Hydrodynamics and mass transfer behavior in multiple draft tube airlift contactors

The draft tube configuration significantly affected the performance of an airlift contactor. The multiple draft tube configuration was demonstrated to give a better gas-liquid mass transfer when compared with a conventional one-draft-tube system. The airlift with a larger number of draft tubes allowed a higher level of bubble entrainment, which rendered a high downcomer gas holdup. This resulted in a higher overall gas holdup in the contactor. Liquid velocity was also enhanced by increasing the number of draft tubes. The ratio between downcomer and riser cross sectional areas, A _d /A _r , had a great effect on the system performance, where a larger A _d /A _r led to a lower downcomer liquid velocity and smaller quantity of gas bubbles being dragged into the downcomer. This resulted in low gas holdup, and consequently, low gas-liquid interfacial mass transfer area, which led to a reduction in the overall volumetric mass transfer coefficient. The presence of salinity in the system drastically reduced the bubble size and subsequently led to an enhancement of gas entrainment within the system. As a result, higher gas holdups and gas-liquid interfacial area were observed, and hence, a higher rate of gas-liquid mass transfer was obtained.     

Formation, physical stability and in vitro antimalarial activity of dihydroartemisinin nanosuspensions obtained by co-grinding method

The purpose of this study was to investigate the formation of drug nanoparticles from binary and ternary mixtures, consisting of dihydroartemisinin (DHA), a poorly water-soluble antimalarial drug, with water-soluble polymer and/or surfactant. Binary mixtures of drug/polyvinyl pyrrolidone K30 (PVP K30), binary mixtures of drug/sodium deoxycholate (NaDC), and ternary mixtures of drug/PVP K30/NaDC were prepared at different weight ratios and then ground by vibrating rod mill to obtain ground mixtures. Nanosuspension was successfully formed after dispersing ternary ground mixtures or DHA/NaDC ground mixtures in water. The ternary ground mixtures did not give superior nanosuspension in terms of particle size reduction and recovery of drug nanoparticles, but they provided more physically stable nanosuspensions than DHA/NaDC ground mixtures. The size of drug nanoparticles was decreased with increasing grinding time and lowering amount of PVP K30 and NaDC. About 95% of drug nanoparticles were found in the nanosuspension from ternary ground mixtures. Zeta potential measurement suggested that stable nanosuspension was attributable to adsorption of NaDC and PVP K30 onto surface of drug particles. Atomic force microscopy and transmission electron microscopy with selected area diffraction indicated that DHA in nanosuspension was existed as nanocrystals. The obtained nanosuspensions had higher in vitro antimalarial acitivity against Plasmodium falciparum than microsuspensions. The results suggest that co-grinding of DHA with PVP K30 and NaDC seems to be a promising method to prepare DHA nanosuspension.     

Resistivity of conductive polymer–coated fabric

Preparation of conductive polymer–coated fabrics was carried out by admicellar polymerization. By this method, a thin layer of conductive polymers (polypyrrole, polyaniline, and polythiophene) was formed on cotton and polyester fabrics by a surfactant template. The effects of monomer concentration, oxidant to monomer ratio, and addition of salt on the resistivity of the resulting fabrics were studied. The results showed that the apparent surface and volume resistivity decreased with an increase in monomer concentration in the range 5–15 mM, but was not strongly dependent on the oxidant to monomer ratio over the range of 1 : 1 to 2 : 1. Addition of 0.5M salt was found to reduce the resistivity significantly. The lowest resistivity obtained was with polypyrrole‐coated fabric, with resistivity around 10⁶ ohm. SEM micrographs of the treated fabric surface showed a filmlike polymer coating, confirming that the fabrics were successfully coated by admicellar polymerization. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2629–2636, 2004     

Self-Cleaning Properties of Silk Fabrics Functionalized with Tio2/Sio2 Composites

Silk fabrics were treated with TiO₂/SiO₂ composites using the pad-dry-cure method. TiO₂/SiO₂ composites were prepared through a low-temperature sol-gel method with five different TiO₂:SiO₂ weight ratio of 100:0, 70:30, 50:50, 30:70, and 0:100. The photocatalytic self-cleaning properties of the TiO₂/SiO₂ composite of samples were assessed by analyzing the degradation of coffee stain under UV irradiation. The presence of anatase crystalline structure in synthesized composites was confirmed using the X-ray diffraction patterns. Fourier transform infrared study confirmed the existence of Si-O-Si and Ti–O–Si bonds in the composites. Surface modifications were confirmed by scanning electron microscopy images. The EDS spectrum of samples showed a well-defined peak for the carbon, oxygen, titanium, and silicon elements, also indicating the existence of TiO₂/SiO₂ on the treated silk fabrics. The samples treated with TiO₂/SiO₂ (70:30) composite showed the highest efficiency in coffee stain removal, followed by samples treated with TiO₂/SiO₂ (50:50). The laundering durability of treated sample showed the strongly interaction between the silk fabrics and the TiO₂/SiO₂ nanoparticles. The physical properties of treated silk fabrics were investigated.     

