Papers by Keyword: Freeze-Drying

Abstract: The structure and properties of graphene oxide aerogels (GOA), prepared by a modified Hummer’s method followed by a freezing-drying process in addition to a pre-oxidized procedure, were studied through FTIR, Raman, SEM and XDR techniques. FTIR results indicated the existence of -C-O, -C-OH and -C=O function groups on the GOA surface. Therefore, the D band intensity of GOA sample exhibited remarkable increasing in the Raman spectra compared with of graphite; it may be due to change the order-structure of graphite to disorder-structure of GOA. The diffractive peak for the graphite at 2θ of 26.5° vanishes instead the one around 10.0° occurred in the XRD pattern for the GOA supported that the structure and d-spacing changed seriously from graphite to GOA. The SEM images revealed that the micro-structure of graphene layer of GOA was wrinkler and softer than that of graphite, however, the former involved fewer lamellar layer appearance with wrinkles on the edges of the graphene. All the characterized evaluation confirmed that the graphite powder has been transformed into a GOA structure through the modified Hummers’ method.

Abstract: Bacterial cellulose (BC) has applied as a versatile biomaterial in a wide variety of applications, such as biomedical devices, acoustics, electronics, and paper products. The controlling of the procedure could significantly improve the chemical and structure properties of the BC foams. This study aims to compare the features of BC foam that synthesized from BC disintegrated by a high-speed blender (HSB) and high-pressure homogenizer (HPH). The methods are the synthesis of BC using pineapple skin extract, disintegration process using both HSB and HPH following by freeze-drying process and characterization using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and FTIR. The results show that freeze-drying to the pellicle did not produce a foam structure of BC. SEM morphology indicates that the disintegration process using HPH produces a better porous BC foam compared than HBS process. XRD analysis shows three peaks associated with the structure of BC, which are at 14.47°, 16.85°, and 22.69°. The crystalline structure of BC foam produced from HPH process has higher than BC foam produced from HBS process. FTIR analysis shows that there is a new peak find out in BC foam after the disintegration process.

Abstract: Three-dimensional (3D) porous alginate/soy protein isolated (Alg/SPI) tissue engineering scaffolds were achieved by freeze-drying. The physico-chemical attributes of the scaffolds including morphology, chemical structure, mechanical properties and in vitro cytotoxicity were investigated for different SPI blends. Results indicated that increasing SPI content to 40 wt% in the blends resulted in the partial existence of closed pores and reduced pore size. The mechanical values of the scaffolds under compression also reduced with increasing SPI in the blends. The addition of SPI did not significantly enhance the cell viability of the scaffolds investigated for in vitro culture with human fibroblasts, which remained in the high (90 – 100%) range. Results demonstrated that Alg/SPI scaffolds have potential for use as tissue engineering scaffolds.

Abstract: Graphene (GR) aerogels with three-dimensional interconnected network were prepared from freeze drying graphene oxide (GO) dispersions for adsorbing organic reagents. Microstructures of GR aerogels were observed by field-emission scanning electron microscopy, and the components were analyzed by X-ray photoelectron spectroscopy and X-ray diffraction. Their adsorption abilities and recycling performances for organic reagents were investigated in detail. The results showed that the adsorption capacity of GR aerogels was dependent on the concentration of GO dispersion. For example, the adsorption capacity of ethanol increased from 7.04 to 32 g/g when the GO concentration changed from 5 to 10 mg/ml. The GR aerogels also exhibited good adsorption performance for other organic reagents, reaching 44.78, 93.41 and 56.56 g/g for cyclohexane, acetone and methanol, respectively. Moreover, the 7GR had good cyclic adsorption capacity for cyclohexane, acetone and methanol, and the relative standard deviation was 3.7%, 4.3%, 3%, respectively.

