All issues / Volume 12 (2018) / Issue 7 (July)
This is an editorial article. It has no abstract.
Supramolecular β-cyclodextrin (β-CD) was used as a soft template for the fabrication of long silver nanowires. A novel design using self-assembled β-CD for the reduction of silver ions was studied. The concentrations of iron chloride, silver nitrate, and the template were controlling factors for the growth of the silver nanowires. Iron chloride was used to accelerate and facilitate the formation of the silver nanowires and inhibit oxidative etching. However, an excessive concentration of Fe+3 resulted in etching of the silver nanostructures. Furthermore, the silver concentration was another controlling factor. The length of the silver nanowires increased as the concentration of silver cations increased. Nevertheless, an excess concentration of silver cations formed various silver crystalline structures. In this study, the optimal ratio between iron chloride and silver nitrate was determined to be 1:13.3. A maximum length of 20 µm was achieved using a concentration of 0.23 M for the soft template. Moreover, the junction of two growing silver nanowires was observed, forming a long fused nanowire, and some significant boundaries were observed. The observed results were further confirmed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. X-ray diffraction (XRD) and energy dispersive spectrometer (EDS) analyses were used to indicate the presence of silver and the formation of crystalline materials.
The structure and properties of ethylene-co-vinyl acetate (EVA) and poly(3-hydroxybutyrate) (PHB) blends depended on their PHB content, i.e. PHB phase dominated the structure for amounts of PHB higher than 50 wt%, whereas EVA phase is dominant for PHB content lower than 50 wt%. EVA/PHB (70:30) blend showed unexpected different structure because of higher miscibility and the creation of new interfacial interactions between C=O and CH3 groups of PHB and CH3 and C=O groups of EVA, these interactions led changing of the phase structure of ethylene and vinyl acetate domains in EVA. As a consequence, improved thermal, viscoelastic and morphological properties were obtained. EVA+PHB blends containing 60 wt% or more PHB did not show tack and, interestingly, the addition of 20–30 wt% PHB enhanced the tack and displaced the maximum tack of pure EVA to lower temperature. The tack of EVA/PHB (70:30) blend was the highest among all blends because of its particular structure, fibrillation was also shown. Finally, the adhesion of EVA+PHB blends containing 20–30 wt% PHB to polypropylene (PP) substrate was higher than the one of pure EVA because of the interactions between the ethylene domains in EVA phase of the blend and PP substrate surface.
The addition of inorganic fillers into a bioplastic could increase its mechanical properties, which will be influenced strongly by the type of the clay dispersion. In this work, we have used montmorillonite nanoclays (MMT) to prepare biocomposites by means of an extrusion process. We present herein the effect of the pH and the addition of montmorillonite nanoclays (MMT) on the barrier and mechanical properties of wheat gluten based bioplastics. The pH of the samples was modified by adding aqueous solution of a strong acid or base (H2SO4 and NaOH). Tensile, dynamic mechanical thermal analysis (DMTA), water absorption and X-ray tests were carried out to study the influence of the above-mentioned variables on the physicochemical properties and rheological behaviour of bioplastics and biocomposites obtained. Tensile results showed that both Young’s modulus and tensile strength are higher at unmodified pH. However, the addition of MMT to an alkaline biopolymer matrix produced remarkable improvements in the rheological and mechanical properties because of a high exfoliation of the nanoclay noticeable in X-ray results. To summarise, extrusion process and the use of nanoclays present an excellent opportunity to develop wheat gluten bioplastics able to replace conventional products.
By combining a trifunctional urethane acrylate synthesized from a hexamethylene diisocyanate trimer and caprolactone acrylate with a bifunctional urethane acrylate prepared from hydroxyethyl acrylate and isophorone diisocyanate, a new reactive resin mixture was prepared, and trimethylolpropane triacrylate was chosen as the thinner to constitute a novel coating matrix. Different amounts of multi-functionalized carbon nanotubes (CNTs) and graphene oxide (GO) were introduced into the matrix and cured by ultraviolet radiation, producing different coatings. Utilizing the methods of Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-VIS) spectroscopy, wide angle X-ray diffraction (WAXS) and thermogravimetric analysis (TGA), the chemical structures and physical properties of the coatings were analyzed. A series of ASTM methods, such as pencil hardness classification, RCA abrasion, crosscut adhesion test classification, and chemical resistance rub testing, were applied to investigate the performances of the coatings. It was found that introducing a small amount of carbon nanomaterials can improve the thermal stability, surface hardness, adhesion, abrasive resistance, and chemical resistance performance of the UV-curable coatings. The reasons and mechanisms of the performance improvements are discussed in this work.
Porous glass fiber and paper layers were tested for application in thermally induced self healing epoxy laminates as healing porous layers. Both types of layers were impregnated using high purity bisphenol A diglycidyl ether (BADGE) epoxy with ability to crystallize during storage under 25 °C. Absorption capacity of porous layers was evaluated. Differential scanning calorimetry was used to investigate BADGE healing agent recrystallization process. Healing porous glass layers (HPGL) were selected for further tests. Liquid chromatography and Fourier transform infrared (FT IR) spectroscopy provided information about average molecular mass of embedded healing agent and functional groups in HPGL layers. Self-healing efficiency of three different laminates with HPGL layers was calculated based on the results of three-point bending test and Charpy impact test. Also, flexural properties and impact strength of laminates were evaluated. The obtained results confirm competitive self healing ability of composites with HPGL.
Electrochromic polymers have attracted much attention due to their potential applications in displays, smart windows, intelligent mirrors, and wearable devices. Here, a novel polyamic acid containing aniline pentamer with improved electrochromic properties and new functionalities was synthesized via oxidative coupling polymerization, followed by postpolymerization of tetraaniline, polyhedral oligomeric silsesquioxane, and fluorene, respectively. With the introduction of tetraaniline pendants, the resultant polymer exhibits improved electrochromic performance with high optical contrast value and rapid switching rate, because of the high content of electrochromic units in the polymeric structure. The polyamic acid functionalized with polyhedral oligomeric silsesquioxane, demonstrates a great enhancement of switching rate in the electrochromism, due to the rapid electrolyte migration through polymer film under electrochemical potentials. In addition, a new electrofluorochromic feature is easily achieved through the introduction of fluorescent fluorene groups into the polymeric architecture.
Polymeric materials with temperature-dependent gas permeabilities using a phase change material are designed and their applicability as a packaging system investigated. Polypropylene/octadecane/zeolite (PP/OD/ZL) composite films were prepared via extrusion process. ZL was used as a filler to enhance the dispersion and interfacial interaction between the OD and the PP originating from different flowabilities during the extrusion process. (FTIR) and (WAXD) analyses showed that the incorporation of ZL increased the interfacial interaction between PP and OD, resultantly enhancing the thermal stability, mechanical properties, and the oxygen transmittance rate and mechanical properties after contact with food simulants and thermal treatment. When the temperature was elevated from 10 to 30 °C, oxygen and water vapor transmittance rate of the composite films increased sharply because of the influence of the OD content. It was surmised that temperaturedependent permeation jump caused by increasing of segmental mobility of OD phase and converting the crystalline structure to an amorphous one of OD phase in the composite films. However, the permeation jump in the composite films was weakened as the ZL content increased. These results are related to changes in the interfacial interaction and crystallinity in the composite films due to the addition of ZL.