دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و دوم شماره 1 (پیاپی 99، فروردین و اردیبهشت 1388)

In this study, the slurry polymerization of ethylene over TiCl4/MgCl2/AlEt3 was obtained. Firstly, to obtain the optimum value of [Al]/[Ti], the effect of [Al]/[Ti] on polymerization rate and catalyst yield was studied. Also, the effect of catalyst content on yielding, crystallization, melting point and density of product were obtained. To determine the order of reaction, the monomer pressure was varied, and hyedrogen was used as transfer agent. Also, we used 1-butene as comomomer. According to the results, hydrogen decreases the catalyst efficiency, melting temperature and molecular weight and increases the melt flow index. The crystallinity is increased first and then it is reduced with increasing H2 content and the density of the product has changed slightly by variation of hydrogen pressure. Also, with increase in 1-butene content, as a comonomer to control polymer density, the density, crystallinity, melting temperature and thickness of crystal lamella decrease and the melt flow index increases. Likewise, the rate of polymerization is initially increased and then it is decreased with comonomer content.

Atom transfer radical polymerization (ATRP) of styrene was carried out at 105°C and a Monte Carlo simulation was employed to model the system. The variations of monomer conversion, the initiator concentration, average molecular weight, and molecular weight distribution were evaluated as the reaction proceeded. According to the results obtained, for similar reaction time, monomer conversion is higher when gel effect is taken into account. Also, the concentration of initiator suddenly drops at the initial stages of polymerization, and finally reaches zero. In addition, in the presence of gel effect, bimolecular termination rate constant decreases during the polymerization. Moreover, number- and weight-average molecular weights linearly rise as the polymerization progresses; this also is a confirmation to the living nature of the polymerization. Finally, the molecular weight distribution of polymers synthesized narrows at high monomer conversion. In effect, polydispersity index decreases from about 2 (at the onset of polymerization) to around 1.3 (towards the end of polymerization).

Unsymmetrical composite laminates deform from the flat state in curing process. According to the "lamination theory" the cured shape of unsymmetrical laminates should always be saddle-like, while considering parameters like specimen lengths and cure temperature, it may lead to two cylindrical shapes. In addition it is necessary to consider geometrical non-linearity for the uneven plates. By considering specimen dimensions, Rayleigh-Ritz energy method precisely predicts the room-temperature shapes of the unsymmetrical polymer composite laminates. In this research, energy equations are developed to determine curvatures of unsymmetrical composite thin laminates at higher scales. Cylindrical cross-ply composite shells are selected to investigate energy method with higher degrees. Cured shape of composite shells is mainly dependent on the stacking sequences, mold radius, layer thickness and cure temperature. Therefore, the changes of these parameters are studied and consequently appropriate assessments are made on the results obtained.

The idea of combining low weight and good mechanical properties has led to efforts to develop a new light fiber/metal laminate (FML) in the last decade. FMLs are hybrid composites consisting of alternating thin layers of metal sheets and fiber-reinforced epoxy prepregs. In this study, the effect of fiber orientation on tensile properties of this material is investigated both analytically and experimentally. An analytical constitutive model based on classical lamination theory by using Kirchhoff-Love assumption, which incorporates the elastic-plastic behavior of the aluminium alloy was applied. Test results show that fiber sheet, with zero angle in laminates, improve the tensile strength. The composite layers with different fiber orientation change specimen's mode of fracture. Good agreement is obtained between the model predictions and experimental results.

The simultaneous cross-linking and antimicrobial finishing of bleached cotton and cationized cotton by 3-chloro2-hydroxypropyl trimethyl ammonium chloride (Quat-188) with butane tetracarboxylic acid and nano titanium dioxide is studied and explored in the current study. Butane tetracarboxylic acid (BTCA) as a cross-linking agent can be linked to the cotton cellulosic chains by covalent bonds and to the cationized cotton by ionic bonds. Different concentrations of nano titanium dioxide and BTCA were examined to obtain the highest crosslinking and antimicrobial effects. Certain haracteristics of the samples such as antimicrobial against different microorganisms including two gram positive bacteria (Bacillus cereus, Staphylococous aureus), one gram negative bacteria (Escherichia coli) and one fungi (Candida albicans), crease recovery angle, bending length, yellowness index,weight changes, water drop absorption time were investigated. The results showed that both the bleached cotton and cationized cotton can be finished by optimum concentration of nano titanium dioxide and BTCA for producing cotton fabric with anticrease and antimicrobial properties.

Non-isothermal crystallization kinetics of polypropylene (PP) and PP containing 0.5 wt% singlewalled carbon nanotubes (PP/SWNT) were studied at various cooling rates using differential scanning calorimetry technique. The non-isothermal melt crystallization data were analyzed according to Ozawa and Cazé-Chuah models. Although Ozawa model was successful in describing the nonisothermal crystallization of PP, it failed to do so for PP/SWNT nanocomposite. The results obtained from Cazé-Chuah model show that the model was successful in describing non-isothermal crystallization kinetics of the nanocomposite and the pristine polymer. Using a method developed by Dobreva and Gutzow, it was found that the nucleation activity of SWNT on PP crystallization was around 0.65. This is consistent with the fact that SWNT acted as nucleating agents for PP.

Sudden fracture is one of the major failure modes in brittle materials. Plexiglass (polymethyl methacrylate) is a well known brittle polymer, widely used in various industries. Many types of notches, particularly V-shaped notches, are sometimes used in the components made of plexiglass. These notches can dramatically decrease the load bearing capacity of components due to the concentration of stress at the vicinity of their tips. The stress concentration may result in the crack nucleation and fracture from the tip of a V-notch. In the present paper, a set of notched specimens of plexiglass are subjected to pure mode II loading, in order to determine the mode II fracture toughness and the fracture initiation angle experimentally. These specimens contain rounded-tip V-notches with variable notch opening angles and different notch radii. The experimental results are then predicted by using a failure criterion, suggested for estimating brittle fracture in rounded-tip V-notches under pure shear deformation. A good agreement is shown to exist between the theoretical predictions and the experimental results.