دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و ششم شماره 4 (پیاپی 126، آبان 1392)

In the some applications like as morphing technology, high strain and anisotropic behavior are essential design requirements. The corrugated composite sheets due to their special geometries have potential to high deflection under axial loading through longitudinal direction of corrugation. In this research, the strain and the anisotropic behavior of corrugated composite sheets are investigated by fabricating glass/epoxy samples with trapezoidal geometries. For evaluation of the mechanical behavior of the composites the samples were subjected to tension and flexural tests in the longitudinal and transverse directions of corrugation. In order to determine anisotropic behavior of the corrugated sheets, two approaches were introduced: (1) tensile anisotropic (E*) and (2) flexural anisotropic (D*). The anisotropic behavior and ultimate deflections were investigated theoretically and experimentally. In this paper, mechanical behaviors based on theoretical and experimental analysis including the elastic constants and stiffness matrices of trapezoidal corrugated composite sheets were studied and the results were verified by finite element method. The results of the numerical and analytical solutions were compared with those of experimental tests. Finally, the load-displacement curves of tensile tests in longitudinal direction of corrugation, the ultimate deflection and anisotropy behavior of these exclusive composite sheets in the corrugated composite sheets were studied experimentally. The experimental results of the trapezoidal corrugated sheets showed that one of the most important parameters in the ultimate strain was amplitude of the corrugation elements. Generally, increasing the amplitude and element per length unit of trapezoidal corrugated specimen led to higher ultimate strain.

Oleic acid was used as a hydrophobic agent to modify cellulose nanofiber (CNF) and the reaction time and fatty acid content were tested in relation to the hydrophilic properties of the products as well as the physicochemical properties of CNF. It was found that the degree of substitution (DS) increased by extending the reaction time though the fatty acid content had no effect on hydrophobicity of CNF. The success of the esterification reaction was confirmed by Fourier transform infrared spectroscopy. Higher degree of substitution led to increased contact angle of CNF surfaces with water, which indicated the increased surface hydrophobicity of modified CNF. The X-ray diffraction analyses showed a lowering trend in crystallinity index and crystallite size with increases in DS value. Surface modification changed the thermal stability of CNF by lowering the degradation temperature from 290.8°C for unmodified cellulose to 195.4°C for highly esterified cellulose. Scanning electron microscopy micrographs revealed that after esterification of CNF with oleic acid, its filamentous shape was preserved. As a result, although the surface modification of CNF by fatty acid increased its hydrophobicity and its ability to mix with non-polar polymers, but it changed CNF physicochemical characteristics and weakened its functional properties.

The effects of interchange reactions on the crystallization, melting, and dynamic mechanical thermal behavior of poly(ethylene terephthalate)/poly(ethylene naphthalate) (PET/PEN) blends prepared by melt mixing have been investigated. The occurrence of interchange reactions has been verified by proton nuclear magnetic resonance (1H NMR). Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used to study the effect of transesterification reaction on crystallinity, melting and dynamic mechanical properties of the blends. It was found that by extension of transesterification, the miscibility of the blend increased. Time and temperature of mixing were most important parameters affecting the transesterification level. On blending, the melt crystallinity of poly(ethylene terephthalate) was reduced and in contrast that of poly(ethylene naphthalate) was increased; where melt crystallization temperatures of both phases were depressed. A single composition-dependent glass transition peak, which was indicative of miscibility, was detected in second heating thermograms of the blends. It was observed that cold crystallization of poly(ethylene terephthalate) phase decreases while that of poly(ethylene naphthalate) was suppressed on blending. It was found that each phase crystallized individually and a melting point depression which was an indication of compatibility was evident at the same time. Dynamic mechanical analysis confirmed the proton nuclear magnetic resonance and differential scanning calorimetry results. The secondary viscoelastic transitions of each phase in blend samples were also probed. Increment of peak area in the loss factor has implied the miscibility of blend due to formation of poly(ethylene terephthalate)/poly(ethylene naphthalate) random copolymer.

Poly (vinylacetate-co-butylmethacrylate) was prepared in presence of potassium persulphate as an oxidizing agent in aqueous solution of dodecylbenzene sulfonate sodium as an emulsifying agent. Then, aniline was polymerized by chemical oxidation method at three different concentrations of aniline monomer (0.1, 0.2 and 0.3 M) in toluene in presence of poly(vinylacetate-co-butylmethacrylate) in order to obtain polyaniline/poly(vinylacetate-co-butylmethacrylate). To prepare conducting-latex of polyanisidine/poly(vinylacetate-co-butylmethacrylate) the same method was employed as above for aniline monomer in obtaining conducting polyaniline/poly(vinylacetate-co-butylmethacrylate) latex. In addition, the purification of conducting-latex polymers, polyaniline/poly(vinylacetate-co-butylmethacrylate) and polyanisidine/poly(vinylacetate-co-butylmethacrylate) was conducted and preparation of tin layer films of conducting-latex polymers was carried out by casting method on glassy lames. The electroactivity properties of the prepared latex-polymers, polyaniline/poly(vinylacetate-co-butylmethacrylate) and polyanisidine/poly(vinylacetate-co-butylmethacrylate) were investigated by cyclic voltammetery (CV). The voltamogrames showed that the latex films were electroactive. Because of conductivity and electroactivity, the obtained films may find applications in anti-corrosion coatings. The anti-corrosion properties of conducting-latex polymers were studied on aluminum surface by impedance technique. The structure of the prepared conducting-latex polymers was confirmed by Fourier transform infrared (FTIR). Finally, the electrical conductivity of synthesized conducting-latex polymers, polyaniline/poly(vinylacetate-co-butylmethacrylate) and polyanisidine/poly(vinylacetate-co-butylmethacrylate) was measured by four probe technique.

