Calorimetric study of the crystallization and melting of polypropylene

Crystallization of Polypropylene and Poly(Ethylene Terephthalate)

“…under cooling. The dependences of T Xthw and T sMgh on R Tx , observed by Koppelmann [59] and Varga, Menczel, and Solti [39] in unrelated experiments, and curves for our best-fit equations to these sets of data are shown in Fig. 18.…”

“…Varga et al [39] also provided T z<mix data, so Fig. 18 [59], for the temperature limits T^ and 7^ of nonisothermal crystallization under cooling, as functions of the cooling rate R Tx (in C C/ min) and our best-fit equations to these data, (b) Data of Varga et al [39] for T At>H ., T tmal , and T lhish in nonisothermal crystallization under cooling and our best-fit equations to these data. The two sets of results are plotted using the same axes to facilitate comparison.…”

“…These trends agree with expectations based on data shown earlier. (a) lei- [7,27,29,30,39,44,45,[52][53][54][55][56][57] for the half-time t m for the primary crystallization of iPP as a function of crystallization temperature T, and a descriptor of the average molecular weight (with Af n used whenever possible); also shown is the curve for our empirical equation providing the best fit for the dependence of the logarithm of t m on 7;. (b) Quality of fit after removing the three outlying data sets (two for resins of very low A/ n [27] and one for very old data [56]) and combining the other data into one data set.…”

“…Values of x c measured by calorimetric or crystallographic methods will be preferred when available as we consider densitometry to be less reliable. The highest observed values were 0.68 by DSC for PP samples off iso = 0.975 andf iso = 0.960 synthesized using a high-yield catalyst system and crystallized isothermally [29], 0.68 by x-ray crystallography for a PP resin with/ M = 0.988 crystallized isothermally [31], 0.65 by x-ray crystallography for a sample annealed at a r a near T m [37], 0.67 for oriented heat-set PP fibers [22] and 0.70 for oriented films [38] characterized by several methods, 0.73 by DSC for a slowly cooled sample in a nonisothermal crystallization experiment [39], and 0.72 by DSC for an oriented sample at a draw ratio of 7 [40]. These highest observed jc r values are quite obviously consistent with the predicted range of 0.71 < x c ,"" < 0.75'.…”

“…It is also the most important practical quantifier of the progress of crystallization since it describes the time required for 50% conversion. We assembled data [7,27,29,30,39,44,45,[52][53][54][55][56][57] on the dependence of r, /2 on T x , M n ,f h0 , and the catalyst used in synthesis. Whenever such data were shown for both primary and secondary crystallization processes [27,29], with the latter usually occurring after spherulitic impingement [58], only the primary crystallization data were considered.…”