Crystallization regimes and reptation in polypropylene molecular weight fractions

Abstract

Crystal growth rate data based on the kinetic nucleation theory of chain folding and the effect of reptation, have been used to predict the rate of crystal growth at moderate to high supercoolings in iPP molecular weight fractions. Growth rate data obtained for the fractions seem to be in agreement with the theoretical predictions of the regime theory. However, an extension of the gambler ruin treatment to the iPP data has not been successful with regard to the dominant morphology in regime II. The variable cluster model suggested as the morphology for polyethylene in regime II does not appear to be evident from this study. The effect of polydispersity, molecular weight, and tacticity on the crystallization behavior of iPP fractions have also been studied and correlated with the structure of polymer samples investigated.

The crystallization of polypropylene in multiwall carbon nanotube‐based composites

“…In agreement with the kinetic theory of crystallization [58–60], independent of the type of regime, the crystallization rate G can be given by: where K g(III) = 4 σ u σ e b 0 T m0 / k Δ H m for Regime III [61–64], k being the Boltzmann constant, 1.38 × 10 −26 kJ K −1 , b 0 = 6.26 Å, represents the thickness of a crystalline monolayer added during growth, σ e and σ u are the basal and lateral interfacial free energies of the crystallite, respectively, and U /2.3 R(T c ‐ T ∞ ) represents the transport term through the liquid–crystal interface at the crystallization temperature T c [65]. The temperature T ∞ is that at which the viscosity of the system is infinite, and is equivalent to the value T g ‐ 30 which is 231.1 K for polypropylene.…”

The crystallization of polypropylene with reduced density of entanglements

“…should be two times higher for Regime III than for Regime II. Experimental values are different, in range of 1.4–2.6 or even more, as 3.2 found by Ibhadon (see Fig. in his paper).…”

The effect of molecular composition and heterogeneity on the environmental stress cracking resistance (ESCR) of propylene impact copolymers

“…The properties of impact polypropylenes, including ESCR, can also be related to the size and distribution of the rubbery component [34][35][36]. The optimum size of the rubber particles and the distance between these particles could be one of the most important factors in controlling the mechanical behaviour of polymers, but there is some debate as to what the optimum values for these variables are, but values of around 0.3-0.4 mm are generally reported [35].…”