Effects of nucleating agent on thermally induced phase separation membrane formation.

摘要

Thermally-induced phase separation, TIPS, is perhaps the most versatile and simplest technique to form microporous polymeric membranes from a variety of semi-crystalline and thermoplastic polymers. The primary objective of this work was to investigate how the addition of nucleating agent affected the crystallization kinetics of polymer-diluent mixtures undergoing solid-liquid thermally-induced phase separation (that is, the rate at which the membrane is formed) and how this influenced membrane structure.; The work focussed on the model system isotactic polypropylene (iPP)-dotriacontane (C{dollar}sb{lcub}32{rcub}{dollar}H{dollar}sb{lcub}66{rcub}{dollar}), with adipic acid (Aa) as the nucleating agent. Differential scanning calorimetry (DSC) was used to study the overall crystallization kinetics, and thermal optical microscopy (TOM) was used to determine the spherulitic growth rates. This study used isothermal and non-isothermal modes of crystallization to characterize the crystallization kinetics of non-nucleated and nucleated iPP-C{dollar}sb{lcub}32{rcub}{dollar}H{dollar}sb{lcub}66{rcub}{dollar} system.; The Avrami analysis was used to study the isothermal overall crystallization kinetics, yielding information regarding the effects of iPP concentration, the addition of nucleating agent, and crystallization temperature on spherulitic morphology and crystallization rate. The Lauritzen and Hoffman (L&H) growth rate analysis was used to study the isothermal growth rate, yielding information regarding the effects of iPP concentration and the addition of nucleating agent on fold surface energies.; The Ozawa and Ziabicki analyses were used to determine the effects of iPP concentration, the addition of nucleating agent, and cooling rate on overall non-isothermal crystallization kinetics. A method was developed to determine growth rates from non-isothermal crystallization data. The L&H equation was modified to approximate non-isothermal growth rate and to predict isothermal growth rate.; TIPS membranes were prepared under various thermal conditions. Cross-sections of the membranes were examined using the scanning electron microscope. The largest pore size was obtained by bubble-point method, and porosity was obtained by ASTM Method D 792-66.; Wide-angle x-ray scattering was used to characterize the different iPP polymorphs and determine the presence of the smectic phase in TIPS membranes. Knowledge of the polymorphs aided in the interpretation of the internal structure of the membranes.