Unprecedented Cell Structure Variation in Multilayered Alternating PS/PS–SiO₂ Foams

Abstract

The objective of the present work was to report the unprecedented cell structure variation in multilayered alternating polystyrene (PS)/PS−SiO 2 foams. The multilayered alternating PS/PS−SiO 2 foams were prepared via a coextrusion technique and a subsequent batch foaming process with high-pressure carbon dioxide (CO 2 ). The multilayered PS/PS−SiO 2 stacks were controlled of different layers (2, 4, 8, 16, 32, 64, and 128) using the layer-multiplying elements (LMEs). The PS−SiO 2 nanocomposite was prepared using a twin-screw extruder with 99 wt % PS resins and 1 wt % SiO 2 nanoparticles. With the increase of the layer number, three types of cell structures were observed: alternating big-cell/small-cell layers, a single big-cell layer in small-cell layers, and alternating film/small-cell layers. The original big cells were formed in the pure PS layer, and the small ones in the PS−SiO 2 layers. It was considered that the decrease in the thickness of the pure PS layer and the increase in the thickness of the PS−SiO 2 layer due to the interfacial mixing between the adjacent layers is the reason for the unprecedented cell structure variation. A possible mechanism was proposed for interpreting the cell structure variation in the preparation of multilayered PS/PS−SiO 2 foams. The interfacial mixing can be taken as the strategy to tune the cell structures for the purpose of end-use demands in preparing multilayered foams using the same polymer in adjacent layers.

Supercritical CO2 Extrusion Foaming and Steam-Chest Molding of Polypropylene/Thermoplastic Polyurethane Bead Foams

“…Bead foams and their molded products, with the characteristics of light weight, thermal and sound insulation, etc., , have been widely used in our daily lives, such as expanded polypropylene (EPP), − expanded poly­(lactic acid) (EPLA), − expanded thermoplastic polyurethane (ETPU), , expanded polycarbonate (EPC), expanded polyethylene (EPE), expanded polyamide (EPA), expanded polystyrene (EPS), − etc. Today, expanded bead foams are mainly prepared by autoclave foaming technology, which has the outstanding advantage of preparing three-dimensional complex shapes . But for the semicontinuous batch foaming method, there are many areas worth improving, such as complex process steps, energy consumption, and long production period. − Therefore, this study intends to propose a facile and continuous method to prepare bead foams, where the procedure of polymer melting, gas dispersion, foaming, and pelletizing can be completed in a one-step continuous process.…”