All issues / Volume 13 (2019) / Issue 5 (May)
This is an editorial article. It has no abstract.
This works aims at the development thermosetting resins derived from epoxidized linseed oil (ELO) of high biobased content, by using a mixture of crosslinking agents, i.e. methyl nadic anhydride (MNA) and maleinized linseed oil (MLO). By using only MNA as crosslinking agent, the obtained resins are characterized by high stiffness and, consequently, high fragility. When MLO content increasing in the crosslinking mixture, up to 25 wt%, a decrease in mechanical resistant and thermomechanical is detected, thus indicating that MLO can provide flexibility to ELO-based thermosetting resins which is an interesting issue to obtain tailored properties by selecting the appropriate mixture composition. In general, the thermosetting resin crosslinked with 10 wt% MLO and 40 wt% MNA gives balanced properties together with noticeable biobased content, thus broadening the potential of these materials for uses in green composites and coatings.
Magnetic field assisted electrospinning is supplemented by conductive sheets that envelop the magnets and have the same potential as the deposition electrode. By optimizing the experimental conditions, it is possible to produce wires made of polymer nanofibers that incorporate longitudinally oriented magnetic particles. The morphological and magnetic characterizations confirm the preferential orientations. The new nanofiber wires are easily aligned along the maximum intensity line of the applied magnetic field. Moreover, the nanostructured wires have high longitudinal elastomagnetic strain and high transversal deflection as a response to magnetic field stimuli. Therefore, these new threadlike aggregates of magnetic nanofibers could be very appealing for application in all microelectronic or biomedical devices whose functionality requires orientation or deformation.
The purpose of the present study was to investigate the effect of cellular structure on the impact strength of polypropylene/polyolefin elastomers blend foams produced by the continuous extrusion process. To create different cell sizes, two chemical blowing agents were employed: azodicarbonamide and sodium bicarbonate. Sodium bicarbonate created foams with bigger cell size and cell wall thickness than azodicarbonamide. The impact strength of the neat and blend foams were studied and correlated to the foam properties and structure. It was observed that the impact strength of blend foams was directly related to the concentration of polyolefin elastomers (POE). Increasing POE by up to 30 wt% increased the foam impact strength by more than 400%. On the other hand, Increasing POE content caused the cell size and cell wall thickness to be reduced. Moreover, an attempt has been made to establish a relationship between the impact strength and cellular structural parameters. It was found that in the blend foams with higher cell wall thickness the rough fracture of the cell walls was intensified and in turn, the impact strength of the foams improved further.
Nowadays successful recycling of rubber waste has been one of the greatest challenges in waste management. Difficulties in mechanical recycling are especially caused by the variability of raw materials, therefore, a processing simply combining them usually results in end-products with poor mechanical stability. Drawbacks of mechanical recycling of mixed plastics and blends of plastics and rubbers can be overcome by application of compatibilizing additives. Taking the commercial types into account only a few general kinds are available and their effectiveness is hindered by the structure as it cannot be fitted to the chemical structures of plastics processed together. Our study has been addressed to give a comprehensive outlook into a rubber recycling process and successful application of compatibilizing strategies for improving mechanical performance of waste elastomer containing polypropylene. Investigations have been carried out on effective elastomer concentrations, meanwhile on elastomer ratios of various types to each other and on proper structures of compatibilizers. Various mechanical properties could be improved even by 44% due to experimental additives compared to uncompatibilized blends. Mechanical test results have been confirmed by SEM, rheology and FT-IR, to name some of them.
