Melting and swelling

Formulas and Data Sheets, issued yearly, containing all newly established fundamental equations and numerical data on basic properties of polymers. These would include new equations to express viscosity as a function of temperature, concentration, or shear rate new relations between intrinsic viscosity and molecular weight new formulas on the kinetics of polymerization and copolymerization data on second-order transition points of new polymers or copolymers heat and entropy of solution, dilution, melting, and swelling of macromolecules and similar fundamental data as they are contained in the articles appearing during the reference year. They would be similar in purpose to the Technical Data Sheets and complement them in regard to fundamental information. 

All cereals store amylose and amylopectin molecules in simple or compound granules (Chapter 4). Starch grauules from a single cereal differ from one another in size, shape, and other characteristics. The different granules possess different melting and swelling properties and respond differently to enzymatic hydrolysis. A... 

When heated, borax fuses, loses w and swells into a wh porous mass. Finally borax melts(anhyd powd at 561°) and on cooling forms a clear glass. Borax beads fused in a loop of Pt wire are used as tests for oxides which dissolve in the bead and show characteristic colors... 

These phenomena have been the subject of intensive study during the last 50 years and still represent major problems in polymer rheology. From a processing point of view they are very important, since melt fracture represents an upper limit to the rate of extrusion, and swelling and the large pressure drops must be accounted for in product considerations and in the design of the die and processing equipment. 

Extrudate swelling refers to the phenomenon observed with polymer melts and solutions that, when extruded, emerge with cross-sectional dimensions appreciably larger than those of the flow conduit. The ratio of the final jet diameter to that of the capillary D/Dq, for Newtonian fluids varies only from 1.12 at low shear rates to 0.87 at high rates. Polymer... 

Fig. 12.12 Comparison of the viscosity and swelling ratio dependence on shear rate for a polystyrene melt of Mw = 2.2 x 105 and Mw/Mn = 3.1. [Reprinted hy permission from W. W. Graessley, S. D. Glasscock, and R. L. Crawley, Die Swell in Molten Polymers, Trans. Soc. Rheol., 14, 519 (1970).]...

Experimentally, as indicated in Fig. 12.13, we find that D/Dq depends on the shear stress at the wall xw (a flow variable) and the molecular weight distribution (MWD) (a structural variable) (22). The length-to-diameter ratio of the capillary (a geometric variable) also influences D/Dq. The swelling ratio at constant xw decreases exponentially with increasing L/Dq and becomes constant for L/Dq > 30. The reason for this decrease can be explained qualitatively as follows. Extrudate swelling is related to the ability of polymer melts and solutions to undergo delayed elastic strain recovery, as discussed in... 

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