Chapter 3 - Experimental Techniques for Understanding Polymer Crystallization

Abstract

Crystallinity in polymers that are semicrystalline is an important material characteristic that determines many of their physical properties. This chapter discusses the various methods that are commonly used for determining crystallinity and crystallization behavior, and in understanding the crystalline characteristics. Beginning with the simplest of all techniques, the density measurements, the chapter describes the most commonly used differential scanning calorimetry (DSC) and X-ray diffraction (XRD) methods. Spectroscopic methods, such as infrared (IR) spectroscopy, Raman spectroscopy, and nuclear magnetic resonance, are also discussed. Although these are secondary techniques that need to be calibrated using density or XRD methods, they provide important structural information and complement other measurement techniques. Other techniques, small-angle X-ray scattering and microscopy, are discussed to highlight the relation between crystallinity and structures at 10–1000nm, such as lamellae, fibrils, and spherulites. Because the crystallinity is rarely homogeneous across the bulk of a sample, IR spectroscopy, Raman spectroscopy, and μ-XRD techniques are presented as examples of the tools that can be used to map such inhomogeneities. Finally, techniques to monitor the crystallization kinetics and the results that are obtained from such measurements are illustrated with a discussion of the use of DSC, optical microscopy, dilatometry, light scattering, and X-ray scattering to measure the development crystals and larger length scale structures. The strength of each technique and the nature of the structural information obtained by different techniques are compared.