Nanocellular foams confined within PS microfibers obtained by CO2 batch foaming process

Abstract

Nanocellular foams localized in PS (polystyrene) microfibers with 10.0---20.0 µm-diameter were prepared by CO2 (carbon dioxide) one-step foaming method. The CO2-soaking conditions were operated at the slightly above Tg (glass transition temperature) of PS that maintains the fiber structures was investigated. The control of bubble nucleation in the foaming mechanism was driven by the depressurization rate adjustment. The higher depressurization rate and the use of the lower diameter of PS microfibers have resulted in the reduction of the obtained cell diameter and larger of cell density. The average of the smallest cell size diameter of 60---70 nm with the number of cell density of 1.1 × 1014 cmź3 was obtained by the depressurization rate of 3.0 MPa/min using PS microfibers of 10 µm-diameter. The ratio of foamed region (core region) and the fiber radius was slightly increased by the reduction of the depressurization rate and using the larger diameter of PS microfibers. The formation of cellular structures could be clarified by P---T (pressure---temperature) profiles combined phase diagram of CO2---PS system. The changed in thermal properties and mechanical properties of the PS fibers caused by the formation of the nanocellular foams were reported in this study.