Strategy for the preparation of lightweight polypropylene/polyethylene‐octene elastomer composite foams with different phase morphologies using supercritical carbon dioxide

Abstract

Polypropylene (PP)/polyethylene-octene elastomer (POE) composites with a "sea-island" structure and a cocontinuous structure were prepared. With the selection of a suitable foaming temperature, the supercritical carbon dioxide foaming of PP/POE composites with different phase morphologies occurred only in the POE phase. The effects of the POE content, foaming temperature, pressure, and number of layers on the cell size, cell density, apparent density, foaming layer density, and foaming ratio under different phase morphologies were investigated by scanning electron microscopy, polarized optical microscopy, differential scanning calorimetry, and dynamic thermomechanical analysis. This article provides a novel approach for foaming PP at a low temperature. For PP/POE-blended composites with a "sea-island" structure, the foaming temperature is as low as 80 C, and for PP/POE alternating multilayered composites with a cocontinuous structure, foaming can occur at 40 C. Compared with the conventional methods for foaming PP, this method avoids the problems of a high foaming temperature, a narrow range of the foaming temperature, and a low melt strength of the PP. Thus, the PP foaming method was successfully improved, yielding a new technique for the preparation of lightweight PP.

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

“…In addition, with the increase of the foaming temperature, both the average sizes of the big cells and the small ones increase. This is attributed to the increased force for cell growth, and the result is consistent with those reported about the foaming of the nonmultilayered 18,19,26 and multilayered 13 foams.…”

“…Hence, it would be very hard for the cells to grow from the PS layers, and then, the PS layers became the unfoamed film (Figure b 3 ). The gas dissolved in PS layers would then be used for cell nucleation and growth in PS–SiO 2 layers, as the activation energy for heterogeneous cell nucleation is much lower than that for homogeneous cell nucleation. , However, the film thickness in the alternating film/foam assemblies formed in this study is much thinner compared to those about 20–200 μm in the literature ,− prepared via coextrusion with chemical foaming agents. The preparation approach provided in this study can save more materials and obtain film/foam assemblies of lower densities.…”

“…In recent years, multilayered foams have emerged as a new branch of foams that feature alternating layered structures. − Due to the special cell structure, the multilayered foams show excellent mechanical, thermal insulation, and sound absorption properties. Till now, different approaches have been reported about the preparation of multilayered foams.…”

“…Till now, different approaches have been reported about the preparation of multilayered foams. The groups of Baer − and Guo − prepared alternating film/foam assemblies via a multilayered coextrusion technique, with the chemical foaming agent incorporated in the alternating layers to decompose during processing. Generally, the same polymer is used for the film layer and the foam layer, but the foams prepared through this approach have cells only in alternating layers, i.e., the foam layers.…”

“…Generally, the same polymer is used for the film layer and the foam layer, but the foams prepared through this approach have cells only in alternating layers, i.e., the foam layers. Wang et al 13 reported the preparation of multilayered polypropylene/polyethylene− octene elastomer (PP/POE) foams via a coextrusion technique followed by a batch foaming process. Due to the large difference in the foaming windows of PP and POE, only the latter layers can be foamed under their experimental condition.…”