In this work, an isotactic polypropylene (PP) and a polyethylene–octene copolymer (POE) have been blended and injection-molded, obtaining solids and foamed samples with a relative density of 0.76. Different mold temperature and injection temperature were used. The Izod impact strength was measured. For solids, higher mold temperature increased the impact resistance, whereas in foams, the opposite trend was observed. In order to understand the reasons of this behavior, the morphology of the elastomeric phase, the crystalline morphology and the cellular structure have been studied. The presence of the elastomer near the skin in the case of high mold temperature can explain the improvement produced with a high mold temperature in solids. For foams, aspects as the elastomer coarsening in the core of the sample or the presence of a thicker solid skin are the critical parameters that justify the improved behavior of the materials produced with a lower mold temperature.
This paper describes the mechanical behavior in compression, at both low-and high-strain rates, of several low-density open-cell polyolefin-based foams with different gas phase interconnectivities and different levels of gas-phase tortuosity. The mechanical properties of the open-cell polyolefin foams have been compared with two different references: an open-cell low tortuous foam based on flexible polyurethane and closed-cell polyolefin foams. One the one hand, at low-strain rates, it has been observed that the mechanical performance is controlled by the open-cell content and the properties of the polymeric matrix, being the influence of tortuosity small. On the other hand, the influence of the level of tortuosity is critical to high-strain rates. In fact, it has been demonstrated that open-cell polyolefin foams with high tortuosity (HT) present an unexpected mechanical behavior, showing excellent mechanical properties, which are even similar to that of closed-cell polyolefin materials with the same chemical composition. Therefore, low-density polyolefin foams with HT have a unique mechanical performance strongly influenced by the strain rate.
This work deals with the production and characterization of low-density rigid foams with anisotropic cellular structures based on polypropylene filled with nanoclays, which present a high potential to be employed for structural applications. The use of nanoclays and different external pressures during foaming allowed to modify several structural parameters such as anisotropy ratio, cell size, and open cell content which had a huge impact on their mechanical behavior. Moreover, nanoparticles catalyzed the thermal decomposition reaction of the blowing agent, which involved the formation of bimodal cellular structures. The mechanical anisotropy of these foams was characterized by measuring the compressive modulus in three different directions. The results indicate that mechanical properties can be significantly improved due to the introduction of nanoclays and to the structural modifications induced by their presence, especially when it comes to the anisotropy ratio parameter. POLYM. COMPOS., 00:000-000,
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