Iranian Polymer Journal
Year:2011 | Volume:20 | Issue:10 (136)|Papers Count:7

N-Substituted polyaniline (poly (N-octadecylaniline)) was prepared through N-alkylation reaction, by introducing octadecyl chains into a highly stable "leucoemeraldine base" (LEB) form of polyaniline nanostructure synthesized via a new chemical polymerization method. The polymer was characterized by FTIR, 1H NMR and UV-Vis spectroscopy techniques. Thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC) methods were carried out to investigate thermal behaviour of the obtained poly (N-octadecylaniline). Thermal analysis showed two endothermic transitions at 41oC and 60oC during the heating and two exothermic transitions at 20oC and 43oC during the cooling stages. Scanning electron microscopy (SEM) study revealed a significant morphology change by grafting of octadecyl chains onto the polyaniline backbone. The electrical conductivity of poly (N-octadecylaniline) that was doped with dodecylbenzene sulphonic acid (DBSA) was 8×10-4 S.cm-1 and the investigation of cyclic voltammograms (CV) showed that the electroactivity of this polymer is acceptable. The obtained polymer was completely soluble in non-polar organic solvents such as xylene and n-hexane. A thin flexible film of the synthesized poly (N-octadecylaniline) was prepared by casting from n-hexane solution and the electroactivity property of the obtained film was investigated by CV method.

Poly (butylene terephthalate) (PBT) nanofibres containing functionalized multiwalled-carbon nanotubes (F-MWNTs) were prepared by electrospinning technique. The F-MWNTs were prepared by the introduction of aromatic amine (COC6H4-NH2) groups onto their side wall via Friedel-Crafts acylation. The diameter of neat PBT nanofibres was below 500 nm and had smooth surface. The scanning electron microscopy (SEM) also showed that F-MWNTs/PBT composite nanofibres mat had similar morphology with that of pure PBT and without beads. The surface of the composite nanofibres was also smooth even by adding high quantity of F-MWNTs. The F-MWNTs were embedded within nanofibres and well oriented along the nanofibre axis, as confirmed by transmission electron microscopy (TEM). The mechanical properties (specific tensile strength and moduli) of the PBT nanofibres were significantly enhanced by the incorporation of F-MWNTs. It was also observed that the melt-crystallization temperature (Tc) of PBT nanofibres shifted to a higher temperature (about 10oC) by the incorporation of F-MWNTs which might be due to the nucleating effect of the nanotubes.

Poly (methyl methacrylate-co-butyl acrylate) /tetrabutylphosphonium modified montmorillonite (P (MMA-co-BA) /P-MMT) composite films were prepared by simple solution casting technique. P (MMA-co-BA) was synthesized through solution polymerization in the presence of benzoyl peroxide (BPO) as an initiator. After modification via cation exchange reaction by tetrabutylphosphonium bromide, the organoclay was dispersed in toluene and added into P (MMA-co-BA) solution. The well-dispersed mixture was cast by doctor blade technique to obtain the composite films. The P-MMT content in the composites was varied (i.e., 1, 2, 3 and 6 wt%) in order to study its effects on thermal stability, mechanical properties and UV shielding ability. The structure of P-MMT in the composites was investigated by XRD technique. The composites containing 1 and 2 wt% of P-MMT showed the d001 peak slightly shifted to lower 2q, indicating mainly intercalated structure occurred with some agglomerations of particles. The intercalated structure of P (MMA-co-BA) /P-MMT 2% composites was observed by TEM technique. The TGA results showed that degradation of the composites occurred at higher temperatures compared to that of their virgin polymer and the degradation point increased with P-MMT content. Tensile strength and Young's modulus of composites were higher than those of their original copolymer. By addition of 1-3 wt% of P-MMT, it could be seen that the higher the P-MMT loading, the higher would be the tensile strength and Young's modulus. The P (MMA-co-BA) /P-MMT composite films showed their screening ability in UV region, especially in the UV-B range, which is rather higher than that in the visible region.

Scientists and engineers are constantly trying to improve the performance of asphalt mixtures. Modification of the asphalt binder is one approach used to achieve good mixtures. Fibres and polymers are generally two important modifiers in improving pavement performance, though fibres have received much attention for their enhancement effects among other modifiers for asphalt. In this study, therefore, polypropylene (PP) fibres were selected as fibre modifier because of their low-cost and consistency with asphalt pavement. Asphalt specimens were made by a Superpave gyratory compactor (SGC), analyzed by both Marshall and Superpave methods and tested by Marshall stability apparatus. PP Fibres of two different lengths, i.e., 6 and 12 mm were used at four different percentages of 0.1%, 0.2%, 0.3% and 0.5%, by the total weight of the asphalt concrete. The dry procedure was used to blend fibres with aggregates at the optimized dosage of bitumen, i.e., 4.2%, by weight of the total mix. The experimental results show that adding PP fibre increases the Marshall stability (26%) and the air voids (67%) while reducing the flow (38%) properties. The "law of mixtures" was used for composite materials to study the fitness of specific gravity of the fibre-reinforced asphalt concrete mixtures with the theoretically calculated values. Thus, it was revealed that the fitness of the real results with the theoretically calculated values is considerable, especially at low percentages of fibres, e.g., 0.1% and 0.2%. It became evident that the existence of voids in all modified and/or neat asphalt-concrete treatments leads samples to completely unfit with the “law of mixtures”. Finally, the analysis of variance (ANOVA) method and Dennett's test were used to check the accuracy of the results which significantly demonstrates the advantages of using PP fibres in AC mixtures.

