Calcium salts of suberic (Ca-Sub) and pimelic (Ca-Pim) acids were synthesized and implemented as in different grades of isotactic polypropylene (iPP). Propylene homopolymer, as well as random and block copolymers containing these additives, crystallized iPP into pure or nearly pure β modification in the isothermal and nonisothermal crystallization experiments. Recently, Ca-Sub proved to be the most effective β-nucleating agent of iPP. The Ca-Sub nucleating agent widens the upper crystallization temperature range of pure β-iPP formation up to 140°C. In this study the effect of the these additives on the crystallization, melting characteristics, and structure of the PP were studied. The degree of crystallinity of β-iPP was markedly higher than that of α-iPP. A widening in the melting peak of the samples crystallized in a high temperature range was first observed and discussed in regard to literature results of the same phenomenon for α-iPP. The morphology of the β-iPP samples was revealed by scanning electron microscopy. Independent of the type of polymer or nucleating agent, hedritic structures were found in the early stages of growth of the β-spherulites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2357–2368, 1999

Highly active thermally stable β-nucleating agents for isotactic polypropylene

Thermal and crystallization studies of short flax fibre reinforced polypropylene matrix composites: Effect of treatments

http://link.springer.com/content/pdf/10.1007/978-94-011-0567-5_3.pdf

Crystallization, melting and supermolecular structure of isotactic polypropylene

Studies of the temperature dependence of spherulitic growth rates, in the context of the Lauritzen−Hoffman secondary nucleation theory, and investigations of the crystallization time and temperature dependence of the melting behavior, in the context of the nonlinear Hoffman−Weeks (HW) extrapolation, are reported for isotactic polypropylene prepared with Ziegler−Natta catalysts. The quantitative agreement between estimations of the equilibrium melting temperature, Tm, through an analysis of spherulitic growth rate data and use of the nonlinear HW approach provides strong support for the latter method. The results of these studies indicate specifically that Tm (it-PP, α-phase) is in the vicinity of 212−215 °C, some 30 °C above the most commonly quoted value. This new value of the equilibrium melting temperature of it-PP leads to predictions of the crystallization temperature dependence of the initial lamellar thickness and of the correlation between the lamellar thickness and observed melting temperature, w...

Equilibrium Melting Temperature and Undercooling Dependence of the Spherulitic Growth Rate of Isotactic Polypropylene

During nonisothermal crystallization of highly dispersed polypropylene/carbon nanotube (CNT) composites, considerable heterogeneous nucleation is observed to an extent scaling with the CNT surface area. Saturation occurs at higher loadings, reaching a plateau value for the crystallization onset which is 15 °C higher than in the unfilled matrix. Polymorphic behavior does not occur, as revealed from wide-angle X-ray diffraction. Upon subsequent heating, an increase in the melting temperature is observed due to increased crystalline perfection in the presence of CNTs. The complex multiple melting behavior is interpreted in terms of recrystallization phenomena. A study at varying heating and cooling rates reveals that CNTs affect the chain segment mobility of the matrix and largely inhibit recrystallization upon heating. TEM observation of the nanocomposite morphology evidences the occurrence of a transcrystalline layer around the CNTs. A structure model is presented, in which individually dispersed CNTs are separated from a bulklike polymer phase by a highly ordered crystalline interface with reduced polymer mobility.

P.C. Jain

Papers

Melting behaviour of isotactic polypropylene isothermally crystallized from the melt