Manipulating the morphology of poly (ethylene terephthlate) blends by capillary rheometry

The present work describes the formation of co-continuous phase morphologies in uncompatibilized and compatibilized poly(ethylene terephthalate) (PET)/poly(m-xylene adipamide) (MXD6) melt-extruded blends. Phase continuity has been determined by using Jordhamo relationship. Viscosity values which are essential for calculation of the phase continuity have been obtained by using capillary rheometry. Phase continuity has been investigated for the non-compatibilized and the compatibilized blends with scanning electron microscopy (SEM). PET/MXD6 blends (92.35/7.65 v/v and 84.5/15.5 v/v) exhibit a droplet-in-matrix phase morphology, while uncompatibilized PET/MXD6 (75.8/24.2 v/v) blend has a combination of rod-like, droplet/matrix structure, and quasi-interpenetrating network structure

Long time stress relaxation of amorphous networks under uniaxial tension: The Dynamic Constrained Junction Model

Poly-isoprene networks with different degrees of cross-linking and filler amount are studied under uniaxial stress relaxation. Time decay of stress obeys a stretched exponential form with a stretching parameter of 0.4 that is same for all independent variables, i.e., extensions, crosslink density and filler amount. Relaxation time τ increases with increasing strain, and decreases with both cross-link and filler content. Dependence of τ on filler content is less sensitive than on cross-link density. The isochronous Mooney-Rivlin plots show that the phenomenological constant 2C1 is time independent, and all time dependence results from that of 2C2 , which is associated with relaxation of intermolecular interactions at and above the length-scales of network chain dimensions. The relatively low value of the stretching parameter is interpreted in terms of a molecular model where entanglements contribute to relaxation at a wide spectrum of time scales

Long-time stress relaxation of filled amorphous networks under uniaxial tension: The dynamic constrained junction model

The dynamic constrained junction model, based on the equilibrium theory of rubber elasticity, is applied to study the effects of fillers on the relaxation of stress in uniaxially deformed rubbers. Only low degrees of reinforcement are considered where complications such as filler-filler interactions are not pronounced. The proposed model is based on a purely molecular picture of the network and attempts to explain the molecular origins of the deformation and time dependence of stress in filled rubbers. Comparison with experimental data on filled (poly) isoprene networks showed that the deformation and time dependence of lightly filled samples can be predicted satisfactorily by the model

Effects of electrospinning parameters on polyacrylonitrile nanofiber diameter: an investigation by response surface methodology

Effects of material and process parameters on the diameter of electrospun polyacrylonitrile fibers were experimentally investigated. Response surface methodology (RSM) was utilized to design the experiments at the settings of solution concentration, voltage and the collector distance. It also imparted the evaluation of the significance of each parameter on the resultant fiber diameter. The investigations were carried out in the two-variable process domains of several collector distances as applied voltage and the solution concentration were varied at a fixed polymer molecular weight. The mean diameter and coefficient of variation were modeled by polynomial response surfaces as functions of solution concentration and voltage at each collector distance. Effect of applied voltage in micron-scale fiber diameter was observed to be almost negligible when solution concentration and collector distance were high. However, all three factors were found statistically significant in the production of nano-scale fibers. The response surface predictions revealed the parameter interactions for the resultant fiber diameter, and showed that there is a negative correlation between the mean diameter and coefficient of variation for the fiber diameter. A sub-domain of the parameter space consisting of the solution concentration, applied voltage and collector distance, was suggested for the potential nano-scale fiber production

Effect of organoclay on the physical properties of UV-curable coatings

The combination of UV-curing and nanocomposite technology has been studied to produce cost-effective coatings with superior physical and mechanical properties. The clay was modified with dimethyl dihydrogenated-tallow quaternary ammonium salt and made organophilic. The effect of the organoclay(2-10 phr) on curing rate, mechanical, thermal and physical properties of a urethane-acrylate coating has been determined. X-ray diffraction analysis, AFM, SEM and TEM images as well as the tensile properties of different formulations have confirmed the uniform distribution of organoclay in polymer matrix. At 3 phr organoclay addition, the UV-cured film exhibited the best mechanical performance due to the formation of both intercalated and exfoliated morphologies. Curing time was reduced and the initial thermal decomposition temperature shifted 50°C to higher temperature by the incorporation of small amount of organoclay. The nanocomposite coating was also found to be more resistant against scratching compared with clay-free coating