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

Abstract

The rheology of solidifying high-density polyethylene (HDPE) is investigated. Experiments on an HDPE were performed with a novel RheoDSC device. Results agree quantitatively with simulations for a suspension of elastic spheres in a viscoelastic matrix except for very low values of space filling (<5%), indicating that the rheological behavior of the crystallizing melt in the frequency range investigated is purely suspension like. The hardening behavior of the material is characterized in two different ways; a normalized rheological function and a time-hardening superposition (THS) master curve of rheological properties. An improvement is proposed to the procedure for performing THS that was previously used in the literature. Based on this procedure, a novel method for predicting the rheological properties of crystallizing melts is presented.

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

“…Zuidema et al (2001) introduced the above as a necessary addition to the core of the model, which is the coupling between chain stretch and nucleation. Although such a phenomenon would be very hard to measure experimentally, there are clear indications for changes in the rheology of a crystallizing melt during the early stages of crystallization, even when the spherulites are still too small to have a noticeable effect on the viscosity, if the behavior of the material is purely suspension-like [Bove and Nobile (2002) ;Carrot et al (1993); Roozemond et al (2012)]. It is obvious that the nuclei do not create the junction points in a percolating network because they are too far apart (with radius of gyration of chains R g ¼ 10-100 nm and distance between spherulites 10-100 lm), but the mechanism for slowing down of chains involved in nuclei can be of a different nature.…”

“…First, the reptation and Rouse time of the hmw tail increases as described above. Second, the material can be viewed as a suspension of soft particles (the growing spherulites) in a viscoelastic matrix (the amorphous melt) [Roozemond et al (2012); Steenbakkers and Peters (2008)]. As the spherulites grow, the viscosity of the material increases.…”

“…Then, using the same parameters, the model is validated in continuous simple shear and uniaxial extension flow [Acierno et al (2008); Hadinata et al (2007Hadinata et al ( , 2005]. The Schneider rate equations [Schneider et al (1988)] and a suspension model [Roozemond et al (2012); Steenbakkers and Peters (2008)] are used to calculate crystalline volume fraction and resulting viscosity increase in time. The goal of this paper is not to improve or adapt the existing model but rather to investigate how well the experimental data presented here could be captured by the model and, if required, could be used for model improvement in future work.…”

Modeling Flow-Induced Crystallization

“…Alternatively, a rheometer can be used to apply flow and monitor subsequent crystallization in terms of rheology [32][33][34][35][36][37][38]. Using a model for the crystallinity dependence of rheological properties [39,40], it is even possible to extract nucleation density from rheological data [25,35]. The evolution of rheological properties with flow-induced structure formation may also play a complex role when strong flows are concerned; it has been observed that the amount of flow-induced structure saturates at a certain level, presumably as a result of decreasing deformation rate caused by increasing viscosity [41,42].…”

Flow-induced crystallization studied in the RheoDSC device: Quantifying the importance of edge effects

“…(Housmans et al 2009;Vleeshouwers and Meijer 1996), or using continuous shear (Acierno et al 2008;Hadinata et al 2005). It has even been shown that using an appropriate model to link rheological properties and crystalline structure (Steenbakkers and Peters 2008;Roozemond et al 2012), one can extract nucleation density after short-term shear from such experiments (Housmans et al 2009;Ma et al 2011), thus providing an alternative for studies with in situ optical microscopy.…”