In situ preparation of silver nanocomposites on cellulosic fibers--microwave vs. conventional heating.

A green approach for the preparation of silver nanocomposites on viscose fibers using microwave and conventional heating is presented. Reduction of silver nitrate is induced by addition of 6-O chitosan sulfate (S-Chi) in aqueous media which provides steric protection and electrostatic stabilization to prevent agglomeration of the nanoparticles. The particles are formed in close spatial proximity to the fibers and adsorption of the particles via structural similarity takes place to create silver nanocomposites. All nanocomposites have been subjected to antimicrobial tests and high antimicrobial activity toward Escherichia coli bacteria has been determined. Further, the nanocomposites are characterized using different analytical techniques which reveal very similar results for both heating techniques. The only significant difference is observed concerning the shape of the nanoparticles on the viscose fibers which are slightly elongated for the microwave method in comparison to spheres observed by conventional heating. Therefore, detailed investigations on the formation of colloidal silver nanoparticles have been performed, comparing microwave dielectric and conventional heating at the exact same temperature and reaction times. These experiments resulted in nearly identical nanoparticle shape and size for both heating methods as demonstrated by dynamic light scattering, UV-vis spectroscopy and transmission electron microscopy. A wide range of parameters has been varied (temperature, AgNO3 to S-Chi ratio, reaction time, and stirring speed) to study the nanoparticle formation under microwave and conventional conditions. No evidence for the existence of so-called specific microwave effects was obtained.

Design of simultaneous antimicrobial and anticoagulant surfaces based on nanoparticles and polysaccharides.

The rational design of silver nanoparticles encapsulated in an anticoagulant, hemocompatible polysaccharide, 6-O-chitosan sulfate, is presented. Three different approaches are described for the immobilization of these core shell particles on cellulosic surfaces. The mass of the immobilized particles is quantified using a quartz crystal microbalance with dissipation (QCM-D). The antimicrobial activity of the surfaces towards E. coli MG 1655 [R1-16] is investigated by live/dead assays using fluorescence staining. All surfaces treated with the designed nanoparticles exhibit excellent antimicrobial activity towards E. coli MG 1655 [R1-16]. Anticoagulant properties of blood plasma on the nanoparticle treated surfaces have been determined using QCM-D. In comparison with the unmodified substrates, the total coagulation time as well as the thrombin formation time and fibrin clotting time of surfaces modified with nanoparticles are significantly increased.

Archaeal production of polyhydroxyalkanoate (PHA) co- and terpolyesters from biodiesel industry-derived by-products.

The archaeon Haloferax mediterranei was selected for production of PHA co- and terpolyesters using inexpensive crude glycerol phase (CGP) from biodiesel production as carbon source. CGP was assessed by comparison with the application of pure glycerol. Applying pure glycerol, a copolyester with a molar fraction of 3-hydroxybutyrate (3HB) of 0.90 mol/mol and 3-hydroxyvalerate (3HV) of 0.10 mol/mol, was produced at a volumetric productivity of 0.12 g/Lh and an intracellular PHA content of 75.4 wt.-% in the sum of biomass protein plus PHA. Application of CGP resulted in the same polyester composition and volumetric productivity, indicating the feasibility of applying CGP as feedstock. Analysis of molar mass distribution revealed a weight average molar mass M w of 150 kDa and polydispersity P i of 2.1 for pure glycerol and 253 kDa and 2.7 for CGP, respectively; melting temperatures ranged between 130 and 140°C in both setups. Supplying γ -butyrolactone as 4-hydroxybutyrate (4HB) precursor resulted in a poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate-co-4-hydroxybutyrate] (PHBHV4HB) terpolyester containing 3HV (0.12 mol/mol) and 4HB (0.05 mol/mol) in the poly[(R)-3-hydroxybutyrate] (PHB) matrix; in addition, this process runs without sterilization of the bioreactor. The terpolyester displayed reduced melting (melting endotherms at 122 and 137°C) and glass transition temperature (2.5°C), increased molar mass (391 kDa), and a polydispersity similar to the copolyesters.