All issues / Volume 11 (2017) / Issue 9 (September)
This is an editorial article. It has no abstract.
Poly(ε-caprolactone) (PCL) films reinforced with polylactide (PLA) microfibers were prepared by two methodologies: a) melt pressing of an electrospun PLA mat between two PCL films, and b) melt pressing of a co-electrospun mat composed of PLA microfibers and PCL nanofibers. Electrospinning conditions were selected for each polymer to obtain films loaded with 10, 20 and 30 wt% of PLA. Thermal and mechanical properties varied depending on the preparation method. Thus, PLA crystallinity was higher when films were obtained by the co-electrospinning process, as revealed from DSC and synchrotron X-ray diffraction data since cold crystallization of the highly oriented PLA microfibers was favored in the subsequent heating run when they were in close contact with PCL nanofibers. Samples obtained by co-electrospinning also showed higher mechanical properties (e.g. Young modulus) with increasing PLA load. In this case, fracture surfaces showed significant interactions between fibers and the PCL matrix and decreased fiber pull-out. All fabrics were also loaded with chlorhexidine (CHX) as a hydrophilic bactericide agent. A delayed release was observed when the drug was only loaded into the electrospun PLA microfibers, and diffusion varied with the method of preparation. In all cases, samples had a clear bactericide effect against Gram positive and Gram negative bacteria. Nevertheless, the protective effect was slightly lower when CHX was only loaded in the reinforcing PLA microfibers.
Ureido-pyrimidone (Upy) can dimerize in a self-complementary array of quadruple hydrogen bonds. In this paper, supramolecular polymer composites were prepared by blending Upy functionalized nanosilica with Upy end-capped polycarbonatediol. Surface characteristics of Upy functionalized nanosilica and influences of supramolecular forces on interfacial binding were researched. Fourier transform infrared spectroscopy (FTIR), Nuclear magnetic resonance (NMR) and Gel permeation chromatography (GPC) were used to characterize the synthesized molecules. Grafting ratio of Upy segments on the surface of nanosilica was analysed by Thermogravimetic analysis (TGA). Hydrophobicity and morphology of Upy modified nanosilica were analysed by Contact angle tester and Scanning electron microscope (SEM). Furthermore, dynamic thermo mechanical properties, mechanical properties and distribution of nanosilica in supramolecular polymer composites were also researched. Compared with the matrix resin, tensile stress and young's modulus of supramolecular polymer composites containing 5 wt% modified nanosilica were increased by 292 and 198% respectively.
Multiwall carbon nanotubes (MWCNTs) previously treated with a cationic polymer were incorporated on the surface of carbon fibers modified by three different chemical treatments, namely, oxidation, oxidation-silanization and oxidation-pre-impregnation. Prior to the incorporation of the MWCNTs, the physical surface properties of the fibers were studied by contact angle and the chemical surface properties by X-ray photoelectron spectroscopy (XPS). The interfacial shear strength (IFSS) of the different systems carbon fiber-MWCNTs-matrix was evaluated using the single-fiber fragmentation test (SFFT) and it was observed that the IFSS of the oxidized-pre-impregnated fibers, was considerably higher than that observed for the other fiber-matrix systems. This was attributed to enhanced interfacial interactions because the fiber surface treatments improved the wettability of the carbon fiber and the MWCNTs, which resulted in a better fiber-matrix mechanical interlocking and to the formation of covalent bonds between the different phases of the composite.
