Filament stretchability of biopolymer fluids and controlling factors

Filament stretchability of biopolymer fluids composed of casein and waxy maize starch has been investigated as a function of fluid properties (viscosity and viscoelasticity) and stretching speed. The stretching of a filament was conducted at a controlled speed using a Texture Analyzer and was monitored using a high speed camera. The maximum stretchable length, L_max, was used to quantify the stretchability of a filament. Influences of various contributing factors were analyzed using dimensionless numbers (Ohnesorge number Oh, Weber number We, and capillary number Ca). It was found that, for fluids that are dominantly viscous, the capillary number could be the dominant factor determining filament stretching, demonstrated by the master curve of the maximum stretchable length against the capillary number. However, for increasingly viscoelastic fluids, the stretching behaviour showed significant deviation from the master curve, suggesting that viscoelasticity could be another pronounced factor influencing the stretching of such biopolymer fluids.     

Anomalous Viscosity Behavior in Aqueous Solutions of Hyaluronic Acid

Summary Effects of steady shear flows on intermolecular interactions in dilute and semidilute aqueous solutions of hyaluronic acid (HA) are reported. Pronounced shear thinning behavior is observed for solutions of HA at high shear rates, and no hysteresis effects are detected upon the subsequent return to low shear rates. With the aid of the asymmetric flow field-flow fractionation (AFFFF) technique, it is shown that mechanical degradation of the polymer does not take place in these shear viscosity experiments, even at high shear rates. The low shear rate viscosity of a semidilute HA solution decreases by approximately 40% when the temperature is increased from 10 °C to 45 °C. It is shown that when a dilute HA solution is exposed to a low fixed shear rate (0.001 s^-1), a marked viscosification occurs in the course of time and prominent intermolecular complexes are formed. It is argued that shear-induced alignment and stretching of polymer chains promote the evolution of hydrogen-bonded structures, where cooperative zipping of stretched chains generates a network. At a higher constant shear rate (0.1 s^-1), the viscosity decreases as time goes because of the alignment of the polymer chains, but the higher shear flow perturbation prevents the chains in dilute solutions from building up association complexes. The viscosity of an entangled HA solution is not changed in the considered time window at this shear rate, but the network structures breakdown at the highest shear rate (1000 s^-1), and then they are restored upon return to a low shear rate.     

Preparation of PLLA/PDLA stereocomplexes using a novel initiator based on Mg(II) and Ti(IV) alkoxides

Herein we describe the obtention of polylactide stereocomplexes using a novel initiator system comprising Mg(II) and Ti(IV) centers. The stereocomplexes were successfully prepared using two different routes: by PDLA and PLLA co‐precipitation from chloroform solutions and two‐step diblock copolymerization. For the PDLA/PLLA mixing procedure, individual homochiral polymers were prepared in solution at different monomer/initiator ratios; whereas, the PLA stereoblock was prepared employing one‐pot sequential polymerization of both chiral monomers. The products analyzed by WAXD showed the characteristic stereocrystal reflections while the high melting temperatures found in the DSC runs confirmed the formation of PLA stereocomplexes in both cases. Surprisingly, one of the stereocomplexes showed a second endothermic event at 250.1°C and to our knowledge this is the highest melting temperature reported for PLA stereocomplexes till date. These results point to the discovery of an effective initiator based on low toxicity metals for the preparation of biodegradable materials with interesting thermal properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40771.     

Smart porous microparticles based on gelatin/sodium alginate polyelectrolyte complex

Porous microparticles of different sizes were prepared by polyelectrolyte complexation of biopolymers gelatine A and sodium alginate for microencapsulation of food bioactives. The optimum pH and ratio between the polymers sodium alginate and gelatine for maximum complexation was found as 3.7 and 1:3.5 respectively. Effect of various factors like amount of surfactant, concentration of polymer and crosslinker on the formation, size and porous/nonporous nature of the microparticles were investigated. The particles’ diameter on swelling at pH = 7.4 was twice that at pH = 1.2 indicating the pH responsiveness. These microparticles were used as carrier for ascorbic acid. The surface morphology and sizes of the microparticles were investigated by scanning electron microscope (SEM). Fourier transform infrared spectroscopy (FTIR) study indicated the formation of polyelectrolyte complex between gelatine and sodium alginate and successful encapsulation of ascorbic acid into the microparticles. The microparticles were further characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) study.