Modeling the reactive PA6 flow for LCM processes

Abstract

Fiber reinforced thermoplastic composites have shown to be attractive for industry as they can be reused, reshaped, welded and repaired, while keeping mechanical properties on par with thermoset composites. Since thermoplastics usually have high melt viscosities unsuitable for liquid composite molding processes, in-situ synthesis of PA6 from ε-caprolactam is considered. Its reactive mix has low viscosity which allows impregnation. However, the coupled crystallization and polymerization affects the resin viscosity and its flow is altered by the dual-scale permeability of the fiber preform. Thus, to predict the local differences in the thermoplastics properties, a coupled polymerization crystallization model needs to be integrated in the LCM processing simulation at representative scales. This study aims to propose a reliable simulation of the resin flow through a fibrous preform. Hence, viscosity measurements on the reactive mix are achieved using a rheometer with parallel-plate geometry, aiming to associate a viscosity model with the Hillier coupled polymerization-crystallization model previously determined by Vicard. The full chemorheological model will then be integrated into a simulation of LCM process in OpenFOAM®, an open source CFD software in order to follow the extent of the synthesis in the resin flow during the process. As a future work, simulations including microscale tow information extracted from a real textile specimen will permit to investigate the effect of permeability and double scale porosity in fibrous preforms on the final polymerization rate and crystallinity.

Efficient polymerization and crystallization kinetics coupling of polyamide 6 synthesis for liquid composite molding process modeling

“…It is also consistent with PA6 spherulite growth observations by Magill [32] and with fast scan DSC measurements. [33,34] It follows Equation (11), in which U Ã , K g , and T ∞ are parameters relative to macromolecular motion or crystallization growth, while T 0 m is the equilibrium melting temperature of PA6 crystals.…”

“…η r,0 (Equation 23) is calculated following an Arrhenius law determined in a previous work. [11] The influence of crystallization in viscosity is not taken into account.…”

“…[6,7] Therefore, simulations of the kinetics during the manufacturing process allow to optimize cycle time and properties while limiting the need for costly experimental optimizations. Several frameworks for reactive simulation process have been proposed in the literature, coupling flow and polymerization [8][9][10][11] or more rarely flow and crystallization, [12] but to the best of the authors' knowledge, polymerizationcrystallization coupled model for process simulation have rarely been proposed until now.…”