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Shear‐induced crystallization of isotactic poly(1‐butene)
Author(s) -
Bove Lucia,
Nobile Maria Rossella
Publication year - 2002
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/1521-3900(200208)185:1<135::aid-masy135>3.0.co;2-s
Subject(s) - crystallization , materials science , shear rate , nucleation , shear (geology) , shear flow , tacticity , simple shear , rheology , thermodynamics , isothermal process , strain rate , pure shear , composite material , polymerization , physics , polymer
In the present work the kinetics of the isothermal quiescent crystallization of the isotactic Poly(1‐butene) (i‐PB) is analyzed by means of rheological measurements and is used as an internal reference to study the effects of the shear flow. In particular, the flow‐induced crystallization of two i‐PB samples with different molecular weight is investigated by step‐shear experiments at the crystallization temperature, T C , of 95°C. Indeed, with step‐shear experiments the effects of the applied shear rate and shear strain on the crystallization kinetics can be separately analyzed. In all the cases the overall‐crystallization rate constant, k, defined as the inverse of the half‐time of crystallization (t 0.5 ) has been evaluated. The results show that a critical shear rate (at a constant shear strain) and a critical shear strain (at a constant shear rate) are necessary to obtain the enhancement of k. These results significantly depend on the molecular weight revealing a stronger sensitivity to flow for the higher molecular weight sample. On the contrary, in the quiescent experiments no evidence of relevant molecular weight effects is detected. The in‐situ optical analysis has shown that faster growth rates and a strong enhancement of nucleation density are observed in the step‐shear experiments compared to the quiescent case.