date due to its low electrical conductivity. Machining is made possible by reinforcing with a conductive phase which increases the overall electrical conductivity. Present work focuses on machining of multi walled carbon nanotubes filled alumina composites. Samples with concentrations ranging from 2.5 to 12.5 vol.% are considered for machining. At lower concentration of 2.5 vol.%, effective machining is not possible. Wire lag phenomena is observed during machining at 5 vol.% sample concentration. Proper machinability is observed with concentration of 7.5 vol.% or more. Also, long micro-cracks are obtained during machining that leads to the workpiece breakage. Spalling effect is observed as the most dominating material removal mechanism. A comparison between alumina composites and conducting metallic alloys were carried out for surface characteristics.

Keywords

Alumina; MWCNT; Wire EDM; MRR; Ra

Microstructure of plasma sprayed Al2O3-3wt% TiO2 coating using freeze granulated powder

Microstructure of plasma sprayed Al2O3-3wt% TiO2 coating using freeze granulated powder

Yiming Yao, Ola Lyckfeldt, Aurélien Tricoire, Dennis Lundström, Uta Klement

Abstract

This study is aiming at controlling the microstructure of plasma sprayed Al2O3-TiO2 composite coatings using freeze granulated powders. As sprayed and sintered Al2O3 + 3wt% TiO2 powders were air plasma sprayed with industry process parameters and compared with a commercial powder. The resulting coatings were investigated with respect to powder flowability, porosity and microstructure of the granules. The results showed that microstructure and melting fraction in the coatings could be tailored with the freeze granulation process and heat treatment conditions.

Keywords

Al2O3-TiO2, Freeze Granulation, Plasma Spray, Microstructure