All issues / Volume 13 (2019) / Issue 11 (November)
This is an editorial article. It has no abstract.
Novel tough bio-based polyesters poly(ethylene 2,5-thiophenedicarboxylate-co-1,4-cyclohexanedimethylene 2,5-thiophenedicarboxylate)s (PECTFs) were synthesized from 2,5-thiophenedicarboxylic acid (TDCA), 1,4-cyclohexanedimethanol (CHDM) and ethylene glycol (EG). The microstructure, thermal and mechanical properties were investigated. Poly(ethylene 2,5-thiophenedicarboxylate) (PETF) displayed the glass transition temperature (~64 °C) and tensile strength (~72 MPa) similar to poly(ethylene terephthalate) (PET). However, the nonlinear structure of TDCA resulted in an angle of 148° between carboxylic acid carbons and the S atom resulted in a permanent dipole, so the thiophene ring-flipping was hindered and the low elongation at break (~24%) was observed for PETF. The peak corresponding to the secondary relaxation shifted to lower temperature due to the incorporation of CHDM, which yielded ductile copolyesters with high elongation at break. When the CHDM content was equal to or higher than 29%, a high elongation at break (>160%) was observed.
Developing eco-friendly, flexible thermoplastic elastomeric foams based on poly(styrene-(ethylene-co-butylene)-styrene) (SEBS) is a challenging task because of its poor melt strength. A promising approach to overcome this challenge is the use of synergistic technologies, such as combination of irradiation, supercritical fluid foaming, and steam-chest molding technologies. Herein, foamed beads were produced from pre-crosslinked SEBS beads using supercritical nitrogen as blowing agent, followed by subsequently efficient steam-chest molding to obtain midsole part. The crosslinking was accomplished under the assistance of electron beam. The rheology properties and foaming behavior reveals that the viscosity and modulus of the matrix increase with the increase of crosslinking resulting from increasing the irradiation dose (ID). With increasing the ID, successful foaming with larger expansion and improved cell morphology was achieved. SEBS bead foams were successfully obtained from 65 kGy-derived pre-crosslinked beads through steam-chest molding which showed a specific gravity of 0.252 g・cm–3 and comparable/superior mechanical properties to/than that of commercial thermoplastic polyurethane (TPU) or ethylene-vinyl acetate copolymer (EVA) foams. Especially, the higher elasticity and resilience of SEBS foams meet well the desirable properties for footwear application which supports SEBS to be an alternative for TPU or EVA.
Multi walled carbon nanotube (MWCNT)-polyaniline nanofiber-carbon dot (CD) nanohybrid was fabricated using in-situ polymerization of aniline in the presence of MWCNT and CD. Different spectroscopic techniques like Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible (UV-vis) spectroscopy were used to study the formation of the nanohybrid. The obtained nanohybrid was incorporated in different weight percentages in the hyperbranched epoxy derived from renewable resources like sorbitol and monoglyceride of castor oil. The formation of the nanocomposites was also verified using spectroscopic, microscopic and diffraction techniques. The thermosetting nanocomposites with uniform and stable dispersion of nanohybrid demonstrated excellent mechanical properties, such as tensile strength (69 MPa), elongation at break (45%), scratch resistance (>10 kg) and impact resistance (16.7 kJ/m); good thermal stability (above 264 °C) and high chemical resistance. The anticorrosion performances of the cured nanocomposites were studied on mild steel plates in 3.5% sodium chloride (NaCl) solution using potentiodynamic polarization method. The study showed that the nanocomposites with the highest percentage of the nanohybrid exhibited better anticorrosion performance (corrosion rate of 4.62・104 mpy) compared to the pristine thermoset. Thus, this study revealed that the hyperbranched epoxy with stable dispersion of the nanohybrid based nanocomposite can be potentially applied as a high performance anticorrosive material.