Copolymerization of phthalonitrile-based resin containing benzoxazine and cyanate ester: Curing behaviors, fiber-reinforced composite laminates and improved properties
L. Chen, D. X. Ren, S. J. Chen, H. Pan, M. Z. Xu, X. B. Liu
Vol. 13., No.5., Pages 456-468, 2019
Vol. 13., No.5., Pages 456-468, 2019
Curing behaviors and copolymerization mechanisms between phthalonitrile-based resin containing benzoxazine (A-ph) and cyanate ester (CE) were characterized and discussed. Results indicated that copolymerization between A-ph and CE were comprised of ring-opening polymerization of oxazine rings and ring-forming polymerization of cyanate and nitrile groups. From them, ring-opening of oxazine occurred preferentially, followed by ring-forming of cyanate and nitrile groups, which were promoted by active hydrogen and amine structures generated from ring-opening of oxazine. Moreover, with increasing the content of CE (≥40 wt%), self-polymerization of cyanate would dominate the components of the resulting composites and reduces the thermal stability of fiber-reinforced composite laminates. Additionally, mechanical properties of composite laminates were also affected by the content of CE. Composite laminates with 10 wt% CE showed the highest flexural strength (622 MPa). The improved mechanical properties were also verified with investigation of dynamic thermomechanical analysis and morphology of fracture surfaces. These findings are helpful to improve the thermosetting resins in terms of their chemical structure, material properties, and processability.
Effect of ionic liquids on kinetic parameters of dicyanate ester polycyclotrimerization and on thermal and viscoelastic properties of resulting cyanate ester resins
A. Fainleib, O. Grigoryeva, A. Vashchuk, O. Starostenko, S. Rogalsky, A. Rios de Anda, T-T-T. Nguyen, D. Grande
Vol. 13., No.5., Pages 469-483, 2019
Vol. 13., No.5., Pages 469-483, 2019
A strong catalytic effect of 1.0 wt% ionic liquids (ILs) on kinetic parameters of dicyanate ester of bisphenol E(DCBE) polycyclotrimerization was evidenced, and structure-property relationships of resulting densely cross-linked cyanate ester resins (CERs) were investigated. Three different ILs with contrasted reactivity were employed as a catalysts: an aprotic IL, i.e. 1-octyl-3-methyl imidazolium tetrafluoroborate ([OMIm][BF4]), a protic IL, i.e. 2-(hydroxyethylamino) imidazolinium chloride ([HEAIm][Cl]), and a protic polymeric IL, i.e. poly(hexamethylene guanidine) toluene sulfonate ([PHMG][TS]). Both [HEAIm][Cl] and [PHMG][TS] were reactive towards DCBE monomer, whereas [OMIm][BF4] was chemically inert, as confirmed by Fourier Transform Infrared (FTIR) spectroscopy. Noticeably, the conversion (αc) of cyanate groups in the presence of ILs dramatically increased, and a significant dependence of αc values on IL chemical structure was found. The corresponding mechanisms of DCBE polycyclotrimerization in the presence of different ILs were proposed. All the CER/IL networks exhibited a high thermal stability inherent to neat CER, as shown by TGA, whereas unexpected significant changes of the viscoelastic characteristics for CER/IL networks compared to pure CER analogue were observed using DMTA.
Microbial cells immobilized in porous carriers as an effective technique has been recently studied and applied in various applications including wastewater treatment. High mechanical stability and large specific surface area are the key advantages of an ideal porous carrier. Immobilization of microbial cells in novel nanocomposite nanofibrous webs (NCNFWs) for use in bioremediation of heavy crude oil as sole carbon and energy sources in aqueous phase was the main focus of this study. Polyvinyl alcohol (PVA) and alginate (ALG) were selected as the polymer matrices for the electrospinning of nanofibrous webs (NFWs). In this study, preparation and application of PVA/ALG webs that were reinforced by halloysite nanotubes (HNTs) followed by cross-linking with glyoxal (GO) are described for the first time. The synthesized NFWs were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and tensile tests. Results showed that NC-NFWs have a great potential for bioremediation of crude oil, and removal performances were higher in immobilized systems (85 and 64%) compared to freely suspended cell system (48%) after 14 days. Also, maximal bacterial growth in culture containing 500 ppm crude oil was achieved by PVA/ALG/GO/ HNT7.5% which was almost 1.4 and 2.4 times higher than PVA/ALG/GO/HNT5% and free cell system at same inoculum concentration, respectively.