Morphology, crystallization, and thermal behaviour of isotactic polypropylene/low density polyethylene blends

Abstract

The morphology, the crystallization and thermal behaviour of isotactic polypropylene (iPP) in its blends with two different samples of low density polyethylene (LDPE) was investigated at temperatures high enough to prevent any solidification of LDPE. It is found that pre-existing liquid LDPE domains are incorporated in intra-spherulitic regions during the isothermal crystallization of iPP. The radial growth rate of spherulites is almost unaffected by the LDPE content. The overall rate of crystallization of iPP, on the contrary, is strongly depressed by the addition of LDPE. A depression of the equilibrium melting temperature of iPP, due to kinetic and morphological effects, is also observed. The depression of the overall kinetic rate constant is accounted for by the negative effect (decrease in the number of nuclei) that the addition of LDPE has on the primary nucleation process of iPP.

Crystallization of Polypropylene and Poly(Ethylene Terephthalate)

“…x c « 0.5388-0 -2.308-HI) (52) i (53) It is seen that x n is comparable for copolymers of propylene with 1-butene and ethylene. An even more direct comparison can be made by considering the data of Turner-Jones [67], who studied both types of copolymers in the same manner, namely, with 1-butene, Guidetti et al [71] investigated the formation of the y polymorph of iPP in propylene copolymerized with small amounts (m < 0.1) of comonomers, both in binary copolymers with ethylene and in terpolymers with ethylene and 1-butene.…”

“…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.…”

“…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.…”

Nucleation of Polypropylene Homo- and Copolymers

“…Keeping the temperatures of isothermal crystallization experiment around the T m of PE (120 to 130 8C) it can be seen that the overall crystallization rate of blends is depressed, producing spherulites in considerably smaller numbers compared to pure PP. Martuscelli et al (1984) claimed this to be a consequence of deactivation and/ or dissolution of nuclei by PE inclusions. This hypothesis was confirmed by further experiments from the same group on PP/ PE systems with (Batczak et al, 1986) and without (Galeski et al, 1984) external nucleating agent.…”

A Dynamic Study of Crystallization of Poly(ε-caprolactone) and Poly(ε-caprolactone)/Poly(vinyl chloride) Blend

“…The behavior shown in Figure 4 is similar to the Tc dependence of r 112 , a half time of crystallization, obtained by other methods, for instance DSC measurement for a polypropylene/poly- ethylene blend. 24 Figures 5 and 6 show the tc dependence of the long period L, which is defined as the inverse of the wave number of the scattering peak. In both Figures, L is nearly constant or slightly decreased with tc, though some decrease of L was observed at the initial stage of crystallization.…”