ISSN:
0098-1273
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
This paper reports of a study on eutectic solidification of the quasi binary system of unfractionated isotactic polypropylene and the dentritic growing diluent pentacrythrityl tetrabromide. This system was characterized by a eutectic-type experimental phase diagram with a eutectic composition of 68% (w/w) of polypropylene. The eutectic temperature was found to depend on kinetics, and was established by differential scanning calorimetry to be 122 and 102°C at a cooling rate of 0.5 and 32°C/min, respectively. A remarkeable nucleating effect of the primary diluent crystals was observed in the solidification of diluted polypropylene solutions. Here the eutectic horizontal was located at a temperature which was 15°C higher than in the eutectic solutions exceeding the temperature at which the pure polymer crystallized from the melt by 8°C. The eutectic microstructures produced were found to depend on the rate of solidification, which was varied by pulling the polypropylene solutions through a fixed temperature gradient of 3°C/mm at different speeds ranging from 0.2 to 80 mm/hr. At rates lower than 3 mm/hr the polymer and the diluent crystallized simultaneously from the eutectic solution in a uncoupled mode of growth, forming a coarse structure of diluent crystals and isotactic polypropylene spherulites with dimensions of about 0.1 mm. At higher speeds the simultaneous crystallization of the macromolecules and solvent molecules proceeded in a co-operative manner with a nonplanar growth front. A rodlike eutectic microstructure was produced, in which diluent rods, lined up in the growth direction, were dispersed in a polypropylene matrix. The lateral dimension λ1 of these rods were found to depend on the growth rate R in the following way: λ12 R = 10-9 mm3/sec, and ranged from 0.3 to 1.0 μm. This was in accord with values calculated by using the current theory of rod eutectic growth of Jackson and Hunt.
Additional Material:
12 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1977.180150310
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