Avinyl functional microemulsion was successfully prepared via polycondensation between polysiloxane prepolymer and a modifier (vinyl silane coupling agent with alkoxy groups). The polysiloxane prepolymer was prepared by ring-opening of D4 (octamethylcyclotetrasiloxane). The structure and properties of vinyl functional microemulsion were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR), photon correlation spectroscopy (PCS). FTIR Spectroscopy result showed that vinyl groups were successfully introduced into the polysiloxane molecules. The variation in pH, amount of vinyl coupling agent and catalyst were studied in relation to the properties of the final microemulsion. The results indicated that under strong acidic more coagulum and higher percentage of conversion occurred in the microemulsion. TEM results also revealed that particles are densely packed in strong acidic condition but become sparsely distributed in weak acidic condition. An increase in the vinyl coupling agent content leads to an increase in formation of coagulum and in particle size, but it lowers the particle size distribution. The smaller ratio of the average surface coverage of surfactant leads to higher amount of coagulation which is in linear dependence to the increased amount of vinyl coupling agent modifier. Photon correlation spectroscopy results show that increasing the amount of vinyl coupling agent modifier increases the particles size, while reduces the particles size distribution. It can be concluded that the coagulum weight fraction increases linearly with higher amount of catalyst. An increase in the vinyl coupling agent modifier leads to an increase in the coagulum. The microemulsion shows stability when the amount of catalyst is about 3.0-4.0 wt%.

Among different types of nanoparticles, carbon nanotubes have always been the subject of extensive studies. In the present study, the effect of concurrent presence of multi-walled carbon nanotubes (MWNT) s and nanoclay on the electrical and mechanical properties of an epoxy system was investigated using the ultrasonic technique for dispersion of nanoparticles. First, an optimum amount for each type of filler is obtained in order to choose appropriate contents of clay/MWNTs components in nanocomposite samples. A nanocomposite reinforced with 0.5 wt% MWNTs showed higher modulus compared with a nanocomposite enhanced with 5 wt% nanoclay, implying that a lower content of MWNTs can lead to higher Young's modulus. Moreover, it was found that the electrical conductivity could be achieved by adding MWNTs. However, addition of nanoclay to epoxy/MWNTs nanocomposite would hinder its electrical conductivity. Simultaneous presence of MWNTs and nanoclay enhanced the Young's modulus and fracture toughness of the prepared nanocomposites. However, the tensile strength of all nanocomposites decreased except for those reinforced with 0.5 wt% MWNTs which showed an increase of around 7%. The SEM micrographs were used for the fractography of specimens and investigation of the dispersion state of MWNTs in the matrix. It was observed that fillers of different shapes provide different features on the fracture surface due to different mechanisms in their toughening action. The X-ray diffraction (XRD) was used to determine the d-spacing of nanoclay layers. The results showed that d-spacing of layers increased from 18.42 A to 42.28 A and thus an intercalated nanocomposite was obtained.

To avoid the loss of precious metal catalysts on carriers, a simple approach is introduced for sliver colloids having ' anchorages' hooked onto inorganic substrate surfaces. This method is based on the nanoreactor of solubilized copolymer micelles for the fabrication of Ag sphere particles. The hydrolysis of tert-butyl acrylate yields acrylic acid and a tri-block copolymer polystyrene-b-poly (acrylic acid) -bpoly (Y-methacryloxypropyltrimethoxysilane) (PS-PAA-PMPS), with PMPS as active functional moieties, was synthesized and characterized which can play strong interaction with inorganic substrates surface as an "anchorage". The PS-PAA-PMPS copolymer solution was prepared to solubilize metal salts to prepare nanoparticles as nanoreactors for in situ reduction. The degree of solubility increased with the increased hydrophilic PAA units but it was also restricted by its dimensional size resisting solubilization. Spherical particles in diameters of 10~30 nm were well dispersed and SEM images showed the hybrid silver colloids remaining on the glass substrate due to their firm adherence after elution. It was demonstrated that this special polymerprotected system provides a successful way for nanoparticles to form anchorage onto the glass surface with firm adhesion and stable properties. This kind of silver colloids conveniently form firm and stable coatings onto the glass substrate which might give longer service life as catalysts to be used in electromagnetic interference shielding, anti-microbial uses and catalytic reduction of p-nitrophenol.