All issues / Volume 13 (2019) / Issue 9 (September)
This is an editorial article. It has no abstract.
In this study, a novel alumina-covered graphene oxide/polyimide (AlGO/PI) nanocomposite was developed as an anticorrosion coating material. The hydroxyl groups on GO reacted with aluminum isopropoxide via a sol-gel process to yield AlGO nanosheets. The characterization and structure were confirmed by Fourier transform infrared spectrometry, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and field emission transmission electron microscopy. Subsequently, GO and AlGO were incorporated into a PI matrix, leading to the formation of GO/PI and AlGO/PI nanocomposites. Well-dispersed AlGO nanosheets in the PI matrix acted as effective additives to enhance the water barrier properties of GO/PI (58 g/(m2·day)) and AlGO/PI (43 g/(m2·day)) coatings. Most importantly, the resultant AlGO/PI films exhibited excellent optical transparency (>75%) and anticorrosion properties. Electrochemical measurements of corrosion potential, polarization resistance, and corrosion current as well as electrochemical impedance spectroscopy confirmed that the AlGO/PI nanocomposites exhibited better anticorrosion properties than GO/PI nanocomposites. This is likely because the insulating layer of alumina on GO can isolate the charge transfer pathway between GO and the metal substrates, leading to improved anticorrosion behavior.
Physically crosslinked chitosan hydrogels have better biocompatibility and possess unique functional characteristics but suffer from poor mechanical properties. In the current study, we prepared Cu+-containing physically crosslinked chitosan hydrogels by exploiting ammonia fumigation and reduction of Cu2+ by NaHSO3. The content of Cu+ in the prepared hydrogels was in a low range of 4.88–29.27 μmol/g. The mechanical strength of the CTS-Cu+/NH3 hydrogels was remarkably improved up to 0.25 MPa and the elongation at break increased with rising content of Cu+ due to the dynamic crosslinks between chitosan and Cu+. Moreover, the CTS-Cu+/NH3 hydrogels demonstrated evident shape memory after exposure to air by exploiting the different coordination number of Cu2+ and Cu+. Thus, the prepared hydrogels may have good potential applications as biomedical materials.
In order to overcome the issues of rework and height difference in the manufacturing of smart devices, UV/UV stepwise curing was conducted on acrylate-based optically clear adhesives. Photo differential scanning calorimetry was used to confirm the results of curing of samples that were processed both with and without acrylic acid, over a range of UV light exposure times for a primary curing process. The samples processed at 0.6 J/cm2 of UV energy with and without acrylic acid showed the highest amount of residual monomers after primary curing. The amount of residual monomers observed in primary-cured samples decreased as the amount of UV light energy increased, from 0.9 to 1.5 J/cm2. After secondary curing, only the samples cured at 0.6 J/cm2 showed small amounts of residual monomers, while the samples exposed to other UV energies showed very few residual monomers, implying that these samples were completely cured during the secondary curing step. Adhesion properties were evaluated using peel and tack tests, while the viscoelastic properties of the samples were confirmed by dynamic mechanical analysis. Our results indicate that uniform physical properties were achieved after secondary curing. The effects of stepwise curing are demonstrated by the difference in gel fractions determined after primary and secondary curing.
Amphiphilic copolymers containing 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) units were synthesized by controlled atom transfer radical polymerization (ATRP) applying bromoester modified retinol (RETBr) as a novel initiator. Analogous series of copolymers with adjustable hydrophilic-hydrophobic balance was obtained with the use of a standard initiator, i.e. ethyl α-bromoisobutyrate (EBriB). The self-assembling particles, prepared by the solvent evaporation, were loaded with vitamin C (VitC) or ferulic acid (FA). The hydrophilic/hydrophobic ratio in the copolymer was indicated as a crucial factor to regulate efficiencies of encapsulation processes in the range of 53–98%. In vitro release of bioactive substance was carried out in phosphate buffer solution (PBS) at pH 7.4 with the maximum amount of VitC after 1h (27–62%) or FA within 2 h (71–97%). The polymeric systems with satisfactory encapsulation characteristics and release profiles are attractive micellar carriers of antioxidants, which, due to their activities could be also delivered using the popular approaches in cosmetology like masks, under-eye patches, or wraps.
The unique temperature-dependent strain-optical and stress-optical behavior of poly(4-methyl-1-pentene) (P4MP) is reported during uniaxial deformation in the rubbery state. For P4MP the birefringence is found to increase with an increase in deformation temperature, which is opposite to the behavior of other polyolefins such as polypropylene and polyethylene. Real-time stress-strain-birefringence measurements are supplemented with offline wide-angle X-ray diffraction (WAXD) and infrared (FTIR) measurements.
Poly(lactic acid) (PLA) is one of the most extensively investigated and used aliphatic polyesters due to some aspects such as biodegradability and biocompatibility. However, PLA has some disadvantages that restrict its applicability for instance its limited thermal resistance and low crystallization kinetics. In this work, nanoclay mineral sepiolite (Sep) was used to enhance the crystallization of PLA. The samples were prepared by casting and melting to evaluate the influence of the processing type on the PLA crystallization. For this purpose, the crystallization kinetics as a function of (i) Sep content and (ii) different types of processing was evaluated by polarized optical microscopy, flow-induced crystallization and differential scanning calorimetry under isothermal condition and glassy crystallization (Avrami model), X-ray diffraction and small angle X-ray scattering. The results of quiescent crystallization show that the presence of Sep enhanced the nucleation density leading to faster spherulites growing and lower crystallization half-time compared with pure PLA. The Sep also affects the flow-induced crystallization in different way. Altogether, the relevance of the present study lies in the fact that it sheds some light on how the Sep content, processing and molar mass of the initial precursor can affect the crystallization of PLA.
Fullerene decorated by iron compound (C60-Fe) was fabricated via solution reaction and characterized by X-ray photoelectron spectra and wide-angle X-ray diffraction. By a partial replacement of intumescent flame retardant (IFR) in flame retarded polyethylene (PE) by C60-Fe, the flame retardant properties of PE/IFR composites were increased dramatically. When 2 wt% IFR was substituted by C60-Fe, a compact and continuous char barrier was formed, resulting in the reduction of the peak of heat release rate (PHRR) and the total heat released (THR). Also, the ignition time (tign) prolonged form 67 to 114 s and the time to PHRR (tPHRR) prolonged form 208 to 455 s. The improvement on flame retardancy of PE/IFR/C60-Fe composites was due to the synergistic influence between the catalytic charring ability of Fe and the free radical trapping effect of C60.