Analysis of the Process-Structure-Behavior Interaction in Bio-Sourced Polymers: Role of the Crystallization Kinetics

PLA (Poly Lactic Acid) is a bio-sourced and biodegradable polymer. It represents an alternative for polymers issued from petrochemical synthesis. Unfortunately, the crystallization kinetics of PLA is very slow and limits the possibility to extend its application in several industrials domains. The enhancement of the PLA crystallization kinetic can be obtained by addition of nucleating agents of by ordering the molecular chains during flow, as in processing conditions. During processing of thermoplastic polymer experiences several thermomechanical conditions influencing drastically its final properties and mechanical behavior. During injection molding process, macromolecules are oriented and ordered due to the shear and elongation imposed by the melt flow in the mold during the filling step. As a consequence, supplementary nucleation is created in the polymer, leading to the acceleration of the crystallization kinetics. In this work, we propose to analyze and to quantify the role of the flow, the temperature kinetics and the nucleating agent on injected PLA parts structure and their mechanical behavior. A parametric analysis of the relationship between the polymer, its structure and the processing condition will be presented. The competition (sometimes antagonism) between several parameters, as the shear rate, the temperature kinetics and the nucleating agent will be highlighted.