Iranian Journal of Polymer Science and Technology
Year:2010 | Volume:23 | Issue:4 (ISSUE NO. 108)|Papers Count:9

Amodified technique is designed to prepare aligned nanofibers to challenge the existing limitations in collecting methods of nanofibers such as, thickness of collected layer, alignment and productivity of nanofibers. Collecting and simultaneously heating of the aligned nanofibers were carried out by using a rotating drum fixed on top of syringe needles and applying hot air flow. This electrospinning set up can facilitate heating of the nanofiber in electrospinning zone (distance between two syringe needles). Polyacrylonitrile (PAN) nanofibers were electrospun from its 14 wt% solu-tion in dimethylformamide (DMF) under practical conditions. The above method resulted in low rupture rates and increased maximum take up speed for two collections.The obtained results from angular power spectrum analy- sis showed better fiber alignment with increasing take up speed, although SEM studies demonstrated wider diameters of nanofibers being produced by the modified method. The glass transition temperature (Tg) of all the pre- pared samples were between 70oC and 90oC. The recorded spectra from FTIR were close to common PAN fibers with peaks at 2240 cm-1 (CN stretch), 2920 cm-1 (CH2 bend), 1450 cm-1 (CH stretch) and 1730 cm-1 (CO stretch) wavenumbers. The diffraction patterns obtained from WAXD technique show also an equatorial peak in 2q=17o for PAN nanofibers. Our quantita- tive analysis of WAXD and FTIR diagrams have revealed positive effects by the modified method on crystallization degree of nanofibers produced at higher take up speeds.

Apermanent anti-graffiti clear polyurethane coating, using a silicone addi- tive, was prepared and studied. Various techniques, such as contact angle measurements and EDX were employed to characterize and investigate the surface properties of the coatings. The results revealed that with inclusion of silicon additive to clear coating, according to Wu method, surface free energy was decreased from 45.13 mJ/m2 for neat clear polyurethane film to 25.25 mJ/m2 in a coating containing 5% additive. With inclusion of higher mole percentage of additive, surface energies remained constant as revealed by EDX technique, which was considered to be due to the excessively covered surface by silicone additive.Ageing under UV radiation revealed that the inclusion of additive up to 5 mole percentage could improve the anti-graffiti property during the first few aging cycles. However, by increasing the number of aging cycles and higher concentration of silicone additive, the rate of degradation in coatings increased. The results showed that PU5% has the best anti-graffiti and ageing properties among other compositions.

Mixing conditions of NBR/PVC nanocomposites such as mixing tempera- ture, rotor speed and mixing time are determining parameters in rheologi-cal, mechanical and morphological properties of the compound. Three lev-els were chosen for each parameter using Design Expert software via Box-Behnken method.The nanocomposite samples were melt-mixed in Brabender internal mixer. The effect of various mixing parameters such as mixing temperature, rotor speed and mixing time was investigated by stress-strain and rheological curves. The TPE nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic mechanical thermal analysis (DMTA), and mechanical properties. It was found that only at low temperature, high tensile strength, storage modulus and low swelling index were obtained by increasing the rotor speed and mixing time simultaneously. As a consequence by increasing the mixing temperature samples undergo two processes. The former is self-crosslinking that leads to torque rise, and the latter is torque drop due to chain sessions. The morphology of nanoclay layers in polymer matrix was studied by X-ray diffraction and TEM. By studying the mechanical and rheological properties of the nanocomposites the optimum preparation condition was found to be the temperature of 160o C, mixing speed of 50 rpm at 6 min.

Radiation degradation of chitosan is one of the most important methods to prepare antibacterial oligochitosans. In this study, the effect of solvent on the reduction of degradation dose and enhancement of the antibacterial activity of chitosan against Pectobacterium Carotovorum (PC) has been considered.Gamma radiation degradation was applied to chitosan as solid and aqueous solution at dose range of 2-200 kGy. The changes of molecular weight with irradiation dose which were monitored by viscometric measurements showed that the solvent led to the reduction of degradation dose. Therefore, the molecular weight of solid chitosan was reduced from 400, 000 to 48, 000 after irradiation at 50 kGy, whereas the molec- ular weight of aqueous solution of chitosan reached 32, 000 after irradiation at 10 kGy. Antibacterial investigations showed that growth of PC in aqueous solution of chitosan irradiated at 10 kGy is equal to the growth of PC in solid chitosan irradiated at 50 kGy. FTIR spectra of the irradiated samples showed that the radiation degradation of chitosan in solid and aqueous solution must have occurred through the breakage of glycosidic bonds. The variations of glycosidic bond were in consistent with the viscometric results based on the effect of solvent on the reduction of degradation dose of chitosan.

