دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و سوم شماره 4 (پیاپی 108، مهر و آبان 1389)

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 thenanofiber in electrospinning zone (distance between two syringe needles). Polyacrylonitrile (PAN) nanofibers were electrospun from its 14 wt% solutio 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 analysis 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 prepared 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 2θ = 17o for PAN nanofibers. Our quantitative 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 additive,was prepared and studied. Various techniques, such as contact anglemeasurements and EDX were employed to characterize and investigate thesurface properties of the coatings. The results revealed that with inclusion of siliconadditive to clear coating, according to Wu method, surface free energy was decreasedfrom 45.13 mJ/m2 for neat clear polyurethane film to 25.25 mJ/m2 in a coating containing5% additive. With inclusion of higher mole percentage of additive, surfaceenergies remained constant as revealed by EDX technique, which was considered tobe due to the excessively covered surface by silicone additive. Ageing under UVradiation revealed that the inclusion of additive up to 5 mole percentage couldimprove the anti-graffiti property during the first few aging cycles. However, byincreasing the number of aging cycles and higher concentration of silicone additive,the rate of degradation in coatings increased. The results showed that PU5% has thebest anti-graffiti and ageing properties among other compositions

Mixing conditions of NBR/PVC nanocomposites such as mixing temperature,rotor speed and mixing time are determining parameters in rheological,mechanical and morphological properties of the compound. Three levelswere chosen for each parameter using Design Expert software via Box-Behnkenmethod. The nanocomposite samples were melt-mixed in Brabender internal mixer. Theeffect of various mixing parameters such as mixing temperature, rotor speed and mixingtime was investigated by stress-strain and rheological curves. The TPE nanocompositeswere characterized by X-ray diffraction (XRD), transmission electronmicroscopy (TEM), dynamic mechanical thermal analysis (DMTA), and mechanicalproperties.

Radiation degradation of chitosan is one of the most important methods toprepare antibacterial oligochitosans. In this study, the effect of solvent onthe reduction of degradation dose and enhancement of the antibacterialactivity of chitosan against Pectobacterium Carotovorum (PC) has been considered.Gamma radiation degradation was applied to chitosan as solid and aqueous solutionat dose range of 2-200 kGy. The changes of molecular weight with irradiation dosewhich were monitored by viscometric measurements showed that the solvent led tothe reduction of degradation dose. Therefore, the molecular weight of solid chitosanwas reduced from 400,000 to 48,000 after irradiation at 50 kGy, whereas the molecularweight of aqueous solution of chitosan reached 32,000 after irradiation at10 kGy. Antibacterial investigations showed that growth of PC in aqueous solutionof chitosan irradiated at 10 kGy is equal to the growth of PC in solid chitosan irradiatedat 50 kGy. FTIR spectra of the irradiated samples showed that the radiationdegradation of chitosan in solid and aqueous solution must have occurred through thebreakage of glycosidic bonds.

In this research, the tacticity and microstructure of polyvinyl chloride (PVC)were studied through back bone methylene and methine carbons and protonssplitting by carbon (13C NMR), proton (1H NMR) and two-dimensional (2DNMR) nulear magnetic resonance spectroscopy in deuterated tetrahydrofuran.Polyvinyl chloride was synthesized by emulsion polymerization of vinyl chloride(VCM) under pressure to about %90 conversion with %45 solid content at 60C. Theassignments of all stereosequences were done at tetrad and pentad levels of methyleneand methine carbons of the polyvinyl chloride respectively, using by 13C liquidNMR. Bernoullian and first-order Markov statistics models were calculated and theresults are compared with the experimental NMR results. It was shown thatBernoullian and first-order Markov statistics fit almost equal for the assigned methyleneand 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 assignedvia heteronuclear multiple quantum coherence technique (HMQC) for methylene andmethine groups at triad sequence levels. Finally, by increasing the NMR acquisitiontemperature from 20 to 50oC higher resolution in methylene and methine carbonswere achieved. In this case, the atactic sequence peaks splitted more than isotacticand syndiotactic sequence peaks

Present research involves the complete simulation of pultrusion manufacturingprocess of glass/polyester composites. For that purpose, the curingprocess is divided to two liquid and gel-solid phases. The physical characteristicsof the resin consist of specific heat, viscosity and coefficient of heat transferchanges with variations of temperature and increasing the degree of curing process(α). In each of the two liquid and gel-solid phases, some of these parameters play animportant role in the heat transfer and consequently in the simulation results. Thereleased heat during the resin curing process is another important parameter. Thisparameter depends on the absolute temperature of the resin and accelerates the resincuring process. The most important parameter in simulation of the resin curingprocess is the degree of cure of the resin, which is used in calculation of the viscosityof the resin in this process and also helps in indicating the end of the curingprocess. 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 isintroduced which demonstrates the behavior of fibers and the resin during the curingprocess.

Bituminous emulsion insulators are types of bituminous emulsions groups composedof different grades of bitumen emulsified in water by bentonite andemulsifiers at 80-90oC. These emulsions are water resistant after drying andtheir physical and mechanical properties are superior in comparison to bitumen properties.Iranian climate, because of variety and extreme variations in temperature imposeshigh performance insulators. Modification of bitumen is considered as one of the mostpractical applications of polymers to impart more improved properties to bitumen. Thisinvestigation involved the study of polymers and resins such as SBS and heavy vacuumslops (HVS). For this purpose, the effect of each component of emulsions on the physicaland chemical properties of insulators was examined and some insulators are madewith more improved properties.