Influence of electrospinning parameters on poly(hydroxybutyrate) electrospun membranes fiber size and distribution

Poly(hydroxybutyrate) (PHB) obtained from sugar cane waste was dissolved in a blend of chloroform and dimethylformamide (DMF) and electrospun at 40°C. By adding DMF to the solution, the electrospinning process for the PHB polymer becomes more stable, allowing complete polymer crystallization during the jet travelling between the tip and the grounded collector. The influence of processing parameters on fiber size and distribution was systematically studied. It was observed that an increase of tip inner diameter promotes a decrease of the fiber average size and a broader distribution. Conversely, an increase of the electric field and flow rate produces an increase of fiber diameter until a maximum of ～2.0 µm but for electric fields higher than 1.5 kV cm^?1, a decrease of the fiber diameter was observed. Polymer crystalline phase seems to be independent of the processing conditions and a crystallinity degree of 53% was found. Moreover, thermal degradation of the as‐spun membrane occurs in single step degradation with activation energy of 91 kJ mol^?1. Furthermore, MC‐3T3‐E1 cell adhesion was not inhibited by the fiber mats preparation, indicating their potential use for biomedical applications. POLYM. ENG. SCI., 54:1608–1617, 2014. © 2013 Society of Plastics Engineers     

Successive centrifugal grinding and sieving of wheat straw

Grinding plant biomass may allow the lignocellulosic assembly to become more reactive/accessible by providing energy for polymer dissociation, increasing contact surface (particle size reduction) and reducing cellulose crystallinity. Moreover lignocellulosic composition varies considerably affecting biomass processability as resource for bio-based energies, composite materials and chemicals. The aims of this work were: (i) to analyse composition of wheat anatomic parts present into wheat straw, (ii) to characterize the behaviour of major components upon successive centrifugal grinding steps (2 mm-screen cutting milling followed by 4-step centrifugal grinding) and (iii) to relate particle size distribution and component concentrations into the finest sized product (0.12 mm-screen ground). The powders from successive centrifugal grindings were sieved and their chemical compositions were determined. Ground straw powders were heterogeneous according to different particle aspects: size, shapes and roughness. In general fractions with lower particle size had higher ash and protein contents whereas cellulose contents are higher in the larger fractions. Wheat straw exhibited a non homogeneous reduction behaviour when finely ground. Fraction compositions were only slightly distinct suggesting that although sieving can constitute a preliminary fractionation step, it is necessary to reduce still more the particle size to reach more effective dissociation of macromolecules assembly.     

Enhancing flame retardancy and optical functionality in multifunctional devices through advanced design of phosphorus-containing copoly(imide-oxadiazole)s

The combination of flame retardance and optical functionality in phosphorus-containing copoly(imide-oxadiazole)s offers a remarkable opportunity for the development of advanced and multifunctional devices, including organic light-emitting diodes, sensors, and photovoltaics. In this context, a series of phosphorus-containing copoly(imide-oxadiazole)s were synthesized through a polycondensation reaction. This involved an aromatic commercial dianhydride, 4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride), a diamine with phosphorus in the main and side chains, and various aromatic diamines with 1,3,4-oxadiazole rings. To achieve this, a solution imidization method was employed, which effectively converted the poly(amic acid) intermediates into the corresponding polyimides with high efficiency. The chemical structure and thermal properties of the resulting polymers were investigated. All polymers exhibited high thermal stability. Moreover, the absorption bands observed in dichloromethane, N,N-dimethylformamide, methanol, and N-methyl-2-pyrrolidone exhibited weak intensities, appearing as shoulders, with maximum values around 270, 303, and 310 nm. In most solvents, the photoluminescence spectra of the polymers showed a single emission band. However, one of the polymers exhibited two emission bands due to pendant groups that disrupted the molecular structure. The fluorescence of these derivatives was influenced by the polarity and proticity of the solvents. Furthermore, they exhibited large Stokes shifts, indicating extended conjugation and the potential to maximize luminescence efficiency. Protonation and deprotonation of polyimides alter their optical properties. These findings provide insights for the design of materials with improved optical performance.     

Kinetic Properties and Enantioselectivity of The Lipases Produced by Four Aspergillus Species

Four high lipase-producing Aspergillus species, selected in our laboratory, were compared in terms of their stability and reactivity for enantioselective esterification between (R, S)-2-octanol with octanoic acid in n-hexane. We determined the pH and temperature reactions dependences of lipases activities, and we found that these enzymes exhibited various pH sensitivities. The optimum pH observed for Aspergillus terreus lipase was 5.5, for A. niger and A. oryzae lipases in the range of 6.0 to 6.5 and pH 7.0 for A. flavus lipase. Good stability was observed at pH ranging from 5.0 to 8.5 after 24 hours at 40° C, and the optimum activity was observed at 35–40° C for all lipases tested. The lipases from A. terreus and A. niger were highly thermostable, retaining 60% and 50% activity at 60° C after 1 hour, respectively. The lipases from A. niger and A. terreus lipases provided the best results in terms of enantioselectivity (E) in the esterification of (R, S)-2-octanol with octanoic acid in n-hexane (E = 4.9 and E = 4.5, respectively). These properties make these lipases good candidates for biocatalysis in organic media.