PhD defense of Cyril GUERS

Abstract:
This thesis work deals with the optimization of cellulosic materials (papers, cardboard and cellulosic based materials). We seek to upgrade those materials for high frequencies applications: radiofrequency and terahertz. Actually the dielectric properties of cellulosic materials, and specifically their dielectric losses, are very high. It means that the efficiency and the yield of those applications are limited. In this work, we first study individually the properties and the dielectric parameters of the different component of cellulosic materials. Using radiofrequencies measuring techniques like the resonant cavity and terahertz measuring techniques like spectroscopy THz-TDS, we point our interest on the impact of those constituents upon the dielectric losses of papers. Thanks to the results, we then present method and techniques allowing to optimize paper reducing its losses. Eventually, we discuss of the transposition effects of those techniques on a paper industrial production line and propose transversal solutions to the exploitation of paper properties in its actual state. During this work, we show specifically the crucial effect of density on the paper losses and present studies upon crystallinity, length and orientation, of cellulose fibers. Two deeper studies present the impact of fillers and moisture on paper dielectric properties. We show moreover that the fillers are very interesting to reduce the losses of cellulosic materials and we highlight the impact of moisture on measured losses. In those studies, we present two effective medium models of filled papers and moist papers. Those predictive models allow the prediction of the evolution of paper properties in function of fillers and moist content. Thanks to those results we determine, in terahertz, the parameters of bound water to cellulose, unknown yet.
 

• Tan Phu VUONG - Supervisor
•  Ke WU - Examiner
•  Frédéric GARET - CoSupervisor
•  Patrick MOUNAIX - Reviewer
•  Philippe LE THUC - Reviewer
•  Romain PERETTI - Examiner