All issues / Volume 11 (2017) / Issue 12 (December)
This is an editorial article. It has no abstract.
Highly soluble fluorinated ethynyl-terminated imide (FETI) oligomers were prepared via a conventional one-step method in m-cresol, using 4, 4′-(hexafluoroisopropylidene) diphthalic anhydride and 2, 2′-bis(trifluoromethyl) benzidine as the monomers, and ethynylphthalic anhydride as the end-capper; then interpenetrating polymer networks (IPN) were formulated from FETI oligomers and bisphenol A dicyanate ester (BADCy) through a solvent-free procedure, and their thermal, mechanical, and dielectric properties were fully characterized. The curing mechanism was studied by model reactions using nitrogen nuclear magnetic resonance. As evidenced by differential scanning calorimetry analysis and rheological measurements, the FETI/BADCy blends exhibited lower curing temperature and shorter gelation time in comparison with pure BADCy due to the catalytic effects of ethynyl and residue amic acid groups. The properties of IPNs were fully compared with those of polycyanurate, and the results revealed that the incorporation of FETI into cyanate ester resins could significantly improve the toughness, glass transition temperatures, mechanical and dielectric properties of the resultant IPNs.
Antibacterial polymeric nanocomposites synthesized by in-situ photoreduction of silver ions without additives inside biocompatible hydrogel matrices based on N-isopropylacrylamide and derivatives
M. Monerris, M. Broglia, I. Yslas, C. Barbero, C. Rivarola
Vol. 11., No.12., Pages 946-962, 2017
Vol. 11., No.12., Pages 946-962, 2017
Synthesis of antibacterial nanocomposite obtained by in-situ photoreduction of Ag+ ions impregnated inside a biocompatible hydrogel matrix is described. Hydrogel matrixes based on N-isopropylacrylamide (PNIPAM) and copolymers are synthesized by free radical polymerization in aqueous medium. The hydrogels are loaded with Ag+ ions and then silver nanoparticles (Ag-NPs) are obtained in-situ by application of UV light without using additives. Ag-NPs formation inside hydrogels is confirmed by UV–visible spectroscopy, scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM). An extensive characterization of nanocomposites is performed by determining the partition coefficient of Ag+ ions before photoreduction, the Ag-NPs mass loaded per gram of hydrogel as a function of irradiation time, swelling capacity and volume phase transition temperature. Fourier Transform Infrared (FTIR) spectra indicate the loss of some functional groups of the polymer backbone during reduction of Ag+ ions whereas 13C NMR spectra do not show any change in the main carbon chain. Nanocomposites show antibacterial activity against Pseudomonas aeruginosas by release of Ag+ ions while Ag-NPs remain inside matrix. Reducing/stabilizing character of hydrogel and antibacterial activity of nanocomposite depend on the chemical composition of the matrix.
This paper addresses the utilisation of fused deposition modelling (FDM) technology using polyamide 12, incorporated with bioceramic fillers (i.e. zirconia and hydroxyapatite) as a candidate for biomedical applications. The entire production process of printed PA12 is described, starting with compounding, filament wire fabrication and finally, FDM printing. The potential to process PA12 using this technique and mechanical, thermal and morphological properties were also examined. Commonly, a reduction of mechanical properties of printed parts would occur in comparison with injection moulded parts despite using the same material. Therefore, the mechanical properties of the samples prepared by injection moulding were also measured and applied as a benchmark to examine the effect of different processing methods. The results indicated that the addition of fillers improved or maintained the strength and stiffness of neat PA12, at the expense of reduced toughness and flexibility. Melting behaviours of PA12 were virtually insensitive to the processing techniques and were dependent on additional fillers and the cooling rate. Incorporation of fillers slightly lowered the melting temperature, however improved the thermal stability. In summary, PA12 composites were found to perform well with FDM technique and enabling the production of medical implants with acceptable mechanical performances for non-load bearing applications.
A series of thermoplastic polyimide (PI) films (PI-1~PI-5) with intrinsic heat sealability have been synthesized by the high-temperature polycondensation reaction of asymmetrical 2,3,3ꞌ,4ꞌ-oxydiphthalic anhydride (aODPA) and various aromatic diamines in order to meet the demands of advanced flexible copper clad laminates (FCCL). The derived PI resins had good solubility in polar aprotic solvents, such as N-methyl-2-pyrrolidone (NMP) and N,N-dimethylacetamide (DMAc) at a solid content up to 20 wt%. Flexible and tough films could be cast from the PI/NMP solution and the films exhibited tensile strength higher than 83 MPa. Among the developed PIs, those derived from aODPA and benzimidazole-containing diamines, including PI-4 from aODPA and 2-(4-aminophenyl)-5-aminobenzimidazole (4APBI) and PI-5 from aODPA and 2-(3-aminophenyl)-5-aminobenzimidazole (3APBI) exhibited the highest thermal stability (glass transition temperatures, Tg > 340°C), lowest linear coefficients of thermal expansion (CTE < 35·10–6 1/K), and superior adhesion to copper foil (peeling strength >1.0 N/mm). Flexible copper clad laminate (FCCL) with no curling was successfully prepared from PI-4 and copper foil.
