The results of standard analytical determinations on coconut shells agree well with those recorded by Fleck and colleagues except for the higher value found for cellulose.It is proposed to investigate further the nature of the association of xylan and cellulose in coconut shells.
Notes 761 them to differ sharply with respect to their solubility in acids. The semicarbazones which we have considered may be divided into two groups, those that are soluble and those that are insoluble in dilute hydrochloric acid.
synopsisMonofilament fibers were spun continuously from the free surface of a pool of molten poly(ethy1ene terephthalate) without the aid of a spinneret. For take-up velocities in the range of 12 to 400 ft/min, the denier of the filaments produced was an inverse power function of take-up velocity, and the birefringence was an inverse power function of the filament diameter. Production rate and product uniformity were strongly dependent on take-up velocity and surface temperature of the melt pool.
An apparatus for measuring stress relaxation of plastics at constant strain in the time range of 0.01 to 2.5 sec after load application is described. Experimental results obtained indicate that rigid plastics at room temperature may be classified as either brittle or ductile. Brittle plastics sustain only low strains without fracture at the testing speed of the apparatus and undergo little relaxation of stress in this time range; ductile plastics sustain higher strains and undergo considerable relaxation of stress. The factors affecting relaxation behavior are briefly discussed. Increasing the strain, temperature, or plasticizer content generally increases the relaxation rate.
Many of the results yield a linear plot of stress vs logarithmic time, as has been reported in the literature for various materials tested at longer times. By application of one form of the Eyring absolute rate theory, an average free energy of activation for the relaxation process can be calculated. The value thus calculated for polymethyl methacrylate is in the range reported in the literature for other polymers.
An empirical measure of ``toughness'' can be based on these results. For many plastics this measurement is in accord with service performance.
The viscosity of cellulose acetate butyrate as a function of nature and amount of plasticizer, and of temperature, was measured by means of a parallel plate plastometer. These data were used to assess numerical values for plasticizer efficiency, applying to the range of temperatures associated with molding, extruding, etc. The efficiency so found was discovered to be somewhat different at some temperatures from that determined by plasticizer solvent power, and at other temperatures, similar to it. The connection between the measurements of principal viscosity and molding conditions appears to be well established. The consequences of too low a molding temperature are clearly shown in terms of sharply increasing viscosity and onset of viscoelastic processes which may be responsible for permanent strains in molded pieces. A four-element mechanical model consisting of springs and viscous dashpots appears to fit these high-temperature phenomena quite w d l . All constants of this system are decreased as either temperature or plasticizer content increases.
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