Iranian Journal of Polymer Science and Technology
Year:2017 | Volume:30 | Issue:1 |Papers Count:7

An epoxy resin was modified by silica nanoparticles and cured with an anhydride. The particles with different batches of 12, 20, and 40 nm sizes were each distributed into the epoxy resin ultrasonically. Electron microscopy images showed that the silica particles were well dispersed throughout the resin.Tensile test results showed that Young’s modulus and tensile strength increased with the volume fraction and surface area of the silica particles. The simultaneous use of two average sizes of 20 and 40 nm diameter silica particles still increased these mechanical properties but other combinations of silica particles were unsuccessful.A three-point bending test on each pre-cracked specimen was performed to measure the mode I fracture toughness energy. The fracture energy increased from 283 J/m2 for the unmodified epoxy to about 740 J/m2 for the epoxy with 4.5 wt% of 12 nm diameter silica nanoparticles. The fracture energy of smaller particles was greater because of their higher surface to volume ratio. The fracture energy results showed also that the combined nanoparticles has a synergic effect on the fracture toughness of nanocomposites. Simultaneous use of 10 and 20 nm particles increased the fracture energy to about 770 J/m2. Finally, crack-opening displacement was calculated and found to be in the range of several micrometers which was much larger than the sizes of particles studied. Thus, the toughening mechanisms of crack pinning and crack deflection have a negligible effect on improvement of toughness, nevertheless, the plastic deformation and plastic void growth are dominant mechanisms in epoxy toughening by nanoparticles.

Microcellular thermoplastic polyurethane foams are examined as absorbing materials in the X-band (8.2-12.4 GHz) frequency range by means of experiment. In this work, we aim to establish relationships between foam morphology including cell size and air volume fraction and electromagnetic properties including absorption, transmission and reflection quality. Nanocomposites based on thermoplastic polyurethane containing carbon black were prepared by coagulation method. In this procedure 15 wt% carbon black-containing nanocomposite was converted to microcellular foams using batch foaming process and supercritical carbon dioxide as physical foaming agent. The morphology of the foams were evaluated by scanning electron microscopy. S-parameters of the samples were measured by a vector network analyzer (VNA) and the effect of morphological parameters such as cell size and air volume fraction on the absorbing properties were investigated. We also established structure/properties relationships which were essential for further optimizations of the materials used in the construction of radar absorbing composites.Foaming reduced the percolation threshold of the nanocomposites by reducing the average distance between nanoparticles. Foaming and dielectric constant reduction reduced the reflection of the samples significantly. The increase in air volume fraction in the foam increased absorption per weight, due to multiple scattering in the composite media. The sensitivity of electromagnetic wave due to the variation of cell size is strongly weaker than that of the variation of air volume fraction. Electromagnetic properties of the microcellular foams deviated a little from effective medium theories (EMTs). Air volume fraction of the cells were a function of cell size and smaller cells showed higher absorption.

The physical, chemical and mechanical properties of polymer systems depend on the micro-structural characteristics of their macromolecular chains. Along with the most characteristic kinetic parameters in copolymerization reactions are the reactivity ratios, which give a clear idea of the average composition and the monomer sequence distribution in copolymer systems. This research studies the solution radical copolymerization of methacrylic acid (MAA) - ethyl acrylate (EA) system at low conversion with 2, 2' -azobisisobutyronitrile (AIBN) as thermal initiator at 60°C in deuterated dimethyl sulfoxide (DMSO-d6) as a reaction solvent.In this case, the monomer reactivity ratios were determined using linear off-line1H nuclear magnetic resonance spectroscopy (1H NMR) methods such as Mayo-Louis, Finemann-Ross, Inverted Finemann-Ross, Ezrielev-Brokhina-Roskin, Joshi-Joshi, Kelen-Tudos, extended Kelen- Tudos, Mao-Huglin at low and high conversions. The next estimation process in off-line 1H NMR methods were performed by applying techniques based on ordinary least square (OLS) and generalized least square (GLS).The results showed that the GLS approach compared to the OLS increased regression coefficients (R2) and the order of magnitude of parameter variances obtained from GLS was many times lower than that obtained from OLS. In addition, the monomer reactivity ratios obtained by the Mao-Huglin method and the GLS approach showed the best linear estimation.

In recent years considerable efforts have been made to develop gas impermeable polymer systems. Compared with metal system counterparts they have advantages such as low density and production costs. The most important challenge in development of impermeable polymer systems is to reduce their gas permeability by proper selection of system composition and process conditions. In this work, nanoparticles were initially synthesized using Al (NO3) 3•9H2O and sodium dodecyl sulfate as a structure-directing agent via hydrothermal method and a plate-like structure was characterized by FESEM and EDAX analyses. In the second step, epoxy/platelike nanoalumina nanocomposites and epoxy-carbon fiber composites containing 1, 2.5, and 5 wt% nanoalumina were prepared. The effect of nanoparticle loading level on permeability of nitrogen, argon, and carbon dioxide in epoxy/plate-like nanoalumina nanocomposites was investigated. It was observed that the permeability of epoxy/ plate-like nanoalumina nanocomposites toward nitrogen, argon, and carbon dioxide gases reduced 83%, 74%, and 50%, respectively. It was deduced that the permeability reduction was clearly associated with the diameter of gas molecules. Generally speaking, the results showed that the incorporation of plate-like nanoalumina particles significantly reduced the gas permeability. Also, carbon dioxide gas permeability of carbon fiber epoxy composites containing plate-like nanoalumina was investigated to show the effect of ingredients on the gas permeability of the system. The results indicated that carbon dioxide gas permeability of epoxy carbon fiber composite containing 5 wt% of plate-like nanoalumina was totally reduced 84%.