Abstract: In this research aerogels were synthesized by homogenization of carbon nanotubes and chitosan under ultrasonic treatment and active magnetic stirring, followed by freeze-drying in order to remove the liquid from its structure. Freeze-drying is characterized by a certain ratio of pressure and temperature at which the solid phase, in our case - the ice, turns into a gas without passing through a liquid phase. Freeze-drying was carried out at a temperature of-5 ° C and a pressure of 30-80 Pa. After freeze-drying which lasted for 20 hours, the as-obtained aerogels were carbonized at temperature of 800 °C in an inert atmosphere. Surface morphology of resulting aerogels was studied using scanning electron microscopy. The hydrophobicity and sorption capacity of these aerogels to organic liquids characterized by different densities were investigated. In addition, composite aerogels with the presence of graphene layers in the structure were obtained and the influence of introduction of graphene on aerogel’s properties was analyzed. It was found that composite aerogels based on graphene and carbon nanotubes with chitosan as a glue matrix are characterized by a better-developed porosity of surface with a smaller pore sizes, and their sorption capacity for organic liquids is also higher compared with the aerogels based on carbon nanotubes.

Abstract: This paper provides a novel route to prepare silica monoliths with hierarchical porous structure via freeze drying. In this method, macroporous silica monoliths were first produced by freeze-drying and calcination. By adjusting the concentration of cetyltrimethylammonium bromide in ethylsilicate, a layer of mesoporous thin film was attached on the macroporous silica monolith. The structural characterization of the hierarchical porous monoliths were studied by field emission scanning electron microscopy, mercury porosimeter and nitrogen adsorption-desorption techniques (BET). It turned out that the pore distribution of the obtained monoliths was ranged from 3.72 nm to 23.21nm and the maximum specific surface area calculated from BET was about 288 m^2/g, which indicated the existence of hierarchical structure in the obtained material.

Abstract: Freeze-dried gelatinization glutinous rice starch (FGGRS) was prepared, characterized and evaluated. The functional properties of native starch and FGGRS were studied, respectively. Scanning electron microscopy (SEM) suggested the structure of FGGRS is looser and more porous, and the surface is rough and scaly. Due to the rapidly cooling process, the movement of starch chains was curded and X-ray diffraction (XRD) showed the peak strength of FGGRS is lower than the original, presented as a diffuse state and indicated that it is a V-type structure. Its particle was determined by mastersizer 2000 particle size analyzer and resulted in particles with a mean size of 11.33μm. Rheological tests confirmed FGGRS is pseudoplastic fluids and demonstrated that it belonged to shear thinning system. FGGRS presented a lower apparent viscosity and performed better freeze-thaw stability. The light transmittance of FGGRS was 27.67%, and presented a better transparency. In addition, due to its formation of new crystal types and its loose microstructure after lyophilization the cold water solubility of FGGRS is excellent.

Abstract: The intelligent instrument for measuring eutectic and co-melting point of freeze-drying material were designed based on resistivity method. Series and parallel joint divide voltage method were designed to increased the measurement rang of impedance. The Relative error of the impedance measuring method was tested. The results show that in the measurement range of 1kΩ~9000kΩ, the relative error of the impedance is less than 8%. Determinant for the eutectic and co-melting point was choosed according to the temperature-impedance curve. Several material were tested, the experiment results show that the instrument can measured the eutectic and co-melting point automatically.

Abstract: A kind of drug releasing 3D porous material was designed and fabricated, which could used for bone repairing. The β-tricalcium phosphate (β-TCP) material were fabricated through the rapid prototyping (RP) combining with the freeze-drying, where the scaffold-mould was fabricated by RP. The material was fabricated with ball-milled slurry which solid content was 40%, the pre-freezing temperature was-10°C, and then the material was freeze-dried under vacuum environment at-30°C without sintering. The test results showed that the material had good structure pores with the mean size of 150μm through controlling the pre-freezing temperature, and the compressive strength of the samples was 0.216Mpa.

Abstract: An investigation was conducted to determine an effective media condition for the growth of fresh and freeze-dried oyster mushroom mycelium. Fresh and freeze-dried mycelium sub-culture on liquid media obtained 0.3022 and 0.5081 maximum specific growth rate respectively. The doubling time for fresh and freeze-dried mycelium was calculated 2.2937 and 1.3642 correspondingly. On solid media, maximum specific growth rate for fresh and freeze-dried mycelium was obtained lower at 0.1636 and 0.3719 respectively. The doubling time for fresh and freeze-dried however, was calculated higher at 4.2368 and 1.8683 correspondingly. Freeze dried mycelium showed good recovery tendency after preservation at low temperature.