Microcellular foaming of PP/EPDM/organoclay nanocomposites: the effect of the distribution of nanoclay on foam morphology

Abstract

In this study, microcellular foams based on polypropylene/ethylene propylene diene monomer/organoclay (PP/EPDM/organoclay) nanocomposites were produced via a batch process using supercritical nitrogen (N 2 ) as the physical blowing agent. The foaming temperature and morphological observation demonstrated that foaming occurred mostly in the PP phase. To evaluate the effect of organoclay distribution on the cell nucleation step and the final foam morphology, the location of the nanofillers in the nanocomposite blend was traced by means of surface energies and Young's equation. The calculated wetting coefficient predicted that the organoclays would have more affinity with PP and would primarily distribute into the PP phase. These results were confirmed by atomic force microscopy (AFM), dynamic mechanical thermal analysis (DMTA) and transmission electron microscopy (TEM). The cell density and average cell sizes are the main foam characteristics that were determined using SEM micrographs, and it was found that these parameters were influenced by the presence of nanoclays. An improved foam morphology was obtained in the nanocomposite samples. INTRODUCTIONBecause polymeric materials are widely used in daily life, the need to reduce the amount of consumed materials has received significant attention. Currently, polymeric foams have become more popular because conventional foams exhibit two important limitations: weak mechanical properties and harmful residues. Hence, the idea of microcellular foaming was invented by Martini et al. 1 at the Massachusetts Institute of Technology to produce lightweight materials without compromising their functional performance. Microcellular foams are defined as foams with cell populations 410 9 cells cm -3 and cell sizes of approximately 10 mm. 2 The tiny size and uniform distribution of bubbles, which are smaller than the critical flaws that already exist in polymers, make microcellular plastics possible for use in daily life applications instead of conventional foams. 3 Microcellular foaming technology has been rapidly developed in the past 2 decades, and microcellular parts have been produced via batch, injection molding and extrusion processes. 4-9 Despite a variety of production methods, the main foaming mechanism is the same. In the first step, the polymer is saturated with an inert gas at high pressure. In the second step, by means of rapid depressurization, the solubility of the dissolved gas decreases, and a super-saturation state occurs. As a result, cell nucleation is thermodynamically favored, and then microcells form through stabilization. 8

Role of chain extension in the rheological properties, crystallization behaviors, and microcellular foaming performances of poly (butylene adipate‐co‐terephthalate)

“…To solve the aforementioned problems, numerous methods were used in preparing microcellular semicrystalline polymer foam, such as introducing special nanofillers, adjusting molecular structure of polymers (chain extension, crosslinking, etc. ), and blending with other polymers .…”

“…Microcellular foams based on polypropylene (PP)/ethylene propylene diene monomer/organoclay nanocomposites were fabricated via a batch foaming process using supercritical N 2 as a physical blowing agent. It showed that the cell structure, cell size, and cell density were improved by the introduction of small amounts of nanoclays . Microcellular injection‐molded PP foam was prepared by introducing long‐chain branches and nucleating agents, the prepared microcellular foam possessed an average cell size of about 2.5 μm and a cell density on the order of 10 10 cells cm −3 .…”

“…had studied the influence of material properties and foaming temperature on the transition from microcellular to nanocellular PLA foam by controlling viscosity, branching, and crystallization, using supercritical N 2 as a physical blowing agent . Throughout the literatures, it could be found that chain extension had a more significant effect on the viscoelasticity and foamability of semicrystalline polymers without the problems of poor interface and dispersity, compared with other methods.…”

“…[13][14][15] The other was that the formed crystalline region would restrict cell nucleation, leading to less cell density and thicker cell wall. 4,16 To solve the aforementioned problems, numerous methods were used in preparing microcellular semicrystalline polymer foam, such as introducing special nanofillers, 17 adjusting molecular structure of polymers (chain extension, crosslinking, etc. ), [18][19][20] and blending with other polymers.…”

The effect of different parameters on mechanical properties of PA-6/clay nanocomposite through genetic algorithm and response surface methods

“…While the effects of chemical structures of polymer and nanoclay (NC) on mechanical properties of polymer nanocomposites (PNCs) have been studied extensively, few studies [22][23][24][25][26][27][28][29][30][31][32][33][34][35] consider the optimization of material and processing parameters. Therefore, the main objective of this study is using a powerful method to optimize material and processing conditions in the twin-screw compounding of PA-6/NC nanocomposites and evaluating their effects on mechanical properties which is not considered in detail in other reports.…”