Thermal and mechanical behavior of thermoplastic composites reinforced with fibers enzymatically extracted from Ampelodesmos mauritanicus

This work investigates the morphology, the thermal, and mechanical properties of technical fibers extracted from the Ampelodesmos mauritanicus (Diss) grass using a process that combines mechanical, mild chemical, and enzymatic steps. The structure and the thermal stability of Diss fibers make them suitable as a reinforcing filler in polymer composites, which was assessed by manufacturing biocomposites with improved stiffness and a tensile strength not degraded by Diss fibers when compared to those of a commodity polymer and a biodegradable one, namely polypropylene and poly(lactic acid). This work confirms that enzyme mixtures obtained from commercially available products of relatively low cost can represent a simple and environmentally friendly means to extract less common natural fibers. POLYM. ENG. SCI., 59:2418–2428, 2019. © 2019 Society of Plastics Engineers     

Development and performance analysis of PCL/silica nanocomposites for bone regeneration

In the present article, several developments of biocomposites containing silica nanoparticles intended for bone regeneration are reported. Nanocomposites of poly(ε-caprolactone) (PCL) and silica, in which either the silica nanoparticles or the PCL have been modified in order to improve interfacial adhesion through chemical graft between the phases are hereafter described. The composites are characterized with respect to their chemical–physical and mechanical properties. Their biocompatibility and capacity to induce the osteoblastic phenotype in human bone marrow mesenchymal stem cells have been assessed.     

Image processing and fractal box counting: user-assisted method for multi-scale porous scaffold characterization

Image analysis has gained new effort in the scientific community due to the chance of investigating morphological properties of three dimensional structures starting from their bi-dimensional gray-scale representation. Such ability makes it particularly interesting for tissue engineering (TE) purposes. Indeed, the capability of obtaining and interpreting images of tissue scaffolds, extracting morphological and structural information, is essential to the characterization and design of engineered porous systems. In this work, the traditional image analysis approach has been coupled with a probabilistic based percolation method to outline a general procedure for analysing tissue scaffold SEM micrographs. To this aim a case study constituted by PCL multi-scaled porous scaffolds was adopted. Moreover, the resulting data were compared with the outputs of conventionally used techniques, such as mercury intrusion porosimetry. Results indicate that image processing methods well fit the porosity features of PCL scaffolds, overcoming the limits of the more invasive porosimetry techniques. Also the cut off resolution of such IP methods was discussed. Moreover, the fractal dimension of percolating clusters, within the pore populations, was addressed as a good indication of the interconnection degree of PCL bi-modal scaffolds. Such findings represent (i) the bases for a novel approach complementary to the conventional experimental procedure used for the morphological analysis of TE scaffolds, in particular offering a valid method for the analysis of soft materials (i.e., gels); also (ii) providing a new perspective for further studies integrating to the structural and morphological data, fluid-dynamics and transport properties modelling.     

An experimental study on the conditions of safe oxidation of toluene with oxygen—carbon dioxide mixtures

The flammability limits of saturated vapours of toluene in oxygen—carbon dioxide mixtures have been measured up to 180°C and 10 atm using a directThe flammability data have been presented in a pressure versus temperature diagram. The convenience of this form of diagram to determine the conditions     

Effect of finite element choice in blunt crack band analysis

The previously developed method of element-wide blunt smeared crack bands, which allows an effective finite element analysis of cracks that are not fixed but propagate and do so in any direction, has so far been numerically studied and demonstrated only for the constant-strain triangular elements. Here this is accomplished for linear strain triangles and for all three methods developed in [1], including the methods of energy variation, of equivalent strength, and of fitting asymptotic series to nodal displacements. Meshes of greatly different sizes are shown to give again the same results except for a negligible error; this indicates satisfactory convergence. Accuracy of the stress intensity factor, compared to the exact solutions for sharp cracks, is found to be sufficient but not better than that achieved previously with constant strain triangles. However, the accuracy may well be better in case of concrete structures in which the element-wide crack band serves not merely as a convenient approximate representation of a sharp crack but as a better representation of the actual fracture process.     

THE EFFECT OF IMPERFECT MIXING ON POLYMER QUALITY IN LOW DENSITY POLYETHYLENE VESSEL REACTORS

A mathematical model is developed for the calculation of polymer quality in low density polyethylene vessel reactors, taking into account mixing limitations at the initiator feed point. Model predictions show that imperfect mixing in the reactor can produce considerable variations in polymer molecular weight distribution. The effect of the most important process conditions, input feed temperature, solvent concentration, monomer flow rate and initiator type, on the final polymer quality is analyzed. The advantages of the design solution which divides the reactor in more compartments in series are also discussed.     

Poly(vinyl alcohol) hydrogels as hydrophilic matrices for the release of lipophilic drugs loaded in PLGA nanoparticles

Poly(vinyl alcohol) (PVA) hydrogels prepared by a freeze-thawing procedure were evaluated as matrices for the release of water-insoluble drugs such as dexamethasone. As it is impossible to directly entrap a lipophilic drug into a hydrophilic matrix, a novel mechanism has been designed based on producing biodegradable nanoparticles loaded with the drug, that could then be entrapped into the hydrogels. Nanoparticles were prepared by a solvent evaporation technique using a biodegradable copolymer of poly(lactic acid)-poly(glycolic acid) (PLGA). The effects of several processing parameters on particle properties were investigated. The drug release from free nanoparticles was compared to that from the nanoparticles entrapped into the PVA matrices. It was observed that the release profile of the drug is not significantly affected by the PVA matrix. A correlation was found between the amount of drug released and the PVA concentration in the hydrogels: the percentage of drug released, as a function of time, decreased by increasing PVA concentration, indicating that PVA concentration can be used as a tool in modulating the release of the drug.     

On Performance Improvement of a Speaker Verification System Using Vector Quantization, Cohorts and Hybrid Cohort-World Models

This paper presents the use of distance normalization techniques in order to improve speaker verification system performance. These techniques provide a dynamic threshold that compensates for the trial-to-trial variations and replaces the fixed threshold used in the classical speaker verification approach. Two methods are described: the cohort model normalization and a new and original hybrid cohort-world model normalization. These methods are compared from the point of view of storage space requirements and computational effort. Two algorithms are proposed: one uses existing user models, and the other creates new models. The algorithms were evaluated using the YOHO database and a proprietary database. The results showed that using these methods, the errors of false rejection are significantly reduced for a constant false acceptance error, when the cohort size is increasing. The algorithms also involve fewer computational resources than other algorithms, making them more suitable for commercial application.