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

Modeling Flow-Induced Crystallization

“…Because timescales for flow and crystallization are separated, this protocol isolates flow-induced structure formation. Using this protocol, flow-induced point-like nucleation (appearing for low to mild flow rates) has been thoroughly characterized, using a shear cell combined with optical microscopy, for iPP [19][20][21][22][23][24][25][26][27][28], isotactic poly(1-butene) [29][30][31], and poly(lactic acid) [32]. Alternatively, a rheometer can be used to apply flow and monitor subsequent crystallization in terms of rheology [32][33][34][35][36][37][38].…”

“…Their approach was extended by the Peters group, who coupled flow-induced nucleation rate to backbone stretch [63][64][65][66]. Because the chains on the high side of the molecular weight distribution are most likely to be stretched, this effect is dominated by the longest chains in the material [21,29,63,67], that is, in a multimode viscoelastic model by the mode with the highest relaxation time(s). Based on an extension of the Schneider rate equations [68] proposed by Eder and coworkers [18,69], Zuidema et al proposed a model that calculates shish density (i.e., the line nucleation density for kebabs) from continuum-level deformation [63].…”

“…Because flow-induced point-like nucleation has been extensively described in the literature, we focus here on FIC under strong flow conditions, yielding highly oriented crystal structures. We focus on experimental data obtained for iPP, but similar modeling has been successfully used to predict FIC kinetics for linear low density polyethylene (LLDPE) and poly(1-butene) [29,81] and is now being applied to poly(lactic acid).…”

“…Liedauer et al coupled the parameter _ γ 4 t 2 s , with shear rate _ γ : and flow time t s , to the density of shish [18], see also [69]. Their approach was used as a starting point for the Eindhoven group, who linked nucleation rate to deformation of the high molecular weight mode on a continuum level [21,29,63] and subsequent shish growth (after overcoming a critical flow criterion) to deformation of a mode corresponding to the average molecular weight [63,64,66]. This approach was validated in terms of shear layer thickness in both channel flow and capillary rheometer.…”

“…Extensive research during the past decade into the phenomenon of FIC has indicated that flow-enhanced point-like nucleation is dominated by the chains at the high end of the molecular weight distribution [21,29,106]. Following earlier experiences by Steenbakkers and Peters [21], Roozemond and Peters [29], Custódio et al [66], and van Erp et al [82], the creation rate of point-like nuclei is coupled in a phenomenological way to the momentary stretch in the high molecular weight tail of the material (corresponding to the mode having the longest relaxation time; mode 7 in Table 3) on a continuum level,…”