A new and convenient route to the regiocontrolled synthesis of a cellulose-based derivate copolymer (2,3-di-O-polycaprolactone-cellulose) grafting ε-caprolactone (ε-CL) from α-cellulose, cellulose-graft-polycaprolactone (cellulose-g-PCL), by a classical ring-opening polymerization (ROP) reaction, using stannous octoate (Sn(Oct)2) as catalyst, in 68% concentration of zinc chloride aqueous solution at 120 °C was presented. By controlling the hydroxyl of cellulose/ε-CL, catalyst/monomer ratio and the reaction time, the molecular architecture of the copolymers can be altered. The solubility of cellulose in zinc chloride aqueous was indicated by UV/VIS spectrometer and rheological measurements. The structures and thermal properties of cellulose-g-polycaprolactone copolymers were characterized using Fourier Transform Infrared (FT-IR), Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR), X-ray Diffraction (XRD), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The interesting results confirm that zinc chloride solution can break the intra-molecular hydrogen bonds of cellulose selectively (not only O3H···O5, but also O2H···O6), and has no effect on the inter-molecular hydrogen bonds (O6H···O3). And the grafting reactivity of hydroxyl on cellulose is C2–OH > C3–OH >> C6–OH in zinc chloride solution, and this is clearly different from other researches. Most importantly, this work confirms that the method to regiocontrolled synthesis cellulose-based derivative polymers by regiobreaking hydrogen bonds is feasible. It is strongly believed that the new discovery may give a novel, environmental, simple and inexpensive method to modify cellulose chemically with various side chains grafted on a given hydroxyl, through liberating hydroxyl as reactive group from hydrogen bonds broken selectively by different solvents.
Natural Rubber (NR) grafted with 3-octanoylthio-1-propyltriethoxysilane (NXT) was prepared by melt mixing using 1,1′-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane as initiator at 140 °C with NXT contents of 10 and 20 parts per hundred rubber [phr] and initiator 0.1 phr. The silane grafted on NR molecules was confirmed by Fourier transform infrared (FTIR), proton nuclear magnetic resonance (1H-NMR) and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDX). Based on 1H-NMR, the use of 10 and 20 phr (parts per hundred resin) of silane resulted in grafted NXT onto NR of 0.66 and 1.32 mol%, respectively, or a grafting efficiency of approx. 38%. The use of NXT-grafted NR as compatibilizer in silica-filled NR compounds, to give a total amount of NXT in both grafted and non-grafted forms in the range of 0.8–6.1 wt% relative to the silica, decreases the Mooney viscosity and Payne effect of the compounds, improves filler-rubber interaction, and significantly increases the tensile properties of the silica-filled NR-compounds compared to the non-compatibilized one. At the same silane-content, the use of silane-grafted NR gives slightly better properties than the straight use of the same silane. With sulfur compensation, the use of NXT-grafted-NR with about 6 wt% NXT relative to the silica gives technical properties that reach the levels obtained for straight use of bis-(3-triethoxysilyl-propyl)tetrasulfide (TESPT) at 8.6 wt% relative to the silica.
In this study, we systematically investigated the effect of various process parameters, such as surfactant concentration, core-to-shell ratio taken in the initial feed, temperature and agitation speed on the core content of microcapsules. For this study epoxy loaded poly(methyl methacrylate) microcapsules were prepared by solvent evaporation method. Taguchi orthogonal array with L25 matrix was implemented to optimize the experimental parameters for such microcapsules. The signal-to-noise ratio (SNR) and analysis of variance (ANOVA) were also performed to determine the optimum parameters and significance of various parameters. Morphological characterization (optical microscopy, scanning electron microscopy and transmission electron microscopy) and particle size analysis (mean particle size and particle size distribution) was done to investigate the effect of various parameters on the prepared microcapsules. SNR analysis identified the optimum levels of various parameters as: surfactant concentration- 10 wt%, core-to-shell ratio- 3:1, temperature- 40 °C and agitation speed- 300 rpm. ANOVA analysis showed that surfactant concentration was the most significant parameter in improving the core content of such microcapsules. The findings of Taguchi method were also verified with contour plots. Maximum core content obtained under optimum conditions was 63.53 wt% and such microcapsules can find applications for the development of self-healing polymer composites.