The impact resistance of injection‐molded polypropylene (PP) parts is severely reduced when they are foamed. It is necessary to implement strategies, such as elastomer toughening, to increase the impact behavior of foamed parts. However, the knowledge on the effect of elastomer addition on the morphology, cellular structure, and impact of injection‐molded cellular parts is very limited. In this work, foamed parts based on blends of PP and polyolefin elastomers have been produced and characterized. A high and a low viscosity octene‐ethylene copolymer (EOC) and a high viscosity butene‐ethylene copolymer (EBC) were employed. The blends have been thermally and rheological characterized. Solids materials and foams (relative density 0.76) were injection‐molded. The solid phase and cellular structure morphologies were studied using scanning electron microscopy. The results showed that elastomer toughening has been successful to obtain an improvement of the impact behavior in solid and cellular polymers. In this case, EOC materials provide an appropriate interfacial adhesion and optimized cellular structure which results in high impact resistance. The optimum elastomer to improve the properties is the EOC with a higher viscosity which provides impact resistance with n values below 3 due to the toughening of polymer matrix, thick skin thickness, and low cell size.
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.
Different blends of a linear polypropylene (L‐PP), a long‐chain branched polypropylene (LCB‐PP), and a polyolefin elastomer (POE) are prepared and foamed using core‐back injection molding. The objective is to analyze the use of POE and LCB‐PP as complementary strategies to improve cellular polymers’ impact response. Different parameters are then studied in blends and injection molded plaques to understand the samples’ mechanical behavior. Parameters such as the interfacial tension, elastomer morphology, extensional rheology, cellular structure, and crystallization behavior are characterized in detail. The addition of POE allows improving the impact response of both the solids and cellular polymers, but the stiffness is reduced. On the other hand, the substitution of L‐PP by LCB‐PP, in blends containing POE, results in solids and cellular materials with both better stiffness and better impact properties, due to the different crystalline morphology comprising the samples, a different cellular orientation, and thicker solid skin.
In this work, formulations based on composites of a linear polypropylene (L-PP), a long-chain branched polypropylene (LCB-PP), a polypropylene–graft–maleic anhydride (PP-MA), a styrene-ethylene-butylene-styrene copolymer (SEBS), glass fibers (GF), and halloysite nanotubes (HNT-QM) have been foamed by using the improved compression molding route (ICM), obtaining relative densities of about 0.62. The combination of the inclusion of elastomer and rigid phases with the use of the LCB-PP led to foams with a better cellular structure, an improved ductility, and considerable values of the elastic modulus. Consequently, the produced foams presented simultaneously an excellent impact performance and a high stiffness with respect to their corresponding solid counterparts.
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.
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