Loianno, Valerio (2018) Thermodynamics of Thermoplastic Polymers and their Solutions. [Tesi di dottorato]

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Glassy organic polymers are technologically important across the gamut of materials applications from structural (hyperbaric windows) to electronic (ionic conductors, surface coatings for printed circuit boards) to environmental (membranes for industrial gas separation). A formal description and understanding of the glass transition temperature is necessary in order to determine the configurational state and hence physical properties of the glass. Moreover, the non-equilibrium glassy state appears to be unstable: volume-relaxation studies of glassy materials have revealed that they undergo slow processes, which attempt to establish equilibrium. These types of retardation/ relaxation phenomena are called physical ageing. As well as pressure and temperature, sorption of a plasticizer may affect in several ways the membrane physical properties. Generally speaking structural rearrangement of the chains is enhanced and, consequently, the glass transition temperature decreases, physical ageing is usually speed up, the membrane is affected by swelling and/or plasticization and even crystallization can be activated. The research work focuses on the investigation of industrial polymers’ glassy – rubbery behaviour due to thermodynamic state variables change (e.g. temperature T, mechanical pressure P and solvent content ) within the polymer matrix. The goal is to obtain a fundamental insight of the sorption process on both macroscopic and microscopic levels. As a result several polymer—penetrant systems have been studied. Different techniques have been implemented to achieve this goal: dilatometry, MTDSC, gravimetry, manometry and in situ FTIR. The instruments used are: a PVT apparatus from GNOMIX®; a MDSC from TA Instruments®; four different handmade systems consisting of a CAHN microbalance from Thermo Fisher Scientific®, a QSM from RUSKA Co.®, a pressure decay system from MKS® and finally a FTIR from Perkin-Elmer®. All data have been modelled with statistical thermodynamic theories and empirical approaches . The study is divided as follows: the first chapter introduces the research goal and fields of application along with the theoretical background for membrane science; the second chapter reports the study conducted on the system PEI—CO2; the third chapter describes the results obtained on the PS—Toluene system; finally in the fourth chapter the results for the PPO—benzene system are given. The order in which these systems are presented is related to the increase of structural modifications as a result of polymer— penetrant interactions.

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