Influence of copolymer composition on the crystallization in PCL/SAN blends
1993; Elsevier BV; Volume: 34; Issue: 15 Linguagem: Inglês
10.1016/0032-3861(93)90395-q
ISSN1873-2291
AutoresJörg Kreßler, Petr Svoboda, Takashi Inoue,
Tópico(s)Polymer Nanocomposites and Properties
ResumoBlends of poly(ε-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) show a miscibility window, i.e. for a fixed blend ratio ф, they are able to form a one-phase mixture in the liquid state, which is dependent on the copolymer composition β, and the temperature T. For miscible blends the Flory interaction parameter χ is smaller than χs, the χ parameter at the spinodal. The minimum of χ, for a fixed T and ф, is at approximately 20 wt% acrylonitrile in SAN. Below the melting point the homogeneous liquid undergoes a liquid-solid phase transition (i.e. crystallization). We have studied the crystallization kinetics of miscible PCL/SAN blends as a function of β, ф and the crystallization temperature Tc. The rate of crystallization G, which is equivalent to the radial spherulite growth rate, also exhibits a minimum, at a fixed Tc and ф, for blends containing SAN with 20 wt% acrylonitrile. This behaviour is described in terms of a modified Hoffman-Lauritzen (HL) theory. From secondary nucleation plots it was shown, in addition, that the surface free energy (σσe)12 has a minimum at a copolymer composition with 20 wt% acrylonitrile, again for fixed values of ф and Tc. In contrast, according to the HL theory the lower surface free energy would lead to a faster crystallization. In order to explain the influence of polymer-polymer interactions on the crystallization kinetics it has to be assumed that the reptation of a crystallizable polymer chain towards the growing front of the crystal is slowed down by favourable interactions. Therefore, an additional term, ΔU∗, was introduced into the mobility expression used in the HL theory. The experimental findings show that the influence of U∗, the activation energy for the transport of crystallizable material, on the rate of crystallization predominates over the influence of (σσe)12.
Referência(s)