In this research, the tacticity and microstructure of polyvinyl chloride (PVC) were studied through back bone methylene and methine carbons and protons splitting by carbon (13C NMR), proton (1H NMR) and two-dimensional (2D NMR) nulear magnetic resonance spectroscopy in deuterated etrahydrofuran. Polyvinyl chloride was synthesized by emulsion polymerization of vinyl chloride (VCM) under pressure to about %90 conversion with %45 solid content at 60­ C. The assignments of all stereosequences were done at tetrad and pentad levels of methylene and methine carbons of the polyvinyl chloride respectively, using by 13C liquid NMR. Bernoullian and first-order Markov statistics models were calculated and the results are compared with the experimental NMR results. It was shown that Bernoullian and first-order Markov statistics fit almost equal for the assigned methylene and methine carbons and that the probability of meso addition (Pm) value inpolyvinyl chloride chains was calculated to be 0.447.1H NMR of PVC was assigned via heteronuclear multiple quantum coherence technique (HMQC) for methylene and methine groups at triad sequence levels. Finally, by increasing the NMR acquisition temperature from 20 to 50oC higher resolution in methylene and methine carbons were achieved. In this case, the atactic sequence peaks splitted more than isotactic and syndiotactic sequence peaks.

Present research involves the complete simulation of pultrusion manufactur-ing process of glass/polyester composites. For that purpose, the curing process is divided to two liquid and gel-solid phases. The physical charac-teristics of the resin consist of specific heat, viscosity and coefficient of heat transfer changes with variations of temperature and increasing the degree of curing process (a).In each of the two liquid and gel-solid phases, some of these parameters play an important role in the heat transfer and consequently in the simulation results. The released heat during the resin curing process is another important parameter. This parameter depends on the absolute temperature of the resin and accelerates the resin curing process. The most important parameter in simulation of the resin curing process is the degree of cure of the resin, which is used in calculation of the viscosity of the resin in this process and also helps in indicating the end of the curing process. The physical properties of fibers do not change during the curing process, while they affect the heat transfer of the resin and duration of the curing process. Therefore, instead of modeling the fibers and the resin, an equivalent material is introduced which demonstrates the behavior of fibers and the resin during the curing process.

Bituminous emulsion insulators are types of bituminous emulsions groups com-posed of different grades of bitumen emulsified in water by bentonite and emulsifiers at 80-90oC. These emulsions are water resistant after drying and their physical and mechanical properties are superior in comparison to bitumen properties. Iranian climate, because of variety and extreme variations in temperature imposes high performance insulators. Modification of bitumen is considered as one of the most practical applications of polymers to impart more improved properties to bitumen. This investigation involved the study of polymers and resins such as SBS and heavy vacuum slops (HVS). For this purpose, the effect of each component of emulsions on the physical and chemical properties of insulators was examined and some insulators are made with more improved properties. Moreover, the bitumen was modified by styrene-butadiene-styrene blocked copolymer (SBS) blends and HVS and their roles on the behavior of the emulsion were studied. The results show that: 1- the bentonite content of the emulsion should not be more than 11%; 2-addition of SBS/HVS blend increased physical and chemical properties (thermal stability, flexibility and adhesion); 3- increased water content of the production process improved the thermal stability and flexibility of the insulators, whereas it did not so the stability of emulsion. Finally, it is found that the best formulation must contain: (1) bentonite with maximum content of 11%; (2) water content of 44% and (3) SBS/HVS blend of about 7%.

Biopolymers are environmental friendly sources as renewable and sustain-able substituents for petroleum-based polymers. Application of these poly-mers is common in variety of industries including papermaking. Herbal exudate gums have been used in papermaking industry for decades, especially paper recycling. In this study, gum polysaccharide exudates from Baridje plant (Ferula Gummosa) extracted and purified with ethanol, analyzed by using Saeman method and added as a dry strength additive to improve the mechanical properties (burst, breaking length and Scott internal bonding) of recycled paper, 60 g/m2 grammage, produced from old corrugated cartons. The purified monosaccharide contained: galactose 60%, arabinose 15% and galacturonic acid 25%. The effects of the biopolymer on mechanical properties of the recycled paper showed statistical significance at 99% level. The anionic nature of the biopolymer, fibres and paper recycling system was neutralized by addition of polyaluminium chloride (PAC) to adjust zeta potential to about zero and improve system’s strength properties. Interaction effects of cationic oligomer (PAC) and biopolymer were also statistically significant at 99% level and displayed stronger material with improved mechanical strength.