Kinetics Comparison of Solid-State Polycondensation and Melt Postpolycondensation for Polyamide 6 with Controllable Extractive Content

This research delves into the kinetics of solid-state polycondensation (SSP) and melt postpolycondensation (MPP) of polyamide 6, with a particular focus on managing extractable content. We scrutinize how reaction time and temperature influence key properties, such as relative viscosity, oligomer content, and end group content in PA6 during SSP and MPP. A sophisticated kinetic model was formulated to discern the reaction rate constants and activation energies of PA6, especially considering the presence of low-molecular-weight extractable small molecules. The results indicate that MPP surpasses SSP in swiftly lowering monomer and oligomer concentrations, with minimal impact from reaction temperature. Extractable small molecules inhibit PA6 chain expansion, with a higher initial oligomer content leading to slower chain growth. Analysis of end group content and reaction kinetic models revealed activation energies of 124.25 and 146.39 kJ/mol for the P4 and P8 stations during SSP, related to viscosity increases. In contrast, melt postpolycondensation showed activation energies of 127.62 and 137.43 kJ/mol for P4 and P8, suggesting its superiority for high-extractable materials due to its dual role in devolatilization and viscosity enhancement. This integrated approach eliminates the need for separate extractable small molecules removal, offering a technological edge by directly producing processable melts and streamlining the production workflow.