Abstract
The non-isothermal crystallization behavior of poly(vinylidene fluoride) (PVDF) in dialkyl phthalate diluents during the thermally induced phase separation (TIPS) process was investigated by differential scanning calorimetry (DSC) at various cooling rates. Dialkyl phthalates with different alkyl chain-length, namely dimethyl phthalate (DMP), diethyl phthalate (DEP) and dibutyl phthalate (DBP), were used as the diluent. The effects of alkyl chain-length of dialkyl phthalate and cooling rate on the non-isothermal crystallization behavior as implied by the Avrami analysis modified by Jeziorny and Mo’s analysis were determined. The values of half-time, t1/2, and the parameters Zc and F(t), which characterized the kinetics of non-isothermal crystallization, showed that the crystallization rate increased with the increase of the alkyl chain-length of dialkyl phthalate due to the lower compatibility between PVDF and dialkyl phthalate. Moreover, the alkyl chain-length of dialkyl phthalate also has a great impact on the compact spherulitic structure of PVDF membranes prepared from different PVDF/dialkyl phthalate blends. With the decrease of the alkyl chain-length of dialkyl phthalate, the number of spherulites increased and the size of spherulites became smaller. This research thus not only proves the effects of alkyl chain-length of dialkyl phthalate on the non-isothermal crystallization behavior of PVDF, but also provides a systematic strategy to evaluate a single diluent during the TIPS process.
Highlights
Microporous semi-crystalline polymeric membranes with controlled pore size, shape and distribution can be prepared via the thermally induced phase separation (TIPS) method, which was first introduced by Castro in the late 1970s [1]
It clearly shows that an increase of the alkyl chain-length of dialkyl phthalate o f temperature
Crystallization peak crystallization temperature, final crystallization temperature, Tc f,The all increased with c, and behavior of the poly(vinylidene fluoride) (PVDF)/dialkyl phthalate blend was analyzed in terms of the compatibility between the increase of the alkyl chain-length of dialkyl phthalate
Summary
Microporous semi-crystalline polymeric membranes with controlled pore size, shape and distribution can be prepared via the thermally induced phase separation (TIPS) method, which was first introduced by Castro in the late 1970s [1]. In the TIPS process, an appropriate polymer/diluent system is heated to achieve a homogeneous solution During cooling, both by isothermal or non-isothermal quenching, TIPS can proceed either solid–liquid phase separation or liquid–liquid phase separation. The non-isothermal crystallization behavior of the crystalline polymer in the diluted system would predominate the pore structure of the resulted membrane. No such work has so far been carried out to analyze the non-isothermal crystallization behavior of PVDF in PVDF/single diluent blend though these single diluents have been widely used in the TIPS process. Three dialkyl phthalates, with similar structure but different alkyl chain-length, including dimethyl phthalate (DMP), diethyl phthalate (DEP) and dibutyl phthalate (DBP), were utilized as the single diluent of PVDF. The morphologies of PVDF membranes prepared from different PVDF/dialkyl phthalate systems were studied through scanning electron microscopy (SEM)
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