Understanding the foamability and mechanical properties of foamed polypropylene blends by using extensional rheology

Abstract

In this article, the influence of the rheological behavior of miscible blends of a linear and a high melt strength, branched, polypropylene (HMS PP), on the cellular structure and mechanical properties of cellular materials, with a fixed relative density, has been investigated. The rheological properties of the PP melts were investigated in steady and oscillatory shear flow and in uniaxial elongation in order to calculate the strain hardening coefficient. While the linear PP does not exhibit strain hardening, the blends of the linear and the HMS PP show pronounced strain hardening, increasing with the concentration of HMS PP. Related to the cellular structure, in general, the amount of open cells, the cell size, and the width of the cell size distribution increase with the amount of linear PP in the blends. Also mechanical properties are conditioned by the extensional rheological behavior of PP blends. Cellular materials with the best mechanical properties are those that have been fabricated using large amounts of HMS PP. The results demonstrate the importance of the extensional rheological behavior of the base polymers for a better understanding and steering of the cellular structure and properties of the cellular materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42430.

Mechanical Properties of PMMA‐Sepiolite Nanocellular Materials with a Bimodal Cellular Structure

“…Another possible rationale behind the reinforcement detected in the cellular nanocomposites compared to the solid nanocomposites with the same sepiolite content is the improved dispersion of the particles in the cellular materials due to the foaming process. Multiple studies have demonstrated that foaming can lead to better dispersion of particles . To validate this hypothesis, the number of particle aggregates was determined before and after the foaming process for the material with 2 wt% of sepiolites (for which the highest enhancement of the modulus was observed at a relative density close to 0.5) using tomography and image analysis.…”

“…These outcomes indicate that the particles are less aggregated in the cellular samples than in the solids. This effect is related to the stretching suffered by the polymer chains during the cell growth . The enhanced dispersion is expected to enhance the mechanical properties of the solid phase.…”

Effects of extrusion process, type and content of clays, and foaming process on the clay exfoliation in HMS PP composites

“…These foams are discs with a diameter of 180 mm and a height of 10 mm. A more detailed description of the ICM technique can be found elsewhere …”

“…Moreover, composites containing three different clay contents (2.5, 5, and 7.5 wt %) were generated in order to analyze the effect of the clay content. Finally, cellular materials were produced by the Improved Compression Moulding (ICM) route in order to analyze the effect of the foaming process . ICM was selected because in this foaming process the material is only subjected to temperature and pressure and hence, there are no other forces associated to the foaming process which could contribute to the clay exfoliation (such as shear forces in extrusion foaming).…”

Highly anisotropic crosslinked HDPE foams with a controlled anisotropy ratio: Production and characterization of the cellular structure and mechanical properties

“…To obtain larger anisotropy ratios, processes designed specifically are required. In the work of Laguna-Gutierrez et al [30] the improve compression molding (ICM) technique was employed to produce polypropylene foams with controlled expansion ratios of the order of 5 and anisotropy ratios around 3. In the work of Arora et al [31] anisotropic polystyrene foams were produced using supercritical carbon dioxide as blowing agent.…”