Immense work has been conducted in the field of thermoresponsive polymers specifically of lower critical solution temperature (LCST) type, but upper critical solution temperature (UCST) type polymers remain a significantly unexplored domain. However, in recent years, UCST polymers have attracted increased attention as evidenced by the rise in publications in the same domain, and therefore, this review is an attempt to compile the reported UCST-type polymers. Unlike LCST, UCST polymers are insoluble at low temperature but solubilize in a given solvent as the temperature increases. The synthesis approaches and applications of reported UCST polymers are discussed in this article. Emphasis has been given to the polymers exhibiting UCST behavior in aqueous medium, due to the obvious advantage of their wide applicability. It is quite apparent from this study that the attempts to synthesize novel polymers and copolymers exhibiting UCST has faced an upsurge, but their application part still requires considerable attention.
Epoxy fibers with different diameters were prepared by hot drawing and their mechanical properties were measured under tension. The stiffness, strength, ultimate strain, and toughness revealed substantial scale-dependent effects as they all significantly increased with a decrease in size. Compared to bulk epoxy, an intrinsically brittle material, thin epoxy fibers displayed a highly ductile behavior under tension. A drop in stress observed immediately beyond the yield point was followed by the development of a stable necking region propagating through the entire fiber length, then by strain-hardening up to final rupture. Necked fiber segments tested in tension were found to have even higher strength and modulus compared to the initial as-prepared fibers. Possible reasons for the highly ductile mechanical behavior and the size effects of epoxy fibers are discussed. Size effects for the strength of epoxy can be elucidated in principle either by means of a classical fracture mechanics argument (strength ~ 1/d1/2), or via a stochastic model argument (strength ~ 1/d1/β, where β is a function of the material and is generally larger than 2). In both models the presence and size of critical defects play a key role. However, defects cannot explain the colossal ductility (plastic deformation) seen in our experiments, nor can the presence of defects justify a size effect in an elastic property, namely Young’s modulus. Only scarce evidence exists in the literature for similar (milder) size effects in epoxy fibers but without any structural justification. We find here that highly cross-linked necked epoxy fibers exhibit partial macromolecular anisotropy which likely explains the observed high mechanical characteristics.
Bioprobes immobilization methods that elevate the probes from the substrate are generally preferred in microarray technology because they prevent steric limitations during the hybridization of the target to probes. A versatile approach to control the thickness of a polymeric coating based on click chemistry to obtain covalently linked layer-by-layer coatings for surface functionalization is presented. By alternating cycles of coating using copolymers bearing click groups, the thickness of the film increases, while remaining functional and stable. Click chemistry reactions provide numerous advantages over standard conjugation procedures typically used in microarrays. They include: quantitative yields and insensitivity of the reaction to pH and hydrolysis. Moreover, click reactions do not interfere with organic groups naturally present in DNA, proteins and peptides such as amino and carboxyl groups allowing orthogonal and chemoselective probe immobilization. In addition to the formation of multilayers, click reactions allow to bind biomolecules to polymer chains generating so-called polymeric probes, which are then immobilized on microarray supports. In a microarray assay of clinical relevance, this methodology provides a miniaturized, tri-dimensional multilayer with higher density of capture probe, improved hybridization efficiency and sensitivity.
Graphene nanoplatelet (GNP)/poly(methyl methacrylate) (PMMA) nanocomposite solution was spray coated on a glass fibre reinforced polymer composite (GFRP) beam with different initial electrical resistance (R0). Scotch tape erosion method was used to tailor the R0 of the sensors. Beams and the sensors were characterized by computed tomography (CT) and scanning electron microscopy (SEM) respectively. The piezoresistive behaviour of these sensors was evaluated in monotonic, step and cyclic loading conditions. These spray coated sensors offered good sensitivity (38.5 times) as compared to a strain gauge. A gauge factor (GF) of 55±0.5, 70±2, and 77±1 was obtained for R0 of 1, 7 and 21 kΩ GNP layers, respectively. Sensors showed good response and stability under the step and cyclic loading conditions. The ease in the process of application coupled with good sensitivity demonstrates that the GNP/PMMA spray coated sensor can be a potential candidate for the futuristic multi-functional materials for structural health monitoring.