The progress in scientific and technical products and increasing needs for advanced electrical and electronic devices have motivated researchers to investigate new ideas in this field. One of the main challenges in this way is the connection between microchips and other parts of electrical boards. Leadbased alloys, especially tin-lead solders are the conventional materials which have destructive effects on living organisms and the environment. Electrical conductive adhesives, used as replacement for lead-based solders, are composites comprised of a polymer matrix as adhesive material and conductive fillers for conduction of electricity. In this research conductive adhesives were prepared using diglycidyl ether of bisphenol A epoxy resin as the polymer matrix and various amounts of silvercoated copper powder as conductive filler. The copper powder was coated with silver using electroless plating. The structural properties of the filler was characterized by inductivity coupled plasma analysis. The morphology of the samples was investigated by scanning electron microscopy. The conductive properties, shear strength and thermal stability of adhesives were also evaluated. The conductive adhesive containing 70 percent by weight of silver-coated copper powder showed optimum properties. For this sample an electrical resistivity of 2.8×10-2  W.cm and a shear strength of 10.77 MPa were obtained. In addition, the weight loss during thermogravimetric reduction was 23.69% for the optimum sample, while it was 88.71% for the sample with no filler, indicating an improvement in thermal stability due to adding filler.

Asymmetrically mixed matrix Matrimid-MIL-53 membranes with silicone cover layer were fabricated. For better understanding of membrane fabrication process, three main parameters of fabrication, Matrimid concentration, silicone concentration and weight percentage of metal organic framework (MIL-53) particles, were optimized by an experimental design method. Cross-section SEM images were used to study the membrane structure and polymer-particles interface. Moreover, thermal resistance of the membranes and the existence of various bonds in them were investigated by FTIR and TGA analyses. The results showed that membranes had porous structure with finger-like morphology. At low and moderate percentages of particles, there were no non-selective voids observed at polymer-particles interface.The thermal resistance of membranes increased with the increase of MIL-53 weight percentage and the destruction temperature of polymer increased from 410°C to 450°C.The permeability tests results showed that the Matrimid (20% wt) -MIL-53 (15% wt) / PMHS (10%wt) membrane exhibited the highest level of CO2/CH4 selectivity (23.6).However, in the membrane with 30 wt% particles loading, selectivity decreased due to particles agglomeration and void formation. The experimental design results showed that the concentration of silicone in covering solution had significant effect. CO2 and CH4 permeability decreased and ideal selectivity of CO2/CH4 increased with silicone concentration enhancement. Although the Matrimid concentration had a little effect on CO2/CH4 ideal selectivity, its enhancement increased the selectivity of the gases.The optimization results showed the membrane with 17.8% of Matrimd polymer, 13.2% of silicone polymer and 15.5 wt% of MIL-53 particle displayed the highest selectivity and CO2 permeability.

Polysulfone (PSf) mixed matrix membranes were prepared by embedding pristine montmorillonite (Mt) together with amino acid (M-AA) -modified Mt in order to remove arsenic from water. The qualitative and quantitative comparisons were made between mixed matrix membranes and pure PSf membrane by FE-SEM, XRD, contact angle, AFM, pure water flux (PWF) and mechanical strength tests. The XRD and FTIR results showed that Mt was successfully modified with amino acid, and the amino functional groups were protonated. After modification with amino acid, the Zeta potential of Mt changed from negative to positive. Maximum improvement in PWF, porosity and hydrophilicity was obtained for PSf/Mt mixed matrix membrane due to hydrophilic properties of Mt. However, the modified Mt showed good interaction with PSf and increased the mechanical strength of mixed matrix membranes. Furthermore, the adsorption experiments showed the PSf/M-AA membranes with better arsenic removal efficiency because of positive surface charge of M-AA. The obtained results showed that by increasing M-AA content from 0 to 1.5 wt%, pure water flux, surface hydrophilicity, roughness, mechanical strength and arsenic adsorption capacity of the membranes increased. The neat PSf membrane showed a very low adsorption capacity for As (V), however the adsorption capacities of 1.4 and 16 mg/g were obtained for the mixed matrix membranes each containing 1.5 wt% of Mt and M-AA. Finally, membrane re-usability of the 1.5 wt% M-AA embedded PSf membrane was assessed by conducting five cycles of adsorption experiments and membrane regeneration in a dead-end filtration system. The obtained results confirmed the applicability of the prepared membrane for multiple cycles.