In this work, a novel semi-interpenetrating polymer network (semi-IPN) hydrogel scaffold based on silk sericin (SS) and poly(N-hydroxyethyl acrylamide) (PHEA) was successfully fabricated via conventional free-radical polymerization. The porous structure of the scaffolds was introduced using a lyophilization technique and the effect of cross-linker (XL) on morphology, gelation time and physical properties of hydrogel scaffold was first studied. The results show that using low cross-linker content (0.125, 0.25 and 0.5 wt% XL) produced flexible scaffolds and appropriate gelation times for fabricating the scaffold. Therefore, the polymerization system with a constant percentage of XL at 0.5 wt% was chosen to study further the effect of SS on the physical properties and cell culture of the scaffolds. It was observed that the hydrogel scaffold of PHEA without SS (PHEA/SS-0) had no cell proliferation, whereas hydrogel scaffolds with SS enhanced cell viability when compared to the positive control. The sample of PHEA/SS at 1.25 wt% of SS and 0.5 wt% of cross-linker was the most suitable for HFF-1 cells to migrate and cell proliferation due to possessing a connective porous structure, along with silk sericin. The results proved that this novel porous semi-IPN hydrogel has the potential to be used as dermal reconstruction scaffold.
There is a big demand for the development of polymer materials for flexible electronics, among them polymers with a high dielectric constant play an important role. Here the preparation and properties of a polymer blend composed of poly(2-cyanoethyl vinyl ether) (CEPVA) as an amorphous polymer with dielectric constant (ε') ~ 15 but glass temperature (Tg) close to room temperature, and poly(methyl methacrylate) (PMMA), a polymer with low ε' ~ 5 and high Tg, are reported. The film forming ability, structure and dielectric properties of the blend are reported to verify its applicability for capacitors and field effect transistors. PMMA:CEPVA ratios 10:90 and 30:70 represent the best composition for obtaining a monophasic system with increased dielectric constant and Tg well above the room temperature. The improved properties have been attributed to the impact of PMMA on the relaxation phenomena of CEPVA, namely to an increased mobility of cyano-groups responsible for the dielectric behavior, as it was observed by the broadband dielectric and nuclear magnetic resonance (NMR) spectroscopies.
The aim of this paper is to develop new elastomeric phase change materials (PCM) for the thermal energy storage/release below room temperature. In particular, poly(cyclooctene) (PCO)/paraffin blends filled with various concentrations of carbon nanotubes (CNTs), were prepared by a melt compounding process. The microstructural, thermo-mechanical and electrical properties of the resulting materials were investigated. The microstructure of these materials was characterized by the presence of paraffin domains inside the PCO, and CNTs were located only inside the paraffin domains in forms of aggregated clusters. DSC tests evidenced the existence of two distinct crystallization peaks at –10 and at 6 °C, respectively associated to the paraffin and the PCO phases, indicating that both the polymeric constituents are thermally active below room temperature. Moreover, CNT addition did not substantially alter the melting/crystallization properties of the material. Noticeable improvements of the mechanical properties and of the electrical conductivity with respect to the neat PCO/paraffin blend could be obtained upon CNT addition, and also thermal conductivity/diffusivity values were considerably enhanced above the percolation threshold. Finite element modeling demonstrated the efficacy of the prepared nanocomposites for applications in the thermal range from –30 to 6 °C.
Poly (styrene-co-butyl acrylate)/nanoporous cellulose gel nanocomposites [P (St/BA)/NCG] were synthesized by in-situ polymerization of styrene/butyl acrylate (St/BA) monomer mixtures in nanoporous regenerated cellulose gels. The three-dimensional nanoporous cellulose gels (NCGs) were fabricated via dissolution and coagulation of cellulose from aqueous sodium hydroxide (NaOH)/urea solution. The NCG contents in nanocomposites were controlled between 16 and 44% v/v by changing water content of starting hydrogels via compression dewatering. Scanning electron microscopy (SEM) analysis showed that the interconnected nanofibrillar network structure of NCGs was preserved well in the nanocomposites after insitu polymerization. The resulting nanocomposites exhibited excellent transparency (up to 82%) in the visible region and high mechanical strength, with a tensile strength of up to 56.0 MPa, Young’s modulus of up to 2195 MPa and elongation at break up to 80.9%. Dynamic mechanical analysis (DMA) showed a remarkable improvement (by over 3 orders of magnitude) in tensile storage modulus above glass transition temperature of the copolymer. The nanocomposites also showed significant improvements in thermal stability as well as water resistance over NCG.