In vitro synthesis of high molecular weight rubber by Hevea small rubber particles

Hevea brasiliensis is one of few higher plants producing the commercial natural rubber used in many significant applications. The biosynthesis of high molecular weight rubber molecules by the higher plants has not been clarified yet. Here, the in vitro rubber biosynthesis was performed by using enzymatically active small rubber particles (SRP) from Hevea. The mechanism of the in vitro rubber synthesis was investigated by the molecular weight distribution (MWD). The highly purified SRP prepared by gel filtration and centrifugation in the presence of Triton^® X-100 showed the low isopentenyl diphosphate (IPP) incorporation for the chain extension mechanism of pre-existing rubber. The MWD of in vitro rubber elongated from the pre-existing rubber chains in SRP was analyzed for the first time in the case of H. brasiliensis by incubating without the addition of any initiator. The rubber transferase activity of 70% incorporation of the added IPP (w/w) was obtained when farnesyl diphosphate was present as the allylic diphosphate initiator. The in vitro synthesized rubber showed a typical bimodal MWD of high and low molecular weight fractions in GPC analysis, which was similar to that of the in vivo rubber with peaks at around 10⁶ and 10⁵ Da or lower. The reaction time independence and dependence of molecular weight of high and low molecular weight fractions, respectively, indicated that the high molecular weight rubber was synthesized from the chain extension of pre-existing rubber molecules whereas the lower one was from the chain elongation of rubber molecules newly synthesized from the added allylic substrates.     

Effect of hexanal vapour on longan fruit decay,quality and phenolic metabolism during cold storage

The effects of postharvest treatment with hexanal vapour on longan fruit decay, quality, hexanal residue, phenolic compound content, and polyphenoloxidase (PPO) and peroxidase (POD) activities were studied during storage at 5 °C for 30 days. Hexanal exposure for 2 h at 900 μL L^?1 before cold storage reduced the percentage of fruit with decay and was deemed the optimum treatment. Hexanal exposure resulted in a pericarp that was more reddish brown and less intense in colour. Hexanal residue in the pericarp and aril of fumigated fruit was several fold higher than that of nonfumigated fruit, although levels were low at the end of cold storage. Electrolyte leakage of pericarp increased during 5 °C storage and was further increased by hexanal exposure. Hexanal reduced pericarp phenolic content, and increased PPO and POD activities. Overall, use of hexanal vapour reduced postharvest disease of longan fruit but increased the likelihood of pericarp browning.     

Formation,Physical Stability and In Vitro Antimalarial Activity of Dihydroartemisinin Nanosuspensions Obtained by Co-grinding Method

The purpose of this study was to investigate the formation of drug nanoparticles from binary and ternary mixtures, consisting of dihydroartemisinin (DHA), a poorly water-soluble antimalarial drug, with water-soluble polymer and/or surfactant. Binary mixtures of drug/polyvinyl pyrrolidone K30 (PVP K30), binary mixtures of drug/sodium deoxycholate (NaDC), and ternary mixtures of drug/PVP K30/NaDC were prepared at different weight ratios and then ground by vibrating rod mill to obtain ground mixtures. Nanosuspension was successfully formed after dispersing ternary ground mixtures or DHA/NaDC ground mixtures in water. The ternary ground mixtures did not give superior nanosuspension in terms of particle size reduction and recovery of drug nanoparticles, but they provided more physically stable nanosuspensions than DHA/NaDC ground mixtures. The size of drug nanoparticles was decreased with increasing grinding time and lowering amount of PVP K30 and NaDC. About 95% of drug nanoparticles were found in the nanosuspension from ternary ground mixtures. Zeta potential measurement suggested that stable nanosuspension was attributable to adsorption of NaDC and PVP K30 onto surface of drug particles. Atomic force microscopy and transmission electron microscopy with selected area diffraction indicated that DHA in nanosuspension was existed as nanocrystals. The obtained nanosuspensions had higher in vitro antimalarial acitivity against Plasmodium falciparum than microsuspensions. The results suggest that co-grinding of DHA with PVP K30 and NaDC seems to be a promising method to prepare DHA nanosuspension.