دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و سوم شماره 3 (پیاپی 107، امرداد و شهریور 1389)

The blending of NR and BR rubber blend with N330 carbon black is studiedon curing behavior and the physico-mechanical properties of a SBR rubberbased tire tread compound containing N234 carbon black. The effect of sulphurand accelerator contents on different properties of rubber compound is also testedwith a wide range of curing agents. Partial substitution of SBR with NR shows significantimprovement in cure characteristics, tear resistance, crack growth, resilienceand abrasion without much changes in its hardness, dispersion and tensile properties.Partial substituted BR delivers the same results except a considerable increase in therate of crack growth. A partial substitution of N234 with N330 has a relatively negativeeffect on the abrasion and tear resistance, but decreases the crack growth rate. Thecrack growth rate increases with increased level of sulphur and accelerator and theabrasion decreases at certain level of curing agent, although it increases thereafter(crosslink density).

Inhibitory effect of double-base solid propellants is exerted to control andprevent the burning degree of the exposed area which is due to longerburning time. In this research a composite inhibitor based on cottonfibers/epoxy resin was manufactured by filament winding technique. Someflame retardant materials such as antimony trioxide and tetrachlorophthalicanhydride were employed as the components of an inhibitor to control theburning process. A desirable viscosity of an epoxy resin should idealisticincrease the wettability of fibers and create stronger adhesion to the propellantsurface, as low density cotton fibers show high fracture strain. Somesamples of composite inhibitors have been produced according to ASTMstandards and their mechanical and thermal properties have been studied byseveral tests such as tensile and adhesive tests, thermogravimetric analysis,differential scanning calorimetry, thermomechanical analysis and flameretardancy. Finally the inhibited propellant charge, statically fired at ambienttemperature, was found to display a smooth and flat pressure-time profilewhich confirmed the successful performance of cotton/epoxy composite inhibitionsystem without the application of any coating barrier. Also, it is evidentthat the burning time is increased as well

The role of polymeric additives such as PVP and PEG is studied with respectto the morphology of PES porous layer as a sublayer of nanofiltration compositemembranes based on PES/PA. Results show that by phase inversion process of quaternary systems comprised of four components of polymer/solvent/nonsolvent/additive and the diffusion of intertwined polymers some changes occur inmembrane morphology with changes in their concentration. With addition of PVP,tear-like pores, finger-like and channel-like morphology change to enlarged channelcavities and by adding more PVP, membrane morphology changes further and spongyregions are extended in the membrane. Presence of PEG in casting solution delayedthe precipitation time. By adding PEG, the solution viscosity is increased which is followedby decreases in diffusion rates of solvent/non-solvent in coagulation bath.Therefore, membrane morphology shifts to small pores and spongier region. Anothereffect of increased PEG content would be deformed PA layer formation in PES sublayerwhich affects membrane performance. However, PVP as an additive does notchange membrane salt rejection very much while it leads to higher fluxes. A membranewith 2.5 percent PVP would perform by 40 percent flux increases, while amembrane with 5% PVP shows flux reductions even below the initial value. Contraryto PVP, the PEG content of 20 percent leads to 4 folds flux increases and in a membranewith 50 percent PEG, there is a flux increase by 7 folds and drop in salt rejectionoccurs by 50 percent and 70 percent, respectively

Open-celled foams are capable to allow the passage of fluids through theirstructure, because of interconnections between the open cells or bubblesand therefore these structures can be used as a membrane and filter. In thiswork, we have studied the production of polystyrene open-celled microcellular foamby using CO2 as blowing agent. To achieve such structures, it is necessary to controlthe stages of growth in such a way that the cells would connect to each other throughthe pores without any coalescence. The required processing condition to achieveopen-celled structures is predictable by a model theory of opened-cell. This modelsuggests that at least a 130 bar saturation pressure and foaming time between 9 and58 s are required for this system. The temperature range has been selected for to beboth higher than polymer glass transition temperature and facilitating the foamingprocess. Experimental results in the batch foaming process has verified the modelquite well. The SEM and mercury porousimetry tests show the presence of poresbetween the cells with open-celled structure.

The high costs of experimental works on the nanocomposites can be reducedthrough implementation of analytical and numerical studies. To study theeffect of impact energy on the nanocomposites, a nanocomposite composedof polyurethane and clay nanoparticles is selected as a case study. The finite elementmodeling is carried out using the ANSYS software, and the impact analysis is performedusing LSDYNA. Three distinct regions: namely the polymer, the clay particles,and the interface are considered in the modeling. Subsequently, the effects ofstaggering factor, vertical distance between nanoparticles, aspect ratio, and volumefraction of clay nanoparticles on the reaction of the nanocomposite to the impactforces are investigated. The magnitude of the displacement of the specimen and themaximum force at the contact point are important parameters in impact analysis. Inorder to study the effect of structural parameters, two different impact velocities areconsidered, and for each 160 finite element modelings are performed. In each case,the effective parameters together with their limitations are considered. Differentgraphs are presented and analyzed for the effect of every structural parameter on theimpact. The results of this study show that for a nanocomposite of aspect ratio equal100, staggering factor of 0.5, and exfoliation factor of 0.51, the volume fraction ofthe clay nanoparticles is the range of 1.5 to 3 percent which can be considered optimumas far as the effect of impact forces are concerned

Afinite element model of a bias truck tire under static vertical load using aglobal/local technique is designed in two parts. In the first part a previouslycreated model for radial tires is developed to take the constructionalvariables of bias tires into account. It is shown that the technique can successfullybe used for bias tires. The main challenge here is the selection of the initial layout ofthe tire, which due to the use of nylon fibers in bias tires undergo considerable variationin shapes on being released from mold. Therefore, the selection of the tire layoutin the mold as the initial starting point for finite element calculations leads to significanterrors in the final results. In the second part, a highly refined mesh has beencreated from contacting region of the tire tread pattern as a local model. This modelis analyzed using the results of the first (global) model as the boundary condition. Itis also shown that the developed method is capable of precisely predicting the geometryof the footprint area without any extra computational cost and efforts needed infinite element calculations of full tire models

Acrylonitrile butadiene rubber (NBR) composites are prepared from wastenylon 66 short fiber using a two-roll mill mixer. The effects of fiber contentand bonding agent on the mechanical and morphological properties of thecomposites are studied. The curing characteristics of the composites have been studiedby using cure rheometer. The cure and scorch time of the composites decrease whilecure rate is increased when short fiber content is increased. The mechanical propertiesof the composites show improvement in both longitudinal and transverse directions withincrease in short fiber content. The adhesion between the fiber and rubber is enhancedby using a dry bonding system consisting of resorcinol, hexamethylenetetramine andhydrated silica (HRH). The swelling behavior of the composites in N,N-dimethylformamideis tested to find the effect of bonding agent on adhesion strength of the matrixand fibers. Fracture surface morphology of composites is studied by scanning electronmicroscopy. The restriction to swelling is higher for composites containing bondingagent, especially, in the longitudinal direction. The morphology of the fracture surfaceshows less fiber pull out when the bonding agent is introduced