Flow‐Induced Crystallization

Fibrillar Morphology in Shear-Induced Crystallization of Polypropylene

“…Recent developments in shear‐induced crystallization (SIC) have demonstrated the existence of three regimes which, for the same polymer at the same temperature and pressure, occur on increasing the flow intensity: (i) the effect of flow upon the final morphologies and crystallization kinetics is negligible, (ii) the flow causes a strong enhancement of crystallization kinetics, increasing the number of nuclei and thus the average dimension decreases, but the spherulitic morphology is kept, (iii) the flow deeply influences both morphology and kinetics by causing the formation of fibrillar structures in the polymer melt. However, apart from a qualitative understanding of the phenomena, a quantitative description of the phenomena is still discussed and it is currently under investigation …”

Structural Basis of High‐Strength High‐Modulus Polymers

“…At the same time, PE samples of similar molecular weight and molecular weight distribution obtained by multistage zone drawing exhibit a similar modulus (50 GPa) but a much higher tensile strength (1.5 GPa) [159,160]. This problem was extensively discussed in the literature [171,172]. The lower tensile strength of the solid-state extruded samples was attributed to their substantially larger cross-section area as compared to that of the meltcrystallized/drawn filaments, since it was established that for samples of similar sizes and similar M , and MWD produced through various technique (surface growth/drawing and gel-spun/drawing) the tensile strengthmodulus relationship is the same [172].…”

Molecular simulation of flow-enhanced nucleation in n-eicosane melts under steady shear and uniaxial extension

“…Meerveld et al classified FIC behavior under shear based on the strain rateε in terms of the reptation time τ d and Rouse time τ R of the melt. 7,9 They determined that there are three important ranges: (i) whenε < 1/τ d , nucleation is effectively quiescent, (ii) when 1/τ d <ε < 1/τ R the molecular orientation induces a modest increase in sporadic, isotropic nucleation, and (iii) whenε > 1/τ R , the molecular stretching causes a drastic increase in the nucleation of oriented, fibrillar structures. This analysis indicated that chain stretching has the most dramatic effect, a result that has also been observed in continuum and meso-scale modelling.…”

“…5 Numerous studies have shown that FIC is strongly dependent on the rheological behavior of the highest molecular weight chains in the melt. [5][6][7][8] This observation has given rise to the concept of precursors, which form during flow from perturbed high molecular weight chains and have an increased capacity to induce crystallization in a polydisperse melt upon cooling. 5,8 This manuscript focuses on nucleation from the monodisperse melt, and therefore the rheology of only the single length of chain present is important, and precursors are not expected to form.…”

“…Continuum models have proven effective for describing the later stages of FIC, including structure development and rheological properties. 7 At the mesoscale, Graham and Olmsted developed a coarse-grained kinetic Monte Carlo model that uses the GLaMM continuum rheological model 12 to sample chain configurations and adds segments of chains to a discretized nucleus using an acceptance criterion based on the segment-wise free energy. 5,11 Their model exhibited good agreement with experimental data, in support of the viewpoint that FEN can be explained by flow-induced entropy reduction in the melt; however, it must be considered to be a phenomenological model due to its rigid assumptions about the nucleus shape and its reliance on unknown thermodynamic parameters.…”