Anisotropic Crystallization in Polypropylene Induced by Deformation of a Nucleating Agent Network

Abstract

Memory effects on polypropylene systems with differents amounts of a nucleating agent (Dybenzylidene Sorbitol DBS) have been studied by Wide Angle X ray scattering methods. It has been observed that deformation applied in polypropylene melts, where even small amounts of DBS are included, is templated into the crystalline state. After crystallising a sheared polypropylene/DBS melt, an anysotropic texture is observed by X ray scattering, whereas the crystals produced from sheared pure PP melts are randomly distributed. This fact is directly addressed how the DBS is spread into the polypropylene melts. Different concentration and deformation conditions are explored allowing to conclude that, below a certain temperature, the DBS self-organize into a three dimensional network producing the gelation of the PP melt. When the deformation is applied in this gel state, it is templated into the crystals, whereas when it is applied at temperatures above this self organisation, there is not memory of the deformation process when the sample crystallise.

Influence of nucleating agent on the crystallization kinetics and morphology of polypropylene

“…It is verified the presence of a very thin and unique fibrillar structure intertwining networks without the formation of specific nuclei. Similar structures were also observed in some studies carried out with derivatives of sorbitol nucleating agents [15,17,18] . Probably this morphology is responsible for the improvement in the optical properties, reducing the interaction between the polymer crystalline phase and visible light.…”

Directed Crystallisation of Poly(ε‐caprolactone) using a Low‐Molar‐Mass Self‐Assembled Template

“…Nogales et al reported that the shear-induced anisotropy in DBS/poly(propylene) was only possible during shear flow at temperatures less than 180 8C. [20] We Figure 11. (a) A map of the WAXS intensity I(a,jQj) obtained for a sample of 3% DBS/PCL crystallised from a melt after a shear flow of 10 000 su at 10 s À1 at 80 8C.…”

“…The modest molecular weight of the PCL melt matrix means that higher shear rates are required to induce a substantial level of macroscopic orientation of these nanoscale fibrils than was observed for equivalent isotactic poly(propylene)-based systems. [20] We can judge that the relaxation rate of this preferred orientation after the cessation of shear flow is relatively fast as the rate of cooling after crystallisation has an impact on the level of templating that occurs (Figure 12). …”

“…[12,20] The crystal structure for PCL has a basal arrangement similar to that for polyethylene but it differs greatly from that for i-poly(propylene). [23] The inclusion of the ester groups in PCL leads to a larger c-value of 17.05 Å [11] while for polyethylene it is 2.55 Å and for i-poly(propylene) it is 6.50 Å .…”

Investigating the Morphological Variations Due to Processing and Thermomechanical Treatment of Poly(propylene) Using Raman Microscopy

“…[ 25 ] Micro SAXS-WAXS has been used to investigate the morphology of PP spherulites; however, a spatial profi ling across the whole spherulite has not been reported. [25][26][27] This can be attributed to the requirement of a synchrotron beam source for achieving a higher resolution, making laboratory measurements unfeasible. Hence, it is extremely valuable to have a method that can provide quantitative information about the X c distribution across a spherulite at a high resolution and also distinctly identify the two different polymorphs of PP.…”