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Purpose: To assess the influence of rheological properties of an artificial vitreous (AV) on the performance of double-blade (DB) and single-blade (SB) guillotine vitreous cutters, with 23-, 25-, and 27-gauge (G) probes. Methods: We evaluate the aspiration flow rate, using an optical method, based on image processing. Experiments are conducted using ten viscoelastic vitreous phantoms, with different properties that are measured with rheological tests. Results: Aspiration rate strongly varies with fluid properties. Regardless of cutter geometry and operational conditions, the flow rate significantly decreases as vitreous viscosity and elasticity increase. Conclusions: All tested vitreous probes are very sensitive to changes in fluid rheology. SB cutters produce smaller flow rates compared with DB ones of the same caliber; however, they are less sensitive to fluid properties at low aspiration pressures. The use of vitreous substitutes for test performance guarantees comparability between flow rate results achieved with different vitrectomy systems operating in different media. This outcome is further confirmed by the low values of estimated flow rate relative errors. [ABSTRACT FROM AUTHOR]

Filler formulations are complex systems, characterized by a high number of components with different nature, as resins, extenders, additives. One of the main properties of a two‐component epoxy filler used for yacht application is the rheology. Thus, rheological additives are studied in both components after different times from the production. Rheological analysis produces a very large amount of information so statistical methods are useful to elaborate the data. In this study, a univariate approach (ANOVA) and a multivariate data processing, namely, principal component analysis after low‐level data fusion are carried out. It is shown that the multivariate approach provides the maximum useful information on the system. No differences are highlighted in the rheological behavior for the epoxy component, by using different additives while, for the polyamide component, the best rheological additive among the tested is the one that has a polyamide nature, being a polar system as itself. [ABSTRACT FROM AUTHOR]

In the present work, different sodium alginates were used to prepare nanofibrous mats by means of electrospinning technique. Firstly, a molecular characterization of each sample was carried out: the molecular mass and the composition, i.e. mannuronic/guluronic acid ratio, were determined using the Mark-Houwink-Sakurada relation and FTIR spectroscopy, respectively. Afterwards, the polyelectrolyte nature and the characteristic concentration regimes of each alginate were studied through rheological tests. The results indicated that both the molecular mass and the composition strongly influence the properties of the polymer in solution; in particular, long chains and the predominance of guluronic moiety lead to a marked polyelectrolyte behaviour. Subsequently, in order to obtain a good spinnability, polyethylene oxide and Triton X-100 were added to alginate-based solutions. The resulting solutions were carefully characterized by a rheological point of view; the viscosity, viscoelasticity, thixotropy and thermal stability were investigated and correlated with their capability of being electrospun. Two different set-ups were used for electrospinning: one consisted in a dry collector and the other one in a wet collector (immersed in a collecting solution). The morphology of the membranes was characterized through scanning electron microscopy; moreover, thermogravimetric analysis was performed in order to study the final composition and the thermal degradation. The preliminary results indicated that the membrane obtained using guluronic-rich alginate and the wet-collector system is composed of only sodium alginate and characterized by thin fibres and a high porosity, which could make it suitable for pharmaceutical and biomedical applications. [ABSTRACT FROM AUTHOR]

ABSTRACT: The methodology to create alginate and alginate/hyaluronic acid membranes, which involves wet conditions electrospinning, is presented in this paper. The wet conditions allow simultaneously to work in water solutions avoiding the toxic solvents and to obtain crosslinked alginate. An accurate rheological characterization of all solutions examined is performed. By optimizing the electrospinning parameters, it is possible to obtain alginate membranes with homogeneous nanofibers and a narrow diameter distribution (i.e., around 100 nm) as well as alginate/hyaluronic acid membranes characterized by a network of bimodal distribution of the dimensions, namely nanofibers with a diameter comparable to the ones of the alginate membrane, in which are blocked microfibers with a ribbon like appearance, as observed in the SEM images. In order to facilitate the electrospinning process, poly(ethylene oxide) is added to the solutions and then removed after membranes preparation, as demonstrated by the differential scanning calorimetry results, obtaining membranes made up only biopolymers. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46390. [ABSTRACT FROM AUTHOR]

