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Effects of thermal history on isotactic polypropylene
Author(s) -
Pae K. D.,
Sauer J. A.
Publication year - 1968
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1968.070120811
Subject(s) - endotherm , crystallinity , tacticity , annealing (glass) , materials science , melting point , endothermic process , melting temperature , degree (music) , thermodynamics , analytical chemistry (journal) , composite material , differential scanning calorimetry , chemistry , polymer , polymerization , organic chemistry , adsorption , acoustics , physics
The effect of past thermal history on the melting behavior of isotactic polypropylene is investigated in some detail. It is shown that a series of stepwise annealing treatments at steadily increasing temperatures will raise the final melting point and will result in a double endothermic peak if the final anneal temperature is at or close to 160°C. It is also shown that a series of stepwise annealing treatments at steadily decreasing temperature will lead to multiple DSC peaks. The number of such separate peaks is equal to or greater than the number of annealing steps. Even low‐temperature anneals (100–130°C) affect the melting endotherm, while high‐temperature anneals have a marked effect on both the degree of crystallinity of the sample and the final melting temperature. For a 3‐min anneal, the highest degree of crystallinity is produced by an anneal temperature of 155°C. The highest melting temperature (∼182°C) is produced by a 30‐min, or longer, anneal at about 160°C. The implications of these results in terms of crystal thickening and perfection are discussed.