Structure and properties of nucleated random and block copolymers of propylene

Abstract

The addition of various nucleating agents to a polymer leads to the modification of its crystalline structure, i.e., the formation of small spherulites with consequent changes in mechanical and optical properties. The aim of our research was to determine the role of nucleating agents on the crystallization of propylene copolymers. Random and block copolymers containing propylene and low amounts of ethylene were used in formulations with nucleating agents based on derivatives of sorbitol such as dibenzylidene sorbitol (DBS) and para‐methyldibenzylidene sorbitol (MDBS). The introduction of low concentrations of DBS and MDBS leads to significant changes in the crystalline structure with respect to α and β phases, as well as in the kinetics of crystallization. Using WAXS, DSC, optical microscopy, and tensile testing, the following changes of nucleated propylene copolymers were observed: (a) an increase in the crystallization temperature; (b) an increase of the level of crystallinity; (c) a considerable decrease of the size of spherulites (i.e., an improvement of the transparency of the random copolymers); (d) a decrease of the amount of the β phase in block copolymers; (e) an increase in tensile strength at yield; and (f) an increase in secant modulus. In most cases we found that the most efficient nucleating agent was the MDBS. © 1994 John Wiley & Sons, Inc.

Nucleation and crystallization of blends of poly(propylene) and ethylene/α-olefin copolymers

“…Applying this concept, the sorbitol has a 60% efficiency in nucleating PP (12 8C shift in peak T c ), since the maximum efficiency (100%) is achieved by the PP crystal fragments during self-nucleation (20 8C shift in peak T c ). Similar shifts in PP crystallization temperature as a consequence of the addition of sorbitol have been reported in the literature [22][23] .…”

“…In this work, Sorbitol was used as nucleating agent, since is well known as a good nucleating agent for a-PP (monoclinic) [22][23] . Fig.…”

Effect of the Molecular Structure of the Polymer and Nucleation on the Optical Properties of Polypropylene Homo- and Copolymers

“…After the quantitative analysis of these correlations an attempt is made to relate the determined parameters to the molecular structure of the polymer. Nucleation is very often used in polypropylene to increase stiffness and strength [23][24][25][26][27][28][29] , to improve productivity by increasing the temperature of crystallization [27][28][29][30] and to modify optical properties [17][18]31 . The efficiency of nucleation is usually estimated by DSC measurements, by changes in the peak temperature of crystallization (T cp ) 32 , which can be related to the thickness of the lamellae formed 33 .…”

Crystallization of Polypropylene: Application of Differential Scanning Calorimetry Part Ii. Crystal Forms and Nucleation

“…Derivatives of sorbitol (known as DBS, MDBS and EDBS) are the most effective known nucleating agents of iPP, leading exclusively to the creation of the monoclinic α-form [53][54][55]. The best-known β-nucleating agents are the trans-quinacridone Permanent Red [56] and a bicomponent mixture consisting of equivalent amounts of pimelic acid and calcium stearat [57].…”