Micro- and Nano-Structural Analysis of Poly (Lactic Acid) with Thermal, Mechanical, Transmission Electron Microscopy and X-ray Diffractometry Techniques

The PhD research activity is aimed at understanding how the structural and morphological characteristics of biopolymers shape and/or influence their intrinsic macroscopic properties. This is with a view to gaining relevant information that could be used to optimize various parameters, such as relative performance, industrial processing, and future development. In addition to the well-known polymer characterization techniques, the research is also carried out through new investigation methodologies. Among these, the most innovative one is performed with the electron pair distribution function (ePDF) technique, which allows to get structural information on the semi-crystalline state from electron diffraction data collected over areas of a few ten of nanometres. Moreover, the characterization of crystalline polymeric phase is carried out by means of X-ray diffraction (XRD) which a global view of the crystallinity of the samples and allows to estimate the amorphous vs. crystalline ratio. These data are supported by the morphological investigation through transmission electron microscopy (TEM) imaging. Furthermore, temperature-modulated differential scanning calorimetry (TMDSC) is jointly employed to get macroscopical thermal insights directly related to micro- and nano-structural data. By using a linear temperature scan superimposed on a low-frequency sinusoidal perturbation (0.001 and 0.1 Hertz), TMDSC has significant advantages related to signal resolution and increased sensitivity, as well as the possibility of detecting overlapping phenomena, specifics of biopolymers. These results are essential for the resolution of the intrinsic polymer structure, with particular emphasis on the different amorphous (RAF and MAF) and crystalline (CRY) phases. Finally, an appropriate tuning of the industrial processing as well as the related processed samples engineering characterizations generally provide information on many aspects of the mechanical behaviours exhibited by the material. All together, these data would enable the development of new analytical theoretical models to be used to predict typical features and behaviours with the aim of improving their relative use and production.