Solid-state microcellular foaming of PE/PE composite systems, investigation on cellular structure and crystalline morphology (original) (raw)
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Journal of Cellular Plastics, 2010
This article discusses the development of microcellular HDPE and HDPE-clay nanocomposites via a batch high temperature process using supercritical N 2 . The study incorporates the effects of clay content and nanocomposite microstructure on the foaming process performance and cellular morphology under investigation. It was possible to produce much nucleated and more expanded microcellular foams with the nanocomposites than with the pure HDPE, as over 14 vol% void fraction could be reached at 6 wt% clay containing nanocomposite as a good result for foaming by N 2 gas via a batch foaming process. We found that the state of nanoparticle dispersion affects the microcellular morphology, so a better dispersed nanocomposite results in a more nucleated system in the microcellular foaming process. Moreover, the relationship between crystalline morphology and cell structure was investigated. Crystallinity and melting point were the important parameters for controlling the cell growth mechanism in this foaming method.
Foam processing and cellular structure of polypropylene/clay nanocomposites
Polymer Engineering and Science, 2002
Polypropylene (PP)/clay nanocomposites (PPCNs) were autoclave-foamed in a batch process. Foaming was performed using supercritical CO2 at 10 MPa, within the temperature range from 130.6°C to 143.4°C, i.e., below the melting temperature of either PPCNs or maleic anhydride-modified PP (PP-MA) matrix without clay. The foamed PP-MA and PPCN2 (prepared at 130.6°C and containing 2 wt% clay) show closed cell structures with pentagonal and/or hexagonal faces, while foams of PPCN4 and PPCN7.5 (prepared at 143.4°C, 4 and 7.5 wt% clay) had spherical cells. Scanning electron microscopy confirmed that foamed PPCNs had high cell density of 107–108 cells/mL, cell sizes in the range of 30–120 μm, cell wall thicknesses of 5–15 μm, and low densities of 0.05–0.3 g/mL. Interestingly, transmission electron microscopic observations of the PPCNs' cell structure showed biaxial flow-induced alignment of clay particles along the cell boundary. In this paper, the correlation between foam structure and rheological properties of the PPCNs is also discussed.
Effects of clay dispersion on the foam morphology of LDPE/clay nanocomposites
Journal of Applied Polymer Science, 2007
Intercalated and exfoliated low-density polyethylene (LDPE)/clay nanocomposites were prepared by melt blending with and without a maleated polyethylene (PE-g-MAn) as the coupling agent. Their morphology was examined and confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effects of clay content and dispersion on the cell morphology of nanocomposite foams during extrusion foaming process were also thoroughly investigated, especially with a small amount of clay of 0.05-1.0 wt%. This research shows the optimum clay content for achieving microcellular PE/clay nanocomposite foams blown with supercritical CO 2 . It is found that < 0.1 wt% of clay addition can produce the microcellular foam structure with a cell density of > 10 9 cells/cm 3 and a cell size of $ 5 mm.
Polymer Journal, 2012
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.
Processing of microcellular nanocomposite foams by using a supercritical fluid
Fibers and Polymers, 2004
Polystyrene/layered silicate nanocomposites were prepared by melt intercalation. To examine the distribution of the clay in polymer matrix, small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) were used. Intercalated nanocomposites were obtained and their rheological properties were investigated. Microcellular nanocomposite foams were produced by using a supercritical fluid. As clay contents increased, the cell size decreased and the cell density increased. It was found that layered silicates could operate as heterogeneous nucleation sites. As the saturation pressure increased and the saturation temperature decreased, the cell size decreased and the cell density increased. Microcellular foams have different morphology depending upon the dispersion state of nanoclays.
Microcellular foaming of low-density polyethylene using nano-CaCo3 as a nucleating agent
In this study, microcellular foaming of low-density polyethylene (LDPE) using nano-calcium carbonate (nano-CaCO3) were carried out. Nanocomposite samples were prepared in different content in range of 0.5–7 phr nano-CaCO3 using a twin screw extruder. X-ray diffraction and scanning electron microscopy (SEM) were used to characterize of LDPE/nano-CaCO3 nanocomposites. The foaming was carried out by a batch process in compression molding with azodicarbonamide (ADCA) as a chemical blowing agent. The cell structure of the foams was examined with SEM, density and gel content of different samples were measured to compare difference between nanocomposite microcellular foam and microcellular foam without nanomaterials. The results showed that the samples containing 5 phr nano-CaCO3 showed microcellular foam with the lowest mean cell diameter 27 μm and largest cell density 8 × 108 cells/cm3 in compared other samples.
Polymer Engineering & Science , 1996
Microcellular foam processing of polymers requires a nucleated cell density greater than 109 cells/cm3 so that the fully grown cells are smaller than 10 μm. A microcellular foam can be developed by first saturating a polymer sample with a volatile blowing agent, followed by rapidly decreasing its solubility in the polymer. In general, the cellular structure of semicrystalline polymer foams is difficult to control, compared to that of amorphous polymer foams. Since the gas does not dissolve in the crystallites (1), the polymer/gas solution formed during the microcellular processing is nonuniform. Moreover, the bubble nucleation is nonhomogeneous because of the heterogeneous nature of the semicrystalline polymer. In this paper, the effects of the crystallinity and morphology of semicrystalline polymers on the microcellular foam processing and on the cellular structure of products are investigated. First, polymer specimens with various crystallinities and morphologies were prepared by varying the cooling rate of the polymer melt. Then, the solubility and diffusivity of the blowing agent in and through specimens were studied. The specimens with differing crystallinities and morphologies were foamed and their cellular structures were compared. The experimental results agree with theoretical predictions, indicating that the crystallinity and morphology of semicrystalline polymers exert a strong influence on the foam processing and the structure of the product. (citation # 274)
Optimization of Process Parameters for Generation of Nanocellular Polymer Foams
Journal of Research Updates in Polymer Science, 2013
High melt strength polypropylene nanocomposites, PPNC/Cloisite 20A (clay) with exfoliated and intercalated morphologies were prepared and subsequently foamed in a batch setup under different foaming conditions. The foaming parameters were varied to relate the foam cell structure to these parameters and determine the efficiency of clay in producing fine cell foams. A Box Benkhen design approach was used initially to determine the effect of processing parameters on foam cell morphology and also to perform optimization studies. The optimization process helped in identifying the range of operating conditions needed to minimize foam cell sizes. Saturation pressure and temperature and foaming time and temperature are the four processing variables used in these studies. Nanocellular foam cells were effectively generated for the first time in Polypropylene nanocomposites.
Journal of Polymer Engineering, 2019
Polystyrene/poly(methyl methacrylate) (PS/PMMA) blends in 80:20, 50:50, and 20:80 ratios with and without calcium carbonate nanoparticles were prepared. n-Pentane was then used to foam the samples in an autoclave. After the diffusion of n-pentane gas into the polymer matrix, the samples and the gas were simultaneously cooled to obtain the liquid n-pentane phase. Phase change to liquid provided the required pressure drop for cell nucleation and consequent cell growth. The solubility of n-pentane in the samples was measured. Liquid n-pentane trapped inside created micro- and nanopores, forming a foam with closed cells. Experiments were carried out in different compositions of the materials, with and without nanoparticles, and the cell morphologies were characterized. The results of this work show that nanocellular structures can be achieved when calcium carbonate nanoparticles are added to PS/PMMA blends.