Structure-properties relations of starch-based materials: impact of orientation and electron beam irradiation

This work is part of the general approach aiming to understand and improving the mechanical properties of thermoplastics starch materials by proposing a new and original approach to the structural modification of thermoplastic starch through the combination of two techniques: radiation crosslinking and macromolecular orientation. The first part of the thesis focuses on the thermo-mechanical properties of plasticised starch and proposes an update to the master Stress-strain curve highlighting 'antiplasticization' and 'over-plasticization' phenomena thanks to the study of properties at equivalent Tg. The evolution of materials β transition temperature (Tβ) could also be linked to the different plasticization stages and TGA results highlighted the sorption and desorption phenomenon of the plasticizer. The damage and fracture mechanisms of plasticized starch were also explored with video-traction technology. The second chapter of the document is devoted to the study of crosslinking of thermoplastic starch at solid state under an electron beam radiation. Many factors were explored like the absorbed dose, water content, plasticizer content, nature and amount of crosslinking agents introduced, and their impact on curing mechanisms and retrogradation of the plasticized starch. The third and final chapter deals with the specific mechanism of molecular orientation of the thermoplastic starch and its impact on mechanical properties. The coupling of orientation and irradiation under an electron beam was also investigated. (author)