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

Abstract

Differences in the Raman spectrum of the α-and β-polymorph of poly(propylene) (PP) have been identifi ed in the form of band shifts distinct for the specifi c polymorph. A new method has been developed, which can ascertain the presence of the α-polymorph. These band shifts have been used to profi le both the polymorphs and variations in the crystallinity across the whole spherulite have been ascertained by carrying out a spatially resolved profi ling of the degree of crystallinity. The crystalline domains in PP have been qualitatively assessed using the band shifts in the Raman spectra. This approach has then been applied to study local variations in the morphology of welds between PP plates, wherein the complex interplay between the heating and cooling patterns as well as the mechanical forces due to shearing gives rise to the development of a different morphological structure in the weld. Using Raman microscopy, a reduction in the crystallinity (≈18%) in the region of the weld seams and sporadic formation of β-spherulites in the weld core is observed. The methodology developed has been applied to investigate a weld between PP-H and PP-R (PP with random ethylene copolymer), to ascertain the variations occurring upon welding in such materials. various components. [ 1,2 ] Processing PP into the fi nal product regularly infers anisotropies in the melt due to shear forces, which result in structural variations in the solidifi ed polymer. The latter embody themselves in the form of spatial variations in morphology, with their length scale and variance depending on the specifi c process and conditions. 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. [ 7,8 ] The crystallization into a specifi c form depends on the crystallization

Effect of Nucleating Additives on Short- and Long-Term Tensile Strength and Residual Stresses of Welded Polypropylene Samples

“…These differences can be distinguished by dynamic differential calorimetry, e.g., with a heating rate of 2 °C/min [13]. Furthermore, both modifications can be distinguished by a polarization microscope on the basis of their birefringence [15][16][17][18]. The microstructures determine macroscopic me-chanical properties of polypropylene samples.…”