All issues / Volume 11 (2017) / Issue 11 (November)
This is an editorial article. It has no abstract.
Rapid retardation and arresting of fatigue crack are successfully realized in the epoxy composite containing microencapsulated epoxy and ethanol solution of antimony pentafluoride-ethanol complex (SbF5·HOC2H5/HOC2H5). The effects of (i) microcapsules induced-toughening, (ii) hydrodynamic pressure crack tip shielding offered by the released healing agent, and (iii) polymeric wedge and adhesive bonding of cured healing agent account for extension of fatigue life of the material. The two components of the healing agent can quickly react with each other soon after rupture of the microcapsules, and reconnect the crack only 20 seconds as of the test. The applied stress intensity range not only affects the healing efficiency, but also can be used to evaluate the healing speed. The present work offers a very fast healing system, and sets up a framework for characterizing speed of self-healing.
Self-healing epoxy coatings were prepared with different nanotubes as reservoirs for epoxy monomer (healing agent). The nanotubes selected for the current study were TiO2 nanotubes with two different tube diameter (TNT1 and TNT2) and naturally occurring hallyosite nanotubes (HNT). These self-healing coatings were subjected to accelerated weathering exposure. The weathering stability of the coatings were observed. The surface morphology, chemical changes and surface roughness were studied as a function of weathering exposure period. These studies confirmed that the long term stability of the coatings highly depend on the nanotube parameters such as nature, surface area and diameter. It was found that the photocatalytic degradation of epoxy matrix with TiO2 nanotubes was prominent in TNT1 filled coating compared with their TNT2 variant. The higher possibility of exposure of epoxy monomer encapsulated inside both HNT and TNT2 facilitated the cure reaction with UV light to create new chains during weathering.
A simple and environmentally-friendly approach for the preparation of porous melamine-formaldehyde resins (PMFRs) was developed by using low-boiling-point solvents, such as water, as pore-forming agent. With using dimethyl sulfoxide (DMSO) and low-boiling solvents cosolvent method, PMFRs with a high specific surface area and well-defined pore structure can be synthesized at a low reaction temperature of 140 °C for a short reaction duration in 20 hours, which can replace the conventional methods that use dimethyl sulfoxide (DMSO) as reaction medium and require 3 days at 170 °C to achieve similar surface area. When loaded with polyethylenimine (PEI), the PMFR-PEI-30% showed good CO2 adsorption performance with a capacity of up to 2.89 mmol/g at 30 °C. These results bring new perspectives for the development of lowcost and environmentally-friendly synthetic methods for porous materials, which can boost their widespread applications.
The main goal of this work was the development of fully biobased unsaturated polyesters (UPs) that upon crosslinking with unsaturated monomers (UM) could lead to greener unsaturated polyester resins (UPRs) with similar thermomechanical properties to commercial fossil based UPR. After the successful synthesis of the biobased UPs, those were crosslinked with styrene (Sty), the most commonly used monomer, and the influence of the chemical structure of the UPs on the thermomechanical characteristics of UPRs were evaluated. The properties were compared with those of a commercial resin (Resipur 9837©). The BioUPRs presented high gel contents and contact angles that are similar to the commercial resin. The thermomechanical properties were evaluated by dynamic mechanical thermal analysis (DMTA) and it was found that the UPR synthesized using propylene glycol (PG), succinic acid (SuAc) and itaconic acid (ItAc) presented very close thermomechanical properties compared to the commercial resin.
This paper reports on the photocatalytic activity showed by nanocomposites of TiO2 with low density polyethylene (LDPE) and high density polyethylene (HDPE) (10, 20 wt%) for the degradation of methyl orange in aqueous medium under visible light irradiation. TiO2 was synthetized by sol-gel process, and the polymers were incorporated by impregnation. Both the pure TiO2 and the nanocomposites were characterized using different physico-chemical techniques including specific surface area analysis, X-ray diffraction analysis, transmission electron microscopy, ultraviolet-visible and photoluminescence spectroscopy, and X-ray photoelectron spectroscopy. All the prepared nanocomposites showed an absorption edge in the visible region. TiO2(90)/LDPE photocatalyst showed the best degradation efficiency after 180 minutes of reaction, without notorious decrease of degradation efficiency after three consecutive uses. Photoluminescence and X-ray photoelectron spectroscopy analyses suggested the presence of vacancies in the TiO2 structure promoted by a Ti–O–C interaction being responsible for the photocatalytic activity enhancement under visible light irradiation.
Three donor/acceptor (D/A)-type two-dimensional polythiophenes (PTs; PBTFA13, PBTFA12, PBTFA11) featuring difluorobenzothiadiazole (DFBT) derivatives as the conjugated (acceptor) units in the polymer backbone and tertbutyl–substituted triphenylamine (tTPA)-containing moieties as (donor) pendants have been synthesized and characterized. These PTs exhibited good thermal stabilities, broad absorption spectra, and narrow optical band gaps. The cutoff wavelength of the UV–Vis absorption band was red-shifted upon increasing the content of the DFBT units in the PTs. Bulk heterojunction solar cells having an active layer comprising blends of the PTs and fullerene derivatives [6,6] phenyl-C61/71-butyric acid methyl ester (PC61BM/PC71BM) were fabricated; their photovoltaic performance was strongly dependent on the content of the DFBT derivative in the PT. Incorporating a suitable content of the DFBT derivative in the polymer backbone enhanced the solar absorption ability and conjugation length of the PTs. The photovoltaic properties of the PBTFA13-based solar cells were superior to those of the PBTFA11- and PBTFA12-based solar cells.
Binary blends composed of 1,3-bis (3,4-dicyanophenoxy) benzene (3BOCN) and ionic liquids (ILs) with different molecular structures were prepared. The curing behavior of these 3BOCN/ILs blends were studied by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and rheological analysis. The study suggested that the blends possessed a wide processing window and the structures of ILs (anion, cation and alkyl chain length at cation) had an effect on curing behavior. The 3BOCN/[EPy]BF4 resins were prepared at elevated temperature. IR spectra of the resins showed that there were triazine and isoindoline formed in curing process. The TGA and dynamic mechanical analysis (DMA) revealed that the resins have excellent thermal stability together with high storage modulus and high glass transition temperature (Tg). Dielectric properties, long term oxidative aging and water uptake measurements of the resins suggested the IL brought some unique properties to the resins.