Effect of cellular uniformity on the necking propagation of foam injection Molded PP/HDPE blend parts

Abstract

Necking propagation (NP) is an important phenomenon that is facilitated by the superductility of many materials, although necking is often considered to be a type of unstable and heterogeneous deformation under tensile loading. In this study, the NP of samples produced with injection molding of polypropylene (PP) and high‐density polyethylene (HDPE) blends with or without a blowing agent was investigated by standard tensile testing, and the foam morphology and cellular structure were characterized with scanning electron microscopy. It was found that the foam parts fabricated with the PP/HDPE blends had the ability to be superductile under a low tensile test speed, which was attributed to the necking spreading throughout the tested gauge section stably and reliably. However, the NP of the foam PP/HDPE blend samples strongly depended on the distribution of the cellular foam. To investigate the relationship between the cellular structure and NP, a design of experiment approach based on the Taguchi method was used to fabricate many samples with different foam structures. The tensile test results of these samples suggested that the cellular uniformity, which was determined based on the statistical results of the fracture surface morphology, played an important role in the NP. The results suggested that there is a close relationship between the NP and the cellular uniformity. Using nonlinear fitting, it was straightforward to obtain a model between the NP length and cellular uniformity index for PP/HDPE molded foam parts.

Foams with Enhanced Ductility and Impact Behavior Based on Polypropylene Composites

“…In this mechanism, the reduced cell size plays a key role. In the PP/HDPE system, the importance of the uniformity of the cellular structure in the deformation mechanism was also studied in depth by Zhou in several articles [51][52][53]. So, it is clear that the inclusion of the LCB-PP combined with foaming in our complex blend led to the formation of foams with a more ductile character.…”

“…In our case, the elongation was not reduced when foaming, in fact, it was increased and this increment in ductility could lead to an increment in the toughness of the foams. This increment of elongation at break in foams when the LCB-PP content was raised to values above to those achieved for the solids with the same composition can be also explained by an optimized quality of the cellular structure [51][52][53].…”

Chemistry, Processing, Properties, and Applications of Rubber Foams

“…The effect of the size, shape, and surface chemistry of nanoparticles on the rubber foam structure and properties still needs further study. On the other hand, the literature is full of blends of thermoplastic foams with several types of thermoplastics being used [ 304 , 305 , 306 , 307 , 308 , 309 ]. However, few studies were found on the foaming of rubber blends or/and thermoplastic/rubber blended foams.…”

Effect of the shape and the distribution of cells on the effective thermal conductivity of polyurethane foam

“…The distribution of cellular uniformity is an important parameter to quantify the cellular distribution in different foam zones. 57 However, this study considers a periodic representation of the structure based on a pavement of unit cells with the same cell diameter to focus on the effect only. Whereas the distribution of closed and open cells is considered, in fact, this is a particular and important parameter of the category of mixed cell foams even with periodic approach of REV.…”