All issues / Volume 14 (2020) / Issue 11 (November)
This is an editorial article. It has no abstract.
In this work, an intelligent approach is applied for the first time in the modelling and optimization of electrospun Polyacrylonitrile/Poly(Vinylidene Fluoride) (PAN/PVdF) nanofiber properties. A genetic algorithm-based computer code was developed to optimize the architecture of an artificial neural network, by which an accurate model was developed for the prediction of nanofiber diameter, the standard deviation of nanofiber diameter and porosity of electrospun membrane. Electrospinning of polyacrylonitrile/poly(vinylidene fluoride) (PAN/PVdF) was applied to obtain a quantitative relationship between selected electrospinning parameters (namely applied voltage, solution concentration, and PVdF composition) and nanofiber diameter, the standard deviation of nanofiber diameter and porosity of electrospun membrane. The morphology and nanofiber diameter were investigated by field emission scanning electron microscopy (FESM). The range of produced nanofiber diameters was from 116 to 379 nm. It seemed that the nanofiber diameter and standard deviation of nanofiber diameter decrease with PVdF composition and increase with solution concentration. The applied voltage had no important effect on the nanofiber diameters. The porosity of the electrospun membrane decreases with solution concentration and increases with PVdF composition.
Waterborne polyurethane and graphene/graphene oxide-based nanocomposites: Reinforcement and electrical conductivity
I. Larraza, B. Alonso-Lerma, K. Gonzalez, N. Gabilondo, R. Perez-Jimenez, M. A. Corcuera, A. Arbelaiz, A. Eceiza
Vol. 14., No.11., Pages 1018-1033, 2020
Vol. 14., No.11., Pages 1018-1033, 2020
Polyurethane based materials show great potential for many applications, and their reinforcement with different kinds of nano-entities can improve their properties or supply them with new ones, widening their fields of applications to new opportunities. In this work, nanocomposites composed of a biobased waterborne polyurethane and carbonaceous reinforcements were prepared and characterized. Parting from graphite, graphene, and graphene oxide were obtained through a mechanical and a chemical route, respectively, and graphene oxide was reduced into graphene through a thermal process. Successful exfoliation, oxidation, and reduction processes were proven when characterizing graphene, graphene oxide, and reduced graphene oxide. Nancomposites reinforced with graphene and graphene oxide showed improved mechanical and thermomechanical properties, whereas they did not show electrical conductivity. Coatings of the systems with graphene and reduced graphene oxide were studied, to grant electrical properties to the composites. Electrical conductor materials were obtained after coating the systems, as shown by Electrostatic Force Microscopy and electrical conductivity measurements.
This work deals with the influence of biaxial orientation on the mechanical behavior of Polylactide (PLA) films. Comparisons between a crystallizable grade and a non-crystallizable one have been made in order to separate the effect of macromolecular orientation from the potential influence of the crystalline phase induced during the thermomechanical treatment. While unstretched PLAs exhibited brittle behavior at room temperature, it was observed for both types of PLA the strains at break for biaxially drawn films were remarkably enhanced to values over 100%. This study highlights for the first time, in the case of PLA, that a critical molecular chain orientation of the amorphous phase is the necessary condition to induce a ductile behavior. In-situ small-angle X-ray scattering (SAXS) experiments and post-mortem microscopic observations have revealed that it is a change of elementary plastic deformation mechanisms that is at the origin of this Brittle-to-Ductile (B-D) transition.
Development of self-assembled poly(2-ethyl-2-oxazoline)-b-poly(ε-caprolactone) (PEtOx-b-PCL) copolymeric nanostructures in aqueous solution and evaluation of their morphological transitions
U. U. Ozkose, S. Gulyuz, U. C. Oz, M. A. Tasdelen, O. Alpturk, A. Bozkir, O. Yilmaz
Vol. 14., No.11., Pages 1048-1062, 2020
Vol. 14., No.11., Pages 1048-1062, 2020
Amphiphilic block copolymers are known to self-assemble into various morphologies, including ellipsoids, tubular structures, toroids, vesicles, micellar structures. In this paper, we discuss the synthesis of copolymeric nanostructures (CNs) using poly(2-ethyl-2-oxazoline)-block-poly(ε-caprolactone) (PEtOx-b-PCL) amphiphilic block copolymers. Our data indicate that - varying the molecular weight and the number of repeating units dictate the nature of morphology. That is, the formation of self-assembled morphologies from ellipsoid to rod-like architectures are observed in aqueous solution, depending on the mass ratio of the hydrophilic block (fPEtOx). To best of our knowledge, this is the first report on the morphological transitions of PEtOx-b-PCL amphiphilic block copolymer-based CNs with different fPEtOx values in the literature.
In this work, low-temperature photoionized plasma, induced in N2 by extreme ultraviolet (EUV) pulses, was used for surface modification of poly(L-lactic acid) (PLLA). Polymer samples were irradiated with 100, 200, and 300 pulses at a 10 Hz repetition rate. The physical and chemical properties of PLLA samples were examined using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The human dermal fibroblast adult cells (NHDF-Ad) were used for the cell culture and viability tests on modified PLLA surfaces. The N2-plasma and EUV treatment caused alteration of the surface morphology resulting in increased surface roughness, incorporation of nitrogen atoms, and appearing of new functional groups on the surface. Cell culture results showed an increase in the number of fibroblasts attached to the modified surfaces compared to the pristine PLLA. The modified surfaces demonstrated high cell viability and no cytotoxic effects were observed.
The goal of this work was to prepare a honeycomb-like pattern (HCP) structure by a combination of acetate cellulose and poly-L-lactic as biocompatible and biodegradable polymers used in tissue engineering. The formation was obtained by a fast and cheap solution-immersion phase separation method based on the presence of nonsolvent, which induces phase separation in normal air without surfactants and supports the formation of the honeycomb structure. As a substrate, we used plasma modified fluorinated polymer, which can significantly improve the possibility of successful preparation HCP formation and control pore size and dimension of the prepared porous layer. Honeycomb-like pattern structure from composite acetate cellulose-PLLA on the surface of plasma-treated perfluorinated polymer FEP was prepared with a simple technique. Plasma modification changed the surface chemistry, wettability and thus allowed the creation of HCP microporous structure on the perfluorinated substrate. The regularity, surface morphology, and wettability of HCP film can be effectively controlled by changing of plasma activation.
The present work proposed a simple approach for producing a fibrous flexible resistive-type pressure sensor from wool. By dip-coating polyurethane (PU) and silver nanowires (AgNWs) onto wool yarn, the latter was turned into a coaxial cable-like structure with the electrically conductive AgNWs/PU composite sheath for the sensing functionality and the wool core for providing a pliable substrate of the sensor. Afterward, the overlapping region of two strands of orthogonally stacked conductive composite yarns was employed to act as the pressure sensor. The experimental results indicated that conductivity and durability of the conductive yarn and sensitivity of the pressure sensor are closely correlated and can be effectively tuned through changing the amounts of PU and AgNWs. The surface fine structure of the composite yarns is a key factor determining responsive behavior. As a result of optimization, the pressure sensor has acquired high sensitivity and longterm working stability. Moreover, the homemade PU imparted the sensor with sunlight triggered self-healability of microcracks. It is anticipated that the pressure sensor possesses promising application potential in a variety of areas, including wearable electronics and e-textiles.