All issues / Volume 13 (2019) / Issue 10 (October)
This is an editorial article. It has no abstract.
Donor-acceptor (DA) type monomers namely 2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole (TTzTh) and 2,5-bis(3-methylthiophen-2-yl)thiazolo[5,4-d]thiazole (TTzMTh) were synthesized and their electrochemical and optoelectronic properties were investigated in detail. The spectro-electrochemical analysis showed that the alkyl chain substitution results in a shift in the onset of the π-π* transition towards longer wavelengths. Depending on the donor substituents, the polymers exhibited optical band gaps 1.65 and 1.85 eV for PTTzTh and PTTzMTh, respectively. Electrochromic studies revealed that both polymers are p-dopable and multichromic. Moreover, polymer of TTzTh (PTTzTh) has been used for the development of a glucose biosensor. Glucose oxidase (GOx) was anchored on a graphite electrode which was previously modified with a film of the conjugated polymer, PTTzTh by electropolymerization. Such a sensor showed a wide linear range (0.05–2.0 mM), good sensitivity (36.32 µA/(mM・cm2) and low limit of detection (LOD) (0.075 mM) under formerly optimized conditions. Moreover, the accuracy of the biosensor was successfully tested using two different beverages to detect glucose. Electrochemical characterizations of the polymers and their biosensor application were investigated for the first time in this work.
Thermo-mechanical and gas transport properties of polylactic acid (PLA) matrix containing various amounts (from 1 to 20 wt%) of nanocellulose esterified with lauryl chains (LNC) were investigated on solvent cast film of about 50 micron. Scanning electron microscopy indicated that, up to a filler content of 6.5 wt%, LNC was well dispersed or formed small, sub-micrometric clusters. At higher filler contents, oval aggregates in the micrometric range were detected. The addition of LNC did not change the matrix glass transition temperature and melting temperature. Concurrently, as LNC content increased, both elastic and storage moduli at room temperature exhibited a sharp decrease up to 5 wt% of filler, and a lower reduction for LCN concentration of 10–20 wt.%. Nanocomposites with 3 and 5 wt% of LNC showed the highest strain at break and a large amount of plastic deformation due to a strong interfacial adhesion between the PLA and filler particles. For higher LNC fractions the presence of aggregates weakened the nanocomposite leading to lower values of maximum stress and strain at break. With the addition of LNC particles, gas barrier properties of the PLA film versus deuterium, nitrogen and carbon dioxide were improved up to a critical LNC concentration of 6.5 wt%, where the gas permeability of the nanocomposite resulted to be 70% lower than that of the PLA matrix. At higher filler contents, large LNC aggregates increased the gas permeability of the nanocomposites.
The ability of Bacillus cereus TISTR 2651 to perform biological devulcanization of natural rubber cured by conventional vulcanization (CV), semi-efficient vulcanization or efficient vulcanization was studied. Among the three curing systems, B. cereus TISTR 2651 could specifically devulcanize rubber products formed from the CV system the best, removing 26.44% of the sulfur within 20 days. Moreover, B. cereus TISTR 2651 could oxidize and desulfurize the sulfide crosslinks in the CV rubber and transform them to oxygen-containing sulfur-based groups via the 4S pathway. Additionally, the molecular weight, crosslink density and gel fraction of the CV rubber were also significantly decreased from the original levels. Horikx analysis was used to propose the mechanism of bacterial devulcanization. Finally, ground tire rubber (GTR) was devulcanized by B. cereus TISTR 2651 and the percentage of sulfur removal was about 27.98 for 20 days, where similar results were also obtained. Accordingly, B. cereus TISTR 2651 can be applied for the management of rubber waste, leading towards a solution of this environmental problem.
Nowadays, two of the most important polymer processing technologies are injection molding and 3D printing. Injection molding is ideal for mass production, while 3D printing is ideal for producing products with a complicated geometry. When these two technologies are combined, such complex products can be manufactured economically that would be too costly if produced traditionally. We present the possibilities of combining injection molding and 3D printing. We introduced a novel concept to study and compare the bonding strength of polylactic acid (PLA) parts prepared by overprinting and overmolding. We developed a special injection mold for overmolding, with which we injection molded ribs on a preform. The geometry of the overprinted part was similar for comparability. The thermal properties of the samples were determined by differential scanning calorimetry and thermogravimetric analysis. To analyze the strength of mechanical bonding, we developed a rib pull-off test. We tested all four manufacturing combinations with this test: overmolding onto a molded or printed plate and also overprinting onto a molded or printed plate.
