1,721,006 research outputs found
On the sub-Tg annealing of uniaxially oriented and unoriented atactic polystyrene
No full textDSC analysis was performed on uniaxially oriented and unoriented atactic polystyrene samples prior to and after annealing at 80 °C. With increasing annealing times, an endothermic peak appeared, whose area increased with the duration of the annealing period. No difference was found between the endotherm areas for the oriented and the unoriented polymer. The DSC curve of the unannealed oriented polystyrene exhibited a relaxation exotherm. DSC and relaxation studies indicated that this relaxation exotherm was independent of the main chain orientation; it may rather be due to sample densification
Effect of composition on the performance of epoxy paints
No full textWater-diffusion coefficient, water solubility and oxygen permeability measurements have been performed on free-standing membranes of epoxy-based organic coatings for different compositions. Concomitant direct (d.c.) and alternating (a.c.) current measurements were carried out on coated mild steel in order to investigate protection in neutral aerated 0.5 M NaCl. A general model has been used to analyse the a.c. data in terms of reactions occurring during the interaction of the coated metal with the aggressive environment. A correlation between transport properties of free films and the protective properties of paints has also been attempted. No relationship was found between the water permeability and the coating performance over exposure time, whereas the oxygen permeability seems to be responsible for coating effectiveness at later stages. The electrical resistivity of the coatings and its dependence on the composition and water content is related to early failure
EFFECT OF ORIENTATION ON THE CO2 SORPTION OF POLYSTYRENE.
No full textThe chain orientation, induced by hot drawing, decreases the sorption capacity of polystyrene due to the tighter packing of macromolecules in the oriented material. Density measurements and decay of birefringence indicate that the loss of orientation is a much more rapid phenomenon than the thermal shrinkage of the polymer
Iron dissolution in acid water-methanol mixtures
No full textDissolution rates of Armco iron in de-aereated and aereated acid (10-3 M H2SO4) water-methanol mixtures have been evaluated by accurate weight loss measurements, by extrapolation of Tafel lines to the corrosion potential and by using the linear polarization method. The corrosion rate was found to decrease and then to increase at increasing molar fraction of methanol both in aereated and aereated solutions, showing a minimum at an intermediate solvent composition which is significantly different from the values observed in pure solvents. Furthermore the corrosion rate in de-aereated acid pure methanol is greater than that in pure water by a factor of nearly two. The experimental results have been plotted in terms of rs rw ratio versus methanol mole fraction, where rs is the corrosion rate in the mixture and rw that in pure water. A behaviour was found quite similar to that exhibited by the ratio of exchange current density for the hydrogen evolution reaction. This similarity leads to a theoretical expression for the ratio rs rw as well as to a physical explanation for the greatest iron dissolution rate in de-aereated acid methanol solution compared to that in pure water which is in satisfactory agreement with experimental results. © 1987
Impedance spectroscopy of reactive polymers .4. An improved experimental procedure for measurement of effective resistivity
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