Spatially resolved monitoring of crystalline suprastructure and molecular orientation in α‐ and β‐nucleated polypropylene pipes using differential scanning calorimetry, infrared microscopy, and polarized light microscopy

Abstract

Differently nucleated polypropylene (PP) pipes were studied by polarized light and infrared (IR) microscopy and differential scanning calorimetry (DSC). Although Fourier transform IR microscopy (mFTIR) excels by high spatial resolution and ease of measurement over the classical approach with manually prepared sections and individual analysis, a disadvantage is that the vibrational bands used to calculate the degree of crystallinity may be influenced by the polymorphism of PP. While this does not play a role for the a-polymorph, in the case of b-nucleated PP the calculated profile of crystallinity derived from the so called crystallinity bands depends on the direction of inspection. We could show that in the case of b-nucleation the results from mFTIR and DSC of cross-sections can be correlated, and thus the crystallinity profile obtained from mFTIR becomes independent from the direction of consideration. Consequently the advantages of mFTIR with regard to spatial resolution and reproducibility can now be exploited for b-nucleated PP as well. Using the differently nucleated specimen we give the first practical validation of a previously on a theoretical basis derived model to determine the molecular orientation in all three dimensions (machine, transverse, and normal). It could be shown that the profiles of molecular orientation are a function of both, the extrusion process with its post extrusion cooling conditions, and the type of nucleating agent.

Measuring the orientation of chains in polypropylene welds by infrared microscopy: A tool to understand the impact of thermo-mechanical treatment and processing

“…PP-H1 shows two peaks with maxima at 159 and 166 C, which can be assigned to the melting endotherms of the b-and apolymorph of PP [24], respectively. However, PP-H2 shows only one melting peak at 164 C that corresponds to the a-polymorph [24,28]. X c was calculated from the melting endotherm according to [24] (Eqs.…”

“…However, PP-H2 shows only one melting peak at 164 C that corresponds to the a-polymorph [24,28]. X c was calculated from the melting endotherm according to [24] (Eqs. (4)e(7)) and IR-spectroscopy using the method reported in (Eq.…”

“…All samples were measured using a heating rate of 10 C/min under an inert atmosphere of nitrogen between 25 and 230 C, and the first heating cycle was used for morphological analysis. The heat of fusion of completely crystalline a-and b-crystalline iPP was taken as 177 J/g and 168 J/g, respectively [24].…”

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

“…The heat of fusion of completely crystalline α-and β-crystalline isotactic PP (iPP) was taken as 177 and 168 J g −1 , respectively. [ 4 ] X c was calculated from the melting endotherm according to ref. [ 4 ] (Equations ( 2) -( 5) )…”

“…These in turn have a signifi cant impact on the macroscopic properties, such as mechanical properties and crack propagation. [3][4][5] Hence, spatially mapping the morphology in a comprehensive manner is an important task in order to establish process→structure→property relationships and use these to optimize manufacturing. [ 6 ] The morphology of PP has been well studied and it has been known that PP crystallizes in three different polymorphs, namely, the α-, β-and γ-form.…”