Iranian Journal of Polymer Science and Technology
Year:2010 | Volume:23 | Issue:3 (ISSUE NO. 107)|Papers Count:8

The blending of NR and BR rubber blend with N 330 carbon black is studied on curing behavior and the physico-mechanical properties of a SBR rubber based tire tread compound containing N 234 carbon black. The effect of sul- phur and accelerator contents on different properties of rubber compound is also tested with a wide range of curing agents. Partial substitution of SBR with NR shows significant improvement in cure characteristics, tear resistance, crack growth, resilience and abrasion without much changes in its hardness, dispersion and tensile properties. Partial substituted BR delivers the same results except a considerable increase in the rate of crack growth. A partial substitution of N 234 with N 330 has a relatively negative effect on the abrasion and tear resistance, but decreases the crack growth rate. The crack growth rate increases with increased level of sulphur and accelerator and the abrasion decreases at certain level of curing agent, although it increases thereafter (crosslink density). The tensile and tear resistance increase first and then decrease with further increase of crosslink density. The study on the governing mechanisms shows that beside rubber chains induced crystallinity, the rubber chain mobility dominates the crack growth rate, while a competition exists between this mechanism and reinforcement mechanism for other failed properties. Finally, an optimized formulation based on SBR/BR/NR and N 234 /N 330 with optimum crosslink density and sulphur/accelerator ratio has been calculated.

Inhibitory effect of double-base solid propellants is exerted to control and prevent the burning degree of the exposed area which is due to longer burning time. In this research a composite inhibitor based on cotton fibers/epoxy resin was manufactured by filament winding technique. Some flame retardant materials such as antimony trioxide and tetrachlorophthalic anhydride were employed as the components of an inhibitor to control the burning process. A desirable viscosity of an epoxy resin should idealistic increase the wettability of fibers and create stronger adhesion to the propel- lant surface, as low density cotton fibers show high fracture strain. Some samples of composite inhibitors have been produced according to ASTM standards and their mechanical and thermal properties have been studied by several tests such as tensile and adhesive tests, thermogravimetric analysis, differential scanning calorimetry, thermomechanical analysis and flame retardancy. Finally the inhibited propellant charge, statically fired at ambient temperature, was found to display a smooth and flat pressure-time profile which confirmed the successful performance of cotton/epoxy composite inhi- bition system without the application of any coating barrier. Also, it is evi- dent that the burning time is increased as well.

The role of polymeric additives such as PVP and PEG is studied with respect to the morphology of PES porous layer as a sublayer of nanofiltration com-posite membranes based on PES/PA. Results show that by phase inversion process of quaternary systems comprised of four components of polymer/solvent/non-solvent/additive and the diffusion of intertwined polymers some changes occur in membrane morphology with changes in their concentration.With addition of PVP, tear-like pores, finger-like and channel-like morphology change to enlarged channel cavities and by adding more PVP, membrane morphology changes further and spongy regions are extended in the membrane. Presence of PEG in casting solution delayed the precipitation time. By adding PEG, the solution viscosity is increased which is followed by decreases in diffusion rates of solvent/non-solvent in coagulation bath. Therefore, membrane morphology shifts to small pores and spongier region. Another effect of increased PEG content would be deformed PA layer formation in PES sublayer which affects membrane performance. However, PVP as an additive does not change membrane salt rejection very much while it leads to higher fluxes. A membrane with 2.5 percent PVP would perform by 40 percent flux increases, while a membrane with 5% PVP shows flux reductions even below the initial value. Contrary to PVP, the PEG content of 20 percent leads to 4 folds flux increases and in a membrane with 50 percent PEG, there is a flux increase by 7 folds and drop in salt rejection occurs by 50 percent and 70 percent, respectively.