A new approach for obtaining a controlled gelling process of sodium alginate, based on the use of bivalent ions rich alginate microbeads added as crosslinkers, is presented. Normally, calcium ions are used in the gelation of alginate solutions. In this article, alginate microspheres, obtained by electrospray, and enriched with different bivalent ions (Ca2+, Ba2+, and Mg2+) are described. Because of the solvent/non-solvent system, it is possible to use also Mg2+ as a crosslinker for alginate, despite the fact that it had long been regarded as a nongelling bivalent ion. The morphology and the ions content of the microspheres are evaluated. Gels are characterized according to type and amount of the ions added to the alginate solution, using rheological measurements to assess the variation in the storage modulus ( G′) and loss modulus ( G″). The gel point is then detected using magnesium ions. The new approach guarantees a working system that could be easily applied in different fields. POLYM. ENG. SCI., 57:531-536, 2017. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The molecular mass of two sodium alginates with the same composition but different chain length is reduced via a simple ultrasonic treatment and monitored by rheological measurements. The polymer molecular mass decreases until a lower limiting value of 100 kg/mol is reached, with the degradation occurring via a mid-point-chain kinetic consisting into the breakage of the glycosidic bonds towards the middle of the macromolecules. The evaluation of the concentration regimes (i.e. viscosity dependence upon the polymer concentration) demonstrates that short chains are characterized by higher critical concentrations and lower scaling factors, most likely owing to their poor ability to form entanglements. Nevertheless, the typical behaviour of neutral polymer in θ solvent is observed independently of the alginate molecular mass. The viscosity temperature dependence of the investigated solutions obeys Arrhenius law in a wide temperature range. Additionally, the flow activation energy is observed to follow a linear relationship with the polymer molecular mass with values of 26.2 kJ/mol for the longest chains and 18.2 kJ/mol for the shortest ones. Consequently, ultrasonic treatment is here proved to be extremely efficient to reduce the molecular mass of alginate, thus representing a fast, safe and cost-effective approach to obtain materials with tailored properties. Image 1 • Two sodium alginates were degraded via ultrasonic treatments. • Rheological measurements were used as easy tool to follow the degradation kinetic. • Alginate molecular mass decreased with the ultrasonic treatment time. • Chain breakage occurred via a mid-point chain model. • Flow activation energy was linearly related to the polymer molecular mass. [ABSTRACT FROM AUTHOR]

• Electrospinning of alginate-based formulations containing zinc oxide nanoparticles. • "Green" synthesis of ZnO nanoparticles to maintain a high biocompatibility. • Rheological investigations to select the most suitable systems to be electrospun. • Study of the electrostatic interactions between ZnO nanoparticles and alginate chains. • Development of an innovative washing-crosslinking process to obtain stable products. In the present work alginate-based nanofibrous membranes embedding zinc oxide nanoparticles (ZnO-NPs) were prepared via electrospinning technique. ZnO-NPs were synthesized by means of a "green" sol-gel method by using alginate itself as stabilizing agent and characterized through UV–vis spectroscopy, thermogravimetric and morphological analysis. Formulations containing sodium alginate, poly(ethylene oxide) and ZnO-NPs were rheologically studied to identify the most suitable ones to be electrospun; alginate molecular structure played an important role on the solution spinnability due to the polysaccharide capability to establish electrostatic interactions and hydrogen bonds with ZnO-NPs. An innovative washing-crosslinking protocol was developed to obtain stable products which composition was assessed using Fourier Transform InfraRed spectroscopy and thermogravimetric analysis. Morphological investigation combined with EDX spectroscopy proved the obtained mats were highly porous and composed by thin homogenous nanofibers with a good distribution of the used nanofillers, thus representing potential products for several purposes (e.g. biomedical, pharmaceutical and environmental applications). [ABSTRACT FROM AUTHOR]

Highlights • Hyaluronic acid used as injectable fillers containing nanoparticles or biomolecules. • Combination of Dynamic Light Scattering and traditional rotational rheometry. • Hydrodynamic radius and conformation of a polyelectrolyte in a saline environment. • Accessible frequency range significantly extended. • Parameters of the network created by the chain entanglements. Abstract Hyaluronic acid (HA) solutions represent an important class of biomedical products, mostly used as viscosupplements in orthopaedics and as fillers in the cosmetic industry. The focus of the present work is the hydrodynamic, micro-rheological and rheological characterization of HA in physiological saline. Standard viscoelastic characterization techniques were coupled with micro-rheological measurements, i.e. by measuring the passive motions of particles embedded in the samples via Dynamic Light Scattering (DLS), effectively extending the accessible frequency range typical of standard rheometers. The influence of molecular weight and polymer concentration on the storage modulus (G'), loss modulus (G") and complex viscosity (η*) of HA saline solutions was investigated. A brief comparison with theoretical models was made showing such concentrated solutions to be of a semi-flexible nature. In addition, the entanglement concentration ν, the critical molecular weight M ¯ c , and the mesh size ξ of the physical network created by the entangled polymer chains were calculated. [ABSTRACT FROM AUTHOR]

Alginate is a seaweed derivative used as thickener in the food and biomedical industries. It is mainly known for its gelling ability with divalent cations and can exist as salt of the alginic acid with different monovalent cations. In this study, a multifunctional approach was used to evaluate the influence of different types of alginate salts on the microstructural properties of a water-based architectural coating. A basic formulation containing cellulose as thickener was considered as benchmark; three different salts of alginic acid, specifically sodium, potassium and ammonium, were investigated as alternative thickeners. The performance of alginate and the role of the counterion were evaluated through rheological, application and tensile tests. Strain sweep test was used to evaluate the paints viscoelastic nature; in particular, it is useful to investigate the storage stability. The evaluation of viscosity curves and Three Interval Thixotropy Test, 3ITT, predicted the application phase and the possible occurrence of surface defects. In addition, the coatings behavior was practically verified through the analysis of the brush application process on gypsum boards. Tensile properties of dried films were measured as well to evaluate the counterion effect in the solid state. The results showed that alginate counterions slightly influence the properties of the formulations during the storage. On the other hand, a greater influence is evidenced from 3ITT results, which foresee their application. Finally, the dried samples showed different tensile properties mainly depending on the concentration of the alginates rather than their type. [Display omitted] • Alginate salts in architectural coating • The counterion affects the homogeneity of the samples. • Rheology to evaluate interactions and viscoelastic properties • Tensile test to evaluate influence of the counterion [ABSTRACT FROM AUTHOR]

