Model Development and Validation of Crystallization Behavior in Injection Molding Prototype Flows

Abstract

To control the final properties of semi‐crystalline polymer products, an accurate prediction of the material microstructure developed upon processing is required. For that purpose a model for flow‐enhanced nucleation of semi‐crystalline polymers is proposed, which relates molecular deformation with the enhancement of crystallization. Flow kinematics, computed in a decoupled fashion, are used to solve a coupled viscoelastic stress—crystallization problem. Morphological features concerning the number, size, and shape of crystalline structures are predicted and a comparison is made with experimental results reported by Housmans et al.1,2 in which the morphology development of an isotactic polypropylene (iPP) resin was studied.magnified image

Application of a multi-phase multi-morphology crystallization model to isotactic polypropylenes with different molecular weight distributions

“…The pioneering work in understanding and modelling flow-induced crystallization started by the Janeschitz-Kriegl group [24] was developed and implemented during the last twenty years in our group [25][26][27][28]19,29,30]: the temperature and pressure dependence of growth of different crystal phases and of the overall nucleation density was determined using an optimization routine to fit experimental data and described by phenomenological equations, the effect of flow on the increase in the number of nuclei and on oriented structures formation was evaluated by considering the momentary stretch of the high molecular weight tail of the material, using different approaches over the past years. The structure development in non-isothermal conditions after flow at different pressures was computed using a modified set of Schneider rate equations [31] combined with Kolmogorov-Avrami equation [32] to account for impingment.…”

Flow-enhanced nucleation of poly(1-butene): Model application to short-term and continuous shear and extensional flow

“…The nucleation model was studied and validated further by Custodio et al (2009) and Steenbakkers and Peters (2011). Applied to iPP, the model captures short-term shear experimental results very well, in simple shear [Roozemond et al (2011);Steenbakkers and Peters (2011);van Erp (2012)] as well as in channel flow [Custodio et al (2009);Zuidema et al (2001)]. Steenbakkers (2009) applied the model to data on poly(1-butene) from the group in Leuven, who studied this material extensively ; ].…”

Suspension-like hardening behavior of HDPE and time-hardening superposition

“…because the rheological properties, flow field, and crystallization kinetics are all intimately coupled (Custódio et al 2009;Steenbakkers and Peters 2010). A vast amount of experiments investigating the change of rheological properties can be found in the literature, cf.…”

“…An empirical relation for the space filling shift factor was proposed. Custódio et al (2009) implemented this method of predicting viscosity as a function of space filling in their code for the simulation of shear flow in a multipass rheometer.…”