Nanostructure Evolution in Poly(propylene) During Mechanical Testing

ipyChord: a package for evaluating small-angle X-ray scattering data of fiber symmetry

This article presents a Python-based package, ipyChord, to compute the 2D chord distribution function (CDF) from the small-angle X-ray scattering (SAXS) pattern from polymer materials with fiber-symmetrical nanostructure. The program allows construction of a harmonized SAXS pattern from a raw SAXS pattern, by normalization of the incident-beam intensity, absorption correction for sample thickness, masking blind areas on the detector, and filling in the shadow of the beamstop and its holder using symmetry operations. Patterns from modular detectors with inter-module gaps can still be fully constructed satisfactorily after determining the optimized beam position and a radial basis function. A CDF pattern computed from the full SAXS pattern can be used to determine the domain size and its variability using a graphical method. An interface distribution function computed from Bonart's longitudinal projection or sliced from a CDF meridian can quantify differently stacked hard and soft domains. Two cases of the application of ipyChord are presented. The software is open source and available at https://github.com/isaxs/ipyChord.

Extruded blend films of poly(vinyl alcohol) and polyolefins: common and hard-elastic nanostructure evolution in the polyolefin during straining as monitored by SAXS

Straining of PVA/PE and PVA/PP blends (70:30) is monitored by small-angle x-ray scattering (SAXS). Sheet-extruded films with different predraw ratio are investigated. The discrete SAXS of predrawn samples originates from polyolefin nanofibrils inside of polyolefin microfibrils immersed in a PVA matrix. PE nanofibrils deform less than the macroscopic strain without volume change. PP nanofibrils experience macroscopic strain. They lengthen but their diameter does not decrease. This is explained by strain-induced crystallization of PP from an amorphous depletion shell around the core of the nanofibril. The undrawn PVA/PE film exhibits isotropic semicrystalline nanostructure. Undrawn PVA/PP holds PP droplets containing oriented stacks of semicrystalline PP like neat precursors of hard-elastic thermoplasts. Respective predrawn films are softer than the undrawn material, indicating conversion into the hard-elastic state. Embedding of the polyolefin significantly retards neck formation. The polyolefin microfibrils can easily be extracted from the water-soluble matrix.