• Sodium alginate can be used as thickener in water paint formulations. • Sodium alginate interacts with water molecules and calcium carbonate filler. • Average molecular mass and concentration must be tuned to obtain a good product. Non-ionic polysaccharides, mainly cellulose ethers, have been extensively studied as thickeners in paint formulation. Their mechanism of interaction with the surrounding system is well known and, due to their easy dissolution properties and availability on the market, they are the most used thickening agents. On the other hand, ionic polysaccharides, having possible interaction with the components of the formulation, are less used. In this work, the role of an anionic polysaccharide, sodium alginate (SA), as a thickener, was investigated in a typical wall paint formulation by evaluating its interaction with the principal components of the formulation: water, binder, pigment and extender. Rheology and FTIR spectroscopy were used to evaluate the occurrence of chemical bonds between the polysaccharide chains and the surrounding system. Contemplating the results, sodium alginate, depending on its molecular weight, M ¯ w , and concentration, turns out to be a suitable thickener for wall paint formulations. In particular, the possibility of building-up a network due to the presence of entanglements, and the interaction with water molecules and extender, demonstrated that the formulation prepared with 0.2 wt. % of a medium M ¯ w alginate was the most promising one. On the other hand, low M ¯ w alginate exhibited a weaker gel structure and only if present at 0.4 wt. % was appropriate concentration for a ready-to-use product. [ABSTRACT FROM AUTHOR]

• Chitosan electrospun membranes were obtained using a low amount of acetic acid. • The effect of polymer concentration on fibre morphology was established. • The best coagulation medium for chitosan was found to have a slightly basic pH. • Chitosan was successfully crosslinked via phosphate ions. • The obtained membranes represent a promising class of biomedical products. Chitosan-based membranes were prepared via electrospinning technique using a low concentrated acetic acid solution as solvent and poly(ethylene oxide) as co-spinning agent. Different solutions were rheologically characterized and increasing the solution viscosity was found to correspond to a better-defined morphology. The membranes were first subjected to a coagulation process with different baths in order to stabilize chitosan and the mats were found not able to withstand a strongly basic environment. Subsequently, a physical and a chemical crosslinking approach were separately optimized to obtain stable mats whose composition was assessed via thermogravimetric and spectroscopic techniques, proving in both cases the elimination of the co-spinning agent. Above all, the ionically crosslinked mats represent a class of extremely promising biomedical products being probably highly biocompatible and characterized by thin and homogenous nanofibers with a diameter of 200 nm, thus showing the ideal structure to foster cell viability. [ABSTRACT FROM AUTHOR]

• Raw agars have a different amount of anhydro units, responsible for gel strength. • The greater the amount of anhydro units, the greater the mechanical performances. • The strength of agar gels increases with increasing the polymer concentration. • The annealing process promotes the formation of additional crosslinking points. • Addition of the chelating agent leads to an enhancement of the gel stiffness. Agar is a natural polymer commonly used in various fields of application ranging from cosmetics to the food industry. In particular, for over forty years agar gels have been used in the field of conservation of Cultural Heritage where they are considered as one of the main well-performing tools in cleaning procedures. In the present work, the relation between the chemical composition and the mechanical strength of four different agar hydrogels was evaluated by comparing the results obtained via pyrolysis-gas chromatography/mass spectrometry and rheological characterization. Agar composition was studied by means of a pyrolysis-gas chromatography/mass spectrometry approach in order to differentiate the anhydrous, galactose and glucose units. Pristine agar gels, gels after double annealing, and gels with and without chelating agent were studied by means of amplitude, frequency and time sweep rheological tests to evaluate all the preparation approaches commonly used by conservators, also taking into account changes in the transparency via UV–vis spectroscopy. A high percentage of anhydrous units in the polymer backbone was found to provide superior mechanical stiffness to the pristine hydrogels, even if it did not seem to affect their long-term stability. The annealing process significantly improved the rheological response of galactose-rich agar hydrogels being able to promote the establishment of additional crosslinking points, whereas the additive presence showed to improve the hydrogel stiffness owing to a more structured polymer network. Moreover, the progressive reduction of the impurities and/or network defects within the hydrogels occurring due to the annealing process slightly increased the transparency of the hydrogels, which is an important aspect for applications in the conservation of Cultural Heritage. [ABSTRACT FROM AUTHOR]