This is an editorial article. It has no abstract.
The chemical recycling of the poly(ethylene terephthalate), (PET), has been successfully carried out by glycolysis in the presence of bis (2-hydroxyethyl) terephthalate (BHET) resulting in the formation of hydroxytelechelic oligomers. These oligomers were then treated with carboxytelechelic poly(ε-caprolactone) oligomers of Mn = 2300 and Mn = 730 g•mol–1 molecular weight, in the absence or presence of the titanium tetrabutyloxide (Ti(OBu)4) as a catalyst to get multiblock copolyesters. The chemical structure of the synthesized copolyesters was investigated by size exclusion chromatography (SEC) and proton Nuclear Magnetic Resonance (1H NMR) spectroscopy. Moreover the differential scanning calorimetry (DSC) was used to explore their thermal properties. The ester-ester interchange reaction was observed between the two oligopolyesters, was studied and discussed in detail.
Wet electrospinning is a useful method for 3-dimensional structure control of nanofibrous materials. This innovative technology uses a liquid collector instead of the metal one commonly used for standard electrospinning. The article compares the internal structural features of polycaprolactone (PCL) nanofibrous materials prepared by both technologies. We analyze the influence of different water/ethanol compositions used as a liquid collector on the morphology of the resultant polycaprolactone nanofibrous materials. Scanning electron micro-photographs have revealed a bimodal structure in the wet electrospun materials composed of micro and nanofibers uniformly distributed across the sample bulk. We have shown that the full-faced, twofold fiber distribution is due to the solvent composition and is induced and enhanced by increasing the ethanol weight ratio. Moreover, the comparison of fibrous layers morphology obtained by wet and dry spinning have revealed that beads that frequently appeared in dry spun materials are created by Plateau-Rayleigh instability of the fraction of thicker fibers. Theoretical conditions for spontaneous and complete immersion of cylindrical fibers into a liquid collector are also derived here.
In this study, poly(vinyl alcohol) (PVA)/Glucose oxidase (GOx)/graphene biocomposite membranes were prepared using an electrospinning technique and used for enzyme immobilization. The PVA/GOx/graphene membrane’s morphology was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), while its electrochemical sensitivity was studied by chronoamperometry. Kinetic parameters were determined to clarify the role of graphene in enzyme immobilization, while a spectrophotometric assay was used to quantify the active enzyme. The results indicated that the presence of graphene helps to stabilize the enzyme’s conformation, facilitate the catalytic reaction, and increase the survivability of the enzyme.
Novel epoxy-benzoxazine emulsions designed for water-based coatings were prepared and investigated. Bisphenol A-based epoxy resins with molar weights of 340, 377 and 1750 g/mol along with epoxidized soybean oil were emulsified using mono- and bi-functional benzoxazine surfactants, which are able to react with epoxy resins at their cure temperature. The structure of synthesized surfactants carrying one or two polyether chains was confirmed using Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance and differential scanning calorimetry. Stability of emulsions was verified by particle diameters measurements. Coatings, made directly from emulsions, were dried and cured at elevated temperature using 3,3'-dimetoxybenzidine as curing agent to ensure a highly cross-linked structure of thermosetting films. Curing process, thermal properties and hardness of cured films were investigated. It was found that benzoxazine molecules were well incorporated into the epoxy network upon curing, which ensures no void structure of cured copolymer and enhanced coating properties.
UV photo-oxidation was first applied to fabricate superhydrophobic polyimide (PI) films in combination with fluoroalkylsilane (FAS) modification. During prolonged UV irradiation, commercial flat PI films evolved to form unique micro/nanostructures. Meanwhile, the root mean square (RMS) surface roughness increased from 1.74 to 53.70 nm, leading to a gradual increase of WCA from 105.1 to 159.2° after FAS treatment. After 72 h of UV radiation exposure, the micro/nano-structured and FAS-modified PI films exhibited superhydrophobicity with water contact angle (WCA) larger than 150° and sliding angle (SA) less than 5°. The superhydrophobicity remained even after annealing at 350°C, which enabled stable utilization under elevated temperature. Stable micro/nanostructures and chemical bonding of FAS were found to contribute to the high thermal endurance. Moreover, the formation mechanism of the superhydrophobic PI films was investigated. The proposed UV photo-oxidation method provides a new route for the industrial fabrication of thermally stable superhydrophobic PI films.
The state of carbon nanotube (CNT) dispersion in epoxy is likely to change in the process of composite production. In the present work CNT dispersion is characterized at different stages of nanocomposite preparation: in the original masterbatch with high CNT concentration, after masterbatch dilution, in the process of curing and in the final nanocomposite. The evaluation techniques included dynamic rheological analysis of the liquid phases, optical, environmental and charge contrast scanning electron microscopy, electrochemical impedance spectroscopy and dynamic mechanical analysis. The evolution of the CNT dispersion was assessed for two CNT/epoxy systems with distinctly different dispersion states induced by different storage time. Strong interactions between CNT clusters were revealed in the masterbatch with a longer storage time. Upon curing CNT clusters in this material formed a network-like structure. This network enhanced the elastic behaviour and specific conductivity of the resulting nanocomposite, leading to a partial electrical percolation after curing.
The morphology and the mechanical properties of polylactide/poly(hydroxybutyrate-co-hydroxyvalerate) blends of various compositions were studied. The statistical analysis of the scanning electron microscopy images allowed finding two statistical ensembles of the minor-phase particles. The first ensemble involves the dispersed particles, whereas the second one contains the coalesced particles. The mean diameters of both dispersed and coalesced minor-phase particles were calculated and plotted against the blend composition. Young’s modulus, tensile strength, elongation at break, and Charpy impact strength of the blends were determined and examined as a function of the blend composition. The Young’s modulus values were shown to be in accordance with theoretical predictions.