Improving of Cell Structure of Microcellular Foams Based on Polypropylene/High-density Polyethylene Blends

Abstract

Polypropylene/high-density polyethylene (PP/HDPE) blends and their nanocomposites are melt compounded using twin-screw extruder. The as-extruded samples are then batch foamed with supercritical carbon dioxide. It is demonstrated that the blend with a viscosity ratio close to unity produces a microcellular foam with very uniformly distributed finer cell structure, whereas nonuniformly distributed cells may be obtained in the foamed blend with a viscosity ratio greater than unity. Then three methods are tried to improve the cellular structure of the latter. The results show that the increase of HDPE content improves the uniformity of cellular size and distribution, but results in the increase of cell diameter and the decrease of cell density. Properly lowering the foaming temperature reduces the cell diameter and improves the cellular distribution. Incorporating nanoparticles, including nano-calcium carbonate and nanoclay, into the blend leads to a significantly smaller cell size and more homogeneous cell distribution. A critical content of nanoparticles exists to obtain dramatically improved cell structure. Moreover, the results show that most cells in foamed blends are nearly reticulated. So open-celled foams are achieved in this work.

Effect of clay dispersion on the cell structure of LDPE/clay nanocomposite foams

“…The interface between the compatibilizer and PE matrix was found to have much lower activation energy for bubble nucleation, and therefore can provide more cells in unit volume, leading to a decrease in the mean cell size [42]. On the other hand, the different viscosities of the components (PE and PE‐ g ‐MA) led to different bubble growth rates, which in turn increased the cell size distribution [43]. The results also showed that the addition of clay, without compatibilizer, reduced the average cell size and cell size distribution, and increased the cell density.…”

Recent Developments of Foamed Polymer/Layered Silicates Nanocomposites

“…It has been also found that the diluting of the masterbatch by pristine PP efficiently helps to disperse nanoclay in the polymer matrix [49][50][51].…”

Characterization of microcellular plastics for weight reduction in automotive interior parts

“…Low solubility and diffusivity of blowing agents in PP have been determined [258,259], leading to inhomogeneous morphology along the part. On the other hand, the [261,262], ramified molecular structures [157,260] and blending with other polymer [125,[263][264][265][266]. Furthermore, it has been reported that inorganic fillers dramatically enhance cell structure of foamed polymers acting as nucleating agents.…”