The late transition metal catalysts based on end group of transition metals in the periodic table like Ni, Fe, Co, Pd, Pt were developed rapidly in polyolefin industrial productions. These metals with suitable ligands exhibited specific properties and appropriate activities in the production of polyolefins. These catalysts based on bulky bisimine ligands usually depend on the structures of the ligands and the ortho group position on the aryl ligands show very interesting behaviors in olefin polymerization. When these groups, located in the ortho positions of aryl ligands, become larger, it would have lesser chance in leading to β hydrogen elimination reactions. The ligand 1,4-bis (2,6-diisopropyl phenyl) acenaphthene was synthesized by reaction of 2,6- diisopropyl aniline and acenaphthene quinone. The synthesized ligand was then added on nickel (II) dibromide salt that produced the 1,4-bis(2,6-diisopropyl phenyl) acenaphthene nickel (II) dibromide catalyst. The structure of the catalyst was fully characterized by IR, NMR techniques. Ethylene polymerization was performed using the prepared catalyst and the effects of parameters such as, polymerization temperature, cocatalyst, to catalyst molar ratio and monomer pressure, were investigated. One of experimental design methods (Box Behnken) was used to minimize the number of tests. The highest activity of catalyst [1420 kgPE/molNih] was obtained at monomer pressure 5 atm, [Al]:[Ni] = 1000 and polymerization temperature of 25°C. Some of the produced polymers were characterized by DSC and 13CNMR. The branched structures with higher methyl branch contents were observed in some polyethylene products.

Blend membranes of synthesized polyurethane based on toluene diisocyanate (TDI), polydimethylsiloxane (PDMS) and polytetramethylene glycol (PTMG) with polyamide12-b-PTMG were prepared by solution casting technique. The synthesized polyurethane-polydimethylsiloxane and PU-PDMS/polyamide12-b-PTMG blend membranes were characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). In the FTIR spectrum of the synthesized PU-PDMS, the disappearance of NCO stretching vibration at 2270 cm−1 was used to confirm the completion of the reaction. According to our DSC results, the use of higher polyamide12-b-PTMG content in PU-PDMS/polyamide12-b-PTMG blends led to greater compatibility between the two phases. The SEM images showed that the blends with polyamide12-b-PTMG (20 wt%) were significantly more homogeneous in the micrometric scale compared to other samples. Gas transport properties have been determined for N2, CO2 and He gases and the obtained permeability values were correlated with the properties of the blends. The comparison of the results with that of the pure PU-PDMS membrane showed that the blend membranes had a higher permeability toward CO2 and lower toward N2 gas. The blend membrane with 20 wt% polyamide12-b-PTMG showed higher CO2 permeability (≈105 Barrer) compared to PU-PDMS membrane. By introduction of polyamide12-b-PTMG into PU-PDMS matrix a perceptible rise in helium ideal selectivity of the blend membranes was observed. In blend membranes with 5-20 wt% polyamide12-b-PTMG contents, an enhancement of CO2/N2 (244%), He/N2 (20%) and CO2/He (103%) selectivity factor was observed. The experimental permeability values of the blend membranes were compared with the calculated permeability based on a modified additive logarithmic model.

Rapeseed oil-filled ethyl cellulose microcapsules were prepared using a two-step solvent evaporation method. The prepared oil-filled microcapsules were characterized by; optical microscopy, scanning electron microscopy and particle size analyzer. The mechanical properties of carboxylated styrene/butadiene copolymer latex films containing various levels of microcapsules were studied using DMTA and tensile strength measurements. The characterization test results showed that rapeseed oil-contained microcapsules with a regular spherical shape, diameter range of 10-45 μm, and a relatively rough porous shell were successfully prepared. The results also revealed that the overall mechanical properties of the latex films containing oil-filled microcapsules improved, due to reinforcing effect of capsules within the latex films; with the best results using 1-2 wt% of oil-filled microcapsules. The improved results were obtained in reinforcing the samples before tests such as tensile tension, capsule rupturing and the oil release within the polymeric network by maintaining the integrity of the films by plasticization of the surrounding polymeric network, increased elongation-at-break, and enhanced resistance against tear or break. With further increasing of microcapsules content up to 3 wt%, there was a drop in overall mechanical properties of latex films, due to possible aggregation of microcapsules, presence of free rapeseed oil within the latex film and weak polymer/microcapsules interface. A proper distribution and dispersion of oil-filled microcapsules within the latex film, and rupture of sufficiently large microcapsules under stress, oil release within the polymeric network and easy movement of the chains were the main requirements for achieving latex film with good mechanical properties.