Foaming behavior of high‐melt strength polypropylene/clay nanocomposites

Abstract

The foaming behavior of high‐melt strength polypropylene (HMS‐PP) and HMS‐PP/Cloisite 20A nanocomposites (PPNC) was studied in a batch process. PPNCs with 2, 4, 8, and 10 wt% clay were prepared in a twin screw extruder. The morphology of the nanocomposites was studied using XRD and TEM. Subsequently, foaming experiments were conducted using supercritical CO2 as the blowing agent in a batch process, and foams with cell sizes varying from the sub micrometer to the micro meter range were prepared. The effect of variation in saturation pressure and temperature, foaming temperature, foaming time, and quench temperature was determined experimentally. Dynamic rheological measurements were conducted to relate the influence of nanocomposites morphology with foam cell growth and nucleation. Extensional rheological measurements were also conducted to detect the presence of strain hardening effect at the foaming temperatures used in the experiment. It was found that the nucleation efficiency of clay reduces with increase in clay loading. Also, the optimum amount of filler for generation of fine celled foams was found to be around the percolation threshold of the polymer. The extended strain hardening effect shown by the polymer in presence of clay plays an important role in stabilizing foam cell sizes. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Sub-critical gas-assisted processing using CO 2 foaming to enhance the exfoliation of graphene in polypropylene + graphene nanocomposites

“…Polymers injection molded or extruded with a supercritical fluid (SCF), such as carbon dioxide (CO 2 ) or nitrogen (N 2 ), can be foamed to achieve lighter weights and improved dimensional stabilities compared to their solid counterparts [16], [17]. This process is known as microcellular processing.…”

Moulded polypropylene foams produced using chemical or physical blowing agents: structure–properties relationship

“…On the one hand, by filling PP with inorganic compounds such as talc or nanoparticles [10][11][12] and on the other hand by using special PP grades known as high melt strength PPs, on which by promoting a high degree of branching the melt strength is significantly increased [6,11,13]. Finally the less desirable solution because turn the polymer non-recyclable, is crosslinking the PP matrix [1].…”

Mechanical behaviour of cyclic olefin copolymer/exfoliated graphite nanoplatelets nanocomposites foamed through supercritical carbon dioxide

“…In the open literature a few papers can be found on the preparation and physical properties of polymer nanocomposites foamed through supercritical carbon dioxide (scCO 2 ) [9,10]. For instance, Bhattacharya et al [5] studied the effect of the foaming parameters (i.e. saturation pressure and temperature, foaming temperature, foaming time and quench temperature) on the physical properties of polypropylene/clay nanocomposites of the prepared materials.…”

“…Therefore, traditional blowing agents (such as pentane, butane, chlorofluoro hydrocarbons) have been withdrawn and replaced by gases like argon, nitrogen and carbon dioxide [1,4]. Recently, the usage of supercritical fluids (SFCs) has been considered as a valuable path to produce polymer foams [5][6][7][8][9][10][11][12][13]. SCFs possess physical properties intermediate between those of gases and fluids.…”