Open-celled foams are capable to allow the passage of fluids through their structure, because of interconnections between the open cells or bubbles and therefore these structures can be used as a membrane and filter. In this work, we have studied the production of polystyrene open-celled microcellular foam by using CO2 as blowing agent. To achieve such structures, it is necessary to control the stages of growth in such a way that the cells would connect to each other through the pores without any coalescence. The required processing condition to achieve open-celled structures is predictable by a model theory of opened-cell. This model suggests that at least a 130 bar saturation pressure and foaming time between 9 and 58 s are required for this system. The temperature range has been selected for to be both higher than polymer glass transition temperature and facilitating the foaming process. Experimental results in the batch foaming process has verified the model quite well. The SEM and mercury porousimetry tests show the presence of pores between the cells with open-celled structure. Experimental results show that by increasing the saturation pressure and the foaming temperature, there is a drop in the time required for open-celled structure formation. A 130 bar saturation pressure, 150o C foaming temperature and 60 s foaming time, suggest the attainment of open-celled microcellular foam based on polystyrene/CO2 system in the batch process

The high costs of experimental works on the nanocomposites can be reduced through implementation of analytical and numerical studies. To study the effect of impact energy on the nanocomposites, a nanocomposite composed of polyurethane and clay nanoparticles is selected as a case study. The finite element modeling is carried out using the ANSYS software, and the impact analysis is performed using LSDYNA. Three distinct regions: namely the polymer, the clay particles, and the interface are considered in the modeling. Subsequently, the effects of staggering factor, vertical distance between nanoparticles, aspect ratio, and volume fraction of clay nanoparticles on the reaction of the nanocomposite to the impact forces are investigated. The magnitude of the displacement of the specimen and the maximum force at the contact point are important parameters in impact analysis. In order to study the effect of structural parameters, two different impact velocities are considered, and for each 160 finite element modelings are performed. In each case, the effective parameters together with their limitations are considered. Different graphs are presented and analyzed for the effect of every structural parameter on the impact. The results of this study show that for a nanocomposite of aspect ratio equal 100, staggering factor of 0.5, and exfoliation factor of 0.51, the volume fraction of the clay nanoparticles is the range of 1.5 to 3 percent which can be considered opti-mum as far as the effect of impact forces are concerned.

Afinite element model of a bias truck tire under static vertical load using a global/local technique is designed in two parts. In the first part a previ- ously created model for radial tires is developed to take the construction- al variables of bias tires into account. It is shown that the technique can successfully be used for bias tires. The main challenge here is the selection of the initial layout of the tire, which due to the use of nylon fibers in bias tires undergo considerable variation in shapes on being released from mold. Therefore, the selection of the tire lay out in the mold as the initial starting point for finite element calculations leads to significant errors in the final results.In the second part, a highly refined mesh has been created from contacting region of the tire tread pattern as a local model. This model is analyzed using the results of the first (global) model as the boundary condition. It is also shown that the developed method is capable of precisely predicting the geometry of the footprint area without any extra computational cost and efforts needed in finite element calculations of full tire models.

Acrylonitrile butadiene rubber (NBR) composites are prepared from waste nylon 66 short fiber using a two-roll mill mixer. The effects of fiber content and bonding agent on the mechanical and morphological properties of the composites are studied. The curing characteristics of the composites have been studied by using cure rheometer. The cure and scorch time of the composites decrease while cure rate is increased when short fiber content is increased. The mechanical properties of the composites show improvement in both longitudinal and transverse directions with increase in short fiber content. The adhesion between the fiber and rubber is enhanced by using a dry bonding system consisting of resorcinol, xamethylenetetramine and hydrated silica (HRH). The swelling behavior of the composites in N, N-dimethylformamide is tested to find the effect of bonding agent on adhesion strength of the matrix and fibers.Fracture surface morphology of composites is studied by scanning electron microscopy. The restriction to swelling is higher for composites containing bonding agent, especially, in the longitudinal direction. The morphology of the fracture surface shows less fiber pull out when the bonding agent is introduced.