3D printing has attracted a lot of attention over the past three decades. In particular the Fuse Filament Fabrication (FFF) technique, general materials require low shrinkage during cooling and viscous behavior during extrusion through a nozzle. Semi-crystalline thermoplastics and their composites are of the relevance of new materials for 3D printing. However, the crystalline structures, for instance, may have a favorable impact on their printability. In this study, polypropylene/organoclay nanocomposites were prepared by melt extrusion using a twin-screw extruder. The effects of organoclay on the thermal, rheological and morphological properties were studied to evaluate the possibility of using the polypropylene/organoclay nanocomposites as the FFF 3D printing feedstock. Dioctadecyl dimethyl ammonium chloride (D18) was successfully used to modify the clay surfaces, providing a good dispersity and wettability of organoclay in the PP matrix.
Polymethylmethacrylate (PMMA) and nanocomposites containing 0.5 wt.% graphene oxide (GO), graphene oxide-multiwalled carbon nanotubes (NT) or graphene oxide-ionic liquid 1-octyl-3-methylimidazolium tetrafluoroborate (IL) (PMMA+GO; PMMA+GO-NT; PMMA+GO-IL) were processed by a single step twin-screw micro-extrusion. The effect of two extrusion temperature profiles and two specific mechanical energy (SME) values has been studied. Results of Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analysis show changes in GO composition and morphology, and better dispersion due to interaction with IL. Dynamic mechanical analysis shows that extrusion conditions affect storage modulus of hybrid nanocomposites. Rheological measurements show that the complex viscosity of the nanocomposites is higher than that of PMMA at low shear rates for materials processed under the lower value of SME. A maximum viscosity increase of 62.6% is found for PMMA+GO-NT. The lowest increase found for PMMA+GOIL, is attributed to the better dispersion of the hybrid GO-IL nanofiller.
Synthesis and characterization of soluble ester-containing polyimide alignment layers with high voltage holding ratio features and potential applications in TFT-LCDs
X. X. Zhi, H. S. Bi, J. G. Liu, Y. S. Gao, Y. L. Zhang, Y. C. Zhou, Y. Zhang, X. Wu, X. M. Zhang
Vol. 13., No.10., Pages 923-936, 2019
Vol. 13., No.10., Pages 923-936, 2019
Novel ester-containing polyimide (PI) resins have been synthesized from an alicyclic dianhydride monomer, 4,4'-dihydroxybiphenyldicyclohexanecarboxylate-3,3',4,4'-tetracarboxylic acid dianhydride (HTABP) and various aromatic diamines. The derived PI resins (PI-1~PI-5) were easily soluble in N-methyl-2-pyrrolidinone (NMP) and gamma-butyrolactone (GBL). The PI alignment agents prepared from the HTABP-PI resins, NMP solvent, and the butyl cellulose (BC) leveling agent with a solid content of 6 wt% showed good stability during the storage at 25 °C for half a year. Smooth and uniform PI alignment layers were formed by spin-coating the PI varnishes onto indium tin oxide (ITO) substrates, followed by thermally baking at the temperature up to 230 °C. Liquid crystal (LC) cells were successfully fabricated by using the rubbing treated PI layers as the alignment components for LC molecules. The LC cells fabricated with the newly-developed PI alignment layers exhibited good electro-optical properties with the pretilt angles around 1.26–2.82° and voltage holding ratio (VHR) as high as 98.36% at room temperature. The residual direct current voltage (RDC) values of the HTABP-PI alignment layers were in the range of 915–2146 mV due to the high volume resistivity values of the PI layers. In addition, the HTABPPI layers showed good thermal stability with the 5% weight loss temperatures (T5%) higher than 415 °C and glass transition temperatures (Tg) in the range of 150.5–201.4 °C.